Influences of Land Use on Water Quality of a Diverse New England Watershed

Analysis of variations in major ion chemistry in the Mill River watershed reveals the importance of anthropogenic activities in controlling streamwater chemistry. Average concentrations of NO3 - and SO4 2- show a positive correlation with percent catchment area altered by human land uses, and concentrations of Cl- increase with road density. Water removal from municipal reservoirs increases the downstream concentration of NO3 - and SO4 2- over that predicted by land use changes, showing that removal of high quality upstream water concentrates pollutants downstream. In salt-impacted streams, Cl- exceeds Na+ by 10−15% due to cation exchange reactions that bind Na+ to soil. The net effect of nonpoint source pollution is to elevate ANC in the most developed areas, which impacts the natural acidity of a large swamp. The sum of base cations (CB) exceeds ANC for all samples. Plotting CB against ANC and subtracting Cl- quantifies the impact of road salt from the impact of the addition of strong acids.