CC-26: Mapping Loading Rates and Sources of Reactive Nitrogen across the United States suggests Regional Interactions with Climate Change Daniel J. a,b Sobota , [email protected] [email protected] Shweta a,d Singh , and Douglas J. e Norton [email protected] [email protected] Ecology Division, US Environmental Protection Agency, Corvallis, OR: bOak Ridge Institute for Science and Education; cNational Health and Environmental Effects Research Laboratory; dNational Research Council eOffice of Water, US Environmental Protection Agency, Washington, DC Colin Bishop kg N ha-1 yr-1 0-1 1-3 3-5 5 - 10 10 - 30 30 - 50 50 - 100 100 - 130 0 250 500 1,000 km Products & Energy Colin Bishop O Energy & products Harmful Algal Blooms & Hypoxia Human-created N is critical for our modern society and economy. However, its overabundance in the environment harms human health, alters ecosystem function, and contributes to climate change. Air pollution Largest human-created reactive N sources 8-digit USGS Hydrologic Units The Nitrogen Cascade Stratospheric effects Particulate N 2O Matter effects Greenhouse effects N2 O Air Ozone effects Project mid-century shifts in riverine N export due to climate change. NHx Biological N fixation NOy NH3 Land Forests & Grasslands effects Agroecosystem effects Animal Crop NHx NOy Plant N2O (terrestrial) Soil Soil Human consumption Coastal effects Surface water effects Groundwater effects 20 15 10 5 0 w Ne atu n hu ral a e r -c ted n a m Percent -13.6 to -5.0 -5.0 to -2.5 -2.5 to 0 0 to 2.5 2.5 to 5.0 5.0 to 11.1 Riverine N export data 100 10 1 0 5 10 15 20 Mean Annual Temperature (oC) 100 10 1 ln(annual riverine export of watershed N inputs) = 1.83+0.0018*Mean Annual Temperature - 0.11*Mean Annual Precipitation n=71; p<0.0001; r2=0.66 0 500 1000 1500 2000 Mean Annual Precipitation (mm yr-1) Changes in annual temperature and precipitation regimes may reduce or increase riverine N export depending on region. www.whoi.edu NOx Identify important reactive N sources across conterminous US watersheds. Projected changes in riverine N export, 2040 -2059 8-digit USGS Hydrologic Units 25 Human activities currently put 7.5 times more new reactive N into the US annually than do natural processes alone. Objectives Agricultural production 30 w e N Water pollution Projected changes in climate for the 21st century may dampen or exacerbate human health and ecosystem effects of overabundant, human-created N. Understanding the interactions between reactive N and climate change is critical. Energy consumption National reactive N inputs Annual riverine export of watershed N inputs (%) Technology now allows us to create N fertilizers, increasing food production. Currently, 50% of N in the human body is synthetic N fertilizer. N also is an important component of many industrial products. New human-created reactive N inputs 8-digit USGS Hydrologic Units Reactive N input (Tg N yr -1) Enhanced crop production Reactive nitrogen (N) is essential to life, making up compounds such as proteins and nucleic acids. Estimate reactive N inputs across the conterminous United States (US). Shifts in riverine N exports due to climate change Reactive nitrogen inputs and sources, circa 2000 Reactive nitrogen is a wicked problem N2O (aquatic) Water Ocean effects Galloway JN, Aber JD, Erisman JW, et al. 2003. The nitrogen cascade. Biosci 53:341-356. National reactive N sources Reactive N input (Tg N yr -1) aWestern Jana E. a,c Compton , Atmospheric deposition Legumes Manure Synthetic fertilizer Sewage 12 Methods Source data for reactive N inputs Reactive N source Spatial resolution Time scale Synthetic fertilizer County 1997-2001 8 Legumes County 1997, 2001 6 Atmospheric deposition 36 km grid 2002 4 Industrial products National 2002 - 2009 Manure County 1997 Sewage County 2000 Trade export National 2002 10 2 0 Spatial data were reformatted to 8-digit USGS Hydrologic Unit Codes (HUC8s) using the Zonal Statistics Tool in ArcMap 10.0 (ESRI Inc., Redlands, CA). For data references, see: Sobota DJ, Compton JE, Harrison JA. 2013. Reactive nitrogen in US lands and waterways: How certain are we about sources and fluxes? Fron Ecol Environ 11:82-90. -2 -4 r es on ts re ge ort e z li um siti duc anu wa xp i t er Leg epo pro M Se de e f d rial tic ra e c T i t er us nth h y S sp Ind o m At Synthetic fertilizer is clearly the largest national reactive N source. However, atmospheric deposition is important in the East and Southwest, while legumes are important in the West. Changes in riverine N exports due to climate change We compiled data from 71 watersheds in the US that described riverine export of annual watershed N inputs (fractional N export): Boyer, EW, Goodale CL, Jaworski NA, Howarth RW. 2002. Anthropogenic nitrogen sources and relationships to riverine nitrogen export in the northeastern USA. Biogeochem 57/58: 137-169 Schafer SC, Alber M. 2007. Temperature controls a latitudinal gradient in the proportion of watershed nitrogen exported to coastal ecosystems. Biogeochem 85:333-346. Schafer SC, Hollibaugh JT, Alber M. 2009. Watershed nitrogen input and riverine export on the west coast of the US. Biogeochem 93:219-233. Sobota DJ, Harrison JA, Dahlgren RA. 2009. Influences of climate, hydrology, and land use on input and export of nitrogen in California watersheds. Biogeochem 94:43-62. Mean annual temperature and precipitation were used to predict fractional N export (see equation in climate change panel). Acknowledgements: Funding was provided by Oak Ridge Institute for Science and Education, the National Research Council, and the US Environmental Protection Agency. Ensemble average data (4.5 km grids) for mean annual temperature and precipitation changes for 2040 – 2059 were downloaded from the National Center for Atmospheric Research (https://gisclimatechange.ucar.edu). Ensemble temperature and precipitation data were scaled to HUC8s using ArcMap 10.0. Coefficients for the fractional N export~precipitation and temperature regression equation presented in the climate change panel were applied to HUC8 climate change data.