Chesapeake Bay Tributaries Research Articles

Efficacy and effects of three desiccation intervals on biofouling and Eastern oysters (Crassostrea virginica) at three commercial oyster farms in the Chesapeake Bay, MD

Oyster aquaculture is a growing industry both globally and nationally. Productive coastal waters support high-density containerized culture of oysters, but also sustain many other macrofaunal species which can settle on oysters and cage materials (biofouling), causing problems for oyster farms. Desiccation, or periodic air drying, of farm infrastructure and oysters has been used to control colonization and growth of biofouling organisms on oyster farms worldwide, but the minimum necessary interval of desiccation has yet to be thoroughly assessed. Given the known stresses to oysters associated with periods of emersion, an understanding of the effects of different weekly desiccation intervals is needed. This study investigated the use of desiccation in controlling biofouling and the associated impacts to oyster growth and mortality at three oyster farms within Maryland's portion of the Chesapeake Bay, including one low salinity site in an upper Chesapeake Bay tributary and two sites in the middle portion of the Chesapeake Bay. Three desiccation treatments were applied at each site: control (no desiccation), 8 consecutive hours of desiccation per week, and 24 consecutive hours of desiccation per week. Oysters were deployed between July–December 2018 and the percent valve coverage by individual biofouling species was monitored, along with worm abundance, oyster growth, and oyster mortality. Total biofouling was significantly greater on non-desiccated oysters but minimal differences in biofouling coverage were observed among oysters desiccated for 8 or 24 h weekly. Seven biofouling species were observed among the sites, and all except for a single macroalgal species (Ulva intestinalis) were controlled by the 8- and 24-h desiccation treatments. No clear treatment-derived differences in oyster growth or mortality were observed. Overall, results suggest desiccating weekly for either 8 or 24 consecutive hours may be a suitable biofouling management strategy for gross biofouling reduction on oyster farms.

Ontogenetic patterns in juvenile blue crab density: effects of habitat and turbidity in a Chesapeake Bay tributary

Nursery habitats are characterized by favorable conditions for juveniles, including higher food availability and lower predation risk, and disproportionately contribute more individuals per unit area to adult populations compared to other habitats. However, nursery habitat inference is complicated by changes in habitat preferences with ontogeny; individuals in early-life stages frequently inhabit different habitats than older juveniles or adults. In this field experiment, we modeled the density of 4 size classes of juvenile blue crabs Callinectes sapidus based on carapace width (CW) across multiple habitats at various locations within an estuarine seascape during the blue crab recruitment season. We examined 4 habitat types—unstructured sand, seagrass meadows, salt marsh edges (SME), and shallow detrital habitat (SDH). Results indicated that densities of small juvenile blue crabs (≤10 mm CW) were highest in seagrass, whereas densities of larger juveniles (16-25 mm CW) were highest in SME. Although densities of juveniles declined in seagrass habitat as a function of size, densities in SME remained consistently high, suggesting that secondary dispersal to SME by smaller juveniles after settlement and recruitment in seagrass may supplement losses in SME due to mortality. Turbidity was positively correlated with densities of both size classes, although our model did not address whether this was due to top-down (refuge) or bottom-up (food availability) mechanisms. Observed patterns in size-specific habitat utilization may result from changing requirements of juvenile blue crabs with size, as animals minimize mortality-to-growth ratios. Our findings emphasize the role of both seagrass and salt marsh habitat within juvenile blue crab ontogeny and emphasize the significance of structurally complex SME habitat in supporting juvenile blue crabs at sizes smaller than previously recognized, challenging past notions about the singular importance of seagrass habitat in this system. Our findings also underscore the need to quantify and preserve the complete chain of habitats used by juveniles.

