Long-term Water Quality Trends in Barnegat Bay, New Jersey

Abstract

Climate change has become one of the major challenges and imposes a serious threat to our environment and economics. Estuarine and coastal ecosystems are heavily influenced by not only human activities, but also climate change associated with temperature increase, sea level rise, and extreme weather events. For this study, eleven years of monitoring data were compiled and analyzed to evaluate the long-term trends of water quality and the impact of climate change in Barnegat Bay, New Jersey. Time-series of seven key water quality parameters, including water temperature, salinity, chlorophyll-a (Chl-a), total nitrogen (TN), total phosphorus (TP), dissolved oxygen (DO), and turbidity collected from 2011-2022 were retrieved from the EPA Water Quality Portal for four sites within the bay. Water temperature at all sites showed a general decreasing trend during this period. Further analysis revealed that summer temperatures increased over the time period whereas winter temperatures decreased. The increase in summer temperatures is in agreement with the long-term trends in the Barnegat Bay watershed since the 1970s. The decreasing trends in winter are consistent with trends from the 2000s to the present in the bay. Salinity exhibited high spatial and temporal variabilities due to the effects of freshwater discharges and seasonal and year-to-year differences in precipitation. TN and TP showed strong intra-annual variation but remained relatively stable (or slightly decreased) over the past decade. Despite monthly variation, DO at all four sites increased during the study period, showing its inverse relationship to water temperature. Meanwhile, turbidity, an indicator of water clarity, decreased over the 11-year period at most of the study sites. This work serves as the first step to assess long-term water quality changes and to evaluate human and climate impact on Barnegat Bay and the adjacent New Jersey coast.