The Missouri Resource Assessment Partnership ( MoRAP) has developed an eight-level hierarchical classification system to characterize and map Missouri's riverine ecosystems into distinct ecological units. The fifth level in the MoRAP riverine ecosystem classification system is described here and shown on the map below.
The Ecological Drainage Units (EDUs) were compiled at a scale of 1:100,000 using existing sampling data for fish, mussel, crayfish and snail species linked to Hydrologic Units(HUs), version 4. Jacaard Similarity Coefficients were calculated for each pair of Level IV Subregions in the classification hierarchy and each pair of the 66, eight-digit HUs that occur within Missouri. HUs with similar coefficients greater than the average similarity among the Level IV Subregions were combined into units called "Major Drainages." These boundaries were refined by examining shared endemics among HUs and the natural barriers to dispersal separating HUs.
Giving equal weight to the Level IV Subregions and Major Drainages, the Major Drainages boundaries were clipped with the Subregion boundaries to generate a final map of EDUs. MoRAP is working with the Nature Conservancy to develop a national map of EDUs using this process.