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Abstract: Salt marshes exist at the terrestrial-marine interface, providing important ecosystem services such as nutrient cycling and carbon sequestration. Tidal inputs play a dominant role in salt marsh porewater mixing, and terrestrially derived freshwater inputs are increasingly recognized as important sources of water and solutes to intertidal wetlands. However, there remains a critical gap in understanding the role of freshwater inputs on salt marsh hydrology, and how this may impact marsh subsurface salinity and plant productivity. Here, we address this knowledge gap by examining the hydrologic behavior, porewater salinity, and pickleweed (Sarcocornia pacifica also known as Salicornia pacifica) plant productivity along a salt marsh transect in an estuary along the central coast of California. Through the installation of a suite of hydrometric sensors and routine porewater sampling and vegetation surveys, we sought to understand how seasonal changes in terrestrial freshwater inputs impact salt marsh ecohydrologic processes. We found that salt marsh porewater salinity, shallow subsurface saturation, and pickleweed productivity are closely coupled with elevated upland water level during the winter and spring, and more influenced by tidal inputs during the summer and fall. This seasonal response indicates a switch in salt marsh hydrologic connectivity with the terrestrial upland that impacts ecosystem functioning. Through elucidating the interannual impacts of drought on salt marsh hydrology, we found that the severity of drought and historical precipitation can impact contemporary hydrologic behavior and the duration and timing of the upland-marsh hydrologic connectivity. This implies that the sensitivity of salt marshes to climate change involves a complex interaction between sea level rise and freshwater inputs that vary at seasonal to interannual timescales.

Estuaries are essential habitats for recreational and commercial fish that are shaped by both natural and anthropogenic processes. In Louisiana a combination of climate change and planned coastal restoration actions is predicted to increase freshwater introduction to coastal estuaries. As such there is a need to quantify the relationships between estuarine fish ecology and salinity to aid in predicting how species will respond to shifts in salinity. We investigated the relative abundance and dietary niches of adult (24.5 ± 5.4 cm standard length) spotted seatrout Cynoscion nebulosus across varying salinity regimes (oligohaline, mesohaline, and polyhaline) within Barataria Bay, Louisiana, using a combination of net sampling and gut content and stable isotopes analysis. We found that the relative abundance of C. nebulosus was lowest at the oligohaline site, translating to approximately five fewer fish captured for every single psu decrease in a site's average annual salinity. In contrast, we found that diets and, to a lesser extent, isotopic niches had a high degree of overlap across sites with differing salinity regimes. Fish and penaeid shrimp were the most common and important prey taxa recovered from guts at all sites. The small isotopic differences found among sites were likely due to spatial variation in hydrogeochemical baselines, and the observed isotopic overlap provides support for the idea that C. nebulosus move between adjacent salinity regimes and forage throughout Barataria Bay. Our results contribute to a greater understanding of the salinity preference and trophic ecology of C. nebulosus that can aid in predicting their responses to future salinity and habitat changes within Barataria Bay associated with predicted climate change and planned coastal restoration actions. [ABSTRACT FROM AUTHOR]

Rangarajan, R. and Prasanna, K., 2024. Stable oxygen and strontium isotopic evidence of submarine groundwater forcing on the sea salinity in the northern Indian Ocean. In: Phillips, M.R.; Al-Naemi, S., and Duarte, C.M. (eds.), Coastlines under Global Change: Proceedings from the International Coastal Symposium (ICS) 2024 (Doha, Qatar). Journal of Coastal Research, Special Issue No. 113, pp. 407–411. Charlotte (North Carolina), ISSN 0749-0208. Understanding the dynamics of freshwater inputs in the Indian Ocean is crucial for elucidating the regional variability and its implications for marine ecosystems. In this study, we utilize stable oxygen (δ18O) and strontium (87Sr/86Sr) isotopic compositions of water samples to investigate the influence of freshwater forcing and the corresponding estimates of sub-marine groundwater fluxes in the Indian Ocean. We present high-resolution stable isotopic records of depth bound seawater samples collected from key locations across the northern Bay of Bengal region of the Indian Ocean. Our findings reveal significant variability in δ18O and 87Sr/86Sr ratios, indicative of freshwater influxes at depths of around 800m. These distinct shifts in isotopic signatures corresponding to increased influx of sub-marine groundwater discharges in the study region. In addition, we calculated the volume of the SGD using a simple compartment box model to elucidate its key role in salinity variability and potential impacts in marine strontium biogeochemistry. The estimates indicated overall SGD flux to be ∼8.3 x 1015 m3 year-1, a much higher value than available published values of SGD flux in the northern Bay of Bengal region. The current research provides valuable insights into the mechanisms driving salinity changes in the northern most sector of Indian Ocean and further elucidates the importance of systematically studying the SGDs in the region. [ABSTRACT FROM AUTHOR]

