Influence Of Freshwater Discharge Research Articles

Salinity data curation using CMIP6 projections and artificial neural network for the Bay of Bengal

ABSTRACT This study addresses the underrepresentation of the Bay of Bengal (BoB) in CMIP6 models, despite its significance in climate change research. Our objective is to propose a methodology to bridge this gap. Through skill score analysis, we identify CIESM as the optimal CMIP6 model for accurately estimating sea surface salinity in the northern BoB. Furthermore, we introduce the novel application of machine learning, specifically artificial neural networks, to enhance predictions from CIESM. This study pioneers the use of ML techniques to improve CMIP6 data for the BoB. Moreover, we examine the relationship between salinity and pH in the BoB, considering the influence of freshwater discharge from multiple rivers. Our findings demonstrate a positive correlation between salinity and pH, highlighting the role of freshwater influx in suppressing acidification. As the intensity of freshwater spread increases, the rate of acidification diminishes. This analysis method presents an efficient approach to curate oceanic parameter data like salinity, contributing to a better understanding of the BoB’s dynamics.

Hydrostatic Densitometer for Monitoring Density in Freshwater to Hypersaline Water Bodies

Density, temperature, salinity, and hydraulic head are physical scalars governing the dynamics of aquatic systems. In coastal aquifers, lakes, and oceans, salinity is measured with conductivity sensors, temperature is measured with thermistors, and density is calculated. However, in hypersaline brines, the salinity (and density) cannot be determined by conductivity measurements due to its high ionic strength. Here, we resolve density measurements using a hydrostatic densitometer as a function of an array of pressure sensors and hydrostatic relations. This system was tested in the laboratory and was applied in the Dead Sea and adjacent aquifer. In the field, we measured temporal variations of vertical profiles of density and temperature in two cases, where water density varied vertically from 1.0 × 103 kg·m−3 to 1.24 × 103 kg·m−3: (i) a borehole in the coastal aquifer, and (ii) an offshore buoy in a region with a diluted plume. The density profile in the borehole evolved with time, responding to the lowering of groundwater and lake levels; that in the lake demonstrated the dynamics of water-column stratification under the influence of freshwater discharge and atmospheric forcing. This method allowed, for the first time, continuous monitoring of density profiles in hypersaline bodies, and it captured the dynamics of density and temperature stratification.

Studies in Tidal Phenomena.(Dept.C)

As a result of complexity of the tidal current and water level prediction problem; before the computer time, reliance has mainly been placed on field measurements and tidal model studies to obtain a reliable picture of water levels and tidal currents in inlets, bays, and estuaries. The expense connected with either of these two methods has greatly restricted to amount of tidal current end tidal range informations. At the present, due to the increasing capacity of high speed digital computer end the different numerical techniques for solving the governing equations of motion, the use of mathematical models for tidal flow computation is quite well established. The main objective of this present study is to investigate the influence of boundary resistance on tidal wave propagating along an estuary or inlet and also on the tidal curerents. An increase of boundary resistance will decrease the tidal range and the corresponding tidal current. Resonance could occur at low value of boundary resistance, which will influence both the characteristics of tidal wave and tidal current. The influence of fresh water discharge in conjunction with boundary resistance on the tidal phenomena is also investigated.

Salinity drives growth dynamics of the mangrove tree Sonneratia apetala Buch. -Ham. in the Sundarbans, Bangladesh

Mangroves throughout the world are threatened by environmental changes apart from anthropogenic disturbances. Many of these changes may inhibit the growth and survival of mangrove species. To understand and predict the effects of global change on mangrove forests, it is necessary to obtain insights on the growth dynamics of mangroves in relation to environmental factors. This study was conducted on Sonneratia apetala, a mangrove species which grows under a range of salinity conditions across the Sundarbans in Bangladesh. We studied trees growing under respectively high, medium, and low salinity conditions based on the influence of freshwater discharge. First, the periodicity of radial growth across the year was detected by applying cambial analyses. Based on tree-ring analyses, we calculated the growth response of S. apetala to monthly variation in precipitation and temperature as well as river discharge, as a proxy for salinity. We found the cambium of S. apetala being active during the monsoon and post-monsoon period whereas it was dormant in the pre-monsoon. This periodicity in radial growth leads to the formation of distinct annual rings with ring boundaries being marked by radially flattened fibres. S. apetala trees growing under low salinity conditions generally show higher growth rates indicating the positive impact of river discharge, i.e. freshwater input on mangrove growth. Wet and warm conditions during the monsoon period positively affected S. apetala growth, especially in the low salinity zone. Our results show that salinity is the primary driver of growth dynamics of S. apetala in the Sundarbans. A gradual or seasonal increase in salinity, e.g. as a consequence of sea-level rise may therefore importantly alter the growth of this species, possibly leading to changes in mangrove forest dynamics and zonation.

