Examining the Relationship Between Wet Weather and Fecal Contamination in a North Carolina Estuary

The Newport River Estuary (NPRE) was recently included on the United States Environmental Protection Agency's 303(d) list of impaired waters for fecal coliforms. Therefore, the estuary is the focus of current total maximum daily load (TMDL) development and implementation. The NPRE is a coastal estuary in eastern North Carolina, and is vital for the local economy in regards to commercial shellfish harvesting and recreational activities (fishing, shrimping, boating, swimming). There is a delicate balance in maintaining the water quality for the NPRE's beneficial uses, and protecting environmental integrity, given the growing coastal population and increasing development along the banks of the NPRE. The increasing levels of development and anthropogenic influence is exacerbating stormwater runoff problems, which is contributing to heightened levels of fecal coliforms and subsequent shellfish harvesting area closures. To assist with the NPRE TMDL development, fecal indicator bacteria (FIB, E. coli and Enterococcus sp. ) and environmental parameter measurements (including but not limited to rainfall, temperature, salinity, and turbidity) were taken from September 2004 to August 2006 over relevant spatial, temporal, and event-driven scales throughout the estuary. Selected water samples from rain and non-rain events were further characterized beyond the traditional FIB analyses using Bacteroides spp. molecular analyses to determine whether fecal contamination signals were either predominantly human or non-human. The results from this study demonstrated a significant correlation between rainfall and FIB after 3.00 cm (1.2 inches) of rainfall over 48 hours and a mixed signal from our preliminary molecular marker analyses. In addition, further analyses indicate that the current management strategy of closing the shellfish harvesting areas after 3.81 cm of rain (1.5 inches) within 24 hours may not be as protective of public health as desired. Accurate models to determine the causal relationship between environmental variables and FIB levels are a major goal of this TMDL project. Thus, the results from this research are being utilized to parameterize both space/time and Bayesian (probabilistic) models of FIB distribution. The goal of these modeling efforts is to provide tools to predict loading of microbial contaminants to shellfish harvesting areas, as well as to provide information on fate and transport of FIB and potential pathogens of concern in the NPRE.