Home on the great river, part 3: An integrated habitat and hydrology index

The U.S. EPA’s Environmental Monitoring and Assessment Program sampled 395 sites in the Upper Mississippi, Lower Missouri and Ohio Rivers in 2004-2006 as part of an integrated assessment of ecological condition.  Using principal components and cluster analyses, we developed fish habitat indices at the site scale and integrated these results with landscape data and with hydrologic measures of flow.  On the impounded Mississippi River, channel complexity, substrate, human impacts, and relief within 50 km of the river explained 52 percent of the variation in a Great River Fish Index (GRFIn).  On the Lower Missouri and unimpounded Mississippi Rivers, GRFIn scores were best described by channel complexity, relief, and agriculture (adj. r² = 0.37).  Ohio River GRFIn scores were related to the fraction of gravel in the riverbed, distance to nearest upriver dam, and extent of forested lands within 50 km of the river (adj. r² = 0.23).