Driving forces that structure sublittoral macrobenthic communities in sandy beaches along environmental gradients

Sandy beaches are very dynamic and changeable environments that present a wide variety of life forms, and, in some areas, high productivity. In the Gulf of Valencia (Western Mediterranean Sea, Spain) these areas have endured an economically important shellfishery of clams (Donax trunculus and Chamelea gallina). In the Mediterranean, a sea with a notable oligotrophic character, rivers are particularly important because of the contributions of fresh water that carry nutrients and organic matter to coastal ecosystems. Consequently, close to the mouths of the rivers, it is possible to investigate the functions of physical, chemical and biological gradients on the macrofauna structuring of sandy beach communities. The objective of this study was to determine the response of sublittoral benthic communities to environmental variables in microtidal intermediate sandy beaches of the south of the Gulf of Valencia. Samples of benthic macrofauna, water and sediment were collected at 5 stations located in the sublittoral zone at different distances to freshwater sources, each one sampled at five depths, in three sampling campaigns. In general, the physicochemical and nutritional variables of water showed a spatial variation alongshore, and only a few variables (dissolved inorganic nitrogen, suspended solids and salinity) also had an across-shore variation. This variability was due to the different freshwater contributions. The sediment variables (mean grain size and organic matter) presented clear patterns related to depth. With respect to the macrofauna, positive relationships with depth were observed for the total density, density of bivalves, polychaetes, crustaceans and C. gallina, while D. trunculus showed the opposite pattern. The proximity to freshwater sources, favoured a greater abundance of organisms. Regarding temporal variation, two very different phytoplanktonic compositions between winter and summer could be distinguished, while, for the macrofauna, differences in abundance were observed with maximum values in summer. The influence of freshwater discharges on the phytoplankton primary production will have an influence on the abundance of macrobenthic fauna, but after a time lag. By means of CCA analyses, it was found that the communities of benthic macrofauna were strongly influenced by physical factors such as mean grain size, as well as the nutritional variables (organic matter in sediment and microalgae in the water column) and the distance to the freshwater discharges. The identification of these variables is crucial in order to develop an adequate coastal management, paying special attention to the anthropogenic activities that may be modifying the environment and, therefore will affect the biocoenoses.

Hydrodynamic modelling of a polluted tropical bay: Assessment of anthropogenic impacts on freshwater runoff and estuarine water renewal

A bay's capacity to buffer fluvial fluxes between the land and sea is sensitive to hydrological changes that can affect its water renewal rates. In Cartagena Bay, Colombia, pollution issues have been associated with freshwater fluxes which are projected to increase in future years. This has led to plans to reduce freshwater flows by constructing upstream hydraulic doors. Given the influence of freshwater discharge on coastal water renewal, it is important to assess how these upstream changes will affect the bay's hydrodynamic processes. This study calibrated the 3D MOHID Water model, configured with a high-resolution mixed vertical discretization to capture the bay's characteristic processes of vertical stratification and mixing. A Lagrangian transport model was used to analyze the flow of passive particle tracers and calculate water renewal time scales. Mean residence times of 3–6 days and flushing times of 10–20 days for canal water were found, while mean residence times of 23–33 days and flushing times of 70–99 days were calculated for the bay's complete water volume. An assessment of future scenarios showed that increases in freshwater runoff would result in faster water renewal in the bay, while plans to decrease freshwater discharge would result in slower water renewal in the bay. It is therefore imperative that any plans for reducing fluvial fluxes into the bay be accompanied by the control of local pollution sources, which are abundant and could worsen the bay's water quality issues should water renewal times become longer.

