Flow regulation manipulates contemporary seasonal sedimentary dynamics in the reservoir fluctuation zone of the Three Gorges Reservoir, China.

PubMed

Tang, Qiang; Bao, Yuhai; He, Xiubin; Fu, Bojie; Collins, Adrian L; Zhang, Xinbao

2016-04-01

Since the launch of the Three Gorges Dam on the Yangtze River, a distinctive reservoir fluctuation zone has been created and significantly modified by regular dam operations. Sediment redistribution within this artificial landscape differs substantially from that in natural fluvial riparian zones, due to a specific hydrological regime comprising steps of water impoundment with increasing magnitudes and seasonal water level fluctuation holding a range of sediment fluxes. This study reinterpreted post-dam sedimentary dynamics in the reservoir fluctuation zone by stratigraphy determination of a 345-cm long sediment core, and related it to impact of the hydrological regime. Seasonality in absolute grain-size composition of suspended sediment was applied as a methodological basis for stratigraphic differentiation. Sedimentary laminations with relatively higher proportions of sandy fractions were ascribed to sedimentation during the dry season when proximal subsurface bank erosion dominates source contributions, while stratigraphy with a lower proportion of sandy fractions is possibly contributed by sedimentation during the wet season when distal upstream surface erosion prevails. Chronology determination revealed non-linear and high annual sedimentation rates ranging from 21.7 to 152.1cm/yr. Although channel geomorphology may primarily determine the spatial extent of sedimentation, seasonal sedimentary dynamics was predominantly governed by the frequency, magnitude, and duration of flooding. Summer inundation by natural floods with enhanced sediment loads produced from upstream basins induced higher sedimentation rates than water impoundment during the dry season when distal sediment supply was limited. We thus conclude that flow regulation manipulates contemporary seasonal sedimentary dynamics in the reservoir fluctuation zone, though little impact on total sediment retention rate was detected. Ongoing reductions in flow and sediment supply under human disturbance may have profound implications in affecting sedimentary equilibrium in the reservoir fluctuation zone. The results herein provide insights of how big dams have disrupted the sediment conveyance processes of large scale fluvial systems. Copyright © 2016 Elsevier B.V. All rights reserved.

The Dynamics of Sediment Oxygenation in Marsh Rhizospheres

NASA Astrophysics Data System (ADS)

Koop-Jakobsen, K.

2014-12-01

Many marsh grasses are capable of internal oxygen transport from aboveground sources to belowground roots and rhizomes, where oxygen may leak across the rhizodermis and oxygenate the surrounding sediment. In the field, the extent of sediment oxygenation in marshes was assessed in the rhizosphere of the marsh grass; Spartina anglica, inserting 70 optical fiber oxygen sensors into the rhizosphere. Two locations with S. anglica growing in different sediment types were investigated. No oxygen was detected in the rhizospheres indicating that belowground sediment oxygenation in S. anglica has a limited effect on the bulk anoxic sediment and is restricted to sediment in the immediate vicinity of the roots. In the laboratory, the presence of 1.5mm wide and 16mm long oxic root zones was demonstrated around root tips of S. anglica growing in permeable sandy sediment using planar optodes recording 2D-images of the oxygen distribution. Oxic root zones in S. anglica growing in tidal flat deposits were significantly smaller. The size of oxic roots zones was highly dynamic and affected by tidal inundations as well as light availability. Atmospheric air was the primary oxygen source for belowground sediment oxygenation, whereas photosynthetic oxygen production only played a minor role for the size of the oxic root zones during air-exposure of the aboveground biomass. During tidal inundations (1.5 h) completely submerging the aboveground biomass cutting off access to atmospheric oxygen, the size of oxic root zones were reduced significantly in the light and oxic root zones were completely eliminated in darkness. Sediment oxygenation in the rhizospheres of marsh grasses is of significant importance for marshes ability to retain inorganic nitrogen before it reaches the coastal waters. The presence of oxic roots zones promotes coupled nitrification-denitrification at depth in the sediment, which can account for more than 80% of the total denitrification in marshes.

Effect of Sediments on Rupture Dynamics of Shallow Subduction Zone Earthquakes and Tsunami Generation

NASA Astrophysics Data System (ADS)

Ma, S.

2011-12-01

Low-velocity fault zones have long been recognized for crustal earthquakes by using fault-zone trapped waves and geodetic observations on land. However, the most pronounced low-velocity fault zones are probably in the subduction zones where sediments on the seafloor are being continuously subducted. In this study I focus on shallow subduction zone earthquakes; these earthquakes pose a serious threat to human society in their ability in generating large tsunamis. Numerous observations indicate that these earthquakes have unusually long rupture durations, low rupture velocities, and/or small stress drops near the trench. However, the underlying physics is unclear. I will use dynamic rupture simulations with a finite-element method to investigate the dynamic stress evolution on faults induced by both sediments and free surface, and its relations with rupture velocity and slip. I will also explore the effect of off-fault yielding of sediments on the rupture characteristics and seafloor deformation. As shown in Ma and Beroza (2008), the more compliant hanging wall combined with free surface greatly increases the strength drop and slip near the trench. Sediments in the subduction zone likely have a significant role in the rupture dynamics of shallow subduction zone earthquakes and tsunami generation.

Ecophysiology of wetland plant roots: A modelling comparison of aeration in relation to species distribution

USGS Publications Warehouse

Sorrell, B.K.; Mendelssohn, I.A.; McKee, K.L.; Woods, R.A.

2000-01-01

This study examined the potential for inter-specific differences in root aeration to determine wetland plant distribution in nature. We compared aeration in species that differ in the type of sediment and depth of water they colonize. Differences in root anatomy, structure and physiology were applied to aeration models that predicted the maximum possible aerobic lengths and development of anoxic zones in primary adventitious roots. Differences in anatomy and metabolism that provided higher axial fluxes of oxygen allowed deeper root growth in species that favour more reducing sediments and deeper water. Modelling identified factors that affected growth in anoxic soils through their effects on aeration. These included lateral root formation, which occurred at the expense of extension of the primary root because of the additional respiratory demand they imposed, reducing oxygen fluxes to the tip and stele, and the development of stelar anoxia. However, changes in sediment oxygen demand had little detectable effect on aeration in the primary roots due to their low wall permeability and high surface impedance, but appeared to reduce internal oxygen availability by accelerating loss from laterals. The development of pressurized convective gas flow in shoots and rhizomes was also found to be important in assisting root aeration, as it maintained higher basal oxygen concentrations at the rhizome-root junctions in species growing into deep water. (C) 2000 Annals of Botany Company.

Biogeochemical factors influencing net mercury methylation in contaminated freshwater sediments from the St. Lawrence River in Cornwall, Ontario, Canada.

PubMed

Avramescu, Mary-Luyza; Yumvihoze, Emmanuel; Hintelmann, Holger; Ridal, Jeff; Fortin, Danielle; Lean, David R S

2011-02-01

The activity of various anaerobic microbes, including sulfate reducers (SRB), iron reducers (FeRP) and methanogens (MPA) has been linked to mercury methylation in aquatic systems, although the relative importance of each microbial group in the overall process is poorly understood in natural sediments. The present study focused on the biogeochemical factors (i.e. the relative importance of various groups of anaerobic microbes (FeRP, SRB, and MPA) that affect net monomethylmercury (MMHg) formation in contaminated sediments of the St. Lawrence River (SRL) near Cornwall (Zone 1), Ontario, Canada. Methylation and demethylation potentials were measured separately by using isotope-enriched mercury species ((200)Hg(2+) and MM(199)Hg(+)) in sediment microcosms treated with specific microbial inhibitors. Sediments were sampled and incubated in the dark at room temperature in an anaerobic chamber for 96h. The potential methylation rate constants (K(m)) and demethylation rates (K(d)) were found to differ significantly between microcosms. The MPA-inhibited microcosm had the highest potential methylation rate constant (0.016d(-1)), whereas the two SRB-inhibited microcosms had comparable potential methylation rate constants (0.003d(-1) and 0.002d(-1), respectively). The inhibition of methanogens stimulated net methylation by inhibiting demethylationand by stimulating methylation along with SRB activity. The inhibition of both methanogens and SRB was found to enhance the iron reduction rates but did not completely stop MMHg production. The strong positive correlation between K(m) and Sulfate Reduction Rates (SRR) and between K(d) and Methane Production Rates (MPR) supports the involvement of SRB in Hg methylation and MPA in MMHg demethylation in the sediments. In contrast, the strong negative correlation between K(d) and Iron Reduction Rates (FeRR) shows that the increase in FeRR corresponds to a decrease in demethylation, indicating that iron reduction may influence net methylation in the SLR sediments by decreasing demethylation rather than favouring methylation. Copyright © 2010 Elsevier B.V. All rights reserved.

Study of the influence of different organic pollutants on Cu accumulation by Halimione portulacoides

NASA Astrophysics Data System (ADS)

Almeida, C. Marisa R.; Claúdia Dias, A.; Mucha, Ana P.; Bordalo, A. A.; Vasconcelos, M. Teresa S. D.

2009-12-01

The influence of each of four organic pollutants selected from among those commonly found in coastal areas, 1,1-dichloro-2,2-bis(p-chlorophenyl) ethylene (DDE), monobutyltin (MBT), Triton X-100 and polycyclic aromatic hydrocarbons (PAHs), on Cu accumulation by Halimione portulacoides was investigated. Experiments were carried out in a laboratory setting, either in hydroponics (sediment elutriate) or in a salt marsh sediment ( Cávado River, NW Portugal) soaked in elutriate. Groups of H. portulacoides were exposed to media for 6 days spiked with 10 mg/L Cu(II) and with one of the selected pollutants, at an environmentally realistic concentration. DDE and MBT did not cause any major change on Cu accumulation by H. portulacoides, whereas PAHs slightly increased accumulation only in hydroponics i.e. in the absence of sediment. On the other hand, the non-ionic surfactant Triton X-100 markedly favoured Cu accumulation on plant roots both in the presence and absence of sediment. The addition of DDE, MBT and Triton X-100 also favoured Cu solubility from sediments. Therefore, the simultaneous presence of pollutants from different nature (inorganic and organic) in the estuarine environment may result in a composition of water column, pore water, sediment or biota different of that expected considering the effect of each individual pollutant.

Rare earth element geochemistry of oceanic ferromanganese nodules and associated sediments

NASA Astrophysics Data System (ADS)

Elderfield, H.; Hawkesworth, C. J.; Greaves, M. J.; Calvert, S. E.

1981-04-01

Analyses have been made of REE contents of a well-characterized suite of deep-sea (> 4000 m.) principally todorokite-bearing ferromanganese nodules and associated sediments from the Pacific Ocean. REE in nodules and their sediments are closely related: nodules with the largest positive Ce anomalies are found on sediments with the smallest negative Ce anomalies; in contrast, nodules with the highest contents of other rare earths (3 + REE) are found on sediments with the lowest 3 + REE contents and vice versa. 143Nd /144Nd ratios in the nodules (˜0.51244) point to an original seawater source but an identical ratio for sediments in combination with the REE patterns suggests that diagenetic reactions may transfer elements into the nodules. Analysis of biogenic phases shows that the direct contribution of plankton and carbonate and siliceous skeletal materials to REE contents of nodules and sediments is negligible. Inter-element relationships and leaching tests suggest that REE contents are controlled by a P-rich phase with a REE pattern similar to that for biogenous apatite and an Fe-rich phase with a pattern the mirror image of that for sea water. It is proposed that 3 + REE concentrations are controlled by the surface chemistry of these phases during diagenetic reactions which vary with sediment accumulation rate. Processes which favour the enrichment of transition metals in equatorial Pacific nodules favour the depletion of 3 + REE in nodules and enrichment of 3 + REE in associated sediments. In contrast, Ce appears to be added both to nodules and sediments directly from seawater and is not involved in diagenetic reactions.

Microbial diversity in Cenozoic sediments recovered from the Lomonosov Ridge in the Central Arctic basin.

PubMed

Forschner, Stephanie R; Sheffer, Roberta; Rowley, David C; Smith, David C

2009-03-01

The current understanding of microbes inhabiting deeply buried marine sediments is based largely on samples collected from continental shelves in tropical and temperate latitudes. The geographical range of marine subsurface coring was expanded during the Integrated Ocean Drilling Program Arctic Coring Expedition (IODP ACEX). This expedition to the ice-covered central Arctic Ocean successfully cored the entire 428 m sediment stack on the Lomonosov Ridge during August and September 2004. The recovered cores vary from siliciclastic sediment low in organic carbon (< 0.2%) to organic rich ( approximately 3%) black sediments that rapidly accumulated in the early middle Eocene. Three geochemical environments were characterized based on chemical analyses of porewater: an upper ammonium oxidation zone, a carbonate dissolution zone and a deep (> 200 m below sea floor) sulfate reduction zone. The diversity of microbes within each zone was assessed using 16S rRNA phylogenetic markers. Bacterial 16S rRNA genes were successfully amplified from each of the biogeochemical zones, while archaea was only amplified from the deep sulfate reduction zone. The microbial communities at each zone are phylogenetically different and are most closely related to those from other deep subsurface environments.

Recovery of gravitropism after basipetal centrifugation in protonemata of the moss Ceratodon purpureus

NASA Technical Reports Server (NTRS)

Walker, L. M.; Sack, F. D.

1991-01-01

Apical cells of 5-day-old dark-grown protonemata of the moss Ceratodon purpureus (Hedw.) Brid. are negatively gravitropic and appear to utilize amyloplasts as statoliths. These cells exhibit a characteristic plastid zonation (five zones) with one zone (No. 3) specialized for the lateral sedimentation of amyloplasts. Basipetal centrifugation displaces all amyloplasts in the apical cell to the end wall. In basipetally centrifuged protonemata observed using infrared videomicroscopy, tip extension occurred with or without amyloplasts present in the apical dome. The initial return of upward curvature was always correlated with the return and sedimentation of amyloplasts in zone 3. Subsequent vigorous upward curvature was correlated with distinct amyloplast zonation and further sedimentation in zone 3. Initial downward ("wrong way") curvature, which often preceded upward curvature, correlated with the presence of amyloplasts in the apical dome (zone 1). These data support the hypotheses that nonsedimenting amyloplasts in zone 1 are necessary for initial downward curvature and that amyloplast sedimentation in zone 3 is necessary for upward curvature.

Reconstruction of Landscape Evolution Zones (LEZ) from laminated Eifel maar sediments of the last 60 000 years

NASA Astrophysics Data System (ADS)

Sirocko, Frank

2016-04-01

Tephra, eolian dust, organic carbon, pollen and botanical macroremains from the dry maar lake structures auf Auel and Dehner are used to synthesize and define Landscape Evolution Zones (LEZ) for the Eifel during the last 60 000 years. LEZ 1-3 reiterate the established succession of vegetation during the Holocene and late glacial. The maximum of the last glaciation (LEZ 4: 14 700 - 23 000 b2k) was characterized by extremely sparse vegetation of some moss and characeae, however, characterized by annual activity of eolian dust. These sediments are generally devoid of clay and sand and reveal no indication of snow-meltwater events; accordingly, the Last Glacial Maximum (LGM) must have been extremely arid in central Europe. The sediments of the subsequent LEZ 5 from 23 000 ‒ 28 500 b2k preserve however distinct layers of clay and coarse sand, which indicates running water with clay in suspension and ephemeral coarse grained fluvial sediment discharge; abundant Ranunculaceae macroremains (used for 14C dating), insects, moss and fungi sclerotia reflect a tundra environment during a time of frequent strong snow melt events. Total carbon content and Betula-Pinus pollen reach increased concentrations during all MIS 3 interstadials that occurred between 28 500 - 36 500 b2k (LEZ 6). Grass pollen and heliophytes indicate a steppe environment with scattered/patchy trees during the interstadials. The stadial phases of LEZ 6 reveal first activity of eolian dust deflation. The opening of the early MIS 3 forested landscape to a steppe occurred with the LEZ 7 - LEZ 6 transition at 36 500 b2k. This is the time when modern man arrived in central Europe; possibly because the vegetation change must have favoured the spread of horse, which was the favoured hunting prey of the modern humans. Accordingly, we postulate that the migration of the modern humans into central Europe could have been mainly driven by climate and vegetation change. The LEZ 7 encompassing the time interval from 36 500 to 49 000 b2k was characterized by a boreal forest with high abundance of pine, birch, and also spruce during the interstadial events. Abundant charcoal fragments indicate that this taiga was under frequent drought stress. The most unexpected finding, but corroborated by all maar records studied, are the abundant thermophilous tree taxa characterizing the time interval 49 000 - 55 000 b2k, representing LEZ 8. The Greenland interstadials 13 and 14 were apparently the warmest part of MIS 3. The proceeding LEZ 9 from 55 000 - 60 000 b2k is also dominated by spruce, but thermophilous trees were only very rare. A continuously warm GI 13/14 appears plausible, because summer insolation was higher in the early MIS 3 than today, ice cover was low in Scandinavia and sea-surface temperatures of the North Atlantic were almost comparable to modern values during GI-14.

Nutrient Enrichment Increases Mortality of Mangroves

PubMed Central

Lovelock, Catherine E.; Ball, Marilyn C.; Martin, Katherine C.; C. Feller, Ilka

2009-01-01

Nutrient enrichment of the coastal zone places intense pressure on marine communities. Previous studies have shown that growth of intertidal mangrove forests is accelerated with enhanced nutrient availability. However, nutrient enrichment favours growth of shoots relative to roots, thus enhancing growth rates but increasing vulnerability to environmental stresses that adversely affect plant water relations. Two such stresses are high salinity and low humidity, both of which require greater investment in roots to meet the demands for water by the shoots. Here we present data from a global network of sites that documents enhanced mortality of mangroves with experimental nutrient enrichment at sites where high sediment salinity was coincident with low rainfall and low humidity. Thus the benefits of increased mangrove growth in response to coastal eutrophication is offset by the costs of decreased resilience due to mortality during drought, with mortality increasing with soil water salinity along climatic gradients. PMID:19440554

Nutrient enrichment increases mortality of mangroves.

PubMed

Lovelock, Catherine E; Ball, Marilyn C; Martin, Katherine C; C Feller, Ilka

2009-01-01

Nutrient enrichment of the coastal zone places intense pressure on marine communities. Previous studies have shown that growth of intertidal mangrove forests is accelerated with enhanced nutrient availability. However, nutrient enrichment favours growth of shoots relative to roots, thus enhancing growth rates but increasing vulnerability to environmental stresses that adversely affect plant water relations. Two such stresses are high salinity and low humidity, both of which require greater investment in roots to meet the demands for water by the shoots. Here we present data from a global network of sites that documents enhanced mortality of mangroves with experimental nutrient enrichment at sites where high sediment salinity was coincident with low rainfall and low humidity. Thus the benefits of increased mangrove growth in response to coastal eutrophication is offset by the costs of decreased resilience due to mortality during drought, with mortality increasing with soil water salinity along climatic gradients.

Biostratigraphy and paleoecology of the Burdigalian-Serravallian sediments in Wadi Sudr (Gulf of Suez, Egypt): comparison with the Central Paratethys evolution

NASA Astrophysics Data System (ADS)

Ied, Ibrahim M.; Holcová, Katarína; Abd-Elshafy, Ezzat

2011-06-01

Two main Miocene facies were recorded in the Gulf of Suez area: a deep marine and a coastal facies. The analysed sections in the Wadi Sudr area belong to the marine facies. The Lower Miocene (Burdigalian) is represented by coastal, shallow marine sediments, rich in coral, algae, gastropods and large pectinids followed by Langhian open marine sediments and Serravallian lagoonal carbonates. The open marine sediments contain well preserved planktonic and benthic foraminifers and abundant ostracods. The parts of the sections containing foraminifers have been correlated with three planktonic foraminiferal zones (Praeorbulina glomerosa Zone, Orbulina Zone and Globorotalia praemenardii-Globorotalia peripheroronda Zone). Two benthic ecozones were defined (Heterolepa dutemplei-Laevidentalina elegans Zone and Bolivina compressa-Elphidium spp. Zone). Two cycles of sea-level changes can be distinguished and correlated with global sea-level cycles Bur5/Lan1 and Ser1. The first (Langhian) cycle culminated in open marine sublittoral to upper bathyal well aerated sediments. The second (Serravallian) cycle was shallower, littoral suboxic sediments were overlaid by euryhaline carbonates. The studied foraminifera-bearing sediments can be correlated with the lower and Middle Badenian of the Central Paratethys. Though the area of the Gulf of Suez and the Central Paratethys were situated in different climatic zones, and influenced by different tectonic events, the main paleoenvironmental events (sea-level changes, oxygen decrease, salinity changes) are comparable. This correspondence shows that the decisive factors triggering these events were global climatic events.

Sediment transport by fishes in Harrington Sound, Bermuda

NASA Astrophysics Data System (ADS)

Alheit, Jürgen

1983-11-01

Harrington Sound, Bermuda, is a shallow subtropical lagoon with carbonate sediments. The most important fishes in this lagoon, in terms of biomass, are grunts (Haemulon aurolineatum, H. flavolineatum, H. sciurus) and a sea-bream (Diplodus bermudensis). These undertake diel feeding migrations from the shallow rocky zone towards the deeper sand and mud zones. When feeding on zoobenthos they cannot avoid swallowing carbonate sediment particles. These sediment particles pass through the alimentary canal of the fishes and are deposited again, after digestion of the food, as faeces in the shallow zones. Thus, the fishes transport the sediment in an unusual direction, from the deep to the shallow zones, in effect against the force of gravity. By recording the fish stock densities, digestion rates, and calcium carbonate content of fish stomach and guts, it was possible to estimate the amount of sediment transported by the fishes. In Harrington Sound, this amounts annually to 4530 kg calcium carbonate, 40% of which is deposited in the very shallow areas. The pH-values measured in fish stomachs seem to be acidic enough for the dissolution of carbonate sediment particles when transported by fishes.

Geochemical, mineralogical and microbiological characteristics of sediment from a naturally reduced zone in a uranium-contaminated aquife

DOE Office of Scientific and Technical Information (OSTI.GOV)

Campbell, K M; K Kukkadapu, R K; Qafoku, N P

2012-05-23

Localized zones or lenses of naturally reduced sediments have the potential to play a significant role in the fate and transport of redox-sensitive metals and metalloids in aquifers. To assess the mineralogy, microbiology and redox processes that occur in these zones, several cores from a region of naturally occurring reducing conditions in a U-contaminated aquifer (Rifle, CO) were examined. Sediment samples from a transect of cores ranging from oxic/suboxic Rifle aquifer sediment to naturally reduced sediment were analyzed for U and Fe content, oxidation state, and mineralogy; reduced S phases; and solid-phase organic C content using a suite of analyticalmore » and spectroscopic techniques on bulk sediment and size fractions. Solid-phase U concentrations were higher in the naturally reduced zone, with a high proportion of the U present as U(IV). The sediments were also elevated in reduced S phases and Fe(II), indicating it is very likely that U(VI), Fe(III), and SO4 reduction has occurred or is occurring in the sediment. The microbial community was assessed using lipid- and DNA-based techniques, and statistical redundancy analysis was performed to determine correlations between the microbial community and the geochemistry. Increased concentrations of solid-phase organic C and biomass in the naturally reduced sediment suggests that natural bioreduction is stimulated by a zone of increased organic C concentration associated with fine-grained material and lower permeability to groundwater flow. Characterization of the naturally bioreduced sediment provides an understanding of the natural processes that occur in the sediment under reducing conditions and how they may impact natural attenuation of radionuclides and other redox sensitive materials. Results also suggest the importance of recalcitrant organic C for maintaining reducing conditions and U immobilization.« less

Geochemical, mineralogical and microbiological characteristics of sediment from a naturally reduced zone in a uranium-contaminated aquifer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Campbell, Kate M.; Kukkadapu, Ravi K.; Qafoku, Nikolla

2012-05-23

Localized zones or lenses of naturally reduced sediments have the potential to play a significant role in the fate and transport of redox-sensitive metals and metalloids in aquifers. To assess the mineralogy, microbiology, and redox processes that occur in these zones, we examined several cores from a region of naturally occurring reducing conditions in a uranium-contaminated aquifer (Rifle, CO). Sediment samples from a transect of cores ranging from oxic/suboxic Rifle aquifer sediment to naturally reduced sediment were analyzed for uranium and iron content, oxidation state, and mineralogy, reduced sulfur phases, and solid phase organic carbon content using a suite ofmore » analytical and spectroscopic techniques on bulk sediment and size fractions. Solid-phase uranium concentrations were higher in the naturally reduced zone, with a high proportion of the uranium present as reduced U(IV). The sediments were also elevated in reduced sulfur phases and Fe(II), indicating it is very likely that U(VI), Fe(III), and sulfate reduction occurred or is occurring in the sediment. The microbial community was assessed using lipid- and DNA-based techniques, and statistical redundancy analysis was performed to determine correlations between the microbial community and the geochemistry. Increased concentration of solid phase organic carbon and biomass in the naturally reduced sediment suggests that natural bioreduction is stimulated by a zone of increased organic carbon concentration associated with fine-grained material and lower permeability to groundwater flow. Characterization of the naturally bioreduced sediment provides an understanding of the natural processes that occur in the sediment under reducing conditions and how they may impact natural attenuation of radionuclides and other redox sensitive materials. Results also suggest the importance of recalcitrant organic carbon for maintaining reducing conditions and uranium immobilization.« less

Geochemical, mineralogical and microbiological characteristics of sediment from a naturally reduced zone in a uranium-contaminated aquifer

DOE Office of Scientific and Technical Information (OSTI.GOV)

Campbell, K. M.; Kukkadapu, R. K.; Qafoku, N. P.

2012-08-01

Localized zones or lenses of naturally reduced sediments have the potential to play a significant role in the fate and transport of redox-sensitive metals and metalloids in aquifers. To assess the mineralogy, microbiology and redox processes that occur in these zones, several cores from a region of naturally occurring reducing conditions in a U-contaminated aquifer (Rifle, CO) were examined. Sediment samples from a transect of cores ranging from oxic/suboxic Rifle aquifer sediment to naturally reduced sediment were analyzed for U and Fe content, oxidation state, and mineralogy; reduced S phases; and solid-phase organic C content using a suite of analyticalmore » and spectroscopic techniques on bulk sediment and size fractions. Solid-phase U concentrations were higher in the naturally reduced zone, with a high proportion of the U present as U(IV). The sediments were also elevated in reduced S phases and Fe(II), indicating it is very likely that U(VI), Fe(III), and SO 4 reduction has occurred or is occurring in the sediment. The microbial community was assessed using lipid- and DNA-based techniques, and statistical redundancy analysis was performed to determine correlations between the microbial community and the geochemistry. Increased concentrations of solid-phase organic C and biomass in the naturally reduced sediment suggests that natural bioreduction is stimulated by a zone of increased organic C concentration associated with fine-grained material and lower permeability to groundwater flow. Characterization of the naturally bioreduced sediment provides an understanding of the natural processes that occur in the sediment under reducing conditions and how they may impact natural attenuation of radionuclides and other redox sensitive materials. Results also suggest the importance of recalcitrant organic C for maintaining reducing conditions and U immobilization.« less

Nearshore sediment thickness, Fire Island, New York

USGS Publications Warehouse

Locker, Stanley D.; Miselis, Jennifer L.; Buster, Noreen A.; Hapke, Cheryl J.; Wadman, Heidi M.; McNinch, Jesse E.; Forde, Arnell S.; Stalk, Chelsea A.

2017-04-03

Investigations of coastal change at Fire Island, New York (N.Y.), sought to characterize sediment budgets and determine geologic framework controls on coastal processes. Nearshore sediment thickness is critical for assessing coastal system sediment availability, but it is largely unquantified due to the difficulty of conducting geological or geophysical surveys across the nearshore. This study used an amphibious vessel to acquire chirp subbottom profiles. These profiles were used to characterize nearshore geology and provide an assessment of nearshore sediment volume. Two resulting sediment-thickness maps are provided: total Holocene sediment thickness and the thickness of the active shoreface. The Holocene sediment section represents deposition above the maximum flooding surface that is related to the most recent marine transgression. The active shoreface section is the uppermost Holocene sediment, which is interpreted to represent the portion of the shoreface thought to contribute to present and future coastal behavior. The sediment distribution patterns correspond to previously defined zones of erosion, accretion, and stability along the island, demonstrating the importance of sediment availability in the coastal response to storms and seasonal variability. The eastern zone has a thin nearshore sediment thickness, except for an ebb-tidal deposit at the wilderness breach caused by Hurricane Sandy. Thicker sediment is found along a central zone that includes shoreface-attached sand ridges, which is consistent with a stable or accretional coastline in this area. The thickest overall Holocene section is found in the western zone of the study, where a thicker lower section of Holocene sediment appears related to the westward migration of Fire Island Inlet over several hundred years.

In-situ Geotechnical Investigation of Arctic Nearshore Zone Sediments, Herschel Island, Yukon

NASA Astrophysics Data System (ADS)

Stark, N.; Quinn, B.; Radosavljevic, B.; Lantuit, H.

2016-02-01

The Arctic is currently undergoing rapid changes with regard to ice coverage, permafrost retreat and coastal erosion. In addition to hydrodynamic processes, the sediments in the Arctic nearshore zone are affected by potential variations in freeze-thaw cycles, as well as an increase of abundant suspended sediment introduced by active retrogressive thaw slumps and increased river discharge. During the YUKON14 expedition to Herschel Island, Yukon, in-situ geotechnical testing of nearshore zone sediments was conducted using a portable free fall penetrometer. The research goals were mapping of sediment types, identification of surficial sediment stratification related to recent sediment remobilization or deposition processes, and the investigation of the soil mechanical characteristics of the uppermost seabed surface in the nearshore zone. Approximately 200 sites were tested using the portable free fall penetrometer, and five different geotechnical signatures identified and grouped. Most locations were characterized by a soft sediment top layer that exhibited a noticeably lower sediment strength than the underlying sediment. The results were correlated to existing sediment grain size records and a sediment type interpretation based on side scan sonar backscatter information. Strong spatial variations in sediment type and stiffness were observed, as well as in abundance and thickness of a top layer of very soft and loose sediment. It was attempted to relate the geotechnical signature to site-specific hydrodynamic energy, morphology, and vicinity to thaw slumps. The results will contribute to a detailed investigation of Arctic coastal erosion in the region, and the investigation of the role of geotechnical parameters for Arctic coastal erosion.

Microbial distributions detected by an oligonucleotide microarray across geochemical zones associated with methane in marine sediments from the Ulleung Basin

DOE Office of Scientific and Technical Information (OSTI.GOV)

Briggs, Brandon R; Graw, Michael; Brodie, Eoin L

2013-11-01

The biogeochemical processes that occur in marine sediments on continental margins are complex; however, from one perspective they can be considered with respect to three geochemical zones based on the presence and form of methane: sulfate–methane transition (SMTZ), gas hydrate stability zone (GHSZ), and free gas zone (FGZ). These geochemical zones may harbor distinct microbial communities that are important in biogeochemical carbon cycles. The objective of this study was to describe the microbial communities in sediments from the SMTZ, GHSZ, and FGZ using molecular ecology methods (i.e. PhyloChip microarray analysis and terminal restriction fragment length polymorphism (T-RFLP)) and examining themore » results in the context of non-biological parameters in the sediments. Non-metric multidimensional scaling and multi-response permutation procedures were used to determine whether microbial community compositions were significantly different in the three geochemical zones and to correlate samples with abiotic characteristics of the sediments. This analysis indicated that microbial communities from all three zones were distinct from one another and that variables such as sulfate concentration, hydrate saturation of the nearest gas hydrate layer, and depth (or unmeasured variables associated with depth e.g. temperature, pressure) were correlated to differences between the three zones. The archaeal anaerobic methanotrophs typically attributed to performing anaerobic oxidation of methane were not detected in the SMTZ; however, the marine benthic group-B, which is often found in SMTZ, was detected. Within the GHSZ, samples that were typically closer to layers that contained higher hydrate saturation had indicator sequences related to Vibrio-type taxa. These results suggest that the biogeographic patterns of microbial communities in marine sediments are distinct based on geochemical zones defined by methane.« less

Numerical simulation of two-phase flow for sediment transport in the inner-surf and swash zones

NASA Astrophysics Data System (ADS)

Bakhtyar, R.; Barry, D. A.; Yeganeh-Bakhtiary, A.; Li, L.; Parlange, J.-Y.; Sander, G. C.

2010-03-01

A two-dimensional two-phase flow framework for fluid-sediment flow simulation in the surf and swash zones was described. Propagation, breaking, uprush and backwash of waves on sloping beaches were studied numerically with an emphasis on fluid hydrodynamics and sediment transport characteristics. The model includes interactive fluid-solid forces and intergranular stresses in the moving sediment layer. In the Euler-Euler approach adopted, two phases were defined using the Navier-Stokes equations with interphase coupling for momentum conservation. The k-ɛ closure model and volume of fluid approach were used to describe the turbulence and tracking of the free surface, respectively. Numerical simulations explored incident wave conditions, specifically spilling and plunging breakers, on both dissipative and intermediate beaches. It was found that the spatial variation of sediment concentration in the swash zone is asymmetric, while the temporal behavior is characterized by maximum sediment concentrations at the start and end of the swash cycle. The numerical results also indicated that the maximum turbulent kinetic energy and sediment flux occurs near the wave-breaking point. These predictions are in general agreement with previous observations, while the model describes the fluid and sediment phase characteristics in much more detail than existing measurements. With direct quantifications of velocity, turbulent kinetic energy, sediment concentration and flux, the model provides a useful approach to improve mechanistic understanding of hydrodynamic and sediment transport in the nearshore zone.

Sulphide-sulphate stability and melting in subducted sediment and its role in arc mantle redox and chalcophile cycling in space and time

NASA Astrophysics Data System (ADS)

Canil, Dante; Fellows, Steven A.

2017-07-01

The redox budget during subduction is tied to the evolution of oxygen and biogeochemical cycles on Earth's surface over time. The sulphide-sulphate couple in subducted crust has significant potential for redox and control on extraction of chalcophile metals from the arc mantle. We derive oxygen buffers for sulphide-sulphate stability ('SSO buffers') using mineral assemblages in subducted crust within the eclogite facies, and examine their disposition relative to the fO2 in the arc mantle along various P-T trajectories for subduction. The fO2 required for sulphide stability in subducted crust passing beneath an arc is shifted by variations in the bulk Ca/(Ca + Mg + Fe) of the subducting crust alone. Hotter slabs and more Fe-rich sediments stabilize sulphide and favour chalcophile sequestration deep into the mantle, whereas colder slabs and calcic sediment will stabilize anhydrite, in some cases at depths of melt generation in the arc mantle (<130 km). The released sulphate on melting potentially increases the fO2 of the arc mantle. We performed melting experiments on three subducted sediment compositions varying in bulk Ca/(Ca + Mg + Fe) from 0.3 to 0.6 at 2.5 GPa and 900-1100 °C to confirm how anhydrite stability can change by orders of magnitude the S, Cu, As, Zn, Mo, Pb, and Sb contents of sediment melts, and their subsequent liberation to the arc mantle. Using Cu/Sc as a proxy for the behaviour of S, the effect of variable subducted sediment composition on sulphide-sulphate stability and release of chalcophiles to the arc mantle is recognizable in volcanic suites from several subduction zones in space and time. The fO2 of the SSO buffers in subducted sediment relative to the arc mantle may have changed with time by shifts in the nature of pelagic sedimentation in the oceans over earth history. Oxidation of arc mantle and the proliferation of porphyry Cu deposits may be latter-day advents in earth history partly due to the rise of planktic calcifiers in the oceans in only the past 250 million years.

Magnetic Hysteresis of Deep-Sea Sediments in Korea Deep Ocean Study(KODOS) Area, NE Pacific

NASA Astrophysics Data System (ADS)

Kim, K.; Park, C.; Yoo, C.

2001-12-01

The KODOS area within the Clarion-Clipperton fracture zone (C-C zone) is surrounded by the Hawaiian and Line Island Ridges to the west and the central American continent to the east. Topography of the seafloor consists of flat-topped abyssal hills and adjacent abyssal troughs, both of which run parallel in N-S direction. Sediments from the study area consist mainly of biogenic sediments. Latitudinal zonation of sedimentary facies was caused by the accumulation of biogenic materials associated with the equatorial current system and movement of the Pacific plate toward the north or northwest. The KODOS area belongs to the latitudinal transition zone having depositional characteristics between non-fossiliferous pelagic clay-dominated zone and calcareous sediment-dominated zone. The box core sediments of the KODOS area are analyzed in an attempt to obtain magnetic hysteresis information and to elucidate the relationship between hysteresis property and lithological facies. Variations in magnetic hysteresis parameters with unit layers reflect the magnetic grain-size and concentrations within the sediments. The ratios of remanant coercivity/coercive force (Hcr/Hc) and saturation remnance/saturation magnetization (Mrs/Ms) indicate that coarse magnetic grains are mainly distributed in dark brown sediments (lower part of the sediment core samples) reflecting high Hcr/Hc and low Mrs/Ms ratios. These results are mainly caused by dissolution differences with core depth. From the plotting of the ratios of hyteresis parameters, it is indicated that magnetic minerals in cubic samples are in pseudo-single domain (PSD) state.

Anaerobic methane oxidation coupled to denitrification is the dominant methane sink in a deep lake

PubMed Central

Deutzmann, Joerg S.; Stief, Peter; Brandes, Josephin; Schink, Bernhard

2014-01-01

Anaerobic methane oxidation coupled to denitrification, also known as “nitrate/nitrite-dependent anaerobic methane oxidation” (n-damo), was discovered in 2006. Since then, only a few studies have identified this process and the associated microorganisms in natural environments. In aquatic sediments, the close proximity of oxygen- and nitrate-consumption zones can mask n-damo as aerobic methane oxidation. We therefore investigated the vertical distribution and the abundance of denitrifying methanotrophs related to Candidatus Methylomirabilis oxyfera with cultivation-independent molecular techniques in the sediments of Lake Constance. Additionally, the vertical distribution of methane oxidation and nitrate consumption zones was inferred from high-resolution microsensor profiles in undisturbed sediment cores. M. oxyfera-like bacteria were virtually absent at shallow-water sites (littoral sediment) and were very abundant at deep-water sites (profundal sediment). In profundal sediment, the vertical distribution of M. oxyfera-like bacteria showed a distinct peak in anoxic layers that coincided with the zone of methane oxidation and nitrate consumption, a strong indication for n-damo carried out by M. oxyfera-like bacteria. Both potential n-damo rates calculated from cell densities (660–4,890 µmol CH4⋅m−2⋅d−1) and actual rates calculated from microsensor profiles (31–437 µmol CH4⋅m−2⋅d−1) were sufficiently high to prevent methane release from profundal sediment solely by this process. Additionally, when nitrate was added to sediment cores exposed to anoxic conditions, the n-damo zone reestablished well below the sediment surface, completely preventing methane release from the sediment. We conclude that the previously overlooked n-damo process can be the major methane sink in stable freshwater environments if nitrate is available in anoxic zones. PMID:25472842

Anaerobic methane oxidation coupled to denitrification is the dominant methane sink in a deep lake.

PubMed

Deutzmann, Joerg S; Stief, Peter; Brandes, Josephin; Schink, Bernhard

2014-12-23

Anaerobic methane oxidation coupled to denitrification, also known as "nitrate/nitrite-dependent anaerobic methane oxidation" (n-damo), was discovered in 2006. Since then, only a few studies have identified this process and the associated microorganisms in natural environments. In aquatic sediments, the close proximity of oxygen- and nitrate-consumption zones can mask n-damo as aerobic methane oxidation. We therefore investigated the vertical distribution and the abundance of denitrifying methanotrophs related to Candidatus Methylomirabilis oxyfera with cultivation-independent molecular techniques in the sediments of Lake Constance. Additionally, the vertical distribution of methane oxidation and nitrate consumption zones was inferred from high-resolution microsensor profiles in undisturbed sediment cores. M. oxyfera-like bacteria were virtually absent at shallow-water sites (littoral sediment) and were very abundant at deep-water sites (profundal sediment). In profundal sediment, the vertical distribution of M. oxyfera-like bacteria showed a distinct peak in anoxic layers that coincided with the zone of methane oxidation and nitrate consumption, a strong indication for n-damo carried out by M. oxyfera-like bacteria. Both potential n-damo rates calculated from cell densities (660-4,890 µmol CH4⋅m(-2)⋅d(-1)) and actual rates calculated from microsensor profiles (31-437 µmol CH4⋅m(-2)⋅d(-1)) were sufficiently high to prevent methane release from profundal sediment solely by this process. Additionally, when nitrate was added to sediment cores exposed to anoxic conditions, the n-damo zone reestablished well below the sediment surface, completely preventing methane release from the sediment. We conclude that the previously overlooked n-damo process can be the major methane sink in stable freshwater environments if nitrate is available in anoxic zones.

Environmental and engineering effects of sinkholes - the processes behind the problems

DOE Office of Scientific and Technical Information (OSTI.GOV)

Beck, B.F.

1988-10-01

Karstic erosion of the land surface is controlled by processes occurring in the epikarstic zone-the upper portion of the limestone which is most intensely dissolved. Sinkholes developing today are generally the effects of downward movement of mantling sediment into the major karren shafts which drain the epikarstic zone deeper into the true karstic aquifer. Dissolution of the limestone itself does not cause significant changes in man's time frame. The downward erosion of mantling sediment is termed ravelling. Only in uniform sediment will an arched cavity occur. In unconsolidated sediment which is stratified, lateral tunneling may even occur. Only the majormore » karren can transmit sediment downward, the majority are ineffective. In mantled karst the location of surficial depressions and photo-linears does not necessarily correlate to areas of new collapse. The irregular and highly dissolved character of the epikarstic zone complicates foundation engineering. Downward drainage through this zone may be limited and cause flooding. An understanding of processes in the epikarstic zone is essential in developing on karst.« less

Nitrogen fluxes across hydrogeomorphic zones in coastal deltaic floodplain using flow-through technique

NASA Astrophysics Data System (ADS)

Li, S.; Twilley, R.; Christensen, A.

2017-12-01

Coastal floodplain deltas are the region of continental margins of major river basins that can remove excess nitrogen before entering the coastal ocean. We propose that the processing of nitrogen in active deltaic wetlands varies with soil organic content in response to different hydrogeomorphic zones. Continuous flow-through core system was used to incubate sediment cores from supratidal, intertidal, and subtidal hydrogeomorphic zones along a chronosequence in Wax Lake Delta during summer of 2017. Ambient water from Wax Lake Outlet was continuously pumped through sealed cores to estimate fluxes of inorganic nitrogen and phosphorus across the sediment-water interface by calculating the difference between inflow and outflow concentrations. The average respiration rate of sediment cores from intertidal zone was about 1.5 g m-2 d-1 while the rate in supratidal zone was more than doubled to 3.7 g m-2 d-1. Under the constant inflow concentration of nitrate (about 107.1 umol/L), sediment cores in supratidal zone exhibited greater NO3- uptake (1329.7 umol m-2 h-1) and N2 release (499.0 umol N m-2 h-1) than that in intertidal zone (421.5 umol m-2 h-1 of NO3- uptake and 67.6 umol N m-2 h-1 of N2 flux respectively). These results indicate greater rate of net denitrification in supratidal zone than intertidal zone in the older chronosequence of the active delta (which formed approximately in 1980). Also, lower NH4 flux (mean 70.0 umol m-2 h-1) from sediment to water column in supratidal zone together with higher NO2- flux (mean 94.2 umol m-2 h-1) illustrated strong signal of nitrification. In conclusion, sediment cores at the intertidal zone helped to remove 12% of NO3- from the water column while cores at supratidal zone removed 35% of NO3-. Based on the correlation between NO3- and N2 fluxes, about 60% of NO3- removed could be converted to N2 under sediment organic concentrations of about 12%. Comparisons of NO3 removal and conversion to N2 by denitrification will be compared along the chronosequence to test the effects of shifts from mineral to organic soils as active deltas develop at the mouths of major river basins.

Conservation of the plastid sedimentation zone in all moss genera with known gravitropic protonemata

NASA Technical Reports Server (NTRS)

Schwuchow, J. M.; Kern, V. D.; White, N. J.; Sack, F. D.

2002-01-01

Moss protonemata from several species are known to be gravitropic. The characterization of additional gravitropic species would be valuable to identify conserved traits that may relate to the mechanism of gravitropism. In this study, four new species were found to have gravitropic protonemata, Fissidens adianthoides, Fissidens cristatus, Physcomitrium pyriforme, and Barbula unguiculata. Comparison of upright and inverted apical cells of P. pyriforme and Fissidens species showed clear axial sedimentation. This sedimentation is highly regulated and not solely dependent on amyloplast size. Additionally, the protonemal tip cells of these species contained broad subapical zones that displayed lateral amyloplast sedimentation. The conservation of a zone of lateral sedimentation in a total of nine gravitropic moss species from five different orders supports the idea that this sedimentation serves a specialized and conserved function in gravitropism, probably in gravity sensing.

Trends in the distribution of recent foraminifera in San Francisco Bay

USGS Publications Warehouse

Arnal, R.E.; Quinterno, P.J.; Conomos, T.J.; Gram, Ralph

1980-01-01

Thirty-one species of benthonic foraminifera were identified in surficial sediments of San Francisco Bay estuary; of these, 20 species were stained red by rose Bengal and are considered as live. Water depth, sediment textural characteristics, salinity, organic matter, sediment pH, and biological competition were considered as factors that might affect distribution of foraminifera. Four ecologic zones based on observed trends in the distribution and abundance of several species correlate well with some environmental factors. Four groups based on the Q-mode analysis of frequency counts of foraminiferal assemblages are reasonably similar to the four ecologic zones. These zones, showing restricted depth ranges, are: Inner Coastal Zone, where Elphidium incertum obscurum and Trochammina infiata are prominent; Outer Coastal Zone, dominated by Ammonia beccarii tepida and Elphidium incatum; Deep Bay Zone, where Elphidietla hannai, Elphidium incertum clavatum, Hopkinsina pacifica, and Bolivina spp. appear in abundance; and Deep Channel Zone, where Elphidiella hannai is most abundant. In the Inner Coastal Zone, salinity due to large fluctuations is a limiting factor for many species. Substrate textural characteristics are primary determinants of the distribution of agglutinated foraminifers. The percentage of organic matter in the sediment correlates well with the abundance of Elphidium incertum obscurum, a ubiquitous species in San Francisco Bay. Sediment pH is not critical. Biologic competition can be estimated by comparing the percentage of a species with the number of species present in the assemblage, as shown for Ammonia beccarii tepida and Elphidiella hannai.

Subglacial Depositional Processes in the Port Askaig Formation (Neoproterozoic) of Ireland

NASA Astrophysics Data System (ADS)

Knight, J.

2004-12-01

The Port Askaig Formation was deposited during the Vendian glaciation (c. 650 Ma) and is a range of tillites that outcrop discontinuously from Banffshire (Scotland) to Connemara (Ireland). Sedimentary structures commonly observed include dropstones and sediment drapes, interpreted as deposition from a floating glacial ice shelf in a shallow marginal sea. Other structures, such as intersecting clastic dikes, have been interpreted as evidence for subaerial exposure of the tillite surface. Exposures of the Port Askaig Formation were examined at its Irish type area at Kiltyfanned Lough, County Donegal. Here, homogeneous sandy beds with internal planar bedding structures are separated by laminated fine sand beds which have erosional upper surfaces. The laminated beds are clast-free and individual laminae are laterally continuous and undisturbed. Larger clasts lie bed-parallel and are draped by overlying beds. Occasionally drapes are asymmetric with a thickened sediment prow, suggestive of flow direction. The clastic dikes are polygonal in plan view, may be isolated or interconnected, and are often arranged in parallel sheets which pinch out laterally. Internally, the clastic dikes are infilled with coarse sand to gravel. Infills are often aligned parallel to dike margins. The presence of draped and deformed sediments suggest a subglacial environment with free water availability. The flat-lying morphology of clasts also favours a subglacial rather than a full marine environment. The morphology and disposition of clastic dikes is interpreted as due to subglacial hydrofracturing of a till sheet and upward passage of sediment-charged water through the fracture zone, which is known from late Pleistocene and Precambrian tillites elsewhere. Variations in water availability can be reconciled by a sub-ice shelf depositional model with spatial and temporal changes in tidally-induced ice-bed coupling.

Faulting of gas-hydrate-bearing marine sediments - contribution to permeability

USGS Publications Warehouse

Dillon, William P.; Holbrook, W.S.; Drury, Rebecca; Gettrust, Joseph; Hutchinson, Deborah; Booth, James; Taylor, Michael

1997-01-01

Extensive faulting is observed in sediments containing high concentrations of methane hydrate off the southeastern coast of the United States. Faults that break the sea floor show evidence of both extension and shortening; mud diapirs are also present. The zone of recent faulting apparently extends from the ocean floor down to the base of gas-hydrate stability. We infer that the faulting resulted from excess pore pressure in gas trapped beneath the gas hydrate-beating layer and/or weakening and mobilization of sediments in the region just below the gas-hydrate stability zone. In addition to the zone of surface faults, we identified two buried zones of faulting, that may have similar origins. Subsurface faulted zones appear to act as gas traps.

Differences in the Composition of Archaeal Communities in Sediments from Contrasting Zones of Lake Taihu

PubMed Central

Fan, Xianfang; Xing, Peng

2016-01-01

In shallow lakes, different primary producers might impact the physiochemical characteristics of the sediment and the associated microbial communities. Until now, little was known about the features of sediment Archaea and their variation across different primary producer-dominated ecosystems. Lake Taihu provides a suitable study area with cyanobacteria- and macrophyte-dominated zones co-occurring in one ecosystem. The composition of the sediment archaeal community was assessed using 16S rRNA gene amplicon sequencing technology, based on which the potential variation with respect to the physiochemical characteristics of the sediment was analyzed. Euryarchaeota (30.19% of total archaeal sequences) and Bathyarchaeota (28.00%) were the two most abundant phyla, followed by Crenarchaeota (11.37%), Aigarchaeota (10.24%) and Thaumarchaeota (5.98%). The differences found in the composition of the archaeal communities between the two zones was significant (p = 0.005). Sediment from macrophyte-dominated zones had high TOC and TN content and an abundance of archaeal lineages potentially involved in the degradation of complex organic compounds, such as the order Thermoplasmatales. In the area dominated by Cyanobacteria, archaeal lineages related to sulfur metabolism, for example, Sulfolobales and Desulfurococcales, were significantly enriched. Among Bathyarchaeota, subgroups MCG-6 and MCG-15 were significantly accumulated in the sediment of areas dominated by macrophytes whereas MCG-4 was consistently dominant in both type of sediments. The present study contributes to the knowledge of sediment archaeal communities with different primary producers and their possible biogeochemical functions in sediment habitats. PMID:27708641

Retardation and Sedimentation of Chernobyl-derived Radiocesium in the Photic Zone Sedimenttrap Deployment Studies in the Norwegian Sea

NASA Astrophysics Data System (ADS)

Baumann, Marion

One long-term and three short-term sedimenttrap-deployments have been installed in the Norwegian Sea shortly after the reactor-accident at Chernobyl in April 1986. Radiocesium investigations of the sedimenttrap material were combined with detailed biological investigations on sedimentation processes in the photic Zone. Lacking efficient export processes in the photic Zone, radiocesium first was retained in the photic Zone for several weeks. Then the break down and successive sedimentation of the heterotrophic community exported about 10 % of surface deposition of radiocesium to larger water depths and to the seafloor at 1450 m.

Size matters: The effects of displacement magnitude on the fluid flow properties of faults in poorly lithified sediments

NASA Astrophysics Data System (ADS)

Loveless, S. E.; Bense, V.; Turner, J.

2011-12-01

Many aquifers worldwide occur in poorly lithified sediments, often in regions that experience active tectonic deformation. Faulting of these sediments introduces heterogeneities that may affect aquifer porosity and permeability, and consequently subsurface fluid flow and groundwater storage. The specific hydrogeological effects of faults depend upon the fault architecture and deformation mechanisms. These are controlled by factors such as rheology, stratigraphy and burial depth. Here, we analyse fault permeability in poorly lithified sediments as a function of fault displacement. We have carried out detailed outcrop studies of minor normal faults at five study sites within the rapidly extending Corinth rift, Central Greece. Gravel conglomerates of giant Gilbert delta facies form productive but localised shallow aquifers within the region. Exposures reveal dense (average 20 faults per 100 m) networks of minor (0.1 to 50 m displacement) normal faults within the uplifted sequences, proximal to many of the crustal-scale normal faults. Analysis of 42 faults shows that fault zones are primarily composed of smeared beds that can either retain their definition or mix with surrounding sediment. Lenses or blocks of sediment are common in fault zones that cut beds with contrasting rheology, and a few faults have a clay core and/or damage zone. Fault thickness increases at a rate of about 0.4 m per 10 m increase in displacement. Comparison of sediment micro-structures from the field, hand samples and thin sections show grain-scale sediment mixing, fracturing of clasts, and in some cases cementation, within fault zones. In faults with displacements >12 m we also find a number of roughly parallel, highly indurated shear planes, up to 20 mm in thickness, composed of highly fragmented clasts and a fine grained matrix. Image analysis of thin sections from hand samples collected in the field was used to quantify the porosity of fault zones and adjacent undeformed sediment. These data show a reduction in average porosity from 21% (± 4) in undisturbed sediments to 14% (± 8) within fault zones. We find that fault zone porosity decreases by approximately 5% per 1 m displacement (up to 2 m displacement), as sediments undergo greater micro-scale deformation. Porosity within the shear planes of larger displacement faults (> 12 m) is significantly less than 5%. In summary, with an increase in fault displacement there is an increase in fault thickness and decrease in fault zone porosity, in addition to the occurrence of extremely low porosity shear planes. Consequently, the impact of faults in poorly lithified sediment on fluid flow is, to a large degree, dependent upon the magnitude of fault displacement.

On the ecogeomorphological feedbacks that control tidal channel network evolution in a sandy mangrove setting

PubMed Central

van Maanen, B.; Coco, G.; Bryan, K. R.

2015-01-01

An ecomorphodynamic model was developed to study how Avicennia marina mangroves influence channel network evolution in sandy tidal embayments. The model accounts for the effects of mangrove trees on tidal flow patterns and sediment dynamics. Mangrove growth is in turn controlled by hydrodynamic conditions. The presence of mangroves was found to enhance the initiation and branching of tidal channels, partly because the extra flow resistance in mangrove forests favours flow concentration, and thus sediment erosion in between vegetated areas. The enhanced branching of channels is also the result of a vegetation-induced increase in erosion threshold. On the other hand, this reduction in bed erodibility, together with the soil expansion driven by organic matter production, reduces the landward expansion of channels. The ongoing accretion in mangrove forests ultimately drives a reduction in tidal prism and an overall retreat of the channel network. During sea-level rise, mangroves can potentially enhance the ability of the soil surface to maintain an elevation within the upper portion of the intertidal zone, while hindering both the branching and headward erosion of the landward expanding channels. The modelling results presented here indicate the critical control exerted by ecogeomorphological interactions in driving landscape evolution. PMID:26339195

78 FR 60218 - Safety Zone; Old Mormon Slough, Stockton, CA

Federal Register 2010, 2011, 2012, 2013, 2014

2013-10-01

... decontaminate soil, groundwater, and sediment in Old Mormon Slough and the surrounding basin. This safety zone... safety zone in Old Mormon Slough to further the efforts of the EPA to rehabilitate soil, sediment, and... water collection ponds. The unlined oily waste ponds were closed in 1981. Sampling has shown that soils...

Amyloplasts as possible statoliths in gravitropic protonemata of the moss Ceratodon purpureus

NASA Technical Reports Server (NTRS)

Walker, L. M.; Sack, F. D.

1990-01-01

The kinetics of gravitropism and of amyloplast sedimentation were studied in dark-grown protonemata of the moss Ceratodon purpureus (Hedw.) Brid. The protonemata grew straight up at a rate of 20-25 micromoles h-1 in nutrient-supplemented agar. After they were oriented to the horizontal, upward curvature was first detected after 1-1.5 h and reached 84 degrees by 24 h. The tip cells exhibited an amyloplast zonation, with a tip cluster of non-sedimenting amyloplasts, an amyloplast-free zone, and a zone with pronounced amyloplast sedimentation. This latter zone appears specialized more for lateral than for axial sedimentation since amyloplasts sediment to the lower wall in horizontal protonemata but do not fall to the basal wall in vertical protonemata. Amyloplast sedimentation started within 15 min of gravistimulation; this is within the 12-17-min presentation time. The data support the hypothesis that some amyloplasts function as statoliths in these cells.

Occurrence and distribution of Vibrio vulnificus and Vibrio parahaemolyticus--potential roles for fish, oyster, sediment and water.

PubMed

Givens, C E; Bowers, J C; DePaola, A; Hollibaugh, J T; Jones, J L

2014-06-01

Vibrio vulnificus and Vibrio parahaemolyticus are Gram-negative marine bacteria naturally found in estuaries such as the Gulf of Mexico and can be pathogenic to humans. We quantified both of these organisms in fish, oyster, sediment, and water using culture-independent (quantitative PCR; qPCR) and culture-dependent (direct plating-colony hybridization; DP-CH) techniques during the transition period between winter and spring. We correlated these levels to environmental conditions and to abundance of total bacteria and total vibrio. By qPCR, fish intestine samples had the highest V. vulnificus densities and were 2·7, 3·5, and 4·2 logs greater than oyster, sediment and water samples, respectively. Densities of V. parahaemolyticus in fish samples by qPCR were 1·0, 2·1, and 3·1 logs greater than oyster, sediment and water samples, respectively. Similar differences between sample types were also observed by DP-CH. The difference between the more favourable and less favourable environmental conditions identified in this study was small (mean salinity 4·3 vs. 13 ppt). However, V. vulnificus and V. parahaemolyticus were consistently detected in fish intestines, but infrequently detected and at lower levels in oysters and during the less favourable period. This trend was observed by qPCR and DP-CH, indicating fish intestines are a significant source of pathogenic vibrios in the environment. This is the first study to report the densities of Bacteria 16S rRNA, Vibrio 16S rRNA, Vibrio vulnificus, and V. parahaemolyticus in fish intestine, oyster, sediment and water samples, as well as compare these values through culture-dependent and culture-independent methodology. Vibrio vulnificus and V. parahaemolyticus were detected in samples of fish intestines by qPCR and colony hybridization when conditions were less favourable for their occurrence in the environment. In contrast, V. vulnificus and V. parahaemolyticus were infrequently detected and at lower levels in other niches examined. These results indicate that fish intestinal tracts are a significant source of these pathogens. © 2014 Society for Applied Microbiology. This article has been contributed to by US Government employees and their work is in the public domain in the US.

Field Observations of Swash-Zone Dynamics on a Sea-Breeze Dominated Beach at the Yucatán Peninsula, México

NASA Astrophysics Data System (ADS)

Chardon-Maldonado, P.; Puleo, J. A.; Torres-Freyermuth, A.

2016-02-01

Sea breezes can modify the nearshore processes and alter beach morphology depending on the geographical location. Prior studies have shown that surf zone wave energy intensifies during strong sea-breeze conditions (wind speeds > 10 ms-1) and the impact on the coast can be similar to a small storm. However, few research efforts have investigated the coastal dynamics on sea-breeze dominated beaches (e.g., Masselink and Pattiaratchi, 1998, Mar. Geol.; Pattiaratchi et al., 1997, Cont. Shelf Res.) and, to the authors' knowledge, only one study has focused on swash-zone processes (Sonu et al., 1973, EOS). A field study was performed on a microtidal, low wave energy, sea-breeze dominated sandy beach in order to investigate the effects of local (sea breeze) and synoptic (storm) scale meteorological events on swash-zone dynamics. In-situ measurements of swash-zone hydrodynamics and sediment transport processes were collected from March 31st to April 12th, 2014 in Sisal, Yucatán located on the northern coast of the Yucatán Peninsula. Flow velocities and suspended sediment concentrations were measured concurrently, at multiple cross-shore and alongshore locations, using Vectrino-II profiling velocimeters and optical backscatter sensors, respectively. The high resolution data allowed the quantification of bed shear stress, turbulent dissipation rate, sediment loads and sediment flux during a mesoscale frontal system (cold-front passage referred to as an El Norte) and local sea-breeze cycles. Field observations showed that strong swash-zone bed shear stresses, turbulence intensity and sediment suspension occur during energetic conditions (i.e., El Norte event). On the other hand, despite milder energy conditions during the sea-breeze events, the alongshore component of bed-shear stresses and velocities can be significant owing to the high incidence wave angle associated with the sea-breeze system in the study area. The increased forcing in the swash zone induced sediment suspension, eroding the foreshore and causing accretion in the surf zone. The preliminary analysis demonstrates that strong sea-breeze events induce a significant alongshore swash-zone sediment transport that may be more important than that observed during an El Norte event.

Potential geologic hazards on the eastern Gulf of Cadiz slope (SW Spain)

USGS Publications Warehouse

Baraza, J.; Ercilla, G.; Nelson, C.H.

1999-01-01

Geologic hazards resulting from sedimentary, oceanographic and tectonic processes affect more than one third of the offshore Gulf of Cadiz, and are identified by interpreting high-resolution seismic profiles and sonographs. Hazards of sedimentary origin include the occurrence of slope instability processes in the form of single or multiple slumps occupying up to 147 km2 mainly concentrated in the steeper, upper slope area. Besides the presence of steep slopes, the triggering of submarine landslides is probably due to seismic activity and favoured by the presence of biogenic gas within the sediment. Gassy sediments and associated seafloor pockmarks cover more than 240 km2 in the upper slope. Hazards from oceanographic processes result from the complex system of bottom currents created by the interaction of the strong Mediterranean Undercurrent and the rough seafloor physiography. The local intensification of bottom currents is responsible for erosive processes along more than 1900 km2 in the upper slope and in the canyons eroded in the central area of the slope, undermining slopes and causing instability. The strong bottom currents also create a mobile seafloor containing bedforms in an area of the Gulf that extends more than 2500 km2, mostly in the continental slope terraces. Hazards of tectonic origin are important because the Gulf of Cadiz straddles two major tectonic regions, the Azores-Gibraltar fracture zone and the Betic range, which results in diapir uplift over an area of more than 1000 km2, and in active seismicity with earthquakes of moderate magnitude. Also, tsunamis produced by strong earthquakes occur in the Gulf of Cadiz, and are related to the tectonic activity along the Azores-Gibraltar fracture zone.

Determining soil erosion from roads in coastal plain of Alabama

Treesearch

McFero Grace; W.J. Elliot

2008-01-01

This paper reports soil losses and observed sediment deposition for 16 randomly selected forest road sections in the National Forests of Alabama. Visible sediment deposition zones were tracked along the stormwater flow path to the most remote location as a means of quantifying soil loss from road sections. Volumes of sediment in deposition zones were determined by...

Sediment trapping by streamside management zones of various widths after forest harvest and site preparation

Treesearch

William Lakel; Wallace Aust; M. Aust; Chad Bolding; C. Dolloff; Patrick Keyser; Robert Feldt

2010-01-01

Recommended widths for streamside management zones (SMZs) for sediment protection vary. The objectives of this study were to compare the effects of SMZ widths and thinning levels on sediment moving through SMZs. Four SMZ treatments were installed within 16 harvested watersheds where intermittent streams graded into small perennial streams. Sites were clearcut,...

Sediment Flux of Particulate Organic Phosphorus in the Open Black Sea

NASA Astrophysics Data System (ADS)

Parkhomenko, A. V.; Kukushkin, A. S.

2018-03-01

The interannual variation of the monthly average (weighted average) concentrations of particulate organic phosphorus (PPOM) in the photosynthetic layer, oxycline, redox zone, and H2S zone in the open Black Sea is estimated based on long-term observation data. The suspension sedimentation rates from the studied layers are assessed using model calculations and published data. The annual variation of PPOM sediment fluxes from the photosynthetic layer, oxycline, redox zone, and upper H2S zone to the anaerobic zone of the sea and the correspondingly annual average values are estimated for the first time. A regular decrease in the PPOM annual average flux with depth in the upper active layer is demonstrated. A correlation between the annual average values of PPOM sediment flux from the photosynthetic layer and ascending phosphate flux to this layer is shown, which suggests their balance in the open sea. The results are discussed in terms of the phosphorus biogeochemical cycle and the concept of new and regenerative primary production in the open Black Sea.

Determining earthquake recurrence intervals from deformational structures in young lacustrine sediments

USGS Publications Warehouse

Sims, John D.

1975-01-01

Examination of the silty sediments in the lower Van Normal reservoir after the 1971 San Fernando, California earthquake revealed three zones of deformational structures in the 1-m-thick sequence of sediments exposed over about 2 km2 of the reservoir bottom. These zones are correlated with moderate earthquakes that shook the San Fernando area in 1930, 1952, and 1971. The success of this study, coupled with the experimental formation of deformational structures similar to those of the Van Norman reservoir, led to a search for similar structures in Pleistocene and Holocene lakes and lake sediments in other seismically active areas. Thus, studies have been started in Pleistocene and Holocene silty and sandy lake sediments in the Imperial Valley, southeastern California; Clear Lake, in northern California; and the Puget Sound area of Washington. The Imperial Valley study has yielded spectacular results: five zones of structures in the upper 10 m of Late Holocene sediments near Brawley have been correlated over an area of approximately 100 km2, using natural outcrops. These structures are similar to those of the Van Norman reservoir and are interpreted to represent at least five moderate to large earthquakes that affected the southern Imperial Valley area during Late Holocene time. The Clear Lake study has provided ambiguous results with respect to determination of earthquake recurrence intervals because the cores studied are in clayey rich in organic material sediments that have low liquefaction potential. A study of Late Pleistocene varved glacio-lacustrine sediments has been started in the Puget Sound area of Washington, and thirteen sites have been examined. One has yielded 18.75 m of sediments that contains 1,804 varves and fourteen deformed zones interpreted as being caused by earthquake, because they are identical to structures formed experimentally by simulated seismic shaking. Correlation of deformational structures with seismic events is based on:(1) proximity to presently active seismic zones;(2) presence of potentially liquefiable sediments;(3) similarity to structures formed experimentally;(4) small-scale internal structures within deformed zones that suggest liquefaction;(5) structures restricted to single stratigraphic intervals;(6) zones of structures correlatable over large areas; and(7) absence of detectable influence by slopes, slope failures, or other sedimentological, biological, or deformational processes.

Effect of logging on streamflow, sedimentation, and fish habitat

Treesearch

Robert R. Ziemer

1968-01-01

Cooperative Watershed Management research in the Lower Conifer Zone of California started in 1961. Research in the Lower Conifer Zone was designed to obtain information and develop principles about the effect of land management in the Zone upon water quality, floods and sedimentation, water timing, and water yield. The research was conducted by the Pacific Southwest...

Spatial variation of sediment mineralization supports differential CO2 emissions from a tropical hydroelectric reservoir.

PubMed

Cardoso, Simone J; Vidal, Luciana O; Mendonça, Raquel F; Tranvik, Lars J; Sobek, Sebastian; Fábio, Roland

2013-01-01

Substantial amounts of organic matter (OM) from terrestrial ecosystems are buried as sediments in inland waters. It is still unclear to what extent this OM constitutes a sink of carbon, and how much of it is returned to the atmosphere upon mineralization to carbon dioxide (CO2). The construction of reservoirs affects the carbon cycle by increasing OM sedimentation at the regional scale. In this study we determine the OM mineralization in the sediment of three zones (river, transition, and dam) of a tropical hydroelectric reservoir in Brazil as well as identify the composition of the carbon pool available for mineralization. We measured sediment organic carbon mineralization rates and related them to the composition of the OM, bacterial abundance and pCO2 of the surface water of the reservoir. Terrestrial OM was an important substrate for the mineralization. In the river and transition zones most of the OM was allochthonous (56 and 48%, respectively) while the dam zone had the lowest allochthonous contribution (7%). The highest mineralization rates were found in the transition zone (154.80 ± 33.50 mg C m(-) (2) d(-) (1)) and the lowest in the dam (51.60 ± 26.80 mg C m(-) (2) d(-) (1)). Moreover, mineralization rates were significantly related to bacterial abundance (r (2) = 0.50, p < 0.001) and pCO2 in the surface water of the reservoir (r (2) = 0.73, p < 0.001). The results indicate that allochthonous OM has different contributions to sediment mineralization in the three zones of the reservoir. Further, the sediment mineralization, mediated by heterotrophic bacteria metabolism, significantly contributes to CO2 supersaturation in the water column, resulting in higher pCO2 in the river and transition zones in comparison with the dam zone, affecting greenhouse gas emission estimations from hydroelectric reservoirs.

Generalized mathematical model of red muds’ thickener of alumina production

NASA Astrophysics Data System (ADS)

Fedorova, E. R.; Vinogradova, A. A.

2018-03-01

The article describes the principle of a generalized mathematical model of the red mud’s thickener construction. The model of the red muds’ thickener of alumina production consists of sub-models of flocculation zones containing solid fraction feed slurry, free-fall and cramped sedimentation zones or effective sedimentation zones, bleaching zones. The generalized mathematical model of thickener allows predicting the content of solid fraction in the condensed product and in the upper discharge. The sub-model of solid phase aggregation allows one to count up average size of floccules, which is created during the flocculation process in feedwell. The sub-model of the free-fall and cramped sedimentation zone allows one to count up the concentration profile taking into account the variable cross-sectional area of the thickener. The sub-model of the bleaching zone is constructed on the basis of the theory of the precipitation of Kinc, supplemented by correction factors.

In-situ Observations of Swash-zone Flow Velocities and Sediment Transport on a Steep Beach

NASA Astrophysics Data System (ADS)

Chardon-Maldonado, P.; Puleo, J. A.; Figlus, J.

