A “watershed Approach” to Tmdl Development

The State of Minnesota, in an effort to streamline the identification of impaired waters and subsequent TMDL development, has developed a watershed approach to condition monitoring and assessment similar to other states such as Ohio and Indiana. The watershed approach uses intensive biological monitoring (fish and macroinvertebrates) to determine biologically impaired stream reaches. Follow up water quality monitoring in the identified impaired reaches is then used to identify the cause of the impairment through a stressor identification process. The idea behind the watershed approach is to identify all of the impairments at once providing an opportunity to address the impairments through a coordinated TMDL process. Although the “Watershed Approach” provides a focused framework for the identification of impaired waters and TMDLs, this approach is highly dependent on the development of biological indices for the evaluation of biological communities. These indices require a significant investment in time and resources to develop. Furthermore, the results of the Stressor Identification process routinely results in identifying stressors such as lack of habitat or altered hydrology not easily addressed in the TMDL framework. As a result, a large amount of creativity is required in the development of these TMDLs. This paper will review the “Watershed Approach” using several examples where the process has been applied in Minnesota. The authors will review the necessary scientific information required for this approach, identify the strengths and weaknesses, and outline how this approach may be applicable to Southeast US watersheds.