Large Estuary Research Articles

Connecting foraging and roosting areas reveals how food stocks explain shorebird numbers

Shorebird populations, especially those feeding on shellfish, have strongly declined in recent decades and identifying the drivers of these declines is important for conservation. Changing food stocks are thought to be a key driver of these declines and may also explain why trends have not been uniform across Europe's largest estuary. We therefore investigated how winter population trends of Eurasian oystercatchers (Haematopus ostralegus) were linked to food availability in the Dutch Wadden Sea. Our analysis incorporated two spatial scales, a smaller scale focused on roost counting areas and food available to birds in these areas and a larger spatial scale of tidal basins. A novelty in our study is that we quantify the connectivity between roosting and foraging areas, identified from GPS tracking data. This allowed us to estimate food available to roosting birds and thus how food availability may explain local population trends. At the smaller spatial scale of roost counting areas, there was no clear relationship between available food and the number of roosting oystercatchers, indicating that other factors may drive population fluctuations at finer spatial scales. At the scale of tidal basins, however, there was a significant relationship between population trends and available food, especially cockle Cerastoderma edule,. Mortality and recruitment alone could not account for the large fluctuations in bird counts, suggesting that the site choice of wintering migratory oystercatchers may primarily drive these large fluctuations. Furthermore, the relationship between oystercatcher abundance and benthic food stocks, suggests winter shorebird counts could act as ecological indicators of ecosystem health, informing about the winter status of food stocks at a spatial scale of tidal basins.

Integrated transcriptomics and proteomics revealed the distinct toxicological effects of multi-metal contamination on oysters

The Pearl River Estuary (PRE) is the largest estuary in southern China and under high metal stress. In the present study, we employed an integrated method of transcriptomics and proteomics to investigate the ecotoxicological effects of trace metals on the Hong Kong oyster Crassostrea hongkongensis. Three oyster populations with distinct spatial distributions of metals were sampled, including the Control (Station QA, the lowest metal levels), the High Cd (Station JZ, the highest Cd), and the High Zn–Cu–Cr–Ni (Station LFS, with the highest levels of zinc, copper, chromium, and nickel). Dominant metals in oysters were differentiated by principal component analysis (PCA), and theirgene and protein profiles were studied using RNA-seq and iTRAQ techniques. Of the 2250 proteins identified at both protein and RNA levels, 70 proteins exhibited differential expressions in response to metal stress in oysters from the two contaminated stations. There were 8 proteins altered at both stations, with the potential effects on mitochondria and endoplasmic reticulum by Ag. The genotoxicity, including impaired DNA replication and transcription, was specifically observed in the High Cd oysters with the dominating influence of Cd. The structural components (cytoskeleton and chromosome-associated proteins) were impaired by the over-accumulated Cu, Zn, Cr, and Ni at Station LFS. However, enhanced tRNA biogenesis and exosome activity might help the oysters to alleviate the toxicities resulting from their exposure to these metals. Our study provided comprehensive information on the molecular changes in oysters at both protein and RNA levels in responding to multi-levels of trace metal stress.

Comprehensive bathymetry and intertidal topography of the Amazon estuary

Abstract. The characterization of estuarine hydrodynamics primarily depends on knowledge of the bathymetry and topography. Here, we present the first comprehensive, high-resolution dataset of the topography and bathymetry of the Amazon River estuary, the world's largest estuary. Our product is based on an innovative approach combining spaceborne remote sensing data, an extensive and processed river depth dataset, and auxiliary data. Our goal with this mapping is to promote the database usage in studies that require this information, such as hydrodynamic modeling or geomorphological assessments. Our twofold approach considered 500 000 sounding points digitized from 19 nautical charts for bathymetry estimation, in conjunction with a state-of-the-art topographic dataset based on remote sensing, encompassing intertidal flats, riverbanks, and adjacent floodplains. Finally, our estimate can be accessed in a unified 30 m resolution regular grid referenced to the Earth Gravitational Model 2008 (EGM08), complemented both landward and seaward by land (Multi-Error-Removed Improved-Terrain digital elevation model, MERIT DEM) and ocean (General Bathymetric Chart of the Oceans version 2020, GEBCO_2020) topographic data. Extensive validation against independent and spatially distributed data, from an airborne lidar survey, from ICESat-2 altimetric satellite data, and from various in situ surveys, shows a typical vertical accuracy of 7.2 m (riverbed) and 1.2 m (non-vegetated intertidal floodplains). The dataset is available at https://doi.org/10.17632/3g6b5ynrdb.2 (Fassoni-Andrade et al., 2021).

