Cerralbo, Pablo; Grifoll, Manel; Valle-Levinson, Arnoldo; Espino, Manuel
Tidal and subtidal waves are analyzed with sea-level data and numerical modeling in a short and micro-tidal embayment, Alfacs Bay (NW Mediterranean Sea). Data analysis exhibits tidal wave amplification and seiching (characteristic period of 3.5 h) along the bay. Numerical results show an eight-fold increase in quarter-wave resonant wave amplitudes from the mouth to the head of the bay. This amplification follows the classical description of a standing wave. Moreover, resonant wave velocities measured and computed at the bay mouth (node location) are about one order of magnitude higher than tidal currents. Analysis of astronomic tidal propagation in the bay reveals similar behavior for diurnal and semidiurnal constituents. Tidal waves amplify along the bay by 3% for diurnal and 10% for semidiurnal constituents. Numerical simulations conducted with different domains indicate that geometric effects dominate over frictional influences in causing the wave behavior. This behavior is consistent with the existence of a quasi-steady standing wave within the bay.
Llebot, Clara; Rueda, Francisco J.; Solé, Jordi; Artigas, Mireia Lara; Estrada, Marta
A conceptual model of the physical behavior of a shallow (6 m deep) micro-tidal estuary (Alfacs Bay) is proposed, based on the interpretation of a field data set, and subsequently tested against the results of three-dimensional hydrodynamic simulations. At seasonal timescales, the buoyancy associated with freshwater inflows dominates the tidal forcing, yielding a strongly stratified two-layered system, with the surface and the bottom layers flowing in opposite directions (classical estuarine circulation). Wind controls the physical behavior of the bay at shorter (days to weeks) timescales. Three scenarios or states have been defined, depending on the strength of stratification relative to the predominant direction and magnitude of the wind forcing, parameterized through the Wedderburn number, W. For weak winds (scenario 1), with W ≫ 1, mixing occurs as a consequence of stirring and convective cooling, and the mixed layer deepens slowly. For strong winds, with W ≪ 1/2, mixing is fast and is largely driven by shear at the pycnocline. Two scenarios are further identified for W ≪ 1/2 depending on the directionality of the winds: one for persistent NW winds (scenario 2) and another for diurnal SW winds (scenario 3). In scenario 2, the water is pushed laterally, overturning the stratification and generating transverse density gradients. In scenario 3, the estuarine circulation is weakened and even reversed, yielding strong longitudinal density gradients. The bay waters relax quickly (within 10-18 h) back to the original state, after the wind ceases, as a result of the horizontal density gradients developed under wind forcing. Bay-sea exchange rates are shown to decrease significantly in the low W scenarios, the magnitudes of these changes being largely dependent on wind direction. These scenarios have important implications for the ecology of the bay, including the occurrence of phenomena such as harmful algal blooms.
Loureiro, Sofia; Garcés, Esther; Fernández-Tejedor, Margarita; Vaqué, Dolors; Camp, Jordi
Samples were collected during one annual cycle (April 2007-March 2008) at Alfacs Bay (NW Mediterranean Sea) central station in order to assess the influence of organic nutrients in the growth of the microalgae assemblage, with special reference to Pseudo-nitzschia spp. This potentially toxic diatom forms natural and recurrent blooms in the study area. To assess further the relationship between Pseudo-nitzschia spp. and nutrients an enrichment experiment with high molecular weight dissolved organic matter (HMWDOM) was performed with field samples obtained during a Pseudo-nitzschia spp. bloom. HMWDOM was extracted from water collected at Alfacs Bay. Five bioassays were prepared: N + P (seawater with addition of nitrate and phosphate), DOM (addition of HMWDOM), (-N + P) + DOM (nitrogen deficient, with addition of phosphate and HMWDOM), (N + P) + DOM (addition of nitrate, phosphate and HMWDOM), seawater control (without added nutrients), and B + DOM (control of bacteria, without microalgae). The experiment was run in batch mode over 4 days. Results from the field study revealed that the concentrations of organic nutrients mostly surpassed the inorganic pool. Pseudo-nitzschia spp. was the most frequent and abundant taxa of the microalgae community. The micro-planktonic assemblage was arranged according to a seasonal factor (ANOSIM and cluster analysis). DON, nitrate and silicate were the most important abiotic parameters contributing to the dissimilarities between seasons (SIMPER analysis) and thereby potentially influencing the seasonal distribution of microalgae in the representative station. In the experimental investigation, Pseudo-nitzschia cells increased by the end of the experiment in the DOM bioassay but no respective increase was observed for chlorophyll a. This could point to an acquisition of nutrients through the DOM fraction that would conjointly reduce the need of chlorophyll a. The data obtained suggest that organic nutrients may exert an important role
This study investigated the effects of green tea polyphenols (GTP) and alfacalcidol on bone microstructure and strength along with possible mechanisms in rats with chronic inflammation. A 12-week study using a 2 (no GTP vs. 0.5%, w/v GTP in drinking water) × 2 (no alfacalcidol vs. 0.05 ug/kg alfacal...