Climate-change driven increases in temperature and precipitation are leading to increased discharge of freshwater and terrestrial material to Arctic coastal ecosystems. These inputs bring sediments, nutrients and organic matter (OM) across the land-ocean interface with a range of implications for coastal ecosystems and biogeochemical cycling. To investigate responses to terrestrial inputs, physicochemical conditions were characterized in a river- and glacier-influenced Arctic fjord system (Isfjorden, Svalbard) from May to August in 2018 and 2019. Our observations revealed a pervasive freshwater footprint in the inner fjord arms, the geochemical properties of which varied spatially and seasonally as the melt season progressed. In June, during the spring freshet, rivers were a source of dissolved organic carbon (DOC; with concentrations up to 1410 μmol L–1). In August, permafrost and glacial-fed meltwater was a source of inorganic nutrients including NO2 + NO3, with concentrations 12-fold higher in the rivers than in the fjord. While marine OM dominated in May following the spring phytoplankton bloom, terrestrial OM was present throughout Isfjorden in June and August. Results suggest that enhanced land-ocean connectivity could lead to profound changes in the biogeochemistry and ecology of Svalbard fjords. Given the anticipated warming and associated increases in precipitation, permafrost thaw and freshwater discharge, our results highlight the need for more detailed seasonal field sampling in small Arctic catchments and receiving aquatic systems.

Highlights • Samples in salt marshes and freshwater restoration wetlands were clearly separated. • Higher soil quality index value was observed in salt marshes with Suaeda salsa. • Salinity, silt and SOM were key factors influencing soil quality. Abstract With the degradation or loss of coastal wetlands, more and more restoration projects have been widely conducted. Freshwater inputs have been proved to be an effective restoration way for degraded coastal wetlands. However, little information is available on the changes in soil quality caused by freshwater inputs. Soil samples were collected to a depth of 50 cm in freshwater restoration wetlands (FRW), tidal salt marshes with Suaeda salsa (SSM) and tidal salt marshes with Tamarix chinensis (TSM) in the Yellow River Delta, China, in August 2015, to investigate the changes in soil quality after freshwater inputs. Our results showed that soil salinity was significantly higher in natural wetlands than that in freshwater restoration wetlands (p < 0.05), while no significant differences in soil organic matter (SOM) were observed among three wetlands (p > 0.05). Cluster analysis and principal component analysis exhibited that soil samples in natural wetlands and freshwater restoration wetlands were clearly distinguished. Soil properties were screened and transformed to establish a soil quality index (SQI) for the assessment of soil quality. Soil salinity, SOM and silt were selected in the minimum data set in this study. Although there were no statistical differences in SQIs (p > 0.05), both linear SQI (SQI L) and non-linear SQI (SQI NL) for three wetlands followed the order: SSM > FRW > TSM. And the SQI L values were lower compared with SQI NL. The contributions of soil salinity to SQI L for three wetlands and SQI NL for TSM and SSM were the highest in the minimum data for three wetlands, while SOM showed the highest contribution proportion of SQI NL for FRW. [ABSTRACT FROM AUTHOR]

