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Oxygen depletion in coastal waters is increasing globally due primarily to eutrophication and warming. Hypoxia responses to nutrient loading and climate change have been extensively studied in large systems like the Chesapeake Bay and the Baltic Sea, while fewer studies have investigated smaller, shallower hypoxic zones. Thus, an improved understanding of the interactions of eutrophication and warming on hypoxia expansion (or reduction) in the wide variety of different estuarine environments is needed. We examined interannual controls on oxygen depletion in the Patuxent River estuary, a eutrophic sub-estuary of Chesapeake Bay where seasonal hypoxia develops annually. We conducted a spatial and temporal analysis of dissolved oxygen (DO) trends, timing, and several metrics of depletion over a long-term record (1985–2021). We found an internally generated hypoxic zone that initiates in the middle estuary, spreading upstream and downstream as the summer progresses, and that hypoxic volume days (HVD) have been increasing (0.11 per year, p = 0.03) over the record despite reduced watershed nitrogen loads and stable phosphorus loads. River flow and temperature have been increasing and are major drivers of increased HVD, with river flow explaining 40% of the interannual variation in HVD (temperature has increased 0.03 and 0.06 °C per year in summer and fall, respectively). Apparent oxygen utilization (AOU) is increasing in bottom waters in the fall, consistent with increasing trends of both water temperature and stratification strength. HVD was negatively related (r2 = 0.34, slope = −0.59*HVD) to the biomass of benthic invertebrates in the middle region of the estuary, suggesting that benthic forage for higher trophic levels will be limited by sustained hypoxia. These results indicate that current and future climate variability plays an important role in regulating oxygen depletion in the Patuxent River estuary, which reinforces the need to factor climate change into strategies for the restoration and management of estuaries. [ABSTRACT FROM AUTHOR]

Hypoxia in coastal waters is a pressing ecological problem caused by continued eutrophication and climatic change that has widespread consequences for metazoan life and biogeochemical cycles. Numerous studies have investigated the controls on seasonal hypoxia formation and persistence in many of the world's large estuaries and coastal hypoxic zones, but far fewer studies have examined the controls on short-term oxygen variability that leads to diel-cycling hypoxia in shallow-water environments. We utilized a unique, comprehensive (181 stations) record of dissolved oxygen concentrations collected at shallow water sites (primarily < 2 m) at high frequency (15 min) throughout the estuarine complex of the Chesapeake Bay and its tributaries to quantify how internal and external variables co-varied with dissolved oxygen. We used a combination of time-series analysis, harmonic analysis, and machine learning (e.g., classification and regression trees (CART)) approaches to identify spatial patterns in major controls on oxygen variability and the duration of moderate hypoxia. We found that key controls on oxygen variability varied substantially over space. For example, photosynthetically active radiation (PAR) was a strong predictor of oxygen dynamics in the majority of mesohaline waters. In more fetch-exposed stations, wind strongly controlled hypoxic duration, but in eutrophic, inshore locations, chlorophyll a, or turbidity were often better predictors. Specifically, diel oxygen variability was muted in upstream regions characterized by high turbidity. The duration of low oxygen conditions, which we defined conservatively as less than 4.8 mg O2 L−1 (156 µM), was strongly controlled by temperature, and simple projections of regional warming and CART-derived oxygen thresholds suggest that the Bay could experience a 10% increase in this type of hypoxia duration by mid-to-late twenty-first century. The ratio of tidal to biological variability in oxygen was found to increase under conditions of higher turbidity, stronger wind, and lower salinity, but biological variability was typically a factor of two higher than tidal variability. Although chlorophyll-a generated high oxygen concentrations at some locations, those stations with exceptionally high chlorophyll a (> 30 µg L−1) were the most vulnerable to hypoxia. Because conventional water quality modeling frameworks are designed to capture hypoxia on relatively long time scales, these new insights can help inform updated oxygen models to support the management of shallow-water estuaries in the face of managed nutrient reductions and climate change. [ABSTRACT FROM AUTHOR]

The high concentration of chlorophyll a (Chl-a) and pollutants in estuaries has led to the deterioration of marine environmental quality and a reduction in the sustainability and safety of marine ecosystems. This study analyzed the distribution characteristics of Chl-a and pollutants in the Liugu Estuary (LE) based on field survey data. By incorporating environmental factors, the water's nutritional status and nutrient limitations were evaluated. The results indicated that there were variations in the concentration range of Chl-a and pollutants between flood and non-flood seasons in the LE, with nitrogen identified as the main limiting nutrient. The correlation indicated that Chl-a and nutrient levels in the LE were influenced by a complex interplay of multiple factors. River inputs with higher pollution levels increased concentrations and reduced DO levels, limiting the rise in Chl-a concentration and the uptake of nutrients by phytoplankton. The findings of this study could provide essential information for an in-depth examination of the eutrophication characteristics of the LE and offer a scientific foundation for the restoration and management of the estuary's ecological environment. [ABSTRACT FROM AUTHOR]

Since 1958, there have been significant changes in the Yangtze River estuary. Due to extensive reclamation and construction of ports and channels, the water area has drastically decreased, resulting in corresponding changes in hydrodynamics and riverbeds at the mouth of the river. According to the analysis of measured topographic data and Delft3D-FLOW model for seven typical historical periods since 1958 at the Yangtze River Estuary, this study investigates the characteristics of riverbed evolution and tidal flow dynamics. From 1958 to 2019, driven by strong human activities, the total area of the Yangtze River Estuary decreased from 2084 km2 to 1403 km2, with a decrease of 32.7%, while the total volume of the corresponding river channel changed slightly and remained stable. Compared with 1958, the volume of the Yangtze River Estuary in 2019 only increased by 345 million m3, with an increase of about 4.1%. The tidal dynamic change of the Yangtze Estuary is closely related to the riverbed evolution of each reach, which not only shapes the estuary landform, but also is affected by the riverbed evolution. Tidal level, tidal range and water area change are closely related. With the decrease of water area in the Yangtze River Estuary, tidal range tends to increase. Tidal prism change is closely related to channel volume. In the past 60 years, the tidal volume at the mouth of the Yangtze River has decreased by 8%. The research findings will provide technical support for enhancing flood control and tide resistance measures at the Yangtze River Estuary, as well as formulating comprehensive management plans for estuaries, contributing to the protection and sustainable development of the Yangtze River Estuary. [ABSTRACT FROM AUTHOR]