Assessing the presence, concentration, and impacts of trace element contamination in a Chesapeake Bay tributary adjacent to a coal ash landfill (Possum Point, VA)

Coal ash (CA) is an industrial waste product that has been shown to contain several neurotoxic constituents such as cadmium, selenium, mercury, lead, and arsenic. Contaminant-laced leachates enter the environment via seepage, runoff, permitted discharge, or accidental spills from CA storage ponds or landfills which may pose a risk to wildlife residing in receiving waterways. In this study, we assessed 1) the presence and concentration of thirteen trace elements (Al, Ca, Mg, Cr, Cd, As, Se, Pb, Cu, Zn, Mn, Fe, B) in surface water and sediment grab samples using ICP-OES, 2) the temporal variability of trace elements using Pb-210 dated sediment core samples, 3) differences in species diversity using environmental DNA (eDNA) analyses, and 4) the presence and concentration of trace metals in banded killifish (Fundulus diaphanus) epaxial muscle tissue collected from waterways surrounding the Possum Point Power Station (Stafford, VA). Results showed the highest concentrations of As, Cd, Cr, Cu, Fe, Mg, Se, Zn, and B in Quantico Creek (QC) adjacent to the coal ash ponds and elevated average cadmium and zinc concentrations compared to both upstream and downstream locations along the Potomac River. Sediment core profiles and Pb-210 analyses showed historical enrichment of several trace elements in QC beginning after the commissioning of the power plant in 1948. When compared to upstream and downstream sites, species diversity was drastically reduced in Quantico Creek based on eDNA identification. Muscle tissues of banded killifish collected in Quantico Creek displayed increased Al, Cd, and Zn concentrations compared to upstream and downstream sites. Collectively, our results demonstrate the potential impacts of coal ash landfills on aquatic ecosystems and suggest that further research is needed to fully inform risk assessment and remediation efforts.

Juvenile Striped Bass consume diverse prey in Chesapeake Bay tributaries

AbstractObjectiveAnadromous Striped Bass Morone saxatilis are dominant predators in estuaries and coastal areas along the U.S. Atlantic coast, with the potential to exert top‐down control on prey populations. Although Striped Bass diets have been studied previously, spatiotemporal patterns of diet across ontogeny remain poorly understood, especially for young fish in shallow nursery habitats.MethodsWe collected and examined gut contents from adult, juvenile, and young‐of‐year (age‐0) Striped Bass from nine rivers across the Maryland and Virginia portions of Chesapeake Bay during summer and fall 2018. We compared the use of traditional morphological inspection and new amplicon‐based next‐generation sequencing methods for identifying gut contents.ResultStriped Bass in shallow tributary habitats of Chesapeake Bay had diverse diets that varied strongly with ontogeny and salinity zone. In particular, the diet of age‐0 Striped Bass varied greatly from those of juveniles and adults when age‐0 fish foraged in freshwater habitats. Although our results on prey consumed aligned with previous surveys, we identified additional taxa as important prey for these young fish, including dipteran insects, Banded Killifish Fundulus diaphanus, Inland Silverside Menidia beryllina, bay barnacle Amphibalanus improvisus, and grass shrimp Palaemon spp. Comparison of methodologies indicated that 40% of prey by weight could not be identified with morphological analysis, while 76% of mitochondrial cytochrome oxidase I sequences could be assigned binomial names, allowing for high‐resolution taxonomic comparisons.ConclusionThis study adds to the growing body of evidence that amplicon‐based next‐generation sequencing methods are far superior to traditional morphological analyses of gut contents for fine‐scale taxonomic resolution of prey.

