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Do US stream nitrogen concentrations reflect changing inputs over time? Results from the U.S. EPA National Rivers and Streams Assessments (2000-2014)
Citation:
Lin, J., R. Hill, R. Sabo, A. Herlihy, M. Weber, Jacqueline Brooks, C. Clark, S. Leibowitz, J. Stoddard, AND J. Compton. Do US stream nitrogen concentrations reflect changing inputs over time? Results from the U.S. EPA National Rivers and Streams Assessments (2000-2014). Society for Freshwater Science, SLC, UT, May 19 - 23, 2019.
Impact/Purpose:
The US EPA National Rivers and Streams Assessment (NRSA) surveys allow for the examination of large-scale changes in stream nutrient concentrations over time. EPA staff have also been preparing an inventory of N inputs to HUC8 watersheds across the continental US in 2002, 2007 and 2012. This inventory showed that while nitrogen (N) input to the entire continental US was similar in 2002 and 2012, N inputs increased in much of the Central Plains, decreased in the eastern US and showed little change across most of the West. WED-FEB staff examined temporal and spatial variations in total nitrogen (TN) concentrations in a spatially-balanced survey of over 3,000 wadeable streams in the NRSA between 2000 and 2014. The results indicate that streams N concentration and N inputs for the US have not changed significantly over the time period. Future analyses will look into the spatial patterns in these time trends in and relationships between concentrations and inputs.
Description:
The US EPA National Rivers and Streams Assessment (NRSA) surveys allow for the examination of large-scale changes in stream nutrient concentrations over time. A recent inventory of N inputs to HUC8 watersheds over time showed that while nitrogen (N) input to the entire continental US was similar in 2002 and 2012, N inputs increased in much of the Central Plains, decreased in the eastern US and showed little change across most of the West. We examined temporal and spatial variations in total nitrogen (TN) concentrations in a spatially-balanced survey of over 3,000 wadeable streams in the NRSA between 2000 and 2014. At the national scale, TN concentrations did not change significantly over this time, consistent with the lack of a national trend in N inputs for the entire US. Streams in the Central Plains had significantly greater TN concentration than streams in the West and Appalachians, reflecting the pattern in N inputs for those areas. Surveyed stream chemistry will be combined with national nitrogen input spatial data to model the response to changes in landscape nutrient loading at regional and finer scales.