Using samples of spring baseflow chemistry on 56 Pennsylvania watersheds with predominantly forested to mixed land-uses and widely varying geology/physiography, we attempted to determine spatial patterns in stream chemistry due to insect defoliation and atmospheric deposition. Land use and land form relations to stream chemistry were examined as well. Defoliation effects on stream chemistry due to repeated, and sometimes intense, insect defoliation over the past several years were seen as reduced stream nitrate concentrations in a watershed data set (n = 11) that included 100% forested lands only. Basins in regions with higher atmospheric sulfate deposition loads had higher stream concentrations of sulfate in 100% forested basins. Significant positive correlations of stream nitrogen and potassium with agricultural land use indicated possible contamination of stream waters by excess fertilizers and/or animal wastes. Weak positive correlations were also found with many of the stream chemistry parameters and percentage urban/barren land use. Ridge-top versus valley bottom watersheds also showed differences in baseflow chemistry due to changing surficial geology and/or land use. Overall, the study showed that agricultural, urban, geologic, and physiographic influences on spring baseflow chemistry mask the effects of insect defoliation and atmospheric deposition on mixed land-use basins (<100% forest). Regional differences in atmospheric deposition on 100% forested basins were directly reflected in spring baseflow SO4 concentrations. When restricted to 100% forested basins with relatively uniform geology, insect defoliation appeared to reduce stream nitrogen concentrations in the long term. This is believed to be due in part to nitrogen bound in vegetative growth and a dilution of nitrogen from increased flows as a result of defoliation and tree mortality bringing about reduced evapotranspiration.
All Science Journal Classification (ASJC) codes
- Environmental Engineering
- Environmental Chemistry
- Ecological Modeling
- Water Science and Technology