Open ocean carbonate chemistry is altered by the dissolution of atmospheric CO 2 in seawater. Up to 40% of anthropogenic CO 2 emissions have dissolved in the surface ocean since the pre-industrial era, driving changes in marine carbonate pools and promoting ocean acidification. Under open ocean conditions, Total Alkalinity (TA) generally relates with salinity and temperature due to the conservative nature of its constituents. In coastal areas, however, land-ocean interactions may greatly contribute to making TA far less predictable, since freshwater inputs can affect the chemistry of coastal water masses by increasing TA and Dissolved Inorganic Carbon (DIC) or, alternatively, lowering them through dilution. Here we analysed and compared coastal carbonate chemistry dynamics in selected coastal areas of Ireland, in order to assess whether rivers and their catchment geology can influence coastal water chemistry and to verify the occurrence of local ocean acidification processes. Data on TA, DIC, salinity, temperature, and nutrients (total nitrogen, phosphate, and silicate) collected during several surveys along the Irish coastline by The Marine Institute Foras Na Mara (MIFNM) from 2009 to 2018 were analysed against those available on the main watercourses feeding the selected coastal areas. The relationships among the different variables were scrutinized, also considering the geological characteristics of river catchments. Results showed a clear linkage between coastal water chemistry and local freshwater inputs, whereas changes in the geology of catchment areas exerted only a secondary influence. An in-depth scrutiny of the Galway Bay sector performed by comparing MIFNM data with those collected during an oceanographic cruise carried out in October 2017 further indicated remarkable effects of the interaction between river inputs and submarine groundwater discharges on seasonal variations in the water chemistry of the area. Future studies, integrating chemical data across the land-ocean boundary, may provide additional, useful information on the factors actually affecting the variation in water carbonates in coastal areas. Elucidating how land-ocean interactions influence the coastal carbonate system may ultimately provide a key for a more advanced understanding of the resilience of coastal areas to ocean acidification. • Coastal carbonate chemistry depends on land-ocean interactions. • Multiple drivers should be considered: bedrock geology, freshwater inputs typology. • Human activities and SGD might affect coastal buffering capacity and TA:DIC ratio. • TA and DIC should be included in all coastal monitoring programs. [ABSTRACT FROM AUTHOR]

Large stands of free living (calcareous) coralline algae — called maerl beds — play a major role as ecosystem engineers in coastal areas throughout the world. They are also subject to strong anthropogenic pressures at global and local scales, which threaten their survival. However, the macroalgal epiphytes growing on maerl may benefit from these pressures, developing to the detriment of maerl algae. Here, we sought to gain insight into how maerl beds and their epiphytic algae are disturbed by variations in the local environment, and how these variations affect their capacity to respond to global change. In 2015, we monitored three maerl beds located in the Bay of Brest (Brittany, France). Sites with contrasting conditions were selected, with one station lying in a zone close to the harbor (northern basin S1) and two stations (S2 and S3) located in areas away from the main urban effluents but subject to other sources of local change: higher currents at S3 (PREVIMER Ocean Forecast) and higher sedimentation rates at S2 (Ehrhold et al., 2016). We observed significant temporal variations of physico-chemical parameters, on an annual but also on a daily basis. Results showed that S2 differentiated itself from the other stations, this station experienced higher fluctuations of salinity, nutrient concentrations and carbonate system parameters and hosted the lowest (living) maerl biomass (4.38 ± 1.54 kg DW m −2 ). S3 observed the highest living maerl biomass (14.56 ± 1.61 kg DW m −2 ) and the lowest non-calcareous epiphytic macroalgal abundance (0.1–7.9 g DW m −2 ). S1 displayed the highest heterogeneity in terms of living maerl biomass (it varied from 0.8 to 8.6 kg DW m −2 ), and the highest Chl a content. However, we did not record differences in terms of physico-chemical parameters between S1 and S3. No positive relationship was observed between nutrient enrichment and macroalgal epiphyte abundance, but epiphyte abundance was higher at stations with lower maerl biomass (S1 and S2) (mean value ranged from 4.6 to 49.0 g DW m −2 at S1 and from 7.4 to 23.7 g DW m −2 at S2). Our results highlight the importance of local changes on the development, survival and capacity to adapt to global change of maerl beds. [ABSTRACT FROM AUTHOR]

The Ciénaga Grande de Santa Marta (CGSM), Colombia is possibly the wetland that has experienced the largest mangrove mortality on record due to modification of hydrologic connectivity and consequent hypersaline conditions. We used hydroclimatic, salinity and mangrove basal area data collected in five stations from 1993 to 2015 to study the relation between ongoing mangrove recovery, changes in salinity in the wetland and hydroclimatic changes in precipitation, potential evapotranspiration and freshwater inputs. We found that until 2015, the mangrove ecosystems in CGSM are in general terms in a path of recovery due to the combined effect of favorable hydroclimatic conditions and management operations to increase freshwater inputs into the wetland. We observed in three stations that the annual growth of mangrove basal area increased as pore water salinity decreased. Regarding surface water salinity, El Niño/Southern Oscillation explained most of the inter-annual variability in the wet season by regulating freshwater and in the dry season by regulating potential evaporation from the wetland. However, persistent channel reopening appeared to be the cause for the largest salinity decreases, whereas lack of persistent dredging slowed recovery in other areas. The monitoring of the mangrove-salinity-hydroclimate system must continue in order to increase its understanding and to avoid more recurring episodes of mangrove mortality. [ABSTRACT FROM AUTHOR]

