Long-term Water Quality and Stream Nutrient Responses to Forest Harvest and Disturbance at US Forest Service Experimental Forests and Ranges

Changes in land use and management as well as natural disturbances can dramatically affect water quality in some but not all headwater streams and downstream rivers. For decades, researchers have studied stream hydrology and solute chemistry in disturbed and undisturbed watersheds at Experimental Forests - a continental-scale research platform that spans gradients of precipitation, atmospheric deposition, nutrient limitation, biomes, topography, and soil types. To increase our understanding of water quality responses to disturbance, we examine: 1) How the short and long-term responses of stream nutrients to forest harvest, biomass removal, and disturbances vary across North America; 2) Which biotic and abiotic factors explain why the magnitude and timing of stream solutes responses vary within and among sites; 3) What factors control the magnitude and duration of disturbance responses; and 4) How atmospheric deposition, geologic, climatic, topographic, and hydrologic parameters affect responses. We find that the magnitude and longevity of nutrient responses varies within and among ecoregions. Following harvest or disturbance, concentrations and fluxes of stream nutrients generally increased but with varying response times 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. These findings have implications about the role of watershed disturbances on instream biotic communities and downstream users.