Predatory impacts of invasive Blue Catfish in an Atlantic coast estuary

AbstractObjectivePredatory invasive fishes may consume species of management interest and alter food webs. Blue CatfishIctalurus furcatusis a large‐bodied, salinity‐tolerant species that exhibits broad diet breadth and preys on species of both conservation concern and fisheries management interest. To better understand the ecological consequences of the establishment of Blue Catfish fisheries, estimates of predatory impacts are needed.MethodsUsing a Monte Carlo simulation, we integrated abundance estimates, diet information, and consumption‐to‐biomass ratios to estimate population‐level Blue Catfish predation for a large Chesapeake Bay tributary along the mid‐Atlantic coast of the United States, the James River.ResultPopulation‐level annual predation estimates by Blue Catfish exceeded 100 metric tons for several species or taxa of interest, including an estimated 400.7 metric tons (95% CI = 272.6–613.2) of blue crabCallinectes sapidus. Prey species abundances were unknown and thus limited opportunities to evaluate prey population responses. For instance, effects of Blue Catfish on blue crab populations remain unknown without tributary‐specific estimates of blue crab abundance, but comparisons to landings data suggests that Blue Catfish predation on blue crab in the James River may be low compared with harvest.ConclusionEstimation of Blue Catfish predatory effects may inform development of management goals and objectives that balance diverse stakeholder interests. This work provides beneficial information to assess trade‐offs of Blue Catfish fisheries and their effects on coastal aquatic resources.

White perch health relative to urbanization and habitat degradation in Chesapeake Bay tributaries. II. Hepatic and splenic macrophage aggregates.

Macrophage aggregate (MA) abundance in fish is a useful general biomarker of contaminant exposures and environmental stress. Hepatic and splenic MAs were evaluated in semi-anadromous white perch Morone americana (Gmelin, 1789) from the urbanized Severn River (S) and the more rural Choptank River (C), Chesapeake Bay. Fish were collected from different sites in the annual migratory circuit in each river that corresponded to active spawning in late winter-early spring, summer regenerating, autumn developing, and winter spawning-capable phases. An age-associated progressive increase in the total volume of MAs (MAV) was evident in the liver and spleen. Mean hepatic MAV (range in seasonal means, C: 6.4-23.1 mm3; S: 15.7-48.7 mm3) and mean splenic MAV (C: 7.3-12.6 mm3; S: 16.0-33.0 mm3) differed significantly among seasons and were significantly greater in females and in Severn River fish. Age and river were the most influential factors, suggesting that increased MAV in Severn River fish resulted from chronic exposures to higher concentrations of environmental contaminants. Hepatic MAV was directly related to the relative volume of copper granules in the liver. Less influential factors on splenic MAV included fish condition, trematode infections, and granulomas, indicating possible functional differences in MAs by organ. While organ volumes were strongly linked to gonadosomatic index (GSI) and reproductive phase, the reason for seasonal differences in MAV was less clear. Water temperature, salinity, and dissolved oxygen were not significantly related to MAV, and indicators of reproductive phase (hepatosomatic index and GSI) were significant but less important in explaining variation in MAV.

White perch health relative to urbanization and habitat degradation in Chesapeake Bay tributaries. I. Biliary neoplasms and hepatic lesions.

White perch Morone americana (Gmelin, 1789) from the Chesapeake Bay (USA) watershed have a high incidence of liver disease, including neoplasms of bile duct origin. Fish collected seasonally from spring 2019 to winter 2020 from the urban Severn River and the more rural Choptank River were evaluated for hepatic lesions. Biliary hyperplasia (64.1%), neoplasms (cholangioma and cholangiocarcinoma, 27%), and dysplasia (24.9%) were significantly higher in Severn River fish compared to Choptank River fish (52.9, 16.2, and 15.8%, respectively). Hepatocellular lesions were less common, including foci of hepatocellular alteration (FHA, 13.3%) and hepatocellular neoplasms (1%). There was also a progressive age-related increase in copper-laden granules in hepatocytes, which was a significant risk factor for FHA and could be a source of oxidative stress in the liver. Significant risk factors for biliary neoplasms included age, bile duct fibrosis, and infections by the myxozoan parasite Myxidium murchelanoi, but the prevalence and relative intensity of M. murchelanoi infections did not differ significantly between fish populations. Hepatic disease in this species appears to be chronic and may stem from an age-related accumulation of damage, possibly from parasitic infections and contaminants such as polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), and copper. Watershed development and exposures to PCBs and PAHs were generally higher for white perch in the Severn River, but similar suites of chemical contaminants were detected in the Choptank River. A broader survey of white perch within and outside Chesapeake Bay may allow determination of the extent of biliary neoplasia in this species.

