Flow and chemical contributions to streamflow in an upland watershed: a baseflow survey

We sampled an east-central Pennsylvania watershed to investigate controls on baseflow and the associated water quality in the upland agricultural watershed setting. Tributaries and upgradient reaches of two main streams exhibited increasing flow from influent groundwater, but rates of increase were different depending on topographic position. Approximately midway through the watershed, the main streams showed loss of flow to groundwater, but reverted to gaining conditions near the watershed outlet, a zone of groundwater discharge. Tributaries draining a forested ridge exhibited low ionic concentrations, while those originating within agricultural areas exhibited higher concentrations of all ions, including NO3-N upto 20 mg l(-1). These concentrations represent drainage from a surficial aquifer with water quality affected by overlying land use. From midway down the main streams to the watershed outlet, baseflow exhibited stable and moderate chemical concentrations; Ca, Mg, SO4, Cl, NO3, and HCO3 were the dominant ions, and NO3-N concentrations were about 5 mg l(-1). A simple model was developed to explain nitrate concentrations within baseflow. It showed that nitrate was predictable down to the subwatershed scale based on percentage of major land use categories. Published by Elsevier Science B.V.