Juvenile fish assemblage recruitment dynamics in a mid-Atlantic estuary: before and after Hurricane Sandy

Hurricanes can have long-term effects on estuarine fauna. Understanding these effects is important as climate change may influence the severity and frequency of these storms. On 29 October 2012, Hurricane Sandy, a large storm spanning roughly 1850 km in diameter, made landfall in Brigantine, New Jersey (USA), approximately 20 km south of Barnegat Bay, during an ongoing study of the bay’s ichthyofauna, providing an opportunity to observe fish recruitment dynamics coincident with hurricane passage. The objective of this study was to measure variance in the Barnegat Bay pre-Sandy fish assemblage relative to that of 1 and 2 yr after the storm. Barnegat Bay fishes were surveyed with an extensive otter trawl study in April, June, August, and October of 2012 (pre-Sandy), 2013 (1 yr post-Sandy), and 2014 (2 yr post-Sandy). Species composition of the fish assemblage was similar across years. Analyzed structural characteristics (abundance, diversity, richness) of the fish assemblage were occasionally more likely to occur or were larger pre-Sandy and 2 yr post-Sandy relative to 1 yr post-Sandy, but this trend was inconsistent across seasons and between structural characteristics. Furthermore, odds of occurrence and length frequency distributions for many resident species and sentinel fall/winter spawners did not indicate that variance could be definitively explained as a hurricane effect. The capability of fish to relocate from areas of temporarily unsuitable habitat and annual new recruitment of larvae and juveniles to the bay likely contributed to the observed stability in the fish assemblage.

Carbon Sequestration Rate Estimates in Delaware Bay and Barnegat Bay Tidal Wetlands Using Interpolation Mapping

Quantifying carbon sequestration by tidal wetlands is important for the management of carbon stocks as part of climate change mitigation. This data publication includes a spatial analysis of carbon accumulation rates in Barnegat and Delaware Bay tidal wetlands. One method calculated long-term organic carbon accumulation rates from radioisotope-dated (Cs-137) sediment cores. The second method measured organic carbon density of sediment accumulated above feldspar marker beds. Carbon accumulation rates generated by these two methods were interpolated across emergent wetland areas, using kriging, with uncertainty estimated by leave-one-out cross validation. This spatial analysis revealed greater carbon sequestration within Delaware, compared to Barnegat Bay. Sequestration rates were found to be more variable within Delaware Bay, and rates were greatest in the tidal freshwater area of the upper bay.

Sediment accumulation, elevation change, and the vulnerability of tidal marshes in the Delaware Estuary and Barnegat Bay to accelerated sea level rise

Tidal marshes protect coastal communities from the effects of sea level rise and storms, yet they are vulnerable to prolonged inundation and submergence. Uncertainty regarding their vulnerability to sea level rise motivated the establishment of a monitoring network in the Delaware Estuary and Barnegat Bay. Using data collected through these efforts, we determined whether rates of tidal marsh sediment accumulation and elevation change exceeded local sea level rise and how these dynamics varied along geographic and environmental gradients. Marker horizons, surface elevation tables, elevation surveys, water level data, and water column suspended sediment concentrations were used to evaluate sea level rise vulnerability. Of 32 study sites, 75% had elevation change that did not keep pace with long-term rising sea levels (1969–2018) and 94% did not keep pace with recent sea level rise (2000–2018). Mean high water rose most rapidly in the freshwater tidal portion of the Delaware Estuary with rates nearing 1 cm yr-1 from 2000–2018. We noted that greater sediment accumulation rates occurred in marshes with large tidal ranges, low elevations, and high water column suspended sediment concentrations. We found correlations between rates of shallow subsidence, increasing salinity, and decreasing tidal range. Marsh elevation and water level surveys revealed significant variability in elevation capital and summer flooding patterns (12–67% inundation). However, rapid increases in mean high water over the past 19 years suggests that all marsh platforms currently sit at or below mean high water. Overall, these data suggest that tidal marshes in the Delaware Estuary and Barnegat Bay are vulnerable to submergence by current rates of sea-level rise. While we observed variability in marsh elevation capital, the absence of strong correlations between elevation trends and environmental parameters makes it difficult to identify clear patterns of sea level rise vulnerability among wetlands.

Spatial distribution of water level impacting back-barrier bays

Water level in semi-enclosed bays, landward of barrier islands, is mainly driven by offshore sea level fluctuations that are modulated by bay geometry and bathymetry, causing spatial variability in the ensuing response (transfer). Local wind setup can have a complementary role that depends on wind speed, fetch, and relative orientation of the wind direction and the bay. Bay area and inlet geometry and bathymetry primarily regulate the magnitude of the transfer between open ocean and bay. Tides and short-period offshore oscillations are more damped in the bays than longer-lasting offshore fluctuations, such as a storm surge and sea level rise. We compare observed and modeled water levels at stations in a mid-Atlantic bay (Barnegat Bay) with offshore water level proxies. Observed water levels in Barnegat Bay are compared and combined with model results from the Coupled Ocean–Atmosphere–Wave–Sediment Transport (COAWST) modeling system to evaluate the spatial structure of the water level transfer. Analytical models based on the dimensional characteristics of the bay are used to combine the observed data and the numerical model results in a physically consistent approach. Model water level transfers match observed values at locations inside the bay in the storm frequency band (transfers ranging from 50 %–100 %) and tidal frequencies (10 %–55 %). The contribution of frequency-dependent local setup caused by wind acting along the bay is also considered. The wind setup effect can be comparable in magnitude to the offshore transfer forcing during intense storms. The approach provides transfer estimates for locations inside the bay where observations were not available, resulting in a complete spatial characterization. An extension of the methodology that takes advantage of the ADCIRC tidal database for the east coast of the United States allows for the expansion of the approach to other bay systems. Detailed spatial estimates of water level transfer can inform decisions on inlet management and contribute to the assessment of current and future flooding hazard in back-barrier bays and along mainland shorelines.