River‐of‐origin assignment of migratory Striped Bass, with implications for mixed‐stock analysis

AbstractObjectiveThe Striped Bass Morone saxatilis is an anadromous teleost with a native range extending north from the Gulf of Mexico into Canadian waters. Far‐ranging coastal migrations support one of the most popular recreational fisheries in the United States. Identifying the underlying population genetic structure of the spawning populations and the genetic markers capable of differentiating among them advances our understanding of these economically and ecologically important fish and enables more targeted management to occur.MethodsWe used a restriction site‐associated DNA sequencing approach to identify neutral and adaptive single‐nucleotide polymorphisms (SNPs), and we determined the population genetic structure of 438 adult Striped Bass sampled from nine spawning locations along the Atlantic coast from the Roanoke River, United States, to the Miramichi River, Canada.ResultThe two Canadian populations (Shubenacadie and Miramichi rivers) were genetically distinct from U.S. populations and from each other. Neutral loci differentiated Striped Bass from U.S. waters into four genetically distinct populations: Roanoke River, Hudson–Kennebec River, Upper Chesapeake Bay–Potomac River–Delaware River, and Choptank River (eastern Chesapeake Bay). Outlier loci further differentiated the Delaware River from the Chesapeake Bay tributaries, suggesting that there may be local adaptation in the face of gene flow. We identified 1300 highly informative SNPs (the top 10% [with respect to the genetic differentiation index FST] of the full suite of 13,361 SNPs in our study) capable of assigning fish with at least 90% accuracy to their river of origin; through simulations, we established their applicability for conducting robust mixed‐stock analyses of the coastal migratory Striped Bass fishery.ConclusionThis study demonstrated that neutral and adaptive loci together provide evidence for fine‐scale population structure of migratory Striped Bass, and these loci provide the most informative genetic panel for mixed‐stock analysis of Striped Bass to date, capable of assigning fish to their spawning river of origin.

Environmental and anthropogenic influences on spatiotemporal dynamics ofAlosain Chesapeake Bay tributaries

AbstractAmerican Shad (Alosa sapidissima), Hickory Shad (A. mediocris), and river herrings (AlewifeA. pseudoharengusand Blueback HerringA. aestivalis) are anadromous pelagic fishes, which as adults spend most of the annual cycle at sea, but enter the coastal rivers in spring to spawn. Once as one of the most valuable fisheries along the Atlantic coast,Alosapopulations have declined in recent decades and current populations are at historic lows. Various management actions have been conducted to restore the populations, and stocks in different river systems display different demographic trends. Demonstration of synthetic diagnostics on the factors impacting these populations is important to better conserve this species group. We developed a Bayesian hierarchical spatiotemporal model to identify the population trends of these species among rivers in the Chesapeake Bay based on results of surveys conducted by the Virginia Department of Game and Inland Fisheries and Maryland Department of Natural Resources and to identify environmental and anthropogenic factors influencing their distribution and abundance. The hierarchical model structure helped to diagnose river‐specific population trends and impacts of surrounding factors, and decrease uncertainties in rivers with less samples available. The results demonstrate river‐specific heterogeneity of spatiotemporal dynamics of these species and indicate river‐specific impacts of multiple factors, including water temperature, river flow, chlorophyllaconcentration, and total phosphorus concentration, on their population dynamics. Atlantic Multidecadal Oscillation and Gulf Stream meanders displayed significant influence on the inter‐annual trends ofAlosaspecies in rivers with more data available. The results would help to develop river‐ and species‐specific management strategies to recover these species.