Mangrove wetland restoration projects have been conducted for many years and it is important to evaluate their success. In this study, we explored the role of monitoring macrobenthos in assessing the success of mangrove restoration. In particular, we sampled soil and macrobenthos from a mangrove wetland area after restoration for one, three, and five years in the Pearl River Estuary Delta in China to explore the effects of different restoration periods on the macrobenthos community structure. The results showed that the macrobenthos collected in the study area mainly comprised Polychaete annelids and Bivalvia mollusks, and there were no significant differences in the species, biomass, richness index, diversity index, and evenness index among different mangrove wetland restoration stages. The macrobenthos biomass, species richness, diversity index, and evenness index were mainly correlated with the soil electrical conductivity, pH, total phosphorus, and soil organic carbon. Compared with mangrove restoration for one year, the average species richness, Margalef richness index, Shannon diversity index, and Pielou evenness index for macrobenthos were significantly higher after three years, thereby indicating that the macrobenthos species diversity increased significantly after mangrove wetland restoration for three years. However, the macrobenthos diversity was lower after mangrove wetland restoration for five years, which may have been due to human activities and soil pollution. The findings obtained in this study provide basic information to facilitate mangrove wetland restoration and conservation. [ABSTRACT FROM AUTHOR]

The theory and practice of adaptive management and adaptive governance have been widely studied in the complex social contexts that mediate how humans interact with ecosystems. Adaptive governance is thought to enable adaptive management in such contexts. In this study, we examine four often-used principles of adaptive governance (polycentric institutions, collaboration, social learning and complexity thinking) to develop a framework for reflecting on adaptive governance of a social-ecological system—the Knysna Estuary in South Africa. This estuary is a priority for biodiversity conservation, as well as a common-pool resource central to livelihoods. We used the framework to structure dialogue on the extent to which the four principles of adaptive governance were being applied in the management of the Knysna Estuary. The dialogue included diverse stakeholders, from those who have the power to influence adaptive management to those most dependent on the resource for their livelihoods. Based on a combination of theory and current reality we then identified eight indicators that could be used to guide a transition towards improved adaptive governance of the estuary. These indicators were assessed and supported by most stakeholders. The main contributions of our research are (a) a process for combining theory and stakeholder dialogue to reflect on adaptive governance of a social-ecological system; (b) a set of indicators or conditions that emerged from our participatory process that can be used for reflexive monitoring and adaptation of adaptive governance of Knysna Estuary; and (c) a real-world example of seeking complementary links between adaptive governance and adaptive management to promote effective management of complex social-ecological systems. [ABSTRACT FROM AUTHOR]

Coastal environments are at the frontline of sea-level rise effects, and seawater intrusion constitutes one of the most important causes of salinization, changing the ecological patterns. Hence, we hypothesized that seawater intrusion would alter environmental gradients, causing either abrupt or gradual changes in the phytoplankton of Itapecuru River estuary. Physical and chemical and biological variables were collected bimonthly at six sites between 2019 and 2020. Seventy-six phytoplankton indicators were selected based on their specific functional traits and indicator value. Polymyxus coronalis was a good indicator of the limit of seawater intrusion. Multivariate analyses revealed high species dispersion among the estuarine sectors governed by variations in salinity, suspended particulate matter, cell size, and silicate. The distribution of freshwater species in the upper sector was correlated with low nutrient values and salinity. The marine species were transported between the middle and lower sectors under the opposite conditions. The seawater intrusion negatively affected the community, primarily in the dry season when the displacement of the turbidity maximum zone estuarine altered the structure, reducing its density, diversity, and biomass. The present study generated important information about seawater intrusion effects on the spatiotemporal variation in the phytoplankton community and provided a tool for the sustainable management of tropical estuaries. [ABSTRACT FROM AUTHOR]

Estuarine nekton (fishes, crabs, and shrimps) play key ecological roles and support valuable commercial and recreational fisheries. Long-term research programs focused on nekton can provide insight into community and population-level changes over time, but are uncommon due to funding and logistical constraints. We describe patterns and changes in a nekton assemblage from an intertidal creek in the North Inlet estuary, South Carolina, USA based on 19 years of observations. From 1984 to 2002, biweekly seine collections (approximately every 2 weeks, n = 469) were made in a pool isolated within an intertidal creek at low tide. The assemblage was composed of juvenile and small adult (mostly < 100 mm) fishes, shrimps, and crabs. The 10 most abundant species made up > 97% of the catch; these species included (in descending order): Leiostomus xanthurus, Litopenaeus setiferus, Fundulus heteroclitus, Mugil cephalus, Farfantepenaeus aztecus, Eucinostomus spp., Mugil curema, Fundulus majalis, Menidia menidia, and Brevoortia tyrannus. The assemblage exhibited a distinct seasonality across years, with peak total abundance in mid-spring, peak total biomass in late spring, and highest species richness in late summer and early fall. Total abundance and species richness showed evidence of significant increases across years, total biomass and the Shannon diversity index remained unchanged, and evenness significantly declined. The composition of the assemblage shifted during the sampling period, with the abundance of key year-round residents (F. heteroclitus, M. cephalus) decreasing and warm-season species (L. xanthurus) increasing. Most of the five metrics of the nekton assemblage and the abundances of the five top species were positively correlated with both water temperature and salinity. Direct and indirect effects of hurricanes and storm events on the hydrogeomorphology of the creek and pool were also recognized as influences on the long-term patterns and trends. Long-term (decadal) sampling programs like this can provide important baseline information, and thus insight into the influence of significant weather events and global climate change on nekton populations and their roles in ecosystem dynamics, as well as inform the management of estuaries and fisheries in the southeastern US. [ABSTRACT FROM AUTHOR]

This study aimed to analyze the relationship between Cygnus spp. population trends and land-use changes and artificial development activities in the Nakdonggang Estuary for the necessity of management to the buffer area outside the protected area boundary in Korea. Analysis of the 15-year population change revealed a sharp decline in the Cygnus columbianus population in the winter, which could be attributed to the Nakdonggang Estuary becoming unfeasible as their wintering site. In contrast, there was no sharp decline in the Cygnus cygnus population, although a moderate decline was identified. Over the past 30 years, farmland activities decreased by approximately 10% in the areas adjacent to the protected area resulting from the expansion of the urbanized area. The rate of decrease in the water body area was high, attributed to urban development through reclamation. The correlation analysis between the area (ha) of paddy fields and the monthly (Nov.–Feb.) population of C. columbianus indicated that the populations in December (R2 = 0.768) and January (R2 = 0.743) were more correlated with the change in paddy field areas than those in the early winter (November: R2 = 0.457) and at the end of winter (February: R2 = 0.582). In the case of C. cygnus, the population tended to increase with increases in the areas of paddy fields, but the statistical explanatory power was low. We identified a distinct difference in that C. columbianus was more sensitive to urbanization than C. cygnus in the Nakdonggang Estuary. [ABSTRACT FROM AUTHOR]