Integrative Taxonomy Reveals That the Marine Brachyuran Crab Pyromaia tuberculata (Lockington, 1877) Reached Eastern Atlantic

Pyromaia tuberculata is native to the north-eastern Pacific Ocean and currently established in distant regions in the Pacific Ocean and southwest Atlantic. Outside its native range, this species has become established in organically polluted enclosed waters, such as bays. The Tagus estuary, with a broad shallow bay, is one of the largest estuaries in the west coast of Europe, located in western mainland Portugal, bordering the city of Lisbon. In this study, sediment samples were collected in the estuary between 2016 and 2017. Several adult specimens of P. tuberculata, including one ovigerous female, were morphologically and genetically identified, resulting in accurate identification of the species. The constant presence of adults over a 16-month sampling period suggests that the species has become established in the Tagus estuary. Moreover, their short life cycle, which allows for the production of at least two generations per year, with females reaching maturity within six months after settlement, favours population establishment. Despite being referred to as invasive, there are no records of adverse effects of P. tuberculata to the environment and socio-economy in regions outside its native range. However, due to its expanding ability, its inclusion in European monitoring programmes would indeed be desirable.

Habitat and humans predict the distribution of juvenile and adult snapper (Sparidae: Chrysophrys auratus) along Australia's most populated coastline

Ecosystem-based fisheries managers are increasingly seeking quantitative and spatially-explicit information on species distributions to assist with the management of fisheries and aquatic habitats. In this study, we used boosted regression trees (BRT) to build species distribution models for a highly valued coastal teleost – pink snapper (Sparidae: Chrysophrys auratus ) across rocky reefs adjacent to Australia's most urbanised coastline. BRT models for juvenile (<25 cm total length) and adult (>32 cm total length) snapper were created using a suite of environmental and habitat predictors. A surrogate for multiple anthropogenic stressors, measured as surrounding human population density, was also included in the models. The BRT model for juvenile snapper performed well (cross-validated AUC = 0.78) and identified habitat features as the most important drivers of their distribution across the region. Juvenile snapper were commonly associated with small patch reefs of low relief adjacent to large estuarine water bodies. In contrast, the performance of the BRT model for adult snapper was weak (cross-validated AUC = 0.68) but identified human population density over habitat features as the strongest predictor of adult snapper distributions. Lower occurrences of adult snapper were associated with reef habitats adjacent to large metropolitan centres, suggesting anthropogenic stressors, such as water pollution, noise and fishing may be negatively impacting adult snapper in the region. Our results highlight essential habitats for snapper populations, notably the importance of large estuaries in the coastal seascape, which are nurseries for juvenile snapper. Knowledge of the demographic habitat associations and spatial distribution of snapper across this highly urbanised coastline will support ongoing management and monitoring of snapper populations and their key habitats. • Juvenile snapper associated with small, low relief reefs adjacent to estuaries • Adult snapper negatively associated with human population density • Results suggest impacts of human stressors on the occurrence of adult snapper • Knowledge of snapper distributions and essential habitats will assist management