Reproductive Characteristics Differ in Two Invasive Populations of Blue Catfish

AbstractThe management of invasive Blue Catfish Ictalurus furcatus in Chesapeake Bay tributaries is hindered by the lack of information on its reproductive biology, which is a key component of population models used to forecast abundance. We quantified and compared the reproductive traits of female Blue Catfish from two populations from the tidal reaches of the James and York River subestuaries during 2015–2017. In these systems, Blue Catfish matured between the ages of 6 and 10 years and spawned between May and July, with larger fish spawning earlier in the season. During spawning events, Blue Catfish produced 2,613–68,356 eggs, with larger and older fish producing more eggs. Fish in the more densely populated James River matured at a marginally older age but a significantly smaller size than fish in the York River, but James River fish allocated more energy to reproduction. Fish in the James River also had greater mean values of the gonadosomatic index, relative fecundity, egg organic content, and proportion of organic content in the eggs. Relative fecundity of Blue Catfish decreased with fish size, contrary to observations in most other fishes. Based on the observed variability in reproductive traits and the size dependence of relative fecundity, we recommend incorporation of population‐specific reproductive rates into stock assessment models for invasive Blue Catfish.

Seasonal variation of polycyclic aromatic hydrocarbon metabolites in bile of white perch Morone americana from two Chesapeake Bay tributaries.

Polycyclic aromatic hydrocarbon (PAH) accumulation in the bile is a reliable biomarker of recent exposure to environmental PAH and elevated concentrations have been identified as significant risk factors for hepatic disease in some fish species. Recent surveys (spring 2019) revealed a high incidence of hepatic lesions in white perch Morone americana from Chesapeake Bay, but this initial survey did not detect an association between PAH metabolites and lesions. Seasonal sampling of fish was extended through the winter 2020 to increase the metabolite and hepatic lesion database and better understand annual PAH exposures to white perch. Naphthalenes, phenanthrenes, and benzo[a]pyrenes (equivalents) were analyzed in bile specimens (n = 400) using high-performance liquid chromatography with fluorescence detection. Mean concentrations of metabolites were highest in fish collected from the urbanized Severn River in summer and were lowest in fish from the more rural Choptank River in winter. Variance in metabolite concentrations were primarily due to location and season. Seasonal fluctuations in water temperature, river discharge, or feeding status had little influence on the pattern of metabolite concentrations observed. The results suggest higher exposures of fish to environmental PAH in the more developed Severn River with significant increases during summer, which could correspond to a spike in seasonal recreational motor boat use or other human activities. A better understanding of the factors that contribute to variability in PAH metabolism and the enterohepatic biliary circulation in white perch will improve the usefulness of biliary metabolites as a biomarker of PAH exposure in Chesapeake Bay and elsewhere.

Comparing larval microbiomes of the eastern oyster (Crassostrea virginica) raised in different hatcheries

An ongoing goal of the aquaculture industry is the improvement of oyster larval growth and production. One component of oyster hatcheries that may contribute to the health of oyster larvae is the early establishment and subsequent development of the oyster larval microbiome. The main objectives of this study were to investigate the effects of environmental conditions (hatchery types and spawning seasons) and oyster phenotypes (larval developmental stages) on the composition and diversity of the larval microbiome. In addition, the members of core larval microbiomes were identified and quantified. Microbiome composition and diversity of larval and corresponding hatchery water samples were examined using high throughput sequencing of 16S rRNA gene amplicons and represented three development stages from two different spawning events at four different hatcheries located in Chesapeake Bay tributaries. Larval and water samples from each spawning cohort were taken at 24-hours ‘D’ shape (D-stage), 1-week veliger (V-stage), and 2-weeks pediveliger (PV-stage). Larval microbiomes were significantly different from water microbiomes and were significantly influenced by hatchery and spawning, with hatchery having the greatest effect on microbiome composition. While development stage did not show a significant effect on the larval microbiomes, there was a decrease in species richness from the initial D-stage larvae through the final PV-stage and nMDS clustering patterns showed some separation between early (D- and V-) and late stages (PV-) of development, suggesting a shift towards a more selective microbiome as the larvae developed. A total of 25 members (OTU level) were identified as the core larval microbiome (core OTUs), comprising approximately one quarter of the total relative abundance of the larval microbiome. Core OTUs belonging to genera Alteronomonas and Roseobacter have been shown to offer bivalve larvae some protection against pathogens, while those belonging to family Cryomorphaceae are commonly isolated from microalgal species and most likely indicate an association with oyster larval feeding. These findings underscore the importance of environmental conditions on microbiome development of oyster larvae associated with hatchery success of larval cultivation. Further studies are needed to determine the contribution of the core larval microbiome to oyster health and disease resistance.

