Environmental Controls on the Transport of Bacteria in Estuaries: Human Health Implications of Sediment Transport and Hurricanes

Estuarine dynamics play a critical role in the transport and fate of bacteria, including those of importance to human health. In this work, the Neuse River Estuary (NRE) in eastern North Carolina was observed through a two-year period to detect links between environmental attributes (e.g., salinity, suspensions) and the transport of two groups of bacteria: fecal indicators and Vibrio sp. (VIB). These bacterial groups differ in their sources and ability to grow once in the environment. Indicators, in this case E. coli (EC) and Enterococcus sp. (ENT), are presumed to be introduced in fecal contamination and simply decay once in the estuary. Large fractions of both indicators have been found attached to particles. On the other hand, VEB are native to the NRE and highly dependent on salinity and temperature. The potential impact of estuarine disturbance on bacterial transport was exemplified by the passage of Hurricane Ophelia in September 2005. The NRE experienced a significant storm surge of salt water, followed by a large runoff input. Water samples and sediment cores were collected, including samples from an in-situ sampler during the storm. Patterns were seen in the salinity and suspension that defined periods of surge, resuspension and runoff during the storm. ENT appeared to have two sources (resuspension and runoff), while EC appeared late in the storm, supporting the conclusion that runoff was its primary source. VTB showed more variability, with high concentrations prior to the storm dissipated, then replaced by the receding storm surge. Sediment ENT concentrations in the sediment bed remained fairly constant throughout the storm period, while EC and VIB both significantly increased following Ophelia. The sediment bed represents an environment that may harbor these bacterial populations through periods of harsh conditions in shallow estuaries (low temperature, salinity changes, nutrient limits, sunlight). The results of this study reinforce the importance of high-frequency sampling and coring of surface sediments to complement water quality monitoring, especially for efforts targeting bacterial groups with potential human health impacts.