Environmental and Anthropogenic Impacts on Surface Water Quality in a Mixed-use Watershed

ABSTRACT Degradation of urban surface water quality has increased the importance of understanding the spatial and temporal distribution of pollutants within aquatic systems. Poor water quality damages aquatic habitats and poses a human health risk. The purpose of this study was to investigate environmental and anthropogenic factors that impact water quality in the Rock Creek Watershed in Maryland and the District of Columbia by monitoring microbiological (E. coli and total coliforms), chemical, and physical water quality parameters. Sampling weekly and following >13 mm rain events during a four-month period obtained 295 total water samples. The geometric mean E. coli concentration for each month exceeded the permissible standard. Spatial and temporal data analysis using Geographic Information Systems software and statistical analysis determined that water quality is not uniform along Rock Creek. Areas with more than 50 percent agricultural and low-density land use had higher mean nitrate concentrations but lower electrical conductivity and phosphate concentrations compared with urbanized areas with a high density of older, potentially leaking sewers. Impervious surface coverage was positively correlated with mean electrical conductivity and negatively correlated with mean nitrate concentration. Precipitation and creek discharge rate were positively correlated with mean enteric bacteria concentration. Temporal (distribution of rainfall) as well as spatial (pet waste from dog walking) influences may impact the dynamics of microbial contamination in the watershed. These data may assist decision makers in understanding the relationship between water quality of Rock Creek, the factors studied, and the potential health hazards resulting from precipitation events.