Salinity Tolerance and Occurrence of Salix nigra Marshall (Black Willow) in Tidal Wetlands of Chesapeake Bay Tributaries

Salix nigra Marshall (Black Willow) is a pioneer tree species that establishes in North American river floodplains and is widely used for bank stabilization. However, its salinity tolerance and occurrence in tidal wetlands of estuarine systems along the North American Atlantic coast is largely unknown. Climate change accompanied by land subsidence and changes in precipitation pattern induce increases in salinity that may affect coastal vegetation. Alteration of hydromorphology of coastal plain estuaries causes additional increases in salinity that affects forested tidal freshwater wetlands. We investigated the salinity tolerance and occurrence of Black Willow in tidal wetlands of 2 Chesapeake Bay tributaries and in a greenhouse hydroponic experiment. A salinity of more than 1 part per thousand (ppt) salt limited the willows' occurrence in the field and the cuttings' performance in the experiment. Dry mass was significantly lower in salinity of 2 and 3 ppt compared to the control and salinity of 1 ppt. Cuttings originating from tidal freshwater wetlands developed more belowground biomass and leaves than cuttings from brackish wetlands. The better performance of cuttings originating from tidal freshwater wetlands may indicate a higher resilience to short-term increases in salinity in tidal freshwater wetland forests with implications for tidal forest restoration in eastern North America.

High salinity tolerance of invasive blue catfish suggests potential for further range expansion in the Chesapeake Bay region.

In estuaries, salinity is believed to limit the colonization of brackish water habitats by freshwater species. Blue catfish Ictalurus furcatus, recognized as a freshwater species, is an invasive species in tidal rivers of the Chesapeake Bay. Salinity tolerance of this species, though likely to determine its potential range expansion and dispersal in estuarine habitats, is not well-known. To address this issue, we subjected blue catfish to a short-term salinity tolerance experiment and found that this species tolerates salinities higher than most freshwater fishes and that larger blue catfish tolerate elevated salinities for longer periods compared with smaller individuals. Our results are supported by spatially extensive, long-term fisheries surveys in the Chesapeake Bay region, which revealed a gradual (1975–2017) down-estuary range expansion of blue catfish from tidal freshwater areas to habitats exceeding 10 psu [practical salinity units] and that large blue catfish (> 200 mm fork length) occur in salinities greater than 10 psu in Chesapeake Bay tributaries. Habitat suitability predictions based on our laboratory results indicate that blue catfish can use brackish habitats to colonize new river systems, particularly during wet months when salinity decreases throughout the tidal rivers of the Chesapeake Bay.

River Water‐Quality Concentration and Flux Estimation Can be Improved by Accounting for Serial Correlation Through an Autoregressive Model

AbstractAccurate quantification of riverine water‐quality concentration and flux is challenging because monitoring programs typically collect concentration data at lower frequencies than discharge data. Statistical methods are often used to estimate concentration and flux on days without observations. One recently developed approach is the Weighted Regressions on Time, Discharge, and Season (WRTDS), which has been shown to provide among the most accurate estimates compared to other common methods. The main objective of this work was to improve WRTDS estimation by accounting for the autocorrelation structure of model residuals using the first‐order autoregressive model (AR1). This modified approach, called WRTDS‐Kalman Filter (WRTDS‐K), was compared with WRTDS for six constituents including nitrate‐plus‐nitrite (NOx), total phosphorus, total Kjeldahl nitrogen, soluble reactive phosphorus, suspended sediment, and chloride. Near‐daily concentration records at nine sites were used to generate subsets through Monte Carlo sampling for five different sampling scenarios. Results show that WRTDS‐K provided generally better daily estimates of concentration and flux than WRTDS under these sampling scenarios for all constituents, especially NOx. The degree of improvement is strongly affected by the underlying sampling scenario, with WRTDS‐K gaining more advantage when more samples are available, and hence more residuals can be exploited. The performance of WRTDS‐K depends on the AR1 coefficient (ρ) and that relationship varies with constituents and sampling scenarios. These results provided recommendations on the optimal ρ for each constituent and sampling scenario. Overall, WRTDS‐K has the potential for broad applications to monitoring records elsewhere, as demonstrated by a pilot application to Chesapeake Bay tributaries.