Spatiotemporal patterns of phytoplankton composition and abundance in the Maryland Coastal Bays: The influence of freshwater discharge and anthropogenic activities

The spatial and temporal variations in phytoplankton abundance and community structure in the northern and southern parts of the Maryland Coastal Bays (MCBs) that differ in anthropogenic activities and hydrological characteristics were studied in 2012 and 2013 using photosynthetic pigments as biomarkers. Phytoplankton pigment biomass and diversity were generally higher in the northern bays that receive high nutrient input from St. Martin River, than in the southern bays where nutrient levels were comparatively low. Sites close to the mouths of tributaries in northern and southern bays had higher nutrient levels, which favored the development of dinoflagellates, and nano- and picophytoplankton, than sites closer to the inlets. The microplankton dominated the phytoplankton community in spring (>90%) and decreased in relative abundance into fall (<60%) whereas nanoplankton peaked in summer or fall. Picoplankton relative abundance increased from late spring (<10%, March 2012 & 2013) to summer (40%, July 2012 and August 2013) and was correlated positively with NH4+ and negatively with salinity. The observed spatial and seasonal patterns of phytoplankton relative abundance and diversity are likely due to changes in nutrient concentrations and ratios, driven by variations in freshwater discharge, and selective grazing of phytoplankton. Water quality management in the MCBs should continue to focus on reducing nutrient inputs into the bays.

Influence of freshwater discharge on the microbial degradation processes of dissolved organic nitrogen in a subtropical estuary.

River bacterioplankton communities, influenced by watershed usage, are responsible for water purification. Bacterioplankton may be critical in the degradation of dissolved organic nitrogen (DON), the major nitrogen pool in the Caloosahatchee River, Florida. We investigated how freshwater discharge influences estuarine bacterioplankton and how the freshwater-originated DON is utilized by estuarine bacterioplankton. Microcosm experiments were conducted during low and high discharge using two upstream freshwater samples: one site primarily influenced by Lake Okeechobee and the other site moderately influenced by an agricultural watershed. These freshwater samples were filtered to eliminate indigenous microbial populations, then mixed with estuarine bacterioplankton. High-throughput sequencing revealed that bacterioplankton differed between low and high discharge and were influenced by salinity. Alphaproteobacteria and Bacteroidetes dominated in low discharge while Bacteroidetes and Cyanobacteria dominated during high discharge. In the microcosm experiment, DON concentration decreased with increasing cell densities, suggesting that the DON was utilized as a carbon and nitrogen source. Band signals in denaturing gradient gel electrophoresis corresponding to Alphaproteobacteria and Actinobacteria decreased while Gammaproteobacteria increased during the 1 month incubation. This data suggests that estuarine bacterioplankton communities are influenced by variations in discharge patterns and use freshwater-originated DON as demonstrated by a shift in community structure.

Seasonal variability of phytoplankton blooms in the coastal waters along the East coast of India

Abstract. Bay of Bengal (BOB) is a semi enclosed tropical basin located in the north eastern part of the Indian Ocean with high influence of fresh water discharge from major rivers and rainfall. Bay of Bengal (BOB) is highly influenced by monsoons and represents a natural laboratory to study the effect of fresh water fluxes on the marine ecosystem. Bay of Bengal (BOB) is very low in productivity often with the observations of Phytoplankton Blooms. Phytoplankton blooms are one of the prominent features of biological variability in the coastal ecosystems such as estuaries, lagoons, bays, and tidal rivers with rapid production and accumulation of phytoplankton biomass in the ocean. These blooms usually respond to changing physical forcings originating in the coastal ocean like tides, currents and river runoff and to the atmospheric forcing like wind. These physical forcings have different timescales of variability, so algal blooms can be short-term episodic events, recurrent seasonal phenomena, or rare events associated with exceptional climatic or hydrologic conditions. Bloom events and their variability on spatial &amp;amp; temporal scales monitoring through field measurements is difficult. Based on this key hypothesis an effort is made to understand the seasonal and spatial variability of Phytoplankton Blooms along the East Coast of India. In this paper we present the bloom dynamics in their context to the chlorophyll concentration along with species composition and abundance in estuarine and near shore coastal waters of Godavari basin using Oceansat-2 Ocean Colour Monitor (OCM). The initial results revealed that the quasi permanent phytoplankton blooms initiates in the month of mid- February and evolves for a period of two months and then slowly starts decaying by the mid of May month. The results also stand as a base for the study of influence of Phytoplankton Blooms on the carbon flux estimations and bio-geo-chemical processes in the Bay of Bengal.

