Explore the vast range of titles available.

Constructed oyster reefs (CORs) provide shore protections and habitats for fish and shellfish communities via wave energy attenuation. However, the processes and mechanism of CORs on wave attenuation remain unclear, thus limiting the effective assessment of CORs for shoreline protection. This paper presents results of a field investigation on wave characteristics and wave spectral variations along a shoreline with CORs in an estuary with a large tidal range as well as large wind waves and swell energy. Six pressure transducers were deployed from January 31 to April 2, 2018, in Gandy’s Beach, New Jersey, in upper Delaware Bay. CORs were constructed at the study site in 2016 as living shoreline structures after Hurricane Sandy. The data collected from the study site exhibits the wave variations and spectral characteristics over the span of 2 months, including four winter storms (i.e., nor’easters). The spatial variations of wave heights measured on both sides of CORs show a strong dependence on the ratio between the freeboard of CORs and the offshore wave heights. Due to the large tidal range (> 2 m), the crests of CORs remain submerged over 85% of the time. The submerged CORs only provide partial attenuation of wave energy. The wave environment in the estuary is complex, especially during nor’easters. For instance, winds with rapid changing fetches could lead to bi-modal wind seas. Due to the complex wave spectra, the bulk wave heights such as the significant wave heights cannot be adopted to adequately reveal the capacity of CORs to attenuate wave energy. Spectral analysis is conducted to investigate the spatial and temporal variations of wave energy in targeted frequency bins. The spectral analysis results reveal the energy transfer from the primary waves to the high harmonics after waves propagate over the submerged CORs. Moreover, it is found that swell energy originated from the Atlantic Ocean can penetrate CORs without any dampening even when CORs are emergent. This study could help resource managers for indepth evaluation of living shoreline effectiveness and improvement of living shoreline structures such as CORs.

Intertidal aquifers host a reactive zone comprised of Fe mineral-coated sands where fresh and saline groundwaters mix. This zone may significantly influence the export of C, N, P, Fe, and other metals in submarine groundwater discharge (SGD). Toward determining the roles of microbes in Fe and S mineralization, and the interplay of microbiology with geochemistry and physical hydrology, we conducted a biogeochemical study of pore waters at Cape Shores, Delaware. Here, fresh groundwater provides Fe(II), which precipitates as FeIIIOOH predominantly through microbial Fe(II) oxidation. Candidate division OP3 was the dominant microbial group associated with Fe(II)- and Fe(III)-rich regions of the aquifer, suggesting that this uncharacterized phylum may be involved in Fe(II) oxidation. Saline water brings O₂, sulfate, and organic C into the intertidal mixing zone. Microbial reduction of sulfate produces sulfide that is transported to the Fe-mineralized zone leading to the transformation of FeOOH to Fe(II) sulfides. Microbial populations are structured by the availability of chemical species supplied along groundwater flow paths. Seasonal changes in the relative supply of fresh and saline groundwater affect solute fluxes, and therefore, microbial controls on the location and composition of the Fe-mineralized zone. Ultimately, the composition, extent, and dynamics of the Fe-mineralized zone will affect the sequestration, affinity, and residence time of solutes bound for export to coastal oceans through SGD.

Salinity distribution in a large tidal estuary is subject to estuarine adjustment under the influences of multiple physical drivers such as freshwater pulses and sea level rise, and is crucial to upstream water quality, aquaculture, and ecosystem functions of the estuary. To better understand the estuarine salinity response to climate change, the unstructured-grid Finite Volume Community Ocean Model was implemented to simulate the salt intrusion in the Delaware Bay Estuary. The model was first validated by multiple observational data sets and subsequently applied in an idealized setting to examine the response of salt front to freshwater pulses in high flow conditions, followed by a long-term drought condition supported by a multi-decadal streamflow drought analysis in the estuary. The model results showed that after the freshwater pulses the salt front location moved further upstream with sea level rise. Under the simulated long-term drought condition, the adjustment timescale of salt intrusion varies nonlinearly with sea level rise. With a significant increase in sea level rise, the adjustment timescale starts to decrease. This shift suggests a transition into a different regime where the estuary becomes more stratified, as indicated by an increasing bulk Simpson number with rising sea levels.

