ANTHROPOGENIC INFLUENCES ON WATER QUALITY IN A SMALL COASTAL CATCHMENT BASIN IN THE NORTHEASTERN USA

Two small drainage subbasins of approximately 3.63 and 3.35 square miles each are part of a coastal drainage system in SE Massachusetts. Both subbasins converge over a glacial outwash aquifer, currently a source of municipal water supply. Both streams (1) drain an area underlain by granites and minor gabbro bodies; (2) flow through a typical semi-urban community with no municipal sewer system but with landscaped lawns; and (3) is cross cut by a network of roads treated by road salt during the winter season. One stream flows near a more developed zone whereas the other one is in a more semi-rural region. The region is a forested land with many interweaving wetlands and only a minor agricultural land use. The study is based on a monitoring of water quality parameters and sampling of surface water at 15 pre-selected locations from the headwaters toward the aquifer and sampling of ground water from a set of about a dozen monitoring wells within the aquifer. Water samples were analyzed in the laboratory for major and minor constituents and in the field by Hydrolab multiprobe for temperature, pH, ORP, dissolved oxygen, conductance, and for nitrates and ammonia by ion selective electrodes. The program was carried over a period of two years. The objective of the study was to test if hydrochemical links exist between the surface water and ground water systems and to quantify the influence of natural and anthropogenic factors on water quality in a non-agricultural catchment basin typical of the northeastern US. Factors that influence most significantly the quality of surface waters are related to land use. Sodium patterns and variations (2.1 mg/kg to 84) represent effects of application of salt on road surfaces, nitrates (up to 40 mg/L) from runoffs of fertilizers and from waste water discharge though a minor effect by nutrient cycling can be also observed. The ground water quality reflects more its geological and ecological environments. High iron and manganese (typically up to 50 mg/kg, occasionally up to 100 mg/kg and up to 2.5 mg/kg, respectively) are related to reducing environments near wetlands and Na to Mg ratio to the bedrock type, for example. Generally, there is a weak observed link between water quality of the surface and ground water systems. However, an induced infiltration due to ground water withdrawal can be a significant factor.