I have had a few inquiries for other science agencies; may be of interest to others:

Real-Time Tracking of Nitrate Concentrations in the Mississippi River Basin:

example station, Mississippi River at Baton Rouge, LA: http://waterdata.usgs.gov/nwis/uv?cb_00060=on&cb_99137=on&format=gif_mult_parms&period=&begin_date=2013-07-16&end_date=2013-07-23&site_no=07374000

USGS news release: Real-time Monitoring Pays Off for Tracking Nitrate Pulse in Mississippi River Basin to the Gulf of Mexico: http://www.usgs.gov/newsroom/article.asp?ID=3668&from=rss_home#.UhUWg7HR7Tg

Just a reminder, the NAWQA program (http://water.usgs.gov/nawqa/) data retrievable by constituent: http://infotrek.er.usgs.gov/apex/f?p=NAWQA:HOME:0
constituent finder: http://infotrek.er.usgs.gov/apex/f?p=NAWQA:23:0

Also, SPARROW Surface Water-Quality Modeling: http://water.usgs.gov/nawqa/sparrow/

USGS NWIS: USGS Water Data for the Nation:  http://waterdata.usgs.gov/nwis

Most library users find it easiest to use the NWIS Mapper interface to search for data: http://maps.waterdata.usgs.gov/mapper/index.html

for mobile users (beta): http://m.waterdata.usgs.gov/

Enjoy the day,

Emily Wild
Librarian (Physical Scientist)
U.S. Geological Survey
Denver Library
Box 25046, MS 914
Denver Federal Center
Denver, CO 80225-0046
ph: (303) 236-1003
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USGS Libraries: http://library.usgs.gov
Professional Page: http://profile.usgs.gov/ecwild