Phosphorus and carbohydrate limtation [i.e. limitation] of fecal coliform and fecal enterococcus within tidal creek sediments

Aquatic sediments have been shown to be a significant reservoir for fecal bacteria and at concentations two to three orders of magnitude higher than the waters directly above them. These bacteria represent a potentially serious health threat to humans using these waters. This study was conducted to determine the abundance of fecal bacteria within tidal creek sediments of Bradley Creek and determine if their residence or growth may be limited by concentrations of sediment phosphorus (P), sediment carbon (C), salinity, and water temperature. Sediment fecal coliforms had a mean of 179 CFU/cm2 (std. dev. = 411, range = 0-3230) for samples collected monthly at 6 stations over the course of this study. Were the bacteria and sediments to be suspended through a 100 cm water column this value would be the equivalent of 179 CFU/100ml which is just below the water quality standard for human contact (200 CFU/100ml). Such disturbances could easily be produced by natural or human activities. Samples for enterococcus had a mean of 285 CFU/cm2 (std. dev. = 473, range = 0-1730). If these sediments and bacteria were similarly suspended they would equate to 285 CFU/100ml and greatly exceede the standard for human contact in the water column (33 CFU/100ml). Overall, only fecal coliform bacteria were correlated to sediment C, however, the signal from bioavailable C was probably masked by the presence of insoluble C from detrital cellulose. Neither bacteria were correlated to sediment P concentrations which were found to be greater in Bradley Creek sediments than limiting concentrations for coliforms in sediments concluded by previous research. Sediments were a significant reservoir of P as concentrations were recorded as high as 4-5 orders of magnitude greater than in overlying waters. Sediment fecal coliforms were shown to be negatively correlated with salinity and positively correlated with temperature conforming to patterns established by previous research. However, fecal enterococcus was not shown to have a significant relationship with either salinity or temperature. Fecal coliforms were positively correlated to precipitation over the previous 24 hours. Experimental addition of bioavailable P (potassium phosphate monobasic) and bioavailable C (dextrose) showed a positive relationship between both fecal bacteria and bioavailable C. Enterococcus was significantly correlated to P in trials with low initial sediment P concentrations. Fecal coliform was significantly correlated to P at a = 0.1 where initial P concentrations were low. A higher a was taken into consideration due to the high variability of coliform data and relatively low degrees of freedom for individual experimental trials. It was concluded that while P and C are important to fecal bacterial residence within sediments, P may no longer be limiting in Bradley Creek due to relatively high background concentrations. Elevated P and bioavailable C concentrations have been correlated to storm water runoff. Limitation of sediment fecal bacteria in Bradley Creek by these nutrients may be alleviated from their introduction via this mechanism

Multiple modes of water quality impairment by fecal contamination in a rapidly developing coastal area: southwest Brunswick County, North Carolina

Fecal contamination of surface waters is a significant problem, particularly in rapidly developing coastal watersheds. Data from a water quality monitoring program in southwest Brunswick County, North Carolina, gathered in support of a regional wastewater and stormwater management program were used to examine likely modes and sources of fecal contamination. Sampling was conducted at 42 locations at 3–4-week intervals between 1996 and 2003, including streams, ponds, and estuarine waters in a variety of land use settings. Expected fecal sources included human wastewater systems (on-site and central), stormwater runoff, and direct deposition by animals. Fecal coliform levels were positively associated with rainfall measures, but frequent high fecal coliform concentrations at times of no rain indicated other modes of contamination as well. Fecal coliform levels were also positively associated with silicate levels, a groundwater source signal, indicating that flux of fecal-contaminated groundwater was a mode of contamination, potentially elevating FC levels in impacted waters independent of stormwater runoff. Fecal contamination by failing septic or sewer systems at many locations was significant and in addition to effects of stormwater runoff. Rainfall was also linked to fecal contamination by central sewage treatment system failures. These results highlight the importance of considering multiple modes of water pollution and different ways in which human activities cause water quality degradation. Management of water quality in coastal regions must therefore recognize diverse drivers of fecal contamination to surface waters