Salinity distribution in a large tidal estuary is subject to estuarine adjustment under the influences of multiple physical drivers such as freshwater pulses and sea level rise, and is crucial to upstream water quality, aquaculture, and ecosystem functions of the estuary. To better understand the estuarine salinity response to climate change, the unstructured-grid Finite Volume Community Ocean Model was implemented to simulate the salt intrusion in the Delaware Bay Estuary. The model was first validated by multiple observational data sets and subsequently applied in an idealized setting to examine the response of salt front to freshwater pulses in high flow conditions, followed by a long-term drought condition supported by a multi-decadal streamflow drought analysis in the estuary. The model results showed that after the freshwater pulses the salt front location moved further upstream with sea level rise. Under the simulated long-term drought condition, the adjustment timescale of salt intrusion varies nonlinearly with sea level rise. With a significant increase in sea level rise, the adjustment timescale starts to decrease. This shift suggests a transition into a different regime where the estuary becomes more stratified, as indicated by an increasing bulk Simpson number with rising sea levels.

Relationships between bacterial community and dissolved organic matter (DOM) include microbial uptake, transformation and secretion, all of which influence DOM composition. In this study, we explore diversity and similarity metrics of dissolved organic molecules (Fourier-transform ion cyclotron resonance mass spectrometry) and bacterial communities (tag-sequencing of 16S rRNA genes) along the salinity gradient of the Delaware Estuary (USA). We found that even though mixing, discharge and seasonal changes explained most of the variation in DOM and bacterial communities, there was still a relationship, albeit weak, between the composition of DOM and bacterial communities in the estuary. Overall, many DOM molecular formulas (MFs) and bacterial operational taxonomic units (OTUs) reoccurred over years and seasons, while the frequency of MF-OTU correlations varied. Diversity based on MFs and OTUs was significantly correlated, decreasing towards the open ocean. However, while the diversity of bacterial OTUs dropped markedly with low salinity, MF diversity decreased strongly only at high salinities. We hypothesize that the different turnover times of DOM and bacteria lead to different abundance distributions of OTUs and MFs. A significant portion of the detected DOM is of a more refractory nature with lifetimes largely exceeding the mixing time of the estuary, while bacterial community turnover times in the Delaware Estuary are estimated at several days.

Earth-observing satellites are a major research tool for spatially explicit ecosystem nowcasting and forecasting. However, there are practical challenges when integrating satellite data into usable real-time products for stakeholders. The need of forecast immediacy and accuracy means that forecast systems must account for missing data and data latency while delivering a timely, accurate, and actionable product to stakeholders. This is especially true for species that have legal protection. Acipenser oxyrinchus oxyrinchus (Atlantic sturgeon) were listed under the United States Endangered Species Act in 2012, which triggered immediate management action to foster population recovery and increase conservation measures. Building upon an existing research occurrence model, we developed an Atlantic sturgeon forecast system in the Delaware Bay, USA. To overcome missing satellite data due to clouds and produce a 3-d forecast of ocean conditions, we implemented data interpolating empirical orthogonal functions (DINEOF) on daily observed satellite data. We applied the Atlantic sturgeon research model to the DINEOF output and found that it correctly predicted Atlantic sturgeon telemetry occurrences over 90% of the time within a 3-d forecast. A similar framework has been utilized to forecast harmful algal blooms, but to our knowledge, this is the first time a species distribution model has been applied to DINEOF gap-filled data to produce a forecast product for fishes. To implement this product into an applied management setting, we worked with state and federal organizations to develop real-time and forecasted risk maps in the Delaware River Estuary for both state-level managers and commercial fishers. An automated system creates and distributes these risk maps to subscribers’ mobile devices, highlighting areas that should be avoided to reduce interactions. Additionally, an interactive web interface allows users to plot historic, current, future, and climatological risk maps as well as the underlying model output of Atlantic sturgeon occurrence. The mobile system and web tool provide both stakeholders and managers real-time access to estimated occurrences of Atlantic sturgeon, enabling conservation planning and informing fisher behavior to reduce interactions with this endangered species while minimizing impacts to fisheries and other projects.