Grifoll, Manel; Solà, Laura; Cerralbo, Pablo; Espino, Manuel
Suspended matter near the bed have been recorded through Optical Backscatter Sensors (OBS), jointly with water current and sea-level measurements, in Alfacs Bay (NW Mediterranean Sea). This bay (16 km length and 4 km width) is characterized by a micro-tidal environment, relative shallow depth (max. 6.5 m) and freswater discharges from the drainage channels of the sourrounding rice fields. OBS voltage gain show an evident relation with energetic hydrodynamic processes, which included strong wind events and seiche episodes. The periodic traffic vessel is also a mechanism responsible of the resuspension of fine bed sediment. Still most of the OBS signal have been well characterized with physical conditions, some peaks remains unexplained. This work is a first step of a complete investigation of fine sediment dynamics in Alfacs Bay, which also include a wave-current numerical model implementation.
Cerralbo, Pablo; Grifoll, Manel; Espino, Manuel
In this contribution we investigate the hydrodynamic response in a micro-tidal and shallow semi-enclosed domain. We chose a set of observations which include currents, hydrography and meteorological data obtained in Alfacs Bay (NW Mediterranean Sea). Short-term response to energetic wind events was found in the hydrography and water velocity observations, sometimes inverting the estuarine circulation or developing one-layered flow. In comparison to previous investigations in Alfacs Bay, we observed that water current variability, and also maximum velocities, were directly related to the development of surface standing waves (i.e. seiches). Mixing mechanisms versus buoyancy sources are studied through potential energy anomaly equation, proving the leading freshwater contribution to stratification, enhanced by heat fluxes in summer. On the other hand, mixing is directly related to winds, mainly in winter and early spring when both buoyancy forces are lower. We also study turbulent bottom mixing by seiches through observations, dimensionless relations and numerical modeling. Seiche induced mixing is suggested as an eventual mechanism that may break the stratification within the Bay under special circumstances.
Cerralbo, Pablo; Grifoll, Manel; Espino, Manuel
The Ebro Delta (NW Mediterranean Sea) is characterized by the presence of two semi-enclosed bays: Alfacs and Fangar. Both bays receive direct freshwater input from drain channels of rice fields. Southern Bay, Alfacs, is about 14km long by 4km wide with an average depth of about 3.1 m (maximum of 6.5 m in the middle). The mouth is about 2.5 km wide. The non-tidal flow in the area has been studied in the past, showing a persistent structure during most of the year: a salty layer in the bottom and freshwater layer on top due to freshwater input. The bay is micro-tidal, with a mixed tidal regime. An extensive field campaign was designed in order to characterize the hydrodynamic and T/S patterns during summer. First CTD transects were conducted during June 2012 and July 2013. Moreover, the positions of lagrangian drifters were tracked recording trajectories at sub-surface waters. Finally, two moored stations (within the Bay and Mouth) allowed to obtain hydrodynamic and T/S conditions during two-month period in summer 2013. Atmospheric data were obtained from three fixed land stations. Data analysis showed density differences from surface to bottom in the middle of the bay around 3-5 kg/m3 and almost constant over all the period. The density profiles seems to be controlled mainly from freshwater contributions (differences of 1.5 in salinity), although heat fluxes in summer contributes positively to the column stabilization (maximum vertical temperature differences of 5-6ºC). Observed well-mixed conditions were related with energetic wind events (northerly winds). The variability on water circulation is dominated by seiches (3h and 1h), with a clear barotropic mode and maximum intensities of 50 cm·s-1. These variability is modulated by diurnal winds (sea breeze regimes). On the other hand, low frequency motion is controlled by baroclinic estuarine circulation.