Geochemistry of reduced fluids from shallow cold vents hosting chemosynthetic communities (Comau Fjord, Chilean Patagonia, ∼42°S)

Reduced fluids from shallow-marine vents sustain chemosynthetic bacterial mats located at the base of the volcano Barranco Colorado in Comau Fjord (X-Huinay; 42°23.279′S, 72°27.635′W). We characterized the chemical environment in which these bacteria thrive. To this end, we analyzed CH4, ∑H2S, O2, DIC, and stable isotopes (δ13C, δ2H and δ18O) and compared them with readings taken at a control station (which lacks evidence of fluid venting and mat-forming bacteria). In addition, CTD measurements, chlorophyll-a, and nutrient analyses were performed. At depths of approximately 5–7m, the water column exhibited a pycnocline that formed under the influence of fresh water discharges, especially during the summer season, which also affected the surface temperature. Bacterial mats and elemental sulfur flocs were observed in the vicinity of the vents (X-Huinay station), and higher concentrations of reduced compounds (CH4 and ∑H2S) were found in the vent fluids, in particular at a depth of 36m. No significant differences in the temperatures of vent and ambient waters were detected. The bottom water close to the vents possessed notably low concentrations of reduced compounds, indicating a rapid and large-quantity dilution of the chemicals from vents. The surface water featured light isotopic values of δ2H and 18O due to the freshwater input from melting ice and precipitation. A linear mixing trend was observed between the freshwater (negative isotopic values) and the fjord bottom water (positive values) that was not influenced by vent fluid. This trend suggests that the venting water corresponds to the mixing among local meteoric water, spring water, and seawater. This result is relevant to understanding how freshwater and meteoric water influence the chemical composition of seawater and how this mixing could impact the marine biota in the vicinities of the vents.

CO2-Driven Ocean Acidification Disrupts the Filter Feeding Behavior in Chilean Gastropod and Bivalve Species from Different Geographic Localities

We present experimental data obtained with newly hatched veliger larvae of the gastropod Concholepas concholepas and juveniles of the mussel Perumytilus purpuratus exposed to three pCO2 levels. Egg capsules of C. concholepas were collected from three geographic locations in northern (Antofagasta), central (Las Cruces), and southern Chile (Calfuco), and then incubated throughout their entire intra-capsular life cycle at three nominal pCO2 levels, ~400, 700, and 1,000 ppm. Similarly, P. purpuratus were collected from both Las Cruces and Calfuco and exposed to the same pCO2 levels during 6 weeks. Hatched gastropod larvae and mussel juvenile were fed with the haptophyte Isochrysis galbana. Clearance and ingestion rates were estimated for newly hatched larvae, and for juvenile mussel these rates were measured at two observation times (3 and 6 weeks). Our results clearly showed a significant negative effect of elevated pCO2 on the clearance and ingestion for both C. concholepas larvae and P. purpuratus juveniles, which dropped between 15 up to 70 % under high pCO2 conditions. The present study has also shown large variations in the sensitivities of C. concholepas larvae from different local populations (i.e. Antofagasta, Las Cruces, and Calfuco). The influence of both corrosive upwelling waters and the influence of freshwater discharges from Maipo River may explain the minor negative effect of high pCO2 conditions in hatched larvae from Las Cruces’ egg capsules, which would suggest that they are inherently more tolerant to ocean acidification (OA) than organisms that live on regions with a lower pCO2 variability. The present study suggests the need for site-specific studies and reveals the important effect of low pH conditions on feeding activity. Furthermore, this study supports the notion that feeding is a key physiological process susceptible to the effects of OA in marine invertebrates.

