Development of Sediment TMDLs: Need for Improved Integration of Sediment, Geomorphological, Habitat, and Ecological Data

A conceptual framework to link ecological response with the dynamics of fluvial processes, habitat maintenance, and sediment characteristics is presented that organizes relationships between biological and physical environmental domains. In human-dominated watersheds in which the sediment regime is in disequilibrium, the proposed framework promotes two important ideas. They are that 1) ecological impairment due to watershed disturbances is species dependent, expressed individually by the organism's species traits and life histories; and 2) the relationship between ecological impairment and sedimentation is dependent on sediment particle size class. Relationships between ecological impairment and transported particle size classes may be direct or indirect. The goal of introducing this framework is to advance our ecological understanding of impacts from sedimentation and habitat alteration in streams. In particular, researchers and practitioners need to question whether ecological impairment can be related to a single sediment yield threshold as designated for some specified discharge. Advancement of our thinking in this area is critical to develop sediment TMDLs that can be related to the loss of ecological functions.