2014-12-01

A 45 m scaffolding frame containing an array of instruments was installed at South Bethany Beach, Delaware, to obtain in-situ measurements in the swash zone. Six cross-shore stations were established to simultaneously measure near-bed velocity profiles, sediment concentration and water level fluctuations on a steep beach. Measurements of swash-zone hydrodynamics and morphological change were collected from February 12 to 25, 2014, following a large Nor'easter storm with surf zone significant wave height exceeding 5 m. Swash-zone flow velocities (u,v,w) were measured at each cross-shore location using a Nortek Vectrino profiling velocimeter that measured a 30 mm velocity profile at 1 mm vertical increments at 100 Hz. These velocity profiles were used to quantify the vertical flow structure over the foreshore and estimate hydrodynamic parameters such as bed shear stress and turbulent kinetic energy dissipation. Sediment concentrations were measured using optical backscatter sensors (OBS) to obtain spatio-temporal measurements during both uprush and backwash phases of the swash cycle. Cross-shore sediment transport rates at each station were estimated by taking the product of cross-shore velocity and sediment concentration. Foreshore elevations were sampled every low tide using a Leica GPS system with RTK capability. Cross-shore sediment transport rates and gradients derived from the velocities and bed shear stress estimates will be related to the observed morphological change.

Enhanced cellular preservation by clay minerals in 1 billion-year-old lakes.

PubMed

Wacey, David; Saunders, Martin; Roberts, Malcolm; Menon, Sarath; Green, Leonard; Kong, Charlie; Culwick, Timothy; Strother, Paul; Brasier, Martin D

2014-07-28

Organic-walled microfossils provide the best insights into the composition and evolution of the biosphere through the first 80 percent of Earth history. The mechanism of microfossil preservation affects the quality of biological information retained and informs understanding of early Earth palaeo-environments. We here show that 1 billion-year-old microfossils from the non-marine Torridon Group are remarkably preserved by a combination of clay minerals and phosphate, with clay minerals providing the highest fidelity of preservation. Fe-rich clay mostly occurs in narrow zones in contact with cellular material and is interpreted as an early microbially-mediated phase enclosing and replacing the most labile biological material. K-rich clay occurs within and exterior to cell envelopes, forming where the supply of Fe had been exhausted. Clay minerals inter-finger with calcium phosphate that co-precipitated with the clays in the sub-oxic zone of the lake sediments. This type of preservation was favoured in sulfate-poor environments where Fe-silicate precipitation could outcompete Fe-sulfide formation. This work shows that clay minerals can provide an exceptionally high fidelity of microfossil preservation and extends the known geological range of this fossilization style by almost 500 Ma. It also suggests that the best-preserved microfossils of this time may be found in low-sulfate environments.

Enhanced cellular preservation by clay minerals in 1 billion-year-old lakes

PubMed Central

Wacey, David; Saunders, Martin; Roberts, Malcolm; Menon, Sarath; Green, Leonard; Kong, Charlie; Culwick, Timothy; Strother, Paul; Brasier, Martin D.

2014-01-01

Organic-walled microfossils provide the best insights into the composition and evolution of the biosphere through the first 80 percent of Earth history. The mechanism of microfossil preservation affects the quality of biological information retained and informs understanding of early Earth palaeo-environments. We here show that 1 billion-year-old microfossils from the non-marine Torridon Group are remarkably preserved by a combination of clay minerals and phosphate, with clay minerals providing the highest fidelity of preservation. Fe-rich clay mostly occurs in narrow zones in contact with cellular material and is interpreted as an early microbially-mediated phase enclosing and replacing the most labile biological material. K-rich clay occurs within and exterior to cell envelopes, forming where the supply of Fe had been exhausted. Clay minerals inter-finger with calcium phosphate that co-precipitated with the clays in the sub-oxic zone of the lake sediments. This type of preservation was favoured in sulfate-poor environments where Fe-silicate precipitation could outcompete Fe-sulfide formation. This work shows that clay minerals can provide an exceptionally high fidelity of microfossil preservation and extends the known geological range of this fossilization style by almost 500 Ma. It also suggests that the best-preserved microfossils of this time may be found in low-sulfate environments. PMID:25068404

Fluidization of host sediments and its impacts on peperites-forming processes, the Cretaceous Buan Volcanics, Korea

NASA Astrophysics Data System (ADS)

Kwon, Chang Woo; Gihm, Yong Sik

2017-07-01

In the Cretaceous Buan Volcanics (SW Korea), blocky and fluidal peperites are developed in a bed of poorly sorted, massive pumiceous lapilli tuff (hot sediments) as a result of the vertical to subvertical intrusion of the trachyandesitic dikes into the bed. Blocky peperites are composed of polyhedral or platy juvenile clasts with a jigsaw-crack texture. Fluidal peperites are characterized by fluidal or globular juvenile clasts with irregular or ragged margins. The blocky peperites are ubiquitous in the host sediments, whereas the fluidal peperites only occur in fine-grained zone (well sorted fine to very fine ash) that are aligned parallel to the dike margin. The development of the fine-grained zone within the poorly sorted host sediments is interpreted to form by grain size segregation caused by upward moving pore water (fluidization) that has resulted from heat transfer from intruding magma toward the waterlogged host sediments during intrusion. With the release of pore water and the selective entrainment of fine-grained ash, the fine-grained zone formed within the host sediments. Subsequent interactions between the fine-grained zone and the intruding magma resulted in ductile deformation of the magma, which generated fluidal peperites. Outside the fine-grained zone, because of the relative deficiency of both pore water and fine-grained ash, intruding magma fragmented in a brittle manner, resulting in the formation of blocky peperites. The results of this study suggest that redistribution of constituent particles (ash) and interstitial fluids during fluidization resulted in heterogeneous physical conditions of the host sediments, which influenced peperite-forming processes.

Molybdenum isotope systematics in subduction zones

NASA Astrophysics Data System (ADS)

König, Stephan; Wille, Martin; Voegelin, Andrea; Schoenberg, Ronny

2016-08-01

This study presents Mo isotope data for arc lavas from different subduction zones that range between δ 98 / 95 Mo = - 0.72 and + 0.07 ‰. Heaviest isotope values are observed for the most slab fluid dominated samples. Isotopically lighter signatures are related to increasing relevance of terrigenous sediment subduction and sediment melt components. Our observation complements previous conclusions that an isotopically heavy Mo fluid flux likely mirrors selective incorporation of isotopically light Mo in secondary minerals within the subducting slab. Analogue to this interpretation, low δ 98 / 95 Mo flux that coincides with terrigenous sediment subduction and sediment melting cannot be simply related to a recycled input signature. Instead, breakdown of the controlling secondary minerals during sediment melting may release the light component and lead to decreasing δ 98 / 95 Mo influx into subarc mantle sources. The natural range between slab dehydration and hydrous sediment melting may thus cause a large spread of δ 98 / 95 Mo in global subduction zone magmas.

Appendix D: Use of wave scenarios to assess potential submerged oil mat (SOM) formation along the coast of Florida and Alabama

USGS Publications Warehouse

Dalyander, P. Soupy; Long, Joseph W.; Plant, Nathaniel G.; Thompson, David M.

2013-01-01

During the Deepwater Horizon oil spill, oil in the surf zone mixed with sediment in the surf zone to form heavier-than-water sediment oil agglomerates of various size, ranging from small (cm-scale) pieces (surface residual balls, SRBs) to large mats (100-m scale, surface residue mats, SR mats). Once SR mats formed in the nearshore or in the intertidal zone, they may have become buried by sand moving onshore or alongshore. To assist in locating possible sites of buried oil, wave scenarios previously developed by the U.S. Geological Survey (USGS) were used to determine the depths at which surface oil had the potential to mix with suspended sediment. For sediment to mix with floating oil and form an agglomerate of sufficient density to sink to the seafloor, either the water must be very shallow (e.g., within the swash zone) or sediment must be suspended to the water surface in sufficient concentrations to create a denser-than-sea water agglomerate. The focus of this study is to analyze suspended sediment mixing with surface oil in depths beyond the swash zone, in order to define the seaward limit of mat formation. A theoretical investigation of sediment dynamics in the nearshore zone revealed that non-breaking waves do not suspend enough sediment to the surface to form sinking sand/oil agglomerates. For this study, it was assumed that the cross-shore distribution of potential agglomerate formation is associated with the primary breaker line, and the presence of plunging breakers, over the time frame of oiling. The potential locations of submerged oil mats (SOMs) are sites where (1) possible agglomerate formation occurred, where (2) sediment accreted post-oiling and buried the SOM, and where (3) the bathymetry has not subsequently eroded to re-expose any mat that may have formed at that site. To facilitate identification of these locations, the range of water level variation over the time frame of oiling was also prescribed, which combined with the wave-breaking depth analysis and pre-oiling bathymetry would identify the potential geographic locations of SOMs.

Rapid Sediment Accumulation Results in High Methane Effluxes from Coastal Sediments

PubMed Central

Lenstra, Wytze; Jong, Dirk; Meysman, Filip J. R.; Sapart, Célia J.; van der Veen, Carina; Röckmann, Thomas; Gonzalez, Santiago; Slomp, Caroline P.

2016-01-01

Globally, the methane (CH4) efflux from the ocean to the atmosphere is small, despite high rates of CH4 production in continental shelf and slope environments. This low efflux results from the biological removal of CH4 through anaerobic oxidation with sulfate in marine sediments. In some settings, however, pore water CH4 is found throughout the sulfate-bearing zone, indicating an apparently inefficient oxidation barrier for CH4. Here we demonstrate that rapid sediment accumulation can explain this limited capacity for CH4 removal in coastal sediments. In a saline coastal reservoir (Lake Grevelingen, The Netherlands), we observed high diffusive CH4 effluxes from the sediment into the overlying water column (0.2–0.8 mol m-2 yr-1) during multiple years. Linear pore water CH4 profiles and the absence of an isotopic enrichment commonly associated with CH4 oxidation in a zone with high rates of sulfate reduction (50–170 nmol cm-3 d-1) both suggest that CH4 is bypassing the zone of sulfate reduction. We propose that the rapid sediment accumulation at this site (~ 13 cm yr-1) reduces the residence time of the CH4 oxidizing microorganisms in the sulfate/methane transition zone (< 5 years), thus making it difficult for these slow growing methanotrophic communities to build-up sufficient biomass to efficiently remove pore water CH4. In addition, our results indicate that the high input of organic matter (~ 91 mol C m-2 yr-1) allows for the co-occurrence of different dissimilatory respiration processes, such as (acetotrophic) methanogenesis and sulfate reduction in the surface sediments by providing abundant substrate. We conclude that anthropogenic eutrophication and rapid sediment accumulation likely increase the release of CH4 from coastal sediments. PMID:27560511

Preliminary estimating the contemporary sedimentation trend in dry valley bottoms of first-order catchments of different landscape zones of the Russian Plain using the 137Cs as a chronomarker

NASA Astrophysics Data System (ADS)

Sharifullin, A.; Gusarov, A.; Gafurov, A.; Essuman-Quainoo, B.

2018-01-01

A general trend of erosion processes over the last 50-60 years can be estimated by dating sediments washed off from arable lands and accumulated in the first-order dry valleys bottoms. Three small (first-order) catchments were chosen as objects of the study. They are located, respectively, in the southern part of the taiga zone, the zone of temperate broad-leaf forests and the forest-steppe zone of the Russian Plain. To date the sediments accumulated in the bottoms the radioactive caesium-137 (137Cs) of global (since 1954) and Chernobyl origin (1986) had been used as a chronomarker. The average (for all the catchments) sedimentation rates during the global 137Cs fallout period (1963(1954)-1986) are at least 0.88-2.71 cm per year.For the period that has passed since the Chernobyl accident (1986-2015(2016)) the average rates were 0.15-1.07 cm per year. The greatest reduction in the sedimentation rates is observed in the subzone of the southern taiga, the lowest one is in the forest-steppe zone of the Russian Plain. The main reason for such significant reduction in the rates of sedimentation of the soil erosion products in the dry valley bottoms was a reduction of surface runoff within the catchments during a snowmelt period, as well as crop-rotation changes there.

Heterogeneous structure of the incoming plate in the Japan Trench

NASA Astrophysics Data System (ADS)

Nakamura, Y.; Fujie, G.; Yamaguchi, A.; Kodaira, S.; Miura, S.

2017-12-01

We have conducted seismic surveys in around the Japan Trench subduction zone, northeastern Japan, to investigate the structural features of the incoming Pacific plate and the frontal prism. Thickness of the hemiplegic sediments on the deposited on the incoming Pacific plate shows the variation along trench axis between 200 and 600 ms two-way travel time (TWT). This is remarkably thinner than other subduction zones with megathrust earthquakes like Sumatra subduction zone. Off Miyagi, central part of the Japan Trench which is the main ruptured region of 2011 Tohoku earthquake, has 200 - 300 ms TWT of the incoming sediments thickness. Off Iwate, northern part of the Japan Trench, has thicker incoming sediments 500 ms TWT, and Off Fukushima, southern part of the Japan Trench, has 300 - 400 ms TWT. We found at least three areas with anomalously thin sediments; Area I: 38N 145N, Area II: 39.5N 144.5E, Area III: 39N 144.5N. At the Area I, located on the outer rise off Miyagi, the receiver function analysis using Ocean Bottom Seismograph data revealed the existence of PS conversion surfaces below the interpreted basement on the seismic sections. This implies that the interface between sediments and the igneous basement is located below the interpreted basement reflections. Previous studies suggested the existence of the petit spots in this Area I. Area II shows apparently very thin sediments near the trench axis on seismic profiles, where the petit spot volcanism was observed. Shallow sediment sampling conducted in this area indicates no major surface erosion. These observations suggest that the petit spot volcanism, like sill intrusion, masked the original deeper basement reflections and caused the apparent thin sediments on seismic profiles. Area III also has thin sediments and rough basement topography, which has possibly been caused by another petit spot activity. Petit spot area with apparent very thin sediments in the trench axis (Area II) is located next to the northern edge of the large slip zone of the 2011 Tohoku earthquake. The volcanic activities like petit spots on the incoming plate introduce heterogeneous input into the subduction zone, which could be important factors to control the megathrust seismo- and tsunamigenesis in the subduction zone.

Prokaryotic functional diversity in different biogeochemical depth zones in tidal sediments of the Severn Estuary, UK, revealed by stable-isotope probing.

PubMed

Webster, Gordon; Rinna, Joachim; Roussel, Erwan G; Fry, John C; Weightman, Andrew J; Parkes, R John

2010-05-01

Stable isotope probing of prokaryotic DNA was used to determine active prokaryotes using (13)C-labelled substrates (glucose, acetate, CO(2)) in sediment slurries from different biogeochemical zones of the Severn Estuary, UK. Multiple, low concentrations (5 x 100 microM) of (13)C-substrate additions and short-term incubations (7 days) were used to minimize changes in the prokaryotic community, while achieving significant (13)C-incorporation. Analysis demonstrated clear metabolic activity within all slurries, although neither the net sulphate removal nor CH(4) production occurred in the anaerobic sulphate reduction and methanogenesis zone slurries. Some similarities occurred in the prokaryotic populations that developed in different sediment slurries, particularly in the aerobic and dysaerobic zone slurries with (13)C-glucose, which were dominated by Gammaproteobacteria and Marine Group 1 Archaea, whereas both anaerobic sediment slurries incubated with (13)C-acetate showed incorporation into Epsilonproteobacteria and other bacteria, with the sulphate reduction zone slurry also showing (13)C-acetate utilization by Miscellaneous Crenarchaeotic Group Archaea. The lower potential energy methanogenesis zone slurries were the only conditions where no (13)C-incorporation into Archaea occurred, despite Bacteria being labelled; this was surprising because Archaea have been suggested to be adapted to low-energy conditions. Overall, our results highlight that uncultured prokaryotes play important ecological roles in tidal sediments of the Severn Estuary, providing new metabolic information for novel groups of Archaea and suggesting broader metabolisms for largely uncultivated Bacteria.

Sequential Sedimentation-Biofiltration System for the purification of a small urban river (the Sokolowka, Lodz) supplied by stormwater.

PubMed

Szklarek, S; Wagner, I; Jurczak, T; Zalewski, M

2018-01-01

The study analyses the efficiency of a Sequentional Sedimentation-Biofiltration System (SSBS) built on the Sokolowka river in Lodz (Poland). It was constructed to purify a small urban river whose hydrological regime is dominated by stormwater and meltwater. The SSBS was constructed on a limited area as multi-zone constructed wetlands. The SSBS consists of three zones: sedimentation zone with structures added to improve sedimentation, a geochemical barrier made of limestone deposit and biofiltration zone. The purification processes of total suspended solids (TSS), total phosphorus (TP), total nitrogen (TP) and other nutrients: phosphates (PO 4 3- ), ammonium (NH 4 + ) and nitrates (NO 3 - ) of the SSBS were analyzed. Chloride (Cl - ) reduction was investigated. Monitoring conducted in the first two hydrological years after construction indicated that the SSBS removed 61.4% of TSS, 37.3% of TP, 30.4% of PO 4 3- , 46.1% of TN, 2.8% of NH4+, 44.8% of NO 3 - and 64.0% of Cl - . The sedimentation zone played a key role in removing TSS and nutrients. The geochemical barrier and biofiltration zone each significantly improved overall efficiency by 4-10% for TSS, PO 4 3- , TN, NO 3 - and Cl - . Although the system reduced the concentration of chloride, further studies are needed to determine the circulation of Cl - in constructed wetlands (CWs), and to assess its impact on purification processes. Copyright © 2017 Elsevier Ltd. All rights reserved.

Use of Polyphosphate to Decrease Uranium Leaching in Hanford 300 Area Smear Zone Sediments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Szecsody, James E.; Zhong, Lirong; Oostrom, Martinus

2012-09-30

The primary objective of this study is to summarize the laboratory investigations performed to evaluate short- and long-term effects of phosphate treatment on uranium leaching from 300 area smear zone sediments. Column studies were used to compare uranium leaching in phosphate-treated to untreated sediments over a year with multiple stop flow events to evaluate longevity of the uranium leaching rate and mass. A secondary objective was to compare polyphosphate injection, polyphosphate/xanthan injection, and polyphosphate infiltration technologies that deliver phosphate to sediment.

Influence of hydropower dams on the composition of the suspended and riverbank sediments in the Danube.

PubMed

Klaver, Gerard; van Os, Bertil; Negrel, Philippe; Petelet-Giraud, Emmanuelle

2007-08-01

Large hydropower dams have major impacts on flow regime, sediment transport and the characteristics of water and sediment in downstream rivers. The Gabcikovo and Iron Gate dams divide the studied Danube transect (rkm 1895-795) into three parts. In the Gabcikovo Reservoir (length of 40km) only a part of the incoming suspended sediments were deposited. Contrary to this, in the much larger Iron Gate backwater zone and reservoir (length of 310km) all riverine suspended sediments were deposited within the reservoir. Subsequently, suspended sediments were transported by tributaries into the Iron Gate backwater zone. Here they were modified by fractional sedimentation before they transgressed downstream via the dams. Compared with undammed Danube sections, Iron Gate reservoir sediment and suspended matter showed higher clay contents and different K/Ga and Metal/Ga ratios. These findings emphasize the importance of reservoir-river sediment-fractionation.

Young inversion with multiple linked QTLs under selection in a hybrid zone.

PubMed

Lee, Cheng-Ruei; Wang, Baosheng; Mojica, Julius P; Mandáková, Terezie; Prasad, Kasavajhala V S K; Goicoechea, Jose Luis; Perera, Nadeesha; Hellsten, Uffe; Hundley, Hope N; Johnson, Jenifer; Grimwood, Jane; Barry, Kerrie; Fairclough, Stephen; Jenkins, Jerry W; Yu, Yeisoo; Kudrna, Dave; Zhang, Jianwei; Talag, Jayson; Golser, Wolfgang; Ghattas, Kathryn; Schranz, M Eric; Wing, Rod; Lysak, Martin A; Schmutz, Jeremy; Rokhsar, Daniel S; Mitchell-Olds, Thomas

2017-04-03

Fixed chromosomal inversions can reduce gene flow and promote speciation in two ways: by suppressing recombination and by carrying locally favoured alleles at multiple loci. However, it is unknown whether favoured mutations slowly accumulate on older inversions or if young inversions spread because they capture pre-existing adaptive quantitative trait loci (QTLs). By genetic mapping, chromosome painting and genome sequencing, we have identified a major inversion controlling ecologically important traits in Boechera stricta. The inversion arose since the last glaciation and subsequently reached local high frequency in a hybrid speciation zone. Furthermore, the inversion shows signs of positive directional selection. To test whether the inversion could have captured existing, linked QTLs, we crossed standard, collinear haplotypes from the hybrid zone and found multiple linked phenology QTLs within the inversion region. These findings provide the first direct evidence that linked, locally adapted QTLs may be captured by young inversions during incipient speciation.

Preliminary Nearshore Sedimentation Rate Analysis of the Tuungane Project Northern Mahale Conservation Area, Lake Tanganyika (Tanzania)

NASA Astrophysics Data System (ADS)

Smiley, R. A.; McGlue, M. M.; Yeager, K. M.; Soreghan, M. J.; Lucas, J.; Kimirei, I.; Mbonde, A.; Limbu, P.; Apse, C.

2017-12-01

The combined effects of climate change, overfishing, and sediment pollution are altering Lake Tanganyika's littoral fisheries in profoundly negative ways. One method for conserving critical fish resources and safeguarding biodiversity in Lake Tanganyika is by establishing small-scale nearshore protected zones, which can be administrated by lakeshore villagers organized into beach management units (BMUs). Each BMU endeavors to manage offshore "no-catch" protected zones, prohibit the use of illegal fishing gear, and promote sustainable agriculture that abates erosion in the lake watershed, in order to mitigate sediment pollution in the lake. We adopted a limnogeological approach to assist in characterizing the littoral zone associated with BMUs in the northern Mahale region of Lake Tanganyika (Tanzania), a critical conservation area for the Nature Conservancy's Tuungane Project (https://www.nature.org/ourinitiatives/regions/africa/wherewework/tuungane-project.xml). We hypothesized that BMUs with heavy onshore agricultural activity would experience relatively high offshore sedimentation rates, due to enhanced sediment-laden runoff in the wet season. Such changes are predicted to alter benthic substrates and degrade habitat available for fish spawning. We mapped bathymetry and sediment types along a 29 km2 area of the littoral zone using high-resolution geophysical tools, and assessed short-term sedimentation rates using sediment cores and radionuclide geochronology (210Pb). Initial results from 210Pb analyses show that sedimentation rates at the mud-line ( 85-100 m water depth) are relatively slow but spatially variable in the northern Mahale area. Offshore of the Kalilani village BMU, linear sedimentation rates are 0.50 mm/yr. By contrast, sedimentation rates offshore from the Igualula village BMU are 0.90-1.30 mm/yr. Higher sedimentation rates near Igualula are consistent with greater sediment inputs from the nearby Lagosa River and its watershed, which has been extensively cultivated for oil palm and cassava. Additional sediment cores from the northern Mahale region are presently being analyzed, and 210Pb data from sediment cores associated with the different BMU areas will shed further light on the impacts of land use change on the littoral fisheries.

Depth Distribution and Assembly of Sulfate-Reducing Microbial Communities in Marine Sediments of Aarhus Bay

PubMed Central

Jochum, Lara M.; Chen, Xihan; Lever, Mark A.; Loy, Alexander; Jørgensen, Bo Barker; Schramm, Andreas

2017-01-01

ABSTRACT Most sulfate-reducing microorganisms (SRMs) present in subsurface marine sediments belong to uncultured groups only distantly related to known SRMs, and it remains unclear how changing geochemical zones and sediment depth influence their community structure. We mapped the community composition and abundance of SRMs by amplicon sequencing and quantifying the dsrB gene, which encodes dissimilatory sulfite reductase subunit beta, in sediment samples covering different vertical geochemical zones ranging from the surface sediment to the deep sulfate-depleted subsurface at four locations in Aarhus Bay, Denmark. SRMs were present in all geochemical zones, including sulfate-depleted methanogenic sediment. The biggest shift in SRM community composition and abundance occurred across the transition from bioturbated surface sediments to nonbioturbated sediments below, where redox fluctuations and the input of fresh organic matter due to macrofaunal activity are absent. SRM abundance correlated with sulfate reduction rates determined for the same sediments. Sulfate availability showed a weaker correlation with SRM abundances and no significant correlation with the composition of the SRM community. The overall SRM species diversity decreased with depth, yet we identified a subset of highly abundant community members that persists across all vertical geochemical zones of all stations. We conclude that subsurface SRM communities assemble by the persistence of members of the surface community and that the transition from the bioturbated surface sediment to the unmixed sediment below is a main site of assembly of the subsurface SRM community. IMPORTANCE Sulfate-reducing microorganisms (SRMs) are key players in the marine carbon and sulfur cycles, especially in coastal sediments, yet little is understood about the environmental factors controlling their depth distribution. Our results suggest that macrofaunal activity is a key driver of SRM abundance and community structure in marine sediments and that a small subset of SRM species of high relative abundance in the subsurface SRM community persists from the sulfate-rich surface sediment to sulfate-depleted methanogenic subsurface sediment. More generally, we conclude that SRM communities inhabiting the subsurface seabed assemble by the selective survival of members of the surface community. PMID:28939599

Influence of land use on hyporheos in catchment of the Jarama River (central Spain)

NASA Astrophysics Data System (ADS)

Iepure, S.; Martínez-Hernández, V.; Herrera, S.; de Bustamante, I.; Rasines, R.

2012-04-01

The Water Framework Directive (2000) requires integrated assessment of water bodies based on water resources but also the evaluation of land-use catchment effect on chemical and ecological conditions of aquatic ecosystems. The hyporheic zone (HZ) supporting obligate subterranean species are particularly vulnerable in river ecosystems when environmental stress occurs at surface and require management strategies to protect both the stream catchment and the aquifer that feed the stream channel. The influence of catchment land-use in the Jarama basin (central Spain) on river geomorphology and hyporheic zone granulometry, chemical and biological variables inferred from crustacean community biodiversity (species richness, taxonomic distinctness) and ecology was assessed. The study was conducted in four streams from the Madrid metropolitan area under distinct local land-use and water resource protection: i) a preserved forested natural sites where critical river ecosystem processes were unaltered or less altered by human activities, and ii) different degree of anthropogenic impact sites from agriculture, urban industrial and mining activities. The river bed permeability reduction and the increase of low sediment size input associated with changes in geomorphology of the stream channels are greatly affected by land-use changes in the Jarama watershed. Water chemical parameters linked to land-use increase from the natural stream to the urban industrial and agricultural dominated catchment. Principal coordinate analysis (PCO) and multidimensional scaling (MDS) clearly discriminate the pristine sites from forested areas by those under anthropogenic stressors. In streams draining forested areas, groundwater discharge and regular exchange between groundwater and surface water occur due to relatively high permeability of the sediments. Consequently, forested land-use produce sites of high water quality and crustacean richness (both groundwater dwellers and surface-benthos species), as indicate the expected diversity pattern after the simulation procedure for taxonomic distinctness. Crustacean diversity (Shannon index) was greatest in less extensive agricultural land-use sites where riparian zone is slightly developed, while intensive agricultural activities cause a decline of water quality and therefore of crustacean richness. Intensively urban industrial land-use yield highly contaminated hyporheic water with heavy metals and VOC (i.e. toluene, benzene). Complementarily, the streams geomorphology and low rates of water flow favour the deposition of fine sediments that clog the interstices, generate a reverse dynamic of river channel and induce a reduction of groundwater discharge. In results, the hyporheic is unsuitable for hyporheos that are missing or harbour reduced populations of exclusively surface-water taxa. There are sites of intermediate biodiversity including hypogeans, located in natural regional parks thriving well-established riparian zone and relatively good water quality. The differences among sites in the Jarama basin indicate the impact that changes in land-use have upon the hyporheic ecology as shown the pattern of crustacean community distribution, diversity and ecological structure. We suggest that in rehabilitation processes of streams sectors require the understanding and recognition of the potential roles of the hyporheic zone and its biota in the whole stream ecosystem.

Holocene paleoecology of an estuary on Santa Rosa Island, California

USGS Publications Warehouse

Cole, K.L.; Liu, Gaisheng

1994-01-01

The middle to late Holocene history and early Anglo-European settlement impacts on Santa Rosa Island, California, were studied through the analysis of sediments in a small estuarine marsh. A 5.4-m-long sediment core produced a stratigraphic and pollen record spanning the last 5200 yr. Three major zones are distinguishable in the core. The lowermost zone (5200 to 3250 yr B.P.) represents a time of arid climate with predominantly marine sediment input and high Chenopodiaceae and Ambrosia pollen values. The intermediate zone (3250 yr B.P. to 1800 A.D.) is characterized by greater fresh water input and high values for Asteraceae and Cyperaceae pollen and charcoal particles. The uppermost zone (1800 A.D. to present) documents the unprecedented erosion, sedimentation, and vegetation change that resulted from the introduction of large exotic herbivores and exotic plants to the island during Anglo-European settlement. The identification of pollen grains of Torrey Pine (Pinus torreyana) documents the persistence of this endemic species on the island throughout the middle to late Holocene.

Analysis of the Sediment Hydrograph of the alluvial deltas in the Apalachicola River, Florida

NASA Astrophysics Data System (ADS)

Daranpob, A.; Hagen, S.; Passeri, D.; Smar, D. E.

2011-12-01

Channel and alluvial characteristics in lowlands are the products of boundary conditions and driving forces. The boundary conditions normally include materials and land cover types, such as soil type and vegetation cover. General driving forces include discharge rate, sediment loadings, tides and waves. Deltas built up of river-transported sediment occur in depositional zones of the river mouth in flat terrains and slow currents. Total sediment load depends on two major abilities of the river, the river shear stress and capacity. The shear stress determines transport of a given sediment grain size, normally expressed as tractive force. The river capacity determines the total load or quantity of total sediments transported across a section of the river, generally expressed as the sediment loading rate. The shear stress and sediment loading rate are relatively easy to measure in the headwater and transfer zones where streams form a v-shape valley and the river begins to form defined banks compared to the deposition zone where rivers broaden across lower elevation landscapes creating alluvial forms such as deltas. Determinations of deposition and re-suspension of sediment in fluvial systems are complicated due to exerting tidal, wind, and wave forces. Cyclic forces of tides and waves repeatedly change the sediment transport and deposition rate spatially and temporally in alluvial fans. However, the influence decreases with water depth. Understanding the transport, deposition, and re-suspension of sediments in the fluvial zone would provide a better understanding of the morphology of landscape in lowland estuaries such as the Apalachicola Bay and its estuary systems. The Apalachicola River system is located in the Florida Panhandle. Shelf sedimentation process is not a strong influence in this region because it is protected by barrier islands from direct ocean forces of the Gulf of Mexico. This research explores the characteristic of suspended sediment loadings in fluvial zones of the Apalachicola River and its distributaries through field investigation and laboratory analysis of a series of total suspended solid (TSS) samples. Time-series TSS samples are collected at the alluvial zone. TSS and particle-size distribution analyses are performed to determine the TSS hydrograph and particle-size distribution of suspended solids. Relationships between the TSS hydrograph, discharge hydrograph, and tidal data provide a better understanding of the deposition and re-suspension of the fluvial system in the region. Total suspended particle-size distribution data are used to determine the deposition rate or diminishing rate of alluvial landform in the estuarine system. This dataset and analysis provide excellent information for future modeling work and wetland morphologic studies in the Apalachicola River and similar systems.

Interaction between shallow groundwater, saline surface water and contaminant discharge at a seasonally and tidally forced estuarine boundary

NASA Astrophysics Data System (ADS)

Westbrook, S. J.; Rayner, J. L.; Davis, G. B.; Clement, T. P.; Bjerg, P. L.; Fisher, S. J.

2005-02-01

This paper presents findings from a 2-year field investigation of a dissolved hydrocarbon groundwater plume flowing towards a tidally and seasonally forced estuarine river system in Perth, Western Australia. Samples collected from transects of multiport wells along the riverbank and into the river, enabled mapping of the fine scale (0.5 m) vertical definition of the hydrocarbon plume and its longitudinal extent. Spear probing beneath the river sediments and water table, and transient monitoring of multiport wells (electrical conductivity) was also carried out to define the zone of mixing between river water and groundwater (the hyporheic zone) and its variability. The results showed that groundwater seepage into the estuarine surface sediments occurred in a zone less than 10 m from the high tide mark, and that this distance and the hyporheic transition zone were influenced by tidal fluctuations and infiltration of river water into the sediments. The dissolved BTEXN (benzene, toluene, ethylbenzene, the xylene isomers and naphthalene) distributions indicated the behaviour of the hydrocarbon plume at the groundwater/surface water transition zone to be strongly influenced by edge-focussed discharge. Monitoring programs and risk assessment studies at similar contaminated sites should therefore focus efforts within the intertidal zone where contaminants are likely to impact the surface water and shallow sediment environments.

Climatic and palaeoceanographic changes during the Pliensbachian (Early Jurassic) inferred from clay mineralogy and stable isotope (C-O) geochemistry (NW Europe)

NASA Astrophysics Data System (ADS)

Bougeault, Cédric; Pellenard, Pierre; Deconinck, Jean-François; Hesselbo, Stephen P.; Dommergues, Jean-Louis; Bruneau, Ludovic; Cocquerez, Théophile; Laffont, Rémi; Huret, Emilia; Thibault, Nicolas

2017-02-01

The Early Jurassic was broadly a greenhouse climate period that was punctuated by short warm and cold climatic events, positive and negative excursions of carbon isotopes, and episodes of enhanced organic matter burial. Clay minerals from Pliensbachian sediments recovered from two boreholes in the Paris Basin, are used here as proxies of detrital supplies, runoff conditions, and palaeoceanographic changes. The combined use of these minerals with stable isotope data (C-O) from bulk carbonates and organic matter allows palaeoclimatic reconstructions to be refined for the Pliensbachian. Kaolinite/illite ratio is discussed as a reliable proxy of the hydrological cycle and runoff from landmasses. Three periods of enhanced runoff are recognised within the Pliensbachian. The first one at the Sinemurian-Pliensbachian transition shows a significant increase of kaolinite concomitant with the negative carbon isotope excursion at the so-called Sinemurian Pliensbachian Boundary Event (SPBE). The Early/Late Pliensbachian transition was also characterised by more humid conditions. This warm interval is associated with a major change in oceanic circulation during the Davoei Zone, likely triggered by sea-level rise; the newly created palaeogeography, notably the flooding of the London-Brabant Massif, allowed boreal detrital supplies, including kaolinite and chlorite, to be exported to the Paris Basin. The last event of enhanced runoff occurred during the late Pliensbachian (Subnodosus Subzone of the Margaritatus Zone), which occurred also during a warm period, favouring organic matter production and preservation. Our study highlights the major role of the London Brabant Massif in influencing oceanic circulation of the NW European area, as a topographic barrier (emerged lands) during periods of lowstand sea-level and its flooding during period of high sea-level. This massif was the unique source of smectite in the Paris Basin. Two episodes of smectite-rich sedimentation ('smectite events'), coincide with regressive intervals, indicating emersion of the London Brabant Massif and thus suggesting that an amplitude of sea-level change high enough to be linked to glacio-eustasy. This mechanism is consistent with sedimentological and geochemical evidences of continental ice growth notably during the Latest Pliensbachian (Spinatum Zone), and possibly during the Early Pliensbachian (late Jamesoni/early Ibex Zones).

Morphology, spatial pattern and sediment of Nitraria tangutorum nebkhas in barchans interdune areas at the southeast margin of the Badain Jaran Desert, China

NASA Astrophysics Data System (ADS)

Yang, YanYan; Liu, LianYou; Shi, PeiJun; Zhang, GuoMing; Qu, ZhiQiang; Tang, Yan; Lei, Jie; Wen, HaiMing; Xiong, YiYing; Wang, JingPu; Shen, LingLing

2015-03-01

To understand the characteristics of the nebkhas in barchan interdune areas, isolated barchan dunes at the southeast margin of the Badain Jaran Desert in China and Nitraria tangutorun nebkhas in the interdune areas were selected, and the morphometric parameters, spatial patterns, and granulometric characteristics of the nebkhas in various interdune zones were compared. According to the locations relative to barchan dunes, the interdune areas were divided into three zones: the windward interdune zone (Zw), the leeward interdune zone (Zl), and the horn interdune zone (Zh). The zone that is proximal to barchan dunes and has never been disturbed by barchan dunes was also selected (Zi). The morphometric parameters were measured through a satellite image and field investigation. The population density and spatial patterns were analyzed using the satellite image, and surface sediment samples of the nebkhas and barchan dunes were collected for grain size analysis. The morphometric parameters of Nitraria tangutorun nebkhas in the interdune zones differ significantly. The nebkhas in Zh are larger than those observed in the other zones, and the nebkhas are the smallest in Zl. In all of the zones, the long-axis orientation of the nebkhas is perpendicular to the prevailing wind direction. The population density of the nebkhas in Zw is relatively higher, whereas the density in Zh and Zl becomes obviously lower. The spatial distribution of nebkhas in all of the zones can be categorized as a dispersed pattern. The sediments of the nebkhas are coarsest in Zh and finest in Zl. In addition, the sediments of the nebkhas in all of the zones are finer than those of barchan dunes. The amount of sand captured by the nebkhas in the interdune areas is approximately 20% of the volume of barchan dunes. The variations of the nebkhas' sizes, spatial pattern and sediment are subjected to migration, flow field and sand transport of barchan dunes and sand accumulation with plant growth in the interdune areas, which suggest complex mutual interactions between barchan dunes and the nebkhas in the interdune areas.

Use of borehole geophysical logs for improved site characterization at Naval Weapons Industrial Reserve Plant, Dallas, Texas

USGS Publications Warehouse

Anaya, Roberto; Braun, Christopher L.; Kuniansky, Eve L.

2000-01-01

A shallow alluvial aquifer at the Naval Weapons Industrial Reserve Plant near Dallas, Texas, has been contaminated by organic solvents used in the fabrication and assembly of aircraft and aircraft parts. Natural gamma-ray and electromagnetic-induction log data collected during 1997 from 162 wells were integrated with existing lithologic and cone-penetrometer test log data to improve characterization of the subsurface alluvium at the site. The alluvium, consisting of mostly fine-grained, low-permeability sediments, was classified into low, intermediate, and high clay-content sediments on the basis of the gamma-ray logs. Low clay-content sediments were interpreted as being relatively permeable, whereas high clay-content sediments were interpreted as being relatively impermeable. Gamma-ray logs, cone-penetrometer test logs, and electromagnetic-induction logs were used to develop a series of intersecting sections to delineate the spatial distribution of low, intermediate, and high clay-content sediments and to delineate zones of potentially contaminated sediments. The sections indicate three major sedimentary units in the shallow alluvial aquifer at NWIRP. The lower unit consists of relatively permeable, low clay-content sediments and is absent over the southeastern and northwestern part of the site. Permeable zones in the complex, discontinuous middle unit are present mostly in the western part of the site. In the eastern and southeastern part of the site, the upper unit has been eroded away and replaced by fill material. Zones of potentially contaminated sediments are generally within the uppermost clay layer or fill material. In addition, the zones tend to be local occurrences.

Organelle sedimentation in gravitropic roots of Limnobium is restricted to the elongation zone

NASA Technical Reports Server (NTRS)

Sack, F. D.; Kim, D.; Stein, B.

1994-01-01

Roots of the aquatic angiosperm Limnobium spongia (Bosc) Steud. were evaluated by light and electron microscopy to determine the distribution of organelle sedimentation towards gravity. Roots of Limnobium are strongly gravitropic. The rootcap consists of only two layers of cells. Although small amyloplasts are present in the central cap cells, no sedimentation of any organelle, including amyloplasts, was found. In contrast, both amyloplasts and nuclei sediment consistently and completely in cells of the elongation zone. Sedimentation occurs in one cell layer of the cortex just outside the endodermis. Sedimentation of both amyloplasts and nuclei begins in cells that are in their initial stages of elongation and persists at least to the level of the root where root hairs emerge. This is the first modern report of the presence of sedimentation away from, but not in, the rootcap. It shows that sedimentation in the rootcap is not necessary for gravitropic sensing in at least one angiosperm. If amyloplast sedimentation is responsible for gravitropic sensing, then the site of sensing in Limnobium roots is the elongation zone and not the rootcap. These data do not necessarily conflict with the hypothesis that sensing occurs in the cap in other roots, since Limnobium roots are exceptional in rootcap origin and structure, as well as in the distribution of organelle sedimentation. Similarly, if nuclear sedimentation is involved in gravitropic sensing, then nuclear mass would function in addition to, not instead of, that of amyloplasts.

Effect of goethite coating and humic acid on the transport of bacteriophage PRD1 in columns of saturated sand

NASA Astrophysics Data System (ADS)

Foppen, J. W. A.; Okletey, S.; Schijven, J. F.

2006-05-01

The transport of bacteriophage PRD1, a model virus, was studied in columns containing sediment mixtures of quartz sand with goethite-coated sand and using various solutions consisting of monovalent and divalent salts and humic acid (HA). Without HA and in the absence of sand, the inactivation rate of PRD1 was found to be as low as 0.014 day - 1 (at 5 ± 3 °C), but in the presence of HA it was much lower (0.0009 day - 1 ), indicating that HA helps PRD1 to survive. When the fraction of goethite in the sediment was increased, the removal of PRD1 also increased. However, in the presence of HA, C/ C0 values of PRD1 increased by as much as 5 log units, thereby almost completely eliminating the effect of addition of goethite. The sticking efficiency was not linearly dependent on the amount of goethite added to the quartz sand; this is apparently due to surface charge heterogeneity of PRD1. Our results imply that, in the presence of dissolved organic matter (DOM), viruses can be transported for long distances thanks to two effects: attachment is poor because DOM has occupied favourable sites for attachment and inactivation of virus may have decreased. This conclusion justifies making conservative assumptions about the attachment of viruses when calculating protection zones for groundwater wells.

Geologic framework, evolution, and sediment resources for restoration of the Louisiana Coastal Zone

USGS Publications Warehouse

Kulp, Mark; Penland, Shea; Williams, S. Jeffress; Jenkins, Chris; Flocks, Jim; Kindinger, Jack

2005-01-01

The Louisiana Coastal Zone along the north-central Gulf of Mexico represents one of America's most important coastal ecosystems in terms of natural resources, human infrastructure, and cultural heritage. This zone also has the highest rates of coastal erosion and wetland loss in the nation because of a complex combination of natural processes and anthropogenic activities during the past century. In response to the dramatic land loss, regional-scale restoration plans are being developed through a partnership of federal and state agencies. One objective is to maintain the barrier island and tidal inlet systems, thereby reducing the impact of storm surge and interior wetland loss. Proposed shore line restoration work relies primarily upon the use of large volumes of sand-rich sediment for shoreline stabilization and the implementation of the shoreline projects. Although sand-rich sediment is required for the Louisiana restoration projects, it is of limited availability within the generally clay to silt-rich, shallow strata of the Louisiana Coastal Zone. Locating volumetrically significant quantities of sand-rich sediment presents a challenge and requires detailed field investigations using direct sampling and geophysical sensing methods. Consequently, there is a fundamental need to thoroughly understand and map the distribution and textural character {e.g., sandiness) of sediment resources within the Coastal Zone for the most cost-effective design and completion of restoration projects.

Contamination of port zone sediments by metals from Large Marine Ecosystems of Brazil.

PubMed

Buruaem, Lucas M; Hortellani, Marcos A; Sarkis, Jorge E; Costa-Lotufo, Leticia V; Abessa, Denis M S

2012-03-01

Sediment contamination by metals poses risks to coastal ecosystems and is considered to be problematic to dredging operations. In Brazil, there are differences in sedimentology along the Large Marine Ecosystems in relation to the metal distributions. We aimed to assess the extent of Al, Fe, Hg, Cd, Cr, Cu, Ni, Pb and Zn contamination in sediments from port zones in northeast (Mucuripe and Pecém) and southeast (Santos) Brazil through geochemical analyses and sediment quality ratings. The metal concentrations found in these port zones were higher than those observed in the continental shelf or the background values in both regions. In the northeast, metals were associated with carbonate, while in Santos, they were associated with mud. Geochemical analyses showed enrichments in Hg, Cd, Cu, Ni and Zn, and a simple application of international sediment quality guidelines failed to predict their impacts, whereas the use of site-specific values that were derived by geochemical and ecotoxicological approaches seemed to be more appropriate in the management of the dredged sediments. Copyright © 2012 Elsevier Ltd. All rights reserved.

The potential influence of the annual invasive plant, Impatiens glandulifera (Himalayan Balsam), on the hydro-geomorphic functioning of inland river systems

NASA Astrophysics Data System (ADS)

Kuhn, N. J.; Greenwood, P.; Fister, W.

2014-12-01

The invasive plant, Impatiens glandulifera (Himalayan Balsam), is now found in most European countries, as well as across large parts of North America and on some Australasian islands. It favours damp, nutrient-rich soils that experience frequent natural disturbance, such as riparian zones. Its ability to out-compete native vegetation and tendency to suffer rapid dieback during cold weather has led to speculation that it may promote soil erosion, particularly along riverbanks. Despite the strong implication, its ability to promote erosion has only recently been shown during an investigation over one dieback and regrowth cycle along a small watercourse in northwest Switzerland. This presentation now benefits from additional results covering further dieback and regrowth cycles obtained from the same watercourse as above, and from a different river system in southwest UK. These additional results support the original conclusion that I. glandulifera promotes soil erosion along riverbanks and the riparian zone. Importantly, the equivalent ground surface retreat from each group of contaminated locations over the three dieback and regrowth cycles are comparable with erosion in regions where high magnitude events are often recorded. Given these very high erosion rates, albeit over three monitoring phases, it is hypothesised that I. glandulifera may act as a catalyst for repeat cycles of colonisation, dieback and extreme erosion. Aside from the deleterious effect of large quantities of nutrient-rich sediment entering into watercourses, high magnitude soil loss such as this could result in reach-scale sections of riverbank undergoing profound morphological changes and reduced structural stability. Dynamic modifications such as those could ultimately impede the ability of riverbanks to moderate stream flow and offer flood protection, as well as hamper the capacity of riparian zones to buffer and retain sediment and associated contaminants during their passage from terrestrial to aquatic environments. Given the dearth of effective intervention measures to halt, or even slow, the spread of I. glandulifera, the impact of extreme erosion driven by this invasive plant could eventually affect the ecohydromorphic functioning of whole river systems, thus making their management extremely difficult and complex.

The potential influence of the invasive plant, Impatiens glandulifera (Himalayan Balsam), on the ecohydromorphic functioning of inland river systems

NASA Astrophysics Data System (ADS)

(Phil) Greenwood, Philip; Fister, Wolfgang; Kuhn, Nikolaus

2014-05-01

The invasive plant, Impatiens glandulifera (common English name: Himalayan Balsam), is now found in most temperate European countries, as well as across large parts of North America and on some Australasian islands. As a ruderal species, it favours damp, nutrient-rich soils that experience frequent natural disturbance, such as riparian zones. Its ability to out-compete native vegetation and tendency to suffer rapid dieback during cold weather has led to repeated speculation that it may promote soil erosion, particularly along riverbanks. Despite the strong implication, its ability to promote erosion has only recently been empirically proven during an investigation over one dieback and regrowth cycle along a small watercourse in northwest Switzerland. This presentation now benefits from additional results covering further dieback and regrowth cycles obtained from the same watercourse as above, and from a different river system in southwest UK. These additional results support the original conclusion that I. glandulifera promotes soil erosion along riverbanks and the riparian zone. Importantly, the equivalent ground surface retreat from each group of contaminated locations over the three dieback and regrowth cycles are comparable with erosion in regions where high magnitude events are often recorded. Given these very high erosion rates, albeit over three monitoring phases, it is hypothesised that I. glandulifera may act as a catalyst for repeat cycles of colonisation, dieback and extreme erosion. Aside from the deleterious effect of large quantities of nutrient-rich sediment entering into watercourses, high magnitude soil loss such as this could result in reach-scale sections of riverbank undergoing profound morphological changes and reduced structural stability. Dynamic modifications such as those could ultimately impede the ability of riverbanks to moderate stream flow and offer flood protection, as well as hamper the capacity of riparian zones to buffer and retain sediment and associated contaminants during their passage from terrestrial to aquatic environments. Given the dearth of effective intervention measures to halt, or even slow, the spread of I. glandulifera, the impact of extreme erosion driven by this invasive plant could eventually affect the ecohydromorphic functioning of whole river systems, thus making their management extremely difficult and complex.

High Levels of Sediment Contamination Have Little Influence on Estuarine Beach Fish Communities

PubMed Central

McKinley, Andrew C.; Dafforn, Katherine A.; Taylor, Matthew D.; Johnston, Emma L.

2011-01-01

While contaminants are predicted to have measurable impacts on fish assemblages, studies have rarely assessed this potential in the context of natural variability in physico-chemical conditions within and between estuaries. We investigated links between the distribution of sediment contamination (metals and PAHs), physico-chemical variables (pH, salinity, temperature, turbidity) and beach fish assemblages in estuarine environments. Fish communities were sampled using a beach seine within the inner and outer zones of six estuaries that were either heavily modified or relatively unmodified by urbanization and industrial activity. All sampling was replicated over two years with two periods sampled each year. Shannon diversity, biomass and abundance were all significantly higher in the inner zone of estuaries while fish were larger on average in the outer zone. Strong differences in community composition were also detected between the inner and outer zones. Few differences were detected between fish assemblages in heavily modified versus relatively unmodified estuaries despite high concentrations of sediment contaminants in the inner zones of modified estuaries that exceeded recognized sediment quality guidelines. Trends in species distributions, community composition, abundance, Shannon diversity, and average fish weight were strongly correlated to physico-chemical variables and showed a weaker relationship to sediment metal contamination. Sediment PAH concentrations were not significantly related to the fish assemblage. These findings suggest that variation in some physico-chemical factors (salinity, temperature, pH) or variables that co-vary with these factors (e.g., wave activity or grain size) have a much greater influence on this fish assemblage than anthropogenic stressors such as contamination. PMID:22039470

Characteristics of Holocene sediments in the Gunsan Basin, central Yellow Sea

NASA Astrophysics Data System (ADS)

Woo, H. J.; Huh, S.; Jeong, K. S.; Lee, J. H.; Ham, A.; Kang, J.

2016-12-01

The Gunsan Basin, in the eastern part of the South Yellow Sea Basin, is filled by terrestrial sedimentary rocks, maximally up to 8 km deep on the basement of metamorphic rocks that constitutes the Yangtze Platform. The uppermost sedimentary layer (generally less than 1 km) appears to have formed experiencing the repeated marine environments since the middle Miocene. This study is to investigate the characteristics of Holocene sediments in the Gunsan Basin, based on interpretation of core sediments and high-resolution shallow (Sparker and Chirp) seismic profiles. The surface sediments in the basin consist of sand (56.6% on the average), silt (18.4%), and clay (25.0%) with a mean grain size of 1.5 to 7.8 Ø. Sand is prevalent (63.8 to 98.3%) in and around the Yellow Sea Trough lying in the eastern part of the basin. The sandy sediments are regarded as relict sediments deposited in the last glacial maximum (LGM). The sedimentary environments are classified, based on the acoustic and morphological characters of high-resolution shallow (Sparker and Chirp) seismic profiles, into mud zone, deformed zone, and sand ridges with sand waves zone from the west to the east in the Gunsan Basin. The deformed zone in the central Yellow Sea is a mixing area of sediments derived from China and Korea, where there are a number of paleochannels and erosional surfaces in the direction of northwest-southeast. The deformed zone represents non-deposition or erosion in the central Yellow Sea during the Holocene. Tidal sand ridges and sand waves are well developed along the coast of Korea. Modern sand ridges are generally moving in the northeast-southwest direction, which coincide with dominant tidal current direction. Fifteen piston cores were collected in the basin to investigate the general geological characters of the marine sedimentary sequence. In comparison with three cores in the southern basin, the sand contents tend to increase in the direction of east. 14C dates from three cores near border of Exclusive Economic Zone (EEZ) of Korea reveal that Holocene sediments have accumulated at the rate 6-18 cm/ka. The mud sediments sequentially change sandy mud to mud after the sea-level rise. In the Gunsan Basin, paleochannels played an important role in sedimentary processes during low sea-level periods of Quaternary.

Naphthalene and benzene degradation under Fe(III)-reducing conditions in petroleum-contaminated aquifers

USGS Publications Warehouse

Anderson, Robert T.; Lovely, Derek R.

1999-01-01

Naphthalene was oxidized anaerobically to CO2 in sediments collected from a petroleum-contaminated aquifer in Bemidji, Minnesota in which Fe(III) reduction was the terminal electron-accepting process. Naphthalene was not oxidized in sediments from the methanogenic zone at Bemidji or in sediments from the Fe(III)-reducing zone of other petroleum-contaminated aquifers studied. In a profile across the Fe(III)-reducing zone of the Bemidji aquifer, rates of naphthalene oxidation were fastest in sediments with the highest proportion of Fe(III), which was also the zone of the most rapid degradation of benzene, toluene, and acetate. The comparative studies attempted to elucidate factors that might account for the fact that unsubstituted aromatic hydrocarbons such as benzene and naphthalene were degraded under Fe(III)-reducing conditions at Bemidji, but not at the other aquifers examined. These studies indicated that the ability of Fe(III)-reducing microorganisms to degrade benzene and naphthalene at the Bemidji site cannot be attributed to groundwater components that make Fe(III) more available for reduction or other potential factors that were evaluated. However, unlike the other aquifers evaluated, uncontaminated sediments at the Bemidji site could be adapted for anaerobic benzene degradation merely with the addition of benzene. These findings indicate that Bemidji sediments naturally contain Fe(III) reducers capable of degradation of unsubstituted aromatic hydrocarbons.

The annual invasive plant, Impatiens glandulifera (Himalayan Balsam) as a trigger for high-magnitude soil erosion in temperate river systems

NASA Astrophysics Data System (ADS)

Greenwood, Philip; Kuhn, Nikolaus

2015-04-01

The invasive plant, Impatiens glandulifera (common English name: Himalayan Balsam), is now found in most temperate European countries, as well as across large parts of North America and on some Australasian islands. As a ruderal species, it favours damp, fertile soils that experience frequent disturbance. Riverbanks and the riparian zone thus represent prime habitat. Its ability to out-compete most perennial vegetation yet tendency to suddenly die during seasonally cold weather has led to claims that it may promote soil erosion, particularly along inland watercourses. Despite the strong implication, this was only recently proven during an investigation conducted over one dieback and regrowth cycle in 2012/13 along a watercourse in northwest Switzerland. Here we reinterpret those initial findings and also present additional data from the same watercourse which now covers three die-off and regrowth cycles, as well as data over two die-off and regrowth cycles from a river system in southwest UK. Results from all monitoring campaigns strongly support the original conclusion that I. glandulifera promotes significant soil erosion along contaminated sections of riverbank and riparian zone. More specifically, however, approximately one third of the total number of contaminated locations monitored (n=41) recorded net ground surface retreat that exceeded, by at least one order of magnitude, equivalent annual erosion rates documented on cultivated hillslopes in temperate regions. Not only does I. glandulifera induce repeat cycles of colonization and die-off, therefore, but collectively, the results generated so far strongly infer that under certain circumstances, this cycle of events can commonly trigger severe or even extreme erosion. Seasonally induced soil loss of this magnitude, particularly along short sections of watercourses, is unsustainable in the long-term and may lead to key fluvial features undergoing profound morphological and structural changes. Such an effect could reduce the stability, and hence the ability, of riverbanks to offer natural, sustainable flood protection, as well as hamper the capacity of riparian zones to buffer and retain sediment and contaminants during their passage from terrestrial to aquatic environments. Aside from the deleterious effect of large amounts of fine-sediment entering receiving watercourses, a failure of those key geomorphic components to fulfil those fundamental ecosystem services could lead to an eventual breakdown in the hydrogeomorphic functioning of whole river systems. This could make the delivery of effective sediment reduction strategies extremely challenging in the future.

Inorganic nitrogen transformations in the bed of the Shingobee River, Minnesota: Integrating hydrologic and biological processes using sediment perfusion cores

USGS Publications Warehouse

Sheibley, R.W.; Duff, J.H.; Jackman, A.P.; Triska, F.J.

2003-01-01

Inorganic N transformations were examined in streambed sediments from the Shingobee River using sediment perfusion cores. The experimental design simulated groundwater-stream water mixing within sediment cores, which provided a well-defined one-dimensional representation of in situ hydrologic conditions. Two distinct hydrologic and chemical settings were preserved in the sediment cores: the lowermost sediments, perfused with groundwater, remained anaerobic during the incubations, whereas the uppermost sediments, perfused with oxic water pumped from the overlying water column, simulated stream water penetration into the bed. The maintenance of oxic and anoxic zones formed a biologically active aerobic-anaerobic interface. Ammonium (NH4+) dissolved in groundwater was transported conservatively through the lower core zone but was removed as it mixed with aerated recycle water. Concurrently, a small quantity of nitrate (NO3-) equaling ???25% of the NH4+ loss was produced in the upper sediments. The NH4+ and NO3- profiles in the uppermost sediments resulted from coupled nitrification-denitrification, because assimilation and sorption were negligible. We hypothesize that anaerobic microsites within the aerated upper sediments supported denitrification. Rates of nitrification and denitrification in the perfusion cores ranged 42-209 and 53-160 mg N m-2 day-1, respectively. The use of modified perfusion cores permitted the identification and quantification of N transformations and verified process control by surface water exchange into the shallow hyporheic zone of the Shingobee River.

Modern configuration of the southwest Florida carbonate slope: Development by shelf margin progradation

USGS Publications Warehouse

Brooks, G.R.; Holmes, C.W.

1990-01-01

Depositional patterns and sedimentary processes influencing modern southwest Florida carbonate slope development have been identified based upon slope morphology, seismic facies and surface sediment characteristics. Three slope-parallel zones have been identified: (1) an upper slope progradational zone (100-500 m) characterized by seaward-trending progradational clinoforms and sediments rich in shelf-derived carbonate material, (2) a lower gullied slope zone (500-800 m) characterized by numerous gullies formed by the downslope transport of gravity flows, and (3) a base-of-slope zone (> 800 m) characterized by thin, lens-shaped gravity flow deposits and irregular topography interpreted to be the result of bottom currents and slope failure along the basal extensions of gullies. Modern slope development is interpreted to have been controlled by the offshelf transport of shallow-water material from the adjacent west Florida shelf, deposition of this material along a seaward advancing sediment front, and intermittent bypassing of the lower slope by sediments transported in the form of gravity flows via gullies. Sediments are transported offshelf by a combination of tides and the Loop Current, augmented by the passage of storm frontal systems. Winter storm fronts produce cold, dense, sediment-laden water that cascades offshelf beneath the strong, eastward flowing Florida Current. Sediments are eventually deposited in a relatively low energy transition zone between the Florida Current on the surface and a deep westward flowing counter current. The influence of the Florida Current is evident in the easternmost part of the study area as eastward prograding sediments form a sediment drift that is progressively burying the Pourtales Terrace. The modern southwest Florida slope has seismic reflection and sedimentological characteristics in common with slopes bordering both the non-rimmed west Florida margin and the rimmed platform of the northern Bahamas, and shows many similarities to the progradational Miocene section along the west Florida slope. As with rimmed platform slopes, development of non-rimmed platform slopes can be complex and controlled by a combination of processes that result in a variety of configurations. Consequently, the distinction between the two slope types based solely upon seismic and sedimentological characteristics may not be readily discernible. ?? 1990.

The influence of groundwater chemistry on arsenic concentrations and speciation in a quartz sand and gravel aquifer

USGS Publications Warehouse

Kent, D.B.; Fox, P.M.

2004-01-01

We examined the chemical reactions influencing dissolved concentrations, speciation, and transport of naturally occurring arsenic (As) in a shallow, sand and gravel aquifer with distinct geochemical zones resulting from land disposal of dilute sewage effluent. The principal geochemical zones were: (1) the uncontaminated zone above the sewage plume [350 ??M dissolved oxygen (DO), pH 5.9]; (2) the suboxic zone (5 ??M DO, pH 6.2, elevated concentrations of sewage-derived phosphate and nitrate); and (3) the anoxic zone [dissolved iron(II) 100-300 ??M, pH 6.5-6.9, elevated concentrations of sewage-derived phosphate]. Sediments are comprised of greater than 90% quartz but the surfaces of quartz and other mineral grains are coated with nanometer-size iron (Fe) and aluminum (Al) oxides and/or silicates, which control the adsorption properties of the sediments. Uncontaminated groundwater with added phosphate (620 ??M) was pumped into the uncontaminated zone while samples were collected 0.3 m above the injection point. Concentrations of As(V) increased from below detection (0.005 ??M) to a maximum of 0.07 ??M during breakthrough of phosphate at the sampling port; As(III) concentrations remained below detection. These results are consistent with the hypothesis that naturally occurring As(V) adsorbed to constituents of the coatings on grain surfaces was desorbed by phosphate in the injected groundwater. Also consistent with this hypothesis, vertical profiles of groundwater chemistry measured prior to the tracer test showed that dissolved As(V) concentrations increased along with dissolved phosphate from below detection in the uncontaminated zone to approximately 0.07 and 70 ??M, respectively, in the suboxic zone. Concentrations of As(III) were below detection in both zones. The anoxic zone had approximately 0.07 ??M As(V) but also had As(III) concentrations of 0.07-0.14 ??M, suggesting that release of As bound to sediment grains occurred by desorption by phosphate, reductive dissolution of Fe oxides, and reduction of As(V) to As(III), which adsorbs only weakly to the Fe-oxide-depleted material in the coatings. Results of reductive extractions of the sediments suggest that As associated with the coatings was relatively uniformly distributed at approximately 1 nmol/g of sediment (equivalent to 0.075 ppm As) and comprised 20%-50% of the total As in the sediments, determined from oxidative extractions. Quartz sand aquifers provide high-quality drinking water but can become contaminated when naturally occurring arsenic bound to Fe and Al oxides or silicates on sediment surfaces is released by desorption and dissolution of Fe oxides in response to changing chemical conditions. ?? 2004 American Institute of Physics.

Modeling of sediment transport in a saltwater lake with supplemental sandy freshwater.

PubMed

Liang, Li; Deng, Yun; Li, Ran; Li, Jia

2018-06-22

Considering the highly complex flow structure of saltwater lakes during freshwater supplementation, a three-dimensional numerical model was developed to simulate suspended sediment transport in saltwater lakes. The model was validated using measurements of the salinity and sediment concentration during a pumping test at Yamdrok Lake. The simulation results were in quantitative agreement with the measured data. The observed and simulated results also indicated that the wind stress and vertical salinity gradient have a significant influence on salinity and sediment transport in a saltwater lake. The validated model was then used to predict and analyze the contributions of wind, the supplement flow rate and salinity stratification to the sediment transport process in Yamdrok Lake during continuous river water supplementation. The simulation results showed that after the sandy river water was continuously discharged into the saltwater lake, the lateral diffusion trends of the sediment exhibited three stages: linear growth in the inflow direction, logarithmic growth in the wind direction, and stabilization. Furthermore, wind was the dominant factor in driving the lake flow pattern and sediment transport. Specifically, wind can effectively reduce the area of the sediment diffusion zone by increasing the lateral sediment carrying and dilution capacities. The effect of inflow on the lake current is negligible, but the extent of the sediment turbidity zone mainly depends on the inflow. Reducing the inflow discharge can decrease the area of the sediment turbidity zone to proportions that far exceed the proportions of inflow discharge reductions. In addition, the high-salinity lake water can support the supplemented freshwater via buoyancy forces, which weaken vertical mixing and sediment settlement and increase lake currents and sediment diffusion near the surface.

Artificial soft sediment resuspension and high density opportunistic macroalgal mat fragmentation as method for increasing sediment zoobenthic assemblage diversity in a eutrophic lagoon.

PubMed

Martelloni, Tatiana; Tomassetti, Paolo; Gennaro, Paola; Vani, Danilo; Persia, Emma; Persiano, Marco; Falchi, Riccardo; Porrello, Salvatore; Lenzi, Mauro

2016-09-15

Superficial soft sediment resuspension and partial fragmentation of high density opportunistic macroalgal mats were investigated by boat to determine the impact on zoobenthic assemblages in a eutrophic Mediterranean lagoon. Sediment resuspension was used to oxidise superficial organic sediments as a method to counteract the effects of eutrophication. Likewise, artificial decay of macroalgal mat was calculated to reduce a permanent source of sediment organic matter. An area of 9ha was disturbed (zone D) and two other areas of the same size were left undisturbed (zones U). We measured chemical-physical variables, estimated algal biomass and sedimentary organic matter, and conducted qualitative and quantitative determinations of the zoobenthic species detected in sediment and among algal mats. The results showed a constant major reduction in labile organic matter (LOM) and algal biomass in D, whereas values in U remained stable or increased. In the three zones, however, bare patches of lagoon bed increased in size, either by direct effect of the boats in D or by anaerobic decay of the algal mass in U. Zoobenthic assemblages in algal mats reduced the number of species in D, probably due to the sharp reduction in biomass, but remained stable in U, whereas in all three areas abundance increased. Sediment zoobenthic assemblages increased the number of species in D, as expected, due to drastic reduction in LOM, whereas values in U remained stable and again abundance increased in all three zones. In conclusion, we confirmed that reduction of sediment organic load enabled an increase in the number of species, while the algal mats proved to be an important substrate in the lagoon environment for zoobenthic assemblages, especially when mat alternated with bare intermat areas of lagoon bed. Sediment resuspension is confirmed as a management criterion for counteracting the effects of eutrophication and improving the biodiversity of zoobenthic assemblages in eutrophic lagoon environments. Copyright © 2016 Elsevier Ltd. All rights reserved.

River Suspended Sediment and Particulate Organic Carbon Transport in Two Montane Catchments in the Luquillo Critical Zone Observatory of Puerto Rico over 25 years: 1989 to 2014

NASA Astrophysics Data System (ADS)

Clark, K. E.; Plante, A. F.; Willenbring, J. K.; Jerolmack, D. J.; Gonzalez, G.; Stallard, R. F.; Murphy, S. F.; Vann, D. R.; Leon, M.; McDowell, W. H.

2015-12-01

Physical erosion in mountain catchments mobilizes large amounts of sediment, while exporting carbon and nutrients from forest ecosystems. This study expands from previous studies quantifying river suspended sediment and particulate organic carbon loads in the Luquillo Critical Zone Observatory, in Puerto Rico. We evaluate the influences on river suspended load due to i) underlying basin geology, ii) hillslope debris and biomass supply, and iii) hurricanes and large storms. In the Mameyes and Icacos catchments of the Luquillo Mountains, we estimate suspended sediment and particulate organic carbon yields over a 25-year period using streamflow discharge determined from stage measurements at 15-intervals, with estimates of discharge replacing gaps in data, and over 3000 suspended sediment samples. We estimate variation in suspended sediment loads over time, and examine variation in particulate organic carbon loads. Mass spectrometry was used to determine organic carbon concentrations. We confirm that higher suspended sediment fluxes occurred i) in the highly weathered quartz diorite catchment rather than the predominantly volcaniclastic catchment, ii) on the rising limb of the hydrograph once a threshold discharge had been reached, and iii) during hurricanes and other storm events, and we explore these influences on particulate organic carbon transport. Transport of suspended sediment and particulate organic carbon in the rivers shows considerable hysteresis, and we evaluate the extent to which hysteresis affects particulate fluxes over time and between catchments. Because particulate organic carbon is derived from the critical zone and transported during high flow, our research highlights the role of major tropical storms in controlling carbon storage in the critical zone and the coastal ocean.

SEDIMENT TOXICITY AND COMMUNITY COMPOSITION OF BENTHOS AND COLONIZED PERIPHYTON IN THE EVERGLADES - FLORIDA BAY TRANSITIONAL ZONE.

EPA Science Inventory

Lewis, Michael A., Larry R. Goodman, John M. Macauley and James C. Moore. 2004. Sediment Toxicity and Community Composition of Benthos and Colonized Periphyton in the Everglades-Florida Bay Transitional Zone. Ecotoxicology. 13(3):231-244. (ERL,GB 1164).

This survey provid...

Microbial respiration and extracellular enzyme activity in sediments from the Gulf of Mexico hypoxic zone

EPA Science Inventory

This study explores the relationship between sediment chemistry (TC, TN, TP) and microbial respiration (DHA) and extracellular enzyme activity (EEA) across the Gulf of Mexico (GOM) hypoxic zone. TC, TN, and TP were all positively correlated with each other (r=0.19-0.68). DHA was ...

Mobilization of beryllium in the sedimentary column at convergent margins

USGS Publications Warehouse

You, C.-F.; Morris, J.D.; Gieskes, J.M.; Rosenbauer, R.; Zheng, S.H.; Xu, X.; Ku, T.-L.; Bischoff, J.L.

1994-01-01

Studies of Be distributions in subduction zone sediments will help to understand questions regarding the enrichments of cosmogenic Be-10 in arc volcanic rocks. Analyses of Be-10 and Be-9 in sediments of Ocean Drilling Program Site 808, Nankai Trough and Be-9 in porewaters of Site 808 and Sites 671 and 672, Barbados ridge complex, show significant decreases in solid phase Be-10 and large increases of porewater Be-9 at the location of the de??collement zone and below or at potential flow conduits. These data imply the potential mobilization of Be during pore fluid expulsion upon sediment burial. Experiments involving reaction between a de??collement sediment and a synthetic NaCl-CaCl2 solution at elevated pressure and temperatures were conducted in an attempt to mimic early subduction zone processes. The results demonstrate that Be is mobilized under elevated pressure and temperature with a strong pH dependence. The Be mobilization provides an explanation of Be-10 enrichment in arc volcanic rocks and supports the argument of the importance of the fluid processes in subduction zones at convergent margins. ?? 1994.