It is essential to make an accurate prediction of the concentration of dissolved oxygen (DO), hydrogen ion concentration (pH), and potassium permanganate (KMnO4) in order to ensure the quality of the drinking water. The lack of monitoring data and the large fluctuation increase the difficulty of predicting DO, pH, and KMnO4 in the tide-sensing estuary. In this research, improved grey association analysis (IGRA) was provided to determine the correlation between DO, pH, KMnO4, and other water quality indicators, thereby resolving the dimension disaster problem of long short-term memory (LSTM). Furthermore, LSTM based on the improved sparrow search algorithm (ISSA) was established, and five LSTM parameters—learning rate, batch size, training times, hidden layer nodes, and fully connected hidden layer nodes—are automatically optimized, which could accurately predict the concentration of DO, pH, and KMnO4. Using the data from the Qiantang River Gate Observation Station from November 8, 2020, to June 27, 2021, 70% of which were training sets and 30% of which were test sets, predicted data for day 4. The results show that the coefficient of determination (R2) of the IGRA-ISSA-LSTM model for DO, pH, and KMnO4 were 0.92, 0.93, and 0.726, respectively, which are greater than that of IGRA-BP model, IGRA-LSTM model, and IGRA-SSA-LSTM model. Therefore, this research provides technical support for water quality management in tidal estuaries. [ABSTRACT FROM AUTHOR]

Reliable predictions of future inundation extent within estuaries require a precise evaluation of future extreme sea levels and the application of accurate numerical models that account for the physical processes driving estuarine hydrodynamics. In this study, a methodology that integrates the estimation of local extreme sea levels with high-resolution numerical modeling was applied to assess the future inundation extent in five estuarine systems located on the Portuguese Coast. The main findings obtained were compared with available results from the popular bathtub approach, that disregards the physical processes driving estuarine hydrodynamics and therefore provide imprecise predictions of inundation extent and associated socio-economic impacts. The inundation extent is revealed to be highly dependent on the extreme sea levels and on the estuarine geomorphology, which controls the propagating long-wave. As the long-wave height is highly attenuated within estuaries that have adjacent low-lying areas, restricted inlets, or extensive tidal flats, the results of this study revealed that the extent of inundation is considerably smaller than that obtained by the bathtub approach. The uncertainties associated with mean sea level rise and the estuarine geomorphological evolution constitute the greatest difficulty in assessing the extent of flooding, posing major challenges to the efficient and sustainable management of estuaries. [ABSTRACT FROM AUTHOR]

Mosquito populations associated with the heavily urbanised Cooks River and Wolli Creek estuaries, Sydney, Australia, were investigated to assist in identifying potential pest and public health threats and assist local authorities in developing management strategies. Adult mosquitoes were sampled using carbon dioxide baited light traps at five locations, including two sites alongside Cooks River (Steel Park and Gough Whitlam Park), two sites alongside Wolli Creek (Jackson Track and Turella Reserve) as well as an additional location, Barton Park (Muddy Creek). These locations represented at least one of three distinct landscape characteristics, dominated either by bushland, parkland, or estuarine wetland habitats. Three trap sites were established at each location and sampling adult host-seeking mosquitoes took place on a weekly basis for 4 weeks. All mosquito specimens were identified to determine differences in relative abundance and community composition. There was a distinct difference in the abundance and community composition of mosquitoes collected between the five locations with the differences due to the presence and abundance of Aedes vigilax, Culex sitiens, Aedes notoscriptus Those locations close to estuarine wetlands were dominated by A. vigilax while other sites were dominated by mosquitoes associated with urban habitats such as stormwater infrastructure or backyard water-holding containers (e.g. A. notoscriptus and Culex quinquefasciatus). Sites adjacent to urban bushland contained a higher species richness, but not necessarily greater abundance, of mosquitoes than other sites. This study provided an insight into mosquito populations within a previously unstudied area of Sydney and highlight that local authorities should carefully consider wetland management and urban planning strategies in the future to assist in identifying potential risks of nuisance-biting, mosquito-borne disease and in determining the need for further public health action. [ABSTRACT FROM AUTHOR]

We developed a method to predict the susceptibility of New Zealand estuaries to eutrophication. This method predicts macroalgae and phytoplankton responses to potential nutrient concentrations and flushing times, obtained nationally from simple dilution models, a GIS land-use model and physical estuary properties. Macroalgal response was based on an empirically derived relationship between potential nitrogen concentrations and an established macroalgal index (EQR) and phytoplankton response using an analytical growth model. Intertidal area was used to determine which primary producer was likely to lead to eutrophic conditions within estuaries. We calculated the eutrophication susceptibility of 399 New Zealand estuaries and assigned them to susceptibility bands A (lowest expected impact) to D (highest expected impact). Twenty-seven percent of New Zealand estuaries have high or very high eutrophication susceptibilities (band C or D), mostly (63% of band C and D) due to macroalgae. The physical properties of estuaries strongly influence susceptibility to macroalgae or phytoplankton blooms, and estuaries with similar physical properties cluster spatially around New Zealand's coasts. As a result, regional patterns in susceptibility are apparent due to a combination of estuary types and land use patterns. The few areas in New Zealand with consistently low estuary eutrophication susceptibilities are either undeveloped or have estuaries with short flushing times, low intertidal area and/or minimal tidal influx. Estuaries with conditions favourable for macroalgae are most at risk. Our approach provides estuary-integrated susceptibility scores likely to be of use as a regional or national screening tool to prioritise more in-depth estuary assessments, to evaluate likely responses to altered nutrient loading regimes and assist in developing management strategies for estuaries. [ABSTRACT FROM AUTHOR]