Tidal stream energy resource characterization in the Salish Sea

The Salish Sea, a large estuary on the Pacific Northwest coast, represents a great tidal stream resource because of its strong tidal currents in many tidal channels. However, the tidal energy resource in the Salish Sea has not been systematically characterized. This paper presents a modeling study conducted to characterize the tidal energy resource in the Salish Sea based on a high-resolution tidal hydrodynamic model, which was validated using data derived from 10 tide gauges and 132 current stations. A total of 16 tidal channels with strong currents were identified as hotspots for potential tidal energy development in the Salish Sea. Probability distributions and exceedance of the cross-channel average velocity were calculated at all 16 channels based on international standards for tidal energy resource characterization. The tidal energy resource at the 16 hotspots was also characterized using power density distributions and kinetic energy fluxes. The ranking of the kinetic energy fluxes suggested that Admiralty Inlet, Rosario Strait, and Middle Channel are the top three tidal energy hotspots in the Salish Sea. The study demonstrated the need of a high-resolution modeling framework for accurate simulation of tidal currents in large complex estuarine systems, in the context of tidal resource characterization and assessment.

Organochlorine pesticide accumulation in fish and catchment sediments of Lake St Lucia: Risks for Africa’s largest estuary

Although use of organochlorine pesticides (OCPs) has been banned or severely limited on a global basis, concerning concentrations continue to be reported in many tropical and subtropical regions of the world. These habitats often support high levels of unique biodiversity and vulnerable communities that depend on the environment for their survival. We investigated threats associated with OCP contamination at Lake St Lucia, a global hotspot for biodiversity and a UNESCO World Heritage Site in South Africa. Lake St Lucia is sustained largely by surface runoff from catchment areas where significant quantities of OCPs have historically been used in agriculture and where DDT continues to be used for disease control. Sediments (n = 40) collected from the two largest fluvial inputs to Lake St Lucia showed that these rivers represent important sources of contaminants, with ∑OCP concentrations ranging between 74 and 510 ng g−1. Measured HCH, dieldrin, ∑DDT and ∑chlor concentrations exceeded NOAA sediment toxicity guidelines in the majority of samples analysed. Bioaccumulation was assessed by examining residue concentrations in muscle tissues from two abundant fish species from Lake St Lucia. OCPs were detected in all samples analysed, with total concentrations ranging 860–5000 ng g−1 lw and 390–3200 ng g−1 lw for Oreochromis mossambicus (n = 17) and Clarias gariepinus (n = 41), respectively. A health risk assessment indicated potential dietary risk associated with exposure to aldrin, dieldrin and heptachlor, although the cumulative effect of OCPs on human health, ecosystem biodiversity and long-term ecotourism sustainability remains unknown.

Normalizing home ranges of immature Kemp’s ridley turtles (Lepidochelys kempii) in an important estuarine foraging area to better assess their spatial distribution

ABSTRACT Kemp’s ridley turtles (Lepidochelys kempii) are critically endangered sea turtles that forage seasonally in Chesapeake Bay, a large estuary on the east coast of the United States. Most of the Kemp’s ridley turtles foraging in the bay are immature. When tracking these animals, satellite transmitter retention times have been low compared with adult marine turtles of other species. The immature Kemp’s ridleys’ small size and rapid growth leads to shorter, more variable deployments, limiting the use of data. These limited data leave critical questions remaining about the animals’ habitat usage that are difficult to answer without substantially more deployments. A novel sensitivity analysis using simulated deployments indicated that too few animals were tagged with satellite transmitters to identify all possible home-range areas in the Bay. We used simulation to create animal deployments of equal duration to address biases (differing lengths of deployments and time between locations) in home-range analyses and boost the information available from relatively short deployments. Combined home ranges from simulated deployments identified important areas for these animals in the south-western portions of the Chesapeake Bay and in the nearshore areas of the Bay north to the middle of the Bay. These areas represent opportunities for managers to mitigate impacts from boating, dredging, military activities and fishing, and could inform critical habitat designations under the United States Endangered Species Act. Habitat modelling may be needed to identify additional important areas in the Bay where animals were not observed via satellite tracking.

