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BALANCING POINT SOURCE AND AGRICULTURAL CONTROLS IN THE MISSISSIPPI RIVER BASIN
Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org
Citation: Watershed Management to Meet Water Quality Standards and Emerging TMDL (Total Maximum Daily Load) Proceedings of the Third Conference 5-9 March 2005 (Atlanta, Georgia USA) Publication Date 5 March 2005 701P0105.(doi:10.13031/2013.18050)Authors: Theodore A.D. Slawecki, Timothy Bondelid, Andrew Stoddard
Keywords: Mississippi River Basin, point sources, nonpoint sources, policy support, Clean Water Act, Safe Drinking Water Act, Farm Security and Rural Investment Act, TMDL, SWP
For the past thirty years or more, elevated levels of dissolved inorganic nitrogen delivered to the
Gulf of Mexico by the Mississippi River have contributed to the seasonal occurrence of an
extended hypoxic zone an area where marine life is threatened by oxygen depletion. These
elevated nitrogen levels are attributed to increased point and nonpoint sources, and to alterations
in the landscape and river channel that promote delivery instead of uptake and sequestration. In
this paper, we examine estimates of nitrogen loads in the Mississipi River Basin, look at some
simplistic load reduction scenarios, and discuss the difficulties in balancing different controls to
address hypoxia.
Load estimates are taken from the National Water Pollution Control Assessment Model
(NWPCAM), a policy support tool being developed for EPA by Research Triangle Institute.
NWPCAM combines point source discharge information from the Permit Compliance System
database with nonpoint source loading models for urban and rural areas to provide end-of-pipe
and edge-of-field source estimates for conventional pollutant loadings. Load estimates for
current conditions and for hypothetical control scenarios (e.g. point source nitrogen limits,
feedlot regulation) will be compared in order to suggest potential benefits.
Although point source and agricultural controls both have tangible benefits in load reductions,
there is considerable debate as to whether one approach is more effective and efficient than the
other. This uncertainty reflects both the difficulties inherent in the large-scale analysis presented
here and the realities of the regulatory climate. Point and agricultural sources and their controls
are administered under different programs and authorities, and understanding and appreciation of
the similarities and differences in these programs is vital to effective partnering between point
source and nonpoint source stakeholders.