Spatial variability of flow over a river-influenced inner shelf in coastal Alabama during spring

Spring-time water column velocity data in 2011 and density data from a series of spring-time hydrographic surveys from 2008 to 2011 were used to examine the spatial variability of the circulation over the inner shelf of the Mississippi Bight off Mobile Bay. Spring-time depth-averaged currents were eastward at all sites, but the vertical profiles were different. East of Mobile Bay the along-shelf flow was eastward, with an offshore component at the surface and an onshore component at depth, indicative of upwelling circulation. West of Mobile Bay the along-shelf flow was also eastward, with a characteristic region of negative vertical shear in the upper layer of the water column. The deeper site had an across-shelf flow structure similar to the east sites, while the shallower site exhibited onshore flow throughout the water column. These spatial differences are attributed, in part, to the seasonally averaged effects of local wind forcing and discharge. In terms of wind forcing, the depth-averaged along-shelf current responded to along-shelf wind asymmetrically in favor of upwelling (more transport in upwelling than during downwelling). Thus, weak seasonal downwelling favorable wind conditions did not inhibit the velocity profiles from having upwelling circulation. West of Mobile Bay, negative vertical shears in the upper portion of the velocity profiles were consistent with the influence of freshwater discharge. This freshwater influence is supported with available chlorophyll-a data (as a freshwater proxy), which showed an enhanced freshwater influence west of Mobile Bay. In addition, across-shelf density data showed a shallow lens of freshwater west of Mobile Bay. These findings have implications for understanding the transport of river-derived nutrients on the Mississippi–Alabama shelf.

Influence of freshwater discharges and tides on the abundance and distribution of larval and juvenile Munida gregaria in the Baker river estuary, Chilean Patagonia

Zooplankton time series collected with different temporal resolution and coverage were examined to characterize seasonal and diel patterns in the abundance of Munida gregaria larvae and juveniles in the Baker river estuary. Zoeae were more abundant in late winter and spring, coinciding with the season of lower sediment transport and higher primary production in the region. The occurrence of juveniles was exclusively in summer. There was a significant correlation between the abundance of zoeae and high-frequency temperature variability near the pycnocline over periods of 7–20 and 26–30 days prior to each plankton sampling. These time scales of correlation suggest that internal motions may be a proximal environmental cue for lunar rhythms in larval hatching, rather than directly causing the aggregation of larvae at the sampling area. To characterize shorter-term patterns in larval abundance and vertical distribution, stratified samples were collected every 3h over a full late-spring day (November 2008) near one of the monitoring stations. Zoeae were significantly more abundant at 10–25m depth (p=0.039), and changes in depth-integrated abundance of both zoea and megalopae were strongly associated with the tidal cycle. Together, these results suggest that the spatial structure and population dynamics of M. gregaria in this region may respond to the combined forcing of seasonal changes in freshwater inputs, tidally-driven processes such as lateral transport of larvae and juveniles, and internal-wave mediated changes in local conditions.

Otolith chemistry of juvenile spotted seatrout Cynoscion nebulosus reflects local natal regions of coastal Mississippi, USA

Early juvenile spotted seatrout Cynoscion nebulosus (n = 199) were collected during late summer and autumn 2001 from shoreline habitats within 9 coastal regions bordering Mississippi Sound in the north-central Gulf of Mexico to ascertain how well fish could be spatially classified based on otolith chemistry. Left otoliths were assayed for trace element:Ca ratios of Ba, Li, Mg, Mn and Sr, and right otoliths for δ 13 C and δ 18 O. Significant overall differences in otolith chemistry existed among the 9 regions; 61% of the joint variance in the 7 otolith chemistry variables was explained by the regional factor in a multivariate analysis of variance (MANOVA). All 7 otolith chemistry variables differed significantly among the 9 regions. The isotopes δ 13 C and δ 18 O showed the highest regional affinities, and Li showed the strongest regional association of all the trace elements. Canonical dis- criminant function analysis (CDFA) maximally separated regional groups of early juvenile fish. The first 3 of 7 discriminant functions accounted for 97.5% of the cumulative variance in the 7 otolith chemistry variables. CDF 1 was influenced primarily by δ 18 O and Li, CDF 2 by Mn and δ 13 C, and CDF 3 by Mg and Ba. In the all-inclusive CDFA, 93.4% of cases were classified correctly, and classifica- tion success among regions ranged from 83.3 to 100%. The influence of freshwater discharge from 7 rivers along the Mississippi coastline likely made it possible to detect the relatively fine-scale spatial differences seen in this study, as defined by a mean interregional distance of only 25 km.