Recruitment and abundance estimation of glass eel genus Anguilla in three large estuaries on the coast of Sukabumi West Java

The rivers on the Sukabumi Coast flow into the Indian Ocean. Three major rivers, namely the Cimandiri River, Cikaso River, and Cibuni River, are sources of glass eel fishing. This study aims to determine the recruitment and estimate of glass eel abundance for future glass eel management. The study was conducted from November 2020-April 2021. Estimation of glass eel abundance was carried out using a fyke net. The glass eel calculation is determined based on the number of glass eels caught, the water discharge entering the fyke net, the water discharge in the estuary, and other variables. The results showed that glass eel recruitment began at the beginning of the rainy season in November 2020 and lasted at the end of the study in April 2021.Anguilla bicolor bicoloris a dominant species of glass eel found in the three river estuaries. The estimated abundance of glass eel was approximately 2,583,438-13,556,650 ind./year or 326,24-1,812 kg/year. The abundance of glass eels at the estuary of Cimandiri River was higher than that of the estuary of Cibuni River and the estuary of Cikaso River.

Habitat models and assessment of habitat partitioning for Kemp’s ridley and loggerhead marine turtles foraging in Chesapeake Bay (USA)

Understanding the spatial distribution of a species is required to enact effective conservation. Complications to effective conservation can arise when the distributions of multiple target species are non-overlapping. Conservation efforts meant to protect one species may shift threats into the distribution of another species. Two species of marine turtle, loggerhead Caretta caretta and Kemp’s ridley Lepidochelys kempii, are common seasonally in Chesapeake Bay, a large estuary on the US east coast. Both species are protected under the US Endangered Species Act and face spatially complex threats in the region. We created habitat suitability models for these 2 species to inform conservation efforts in the region and explore the extent of overlap between their distributions. Argos satellite tags were deployed on 24 Kemp’s ridley and 10 loggerhead turtles to record animal locations within the Bay. Boosted regression tree models were created for each species using presence-only animal locations, predicting suitable habitat within the Bay. Habitat for Kemp’s ridley turtles was predicted in shallow, coastal areas of the southern Bay as well as in brackish areas of rivers. Loggerhead turtle habitat was predicted to extend farther north than Kemp’s ridley habitat and was generally found in deeper areas of the middle Bay. There is some evidence that these 2 species are partitioning habitat. Any conservation measures adopted to conserve marine turtles in the Chesapeake Bay should consider the habitat of both species holistically to avoid shifting impacts from one species to another.

Shifting Baselines in the Chesapeake Bay: An Environmental History by Victor S. Kennedy

