During 1945 to 1980, nitrate levels in large U.S. rivers increased up to fivefold in intensively managed agricultural areas of the Midwest, according to a new U.S. Geological Survey study.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/historic-nitrate-levels-still-plague-us-rivers
[2] http://admin.indiaenvironmentportal.org.in/category/newspaper/environment-news-network
[3] http://admin.indiaenvironmentportal.org.in/category/thesaurus/water-pollution
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/river-pollution
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/united-states-america-us
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/pesticides
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/chemical-fertilisers
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/freshwater-ecosystems
[9] http://admin.indiaenvironmentportal.org.in/category/thesaurus/fisheries-0