Stream N and other water chemistry measurements originate from three national-scale, randomized, unequally weighted probability surveys of the U.S. EPA's National Rivers and Streams Assessment (NRSA) between 2000 and 2014, conducted as part of the National Aquatic Resource Surveys (NARS; https://www.epa.gov/national-aquaticresource-surveys/data-national-aquatic-resource-surveys). The NRSA sampling design assures a statistically valid assessment of the physical, chemical, and biological conditions of the population of U.S. streams and rivers. The first of the NRSA surveys (2000–2004) also known as the Wadeable Streams Assessment (WSA) sampled wadeable (1st through 4th Strahler Order) streams in the 48 conterminous states. Additional surveys were conducted in 2008–2009 (survey 2) and 2013–2014 (survey 3), and included larger, non-wadeable sites. Each of the three surveys sampled roughly 2000 perennial stream/river sites, using a standardized probability-based sampling method that did not change over time. Since large rivers and streams were not sampled during the 2000–2004 survey, we restricted our analyses to survey datasets with associated watershed areas <1000km2, sampled roughly 5 years apart. Analyses in this study were limited to watersheds where deposition was the largest source of anthropogenic N, determined using the fine-scaled National Nutrient Inventory (NNI) dataset that are based on downscaled HUC-8 level N inventory of the CONUS (improved based on (Sabo et al., 2019) and (Lin et al., 2021)).

Sabo, R.D., Clark, C.M., Bash, J., Sobota, D., Cooter, E., Dobrowolski, J.P., Houlton, B.Z., Rea, A., Schwede, D., Morford, S.L. and Compton, J.E., 2019. Decadal shift in nitrogen inputs and fluxes across the contiguous United States: 2002–2012. Journal of Geophysical Research: Biogeosciences, 124(10), pp.3104-3124.

Lin, J., Compton, J.E., Hill, R.A., Herlihy, A.T., Sabo, R.D., Brooks, J.R., Weber, M., Pickard, B., Paulsen, S.G. and Stoddard, J.L., 2021. Context is everything: interacting inputs and landscape characteristics control stream nitrogen. Environmental science & technology, 55(12), pp.7890-7899.

This dataset is associated with the following publication: Lassiter, M., J. Lin, J. Compton, J. Phelan, R. Sabo, J. Stoddard, S. McDow, and T. Greaver. Shifts in the Composition of Nitrogen Deposition in the Conterminous United States are Discernable in Stream Chemistry.. SCIENCE OF THE TOTAL ENVIRONMENT. Elsevier BV, AMSTERDAM, NETHERLANDS, 881: 163409, (2023).