Monthly surface currents at 2 km resolution near the mouths of three U.S. east coast bays were obtained from high-frequency radars (Coastal Ocean Dynamics Application Radar, CODAR) during 2012–2024. The currents near these bays, the Chesapeake Bay (CB), the Delaware Bay (DB) and the New York Bay (NB) were analyzed to infer similarity and differences, as well as potential common forcing from regional and basin-scale factors. The contribution to flow variability from local and remote forcing is evaluated by comparing surface currents with (a) river discharges into each bay, (b) with local and regional winds, and (c) with the North Atlantic Oscillation (NAO). The results show that surface flow variability near the mouth of the bays is linked with all three driving factors. The three bays often show similar flow patterns not only of the seasonal cycle, but also during extreme weather events. For example, increased surface flow into the bays from the Atlantic Ocean is seen when hurricanes are observed offshore in the fall, and increased surface flow from the bays is seen during winter storms. During positive NAO phases, eastward flow from all three bays increased due to intensified westerly winds, while during negative NAO phases flow decreased with weakening winds in the region. River discharges into the bays increased during 2012–2019 but decreased during 2019–2024. This change in river discharge trend was especially large in the CB, resulting in a change in trends of the surface currents. Monthly currents of each bay are only weakly correlated with the monthly river flow ( R  ~ 0.2–0.3; P  < 0.05), while the seasonal cycles of rivers and currents have higher correlations ( R  ~ 0.6–0.7). Local winds show high correlations with the monthly currents ( R  ~ 0.75) with the current direction ~ 45° to the right of the wind, as expected from Ekman theory. However, contributions to current variability from regional and remote factors cannot be ignored. The results demonstrate the complex nature of the currents near the mouth of bays since multiple drivers, including estuarine, coastal and open ocean dynamics contribute to the observed variability.

During spring migration, thousands of shorebirds gather in Delaware Bay at the same time as horseshoe crabs (Limulus polyphemus) are spawning. During their stopover, the birds store enough fuel in the form of fat and muscle protein to complete their migration to the Canadian breeding grounds. We documented the changes in body mass of shorebirds migrating through Delaware Bay and determined how much of the shorebird diet during this period consisted of horseshoe crab eggs. Migrating shorebirds were captured, morphometric measurements taken, and gut samples collected by stomach flushing. Red Knots (Calidris canutus), Ruddy Turnstones (Arenaria interpres), Sanderlings (C. alba), and Semipalmated Sandpipers (C. pusilla) increased their body mass up to 70-80% while staging on Delaware Bay. Horseshoe crab egg membranes constituted the bulk of the gut contents for all species at all collection sites. Polychaete and oligochaete worms were found in substantial concentrations in gut samples collected from shorebirds in certain beaches. Sand and un-identified decomposed material were found in varying amounts in gut samples of all species and locations. Apparent declines in spawning horseshoe crab populations may adversely affect migratory shorebirds.

Estuaries include some of the most productive yet anthropogenically impacted marine ecosystems on the planet, and provide critical habitat to many ecologically and economically important marine species. In order to elucidate ecological function in estuaries, we must understand what factors drive community dynamics. Delaware Bay is the third largest estuary in the United States and hosts over 200 species of migrant and resident fishes and invertebrates. The Delaware Division of Fish and Wildlife has conducted two long-term trawl surveys at monthly intervals in Delaware Bay since 1966. The two surveys collect data on environmental conditions, species composition, and number of fishes and macroinvertebrates across different size classes and life histories. Using a suite of multivariate approaches including hierarchical cluster analysis, canonical correlation analysis, and permutational multivariate analysis of variance, we characterized the fish and macroinvertebrate community in Delaware Bay and found that community composition and environmental conditions varied across spatial and seasonal scales. We identified four distinct biogeographic regions, based on environmental conditions and community composition, which were consistent across surveys. We found that the community was driven primarily by gradients in temperature and salinity and that abundant, frequently occurring species in the Bay have well-defined environmental associations. Our work represents the first attempt to use an existing historical survey to better understand how environmental parameters influence diversity and distribution of macrofauna within Delaware Bay, providing insight into how abiotic variables, influenced by climate, may impact the Delaware Bay ecosystem and similar estuarine ecosystems worldwide.