Attachment of Fecal Indicator Bacteria to Particles in the Neuse River Estuary, N.C.

Observations of microbial contamination and particle suspensions represent valuable inputs to water quality models that form the basis of regulatory decisions regarding the use of surface waters. The Neuse River Estuary in eastern North Carolina is experiencing a decline in water quality due to increasing anthropogenic inputs. Potentially serious consequences of these inputs are the introduction and persistence of bacterial pathogenic organisms from human and animal waste. A critical factor in determining human health risk is the partitioning of these organisms between particle-attached and free-living cells in the water column. Particle-associated bacteria are generally less mobile in the environment, settle faster, and may have different rates of mortality than their free phase counterparts. Surface and bottom water samples were collected during both dry weather and storm events throughout the summer of 2004 to gage changes in particle concentration, particulate organic carbon and nitrogen, and the partitioning of two indicators of fecal contamination: Enterococcus sp. (ENT) and E. coli (EC). Increases in concentrations of these indicators coincided with increases in particles in suspension following storm events. In surface waters, both ENT and EC exhibited similar patterns, controlled primarily by runoff inputs (i.e., storms). In bottom waters, resuspension of sediments was additional source of particles and both indicators. Partitioning of these indicators between particle attached and free living exhibited an overall average of 38% of bacteria associated with particles capable of settling out of the water column. This fraction compares well with previous estimates of attachment of indicators in stormwater. The ability to estimate attachment rates and characterize particle suspensions provides a powerful tool for management and assessment of water quality in estuaries.