Water and salinity regulation measures have been widely taken to restore the ecological structures and functions of degraded coastal wetlands. To investigate the effects of different water and salinity regulation measures on soil carbon stocks in coastal wetlands, soil samples were collected to a depth of 50 cm in four types of wetlands (i.e., restored tidal salt marshes (RTSM, covered with Suaeda salsa ) and degraded tidal salt marshes (DTSM, bare land); freshwater restored wetlands (FRW) and degraded wetlands without freshwater inputs (DWFI), covered with Phragmites australis ) during the period from August to October in 2015 in the Yellow River Delta, China. Our results showed that the mean values of total carbon (TC), soil organic carbon (SOC), readily oxidizable organic carbon (ROOC) and dissolved organic carbon (DOC) were higher in restored wetlands (e.g., RTSM and FRW) than those in degraded wetlands (e.g., DTSM and DWFI). Along the whole soil profile, TC, SOC, ROOC and DOC were higher in RTSM soils than those in DTSM soils except for TC and SOC in the 0–10 cm soils and DOC in the 40–50 cm soils. FRW soils contained higher TC, SOC, ROOC and DOC than DWFI except for DOC in the 0–10 cm soils. Soil TC density (TCD), SOC density (SOCD), ROOC density (ROOCD) and DOC density (DOCD) in the top 50 cm soils in restored wetlands were higher compared with degraded wetlands. Multivariate analysis showed that soil carbon was significantly influenced by EC, soil base cations and anions (e.g., K + , Ca 2 + , Cl − and SO 4 2 − ), pH, TN, C/N ratio, bulk density (BD) and soil texture ( p < 0.05). The findings of this study indicated that these two water and salinity regulation measures are effective in increasing soil carbon stocks of coastal wetlands. [ABSTRACT FROM AUTHOR]

A weekly time-series of oxygen isotope (δ 18 O) measurements was collected over a 16-month period from near-surface (1 m) and near-bottom (60 m) waters of Bedford Basin, a coastal fjord adjacent to the Scotian Shelf, off eastern Canada. The time-series was complemented with δ 18 O measurements of local precipitation (rain and snow), river, and wastewater runoff. The isotopic composition of precipitation displayed strong seasonality with an average (volume-weighted) δ 18 O value of −5.39‰ (±0.96) for summer and a depleted value of −10.37‰ (±2.96) over winter. Winter precipitation exhibited more depleted and variable δ 18 O of solid precipitation relative to rainfall. The annual, amount-weighted average δ 18 O of Sackville River discharge (−6.49‰ ± 0.82) was not statistically different from precipitation (−7.24‰ ± 0.92), but exhibited less seasonal variation. Freshwater end-members (zero-salinity intercepts) estimated from annual and seasonal regressions of δ 18 O versus salinity (S) for Bedford Basin near-surface samples were consistent with the δ 18 O of summer precipitation and the annual, amount-weighted average for the Sackville River. However, the isotopically depleted signature of winter precipitation was not observed clearly in near-surface waters of Bedford Basin, which might reflect isotope enrichment during sublimation from accumulated snowfall prior to melting and discharge, or retention and mixing within the drainage basin. In near bottom waters, most of the δ 18 O-S variation (average freshwater end-member: 7.47‰ ± 2.17) could be explained by vertical mixing with near-surface waters (average freshwater end-member: −6.23‰ ± 0.34) and hence with locally-derived freshwater. However the near-bottom δ 18 O-S variation suggested an additional contribution of a freshwater end-member with a δ 18 O of −15.55‰ ± 2.3, consistent with a remotely-derived freshwater end-member identified previously for the Scotian Shelf. Residuals from a long-term regression of δ 18 O-S were generally within the range expected due to analytical uncertainty (±0.05); however near-surface waters exhibited seasonal variability of small amplitude, which was consistent with the timing and δ 18 O variability of local freshwater inputs. [ABSTRACT FROM AUTHOR]

