Spatial distributions of biophysical conditions on the Ohio River
Bolgrien, David W.; Meyer, Roger; Pearson, Mark S.; Jicha, Terri M.; Angradi, Ted R.; Taylor, Debra L.; Moffett, Mary F.; Hill, Brian H.
We examined longitudinal and patchy distributions of water quality, fish assemblage, and land cover metrics from 59 sites on the Ohio River to determine if they were responses to geophysical, biological, and/or anthropogenic constraints. Conceptual models of river ecology hold that longitudinal trends are associated with river size and spatial heterogeneity or patchiness results from interactions between biology and hydromorphology, and in-channel and landscape process. Spatial autocorrelation was used to estimate patch length or the river distance between sites at which conditions are no longer spatially dependent. Significant linear (p < 0.01) longitudinal trends in the ohio river were downriver increases in temperature and chlorophyll a concentrations and decreases in dissolved components (sulfate, chloride, conductivity, silica, nitrate, and total dissolved solids). there was a downriver increase in the proportion of developed riparian lands. in main channel and tributary catchments within 10 km upriver from sites the proportion of agriculture increased and forest decreased moving downriver. littoral substrate types lacked any longitudinal or patchy spatial structure. there was a downriver increase in the richness of great river species and a decrease in the richness of intolerant species. patch lengths were relatively short for nutrients ( 400 km). The exceptionally long patch length of silica suggests its distribution was constrained more by advection than biological assimilation like other nutrients. Turbidity, total suspended sediments, and Secchi depth had similar patch lengths. Their distributions were not related to the positions of dams or tributaries. The relatively small patch lengths for the proportion of fish with deformities or of native species, or of nonindigenous species contrasted with the large patch length for the proportion of detritivores. Patch length of riparian development was less than agriculture and forest suggesting that the distribution of development was relative more constrained by valley walls and vulnerability to flooding. Analyses of the spatial distributions of fish, habitat, and water chemistry in large rivers can inform restoration and conservation decisions that maintain or increase biological diversity.