SEASONAL AND SPATIAL VARIATIONS IN DISSOLVED ION CONCENTRATIONS IN PATROON CREEK, A SMALL URBAN WATERSHED IN ALBANY COUNTY, NEW YORK

The Patroon Creek watershed (33 km²) is highly urbanized with many impervious surfaces and few natural areas. For much of its 10-km length, the creek flows within 200 m of an interstate highway and a major rail route, mostly through artificial channels before reaching the Hudson River. It is listed as one of the ten most severely impacted streams in New York State, based on conditions of sedimentation, sewage discharge, and non-point-source pollution. Sediments of the creek and its impoundments are contaminated with heavy metals and PCB’s. In 2002, we began monitoring creek water quality as part of a consortium of federal, state, and local government agencies, local universities, and community groups in order to provide critical data for future management and restoration efforts.

Seven sampling sites were selected along the creek to characterize the effects of land use, point and non-point pollution on water quality. Temperature and dissolved oxygen were measured at each site weekly for one year. Specific conductance, stage height, and temperature were measured continuously (15 minute intervals) at a gage site near the creek mouth. Alkalinity and pH were determined in the laboratory by standard methods, and major ion concentrations were determined by ion chromatography.

During the summer, mean concentrations for all sites (in mg/L) were Na (123), NH₄ (2.5) K (4.2), Mg (18), Ca (86), F (0.5), Cl (186), NO₃ (1.9), SO₄ (27), and total dissolved solids (TDS; 437). Winter monthly means for Na (240), Ca (50), Cl (391), SO₄ (36), and TDS (790) were 13-100 % higher than during summer, whereas other ions were unchanged. These increases are related to the use of road de-icing salts within the watershed, as specific conductance increases with stage height during winter storm events. This effect is also more pronounced at sites in close proximity to and downstream of paved areas, than at more distant and upstream sites. In contrast, during summer storms, specific conductance is negatively correlated with stage height, because of the diluting effects of surface run-off on ion concentrations. High concentrations of dissolved anions, particularly chloride, have the potential to adversely affect aquatic ecosystems and aqueous phase speciation and transport of heavy metals.