Reviewed by: Shifting Baselines in the Chesapeake Bay: An Environmental History by Victor S. Kennedy Geoffrey L. Buckley Shifting Baselines in the Chesapeake Bay: An Environmental History. Victor S. Kennedy. Baltimore, MD: Johns Hopkins University Press, 2018. Pp. 146, charts, drawings, maps, photographs. $38.50, hardcover, ISBN 978-1-4214-2654-9. When I was a graduate student at the University of Oregon in the 1990s, one of my professors, Alvin Urquhart, assigned us to read one of his articles titled "Stripping the Urban Landscape" (1981). The paper, which had served as his presidential address to the Association of Pacific Coast Geographers a decade earlier, focused on environmental transformation—more specifically, the development of an urban strip in Eugene, Oregon. Two sentences in particular made a lasting impression: "That the trend toward environmental artificiality has accelerated in recent decades and that we accept, often unquestioningly, these trends, scarcely needs reiterating" and "Yet the forms which environmental alterations have taken," he noted, "and the direction of the changes do need to be discussed before we forget what the world of some of our grandparents and almost all of our more remote ancestors was like" (Urquhart 1981) (emphasis added). After reading Victor Kennedy's concise and thought-provoking book, I was reminded of this passage because it described a concept that few of us who study past environments knew what to call at the time but recognize today as shifting baseline syndrome. So, what is "shifting baseline" syndrome and why does Kennedy use it to frame his environmental history of the Chesapeake Bay? According to the author, it can best be described as a form of "generational amnesia" (x). As time passes, and the resources on which growing human populations depend begin to dwindle, we become increasingly detached from the natural abundance that previously animated the world and supported the economies of those who came before us. The result is that successive generations accept their increasingly impoverished environments as normal, thereby establishing lower baselines against which to measure future changes. Using a wide range of historical sources, including historical scientific papers, newspaper articles, government reports, port records, and journal accounts—and buttressed by quantitative fisheries data when they became available in the latter part of the nineteenth century—Kennedy seeks to reinstate our understanding and knowledge of the Chesapeake Bay's ecology and past abundance. More important, he admonishes scientists, politicians, state and federal [End Page 113] agency officials, commercial fishers, and others to use this information to raise the bar for ecological restoration. Kennedy's book is divided into nine chapters plus an afterword. The author also includes a helpful appendix that catalogs some of the significant technological innovations in fishing gear—particularly more efficient nets, seines, and pots—that permitted tremendous increases in harvests over the last century and a half. The first two chapters introduce the reader to the concept of shifting baselines; review the ecological factors that made the Chesapeake Bay, in the words of Baltimore's renowned literary critic and contrarian journalist H. L. Mencken, an "immense protein factory"; and then chart the vast fishery's deterioration since the Civil War. Increased sedimentation, nutrient runoff, and pollution in all its forms, not to mention overharvesting of fish and other creatures using increasingly sophisticated technology—all occurring against the backdrop of rapid urbanization and industrialization—are implicated in the decline. Kennedy dedicates the next several chapters to individual species, tracking their rise and fall and, in some cases, their remarkable resilience. These include shad and river herring; oysters; diamond-backed terrapins; waterfowl, especially canvasbacks; sturgeon; and, of course, the iconic blue crab. Relying on "anecdotal accounts of animal abundance" that predate the collection of quantitative data by government authorities—including journals from the seventeenth and eighteenth centuries—Kennedy marvels at the degree to which estimates of fish, oyster, crab, and waterfowl abundance corroborate one another. Reinforcing his thesis of past abundance are industry figures that point to the region's economic dependence on North America's largest estuary, including numbers of workers employed in the combined seafood industries of Maryland and Virginia, as well as various ancillary industries—from coopers to sailmakers to net menders. Although the commercial...

Multidisciplinary assessment of nearshore nursery habitat restoration for an exploited population of marine fish

Nearshore habitats are essential for many marine fish species but are subject to anthropogenic stressors. Assessing the consequences of essential fish habitat degradation on population dynamics and productivity is challenging. We address this by focusing on a metapopulation of the common sole Solea solea, a high-value, exploited flatfish in the Eastern English Channel (EEC). Multidisciplinary data and expert knowledge were compiled to build feasible restoration scenarios for the availability of suitable habitat (measured in habitat surface extent) and chemical quality of juvenile habitats in the highly anthropized Seine estuary, the largest estuary and potentially a sole nursery area of primary interest in the EEC. Scenarios were simulated with a spatially structured life-cycle model to investigate the consequences of local restoration on restricted nursery habitats in the estuary. Restoring surface extent and habitat quality in the Seine estuary dramatically enhances spawning stock biomass (+18%) and fishery catches (+13%) in the EEC. Restoring habitat quality has a greater effect than restoring habitat surface. Because of the low connectivity between subpopulations of sole in the EEC, most of the local restoration benefits remain regional and affect the subpopulation that directly depends on the Seine nursery, with only moderate spread to the entire EEC. Our study emphasizes the utility of spatial simulation models for integrating multidisciplinary knowledge and assessing the consequences of local anthropogenic pressures at wider metapopulation scales. We provide a means of building robust methods to assess the benefits of nearshore habitat restoration for enhancing fish populations and fisheries and integrate habitat value into the sustainable management of exploited species.