Mhlathuze Estuary constitutes one of the ecological most important estuaries in southern Africa and is regarded as an estuary of high conservation importance. The ongoing expansion of the adjacent industrialized Richards Bay Harbour increases the risk of metal pollution to the estuary. This study provides insight into the extent and sources of trace metal contamination using pollution indices and sediment quality guidelines and the effect on macrobenthic habitat quality. Sediment samples for sediment metal and macrobenthic analysis were collected quarterly during 2016–2017 at five sites in the estuary using a marine-grade Zabalocki grab. Metal concentrations were determined using an ICP-OES. Sediment metal concentrations were consistently highest in the subtidal mudflats and lowest in marine sand at the mouth of the estuary. Concentrations of all metals displayed significant differences between sites (P < 0.05). Pollution indices indicated moderate enrichment of Cr at all sites, although the mean pollution load index showed the estuary to be unpolluted. Comparison with sediment quality guidelines revealed that concentrations of Ni and Cr were potentially toxic to biota. Using multivariate analysis, metal concentrations appeared not to significantly affect the macrobenthic community. The multi-metric biotic index M-AMBI proved to be a robust tool in the habitat quality assessment of the estuary. The continuing use of M-AMBI as a biomonitoring tool for ecological management of the estuary is advocated. [ABSTRACT FROM AUTHOR]

The present work represented first study of the spatio-seasonal distribution of the multi-elements in the suspended particulate matter (SPM) of the tropical Hooghly river estuary (HRE), eastern part of India. The high load of SPM (20–3460 mg/l) might have induced negative impact on the phytoplankton density. The relative abundance of the studied elements exhibited the following decreasing trend (concentration in μg/g and %): Si(26.44 ± 3.75%) > Al(7.94 ± 1.52%) > Fe(6.17 ± 1.9%) > K(3.05 ± 1.5%) > Ca(1.97 ± 1.11%) > Mg(1.57 ± 1.71%) > Na(1.45 ± 8.40%) > Mn(1273 ± 2003) > Zn(178.43 ± 130.95) > V(151.54 ± 27.13) > Cr(147.08 ± 32.21) > Cu(62.06 ± 14.03) > Ni(49.64 ± 12.09) > Pb(21.5 ± 10.45). The accumulation of Ni, Cr, Pb, and Cu is mainly controlled by the formation of Fe hydroxides along with particulate organic carbon (POC) and salinity. The average geo-accumulation index (Igeo) and enrichment factor (EF) endorsed the substantial input of Cr (Igeo = 0.037; EF = 1.61) and Zn (Igeo = 0.123; EF = 2.07) from diffused pollution sources. From ecotoxicological point of view, the quality guidelines (QGs) suggested that Cr and Ni might possess frequent adverse biological effects. However, the mean probable effect level (PEL) quotient values revealed 49% probability of toxicity to the aquatic biota for five toxic elements (Cr, Ni, Cu, Zn, and Pb). The geochemical approaches, pollution indices, and statistical evaluation together revealed low to moderate contamination in the estuary. This baseline data would be beneficial in adopting proper management strategies for sustainable utilization and restoration of the water resources. The authors strongly recommend continuous systematic monitoring and installation of treatment plants for management of this stressed estuary. [ABSTRACT FROM AUTHOR]

Seagrass meadows are a critical component of estuarine and coastal seascapes, and their structure influences fish assemblages at multiple spatial scales. The patch mosaic model, which defines the seascape as a collection of interacting habitat types, is increasingly adopted to prioritise protected areas and design ecological restoration schemes, hence helping to preserve seagrass meadows and the associated fish assemblages. Despite that, there are few studies investigating the relative contribution of environmental characteristics measured at different spatial scales in determining the distribution of seagrass fish. This study collects fish and environmental observations taken at both site and seascape scales in seagrass meadows in the Venice lagoon (Adriatic Sea, Italy). By means of generalised linear models, it aims to disentangle the relative influence of local water quality and habitat characteristics from that of habitat mosaic properties, investigating the response of whole fish assemblage descriptors, feeding guilds and dominant species. While confirming the primary importance of local habitat quality, the study highlights that also seagrass habitat structure at the seascape scale is relevant for seagrass fish assemblages, influencing total biomass, biomass of macrobenthivorous and hyperbenthivorous/piscivorous species and seagrass specialists such as syngnathids. Conservation of seagrass fish assemblages can therefore be promoted in Mediterranean coastal lagoons by preserving or restoring some features of the habitat mosaic, namely the extension of seagrass patches and their shape complexity, in addition to local water quality and seagrass cover. [ABSTRACT FROM AUTHOR]

Once viewed as an inexhaustible fishery resource, eastern oyster reefs (Crassostrea virginica) have been dramatically depleted. In North Carolina alone, eastern oyster harvests have declined by 90% since the early 1900s. However, eastern oyster restoration and management efforts have substantially increased since the 1970s. Oyster reefs provide habitat and refuge for organisms, improve water quality, and decrease erosion. Oyster restoration projects aim to construct reefs that function similarly to their natural counterparts. Therefore, post-creation monitoring of these reefs is crucial in determining restoration success. However, monitoring is often lacking or focused only on oyster density and size rather than ecosystem functions such as nekton utilization. This study examines nekton utilization among created reefs compared to natural reefs in an estuary in Wilmington, North Carolina. The objective was to determine whether the created reefs function similarly to the natural reefs in abundance, species richness, and fish size. Using seine nets and Breder traps, reefs were sampled over a 5-month period. No significant difference was detected among reefs for nekton abundance, species richness, and standard length. This is a promising result for future management, indicating that created and natural reefs can support similar communities of fishes and shrimp. [ABSTRACT FROM AUTHOR]

This study conducts a meta-analysis and benefit transfer of the value of water clarity in the Chesapeake Bay estuary to estimate the property value impacts of pollution reduction policies. Estimates of the value of water clarity are derived from separate hedonic property value analyses of 14 counties bordering the Bay. The meta-analysis allows us to: (1) estimate the average effect of water clarity in the Chesapeake Bay, (2) investigate heterogeneity of effects across counties based on socioeconomic and ecological factors, (3) evaluate different measures of water clarity used in the original hedonic equations, and (4) transfer the values to Bayfront counties in nearby jurisdictions to estimate the property value impacts of the total maximum daily load (TMDL), a policy to reduce nutrient and sediment pollution entering the Bay that is expected to improve water clarity and ecological health. We also investigate the in-sample and out-of-sample predictive power of different transfer strategies and find that a simpler unit value transfer can outperform more complex function transfers. We estimate that aggregate near-waterfront property values could increase by roughly $400–$700 million in response to water clarity improvements from the TMDL. [ABSTRACT FROM AUTHOR]

