EFFECTS OF ENVIRONMENTAL AND ANTHROPOGENIC FACTORS ON SURFACE WATER QUALITY IN THE ROCK CREEK WATERSHED

The need to understand the spatial and temporal distribution of pollutants within urban aquatic systems has increased in importance as surface water quality continues to degrade. Rock Creek, a tributary of the Potomac River, spans 33 miles originating in the agricultural and suburban areas of Maryland (MD) and continuing through the more urbanized District of Columbia (D.C.), ultimately running into the Chesapeake Bay. Downstream, the land use becomes increasingly more urbanized and the sewer and stormwater systems transition from separate (MD) to combined (D.C). Known contaminants associated with sewer and stormwater discharges as well as stormwater runoff which traverse vegetated and impervious surfaces, include nitrate, phosphate, and Escherichia coli (E. coli).

The purpose of this study is to investigate environmental and anthropogenic factors that impact surface water quality in the Rock Creek watershed. Water quality samples were collected weekly from 15 sites along Rock Creek for approximately four months. The samples were analyzed for physical and chemical parameters including: turbidity, electrical conductivity, nitrogen, and phosphorus. Additionally, concentrations of E. coli and total coliforms were quantitatively assessed. Additional samples were collected following significant rain events, in order to assess the impact of precipitation events on the water quality. Spatial and temporal data analysis using geographic information systems software determined that water quality variation is not uniform along the creek. The most probable factors responsible for the variation in the study area are agricultural runoff, sewer type and condition, and impervious surface coverage. These data may ultimately 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 and sewer/stormwater discharges.