Sedimentary constraints on the development of a narrow deep strait (São Sebastião Channel, SE Brazil)

NASA Astrophysics Data System (ADS)

Alcántara-Carrió, Javier; Sasaki, Dalton Kei; Mahiques, Michel Michaelovitch de; Taborda, Rui; de Souza, Luiz Antonio Pereira

2017-10-01

The São Sebastião Channel (SSC), which separates São Sebastião Island from the continent, is a deep elongated strait on the inner shelf of the São Paulo Bight (SE Brazil). The aim of this study is to explain why it is presently sediment starved, instead of forming a tombolo. Wave data were obtained from both a WW3 model database and buoy records, and wave propagation patterns from the SWAN numerical model. Grain size trend analysis of 579 surficial sediment samples from the strait and the surrounding region served to estimate the residual transport directions. Bedload sediment transport was computed considering in situ currents and bottom sediment grain size. Moreover, six seismic profiles and one gravity core were obtained in the strait in order to evaluate the hickness of the sedimentary deposits. The geometry of the SSC (X/B=0.3, where B is the breakwater or island diameter and X is its cross-shore distance to the mainland) predicts that a tombolo should be formed, and wave patterns confirm that it is a zone sheltered from both S and NE waves. Previous studies have shown that the hydrodynamics of the SSC is controlled by wind-driven currents, which are more intense in the eastern and central sectors of the strait. The western sector is currently covered by sandy mud, whereas very coarse to fine sand prevails in the deeper eastern sector. Sediment patterns show a trend to deposition of fine sediment in the western sector of the SSC and two main depocentres located at the northern limit of the study area and at the southern mouth of the strait. Sandy mud in the western sector forms a 40-m-thick deposit close to the outer limit of Araçá Bay, whereas the remainder of the SSC is covered by a very thin layer of sandy sediments. Dominance of mud in the depositional western sector suggests low availability of sand in the area. Therefore, despite the geometry and wave patterns of the SSC favouring the formation of a tombolo, the dominance of wind-driven currents and the low availability of sand determine that such a sedimentary feature cannot be formed, resulting in a deep strait.

Effects of fluidization of the host sediment on peperite textures: A field example from the Cretaceous Buan Volcanics, SW Korea

NASA Astrophysics Data System (ADS)

Gihm, Yong Sik; Kwon, Chang Woo

2017-04-01

In the Cretaceous Buan Volcanics (SW Korea), blocky and fluidal peperites are hosted in a massive pumiceous lapilli tuff intruded by intermediate dikes. Blocky peperites, the most abundant species, are characterized by polyhedral or platy juvenile clasts and a jigsaw-crack texture. Fluidal peperites occur only along dike margins, where the host sediments are composed of well sorted, fine to very fine ash (fine-grained zone), and are characterized by fluidal or globular juvenile clasts with irregular or ragged margins. The fine-grained zone is interpreted to form by grain size segregation caused by upward moving pore water (fluidization) that has resulted from heat transfer from intruding magma toward waterlogged host sediments during intrusion. With the release of pore water and the selective entrainment of fine-grained ash, fine-grained zones formed within the host sediments. Subsequent interactions between the fine-grained zone and the intruding magma resulted in ductile deformation of the magma before fragmentation, which generated fluidal peperites. Outside the fine-grained zone, intruding magma fragmented in a brittle manner because of the relative deficiency of both pore water and fine-grained ash, resulting in the formation of blocky peperites. The results of this study suggest that redistribution of constituent particles (ash) and interstitial fluids during fluidization resulted in heterogeneous physical conditions of the host sediments, which influenced peperite-forming processes, as reflected by the different peperite textures.

Effect of saline waste solution infiltration rates on uranium retention and spatial distribution in Hanford sediments.

PubMed

Wan, Jiamin; Tokunaga, Tetsu K; Kim, Yongman; Wang, Zheming; Lanzirotti, Antonio; Saiz, Eduardo; Serne, R Jeffrey

2008-03-15

The accidental overfilling of waste liquid from tank BX-102 at the Hanford Site in 1951 put about 10 t of U(VI) into the vadose zone. In order to understand the dominant geochemical reactions and transport processes that occurred during the initial infiltration and to help understand current spatial distribution, we simulated the waste liquid spilling event in laboratory sediment columns using synthesized metal waste solution. We found that, as the plume propagated through sediments, pH decreased greatly (as much as 4 units) at the moving plume front. Infiltration flow rates strongly affect U behavior. Slower flow rates resulted in higher sediment-associated U concentrations, and higher flow rates (> or =5 cm/day) permitted practically unretarded U transport. Therefore, given the very high Ksat of most of Hanford formation, the low permeability zones within the sediment could have been most important in retaining high concentrations of U during initial release into the vadose zone. Massive amount of colloids, including U-colloids, formed at the plume fronts. Total U concentrations (aqueous and colloid) within plume fronts exceeded the source concentration by up to 5-fold. Uranium colloid formation and accumulation at the neutralized plume front could be one mechanism responsible for highly heterogeneous U distribution observed in the contaminated Hanford vadose zone.

Bowers Swell: Evidence for a zone of compressive deformation concentric with Bowers Ridge, Bering Sea

USGS Publications Warehouse

Marlow, M. S.; Cooper, A. K.; Dadisman, S.V.; Geist, E.L.; Carlson, P.R.

1990-01-01

Bowers Swell is a newly discovered bathymetric feature which is up to 90 m high, between 12 and 20 km wide, and which extends arcuately about 400 km along the northern and eastern sides of Bowers Ridge. The swell was first revealed on GLORIA sonographs and subsequently mapped on seismic reflection and 3.5 kHz bathymetric profiles. These geophysical data show that the swell caps an arcuate anticlinal ridge, which is composed of deformed strata in an ancient trench on the northern and eastern sides of Bowers Ridge. The trench fill beneath the swell is actively deforming, as shown by faulting of the sea floor and by thinning of the strata across the crest of the swell. Thinning and faulting of the trench strata preclude an origin for the swell by simple sediment draping over an older basement high. We considered several models for the origin of Bowers Swell, including folding and uplift of the underlying trench sediment during the interaction between the Pacific plate beneath the Aleutian Ridge and a remnant oceanic slab beneath Bowers Ridge. However, such plate motions should generate extensive seismicity beneath Bowers Ridge, which is aseismic, and refraction data do not show any remnant slab beneath Bowers Ridge. Another origin considered for Bowers Swell invokes sediment deformation resulting from differential loading and diapirism in the trench fill. However, diapirism is not evident on seismic reflection profiles across the swell. We favour a model in which sediment deformation and swell formation resulted from a few tens of kilometers of low seismicity motion by intraplate crustal blocks beneath the Aleutian Basin. This motion may result from the translation of blocks in western Alaska to the south-west, forcing the movement of the Bering Sea margin west of Alaska into the abyssal Aleutian Basin. ?? 1990.

Evaluation of toxicity of polluted marine sediments from Bahia Salina Cruz, Mexico.

PubMed

Gonzalez-Lozano, Maria Cristina; Mendez-Rodriguez, Lia C; Maeda-Martinez, Alejandro M; Murugan, Gopal; Vazquez-Botello, Alfonso

2010-01-01

Bahia Salina Cruz, Oaxaca, Mexico is a major center of oil and refined product distribution on the Mexican Pacific coast. From the start of oil industry operations in 1979, negative effects from discharges of treated effluents in the bay have been a constant concern for local communities. We analyzed 28 surface sediment samples obtained in June, 2002 to evaluate the level of toxicity in the littoral zone, port-harbor, and La Ventosa estuary in Bahia Salina Cruz. The extractable organic matter concentration was high (1,213 to 7,505 micro g g(-1)) in 5 of 7 stations from the port and harbor, whereas it was low in 12 of 16 stations in the littoral zone (36 to 98 micro g g(-1)). The total aromatic hydrocarbon concentration was highest (57 to 142 micro g g(-1)) in the port and harbor compared to the La Ventosa estuary and the littoral zone. Among the heavy metals analyzed, cadmium exceeded the effects range-low values associated with adverse biological effects. The geo-accumulation index of sediments was moderate to strong contamination at 5 stations in the nonlittoral and 6 stations in the littoral zone. The enrichment of lead, zinc, and cadmium at 5 stations from the littoral, port, and harbor suggest that these metals are of anthropogenic origin. Bioassay tests of elutriates of sediments on nauplii of Artemia franciscana and Artemia sp. showed that the port and harbor were more toxic than the La Ventosa estuary and the coastal zone. The Microtox test (Vibrio fischeri) did not show a similar response with the solid phase of the sediments. The results of this study indicate that the high levels of organic content and metals in the sediments of port-harbor and the La Ventosa estuary are mainly caused by anthropogenic activities.

Sedimentation and associated trace metal enrichment in the riparian zone of the Three Gorges Reservoir, China.

PubMed

Tang, Qiang; Bao, Yuhai; He, Xiubin; Zhou, Huaidong; Cao, Zhijing; Gao, Peng; Zhong, Ronghua; Hu, Yunhua; Zhang, Xinbao

2014-05-01

Impoundment of the Three Gorges Reservoir has created an artificial riparian zone with a vertical height of 30 m and a total area of 349 km(2), which has been subjected to seasonal inundation and exposure due to regular reservoir impoundment and the occurrence of natural floods. The significant alteration of hydrologic regime has caused numerous environmental changes. The present study investigated the magnitude and spatial pattern of sedimentation and metal enrichment in a typical section of the riparian zone, composed of bench terraces with previous agricultural land uses, and explored their links to the changed hydrologic regime. In particular, we measured the total sediment depths and collected surface riparian sediments and down-profile sectioned riparian soils (at 5 cm intervals) for trace metal determination. Our analysis showed that the annual average sedimentation rates varied from 0.5 to 10 cm·yr(-1) and they decreased significantly with increasing elevation. This lateral distribution was principally attributed to seasonal variations in water levels and suspended sediment concentrations. Enriched concentrations of trace metals were found both in the riparian sediments and soils, but they were generally higher in the riparian sediments than in riparian soils and followed a similar lateral decreasing trend. Metal contamination assessment showed that the riparian sediments were slightly contaminated by Ni, Zn, and Pb, moderately contaminated by Cu, and moderately to strongly contaminated by Cd; while riparian soils were slightly contaminated by As, and moderately contaminated by Cd. Trace metal enrichment in the riparian sediments may be attributed to external input of contaminated sediments produced from upstream anthropogenic sources and chemical adsorption from dissolved fractions during pure sediment mobilization and after sink for a prolonged flooding period due to reservoir impoundment. Copyright © 2014 Elsevier B.V. All rights reserved.

Morphology of sea-floor landslides on Horizon Guyot: application of steady-state geotechnical analysis

USGS Publications Warehouse

Kayen, R.E.; Schwab, W.C.; Lee, H.J.; Torresan, M.E.; Hein, J.R.; Quinterno, P.J.; Levin, L.A.

1989-01-01

Mass movement and erosion have been identified on the pelagic sediment cap of Horizon Guyot, a seamount in the Mid-Pacific Mountains. Trends in the size, shape and preservation of bedforms and sediment textural trends on the pelagic cap indicate that bottom-current-generated sediment transport direction is upslope. Slumping of the sediment cap occurred on and that the net bedload transport direction is upslope. Slumping of the sediment cap occurred on the northwest side of the guyot on a 1.6?? to 2.0?? slope in the zone of enhanced bottom-current activity. Submersible investigations of these slump blocks show them to be discrete and to have a relief of 6-15 m, with nodular chert beds cropping out along the headwall of individual rotated blocks. An evaluation of the stability of the sediment cap suggests that the combination of the current-induced beveling of the sea floor and infrequent earthquake loading accompanied by cyclic strength reduction is responsible for the initiation of slumps. The sediment in the area of slumping moved short distances in relatively coherent masses, whereas sediment that has moved beyond the summit cap perimeter has fully mobilized into sediment gravity flows and traveled large distances. A steady-state geotechnical analysis of Horizon Guyot sediment indicates the predisposition of deeply buried sediment towards disintegrative flow failure on appropriately steep slopes. Thus, slope failure in this deeper zone would include large amounts of internal deformation. However, gravitational stress in the near-surface sediment of the summit cap (sub-bottom depth < 14 m) is insufficient to maintain downslope movement after initial failure occurs. The predicted morphology of coherent slump blocks displaced and rafted upon a weakened zone at depth corresponds well with seismic-reflection data and submersible observations. ?? 1990.

Clay with Desiccation Cracks is an Advection Dominated Environment

NASA Astrophysics Data System (ADS)

Baram, S.; Kurtzman, D.; Sher, Y.; Ronen, Z.; Dahan, O.

2012-04-01

Heavy clay sediments are regarded "safe" from the hydrological point of view due to their low hydraulic conductivities. However, the formation of desiccation cracks in dispersive clays may dramatically change their bulk hydraulic properties. The impact of desiccation cracks on water percolation, dissolved salts and contaminants transport and redox related reactions (microbial ammonium oxidation and denitrification) were investigated in 6 -12 m clay layer near a diary farm waste lagoon. The study implemented unique vadose-zone monitoring systems that enable in-situ measurements of the temporal variation of the sediment's water content along with frequent sampling of the sediment's pore water along the entire vadose zone (> 30 m). Results from four years of continuous measurements showed quick rises in sediment water content following rain events and temporal wastewater overflows. The percolation pattern indicated dominance of preferential flow through a desiccation-cracks network crossing the entire clay sediment layer. High water-propagation velocities (0.4 - 23.6 m h-1) were observed, indicating that the desiccation-crack network remains open and serves as a preferential flow pathway year-round, even at high sediment water content (~0.50 m3 m-3). The rapid percolation bypassed the most bio-geo-active parts of the soil, transporting even highly sorptive contaminants (testosterone and estrogen) in to the deep sections of the vadose zone, accelerating the underlying groundwater contamination. The ammonium and nitrate concentrations in the vadose zone and the high number of nitrifying and denitrifying bacteria (~108 gene copies gdry-sediemt-1, each) found in the sediment indicated that the entire vadose zone is aerated even at high water content conditions (~0.55 m3 m-3). The dissolved salts concentration in the pore-water and the δ2H-H2O and δ18O-H2O values of the pore-water substantially increased with depth (becoming less depleted) in the clay sediment, indicating deep soil evaporation. Daily fluctuation of the air temperature in the desiccation cracks supported thermally induced air convection within the cracks void and could explain the deep soil salinization process. Combination of all the abovementioned observations demonstrated that the formation of desiccation cracks network in dispersive clay sediments generates a bulk advection dominated environment for both air and water flow, and that the reference to clay sediments as "hydrologically safe" should to be reconsidered.

A big data approach to macrofaunal baseline assessment, monitoring and sustainable exploitation of the seabed.

PubMed

Cooper, K M; Barry, J

2017-09-29

In this study we produce a standardised dataset for benthic macrofauna and sediments through integration of data (33,198 samples) from 777 grab surveys. The resulting dataset is used to identify spatial and temporal patterns in faunal distribution around the UK, and the role of sediment composition and other explanatory variables in determining such patterns. We show how insight into natural variability afforded by the dataset can be used to improve the sustainability of activities which affect sediment composition, by identifying conditions which should remain favourable for faunal recolonisation. Other big data applications and uses of the dataset are discussed.

Multipolarization P-, L-, and C-band radar for coastal zone mapping - The Louisiana example

NASA Technical Reports Server (NTRS)

Wu, Shih-Tseng

1989-01-01

Multipolarization P-, L-, and C-band airborne SAR data sets were acquired over a coastal zone and a forested wetland of southern Louisiana. The data sets were used with field-collected surface-parameter data in order to determine the value of SAR systems in assessing and mapping coastal-zone surface features. The coastal-zone surface features in this study are sediments, sediment distribution, and the formation of new isles and banks. Results of the data analysis indicate that the P-band radar with 68-cm wavelength is capable of detecting the submerged sediment if the area is very shallow (i.e., a water depth of less than one meter). The penetration capability of P-band radar is also demonstrated in the forested wetland area. The composition and condition of the ground surface can be detected, as well as the standing water beneath dense tree leaves.

Effects of remediation amendments on vadose zone microorganisms

DOE Office of Scientific and Technical Information (OSTI.GOV)

Miller, Hannah M.; Tilton, Fred A.

2012-08-10

Surfactant-based foam delivery technology has been studied to remediate Hanford 200 area deep vadose zone sediment. However, the surfactants and remediation amendments have an unknown effect on indigenous subsurface microorganisms. Microbial populations are important factors to consider in remediation efforts due to their potential to alter soil geochemistry. This project focuses on measuring microbial metabolic responses to remediation amendments in batch and column studies using Deep Vadose Zone Sediments. Initial studies of the microbes from Hanford 200 area deep vadose zone sediment showed surfactants sodium dodecyl sulfate (SDS) and cocamidopropyl betaine (CAPB) and remediation amendment calcium polysulfide (CPS) had nomore » affect on microbial growth using BiologTM Ecoplates. To move towards a more realistic field analog, soil columns were packed with Hanford 200 Area sediment. Once microbial growth in the column was verified by observing growth of the effluent solution on tryptic soy agar plates, remedial surfactants were injected into the columns, and the resulting metabolic diversity was measured. Results suggest surfactant sodium dodecyl sulfate (SDS) stimulates microbial growth. The soil columns were also visualized using X-ray microtomography to inspect soil packing and possibly probe for evidence of biofilms. Overall, BiologTM Ecoplates provide a rapid assay to predict effects of remediation amendments on Hanford 200 area deep vadose zone microorganisms.« less

Microtubule distribution in gravitropic protonemata of the moss Ceratodon

NASA Technical Reports Server (NTRS)

Schwuchow, J.; Sack, F. D.; Hartmann, E.

1990-01-01

Tip cells of dark-grown protonemata of the moss Ceratodon purpureus are negatively gravitropic (grow upward). They possess a unique longitudinal zonation: (1) a tip group of amylochloroplasts in the apical dome, (2) a plastid-free zone, (3) a zone of significant plastid sedimentation, and (4) a zone of mostly non-sedimenting plastids. Immunofluorescence of vertical cells showed microtubules distributed throughout the cytoplasm in a mostly axial orientation extending through all zones. Optical sectioning revealed a close spatial association between microtubules and plastids. A majority (two thirds) of protonemata gravistimulated for > 20 min had a higher density of microtubules near the lower flank compared to the upper flank in the plastid-free zone. This apparent enrichment of microtubules occurred just proximal to sedimented plastids and near the part of the tip that presumably elongates more to produce curvature. Fewer than 5% of gravistimulated protonemata had an enrichment in microtubules near the upper flank, whereas 14% of vertical protonemata were enriched near one of the side walls. Oryzalin and amiprophos-methyl (APM) disrupted microtubules, gravitropism, and normal tip growth and zonation, but did not prevent plastid sedimentation. We hypothesize that a microtubule redistribution plays a role in gravitropism in this protonema. This appears to be the first report of an effect of gravity on microtubule distribution in plants.

Macro and micro rate zonal analytical centrifugation of polydisperse and slowly diffusing sedimenting systems in isovolumetric density gradients. Application to cartilage proteoglycans.

PubMed

Müller, F J; Pezon, C F; Pita, J C

1989-06-13

A method to study the polydispersity of zonally sedimenting and slowly diffusing macromolecules or particles in isokinetic or isovolumetric density gradients is presented. First, a brief theory is given for predicting the zonal profile after a "triangular" (or "inverse") zone is centrifuged. This type of zone is essential to preserve hydrodynamic stability of the very slowly diffusing polydisperse solutes. It is proven, both by semitheoretical considerations and by computer calculations, that the resulting concentration profile of macrosolute is almost identical with that obtainable with a rectangular zone coextensive with the triangular one and carrying the same total mass. Next, practical procedures are described for the convectionless layering of very small triangular zones (50 microL or less). The linearity and stability of the zones are experimentally tested and verified. Finally, the method is applied to cartilage proteoglycan preparations that included either the monomeric molecules only or both the monomeric and the aggregated ones. The zonal results are compared with those obtained by using conventional boundary sedimentation. The two sets of results are seen to coincide fairly well, thus proving that the present technique can add to preparative zonal centrifugation the analytical precision of boundary sedimentation. A multimodal polydisperse system is suggested to describe the aggregated proteoglycan macromolecules.

Recent Monitoring of Suspended Sediment Patterns along Louisiana's Coastal Zone using ER-2 based MAS Data and Terra Based MODIS Data

NASA Technical Reports Server (NTRS)

Moeller, Christopher C.; Gunshor, M. M.; Menzel, W. P.; Huh, O. K.; Walker, N. D.; Rouse, L. J.

2001-01-01

The University nf Wisconsin and Louisiana State University have teamed to study the forcing of winter season cold frontal wind systems on sediment distribution patterns and geomorphology in the Louisiana coastal zone. Wind systems associated with cold fronts have been shown to model coastal circulation and resuspend sediments along the micro tidal Louisiana coast (Roberts et at. 1987, Moeller et al. 1993). Remote sensing data is being used to map and track sediment distribution patterns for various wind conditions. Suspended sediment is a building material for coastal progradation and wetlands renewal, but also restricts access to marine nursery environments and impacts oyster bed health. Transferring a suspended sediment concentration (SSC) algorithm to EOS MODerate resolution Imaging Spectroradiometer (MODIS; Barnes et al. 1998) observations may enable estimates of SSC globally.

Geomorphic evolution of the Le Sueur River, Minnesota, USA, and implications for current sediment loading

USGS Publications Warehouse

Gran, K.B.; Belmont, P.; Day, S.S.; Jennings, C.; Johnson, Aaron H.; Perg, L.; Wilcock, P.R.

2009-01-01

There is clear evidence that the Minnesota River is the major sediment source for Lake Pepin and that the Le Sueur River is a major source to the Minnesota River. Turbidity levels are high enough to require management actions. We take advantage of the well-constrained Holocene history of the Le Sueur basin and use a combination of remote sensing, fi eld, and stream gauge observations to constrain the contributions of different sediment sources to the Le Sueur River. Understanding the type, location, and magnitude of sediment sources is essential for unraveling the Holocene development of the basin as well as for guiding management decisions about investments to reduce sediment loads. Rapid base-level fall at the outlet of the Le Sueur River 11,500 yr B.P. triggered up to 70 m of channel incision at the mouth. Slope-area analyses of river longitudinal profi les show that knickpoints have migrated 30-35 km upstream on all three major branches of the river, eroding 1.2-2.6 ?? 109 Mg of sediment from the lower valleys in the process. The knick zones separate the basin into an upper watershed, receiving sediment primarily from uplands and streambanks, and a lower, incised zone, which receives additional sediment from high bluffs and ravines. Stream gauges installed above and below knick zones show dramatic increases in sediment loading above that expected from increases in drainage area, indicating substantial inputs from bluffs and ravines.

Changes in ice-margin processes and sediment routing during ice-sheet advance across a marginal moraine

USGS Publications Warehouse

Knight, P.G.; Jennings, C.E.; Waller, R.I.; Robinson, Z.P.

2007-01-01

Advance of part of the margin of the Greenland ice sheet across a proglacial moraine ridge between 1968 and 2002 caused progressive changes in moraine morphology, basal ice formation, debris release, ice-marginal sediment storage, and sediment transfer to the distal proglacial zone. When the ice margin is behind the moraine, most of the sediment released from the glacier is stored close to the ice margin. As the margin advances across the moraine the potential for ice-proximal sediment storage decreases and distal sediment flux is augmented by reactivation of moraine sediment. For six stages of advance associated with distinctive glacial and sedimentary processes we describe the ice margin, the debris-rich basal ice, debris release from the glacier, sediment routing into the proglacial zone, and geomorphic processes on the moraine. The overtopping of a moraine ridge is a significant glaciological, geomorphological and sedimentological threshold in glacier advance, likely to cause a distinctive pulse in distal sediment accumulation rates that should be taken into account when glacial sediments are interpreted to reconstruct glacier fluctuations. ?? 2007 Swedish Society for Anthropology and Geography.

Downstream aggradation owing to lava dome extrusion and rainfall runoff at Volcán Santiaguito, Guatemala

USGS Publications Warehouse

Harris, Andrew J. L.; Vallance, James W.; Kimberly, Paul; Rose, William I.; Matías, Otoniel; Bunzendahl, Elly; Flynn, Luke P.; Garbeil, Harold

2006-01-01

Persistent lava extrusion at the Santiaguito dome complex (Guatemala) results in continuous lahar activity and river bed aggradation downstream of the volcano. We present a simple method that uses vegetation indices extracted from Landsat Thematic Mapper (TM) data to map impacted zones. Application of this technique to a time series of 21 TM images acquired between 1987 and 2000 allow us to map, measure, and track temporal and spatial variations in the area of lahar impact and river aggradation.In the proximal zone of the fluvial system, these data show a positive correlation between extrusion rate at Santiaguito (E), aggradation area 12 months later (Aprox), and rainfall during the intervening 12 months (Rain12): Aprox=3.92+0.50 E+0.31 ln(Rain12) (r2=0.79). This describes a situation in which an increase in sediment supply (extrusion rate) and/or a means to mobilize this sediment (rainfall) results in an increase in lahar activity (aggraded area). Across the medial zone, we find a positive correlation between extrusion rate and/or area of proximal aggradation and medial aggradation area (Amed): Amed=18.84-0.05 Aprox - 6.15 Rain12 (r2=0.85). Here the correlation between rainfall and aggradation area is negative. This describes a situation in which increased sediment supply results in an increase in lahar activity but, because it is the zone of transport, an increase in rainfall serves to increase the transport efficiency of rivers flowing through this zone. Thus, increased rainfall flushes the medial zone of sediment.These quantitative data allow us to empirically define the links between sediment supply and mobilization in this fluvial system and to derive predictive relationships that use rainfall and extrusion rates to estimate aggradation area 12 months hence.

Palaeozoic and Mesozoic tectonic implications of Central Afghanistan

NASA Astrophysics Data System (ADS)

Sliaupa, Saulius; Motuza, Gediminas

2017-04-01

The field and laboratory studies were carried out in Ghor Province situated in the central part of Afghanistan. It straddles juxtaposition of the Tajik (alternatively, North Afghanistan) and Farah Rod blocks separated by Band-e-Bayan zone. The recent studies indicate that Band-e-Bayan zone represents highly tectonised margin of the Tajik block (Motuza, Sliaupa, 2016). The Band-e-Bayan zone is the most representative in terms of sedimentary record. The subsidence trends and sediment lithologies suggest the passive margin setting during (Cambrian?) Ordovician to earliest Carboniferous times. A change to the foredeep setting is implied in middle Carboniferous through Early Permian; the large-thickness flysh-type sediments were derived from continental island arc provenance, as suggested by chemical composition of mudtstones. This stage can be correlated to the amalgamation of the Gondwana supercontinent. The new passive-margin stage can be inferred in the Band-e-Bayan zone and Tajik blocks in the Late Permian throughout the early Late Triassic that is likely related to breaking apart of Gondwana continent. A collisional event is suggested in latest Triassic, as seen in high-rate subsidence associating with dramatic change in litholgies, occurrence of volcanic rocks and granidoid intrusions. The continental volcanic island arc derived (based on geochemical indices) terrigens prevail at the base of Jurassic that were gradually replaced by carbonate platform in the Middle Jurassic pointing to cessation of the tectonic activity. A new tectonic episode (no deposition; and folding?) took place in the Tajik and Band-e-Bayan zone in Late Jurassic. The geological section of the Farah Rod block, situated to the south, is represented by Jurassic and Cretaceous sediments overlain by sporadic Cenozoic volcanic-sedimentary succession. The lower part of the Mesozoic succession is composed of terrigenic sediments giving way to upper Lower Cretaceous shallow water carbonates implying low tectonic regime. There was a break in sedimentation during the upper Cretaceous that is likely related to the Alpine orogenic event. It associated with some Upper Cretaceous magmatic activity (Debon et al., 1987). This event is reflected in the sedimentation pattern in the adjacent Band-e-Bayan zone and Tadjick block. The lower part of the Upper Cretaceous succession is composed of reddish terrigenic sediments. They are overlain by uppermost Cretaceous (and Danian) shallow marine sediments implying establishment of quiet tectonic conditions.

Biogeochemical and Molecular Signatures of Anaerobic Methane Oxidation in a Marine Sediment

PubMed Central

Thomsen, Trine R.; Finster, Kai; Ramsing, Niels B.

2001-01-01

Anaerobic methane oxidation was investigated in 6-m-long cores of marine sediment from Aarhus Bay, Denmark. Measured concentration profiles for methane and sulfate, as well as in situ rates determined with isotope tracers, indicated that there was a narrow zone of anaerobic methane oxidation about 150 cm below the sediment surface. Methane could account for 52% of the electron donor requirement for the peak sulfate reduction rate detected in the sulfate-methane transition zone. Molecular signatures of organisms present in the transition zone were detected by using selective PCR primers for sulfate-reducing bacteria and for Archaea. One primer pair amplified the dissimilatory sulfite reductase (DSR) gene of sulfate-reducing bacteria, whereas another primer (ANME) was designed to amplify archaeal sequences found in a recent study of sediments from the Eel River Basin, as these bacteria have been suggested to be anaerobic methane oxidizers (K. U. Hinrichs, J. M. Hayes, S. P. Sylva, P. G. Brewer, and E. F. DeLong, Nature 398:802–805, 1999). Amplification with the primer pairs produced more amplificate of both target genes with samples from the sulfate-methane transition zone than with samples from the surrounding sediment. Phylogenetic analysis of the DSR gene sequences retrieved from the transition zone revealed that they all belonged to a novel deeply branching lineage of diverse DSR gene sequences not related to any previously described DSR gene sequence. In contrast, DSR gene sequences found in the top sediment were related to environmental sequences from other estuarine sediments and to sequences of members of the genera Desulfonema, Desulfococcus, and Desulfosarcina. Phylogenetic analysis of 16S rRNA sequences obtained with the primers targeting the archaeal group of possible anaerobic methane oxidizers revealed two clusters of ANME sequences, both of which were affiliated with sequences from the Eel River Basin. PMID:11282617

Biogeochemical and molecular signatures of anaerobic methane oxidation in a marine sediment.

PubMed

Thomsen, T R; Finster, K; Ramsing, N B

2001-04-01

Anaerobic methane oxidation was investigated in 6-m-long cores of marine sediment from Aarhus Bay, Denmark. Measured concentration profiles for methane and sulfate, as well as in situ rates determined with isotope tracers, indicated that there was a narrow zone of anaerobic methane oxidation about 150 cm below the sediment surface. Methane could account for 52% of the electron donor requirement for the peak sulfate reduction rate detected in the sulfate-methane transition zone. Molecular signatures of organisms present in the transition zone were detected by using selective PCR primers for sulfate-reducing bacteria and for Archaea. One primer pair amplified the dissimilatory sulfite reductase (DSR) gene of sulfate-reducing bacteria, whereas another primer (ANME) was designed to amplify archaeal sequences found in a recent study of sediments from the Eel River Basin, as these bacteria have been suggested to be anaerobic methane oxidizers (K. U. Hinrichs, J. M. Hayes, S. P. Sylva, P. G. Brewer, and E. F. DeLong, Nature 398:802-805, 1999). Amplification with the primer pairs produced more amplificate of both target genes with samples from the sulfate-methane transition zone than with samples from the surrounding sediment. Phylogenetic analysis of the DSR gene sequences retrieved from the transition zone revealed that they all belonged to a novel deeply branching lineage of diverse DSR gene sequences not related to any previously described DSR gene sequence. In contrast, DSR gene sequences found in the top sediment were related to environmental sequences from other estuarine sediments and to sequences of members of the genera Desulfonema, Desulfococcus, and Desulfosarcina. Phylogenetic analysis of 16S rRNA sequences obtained with the primers targeting the archaeal group of possible anaerobic methane oxidizers revealed two clusters of ANME sequences, both of which were affiliated with sequences from the Eel River Basin.

Use of slow filtration columns to assess oxygen respiration, consumption of dissolved organic carbon, nitrogen transformations, and microbial parameters in hyporheic sediments.

PubMed

Mermillod-Blondin, F; Mauclaire, L; Montuelle, B

2005-05-01

Biogeochemical processes mediated by microorganisms in river sediments (hyporheic sediments) play a key role in river metabolism. Because biogeochemical reactions in the hyporheic zone are often limited to the top few decimetres of sediments below the water-sediment interface, slow filtration columns were used in the present study to quantify biogeochemical processes (uptakes of O2, DOC, and nitrate) and the associated microbial compartment (biomass, respiratory activity, and hydrolytic activity) at a centimetre scale in heterogeneous (gravel and sand) sediments. The results indicated that slow filtration columns recreated properly the aerobic-anaerobic gradient classically observed in the hyporheic zone. O2 and NO3- consumptions (256 +/- 13 microg of O2 per hour and 14.6 +/- 6.1 microg of N-NO3- per hour) measured in columns were in the range of values measured in different river sediments. Slow filtration columns also reproduced the high heterogeneity of the hyporheic zone with the presence of anaerobic pockets in sediments where denitrification and fermentation processes occurred. The respiratory and hydrolytic activities of bacteria were strongly linked with the O2 consumption in the experimental system, highlighting the dominance of aerobic processes in our river sediments. In comparison with these activities, the bacterial biomass (protein content) integrated both aerobic and anaerobic processes and could be used as a global microbial indicator in our system. Finally, slow filtration columns are an appropriate tool to quantify in situ rates of biogeochemical processes and to determine the relationship between the microbial compartment and the physico-chemical environment in coarse river sediments.

The chemistry and mineralogy of haloed burrows in pelagic sediment at DOMES Site A: The equatorial North Pacific

USGS Publications Warehouse

Piper, D.Z.; Rude, P.D.; Monteith, S.

1987-01-01

The chemical and mineralogical composition of burrowed sediment, recovered in 66 box cores at latitude 9??25???N and longitude 151??15???W in the equatorial Pacific, demonstrates the important role of infauna in determining the geochemistry of pelagic sediment. Haloed burrows, approximately 3 cm across, were present in many of the cores. Within early Tertiary sediment that was covered by less than 5 cm of surface Quaternary sediment in several cores, the burrows in cross-section consist of three units: (1) a dark yellowish-brown central zone of Quaternary sediment surrounded, by (2) a pale yellowish-orange zone (the halo) of Tertiary sediment, which is surrounded by (3) a metal-oxide precipitate; the enclosing Tertiary sediment is dusky brown. Several elements - Mn, Ni, Cu, Co, Zn, Sb and Ce - have been leached from the light-colored halo, whereas Cr, Cs, Hf, Rb, Sc, Ta, Th, U, the rare earth elements exclusive of Ce, and the major oxides have not been leached. The metal-oxide zone, 1-5 mm thick, contains as much as 16% MnO2, as the mineral todorokite. The composition of the todorokite, exclusive of the admixed Tertiary sediment, resembles the composition of the metal deficit of the halo and also the composition of surface ferromanganese nodules that have been interpreted as having a predominantly diagenetic origin. Thus bioturbation contributes not only to the redistribution of metals within pelagic sediment, but also to the accretion of ferromanganese nodules on the sea floor. ?? 1987.

Sedimentation across the central California oxygen minimum zone: an alternative coastal upwelling sequence.

USGS Publications Warehouse

Vercoutere, T.L.; Mullins, H.T.; McDougall, K.; Thompson, J.B.

1987-01-01

Distribution, abundance, and diversity of terrigenous, authigenous, and biogenous material provide evidence of the effect of bottom currents and oxygen minimum zone (OMZ) on continental slope sedimentation offshore central California. Three major OMZ facies are identified, along the upper and lower edges of OMZ and one at its core.-from Authors

Implications of tidally-varying bed stress and intermittent estuarine stratification on fine-sediment dynamics through the Mekong's tidal river to estuarine reach

NASA Astrophysics Data System (ADS)

McLachlan, R. L.; Ogston, A. S.; Allison, M. A.

2017-09-01

River gauging stations are often located upriver of tidal propagation where sediment transport processes and storage are impacted by widely varying ratios of marine to freshwater influence. These impacts are not yet thoroughly understood. Therefore, sediment fluxes measured at these stations may not be suitable for predicting changes to coastal morphology. To characterize sediment transport dynamics in this understudied zone, flow velocity, salinity, and suspended-sediment properties (concentration, size, and settling velocity) were measured within the tidal Sông Hậu distributary of the lower Mekong River, Vietnam. Fine-sediment aggregation, settling, and trapping rates were promoted by seasonal and tidal fluctuations in near-bed shear stress as well as the intermittent presence of a salt wedge and estuary turbidity maximum. Beginning in the tidal river, fine-grained particles were aggregated in freshwater. Then, in the interface zone between the tidal river and estuary, impeded near-bed shear stress and particle flux convergence promoted settling and trapping. Finally, in the estuary, sediment retention was further encouraged by stratification and estuarine circulation which protected the bed against particle resuspension and enhanced particle aggregation. These patterns promote mud export ( 1.7 t s-1) from the entire study area in the high-discharge season when fluvial processes dominate and mud import ( 0.25 t s-1) into the estuary and interface zone in the low-discharge season when estuarine processes dominate. Within the lower region of the distributaries, morphological change in the form of channel abandonment was found to be promoted within minor distributaries by feedbacks between channel depth, vertical mixing, and aggregate trapping. In effect, this field study sheds light on the sediment trapping capabilities of the tidal river - estuary interface zone, a relatively understudied region upstream of where traditional concepts place sites of deposition, and predicts how fine-sediment dynamics and morphology of large tropical deltas such as the Mekong will respond to changing fluvial and marine influences in the future.

Sharp Permeability Transitions due to Shallow Diagenesis of Subduction Zone Sediments

NASA Astrophysics Data System (ADS)

James, S.; Screaton, E.

2013-12-01

The permeability of hemipelagic sediments is an important factor in fluid flow in subduction zones and can be affected by porosity changes and cementation-dissolution processes acting during diagenesis. Anomalously high porosities have been observed in cores from the Shikoku Basin sediments approaching the Nankai Trough subduction zone. These high porosities have been attributed to the presence of minor amounts of amorphous silica cement that strengthen the sediment and inhibit consolidation. The porosity rapidly drops from 66-68% to 54-56% at a diagenetic boundary where the amorphous silica cement dissolves. Although the anomalous porosity profiles at Nankai have received attention, the magnitude of the corresponding permeability change has not been addressed. In this study, permeability profiles were constructed using permeability-porosity relationships from previous studies, to estimate the magnitude and rate of permeability changes with depth. The predicted permeability profiles for the Nankai Trough sediment cores indicate that permeability drops by almost one order of magnitude across the diagenetic boundary. This abrupt drop in permeability has the potential to facilitate significant changes in pore fluid pressures and thus to influence the deformation of the sediment onto the accretionary prism. At the Costa Rica subduction zone, results vary with location. Site U1414 offshore the Osa Peninsula shows porosities stable at 69% above 145 mbsf and then decrease to 54% over a 40 m interval. A porosity drop of that magnitude is predicted to correlate to an order of magnitude permeability decrease. In contrast, porosity profiles from Site 1039 offshore the Nicoya Peninsula and Site U1381 offshore the Osa Peninsula show anomalously high porosities but no sharp drop. It is likely that sediments do not cross the diagenetic boundary due to the extremely low (<10°C/km) thermal gradient at Site 1039 and the thin (<100 m) sediment cover at Site U1381. At these locations, the porosity loss and permeability reduction may occur after the sediment is subducted and contribute to high pore pressures at the plate boundary.

Fe(II)- and sulfide-facilitated reduction of 99Tc(VII)O4- in microbially reduced hyporheic zone sediments

NASA Astrophysics Data System (ADS)

Lee, Ji-Hoon; Zachara, John M.; Fredrickson, James K.; Heald, Steve M.; McKinley, James P.; Plymale, Andrew E.; Resch, Charles T.; Moore, Dean A.

2014-07-01

Redox-reactive, biogeochemical phases generated by reductive microbial activity in hyporheic zone sediments from a dynamic groundwater-river interaction zone were evaluated for their ability to reduce soluble pertechnetate [99Tc(VII)O4-] to less soluble Tc(IV). The sediments were bioreduced by indigenous microorganisms that were stimulated by organic substrate addition in synthetic groundwater with or without sulfate. In most treatments, 20 μmol L-1 initial aqueous Tc(VII) was reduced to near or below detection (3.82 × 10-9 mol L-1) over periods of days to months in suspensions of variable solids concentrations. Native sediments containing significant lithogenic Fe(II) in various phases were, in contrast, unreactive with Tc(VII). The reduction rates in the bioreduced sediments increased with increases in sediment mass, in proportion to weak acid-extractable Fe(II) and sediment-associated sulfide (AVS). The rate of Tc(VII) reduction was first order with respect to both aqueous Tc(VII) concentration and sediment mass, but correlations between specific reductant concentrations and reaction rate were not found. X-ray microprobe measurements revealed a strong correlation between Tc hot spots and Fe-containing mineral particles in the sediment. However, only a portion of Fe-containing particles were Tc-hosts. The Tc-hot spots displayed a chemical signature (by EDXRF) similar to pyroxene. The application of autoradiography and electron microprobe allowed further isolation of Tc-containing particles that were invariably found to be ca 100 μm aggregates of primary mineral material embedded within a fine-grained phyllosilicate matrix. EXAFS spectroscopy revealed that the Tc(IV) within these were a combination of a Tc(IV)O2-like phase and Tc(IV)-Fe surface clusters, with a significant fraction of a TcSx-like phase in sediments incubated with SO42-. AVS was implicated as a more selective reductant at low solids concentration even though its concentration was below that required for stoichiometric reduction of Tc(VII). These results demonstrate that composite mineral aggregates may be redox reaction centers in coarse-textured hyporheic zone sediments regardless of the dominant anoxic biogeochemical processes.

Fe(II)- and Sulfide-Facilitated Reduction of 99Tc(VII)O4- in Microbially Reduced Hyporheic Zone Sediments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Ji-Hoon; Zachara, John M.; Fredrickson, Jim K.

Redox-reactive, biogeochemical phases generated by reductive microbial activity in hyporheic zone sediments from a dynamic groundwater-river interaction zone were evaluated for their ability to reduce soluble pertechnetate [99Tc(VII)O4-] to less soluble Tc(IV). The sediments were bioreduced by indigenous microorganisms that were stimulated by organic substrate addition in synthetic groundwater with or without sulfate. In most treatments, 20 µmol L-1 initial aqueous Tc(VII) was reduced to near or below detection (3.82×10-9 mol L-1) over periods of days to months in suspensions of variable solids concentrations. Native sediments containing significant lithogenic Fe(II) in various phases were, in contrast, unreactive with Tc(VII). Themore » reduction rates in the bioreduced sediments increased with increases in sediment mass, in proportion to weak acid-extractable Fe(II) and sediment-associated sulfide (AVS). The rate of Tc(VII) reduction was first order with respect to both aqueous Tc(VII) concentration and sediment mass, but correlations between specific reductant concentrations and reaction rate were not found. X-ray microprobe measurements revealed a strong correlation between Tc hot spots and Fe-containing mineral particles in the sediment. However, only a portion of Fe-containing particles were Tc-hosts. The Tc-hot spots displayed a chemical signature (by EDXRF) similar to pyroxene. The application of autoradiography and electron microprobe allowed further isolation of Tc-containing particles that were invariably found to be ca 100 µm aggregates of primary mineral material embedded within a fine-grained phyllosilicate matrix. EXAFS spectroscopy revealed that the Tc(IV) within these were a combination of a Tc(IV)O2-like phase and Tc(IV)-Fe surface clusters, with a significant fraction of a TcSx-like phase in sediments incubated with SO42-. AVS was implicated as a more selective reductant at low solids concentration even though its concentration was below that required for stoichiometric reduction of Tc(VII). These results demonstrate that composite mineral aggregates may be redox reaction centers in coarse-textured hyporheic zone sediments regardless of the dominant anoxic biogeochemical processes.« less

Rheological implications of sediment transport for continental rifting and its impact in margin geometry and major unconformities

NASA Astrophysics Data System (ADS)

Andres-Martinez, Miguel; Perez-Gussinye, Marta; Armitage, John; Morgan, Jason

2016-04-01

The inner dynamics of the Earth such as mantle convection, geochemical reactions and isostasy have been typically interpreted as the main engine of plate tectonics and crustal deformation. However, nowadays it is well established that processes transporting material along the surface of the Earth influence the inner dynamics. Surface processes play a key role particularly during rifting, where great subsidence rates occur at synrift basins while shoulder uplift provides rock to be eroded for later infilling of these basins. Erosion implies unloading of the crust which favours uplift, and sedimentation at basins results in loading which favours subsidence. Consequently, erosion and sedimentation amplify stresses and the flexural response of the lithosphere in situations with extensive faulting. These changes to the stress field may be large enough to result in changes in the evolution of rifting and its modes of extension. Additionally, higher subsidence rates and thermal blanketing due to sediments may result in higher geotherms and consequently, a weaker/more-viscous behaviour of the crustal rocks. This would also have a large impact on the deformation style during extension. Here, we explore the interactions between surface processes and tectonics using numerical modelling. Experiments are run with the absence of sediment transport and with different sediment transport regimes for 35 and 40 km crustal thicknesses. Tests with higher transport coefficient show more effective localization of deformation into upper crustal faults which results in effective crustal thinning, larger blocks and longer-lived faults. Our experiments also prove that more effective surface processes reduce the length of margins generated by sequential faulting. For our end member situations, high sedimentation rates lead to pure shear extension of the crust induced by high temperatures, which finally results in broad extension and symmetric margins. Furthermore, our model allows for the recovery of predicted sediment stratigraphic patterns. Major unconformities that separate synrift from sag-basin-type sediments are observed in these pseudo-strata patterns. Here, we also address the meaning of these major unconformities and their relationship to the time of breakup.

Features of distribution and quality of organic matter in the bottom sediments of the Great Peter Bay (Sea of Japan)

NASA Astrophysics Data System (ADS)

Nesterova, Olga; Tregubova, Valentina; Semal, Victoria; Vasenev, Ivan

2017-04-01

The nature and distribution of organic carbon in marine waters depends on: 1) biological productivity and revenue of the autochthonous organic matter to the bottom; 2) sediment grain-size composition and conditions of dumping, which in turn depends of hydrothermic regime, topography, speed River mist and received major erosion products; 3) living conditions of the benthos (the quantity consumed of OM, gas regime of habitats, physiological capacity of heterotrophs). Autochthonous OM of phytoplankton plays a dominant role in the processes of formation of humus in aquatic conditions. Bottom sediments at different distance from the shoreline to depths from 0.5 up to 480 m of the Sea of Japan, which are formed in various conditions of facies, were selected as the objects of study. There is no clear relationships to the amount of organic matter in bottom sediments on the characteristics of the distribution and nature of living matter in the oceans and seas. This is because the process of sedimentation and fossilization of organic matter on the seabed and the ocean floor depends on many factors (currents, depth). Humus of studied bottom sediments in composition can be attributed mainly to the humic type. Nonhydrolyzing rest is 70-90%. This is characteristic of bottom sediments formed in facial types of small bays, internal coastal shelf bights and the underwater slope. At a fraction of the carbon of humic acids in organic matter, ranging from 4 to 80% of the amount of humic and fulvic acids. Fulvic acids content is much less. This is due to more favourable conservation situation of humic acids in precipitation with high content of organic matter, whereas fulvic acids in aquatic environments are more labile and almost not dumped. Despite the fact humic acids are not the most stable component (s), however, with increased content of humic acids, the mobility of organic matter and removing it from the bottom sediments are reduced. Internal shelf facies of the Great Peter Bay is the most diverse on the content of the various components of the bottom sediments humus. This is because modern processes of sedimentations and humus formation are active in this zone. The greatest concentration of organic matter in conjunction with the submarine and coastal slope at depths of more than 120 m. Slight variations parameters that characterize the composition of humus, are notable for all bottom sediments, as well as the marine environment, largely cancels the General conditions of humus formation around the basin of the Sea of Japan. Organic substance moving in the water colomn and transforms. Only sustainable to mineralization of organic substance reaches the bottom.

Sediments in marsh ponds of the Gulf Coast Chenier Plain: Effects of structural marsh management and salinity

USGS Publications Warehouse

Bolduc, F.; Afton, A.D.

2005-01-01

Physical characteristics of sediments in coastal marsh ponds (flooded zones of marsh associated with little vegetation) have important ecological consequences because they determine compositions of benthic invertebrate communities, which in turn influence compositions of waterbird communities. Sediments in marsh ponds of the Gulf Coast Chenier Plain potentially are affected by (1) structural marsh management (levees, water control structures and impoundments; SMM), and (2) variation in salinity. Based on available literature concerning effects of SMM on sediments in emergent plant zones (zones of marsh occasionally flooded and associated with dense vegetation) of coastal marshes, we predicted that SMM would increase sediment carbon content and sediment hardness, and decrease oxygen penetration (O2 depth) and the silt-clay fraction in marsh pond sediments. Assuming that freshwater marshes are more productive than are saline marshes, we also predicted that sediments of impounded freshwater marsh ponds would contain more carbon than those of impounded oligohaline and mesohaline marsh ponds, whereas C:N ratio, sediment hardness, silt-clay fraction, and O2 depth would be similar among pond types. Accordingly, we measured sediment variables within ponds of impounded and unimpounded marshes on Rockefeller State Wildlife Refuge, near Grand Chenier, Louisiana. To test the above predictions, we compared sediment variables (1) between ponds of impounded (IM) and unimpounded mesohaline marshes (UM), and (2) among ponds of impounded freshwater (IF), oligohaline (IO), and mesohaline (IM) marshes. An a priori multivariate analysis of variance (MANOVA) contrast indicated that sediments differed between IM and UM marsh ponds. As predicted, the silt-clay fraction and O2 depth were lower and carbon content, C:N ratio, and sediment hardness were higher in IM than in UM marsh ponds. An a priori MANOVA contrast also indicated that sediments differed among IF, IO, and IM marsh ponds. As predicted, carbon content was higher in IF marsh ponds than in ponds of other impounded marsh types. In contrast to our predictions, C:N ratio and sediment hardness were lowest and silt-clay fraction and O2 depth were highest in IO and IM marsh ponds. Our results indicated that SMM has affected physical properties of sediments in coastal marsh ponds. Moreover, sediments in IF marsh ponds were affected more so than were those in IO and IM marsh ponds. Our results, in conjunction with those of previous studies, indicated that sediments of marsh ponds and emergent plant zones differed greatly. We predict that changes in pond sediments due to SMM will promote greater epifaunal macroinvertebrate biomass, which in turn should attract larger populations of wintering waterbirds. However, waterbirds that filter or probe soft sediments may be negatively affected by SMM because of the expected decrease in infaunal invertebrate biomass. ?? Springer 2005.

Anthropopression markers in lake bottom sediments

NASA Astrophysics Data System (ADS)

Nadolna, Anna; Nowicka, Barbara

2014-05-01

Lakes are vulnerable to various types of anthropogenic disturbances. Responses of lake ecosystems to environmental stressors are varied and depend not only on the type of a factor but also on the lake natural resistance to degradation. Within the EULAKES project an evaluation of anthropogenic stress extent in a flow-through, postglacial, ribbon lake (Lake Charzykowskie) was carried out. It was assumed, that this impact manifests unevenly, depending on a type and degree of the pressure on the shore zones, water quality of tributaries, lake basin shape and dynamics of a water movement. It was stated, that anthropogenic markers are substances accumulated in bottom sediments as a result of allochthonous substances inflow from the catchment and atmosphere. Along the selected transects 105 samples from the top layer of sediments (about 20 cm) was collected representing the contemporary accumulation (about 15 years). The content of selected chemical elements and compounds was examined, including nutrients (TN and TP), heavy metals (arsenic, cadmium, lead, chromium, nickel, copper, zinc, mercury, iron, and manganese) and pesticides (DDT, DDD, DDE, DMDT , γ-HCH). The research was conducted in the deepest points of each lake basin and along the research transects - while choosing the spots, the increased intensity of anthropogenic impact (ports, roads with heavy traffic, wastewater discharge zones, built-up areas) was taken into consideration. The river outlets to the lake, where there are ecotonal zones between limnic and fluvial environment, were also taken into account. Analysis of the markers distribution was carried out against the diversity of chemical characteristics of limnic sediments. Ribbon shape of the lake basin and the dominant wind direction provide an opportunity of easy water mixing to a considerable depth. Intensive waving processes cause removal of the matter from the littoral zone towards lake hollows (separated by the underwater tresholds), where the top layer of sediments consists of organic sediment ("sapropel" type). The littoral zone is dominated by sandy material from the shores denudation. In river mouths sandy deltas are formed. The most contaminated sediments are deposited in the central pool, which is a natural trap for the substances flowing with the river that is draining wastewaters from urban areas. At its mouth the sediment samples were significantly contaminated with chromium, zinc, cadmium, copper, nickel, lead and mercury. A high content of total phosphorus was also detected. A different role is played by a large river flowing through the lake. While flushing the sediments it reduces their pollution. The lowest content of markers was detected in headwater areas and in littoral zones exposed to waving.

DIN retention-transport through four hydrologically connected zones in a headwater catchment of the Upper Mississippi River

USGS Publications Warehouse

Triska, F.J.; Duff, J.H.; Sheibley, R.W.; Jackman, A.P.; Avanzino, R.J.

2007-01-01

Dissolved inorganic nitrogen (DIN) retention-transport through a headwater catchment was synthesized from studies encompassing four distinct hydrologic zones of the Shingobee River Headwaters near the origin of the Mississippi River. The hydrologic zones included: (1) hillslope ground water (ridge to bankside riparian); (2) alluvial riparian ground water; (3) ground water discharged through subchannel sediments (hyporheic zone); and (4) channel surface water. During subsurface hillslope transport through Zone 1, DIN, primarily nitrate, decreased from ???3 mg-N/l to <0.1 mg-N/l. Ambient seasonal nitrate:chloride ratios in hillslope flow paths indicated both dilution and biotic processing caused nitrate loss. Biologically available organic carbon controlled biotic nitrate retention during hillslope transport. In the alluvial riparian zone (Zone 2) biologically available organic carbon controlled nitrate depletion although processing of both ambient and amended nitrate was faster during the summer than winter. In the hyporheic zone (Zone 3) and stream surface water (Zone 4) DIN retention was primarily controlled by temperature. Perfusion core studies using hyporheic sediment indicated sufficient organic carbon in bed sediments to retain ground water DIN via coupled nitrification-denitrification. Numerical simulations of seasonal hyporheic sediment nitrification-denitrification rates from perfusion cores adequately predicted surface water ammonium but not nitrate when compared to 5 years of monthly field data (1989-93). Mass balance studies in stream surface water indicated proportionally higher summer than winter N retention. Watershed DIN retention was effective during summer under the current land use of intermittently grazed pasture. However, more intensive land use such as row crop agriculture would decrease nitrate retention efficiency and increase loads to surface water. Understanding DIN retention capacity throughout the system, including special channel features such as sloughs, wetlands and floodplains that provide surface water-ground water connectivity, will be required to develop effective nitrate management strategies. ?? 2007 American Water Resources Association.

Flow and Suspended Sediment Events in the Near-Coastal Zone off Corpus Christi, Texas

DTIC Science & Technology

2003-09-30

redistribution of preexisting shelf sediments during storms and (2) transportation of suspended sediment from the adjacent bay- lagoon system. Snedden et al...and K.E. Schmedes. (1983). Submerged lands of Texas, Corpus Christi area: sediments, geochemistry, benthic macroinvertebrates and associated

Evaluation of ship-based sediment flux measurements by ADCPs in tidal flows

NASA Astrophysics Data System (ADS)

Becker, Marius; Maushake, Christian; Grünler, Steffen; Winter, Christian

2017-04-01

In the past decades acoustic backscatter calibration developed into a frequently applied technique to measure fluxes of suspended sediments in rivers and estuaries. Data is mainly acquired using single-frequency profiling devices, such as ADCPs. In this case, variations of acoustic particle properties may have a significant impact on the calibration with respect to suspended sediment concentration, but associated effects are rarely considered. Further challenges regarding flux determination arise from incomplete vertical and lateral coverage of the cross-section, and the small ratio of the residual transport to the tidal transport, depending on the tidal prism. We analyzed four sets of 13h cross-sectional ADCP data, collected at different locations in the range of the turbidity zone of the Weser estuary, North Sea, Germany. Vertical LISST, OBS and CTD measurements were taken very hour. During the calibration sediment absorption was taken into account. First, acoustic properties were estimated using LISST particle size distributions. Due to the tidal excursion and displacement of the turbidity zone, acoustic properties of particles changed during the tidal cycle, at all locations. Applying empirical functions, the lowest backscattering cross-section and highest sediment absorption coefficient were found in the center of the turbidity zone. Outside the tidally averaged location of the turbidity zone, changes of acoustic parameters were caused mainly by advection. In the turbidity zone, these properties were also affected by settling and entrainment, inducing vertical differences and systematic errors in concentration. In general, due to the iterative correction of sediment absorption along the acoustic path, local errors in concentration propagate and amplify exponentially. Based on reference concentration obtained from water samples and OBS data, we quantified these errors and their effect on cross-sectional averaged concentration and sediment flux. We found that errors are effectively decreased by applying calibration parameters interpolated in time, and by an optimization of the sediment absorption coefficient. We further discuss practical aspects of residual flux determination in tidal environments and of measuring strategies in relation to site-specific tidal dynamics.

Quaternary Sediment Accumulation in the Aleutian Trench: Implications for Dehydration Reaction Progress and Pore Pressure Development Offshore Alaska

NASA Astrophysics Data System (ADS)

Meridth, L. N.; Screaton, E.; Jaeger, J. M.; James, S. R.; Villaseñor, T. G.

2015-12-01

Sediment inputs to subduction zones impart a significant control on diagenetic reaction progress, fluid production and pore pressure development and thus affect hydrologic and tectonic behavior during subduction. Intensified glaciation following the mid-Pleistocene transition increased sediment flux to the Gulf of Alaska. Rapid sediment accumulation (>1 km/my) in the Aleutian Trench increases overburden and should accelerate dehydration of hydrous sedimentary components by elevating temperatures in the incoming sediment column. These processes have the potential to generate fluid overpressures in the mud-dominated, low permeability sediments deposited on the incoming plate, offshore SE Alaska. Mineralogical analyses on incoming sediments from Deep Sea Drilling Project Leg 18 and Integrated Ocean Drilling Program Expedition 341 show that both smectite and Opal-A are present as hydrous mineral phases. A 1-D numerical model was developed to track dehydration reaction progress and pore pressures in the incoming sediment column from the abyssal plain to the Aleutian Trench. Simulated temperatures in the incoming column increase due to the insulating effect of trench sediments. As a result, trench sedimentation causes smectite dehydration to begin and Opal-A dehydration to nearly reach completion at the deformation front. Simulated excess pore pressures in the proto-decollement zone increase from nearly hydrostatic to almost half of lithostatic due to the rapid deposition of trench sediments. The 1-D modeling results were incorporated into a 2-D model that follows the underthrust column at the deformation front into the subduction zone. Simulated results of the 2-D flow model illustrate the effects of lateral flow on pore pressure distribution following subduction.

Anaerobic Benzene Degradation in Petroleum-Contaminated Aquifer Sediments after Inoculation with a Benzene-Oxidizing Enrichment

PubMed Central

Weiner, Jonathan M.; Lovley, Derek R.

1998-01-01

Sediments from the sulfate-reduction zone of a petroleum-contaminated aquifer, in which benzene persisted, were inoculated with a benzene-oxidizing, sulfate-reducing enrichment from aquatic sediments. Benzene was degraded, with apparent growth of the benzene-degrading population over time. These results suggest that the lack of benzene degradation in the sulfate-reduction zones of some aquifers may result from the failure of the appropriate benzene-degrading sulfate reducers to colonize the aquifers rather than from environmental conditions that are adverse for anaerobic benzene degradation. PMID:9464422

The volume of fine sediment in pools: An index of sediment supply in gravel-bed streams

Treesearch

Thomas E. Lisle; Sue Hilton

1992-01-01

Abstract - During waning flood flows in gravel-bed streams, fine-grained bedload sediment (sand and fine gravel) is commonly winnowed from zones of high shear stress, such as riffles, and deposited in pools, where it mantles an underlying coarse layer. As sediment load increases, more fine sediment becomes availabe to fill pools. The volume of fine sediment in pools...

Oceanography and Mine Warfare

DTIC Science & Technology

2000-03-13

of breaking waves , the position and strength of surface currents, and the propagation of the tide into very shallow waters. In the surf zone...6) sediment properties determine shock wave propagation , a method for mine neutralization in the surf zone. 48 OCEANOGRAPHY AND MINE WARFARE...mines will be buried in the sediments, sedimentary explosive shock wave propagation is critical for determining operational performance. Presently, we

Watershed scale assessment of the impact of forested riparian zones on stream water quality

Treesearch

J. A. Webber; K. W. J. Williard; M. R. Whiles; M. L. Stone; J. J. Zaczek; D. K. Davie

2003-01-01

Federal and state land management agencies have been promoting forest and grass riparian zones to combat non-point source nutrient and sediment pollution of our nations' waters. The majority of research examining the effectiveness of riparian buffers at reducing nutrient and sediment inputs to streams has been conducted at the field scale. This study took a...

Eogenetic siderite as an indicator for fluctuations in sedimentation rate in the Oligocene Boom Clay Formation (Belgium)

NASA Astrophysics Data System (ADS)

Laenen, B.; De Craen, M.

2004-01-01

Horizons with septarian concretions are a salient feature of the marine Boom Clay Formation. At most horizons, the concretions consist of ferroan calcite with variable amounts of pyrite, but at stratigraphic level S60 they also contain siderite. S60 is situated at the centre of an intensely bioturbated zone that is underlain by a pyrite-rich layer. Furthermore, the enclosing clay is strongly enriched in iron, manganese and phosphorous. The sedimentological and chemical zoning is indicative for low sedimentation rates, which allowed the concentration of iron in the aerobic zone of the sediment. Concentration of iron was the prerequisite for the formation of the siderite-containing concretions. The co-precipitation with pyrite is an argument for a formation in the sulphate reduction zone, and is indicative for a high rate of iron-reduction. The latter was due to the rapid burial of the iron-enriched layer below the redox boundary. The abrupt fluctuations in sedimentation rate were a response to the maximum flooding event of the second Rupelian third-order relative sea-level cycle, which caused a brief pushback of the detrital sediment wedge to its source areas. As this response is logically explained by the general sequence stratigraphic model [Spec. Publ.-Soc. Econ. Paleontol. Mineral. 42 (1988) 109], early diagenetic siderite may be widespread at maximum flooding surfaces in rapidly prograding marine mudstones.

Harmonised framework for ecological risk assessment of sediments from ports and estuarine zones of North and South Atlantic.

PubMed

Choueri, R B; Cesar, A; Abessa, D M S; Torres, R J; Riba, I; Pereira, C D S; Nascimento, M R L; Morais, R D; Mozeto, A A; DelValls, T A

2010-04-01

This paper presents a harmonised framework of sediment quality assessment and dredging material characterisation for estuaries and port zones of North and South Atlantic. This framework, based on the weight-of-evidence approach, provides a structure and a process for conducting sediment/dredging material assessment that leads to a decision. The main structure consists of "step 1" (examination of available data); "step 2" (chemical characterisation and toxicity assessment); "decision 1" (any chemical level higher than reference values? are sediments toxic?); "step 3" (assessment of benthic community structure); "step 4" (integration of the results); "decision 2" (are sediments toxic or benthic community impaired?); "step 5" (construction of the decision matrix) and "decision 3" (is there environmental risk?). The sequence of assessments may be interrupted when the information obtained is judged to be sufficient for a correct characterisation of the risk posed by the sediments/dredging material. This framework brought novel features compared to other sediment/dredging material risk assessment frameworks: data integration through multivariate analysis allows the identification of which samples are toxic and/or related to impaired benthic communities; it also discriminates the chemicals responsible for negative biological effects; and the framework dispenses the use of a reference area. We demonstrated the successful application of this framework in different port and estuarine zones of the North (Gulf of Cádiz) and South Atlantic (Santos and Paranaguá Estuarine Systems).

Glacimarine sedimentation in Petermann Fjord and Nares Strait, NW Greenland

NASA Astrophysics Data System (ADS)

Hogan, Kelly; Jakobsson, Martin; Mayer, Larry; Mix, Alan; Nielsen, Tove; Kamla, Elina; Reilly, Brendan; Heirman, Katrina An; Stranne, Christian; Mohammed, Rezwan; Eriksson, Bjorn; Jerram, Kevin

2017-04-01

Here we build on preliminary results from 6500 line-km of high-resolution chirp sub-bottom profiles (2-7 kHz) acquired in Petermann Fjord and Nares Strait during the Petermann 2015 Expedition of the Swedish icebreaker Oden. We map the unlithified sediment cover in Peterman Fjord, which consists of up to 3 conformable "drape" units and calculate volumes of this assumed "post-glacial" fill. In Nares Strait we have mapped sediment volumes in local basins just beyond the sill at the Petermann Fjord-mouth: do these sediments represent material flushed out from the grounding zone of Petermann Glacier when it was grounded at the sill? In this vein, and interestingly, some of the thickest sediments that we observe are found close to a grounding-zone wedge (GZW) in Nares Strait that represents a former grounding zone of ice retreating southwards through the strait. We also map conformable units across Nares Strait and consider the similarities between these and the sediment units in the fjord. Do the strong reflections between the units represent the same climatic, oceanographic or process-shift both inside and outside the fjord? We also aim to tie our new acoustic stratigraphy to sediment-core data (lithofacies, dates) and, therefore, to comment on the age of the mapped sediment units and present ideas on the glacimarine flux of material to the Petermann-Nares system. Primary sediment delivery to the seafloor in this environment is thought to be predominantly through sedimentation from meltwater plumes but also of iceberg-rafted debris (IRD). However, sediment redeposition by slope failures on a variety of scales also occurs and has focussed sediments into discrete basins where the seafloor is rugged. This work - which aims to relate past sediment, meltwater and iceberg fluxes to changes in climate - will help us to identify how the system has responded to a past global warming event, namely the last deglaciation. This is particularly relevant in light of the recent thinning and acceleration of NW Greenland's marine-terminating outlet glaciers.

[Formation Mechanism of Aerobic Granular Sludge and Removal Efficiencies in Integrated ABR-CSTR Reactor].

PubMed

Wu, Kai-cheng; Wu, Peng; Xu, Yue-zhong; Li, Yue-han; Shen, Yao-liang

2015-08-01

Anaerobic Baffled Reactor (ABR) was altered to make an integrated anaerobic-aerobic reactor. The research investigated the mechanism of aerobic sludge granulation, under the condition of continuous-flow. The last two compartments of the ABR were altered into aeration tank and sedimentation tank respectively with seeded sludge of anaerobic granular sludge in anaerobic zone and conventional activated sludge in aerobic zone. The HRT was gradually decreased in sedimentation tank from 2.0 h to 0.75 h and organic loading rate was increased from 1.5 kg x (M3 x d)(-1) to 2.0 kg x (M3 x d)(-1) while the C/N of 2 was controlled in aerobic zone. When the system operated for 110 days, the mature granular sludge in aerobic zone were characterized by compact structure, excellent sedimentation performance (average sedimentation rate was 20.8 m x h(-1)) and slight yellow color. The system performed well in nitrogen and phosphorus removal under the conditions of setting time of 0.75 h and organic loading rate of 2.0 kg (m3 x d)(-1) in aerobic zone, the removal efficiencies of COD, NH4+ -N, TP and TN were 90%, 80%, 65% and 45%, respectively. The results showed that the increasing selection pressure and the high organic loading rate were the main propulsions of the aerobic sludge granulation.

Identifying and Quantifying Chemical Forms of Sediment-Bound Ferrous Iron.

NASA Astrophysics Data System (ADS)

Kohler, M.; Kent, D. B.; Bekins, B. A.; Cozzarelli, I.; Ng, G. H. C.

2015-12-01

Aqueous Fe(II) produced by dissimilatory iron reduction comprises only a small fraction of total biogenic Fe(II) within an aquifer. Most biogenic Fe(II) is bound to sediments on ion exchange sites; as surface complexes and, possibly, surface precipitates; or incorporated into solid phases (e.g., siderite, magnetite). Different chemical forms of sediment-bound Fe(II) have different reactivities (e.g., with dissolved oxygen) and their formation or destruction by sorption/desorption and precipitation/dissolution is coupled to different solutes (e.g., major cations, H+, carbonate). We are quantifying chemical forms of sediment-bound Fe(II) using previously published extractions, novel extractions, and experimental studies (e.g., Fe isotopic exchange). Sediments are from Bemidji, Minnesota, where biodegradation of hydrocarbons from a burst oil pipeline has driven extensive dissimilatory Fe(III) reduction, and sites potentially impacted by unconventional oil and gas development. Generally, minimal Fe(II) was mobilized from ion exchange sites (batch desorption with MgCl2 and repeated desorption with NH4Cl). A < 2mm sediment fraction from the iron-reducing zone at Bemidji had 1.8umol/g Fe(II) as surface complexes or carbonate phases (sodium acetate at pH 5) of which ca. 13% was present as surface complexes (FerroZine extractions). Total bioavailable Fe(III) and biogenic Fe(II) (HCl extractions) was 40-50 umole/g on both background and iron-reducing zone sediments . Approximately half of the HCl-extractable Fe from Fe-reducing zone sediments was Fe(II) whereas 12 - 15% of Fe extracted from background sediments was present as Fe(II). One-third to one-half of the total biogenic Fe(II) extracted from sediments collected from a Montana prairie pothole located downgradient from a produced-water disposal pit was present as surface-complexed Fe(II).

Diatoms dominate the eukaryotic metatranscriptome during spring in coastal 'dead zone' sediments.

PubMed

Broman, Elias; Sachpazidou, Varvara; Dopson, Mark; Hylander, Samuel

2017-10-11

An important characteristic of marine sediments is the oxygen concentration that affects many central metabolic processes. There has been a widespread increase in hypoxia in coastal systems (referred to as 'dead zones') mainly caused by eutrophication. Hence, it is central to understand the metabolism and ecology of eukaryotic life in sediments during changing oxygen conditions. Therefore, we sampled coastal 'dead zone' Baltic Sea sediment during autumn and spring, and analysed the eukaryotic metatranscriptome from field samples and after incubation in the dark under oxic or anoxic conditions. Bacillariophyta (diatoms) dominated the eukaryotic metatranscriptome in spring and were also abundant during autumn. A large fraction of the diatom RNA reads was associated with the photosystems suggesting a constitutive expression in darkness. Microscope observation showed intact diatom cells and these would, if hatched, represent a significant part of the pelagic phytoplankton biomass. Oxygenation did not significantly change the relative proportion of diatoms nor resulted in any major shifts in metabolic 'signatures'. By contrast, diatoms rapidly responded when exposed to light suggesting that light is limiting diatom development in hypoxic sediments. Hence, it is suggested that diatoms in hypoxic sediments are on 'standby' to exploit the environment if they reach suitable habitats. © 2017 The Author(s).