Coastal lagoons are important systems for freshwater, estuarine and marine organisms; they are considered important zones of reproduction, nursery and feeding for many fish species. The present study investigates the fish assemblages of the natural reserve of Dzilam and their relationship with the hydrologic variables. A total of 6 474 individuals (81 species) were collected, contributing with more than 50% considering the Importance Value Index (IVI), Sphoeroides testudineus, Fundulus persimilis, Anchoa mitchilli, Eucinostomus gula, Eucinostomus argenteus and Mugil trichodon. Differences in species composition were found between seasons the highest during the cold fronts. Spatially, differences were related with the presence of freshwater seeps, the highest in the ecological characterized eastern part and the lowest with higher difference in specific composition located in the western part of the internal zone, due to a higher abundance and dominance of L. rhomboides. Salinity and temperature were the variables that presented a higher influence in the distribution of some pelagic species such as A. mitchilli and A. hepsetus. Because of the abundant freshwater seeps characteristic of the coastal lagoons of Yucatan Peninsula their community structure and fish assemblage display spatial and temporal differences in specific composition. Rev. Biol. Trop. 57 (1-2): 89-103. Epub 2009 June 30.Las lagunas costeras son sistemas importantes para muchas especies de organismos dulceacuícolas, estuarinos y marinos, ya que son consideradas zonas de reproducción, refugio y alimentación de muchas especies de peces. El presente estudio analizó los ensamblajes de la comunidad íctica de la reserva de Dzilam y su relación con las variables hidrológicas. Se capturaron un total de 6 474 individuos (81 especies), en donde Sphoeroides testudineus, Fundulus persimilis, Anchoa mitchilli, Eucinostomus gula, Eucinostomus argenteus and Mugil trichodon contribuyeron con más del 50% del Indice de Valor de Importancia (IVI). Las diferencias en composición de especies se encontraron entre temporadas, la mayor durante los nortes. Espacialmente, las diferencias fueron relacionadas con la presencia de afloramientos de agua dulce, la mayor en la zona Este de la laguna y la menor con mayor diferencia en composición específica se localizó en la parte Oeste de la zona interna, esto debido a la gran abundancia y dominancia de una sola especie (L. rhomboides). La salinidad y la temperatura fueron las variables que presentaron la mayor influencia en la distribución de algunas especies pelágicas como son A. mitchilli y A. hepsetus. Debido a la abundancia de afloramientos de agua dulce, característicos de las lagunas costeras de la Península de Yucatán, los ensamblajes de peces muestran diferencias espaciales y temporales en la composición específica.

In the Mediterranean-climate zone, recurrent drought events and increasing water demand generally lead to a decrease in freshwater input to estuaries. This water scarcity may alter the proper function of estuaries as nursery areas for marine species and as permanent habitat for estuarine species. A 12-year data set of the aquatic macrofauna (fish, decapod and mysid crustaceans) in a Mediterranean estuary (Guadalquivir estuary, South Spain) was analysed to test if water scarcity favours the nursery function of regional estuaries to the detriment of permanent estuarine inhabitants. Target species typically displayed a salinity-related distribution and estuarine salinisation in dry years resulted in a general upstream community displacement. However, annual densities of marine species were neither consistently higher in dry years nor estuarine species during wet years. Exceptions included the estuarine mysid Neomysis integer and the marine shrimp Crangon crangon , which were more abundant in wet and dry years, respectively. High and persistent turbidity, a collateral effect of water scarcity, altered both the structural (salinity-related pattern) and functional (key prey species and predator density) community characteristics, chiefly after the second drought period of the analysis. The observed high inter-year environmental variability, as well as species-specific effects of water scarcity, suggests that exhaustive and long-term sampling programmes will be required for rigorously monitoring the estuarine communities of the Mediterranean-climate region. [ABSTRACT FROM AUTHOR]