Late Pleistocene Catastrophic Landslide from the Balaganchik Ridge: Evidence from the Mitoga 2 Reference Section (Western Kamchatka)

A new reference section of the Okhotsk seaside of Kamchatka in the Mitoga 2 River area is studied and dated for the first time (14C and 230Th/U). Sedimentary deposits were correlated with the previously known sections in the Khomutina‒Mitoga interfluve. It has been established that the sequence of “gray silts and clays” represents deposits of a large lake-type estuary, which began to swamp about 90–80 ka BP, and all sediments overlapping the silts began to form no earlier than 90 ka BP (second half of MIS 5). Deposits of a catastrophic collapse (clastic mass transport over about 100 km, area ≥1500 km2, volume ≥15 km3), which descended from the Balaganchik Ridge about 90‒80 ka BP, were identified. Two main facies were established: dispersed basal layer (“moraine-type loam” sequence) and landslide proper sediments (conglomerates). Valleys of the Bystraya and Plotnikova rivers were blocked by a collapse, resulting in the formation of a large dammed lake. The catastrophic drainage of the lake could occur about 37 ka BP. Deposits related to the dam breakthrough are recorded between the Mitoga 2 River and Zuikovo Settlement on the Okhotsk coast.

Fecal indicators, pathogens, antibiotic resistance genes, and ecotoxicity in Galveston Bay after Hurricane Harvey

Unprecedented rainfall after Hurricane Harvey caused a catastrophic flood in the southern coast of Texas, and flushed significant floodwater and sediments into Galveston Bay, the largest estuary along the Texas Gulf Coast. This study investigated the immediate and long-term (6 months post-Harvey) fecal indicators, pathogenic bacteria, antibiotic resistance genes (ARGs), and ecotoxicity in the Galveston Bay. Dramatic decrease of salinity profile to zero, increased levels of fecal indicator bacteria and pathogenic bacteria, and detection of various ARGs were observed in the water and sediment samples collected 2 weeks post-Harvey. High levels of BlaTEM and cytotoxicity measured by yeast bioluminescent assay (BLYR) were also observed especially near the river mouths. While Vibrio spp. was dominant in water, much higher abundance of fecal indicator bacteria and pathogen were detected in the sediments. A decreasing trend of BlaTEM and cytotoxicity was observed in March 2018 samples, suggesting the Bay has returned to its pre-hurricane conditions 6 months post-Harvey. Interestingly, the abundance of fecal indicator bacteria and pathogens were shifted dramatically according to high-streamflow and low-streamflow seasons in the Bay. The data are useful to construct the model of risk assessment in coastal estuaries system and predict the effects of extreme flooding events in the future.

Water exchange and its relationships with external forcings and residence time in Chesapeake Bay

Abstract Water exchange, featured by bottom inflow and surface outflow in a typical estuary, determines the transport and redistribution of salt, nutrients, pollutants, and suspended sediments and organisms. Water exchange in Chesapeake Bay, the largest estuary in the US, has been extensively studied, yet its long-term interannual variability and its relationship with the external forcings are not fully understood. Based on a long-term (1980–2011) numerical model simulation, this study examines the water exchanges between Chesapeake Bay and the adjacent coastal shelf, between different regions within the bay, as well as their relationships with river discharge, wind, and residence time. Through an EOF analysis of the bottom inflow and surface outflow at seven selected cross-bay sections, we found that over 90% of the spatiotemporal variations of water exchange can be explained by the first two EOF modes, which are highly correlated with the freshwater discharge and northwesterly wind, respectively. Unlike the outflow that increases linearly with river discharge as commonly expected, the inflow responds non-monotonically to river discharge. The relationship between the river discharge and inflow can be described by a combination of the Michaelis–Menten/Monod equation and a linearly decreasing function, i.e., the inflow initially increases with river discharge due to enhanced gravitational circulation and then levels, and gradually declines due to overwhelming seaward barotropic current. We found a locally enhanced water exchange in the lower-middle bay, which can be attributed to the persistent reflux of surface outflow due to the irregular geometry and rapid shoaling in the channel bathymetry. The water exchange and the mean residence time can be connected reciprocally through the bay volume, yet the validation of this relationship depends on the timescale to be considered since the residence time at a given time is controlled by the future hydrodynamics. A delay effect should be considered when using the relationship to estimate outflow interchangeably with the direct computation of the outflow.