Quaternary geology and geologic hazards of the West Desert Hazardous Industry Area, Tooele County, Utah

USGS Publications Warehouse

Solomon, Barry J.; Black, Bill D.; ,

1990-01-01

The study of Quaternary geology provides information to evaluate geologic conditions and identify geologic constraints on construction in the West Desert Hazardous Industry Area (WDHIA). The WDHIA includes portions of the Great Salt Lake Desert to the west, underlain by several thousand feet of sediments capped by saline mudflats, and Ripple Valley to the east, separated from the Desert by the Grayback Hills and underlain by several hundred feet of sediments in the Cedar Mountains piedmont zone. Quaternary surficial units include marginal, shore-zone, and deep-water lacustrine sediments deposited in Pleistocene Lake Bonneville; eolian deposits; and alluvial sediments. The level of Lake Bonneville underwent major oscillations resulting in the creation of four basin-wide shorelines, three of which are recognized in the WDHIA. Geologic hazards in the WDHIA include the possible contamination of ground water in basin-fill aquifers, debris flows and flash floods in the piedmont zone, and earthquakes and related hazards. Numerous factors contribute to unsafe foundation conditions. Silty and sandy sediments may be subject to liquefaction or hydrocompaction, clayey sediments and mud flats of the Great Salt Lake Desert may be subject to shrinking or swelling, and gypsiferous dunes and salt flats are subject to subsidence due to dissolution.

Thermodynamically controlled preservation of organic carbon in floodplains

NASA Astrophysics Data System (ADS)

Boye, Kristin; Noël, Vincent; Tfaily, Malak M.; Bone, Sharon E.; Williams, Kenneth H.; Bargar, John R.; Fendorf, Scott

2017-06-01

Organic matter decomposition in soils and terrestrial sediments has a prominent role in the global carbon cycle. Carbon stocks in anoxic environments, such as wetlands and the subsurface of floodplains, are large and presumed to decompose slowly. The degree of microbial respiration in anoxic environments is typically thought to depend on the energetics of available terminal electron acceptors such as nitrate or sulfate; microbes couple the reduction of these compounds to the oxidation of organic carbon. However, it is also possible that the energetics of the organic carbon itself can determine whether it is decomposed. Here we examined water-soluble organic carbon by Fourier-transform ion-cyclotron-resonance mass spectrometry to compare the chemical composition and average nominal oxidation state of carbon--a metric reflecting whether microbial oxidation of organic matter is thermodynamically favourable--in anoxic (sulfidic) and oxic (non-sulfidic) floodplain sediments. We observed distinct minima in the average nominal oxidation state of water-soluble carbon in sediments exhibiting anoxic, sulfate-reducing conditions, suggesting preservation of carbon compounds with nominal oxidation states below the threshold that makes microbial sulfate reduction thermodynamically favourable. We conclude that thermodynamic limitations constitute an important complement to other mechanisms of carbon preservation, such as enzymatic restrictions and mineral association, within anaerobic environments.

[Exchange Fluxes and Coupling Relationship of Dissolved Inorganic Carbon and Dissolved Organic Carbon Across the Water-Sediment Interface in Lakes].

PubMed

Wang, Wei-ying; Lü, Chang-wei; He, Jiang; Zuo, Le; Yan, Dao-hao

2015-10-01

In this work, the exchange fluxes and coupling relationship of dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) were investigated across the water-sediment interface in Lake Wuliangsuhai and Daihai by employing columnar simulation method. The results showed that the sediments in non-Phragmitescommunis area from Lake Wuliangsuhai functioned as the sources of DIC and DOC for overlying water, whereas the sediments from Lake Daihai as the sinks during the period of summer (90 days). In the experimental period, the average exchange rates of DIC and DOC were 71.07 mmol x (m2 x d)(-1) and 185.09 mmol x (m2 x d)(-1) in non-Phragmitescommunis area from Lake Wuliangsuhai, respectively; while in Lake Daihai, they were 155.75 mmol x (m2 x d)(-1) and -1478.08 mmol x (m2 x d)(-1) in shoal water zone, and -486.53 mmol x (m2 x d)(-1) and -1274.02 mmol x (m2 x d)(-1) in deep water zone, respectively. The coupling effects between DIC and DOC were governed by hydrobios, microbial uptake, abiotic and microbiological degradation in Lake Wuliangsuhai and in shoal water zone of Lake Daihai; while they were closely related to the coprecipitation process of CaCO3 and the fraction distribution of inorganic carbon in sediments in deep water zone of Lake Daihai. In summary, the sink or source functions of sediments could be considered as the results of synthetic action of lake types, offshore distance, geohydrochemistry and the fraction distribution of inorganic carbon.

Natural and anthropogenic controls on sediment composition of an arid coastal environment: Sharm Obhur, Red Sea, Saudi Arabia.

PubMed

Ghandour, I M; Basaham, A S; Basaham, S; Al-Washmi, H A; Al-Washmi, A; Masuda, H

2014-03-01

The present study investigated the natural and anthropogenic processes that control the composition of the bottom sediments of Sharm Obhur, Red Sea. Mineralogical analysis using XRD indicated that the sediments consist of carbonate and non-carbonate minerals. Elemental interrelationships allowed differentiating two groups of elements of different sources and origin. Elements that are in the same group are positively correlated, while they correlate negatively with elements of the other group. The first group includes silicon, Al, Fe, Mn, Mg, vanadium (V), chromium (Cr), Co, Ni, Cu, and Zn, whereas the other group includes Ca, Sr, and CaCO3. The highest concentration levels of the first group and the highest content of non-carbonate minerals were obtained from the sediments near the head of the sharm (zone A), whereas the sediments near the mouth of the sharm (zone B) yielded high concentrations of second group and carbonate minerals. Metal enrichment and contamination factors and pollution load index were calculated. The values of these indices differentiate two groups of metals: lithogenic and non-lithogenic. Except for lead (Pb) at one sampling site, metals in zone A sediments are of lithogenic source, supplied to the sharm either naturally by aeolian transportation and through Wadi Al-Kuraa'a during rare but major floods or by human activities such as dumping and shore protection. Non-lithogenic Cr, Pb, V, and Mn were documented from some sampling sites in zone B, and their occurrences are related to waste disposal and fossil fuel combustion.

Application of Remote Sensing to Assess the Impact of Short Term Climate Variability on Coastal Sedimentation

NASA Technical Reports Server (NTRS)

Menzel, W. Paul; Huh, Oscar K.; Walker, Nan

2004-01-01

The purpose of this joint University of Wisconsin (UW) and Louisiana State University (LSU) project has been to relate short term climate variation to response in the coastal zone of Louisiana in an attempt to better understand how the coastal zone is shaped by climate variation. Climate variation in this case largely refers to variation in surface wind conditions that affect wave action and water currents in the coastal zone. The primary region of focus was the Atchafalaya Bay and surrounding bays in the central coastal region of Louisiana. Suspended solids in the water column show response to wind systems both in quantity (through resuspension) and in the pattern of dispersement or transport. Wind systems associated with cold fronts are influenced by short term climate variation. Wind energy was used as the primary signature of climate variation in this study because winds are a significant influence on sediment transport in the micro-tidal Gilf of Mexico coastal zone. Using case studies, the project has been able to investigate the influence of short term climate variation on sediment transport. Wind energy data, collected daily for National Weather Service (NWS) stations at Lake Charles and New Orleans, LA, were used as an indicator of short term climate variation influence on seasonal time scales. A goal was to relate wind energy to coastal impact through sediment transport. This goal was partially accomplished by combining remote sensing and wind energy data. Daily high resolution remote sensing observations are needed to monitor the complex coastal zone environment, where winds, tides, and water level all interact to influence sediment transport. The NASA Earth Observing System (EOS) era brings hope for documenting and revealing response of the complex coastal transport mosaic through regular high spatial resolution observations from the Moderate resolution Imaging Spectrometer (MODIS) instrument. MODIS observations were sampled in this project for information content and should continue to be viewed as a resource for coastal zone monitoring. The project initialized the effort to transfer a suspended sediment concentration (SSC) algorithm to the MODIS platform for case 2 waters. MODIS enables monitoring of turbid coastal zones around the globe. The MODIS SSC algorithm requires refinements in the atmospheric aerosol contribution, sun glint influence, and designation of the sediment inherent optical properties (IOPs); the framework for continued development is in place with a plan to release the algorithm to the MODIS direct broadcast community.

Structural architecture and petrophysical properties of the Rocca di Neto extensional fault zone developed in the shallow marine sediments of the Crotone Basin (Southern Apennines, Italy).

NASA Astrophysics Data System (ADS)

Pizzati, Mattia; Balsamo, Fabrizio; Iacumin, Paola; Swennen, Rudy; Storti, Fabrizio

2017-04-01

In this contribution we describe the architecture and petrophysical properties of the Rocca di Neto extensional fault zone in loose and poorly lithified sediments, located in the Crotone forearc basin (south Italy). To this end, we combined fieldwork with microstructural observations, grain size analysis, and in situ permeability measurements. The studied fault zone has an estimated maximum displacement of 80-90 m and separates early Pleistocene age (Gelasian) sands in the footwall from middle Pleistocene (Calabrian) silty clay in the hangingwall. The analysed outcrop consists of about 70 m section through the fault zone mostly developed in the footwall block. Fault zone consists of four different structural domains characterized by distinctive features: (1) <1 m-thick fault core (where the majority of the displacement is accommodated) in which bedding is transposed into foliation imparted by grain preferential orientation and some black gouges decorate the main slip surfaces; (2) zone of tectonic mixing characterized by a set of closely spaced and anastomosed deformation bands parallel to the main slip surface; (3) about 8 m-thick footwall damage zone characterized by synthetic and antithetic sets of deformation bands; (4) zone of background deformation with a few, widely-spaced conjugate minor faults and deformation bands. The boundary between the relatively undeformed sediments and the damage zone is not sharp and it is characterized by a progressive decrease in deformation intensity. The silty clay in the hangingwall damage zone is characterized by minor faults. Grain size and microstructural data indicate that particulate flow with little amount of cataclasis is the dominant deformation mechanism in both fault core rocks and deformation bands. Permeability of undeformed sediments is about 70000 mD, whereas the permeability in deformation bands ranges from 1000 to 18000 mD; within the fault core rocks permeability is reduced up to 3-4 orders of magnitude respect to the undeformed domains. Structural and petrophysical data suggest that the Rocca di Neto fault zone may compartmentalize the footwall block due to both juxtaposition of clay-rich lithology in the hangingwall and the development of low permeability fault core rocks.

Sediment-pore water interactions controlling cementation in the NanTroSEIZE drilling transects

NASA Astrophysics Data System (ADS)

Hong, W.; Spinelli, G. A.; Torres, M. E.

2012-12-01

One goal of the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE) is to understand how changes in subducting sediment control the transition from aseismic to seismogenic behavior in subduction zones. In the sediment entering the Nankai subduction zone, dramatic changes in physical and chemical properties occur across a diagenetic boundary; they are thought to affect sediment strength and deformation. The dissolution of disseminated volcanic ash and precipitation of silica cement may be responsible for these changes in physical properties, but the mechanism controlling cementation was unclear (Spinelli et al., 2007). In this study, we used CrunchFlow (Steefel, 2009) to simulate chemical reactions and fluid flow through 1-D sediment columns at Integrated Ocean Drilling Program (IODP) sites on the incoming plate in Nankai Trough. The simulations include the thermodynamics and kinetics of sediment-water interactions, advection of pore water and sediment due to compaction, and multi-component diffusion in an accumulating sediment column. Key reactions in the simulations are: ash dissolution, amorphous silica precipitation and dissolution, and zeolite precipitation. The rate of ash decomposition was constrained using Sr isotope data of Joseph et al. (2012). Our model reproduces the distinct diagenetic boundary observed in sediment and pore water chemistry, which defines two zones. Above this boundary (zone 1), dissolved and amorphous silicate contents are high and the potassium concentration remains near seawater values or gradually decreases toward the boundary. Below the boundary, both dissolved and amorphous silicate content drop rapidly, concomitant with a decrease in dissolved potassium. Our model shows that these changes in the system are driven by formation of clinoptilolite in response to changes in pore fluid pH. The low pH values (<7.6) above the diagenetic boundary accelerate ash decomposition and maintain clinoptilolite slightly undersaturated. The dissolved silicate released from ash alteration precipitates as cement, inhibiting consolidation. At or below the boundary, the increase in pH (>8.0), leads to oversaturation (and precipitation) of clinoptilolite. Strong demand of dissolved silicate due to clinoptilolite formation soon depletes the dissolved potassium and silicate; ash and silicate cement are forced to dissolve. The exact set of reactions resulting on the observed pH increase is still unclear, but it likely involves the carbon system. It is noteworthy that the diagenetic boundary at all sites in the incoming plate occurs at the same thermal maturity of the sediments (TTI=0.025), similar to observations on onshore sequences in Japan (Sasaki, 1986).

Sediment bacterial community structures and their predicted functions implied the impacts from natural processes and anthropogenic activities in coastal area.

PubMed

Su, Zhiguo; Dai, Tianjiao; Tang, Yushi; Tao, Yile; Huang, Bei; Mu, Qinglin; Wen, Donghui

2018-06-01

Coastal ecosystem structures and functions are changing under natural and anthropogenic influences. In this study, surface sediment samples were collected from disturbed zone (DZ), near estuary zone (NEZ), and far estuary zone (FEZ) of Hangzhou Bay, one of the most seriously polluted bays in China. The bacterial community structures and predicted functions varied significantly in different zones. Firmicutes were found most abundantly in DZ, highlighting the impacts of anthropogenic activities. Sediment total phosphorus was most influential on the bacterial community structures. Predicted by PICRUSt analysis, DZ significantly exceeded FEZ and NEZ in the subcategory of Xenobiotics Biodegradation and Metabolism; and DZ enriched all the nitrate reduction related genes, except nrfA gene. Seawater salinity and inorganic nitrogen, respectively as the representative natural and anthropogenic factor, performed exact-oppositely in nitrogen metabolism functions. The changes of bacterial community compositions and predicted functions provide a new insight into human-induced pollution impacts on coastal ecosystem. Copyright © 2018 Elsevier Ltd. All rights reserved.

Isoprenoid quinones resolve the stratification of microbial redox processes in a biogeochemical continuum from the photic zone to deep anoxic sediments of the Black Sea.

PubMed

Becker, Kevin W; Elling, Felix J; Schröder, Jan M; Lipp, Julius S; Goldhammer, Tobias; Zabel, Matthias; Elvert, Marcus; Overmann, Jörg; Hinrichs, Kai-Uwe

2018-03-09

The stratified water column of the Black Sea serves as a model ecosystem for studying the interactions of microorganisms with major biogeochemical cycles. Here we provide detailed analysis of isoprenoid quinones to study microbial redox processes in the ocean. In a continuum from the photic zone through the chemocline into deep anoxic sediments of the southern Black Sea, diagnostic quinones and inorganic geochemical parameters indicate niche segregation between redox processes and corresponding shifts in microbial community composition. Quinones specific for oxygenic photosynthesis and aerobic respiration dominate oxic waters, while quinones associated with thaumarchaeal ammonia-oxidation and bacterial methanotrophy, respectively, dominate a narrow interval in suboxic waters. Quinone distributions indicate highest metabolic diversity within the anoxic zone, with anoxygenic photosynthesis being a major process in its photic layer. In the dark anoxic layer, quinone profiles indicate occurrence of bacterial sulfur and nitrogen cycling, archaeal methanogenesis, and archaeal methanotrophy. Multiple novel ubiquinone isomers, possibly originating from unidentified intra-aerobic anaerobes, occur in this zone. The respiration modes found in the anoxic zone continue into shallow subsurface sediments, but quinone abundances rapidly decrease within the upper 50 cm below sea floor, reflecting the transition to lower energy availability. In the deep subseafloor sediments, quinone distributions and geochemical profiles indicate archaeal methanogenesis/methanotrophy and potentially bacterial fermentative metabolisms. We observed that sedimentary quinone distributions track lithology, which supports prior hypotheses that deep biosphere community composition and metabolisms are determined by environmental conditions during sediment deposition. Importance Microorganisms play crucial roles in global biogeochemical cycles. Yet, we have only a fragmentary understanding of the diversity of microorganisms and their metabolisms, as the majority remains uncultured. Thus, culture-independent approaches are critical for determining microbial diversity and active metabolic processes. In order to resolve the stratification of microbial communities in the Black Sea, we comprehensively analyzed redox process-specific isoprenoid quinone biomarkers in a unique continuous record from the photic zone through the chemocline into anoxic subsurface sediments. We describe an unprecedented quinone diversity that allowed us to detect distinct biogeochemical processes including oxygenic photosynthesis, archaeal ammonia oxidation, aerobic methanotrophy and anoxygenic photosynthesis in defined geochemical zones. Copyright © 2018 American Society for Microbiology.

The Middle Jurassic microflora from El Maghara N° 4 borehole, Northern Sinai, Egypt

NASA Astrophysics Data System (ADS)

Mohsen, Sayed Abdel

The coal bearing formation in El Maghara area, northern Sinai, yielded abundant, diverse and generally well preserved spores, pollen and marine microflora. The palynological analysis of the fine clastic sediments in this formation yielded (71) species related to (44) genera. Three different palynological assemblage zones can be distinguished. The sediments which contain lower and the upper assemblage zones bearing the coal seems, were deposited in non-marine (swamp) environment. In the middle assemblage zone few marine microflora can be identified, indicating a coastal near shore marine environment. Compared with other palynologic data obtained from Egypt and other countries, the three described assemblage zones belong to Middle Jurassic (Bathonian) age.

Microbial Nitrogen Cycling Associated with the Early Diagenesis of Organic Matter in Subseafloor Sediments

NASA Astrophysics Data System (ADS)

Zhao, R.

2015-12-01

The early diagenesis of organic matter is the major energy source of marine sedimentary biosphere and thus controls its population size; however, the vertical distribution of any functional groups along with the diagenesis of organic matter is remained unclear, especially for those microbes involved in nitrogen transformation which serve as a major control on the nitrogen flux between reservoirs. Here we investigated the vertical distributions of various functional groups in five sediment cores retrieved from Arctic Mid-Ocean Ridge (AMOR), with emphasis on the nitrifiers, denitrifiers and anaerobic ammonium oxidizing bacteria (anammox). We observed the clear geochemical zonation associated with organic matter diagenesis in the sediments based on the pore water profiles of oxygen, nitrate, ammonium, manganese and sulfate, with distinct geochemical transition zones at the boundaries of geochemical zones, including oxic-anoxic transition zone (OATZ) and nitrate-manganese reduction zone (NMTZ). Nitrate was produced in surface oxygenated sediments and nitrate consumption mainly took place at the NMTZ, splitted between re-oxidation of ammonium and manganese (II). Abundances of ammonia oxidizers, nitrite oxidizers, and denitrifiers, estimated through quantitative PCR targeting their respective functional genes, generally decrease with depth, but constantly elevated around the OATZ, NMTZ, and manganese-reduction zone as well. Anammox bacteria were only detected around the NMTZ where both nitrate/nitrite and ammonium are available. These depth profiles of functional groups were also confirmed by the community structure profiling by prokaryotic 16S rRNA gene tag pyrosequencing. Cell-specific rates of nitrification and denitrification, calculated from the bulk net reaction rates divided by functional group abundances, were similar to those values from oligotrophic sediments like North Pond and thus suggested that nitrifiers and denitirifiers populations were in maintenance state. This study illustrated the microbial nitrogen transformation accompanying the early diagenesis of organic matter in marine sediments, which scenario might be occurring in a wide range of stratified environments on Earth.

Organic Geochemistry of Sediments in Nearshore Areas of the Mississippi and Atchafalaya Rivers: I. General Organic Characterization

USGS Publications Warehouse

Orem, William H.; Rosenbauer, Robert J.; Swarzenski, Peter W.; Lerch, Harry E.; Corum, Margo D.; Bates, Anne L.

2007-01-01

This report presents results on the general organic characteristics of sediment cores collected from the coastal zone of the Mississippi River system, including distributions of the important nutrient elements (C, N, P, and S). This was part of a larger study conducted from 2001-2005 to examine the delivery of sediment-associated contaminants to the Gulf of Mexico by the Mississippi River system, funded by the USGS Coastal and Marine Geology Program. Companion reports emphasize organic contaminants (Rosenbauer and others, 2006), and metals (Swarzenski and others, 2006). The level of contamination within the deltaic system of the Mississippi River system was determined through the collection of sediment cores from interdistributary bays, and offshore in the Gulf of Mexico, including the zone of hypoxia. Results provide the basis for reconstructing contaminant inventories from which to develop historic perspectives on nutrient loading and hypoxia, and to better understand how sediment-hosted contaminants either directly or indirectly move through biota and ultimately affect ecosystem health. Concentrations of C, N, P, and S in sediments varied by a factor of 10 between sites, and in down core profiles. Nearshore cores collected in 2001 proved to have erratic downcore C, N, P, and S profiles and sediment deposition rates, suggesting a high energy regime controlled more by variability in river flow rather than by geochemical processes and reactions within the system. These results focused further coring activities further offshore. Atomic C/N ratios suggest that organic matter deposited at all sites is a mix of microbial (algal) and terrestrial (vascular plant) remains, but with algal material dominant. Concentrations of total sulfur in sediments from cores in the zone of hypoxia were often higher than those in nearby zones with oxic water columns. Corresponding atomic C/S ratios were typically lower in sediments from sites in the zone of hypoxia compared to nearby sites with oxic water columns, and thus atomic C/S values may be useful as a proxy for identifying sites impacted by hypoxic conditions in the water column and for examining historical trends in hypoxia. At one site examined in this study, maximum hypoxic conditions were observed in the mid 1960's. The organic elemental composition (C, N, P, and S) of sediments was also used to guide sample selection for contaminant analysis, and to normalize the contaminant data to organic C content of the sediments. Dissolved hydrocarbon gases in sediments showed a dominance of methane, but identifiable concentrations of ethane and hexane, and trace concentrations of propane, butane, and pentane were also detected. All dissolved gases except hexane were dominated by 'bound' gas, gas released only after agitation of the sediment in a blender. Hexane, in contrast was observed mostly as free gas, determined by headspace analysis.

Effect of grain-coating mineralogy on nitrate and sulfate storage in the unsaturated zone

USGS Publications Warehouse

Reilly, T.J.; Fishman, N.S.; Baehr, A.L.

2009-01-01

Unsaturated-zone sediments and the chemistry of shallow groundwater underlying a small (???8-km2) watershed were studied to identify the mechanisms responsible for anion storage within the Miocene Bridgeton Formation and weathered Coastal Plain deposits in southern New Jersey. Lower unsaturated-zone sediments and shallow groundwater samples were collected and concentrations of selected ions (including NO3- and SO42-) from 11 locations were determined. Grain size, sorting, and color of the lower unsaturated-zone sediments were determined and the mineralogy of these grains and the composition of coatings were analyzed by petrographic examination, scanning electron microscopy and energy dispersive analysis of x-rays, and quantitative whole-rock x-ray diffraction. The sediment grains, largely quartz and chert (80-94% w/w), are coated with a very fine-grained (<20 ??m), complex mixture of kaolinite, halloysite, goethite, and possibly gibbsite and lepidocrocite. The mineral coatings are present as an open fabric, resulting in a large surface area in contact with pore water. Significant correlations between the amount of goethite in the grain coatings and the concentration of sediment-bound SO42- were observed, indicative of anion sorption. Other mineral-chemical relations indicate that negatively charged surfaces and competition with SO 42- results in exclusion of NO3- from inner sphere exchange sites. The observed NO3- storage may be a result of matrix forces within the grain coatings and outer sphere complexation. The results of this study indicate that the mineralogy of grain coatings can have demonstrable effects on the storage of NO 3- and SO42- in the unsaturated zone. ?? Soil Science Society of America. All rights reserved.

Glacially-derived overpressure in the northeastern Alaskan subduction zone: combined tomographic and morphometric analysis of shallow sediments on the Yakutat shelf and slope, Gulf of Alaska

NASA Astrophysics Data System (ADS)

Clary, W. A.; Worthington, L. L.; Scuderi, L. A.; Daigle, H.; Swartz, J. M.

2017-12-01

The Pamplona zone fold and thrust belt is the offshore expression of convergence and shallow subduction of the Yakutat microplate beneath North America in the northeastern Alaska subduction zone. The combination of convergent tectonics and glaciomarine sedimentary processes create patterns of deformation and deposition resulting in a shallow sedimentary sequence with varying compaction, fluid pressure, and fault activity. We propose that velocity variations observed in our tomographic analysis represent long-lived fluid overpressure due to loading by ice sheets and sediments. Regions with bathymetric and stratigraphic evidence of recent ice sheets and associated sedimentation should be collocated with evidence of overpressure (seismic low velocity zones) in the shallow sediments. Here, we compare a velocity model with shelf seismic stratigraphic facies and modern seafloor morphology. To document glacially derived morphology we use high resolution bathymetry to identify channel and gully networks on the western Yakutat shelf-slope then analyze cross-channel shape indices across the study area. We use channel shape index measurements as a proxy of recent ice-proximal sedimentation based on previously published results that proposed a close correlation. Profiles taken at many locations were fitted with a power function and assigned a shape - U-shape channels likely formed proximal to recent ice advances. Detailed velocity models were created by a combination of streamer tomography and pre-stack depth migration velocities with seismic data including: a 2008 R/V Langseth dataset from the St. Elias Erosion and Tectonics Project (STEEP); and a 2004 high-resolution R/V Ewing dataset. Velocity-porosity-permeability relationships developed using IODP Expedition 341 drilling data inform interpretation and physical properties analyses of the shallow sediments. Initial results from a 35 km profile extending SE seaward of the Bering glacier and subparallel to the Bering trough suggest a spatial relationship between the extent of U-shaped profiles and low-velocity shallow sediments. Towards the SE end of the model we observe a large overlap of U-shaped indices, and a shallow low-velocity zone in the mapped extent of the last glacial maximum suggestive of overpressure due to loading by ice sheet activity.

Nearshore Coastal Dynamics on a Sea-Breeze Dominated Micro-Tidal Beach (NCSAL)

NASA Astrophysics Data System (ADS)

Torres-Freyermuth, A.; Puleo, J. A.; Ruiz de Alegría-Arzaburu, A.; Figlus, J.; Mendoza, T.; Pintado-Patino, J. C.; Pieterse, A.; Chardon-Maldonado, P.; DiCosmo, N. R.; Wellman, N.; Garcia-Nava, H.; Palemón-Arcos, L.; Roberts, T.; López-González, J.; Bravo, M.; Ojeda, E.; Medellín, G.; Appendini, C. M.; Figueroa, B.; González-Leija, M.; Enriquez, C.; Pedrozo-Acuña, A.; Salles, P.

2014-12-01

A comprehensive field experiment devoted to the study of coastal processes on a micro-tidal beach was conducted from March 30th to April 12th 2014 in Sisal, Yucatán México. Wave conditions in the study area are controlled by local (i.e., sea-breezes) and meso-scale (i.e., Nortes) meteorological events. Simultaneous measurements of waves, tides, winds, currents, sediment transport, runup, and beach morphology were obtained in this experiment. Very dense nearshore instrumentation arrays allow us the study of the cross-/along- shore variability of surf/swash zone dynamics during different forcing conditions. Strong sea-breeze wind events produced a diurnal cycle with a maximum wind speed of 14 m/s. The persistent sea-breeze system forces small-amplitude (Hs<1 m) short-period (Tp<4 s) NE waves approaching with a high incidence wave angle. These wave conditions drive westward alongshore currents of up to 0.6 m/s in the inner surf zone and hence produce an active sediment transport in the swash zone. On the other hand, the more energetic (Hs>1 m) Norte event, lasting 48 hours, reached the coast on April 8th generating a long-period swell (Tp>10 s) arriving from the NNW. This event induced an eastward net sediment transport across a wide surf zone. However, long-term observations of sand impoundment at a groin located near the study area suggests that the net sediment transport in the northern Yucatan peninsula is controlled by sea-breeze events and hence swash zone dynamics play an important role in the net sediment budget of this region. A comparative study of surf and swash zone dynamics during both sea-breeze and Norte events will be presented. The Institute of Engineering of UNAM, throughout an International Collaborative Project with the University of Delaware, and CONACYT (CB-167692) provided financial support. The first author acknowledges ONR Global for providing financial support throughout the Visiting Scientist Program.

Frictional behavior of carbonate-rich sediments in subduction zones

NASA Astrophysics Data System (ADS)

Rabinowitz, H. S.; Savage, H. M.; Carpenter, B. M.; Collettini, C.

2016-12-01

Deformation in rocks and sediments is controlled by multiple mechanisms, each governed by its own pressure- (P), temperature- (T), and slip velocity- (v) dependent kinetics. Frictional behavior depends on which of these mechanisms are dominant, and, thus, varies with P, T, and v. Carbonates are a useful material with which to interrogate the PTv controls on friction due to the fact that a wide range of mechanisms can be easily accessed in the lab at geologically relevant conditions. In addition, carbonate-rich layers make up a significant component of subducting sediments around the world and may impact the frictional behavior of shallow subduction zones. In order to investigate the effect of carbonate subduction and the evolution of friction at subduction zone conditions, we conducted deformation experiments on input sediments for two subduction zones, the Hikurangi trench, New Zealand (ODP Site 1124) and the Peru trench (DSDP Site 321), which have carbonate/clay contents of 40/60 wt% and 80/20 wt%, respectively. Samples were saturated with distilled water mixed with 35g/l sea salt and deformed at room temperature. Experiments were conducted at σeff = 1-100 MPa and T = 20-100 °C with sliding velocities of 1-300 μm/s and hold times of 1-1000 s. We test the changes in velocity dependence and healing over these PT conditions to elucidate the frictional behavior of carbonates in subduction zone settings. The mechanical results are complemented by microstructural analysis. In lower stress experiments, there is no obvious shear localization; however, by 25 MPa, pervasive boundary-parallel shears become dominant, particularly in the Peru samples. Optical observations of these shear zones under cross-polarized light show evidence of plastic deformation (CPO development) while SEM-EDS observations indicate phase segregation in the boundary shears. Degree of microstructural localization appears to correspond with the trends observed in velocity-dependence. Our preliminary results indicate that carbonate/clay compositions could have a significant impact on the frictional behavior of subducting sediments.

Quantifying hyporheic exchange in a karst stream using 222Rn

NASA Astrophysics Data System (ADS)

Khadka, M. B.; Martin, J. B.; Kurz, M. J.

2013-12-01

The hyporheic zone is a critical interface between groundwater and river water environments and is characterized by steep biogeochemical gradients. Understanding how this interface affects solute transport, nutrient cycling and contaminant attenuation is essential for better water resource management of streams. However, this understanding is constrained due to difficulty associated with quantification of exchange of water through the hyporheic zone. We tested a radon (222Rn) method to estimate the hyporheic water residence time and exchange rate in the bottom sediment of the spring-fed Ichetucknee River, north-central Florida. The river, which flows over the top of the unconfined karstic Floridan Aquifer, is characterized by a broad bedrock channel partially in-filled with unconsolidated sediments. Radon (222Rn) activity in the pore waters of the channel sediments differs from the amount expected from sediment production and decay. Although most radon in streams originates from sources in bottom sediments, the Ichetucknee River water has 222Rn activities (251×5 PCi/L) that are nearly twice that of the pore water (128×15 PCi/L). The river water 222Rn activity is consistent with that of the source springs, suggesting the source of Rn in the river is from deep within the aquifer rather than bottom sediments and that the excess 222Rn in the pore water results from hyporheic exchange. Profiles of radon concentrations with depth through the sediments show that the mixing of stream water and pore water extends 35-45 cm below the sediment and water interface. Based on a model that integrates the excess radon with depth, we estimate the water exchange rate to be between 1.1 and 1.6 cm/day with an average value of 1.3×0.2 cm/day. Water that exchanges across the sediment-water interface pumps oxygen into the sediments, thereby enhancing organic carbon remineralization, as well as the production of NH4+ and PO43- and their fluxes from sediments to the stream. As opposed to conventional in-stream tracer injection method which estimates exchange between the stream and both the hyporheic zone and the surface transient storage zone, the 222Rn approach measures the water exchange between stream and hyporheic sediments only. Although the present method is tested on a spring-fed karst stream, it has potential for any freshwater system (e.g. wetland, lake) where distinct radon activity and production between surface water and underlying sediments occur.

The role of suspension events in cross-shore and longshore suspended sediment transport in the surf zone

USGS Publications Warehouse

Jaffe, Bruce E.

2015-01-01

Suspension of sand in the surf zone is intermittent. Especially striking in a time series of concentration are periods of intense suspension, suspension events, when the water column suspended sediment concentration is an order of magnitude greater than the mean concentration. The prevalence, timing, and contribution of suspension events to cross-shore and longshore suspended sediment transport are explored using field data collected in the inner half of the surf zone during a large storm at Duck, NC. Suspension events are defined as periods when the concentration is above a threshold. Events tended to occur during onshore flow under the wave crest, resulting in an onshore contribution to the suspended sediment transport. Even though large events occurred less than 10 percent of the total time, at some locations onshore transport associated with suspension events was greater than mean-current driven offshore-directed transport during non-event periods, causing the net suspended sediment transport to be onshore. Events and fluctuations in longshore velocity were not correlated. However, events did increase the longshore suspended sediment transport by approximately the amount they increase the mean concentration, which can be up to 35%. Because of the lack of correlation, the longshore suspended sediment transport can be modeled without considering the details of the intensity and time of events as the vertical integration of the product of the time-averaged longshore velocity and an event-augmented time-averaged concentration. However, to accurately model cross-shore suspended sediment transport, the timing and intensity of suspension events must be reproduced.

Stratigraphic test well, Nantucket Island, Massachusetts

USGS Publications Warehouse

Folger, David W.; Hathaway, J.C.; Christopher, R.A.; Valentine, P.C.; Poag, C.W.

1978-01-01

The U.S. Geological Survey, in cooperation with the Massachusetts Water Resources Commission and the Nantucket Conservation Foundation, continuously cored 514 m of sediment and volcanic rock in a stratigraphic and water-quality test near the geographic center of Nantucket Island. Stratified sediments were divided texturally into three zones: the upper zone (0-128 m) contains mostly coarse sand and gravel; the middle zone (128-349 m) contains mostly silty clay and a few beds of sand and silt; and the lower zone (349-457 m) contains soft, unconsolidated, clayey sand. Below the lower zone, a saprolite, composed mostly of clay, grades abruptly downward at 470 m into partially altered basalt that extends to the bottom of the hole at 514 m. Calculations based on the Ghyben-Herzberg principle predicted a zone of freshwater 120-150 m thick. This principle is the theory of hydrostatic equilibrium between freshwater and more dense seawater in a coastal aquifer; it states that for each meter of ground-water elevation above sea level, the freshwater lens will depress the saltwater interface about 40 m below sea level. Freshwater or low-salinity brackish water was found in sediments far below the depth predicted by the Ghyben-Herzberg principle. These interstitial waters are probably relict ground water emplaced during times of low sea level during the Pleistocene. (Woodard-USGS)

Microbial abundance in the deep subsurface of the Chesapeake Bay impact crater: Relationship to lithology and impact processes

USGS Publications Warehouse

Cockell, Charles S.; Gronstal, Aaron L.; Voytek, Mary A.; Kirshtein, Julie D.; Finster, Kai; Sanford, Ward E.; Glamoclija, Mihaela; Gohn, Gregroy S.; Powars, David S.; Horton, J. Wright

2009-01-01

Asteroid and comet impact events are known to cause profound disruption to surface ecosystems. The aseptic collection of samples throughout a 1.76-km-deep set of cores recovered from the deep subsurface of the Chesapeake Bay impact structure has allowed the study of the subsurface biosphere in a region disrupted by an impactor. Microbiological enumerations suggest the presence of three major microbiological zones. The upper zone (127–867 m) is characterized by a logarithmic decline in microbial abundance from the surface through the postimpact section of Miocene to Upper Eocene marine sediments and across the transition into the upper layers of the impact tsunami resurge sediments and sediment megablocks. In the middle zone (867–1397 m) microbial abundances are below detection. This zone is predominantly quartz sand, primarily composed of boulders and blocks, and it may have been mostly sterilized by the thermal pulse delivered during impact. No samples were collected from the large granite block (1096–1371 m). The lowest zone (below 1397 m) of increasing microbial abundance coincides with a region of heavily impact-fractured, hydraulically conductive suevite and fractured schist. These zones correspond to lithologies influenced by impact processes. Our results yield insights into the influence of impacts on the deep subsurface biosphere.

The winter pack-ice zone provides a sheltered but food-poor habitat for larval Antarctic krill.

PubMed

Meyer, Bettina; Freier, Ulrich; Grimm, Volker; Groeneveld, Jürgen; Hunt, Brian P V; Kerwath, Sven; King, Rob; Klaas, Christine; Pakhomov, Evgeny; Meiners, Klaus M; Melbourne-Thomas, Jessica; Murphy, Eugene J; Thorpe, Sally E; Stammerjohn, Sharon; Wolf-Gladrow, Dieter; Auerswald, Lutz; Götz, Albrecht; Halbach, Laura; Jarman, Simon; Kawaguchi, So; Krumpen, Thomas; Nehrke, Gernot; Ricker, Robert; Sumner, Michael; Teschke, Mathias; Trebilco, Rowan; Yilmaz, Noyan I

2017-12-01

A dominant Antarctic ecological paradigm suggests that winter sea ice is generally the main feeding ground for krill larvae. Observations from our winter cruise to the southwest Atlantic sector of the Southern Ocean contradict this view and present the first evidence that the pack-ice zone is a food-poor habitat for larval development. In contrast, the more open marginal ice zone provides a more favourable food environment for high larval krill growth rates. We found that complex under-ice habitats are, however, vital for larval krill when water column productivity is limited by light, by providing structures that offer protection from predators and to collect organic material released from the ice. The larvae feed on this sparse ice-associated food during the day. After sunset, they migrate into the water below the ice (upper 20 m) and drift away from the ice areas where they have previously fed. Model analyses indicate that this behaviour increases both food uptake in a patchy food environment and the likelihood of overwinter transport to areas where feeding conditions are more favourable in spring.

Thermal Alteration of Pyrite to Pyrrhotite During Earthquakes: New Evidence of Seismic Slip in the Rock Record

NASA Astrophysics Data System (ADS)

Yang, Tao; Dekkers, Mark J.; Chen, Jianye

2018-02-01

Seismic slip zones convey important information on earthquake energy dissipation and rupture processes. However, geological records of earthquakes along exhumed faults remain scarce. They can be traced with a variety of methods that establish the frictional heating of seismic slip, although each has certain assets and disadvantages. Here we describe a mineral magnetic method to identify seismic slip along with its peak temperature through examination of magnetic mineral assemblages within a fault zone in deep-sea sediments cored from the Japan Trench—one of the seismically most active regions around Japan—during the Integrated Ocean Drilling Program Expedition 343, the Japan Trench Fast Drilling Project. Fault zone sediments and adjacent host sediments were analyzed mineral magnetically, supplemented by scanning electron microscope observations with associated energy dispersive X-ray spectroscopy analyses. The presence of the magnetic mineral pyrrhotite appears to be restricted to three fault zones occurring at 697, 720, and 801 m below sea floor in the frontal prism sediments, while it is absent in the adjacent host sediments. Elevated temperatures and coseismic hot fluids as a consequence of frictional heating during earthquake rupture induced partial reaction of preexisting pyrite to pyrrhotite. The presence of pyrrhotite in combination with pyrite-to-pyrrhotite reaction kinetics constrains the peak temperature to between 640 and 800°C. The integrated mineral-magnetic, microscopic, and kinetic approach adopted here is a useful tool to identify seismic slip along faults without frictional melt and establish the associated maximum temperature.

Tidal controls on riverbed denitrification along a tidal freshwater zone

NASA Astrophysics Data System (ADS)

Knights, Deon; Sawyer, Audrey H.; Barnes, Rebecca T.; Musial, Cole T.; Bray, Samuel

2017-01-01

In coastal rivers, tidal pumping enhances the exchange of oxygen-rich river water across the sediment-water interface, controlling nitrogen cycling in riverbed sediment. We developed a one-dimensional, fluid flow and solute transport model that quantifies the influence of tidal pumping on nitrate removal and applied it to the tidal freshwater zone (TFZ) of White Clay Creek (Delaware, USA). In field observations and models, both oxygenated river water and anoxic groundwater deliver nitrate to carbon-rich riverbed sediment. A zone of nitrate removal forms beneath the aerobic interval, which expands and contracts over daily timescales due to tidal pumping. At high tide when oxygen-rich river water infiltrates into the bed, denitrification rates decrease by 25% relative to low tide. In the absence of tidal pumping, our model predicts that the aerobic zone would be thinner, and denitrification rates would increase by 10%. As tidal amplitude increases toward the coast, nitrate removal rates should decrease due to enhanced oxygen exchange across the sediment-water interface, based on sensitivity analysis. Denitrification hot spots in TFZs are more likely to occur in less permeable sediment under lower tidal ranges and higher rates of ambient groundwater discharge. Our models suggest that tidal pumping is not efficient at removing surface water nitrate but can remove up to 81% of nitrate from discharging groundwater in the TFZ of White Clay Creek. Given the high population densities of coastal watersheds, the reactive riverbeds of TFZs play a critical role in mitigating new nitrogen loads to coasts.

Water and sediment dynamics in the Red River mouth and adjacent coastal zone

NASA Astrophysics Data System (ADS)

van Maren, D. S.

2007-02-01

The coastline of the Red River Delta is characterized by alternating patterns of rapid accretion and severe erosion. The main branch of the Red River, the Ba Lat, is presently expanding seaward with a main depositional area several km downstream and offshore the Ba Lat River mouth. Sediment deposition rates are approximately 6 m in the past 50 years. Field measurements were done to determine the processes that regulate marine dispersal and deposition of sediment supplied by the Ba Lat. These measurements reveal that the waters surrounding the Ba Lat delta are strongly stratified with a pronounced southward-flowing surface layer. This southward-flowing surface layer is a coastal current which is generated by river plumes that flow into the coastal zone north of the Ba Lat. However, outflow of turbid river water is not continuous and most sediment enters the coastal zone when the alongshore surface velocities are low. As a consequence, most sediment settles from suspension close to the river mouth. In addition to the southward surface flow, the southward near-bottom currents are also stronger than northward currents. Contrasting with the residual flow near-surface, this southward flow component near-bottom is caused by tidal asymmetry. Because most sediment is supplied by the Ba Lat when wave heights are low, sediment is able to consolidate and therefore the long-term deposition is southward of, but still close to, the Ba Lat mouth.

Groundwater quality in the Coastal Los Angeles Basin, California

USGS Publications Warehouse

Fram, Miranda S.; Belitz, Kenneth

2012-01-01

The Coastal Los Angeles Basin study unit is approximately 860 square miles and consists of the Santa Monica, Hollywood, West Coast, Central, and Orange County Coastal Plain groundwater basins (California Department of Water Resources, 2003). The basins are bounded in part by faults, including the Newport-Inglewood fault zone, and are filled with Holocene-, Pleistocene-, and Pliocene-age marine and alluvial sediments. The Central Basin and Orange County Coastal Plain are divided into a forebay zone on the northeast and a pressure zone in the center and southwest. The forebays consist of unconsolidated coarser sediment, and the pressure zones are characterized by lenses of coarser sediment divided into confined to semi-confined aquifers by lenses of finer sediments. The primary aquifer system in the study unit is defined as those parts of the aquifer system corresponding to the perforated intervals of wells listed in the California Department of Public Health (CDPH) database of public-supply wells. The majority of public-supply wells are drilled to depths of 510 to 1,145 feet, consist of solid casing from the land surface to a depth of about 300 to 510 feet, and are perforated below the solid casing. Water quality in the primary aquifer system may differ from that in the shallower and deeper parts of the aquifer systems.

Modelling the Deformation Front of a Fold-Thrust Belt: the Effect of an Upper Detachment Horizon

NASA Astrophysics Data System (ADS)

Burberry, C. M.; Koyi, H.; Nilfouroushan, F.; Cosgrove, J. W.

2008-12-01

Structures found at the deformation fronts of fold-thrust belts are variable in type, geometry and spatial organisation, as can be demonstrated from comparisons between structures in the Zagros Fold-Thrust Belt, Iran and the Sawtooth Range, Montana. A range of influencing factors has been suggested to account for this variation, including the mechanical properties and distribution of any detachment horizons within the cover rock succession. A series of analogue models was designed to test this hypothesis, under conditions scaled to represent the Sawtooth Range, Montana. A brittle sand pack, containing an upper ductile layer with variable geometry, was shortened above a ductile base and the evolution of the deformation front was monitored throughout the deformation using a high-accuracy laser scanner. In none of the experiments did the upper detachment horizon cover the entire model. In experiments where it pinched out perpendicular to the shortening direction, a triangle zone was formed when the deformation front reached the pinch out. This situation is analogous to the Teton Canyon region structures in the Sawtooth Range, Montana, where the Cretaceous Colorado Shale unit pinches out at the deformation front, favouring the development of a triangle zone in this region. When the pinch out was oblique to the shortening direction, a more complex series of structures was formed. However, when shortening stopped before the detachment pinch out was reached, the deformation front structures were foreland-propagating and no triangle zone was observed. This situation is analogous to foreland-propagating thrust structures developed at the deformation front in the Swift Dam region of the Sawtooth Range, Montana and to the development of fault-bend folds at the deformation front of the Zagros Fold-Thrust Belt, Iran. We suggest that the presence of a suitable intermediate detachment horizon within a sediment pile can be invoked as a valid explanation for the development of varied deformation front structures in fold-thrust belts. Specifically, the spatial extent of the upper detachment horizon with respect to the spatial extent of the deformed region is a key influence on the development of deformation front structures. However, we acknowledge that factors such as basement structure and variable sedimentation within the foreland basin may also be key influences on deformation front structures in other fold-thrust belts.

Shallow geology, sea-floor texture, and physiographic zones of Buzzards Bay, Massachusetts

USGS Publications Warehouse

Foster, David S.; Baldwin, Wayne E.; Barnhardt, Walter A.; Schwab, William C.; Ackerman, Seth D.; Andrews, Brian D.; Pendleton, Elizabeth A.

2015-01-07

Geologic, sediment texture, and physiographic zone maps characterize the sea floor of Buzzards Bay, Massachusetts. These maps were derived from interpretations of seismic-reflection profiles, high-resolution bathymetry, acoustic-backscatter intensity, bottom photographs, and surficial sediment samples. The interpretation of the seismic stratigraphy and mapping of glacial and Holocene marine units provided a foundation on which the surficial maps were created. This mapping is a result of a collaborative effort between the U.S. Geological Survey and the Massachusetts Office of Coastal Zone Management to characterize the surface and subsurface geologic framework offshore of Massachusetts.

Changes in northern Gulf of Mexico sediment bacterial and archaeal communities exposed to hypoxia

EPA Science Inventory

Biogeochemical changes in marine sediments during coastal water hypoxia are well described, but less is known about underlying changes in microbial communities. Bacterial and archaeal communities in Louisiana continental shelf (LCS) hypoxic zone sediments were characterized by py...

Concentration, composition and sources of PAHs in the coastal sediments of the exclusive economic zone (EEZ) of Qatar, Arabian Gulf.

PubMed

Soliman, Y S; Al Ansari, E M S; Wade, T L

2014-08-30

Surface sediments were collected from sixteen locations in order to assess levels and sources of polycyclic aromatic hydrocarbons (PAHs) in sediments of Qatar exclusive economic zone (EEZ). Samples were analyzed for 16 parent PAHs, 18 alkyl homologs and for dibenzothiophenes. Total PAHs concentration (∑PAHs) ranged from 2.6 ng g(-1) to 1025 ng g(-1). The highest PAHs concentrations were in sediments in and adjacent to harbors. Alkylated PAHs predominated most of the sampling locations reaching up to 80% in offshore locations. Parent PAHs and parent high molecular weight PAHs dominated location adjacent to industrial activities and urban areas. The origin of PAHs sources to the sediments was elucidated using ternary plot, indices, and molecular ratios of specific compounds such as (Ant/Phe+Ant), (Flt/Flt+Pyr). PAHs inputs to most coastal sites consisted of mixture of petroleum and combustion derived sources. However, inputs to the offshore sediments were mainly of petroleum origin. Copyright © 2014 Elsevier Ltd. All rights reserved.

Cellular polarity and interactions in plant graviperception

NASA Technical Reports Server (NTRS)

Sack, Fred D.

1993-01-01

Presented are results of studies on the mechanisms of gravitropic sensing in higher and lower plants. Gravitropic roots of the aquatic angiosperm, Limnobium, were found to have sedimented amyloplasts in their elongation zone but not in their rootcap; nuclei were found to sediment in the elongation zone as well. Another study attempted to understand how plastid sedimentation occurs in vertical Ceratodon cells and how this sedimentation is regulated. To determine whether the cytoskeleton restricts plastid sedimentation, the effects of amiprophos-methyl (APM) and cytochalasin (CD) on plastid position were qualified. Results suggest that microtubules restrict the sedimentation of plastids along the length of the cell and that microtubules are load-bearing for all the plastids in the apical cell, demonstrating the importance of the cytoskeleton in maintaining organelle position and cell organization against the force of gravity. Physcomitrella and Funaria were also studied. Results suggest that gravitropism may be relatively common in moss protonemata and reinforce the idea that amyloplast mass functions in gravitropic sensing.

Linking channel hydrology with riparian wetland accretion in tidal rivers

USGS Publications Warehouse

Ensign, Scott H.; Noe, Gregory B.; Hupp, Cliff R.

2014-01-01

The hydrologic processes by which tide affects river channel and riparian morphology within the tidal freshwater zone are poorly understood, yet are fundamental to predicting the fate of coastal rivers and wetlands as sea level rises. We investigated patterns of sediment accretion in riparian wetlands along the non-tidal through oligohaline portion of two coastal plain rivers in Maryland, U.S.A., and how flow velocity, water level, and suspended sediment concentration (SSC) in the channel may have contributed to those patterns. Sediment accretion was measured over a one year period using artificial marker horizons, channel hydrology was measured over a one month period using acoustic Doppler current profilers, and SSC was predicted from acoustic backscatter. Riparian sediment accretion was lowest at the non-tidal sites (mean and standard deviation = 8 ± 8 mm yr-1), highest at the upstream tidal freshwater forested wetlands (TFFW) (33 ± 28 mm yr-1), low at the midstream TFFW (12 ± 9 mm yr-1), and high at the oligohaline (fresh-to-brackish) marshes (19 ± 8 mm yr-1). Channel maximum flood and ebb velocity was 2-fold faster at the oligohaline than tidal freshwater zone on both tidal rivers, corresponding with the differences in in-channel SSC: the oligohaline zone's SSC was more than double the tidal freshwater zone's, and was greater than historical SSC at the non-tidal gages. The tidal wave characteristics differed between rivers, leading to significantly greater in-channel SSC during floodplain inundation in the weakly convergent than the strongly convergent tidal river. Overall sediment accretion was higher in the embayed river likely due to a single storm discharge and associated sedimentation.

Benthic exchange and biogeochemical cycling in permeable sediments.

PubMed

Huettel, Markus; Berg, Peter; Kostka, Joel E

2014-01-01

The sandy sediments that blanket the inner shelf are situated in a zone where nutrient input from land and strong mixing produce maximum primary production and tight coupling between water column and sedimentary processes. The high permeability of the shelf sands renders them susceptible to pressure gradients generated by hydrodynamic and biological forces that modulate spatial and temporal patterns of water circulation through these sediments. The resulting dynamic three-dimensional patterns of particle and solute distribution generate a broad spectrum of biogeochemical reaction zones that facilitate effective decomposition of the pelagic and benthic primary production products. The intricate coupling between the water column and sediment makes it challenging to quantify the production and decomposition processes and the resultant fluxes in permeable shelf sands. Recent technical developments have led to insights into the high biogeochemical and biological activity of these permeable sediments and their role in the global cycles of matter.

Non-seagrass meadow sedimentary facies of the Pontinian Islands, Tyrrhenian Sea: A modern example of mixed carbonate siliciclastic sedimentation

NASA Astrophysics Data System (ADS)

Brandano, Marco; Civitelli, Giacomo

2007-10-01

The soft bottom of the Mediterranean continental shelf is characterized by a heterozoan skeletal assemblage ( sensu [James, N.P., 1997. The cool-water carbonate depositional realm. In: James, N.P., Clarke, J. (Eds), Cool-water Carbonates. Spec. Publ. Soc. Sediment. Geol., vol. 56, pp.1-20.]). Although the contemporary presence of terrigenous and skeletal carbonate sediments has been well established [Tortora, P., 1996. Depositional and erosional coastal processes during the last postglacial sea-level rise: an example from the Central Tyrrhenian continental shelf (Italy). J. Sed. Res. 66, 391-405.; Fornós, J.J., Ahr, W.M., 1997. Temperate carbonates on a modern, low-energy, isolated ramp: the Balearic Platform, Spain. Journal of Sedimentary Research , 67, 364-373.; Fornós, J.J., Ahr, W.M., 2006. Present-day temperate carbonate sedimentation on the Balearic Platform, western Mediterranean: compositional and textural variation along a low-energy isolated ramp. In: Pedley, H.M., Carannante, G. (Eds.) 2006, Cool-water Carbonates: Depositional Systems and Palaeoenvironmental Controls. Geological Society, London, Special Publications, 255, pp. 121-135], the interactions between carbonate and terrigenous-siliciclastic sedimentation has not been documented well enough. A total of 33 surface sediment samples from the Pontinian shelf (Tyrrhenian Sea, central Mediterranean) have been analysed. Sampling stations range from 15 to 250 mwd (meter water depth) and are located along five transects (PonzaW, PonzaNW, Ponza NE, Ponza E, Zannone), plus four samples collected around Palmarola Island. Sectors colonized by seagrass meadows have not been sampled. A total of 6 sedimentary facies (F) and 10 microfacies (mf) have been recognized by using component analyses, grain size percentage, sorting, carbonate content and authigenic mineralization rate. These facies and microfacies represent the Pontian Islands shelf sedimentation, in the interval between the upper infralittoral and the epibathyal zones that represent shelf-break and upper slope sedimentation. The Maerl facies (F4a,b; mf4a,b) and the skeletal sands (F2a,b; mf2a1, mf2a2, mf2b) fall within the circalittoral zone. The circalittoral zone in the water depth interval between 82 m and 112 m display relict facies (F6, mf6). Finally facies F5 (Siliciclastic sands) includes subfacies F5b (mf5b), located in the circalittoral zone at depths of 49 to 101 mwd and restricted to the western and eastern sectors of Ponza, and subfacies F5a in the upper infralittoral zone (15 mwd/25 mwd) where erosional processes prevail. Carbonate content analyses indicate that maximum carbonate production on the Pontinian shelf took place in the 60-80 mwd interval. Facies F4 (Maerl) represents the environment characterized by the highest carbonate production rates. In the Pontian area siliciclastic-carbonate mixing took place in the infralittoral zone and in the lower circalittoral zone. In the infralittoral zone erosional processes on the rocky shoreline produced lithoclasts and vulcanoclastic deposits that were reworked by wave-induced near-shore currents. In the lower circalittoral zone the prolific production by photic biota (red algae) ends, while skeletal remains of the aphotic environment mixes with planktonic sediments characterized by low carbonate values. Sand (63 μm-2 mm) is the dominant grain size class, however gravel-dominated facies (F4 Maerl) are present in water depths (50 to 112 mwd) which are significantly below the storm wave base. Glauconite mineralization appears on the Pontinian shelf from 50 mwd and increases in abundance along the deeper bathymetries. The compositional characteristics of relict facies F6 shows the concurrence of biota assemblages of the infralittoral and circalittoral zones, likely representing the record of the last Holocene transgressive event (18 ky) and expressed by the overlapping of components of different environments.

Maintaining the Link to The Floodplain: Scour Dynamics in Crevasses

NASA Astrophysics Data System (ADS)

Esposito, C. R.; Liang, M.; Yuill, B. T.; Meselhe, E. A.

2017-12-01

In river deltas, crevasses are the primary geomorphic feature that traverse the levee, connecting the river to its floodplain and facilitating the transfer of water, sediment, and chemical constituents from the trunk channel. Despite their fundamental position linking river and floodplain, the factors that are important to crevasse evolution are not well understood, and their enumeration is the subject of active research across multiple earth surface process subfields. Crevasses are often associated with a zone of intense scour proximal to the trunk channel. Surprisingly little is known about the morphological dynamics in this zone, but there is evidence from studies of river avulsion that scour zone evolution plays an important role in determining crevasse sustainability. Here we use Delft3D to simulate the development of managed crevasse splays - river diversions - for the purpose of landscape management in the Mississippi River Delta. Our model runs vary the erodibility of the substrate in the receiving basin and the extent and location of erosion protection along the conveyance channel. We find that substrate erodibility in the basin plays a critical role in determining the long-term performance of sediment diversions. Crevasses that create large scours tend to maintain their performance over several decades, but those that only create small scours are subject to rapidly declining performance as the scour pit fills in with coarse sediments. Finally, we compare the evolution of our modeled scour zone to the West Bay Sediment Diversion, where regular bathymetric surveys have documented the evolution of the scour zone since 2004.

The morphology, processes, and evolution of Monterey Fan: a revisit

USGS Publications Warehouse

Gardner, James V.; Bohannon, Robert G.; Field, Michael E.; Masson, Douglas G.

2010-01-01

Long-range (GLORIA) and mid-range (TOBI) sidescan imagery and seismic-reflection profiles have revealed the surface morphology and architecture of the complete Monterey Fan. The fan has not developed a classic wedge shape because it has been blocked for much of its history by Morro Fracture Zone. The barrier has caused the fan to develop an upper-fan and lower-fan sequence that are distinctly different from one another. The upper-fan sequence is characterized by Monterey and Ascension Channels and associated Monterey Channel-levee system. The lower-fan sequence is characterized by depositional lobes of the Ascension, Monterey, and Sur-Parkington-Lucia systems, with the Monterey depositional lobe being the youngest. Presently, the Monterey depositional lobe is being downcut because the system has reached a new, lower base level in the Murray Fracture Zone. A five-step evolution of Monterey Fan is presented, starting with initial fan deposition in the Late Miocene, about 5.5 Ma. This first stage was one of filling bathymetric lows in the oceanic basement in what was to become the upper-fan segment. The second stage involved filling the bathymetric low on the north side of Morro Fracture Zone, and probably not much sediment was transported beyond the fracture zone. The third stage witnessed sediment being transported around both ends of Morro Fracture Zone and initial sedimentation on the lower-fan segment. During the fourth stage Ascension Channel was diverted into Monterey Channel, thereby cutting off sedimentation to the Ascension depositional lobe.

Methane and sulfate dynamics in sediments from mangrove-dominated tropical coastal lagoons, Yucatan, Mexico

USGS Publications Warehouse

Chuang, P. C.; Young, Megan B.; Dale, Andrew W.; Miller, Laurence G.; Herrera-Silveira, Jorge A.; Paytan, Adina

2016-01-01

Porewater profiles in sediment cores from mangrove-dominated coastal lagoons (Celestún and Chelem) on the Yucatán Peninsula, Mexico, reveal the widespread coexistence of dissolved methane and sulfate. This observation is interesting since dissolved methane in porewaters is typically oxidized anaerobically by sulfate. To explain the observations we used a numerical transport-reaction model that was constrained by the field observations. The model suggests that methane in the upper sediments is produced in the sulfate reduction zone at rates ranging between 0.012 and 31 mmol m−2 d−1, concurrent with sulfate reduction rates between 1.1 and 24 mmol SO42− m−2 d−1. These processes are supported by high organic matter content in the sediment and the use of non-competitive substrates by methanogenic microorganisms. Indeed sediment slurry incubation experiments show that non-competitive substrates such as trimethylamine (TMA) and methanol can be utilized for microbial methanogenesis at the study sites. The model also indicates that a significant fraction of methane is transported to the sulfate reduction zone from deeper zones within the sedimentary column by rising bubbles and gas dissolution. The shallow depths of methane production and the fast rising methane gas bubbles reduce the likelihood for oxidation, thereby allowing a large fraction of the methane formed in the sediments to escape to the overlying water column.

Chromium distribution in an Amazonian river exposed to tannery effluent.

PubMed

de Sousa, Eduardo Araujo; Luz, Cleber Calado; de Carvalho, Dario Pires; Dorea, Caetano Chang; de Holanda, Igor Bruno Barbosa; Manzatto, Ângelo Gilberto; Bastos, Wanderley Rodrigues

2016-11-01

This study aims to evaluate the Cr concentrations in surface water, suspended particles, and bottom sediments exposed to tannery effluent releases in the Candeias River. Cr concentrations were compared in relation to environmental thresholds imposed by United States Environmental Protection Agency (USEPA) and the Brazilian Environmental Council (CONAMA), and the geoaccumulation index (Igeo) was calculated in bottom sediment. Samples were collected in flood and dry seasons. Cr extraction was done by an acid extraction and quantified by flame atomic absorption spectrometry. Most samples were found to be below the environmental thresholds imposed by CONAMA and USEPA, except in the one from the discharge zone sampled during the dry season, showing values 1.5 and 6.1 higher than CONAMA in water and bottom sediment, respectively. Cr concentrations were significantly higher (P < 0.001) in suspended particles during dry season than flood season. Surface water and bottom sediment did not show significant differences between the seasons. The Igeo revealed an enrichment of Cr in bottom sediments after discharge zone, indicating that the effluent may be contributing to metal accumulation in the sediment. Apparently, the Candeias River shows a wash behavior on the river bottom, leaching the accumulated metal deposited on the riverbed to other areas during the flood pulses, which decreases Cr concentration in the discharge zone during dry seasons. Thus, this behavior can promote Cr dispersion to unpolluted areas.

Coral reef health response to chronic and acute changes in water quality in St. Thomas, United States Virgin Islands.

PubMed

Ennis, Rosmin S; Brandt, Marilyn E; Wilson Grimes, Kristin R; Smith, Tyler B

2016-10-15

It is suspected that land cover alteration on the southern coast of St. Thomas, USVI has increased runoff, degrading nearshore water quality and coral reef health. Chronic and acute changes in water quality, sediment deposition, and coral health metrics were assessed in three zones based upon perceived degree of human influence. Chlorophyll (p<0.0001) and turbidity (p=0.0113) were significantly higher in nearshore zones and in the high impact zone during heavy precipitation. Net sediment deposition and terrigenous content increased in nearshore zones during periods of greater precipitation and port activity. Macroalgae overgrowth significantly increased along a gradient of decreasing water quality (p<0.0001). Coral bleaching in all zones peaked in November with a regional thermal stress event (p<0.0001). However, mean bleaching prevalence was significantly greater in the most impacted zone compared to the offshore zone (p=0.0396), suggesting a link between declining water quality and bleaching severity. Published by Elsevier Ltd.

Relationships between microbial communities and environmental parameters at sites impacted by mining of volcanogenic massive sulfide deposits, Prince William Sound, Alaska

USGS Publications Warehouse

Foster, A.L.; Munk, L.; Koski, R.A.; Shanks, Wayne C.; Stillings, L.L.

2008-01-01

The relations among geochemical parameters and sediment microbial communities were examined at three shoreline sites in the Prince William Sound, Alaska, which display varying degrees of impact by acid-rock drainage (ARD) associated with historic mining of volcanogenic massive sulfide deposits. Microbial communities were examined using total fatty acid methyl esters (FAMEs), a class of compounds derived from lipids produced by eukaryotes and prokaryotes (bacteria and Archaea); standard extraction techniques detect FAMEs from both living (viable) and dead (non-viable) biomass, but do not detect Archaeal FAMEs. Biomass and diversity (as estimated by FAMEs) varied strongly as a function of position in the tidal zone, not by study site; subtidal muds, Fe oxyhydroxide undergoing biogenic reductive dissolution, and peat-rich intertidal sediment had the highest values. These estimates were lowest in acid-generating, intertidal zone sediment; if valid, the estimates suggest that only one or two bacterial species predominate in these communities, and/or that Archeal species are important members of the microbial community in this sediment. All samples were dominated by bacterial FAMEs (median value >90%). Samples with the highest absolute abundance of eukaryotic FAMEs were biogenic Fe oxyhydroxides from shallow freshwater pools (fungi) and subtidal muds (diatoms). Eukaryotic FAMEs were practically absent from low-pH, sulfide-rich intertidal zone sediments. The relative abundance of general microbial functional groups such as aerobes/anaerobes and gram(+)/gram(-) was not estimated due to severe inconsistency among the results obtained using several metrics reported in the literature. Principal component analyses (PCAs) were performed to investigate the relationship among samples as separate functions of water, sediment, and FAMEs data. PCAs based on water chemistry and FAMEs data resulted in similar relations among samples, whereas the PCA based on sediment chemistry produced a very different sample arrangement. Specifically, the sediment parameter PCA grouped samples with high bulk trace metal concentration regardless of whether the metals were incorporated into secondary precipitates or primary sulfides. The water chemistry PCA and FAMEs PCA appear to be less prone to this type of artifact. Signature lipids in sulfide-rich sediments could indicate the presence of acid-tolerant and/or acidophilic members of the genus Thiobacillus or they could indicate the presence of SO4-reducing bacteria. The microbial community documented in subtidal and offshore sediments is rich in SRB and/or facultative anaerobes of the Cytophaga-Flavobacterium group; both could reasonably be expected in PWS coastal environments. The results of this study provide evidence for substantial feedback between local (meter to centimeter-scale) geochemical variations, and sediment microbial community composition, and show that microbial community signatures in the intertidal zone are significantly altered at sites where ARD drainage is present relative to sites where it is not, even if the sediment geochemistry indicates net accumulation of ARD-generated trace metals in the intertidal zone. ?? 2007 Elsevier Ltd. All rights reserved.

Internal architecture, permeability structure, and hydrologic significance of contrasting fault-zone types

NASA Astrophysics Data System (ADS)

Rawling, Geoffrey C.; Goodwin, Laurel B.; Wilson, John L.

2001-01-01

The Sand Hill fault is a steeply dipping, large-displacement normal fault that cuts poorly lithified Tertiary sediments of the Albuquerque basin, New Mexico, United States. The fault zone does not contain macroscopic fractures; the basic structural element is the deformation band. The fault core is composed of foliated clay flanked by structurally and lithologically heterogeneous mixed zones, in turn flanked by damage zones. Structures present within these fault-zone architectural elements are different from those in brittle faults formed in lithified sedimentary and crystalline rocks that do contain fractures. These differences are reflected in the permeability structure of the Sand Hill fault. Equivalent permeability calculations indicate that large-displacement faults in poorly lithified sediments have little potential to act as vertical-flow conduits and have a much greater effect on horizontal flow than faults with fractures.

Approximate Model of Zone Sedimentation

NASA Astrophysics Data System (ADS)

Dzianik, František

2011-12-01

The process of zone sedimentation is affected by many factors that are not possible to express analytically. For this reason, the zone settling is evaluated in practice experimentally or by application of an empirical mathematical description of the process. The paper presents the development of approximate model of zone settling, i.e. the general function which should properly approximate the behaviour of the settling process within its entire range and at the various conditions. Furthermore, the specification of the model parameters by the regression analysis of settling test results is shown. The suitability of the model is reviewed by graphical dependencies and by statistical coefficients of correlation. The approximate model could by also useful on the simplification of process design of continual settling tanks and thickeners.

Hydrocarbon Degradation in Caspian Sea Sediment Cores Subjected to Simulated Petroleum Seepage in a Newly Designed Sediment-Oil-Flow-Through System.

PubMed

Mishra, Sonakshi; Wefers, Peggy; Schmidt, Mark; Knittel, Katrin; Krüger, Martin; Stagars, Marion H; Treude, Tina

2017-01-01

The microbial community response to petroleum seepage was investigated in a whole round sediment core (16 cm length) collected nearby natural hydrocarbon seepage structures in the Caspian Sea, using a newly developed Sediment-Oil-Flow-Through (SOFT) system. Distinct redox zones established and migrated vertically in the core during the 190 days-long simulated petroleum seepage. Methanogenic petroleum degradation was indicated by an increase in methane concentration from 8 μM in an untreated core compared to 2300 μM in the lower sulfate-free zone of the SOFT core at the end of the experiment, accompanied by a respective decrease in the δ 13 C signal of methane from -33.7 to -49.5‰. The involvement of methanogens in petroleum degradation was further confirmed by methane production in enrichment cultures from SOFT sediment after the addition of hexadecane, methylnapthalene, toluene, and ethylbenzene. Petroleum degradation coupled to sulfate reduction was indicated by the increase of integrated sulfate reduction rates from 2.8 SO 4 2- m -2 day -1 in untreated cores to 5.7 mmol SO 4 2- m -2 day -1 in the SOFT core at the end of the experiment, accompanied by a respective accumulation of sulfide from 30 to 447 μM. Volatile hydrocarbons (C2-C6 n -alkanes) passed through the methanogenic zone mostly unchanged and were depleted within the sulfate-reducing zone. The amount of heavier n -alkanes (C10-C38) decreased step-wise toward the top of the sediment core and a preferential degradation of shorter (C30) was seen during the seepage. This study illustrates, to the best of our knowledge, for the first time the development of methanogenic petroleum degradation and the succession of benthic microbial processes during petroleum passage in a whole round sediment core.

Influence of sea level rise on iron diagenesis in an east Florida subterranean estuary

USGS Publications Warehouse

Roy, M.; Martin, J.B.; Cherrier, J.; Cable, J.E.; Smith, C.G.