Short-term water quality variability in two tropical estuaries, central Sumatra

We examined high frequency fluctuations in water quality parameters in two tropical coastal plain estuaries in response to changing tidal flow conditions. The variability in total suspended sediments (TSS), volatile suspended solids (VSS), total organic carbon (TOC) concentrations, and indicators of water quality, including pH, temperature, salinity, and dissolved oxygen, over one spring tidal cycle during the early wet monsoon season was measured in two estuaries in eastern Sumatra. The relatively high rainfall experienced throughout the year, in combination with the recent extensive vegetation clearing and modification of the landscape, resulted in significant concentrations of TSS, VSS, and TOC being discharged to coastal waters. Maximum values are reached on the ebb tide (TSS > 1,013 mg l−1; VSS > 800 mg l−1; TOC >60 mg l−1). The influence of freshwater discharge and tidal flow on water properties of the lower estuaries is also marked by the variability in salinity, dissolved oxygen, and pH over the tidal cycle, with minimum values for each of these parameters following maximum current velocities and after the completion of the strong ebb tide. Estimation of seaward sediment fluxes, which are of significant interest in a region where rapid environmental change is occurring, would require further examination of sedimentary processes, such as resuspension and advection of sediment, as well as a consideration of neap-spring tidal variations and the effect of seasonality on estuarine circulation.

The influence of freshwater discharge on the distribution of zooplankton in the southern Kara Sea

Zooplankton was collected on two cruises to the southern Kara Sea to study the effect of the freshwater outflow of the rivers Ob and Yenisej on plankton distribution. Calanoid copepods dominated the composition with more than 75% of all specimens collected in both years; Drepanopus bungei was the most abundant species. Species composition showed a wide spectrum from freshwater to marine species. The abundance and community composition of the zooplankton communities followed closely the hydrographic pattern along a gradient from the inner to the outer estuaries, as revealed by cluster analysis and Multi-Dimensional Scaling. There were also differences in species composition and abundance between the two rivers. The stable brackish surface layer created a large distribution area for riverine species, while in the underlying marine water masses, oceanic species penetrated far into the estuaries. In 1997 this area was considerably larger, probably due to a higher freshwater discharge. During the 1999 cruise, which took place 3 weeks earlier, salinities were generally higher. Both species composition and overall abundances were higher in 1999 than in 1997, due especially to the enormous increase of Limnocalanus macrurus and Pseudocalanus major.

The role of phosphorus on planktonic production of the Gironde plume waters in the Bay of Biscay

More and more studies emphasize the status of phosphorus (P) as the principal limiting nutrient of phytoplankton growth, especially in coastal waters under the influence of freshwater discharges. The purpose of the present paper is to investigate the role of P on planktonic production in the waters influenced by the Gironde discharges; the Gironde being one of the two largest rivers on the French Atlantic coast. The survey is based on several cruises made in 1998 and 1999. Two different patterns were observed for waters with salinity below and above 34.5. For waters with salinity 34.5. P was found to be the first limiting nutrient of winter and spring phytoplankton blooms, based on undetectable phosphate ( 20 nM), high NO3 : PO4 ratios, typically 100:1, short phosphate turnover time (1 to 2 h), high alkaline phosphatase activities (mean of 176 nM h(-1) in late May 1999) and ultimately great increases of chlorophyll a (Chl a) and primary production in phosphate-enriched samples relative to controls. This limitation could be partly explained by the Gironde nutrient supplies, which were phosphate deficient compared with the mineral nitrogen (N-min : PO4 was 40 within a salinity range 16-33). In summer, corresponding to the period of low influence of Gironde supplies (low runoff and a spreading effect of the plume), phytoplankton growth would be controlled by both P and nitrogen (N), according to low nitrate and the major effect of combined P+N (NH4) enrichment on Chl a and primary production compared with the addition of Nor P singly. In early October, after the first autumn gales, the mixed layer was enriched with a sufficient supply of nutrients to support exponential phytoplankton growth for 4 days in enclosures. The pattern was different for waters at the limit of the Gironde plume and Atlantic oceanic waters (within salinity range 34.5-35.4)...