Rivetti, Claudia; Gómez-Canela, Cristian; Lacorte, Silvia; Barata, Carlos
Microcystins, anatoxins and okadaic acid are toxins produced by freshwater cyanobacteria and marine dinoflagellates. These toxins have been the responsible for the illness and death of biota and humans. To determine their presence in water during blooms, sensitive analytical methods are needed. In this study, we have developed a new liquid chromatography tandem mass spectrometry (LC-MS/MS) method for fast multiresidue determination of five toxins in suspended material and sediment samples. For each target compound, two selected reaction monitoring (SRM) transitions were optimised. Chromatographic conditions were optimised considering that the compounds analysed had different chemical structure and chromatographic behaviour. Using a Luna C18 column and specific SRM transitions, five phytotoxins were resolved. Method detection limits (MDL) for anatoxin-a, microcystins RR, LR and YR and okadaic acid were 7.1, 3.3, 81.7, 102.8 and 28.8 ng g(-1) dry weight in sediment, respectively. The developed analytical method was successfully applied to analyse the presence of toxins in suspended solids and sediment from Ebro River (NE Spain) and Ebro delta-associated lagoons. Anatoxin-a was detected downstream of the Riba-Roja reservoir with levels ranging from 20 to 1120 ng g(-1) dry weight of suspended solids. Okadaic acid was only detected in three samples collected in the Alfacs Bay (Ebro delta, Spain) affected by Dinophysis blooms in 2012. PMID:25619981
Cerralbo, Pablo; Espino, Manuel; Grifoll, Manel
This contribution shows the importance of the cross-shore spatial wind variability in the water circulation in a small-sized micro-tidal bay. The hydrodynamic wind response at Alfacs Bay (Ebro River delta, NW Mediterranean Sea) is investigated with a numerical model (ROMS) supported by in situ observations. The wind variability observed in meteorological measurements is characterized with meteorological model (WRF) outputs. From the hydrodynamic simulations of the bay, the water circulation response is affected by the cross-shore wind variability, leading to water current structures not observed in the homogeneous-wind case. If the wind heterogeneity response is considered, the water exchange in the longitudinal direction increases significantly, reducing the water exchange time by around 20%. Wind resolutions half the size of the bay (in our case around 9 km) inhibit cross-shore wind variability, which significantly affects the resultant circulation pattern. The characteristic response is also investigated using idealized test cases. These results show how the wind curl contributes to the hydrodynamic response in shallow areas and promotes the exchange between the bay and the open sea. Negative wind curl is related to the formation of an anti-cyclonic gyre at the bay's mouth. Our results highlight the importance of considering appropriate wind resolution even in small-scale domains (such as bays or harbors) to characterize the hydrodynamics, with relevant implications in the water exchange time and the consequent water quality and ecological parameters.
Artigas, M. L.; Llebot, C.; Ross, O. N.; Neszi, N. Z.; Rodellas, V.; Garcia-Orellana, J.; Masqué, P.; Piera, J.; Estrada, M.; Berdalet, E.
Understanding the spatio-temporal variability of phytoplankton in aquaculture zones is necessary for the prevention and/or prediction of harmful algal bloom events. Synoptic cruises, time series analyses of physical and biological parameters, and 3D modeling were combined to investigate the variability of phytoplankton biomass in Alfacs Bay at basin scale. This microtidal estuary located in the NW Mediterranean is an important area of shellfish and finfish exploitation, which is regularly affected by toxic outbreaks. Observations showed the existence of a preferential phytoplankton accumulation area on the NE interior of the bay. This pattern can be observed throughout the year, and we show that it is directly linked to the physical forcing in the bay, in particular, the interplay between freshwater input and wind-induced turbulence. Both drivers affect the strength of the estuarine circulation, explaining nearly 75% of the variability in phytoplankton biomass. More cells are retained when stratification is weakened and the estuarine circulation reduced, while flushing rates are higher during times of increased stratification and stronger estuarine flow. This has been confirmed by using a 3D hydrodynamic model with Eulerian tracers. Nutrients, while important to support phytoplankton populations, have been found to play only a secondary role in explaining this variability at basin scale.
Mascaró, O.; Romero, J.; Pérez, M.
In temperate regions, climatic factors impose a general seasonal pattern on seagrass growth that can be observed in leaf growth rates and, in small species, also in shoot density. Large variations in shoot density suggest a strong temporal uncoupling between shoot recruitment and shoot mortality, and the dependence of each of these processes on different drivers. Here we examine seasonal patterns of recruitment and mortality in the seagrass Cymodocea nodosa, one of the species most sensitive to seasonal forcing in the Mediterranean. We sampled two local populations submitted to different nutrient availability in Alfacs Bay (NW Mediterranean) and determined recruitment and mortality rates, as well as other plant traits, on a monthly basis. Our results confirm the hypothesized uncoupling, with maximum mortality 2 months after maximum recruitment. Whereas timing of recruitment was associated with light availability, and was supported by carbohydrate remobilisation, mortality was related to high water temperatures and probably also to light limitation in late summer due to self-shading. In the high-nutrient population, algal overgrowth caused further light deprivation, with mortality rates higher than in the low-nutrient population. It is emphasised that the demographic balance of the studied populations was negative for most of the year, with the exception of August and September. Therefore, caution is necessary when overall population trends are inferred from single annual sampling events.
