The Complexities of Developing Excess Nutrient TMDLs for Shallow Lakes

One of the primary strengths of the Total Maximum Daily Load (TMDL) program is its ability to support the development of water quality strategies based on sound science and readily available information. Due to the strength of the TMDL program, the State of Minnesota is using the Total Maximum Daily Load framework as the basis for developing restoration plans for nutrient impaired lakes, including shallow lakes. However, due to complex biological and sediment interactions with the water column, development of TMDLs for shallow lakes offers a number of challenges that must be overcome if a sound restoration plan is to be accomplished. Some of the challenges in developing TMDLs in shallow lakes include the confounding effects of rough fish, complex internal nutrient cycles, and weak linkages between water quality and aquatic vegetation communities. Paleolimnology is a useful tool in the TMDL process to obtain information on the natural state of the lake and to understand the timing and magnitude of historical ecological changes. Shallow lakes have posed problems with traditional diatom-based nutrient reconstructions; however, analyzing multiple proxies in the sediment record provides important information on the timing and nature of ecological state changes in these systems. Although these challenges may seem daunting, there are a number of tools and datasets available to overcome these challenges to develop an implementation plan that will result in restoration of the impaired shallow lake.