Impacts of rainfall on the water quality of the Newport River Estuary (Eastern North Carolina, USA)

The Newport River Estuary (NPRE), an important North Carolina (NC) shellfish harvesting area, has been experiencing alterations to the land-water interface due to increasing population and coastal development. Water quality degradation in the estuary over the last decade has led to an increase of shellfish harvesting area closures, and has been postulated to be due to non-point source contamination in the form of stormwater. Water samples were taken in the NPRE (n = 179) over a range of weather conditions and all seasons from August 2004 to September 2006. Fecal coliform (FC), as estimated by E. coli (EC), and Enterococcus (ENT) concentrations (MPN per 100 ml) were examined in relation to rainfall levels and distance from land. The relationships among the fecal indicator bacteria (FIB) and environmental parameters were also examined. The data revealed a significant increase in FC concentrations after measured rainfall amounts of 2.54cm (general threshold) and 3.81cm (management action threshold). However, higher than expected FIB concentrations existed during conditions of negligible rainfall (<0.25 cm), indicating a possible reservoir population in the sediment. Overall, stormwater runoff appears to be adversely impacting water quality in the NPRE

Surface currents and winds at the Delaware Bay mouth

Knowledge of the circulation of estuaries and adjacent shelf waters has relied on hydrographic measurements, moorings, and local wind observations usually removed from the region of interest. Although these observations are certainly sufficient to identify major characteristics, they lack both spatial resolution and temporal coverage. High resolution synoptic observations are required to identify important coastal processes at smaller scales. Long observation periods are needed to properly sample low-frequency processes that may also be important. The introduction of high-frequency (HF) radar measurements and regional wind models for coastal studies is changing this situation. Here we analyze synoptic, high-resolution surface winds and currents in the Delaware Bay mouth over an eight-month period (October 2007 through May 2008). The surface currents were measured by two high-frequency radars while the surface winds were extracted from a data-assimilating regional wind model. To illustrate the utility of these monitoring tools we focus on two 45-day periods which previously were shown to present contrasting pictures of the circulation. One, the low-outflow period is from 1 October through 14 November 2007; the other is the high-outflow period from 3 March through 16 April 2008. The large-scale characteristics noted by previous workers are clearly corroborated. Specifically the M2 tide dominates the surface currents, and the Delaware Bay outflow plume is clearly evident in the low frequency currents. Several new aspects of the surface circulation were also identified. These include a map of the spatial variability of the M2 tide (validating an earlier model study), persistent low-frequency cross-mouth flow, and a rapid response of the surface currents to a changing wind field. However, strong wind episodes did not persist long enough to set up a sustained Ekman response