Margulis, L.; Navarrete, A.; Sole, M.
Inocula from organic-rich black muds immediately underlying intertidal laminated microbial mats dominated by Microcoleus chthonoplastes yielded large, variable diameter spirochetes. These unusual spirochetes, previously reported only from the Alfacs Peninsula at the delta of the Ebro river in northeast Spain, contain striking arrays of cytoplasmic granules packed into their protoplasmic cylinders. On several occasions, both in summer and winter, the huge spirochetes were recognized in samples from mats growing in the Sippewissett salt marsh at Woods Hole Massachusetts. They were also seen in similar samples from microbial mats at North Pond, Laguna Figueroa, Baja California Norte, Mexico. The identity of these spirochetes was confirmed by electron microscopy: number and disposition of flagella, composite structure, measurements of their distinctive cytoplasmic granules. The granules, larger, more conspicuous and present in addition to ribosomes, are hypothesized to contain ATPases. As culture conditions worsen, these spirochetes retract into membrane-bounded round bodies in which they form refractile inclusions. From morphology and behavior we conclude the North American spirochetes from both Atlantic and Pacific intertidal microbial mats are indistinguishable from those at the delta of the Ebro river. We conclude a cosmopolitan distribution for Spirosymplokos deltaeiberi.
Grignon-Dubois, Micheline; Rezzonico, Bernadette; Alcoverro, Teresa
Secondary metabolites play an important role in protecting plants from herbivores or pathogens. Despite this, few studies have investigated the presence and the concentration of those compounds over broad spatial scales in seagrasses. Here we analysed the presence and abundance of specific phenolic compounds of Zostera noltii from four different meadows located across the Atlantic and the Mediterranean coast. Three phenolic acids have been found in the samples of Z. noltii: rosmarinic, caffeic and zosteric acids. The proportion of the three compounds varied substantially with the major proportion comprising rosmarinic acid (RA, mean value 94%) followed by zosteric acid (ZA, mean value 4%) and caffeic acid (CAF, mean value 2%). Z. noltii metabolic compounds varied notably between sites. The highest concentrations in RA were found in the Cadiz Bay with values of 11,254 (55 SD) μg g-1 dry wt, while the lowest were observed in the Alfacs Bay (Ebro) with values of 823 (7 SD) μg g-1 dry wt. The highest concentrations in ZA were also observed in the Cadiz Bay with values of 727 (6 SD) μg g-1 dry wt, while the lowest were observed in the Sa Nitja Bay (Menorca Island) with values of 20 (4 SD) μg g-1 dry wt. Finally, the concentrations in CAF remain very low at each site (17-69 μg g-1 dry wt), with the lowest observed in Arcachon. Their proportions remained relatively constant, indicating that most phenolic acids responded together. Documenting the presence of those compounds in living tissues of Z. noltii and how they vary in abundance between seagrass meadows across large geographical scales is a crucial first step to understand the large-scale level response of the plant to potential pathogens, herbivore outbreaks or other ecological processes.
Busch, Julia A.; Price, Ivan; Jeansou, Eric; Zielinski, Oliver; van der Woerd, Hendrik J.
Ocean colour measurements from space are well suited to assess phytoplankton dynamics over broad spatial scales. Closer to the coast however, the quality of these data degrades as a result of the loading of sediments and dissolved matter from terrestrial runoff, the influences of land reflection on atmospheric correction and sea-bottom reflection, which compromise their use in coastal management actions. Recently, the enabling of citizens to provide environmental observations has gained recognition as a way for enhancing the spatio-temporal coverage of satellite observations. In the FP7 funded EU project "Citclops" (Citizens' observatory for coast and ocean optical monitoring), a smart phone app for the classification of water colour, simplified to 21 hues of the Forel Ule (FU) scale, is developed. In this study we examine two bays in the Ebro Delta (NW Mediterranean) where satellite data, hyperspectral measurements, and observations with the citizen tool for colour comparison were available. FU values and their corresponding novel colorimetric parameter, the hue colour angle, were derived in the bay at 12 stations with the traditional FU scale and one automated in-situ radiometric system at the Alfacs Bay aquaculture site. Both methods complied well during the study course of May-June 2011. These measurements were further compared to data from Full Resolution MERIS (Medium Resolution Imaging Spectrometer) satellite images. The quality of the retrieved hue angle varies over the image. For high-quality sites, MERIS hue colour angles and FU values gave a good estimate of seasonal algal dynamics in the bays over the year 2011, while ground measurements revealed colour changes over short space- and time frames, which are indicative of the fast dynamics of phytoplankton in the area that could not be fully resolved with MERIS data. The use of FU values and hue colour angle of water will allow a simple integration of data from hyperspectral measurements, MERIS