Habitat use can be complex, as tradeoffs among physiology, resource abundance, and predator avoidance affect the suitability of different environments for different species. Green sturgeon ( Acipenser medirostris), an imperiled species along the west coast of North America, undertake extensive coastal migrations and occupy estuaries during the summer and early fall. Warm water and abundant prey in estuaries may afford a growth opportunity. We applied a bioenergetics model to investigate how variation in estuarine temperature, spawning frequency, and duration of estuarine residence affect consumption and growth potential for individual green sturgeon. We assumed that green sturgeon achieve observed annual growth by feeding solely in conditions represented by Willapa Bay, Washington, an estuary annually frequented by green sturgeon and containing extensive tidal flats that harbor a major prey source (burrowing shrimp, Neotrypaea californiensis). Modeled consumption rates increased little with reproductive investment (<0.4%), but responded strongly (10-50%) to water temperature and duration of residence, as higher temperatures and longer residence required greater consumption to achieve equivalent growth. Accordingly, although green sturgeon occupy Willapa Bay from May through September, acoustically-tagged individuals are observed over much shorter durations (34 d + 41 d SD, N = 89). Simulations of <34 d estuarine residence required unrealistically high consumption rates to achieve observed growth, whereas longer durations required sustained feeding, and therefore higher total intake, to compensate for prolonged exposure to warm temperatures. Model results provide a range of per capita consumption rates by green sturgeon feeding in estuaries to inform management decisions regarding resource and habitat protection for this protected species. [ABSTRACT FROM AUTHOR]

The productivity gradient between adjacent habitats can fluctuate over time due to seasonal cycles and lead to both habitats being alternately subsidized. Although this process is well known for prey subsidies in stream-riparian forest ecotones, few studies are available for other systems or subsidy types. Moreover, the effects of transport intensity on this expected alternate subsidy exchange are still poorly understood. We assessed whether subsidy input and allochthonous carbon assimilation by resident benthic invertebrates alternated between adjacent mangroves and salt marshes during peaks of detritus productivity (summer and winter, respectively) in a subtropical estuary, by using detritus trapping techniques and stable isotope ratios. Sampling was performed simultaneously in the sheltered (inner sector) and exposed (outer sector) regions of the estuary to assess the influence of different physical conditions on the intensity of subsidy flow. Transport of mangrove litter into the salt marsh occurred mainly in the summer in both sectors; however, most of the litter remained trapped in the marsh boundary. The mixing model also showed that there was little influence of allochthonous carbon in the diet of salt marsh benthic invertebrates. Marsh litter supply to mangroves did not vary significantly between seasons but was significantly higher in the outer than in the inner sector. Likewise, the mixing model showed great contribution of salt marsh carbon to the diet of benthic invertebrates from the outer-sector mangroves, whereas autochthonous carbon predominated in those from the inner mangroves. Our findings reinforce the model that trophic connectivity relies on the relative proportion of allochthonous (subsidy) and autochthonous resources rather than only on asymmetric productivity between habitats. Differences in the proportion of resources result from interaction among productivity, permeability, and transport vectors that lead to many states of trophic connectivity. [ABSTRACT FROM AUTHOR]

Climate change is increasing the need to characterise the vulnerability of coastal landscapes to coastal and flood hazards that result in erosion and inundation. Indices, such as the Coastal Vulnerability Index (CVI), have emerged as useful tools with which coastal managers can prioritise areas for further detailed assessment of vulnerability, risk, resilience and adaptation options. Approaches, such as the use of an index, efficiently characterise the vulnerability of linear, one-dimensional coastal features such as coastlines; however, they do not capture variability in coastal processes affecting more complex, non-linear features, such as estuaries, or interactive effects of coastal processes between linear (e.g. coastlines) and non-linear (e.g. estuaries) landforms. We present an approach that uses geomorphology to indicate biophysical vulnerability of estuaries to coastal and flood hazards. The approach is applied to the South Coast of NSW; a wave-dominated coastline of approximately 400 km length that contains more than 100 estuaries. We demonstrate the simplicity of the approach and its utility in identifying areas requiring higher resolution assessments. Although this approach does not include socio-economic factors, we demonstrate the capacity to incorporate socio-economic components of vulnerability using regional land use mapping. We infer that the most vulnerable estuaries are characterised by large catchment areas, broad estuarine valleys, mature stages of infill, or entrances oriented towards the prevailing wave direction. The area below 15 m elevation was identified as a robust indicator of the total area of vulnerability within a catchment. This approach can be applied to one-dimensional and more complex two-dimensional landscapes, such as estuaries; integrates varying sea-level rise projections; and incorporates a wider range of hazards that operate in the coastal zone. [ABSTRACT FROM AUTHOR]

The resonant interaction of surface and internal waves produces a nonlinear mechanism for energy transfer among wave components in oceans, lakes, and estuaries. In many field situations, the stratification may be well approximated by a two-layer fluid with a diffuse interface. The growth and damping rates of sub-harmonic interfacial waves generated by a surface wave through a three-wave resonant interaction are measured in the laboratory. These measurements are compared with theoretical predictions. A diffuse interface reduces the damping rate and increases the growth rate. The predicted growth rate provides excellent comparison with the laboratory measurements. The inclusion of the effects of a diffuse interface significantly improve the comparison. [ABSTRACT FROM AUTHOR]

Several field studies in bays and estuaries have revealed pronounced subsurface maxima in the vertical profiles of the current amplitude of the principal tidal harmonic, or of its vertical shear, over the water column. To gain fundamental understanding about these phenomena, a semi-analytical model is designed and analysed, with focus on the sensitivity of the vertical structure of the tidal current amplitude to formulations of the vertical shape of the eddy viscosity. The new analytical solutions for the tidal current amplitude are used to explore their dependence on the degree of surface mixing, the vertical shape of eddy viscosity in the upper part of the water column and the density stratification. Sources of surface mixing are wind and whitecapping. Results show three types of current amplitude profiles of tidal harmonics, characterised by monotonically decreasing shear towards the surface, 'surface jumps' (vertical shear of tidal current amplitude has a subsurface maximum) and 'subsurface jets' (maximum tidal current amplitude below the surface), respectively. The 'surface jumps' and 'subsurface jets' both occur for low turbulence near the surface, whilst additionally the surface jumps only occur if the eddy viscosity in the upper part of the water column decreases faster than linearly to the surface. Furthermore, 'surface jumps' take place for low density stratification, while and 'subsurface jets' occur for high density stratification. The physics causing the presence of surface jumps and subsurface jets is also discussed. [ABSTRACT FROM AUTHOR]