Toward Explaining Nitrogen and Phosphorus Trends in Chesapeake Bay Tributaries, 1992–2012

AbstractUnderstanding trends in stream chemistry is critical to watershed management, and often complicated by multiple contaminant sources and landscape conditions changing over varying time scales. We adapted spatially referenced regression (SPARROW) to infer causes of recent nutrient trends in Chesapeake Bay tributaries by relating observed fluxes during 1992, 2002, and 2012 to contemporary inputs and watershed conditions. The annual flow‐normalized nitrogen flux to the bay from its watershed declined by 14% to 127,000 Mg (metric tons) between 1992 and 2012, due primarily (more than 80% of the decline) to reduced point sources. The remainder of the decline was due to reduced atmospheric deposition (13%) and urban nonpoint sources. Agricultural inputs, which contribute most nitrogen to the bay, changed little, although trends in the average nitrogen yield (flux per unit area) from cropland and pasture to streams in some settings suggest possible effects of evolving nutrient applications or other land management practices. Point sources of phosphorus to local streams declined by half between 1992 and 2012, while nonpoint inputs were relatively unchanged. Annual phosphorus delivery to the bay increased by 9% to 9,570 Mg between 1992 and 2012, however, due mainly to reduced retention in the Susquehanna River at Conowingo Reservoir.

Chesapeake Bay's "forgotten" Anacostia River: eutrophication and nutrient reduction measures.

The Anacostia River, a Chesapeake Bay tributary running through Washington, D.C., is small but highly polluted with nutrients and contaminants. There is currently a multi-billion dollar tunnel project underway, being built in several phases, aimed at diverting effluent to sewage treatment, especially during high flow periods, and improving water quality of the Anacostia and the river into which it flows, the Potomac. Here, 4years of biweekly to monthly nutrient and phytoplankton data are analyzed to assess pre-tunnel eutrophication status and relationships to flow conditions. Under all flow conditions, nutrients prior to tunnel implementation were well in excess of values normally taken to be limiting for growth, and hypoxia was apparent during summer. Chlorophyll a was higher in summer (averaging 26.9μgL-1) than in spring (averaging 14.8μgL-1), and based on pigment composition, summer communities had proportionately more cyanobacteria (> 2-fold higher zeaxanthin to chlorophyll a ratios) compared to spring, which had proportionately more diatoms (> 2-fold higher fucoxanthin to chlorophyll a ratios). When all data from all years and sites were considered, there was a decrease in diatoms and increase in cyanobacteria with decreasing NO3- and increasing NH4+ concentrations, increasing ratios of NH4+ to NO3-, and increasing temperature. Tunnel implementation and associated nutrient reductions may reduce the severity of summer blooms but reductions of spring assemblages may be even greater because river flows are typically higher at that time of year.

Environmental DNA analysis of river herring in Chesapeake Bay: A powerful tool for monitoring threatened keystone species.