Hydrology and Nutrient Enrichment at Two Coastal Lagoon Systems in Northern Greece

The lagoons of N.E. Greece, located on the western side of Nestos River, and of N.W. Greece, located at the lower reaches of Kalamas River, are among the most important shallow, semi-enclosed ecosystems in Northern Greece. The temporal variability of nutrients at both lagoonal systems shows the strong influence of fresh water discharge on water quality. Nutrient enrichment factors showed that nitrites and ammonium were six times higher at the lagoons of N.W. Greece than those observed at N.E. Greece, while phosphates were forty times higher at Nestos River lagoons. The flushing half-life was calculated based on a combination of hydrological and tidal processes, for each lagoon of these two systems, allowing for the assessment of water quality changes. Proper management measures for both systems should focus on the control of fresh water quality entering the lagoons, the reduction of phosphoric fertilizers used by agriculture and the better oxygenation of the water column. One way to eliminate massive fish deaths during the winter in N.E. Greece is also the transfer of fresh, warm groundwater, while bathymetric modifications and channel widening are needed at the lagoons of N.W. Greece.

Patterns in Species Composition of Fish and Selected Invertebrate Assemblages in Estuarine Subregions near Ponce de Leon Inlet, Florida

The Florida Fish and Wildlife Conservation Commission's Fisheries-Independent Monitoring program monitored the species composition and relative abundance of fishes and selected invertebrates in the estuarine waters near Ponce de Leon Inlet, Florida, from January 1993 through to December 1996. Sampling sites were located in three distinct physiographic and biotic estuarine subregions: Mosquito Lagoon (ML; 11 stations), Ponce de Leon Inlet (PI; 8 stations), and Tomoka Basin/River (TR; 8 stations). This series of subregions associated with Ponce de Leon Inlet is a species-rich estuarine system that is numerically dominated by a few taxa. A total of 1080477 animals representing 160 species and 56 families were recorded.Anchoa spp. (29·9%) and Menidia spp. (12·6%) were the numerically dominant taxa. Sciaenidae and Gobiidae were the most speciose families, with 12 species each (14·0% and 1·7% of the total animals collected, respectively), followed by the bothids 10 species (0·6% of total animals). Detrended correspondence analysis showed that the subregions could be discriminated by their respective species composition and relative abundance. Spatial differences in species composition were principally attributed to differences in the magnitude of seasonal recruitment events and to habitat characteristics associated with the presence of seagrass, inlet dynamics, or the influence of freshwater discharge. The presence of freshwater taxa (centrarchids) and the seasonal recruitment of juvenile Penaeidae,Micropogonias undulatus , Stellifer lanceolatus and Leiostomus xanthurus, characterize the TR area, whereas the presence of species associated with higher salinities (Opisthonema oglinum and Harengula jaguana) characterize PI and with seagrass (Lucania parva and Lagodon rhomboides) characterize ML.

La dispersion des apports de la Gironde sur le plateau continental. Données in situ, satellitales et numériques

Coastal waters are generally a product of mixing between continental and oceanic originated water masses. Near river mouth areas, as in the Gironde estuary, oceanic waters are modified by the influence of freshwater discharge that introduces suspended and dissolved substances, including pollutants. Within PNOC (Programme National d'Oceanographie Côtière) our objective is to determine the extent of the influence of the Gironde estuary on to the Aquitanian continental shelf. Several cruises for collecting hydrological data have been carried out in this area. The data of every cruise were coupled with a NOAA-11 satellite passage. The recorded images have been analysed and were compared with the results given by a 3D mathematical model. The interaction among different dynamical factors (density, wind-driven and tidal circulation) controls the mixing and the transport of low salinity waters.