TY  - RPRT
TI  - Nutrients in the Nation's waters; identifying problems and progress
AU  - Elisabeth A. Graffy
AU  - Dennis R. Helsel
AU  - David K. Mueller
PY  - 1996
DO  - 10.3133/fs21896
UR  - https://pubs.usgs.gov/publication/fs21896
ID  - fs21896
ER  -