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Long Prairie River Watershed TMDL Project – Lessons Learned from Phase I

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Pp. 141-147 in Total Maximum Daily Load (TMDL) Environmental Regulations: Proceedings of the March 11-13, 2002 Conference, (Fort Worth, Texas, USA)  701P0102.(doi:10.13031/2013.7540)
Authors:   Hafiz M. Munir, Bashar Sinokrot, Dennis E. Ford
Keywords:   TMDL, Long Prairie, SWAT, model, monitoring, DO, Minnesota

Long Prairie River drains a predominantly agricultural 883-square mile watershed in central Minnesota. Designated uses of the River are aquatic life, recreation, industrial consumption, agriculture, wildlife, aesthetic enjoyment, and navigation. Monitoring in recent years has shown dissolved oxygen (DO) concentrations in portions of the river and at Motley intermittently below the state water quality standard of 5 mg/L. As a result, Minnesota Pollution Control Agency (MCPA) placed four lower-river reach segments on the agencys 1998 303(d) list. The objectives of the study are to define the extent, persistence, and severity of the DO depletion problem, and develop a TMDL for the watershed. The project has three phases. Phase I is an analysis of existing data to determine what additional data will be needed to complete the project objectives and what technical issues will need to be addressed within the scope of the project. Additional data will be collected, analyzed, and reported in Phase II. Modeling and TMDL development will be conducted in Phase III. The project is anticipated to complete by December 2002.

Review of the existing water quality data for the Long Prairie River indicates substantial seasonal and inter-annual variability but no significant long-term trends. Longitudinal total phosphorus profiles show a consistent pattern of gradual increase from the headwaters to Long Prairie, followed by a steep increase downstream from City of Long Prairie. Longitudinal nitrogen series profiles indirectly suggest significant nitrification in the reach between the cities of Long Prairie and Browerville. Diurnal DO variations in the vicinity of City of Long Prairie indicate substantial primary productivity. Based on the review and preliminary analysis of existing data, a modeling strategy has been outlined, and data gaps and additional monitoring needs have been defined.

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