2010-01-01

Subterranean estuary occupies the transition zone between hypoxic fresh groundwater and oxic seawater, and between terrestrial and marine sediment deposits. Consequently, we hypothesize, in a subterranean estuary, biogeochemical reactions of Fe respond to submarine groundwater discharge (SGD) and sea level rise. Porewater and sediment samples were collected across a 30-m wide freshwater discharge zone of the Indian River Lagoon (Florida, USA) subterranean estuary, and at a site 250. m offshore. Porewater Fe concentrations range from 0.5 ??M at the shoreline and 250. m offshore to about 286 ??M at the freshwater-saltwater boundary. Sediment sulfur and porewater sulfide maxima occur in near-surface OC-rich black sediments of marine origin, and dissolved Fe maxima occur in underlying OC-poor orange sediments of terrestrial origin. Freshwater SGD flow rates decrease offshore from around 1 to 0.1. cm/day, while bioirrigation exchange deepens with distance from about 10. cm at the shoreline to about 40. cm at the freshwater-saltwater boundary. DOC concentrations increase from around 75 ??M at the shoreline to as much as 700 ??M at the freshwater-saltwater boundary as a result of labile marine carbon inputs from marine SGD. This labile DOC reduces Fe-oxides, which in conjunction with slow discharge of SGD at the boundary, allows dissolved Fe to accumulate. Upward advection of fresh SGD carries dissolved Fe from the Fe-oxide reduction zone to the sulfate reduction zone, where dissolved Fe precipitates as Fe-sulfides. Saturation models of Fe-sulfides indicate some fractions of these Fe-sulfides get dissolved near the sediment-water interface, where bioirrigation exchanges oxic surface water. The estimated dissolved Fe flux is approximately 0.84 ??M Fe/day per meter of shoreline to lagoon surface waters. Accelerated sea level rise predictions are thus likely to increase the Fe flux to surface waters and local primary productivity, particularly along coastlines where groundwater discharges through sediments. ?? 2010 Elsevier Ltd.

Early Stage Evolution of Nourished Beach under High-energy, Macro-tidal Environment

NASA Astrophysics Data System (ADS)

Liu, J. H.; Cai, F.; Zhang, Z. W.; Li, B.

2017-02-01

Beach planform evolution, profile equilibration and sediment grain size change have been studied during the first 4 months from 4th September to 24th December 2011 after the construction of beach nourishment project at Longfengtou Beach, Haitan Bay. Monthly beach profiles, shoreline surveys, sediment sampling and nearshore wave measurements were carried out after implementation of the 1.3km long nourishment project which was completed on 20th August 2011. This study indicates that: (1) rapid beach profile equilibration occurred in the early stage after the construction of the project. A null point was observed, which is equal to the height of mean high tide, basically kept dynamic stable during the process of profile evolution. Shoreface sediment accumulated beneath the height of this point while erosion happened above it, the slope between the beach berm and the landward edge of low tidal zone became more gradual accompanied with seaward transportation of beach sediment. The velocity of beach slope adjustment in earlier period is faster than later. (2) Beach planform adjustment initiated simultaneously with the combination of the process of profile equilibration and longshore sediment transport. Shoreline retreated with an average distance of 11.1m and maximum of 31.02m from 4th September to 24th December, erosion in the south part was more serious than in the north, and 3 erosion hot spots were found along the coast. (3) Sediment redistributed with cross-shore profile equilibration, it showed a pattern across beach profile as medium sand (0.4-0.5mm) in beach berm, smaller (0.3-0.4mm) in high and middle tidal zone, coarse sand(0.6-1mm) in beach slope transitional zone, fine sand(0.1-0.25mm) in low tidal zone. The sediment grain size change of foreshore was rapidly response to the passage of storm surge.

Hydrocarbon Degradation in Caspian Sea Sediment Cores Subjected to Simulated Petroleum Seepage in a Newly Designed Sediment-Oil-Flow-Through System

PubMed Central

Mishra, Sonakshi; Wefers, Peggy; Schmidt, Mark; Knittel, Katrin; Krüger, Martin; Stagars, Marion H.; Treude, Tina

2017-01-01

The microbial community response to petroleum seepage was investigated in a whole round sediment core (16 cm length) collected nearby natural hydrocarbon seepage structures in the Caspian Sea, using a newly developed Sediment-Oil-Flow-Through (SOFT) system. Distinct redox zones established and migrated vertically in the core during the 190 days-long simulated petroleum seepage. Methanogenic petroleum degradation was indicated by an increase in methane concentration from 8 μM in an untreated core compared to 2300 μM in the lower sulfate-free zone of the SOFT core at the end of the experiment, accompanied by a respective decrease in the δ13C signal of methane from -33.7 to -49.5‰. The involvement of methanogens in petroleum degradation was further confirmed by methane production in enrichment cultures from SOFT sediment after the addition of hexadecane, methylnapthalene, toluene, and ethylbenzene. Petroleum degradation coupled to sulfate reduction was indicated by the increase of integrated sulfate reduction rates from 2.8 SO42-m-2 day-1 in untreated cores to 5.7 mmol SO42-m-2 day-1 in the SOFT core at the end of the experiment, accompanied by a respective accumulation of sulfide from 30 to 447 μM. Volatile hydrocarbons (C2–C6 n-alkanes) passed through the methanogenic zone mostly unchanged and were depleted within the sulfate-reducing zone. The amount of heavier n-alkanes (C10–C38) decreased step-wise toward the top of the sediment core and a preferential degradation of shorter (C30) was seen during the seepage. This study illustrates, to the best of our knowledge, for the first time the development of methanogenic petroleum degradation and the succession of benthic microbial processes during petroleum passage in a whole round sediment core. PMID:28503172

Gas composition and isotopic geochemistry of cuttings, core, and gas hydrate from the JAPEX/JNOC/GSC Mallik 2L-38 gas hydrate research well

USGS Publications Warehouse

Lorenson, T.D.

1999-01-01

Molecular and isotopic composition of gases from the JAPEX/JNOC/GSC Mallik 2L-38 gas hydrate research well demonstrate that the in situ gases can be divided into three zones composed of mixtures of microbial and thermogenic gases. Sediments penetrated by the well are thermally immature; thus the sediments are probably not a source of thermogenic gas. Thermogenic gas likely migrated from depths below 5000 m. Higher concentrations of gas within and beneath the gas hydrate zone suggest that gas hydrate is a partial barrier to gas migration. Gas hydrate accumulations occur wholly within zone 3, below the base of permafrost. The gas in gas hydrate resembles, in part, the thermogenic gas in surrounding sediments and gas desorbed from lignite. Gas hydrate composition implies that the primary gas hydrate form is Structure I. However, Structure II stabilizing gases are more concentrated and isotopically partitioned in gas hydrate relative to the sediment hosting the gas hydrate, implying that Structure II gas hydrate may be present in small quantities.

Origin of dolomite in Miocene Monterey Shale and related formations in the Temblor Range, California

USGS Publications Warehouse

Friedman, I.; Murata, K.J.

1979-01-01

Dolomites in thick sections of Miocene Monterey Shale and related formations in the Temblor Range of California acquired their isotopic compositions as they formed at shallow depth in the original sediment rich in organic matter, and retained the composition against the vicissitudes of burial diagenesis. The oxygen isotopes of dolomites of successive beds record changes in temperature of bottom water while the carbon isotopes of the same samples indicate changes in the kind of microbial activity (sulfate reduction vs carbohydrate fermentation) that prevailed at shallow depths in the sediment. In an auxiliary study, two samples of dolomite from sediments of Cariaco Basin off Venezuela (DSDP site 147) were found to have ??5C13 of -14.1 and -9.8 per ml PDB, although they occur in a heavy-carbon zone containing bicarbonate as heavy as +8.4 per ml. These dolomites probably originated at shallow depth in the light-carbon zone of microbial sulfate reducers and were buried under later sediments down into the heavy-carbon zone of microbial fermenters of carbohydrates without losing their original light-carbon composition. ?? 1979.

Influence of forest road buffer zones on sediment transport in the Southern Appalachian Region

Treesearch

Johnny M. Grace; Stanley J. Zarnoch

2013-01-01

A gap exists in the understanding of the effectiveness of forest road best management practices (BMP) in controlling sediment movement and minimizing risks of sediment delivery to forest streams. The objective of this paper is to report the findings of investigations to assess sediment travel distances downslope of forest roads in the Appalachian region, relate...

Compositional changes of surface sediments and variability of manganese nodules in the Peru Basin

NASA Astrophysics Data System (ADS)

Marchig, Vesna; von Stackelberg, Ulrich; Hufnagel, Heinz; Durn, Goran

Two types of manganese nodules were observed in the Peru Basin: large botryoidal nodules in basins and small ellipsoidal nodules on slope positions. The sediment in areas with large botryoidal nodules contains a thinner and weaker oxidation zone than the sediment under small ellipsoidal nodules, indicating that diagenetic processes in the sediment, which supply manganese nodules with metals for their growth, are stronger in sediments on which large botryoidal nodules grow. Organic matter, which activates remobilization of metals, occurs mostly in the form of refractory lipidic compounds in the inner capsule of radiolaria. This material needs bacterial degradation to act as a reducing agent. Easily oxidizable organic components could not be found in the sediments. Other changes in sediment composition do not have a link to manganese nodule growth. Biogenous components (radiolarians, organogenic barite and apatite) increase towards the equatorial high-productivity zone. Authigenous clay minerals (nontronite as well as montmorillonite with high Fe +3 incorporation on positions of ochtaedral Al) increase with distance from the continent. The assessment of environmental impacts will have to take into account the regional differences in sediment composition and the small-scale variability of manganese nodules.

Permeability-Porosity Relationships of Subduction Zone Sediments

NASA Astrophysics Data System (ADS)

Gamage, K.; Screaton, E.; Bekins, B.; Aiello, I.

2008-12-01

Permeability-porosity relationships for sediments from Northern Barbados, Costa Rica, Nankai, and Peru subduction zones were examined based on their sediment type and grain size distribution. Greater correlation was observed between permeability and porosity for siliciclastic sediments, diatom oozes, and nannofossil chalk than for nannofossil oozes. For siliciclastic sediments, grouping of sediments by clay content yields relationships that are generally consistent with results from other marine settings and suggest decreasing permeability for a given porosity as clay content increases. Correction of measured porosities for smectite content generally improves the quality of permeability-porosity relationships. The relationship between permeability and porosity for diatom oozes may be controlled by the amount of clay present in the ooze, causing diatom oozes to behave similarly to siliciclastic sediments. For a given porosity the nannofossil oozes have higher permeability values by 1.5 orders of magnitude than the siliciclastic sediments. However, the use of a permeability-porosity relation may not be appropriate for unconsolidated carbonates such as nannofossil oozes. This study provided insight to the effects of porosity correction for smectite, variations in lithology and grain size in permeability-porosity relationships. However, further progress in delineating controls on permeability will require more careful and better documented permeability tests on characterized samples.

Three-dimensional distribution of gas hydrate beneath southern Hydrate Ridge: Constraints from ODP Leg 204

USGS Publications Warehouse

Trehu, A.M.; Long, P.E.; Torres, M.E.; Bohrmann, G.; Rack, F.R.; Collett, T.S.; Goldberg, D.S.; Milkov, A.V.; Riedel, M.; Schultheiss, P.; Bangs, N.L.; Barr, S.R.; Borowski, W.S.; Claypool, G.E.; Delwiche, M.E.; Dickens, G.R.; Gracia, E.; Guerin, G.; Holland, M.; Johnson, J.E.; Lee, Y.-J.; Liu, C.-S.; Su, X.; Teichert, B.; Tomaru, H.; Vanneste, M.; Watanabe, M. E.; Weinberger, J.L.

2004-01-01

Large uncertainties about the energy resource potential and role in global climate change of gas hydrates result from uncertainty about how much hydrate is contained in marine sediments. During Leg 204 of the Ocean Drilling Program (ODP) to the accretionary complex of the Cascadia subduction zone, we sampled the gas hydrate stability zone (GHSZ) from the seafloor to its base in contrasting geological settings defined by a 3D seismic survey. By integrating results from different methods, including several new techniques developed for Leg 204, we overcome the problem of spatial under-sampling inherent in robust methods traditionally used for estimating the hydrate content of cores and obtain a high-resolution, quantitative estimate of the total amount and spatial variability of gas hydrate in this structural system. We conclude that high gas hydrate content (30-40% of pore space or 20-26% of total volume) is restricted to the upper tens of meters below the seafloor near the summit of the structure, where vigorous fluid venting occurs. Elsewhere, the average gas hydrate content of the sediments in the gas hydrate stability zone is generally <2% of the pore space, although this estimate may increase by a factor of 2 when patchy zones of locally higher gas hydrate content are included in the calculation. These patchy zones are structurally and stratigraphically controlled, contain up to 20% hydrate in the pore space when averaged over zones ???10 m thick, and may occur in up to ???20% of the region imaged by 3D seismic data. This heterogeneous gas hydrate distribution is an important constraint on models of gas hydrate formation in marine sediments and the response of the sediments to tectonic and environmental change. ?? 2004 Published by Elsevier B.V.

The Campanian-Maastrichtian foraminiferal biostratigraphy of the basement sediments from the southern Pannonian Basin (Vojvodina, northern Serbia): implications for the continuation of the Eastern Vardar and Sava zones

NASA Astrophysics Data System (ADS)

Dunčić, Milena; Dulić, Ivan; Popov, Olivera; Bogićević, Goran; Vranjković, Alan

2017-04-01

Micropalaeontological and biostratigraphical studies included Campanian-Maastrichtian complexes from five oil exploration wells drilled in northern Serbia (Vojvodina): the first is a carbonate-clastic complex and second is a complex containing ophiolites intercalated with hemipelagic and pelagic sediments. Within the studied complexes, rich associations of planktonic and benthic foraminifera, calcareous nannoplankton, palynomorphs, as well as shallow and deep-water fossil detritus were determined. The presence of relatively rich associations of planktonic foraminifera allowed recognition of two biozones: the Globotruncana ventricosa Zone, observed in the sediments of the carbonate-clastic complex and the Gansserina gansseri Zone, observed in both complexes. Except biozones, based on documented index species, for some units in both complexes, larger benthic foraminifera species had special biostratigraphical value, and in some of them, the calcareous nannoplankton zones were recognized. The studied complexes represent deep-water formations, generated in oceanic island arc and trough zones. The presence of limestones, which originate from destroyed rudist reefs, is explained by transfer by means of gravitational transport mechanisms of shallow-water sediments to deep-water depositional environments. In this paper, the results of more detailed biostratigraphical and palaeo-ecological studies of foraminifera associations in Campanian-Maastrichtian complexes in Vojvodina are presented. Combined with lithological studies, seven units were determined within the complexes. The obtained results are important as a part of multidisciplinary, regional exploration of both complexes, generated in specific geological conditions, that today constitute a part of the pre-Neogene basement complex in the southeastern part of the Pannonian Basin. The Campanian- Maastrichtian carbonate-clastic complex represents sedimentary cover of the Eastern Vardar Ophiolitic Unit, while the ophiolites intercalated with hemipelagic and pelagic limestones belongs to the Sava Zone.

Nature and Role of Subducting Sediments on the Megathrust and Forearc Evolution in the 2004 Great Sumatra Earthquake Rupture Zone: Results from Full Waveform Inversion of Long Offset Seismic Data

NASA Astrophysics Data System (ADS)

Singh, S. C.; Qin, Y.

2015-12-01

On active accretionary margins, the nature of incoming sediments defines the locking mechanism on the megathrust, and the development and evolution of the accretionary wedge. Drilling is the most direct method to characterise the nature of these sediments, but the drilling is very expensive, and provide information at only a few locations. In north Sumatra, an IODP drilling is programmed to take place in July-August 2016. We have performed seismic full waveform inversion of 12 km long offset seismic reflection data acquired by WesternGeco in 2006 over a 35 km zone near the subduction front in the 2004 earthquake rupture zone area that provide detailed quantitative information on the characteristics of the incoming sediments. We first downward continue the surface streamer data to the seafloor, which removes the effect of deep water (~5 km) and brings out the refraction arrivals as the first arrivals. We carry out travel time tomography, and then performed full waveform inversion of seismic refraction data followed by the full waveform inversion of reflection data providing detailed (10-20 m) velocity structure. The sediments in this area are 3-5 km thick where the P-wave velocity increases from 1.6 km/s near the seafloor to more than 4.5 km/s above the oceanic crust. The high velocity of sediments above the basement suggests that the sediments are highly compacted, strengthened the coupling near the subduction front, which might have been responsible for 2004 earthquake rupture propagation up to the subduction front, enhancing the tsunami. We also find several thin velocity layers within the sediments, which might be due to high pore-pressure fluid or free gas. These layers might be responsible for the formation of pseudo-decollement within the forearc sediments that acts as a conveyer belt between highly compacted subducting lower sediments and accreted sediments above. The presence of well intact sediments on the accretionary prism supports this interpretation. Our results provide first hand information about the sediments properties, which will be ground toothed by drilling.

Gravity-regulated formation of the peg in developing cucumber seedlings

NASA Technical Reports Server (NTRS)

Takahashi, H.; Scott, T. K.

1994-01-01

It has been proposed that peg formation in the vascular transition region (TR zone) between the hypocotyl and the root in Cucurbitaceae seedlings is a gravimorphogenetic phenomenon. Initiation of the peg became visible 36 h after imbibition when cucumber (Cucumis sativus L. cv. Burpee Hybrid II) seeds were germinated in a horizontal position at 24 degrees C in the dark. Simultaneously, sedimented amyloplasts (putative statoliths) were apparent in the sheath cells surrounding the vascular strands, and in the cortical cells immediately adjacent to them, in the TR zone. In contrast, the other cortical cells, some of which were destined to develop into the peg, contained amyloplasts which were not sedimented. These results suggest that the graviperception mechanism for peg formation may be like that of statoliths in shoot gravitropism. By 48 h following imbibition, the cells of the TR zone still had sedimented amyloplasts but had lost their sensitivity to gravity, possibly because of their maturation.

Foraminiferal and radiolarian biostratigraphy of the youngest (Late Albian through Late Cenomanian) sediments of the Tatra massif, Central Western Carpathians

NASA Astrophysics Data System (ADS)

Bąk, Krzysztof; Bąk, Marta

2013-06-01

Bąk, K. and Bąk M. 2013. Foraminiferal and radiolarian biostratigraphy of the youngest (Late Albian through Late Cenomanian) sediments of the Tatra massif, Central Western Carpathians. Acta Geologica Polonica, 63 (2), 223-237. Warszawa. The foraminiferal and radiolarian biostratigraphy of selected sections of the Zabijak Formation, the youngest sediments of the Tatra massif (Central Western Carpathians), have been studied. Benthic foraminifers, mainly agglutinated species, occur abundantly and continuously throughout the studied succession, while planktic foraminifers are generally sparse. Five planktic and two benthic foraminiferal zones have been recognized. The marly part of the Zabijak Formation comprises the Pseudothalmanninella ticinensis (Upper Albian) through the Rotalipora cushmani (Upper Cenomanian) planktic foraminiferal zones, and the Haplophragmoides nonioninoides and Bulbobaculites problematicus benthic foraminiferal zones. The radiolarians were recognized exclusively in the Lower Cenomanian part of the formation.

Dynamic behaviour of coastal sedimentation in the Lions Gulf. [France

NASA Technical Reports Server (NTRS)

Guy, M. (Principal Investigator)

1974-01-01

The author has identified the following significant results. A number of ERTS-1 images covering this geographical zone were studied and compared with cartographic maps, air photographs, and thermal-IR images. Old and recent sediments leave traces in the landscape which are decoded by interpreting the shapes of the clear zones forming a network against the black background representing water and humid zones. Current sedimentation and its mechanism were investigated. It had been hoped that a regular sequence of images would make it possible to follow the dynamics of the Rhone and the coastal rivers in relation to meteorological conditions. In any event only a small number of images spread over a wide period of time were obtained, and a complete study was therefore impossible. However, in comparing some of the ERTS-1 images certain thermal-IR images and information on the flow of the Rhone provided some clarification of mechanisms associated with river dynamics.

CROSS-SHORE TRANSPORT OF BIMODAL SANDS.

USGS Publications Warehouse

Richmond, Bruce M.; Sallenger,, Asbury H.; Edge, Billy L.

1985-01-01

Foreshore sediment level and sediment size were monitored as part of an extensive nearshore processes experiment - DUCK 82. Changes in foreshore texture were compared with computed values of onshore transported material based on current measurements from the surf zone and sediment transport theory. Preliminary results indicate reasonable agreement between predicted size of sediment transported onshore and beach texture changes. It is also demonstrated that coarse sediment may move onshore while finer material may simultaneously move offshore. Refs.

Geochemical and geological factors controlling the spatial distribution of sulfate-methane transition zone in the Ría de Vigo (NW Spain)

NASA Astrophysics Data System (ADS)

Martínez-Carreño, N.; García-Gil, S.; Cartelle, V.; de Blas, E.; Ramírez-Pérez, A. M.; Insua, T. L.

2017-05-01

High-resolution seismic profiles, gravity core analysis and radiocarbon data have been used to identify the factors behind the methane production and free gas accumulation in the Ría de Vigo. Lithological and geochemical parameters (sulfate and methane concentration) from seventeen gravity cores were analyzed to characterize the sediment of the ria. The distribution of methane-charged sediments is mainly controlled by the quantity and quality of organic matter. Geochemical analyses reveal minimum methane concentrations ranging between 1 μM and 1 mM in sediments located outside the acoustic gas field, while gas-bearing sediments, show methane concentrations up to 5 mM. A shallowing of the sulfate-methane transition zone (SMTZ) is observed from the outer to the inner area of the ria. The presence of methane in the sulfate reduction zone (SRZ) likely to reflect the existence of methylotropic methanogenesis and/or migration processes of deeper methane gas in the sediments of the Ría de Vigo. The presence of an 'anomalous' high-sulfate concentration layer below the SMTZ in the inner and middle area of the ria, is attributed to the intrusion of sulfate-rich waters from adjacent areas that could be transported laterally through more porous layers.

Streambeds Merit Recognition as a Scientific Discipline

NASA Astrophysics Data System (ADS)

Constantz, J. E.

2016-12-01

Streambeds are generally viewed as simply sediments beneath streams, sediments topping alluvial aquifers, or sediments housing aquatic life, rather than as distinct geographic features comparable to soils and surficial geologic formations within watersheds. Streambeds should be viewed as distinct elements within watersheds, e.g., as akin to soils. In this presentation, streambeds are described as central features in watersheds, cycling water between the surface and underlying portions of the watershed. Regarding their kinship to soils, soils are often described as surficial sediments largely created by atmospheric weathering of underlying geologic parent material, and similarly, streambeds should be described as submerged sediments largely created by streamflow modification of underlying geologic parent material. Thus, streambeds are clearly overdue for recognition as their own scientific discipline along side other well-recognized disciplines within watersheds; however, slowing progress in this direction, the point is often made that hyporheic zones should be considered comparable to streambeds, but this is as misguided as equating unsaturated zones to soils. Streambeds and soils are physical geographic features of relatively constant volume, while hyporheic and unsaturated zones are hydrologic features of varying volume. Expanded upon in this presentation, 'Streambed Science' is proposed for this discipline, which will require both a well-designed protocol to physically characterize streambeds as well as development of streambed taxonomy, for suitable recognition as an independent discipline within watersheds.

Sediment features at the grounding zone and beneath Ekström Ice Shelf, East Antarctica, imaged using on-ice vibroseis.

NASA Astrophysics Data System (ADS)

Smith, Emma C.; Eisen, Olaf; Hofstede, Coen; Lambrecht, Astrid; Mayer, Christoph

2017-04-01

The grounding zone, where an ice sheet becomes a floating ice shelf, is known to be a key threshold region for ice flow and stability. A better understanding of ice dynamics and sediment transport across such zones will improve knowledge about contemporary and palaeo ice flow, as well as past ice extent. Here we present a set of seismic reflection profiles crossing the grounding zone and continuing to the shelf edge of Ekström Ice Shelf, East Antarctica. Using an on-ice vibroseis source combined with a snowstreamer we have imaged a range of sub-glacial and sub-shelf sedimentary and geomorphological features; from layered sediment deposits to elongated flow features. The acoustic properties of the features as well as their morphology allow us to draw conclusions as to their material properties and origin. These results will eventually be integrated with numerical models of ice dynamics to quantify past and present interactions between ice and the solid Earth in East Antarctica; leading to a better understanding of future contributions of this region to sea-level rise.

Beach-dune dynamics: Spatio-temporal patterns of aeolian sediment transport under complex offshore airflow

NASA Astrophysics Data System (ADS)

Lynch, K.; Jackson, D.; Delgado-Fernandez, I.; Cooper, J. A.; Baas, A. C.; Beyers, M.

2010-12-01

This study examines sand transport and wind speed across a beach at Magilligan Strand, Northern Ireland, under offshore wind conditions. Traditionally the offshore component of local wind regimes has been ignored when quantifying beach-dune sediment budgets, with the sheltering effect of the foredune assumed to prohibit grain entrainment on the adjoining beach. Recent investigations of secondary airflow patterns over coastal dunes have suggested this may not be the case, that the turbulent nature of the airflow in these zones enhances sediment transport potential. Beach sediment may be delivered to the dune toe by re-circulating eddies under offshore winds in coastal areas, which may explain much of the dynamics of aeolian dunes on coasts where the dominant wind direction is offshore. The present study investigated aeolian sediment transport patterns under an offshore wind event. Empirical data were collected using load cell traps, for aeolian sediment transport, co-located with 3-D ultrasonic anemometers. The instrument positioning on the sub-aerial beach was informed by prior analysis of the airflow patterns using computational fluid dynamics. The array covered a total beach area of 90 m alongshore by 65 m cross-shore from the dune crest. Results confirm that sediment transport occurred in the ‘sheltered’ area under offshore winds. Over short time and space scales the nature of the transport is highly complex; however, preferential zones for sand entrainment may be identified. Alongshore spatial heterogeneity of sediment transport seems to show a relationship to undulations in the dune crest, while temporal and spatial variations may also be related to the position of the airflow reattachment zone. These results highlight the important feedbacks between flow characteristics and transport in a complex three dimensional surface.

The importance of benchmarking habitat structure and composition for understanding the extent of fishing impacts in soft sediment ecosystems

NASA Astrophysics Data System (ADS)

Handley, Sean J.; Willis, Trevor J.; Cole, Russell G.; Bradley, Anna; Cairney, Daniel J.; Brown, Stephen N.; Carter, Megan E.

2014-02-01

Trawling and dredge fisheries remove vulnerable fauna, homogenise sediments and assemblages, and break down biogenic habitats, but the full extent of these effects can be difficult to quantify in the absence of adequate control sites. Our study utilised rare control sites containing biogenic habitat, the Separation Point exclusion zone, formally protected for 28 years, as the basis for assessing the degree of change experienced by adjacent areas subject to benthic fishing. Sidescan sonar surveys verified that intensive trawling and dredging occurred in areas adjacent to, but not inside, the exclusion area. We compared sediment composition, biogenic cover, macrofaunal assemblages, biomass, and productivity of the benthos, inside and outside the exclusion zone. Disturbed sites were dominated by fine mud, with little or no shell-gravel, reduced number of species, and loss of large bodied animals, with concomitant reductions in biomass and productivity. At protected sites, large, rarer molluscs were more abundant and contributed the most to size-based estimates of productivity and biomass. Functional changes in fished assemblages were consistent with previously reported relative increases in scavengers, predators and deposit feeders at the expense of filter feeders and a grazer. We propose that the colonisation of biogenic species in protected sites was contingent on the presence of shell-gravel atop these soft sediments. The process of sediment homogenisation by bottom fishing and elimination of shell-gravels from surficial sediments appeared to have occurred over decades - a ‘shifting baseline’. Therefore, benchmarking historical sediment structure at control site like the Separation Point exclusion zone is necessary to determine the full extent of physical habitat change wrought by contact gears on sheltered soft sediment habitats to better underpin appropriate conservation, restoration or fisheries management goals.

[Sediment-water flux and processes of nutrients and gaseous nitrogen release in a China River Reservoir].

PubMed

Chen, Zhu-hong; Chen, Neng-wang; Wu, Yin-qi; Mo, Qiong-li; Zhou, Xing-peng; Lu, Ting; Tian, Yun

2014-09-01

The key processes and fluxes of nutrients (N and P) and gaseous N (N2 and N2O) across the sediment-water interface in a river reservoir (Xipi) of the Jiulong River watershed in southeast China were studied. Intact core sediment incubation of nutrients exchange, in-situ observation and lab incubation of excess dissolved N2 and N2O (products of nitrification, denitrification and Anammox), and determination of physiochemical and microbe parameters were carried out in 2013 for three representative sites along the lacustrine zone of the reservoir. Results showed that ammonium and phosphate were generally released from sediment to overlying water [with averaged fluxes of N (479.8 ± 675.4) mg. (m2. d)-1 and P (4. 56 ± 0.54) mg. (m2 d) -1] , while nitrate and nitrite diffused into the sediment. Flood events in the wet season could introduce a large amount of particulate organic matter that would be trapped by the dam reservoir, resulting in the high release fluxes of ammonium and phosphate observed in the following low-flow season. No clear spatial variation of sediment nutrient release was found in the lacustrine zone of the reservoir. Gaseous N release was dominated by excess dissolved N2 (98% of total), and the N2 flux from sediment was (15.8 ± 12. 5) mg (m2. d) -1. There was a longitudinal and vertical variation of excess dissolved N2, reflecting the combined results of denitrification and Anammox occurring in anoxic sediment and fluvial transport. Nitrification mainly occurred in the lower lacustrine zone, and the enrichment of N2O was likely regulated by the ratio of ammonium to DIN in water.

Integrated quality assessment of sediments from harbour areas in Santos-São Vicente Estuarine System, Southern Brazil

NASA Astrophysics Data System (ADS)

Buruaem, Lucas Moreira; de Castro, Ítalo Braga; Hortellani, Marcos Antonio; Taniguchi, Satie; Fillmann, Gilberto; Sasaki, Silvio Tarou; Varella Petti, Mônica Angélica; Sarkis, Jorge Eduardo de Souza; Bícego, Márcia Caruso; Maranho, Luciane Alves; Davanso, Marcela Bergo; Nonato, Edmundo Ferraz; Cesar, Augusto; Costa-Lotufo, Leticia Veras; Abessa, Denis Moledo de Souza

2013-09-01

Santos-São Vicente Estuarine System is a highly populated coastal zone in Brazil and where it is located the major port of Latin America. Historically, port activities, industrial and domestic effluents discharges have constituted the main sources of contaminants to estuarine system. This study aimed to assess the recent status of sediment quality from 5 zones of Port of Santos by applying a lines-of-evidence approach through integrating results of: (1) acute toxicity of whole sediment and chronic toxicity of liquid phases; (2) grain size, organic matter, organic carbon, nitrogen, phosphorus, trace metals, polycyclic aromatic hydrocarbons, linear alkylbenzenes and butyltins; (3) benthic community descriptors. Results revealed a gradient of increasing contamination for metals and organic compounds, alongside with their geochemical carriers. Sediment liquid phases were more toxic compared to whole sediment. Low number of species and individuals indicated the impoverishment of benthic community. The use of site-specific sediment quality guidelines was more appropriate to predict sediment toxicity. The integration of results through Sediment Quality Triad approach and principal component analysis allowed observing the effects of natural stressors and dredging on sediment quality and benthic distribution. Even with recent governmental efforts to control, pollution is still relevant in Port of Santos and a threat to local ecosystems.

Northern Victoria Land (western Ross Sea-Antarctica): inner shelf fine sedimentation

NASA Astrophysics Data System (ADS)

Colizza, E.; Finocchiaro, F.; Ivaldi, R.; Pittà, A.; Tolotti, R.; Brambati, A.

2003-04-01

The Holocene sedimentation conditions are represented, in the western Ross Sea, by diatomaceous ooze in the uppermost part of sedimentary sequences, while diamicton deposited during Last Glacial Maximum are the basal unit of most cores. Thick layer (> 2 m) of diatomaceous ooze were sampled in the northern Joides Basin and into Granite Harbour. In Drygalski Ice Tongue area and along the coasts of northern Victoria Land, prevails coarse sedimentation, due to seaward flowing of large outlet glacier that drain the Transantarctic Mountain. During 1998-99 and 2001-02 PNRA antarctic cruises, favourable sea ice conditions, has allowed to sample inner shelf area, both in Wood Bay and south of Drygalski ice tongue (Nordenskjold basin). In both sites fine laminated diatomaceous mud are present. Preliminary seismostratigraphy and sedimentological data are here reported. This is the first note of new sites of fine sedimentation in the Ross Sea inner shelf.

Investigating the development of less-mobile porosity in realistic hyporheic zone sediments with COMSOL Multiphysics

NASA Astrophysics Data System (ADS)

MahmoodPoorDehkordy, F.; Briggs, M. A.; Day-Lewis, F. D.; Bagtzoglou, A. C.

2017-12-01

Although hyporheic zones are often modeled at the reach scale as homogeneous "boxes" of exchange, heterogeneity caused by variations of pore sizes and connectivity is not uncommon. This heterogeneity leads to the creation of more- and less-mobile zones of hydraulic exchange that influence reactive solute transport processes. Whereas fluid sampling is generally sensitive to more-mobile zones, geoelectrical measurement is sensitive to ionic tracer dynamics in both less- and more-mobile zones. Heterogeneity in pore connectivity leads to a lag between fluid and bulk electrical conductivity (EC) resulting in a hysteresis loop, observed during tracer breakthrough tests, that contains information about the less-mobile porosity attributes of the medium. Here, we present a macro-scale model of solute transport and electrical conduction developed using COMSOL Multiphysics. The model is used to simulate geoelectrical monitoring of ionic transport for bed sediments based on (1) a stochastic sand-and-cobble mixture and (2) a dune feature with strong permeability layering. In both of these disparate sediment types, hysteresis between fluid and bulk EC is observed, and depends in part on fluid flux rate through the model domain. Using the hysteresis loop, the ratio of less-mobile to mobile porosity and mass-transfer coefficient are estimated graphically. The results indicate the presence and significance of less-mobile porosity in the hyporheic zones and demonstrate the capability of the proposed model to detect heterogeneity in flow processes and estimate less-mobile zone parameters.

Relating modes of extension to the spatial and temporal distribution of major sediment unconformities at passive margins

NASA Astrophysics Data System (ADS)

Andrés-Martínez, Miguel; Pérez-Gussinyé, Marta; Armitage, John; Morgan, Jason P.

2017-04-01

Rifting is a regional process which results in thinning of the crust over hundreds of kilometres. However, basins where deposition takes place could have different subsidence histories due to local graben-bounding fault kinetics. A change in the rift dynamics often results in a displacement of the basin depocenters, with subsequent erosion of old sediments and later deposition, creating an unconformity. Unconformities of regional character are typically studied to unveil the overall rift deformation history, and major ones separating syn- and post-kinematic sediments are often associated with break-up of the continental crust. However, evolution of the basement deformation is typically challenging to study since reflection images are usually diffuse at these depths and boreholes are typically scarce, which complicates the dating of the sediments overlying the basement. Consequently, relating the deformation styles and rift evolution to unconformities is not straight forward. We use numerical models in order to approach the meaning of regional unconformities and to study the sedimentation patterns under different modes of extension. Our models solve 2D Stokes flow for rocks treated as non-Newtonian bodies, together with heat conservation equation. Viscosities and densities depend on temperatures. Elasticity and plasticity are plugged-in in the mechanical formulation. We also use strain softening to simulate faulting and shear zones. The top boundary is a free-surface so that tectonics result in topography. Additionally, we update this topography every time step using a sediment transport model, and we store information about depositional times, paleo-depths and erosional events. These models allow for the recovery of the basement deformation during rift evolution simultaneously to the recovery of sedimentation history. Here, we run models with different crustal rheologies to reproduce different extensional modes. This allows us to contrast sedimentation patterns and unconformities under variable kinetic scenarios, from regional to faulted-block scales. We find that unconformities are generally associated to a change in the locus of extension. In models with intermediate-strength crust, sequential faulting takes place, so that only one fault is active at a time and occur in the hanging wall of the previous fault, resulting in asymmetric conjugate margins. In this case a major unconformity separates syn- and post-kinematic sediments. Both syn- and post-kinematic sediments young oceanwards and the unconformity dates the time in which extension abandons the area in favour of new faults forming oceanwards. Models with weaker crusts display extension along a wide region, with overprinting of different faulting phases. Eventually, deformation localizes in a narrow region due to cooling, and crustal break-up occurs. In this case, a first set of unconformities separates different phases of faulting inside the syn-kinematic sediments, and later unconformities separate syn-kinematic and post-kinematic sediments, dating the time at which extension localizes. We also find that unconformities date the crustal break-up only when they develop in the vicinity of the break-up locus. This stresses on that terms such as syn- and post-rift sediments and break-up unconformity should be handled carefully when seismic interpretation is done, and also provides support for unconformities as rifting story-tellers.

Geochemical evidence for enhanced preservation of organic matter in the oxygen minimum zone of the continental margin of northern California during the Late Pleistocene

USGS Publications Warehouse

Dean, Walter E.; Gardner, James V.; Anderson, Roger Y.

1994-01-01

The present upper water mass of the northeastern Pacific Ocean off California has a well-developed oxygen minimum zone between 600 and 1200 m wherein concentrations of dissolved oxygen are less than 0.5 mL/L. Even at such low concentrations of dissolved oxygen, benthic burrowing organisms are abundant enough to thoroughly bioturbate the surface and near-surface sediments. These macro organisms, together with micro organisms, also consume large quantities of organic carbon produced by large seasonal stocks of plankton in the overlying surface waters, which are supported by high concentrations of nutrients within the California Current upwelling system. In contrast to modern conditions of bioturbation, laminated sediments are preserved in upper Pleistocene sections of cores collected on the continental slope at water depths within the present oxygen minimum zone from at least as far north as the California-Oregon border and as far south as Point Conception. Comparison of sediment components in the laminae with those delivered to sediment traps as pelagic marine “snow” demonstrates that the dark-light lamination couplets are indeed annual (varves). These upper Pleistocene varved sediments contain more abundant lipid-rich “sapropelic” (type II) organic matter than the overlying bioturbated, oxidized Holocene sediments. The baseline of stable carbon isotopic composition of the organic matter in these slope cores does not change with time, indicating that the higher concentrations of type II organic matter in the varved sediments represent better preservation of organic matter rather than any change in the source of organic matter.

Structural characteristics of the décollement zone and underthrust sediments in the Nankai accretionary prism: Geologic architectures in the Site C0023, IODP Expedition 370

NASA Astrophysics Data System (ADS)

Yamamoto, Y.; Okutsu, N.; Yamada, Y.; Bowden, S.; Tonai, S.; Yang, K.; Tsang, M. Y.; Hirose, T.; Kamiya, N.

2017-12-01

Expedition 370 penetrated the accretionary prism, plate boundary décollement zone, and underthrust sediment and touched the basement basalt on the Philippine Sea Plate. The drilling site (C0023) is located 4 km NE from the legacy sites, Sites 808 and 1174. Compared to the legacy sites, the décollement zone is characterized by weak and intermittent negative reflectors in the seismic profile. Onboard physical properties, e.g. porosity and P-wave velocity data, indeed show the smaller gaps at the top of the décollement zone. The nature of the deformation along the décollement zone represented 40 m thick phacoidal deformation zone composed of fragmented mudstone with slickenlines on the surfaces in the Sites 808 and 1174. Compare with this, décollement zone in Site C0023 represented the weaker and non-localized deformation zone comprised of alternating zone of 1 m thick phacoidal deformation zones and a few 10 m of intact intervals in the Site C0023. Many normal faults striking parallel to the trench were identified just below the décollement zone, which is indicative of non-localized deformations along the décollement zone. Many of these faults were accompanied with calcite and sulphate mineral veins (anhydrite and barite), indicative of high-temperature fluid migration just above the ridge-spreading center. Based on the paleomagnetic restoration of structure to the geologic coordinate, attitudes of the bedding and fault planes in the Site C0023 are controlled by two factors: 1) subduction/accretion producing the trench-parallel bedding strikes and trench-perpendicular principal stress and 2) ridge spreading that produces ridge-parallel bedding and vein strikes. The former developed in the accretionary prism and the upper part of the underthrust sediment (<900 mbsf), whereas the latter occurs in the lower part (>900 mbsf). These tectonic variations might affect fluid migration pathways.

Spatial hydrological flow processes, water quality, sediment and vegetation community distributions in a natural floodplain fen - implication for the Flood Pulse Concept

NASA Astrophysics Data System (ADS)

Keizer, Floris; Schot, Paul; Wassen, Martin; Kardel, Ignacy; Okruszko, Tomasz

2017-04-01

We studied spatial patterns in inundation water quality, sediment and vegetation distribution in a floodplain fen in Poland to map interacting peatland hydrological processes. Using PCA and K-means cluster analysis, we identified four water types, related to river water inundation, discharge of clean and polluted groundwater, and precipitation and snowmelt dilution. Spatially, these hydrochemical water types are related to known water sources in the floodplain and occupy distinctive zones. River water is found along the river, clean and polluted groundwater at the valley margins and groundwater diluted with precipitation and snowmelt water in the central part of the floodplain. This implies that, despite the floodplain being completely inundated, nutrient input from river flooding occurs only in a relatively narrow zone next to the river. Our findings question the relevance of the edge of inundation, as presented in the Flood Pulse Concept, as delineating the zone of input and turnover of nutrients. Secondly, we studied rich-fen and freshwater vegetation community distributions in relation to the presented inundation water quality types. We successfully determined inundation water quality preference for 14 out of 17 studied rich-fen and freshwater communities in the floodplain. Spatial patterns in preference show vegetation with attributed river water preference to occur close to the river channel, with increasing distance to the river followed by communities with no preference, diluted groundwater preference in the central part, and clean and polluted groundwater preference at the valley margins. In inundation water, nutrients are known to be transported mainly as attached to sediment, besides in dissolved state. This means that in the zone where sediment deposition occurs, nutrient input can be a relevant contribution to the nutrient input of the floodplain. We found a significant decrease in sediment-attached nutrient deposition with distance from the river. Sediment-attached nutrients correlated better to aboveground standing biomass than dissolved nutrients. These findings further reduce the spatial zone where significant nutrient input is influenced by transport from the river, compared to the zone influenced by dissolved nutrients. Our findings indicate the need for a revision of the Flood Pulse Concept for temperate river with multiple water sources, as peatland hydrological processes significantly influence spatial floodplain vegetation distribution.

Sulfur cycling in an iron oxide-dominated, dynamic marine depositional system: The Argentine continental margin

NASA Astrophysics Data System (ADS)

Riedinger, Natascha; Brunner, Benjamin; Krastel, Sebastian; Arnold, Gail L.; Wehrmann, Laura M.; Formolo, Michael J.; Beck, Antje; Bates, Steven M.; Henkel, Susann; Kasten, Sabine; Lyons, Timothy W.

2017-05-01

The interplay between sediment deposition patterns, organic matter type and the quantity and quality of reactive mineral phases determines the accumulation, speciation and isotope composition of pore water and solid phase sulfur constituents in marine sediments. Here, we present the sulfur geochemistry of siliciclastic sediments from two sites along the Argentine continental slope—a system characterized by dynamic deposition and reworking, which result in non-steady state conditions. The two investigated sites have different depositional histories but have in common that reactive iron phases are abundant and that organic matter is refractory—conditions that result in low organoclastic sulfate reduction rates. Deposition of reworked, isotopically light pyrite and sulfurized organic matter appear to be important contributors to the sulfur inventory, with only minor addition of pyrite from organoclastic sulfate reduction above the sulfate-methane transition (SMT). Pore-water sulfide is limited to a narrow zone at the SMT. The core of that zone is dominated by pyrite accumulation. Iron monosulfide and elemental sulfur accumulate above and below this zone. Iron monosulfide precipitation is driven by the reaction of low amounts of hydrogen sulfide with ferrous iron and is in competition with the oxidation of sulfide by iron (oxyhydr)oxides to form elemental sulfur. The intervals marked by precipitation of intermediate sulfur phases at the margin of the zone with free sulfide are bordered by two distinct peaks in total organic sulfur. Organic matter sulfurization appears to precede pyrite formation in the iron-dominated margins of the sulfide zone, potentially linked to the presence of polysulfides formed by reaction between dissolved sulfide and elemental sulfur. Thus, SMTs can be hotspots for organic matter sulfurization in sulfide-limited, reactive iron-rich marine sedimentary systems. Furthermore, existence of elemental sulfur and iron monosulfide phases meters below the SMT demonstrates that in sulfide-limited systems metastable sulfur constituents are not readily converted to pyrite but can be buried to deeper sediment depths. Our data show that in non-steady state systems, redox zones do not occur in sequence but can reappear or proceed in inverse sequence throughout the sediment column, causing similar mineral alteration processes to occur at the same time at different sediment depths.

Conceptual Regional Sediment Budget for USACE North Atlantic Division

DTIC Science & Technology

2015-03-01

sediment budget is the first phase in development of the working budget and is intended to provide a general framework based on existing transport ...existing literature and databases were reviewed and analyzed to characterize sediment transport pathways and magnitudes, and morphologic zones of...net sediment transport pathways for Region 1 (includes NACCS planning regions VA1 through VA6 and MD2 through MD5

Regional Survey of Structural Properties and Cementation Patterns of Fault Zones in the Northern Part of the Albuquerque Basin, New Mexico - Implications for Ground-Water Flow

USGS Publications Warehouse

Minor, Scott A.; Hudson, Mark R.

2006-01-01

Motivated by the need to document and evaluate the types and variability of fault zone properties that potentially affect aquifer systems in basins of the middle Rio Grande rift, we systematically characterized structural and cementation properties of exposed fault zones at 176 sites in the northern Albuquerque Basin. A statistical analysis of measurements and observations evaluated four aspects of the fault zones: (1) attitude and displacement, (2) cement, (3) lithology of the host rock or sediment, and (4) character and width of distinctive structural architectural components at the outcrop scale. Three structural architectural components of the fault zones were observed: (1) outer damage zones related to fault growth; these zones typically contain deformation bands, shear fractures, and open extensional fractures, which strike subparallel to the fault and may promote ground-water flow along the fault zone; (2) inner mixed zones composed of variably entrained, disrupted, and dismembered blocks of host sediment; and (3) central fault cores that accommodate most shear strain and in which persistent low- permeability clay-rich rocks likely impede the flow of water across the fault. The lithology of the host rock or sediment influences the structure of the fault zone and the width of its components. Different grain-size distributions and degrees of induration of the host materials produce differences in material strength that lead to variations in width, degree, and style of fracturing and other fault-related deformation. In addition, lithology of the host sediment appears to strongly control the distribution of cement in fault zones. Most faults strike north to north-northeast and dip 55? - 77? east or west, toward the basin center. Most faults exhibit normal slip, and many of these faults have been reactivated by normal-oblique and strike slip. Although measured fault displacements have a broad range, from 0.9 to 4,000 m, most are <100 m, and fault zones appear to have formed mainly at depths less than 1,000 m. Fault zone widths do not exceed 40 m (median width = 15.5 m). The mean width of fault cores (0.1 m) is nearly one order of magnitude less than that of mixed zones (0.75 m) and two orders of magnitude less than that of damage zones (9.7 m). Cements, a proxy for localized flow of ancient ground water, are common along fault zones in the basin. Silica cements are limited to faults that are near and strike north to northwest toward the Jemez volcanic field north of the basin, whereas carbonate fault cements are widely distributed. Coarse sediments (gravel and sand) host the greatest concentrations of cement within fault zones. Cements fill some extension fractures and, to a lesser degree, are concentrated along shear fractures and deformation bands within inner damage zones. Cements are commonly concentrated in mixed zones and inner damage zones on one side of a fault and thus are asymmetrically distributed within a fault zone, but cement does not consistently lie on the basinward side of faults. From observed spatial patterns of asymmetrically distributed fault zone cements, we infer that ancient ground-water flow was commonly localized along, and bounded by, faults in the basin. It is apparent from our study that the Albuquerque Basin contains a high concentration of faults. The geometry of, internal structure of, and cement and clay distribution in fault zones have created and will continue to create considerable heterogeneity of permeability within the basin aquifers. The characteristics and statistical range of fault zone features appear to be predictable and consistent throughout the basin; this predictability can be used in ground-water flow simulations that consider the influence of faults.

Velocity-porosity relationships for slope apron and accreted sediments in the Nankai Trough Seismogenic Zone Experiment, Integrated Ocean Drilling Program Expedition 315 Site C0001

NASA Astrophysics Data System (ADS)

Hashimoto, Y.; Tobin, H. J.; Knuth, M.

2010-12-01

In this study, we focused on the porosity and compressional wave velocity of marine sediments to examine the physical properties of the slope apron and the accreted sediments. This approach allows us to identify characteristic variations between sediments being deposited onto the active prism and those deposited on the oceanic plate and then carried into the prism during subduction. For this purpose we conducted ultrasonic compressional wave velocity measurements on the obtained core samples with pore pressure control. Site C0001 in the Nankai Trough Seismogenic Zone Experiment transect of the Integrated Ocean Drilling Program is located in the hanging wall of the midslope megasplay thrust fault in the Nankai subduction zone offshore of the Kii peninsula (SW Japan), penetrating an unconformity at ˜200 m depth between slope apron sediments and the underlying accreted sediments. We used samples from Site C0001. Compressional wave velocity from laboratory measurements ranges from ˜1.6 to ˜2.0 km/s at hydrostatic pore pressure conditions estimated from sample depth. The compressional wave velocity-porosity relationship for the slope apron sediments shows a slope almost parallel to the slope for global empirical relationships. In contrast, the velocity-porosity relationship for the accreted sediments shows a slightly steeper slope than that of the slope apron sediments at 0.55 of porosity. This higher slope in the velocity-porosity relationship is found to be characteristic of the accreted sediments. Textural analysis was also conducted to examine the relationship between microstructural texture and acoustic properties. Images from micro-X-ray CT indicated a homogeneous and well-sorted distribution of small pores both in shallow and in deeper sections. Other mechanisms such as lithology, clay fraction, and abnormal fluid pressure were found to be insufficient to explain the higher velocity for accreted sediments. The higher slope in velocity-porosity relationship for accreted sediments can be explained by weak cementation, critical porosity or differences in loading history.

Depositionally controlled recycling of iron and sulfur in marine sediments and its isotopic consequences

NASA Astrophysics Data System (ADS)

Riedinger, N.; Formolo, M.; Arnold, G. L.; Vossmeyer, A.; Henkel, S.; Sawicka, J.; Kasten, S.; Lyons, T. W.

2011-12-01

The continental margin off Uruguay and Argentina is characterized by highly dynamic depositional conditions. This variable depositional regime significantly impacts the biogeochemical cycles of iron and sulfur. Mass deposit related redeposition of reduced minerals can lead to the reoxidation of these phases and thus to an overprint of their geochemical primary signatures. Due to rapid burial these oxidized phases are still present in deeper subsurface sediments. To study the effects of sediment relocation on the sulfur and iron inventory we collected shallow and deep subsurface sediment samples via multicorer and gravity cores, respectively, in the western Argentine Basin during the RV Meteor Expedition M78/3 in May-July 2009. The samples were retrieved from shelf, slope and deep basin sites. The concentration and sulfur isotope composition of acid volatile sulfur (AVS), chromium reducible sulfur (CRS), elemental sulfur and total organic sulfur were determined. Furthermore, sequential iron extraction techniques were applied assess the distribution of iron oxide phases within the sediment. The investigated sediments are dominated by terrigenous inputs, with high amounts of reactive ferric iron minerals and only low concentrations of calcium carbonate. Total organic carbon concentrations show strong variation in the shallow subsurface sediments ranging between approximately 0.7 and 6.4 wt% for different sites. These concentrations do not correlate with water depths. Pore water accumulations of hydrogen sulfide are restricted to an interval at the sulfate-methane transition (SMT) zone a few meters below the sediment surface. In these deeper subsurface sediments pyrite is precipitated in this zone of hydrogen sulfide excess, whereas the accumulation of authigenic AVS and elemental sulfur (up to 2000 ppm) occurs at the upper and lower boundary of the sulfidic zone due the reaction of iron oxides with limited amounts of sulfide. Furthermore, our preliminary results indicate that there is a link between modern deposition in the shallow subsurface sediments and the long-term signals being buried and preserved in the deep subsurface layers. The data show that the burial of elemental sulfur into deep subsurface sediments can fuel the deep biosphere and has consequences for isotopic overprints tied, for example, to oxidation and disproportionation processes in the deeper sediments.

Spectral Decomposition and Other Seismic Attributes for Gas Hydrate Prospecting

DOE Office of Scientific and Technical Information (OSTI.GOV)

McConnell, Dan

Studying the sediments at the base of gas hydrate stability is ideal for determining the seismic response to gas hydrate saturation. First, assuming gas migration to the shallow section, this area is more likely to have concentrated gas hydrate because it encompasses the zone in which upward moving buoyant gas transitions to form immobile gas hydrate deposits. Second, this zone is interesting because these areas have the potential to show a hydrate filled zone and a gas filled zone within the same sediments. Third, the fundamental measurement within seismic data is impedance contrasts between velocity*density layers. High saturation gas hydratesmore » and free gas inhabit opposite ends of these measurements making the study of this zone ideal for investigating the seismic characteristics of gas hydrate and, hence, the investigation of other seismic attributes that may indicate gas hydrate fill.« less

Effective strength of incoming sediments and its implications for plate boundary propagation: Nankai and Costa Rica as type examples of accreting vs. erosive convergent margins

NASA Astrophysics Data System (ADS)

Kopf, Achim

2013-11-01

The location of the seaward tip of a subduction thrust controls material transfer at convergent plate margins, and hence global mass balances. At approximately half of those margins, the material of the subducting plate is completely underthrust so that no accretion or even subduction erosion takes place. Along the remaining margins, material is scraped off the subducting plate and added to the upper plate by frontal accretion. We here examine the physical properties of subducting sediments off Costa Rica and Nankai, type examples for an erosional and an accretionary margin, to investigate which parameters control the level where the frontal thrust cuts into the incoming sediment pile. A series of rotary-shear experiments to measure the frictional strength of the various lithologies entering the two subduction zones were carried out. Results include the following findings: (1) At Costa Rica, clay-rich strata at the top of the incoming succession have the lowest strength (μres = 0.19) while underlying calcareous ooze, chalk and diatomite are strong (up to μres = 0.43; μpeak = 0.56). Hence the entire sediment package is underthrust. (2) Off Japan, clay-rich deposits within the lower Shikoku Basin inventory are weakest (μres = 0.13-0.19) and favour the frontal proto-thrust to migrate into one particular horizon between sandy, competent turbidites below and ash-bearing mud above. (3) Taking in situ data and earlier geotechnical testing into account, it is suggested that mineralogical composition rather than pore-pressure defines the position of the frontal thrust, which locates in the weakest, clay mineral-rich (up to 85 wt.%) materials. (4) Smectite, the dominant clay mineral phase at either margin, shows rate strengthening and stable sliding in the frontal 50 km of the subduction thrust (0.0001-0.1 mm/s, 0.5-25 MPa effective normal stress). (5) Progressive illitization of smectite cannot explain seismogenesis, because illite-rich samples also show velocity strengthening at the conditions tested.

A unified framework for modelling sediment fate from source to sink and its interactions with reef systems over geological times.

PubMed

Salles, Tristan; Ding, Xuesong; Webster, Jody M; Vila-Concejo, Ana; Brocard, Gilles; Pall, Jodie

2018-03-27

Understanding the effects of climatic variability on sediment dynamics is hindered by limited ability of current models to simulate long-term evolution of sediment transfer from source to sink and associated morphological changes. We present a new approach based on a reduced-complexity model which computes over geological time: sediment transport from landmasses to coasts, reworking of marine sediments by longshore currents, and development of coral reef systems. Our framework links together the main sedimentary processes driving mixed siliciclastic-carbonate system dynamics. It offers a methodology for objective and quantitative sediment fate estimations over regional and millennial time-scales. A simulation of the Holocene evolution of the Great Barrier Reef shows: (1) how high sediment loads from catchments erosion prevented coral growth during the early transgression phase and favoured sediment gravity-flows in the deepest parts of the northern region basin floor (prior to 8 ka before present (BP)); (2) how the fine balance between climate, sea-level, and margin physiography enabled coral reefs to thrive under limited shelf sedimentation rates after ~6 ka BP; and, (3) how since 3 ka BP, with the decrease of accommodation space, reduced of vertical growth led to the lateral extension of reefs consistent with available observational data.

UV filters, ethylhexyl methoxycinnamate, octocrylene and ethylhexyl dimethyl PABA from untreated wastewater in sediment from eastern Mediterranean river transition and coastal zones.

PubMed

Amine, Helmieh; Gomez, Elena; Halwani, Jalal; Casellas, Claude; Fenet, Hélène

2012-11-01

UVF may occur in the aquatic environment through two principal sources: direct inputs from recreational activities and indirect wastewater- and river-borne inputs. The aim of this study was to obtain a first overview of levels of three UVF (EHMC, OC and OD-PABA) in coastal areas subjected to river inputs, untreated wastewater discharges and dumpsite leachates. We selected three eastern Mediterranean rivers that have been impacted for decades by untreated wastewater release and collected sediment in the coastal zone during the hot and humid seasons. Western Mediterranean sites receiving treated wastewaters were analyzed for comparison. The results gave an overview of sediment contamination under these two contrasted situations representative of Mediterranean coastal areas without bathing activities. The analysis of the three UVF revealed the ubiquity and high point source contamination by EHMC and OC in transition and coastal zones, with levels as high as 128 ng g(-1)d.w. OD-PABA was also frequently detected, but at lower concentrations (

Influence of the very polluted inputs of the Tinto-Odiel system on the adjacent littoral sediments of southwestern Spain: a statistical approach.

PubMed

Sainz, A; Ruiz, F

2006-03-01

A spatial and temporal analysis (period 1990-2003) of 15 sampling points distributed along the southwestern Spanish coast permits to delimitate the influence area of the extremely polluted discharges coming from the Tinto-Odiel system in the bottom sediments of the adjacent littoral area. As, Cu, Pb and Zn are the main heavy metals transported by the freshwater runoffs toward the shallow shelf and present very high negative (r < -0.7) and significant (p < 0.001) correlations with the distance to the estuarine mouth. The statistical analysis (index of geoaccumulation, Pearson correlation matrix, cluster analysis) of their concentrations in the littoral sediments located between the Guadiana and Guadalquivir mouths delimitates three zones: (a) Zone 1 (from the estuarine mouth to 6 km to the east), characterized by moderate to strongly polluted bottom sediments and main responsible of the mean annual variations of the former heavy metals in the area studied; (b) Zone 2 (from 21.2 km to the west to 29 km to the east), characterized by moderate pollution levels; and (c) Zone 3, located near the Guadiana and Guadalquivir mouths, with very low As-Cu-Pb contents and unpolluted to moderately levels of Zn due to urban sewages or the presence of local low mobility areas for this element.

Pore pressure development and progressive dewatering in underthrust sediments at the Costa Rican subduction margin: Comparison with northern Barbados and Nankai

NASA Astrophysics Data System (ADS)

Saffer, Demian M.

2003-05-01

At subduction zones, pore pressure affects fault strength, deformation style, structural development, and potentially the updip limit of seismogenic faulting behavior through its control on effective stress and consolidation state. Despite its importance for a wide range of subduction zone processes, few detailed measurements or estimates of pore pressure at subduction zones exist. In this paper, I combine logging-while-drilling (LWD) data, downhole physical properties data, and laboratory consolidation tests from the Costa Rican, Nankai, and Barbados subduction zones, to document the development and downsection variability of effective stress and pore pressure within underthrust sediments as they are progressively loaded by subduction. At Costa Rica, my results suggest that the lower portion of the underthrust section remains nearly undrained, whereas the upper portion is partially drained. An inferred minimum in effective stress developed within the section ˜1.5 km landward of the trench is consistent with core and seismic observations of faulting, and illustrates the important effects of heterogeneous drainage on structural development. Inferred pore pressures at the Nankai and northern Barbados subduction zones indicate nearly undrained conditions throughout the studied intervals, and are consistent with existing direct measurements and consolidation test results. Slower dewatering at Nankai and Barbados than at Costa Rica can be attributed to higher permeability and larger compressibility of near-surface sediments underthrust at Costa Rica. Results for the three margins indicate that the pore pressure ratio (λ) in poorly drained underthrust sediments should increase systematically with distance landward of the trench, and may vary with depth.

Response of invertebrates from the hyporheic zone of chalk rivers to eutrophication and land use.

PubMed

Pacioglu, Octavian; Moldovan, Oana Teodora

2016-03-01

Whereas the response of lotic benthic macroinvertebrates to different environmental stressors is a widespread practice nowadays in assessing the water and habitat quality, the use of hyporheic zone invertebrates is still in its infancy. In this study, classification and regression trees analysis were employed in order to assess the ecological requirements and the potential as bioindicators for the hyporheic zone invertebrates inhabiting four lowland chalk rivers (south England) with contrasting eutrophication levels (based on surface nitrate concentrations) and magnitude of land use (based on percentage of fine sediments load and median interstitial space). Samples of fauna, water and sediment were sampled twice, during low (summer) and high (winter) groundwater level, at depths of 20 and 35 cm. Certain groups of invertebrates (Glossosomatidae and Psychomyiidae caddisflies, and riffle beetles) proved to be good indicators of rural catchments, moderately eutrophic and with high fine sediment load. A diverse community dominated by microcrustaceans (copepods and ostracods) were found as good indicators of highly eutrophic urban streams, with moderate-high fine sediment load. However, the use of other taxonomic groups (e.g. chironomids, oligochaetes, nematodes, water mites and the amphipod Gammarus pulex), very widespread in the hyporheic zone of all sampled rivers, is of limited use because of their high tolerance to the analysed stressors. We recommend the use of certain taxonomic groups (comprising both meiofauna and macroinvertebrates) dwelling in the chalk hyporheic zone as indicators of eutrophication and colmation and, along with routine benthic sampling protocols, for a more comprehensive water and habitat quality assessment of chalk rivers.

Fe-C-S systematics in Bengal Fan sediments

NASA Astrophysics Data System (ADS)

Volvoikar, S. P.; Mazumdar, A.; Goswami, H.; Pujari, S.; Peketi, A.

2017-12-01

Global biogeochemical cycles of iron, carbon and sulfur (Fe-C-S) are interrelated. Sulfate reduction in marine sediments is the major factor controlling the cycling and burial of carbon, sulfur and iron. Organoclastic sulfate reduction and anaerobic oxidation of methane (AOM) are the two main processes responsible for sulfate reduction in marine sediments. The amount and reactivity of organic matter, iron minerals and concentrations of dissolved sulfide in pore water control the burial of iron sulfide and organic bound sulfur in marine sediments. Here we investigate the sulfidization process in a sediment core from the western part of upper Bay of Bengal fan characterized by efficient burial of organic matter with siliclastic load. A 30 m long sediment core (MD 161/29, Lat. 170 18.04' N, Long. 870 22.56' E, water depth: 2434m) was collected onboard Marion Dufresne (May, 2007) and studied for Fe-S speciation and organic matter characterization. Buffered dithionite extractable iron (FeD) varies from 0.71 to 1.43 wt % (Avg. 0.79 wt %). FeD represents Fe oxides and oxyhydroxides mainly, ferrihydrite, lepidocrocite, goethite and hematite. Acid volatile sulfur (AVS) varies from 0.0015 to 0.63 wt % (avg: 0.058 wt %), while chromium reducible sulfur (CRS) varies from 0.00047 to 0.29 wt % (avg. 0.054 wt %). Based on the vertical distribution patterns of FeD, AVS and CRS, the core is divided into three zones, the lower (3000 to 1833 cm), middle (1833 to 398 cm) and upper (398 cm to surface) zones. FeD shows higher concentration in the lower zone. FeTR (FeOx + FeD + FeCRS + FeAVS) also exhibit higher concentration in this zone, suggesting higher availability of reactive iron for iron sulfide precipitation. AVS, elemental sulfur, spikes of CRS and gradual enrichment of δ34SAVS and δ34SCRS with sharp peaks in-between is noted in the lower zone. The gradual enrichment of δ34SAVS and δ34SCRS is the outcome of late diagenetic pyritization with higher availability of sulfide (HS- and H2S) from AOM.

Measurement of Sedimentary Interbed Hydraulic Properties and Their Hydrologic Influence near the Idaho Nuclear Technology and Engineering Center at the Idaho National Engineering and Environmental Laboratory

USGS Publications Warehouse

Perkins, Kim S.

2003-01-01

Disposal of wastewater to unlined infiltration ponds near the Idaho Nuclear Technology and Engineering Center (INTEC), formerly known as the Idaho Chemical Processing Plant, at the Idaho National Engineering and Environmental Laboratory (INEEL) has resulted in the formation of perched water bodies in the unsaturated zone (Cecil and others, 1991). The unsaturated zone at INEEL comprises numerous basalt flows interbedded with thinner layers of coarse- to fine-grained sediments and perched ground-water zones exist at various depths associated with massive basalts, basalt-flow contacts, sedimentary interbeds, and sediment-basalt contacts. Perched ground water is believed to result from large infiltration events such as seasonal flow in the Big Lost River and wastewater discharge to infiltration ponds. Evidence from a large-scale tracer experiment conducted in 1999 near the Radioactive Waste Management Complex (RWMC), approximately 13 km from the INTEC, indicates that rapid lateral flow of perched water in the unsaturated zone may be an important factor in contaminant transport at the INEEL (Nimmo and others, 2002b). Because sedimentary interbeds, and possibly baked-zone alterations at sediment-basalt contacts (Cecil and other, 1991) play an important role in the generation of perched water it is important to assess the hydraulic properties of these units.

Dicamptodon tenebrosus larvae within hyporheic zones of intermittent streams in California

Treesearch

David Feral; Michael A. Camann; Hartwell H. Welsh Jr.

2005-01-01

Lotic ecosystems are increasingly viewed as having three interactive spatial compartments, i.e., channel sediments, the hyporheic zone, and flood plains or riparian areas (Cummins et al. 1983; Ward 1989). The hyporheic zone is the sub-benthic habitat of interstitial spaces between substrate particles in the stream bed, and is the transition zone between surface flow...

Subduction zone earthquake probably triggered submarine hydrocarbon seepage offshore Pakistan

NASA Astrophysics Data System (ADS)

Fischer, David; José M., Mogollón; Michael, Strasser; Thomas, Pape; Gerhard, Bohrmann; Noemi, Fekete; Volkhard, Spiess; Sabine, Kasten

2014-05-01

Seepage of methane-dominated hydrocarbons is heterogeneous in space and time, and trigger mechanisms of episodic seep events are not well constrained. It is generally found that free hydrocarbon gas entering the local gas hydrate stability field in marine sediments is sequestered in gas hydrates. In this manner, gas hydrates can act as a buffer for carbon transport from the sediment into the ocean. However, the efficiency of gas hydrate-bearing sediments for retaining hydrocarbons may be corrupted: Hypothesized mechanisms include critical gas/fluid pressures beneath gas hydrate-bearing sediments, implying that these are susceptible to mechanical failure and subsequent gas release. Although gas hydrates often occur in seismically active regions, e.g., subduction zones, the role of earthquakes as potential triggers of hydrocarbon transport through gas hydrate-bearing sediments has hardly been explored. Based on a recent publication (Fischer et al., 2013), we present geochemical and transport/reaction-modelling data suggesting a substantial increase in upward gas flux and hydrocarbon emission into the water column following a major earthquake that occurred near the study sites in 1945. Calculating the formation time of authigenic barite enrichments identified in two sediment cores obtained from an anticlinal structure called "Nascent Ridge", we find they formed 38-91 years before sampling, which corresponds well to the time elapsed since the earthquake (62 years). Furthermore, applying a numerical model, we show that the local sulfate/methane transition zone shifted upward by several meters due to the increased methane flux and simulated sulfate profiles very closely match measured ones in a comparable time frame of 50-70 years. We thus propose a causal relation between the earthquake and the amplified gas flux and present reflection seismic data supporting our hypothesis that co-seismic ground shaking induced mechanical fracturing of gas hydrate-bearing sediments creating pathways for free gas to migrate from a shallow reservoir within the gas hydrate stability zone into the water column. Our results imply that free hydrocarbon gas trapped beneath a local gas hydrate seal was mobilized through earthquake-induced mechanical failure and in that way circumvented carbon sequestration within the sediment. These findings lead to conclude that hydrocarbon seepage triggered by earthquakes can play a role for carbon budgets at other seismically active continental margins. The newly identified process presented in our study is conceivable to help interpret data from similar sites. Reference: Fischer, D., Mogollon, J.M., Strasser, M., Pape, T., Bohrmann, G., Fekete, N., Spieß, V. and Kasten, S., 2013. Subduction zone earthquake as potential trigger of submarine hydrocarbon seepage. Nature Geoscience 6: 647-651.

Presence, concentrations and risk assessment of selected antibiotic residues in sediments and near-bottom waters collected from the Polish coastal zone in the southern Baltic Sea - Summary of 3years of studies.

PubMed

Siedlewicz, Grzegorz; Białk-Bielińska, Anna; Borecka, Marta; Winogradow, Aleksandra; Stepnowski, Piotr; Pazdro, Ksenia

2018-04-01

Concentrations of selected antibiotic compounds from different groups were measured in sediment samples (14 analytes) and in near-bottom water samples (12 analytes) collected in 2011-2013 from the southern Baltic Sea (Polish coastal zone). Antibiotics were determined at concentration levels of a few to hundreds of ng g -1 d.w. in sediments and ng L -1 in near-bottom waters. The most frequently detected compounds were sulfamethoxazole, trimethoprim, oxytetracycline in sediments and sulfamethoxazole and trimethoprim in near-bottom waters. The occurrence of the identified antibiotics was characterized by spatial and temporal variability. A statistically important correlation was observed between sediment organic matter content and the concentrations of sulfachloropyridazine and oxytetracycline. Risk assessment analyses revealed a potential high risk of sulfamethoxazole contamination in near-bottom waters and of contamination by sulfamethoxazole, trimethoprim and tetracyclines in sediments. Both chemical and risk assessment analyses show that the coastal area of the southern Baltic Sea is highly exposed to antibiotic residues. Copyright © 2017 Elsevier Ltd. All rights reserved.

Response of crayfish to hyporheic water availability and excess sedimentation

USGS Publications Warehouse

Dyer, Joseph J.; Worthington, Thomas A.; Brewer, Shannon K.

2015-01-01

Crayfish in many headwater streams regularly cope with seasonal drought. However, it is unclear how landscape changes affect the long-term persistence of crayfish populations. We designed two laboratory experiments to investigate the acute effects of common landscape stressors on crayfish: water withdrawal and sedimentation. The first experiment tested the interaction among water withdrawals (four 24-h water reductions of 0, 15, 30, or 45 cm) and two substrate treatments (pebble and cobble) on the burrowing depth of crayfish. The second experiment evaluated the effects of excess fine sediment (three treatments of 0, 45, and 90% sediment) and substrate type (cobble and pebble) on crayfish burrowing depth. Crayfish were able to burrow deeper into the simulated hyporheic zone in cobble substrate when compared to pebble. Crayfish subjected to greater water withdrawals in the pebble treatment were not able to reach the simulated hyporheic zone. Excess fine sediment reduced the depth that crayfish burrowed, regardless of substrate type. Results from this study suggest excess fine sediment may reduce crayfish persistence, particularly when seeking refuge during prolonged dry conditions.

