Use of stream order and biological indices to assess water quality in the Osage and Black river basins of Missouri

Significant variations in four biological measures of water quality with stream order and river basin were demonstrated for streams of the Black and Osage river basins of Missouri. Water quality criteria specific for each order and basin were then developed.Benthic macroinvertebrates from springs and stream orders 3–8 in the two river basins were sampled quarterly for one year with riffle nets and artificial substrate samplers. A total of 548 samples were taken at 137 stations. The average annual macroinvertebrate density, index of diversity, number of taxa, and number of mayfly and stonefly taxa were determined for each station. These measures showed significant differences (p < 0.05) across stream order within and between the two river basins. Total taxa, total mayfly and stonefly taxa, and diversity were highest in orders 4 and 5 with decreased values in lower and higher stream orders. Maximum organism densities occurred in intermediate order streams. These differences were attributed to the succession of physical changes from headwaters to mouth within each river and to the unique geomorphology of each catchment basin.Water quality criteria based on three of the four measures described above (with 95% confidence limits) were established for each stream order in each river basin. Criteria for the Osage River basin were then used to identify three streams in the basin affected by environmental disturbances (stream impoundment, channelization and sewage discharge). The use of order- and basin-specific criteria assures that the biological differences between streams caused by environmental disturbance can be distinguished from the natural biological differences between streams of different orders and drainages.