Abstract: Dual δ15N and δ13C analyses and estimates of biomass were used to characterize the food webs of valuable fish species in three coastal lagoons of the Ebro Delta subjected to contrasting salinity regimes (polyhaline in the Tancada lagoon, mesohaline in the Encanyissada and oligohaline in the Clot lagoon). The δ13C signatures of the entire food-web including primary producers, sediment organic matter and consumers showed the most enriched values in the Tancada lagoon (from approx. −4.8‰ in sediments to −19.7‰ in fish) and the most depleted ones in the Clot lagoon (from approx. −11.4‰ in sediments to −25.4‰ in fish), consistent with dominant contributions from marine and continental sources, respectively. For δ15N, particularly high values were detected in the submersed vegetation (11.3 ± 0.3‰) together with more enriched sediment values at lower salinities (by approx. 2.5‰), suggesting that historical loadings of agricultural fertilizers are still retained by the systems and transmitted across trophic levels. Negative relationships between δ15N and salinity were also observed for the amphipod Gammarus aequicauda and the isopod Sphaeroma hookeri, suggesting some consumption of accumulated and resuspended detrital material. In contrast, δ15N signatures of fish showed lower values and inconsistent patterns, possibly because most species have a seasonal use of the lagoons. The biomass of fish species did not show a clear effect of the salinity regime (except for the mosquitofish Gambusia holbrookii), but results for mixing models suggest a diet shift from higher contribution of zooplankton size fractions in the Encanyissada (from 57 to 73%) to macrofauna at the other lagoons (from 40 to 67%). We suggest that alterations in salinity might modify the trophic dynamics of the systems from benthic to planktonic pathways, without large-scale differences in δ15N of fish suggestive of similar trophic levels. [Copyright &y& Elsevier]

Rice cultivation in the Ebro Delta (Catalonia, Spain) has inverted the natural hydrological cycles of coastal lagoons and decreased water salinities for over 150 years. Adjustments in the water management practices-in terms of source and amount of freshwater inputs-have resulted in changes in the diversity, distribution and productivity of submerged angiosperms. Between the 1970s and late 1980s, a massive decline of the aquatic vegetation occurred in the Encanyissada-Clot and Tancada lagoons, but little information on the status is available after the recovery of macrophytes in the 1990s. Here, we evaluate the influence of salinity regimes resulting from current water management practices on the composition, distribution, seasonal abundance and flowering rates of submersed macrophytes, as well as on the occurrence of epiphyte and drift macroalgae blooms in three coastal lagoons. Our results show that Ruppia cirrhosa is the dominant species in the Encanyissada lagoon (185.97 ± 29.74 g DW m year; 12-27 ‰ salinity) and the only plant species found in the Tancada lagoon (53.26 ± 10.94 g DW m year; 16-28 ‰ salinity). Flowering of R. cirrhosa (up to 1,011 ± 121 flowers m) was only observed within the Encanyissada and suggests that mesohaline summer conditions may favor these events. In contrast, low salinities in Clot lagoon (∼3-12 ‰) favor the development of Potamogeton pectinatus (130.53 ± 13.79 g DW m year) with intersperse R. cirrhosa (8.58 ± 1.71 g DW m) and mixed stands of P. pectinatus and Najas marina (up to ∼57 g DW m year) in some reduced areas. The peak biomasses observed during the study are 88 to 95 % lower than maximum values reported in the literature at similar salinities, and there is also little or no recovery in some areas compared to last reports more than 20 years ago. The main management actions to restore the natural diversity and productivity of submersed angiosperms, such as the recovering of the seagrass Zostera noltii, should be the increase of salinity during the period of rice cultivation, by reducing freshwater inputs and increasing flushing connections with the bays. [ABSTRACT FROM AUTHOR]