Applying electrical resistivity tomography and biological methods to assess the surface-groundwater interaction in two Mediterranean rivers (central Spain)

NASA Astrophysics Data System (ADS)

Iepure, Sanda; Gómez Ortiz, David; Lillo Ramos, Javier; Rasines Ladero, Ruben; Persoiu, Aurel

2014-05-01

Delineation of the extent of hyporheic zone (HZ) in river ecosystems is problematic due to the scarcity of spatial information about the structure of riverbed sediments and the magnitude and extent of stream interactions with the parafluvial and riparian zones. The several existing methods vary in both quality and quantity of information and imply the use of hydrogeological and biological methods. In the last decades, various non-invasive geophysical techniques were developed to characterise the streambed architecture and also to provide detailed spatial information on its vertical and horizontal continuity. All classes of techniques have their strengths and limitations; therefore, in order to assess their potential in delineating the lateral and vertical spatial extents of alluvial sediments, we have combined the near-surface images obtained by electrical resistivity tomography (ERT) with biological assessment of invertebrates in two Mediterranean lowland rivers from central Spain. We performed in situ imaging of the thickness and continuity of alluvial sediments under the riverbed and parafluvial zone during base-flow conditions (summer 2013 and winter 2014) at two different sites with distinct lithology along the Tajuña and Henares Rivers. ERT was performed by installing the electrodes (1 m spacing) on a 47 m long transect normal to the river channel using a Wener-Schlumberger array, across both the riparian zones and the river bed. Invertebrates were collected in the streambed from a depth of 20-40 cm, using the Bou-Rouch method, and from boreholes drilled to a depth of 1.5 m in the riparian zone. The ERT images obtained at site 1 (medium and coarse sand dominated lithology) shows resistivity values ranging from ~20 to 80 ohm•m for the in-stream sediments, indicating a permeable zone up to ~ 0.5 m thick and extending laterally for ca. 5 m from the channel. These sediments contribute to active surface/hyporheic water exchanges and to low water retention in stream sediments, as also indicated by the similar physico-chemical parameters in thw two zones, and the composition of hyporheic biota, dominated exclusively by surface-dwellers (e.g. Cladocera, Chironomidae, Cyclopoida (Microcyclops rubellus), Ostracoda (Pryonocypris zenkeri). A low resistivity (< 70 ohm•m) permeable zone located at 2.3 m depth bellow the streambed and unconnected with the river channel was also detected and associated with a shallow floodplain aquifer. In contrast, the resistivity image at site 2 (fine and very fine sand dominated lithology) shows a low permeability zone in the upper ~ 0.5 m of the profile, with resistivity values ranging from ~45 to 80 ohm•m, indicating a reduced HZ extension in both vertical and lateral dimensions. Here, both water retention and interaction between water and sediments are higher than at site 1 and consequently the water chemistry is distinct from that of the river channel (lower conductivity, temperature and dissolved oxygen in hyporheic waters). These features of the sedimentary layers create suitable habitats conditions in HZ for the development of a mixture of both epigean (e.g., Ostracoda (Darwinula stevensoni)) and hypogean stygobites dwellers (e.g., Cyclopoida (Acanthocyclops n. sp)). Furthermore, a low resistivity (< 30 ohm•m) high permeability zone was detected 2 m from the riverbed, at a depth of ca. 3 meters, being associated either to a suspended aquifer supplied with water from the terraces, or to water accumulation within tree roots, that might be temporary connected with the stream-hyporheic system. The two examples show that non-invasive ERT images and biological assessment provides complementary and valuable information about the characterisation of the sub-channel architecture and its potential connection with the parafluvial and riparian zones. Our results provide initial templates for high-resolution in situ studies with broad and integrated methods to identify the boundaries between hyporheic and parafluvial zones and the time-scale fluctuations in response to water exchanges with the surface stream.

Methane Recycling During Burial of Methane Hydrate-Bearing Sediments

NASA Astrophysics Data System (ADS)

You, K.; Flemings, P. B.

2017-12-01

We quantitatively investigate the integral processes of methane hydrate formation from local microbial methane generation, burial of methane hydrate with sedimentation, and methane recycling at the base of the hydrate stability zone (BHSZ) with a multiphase multicomponent numerical model. Methane recycling happens in cycles, and there is not a steady state. Each cycle starts with free gas accumulation from hydrate dissociation below the BHSZ. This free gas flows upward under buoyancy, elevates the hydrate saturation and capillary entry pressure at the BHSZ, and this prevents more free gas flowing in. Later as this layer with elevated hydrate saturation is buried and dissociated, the large amount of free gas newly released and accumulated below rapidly intrudes into the hydrate stability zone, drives rapid hydrate formation and creates three-phase (gas, liquid and hydrate) equilibrium above the BHSZ. The gas front retreats to below the BHSZ until all the free gas is depleted. The shallowest depth that the free gas reaches in one cycle moves toward seafloor as more and more methane is accumulated to the BHSZ with time. More methane is stored above the BHSZ in the form of concentrated hydrate in sediments with relatively uniform pore throat, and/or with greater compressibility. It is more difficult to initiate methane recycling in passive continental margins where the sedimentation rate is low, and in sediments with low organic matter content and/or methanogenesis reaction rate. The presence of a permeable layer can store methane for significant periods of time without recycling. In a 2D system where the seafloor dips rapidly, the updip gas flow along the BHSZ transports more methane toward topographic highs where methane gas and elevated hydrate saturation intrude deeper into the hydrate stability zone within one cycle. This could lead to intermittent gas venting at seafloor at the topographic highs. This study provides insights on many phenomenon associated with methane recycling, such as the formation of free gas zone, concentrated hydrate zone, bottom simulating reflector, and overpressured zone around the BHSZ, and gas venting at seafloor.

Speciation of strontium in particulates and sediments from the Mississippi River mixing zone

NASA Astrophysics Data System (ADS)

Xu, Yingfeng; Marcantonio, Franco

2004-06-01

Sequential extractions were performed on small amounts of particulate and sediment samples (6 to10 mg) from the Mississippi River mixing zone. The leachates were analyzed for Sr concentration and 87Sr/ 86Sr isotope ratio. Mn and Fe contents were also measured as their oxyhydroxides are potential carrier phases for Sr. The largest fraction of Sr in the solid phase (particulates and sediments) was found to be present in the residual, refractory fraction (>70% of total). By comparison with the corresponding sediment, particulates appear to have higher concentrations of nonresidual, labile Sr (30% vs. 15%). Carbonate components seem to play an important role as carriers for labile Sr in particulates and sediments. Changes in the composition and content of the solid phase may significantly modify both the 87Sr/ 86Sr isotope ratio of the total labile fractions and that of the bulk components. However, such modifications, under normal conditions, exert little measurable influence on the Sr isotope composition of the dissolved phase.

The dark side of the hyporheic zone: Depth profiles of nitrogen and its processing in stream sediments

USGS Publications Warehouse

Stelzer, R.S.; Bartsch, L.A.; Richardson, W.B.; Strauss, E.A.

2011-01-01

1.Although it is well known that sediments can be hot spots for nitrogen transformation in streams, many previous studies have confined measurements of denitrification and nitrate retention to shallow sediments (<5cm deep). We determined the extent of nitrate processing in deeper sediments of a sand plains stream (Emmons Creek) by measuring denitrification in core sections to a depth of 25cm and by assessing vertical nitrate profiles, with peepers and piezometers, to a depth of 70cm. 2.Denitrification rates of sediment slurries based on acetylene block were higher in shallower core sections. However, core sections deeper than 5cm accounted for 68% of the mean depth-integrated denitrification rate. 3.Vertical hydraulic gradient and vertical profiles of pore water chloride concentration suggested that deep ground water upwelled through shallow sediments before discharging to the stream channel. The results of a two-source mixing model based on chloride concentrations suggested that the hyporheic zone was very shallow (<5cm) in Emmons Creek. 4.Vertical profiles showed that nitrate concentration in shallow ground water was about 10-60% of the nitrate concentration of deep ground water. The mean nitrate concentrations of deep and shallow ground water were 2.17 and 0.73mgNO3-NL-1, respectively. 5.Deep ground water tended to be oxic (6.9mgO2L-1) but approached anoxia (0.8mgO2L-1) after passing through shallow, organic carbon-rich sediments, which suggests that the decline in the nitrate concentrations of upwelling ground water was because of denitrification. 6.Collectively, our results suggest that there is substantial nitrate removal occurring in deep sediments, below the hyporheic zone, in Emmons Creek. Our findings suggest that not accounting for nitrate removal in deep sediments could lead to underestimates of nitrogen processing in streams and catchments. ?? 2011 Blackwell Publishing Ltd.

Redox transformation and reductive immobilization of Cr(VI) in the Columbia River hyporheic zone sediments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Xu, Fen; Liu, Yuanyuan; Zachara, John

An experimental and modeling study was conducted to investigate the redox transformation and reductive immobilization of groundwater contaminant Cr in hyporheic zone (HZ) sediments from U.S. Department of Energy’s Hanford site, where groundwater Cr(VI) is migrating and discharging to the nearby Columbia River. Experimental results revealed that Cr(VI) can be reduced to immobile reduced Cr by the HZ sediments in the presence/absence of O2. Anaerobic pre-incubation of the sediments increased the effective rate of Cr reduction that was correlated with the increase in HCl-extractable Fe(II) content in the sediments. The reduced Cr was stable in exposure to O2 under field-relevantmore » pH (~7.5) and Mn-containing (~0.02% w/w) conditions. The Cr(VI) reduction rate showed a multi-rate behavior, apparently reflecting the presence of reductants with different reactivity in the sediments. The results from this study indicated that the HZ sediments can reductively immobilize Cr and the sediment redox capacity can be recharged through microbial activities. The results implied that HZ can play a role as a natural permeable redox barrier for removing groundwater Cr before it discharges into a river system.« less

Novel pyropheophorbide steryl esters in Black Sea sediments

NASA Astrophysics Data System (ADS)

King, Linda L.; Repeta, Daniel J.

1991-07-01

A series of non-polar chlorophyll degradation products (NPCs) with greater than 10 components has been isolated from Black Sea sediment and identified as pyropheophorbide steryl esters by visible and mass spectrometry. These compounds have been previously observed in seawater and sediment trap samples, and may be formed during grazing of phytoplankton by zooplanktonic herbivores. In Black Sea sediments, NPCs constitute 14% of the total phorbins determined spectroscopically at 660 nm, and 39% of the total chlorophyll degradation products measured by high pressure liquid chromatography. NPCs therefore constitute a significant sedimentary sink for chlorophyll. The distribution of sterols released by hydrolysis of NPCs most closely resembles sterols in suspended particulate matter collected from the euphotic zone and is quite different from the distribution of solvent-extractable sterols in sediments. Sterols extracted from sediments have high concentrations of 4-methylsterols and high stanol/stenol ratios. NPC-derived sterols have very low concentrations of 4-methylsterols and low stanol/stenol ratios. We suggest that these differences reflect an enhanced preservation of NPCs in sediments relative to free sterols and phorbins. As a result, the original production of sterols in the euphotic zone may be more closely approximated by the distribution of NPC-derived sterols than by the distribution of free sterols in sediments.

Redox transformation and reductive immobilization of Cr(VI) in the Columbia River hyporheic zone sediments

NASA Astrophysics Data System (ADS)

Xu, Fen; Liu, Yuanyuan; Zachara, John; Bowden, Mark; Kennedy, David; Plymale, Andrew E.; Liu, Chongxuan

2017-12-01

An experimental and modeling study was conducted to investigate the redox transformation and reductive immobilization of groundwater contaminant Cr in hyporheic zone (HZ) sediments from U.S. DOE's Hanford Site, where groundwater Cr(VI) is migrating and discharging to the nearby Columbia River. Experimental results revealed that Cr(VI) can be reduced and immobilized by the HZ sediments in the presence/absence of O2. Anaerobic pre-incubation of the sediments increased the effective rate of Cr reduction that was correlated with the increase in HCl-extractable Fe(II) content in the sediments. The reduced Cr was stable when exposed to O2 under field-relevant pH (7.5) with and without dissolved Mn(II), which might be oxidized to form Mn(III/IV) oxides that may oxidize reduced Cr. The Cr(VI) reduction rate showed a multi-rate behavior, apparently reflecting the presence of reductants with different reactivity in the sediments. The results from this study indicated that the HZ sediments can reductively immobilize Cr and the sediment redox capacity can be recharged through microbial activities. The results implied that HZ can play a role as a natural permeable redox barrier for removing groundwater Cr before it discharges into a river system.

Distribution of metal concentrations in sediments of the coastal zone of the Gulf of Riga and open part of the Baltic Sea

NASA Astrophysics Data System (ADS)

Seisuma, Z.; Kulikova, I.

2012-11-01

The comparison of spatial and temporal distribution of Hg, Cd, Pb, Cu, Ni, Zn, Mn and Fe concentrations in sediments from the Gulf of Riga and open Baltic Sea along the coastal zone is presented for the first time. There were considerable differences in Pb, Zn, Mn and Fe levels in sediment at various stations of the Gulf of Riga. A significant difference of Cd, Pb, Cu, Ni, Zn levels was found in sediments of various stations in the open Baltic coast. The amount of Cd, Pb, Cu, Ni, Zn and Fe levels also differed significantly in the sediments of the Gulf of Riga in different years. A considerable yearly difference in amount of Hg, Cd, Pb, Cu, Ni and Mn levels was found in sediments in the open Baltic coast. The essential highest values of Pb and Zn in coastal sediments of the open Baltic Sea are stated in comparison with the Gulf of Riga. The concentrations of other metals have only a tendency to be higher in coastal sediments of the open Baltic Sea in comparison with the Gulf of Riga. Natural and anthropogenic factors were proved to play an important role in determining resultant metals concentrations in the regions.

Using a conceptual model to assess the role of flow regulation in the hydromorphological evolution of riparian corridors

NASA Astrophysics Data System (ADS)

Martínez-Fernández, Vanesa; Gonzalez del Tánago, Marta; García de Jalón, diego

2017-04-01

Riparian corridors result from active vegetation-fluvial interactions, which are highly dependent on flow regime conditions and sediment dynamics. Colonization, establishment and survival of species are constrained by fluvial processes which vary according to topographic and sedimentological complexity of the corridor. In order to manage these dynamic and complex riparian systems there is a need for practical tools based on conceptual models. The objective of this study was to apply the conceptual model of riparian corridors lateral zonation in response to the dominant fluvial processes established by Gurnell et al. (2015) and verify its usefulness as a tool for assessing the effect of flow regulation. Two gravel rivers have been selected for this purpose from the north of Spain, the Porma River regulated by Boñar large dam and the unregulated Curueño River. The historical series of flows and the aerial photographs of 1956 and 2011 on which the river corridor has been delimited have been analyzed and identified the permanent inundated zone (1) and four areas of riparian vegetation dominated respectively by fluvial disturbance with coarse sediment erosion and deposition (zone 2), fluvial disturbance with finer sediment deposition (zone 3), inundation (zone 4) and soil moisture regime (zone 5). Likewise, a two-dimensional hydraulic simulation was performed with avenues of different return periods and calculated the prevailing hydraulic conditions (depths, velocities and drag forces) to characterize each of the vegetation zones mentioned in both rivers. The results show that the most active zone 2 (fluvial disturbance dominated showing coarse sediment erosion and deposition) disappears due to the regulation of flows and vegetation encroachment, while the riparian corridor is dominated by the less active zone where the vegetation is maintained by the humidity of sporadic floods and underground runoff. Moreover, by means of the hydraulic simulation we have found a close relationship between the different areas of fluvial processes recognized through its vegetation and hydraulic conditions, which predicts the expected evolution of vegetation at different scenarios of regulation.

Geological evolution of the Iraqi Mesopotamia Foredeep, inner platform and near surroundings of the Arabian Plate

NASA Astrophysics Data System (ADS)

Sissakian, Varoujan K.

2013-08-01

The Iraqi territory could be divided into four main tectonic zones; each one has its own characteristics concerning type of the rocks, their age, thickness and structural evolution. These four zones are: (1) Inner Platform (stable shelf), (2) Outer Platform (unstable shelf), (3) Shalair Zone (Terrain), and (4) Zagros Suture Zone. The first two zones of the Arabian Plate lack any kind of metamorphism and volcanism. The Iraqi territory is located in the extreme northeastern part of the Arabian Plate, which is colliding with the Eurasian (Iranian) Plate. This collision has developed a foreland basin that includes: (1) Imbricate Zone, (2) High Folded Zone, (3) Low Folded Zone and (4) Mesopotamia Foredeep. The Mesopotamia Foredeep, in Iraq includes the Mesopotamia Plain and the Jazira Plain; it is less tectonically disturbed as compared to the Imbricate, High Folded and Low Folded Zones. Quaternary alluvial sediments of the Tigris and Euphrates Rivers and their tributaries as well as distributaries cover the central and southeastern parts of the Foredeep totally; it is called the Mesopotamian Flood Plain. The extension of the Mesopotamia Plain towards northwest however, is called the Jazira Plain, which is covered by Miocene rocks. The Mesopotamia Foredeep is represented by thick sedimentary sequence, which thickens northwestwards including synrift sediments; especially of Late Cretaceous age, whereas on surface the Quaternary sediments thicken southeastwards. The depth of the basement also changes from 8 km, in the west to 14 km, in the Iraqi-Iranian boarders towards southeast. The anticlinal structures have N-S trend, in the extreme southern part of the Mesopotamia Foredeep and extends northwards until the Latitude 32°N, within the Jazira Plain, there they change their trends to NW-SE, and then to E-W trend. The Mesozoic sequence is almost without any significant break, with increase in thickness from the west to the east, attaining 5 km. The sequence forms the main source and reservoir rocks in the central and southern parts of Iraq. The Cenozoic sequence consists of Paleogene open marine carbonates, which grades upwards into Neogene lagoonal marine; of Early Miocene and evaporitic rocks; of Middle Miocene age, followed by thick molasses of continental clastics that attain 3500 m in thickness; starting from Late Miocene. The Quaternary sediments are very well developed in the Mesopotamia Plain and they thicken southwards to reach about 180 m near Basra city; in the extreme southeastern part of Iraq. The Iraqi Inner Platform (stable shelf) is a part of the Arabian Plate, being less affected by tectonic disturbances; it covers the area due to south and west of the Euphrates River. The main tectonic feature in this zone that had affected on the geology of the area is the Rutbah Uplift; with less extent is the Ga'ara High. The oldest exposed rocks within the Inner Platform belong to Ga'ara Formation of Permian age; it is exposed only in the Ga'ara Depression. The Permian rocks are overlain by Late Triassic rocks; represented by Mulussa and Zor Hauran formations, both of marine carbonates with marl intercalations. The whole Triassic rocks are absent west, north and east of Ga'ara Depression. Jurassic rocks, represented by five sedimentary cycles, overlie the Triassic rocks. Each cycle consists of clastic rocks overlain by carbonates, being all of marine sediments; whereas the last one (Late Jurassic) consists of marine carbonates only. All the five formations are separated from each other by unconformable contacts. Cretaceous rocks, represented by seven sedimentary cycles, overlie the Jurassic rocks. Marine clastics overlain by marine carbonates. Followed upwards (Late Cretaceous) by continental clastics overlain by marine carbonates; then followed by marine carbonates with marl intercalations, and finally by marine clastics overlain by carbonates; representing the last three cycles, respectively. The Paleocene rocks form narrow belt west of the Ga'ara Depression, represented by Early-Late Paleocene phosphatic facies, which is well developed east of Rutbah Uplift and extends eastwards in the Foredeep. Eocene rocks; west of Rutbah Uplift are represented by marine carbonates that has wide aerial coverage in south Iraq. Locally, east of Rutbah Uplift unconformable contacts are recorded between Early, Middle and Late Eocene rocks. During Oligocene, in the eastern margin of the Inner Platform, the Outer Platform was uplifted causing very narrow depositional Oligocene basin. Therefore, very restricted exposures are present in the northern part of the Inner Platform (north of Ga'ara Depression), represented by reef, forereef sediments of some Oligocene formations. The Miocene rocks have no exposures west of Rutbah Uplift, but north and northwestwards are widely exposed represented by Early Miocene of marine carbonates with marl intercalations. Very locally, Early Miocene deltaic clastics and carbonates, are interfingering with the marine carbonates. The last marine open sea sediments, locally with reef, represent the Middle Miocene rocks and fore reef facies that interfingers with evaporates along the northern part of Abu Jir Fault Zone, which is believed to be the reason for the restriction of the closed lagoons; in the area. During Late Miocene, the continental phase started in Iraq due to the closure of the Neo-Tethys and collision of the Sanandaj Zone with the Arabian Plate. The continental sediments consist of fine clastics. The Late Miocene - Middle Pliocene sediments were not deposited in the Inner Platform. The Pliocene-Pleistocene sediments are represented by cyclic sediments of conglomeratic sandstone overlain by fresh water limestone, and by pebbly sandstone. The Quaternary sediments are poorly developed in the Inner Platform. Terraces of Euphrates River and those of main valleys represent pleistocene sediments. Flood plain of the Euphrates River and those of large valleys represent Holocene sediments. Residual soil is developed, widely in the western part of Iraq, within the western marginal part of the Inner Platform.

Mangrove growth in New Zealand estuaries: the role of nutrient enrichment at sites with contrasting rates of sedimentation.

PubMed

Lovelock, Catherine E; Feller, Ilka C; Ellis, Joanne; Schwarz, Ann Maree; Hancock, Nicole; Nichols, Pip; Sorrell, Brian

2007-09-01

Mangrove forest coverage is increasing in the estuaries of the North Island of New Zealand, causing changes in estuarine ecosystem structure and function. Sedimentation and associated nutrient enrichment have been proposed to be factors leading to increases in mangrove cover, but the relative importance of each of these factors is unknown. We conducted a fertilization study in estuaries with different sedimentation histories in order to determine the role of nutrient enrichment in stimulating mangrove growth and forest development. We expected that if mangroves were nutrient-limited, nutrient enrichment would lead to increases in mangrove growth and forest structure and that nutrient enrichment of trees in our site with low sedimentation would give rise to trees and sediments that converged in terms of functional characteristics on control sites in our high sedimentation site. The effects of fertilizing with nitrogen (N) varied among sites and across the intertidal zone, with enhancements in growth, photosynthetic carbon gain, N resorption prior to leaf senescence and the leaf area index of canopies being significantly greater at the high sedimentation sites than at the low sedimentation sites, and in landward dwarf trees compared to seaward fringing trees. Sediment respiration (CO(2) efflux) was higher at the high sedimentation site than at the low one sedimentation site, but it was not significantly affected by fertilization, suggesting that the high sedimentation site supported greater bacterial mineralization of sediment carbon. Nutrient enrichment of the coastal zone has a role in facilitating the expansion of mangroves in estuaries of the North Island of New Zealand, but this effect is secondary to that of sedimentation, which increases habitat area and stimulates growth. In estuaries with high sediment loads, enrichment with N will cause greater mangrove growth and further changes in ecosystem function.

Soil Microbial Community Contribution to Small Headwater Stream Metabolism.

NASA Astrophysics Data System (ADS)

Clapcott, J. E.; Gooderham, J. P.; Barmuta, L. A.; Davies, P. E.

2005-05-01

The temporal dynamics of sediment respiration were examined in seven small headwater streams in forested catchments in 2004. A strong seasonal response was observed with higher respiration rates in depositional zones than in gravel runs. The data were also examined in the context of proportional habitat distributions that highlighted the importance of high flow events in shaping whole stream metabolic budgets. This study specifically examines the question of terrestrial soil respiration contribution to whole stream metabolism by the controlled inundation of terrestrial soils. The experiment included six experimentally inundated terrestrial zones, six terrestrial controls, and six in-stream depositional zones. Sediment bacterial respiration was measured using 14C leucine incorporation and cotton strip bioassays were also employed to provide an indicative measure of sediment microbial activity. Despite high variability and exhibiting significantly lower bacterial activity than in-stream sediments, modelling using flow data and habitat mapping illustrated the important contribution of terrestrial soil respiration to the whole stream metabolic budgets of small headwater streams. In addition, microbial community composition examined using phospholipid fatty acid analysis clearly differentiated between terrestrial and aquatic communities. Freshly inundated terrestrial communities remained similar to un-inundated controls after 28 days.

Sediment record of environmental change at Lake Lop Nur (Xinjiang, NW China) from 13.0 to 5.6 cal ka BP

NASA Astrophysics Data System (ADS)

Wang, Jingzhong; Jia, Hongjuan

2017-09-01

Lake Lop Nur is located in the eastern part of the Tarim Basin in Xinjiang, northwestern China. A 220-cm-long sediment core was collected from the center of the ear-shaped depression forming the basin and dated with AMS14C. Grain size, total organic matter (TOC), total nitrogen (TN), and TOC/TN (C/N) analyses were used to reconstruct climatic conditions from 13.0 to 5.6 cal ka BP. The results showed five main climatic stages. Zone I (13.0-11.3 cal ka BP) was a wet-dry environment, whereas Zone II (11.3-8.9 cal ka BP) consisted of a primarily wet environment. Zone III (8.9-7.7 cal ka BP) was subdivided into Zone IIIa (8.9-8.2 cal ka BP) that indicated lake constriction and dry climate, and Zone IIIb (8.2-7.7 cal ka BP) in which the proxies indicated wet conditions. In Zone IV (7.7-6.6 cal ka BP), the climate presented a bit wet conditions. In Zone V (6.6-5.6 cal ka BP), abundant glauberite is present in the sediment and silt dominates the lithology; these results indicate the lake shrank and the overall climate was dry. Abrupt environmental events were also identified, including six dry events at 11.0, 10.5, 9.3, 8.6, 8.2, and 7.6 cal ka BP and one flood event from 7.8 to 7.7 cal ka BP in the Early-Middle Holocene.

From the Surface to the Deep-Sea: Bacterial Distributions across Polymetallic Nodule Fields in the Clarion-Clipperton Zone of the Pacific Ocean.

PubMed

Lindh, Markus V; Maillot, Brianne M; Shulse, Christine N; Gooday, Andrew J; Amon, Diva J; Smith, Craig R; Church, Matthew J

2017-01-01

Marine bacteria regulate fluxes of matter and energy essential for pelagic and benthic organisms and may also be involved in the formation and maintenance of commercially valuable abyssal polymetallic nodules. Future mining of these nodule fields is predicted to have substantial effects on biodiversity and physicochemical conditions in mined areas. Yet, the identity and distributions of bacterial populations in deep-sea sediments and associated polymetallic nodules has received relatively little attention. We examined bacterial communities using high-throughput sequencing of bacterial 16S rRNA gene fragments from samples collected in the water column, sediment, and polymetallic nodules in the Pacific Ocean (bottom depth ≥4,000 m) in the eastern Clarion-Clipperton Zone. Operational taxonomic units (OTUs; defined at 99% 16S rRNA gene identity) affiliated with JTB255 (Gammaproteobacteria) and Rhodospirillaceae (Alphaproteobacteria) had higher relative abundances in the nodule and sediment habitats compared to the water column. Rhodobiaceae family and Vibrio OTUs had higher relative abundance in nodule samples, but were less abundant in sediment and water column samples. Bacterial communities in sediments and associated with nodules were generally similar; however, 5,861 and 6,827 OTUs found in the water column were retrieved from sediment and nodule habitats, respectively. Cyanobacterial OTUs clustering among Prochlorococcus and Synechococcus were detected in both sediments and nodules, with greater representation among nodule samples. Such results suggest that vertical export of typically abundant photic-zone microbes may be an important process in delivery of water column microorganisms to abyssal habitats, potentially influencing the structure and function of communities in polymetallic nodule fields.

Modeling the Formation of Hydrate-Filled Veins in Fine-Grained Sediments from in Situ Microbial Methane

NASA Astrophysics Data System (ADS)

Malinverno, A.; Cook, A.; Daigle, H.

2016-12-01

Continental margin sediments are dominantly fine-grained silt and clay, and methane hydrates in these sediments are often found in semi-vertical veins and fractures. In several instances, these hydrate veins occupy discrete depth intervals that are a few tens of meters thick and are surrounded by hydrate-free sediments. As they are not connected with gas sources beneath the base of the gas hydrate stability zone (GHSZ), these isolated hydrate-bearing intervals have been interpreted as formed by in situ microbial methane. To investigate the formation of these hydrate deposits, we applied a time-dependent advection-diffusion-reaction model that includes the effects of sedimentation, compaction, solute diffusion, and microbial methane generation. Microbial methane generation depends on the amount of metabolizable organic carbon deposited at the seafloor, whose progressive degradation produces methane beneath the sulfate reduction zone. If the amount of organic carbon entering the methanogenic zone is kept constant in time, we found that the computed amounts of hydrate formed in discrete intervals within the GHSZ are well below those estimated from observations. On the other hand, if the deposition of organic carbon is higher in a given time interval, methane generation during burial is more intense in the corresponding sediment interval, resulting in enhanced hydrate formation. With variations in organic carbon deposition comparable to those generally observed in continental margins, our model was able to reproduce the methane hydrate contents that were estimated from drilling. These results support the suggestion that in situ microbial generation associated with transient organic carbon deposition is the source of methane that forms isolated intervals of hydrate-filled veins in fine-grained sediments.

Modeling the Formation of Hydrate-Filled Veins in Fine-Grained Sediments from in Situ Microbial Methane

DOE Office of Scientific and Technical Information (OSTI.GOV)

Malinverno, Alberto; Cook, Ann; Daigle, Hugh

Continental margin sediments are dominantly fine-grained silt and clay, and methane hydrates in these sediments are often found in semi-vertical veins and fractures. In several instances, these hydrate veins occupy discrete depth intervals that are a few tens of meters thick and are surrounded by hydrate-free sediments. As they are not connected with gas sources beneath the base of the gas hydrate stability zone (GHSZ), these isolated hydrate-bearing intervals have been interpreted as formed by in situ microbial methane. To investigate the formation of these hydrate deposits, we applied a time-dependent advection-diffusion-reaction model that includes the effects of sedimentation, compaction,more » solute diffusion, and microbial methane generation. Microbial methane generation depends on the amount of metabolizable organic carbon deposited at the seafloor, whose progressive degradation produces methane beneath the sulfate reduction zone. If the amount of organic carbon entering the methanogenic zone is kept constant in time, we found that the computed amounts of hydrate formed in discrete intervals within the GHSZ are well below those estimated from observations. On the other hand, if the deposition of organic carbon is higher in a given time interval, methane generation during burial is more intense in the corresponding sediment interval, resulting in enhanced hydrate formation. With variations in organic carbon deposition comparable to those generally observed in continental margins, our model was able to reproduce the methane hydrate contents that were estimated from drilling. These results support the suggestion that in situ microbial generation associated with transient organic carbon deposition is the source of methane that forms isolated intervals of hydrate-filled veins in fine-grained sediments.« less

The role of alluvial aquifer sediments in attenuating a dissolved arsenic plume

USGS Publications Warehouse

Ziegler, Brady A.; Schreiber, Madeline E.; Cozzarelli, Isabelle M.

2017-01-01

In a crude-oil-contaminated sandy aquifer at the Bemidji site in northern Minnesota, biodegradation of petroleum hydrocarbons has resulted in release of naturally occurring As to groundwater under Fe-reducing conditions. This study used chemical extractions of aquifer sediments collected in 1993 and 2011–2014 to evaluate the relationship between Fe and As in different redox zones (oxic, methanogenic, Fe-reducing, anoxic-suboxic transition) of the contaminated aquifer over a twenty-year period. Results show that 1) the aquifer has the capacity to naturally attenuate the plume of dissolved As, primarily through sorption; 2) Fe and As are linearly correlated in sediment across all redox zones, and a regression analysis between Fe and As reasonably predicted As concentrations in sediment from 1993 using only Fe concentrations; 3) an As-rich “iron curtain,” associated with the anoxic-suboxic transition zone, migrated 30 m downgradient between 1993 and 2013 as a result of the hydrocarbon plume evolution; and 4) silt lenses in the aquifer preferentially sequester dissolved As, though As is remobilized into groundwater from sediment after reducing conditions are established. Using results of this study coupled with historical data, we develop a conceptual model which summarizes the natural attenuation of As and Fe over time and space that can be applied to other sites that experience As mobilization due to an influx of bioavailable organic matter.

The role of alluvial aquifer sediments in attenuating a dissolved arsenic plume.

PubMed

Ziegler, Brady A; Schreiber, Madeline E; Cozzarelli, Isabelle M

2017-09-01

In a crude-oil-contaminated sandy aquifer at the Bemidji site in northern Minnesota, biodegradation of petroleum hydrocarbons has resulted in release of naturally occurring As to groundwater under Fe-reducing conditions. This study used chemical extractions of aquifer sediments collected in 1993 and 2011-2014 to evaluate the relationship between Fe and As in different redox zones (oxic, methanogenic, Fe-reducing, anoxic-suboxic transition) of the contaminated aquifer over a twenty-year period. Results show that 1) the aquifer has the capacity to naturally attenuate the plume of dissolved As, primarily through sorption; 2) Fe and As are linearly correlated in sediment across all redox zones, and a regression analysis between Fe and As reasonably predicted As concentrations in sediment from 1993 using only Fe concentrations; 3) an As-rich "iron curtain," associated with the anoxic-suboxic transition zone, migrated 30m downgradient between 1993 and 2013 as a result of the hydrocarbon plume evolution; and 4) silt lenses in the aquifer preferentially sequester dissolved As, though As is remobilized into groundwater from sediment after reducing conditions are established. Using results of this study coupled with historical data, we develop a conceptual model which summarizes the natural attenuation of As and Fe over time and space that can be applied to other sites that experience As mobilization due to an influx of bioavailable organic matter. Copyright © 2017 Elsevier B.V. All rights reserved.

Natural Attenuation in Streambed Sediment Receiving Chlorinated Solvents from Underlying Fracture Networks

DOE PAGES

Şimşir, Burcu; Yan, Jun; Im, Jeongdae; ...

2017-03-22

Contaminant discharge from fractured bedrock formations remains a remediation challenge. Here, we applied an integrated approach to assess the natural attenuation potential of sediment that forms the transition zone between upwelling groundwater from a chlorinated solvent-contaminated fractured bedrock aquifer and the receiving surface water. In situ measurements demonstrated that reductive dechlorination in the sediment attenuated chlorinated compounds before reaching the water column. Microcosms established with creek sediment or in situ incubated Bio-Sep beads degraded C 1-C 3 chlorinated solvents to less-chlorinated or innocuous products. Quantitative PCR and 16S rRNA gene amplicon sequencing revealed the abundance and spatial distribution of knownmore » dechlorinator biomarker genes within the creek sediment and demonstrated that multiple dechlorinator populations degrading chlorinatedC 1-C 3 alkanes and alkenes co-inhabit the sediment. Phylogenetic classification of bacterial and archaeal sequences indicated a relatively uniform distribution over spatial (300 m horizontally) scale, but Dehalococcoides and Dehalobacter were more abundant in deeper sediment, where 5.7 ± 0.4 × 10 5 and 5.4 ± 0.9 × 10 6 16S rRNA gene copies per g of sediment, respectively, were measured. The microbiological and hydrogeological characterization demonstrated that microbial processes at the fractured bedrock-sediment interface were crucial for preventing contaminants reaching the water column, emphasizing the relevance of this critical zone environment for contaminant attenuation.« less

Natural Attenuation in Streambed Sediment Receiving Chlorinated Solvents from Underlying Fracture Networks

DOE Office of Scientific and Technical Information (OSTI.GOV)

Şimşir, Burcu; Yan, Jun; Im, Jeongdae

Contaminant discharge from fractured bedrock formations remains a remediation challenge. Here, we applied an integrated approach to assess the natural attenuation potential of sediment that forms the transition zone between upwelling groundwater from a chlorinated solvent-contaminated fractured bedrock aquifer and the receiving surface water. In situ measurements demonstrated that reductive dechlorination in the sediment attenuated chlorinated compounds before reaching the water column. Microcosms established with creek sediment or in situ incubated Bio-Sep beads degraded C 1-C 3 chlorinated solvents to less-chlorinated or innocuous products. Quantitative PCR and 16S rRNA gene amplicon sequencing revealed the abundance and spatial distribution of knownmore » dechlorinator biomarker genes within the creek sediment and demonstrated that multiple dechlorinator populations degrading chlorinatedC 1-C 3 alkanes and alkenes co-inhabit the sediment. Phylogenetic classification of bacterial and archaeal sequences indicated a relatively uniform distribution over spatial (300 m horizontally) scale, but Dehalococcoides and Dehalobacter were more abundant in deeper sediment, where 5.7 ± 0.4 × 10 5 and 5.4 ± 0.9 × 10 6 16S rRNA gene copies per g of sediment, respectively, were measured. The microbiological and hydrogeological characterization demonstrated that microbial processes at the fractured bedrock-sediment interface were crucial for preventing contaminants reaching the water column, emphasizing the relevance of this critical zone environment for contaminant attenuation.« less

Quantifying retro-foreland evolution in the Eastern Pyrenees.

NASA Astrophysics Data System (ADS)

Grool, Arjan R.; Ford, Mary; Huismans, Ritske S.

2015-04-01

The northern Pyrenees form the retro-foreland of the Pyrenean orogen. Modelling studies show that retro-forelands have several contrasting characteristics compared to pro-forelands: They tend to show a constant tectonic subsidence during the growth phase of an orogen, and no tectonic subsidence during the steady-state phase. Retro-forelands are also not displaced into the core of the orogen once the steady state phase is achieved. This means they tend to preserve the subsidence history from the growth phase of the orogen, but little or no history from the steady state phase. The northeastern Pyrenees (Carcassonne high) are a good location to test these characteristics against real-world data, because syn-orogenic sediments are preserved and the lack of postrift thermal subsidence and Triassic salt reduce complicating factors. In order to test the model, quantification of the following parameters is needed: Timing, amount and distribution of deformation, subsidence and sedimentation. We use subsurface, field, map and literature data to construct 2 balanced and restored cross sections through the eastern north Pyrenean foreland, stretching from the Montagne Noire in the north, to the Axial Zone in the south. We will link this to published thermochronology data to further constrain the evolution of the retro-foreland and investigate the link with the Axial Zone towards the south. We will quantify subsidence, deformation and sedimentation and link them to exhumation phases in the North Pyrenean Zone (NPZ) and the Axial Zone. The north Pyrenean retro-foreland is divided into two parts: the external foreland basin (Aquitaine basin) to the north and the North Pyrenean Zone to the south, separated by the North Pyrenean Frontal Thrust (NPFT). South of the NPZ lies the Axial Zone, separated from the retro-foreland by the North Pyrenean Fault which is believed to be the suture between Iberia and Europe. The NPFT was the breakaway fault on the European continent during the Apto-Albian rifting phase and was strongly inverted during the Pyrenean orogeny. South of the NPFT we find Lower Cretaceous and older sediments, including Triassic salt. These sediments are completely absent north of the NPFT (on Carcassonne high), indicating its significance during the extensional phase. The retro-foreland is deformed by fault-propagation folds above basement-involving thrusts. A slow northward propagation of deformation and sedimentation is clearly visible. The preserved thickness of Upper Cretaceous sediments corresponds with the retro-foreland model's prediction that early subsidence records are preserved. Two distinct deformation phases are recognized, but not the latest Oligocene phase that is found in the pro-foreland (southern Pyrenees). This could indicate a steady state during the late Oligocene.We quantify and constrain the evolution of the eastern Pyrenean retro-foreland basin, investigate the link with the axial zone and investigate the pre-orogenic configuration of the region that currently constitutes the eastern Pyrenean retro-foreland.

Geochemical stability of phosphorus solids below septic system infiltration beds

NASA Astrophysics Data System (ADS)

Zurawsky, M. A.; Robertson, W. D.; Ptacek, C. J.; Schiff, S. L.

2004-09-01

Review of 10 mature septic system plumes in Ontario, revealed that phosphorus (P) attenuation commonly occurred close to the infiltration pipes, resulting in discrete narrow intervals enriched in P by a factor of 2-4 ( Wood, J.S.A. 1993. MSc thesis, Dept. Earth Sci., University of Waterloo, Waterloo, Ont.; Ground Water 36 (1995) 1000; J. Contam. Hydrol. 33 (1998) 405). Although these attenuation reactions appeared to be sustainable under present conditions, the potential for remobilization of this P mass, should geochemical conditions change, is unknown. To test the stability of these P solids, dynamic flow column tests were carried out using sediments from three of the previously studied sites (Cambridge, Langton and Muskoka) focusing on sediments from the 'High-P' and underlying (Below) zones. Tests were continued for 166-266 pore volumes (PVs), during which time varying degrees of water saturation were maintained. During saturated flow conditions, relatively high concentrations of PO 4 were eluted from the Cambridge and Langton High-P zones (up to 4 and 9 mg/l P, respectively), accompanied by elevated concentrations of Fe (up to 1.4 mg/l) and Mn (up to 4 mg/l) and lower values of Eh (<150 mV). The Below zones from Cambridge and Langton, however, maintained lower concentrations of P (generally<2 mg/l), Fe (<0.2 mg/l) and Mn (<1 mg/l) and maintained higher Eh (>250 mV) during saturated flow conditions. During unsaturated flow, P and Fe declined dramatically in the High-P zones (P<1 mg/l, Fe<0.2 mg/l), whereas concentrations remained about the same during saturated and unsaturated flow in the Below zones. This behavior is at least partly attributed to the development of reducing conditions during saturated flow in the High-P zones, leading to reductive dissolution of Fe (III)-P solids present in the sediments. Reducing conditions did not develop in the Below zones apparently because of lower sediment organic carbon (OC) contents (0.03-0.04 wt.%) compared to the High-P zones (0.2-0.65 wt.%). At the Muskoka site, where the sediments were noncalcareous, low values of P (<0.2 mg/l) were maintained in both the High-P and Below columns and reducing conditions did not develop. Results indicate the possibility of remobilizing P accumulated below septic system infiltration beds should conditions become more reducing. This could occur if sewage loading patterns change, for example when a seasonal use, lakeshore cottage is converted to a permanent dwelling.

Shallow geology, sea-floor texture, and physiographic zones of Vineyard and western Nantucket Sounds, Massachusetts

USGS Publications Warehouse

Baldwin, Wayne E.; Foster, David S.; Pendleton, Elizabeth A.; Barnhardt, Walter A.; Schwab, William C.; Andrews, Brian D.; Ackerman, Seth D.

2016-09-02

Geologic, sediment texture, and physiographic zone maps characterize the sea floor of Vineyard and western Nantucket Sounds, Massachusetts. These maps were derived from interpretations of seismic-reflection profiles, high-resolution bathymetry, acoustic-backscatter intensity, bottom photographs/video, and surficial sediment samples collected within the 494-square-kilometer study area. Interpretations of seismic stratigraphy and mapping of glacial and Holocene marine units provided a foundation on which the surficial maps were created. This mapping is a result of a collaborative effort between the U.S. Geological Survey and the Massachusetts Office of Coastal Zone Management to characterize the surface and subsurface geologic framework offshore of Massachusetts.

Influence of Hydrological Perturbations and Riverbed Sediment Characteristics on Hyporheic Zone Respiration of CO2 and N2

NASA Astrophysics Data System (ADS)

Newcomer, Michelle E.; Hubbard, Susan S.; Fleckenstein, Jan H.; Maier, Ulrich; Schmidt, Christian; Thullner, Martin; Ulrich, Craig; Flipo, Nicolas; Rubin, Yoram

2018-03-01

Rivers in climatic zones characterized by dry and wet seasons often experience periodic transitions between losing and gaining conditions across the river-aquifer continuum. Infiltration shifts can stimulate hyporheic microbial biomass growth and cycling of riverine carbon and nitrogen leading to major exports of biogenic CO2 and N2 to rivers. In this study, we develop and test a numerical model that simulates biological-physical feedback in the hyporheic zone. We used the model to explore different initial conditions in terms of dissolved organic carbon availability, sediment characteristics, and stochastic variability in aerobic and anaerobic conditions from water table fluctuations. Our results show that while highly losing rivers have greater hyporheic CO2 and N2 production, gaining rivers allowed the greatest fraction of CO2 and N2 production to return to the river. Hyporheic aerobic respiration and denitrification contributed 0.1-2 g/m2/d of CO2 and 0.01-0.2 g/m2/d of N2; however, the suite of potential microbial behaviors varied greatly among sediment characteristics. We found that losing rivers that consistently lacked an exit pathway can store up to 100% of the entering C/N as subsurface biomass and dissolved gas. Our results demonstrate the importance of subsurface feedbacks whereby microbes and hydrology jointly control fate of C and N and are strongly linked to wet-season control of initial sediment conditions and hydrologic control of seepage direction. These results provide a new understanding of hydrobiological and sediment-based controls on hyporheic zone respiration, including a new explanation for the occurrence of anoxic microzones and large denitrification rates in gravelly riverbeds.

Elevated gas hydrate saturation within silt and silty clay sediments in the Shenhu area, South China Sea

USGS Publications Warehouse

Wang, Xiujuan; Hutchinson, Deborah R.; Wu, Shiguo; Yang, Shengxiong; Guo, Yiqun

2011-01-01

Gas hydrate saturations were estimated using five different methods in silt and silty clay foraminiferous sediments from drill hole SH2 in the South China Sea. Gas hydrate saturations derived from observed pore water chloride values in core samples range from 10 to 45% of the pore space at 190–221 m below seafloor (mbsf). Gas hydrate saturations estimated from resistivity (Rt) using wireline logging results are similar and range from 10 to 40.5% in the pore space. Gas hydrate saturations were also estimated by P wave velocity obtained during wireline logging by using a simplified three-phase equation (STPE) and effective medium theory (EMT) models. Gas hydrate saturations obtained from the STPE velocity model (41.0% maximum) are slightly higher than those calculated with the EMT velocity model (38.5% maximum). Methane analysis from a 69 cm long depressurized core from the hydrate-bearing sediment zone indicates that gas hydrate saturation is about 27.08% of the pore space at 197.5 mbsf. Results from the five methods show similar values and nearly identical trends in gas hydrate saturations above the base of the gas hydrate stability zone at depths of 190 to 221 mbsf. Gas hydrate occurs within units of clayey slit and silt containing abundant calcareous nannofossils and foraminifer, which increase the porosities of the fine-grained sediments and provide space for enhanced gas hydrate formation. In addition, gas chimneys, faults, and fractures identified from three-dimensional (3-D) and high-resolution two-dimensional (2-D) seismic data provide pathways for fluids migrating into the gas hydrate stability zone which transport methane for the formation of gas hydrate. Sedimentation and local canyon migration may contribute to higher gas hydrate saturations near the base of the stability zone.

Observational Data Analysis and Numerical Model Assessment of the Seafloor Interaction and Mobility of Sand and Weathered Oil Agglomerates (Surface Residual Balls) in the Surf Zone

NASA Astrophysics Data System (ADS)

Dalyander, S.; Long, J.; Plant, N. G.; Penko, A.; Calantoni, J.; Thompson, D.; Mclaughlin, M. K.

2014-12-01

When weathered oil is transported ashore, such as during the Deepwater Horizon oil spill, it can mix with suspended sediment in the surf zone to create heavier-than-water sand and oil agglomerates in the form of mats several centimeters thick and tens of meters long. Broken off pieces of these mats and smaller agglomerates formed in situ (called Surface Residual Balls, SRBs) can cause beach re-oiling months to years after the initial spill. The physical dynamics of these SRBs in the nearshore, where they are larger (cm-scale) and less dense than natural sediment, are poorly understood. In the current study, SRB mobility and seafloor interaction is investigated through a combination of laboratory and field experiments with pseudo-SRBs developed to be physically stable proxies for genuine agglomerates. Formulations for mobility prediction based on comparing estimated shear stress to the critical Shields and modified Shields parameters developed for mixed sediment beds are assessed against observations. Processes such as burial, exhumation, and interaction with bedforms (e.g., migrating ripples) are also explored. The observations suggest that incipient motion estimates based on a modified Shields parameter have some skill in predicting SRB movement, but that other forcing mechanisms such as pressure gradients may be important under some conditions. Additionally, burial and exhumation due to the relatively high mobility of sand grains are confirmed as key processes controlling SRB dynamics in the surf zone. This work has broad implications for understanding surf zone sediment transport at the short timescale associated with mobilizing sand grains and SRBs as well as at the longer timescales associated with net transport patterns, sediment budgets, and bed elevation changes.

Sediment export, transient landscape response and catchment-scale connectivity following rapid climate warming and Alpine glacier recession

NASA Astrophysics Data System (ADS)

Lane, Stuart N.; Bakker, Maarten; Gabbud, Chrystelle; Micheletti, Natan; Saugy, Jean-Noël

2017-01-01

In the face of rapid climate warming, rapid glacier recession should lead to a marked increase in the spatial extent of the paraglacial zone in glaciated drainage basins. The extent of the paraglacial zone has been well established to be transient but there are very few studies of this transient response and what it means for sediment export. There is good reason to expect that glacier recession could increase basin-scale sediment connectivity as: sediment becomes less dependent on glacier surface transport; proglacial streams are more able to migrate laterally than subglacial streams and so access sediment for transport; and glacier debuttressing may aid the development of gullies that can dissect moraines and so aid hillslope to proglacial zone connectivity. By using records of the flushing of hydroelectric power installations we were able to develop a record of coarse sediment (sand and gravel) export from a basin with a rapidly retreating valley glacier, the Haut Glacier d'Arolla, from 1977 to 2014. Modelling suggested that these data could only be partially controlled by transport capacity implying an important role for sediment supply and potentially for the influence of changing sediment connectivity. Indeed, there was evidence of the effects of glacial debuttressing upon gullying processes and hence a possible increase in the ease of connection of upstream basins to the proglacial area. More recently, we were able to show possible temperature control on sediment export, which may only have become apparent because of the progressive development of better sediment connectivity. However, whilst rapid glacier recession should result in theory in a progressive increase in connectivity of sediment sources to the basin outlet, the supply to capacity ratio does not increase continually with glacier recession until maximum capacity is reached. We identified two possible examples of why. First, gullying was also accompanied by the sediment accumulation at the base of moraines that was too coarse to be transported by the proglacial stream, maintaining disconnection of the upper basins. Second, the sediment capacity ratio appeared to be elevated during periods of more rapid retreat and we attribute this to the importance of a continued supply of unworked glacial till before fluvial reworking and sorting of freshly exposed sediment increased the resistance of sediment to entrainment and hence export rates. Thus, the transient geomorphic response of glaciated basins to glacier recession may involve negative feedbacks that can reduce the extent to which increases in connectivity elsewhere in the basin lead to increased sediment export.

The dominance of dispersion in the evolution of bed material waves in gravel-bed rivers

Treesearch

Thomas E. Lisle; Yantao Cui; Gary Parker; James E. Pizzuto; Annjanette M. Dodd

2001-01-01

Abstract - Bed material waves are temporary zones of sediment accumulation created by large sediment inputs. Recent theoretical, experimental and field studies examine factors in fluencing dispersion and translation of bed material waves in quasi-uniform, gravel-bed channels. Exchanges of sediment between a channel and its floodplain are...

Quantifying Seepage Flux using Sediment Temperatures

EPA Science Inventory

This report provides a demonstration of different modeling approaches that use sediment temperatures to estimate the magnitude and direction of water flux across the groundwater-surface water transition zone. Analytical models based on steady-state or transient temperature solut...

Development of a new model for batch sedimentation and application to secondary settling tanks design.

PubMed

Karamisheva, Ralica D; Islam, M A

2005-01-01

Assuming that settling takes place in two zones (a constant rate zone and a variable rate zone), a model using four parameters accounting for the nature of the water-suspension system has been proposed for describing batch sedimentation processes. The sludge volume index (SVI) has been expressed in terms of these parameters. Some disadvantages of the SVI application as a design parameter have been pointed out, and it has been shown that a relationship between zone settling velocity and sludge concentration is more consistent for describing the settling behavior and for design of settling tanks. The permissible overflow rate has been related to the technological parameters of secondary settling tank by simple working equations. The graphical representations of these equations could be used to optimize the design and operation of secondary settling tanks.

Ecological evaluation of an experimental beneficial use scheme for dredged sediment disposal in shallow tidal waters.

PubMed

van der Wal, Daphne; Forster, Rodney M; Rossi, Francesca; Hummel, Herman; Ysebaert, Tom; Roose, Frederik; Herman, Peter M J

2011-01-01

An experiment was performed to test an alternative dredging strategy for the Westerschelde estuary. Clean sand dredged from the navigation channel was disposed seawards of an eroding intertidal flat in order to modify morphology and hydrodynamics, improving the multi-channel system with ecologically productive shallow water habitat. Five years of intensive monitoring revealed that part of the disposed sediment moved slowly towards the flat, increasing the very shallow subtidal and intertidal area, as planned. The sand in the impact zone became gradually finer after disposal, possibly due to reduced current velocities. Nevertheless, no changes in macrobenthic biomass, density, species richness and composition were detected in the subtidal zone, also demonstrating rapid macrobenthic recovery. In the intertidal zone, no ecological effects could be revealed superimposed on trends associated with long-term sediment fining. Thus, despite morphological success and absence of detected negative ecological impacts of the experiment, new beneficial habitat was not created. Copyright © 2010 Elsevier Ltd. All rights reserved.

Detrital Cr-spinel in the Šambron-Kamenica Zone (Slovakia): evidence for an ocean-spreading zone in the Northern Vardar suture?

NASA Astrophysics Data System (ADS)

Lenaz, Davide; Mazzoli, Claudio; Spišiak, Jan; Princivalle, Francesco; Maritan, Lara

2009-03-01

The Šambron-Kamenica Zone is situated on the northern margin of the Levočské vrchy mountains and Šarišskà vrchovina Highland, where the Central Carpathian Paleogene joins the Pieniny Klippen Belt. Sandstone outcrops in this area. From Cretaceous to Late Oligocene in age, these sediments suggest transport directions from S and SE. The heavy mineral assemblages of this sandstone include Cr-spinel grains, mainly displaying types II and III alpine-peridotite affinities, and are representative of Ocean Island Basalt volcanism. A sample from Upper Eocene sediments at Vit’az shows a clear change in Cr-spinel composition, which turns out to have types I and II peridotite affinities, and to derive from arc and Middle Ocean Ridge Basalt volcanism, with sediment transport directions from SW and WSW. These data indicate major variations in the Upper Eocene tectonic setting, giving constraints to paleogeographic reconstruction of the Slovak Central Carpathians.

Vertical distribution of radiocesium in soils of the area affected by the Fukushima Dai-ichi nuclear power plant accident

NASA Astrophysics Data System (ADS)

Konoplev, A. V.; Golosov, V. N.; Yoschenko, V. I.; Nanba, K.; Onda, Y.; Takase, T.; Wakiyama, Y.

2016-05-01

Presented are results of the study of radiocesium vertical distribution in the soils of the irrigation pond catchments in the near field 0.25 to 8 km from the Fukushima Dai-ichi NPP, on sections of the Niida River floodplain, and in a forest ecosystem typical of the territory contaminated after the accident. It is shown that the vertical migration of radiocesium in undisturbed forest and grassland soils in the zone affected by the Fukushima accident is faster than it was in the soils of the 30-km zone of the Chernobyl NPP for a similar time interval after the accident. The effective dispersion coefficients in the Fukushima soils are several times higher than those for the Chernobyl soils. This may be associated with higher annual precipitation (by about 2.5 times) in Fukushima as compared to the Chernobyl zone. In the forest soils the radiocesium dispersion is faster as compared to grassland soils, both in the Fukushima and Chernobyl zones. The study and analysis of the vertical distribution of the Fukushima origin radiocesium in the Niida gawa floodplain soils has made it possible to identify areas of contaminated sediment accumulation on the floodplain. The average accumulation rate for sediments at the study locations on the Niida gawa floodplain varied from 0.3 to 3.3 cm/year. Taking into account the sediments accumulation leading to an increase in the radiocesium inventory in alluvial soils is key for predicting redistribution of radioactive contamination after the Fukushima accident on the river catchments, as well as for decision-making on contaminated territories remediation and clean-up. Clean-up of alluvial soils does not seem to be worthwhile because of the following accumulation of contaminated sediments originating from more contaminated areas, including the exclusion zone.

Temporal variation on environmental variables and pollution indicators in marine sediments under sea Salmon farming cages in protected and exposed zones in the Chilean inland Southern Sea.

PubMed

Urbina, Mauricio A

2016-12-15

The impacts of any activity on marine ecosystems will depend on the characteristics of the receptor medium and its resilience to external pressures. Salmon farming industry develops along a constant gradient of hydrodynamic conditions in the south of Chile. However, the influence of the hydrodynamic characteristics (weak or strong) on the impacts of intensive salmon farming is still poorly understood. This one year study evaluates the impacts of salmon farming on the marine sediments of both protected and exposed marine zones differing in their hydrodynamic characteristics. Six physico-chemical, five biological variables and seven indexes of marine sediments status were evaluated under the salmon farming cages and control sites. Our results identified a few key variables and indexes necessary to accurately evaluate the salmon farming impacts on both protected and exposed zones. Interestingly, the ranking of importance of the variables and the temporality of the observed changes, varied depending on the hydrodynamic characteristics. Biological variables (nematodes abundance) and environmental indexes (Simpson's dominance, Shannon's diversity and Pielou evenness) are the first to reflect detrimental impacts under the salmon farming cages. Then the physico-chemical variables such as redox, sulphurs and phosphorus in both zones also show detrimental impacts. Based on the present results we propose that the hydrodynamic regime is an important driver of the magnitude and temporality of the effects of salmon farming on marine sediments. The variables and indexes that best reflect the effects of salmon farming, in both protected and exposed zones, are also described. Copyright © 2016. Published by Elsevier B.V.

Stable isotope hydrology in fractured and detritic aquifers at both sides of the South Atlantic Ocean: Mar del Plata (Argentina) and the Rawsonville and Sandspruit river catchment areas (South Africa)

NASA Astrophysics Data System (ADS)

Glok Galli, Melisa; Damons, Matthew E.; Siwawa, Sitembiso; Bocanegra, Emilia M.; Nel, Jacobus M.; Mazvimavi, Dominic; Martínez, Daniel E.

2017-01-01

The aim of this work is to characterize the isotope composition of water (2H and 18O) in order to establish the relationship between fractured and detritic aquifers in similar hydrological environments located at both sides of the Atlantic Ocean. The Mar del Plata zone, placed in the Argentine Buenos Aires province in South America, and the Rawsonville and Sandspruit river catchment areas, situated in the Western Cape province in South Africa were compared. Rainwater and groundwater samples from fractured and detritic aquifers were analyzed through laser spectroscopy. In both Argentina and South African study sites, stable isotopes data demonstrate an aquifers recharge source from rainfall. For the Mar del Plata region, two different groups of detritic aquifer's samples with distinct recharge processes can be identified due to the close relationship existing between the present hydrogeological environments, the aquifer's grain size sediments and the isotopes contents: one representing rapid infiltration in aquifer sediments of the creeks' palaeobeds and hills zones (sandy or silt sandy sediments) and the other with slow infiltration of evaporated water in plain zones with an aquitard behavior. In the last group, the evaporation process occurs previous infiltration or in the aquifer's non-saturated zone, because of the existence of very low topographic gradients and fine-grained sediments. The evaporation phenomenon is not evident in the Sandspruit river catchment site's detritic aquifer, because its sandy composition allows a faster infiltration rate than in the loess that compounds the Pampeano aquifer in the interfluves zones of the Argentinian study area.

Comparisons of Low-Strain Amplification at Soft-Sediment, Hard-Rock, Topographic, and Fault-Zone Sites in the Hayward Fault Zone, California

NASA Astrophysics Data System (ADS)

Catchings, R.; Strayer, L. M.; Goldman, M.

2014-12-01

We used a temporary network of approximately 600 seismographs to record a seismic source generated by the collapse of a 13-story building near the active trace of the Hayward Fault. These data allow us to evaluate variations in ground shaking across a series of 30 2-km-long radial arrays centered on the seismic source. Individual seismographs were spaced at 200-m intervals, forming a series of 360°concentric arrays around the seismic source. The data show variations in amplification caused by (1) soft sediments within the East Bay alluvial plain (EBAP), (2) hard rocks within the East Bay hills (EBH), (3) low-velocity rocks within the Hayward Fault zone (HFZ), and (4) topography. Given that ground shaking varies strongly with distance from the source, the concentric arrays allowed us to measure variations in ground shaking as a function of azimuth at fixed distances from the source. On individual linear profiles within the concentric arrays, we observed decreases in peak ground velocity (PGV) across the HFZ and other faults within the EBH. However, for a given distance from the source, we observe four to five fold amplification from the EBAP sites compared to most sites in the EBH. Topographic and fault-zone amplification effects within the EBH, however, are greater than the EBAP sediment amplification. Thus, for future earthquakes, shaking at many sites within the EBH may be significantly stronger than many sites within the EBAP. These observations suggest amplification can be expected in unconsolidated sediments, but topographic and fault-zone amplification can be larger. This confirms the importance of site effects for hazard mitigation and in interpreting MMI for future and historical earthquakes.

Rapid sedimentation and overpressure in shallow sediments of the Bering Trough, offshore southern Alaska

NASA Astrophysics Data System (ADS)

Daigle, Hugh; Worthington, Lindsay L.; Gulick, Sean P. S.; Van Avendonk, Harm J. A.

2017-04-01

Pore pressures in sediments at convergent margins play an important role in driving chemical fluxes and controlling deformation styles and localization. In the Bering Trough offshore Southern Alaska, extreme sedimentation rates over the last 140 kyr as a result of glacial advance/retreats on the continental shelf have resulted in elevated pore fluid pressures in slope sediments overlying the Pamplona Zone fold and thrust belt, the accretionary wedge resulting from subduction of the Yakutat microplate beneath the North American Plate. Based on laboratory experiments and downhole logs acquired at Integrated Ocean Drilling Program Site U1421, we predict that the overpressure in the slope sediments may be as high as 92% of the lithostatic stress. Results of one-dimensional numerical modeling accounting for changes in sedimentation rate over the last 130 kyr predicted overpressures that are consistent with our estimates, suggesting that the overpressure is a direct result of the rapid sedimentation experienced on the Bering shelf and slope. Comparisons with other convergent margins indicate that such rapid sedimentation and high overpressure are anomalous in sediments overlying accretionary wedges. We hypothesize that the shallow overpressure on the Bering shelf/slope has fundamentally altered the deformation style within the Pamplona Zone by suppressing development of faults and may inhibit seismicity by focusing faulting elsewhere or causing deformation on existing faults to be aseismic. These consequences are probably long-lived as it may take several million years for the excess pressure to dissipate.

Rainfall simulation experiments to study sediment redistribution using rare earth element oxides as tracers under conventional and conservation agricultural practices

NASA Astrophysics Data System (ADS)

Tóth, Adrienn; Jakab, Gergely; Sipos, Péter; Karlik, Máté; Madarász, Balázs; Zacháry, Dóra; Szabó, Judit; Szalai, Zoltán

2017-04-01

Rare earth elements (REE) have very favourable characteristics for being ideal sediment tracers as they are characterised by strong binding to soil particles, low mobility, low background concentration in soils, environmental benignity, high analytical sensitivity and they can be detected relatively easily and inexpensively in soils. The group of REEs consist of 16 elements with similar chemical properties, but at the same time, they are clearly distinguishable enabling multiple tracking of sediment deriving from different parts of the studied area, as well as mapping redistribution processes by appropriate designing of subareas marked by different REEs. In this study, rainfall simulation experiments were carried out to compare the loss and redistribution of soil sediments in two plots under conventional and conservation agricultural practices. Five different rainfall intensities (up to 80 mm/h) were applied to both plots. Sources and pathways of sediments within the two plots were studied using REE-oxides as tracers. Approximately 1,000 mg/kg of Er2O3, Ho2O3 and Sm2O3 (calculated to the upper 1 cm of the soil) were dispersed to the soil surface with banded distribution; each transversal band covered the third of the surface are of the plots. Concentration of the REE-oxides in the sediment leaving the plots, and that of the surface soil before and after the experiment were analysed by X-Ray fluorescence spectrometry. Significant sediment losses were found for both plots after the experiments, with slightly different characteristics between the conventional and conservation ones. Highest difference in loss of added REEs was found in the upper third of the plots with 81 ± 19% in the conventional and 71 ± 21% in the conservation ones. These values have been equalized downwards with almost complete losses in the lower third of the plots (99 ± 2% and 97 ± 4%, respectively). Only very small part of the removed sediment has been accumulated in the lower parts of the plots, they rather mostly leaved the study area. These accumulation zones showed patchy distribution and could be characterized by slightly higher REE concentrations in the conservation plot. Also, large variances in the REE amounts removed from the study plots were found during the experiment with slight differences between the two plots. Thanks to the use of the REE tracers, information was received not only on the sediment amounts leaving the area due to the individual rainfall events but also on the source of them within the plot. Our data also suggest that differences between the conventional and conservation plots can be observed even in the short term. The authors are grateful to the support of the National Research, Development and Innovation Office (OTKA PD 112729). A. Tóth also thanks for the support of the János Bolyai Research Scholarship of the Hungarian Academy of Sciences.

Sediment properties and water movement through shallow unsaturated alluvium at an arid site for disposal of low-level radioactive waste near Beatty, Nye County, Nevada

USGS Publications Warehouse

Fischer, Jeffrey M.

1992-01-01

A commercial disposal facility for low-level radioactive waste has been in operation near Beatty, Nevada, since 1962. The facility is in the arid Amargosa Desert where wastes are buried in trenches excavated into unsaturated alluvial sediments. Thick unsaturated zones in arid environments offer many potential advantages for disposal of radioactive wastes, but little is known about the natural movement of water near such facilities. Thus, a study was begun in 1982 to better define the direction and rates of water movement through the unsaturated zone in undisturbed sediments near the disposal facility. This report discusses the analyses of data collected between 1983 and 1988.

The Physical, Geochemical and Microbial Conditions and Processes in the Hyporheic Zone of a Large Tidally Influenced River: The Fraser River, British Columbia, Canada

NASA Astrophysics Data System (ADS)

Bianchin, M.; Roschinski, T.; Ross, K.; Leslie, S.; William, M.; Beckie, R.

2006-12-01

The objective of this research is to investigate the physical, chemical and biological conditions and processes that occur in the hyporheic zone of the lower Fraser River, British Columbia. The large flows of between 2000 and 10000 cubic meters per second, the 10 15 m deep, 250 m wide channel, the 1 m tidal fluctuations, the localized scour and redeposition of sediments during freshet and the strong geochemical contrast between groundwater and surface water distinguish this investigation from studies on smaller channels and streams and required the development of novel characterization tools and strategies. The geochemistry of water samples collected with a push-in profiler, bulk electrical conductivity (EC) measurements collected with a push-in tool and hydraulic head measurements indicate that groundwater principally discharges into the river approximately 100 m offshore in a 10 m wide band. River water and groundwater mix to a maximum depth of between 0.75 and 1.5 m. While hydraulic heads show strong tidal reversals, bulk EC profiles show only moderate changes during the tidal cycle. It was hypothesized that high iron (10's mg/L of Fe(II)) in reduced groundwater would precipitate from solution as secondary iron-oxide phases in the zone where groundwater mixes with aerobic river water. Sediments were collected with a freeze-shoe corer and depth profiles through the hyporheic zone and into the underlying aquifer were analyzed by selective extractions. The 15-30 mg/g of total extractable iron in both the aquifer and hyporheic zone is relatively high. The lack of noticeable iron accumulation in the hyporheic zone may indicate that iron precipitates on shallow sediments that are subsequently scoured from the river bed during freshet. Microbial DNA from sediments was analyzed using denaturing gradient gel electrophoresis and showed a relatively diverse community structure but an overall low biomass.

The Effectiveness of Permanent Highway Runoff Controls: Sedimentation/Filtration Systems

DOT National Transportation Integrated Search

1998-09-01

Original Report Date: October 1997. This study evaluates the performance of sedimentation/filtration systems that are the most common control for treating highway runoff in the Edwards Aquifer recharge zone. The study includes: 1) monitoring and eval...

Sedimentary record of relay zone evolution, Central Corinth Rift (Greece): Role of fault propagation and structural inheritance.

NASA Astrophysics Data System (ADS)

Hemelsdaël, Romain; Ford, Mary; Meyer, Nicolas

2013-04-01

Relay zones along rift border fault systems form topographic lows that are considered to allow the transfer of sediment from the footwall into hanging wall depocentres. Present knowledge focuses on the modifications of drainage patterns and sediment pathways across relay zones, however their vertical motion during growth and interaction of faults segments is not well documented. 3D models of fault growth and linkage are also under debate. The Corinth rift (Greece) is an ideal natural laboratory for the study of fault system evolution. Fault activity and rift depocentres migrated northward during Pliocene to Recent N-S extension. We report on the evolution of a relay zone in the currently active southern rift margin fault system from Pleistocene to present-day. The relay zone lies between the E-W East Helike (EHF) and Derveni faults (DF) that lie just offshore and around the town of Akrata. During its evolution the relay zone captured the antecedent Krathis river which continued to deposit Gilbert-type deltas across the relay zone during fault interaction, breaching and post linkage phases. Moreover our work underlines the role that pre-existing structure in the location of the transfer zone. Offshore fault geometry and kinematics, and sediment distribution were defined by interpretation and depth conversion of high resolution seismic profiles (from Maurice Ewing 2001 geophysical survey). Early lateral propagation of the EHF is recorded by synsedimentary fault propagation folds while the DF records tilted block geometries since initiation. Within the relay zone beds are gradually tilted toward the basin before breaching. These different styles of deformation highlight mechanical contrasts and upper crustal partition associated with the development of the Akrata relay zone. Onshore detailed lithostratigraphy, structure and geomorphological features record sedimentation across the subsiding relay ramp and subsequent footwall uplift after breaching. The area is characterised by the successive deposition of the northward prograding Platanos Gilbert-type delta (Middle group; deposited in hangingwall of the Pirgaki-Mamoussia fault) and the NE to E prograding Akrata Gilbert-type delta (Upper group). The Akrata Gilbert-type delta records progressive rotation and lengthening of the relay ramp as the East Helike fault and Derveni fault propagated laterally (from around 0.8 Ma) and started to overlap. The relay ramp was then breached by the Krathis fault (around 0.45 Ma) and the latter reactivated a NW-SE oriented inherited structure. Onshore-offshore correlation and profile restoration of the Upper group demonstrate the presence of this pre-existing structure (detachment fault?) below the Akrata relay zone that was responsible for significant eastward thickening in early rift sediments (Lower to Middle group). Our evolution model is consistent with the 'isolated fault' model where a fault array initially develops from growth of kinematically independent fault segments and fault displacement gradually accumulates during pre- and post-linkage stages. Despite the prominent control of pre-existing fabrics on the location of the transfer zone, lateral fault propagation and interaction can be well documented.

