TY  - RPRT
TI  - Natural background concentrations of nutrients in streams and rivers of the conterminous United States
AU  - R. A. Smith
AU  - R. B. Alexander
AU  - G. E. Schwarz
PY  - 2003
DO  - 10.1021/es020663b
UR  - https://pubs.usgs.gov/publication/70025473
ID  - 70025473
ER  -