Sustainable Exploitation of Dominant Fishes in the Largest Estuary in Southeastern China

Globally, marine fisheries have declined under multiple stresses including overfishing, climate change, and habitat degradation. The Min River Estuary, as the largest estuary in southeastern China, has confronted this situation over recent decades. In this study, the dominant species of fish stocks in the Min River Estuary, including Coilia mystus, Cynoglossus abbreviates, Collichthys lucidus, Amblychaeturichthys hexanema, Polydactylus sextarius, Harpodon nehereus, and Secutor ruconius, were evaluated by the length-based Bayesian biomass estimator method (LBB). Outcomes could be grouped into three categories as healthy, showing the lowest exploitation rate (E: 0.31–0.43) and highest relative biomass (B/Bmsy: 1.30–1.90), including S. ruconius, C. mystus, and H. nehereus; overfished, with a medium E (0.50–0.58) and B/Bmsy (0.68–0.79), including A. hexanema and C. abbreviates; and collapsed, with the highest E (0.89–0.92) and lowest B/Bmsy (0.03–0.21), including C. lucidus and P.sextarius. Corresponding imperative countermeasures such as using larger-sized mesh gears and reducing fishing intensity should be deployed according to the current status of each species for sustainable fishery exploitation and fish conservation.

Influence of River Discharge on the Transport of the Saltwater Group from the North Branch in the Yangtze River Estuary.

The Yangtze River Estuary (YRE) is the largest estuary in China. Recently, due to the increase of extent and frequency, saltwater intrusion has received more and more attention. In this paper, with the adoption of hydrodynamic and salinity transport mode, quantitative research of the influence of river discharge to the North Branch (NB) of the Yangtze River on the saltwater group migration law is conducted. Tide and salinity data are used to validate the model effectively. In different paths, the changes in flow and the movement of the saltwater group are similar. The saltwater group starts to move downward from the sixth day. In the staged downward movement, the larger the runoff volume, the further the distance of the core of the saltwater group, and converges to around 90 km gradually. At different flow rates, the relationship between the average location of each waterway saltwater group core tide cycle and time is consistent with the Gompertz model, and its parameters had a nonlinear relationship with the flow rate. A function is constructed to calculate the length and time of the saltwater group migration. As the flow rate increases, the faster the core of the saltwater group reaches the entrance. The downwards movement takes 3–8 days. Quantitative research on the influence of the saltwater spilling from NB to the three major reservoirs in the South Branch (SB)is conducted. The simulation results are consistent with the function calculation. River discharge has a direct impact on saltwater transport and diffusion in the YRE.

Picophytoplankton dynamics in a large temperate estuary and impacts of extreme storm events