Environmental DNA (eDNA) sampling has emerged as a powerful tool to detect and quantify species abundance in aquatic environments. However, relatively few studies have compared the performance of eDNA-based abundance estimates to traditional catch or survey approaches in the field. Here, we have developed and field-tested a qPCR assay to detect eDNA from alewife and blueback herring (collectively known as ‘river herring’), comparing eDNA-based presence and abundance data to traditional methods of quantification (ichthyoplankton sampling and adult observations). Overall, the qPCR assay showed very high target specificity in lab trials, and was successful in detecting river herring for 11/12 Chesapeake Bay tributaries in spring 2015 and 2016, with 106 out of 445 samples exhibiting positive eDNA hits. We found a strong correlation between eDNA abundance and ichthyoplankton count data (Spearman’s Rho = 0.52), and Phi-tests (correlation of presence/absence data) showed higher correlation between eDNA and ichthyoplankton data (Phi = 0.45) than adult data (Phi = 0.35). Detection probability was significantly lower on western vs. eastern shore tributaries of Chesapeake Bay, and blueback herring and alewife were more likely detected on the western and eastern shores, respectively. Temporal patterns of eDNA abundance over the spring spawning season revealed that alewife were present in high abundances weeks ahead of blueback herring, which aligns with known differences in spawning behavior of the species. In summary, the eDNA abundance data corresponded well to other field methods and has great potential to assist future monitoring efforts of river herring abundance and habitat use.

Influence of Inundation and Suspended-Sediment Concentrations on Spatiotemporal Sedimentation Patterns in a Tidal Freshwater Marsh

Long-term marsh sustainability is threatened by environmental changes, especially accelerated rates of sea-level rise (SLR) and changing fluvial sediment supplies. Although direct observations of long-term marsh responses to these changes are challenging, this study examines shorter-term responses via bimonthly sedimentation measurements over 5 years in Dyke Marsh Preserve (DMP), a tidal freshwater marsh in the Potomac River (Chesapeake Bay tributary, USA). Observed patterns are evaluated with physical drivers (winds, river discharge, water-level changes, suspended-sediment concentrations (SSC)) that influence spatiotemporal variability within the marsh. Linear regression models reveal that water-level changes exert more influence on this variability than SSC in a system with plentiful sediment supply. Sedimentation rates increase linearly with inundation time, but a quadratic regression model explains more of the variability, especially for the inorganic fraction of sediment. This result indicates that fluvial sediment supply is key for marsh accretion and suggests an optimal response of sedimentation to increased inundation that non-linearly affects marsh vulnerability to future SLR. Ultimately, the SSC in adjacent waters is not available to nourish the marsh unless it is transported and retained on the platform. Self-sustaining feedbacks among inundation, sedimentation, elevation, and plants likely aid in maintaining equilibrium elevations over time and thus also marsh sustainability.

Examination of contaminant exposure and reproduction of ospreys (Pandion haliaetus) nesting in Delaware Bay and River in 2015

A study of ospreys (Pandion haliaetus) nesting in the coastal Inland Bays of Delaware, and the Delaware Bay and Delaware River in 2015 examined spatial and temporal trends in contaminant exposure, food web transfer and reproduction. Concentrations of organochlorine pesticides and metabolites, polychlorinated biphenyls (PCBs), coplanar PCB toxic equivalents, polybrominated diphenyl ethers (PBDEs) and other flame retardants in sample eggs were generally greatest in the Delaware River. Concentrations of legacy contaminants in 2015 Delaware Bay eggs were lower than values observed in the 1970s through early 2000s. Several alternative brominated flame retardants were rarely detected, with only TBPH [bis(2-ethylhexyl)-tetrabromophthalate)] present in 5 of 27 samples at <5 ng/g wet weight. No relation was found between p,p′-DDE, total PCBs or total PBDEs in eggs with egg hatching, eggs lost from nests, nestling loss, fledging and nest success. Osprey eggshell thickness recovered to pre-DDT era values, and productivity was adequate to sustain a stable population. Prey fish contaminant concentrations were generally less than those in osprey eggs, with detection frequencies and concentrations greatest in white perch (Morone americana) from Delaware River compared to the Bay. Biomagnification factors from fish to eggs for p,p′-DDE and total PCBs were generally similar to findings from several Chesapeake Bay tributaries. Overall, findings suggest that there have been improvements in Delaware Estuary waterbird habitat compared to the second half of the 20th century. This trend is in part associated with mitigation of some anthropogenic contaminant threats.