To improve the description of long-term changes in water quality, a weighted regression approach developed to describe trends in pollutant transport in rivers was adapted to analyze a long-term water quality dataset from Tampa Bay, Florida. The weighted regression approach allows for changes in the relationships between water quality and explanatory variables by using dynamic model parameters and can more clearly resolve the effects of both natural and anthropogenic drivers of ecosystem response. The model resolved changes in chlorophyll- a (chl- a) from 1974 to 2012 at seasonal and multi-annual time scales while considering variation associated with changes in freshwater influence. Separate models were developed for each of the four Bay segments to evaluate spatial differences in patterns of long-term change. Observed trends reflected the known decrease in nitrogen loading to Tampa Bay since the 1970s. Although median chl- a has remained constant in recent decades, model predictions indicated that variation has increased for upper Bay segments and that low biomass events in the lower Bay occur less often. Dynamic relationships between chl- a and freshwater inputs were observed from the model predictions and suggested changes in drivers of primary production across the time series. Results from our analyses have allowed additional insight into water quality changes in Tampa Bay that has not been possible with traditional modeling approaches. The approach could easily be applied to other systems with long-term datasets. [ABSTRACT FROM AUTHOR]

The ability to determine a bulk estuarine turnover timescale that is well defined under realistic conditions is in high demand for estuarine research and management. We compare how turnover timescales vary with tidal and river forcing from idealized forcing scenarios using a three-dimensional circulation model of the Yaquina Bay estuary in order to understand the limitations and benefits of different timescale methods for future application. Using model results, we compare bulk formula approaches-the tidal prism method, freshwater fraction method, and a relatively new estuarine timescale calculation method based on the total exchange flow (TEF)-to directly calculated timescales from particle tracking in order to assess the utility of the bulk formula timescales. All of the timescales calculated had similar magnitudes during high river discharge but varied significantly at low discharge and had different dependences on tidal amplitude. Even in the application of a single estuary-averaged timescale, we did not find that any of the bulk timescales described the estuary over a realistic range of tidal and river discharge forcing. During high discharge, the Yaquina Bay timescale is on the order of 2-5 tidal cycles based on the particle tracking analysis, but during low discharge, the turnover time varies across methods and spatial considerations appear to be more important. [ABSTRACT FROM AUTHOR]

Classification schemes and ecological evaluation tools based on benthic macrofauna data were applied to the Azini, Jask and Khalasi estuaries. Changes in benthic community structure were investigated using multivariate (MDS and CCA) and univariate analyses (diversity indices and BENTIX). BENTIX indices were applied to the available benthic species data and the succession of the ecological groups. The ANOSIM tests, applied to assess the significance of ecological segregation, confirmed that there was a significant difference in the structure of the assemblages among estuaries for all seasons (Global R > 0.5, P > 0.001). According to results of the BENTIX indices, a significant difference was observed between the Khalasi estuary (as the reference condition) with the Jask and Azini estuaries with regard to BENTIX values. The ecological quality status of the disturbed stations was worse than that of references. Thus, BENTIX indices appeared to work successfully in soft bottom substrates in these subtropical areas. [ABSTRACT FROM AUTHOR]

In estuarine ecosystems, trace metals are mainly associated with fine grain sediments which settle on mudflats. Over time, the layers of sediments accumulate and are then transformed by diagenetic processes, recording the history of the estuary's chemical contamination. In such a specific environment, we investigated to what extent a chronic exposure to contaminants could affect metal-resistant sedimentary bacteria in subsurface sediments. The occurrence and diversity of cadmium resistance genes ( cadA, czcA) was investigated in 5- and 33-year-old sediments from a highly contaminated estuary (Seine France). Primers were designed to detect a 252-bp fragment of the czcA gene, specifically targeting a transmembrane helice domain (TMH IV) involved in the proton substrate antiport of this efflux pump. Although the cadA gene was not detected, the highest diversity of the sequence of the czcA gene was observed in the 5-year-old sediment. According to the percentage of identity at the amino acid level, the closest CzcA relatives were identified among Proteobacteria (α, β, γ, and δ), Verrucomicrobia, Nitrospirae, and Bacteroidetes. The most abundant sequences were affiliated with Stenotrophomonas. In contrast, in the 33-year-old sediment, CzcA sequences were mainly related to Rhodanobacter thiooxydans and Stenotrophomonas, suggesting a shaping of the metal-resistant microbial communities over time by both diagenetic processes and trace metal contamination. [ABSTRACT FROM AUTHOR]

Estuarine barriers may significantly reduce the upstream migration of diadromous fish species like the European eel ( Anguilla anguilla L.). Previous research showed that limited barrier opening during tidal rise was a cost-efficient and effective mitigation option to improve upstream glass eel migration, without significant intrusion of sea water. This paper aims to optimise this adjusted barrier management to improve eel passage at a tidal barrier complex at the mouth of the River Yser, Flanders, Belgium, one of the most important migration routes for glass eel in Flanders. Specifically, three hypotheses were tested. The first hypothesis analysed the impact of the number of barriers opened on the upstream glass eel migration. The second hypothesis evaluated the relation between the size of the barrier opening and glass eel migration. Finally, we tested whether the suggested adjusted barrier management may lead to a significant increase in conductivity in the River Yser. Increased opening of one barrier appeared more efficient than opening several barriers slightly. Conductivity increased during periods of extreme drought and at base flow, but decreased within 24 h after the first peak flow. This indicates that adjusted barrier management does not entail salt intrusion in the Yser basin, as long as this management is not applied in extremely dry periods. Since the adjusted barrier management is easily implemented and could be applied on numerous tidal barriers, the presented results may contribute to restoration of eel populations worldwide and be of interest to a wide range of river managers and stakeholders. [ABSTRACT FROM AUTHOR]