Spatial and temporal variability in sedimentation rates associated with cutoff channel infill deposits: Ain River, France

USGS Publications Warehouse

Piégay, H.; Hupp, C.R.; Citterio, A.; Dufour, S.; Moulin, B.; Walling, D.E.

2008-01-01

Floodplain development is associated with lateral accretion along stable channel geometry. Along shifting rivers, the floodplain sedimentation is more complex because of changes in channel position but also cutoff channel presence, which exhibit specific overflow patterns. In this contribution, the spatial and temporal variability of sedimentation rates in cutoff channel infill deposits is related to channel changes of a shifting gravel bed river (Ain River, France). The sedimentation rates estimated from dendrogeomorphic analysis are compared between and within 14 cutoff channel infills. Detailed analyses along a single channel infill are performed to assess changes in the sedimentation rates through time by analyzing activity profiles of the fallout radionuclides 137Cs and unsupported 210Pb. Sedimentation rates are also compared within the channel infills with rates in other plots located in the adjacent floodplain. Sedimentation rates range between 0.65 and 2.4 cm a−1 over a period of 10 to 40 years. The data provide additional information on the role of distance from the bank, overbank flow frequency, and channel geometry in controlling the sedimentation rate. Channel infills, lower than adjacent floodplains, exhibit higher sedimentation rates and convey overbank sediment farther away within the floodplain. Additionally, channel degradation, aggradation, and bank erosion, which reduce or increase the distance between the main channel and the cutoff channel aquatic zone, affect local overbank flow magnitude and frequency and therefore sedimentation rates, thereby creating a complex mosaic of sedimentation zones within the floodplain and along the cutoff channel infills. Last, the dendrogeomorphic and 137Cs approaches are cross validated for estimating the sedimentation rate within a channel infill.

Tropical Cyclones as a Driver of Global Sediment Flux

NASA Astrophysics Data System (ADS)

Leyland, J.; Darby, S. E.; Cohen, S.

2017-12-01

The world's rivers deliver 19 billion tonnes of sediment to the coastal zone annually. The sediment supplied to the coastal zone is of significant importance for a variety of reasons, for example in acting as a vector for nutrients as well as in supplying sediment to coastal landforms such as deltas and beaches that can buffer those landforms from erosion and flooding. A greater understanding of the factors governing sediment flux to the oceans is therefore a key research gap. The non-linear relationship between river discharge and sediment flux implies that the global sediment flux may be disproportionately driven by large floods. Indeed, in our recent empirical research we have demonstrated that changes in the track locations, frequency and intensity of tropical storms in recent decades exert a significant control on the sediment flux emanating from the Mekong River. Since other large rivers potentially affected by tropical storms are known to make a significant contribution to the global sediment flux, this raises the question of the extent to which such storms play a significant role in controlling sediment loads at the global scale. In this paper we address that question by employing a global hydrological model (WBMsed) in order to predict runoff and sediment load forced by recent historical climate scenarios `with' and `without' tropical cyclones. We compare the two scenarios to (i) make the first estimate of the global contribution of sediment load forced by tropical storms; (ii) evaluate how that contribution has varied in recent decades and to (iii) explore variations in tropical-storm driven sediment loads in selected major river basins that are significantly affected by such storms.

In situ observation of the water-sediment interface in combined sewers, using endoscopy.

PubMed

Oms, C; Gromaire, M C; Chebbo, G

2003-01-01

A new method for water-sediment interface observation has been designed. This system is based on a small diameter endoscope protected by a graduated plastic tube. It makes it possible to visualise in a non-destructive manner the sediments and the water-sediment interface. The endoscope was used to investigate Le Marais catchment (Paris): an immobile organic layer was observed at the water-sediment interface. This layer appears in pools of gross bed sediment, at the upstream of collectors, in zones where velocity is slow and where bed shear stress is less than 0.03 N/m2.

Microbiological and Geochemical Characterization of Fluvially Deposited Sulfidic Mine Tailings

PubMed Central

Wielinga, Bruce; Lucy, Juliette K.; Moore, Johnnie N.; Seastone, October F.; Gannon, James E.

1999-01-01

The fluvial deposition of mine tailings generated from historic mining operations near Butte, Montana, has resulted in substantial surface and shallow groundwater contamination along Silver Bow Creek. Biogeochemical processes in the sediment and underlying hyporheic zone were studied in an attempt to characterize interactions consequential to heavy-metal contamination of shallow groundwater. Sediment cores were extracted and fractionated based on sediment stratification. Subsamples of each fraction were assayed for culturable heterotrophic microbiota, specific microbial guilds involved in metal redox transformations, and both aqueous- and solid-phase geochemistry. Populations of cultivable Fe(III)-reducing bacteria were most prominent in the anoxic, circumneutral pH regions associated with a ferricrete layer or in an oxic zone high in organic carbon and soluble iron. Sulfur- and iron-oxidizing bacteria were distributed in discrete zones throughout the tailings and were often recovered from sections at and below the anoxic groundwater interface. Sulfate-reducing bacteria were also widely distributed in the cores and often occurred in zones overlapping iron and sulfur oxidizers. Sulfate-reducing bacteria were consistently recovered from oxic zones that contained high concentrations of metals in the oxidizable fraction. Altogether, these results suggest a highly varied and complex microbial ecology within a very heterogeneous geochemical environment. Such physical and biological heterogeneity has often been overlooked when remediation strategies for metal contaminated environments are formulated. PMID:10103249

Bioavailability of classical and novel flame retardants: Effect of fullerene presence.

PubMed

Santín, Giselle; Eljarrat, Ethel; Barceló, Damià

2016-09-15

To understand the behavior of some emerging flame retardants (FRs) in the environment, a nonexhaustive extraction using Tenax was applied to study their behavior in aquatic ecosystems. Desorption of 8 polybrominated diphenyl ethers (PBDEs), 8 methoxylated PBDEs, 3 emerging brominated FRs and 6 halogenated norbornenes from sediments spiked in the laboratory was studied. Results showed that emerging FRs have a similar bioavailability than that of legacy FRs, already banned. In addition, some parameters such as sediment total organic carbon (TOC), aging or nanomaterial (NMs) presence in the sediment were modified in order to study their effects on the bioavailability of FRs. Bioavailability increases with a diminution of sediment TOC, while diminishes with an increase of aging. The study of effect of NM presence was performed at three different pH (acidic, neutral and basic), and for the three scenarios, FR bioavailability decreased with NM presence. The retention of pollutants in the sediment seems to be favoured by NM presence, minimizing their impact on living organisms. Copyright © 2016 Elsevier B.V. All rights reserved.

Permeability-porosity relationships of subduction zone sediments

USGS Publications Warehouse

Gamage, Kusali; Screaton, Elizabeth; Bekins, B.; Aiello, I.

2011-01-01

Permeability-porosity relationships for sediments from the northern Barbados, Costa Rica, Nankai, and Peru subduction zones were examined based on sediment type, grain size distribution, and general mechanical and chemical compaction history. Greater correlation was observed between permeability and porosity in siliciclastic sediments, diatom oozes, and nannofossil chalks than in nannofossil oozes. For siliciclastic sediments, grouping of sediments by percentage of clay-sized material yields relationships that are generally consistent with results from other marine settings and suggests decreasing permeability as percentage of clay-sized material increases. Correction of measured porosities for smectite content improved the correlation of permeability-porosity relationships for siliciclastic sediments and diatom oozes. The relationship between permeability and porosity for diatom oozes is very similar to the relationship in siliciclastic sediments, and permeabilities of both sediment types are related to the amount of clay-size particles. In contrast, nannofossil oozes have higher permeability values by 1.5 orders of magnitude than siliciclastic sediments of the same porosity and show poor correlation between permeability and porosity. More indurated calcareous sediments, nannofossil chalks, overlap siliciclastic permeabilities at the lower end of their measured permeability range, suggesting similar consolidation patterns at depth. Thus, the lack of correlation between permeability and porosity for nannofossil oozes is likely related to variations in mechanical and chemical compaction at shallow depths. This study provides the foundation for a much-needed global database with fundamental properties that relate to permeability in marine settings. Further progress in delineating controls on permeability requires additional carefully documented permeability measurements on well-characterized samples. ?? 2010 Elsevier B.V.

Spatial characterization of riparian buffer effects on sediment loads from watershed systems.

PubMed

Momm, Henrique G; Bingner, Ronald L; Yuan, Yongping; Locke, Martin A; Wells, Robert R

2014-09-01

Understanding all watershed systems and their interactions is a complex, but critical, undertaking when developing practices designed to reduce topsoil loss and chemical/nutrient transport from agricultural fields. The presence of riparian buffer vegetation in agricultural landscapes can modify the characteristics of overland flow, promoting sediment deposition and nutrient filtering. Watershed simulation tools, such as the USDA-Annualized Agricultural Non-Point Source (AnnAGNPS) pollution model, typically require detailed information for each riparian buffer zone throughout the watershed describing the location, width, vegetation type, topography, and possible presence of concentrated flow paths through the riparian buffer zone. Research was conducted to develop GIS-based technology designed to spatially characterize riparian buffers and to estimate buffer efficiency in reducing sediment loads in a semiautomated fashion at watershed scale. The methodology combines modeling technology at different scales, at individual concentrated flow paths passing through the riparian zone, and at watershed scales. At the concentrated flow path scale, vegetative filter strip models are applied to estimate the sediment-trapping efficiency for each individual flow path, which are aggregated based on the watershed subdivision and used in the determination of the overall impact of the riparian vegetation at the watershed scale. This GIS-based technology is combined with AnnAGNPS to demonstrate the effect of riparian vegetation on sediment loadings from sheet and rill and ephemeral gully sources. The effects of variability in basic input parameters used to characterize riparian buffers, onto generated outputs at field scale (sediment trapping efficiency) and at watershed scale (sediment loadings from different sources) were evaluated and quantified. The AnnAGNPS riparian buffer component represents an important step in understanding and accounting for the effect of riparian vegetation, existing and/or managed, in reducing sediment loads at the watershed scale. Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.

Relative importance of methylotrophic methanogenesis in sediments of the Western Mediterranean Sea

NASA Astrophysics Data System (ADS)

Zhuang, Guang-Chao; Heuer, Verena B.; Lazar, Cassandre S.; Goldhammer, Tobias; Wendt, Jenny; Samarkin, Vladimir A.; Elvert, Marcus; Teske, Andreas P.; Joye, Samantha B.; Hinrichs, Kai-Uwe

2018-03-01

Microbial production of methane is an important terminal metabolic process during organic matter degradation in marine sediments. It is generally acknowledged that hydrogenotrophic and acetoclastic methanogenesis constitute the dominant pathways of methane production; the importance of methanogenesis from methylated compounds remains poorly understood. We conducted various biogeochemical and molecular genetic analyses to characterize substrate availability, rates of methanogenesis, and methanogen community composition, and further evaluated the contribution of different substrates and pathways for methane production in deltaic surface and subsurface sediments of the Western Mediterranean Sea. Major substrates representing three methanogenic pathways, including H2, acetate, and methanol, trimethylamine (TMA), and dimethylsulfide (DMS), were detected in the pore waters and sediments, and exhibited variability over depth and between sites. In accompanying incubation experiments, methanogenesis rates from various 14C labeled substrates varied as well, suggesting that environmental factors, such as sulfate concentration and organic matter quality, could significantly influence the relative importance of individual pathway. In particular, methylotrophic and hydrogenotrophic methanogenesis contributed to the presence of micromolar methane concentrations in the sulfate reduction zone, with methanogenesis from methanol accounting for up to 98% of the total methane production in the topmost surface sediment. In the sulfate-depleted zone, hydrogenotrophic methanogenesis was the dominant methanogenic pathway (67-98%), and enhanced methane production from acetate was observed in organic-rich sediment (up to 31%). Methyl coenzyme M reductase gene (mcrA) analysis revealed that the composition of methanogenic communities was generally consistent with the distribution of methanogenic activity from different substrates. This study provides the first quantitative assessment of methylotrophic methanogenesis in marine sediments and has important implications for marine methane cycling. The occurrence of methylotrophic methanogenesis in surface sediments could fuel the anaerobic oxidation of methane (AOM) in the shallow sulfate reduction zone. Release of methane produced from methylotrophic methanogenesis could be a source of methane efflux to the water column, thus influencing the benthic methane budgets.

Numerical experiments on breaking waves on contrasting beaches using a two-phase flow approach

NASA Astrophysics Data System (ADS)

Bakhtyar, R.; Barry, D. A.; Kees, C. E.

2012-11-01

A mechanistic understanding of beach environments needs to account for interactions of oceanic forcing and beach materials, in particular the role of waves on the evolution of the beach profile. A fully coupled two-phase flow model was used to simulate nearshore fluid-sediment turbulent flow in the cross-shore direction. It includes the Reynolds-Averaged Navier-Stokes equations and turbulent stress closures for each phase, and accounts for inter-granular stresses. The model has previously been validated using laboratory-scale data, so the results are likely more reliable for that scale. It was used to simulate wave breaking and the ensuing hydrodynamics and sediment transport processes in the surf/swash zones. Numerical experiments were conducted to investigate the effects of varying beach and wave characteristics (e.g., beach slope, sediment grain size, wave periods and heights) on the foreshore profile changes. Spilling and plunging breakers occur on dissipative and intermediate beaches, respectively. The impact of these wave/beach types on nearshore zone hydrodynamics and beach morphology was determined. The numerical results showed that turbulent kinetic energy, sediment concentrations and transport rate are greater on intermediate than on dissipative beaches. The results confirmed that wave energy, beach grain size and bed slope are main factors for sediment transport and beach morphodynamics. The location of the maximum sediment transport is near the breaking point for both beach types. Coarse- and fine-sand beaches differ significantly in their erosive characteristics (e.g., foreshore profile evolutions are erosive and accretionary on the fine and coarse sand beaches, respectively). In addition, a new parameter (based on main driving factors) is proposed that can characterize the sediment transport in the surf and swash zones. The results are consistent with existing physical observations, suggesting that the two-phase flow model is suitable for the simulation of hyper-concentrated mixed water-sediment flows in the nearshore. The model thus has potential as a useful tool for investigating interactions between nearshore hydrodynamics and beach morphology.

Caspar Creek study

Treesearch

Robert R. Ziemer; Eugene Kojan; Robert B. Thomas; Robert A. Muller

1966-01-01

In 1961, the cooperative watershed management research program in the Lower Conifer Zone of California was started. Research in the Lower Conifer Zone was designed to obtain information and develop principles to give greater insight into the effect of land management in the Zone upon water quality, floods and sedimentation, water timing, and water yield. The research...

Nannofossil biostratigraphy, strontium and carbon isotope stratigraphy, cyclostratigraphy and an astronomically calibrated duration of the Late Campanian Radotruncana calcarata Zone

PubMed Central

Wagreich, Michael; Hohenegger, Johann; Neuhuber, Stephanie

2012-01-01

A section from the southern (Austro-Alpine Northern Calcareous Alps) margin of the Penninic Ocean in the NW Tethys realm of Late Campanian age is investigated stratigraphically. Plankton foraminifer and nannofossil biostratigraphy designate the presence of the Globotruncana ventricosa Zone and the Radotruncana (Globotruncanita) calcarata Zone, and standard nannofossil zones CC21–UC15cTP and CC22ab–UC15deTP. The combination of carbon isotope stratigraphy, strontium isotopes, and cyclostratigraphy allows a detailed chronostratigraphic correlation. Periodicity was obtained by power spectral analysis, sinusoidal regression, and Morlet wavelets. The duration of the calcarata Total Range Zone is calculated by orbital cyclicity expressed in thickness data of limestone–marl rhythmites and stable carbon isotope data. Precessional, obliquity, and short and long eccentricity cycles are identified and give an extent of c. 806 kyr for the zone. Mean sediment accumulation rates are as low as 1.99 cm/kyr and correspond well to sediment accumulation rates in similar settings. We further discuss chronostratigraphic implications of our data. PMID:27087718

Nannofossil biostratigraphy, strontium and carbon isotope stratigraphy, cyclostratigraphy and an astronomically calibrated duration of the Late Campanian Radotruncana calcarata Zone.

PubMed

Wagreich, Michael; Hohenegger, Johann; Neuhuber, Stephanie

2012-12-01

A section from the southern (Austro-Alpine Northern Calcareous Alps) margin of the Penninic Ocean in the NW Tethys realm of Late Campanian age is investigated stratigraphically. Plankton foraminifer and nannofossil biostratigraphy designate the presence of the Globotruncana ventricosa Zone and the Radotruncana ( Globotruncanita ) calcarata Zone, and standard nannofossil zones CC21-UC15c TP and CC22ab-UC15de TP . The combination of carbon isotope stratigraphy, strontium isotopes, and cyclostratigraphy allows a detailed chronostratigraphic correlation. Periodicity was obtained by power spectral analysis, sinusoidal regression, and Morlet wavelets. The duration of the calcarata Total Range Zone is calculated by orbital cyclicity expressed in thickness data of limestone-marl rhythmites and stable carbon isotope data. Precessional, obliquity, and short and long eccentricity cycles are identified and give an extent of c. 806 kyr for the zone. Mean sediment accumulation rates are as low as 1.99 cm/kyr and correspond well to sediment accumulation rates in similar settings. We further discuss chronostratigraphic implications of our data.

Novel pyropheophorbide steryl esters in Black Sea sediments

DOE Office of Scientific and Technical Information (OSTI.GOV)

King, L.L.; Repeta, D.J.

1991-07-01

A series of non-polar chlorophyll degradation products (NPCs) with greater than 10 components has been isolated from Black Sea sediment and identified as pyropheophorbide steryl esters by visible and mass spectrometry. These compounds have been previously observed in seawater and sediment trap samples, and may be formed during grazing of phytoplankton by zooplanktonic herbivores. In Black Sea sediments, NPCs constitute 14% of the total phorbins determined spectroscopically at 660 nm, and 39% of the total chlorophyll degradation products measured by high pressure liquid chromatography. NPCs therefore constitute a significant sedimentary sink for chlorophyll. The distribution of sterols released by hydrolysismore » of NPCs most closely resembles sterols in suspended particulate matter collected from the euphotic zone and is quite different from the distribution of solvent-extractable sterols in sediments. Sterols extracted from sediemtns have high concentrations of 4-methylsterols and high stanol/stenol ratios. BNPC-derived sterols have very low concentrations of 4-methylsterols and low stanol/stenol ratios. The authors suggest that these differences reflect an enhanced preservation of HPCs in sediments relative to free sterols and phorbins. As a result, the original production of sterols in the euphotic zone may be more closely approximated by the distribution of NPC-derived sterols than by the distribution of free sterols in sediments.« less

Iron-mediated anaerobic oxidation of methane in brackish coastal sediments.

PubMed

Egger, Matthias; Rasigraf, Olivia; Sapart, Célia J; Jilbert, Tom; Jetten, Mike S M; Röckmann, Thomas; van der Veen, Carina; Bândă, Narcisa; Kartal, Boran; Ettwig, Katharina F; Slomp, Caroline P

2015-01-06

Methane is a powerful greenhouse gas and its biological conversion in marine sediments, largely controlled by anaerobic oxidation of methane (AOM), is a crucial part of the global carbon cycle. However, little is known about the role of iron oxides as an oxidant for AOM. Here we provide the first field evidence for iron-dependent AOM in brackish coastal surface sediments and show that methane produced in Bothnian Sea sediments is oxidized in distinct zones of iron- and sulfate-dependent AOM. At our study site, anthropogenic eutrophication over recent decades has led to an upward migration of the sulfate/methane transition zone in the sediment. Abundant iron oxides and high dissolved ferrous iron indicate iron reduction in the methanogenic sediments below the newly established sulfate/methane transition. Laboratory incubation studies of these sediments strongly suggest that the in situ microbial community is capable of linking methane oxidation to iron oxide reduction. Eutrophication of coastal environments may therefore create geochemical conditions favorable for iron-mediated AOM and thus increase the relevance of iron-dependent methane oxidation in the future. Besides its role in mitigating methane emissions, iron-dependent AOM strongly impacts sedimentary iron cycling and related biogeochemical processes through the reduction of large quantities of iron oxides.

[Evaluating comprehensive quality of sediment in Dianchi Lake using adjusted AHP method and 137Cs dating].

PubMed

Zhang, Yan; Deng, Xi-Hai; Peng, Bu-Zhuo

2006-08-01

It is difficult to evaluate comprehensive quality of sediment and to understand development trend of pollution because of absence of monitoring data, especially history data. Combining the method of 137Cs dating with the ways of general sampling and measurement can easily resolve the problem of absence of data and also provide the possibility for calculating weighted environmental quality comprehensive index using the adjusted analytical hierarchy process (AHP) method. In order to overcome the willfulness the judgment matrix is formed objectively based on calculating monitoring data. Based on the monitoring data of sediment pollution and the weights of various factors gained by adjusted AHP method the comprehensive quality of sediment in each zone of Dianchi Lake was evaluated and the results indicated that the pollution of sediments in each zone at the present be serious more than that in the history. The condition may be related to the industrial development and distribution of industries in Dianchi Lake basin. Therefore, in order to improve the comprehensive quality of sediment in Dianchi Lake and to prevent the secondary pollution of heavy metals in sediment from happening, it is necessary to control the pollutants discharge and to remove the pollutants with various ways.

Offshore gas hydrate sample database with an overview and preliminary analysis

USGS Publications Warehouse

Booth, James S.; Rowe, Mary M.; Fisher, Kathleen M.

1996-01-01

Synopsis -- A database of offshore gas hydrate samples was constructed from published observations and measurements. More than 90 samples from 15 distinct regions are represented in 13 data categories. This database has permitted preliminary description of gas hydrate (chiefly methane hydrate) tendencies and associations with respect to their geological environment. Gas hydrates have been recovered from offshore sediment worldwide and from total depths (water depth plus subseabed depth) ranging from 500 m to nearly 6,000 m. Samples have come from subbottom depths ranging from 0 to 400 m. Various physiographic provinces are represented in the data set including second order landforms such as continental margins and deep-sea trenches, and third order forms such as submarine canyons, continental slopes, continental margin ridges and intraslope basins. There is a clear association between fault zones and other manifestations of local, tectonic-related processes, and hydrate-bearing sediment. Samples of gas hydrate frequently consist of individual grains or particles. These types of hydrates are often further described as inclusions or disseminated in the sediment. Moreover, hydrates occur as a cement, as nodules, or as layers (mostly laminae) or in veins. The preponderance of hydrates that could be characterized as 2- dimensional (planar) were associated with fine sediment, either as intercalated layers or in fractures. Hydrate cements were commonly associated with coarser sediment. Hydrates have been found in association with grain sizes ranging from clay through gravel. More hydrates are associated with the more abundant finer-grained sediment than with coarser sediment, and many were discovered in the presence of both fine (silt and clay) and coarse sediment. The thickness of hydrate zones (i. e., sections of hydrate-bearing sediment) varies from a few centimeters to as much as 30 m. In contrast, the thickness of layers of pure hydrate or the dimensions of individual hydrate grains were most often characterized in terms of millimeters or centimeters, although a pure hydrate layer discovered in the Middle America Trench off Guatemala was as much as 3-4-m-thick. The data suggest that grains, or thin veins or laminae of pure gas hydrate may be ubiquitous in many hydrate zones but that typically they may only comprise a minor component of the thicker zones. In more than 80 percent of the hydrate samples the methane was of biogenic origin. The methane in the remainder was either classified as (or may be at least part) thermogenic. Each site where thermogenic gas was identified is characterized by faults or other manifestions of a dynamic geological environment (e.g., diapirs, mud volcanoes, gas seeps). Every sample in the database came from within the zone of theoretical methane hydrate stability, as determined on the basis of assumed regional pressure and temperature gradients. Most show that they were situated --- expressed in terms of depth --- well above the phase boundary and about 70% of the samples were located more than 100 m above the assumed regional position of that boundary. The calculated subseabed positions of the phase boundaries and the BSRs (bottom simulating reflector) are essentially identical. This may be taken as general corroboration of the regional phase boundary calculations and the concept of the BSR. Three provocative aspects of marine gas hydrates have been disclosed by the database: gas hydrates are frequently situated at much shallower subseabed depths than the assumed contemporary position of the regional phase boundary hydrates are often found in areas typified by faults or other indicators of a dynamic geological environment zones of gas hydrate-bearing sediment tend to be tens of centimeters to tens of meters thick but the hydrate within the thicker zones tends to be only a minor constituent. Whether existing as dispersed particles, cements, or pure layers or vein

Erosion of Perennially Frozen Streambanks,

DTIC Science & Technology

1983-12-01

erosional processes. Factors that determine rates and locations of erosion in- dude physical, thermal and structural properties of bank sediments , stream...Program, Environmental Impact, and Civil Works Work Unit CWIS 31722, Sediment Transport and Deposition in Northern Rivers; Research Area, Flood Control...between bank and bluff zones of eroding, perennially frozen streambanks 4 3. Cantilevered blocks of frozen sediment above thermoerosional niche, northern

Magnetic properties of Surabaya river sediments, East Java, Indonesia

NASA Astrophysics Data System (ADS)

Mariyanto, Bijaksana, Satria

2017-07-01

Surabaya river is one of urban rivers in East Java Province, Indonesia that is a part of Brantas river that flows in four urban and industrial cities of Mojokerto, Gresik, Sidoarjo, and Surabaya. The urban populations and industries along the river pose serious threat to the river mainly for their anthropogenic pollutants. This study aims to characterize the magnetic properties of sediments in various locations along Surabaya river and correlate these magnetic properties to the level of pollution along the river. Samples are taken and measured through a series of magnetic measurements. The mass-specific magnetic susceptibility of sediments ranges from 259.4 to 1134.8 × 10-8 m3kg-1. The magnetic minerals are predominantly PSD to MD magnetite with the grain size range from 6 to 14 μm. The mass-specific magnetic susceptibility tends to decreases downstream as accumulation of magnetic minerals in sediments is affected not only by the amount of household and industrial wastes but also by sediment dredging, construction of embankments, and extensive erosion arround the river. Sediments located in the industrial zone on the upstream area tend to have higher mass-specific magnetic susceptibility than in the non-industrial zones on the downstream area.

Reservoir Bank Erosion Caused and Influenced by Ice Cover.

DTIC Science & Technology

1982-12-01

8 8. Bank sediment deposited on shorefast ice ------------ 9 9. Sediment frozen to the bottom of ice laid down onto the reservoir bed...end of November 1979 during a storm with 45-mph northwesterly winds-- 17 16. Ice and shore sediment uplifted where an ice pres- sure ridge intersects...restarts at breakup when the ice becomes mobile; the ice scrapes, shoves and scours the shore or bank, and transports sediment away. Figure 1. Narrow zone

Trace Element Mobility in Water and Sediments in a Hyporheic Zone Adjacent to an Abandoned Uranium Mine

NASA Astrophysics Data System (ADS)

Roldan, C.; Blake, J.; Cerrato, J.; Ali, A.; Cabaniss, S.

2015-12-01

The legacy of abandoned uranium mines lead to community concerns about environmental and health effects. This study focuses on a cross section of the Rio Paguate, adjacent to the Jackpile Mine on the Laguna Reservation, west-central New Mexico. Often, the geochemical interactions that occur in the hyporheic zone adjacent to these abandoned mines play an important role in trace element mobility. In order to understand the mobility of uranium (U), arsenic (As), and vanadium (V) in the Rio Paguate; surface water, hyporheic zone water, and core sediment samples were analyzed using inductively coupled plasma mass spectroscopy (ICP-MS). All water samples were filtered through 0.45μm and 0.22μm filters and analyzed. The results show that there is no major difference in concentrations of U (378-496μg/L), As (0.872-6.78μg/L), and V (2.94-5.01μg/L) between the filter sizes or with depth (8cm and 15cm) in the hyporheic zone. The unfiltered hyporheic zone water samples were analyzed after acid digestion to assess the particulate fraction. These results show a decrease in U concentration (153-202μg/L) and an increase in As (33.2-219μg/L) and V (169-1130μg/L) concentrations compared to the filtered waters. Surface water concentrations of U(171-184μg/L) are lower than the filtered hyporheic zone waters while As(1.32-8.68μg/L) and V(1.75-2.38μg/L) are significantly lower than the hyporheic zone waters and particulates combined. Concentrations of As in the sediment core samples are higher in the first 15cm below the water-sediment interface (14.3-3.82μg/L) and decrease (0.382μg/L) with depth. Uranium concentrations are consistent (0.047-0.050μg/L) at all depths. The over all data suggest that U is mobile in the dissolved phase and both As and V are mobile in the particular phase as they travel through the system.

Arid Zone Hydrology

USDA-ARS?s Scientific Manuscript database

Arid zone hydrology encompasses a wide range of topics and hydro-meteorological and ecological characteristics. Although arid and semi-arid watersheds perform the same functions as those in humid environments, their hydrology and sediment transport characteristics cannot be readily predicted by inf...

Multivariate statistical analysis to investigate the subduction zone parameters favoring the occurrence of giant megathrust earthquakes

NASA Astrophysics Data System (ADS)

Brizzi, S.; Sandri, L.; Funiciello, F.; Corbi, F.; Piromallo, C.; Heuret, A.

2018-03-01

The observed maximum magnitude of subduction megathrust earthquakes is highly variable worldwide. One key question is which conditions, if any, favor the occurrence of giant earthquakes (Mw ≥ 8.5). Here we carry out a multivariate statistical study in order to investigate the factors affecting the maximum magnitude of subduction megathrust earthquakes. We find that the trench-parallel extent of subduction zones and the thickness of trench sediments provide the largest discriminating capability between subduction zones that have experienced giant earthquakes and those having significantly lower maximum magnitude. Monte Carlo simulations show that the observed spatial distribution of giant earthquakes cannot be explained by pure chance to a statistically significant level. We suggest that the combination of a long subduction zone with thick trench sediments likely promotes a great lateral rupture propagation, characteristic of almost all giant earthquakes.

Sub-seafloor acoustic characterization of seamounts near the Ogasawara Fracture Zone in the western Pacific using chirp (3-7 kHz) subbottom profiles

USGS Publications Warehouse

Lee, T.-G.; Hein, J.R.; Lee, Kenneth; Moon, J.-W.; Ko, Y.-T.

2005-01-01

A detailed analysis of chirp (3-7 kHz) subbottom profiles and bathymetry was performed on data collected from seamounts near the Ogasawara Fracture Zone (OFZ) in the western Pacific. The OFZ, which is a 150 km wide rift zone showing 600 km of right-lateral movement in a NW-SE direction, is unique among the fracture zones of the Pacific in that it includes many old seamounts (e.g., Magellan Seamounts and seamounts on Dutton Ridge). Sub-seafloor acoustic echoes on the seamounts are classified into nine specific types based on the nature and continuity of the echoes, subbottom structure, and morphology of the seafloor: (1) distinct echoes (types I-1, I-2, I-3), (2) indistinct echoes (types II-1, II-2, II-3), and (3) hyperbolic echoes (types III-1, III-2, III-3). Type I-2 pelagic sediments, characterized by thin and intermittent coverage, were probably deposited in topographically sheltered areas when bottom currents were strong, whereas type I-1 pelagic sediments accumulated during continuous and widespread sedimentation. Development of seamount flank rift zones in the OFZ may have been influenced by preexisting structures in the transform fracture zone at the time of volcanism, whereas those on Ita Mai Tai seamount in the Pigafetta Basin originated solely by edifice-building processes. Flank rift zones that formed by dike intrusions and eruptions played an important role in mass wasting. Mass-wasting processes included block faulting or block slides around the summit margin, sliding/slumping, debris flows, and turbidites, which may have been triggered by faulting, volcanism, dike injection, and weathering during various stages in the evolution of the seamounts. ?? 2005 Elsevier Ltd. All rights reserved.

Application of continuous seismic-reflection techniques to delineate paleochannels beneath the Neuse River at US Marine Corps Air Station, Cherry Point, North Carolina

USGS Publications Warehouse

Cardinell, Alex P.

1999-01-01

A continuous seismic-reflection profiling survey was conducted by the U.S. Geological Survey on the Neuse River near the Cherry Point Marine Corps Air Station during July 7-24, 1998. Approximately 52 miles of profiling data were collected during the survey from areas northwest of the Air Station to Flanner Beach and southeast to Cherry Point. Positioning of the seismic lines was done by using an integrated navigational system. Data from the survey were used to define and delineate paleochannel alignments under the Neuse River near the Air Station. These data also were correlated with existing surface and borehole geophysical data, including vertical seismic-profiling velocity data collected in 1995. Sediments believed to be Quaternary in age were identified at varying depths on the seismic sections as undifferentiated reflectors and lack the lateral continuity of underlying reflectors believed to represent older sediments of Tertiary age. The sediments of possible Quaternary age thicken to the southeast. Paleochannels of Quaternary age and varying depths were identified beneath the Neuse River estuary. These paleochannels range in width from 870 feet to about 6,900 feet. Two zones of buried paleochannels were identified in the continuous seismic-reflection profiling data. The eastern paleochannel zone includes two large superimposed channel features identified during this study and in re-interpreted 1995 land seismic-reflection data. The second paleochannel zone, located west of the first paleochannel zone, contains several small paleochannels near the central and south shore of the Neuse River estuary between Slocum Creek and Flanner Beach. This second zone of channel features may be continuous with those mapped by the U.S. Geological Survey in 1995 using land seismic-reflection data on the southern end of the Air Station. Most of the channels were mapped at the Quaternary-Tertiary sediment boundary. These channels appear to have been cut into the older sediments and deepen in a southerly or downgradient direction. If these paleochannels continue beneath the Marine Corps Air Station and are filled with permeable sediment, they may act as conduits for ground-water flow or movement of contaminants between the surficial and underlying freshwater aquifers where confining units are breached.

Vortex-induced suspension of sediment in the surf zone

NASA Astrophysics Data System (ADS)

Otsuka, Junichi; Saruwatari, Ayumi; Watanabe, Yasunori

2017-12-01

A major mechanism of sediment suspension by organized vortices produced under violent breaking waves in the surf zone was identified through physical and computational experiments. Counter-rotating flows within obliquely descending eddies produced between adjacent primary roller vortices induce transverse convergent near-bed flows, driving bed load transport to form regular patterns of transverse depositions. The deposited sediment is then rapidly ejected by upward carrier flows induced between the vortices. This mechanism of vortex-induced suspension is supported by experimental evidence that coherent sediment clouds are ejected where the obliquely descending eddies reach the sea bed after the breaking wave front has passed. In addition to the effects of settling and turbulent diffusion caused by breaking waves, the effect of the vortex-induced flows was incorporated into a suspension model on the basis of vorticity dynamics and parametric characteristics of transverse flows in breaking waves. The model proposed here reasonably predicts an exponential attenuation of the measured sediment concentration due to violent plunging waves and significantly improves the underprediction of the concentration produced by previous models.

The control of palaeo-topography in the preservation of shallow gas accumulation: Examples from Brazil, Argentina and South Africa

NASA Astrophysics Data System (ADS)

Weschenfelder, Jair; Klein, Antonio H. F.; Green, Andrew N.; Aliotta, Salvador; de Mahiques, Michel M.; Ayres Neto, Arthur; Terra, Laurício C.; Corrêa, Iran C. S.; Calliari, Lauro J.; Montoya, Isabel; Ginsberg, Silvia S.; Griep, Gilberto H.

2016-04-01

Acoustic anomalies in seismic records have revealed that gas-charged sediments are very common features in the coastal environments around the world. The ubiquitous gassy sediments challenge the effective acoustic mapping of shallow stratigraphy by seismic means, as well as having an important influence on environmental issues related to the coastal zone occupation and management. This paper documents examples of gassy sediments from coastal lagoons, estuaries, rivers, bays and the inner shelf and nearshore environments of Brazil, Argentina and South Africa. Seismic echograms from selected areas show several gas-related anomalies, which present distinctive morphologies for sediment-trapped gas, leaking or free gas discharge into the water column. In several places the gas-charged sediments occur in areas of palaeo-topographic lows related to fluvial channels and valleys that developed in the coastal zone due to sea level oscillations during the Quaternary period. This forcing by palaeo-topographic features results in the occurrence of shallow gas being controlled in most coastal sites by the previous environmental scenario, the stratigraphic arrangement of the transgressive infilling elements, and the local hydrodynamic conditions.

Anthropogenic and natural variability in the composition of sedimentary organic matter of the urbanised coastal zone of Montevideo (Río de la Plata).

PubMed

Bueno, C; Brugnoli, E; Bergamino, L; Muniz, P; García-Rodríguez, F; Figueira, R

2018-01-01

This study is aimed to identify the different sources of sedimentary organic matter (SOM) within Montevideo coastal zone (MCZ). To this end δ 13 C, δ 15 N and C/N ratio were analysed in surface sediments and a sediment core. Sediment core analysis showed that until ~1950CE SOM was mainly marine, observing a shift towards lower δ 13 C in recent sediments, evidencing an estuarine composition. This trend was associated to the climatic variability, which exerted a major influence on the SOM composition, leading to an increased input of terrigenous material and associated anthropogenic contaminants. Surface sediments collected during different El Niño South Oscillation (ENSO) phases did not show inter-annual variability in SOM composition, which was mainly marine in both eastern and western region of MCZ and estuarine in Montevideo Bay. This spatial pattern provides new insights on the dynamics and factors affecting organic matter sources available for primary consumers along the study region. Copyright © 2017 Elsevier Ltd. All rights reserved.

Bacterial dominance in subseafloor sediments characterized by methane hydrates

USGS Publications Warehouse

Briggs, Brandon R.; Inagaki, Fumio; Morono, Yuki; Futagami, Taiki; Huguet, Carme; Rosell-Mele, Antoni; Lorenson, T.D.; Colwell, Frederick S.

2015-01-01

The degradation of organic carbon in subseafloor sediments on continental margins contributes to the largest reservoir of methane on Earth. Sediments in the Andaman Sea are composed of ~ 1% marine-derived organic carbon and biogenic methane is present. Our objective was to determine microbial abundance and diversity in sediments that transition the gas hydrate occurrence zone (GHOZ) in the Andaman Sea. Microscopic cell enumeration revealed that most sediment layers harbored relatively low microbial abundance (103–105 cells cm−3). Archaea were never detected despite the use of both DNA- and lipid-based methods. Statistical analysis of terminal restriction fragment length polymorphisms revealed distinct microbial communities from above, within, and below the GHOZ, and GHOZ samples were correlated with a decrease in organic carbon. Primer-tagged pyrosequences of bacterial 16S rRNA genes showed that members of the phylum Firmicutes are predominant in all zones. Compared with other seafloor settings that contain biogenic methane, this deep subseafloor habitat has a unique microbial community and the low cell abundance detected can help to refine global subseafloor microbial abundance.

A mid-Permian chert event: widespread deposition of biogenic siliceous sediments in coastal, island arc and oceanic basins

USGS Publications Warehouse

Murchey, B.L.; Jones, D.L.

1992-01-01

Radiolarian and conodont of Permian siliceous rocks from twenty-three areas in teh the circum-Pacific and Mediterranean regions reveal a widespread Permian Chert Event during the middle Leonardian to Wordian. Radiolarian- and (or) sponge spicule-rich siliceous sediments accumulated beneath high productivity zones in coastal, island arc and oceanic basins. Most of these deposits now crop out in fault-bounded accreted terranes. Biogenic siliceous sediments did not accumulate in terranes lying beneath infertile waters including the marine sequences in terranes of northern and central Alaska. The Permian Chert Event is coeval with major phosphorite deposition along the western margin of Pangea (Phosphoria Formation and related deposits). A well-known analogue for this event is middle Miocene deposition of biogenic siliceous sediments beneath high productivity zones in many parts of the Pacific and concurrent deposition of phosphatic as well as siliceous sediments in basins along the coast of California. Interrelated factors associated with both the Miocene and Permian depositional events include plate reorientations, small sea-level rises and cool polar waters. ?? 1992.

Mechanical and hydraulic properties of Nankai accretionary prism sediments: Effect of stress path

NASA Astrophysics Data System (ADS)

Kitajima, Hiroko; Chester, Frederick M.; Biscontin, Giovanna

2012-10-01

We have conducted triaxial deformation experiments along different loading paths on prism sediments from the Nankai Trough. Different load paths of isotropic loading, uniaxial strain loading, triaxial compression (at constant confining pressure, Pc), undrained Pc reduction, drained Pc reduction, and triaxial unloading at constant Pc, were used to understand the evolution of mechanical and hydraulic properties under complicated stress states and loading histories in accretionary subduction zones. Five deformation experiments were conducted on three sediment core samples for the Nankai prism, specifically from older accreted sediments at the forearc basin, underthrust slope sediments beneath the megasplay fault, and overthrust Upper Shikoku Basin sediments along the frontal thrust. Yield envelopes for each sample were constructed based on the stress paths of Pc-reduction using the modified Cam-clay model, and in situ stress states of the prism were constrained using the results from the other load paths and accounting for horizontal stress. Results suggest that the sediments in the vicinity of the megasplay fault and frontal thrust are highly overconsolidated, and thus likely to deform brittle rather than ductile. The porosity of sediments decreases as the yield envelope expands, while the reduction in permeability mainly depends on the effective mean stress before yield, and the differential stress after yield. An improved understanding of sediment yield strength and hydromechanical properties along different load paths is necessary to treat accurately the coupling of deformation and fluid flow in accretionary subduction zones.

Spatial distribution and risk assessment of heavy metals and As pollution in the sediments of a shallow lake.

PubMed

Deng, Jiancai; Wang, Yuansheng; Liu, Xin; Hu, Weiping; Zhu, Jinge; Zhu, Lin

2016-05-01

The concentrations and spatial distributions of eight heavy metals in surface sediments and sediment core samples from a shallow lake in China were investigated to evaluate the extent of the contamination and potential ecological risks. The results showed that the heavy metal concentrations were higher in the northern and southwestern lake zones than those in the other lake zones, with lower levels of As, Hg, Zn, Cu, Pb, Cr, and Ni primarily observed in the central and eastern lake regions and Cd primarily confined to areas surrounding the lake. The concentrations of the eight heavy metals in the sediment profiles tended to decrease with increasing sediment depth. The contents of Ni, Cu, Zn, Pb, and Cd in the surface sediment were approximately 1.23-18.41-fold higher than their background values (BVs), whereas the contents of Cr, As, and Hg were nearly identical to their BVs. The calculated pollution load index (PLI) suggested that the surface sediments of this lake were heavily polluted by these heavy metals and indicated that Cd was a predominant contamination factor. The comprehensive potential ecological risk index (PERI) in the surface sediments ranged from 99.2 to 2882.1, with an average of 606.1. Cd contributed 78.7 % to the PERI, and Hg contributed 8.4 %. Multivariate statistical analyses revealed that the surface sediment pollution with heavy metals mainly originated from industrial wastewater discharged by rivers located in the western and northwestern portion of the lake.

Methane-related metabolisms of deep-sea sediments captured with a colonization experiment.

NASA Astrophysics Data System (ADS)

Carr, S. A.; Wheat, C. G.; Orcutt, B.; Kopf, A.; Saffer, D. M.; Toczko, S.

2016-12-01

NanTroSEIZE is a multi-expedition project of the International Ocean Discovery Program (IODP) designed to investigate the Nankai Trough subduction zone. In 2016, a long-term borehole instrument package known as the "GeniusPlug" was collected from Hole C0010A after a six-year deployment within the sediment of a major fault zone, at a depth of 400 mbsf. This GeniusPlug included a set of osmotically-driven pumps, which continuously pumped in situ deep seated, formation water through a microbiological colonization experiment (flow-through osmo colonization system (FLOCS)). This FLOCS experiment contained cassettes of olivine, barite, and sediment collected from nearby Hole C0004D, to serve as colonization substrates. While similar FLOCS have been deployed within boreholes in the igneous oceanic crust, this FLOCS experiment represents the first to be deployed within a sedimentary environment, and thus represents the first opportunity to observe how pore water communities colonize sediment and rock substrates. Initial geochemistry results suggest that conditions within the FLOCS experiment were similar to a methane-sulfate transition zone, and initial enrichment cultures inoculated with the FLOCS substrates demonstrate methane production. Here, we will present integrated results of culturing experiments and culture-independent genomic investigations as a means to elucidate the methane-related metabolisms of these colonizing communities.

Reservoir vital signs monitoring, 1990: Physical and chemical characteristics of water and sediments

DOE Office of Scientific and Technical Information (OSTI.GOV)

Meinert, D.L.

1991-05-01

As part of Tennessee Valley Authority's (TVA's) Reservoir Vital Signs Monitoring program, physical/chemical measurements of water and sediment were made in 1990 on twelve TVA reservoirs (the nine main steam Tennessee river reservoirs - Kentucky through Fort Loudoun and three major tributary reservoirs - Cherokee, Douglas, and Norris). The objective of this monitoring program is to assess the health or integrity of these aquatic ecosystems. The physical/chemical water quality data collected in 1990 showed the water quality of these reservoirs to be very good. However, hypolimnetic anoxia during the summer months in Watts bars, Douglas, and Cherokee reservoir continues tomore » be a concern. High concentrations of nutrients were measured in the transition zones of Cherokee and Douglas reservoirs, resulting in highly productive and eutrophic conditions in the transition zones of these reservoirs. Fecal coliform organisms were frequently detected in the forebay area of Guntersville reservoir, and higher than expected ammonia nitrogen concentrations were found at the transition zone of Wheeler reservoir. Elevated concentrations of mercury were found in Pickwick and Watts bar reservoir sediment, and high lead concentrations were found in a sediment sample collected from Guntersville reservoir. A TVA Reservoir Water Quality Index (RWQI) was developed and used to summarize water quality conditions on a scale from 0 (worst) to 100 (best).« less

Microbial ecology of arsenic-mobilizing Cambodian sediments: lithological controls uncovered by stable-isotope probing.

PubMed

Héry, Marina; Rizoulis, Athanasios; Sanguin, Hervé; Cooke, David A; Pancost, Richard D; Polya, David A; Lloyd, Jonathan R

2015-06-01

Microbially mediated arsenic release from Holocene and Pleistocene Cambodian aquifer sediments was investigated using microcosm experiments and substrate amendments. In the Holocene sediment, the metabolically active bacteria, including arsenate-respiring bacteria, were determined by DNA stable-isotope probing. After incubation with (13) C-acetate and (13) C-lactate, active bacterial community in the Holocene sediment was dominated by different Geobacter spp.-related 16S rRNA sequences. Substrate addition also resulted in the enrichment of sequences related to the arsenate-respiring Sulfurospirillum spp. (13) C-acetate selected for ArrA related to Geobacter spp. whereas (13) C-lactate selected for ArrA which were not closely related to any cultivated organism. Incubation of the Pleistocene sediment with lactate favoured a 16S rRNA-phylotype related to the sulphate-reducing Desulfovibrio oxamicus DSM1925, whereas the ArrA sequences clustered with environmental sequences distinct from those identified in the Holocene sediment. Whereas limited As(III) release was observed in Pleistocene sediment after lactate addition, no arsenic mobilization occurred from Holocene sediments, probably because of the initial reduced state of As, as determined by X-ray Absorption Near Edge Structure. Our findings demonstrate that in the presence of reactive organic carbon, As(III) mobilization can occur in Pleistocene sediments, having implications for future strategies that aim to reduce arsenic contamination in drinking waters by using aquifers containing Pleistocene sediments. © 2014 The Authors. Environmental Microbiology published by Society for Applied Microbiology and John Wiley & Sons Ltd.

Buried cold-water coral mounds and contourite deposits in the Atlantic Moroccan Coral Province

NASA Astrophysics Data System (ADS)

Vandorpe, Thomas; Hebbeln, Dierk; Wienberg, Claudia; Van den Berghe, Michèle; Van Rooij, David

2016-04-01

The Atlantic Moroccan Coral Province (AMCP) is situated in the southern Gulf of Cadiz roughly between 34° 50'N to 35°35'N and 6°30'W to 7°15'W. The region displays tectonic (ridges and both large transverse as well as small normal and reverse faults) as well as sedimentological features (drifts deposits and sediment waves). Eleven mud volcanoes are present in the northern part of the region as well (Vandorpe et al., in press). Besides the presence of many surfacing small cold-water coral mounds, hundreds to thousands of mounds were discovered in the subsurface through 2D seismic parasound and sparker seismic profiles. Over 90% of the mounds are situated at water depths between 600 and 1000 meters and most of them occur in clusters. The cold-water coral mounds are rather small in this region (compared to the 100 m high mounds in the Belgica Province in the Porcupine basin (Huvenne et al., 2003)). Their widths vary between 20 and 200 m with a modus around 60 m, while their heights vary between 2 and 40 m with a modus around 10 m. Moreover, ten horizons at which mound growth initiated can be distinguished, compared to the single mound growth event observed in the Porcupine Basin (Huvenne et al., 2003). This points towards rapidly changing environmental conditions in the AMCP which were sometimes favourable for initiation and growth of cold-water coral mounds. These favourable periods rapidly switched to periods when corals were not able to settle and the mounds could get buried. Mound growth initiates mostly at elevated places, e.g. tectonic ridges, outcropping bedrock or even previous cold-water coral mounds. Elevated places deflect bottom currents and increase the amount of food particles and sediments delivered to the corals, but also create sedimentological features such as contourites. The contourite deposits in the region greatly depend on the slope of the topography against which they are present (Vandorpe et al., in press). When mounds were able to reach a certain height at which they did not get buried by sediments during subsequent non-favourable periods, they were usually recolonized, leading to complex mound shapes clearly showing the growth phases of the mound. All of these factors indicate that the AMCP is a very promising region to further unravel the conditions (both geographically and environmentally) favourable for mound initiation and how these mounds in turn influence the local stratigraphy. Huvenne, V.A.I., De Mol, B., Henriet, J.P., 2003. A 3D seismic study of the morphology and spatial distribution of buried coral banks in the Porcupine Basin, SW of Ireland. Marine Geology 198, 5-25. Vandorpe, T., Martins, I., Vitorino, J., hebbeln, D., García, M., Van Rooij, D., in press. Bottom currents and their influence on the sedimentation pattern in the El Arraiche Mud Volcano Province, southern Gulf of Cadiz. Marine Geology.

Sediment-peridotite interactions in a thermal gradient: mineralogic and geochemical effects and the "sedimentary signature" of arc magmas

NASA Astrophysics Data System (ADS)

Woodland, Alan; Girnis, Andrei; Bulatov, Vadim; Brey, Gerhard; Höfer, Heidi; Gerdes, Axel

2017-04-01

Strong thermal and chemical gradients are characteristic of the slab-mantle interface in subduction zones where relatively cold sediments become juxtaposed with hotter peridotite of the mantle wedge. The formation of arc magmas is directly related to mass transfer processes under these conditions. We have undertaken a series of experiments to simulate interactions and mass transfer at the slab-mantle interface. In addition to having juxtaposed sediment and peridotite layers, the experiments were performed under different thermal gradients. The sediment had a composition similar to GLOSS (1) and also served as the source of H2O, CO2 and a large selection of trace elements. The peridotite was a depleted garnet harzburgite formed from a mixture of natural hand-picked olivine, opx and garnet. Graphite was added to this mixture to establish a redox gradient between the two layers. Experiments were performed at 7.5-10 GPa to simulate the processes during deep subduction. The thermal gradient was achieved by displacing the sample capsule (Re-lined Pt) from the center of the pressure cell. The gradient was monitored with separate thermocouples at each end of the capsule and by subsequent opx-garnet thermometry across the sample. Maximum temperatures varied from 1400˚ -900˚ C and gradients ranged from 200˚ -800˚ C. Thus, in some experiments melting occurred in the sediment layer and in others this layer remained subsolidus, only devolatilizing. Major and trace elements were transported both in the direction of melt percolation to the hot zone, as well as down temperature. This leads to the development of zones with discrete phase assemblages. Olivine in the peridotite layer becomes converted to orthopyroxene, which is due to Si addition, but also migration of Mg and Fe towards the sediment. In the coldest part of a sample, the sediment is converted into an eclogitic cpx + garnet assemblage. A thin zone depleted in almost all trace elements is formed in peridotite directly above the sediment/peridotite boundary and defines the region of maximum metasomatic alteration. With a low Tmin, fluid-mobile Ba, Rb, Sr and Li are more strongly transported into the melt zone compared to HFSE and REE. At Tmin > 700˚ C, all incompatible elements are extracted from the solid into the melt. However, the mineral assemblage controls which elements are held back in the solid residue (i.e. MREE, HREE, Y, Sc, and to a lesser extent Ti, Zr and Hf in garnet). Peridotite-sediment interaction can produce humite-group minerals, particularly in the presence of F. Negative Nb-Ta anomalies are caused by rutile and/or humite phases. Transport of melt or fluid from the sediment to the overlying mantle wedge produces metasomatized magma sources from which basaltic melts with sedimentary geochemical signatures can be derived. Adding even 1% of melt or fluid to depleted mantle peridotite is sufficient to produce basaltic melts with incompatible element contents similar to those observed in natural subduction-related magmas. Such signatures are retained at 6.5 and even 10 GPa when Tmin < 700˚ C. Plank, T., Langmuir C., 1998. Chem. Geol. 145, 325-394.

Numerical Model of Turbulence, Sediment Transport, and Sediment Cover in a Large Canyon-Bound River

NASA Astrophysics Data System (ADS)

Alvarez, L. V.; Schmeeckle, M. W.

2013-12-01

The Colorado River in Grand Canyon is confined by bedrock and coarse-grained sediments. Finer grain sizes are supply limited, and sandbars primarily occur in lateral separation eddies downstream of coarse-grained tributary debris fans. These sandbars are important resources for native fish, recreational boaters, and as a source of aeolian transport preventing the erosion of archaeological resources by gully extension. Relatively accurate prediction of deposition and, especially, erosion of these sandbar beaches has proven difficult using two- and three-dimensional, time-averaged morphodynamic models. We present a parallelized, three-dimensional, turbulence-resolving model using the Detached-Eddy Simulation (DES) technique. DES is a hybrid large eddy simulation (LES) and Reynolds-averaged Navier Stokes (RANS). RANS is applied to the near-bed grid cells, where grid resolution is not sufficient to fully resolve wall turbulence. LES is applied further from the bed and banks. We utilize the Spalart-Allmaras one equation turbulence closure with a rough wall extension. The model resolves large-scale turbulence using DES and simultaneously integrates the suspended sediment advection-diffusion equation. The Smith and McLean suspended sediment boundary condition is used to calculate the upward and downward settling of sediment fluxes in the grid cells attached to the bed. The model calculates the entrainment of five grain sizes at every time step using a mixing layer model. Where the mixing layer depth becomes zero, the net entrainment is zero or negative. As such, the model is able to predict the exposure and burial of bedrock and coarse-grained surfaces by fine-grained sediments. A separate program was written to automatically construct the computational domain between the water surface and a triangulated surface of a digital elevation model of the given river reach. Model results compare favorably with ADCP measurements of flow taken on the Colorado River in Grand Canyon during the High Flow Experiment (HFE) of 2008. The model accurately reproduces the size and position of the major recirculation currents, and the error in velocity magnitude was found to be less than 17% or 0.22 m/s absolute error. The mean deviation of the direction of velocity with respect to the measured velocity was found to be 20 degrees. Large-scale turbulence structures with vorticity predominantly in the vertical direction are produced at the shear layer between the main channel and the separation zone. However, these structures rapidly become three-dimensional with no preferred orientation of vorticity. Surprisingly, cross-stream velocities, into the main recirculation zone just upstream of the point of reattachment and out of the main recirculation region just downstream of the point of separation, are highest near the bed. Lateral separation eddies are more efficient at storing and exporting sediment than previously modeled. The input of sediment to the eddy recirculation zone occurs near the reattachment zone and is relatively continuous in time. While, the export of sediment to the main channel by the return current occurs in pulses. Pulsation of the strength of the return current becomes a key factor to determine the rates of erosion and deposition in the main recirculation zone.

A cryptic sulfur cycle driven by iron in the methane zone of marine sediment (Aarhus Bay, Denmark)

NASA Astrophysics Data System (ADS)

Holmkvist, Lars; Ferdelman, Timothy G.; Jørgensen, Bo Barker

2011-06-01

Sulfate reduction and sulfur-iron geochemistry were studied in 5-6 m deep gravity cores of Holocene mud from Aarhus Bay (Denmark). A goal was to understand whether sulfate is generated by re-oxidation of sulfide throughout the sulfate and methane zones, which might explain the abundance of active sulfate reducers deep below the main sulfate zone. Sulfate penetrated down to 130 cm where methane started to build up and where the concentration of free sulfide peaked at 5.5 mM. Below this sulfate-methane transition, sulfide diffused downwards to a sulfidization front at 520 cm depth, below which dissolved iron, Fe 2+, accumulated in the pore water. Sulfate reduction rates measured by 35S-tracer incubations in the sulfate zone were high due to high concentrations of reactive organic matter. Within the sulfate-methane transition, sulfate reduction was distinctly stimulated by the anaerobic oxidation of methane. In the methane zone below, sulfate remained at positive "background" concentrations of <0.5 mM down to the sulfidization front. Sulfate reduction decreased steeply to rates which at 300-500 cm depth were 0.2-1 pmol SO 42- cm -3 d -1, i.e., 4-5 orders of magnitude lower than rates measured near the sediment surface. The turn-over time of sulfate increased from 3 years at 12 cm depth to 100-1000 years down in the methane zone. Sulfate reduction in the methane zone accounted for only 0.1% of sulfate reduction in the entire sediment column and was apparently limited by the low pore water concentration of sulfate and the low availability of organic substrates. Amendment of the sediment with both sulfate and organic substrates immediately caused a 10- to 40-fold higher, "potential sulfate reduction" which showed that a physiologically intact community of sulfate reducing bacteria was present. The "background" sulfate concentration appears to be generated from the reaction of downwards diffusing sulfide with deeply buried Fe(III) species, such as poorly-reactive iron oxides or iron bound in reactive silicates. The oxidation of sulfide to sulfate in the sulfidic sediment may involve the formation of elemental sulfur and thiosulfate and their further disproportionation to sulfide and sulfate. The net reaction of sulfide and Fe(III) to form pyrite requires an additional oxidant, irrespective of the formation of sulfate. This could be CO 2 which is reduced with H 2 to methane. The methane subsequently diffuses upwards to become re-oxidized at the sulfate-methane transition and thereby removes excess reducing power and enables the formation of excess sulfate. We show here how the combination of these well-established sulfur-iron-carbon reactions may lead to the deep formation of sulfate and drive a cryptic sulfur cycle. The iron-rich post-glacial sediments underlying Holocene marine mud stimulate the strong sub-surface sulfide reoxidation observed in Aarhus Bay and are a result of the glacial to interglacial history of the Baltic Sea area. Yet, processes similar to the ones described here probably occur widespread in marine sediments, in particular along the ocean margins.

Estimating sediment budgets at the interface between rivers and estuaries with application to the Sacramento-San Joaquin River Delta

USGS Publications Warehouse

Wright, S.A.; Schoellhamer, D.H.

2005-01-01

[1] Where rivers encounter estuaries, a transition zone develops where riverine and tidal processes both affect sediment transport processes. One such transition zone is the Sacramento-San Joaquin River Delta, a large, complex system where several rivers meet to form an estuary (San Francisco Bay). Herein we present the results of a detailed sediment budget for this river/estuary transitional system. The primary regional goal of the study was to measure sediment transport rates and pathways in the delta in support of ecosystem restoration efforts. In addition to achieving this regional goal, the study has produced general methods to collect, edit, and analyze (including error analysis) sediment transport data at the interface of rivers and estuaries. Estimating sediment budgets for these systems is difficult because of the mixed nature of riverine versus tidal transport processes, the different timescales of transport in fluvial and tidal environments, and the sheer complexity and size of systems such as the Sacramento-San Joaquin River Delta. Sediment budgets also require error estimates in order to assess whether differences in inflows and outflows, which could be small compared to overall fluxes, are indeed distinguishable from zero. Over the 4 year period of this study, water years 1999-2002, 6.6 ?? 0.9 Mt of sediment entered the delta and 2.2 ?? 0.7 Mt exited, resulting in 4.4 ?? 1.1 Mt (67 ?? 17%) of deposition. The estimated deposition rate corresponding to this mass of sediment compares favorably with measured inorganic sediment accumulation on vegetated wetlands in the delta.

What multi-beam bathymetric data can tell about morphodynamics and sediment transport in an estuarine environment?

NASA Astrophysics Data System (ADS)

Winterscheid, Axel; Reiß, Marcel

2017-04-01

The Elbe River Estuary is one of the most important waterways for commercial shipping in Europe. It connects the North Sea with the Port of Hamburg located about 100 km inlands. To secure navigation, the Federal Waterways and Shipping Administration (WSV) is operating a fleet of survey vessels all equipped with a multi-beam echo sounder controlling the required water depths. Beyond navigational purposes, this monitoring is creating a comprehensive and ever-growing data base, which can be used for a consistent morphodynamical description of the river bed. The history of multi-beam records in the Elbe River Estuary reaches back to 2008. At particular river sections where large amounts of fine grained sediments accumulate surveys are taken biweekly; at other sections there are monthly surveys. Locally, sedimentation rates of up to 12 cm per day have been observed within the fairway. The time series of multiple multi-beam records have been analyzed with a particular focus on morphodynamics and sedimentation rates. Here we compare the morphodynamical characteristics of two river sections. The first section is located at the downstream end of the estuarine turbidity zone near the city of Cuxhaven; the second section is located 50 km away at the upstream end of the turbidity zone near the city of Hamburg. These two sections have been selected because in both the morphology of the river bed and the sedimentation processes are strongly influenced by the presence of fine grained sediments. The results show that changing sedimentation rates in both sections are conditioned by different site specific factors, e.g. the dynamic shifting of the turbidity zone along the estuary, which is resulting in a temporarily higher availability of suspended sediments and more intense sedimentation rates in the upper part of the estuary and the respective section. In contrast, in the downstream located river section more intense sedimentation rates could be related to periods of strong north-western wind conditions causing increased water levels and higher wave loads on the adjacent wadden areas of the German Bight. These processes were formerly inferred from theory and numerical studies but could not so far be supported on the basis of direct measurements due to a lack of continuous data records on sedimentation rates with a sufficiently high spatial and temporal resolution.

The cost-effectiveness of mandatory 20 mph zones for the prevention of injuries.

PubMed

Peters, Jaime L; Anderson, Rob

2013-03-01

Traffic calming and speed limits are major public health strategies for further reducing road injuries, especially for vulnerable pedestrians such as children and the elderly. We conducted a cost-benefit analysis (CBA-favoured by transport economists) alongside a cost-utility analysis (CUA-favoured by health economists) of mandatory 20 mph zones, providing a unique opportunity to compare assumptions and results. A CUA from the public sector perspective and a CBA from a broader societal perspective. One-way, threshold and probabilistic sensitivity analyses were undertaken. In low casualty areas the intervention was not cost-effective regardless of approach (CUA: cost per QALY = £429 800; CBA: net present value = -£25 500). In high casualty areas, the intervention was cost-effective from the CBA (a saving of £90 600), but not from the CUA [cost per quality-adjusted life year (QALY) = £86 500; assuming National Institute for Health and Clinical Excellence's benchmark for approving health technologies]. Mandatory 20 mph zones may be cost-effective in high casualty areas when a CBA from a societal perspective is considered. Although CBA may appear, in principle, more appropriate, the quality, age or absence of reliable data for many parameters means that there is a great deal of uncertainty and the results should be interpreted with caution.

Biogeochemical transformation of Fe minerals in a petroleum-contaminated aquifer

USGS Publications Warehouse

Zachara, John M.; Kukkadapu, Ravi K.; Glassman, Paul L.; Dohnalkova, Alice; Fredrickson, Jim K.; Anderson, Todd

2004-01-01

The Bemidji aquifer in Minnesota, USA is a well-studied site of subsurface petroleum contamination. The site contains an anoxic groundwater plume where soluble petroleum constituents serve as an energy source for a region of methanogenesis near the source and bacterial Fe(III) reduction further down gradient. Methanogenesis apparently begins when bioavailable Fe(III) is exhausted within the sediment. Past studies indicate that Geobacter species and Geothrix fermentens-like organisms are the primary dissimilatory Fe-reducing bacteria at this site. The Fe mineralogy of the pristine aquifer sediments and samples from the methanogenic (source) and Fe(III) reducing zones were characterized in this study to identify microbiologic changes to Fe valence and mineral distribution, and to identify whether new biogenic mineral phases had formed. Methods applied included X-ray diffraction; X-ray fluorescence (XRF); and chemical extraction; optical, transmission, and scanning electron microscopy; and Mössbauer spectroscopy.All of the sediments were low in total Fe content (≈ 1%) and exhibited complex Fe-mineralogy. The bulk pristine sediment and its sand, silt, and clay-sized fractions were studied in detail. The pristine sediments contained Fe(II) and Fe(III) mineral phases. Ferrous iron represented approximately 50% of FeTOT. The relative Fe(II) concentration increased in the sand fraction, and its primary mineralogic residence was clinochlore with minor concentrations found as a ferroan calcite grain cement in carbonate lithic fragments. Fe(III) existed in silicates (epidote, clinochlore, muscovite) and Fe(III) oxides of detrital and authigenic origin. The detrital Fe(III) oxides included hematite and goethite in the form of mm-sized nodular concretions and smaller-sized dispersed crystallites, and euhedral magnetite grains. Authigenic Fe(III) oxides increased in concentration with decreasing particle size through the silt and clay fraction. Chemical extraction and Mössbauer analysis indicated that this was a ferrihydrite like-phase. Quantitative mineralogic and Fe(II/III) ratio comparisons between the pristine and contaminated sediments were not possible because of textural differences. However, comparisons between the texturally-similar source (where bioavailable Fe(III) had been exhausted) and Fe(III) reducing zone sediments (where bioavailable Fe(III) remained) indicated that dispersed detrital, crystalline Fe(III) oxides and a portion of the authigenic, poorly crystalline Fe(III) oxide fraction had been depleted from the source zone sediment by microbiologic activity. Little or no effect of microbiologic activity was observed on silicate Fe(III). The presence of residual “ferrihydrite” in the most bioreduced, anoxic plume sediment (source) implied that a portion of the authigenic Fe(III) oxides were biologically inaccessible in weathered, lithic fragment interiors. Little evidence was found for the modern biogenesis of authigenic ferrous-containing mineral phases, perhaps with the exception of thin siderite or ferroan calcite surface precipitates on carbonate lithic fragments within source zone sediments.

Beach groundwater dynamics

NASA Astrophysics Data System (ADS)

Horn, Diane P.

2002-11-01

An understanding of the interaction between surface and groundwater flows in the swash zone is necessary to understand beach profile evolution. Coastal researchers have recognized the importance of beach watertable and swash interaction to accretion and erosion above the still water level (SWL), but the exact nature of the relationship between swash flows, beach watertable flow and cross-shore sediment transport is not fully understood. This paper reviews research on beach groundwater dynamics and identifies research questions which will need to be answered before swash zone sediment transport can be successfully modelled. After defining the principal terms relating to beach groundwater, the behavior, measurement and modelling of beach groundwater dynamics is described. Research questions related to the mechanisms of surface-subsurface flow interaction are reviewed, particularly infiltration, exfiltration and fluidisation. The implications of these mechanisms for sediment transport are discussed.

Vertical accumulation of potential toxic elements in a semiarid system that is influenced by an abandoned gold mine

NASA Astrophysics Data System (ADS)

Sánchez-Martínez, Martha A.; Marmolejo-Rodríguez, Ana J.; Magallanes-Ordóñez, Víctor R.; Sánchez-González, Alberto

2013-09-01

The mining zone at El Triunfo, Baja California Sur, Mexico, was exploited for gold extraction for 200 years. This area includes more than 100 abandoned mining sites. These sites contain mine tailings that are highly contaminated with potential toxic elements (PTE), such as As, Cd, Pb, Sb, Zn, and other associated elements. Over time, these wastes have contaminated the sediments in the adjacent fluvial systems. Our aim was to assess the vertical PTE variations in the abandoned mining zone and in the discharge of the main arroyo into a small lagoon at the Pacific Ocean. Sediments were collected from the two following locations in the mining zone near the arroyo basin tailings: 1) an old alluvial terrace (Overbank) and a test pit (TP) and 2) two sediment cores locations at the arroyo discharge into a hypersaline small lagoon. Samples were analyzed by ICP-MS, ICP-OES, and INAA and the methods were validated. The overbank was the most contaminated and had As, Cd, Pb, Sb, and Zn concentrations of 8690, 226, 84,700, 17,400, and 42,600 mg kg-1, respectively, which decreased with depth. In addition, the TP contained elevated As, Cd, Pb, Sb, and Zn concentrations of 694, 18.8, 5001, 39.2, and 4170 mg kg-1, respectively. The sediment cores were less contaminated. However, the As, Cd, Pb, Sb, and Zn concentrations were greater than the concentrations that are generally found in the Earth's crust. The normalized enrichment factors (NEFs), which were calculated from the background concentrations of these elements in the system, showed that extremely severe As, Cd, Pb, Sb, and Zn (NEF > 50) enrichment occurred at the overbank. The TP was severe to very severely enriched with As, Cd, Pb, Sb, and Zn (NEF = 10-50). The sediment cores had a severe enrichment of As, Pb, and Zn (NEF = 10-25). Their vertical profiles showed that anthropogenic influences occurred in the historic sediment deposition at the overbank and TP and in the sediment cores. In addition, the As, Pb, and Zn concentrations in the sediment cores were related to the deposition of fine sediments and organic carbon.

