TY  - RPRT
TI  - Trends in the nutrient enrichment of U.S. rivers during the late 20th century and their relation to changes in probable stream trophic conditions
AU  - R. B. Alexander
AU  - R. A. Smith
PY  - 2006
UR  - https://pubs.usgs.gov/publication/70031059
ID  - 70031059
ER  -