Rocky reef habitat is common in many estuaries, yet its role as a habitat for fishes is poorly understood. There is also limited understanding of how access of coastal species into estuaries and habitat quality can affect the distribution of rocky reef fishes within estuaries. This study used baited remote underwater video stations to determine spatial patterns in fish assemblages associated with rocky reef habitat throughout a barrier estuary with a permanently open but restricted inlet. Estuarine rocky reefs provided habitat for a diverse assemblage of fishes, many of which were large juveniles and subadults. In the absence of a pronounced salinity or temperature gradient, a clear transition in fish assemblages occurred from coastal waters, through the inlet channel, to the central estuary, and into the inner estuary. The inlet channel, notably its narrowness and length, limits tidal input into this estuary, which acts as a significant impediment to the dispersal of many coastal fishes, and insufficient habitat excludes many coastal rocky reef species from the inner estuary. This study highlights the need to recognise estuarine rocky reefs as providing habitat for diverse fish assemblages and the role inlets play in restricting access of coastal species. [ABSTRACT FROM AUTHOR]

The Tampa Bay estuary is a unique and valued ecosystem that currently thrives between subtropical and temperate climates along Florida's west-central coast. The watershed is considered urbanized (42 % lands developed); however, a suite of critical coastal habitats still persists. Current management efforts are focused toward restoring the historic balance of these habitat types to a benchmark 1950s period. We have modeled the anticipated changes to a suite of habitats within the Tampa Bay estuary using the sea level affecting marshes model under various sea level rise (SLR) scenarios. Modeled changes to the distribution and coverage of mangrove habitats within the estuary are expected to dominate the overall proportions of future critical coastal habitats. Modeled losses in salt marsh, salt barren, and coastal freshwater wetlands by 2100 will significantly affect the progress achieved in 'Restoring the Balance' of these habitat types over recent periods. Future land management and acquisition priorities within the Tampa Bay estuary should consider the impending effects of both continued urbanization within the watershed and climate change. This requires the recognition that: (1) the Tampa Bay estuary is trending towards a mangrove-dominated system; (2) the current management paradigm of 'Restoring the Balance' may no longer provide realistic, attainable goals; (3) restoration that creates habitat mosaics will prove more resilient in the future; and (4) establishing subtidal and upslope 'refugia' may be a future strategy in this urbanized estuary to allow sensitive habitat types (e.g., seagrass and salt barren) to persist under anticipated climate change and SLR impacts. [ABSTRACT FROM AUTHOR]

In summer 2009, the effects of 6 years of landscape-level experimental nutrient enrichment on the eastern mudsnail, Nassarius obsoletus (formerly Ilyanassa obsoleta), were examined. The experiment was conducted in five tidal creeks (two nutrient-enriched, three reference creeks) in the Plum Island Estuary, Massachusetts, USA. (42°44′ N, 70°52′ W). After 6 years of enrichment, N. obsoletus size structure differed between treatment creeks with adult snails on average 14 % larger in enriched creeks. N. obsoletus densities (in individuals per square meter) and biomass (in grams dry weight per square meter) were four times higher in nutrient-enriched versus reference creeks. Nutrient enrichment did not significantly affect the biomass of benthic microalgae (a N. obsoletus food resource), but snail density was significantly correlated with benthic microalgal biomass, suggesting bottom-up control of snails. N. obsoletus is abundant on the east and west coast of North America; thus, N. obsoletus density and biomass may be useful variables for monitoring eutrophication effects on North American estuaries. [ABSTRACT FROM AUTHOR]

Flocculation can be considered as an effective mechanism in self-purification of metals during estuarine mixing. In the present investigation, flocculation of metals during mixing of Minab River water with the Strait of Hormuz (The Persian Gulf) water is studied for the first time. Flocculation behavior of metals (except for Pb) is governed by dissolved organic carbon. The source of dissolved organic carbon is terrigenous in the estuarine waters of study area. The general pattern of flocculation of studied metals is manganese (180 μg/L) > zinc (88 μg/L)> nickle (73 μg/L)> copper (30 μg/L)> lead (19 μg/L). The results of present study show that metal species are a very important factor in overall flocculation rate. It is found that solids and oxides have the highest and lowest flocculation levels, respectively. Eh-pH diagram indicated that lead is present as lead oxide in Minab River water and the least flocculation rate is attributed to this element. The results also showed that flocculation rate of metal species could be as solids > free ions ≈ hydroxides > oxides. The amount of metal flocculation is about 30.5, 6.6, 25.3, 10.4 and 62.5 ton/y for zinc, Pb, Ni, Cu and Mn, respectively. [ABSTRACT FROM AUTHOR]

Multi-year nitrogen (N) and phosphorus (P) budgets were developed for the Patuxent River estuary, a seasonally stratified and moderately eutrophic tributary of Chesapeake Bay. Major inputs (point, diffuse, septic, and direct atmospheric) were measured for 13 years during which, large reductions in P and then lesser reductions in N-loading occurred due to wastewater treatment plant improvements. Internal nutrient losses (denitrification and long-term burial of particulate N and P) were measured in tidal marshes and sub-tidal sediments throughout the estuary as were nutrient storage in the water column, sediments, and biota. Nutrient transport between the oligohaline and mesohaline zones and between the Patuxent and Chesapeake Bay was estimated using a salt and water balance model. Several major nutrient recycling terms were directly and indirectly evaluated and compared to new N and P inputs on seasonal and annual time-scales. Major findings included: (1) average terrestrial and atmospheric inputs of N and P were very close to the sum of internal losses plus export, suggesting that dominant processes are captured in these budgets; (2) both N and P export were a small fraction (13% and 28%, respectively) of inputs, about half of that expected for N based on water residence times, and almost all exported N and P were in organic forms; (3) the tidal marsh-oligohaline estuary, which by area comprised ~27% of the full estuarine system, removed about 46% and 74% of total annual upland N and P inputs, respectively; (4) recycled N and P were much larger sources of inorganic nutrients than new inputs during warm seasons and were similar in magnitude even during cold seasons; (5) there was clear evidence that major estuarine processes responded rapidly to inter-annual nutrient input variations; (6) historical nutrient input data and nutrient budget data from drought periods indicated that diffuse nutrient sources were dominant and that N loads need to be reduced by about 50% to restore water quality conditions to pre-eutrophic levels. [ABSTRACT FROM AUTHOR]

