Long-term research in headwater streams of Experimental Forests and Ranges has contributed substantially to our current understanding of forest hydrology and water quality. These long-term studies of forest-stream interactions have been and will continue to be valuable in developing, calibrating, and validating hydrologic and biogeochemical models to address contemporary issues, including the impacts of climate and land use change on hydrology, biogeochemistry, and water supply throughout the country. The network of Experimental Forests and Ranges includes numerous pairs of treated and reference experimental watersheds across gradients of precipitation, atmospheric deposition, nutrient limitation, forest biomes, topography, and soil types. In addition, the reference watersheds provide foundational data and the opportunity to examine for long-term trends in hydrology and stream chemistry. Across sites, anthropogenic and natural disturbances have been shown to have the potential to dramatically affect water quality and quantity. With changing climate and decades of data, is timely to reevaluate how predictable and persistent are responses of water quality and quantity to forest disturbances.
Results/Conclusions
For these small, forested streams across North America, we ask: 1) How consistent are the responses of hydrology and stream nutrients after disturbance? 2) Which biotic and abiotic factors best explain the magnitude, timing and duration of hydrologic and stream solute changes following disturbances? We calculate a dryness index (ratio of monthly ET to precipitation) as a possible metric of energy-limited versus moisture-limited watersheds to compare hydrologic responses to disturbances. Within a year or two following disturbance, many sites show increased annual and low flows; these continue for 5-15 years, followed by reduced flows at some biomes during forest succession. After harvest or disturbance, concentrations of stream nutrients, primarily nitrogen, generally increase but response times vary across gradients of nutrient limitation. Changes in nutrient fluxes reflect gradients of nutrient limitation as well as the role of vegetation as a primary influence on nutrient cycling. Because of the length and quality of data available at these sites, new questions and research opportunities are continually emerging in these experimental watersheds.