Abstract: The aim of this 12-year study was to assess the nekton (fish, decapod crustaceans) response to freshwater inputs (rainfall, dam discharges) in a temperate estuary with regulated riverine inflow. Although interannual variability in river discharges to the Guadalquivir estuary has been extremely high since the construction of a dam in 1930, a significant decreasing trend in the dam''s discharges has been observed in the last 80years. During this study, an alternation of wet, standard and dry years occurred in the estuarine area but no significant long-term trend was observed. River discharge, in turn, showed a considerable interannual variability and a significantly decreasing long-term trend. Freshwater inputs had an immediate effect on estuarine salinity and turbidity, and consequently on prey availability (mysids). Although 124 nektonic species were collected, only 47 of them (adding up to 99.7% of total abundance) were regularly present in the estuary: 32 marine migrants, 13 estuarine species and 2 diadromous species. Well-defined temporal changes in species composition and abundance yielded clear seasonal patterns in the estuarine nektonic community. Considerable intermonth and interannual changes were occasionally observed relating to freshwater inputs, mainly in winter/autumn of wet years. Thus, within each two-month period, some significant interannual differences in the nektonic community were also observed, with marine migrants tending to be more abundant in dry years. However, changes in the studied nektonic community did not show long-term trends. In conclusion, natural and human-controlled freshwater inputs currently play a significant role in determining the physicochemical conditions and the biota of the Guadalquivir estuary. However, although freshwater input seemed to transitorily affect the estuarine nekton, either directly (flushing out) or indirectly (through changes in salinity, turbidity and prey availability), a quick reestablishment of the estuarine nekton (strong resilience) was observed following freshwater inputs together with the recovery of environmental conditions within the estuary. [Copyright &y& Elsevier]

Abstract: In view of increasing environmental awareness and biodiversity conservation, understanding the main forcing mechanism driving biogeochemical cycles in coral reefs and lagoon coastal areas is a priority. La Niña events cause unbalanced situations in the Equatorial Pacific and result in enhanced precipitation in South West Pacific coastal areas. We investigated the impact of heavy rainfalls during the 2008 La Niña event on the New Caledonia lagoon using a 3D coupled on-line hydrodynamic–biogeochemical model. Simulations and data showed that the whole lagoon was impacted by river inputs and stronger hydrodynamics, enhancing chlorophyll-a concentration by a factor between 1.7 and 1.9. The coupled model provided new insights into plume transport, highlighting that eastern plumes can be advected northwards or can reach the South West Lagoon, depending on the balance between regional, tide-induced, and wind-induced surface currents. It also provided a synoptic view of lagoon biogeochemical–hydrodynamic response, when remote sensing data are not available due to cloud coverage. [Copyright &y& Elsevier]

Coastal lagoons are important systems for freshwater, estuarine and marine organisms; they are considered important zones of reproduction, nursery and feeding for many fish species. The present study investigates the fish assemblages of the natural reserve of Dzilam and their relationship with the hydrologic variables. A total of 6 474 individuals (81 species) were collected, contributing with more than 50% considering the Importance Value Index (IVI), Sphoeroides testudineus, Fundulus persimilis, Anchoa mitchilli, Eucinostomus gula, Eucinostomus argenteus and Mugil trichodon. Differences in species composition were found between seasons the highest during the cold fronts. Spatially, differences were related with the presence of freshwater seeps, the highest in the ecological characterized eastern part and the lowest with higher difference in specific composition located in the western part of the internal zone, due to a higher abundance and dominance of L. rhomboides. Salinity and temperature were the variables that presented a higher influence in the distribution of some pelagic species such as A. mitchilli and A. hepsetus. Because of the abundant freshwater seeps characteristic of the coastal lagoons of Yucatan Peninsula their community structure and fish assemblage display spatial and temporal differences in specific composition. [ABSTRACT FROM AUTHOR]

Seasonal and inter-annual variability of environmental characteristics and of plankton were analysed based on monthly surveys of the physical structure of the water column, nutrients, phytoplankton, and zooplankton biomass and abundance in the Gulf of Trieste (1989–1995). Seasonal plankton dynamics were related to Soĉa River run-off, the main freshwater source, and peaks of autotrophic biomass were associated with extended periods of high freshwater inflow. Our results indicate that the freshwater discharge during spring was more important for annual phytobiomass than total yearly input. In 1993, which was characterized by a relatively high total annual freshwater input but by a dry spring, the lowest average chlorophyll biomass (0.85 μg l−1) and cumulative monthly mesozooplanktonic biomass (123 mg AFDW m−3) were observed over the entire period. Annual peaks of phytoplankton biomass were mainly due to increases in diatom abundance, while small-sized cells (microflagellates, coccolithophores) dominated during periods of low Chl a concentrations. Consumer community patterns followed autotrophic biomass evolution with high abundance of herbivores and mixed feeders in spring, and fine-filter feeders and planktonic protists during summer. A large inter-annual variability emphasizes the importance of long-term monitoring in areas like the Gulf of Trieste for distinguishing anthropogenic trends from natural variations of plankton. [ABSTRACT FROM PUBLISHER]