More than ever, there is a need to integrate restoration ecology, as practiced by the scientific community, and ecological restoration, a province that is largely, but not entirely the purview of practitioners. Success in some coastal restoration projects is increasingly measured in the context of practitioner skills and cultural goals rather than by the manifestation of underlying ecological principles and mechanisms in the restoration process. Especially in human-dominated landscapes, restoration practices should attempt to balance human needs with those of extant biota in a consensus based combination of restoration ecology and ecological restoration criteria. The goal is to devise plans at the appropriate scale that allow humans and other biota to share space and resources in an increasingly complex landscape. No matter where restoration takes place, both ecological fidelity (in ecocentric terms) and human dimensions (in anthropocentric terms) must comprise the restoration design, but ultimately in proportion to human density in the landscape. Without this integration, compromise, and balance, restoration will not likely prosper in the mainstream of society. [ABSTRACT FROM AUTHOR]

In the framework of rehabilitation efforts to enhance the ecological value of closed-off estuaries, we studied the effects of restoring a tidal movement and seawater incursion on soil nitrogen conversion rates and vegetation response of semi-natural and agricultural grasslands in an outdoor mesocosm experiment. Intact soil monoliths including vegetation were collected in June 2004 on two locations on the shores of the Haringvliet lagoon in the south-western part of the Netherlands, which used to be a well-developed estuary before closure in 1970. For more than 1 year, soil monoliths were continuously subjected to a full-factorial combination of tidal treatment [stagnant/tidal (0.20 m amplitude)] and water type [(freshwater, oligohaline (salinity = 3)]. Soil, soil moisture and water nitrogen concentrations were monitored for a year, as well as vegetation response and nitrogen conversion rates in the soil. As expected, nitrogen mineralization rates were enhanced by the tidal treatment in comparison with the stagnant treatment. Denitrification rates however, were much less affected by tide and were even lower in the tidal treatments after 3 months in the agricultural grassland soils, implying that in general, soils were more oxic in the tidal treatments. Oligohaline treatments had virtually no effect on soil nitrogen conversion rates compared to freshwater treatments. Vegetation performance, however, was lower under saline conditions, especially in the semi-natural grassland. No further significant differences in response to the tidal and oligohaline treatments were found between the two soils although they differed strongly in soil characteristics. We conclude that if the rehabilitation measures in the former Haringvliet estuary are carried out as planned, drastic changes in soil nitrogen processes and vegetation composition will not occur. [ABSTRACT FROM AUTHOR]

The U.S. Environmental Protection Agency has released a report entitled Condition of the Mid-Atlantic Estuaries. That report summarizes the findings of several studies conducted by federal and state agencies and academic institutions in Chesapeake Bay, Delaware Estuary, and the coastal bays of Delaware, Maryland, and Virginia, and simultaneously addresses two distinct audiences: environmental managers and the general public. This paper documents the process of preparing the Estuaries Report, emphasizing the lessons learned in merging information from a wide-variety of sources and in reporting the results to multiple audiences. The major difficulties in preparing the report included: 1) choosing a format and topics that adequately addressed both environmental managers and the public, 2) resolving spatial and temporal disparities in the assembled data sets, and 3) establishing threshold values that distinguished between acceptable and unacceptable conditions in indicators. Our solutions to these challenges and alternatives are discussed. We conclude that a small team of knowledgeable scientists can effectively merge the information of diverse sources into a document that is useful to both environmental managers and the interested public. However, considerable interaction between the team and other scientists was necessary to resolve ambiguities and assure relevancy and accuracy. These findings support the proposition that the vast sources of existing environmental information can be easily and effectively used to assess the ecological condition across large regions. [ABSTRACT FROM AUTHOR]

In order to examine the condition of biota in Atlantic coast estuaries, "Contaminant Exposure and Effects—Terrestrial Vertebrates" database (CEE-TV) has been compiled through computerized search of published literature, review of existing databases, and solicitation of unpublished reports from conservation agencies, private groups, and universities. Summary information has been entered into the database, including species, collection date (1965–present), site coordinates, estuary name, hydrologic unit code, sample matrix, contaminant concentrations, biomarker and bioindicator responses, and reference source, utilizing a 98-field character and numeric format. Currently, the CEE-TV database contains 3699 geo-referenced records representing 190 vertebrate species and >140,000 individuals residing in estuaries from Maine through Florida. This relational database can be directly queried or imported into a Geographic Information System to examine spatial patterns, identify data gaps and areas of concern, generate hypotheses, and focus ecotoxicological field assessments. Information on birds made up the vast majority (83%) of the database, with only a modicum of data on amphibians (<0.1%). Of the >75,000 chemical compounds in commerce, only 118 commonly measured environmental contaminants were quantified in tissues of terrestrial vertebrates. There were no CEE-TV data records in 15 of the 67 estuaries located along the Atlantic coast and Florida Gulf coast. The CEE-TV database has a number of potential applications including focusing biomonitoring efforts to generate critically needed ecotoxicological data in the numerous "gaps" along the coast, reducing uncertainty about contaminant risk, identifying areas for mitigation, restoration or special management, and ranking ecological conditions of estuaries. [ABSTRACT FROM AUTHOR]

Mudflats and associated mangroves are most important ecosystems of tropical coastal regions. Mangroves play a very important role in maintaining the environmental balance; thus in addition to mangrove reforestation and restoration, afforestation has also been practiced. We studied distribution of sediment components (sand, silt, clay) organic carbon (OC), heavy metals (Fe, Mn, Cu, Zn, Cr and Co) and pH in six cores collected from one of the largest mudflats of Mandovi estuary, west coast of India. The temporal distribution patterns of these proxies suggested that past changes in tidal energy conditions, fresh water inflow and anthropogenic activities over the last few decades, together helped in development of a middle tidal flat in this estuary. In cores collected from the mangroves, trapping and deposition of finer particles and organic matter were enhanced by a complex aerial mangrove root system in recent years. Mangroves were, therefore, suggested to enhance the buildup of mudflats in Mandovi estuary. Cores collected from mudflats also exhibited higher deposition of finer particles and organic matter (except MF2) in recent years, suggesting maturity and greater stability of the entire mudflat in recent years. Middle tidal flats (mudflats) of Mandovi estuary may, therefore, prove to be suitable substrates for mangrove proliferation in the near future. Finer sediments deposited mainly from mining activities in recent years exhibited lower pH and higher metal content. Organisms dwelling in these recently deposited sediments are, therefore, at higher risk of bioaccumulation and metal toxicity. [ABSTRACT FROM AUTHOR]