Picophytoplankton (PicoP) are increasingly recognized as significant contributors to primary productivity and phytoplankton biomass in coastal and estuarine systems. Remarkably though, PicoP composition is unknown or not well-resolved in several large estuaries including the semi-lagoonal Neuse River Estuary (NRE), a tributary of the second largest estuary-system in the lower USA, the Pamlico-Albemarle Sound. The NRE is impacted by extreme weather events, including recent increases in precipitation and flooding associated with tropical cyclones. Here we examined the impacts of moderate to extreme (Hurricane Florence, September 2018) precipitation events on NRE PicoP abundances and composition using flow cytometry, over a 1.5 year period. Phycocyanin-rich Synechococcus-like cells were the most dominant PicoP, reaching ~ 106 cells mL−1, which highlights their importance as key primary producers in this relatively long residence-time estuary. Ephemeral “blooms” of picoeukaryotic phytoplankton (PEUK) during spring and after spikes in river flow were also detected, making PEUK periodically major contributors to PicoP biomass (up to ~ 80%). About half of the variation in PicoP abundance was explained by measured environmental variables. Temperature explained the most variation (24.5%). Change in total dissolved nitrogen concentration, an indication of increased river discharge, explained the second-most variation in PicoP abundance (15.9%). The short-term impacts of extreme river discharge from Hurricane Florence were particularly evident as PicoP biomass was reduced by ~ 100-fold for more than 2 weeks. We conclude that precipitation is a highly influential factor on estuarine PicoP biomass and composition, and show how ‘wetter’ future climate conditions will have ecosystem impacts down to the smallest of phytoplankton.

Features of the Intrinsic L-Band Radiation of the Gulf of Ob during the Freeze-Up Period

This article analyzes seasonal and interannual dependences of brightness temperature in different zones of the Gulf of Ob according to data from the MIRAS radiometer (SMOS satellite). It is shown that, while the brightness temperature dynamics of the freshwater zone of the Gulf of Ob (the estuary and the central zone) is similar to that of freshwater lakes, this dynamics in the seawater zone is different. The authors explain this difference by an increase in water salinity and, consequently, an increase in radiation absorption in the lower ice layer, which is in contact with the water surface. The regularities of seasonal variations of brightness temperature in different zones of the Gulf of Ob and related ice-cover phases can be used to assess salinity and water mixing in large estuaries of the Arctic in winter based on satellite microwave radiometry.

Surveillance of plasticizers, bisphenol A, steroids and caffeine in surface water of River Ganga and Sundarban wetland along the Bay of Bengal: occurrence, sources, estrogenicity screening and ecotoxicological risk assessment

The transboundary River Ganga serves as a conduit for meltwater from the Himalayas and is a major freshwater source for two thirds of Indian population before emptying into the Sundarban Delta, the largest estuary in the Bay of Bengal. Endocrine disrupting compounds (EDCs) such as phthalic acid esters (PAEs) and bisphenol A (BPA) used as organic plastic additives can pollute the aquatic environment receiving plastic litter. Hence, we have investigated these EDCs in water samples from Ganga and Sundarban wetland of India. Since these compounds exhibit estrogenic potential, we have further measured steroids and evaluated the estrogenic activity (estradiol equivalents, BioE2Eqs) using an in-vitro bioassay (E-Screen). Further BioE2Eqs were compared with the sum of predicted estradiol equivalents based on the chemical concentrations of PAEs and BPA by E-Screen (ChemE2Eq) and YES factors (ChemYES). Caffeine was measured as a marker for anthropogenic wastewater discharge. Results showed that the highest BioE2Eq (below the lowest observable effect of E2 on fish) was associated with sites having sewer outfalls in the middle stretch of the river, and concomitantly coinciding with the elevated concentrations of caffeine. Neither ChemE2Eq nor ChemYES correlated with measured BioE2Eqs. River concentrations of BPA (0.04–4.46 µg/L) and ∑7plasticizers (0.43–7.63 µg/L) were higher than BPA (0.21–2.82 µg/L) and ∑7plasticizers (0.85–2 µg/L) in the Sundarban wetland. The only steroids detected were androgens, found at four sites in Ganga (0.007 µg/L± 0.003, mean ± S.D.). The highest estimated ecotoxicological risk to aquatic insect and fish stemmed from BPA. A secondary effect, and a potential impact on human health could be reflected via fish consumption from the productive fisheries region along the lower stretch of River Ganga. Identification of areas of elevated estrogenicity, plasticizer and steroid concentrations in River Ganga can be used to design and implement interventions for the remediation of such emerging contaminants.