Shallow velocity structure of the Alaska Peninsula subduction zone and implications for controls on seismic behavior

NASA Astrophysics Data System (ADS)

Li, J.; Shillington, D. J.; Becel, A.; Nedimovic, M. R.; Kuehn, H.; Webb, S. C.; Abers, G. A.; Keranen, K. M.; Saffer, D. M.

2014-12-01

Downdip and along-strike variations in the seismic behavior of subduction zone megathrust faults are thought to be strongly controlled by changes in the material properties along the plate boundary. Roughness and hydration of the incoming plate, fluid pressure and lithology in the subducting sediment channel are likely to control the distribution of shallower rupture. Here, we focus on the subduction zone offshore of the Alaska Peninsula. In 2011, the ALEUT program acquired deep penetration multichannel seismic (MCS) reflection and ocean bottom seismometer (OBS) data across the apparently freely sliding Shumagin Gap, the locked Semidi segment that last ruptured in 1938 M8.2 earthquake, and the locked western Kodiak asperity, which ruptured in the 1964 M9.2 earthquake. Seismic reflection data from the ALEUT cruise reveal significant variability in the thickness of sediment on the incoming plate and entering the trench, and the roughness and degree of hydration of the incoming plate. Oceanic crust entering the trench in the Shumagin gap is rugged with extensive faults and only a thin layer of sediment (<0.5 km thick). Farther east in the Semidi segment, the subducting plate has a smoother surface with thicker sediments (~1 km thick) and less faulting/hydration. To better constrain the properties of the accretionary prism and shallow part of the plate boundary, we are undertaking travel time tomography using reflection/refraction phases in OBS and MCS data, and constraints on the interface geometry from MCS images to estimate the detailed shallow velocity structure, with particular focus on properties within the shallow subduction channel. We observe refractions and reflections in OBS data from the shallow part of the subduction zone in both the Shumagin Gap and Semidi segment, including reflections off the top and base of what appears to be a layer of subducting sediment, which can be used for this work. We plan to present initial models of the shallow part of the subduction zone from both segments and discuss comparisons between the two.

Modification of the Undertow and Turbulence by Submerged Vegetation in a Laboratory Surf Zone

NASA Astrophysics Data System (ADS)

Mandel, T.; Suckale, J.; Marras, S.; Maldonado, S.; Koseff, J. R.

2016-12-01

Breaking waves in the surf zone are a dominant factor shaping the evolution of our coastlines. The turbulence generated by wave breaking causes sediment resuspension, while wave runup, rundown, and the undertow transport this sediment along and across the shore (Longo et al., 2002). Coastal hazard models must now address the added complications of climate change, including sea level rise, stronger storm events, and ecosystem degradation (Arkema et al., 2013). A robust theoretical understanding of surf zone dynamics is therefore imperative to considering the magnitude and implications of these potential changes. However, little work has been done to extend our current theoretical understanding to realistic beach faces, with aquatic vegetation, reefs, and other roughness elements that might mitigate scour and sedimentation. Clarifying these relationships will help scientists and policy-makers decide where to focus ecosystem restoration and preservation efforts, in order to maximize their protective benefits to infrastructure and economic activity on the coast. In order to evaluate the role of vegetation in coastal protection, we conducted a series of experiments in an idealized laboratory surf zone. We examine the impact of submerged model vegetation on the undertow profile, wave orbital velocities, turbulent kinetic energy, and wave-induced stresses, and compare these results to theoretical formulations that model these quantities. We find that vegetation reduces the wave energy available to be converted to turbulent kinetic energy during breaking, indicating a mechanism to mitigate suspension of sediment. Vegetation also reduces the magnitude of the undertow, likely reducing transport of sediment offshore. These results suggest that vegetation provides significant protective benefits for coastal communities at risk from erosion beyond its well-characterized ability to attenuate wave height, and motivate further work to incorporate these effects into models of near-shore hydrodynamics. Longo S, Petti M, Losada IJ. 2002. Turbulence in the swash and surf zones: a review. Coast Eng 45:129-147. Arkema KK, Guannel G, Verutes G, Wood SA, Guerry A, Ruckelshaus M, Kareiva P, Lacayo M, Silver JM. Coastal habitats shield people and property from sea-level rise and storms. Nat Clim Change 3:913-918.

Redox Zonation and Oscillation in the Hyporheic Zone of the Ganges-Brahmaputra-Meghna Delta: Implications for the Fate of Groundwater Arsenic during Discharge

PubMed Central

Jung, Hun Bok; Zheng, Yan; Rahman, Mohammad W.; Rahman, Mohammad M.; Ahmed, Kazi M.

2015-01-01

Riverbank sediment cores and pore waters, shallow well waters, seepage waters and river waters were collected along the Meghna Riverbank in Gazaria Upazila, Bangladesh in Jan. 2006 and Oct.-Nov. 2007 to investigate hydrogeochemical processes controlling the fate of groundwater As during discharge. Redox transition zones from suboxic (0-2 m depth) to reducing (2-5 m depth) then suboxic conditions (5-7 m depth) exist at sites with sandy surficial deposits, as evidenced by depth profiles of pore water (n=7) and sediment (n=11; diffuse reflectance, Fe(III)/Fe ratios and Fe(III) concentrations). The sediment As enrichment zone (up to ~700 mg kg−1) is associated with the suboxic zones mostly between 0-2 m depth and less frequently between 5-7 m depth. The As enriched zones consist of several 5 to 10 cm-thick dispersed layers and span a length of ~5-15 m horizontally from the river shore. Depth profiles of riverbank pore water deployed along a 32 m transect perpendicular to the river shore show elevated levels of dissolved Fe (11.6±11.7 mg L−1) and As (118±91 μg L−1, mostly as arsenite) between 2-5 m depth, but lower concentrations between 0-2 m depth (0.13±0.19 mg L−1 Fe, 1±1 μg L−1 As) and between 5-6 m depth (1.14±0.45 mg L−1 Fe, 28±17 μg L−1 As). Because it would take more than a few hundred years of steady groundwater discharge (~10 m yr−1) to accumulate hundreds of mg kg−1 of As in the riverbank sediment, it is concluded that groundwater As must have been naturally elevated prior to anthropogenic pumping of the aquifer since the 1970s. Not only does this lend unequivocal support to the argument that As occurrence in the Ganges-Brahmaputra-Meghna Delta groundwater is of geogenic origin, it also calls attention to the fate of this As enriched sediment as it may recycle As into the aquifer. PMID:26855475

Controls on subsurface methane fluxes and shallow gas formation in Baltic Sea sediment (Aarhus Bay, Denmark)

NASA Astrophysics Data System (ADS)

Flury, Sabine; Røy, Hans; Dale, Andrew W.; Fossing, Henrik; Tóth, Zsuzsanna; Spiess, Volkhard; Jensen, Jørn Bo; Jørgensen, Bo Barker

2016-09-01

Shallow gas accumulates in coastal marine sediments when the burial rate of reactive organic matter beneath the sulfate zone is sufficiently high and the methanogenic zone is sufficiently deep. We investigated the controls on methane production and free methane gas accumulation along a 400 m seismo-acoustic transect across a sharp transition from gas-free into gas-bearing sediment in Aarhus Bay (Denmark). Twelve gravity cores were taken, in which the pore water was analyzed for inorganic solutes while rates of organic carbon mineralization were measured experimentally by 35SO42- radiotracer method. The thickness of organic-rich Holocene mud increased from 5 to 10 m along the transect concomitant with a shallowing of the depth of the sulfate-methane transition from >4 m to 2.5 m. In spite of drastic differences in the distribution of methane and sulfate in the sediment along the transect, there were only small differences in total mineralization, and methanogenesis was only equivalent to about 1% of sulfate reduction. Shallow gas appeared where the mud thickness exceeded 8-9 m. Rates of methanogenesis increased along the transect as did the upward diffusive flux of methane. Interestingly, the increase in the sedimentation rate and Holocene mud thickness had only a modest direct effect on methanogenesis rates in deep sediments. This increase in methane flux, however, triggered a shallowing of the sulfate-methane transition which resulted in a large increase in methanogenesis at the top of the methanogenic zone. Thus, our results demonstrate a positive feedback mechanism that causes a strong enhancement of methanogenesis and explains the apparently abrupt appearance of gas when a threshold thickness of organic-rich mud is exceeded.

Rates and extent of microbial debromination in the deep subseafloor biosphere

NASA Astrophysics Data System (ADS)

Berg, R. D.; Solomon, E. A.; Morris, R. M.

2013-12-01

Recent genomic and porewater geochemical data suggest that reductive dehalogenation of a wide range of halogenated organic compounds could represent an important energy source for deep subseafloor microbial communities. At continental slope sites worldwide, there is a remarkably linear relationship between porewater profiles of ammonium and bromide, indicating that the factors controlling the distribution and rates of dehalogenation have the potential to influence carbon and nitrogen cycling in the deep subsurface biosphere. Though this metabolic pathway could play an important role in the cycling of otherwise refractory pools of carbon and nitrogen in marine sediments and provide energy to microbial communities in the deep subsurface biosphere, the rates and extent of dehalogenation in marine sediments are poorly constrained. Here we report net reaction rate profiles of debromination activity in continental slope sediments, calculated from numerical modeling of porewater bromide profiles from several margins worldwide. The reaction rate profiles indicate three common zones of debromination activity in slope sediments: 1) low rates of debromination, and a potential bromine sink, in the upper sediment column correlating to the sulfate reduction zone, with net bromide removal rates from -3.6 x 10^-2 to -4.85 x 10^-1 μmol m^-2 yr^-1, 2) high rates of debromination from the sulfate-methane transition zone to ~40-100 mbsf, with net bromide release rates between 7.1 x 10^-2 to 3.9 x 10^-1 μmol m^-2 yr^-1, and 3) an inflection point at ~40-100 mbsf, below which net rates of debromination decrease by an order of magnitude and at several sites are indistinguishable from zero. These results indicate that dehalogenating activity is widely distributed in marine sediments, providing energy to fuel deep subseafloor microbial communities, with potentially important consequences for the global bromine and nitrogen cycles.

Carbon fluxes within the epipelagic zone of the Humboldt Current System off Chile: The significance of euphausiids and diatoms as key functional groups for the biological pump

NASA Astrophysics Data System (ADS)

González, Humberto E.; Daneri, Giovanni; Iriarte, José L.; Yannicelli, Beatriz; Menschel, Eduardo; Barría, Claudio; Pantoja, Silvio; Lizárraga, Lorena

2009-12-01

The information from 54 drifting sediment traps deployed between 1997 and 2006 along the Humboldt Current System off Chile (from 19.9°S to 42.2°S) was analyzed to contribute to unveiling the recurrent global-ocean issue of the lack of relationship between gross primary production (GPP) and particulate organic carbon (POC) export below 50 m depth. When the proportion of carbon that effectively sinks is relatively low compared to the carbon being fixed through GPP, a significant amount (average of 32%) of the sinking organic matter is composed of diatoms, regardless of GPP rates. Such a fraction seems to be affected by the physiological state of phytoplankton. In contrast, when the fraction of carbon sinking is high relative to GPP, most of sinking organic matter is composed of euphausid faecal strings. Such a situation occurs at relatively low values of GPP and chlorophyll-a. Most of these high sinking rates of pellets and low phytoplankton biomass occur during summer, when physical conditions favour the presence of phytoplankton blooms, and when the GPP/Biomass ratio indicates healthy phytoplankton physiological conditions. All this evidence supports the assessment of the relevance of euphausiids as key species in the Humboldt Current System pointing to (i) the top-down control that euphausiids are capable of exerting over primary producer biomass, and (ii) euphausiids‘ paramount role on total organic carbon flux over the Concepción continental shelf, regarding both POC export to the sediments and possibly the channelling of GPP directly to higher trophic levels.

Guidelines for collecting and processing samples of stream bed sediment for analysis of trace elements and organic contaminants for the National Water-Quality Assessment Program

USGS Publications Warehouse

Shelton, Larry R.; Capel, Paul D.

1994-01-01

A major component of the U.S. Geological Survey's National Water-Quality Assessment program is to assess the occurrence and distribution of trace elements and organic contaminants in streams. The first phase of the strategy for the assessment is to analyze samples of bed sediments from depositional zones. Fine-grained particles deposited in these zones are natural accumulators of trace elements and hydrophobic organic compounds. For the information to be comparable among studies in many different parts of the Nation, strategies for selecting stream sites and depositional zones are critical. Fine-grained surficial sediments are obtained from several depositional zones within a stream reach and composited to yield a sample representing average conditions. Sample collection and processing must be done consistently and by procedures specifically designed to separate the fine material into fractions that yield uncontaminated samples for trace-level analytes in the laboratory. Special coring samplers and other instruments made of Teflon are used for collection. Samples are processed through a 2.0-millimeter stainless-steel mesh sieve for organic contaminate analysis and a 63-micrometer nylon-cloth sieve for trace-element analysis. Quality assurance is maintained by strict collection and processing procedures, duplicate samplings, and a rigid cleaning procedure.

Differences in Hyporheic-Zone Microbial Community Structure along a Heavy-Metal Contamination Gradient

PubMed Central

Feris, Kevin; Ramsey, Philip; Frazar, Chris; Moore, Johnnie N.; Gannon, James E.; Holben, William E.

2003-01-01

The hyporheic zone of a river is nonphotic, has steep chemical and redox gradients, and has a heterotrophic food web based on the consumption of organic carbon entrained from downwelling surface water or from upwelling groundwater. The microbial communities in the hyporheic zone are an important component of these heterotrophic food webs and perform essential functions in lotic ecosystems. Using a suite of methods (denaturing gradient gel electrophoresis, 16S rRNA phylogeny, phospholipid fatty acid analysis, direct microscopic enumeration, and quantitative PCR), we compared the microbial communities inhabiting the hyporheic zone of six different river sites that encompass a wide range of sediment metal loads resulting from large base-metal mining activity in the region. There was no correlation between sediment metal content and the total hyporheic microbial biomass present within each site. However, microbial community structure showed a significant linear relationship with the sediment metal loads. The abundances of four phylogenetic groups (groups I, II, III, and IV) most closely related to α-, β-, and γ-proteobacteria and the cyanobacteria, respectively, were determined. The sediment metal content gradient was positively correlated with group III abundance and negatively correlated with group II abundance. No correlation was apparent with regard to group I or IV abundance. This is the first documentation of a relationship between fluvially deposited heavy-metal contamination and hyporheic microbial community structure. The information presented here may be useful in predicting long-term effects of heavy-metal contamination in streams and provides a basis for further studies of metal effects on hyporheic microbial communities. PMID:12957946

Sediment dynamics and post-glacial evolution of the continental shelf around the Blanes submarine canyon head (NW Mediterranean)

NASA Astrophysics Data System (ADS)

Durán, Ruth; Canals, Miquel; Lastras, Galderic; Micallef, Aaron; Amblas, David; Pedrosa-Pàmies, Rut; Sanz, José Luis

2013-11-01

The Blanes submarine canyon (BC) deeply incises the Catalan continental shelf in the NW Mediterranean Sea. As a consequence of the closeness (only 4 km) of its head to the coastline and the mouth of the Tordera River, the canyon has a direct influence on the shelf dispersal system as it collects large amounts of sediment, mainly during high-energy events. Multibeam bathymetry, backscatter imagery and very-high resolution seismic reflection profiles have allowed characterizing the morphology of the continental shelf around the canyon head, also identifying sediment sources and transport pathways into the canyon. The morphological data have also been used to reconstruct the evolution of the continental shelf during the last sea-level transgression so that the current understanding of shelf-to-canyon sediment exchanges through time could be improved. The continental shelf surrounding the BC consists of both depositional and erosional or non-depositional areas. Depositional areas display prominent sediment bodies, a generally smooth bathymetry and variable backscatter. These include: (i) an area of modern coarse-grained sediment accumulation that comprises the inner shelf; (ii) a modern fine-grained sedimentation area on the middle shelf offshore Tossa de Mar; and (iii) a modern sediment depleted area that covers most of the middle and outer shelf to the west of the canyon head. Erosional and non-depositional areas display a rough topography and high backscatter, and occur primarily to the east of the canyon head, where the arrival of river-fed inputs is very small. In agreement with this pattern, the continental shelf north and west of the canyon head likely is the main source of shelf sediment into the canyon. To the north, a pattern of very high backscatter extends from the coastline to the canyon head, suggesting the remobilization and off-shelf export of fines. Additionally, relict near-shore sand bodies developed over the Barcelona shelf that extend to the canyon head rim constitute a source of coarse sediment. High-energy processes, namely river floods and coastal storms, are the main controls over the river-shelf-canyon sediment exchange. River floods increase the delivery of terrigenous particles to the coastal system. Storms, mainly from the east, remobilize the sediment temporarily accumulated on the shelf towards the canyon head, so that the finer fractions are preferentially removed and a coarse lag is normally left on the shelf floor. Exceptionally, very strong storms also remove the coarse fractions from the shelf drive them into the canyon. Processes like dense shelf water cascading, which is much more intense in canyons to the north of BC, and the Northern Current also contribute to the transport of suspended sediment from far distant northern sources. During the last post-glacial transgression the BC had a strong influence on the evolution of the inner continental margin, as it interrupted the shelf sediment dispersal system by isolating the shelves to its north and south, named La Planassa and Barcelona shelves, respectively. The detailed study of the geomorphology and uppermost sediment cover of the continental shelf surrounding the Blanes submarine canyon yields insight into the past and present shelf sediment dynamics and the shelf-to-canyon sediment exchanges. The continental shelf near the canyon head consists of mosaic where erosional, or non-depositional, and depositional zones coexist. East of the canyon and offshore Tossa de Mar, the modern sediment deposition is mostly confined to the inner and middle shelf, whilst most of the La Planassa shelf is sediment depleted with numerous relict morphosedimentary features cropping out. Rocky outcrops, narrow ridges and relict coarse sand deposits suggesting erosion or non-deposition of fine sediments in modern times occupy the middle and outer shelf floor east and northeast of the canyon head. In contrast, north and west of the canyon head, the middle and outer shelf comprises several large relict sand bodies that point out to long-term deposition. However, the lack of modern sediments on top of these bodies supports active erosion or by-pass in present times. The morphology of the continental shelf near the canyon head records the imprint of the main factors controlling the shelf sediment-dispersal system and provides evidence for the main sources and transport pathways of sediment from the shelf into the canyon. The depletion of fine sediments on the continental shelf, as evidenced by backscatter data, suggests that the Blanes Canyon acts as a sediment trap collecting the finest fractions resuspended primarily from the adjacent shelf to the north. The main processes that control the shelf-to-canyon transfer of sediment are eastern storms, which enhance the off-shelf export of mainly fine sediment from the shelf. Particularly severe storms are also able to remobilize and transport coarse sediment from the shelf and also from the relict sand bodies into the canyon. Other processes, such as DSWC and the Northern Current, contribute to a lesser extent to the transport of sediment along the shelf and into the canyon. During the last post-glacial transgression, the BC played a crucial role in the shaping of the continental shelf surrounding it by cutting the littoral drift of sediment between the shelf areas to the north and south, thus severely modifying the across- and along-shelf sediment pathways. As a result, to the east of the canyon, the poor development of transgressive deposits indicates the prevalence of erosion and non-deposition associated to a limited sediment supply and an effective action of the littoral drift leading to a south-westward transport of sediment towards the canyon head. To the north and west of the canyon the morphology of the continental shelf changed significantly during the sea-level rise. At the early stage of the transgression, the sediment supplied by the Tordera River was discharged directly into the canyon, thus preventing deposition over the shelf. Later, the progressive sea-level rise favoured the development of large depositional bodies on the Barcelona shelf favoured by the increase of accommodation space and the augmenting distance between the river mouth and the canyon head. A drastic change in the configuration of the shelf occurred when the sea-level raised enough to flood the entire continental shelf. The along-shelf sediment transport between the shelf areas to the north and south of the canyon head was then restored and new sediment bodies were formed between the coastline and the canyon tip. At present, these sediment bodies constitute the primary source of coarse sediment into the BC. These results confirm that the Blanes submarine canyon head is highly dynamic and sensitive to a variety of processes that enhance the transport of sediment from the shelf into the canyon, particularly during major storms.

Optimization of remediation strategies using vadose zone monitoring systems

NASA Astrophysics Data System (ADS)

Dahan, Ofer

2016-04-01

In-situ bio-remediation of the vadose zone depends mainly on the ability to change the subsurface hydrological, physical and chemical conditions in order to enable development of specific, indigenous, pollutants degrading bacteria. As such the remediation efficiency is much dependent on the ability to implement optimal hydraulic and chemical conditions in deep sections of the vadose zone. These conditions are usually determined in laboratory experiments where parameters such as the chemical composition of the soil water solution, redox potential and water content of the sediment are fully controlled. Usually, implementation of desired optimal degradation conditions in deep vadose zone at full scale field setups is achieved through infiltration of water enriched with chemical additives on the land surface. It is assumed that deep percolation into the vadose zone would create chemical conditions that promote biodegradation of specific compounds. However, application of water with specific chemical conditions near land surface dose not necessarily results in promoting of desired chemical and hydraulic conditions in deep sections of the vadose zone. A vadose-zone monitoring system (VMS) that was recently developed allows continuous monitoring of the hydrological and chemical properties of deep sections of the unsaturated zone. The VMS includes flexible time-domain reflectometry (FTDR) probes which allow continuous monitoring of the temporal variation of the vadose zone water content, and vadose-zone sampling ports (VSPs) which are designed to allow frequent sampling of the sediment pore-water and gas at multiple depths. Implementation of the vadose zone monitoring system in sites that undergoes active remediation provides real time information on the actual chemical and hydrological conditions in the vadose zone as the remediation process progresses. Up-to-date the system has been successfully implemented in several studies on water flow and contaminant transport in the unsaturated zone including enhanced bioremediation of contaminated deep vadose zone (40 m depth). Manipulating subsurface conditions for enhanced bioremediation was demonstrated through two remediation projects. One site is characterized by 20 m deep vadose zone that is contaminated with gasoline products and the other is a 40 m deep vadose zone that is contaminated with perchlorate. In both cases temporal variation of the sediment water content as well as the variations in the vadose zone chemical and isotopic composition allowed real time detection of water flow velocities, contaminants transport rates and bio-degradation degree. Results and conclusions from each wetting cycle were used to improve the following wetting cycles in order to optimize contaminants degradation conditions while minimizing leaching of contaminants to the groundwater.

Analysis of sediment retention in western riverine wetlands: the Yampa River watershed, Colorado, USA.

PubMed

Arp, Christopher D; Cooper, David J

2004-03-01

We quantified annual sediment deposition, bank erosion, and sediment budgets in nine riverine wetlands that represented a watershed continuum for 1 year in the unregulated Yampa River drainage basin in Colorado. One site was studied for 2 years to compare responses to peak flow variability. Annual mean sediment deposition ranged from 0.01 kg/m(2) along a first-order subalpine stream to 21.8 kg/m(2) at a sixth-order alluvial forest. Annual mean riverbank erosion ranged from 3 kg/m-of-bank at the first-order site to 1000 kg/m at the 6(th)-order site. Total sediment budgets were nearly balanced at six sites, while net export from bank erosion occurred at three sites. Both total sediment deposition (R(2) = 0.86, p < 0.01) and bank erosion (R(2) = 0.77, p < 0.01) were strongly related to bankfull height, and channel sinuosity and valley confinement helped to explain additional variability among sites. The texture and organic fraction of eroded and deposited sediment were relatively similar in most sites and varied among sites by watershed position. Our results indicate that bank erosion generally balances sediment deposition in riverine wetlands, and we found no distinct zones of sediment retention versus export on a watershed continuum. Zones of apparent disequilibrium can occur in unregulated rivers due to factors such as incised channels, beaver activity, and cattle grazing. A primary function of many western riverine wetlands is sediment exchange, not retention, which may operate by transforming materials and compounds in temporary sediment pools on floodplains. These results are considered in the context of the Hydrogeomorphic approach being implemented by the U.S. government for wetland resource management.

OECD Economic Surveys: Canada 2012

ERIC Educational Resources Information Center

OECD Publishing (NJ3), 2012

2012-01-01

Canada weathered the global economic crisis well, mainly reflecting sustained growth in domestic pending, and the economy is continuing to grow despite the persistence of international turbulence, most recently stemming from the euro zone sovereign debt crisis. In Canada's case, several factors are acting in its favour. Federal fiscal plans are…

Microfossil biostratigraphy of prograding Neogene platform-margin carbonates, Bahamas: Age constraints and alternatives

USGS Publications Warehouse

Lidz, B.H.; Bralower, T.J.

1994-01-01

Benthic and planktic foraminifera and calcareous nannofossils were recovered in shallow-water carbonate rock cores from two continuous boreholes drilled 7.5 km apart on the west platform margin of the Great Bahama Bank. The microfossils define six biostratigraphic units in each hole. One unit in each hole represents a correlative condensed section. Seven foraminiferal biozones are recognized in 11 of the units between the holes: middle Miocene Globorotalia fohsi robusta Zone N12, late Miocene G. acostaensis Zone N16 and G. humerosa Zone N17, early Pliocene G. margaritae evoluta Subzone N19, late Pliocene G. exilis Subzone N21 and, tentatively, G. tosaensis tosaensis Zone N21, and early Pleistocene G. crassaformis viola Subzone N22. The twelfth unit is inferred to be of G. crassaformis viola Subzone N22 age. The oldest unit is onshore, the youngest is offshore. As presently interpreted, the nannofossil and foraminiferal zonations are partially correlative. Although the microfossils unequivocally constrain the series ages of the sediments, the incompleteness of the fossil record allows for alternative biozonal age models within the series. The Miocene and Pliocene biozones are common to both holes, but the greatest similarities between the holes are the significant mixing of middle and late Miocene, and late Miocene-early Pliocene faunas, the greatly condensed intervals at the Miocene/Pliocene boundary, and the early Pliocene influx of deep-water benthic and pelagic foraminifera. Of particular importance is the tentative recognition of late Pliocene G. tosaensis tosaensis Zone N21 in one borehole. Subsequent data not available to this phase of the study indicate that much of the zone is likely missing. Its absence will lend support to speculations of a regional unconformity in the Bahamas. The microfossils indicate that (1) several transgressions occurred from the middle Miocene to at least the earliest Pleistocene (> 11.5-> 0.46 Ma), during which banktop-derived sediments accumulating at the margin prograded the platform seaward; (2) a condensed interval on the bank top may represent a late Miocene lowstand, a period of sediment bypassing, or a lack of accommodation space; (3) the slope received thin layers of pelagic sediments in a condensed interval during the late Miocene and early Pliocene, while the bank top accommodated early Pliocene (4.2-3.4 Ma) deep-water indicators prior to a likely period of exposure (2.35 - 1.89 Ma); (4) two cycles of banktop sediment production and starvation occurred during the Pliocene; (5) the Pliocene transgression was punctuated by stillstands or low-amplitude reversals during which parts of biozones did not accumulate; and (6) the sediments containing the most complete microfossil-datum record are the thin pelagic strata that mark interruptions in the regular shedding of transgressive deposits from the platform. Sedimentation-rate patterns varied but were generally higher offshore than onshore. ?? 1994.

Amino acids as indicators to elucidate organic matter degradation profile in the Cochin estuarine sediments, Southwest coast of India.

PubMed

Salas, P M; Sujatha, C H; Ratheesh Kumar, C S; Cheriyan, Eldhose

2018-02-01

Surface sediments from three zones (fresh water, estuarine, and riverine/industrial zones) of the Cochin estuary, Southwest coast of India, were seasonally analyzed to understand the nature and degradation status of organic matter. Amino acid-based indices such as total hydrolyzable amino acids (THAAs), percentage contributions of amino acid carbon to total organic carbon (THAA-C%) and those of amino acid nitrogen to total nitrogen (THAA-N%), and degradation index (DI) were calculated. Elevated levels of amino acids in the sediments of the estuary were attributed to river runoff, autochthonous production, allochthonous inputs, and industrial and domestic effluent discharges. Higher levels of THAA-C%, THAA-N%, THAA, and positive DI found in most of the stations suggest the fresh deposition of organic matter. Multivariate statistical analyses revealed that the dispersal pattern of amino acids depends on the sediment texture, organic matter, redox state, and microbial processes in the study region. Copyright © 2017 Elsevier Ltd. All rights reserved.

Characterization of Archaeological Sediments Using Fourier Transform Infrared (FT-IR) and Portable X-ray Fluorescence (pXRF): An Application to Formative Period Pyro-Industrial Sites in Pacific Coastal Southern Chiapas, Mexico.

PubMed

Neff, Hector; Bigney, Scott J; Sakai, Sachiko; Burger, Paul R; Garfin, Timothy; George, Richard G; Culleton, Brendan J; Kennett, Douglas J

2016-01-01

Archaeological sediments from mounds within the mangrove zone of far-southern Pacific coastal Chiapas, Mexico, are characterized in order to test the hypothesis that specialized pyro-technological activities of the region's prehistoric inhabitants (salt and ceramic production) created the accumulations visible today. Fourier transform infrared spectroscopy (FT-IR) is used to characterize sediment mineralogy, while portable X-ray fluorescence (pXRF) is used to determine elemental concentrations. Elemental characterization of natural sediments by both instrumental neutron activation analysis (INAA) and pXRF also contribute to understanding of processes that created the archaeological deposits. Radiocarbon dates combined with typological analysis of ceramics indicate that pyro-industrial activity in the mangrove zone peaked during the Late Formative and Terminal Formative periods, when population and monumental activity on the coastal plain and piedmont were also at their peaks. © The Author(s) 2015.

Sedimentary loadings and ecological significance of polycyclic aromatic hydrocarbons in a typical mariculture zone of South China.

PubMed

Yu, Huan-Yun; Bao, Lian-Jun; Wong, Charles S; Hu, Yuanan; Zeng, Eddy Y

2012-10-26

Two sediment cores were collected from Hailing Bay located in a typical mariculture zone of Guangdong Province, South China, and analyzed for polycyclic aromatic hydrocarbons (PAHs). The concentrations of the sum of 27 PAHs ranged from 62 to 1200 ng g(-1) dry wt, and sediment in the study area was considered to be moderately polluted by PAHs. Source diagnostics based on PAH composition and principal component analysis suggested that PAHs in the study area were mainly derived from petroleum combustion, with discharge of PAHs from fishing boats as an important source. Ecological risk assessment results indicate that PAHs in sediment of the present study currently have minimal adverse effect on the mariculture environment. Comparison of sedimentary inventory of PAHs in the fish harbor of the study area with those in the Pearl River Estuary and the coastal Bohai Bay indicate that the sediment has become an important reservoir of PAHs.

Benthic foraminiferal assemblage formation: Theory and observation for the European Arctic margin

NASA Astrophysics Data System (ADS)

Loubere, Paul; Rayray, Shan

2016-09-01

We use theory and observation to determine how benthic foraminiferal populations living in a range of sedimentary microenvironments are translated into fossil assemblages along the continental margin of the European Arctic. We examine downcore stained (cell tracker green and rose Bengal) and total species shell abundances through the sediment mixing (bioturbation) zone. This, in combination with porewater geochemical measurements, allows us to establish zones of production and destruction for species' shells, and deduce how the fossil record is being generated by the living community. For many taxa, shell production is high in the upper, oxic, sedimentary layer, but destruction in this zone is also high. Hence, contribution to the fossil record is biased to more infaunal populations and species. Taxa producing near, or below, the anoxic boundary of the sediments are particularly important to the developing fossil record of the fjord environment. We find that taxon relative and absolute abundances change continuously through the biologically active sediment profile. This has implications for reconstructing paleoenvironments using benthic foraminiferal assemblages, and potentially for the geochemistry of individual fossil taxa.

Benthic foraminiferal assemblage formation: Theory and observation for the European Arctic Margin

NASA Astrophysics Data System (ADS)

Loubere, Paul; Rayray, Shan

2016-07-01

We use theory and observation to determine how benthic foraminiferal populations living in a range of sedimentary microenvironments are translated into fossil assemblages along the continental margin of the European Arctic. We examine downcore stained (cell tracker green and rose Bengal) and total species shell abundances through the sediment mixing (bioturbation) zone. This, in combination with porewater geochemical measurements, allows us to establish zones of production and destruction for species' shells, and deduce how the fossil record is being generated by the living community. For many taxa, shell production is high in the upper, oxic, sedimentary layer, but destruction in this zone is also high. Hence, contribution to the fossil record is biased to more infaunal populations and species. Taxa producing near, or below, the anoxic boundary of the sediments are particularly important to the developing fossil record of the fjord environment. We find that taxon relative and absolute abundances change continuously through the biologically active sediment profile. This has implications for reconstructing paleoenvironments using benthic foraminiferal assemblages, and potentially for the geochemistry of individual fossil taxa.

Groundwater-quality data and regional trends in the Virginia Coastal Plain, 1906-2007

USGS Publications Warehouse

McFarland, Randolph E.

2010-01-01

A newly developed regional perspective of the hydrogeology of the Virginia Coastal Plain incorporates updated information on groundwater quality in the area. Local-scale groundwater-quality information is provided by a comprehensive dataset compiled from multiple Federal and State agency databases. Groundwater-sample chemical-constituent values and related data are presented in tables, summaries, location maps, and discussions of data quality and limitations. Spatial trends in groundwater quality and related processes at the regional scale are determined from interpretive analyses of the sample data. Major ions that dominate the chemical composition of groundwater in the deep Piney Point, Aquia, and Potomac aquifers evolve eastward and with depth from (1) 'hard' water, dominated by calcium and magnesium cations and bicarbonate and carbonate anions, to (2) 'soft' water, dominated by sodium and potassium cations and bicarbonate and carbonate anions, and lastly to (3) 'salty' water, dominated by sodium and potassium cations and chloride anions. Chemical weathering of subsurface sediments is followed by ion exchange by clay and glauconite, and subsequently by mixing with seawater along the saltwater-transition zone. The chemical composition of groundwater in the shallower surficial and Yorktown-Eastover aquifers, and in basement bedrock along the Fall Zone, is more variable as a result of short flow paths between closely located recharge and discharge areas and possibly some solutes originating from human sources. The saltwater-transition zone is generally broad and landward-dipping, based on groundwater chloride concentrations that increase eastward and with depth. The configuration is convoluted across the Chesapeake Bay impact crater, however, where it is warped and mounded along zones having vertically inverted chloride concentrations that decrease with depth. Fresh groundwater has flushed seawater from subsurface sediments preferentially around the impact crater as a result of broad contrasts between sediment permeabilities. Paths of differential flushing are also focused along the inverted zones, which follow stratigraphic and structural trends southeastward into North Carolina and northeastward beneath the chloride mound across the outer impact crater. Brine within the inner impact crater has probably remained unflushed. Regional movement of the saltwater-transition zone takes place over geologic time scales. Localized movement has been induced by groundwater withdrawal, mostly along shallow parts of the saltwater-transition zone. Short-term episodic withdrawals result in repeated cycles of upconing and downconing of saltwater, which are superimposed on longer-term lateral saltwater intrusion. Effective monitoring for saltwater intrusion needs to address multiple and complexly distributed areas of potential intrusion that vary over time. A broad belt of large groundwater fluoride concentrations underlies the city of Suffolk, and thins and tapers northward. Fluoride in groundwater probably originates by desorbtion from phosphatic sedimentary material. The high fluoride belt possibly was formed by initial adsorbtion of fluoride onto sediment oxyhydroxides, followed by desorbtion along the leading edge of the advancing saltwater-transition zone. Large groundwater iron and manganese concentrations are most common to the west along the Fall Zone, across part of the saltwater-transition zone and eastward, and within shallow groundwater far to the east. Iron and manganese initially produced by mineral dissolution along the Fall Zone are adsorbed eastward and with depth by clay and glauconite, and subsequently desorbed along the leading edge of the advancing saltwater-transition zone. Iron and manganese in shallow groundwater far to the east are produced by reaction of sediment organic matter with oxyhydroxides. Large groundwater nitrate and ammonium concentrations are mostly limited to shallow depths. Most nitrate a

Dynamics of oxygen and carbon dioxide in rhizospheres of Lobelia dortmanna - a planar optode study of belowground gas exchange between plants and sediment.

PubMed

Lenzewski, Nikola; Mueller, Peter; Meier, Robert Johannes; Liebsch, Gregor; Jensen, Kai; Koop-Jakobsen, Ketil

2018-04-01

Root-mediated CO 2 uptake, O 2 release and their effects on O 2 and CO 2 dynamics in the rhizosphere of Lobelia dortmanna were investigated. Novel planar optode technology, imaging CO 2 and O 2 distribution around single roots, provided insights into the spatiotemporal patterns of gas exchange between roots, sediment and microbial community. In light, O 2 release and CO 2 uptake were pronounced, resulting in a distinct oxygenated zone (radius: c. 3 mm) and a CO 2 -depleted zone (radius: c. 2 mm) around roots. Simultaneously, however, microbial CO 2 production was stimulated within a larger zone around the roots (radius: c. 10 mm). This gave rise to a distinct pattern with a CO 2 minimum at the root surface and a CO 2 maximum c. 2 mm away from the root. In darkness, CO 2 uptake ceased, and the CO 2 -depleted zone disappeared within 2 h. By contrast, the oxygenated root zone remained even after 8 h, but diminished markedly over time. A tight coupling between photosynthetic processes and the spatiotemporal dynamics of O 2 and CO 2 in the rhizosphere of Lobelia was demonstrated, and we suggest that O 2 -induced stimulation of the microbial community in the sediment increases the supply of inorganic carbon for photosynthesis by building up a CO 2 reservoir in the rhizosphere. © 2018 The Authors. New Phytologist © 2018 New Phytologist Trust.

Numerical model of turbulence, sediment transport, and morphodynamics tested in the Colorado River at Grand Canyon

NASA Astrophysics Data System (ADS)

Alvarez, L. V.; Grams, P.

2017-12-01

We present a parallelized, three-dimensional, turbulence-resolving model using the Detached-Eddy Simulation (DES) technique, tested at the scale of the river-reach in the Colorado River. DES is a hybrid large eddy simulation (LES) and Reynolds-averaged Navier Stokes (RANS). RANS is applied to the near-bed grid cells, where grid resolution is not sufficient to fully resolve wall turbulence. LES is applied in the flow interior. We utilize the Spalart-Allmaras one equation turbulence closure with a rough wall extension. The model resolves large-scale turbulence using DES and simultaneously integrates the suspended sediment advection-diffusion equation. The Smith and McLean suspended sediment boundary condition is used to calculate the upward and downward settling of sediment fluxes in the grid cells attached to the bed. Model results compare favorably with ADCP measurements of flow taken on the Colorado River in Grand Canyon during the High Flow Experiment (HFE) of 2008. The model accurately reproduces the size and position of the major recirculation currents, and the error in velocity magnitude was found to be less than 17% or 0.22 m/s absolute error. The mean deviation of the direction of velocity with respect to the measured velocity was found to be 20 degrees. Large-scale turbulence structures with vorticity predominantly in the vertical direction are produced at the shear layer between the main channel and the separation zone. However, these structures rapidly become three-dimensional with no preferred orientation of vorticity. Cross-stream velocities, into the main recirculation zone just upstream of the point of reattachment and out of the main recirculation region just downstream of the point of separation, are highest near the bed. Lateral separation eddies are more efficient at storing and exporting sediment than previously modeled. The input of sediment to the eddy recirculation zone occurs in the interface of the eddy and main channel. Pulsation of the strength of the return current becomes a key factor to determine the rates of erosion and deposition in the main recirculation zone.

Arsenic and antimony geochemistry of mine wastes, associated waters and sediments at the Giant Mine, Yellowknife, Northwest Territories, Canada

USGS Publications Warehouse

Fawcett, Skya E.; Jamieson, Heather E.; Nordstrom, D. Kirk; McCleskey, R. Blaine

2015-01-01

Elevated levels of arsenic (As) and antimony (Sb) in water and sediments are legacy residues found downstream from gold-mining activities at the Giant Mine in Yellowknife, Northwest Territories (NWT), Canada. To track the transport and fate of As and Sb, samples of mine-waste from the mill, and surface water, sediment, pore-water, and vegetation downstream of the mine were collected. Mine waste, pore-water, and sediment samples were analyzed for bulk chemistry, and aqueous and solid-state speciation. Sediment and vegetation chemistry were evaluated using scanning electron microscope imaging, synchrotron-based element mapping and electron microprobe analysis. The distributions of As and Sb in sediments were similar, yet their distributions in the corresponding pore-waters were mostly dissimilar, and the mobility of As was greater than that of Sb. Competition for sorption sites is the most likely cause of elevated Sb concentrations in relatively oxidized pore-water and surface water. The aqueous and solid-state speciation of As and Sb also differed. In pore-water, As(V) dominated in oxidizing environments and As(III) in reducing environments. In contrast, the Sb(V) species dominated in all but one pore-water sample, even under reducing conditions. Antimony(III) appears to preferentially precipitate or adsorb onto sulfides as evidenced by the prevalence of an Sb(III)-S secondary solid-phase and the lack of Sb(III)(aq) in the deeper zones. The As(V)–O solid phase became depleted with depth below the sediment–water interface, and the Sb(V)–O phase persisted under relatively reducing conditions. In the surficial zone at a site populated by Equisetum fluviatile (common horsetail), As and Sb were associated with organic material and appeared mobile in the root zone. In the zone below active plant growth, As and Sb were associated primarily with inorganic phases suggesting a release and reprecipitation of these elements upon plant death. The co-existence of reduced and oxidized As and Sb species, instability of some phases under changing redox conditions, and plant uptake and release pose challenges for remediation efforts at the mine.

A Bayesian method to quantify azimuthal anisotropy model uncertainties: application to global azimuthal anisotropy in the upper mantle and transition zone

NASA Astrophysics Data System (ADS)

Yuan, K.; Beghein, C.

2018-04-01

Seismic anisotropy is a powerful tool to constrain mantle deformation, but its existence in the deep upper mantle and topmost lower mantle is still uncertain. Recent results from higher mode Rayleigh waves have, however, revealed the presence of 1 per cent azimuthal anisotropy between 300 and 800 km depth, and changes in azimuthal anisotropy across the mantle transition zone boundaries. This has important consequences for our understanding of mantle convection patterns and deformation of deep mantle material. Here, we propose a Bayesian method to model depth variations in azimuthal anisotropy and to obtain quantitative uncertainties on the fast seismic direction and anisotropy amplitude from phase velocity dispersion maps. We applied this new method to existing global fundamental and higher mode Rayleigh wave phase velocity maps to assess the likelihood of azimuthal anisotropy in the deep upper mantle and to determine whether previously detected changes in anisotropy at the transition zone boundaries are robustly constrained by those data. Our results confirm that deep upper-mantle azimuthal anisotropy is favoured and well constrained by the higher mode data employed. The fast seismic directions are in agreement with our previously published model. The data favour a model characterized, on average, by changes in azimuthal anisotropy at the top and bottom of the transition zone. However, this change in fast axes is not a global feature as there are regions of the model where the azimuthal anisotropy direction is unlikely to change across depths in the deep upper mantle. We were, however, unable to detect any clear pattern or connection with surface tectonics. Future studies will be needed to further improve the lateral resolution of this type of model at transition zone depths.

Immediate propagation of deglacial environmental change to deep-marine turbidite systems along the Chile convergent margin

NASA Astrophysics Data System (ADS)

Bernhardt, Anne; Schwanghart, Wolfgang; Hebbeln, Dierk; Stuut, Jan-Berend W.; Strecker, Manfred R.

2017-09-01

Understanding how Earth-surface processes respond to past climatic perturbations is crucial for making informed predictions about future impacts of climate change on sediment fluxes. Sedimentary records provide the archives for inferring these processes, but their interpretation is compromised by our incomplete understanding of how sediment-routing systems respond to millennial-scale climate cycles. We analyzed seven sediment cores recovered from marine turbidite depositional sites along the Chile continental margin. The sites span a pronounced arid-to-humid gradient with variable relief and related sediment connectivity of terrestrial and marine environments. These sites allowed us to study event-related depositional processes in different climatic and geomorphic settings from the Last Glacial Maximum to the present day. The three sites reveal a steep decline of turbidite deposition during deglaciation. High rates of sea-level rise postdate the decline in turbidite deposition. Comparison with paleoclimate proxies documents that the spatio-temporal sedimentary pattern rather mirrors the deglacial humidity decrease and concomitant warming with no resolvable lag times. Our results let us infer that declining deglacial humidity decreased fluvial sediment supply. This signal propagated rapidly through the highly connected systems into the marine sink in north-central Chile. In contrast, in south-central Chile, connectivity between the Andean erosional zone and the fluvial transfer zone probably decreased abruptly by sediment trapping in piedmont lakes related to deglaciation, resulting in a sudden decrease of sediment supply to the ocean. Additionally, reduced moisture supply may have contributed to the rapid decline of turbidite deposition. These different causes result in similar depositional patterns in the marine sinks. We conclude that turbiditic strata may constitute reliable recorders of climate change across a wide range of climatic zones and geomorphic conditions. However, the underlying causes for similar signal manifestations in the sinks may differ, ranging from maintained high system connectivity to abrupt connectivity loss.

The Impact of Mass Movement and Fluid Flow during Ridge Subduction inferred from Physical Properties and Zeolite Assemblage in the Upper Plate Slope of the Costa Rica Subduction Zone

NASA Astrophysics Data System (ADS)

Hamahashi, M.; Screaton, E.; Tanikawa, W.; Hashimoto, Y.; Martin, K. M.; Saito, S.; Kimura, G.

2015-12-01

The Costa Rica subduction zone offshore Osa Peninsula is known as an erosive margin with active seismicity and the subduction of the Cocos Ridge. One of the major unknowns in this margin is the nature of the unconformity at the base of the slope sediments in the upper plate and the high velocity materials below. To investigate the geologic processes across the unconformity, we examined the consolidation state and mineral assemblages of the sediments at the mid-slope Site 1380 drilled during IODP Expedition 344 by conducting microstructural observation, particle size analysis, X-ray fluorescence/diffraction analysis and resistivity measurement. The general compaction trend is controlled primarily by grain-size sorting and the physical property transition is likely caused by massive sediment removal under normal fault regime, thickness of which range between ~600-850 m determined from the composite porosity-depth curve. Across the unconformity between the late Pliocene~late Pleistocene silty clay (Unit 1) and late Pliocene~early Pleistocene clayey siltstone (Unit 2), the mineral/element components of the sediments is marked by the transitions in zeolite compositions; Unit 1 consists of laumontite and heulandite, whereas below the unconformity, Unit 2 sediments contain analcime, laumontite, and heulandite, but laumontite become less abundant at lower depth. The experienced temperature of the sediments in Unit 2 is estimated to have reached between ~86 and 122℃ as inferred from analcime burial diagenesis. This may correspond with the greater depth range prior to mass movement and normal faulting. The initial analcime burial diagenetic zone was likely cut off by the sediment removal across the unconformity, and later overprinted by high temperature fluid along the boundary forming laumontite and heulandite in the vicinity. These results illustrate that ridge subduction has substantial potential to cause mass movement, an extensional stress regime, and fluid flow from depth.

The Influence of Coastal Wetland Zonation on Surface Sediment and Porewater Mercury Speciation

NASA Astrophysics Data System (ADS)

Marvin-DiPasquale, M. C.; Windham-Myers, L.; Wilson, A. M.; Buck, T.; Smith, E.

2014-12-01

An investigation of mercury (Hg) speciation in saltmarsh surface sediment (top 0-2 cm) and porewater (integrated 0-50 cm) was conducted along two monitoring well transects established within North Inlet Estuary (S. Carolina, USA) as part of the NOAA sponsored National Estuarine Research Reserve (NERR) network. Transects were perpendicular to the shoreline, from the forested uplands to the edge of the tidal channel, and traversed a range of vegetated zones from the high marsh (pickleweed, rush, and salt panne-dominated) to the low marsh (cordgrass dominated), as mediated by elevation and tidal inundation. Sediment grain size and organic content explained 95% of the variability in the distribution of total Hg (THg) in surface sediment. Tin-reducible 'reactive' mercury (HgR) concentration was 10X greater in the high marsh, compared to the low marsh, and increased sharply with decreasing sediment pH values below pH=6. The percentage of THg as HgR decreased as sediment redox conditions became more reducing. There were no significant differences in surface sediment methylmercury (MeHg) concentrations between high and low marsh zones. In contrast, porewater MeHg concentrations were 5X greater in the high marsh compared to the low marsh. As a percentage of THg, mean porewater %MeHg was 23% in the low marsh and 51% in the high marsh, reaching levels of 73-89% in a number of high marsh sites. Calculations of partitioning between porewater and the solid phase suggest stronger binding to particles in the low marsh and a shift towards the dissolved phase in the high marsh for both THg and MeHg. These results are consistent with a conceptual model for coastal wetlands where the less frequently inundated high marsh zone may be important in terms of MeHg production and enhanced subsurface mobilization, partially due to the subsurface mixing of saline estuarine water and freshwater draining in from the uplands area.

Predicting Martian dune shape and orientation from wind directional variability and sediment availability

NASA Astrophysics Data System (ADS)

Fernandez-Cascales, Laura; Lucas, Antoine; Rodriguez, Sébastien; Narteau, Clément; Spiga, Aymeric; Allemand, Pascal

2016-04-01

Dunes provide a unique set of information to constrain local climatic regimes on planetary bodies where there is no direct meteorological data. Wind directional variability and sediment availability are known to control the dune growth mechanism (i.e. the bed instability or fingering modes) and the subsequent dune shape and orientation (Courrech du Pont at al., 2014; Gao et al., 2015). Here we provide a quantitative analysis of these dependences on Mars using the output of the Martian General Circulation Models (GCM) and satellite imagery such as the Mars Reconnaissance Orbiter (MRO) Context Camera (CTX) images, at a selection of places where there is a high contrast between the dune material and the non-erodible ground. Dunes, mostly composed of unweathered basaltic and andesitic grains, appear dark, whereas the non-erodible ground has a higher albedo. Such a systematic contrast permits to link dune morphology to the local sediment cover. Dune shape, crest orientation and local sediment cover are extracted from CTX images using an automatic linear segment detection method and the local distribution in albedo. In zones of high sediment supply, dune crest alignments are close to the orientation of the bed instability mode predicted from the local winds from the Martian Climate Database (MCD) where is stored the outputs of the IPSL-GCM for Mars (Millour et al., 2014). Using the same wind data, in zones of low sediment supply, the crest angle is close to the orientation of the fingering mode. In addition, there are continuous transitions in dune shape and orientation as the dunes migrate from zone of high to low sediment availability. These results indicate that the prediction of the IPSL-GCM are in good agreement with the present dune shapes and orientations and shed new light on the dynamics of complex dune fields along sand flow path.

Comments on the Parameters and Processes that Affect the Preservation Potential and Style of Oblique-Divergent Plate Boundaries

NASA Astrophysics Data System (ADS)

Umhoefer, P. J.

2014-12-01

Oblique-divergent or transtensional zones present particular challenges in ancient belts because of the poor preservation potential of the thinned continental crust and young oceanic crust. Many oblique belts will preferentially preserve their boundary zones that lie within continents rather than the main plate boundary zone, which will be at a much lower elevation and composed of denser crust. Zones of tectonic escape or strike-slip overprinting of arcs or plateaus deform continental crust and may be better preserved. Here I highlight parameters and processes that have major effects on oblique divergent belts. Strain partitioning is common, but not ubiquitous, along and across oblique boundaries; the causes of partitioning are not always clear and make this especially vexing for work in ancient belts. Partitioning causes complexity in the patterns of structures at all scales. Inherited structures commonly determine the orientation and style of structures along oblique boundaries and can control the pattern of faults across transtensional belts. Regionally, inherited trends of arcs or other 1000-km-scale features can control boundary structures. Experiments and natural examples suggest that oblique boundary zones contain less of a record of strike-slip faulting and more extensional structures. The obliquity of divergence produces predictable families of structures that typify (i) strike-slip dominated zones (obliquity <~20°), (ii) mixed zones (~20° - ~35°), and (iii) extension dominated zones (>~35°). The combination of partitioning and mixed structures in oblique zones means that the boundaries of belts with large-magnitude strike-slip faulting will commonly preserve little of no record of that faulting history. Plate boundaries localize strain onto the main plate boundary structures from the broader plate boundary and therefore the boundary zones commonly preserve the earlier structures more than later structures, a major problem in interpreting ancient belts. Sediment input is critical in some oblique plate boundaries because these belts become more pronounced sediment sinks over time. The evolving topography of oblique boundaries means that they have great variability of sediment flux into differing parts of the system; large rivers enter these belts only in special circumstances.

Hurricane Katrina sediment slowed elevation loss in subsiding brackish marshes of the Mississippi River delta

USGS Publications Warehouse

McKee, K.L.; Cherry, J.A.

2009-01-01

Although hurricanes can damage or destroy coastal wetlands, they may play a beneficial role in reinvigorating marshes by delivering sediments that raise soil elevations and stimulate organic matter production. Hurricane Katrina altered elevation dynamics of two subsiding brackish marshes in the Mississippi River deltaic plain by adding 3 to 8 cm of sediment to the soil surface in August 2005. Soil elevations at both sites subsequently declined due to continued subsidence, but net elevation gain was still positive at both Pearl River (+1.7 cm) and Big Branch (+0.7 cm) marshes two years after the hurricane. At Big Branch where storm sediments had higher organic matter and water contents, post-storm elevation loss was more rapid due to initial compaction of the storm layer in combination with root-zone collapse. In contrast, elevation loss was slower at Pearl River where the storm deposit (high sand content) did not compact and the root zone did not collapse. Vegetation at both sites fully recovered within one year, and accumulation of root matter at Big Branch increased 10-fold from 2005 to 2006, suggesting that the hurricane stimulated belowground productivity. Results of this study imply that hurricane sediment may benefit subsiding marshes by slowing elevation loss. However, long-term effects of hurricane sediment on elevation dynamics will depend not only on the amount of sediment deposited, but on sediment texture and resistance to compaction as well as on changes in organic matter accumulation in the years following the hurricane.

Effects of bottom water dissolved oxygen variability on copper and lead fractionation in the sediments across the oxygen minimum zone, western continental margin of India.

PubMed

Chakraborty, Parthasarathi; Chakraborty, Sucharita; Jayachandran, Saranya; Madan, Ritu; Sarkar, Arindam; Linsy, P; Nath, B Nagender

2016-10-01

This study describes the effect of varying bottom-water oxygen concentration on geochemical fractionation (operational speciation) of Cu and Pb in the underneath sediments across the oxygen minimum zone (Arabian Sea) in the west coast of India. Both, Cu and Pb were redistributed among the different binding phases of the sediments with changing dissolved oxygen level (from oxic to hypoxic and close to suboxic) in the bottom water. The average lability of Cu-sediment complexes gradually decreased (i.e., stability increased) with the decreasing dissolved oxygen concentrations of the bottom water. Decreasing bottom-water oxygen concentration increased Cu association with sedimentary organic matter. However, Pb association with Fe/Mn-oxyhydroxide phases in the sediments gradually decreased with the decreasing dissolved oxygen concentration of the overlying bottom water (due to dissolution of Fe/Mn oxyhydroxide phase). The lability of Pb-sediment complexes increased with the decreasing bottom-water oxygen concentration. This study suggests that bottom-water oxygen concentration is one of the key factors governing stability and lability of Cu and Pb complexes in the underneath sediment. Sedimentary organic matter and Fe/Mn oxyhydroxide binding phases were the major hosting phases for Cu and Pb respectively in the study area. Increasing lability of Pb-complexes in bottom sediments may lead to positive benthic fluxes of Pb at low oxygen environment. Copyright © 2016 Elsevier B.V. All rights reserved.

Bee diversity assemblage on pigeon pea, Cajanus cajan along habitat gradient.

PubMed

Makkar, Gurpreet Singh; Chhuneja, Pardeep K

2016-11-01

The regional bee diversity was investigated on pigeon pea in three agroclimatic zones of Punjab state in northern India. Of the total nine species recorded, population of Megachilids, in particular, was significantly higher in all the three zones. Appraisal of diversity metrics revealed highest bee community diversity in Sub-mountain Undulating zone, followed by Central Plain zone, while least diversity was noted in Western zone, which highlighted the effect of habitat on species richness and abundance. Diurnal variations were evident with the most diverse bee communities recorded at 11:00 hr, followed by at 14:00 and 08:00 hr, with the lowest community diversity at 17:00 hr. The relative abundance of bee species was highly in favour of non-Apis species than Apis species. The results obtained can be used in the application of risk management through planned plant protection measures, study of plant-pollinator interactions along with conservation and augmentation of bee species.

Colloid-facilitated transport of cesium in variably saturated Hanford sediments.

PubMed

Chen, Gang; Flury, Markus; Harsh, James B; Lichtner, Peter C

2005-05-15

Radioactive 137Cs has leaked from underground waste tanks into the vadose zone at the Hanford Reservation in south-central Washington State. There is concern that 137Cs, currently located in the vadose zone, can reach the groundwater. In this study, we investigated whether, and to what extent, colloidal particles can facilitate the transport of 137Cs at Hanford. We used colloidal materials isolated from Hanford sediments. Transport experiments were conducted under variably saturated, steady-state flow conditions in repacked, 20 cm long Hanford sediment columns, with effective water saturations ranging from 0.2 to 1.0. Cesium, pre-associated with colloids, was stripped off during transport through the sediments. The higher the flow rates, the less Cs was stripped off, indicating in part that Cs desorption from carrying colloids was a residence-time-dependent process. Depending on the flow rate, up to 70% of the initially sorbed Cs desorbed from colloidal carriers and was captured in the stationary sediments. Less Cs was stripped off colloids under unsaturated than under saturated flow conditions at similar flow rates. This phenomenon was likely due to the reduced availability of sorption sites for Cs on the sediments as the water content decreased and water flow was divided between mobile and immobile regions.

Gravitropism in caulonemata of the moss Pottia intermedia

NASA Technical Reports Server (NTRS)

Chaban, C. I.; Kern, V. D.; Ripetskyj, R. T.; Demkiv, O. T.; Sack, F. D.

1998-01-01

The gravitropism of caulonemata of Pottia intermedia is described and compared with that of other mosses. Spore germination produces primary protonemata including caulonemata which give rise to buds that form the leafy moss plant, the gametophore. Primary caulonemata are negatively gravitropic but their growth and the number of filaments are limited in the dark. Axenic culture of gametophores results in the production of secondary caulonemata that usually arise near the leaf base. Secondary protonemata that form in the light are agravitropic. Secondary caulonemata that form when gametophores are placed in the dark for several days show strong negative gravitropism and grow well in the dark. When upright caulonemata are reorientated to the horizontal or are inverted, upward bending can be detected after 1 h and caulonemata reach the vertical within 1-2 d. Clear amyloplast sedimentation occurs 10-15 minutes after horizontal placement and before the start of upward curvature. This sedimentation takes place in a sub-apical zone. Amyloplast sedimentation also takes place along the length of upright and inverted Pottia protonemata. These results support the hypothesis that amyloplast sedimentation functions in gravitropic sensing since sedimentation occurs before gravitropism in Pottia and since the location and presence of a unique sedimentation zone is conserved in all four mosses known to gravitropic protonomata.

[Alternative stable states in coastal intertidal wetland ecosystems of Yangtze estuary, China].

PubMed

Li, Hui; Yuan, Lin; Zhang, Li Quan; Li, Wei; Li, Shi Hua; Zhao, Zhi Yuan

2017-01-01

Alternative stable states phenomenon widely exists in a variety of ecosystems and is closely related to ecosystem health and sustainable development. Although alternative stable states research has become the focus and hotspot of the ecology researches, only a few empirical evidences supported its behavior and mechanisms in coastal wetland ecosystems up to now. In our study, ta-king the intertidal wetland ecosystem in Chongming Dongtan Nature Reserve as study area, we aimed to: 1) test the existence of alternative stable states based on judgment conditions (bimodal characteristic and threshold effect) and determine the relative stable state types; 2) explore the formation mechanisms of alternative stable states by monitoring hydrological conditions, sediment accretion dynamics as well as vegetation growth parameters and analyzing the positive feedbacks between saltmarsh vegetation and sedimentary geomorphology. Our results showed that: 1) Normalized difference vegetation index (NDVI) frequentness distribution revealed obvious bimodality at saltmarsh pioneer zone. Propagule biomass threshold limited the establishment of plant patches representing the "saltmarsh" state. The presence of bimodality and biomass threshold demonstrated there are "mudflat" stable state and "saltmarsh" stable state with distinct structure and function in intertidal wetland ecosystem. 2) Current velocities, turbidities and direction perpendicular to the vegetation zone were the most important factors responsible for the sediments rapid accretion at saltmarsh pioneer zone in spring and summer. Sediments accretion significantly promoted the growth of saltmarsh plant. The positive feedbacks between plant growth and sediments accretion resulted in the formation of alternative stable states. 3) The expansion pattern of saltmarshes in the Chongming Dongtan intertidal wetland ecosystem also suggested that increases of sediments accretion could trigger the formation of "mudflat" stable state and "saltmarsh" stable state on landscape scale. The results from this study could enrich regime shift mechanisms researches and provide the scientific supports for coastal zone protection, restoration and comprehensive management, which could have important theoretical and practical meaning.

3D Porosity Estimation of the Nankai Trough Sediments from Core-log-seismic Integration

NASA Astrophysics Data System (ADS)

Park, J. O.

2015-12-01

The Nankai Trough off southwest Japan is one of the best subduction-zone to study megathrust earthquake fault. Historic, great megathrust earthquakes with a recurrence interval of 100-200 yr have generated strong motion and large tsunamis along the Nankai Trough subduction zone. At the Nankai Trough margin, the Philippine Sea Plate (PSP) is being subducted beneath the Eurasian Plate to the northwest at a convergence rate ~4 cm/yr. The Shikoku Basin, the northern part of the PSP, is estimated to have opened between 25 and 15 Ma by backarc spreading of the Izu-Bonin arc. The >100-km-wide Nankai accretionary wedge, which has developed landward of the trench since the Miocene, mainly consists of offscraped and underplated materials from the trough-fill turbidites and the Shikoku Basin hemipelagic sediments. Particularly, physical properties of the incoming hemipelagic sediments may be critical for seismogenic behavior of the megathrust fault. We have carried out core-log-seismic integration (CLSI) to estimate 3D acoustic impedance and porosity for the incoming sediments in the Nankai Trough. For the CLSI, we used 3D seismic reflection data, P-wave velocity and density data obtained during IODP (Integrated Ocean Drilling Program) Expeditions 322 and 333. We computed acoustic impedance depth profiles for the IODP drilling sites from P-wave velocity and density data. We constructed seismic convolution models with the acoustic impedance profiles and a source wavelet which is extracted from the seismic data, adjusting the seismic models to observed seismic traces with inversion method. As a result, we obtained 3D acoustic impedance volume and then converted it to 3D porosity volume. In general, the 3D porosities show decrease with depth. We found a porosity anomaly zone with alteration of high and low porosities seaward of the trough axis. In this talk, we will show detailed 3D porosity of the incoming sediments, and present implications of the porosity anomaly zone for the megathrust fault behavior.

Hydrologically Controlled Arsenic Release in Deltaic Wetlands and Coastal Riparian Zones

NASA Astrophysics Data System (ADS)

Stuckey, J.; LeMonte, J. J.; Yu, X.; Schaefer, M.; Kocar, B. D.; Benner, S. G.; Rinklebe, J.; Tappero, R.; Michael, H. A.; Fendorf, S. E.; Sparks, D. L.

2016-12-01

Wetland and riparian zone hydrology exerts critical controls on the biogeochemical cycling of metal contaminants including arsenic. The role of wetlands in driving geogenic arsenic release to groundwater has been debated in the deltas of South and Southeast Asia where the largest impacted human population resides. In addition, groundwater in coastal areas worldwide, such as those in South and Southeast Asia and the Mid-Atlantic of the U.S., is at risk to largely unexplored biogeochemical and hydrologic impacts of projected sea level rise. First, we present data from fresh-sediment incubations, in situ model sediment incubations and a controlled field experiment with manipulated wetland hydrology and organic carbon inputs in the minimally disturbed upper Mekong Delta. Here we show that arsenic release is limited to near-surface sediments of permanently saturated wetlands where both organic carbon and arsenic-bearing solids are sufficiently reactive for microbial oxidation of organic carbon and reduction of arsenic-bearing iron oxides. In contrast, within the deeper aquifer or seasonally saturated sediments, reductive dissolution of iron oxides is observed only when either more reactive exogenous forms of iron oxides or organic carbon are added, revealing a potential thermodynamic restriction to microbial metabolism. Second, in order to assess the potential impacts of sea level rise on arsenic release to groundwater, we determined the changes in arsenic speciation and partitioning in sediment collected from an anthropogenically contaminated coastal riparian zone under controlled Eh regimes in both seawater and freshwater systems. Here we show greater arsenic release under anoxic/suboxic conditions in the freshwater system than in the seawater system, potentially due to high salinity induced microbial inhibition. Collectively, our work shows that shifting hydrologic conditions in deltaic wetlands and tidally influenced zones impacts the extent of arsenic release to groundwater. Land and water management decisions that increase the duration of wetland inundation may promote arsenic release to groundwater.

Elevated gas hydrate saturation within silt and silty clay sediments in the Shenhu area, South China Sea

USGS Publications Warehouse

Wang, X.; Hutchinson, D.R.; Wu, S.; Yang, S.; Guo, Y.

2011-01-01

Gas hydrate saturations were estimated using five different methods in silt and silty clay foraminiferous sediments from drill hole SH2 in the South China Sea. Gas hydrate saturations derived from observed pore water chloride values in core samples range from 10 to 45% of the pore space at 190-221 m below seafloor (mbsf). Gas hydrate saturations estimated from resistivity (Rt) using wireline logging results are similar and range from 10 to 40.5% in the pore space. Gas hydrate saturations were also estimated by P wave velocity obtained during wireline logging by using a simplified three-phase equation (STPE) and effective medium theory (EMT) models. Gas hydrate saturations obtained from the STPE velocity model (41.0% maximum) are slightly higher than those calculated with the EMT velocity model (38.5% maximum). Methane analysis from a 69 cm long depressurized core from the hydrate-bearing sediment zone indicates that gas hydrate saturation is about 27.08% of the pore space at 197.5 mbsf. Results from the five methods show similar values and nearly identical trends in gas hydrate saturations above the base of the gas hydrate stability zone at depths of 190 to 221 mbsf. Gas hydrate occurs within units of clayey slit and silt containing abundant calcareous nannofossils and foraminifer, which increase the porosities of the fine-grained sediments and provide space for enhanced gas hydrate formation. In addition, gas chimneys, faults, and fractures identified from three-dimensional (3-D) and high-resolution two-dimensional (2-D) seismic data provide pathways for fluids migrating into the gas hydrate stability zone which transport methane for the formation of gas hydrate. Sedimentation and local canyon migration may contribute to higher gas hydrate saturations near the base of the stability zone. Copyright 2011 by the American Geophysical Union.

Idaho National Laboratory Vadose Zone Research Park Geohydrological Monitoring Results

DOE Office of Scientific and Technical Information (OSTI.GOV)

Kristine Baker

2006-01-01

Vadose zone lithology, hydrological characterization of interbed sediments, and hydrological data from subsurface monitoring of Idaho Nuclear Technology and Engineering Center wastewater infiltration are presented. Three-dimensional subsurface lithology of the vadose zone beneath the Vadose Zone Research Park is represented in a 2 dimensional (2 D) diagram showing interpolated lithology between monitoring wells. Laboratory-measured values for saturated hydraulic conductivity and porosity are given for three major interbeds, denoted as the B BC interbed (20 to 35 m bls), the C D interbed (40 to 45 m bls), and the DE 1 2 interbed (55 to 65 m bls), along withmore » an overall physical description of the sediments and geologic depositional environments. Pre-operational pore water pressure conditions are presented to show the presence and location of perched water zones before pond discharge at the New Percolation Ponds. Subsurface infiltration conditions during initial high-volume discharge are presented to show water arrival times and arrival sequences. Steady-state conditions are then presented to show formation and locations of perched water zones and recharge sources after several months of discharge to the New Percolation Ponds.« less

THESIS: terrestrial and habitable zone infrared spectroscopy spacecraft

NASA Astrophysics Data System (ADS)

Vasisht, G.; Swain, M. R.; Akeson, R. L.; Burrows, A.; Deming, D.; Grillmair, C. J.; Greene, T. P.

2008-07-01

THESIS is a concept for a medium class mission designed for spectroscopic characterization of extrasolar planets between 2-14 microns. The concept leverages off the recent first-steps made by Spitzer and Hubble in characterizing the atmospheres of alien gas giants. Under favourable circumstances, THESIS is capable of identifying biogenic molecules in habitable-zone planets, thereby determining conditions on worlds where life might exist. By systematically characterizing many worlds, from rocky planets to gas-giants, THESIS would deliver transformational science of profound interest to astronomers and the general public.

High-resolution chronology of sediment below CCD based on Holocene paleomagnetic secular variations in the Tohoku-oki earthquake rupture zone

NASA Astrophysics Data System (ADS)

Kanamatsu, Toshiya; Usami, Kazuko; McHugh, Cecilia M. G.; Ikehara, Ken

2017-08-01

Using high-resolution paleomagnetic data, we examined the potential for obtaining precise ages from sediment core samples recovered from deep-sea basins close to rupture zones of the 2011 and earlier earthquakes off Tohoku, Japan. Obtaining detailed stratigraphic ages from deep-sea sediments below the calcium compensation depth (CCD) is difficult, but we found that the samples contain excellent paleomagnetic secular variation records to constrain age models. Variations in paleomagnetic directions obtained from the sediments reveal systematic changes in the cores. A stacked paleomagnetic profile closely matches the Lake Biwa data sets in southwest Japan for the past 7000 years, one can establish age models based on secular variations of the geomagnetic field on sediments recovered uniquely below the CCD. Comparison of paleomagnetic directions near a tephra and a paleomagnetic direction of contemporaneous pyroclastic flow deposits acquired by different magnetization processes shows precise depositional ages reflecting the magnetization delay of the marine sediment record.