1. Alexander, R.B., and Smith, R.A., 1990, County-level estimates of nitrogen and phosphorus fertilizer use in the United States, 1945 to 1985: U.S. Geological Survey Open-File Report 90–130, 12 p., accessed August 11, 2022, at https://doi.org/10.3133/ofr90130.
2. American Society of Agricultural Engineers, 2003, Manure production and characteristics: American Society of Agricultural Engineers Standard D384.1 FEB03, 4 p. [Also available at https://elibrary.asabe.org/abstract.asp?aid=32018.]
3. American Veterinary Medical Association, 2018, U.S. pet ownership statistics: American Veterinary Association web page, accessed April 22, 2022, at https://www.avma.org/resources-tools/reports-statistics/us-pet-ownership-statistics.
4. Bachman, L.J., Lindsey, B.D., Brakebill, J.W., and Powars, D.S., 1998, Ground-water discharge and base-flow nitrate loads of nontidal streams, and their relation to a hydrogeomorphic classification of the Chesapeake Bay watershed, middle Atlantic coast: U.S. Geological Survey Water-Resources Investigations Report 98–4059, 71 p. [Also available at https://doi.org/10.3133/wri984059.]
5. Bachman, L.J., and Phillips, P.J., 1996, Hydrologic landscapes on the Delmarva Peninsula part 2—Estimates of base-flow nitrogen load to Chesapeake Bay: Journal of the American Water Resources Association, v. 32, no. 4, p. 779–791. [Also available at https://doi.org/10.1111/j.1752-1688.1996.tb03475.x.]