| Changes in flow management of the Missouri River Mainstem Reservoir System have been proposed to restore more of the ecological functions of the Missouri River. However, uncertainty exists about how the biota will respond to flow management changes. This dissertation explored relationships between three components of the biota and abiotic factors. The dissertation is divided into three studies corresponding to the biota studied: (1) aquatic macroinvertebrates; (2) larval fish; and (3) age-0 and age-1 fish. The objectives of each study were to estimate the relative importance or probability of an effect for key abiotic predictor variables to biotic response variables and to compare the results among reaches of the river. A multi-year, multi-location database of biological sampling was used to develop statistical models relating biotic responses to variables representing discharge, temperature, and turbidity in the Missouri River from Fort Randall Dam, SD to Rulo, NE. The results of the aquatic macroinvertebrate modeling varied by river reach. Greater macroinvertebrate drift densities were related to high flows out of Fort Randall Dam and low flows and reduced turbidity below Gavins Point Dam. The results below Gavins Point Dam suggest that increased macroinvertebrate drift densities are a response to reduced habitat and food availability. Results of the larval fish modeling indicated that water temperature was the most important predictor variable. Greater temperatures or degree days consistently increased the probability of finding larval fish and the resulting drift densities. Discharge-related variables were the most important predictors for age-0 and age-1 fish. Greater catch per unit effort of age-0 or age-1 fish was generally related to less variable discharge in the unchannelized reaches and to greater, rising discharge in the channelized reaches. Overall, the results suggest that more natural discharge, temperature, and turbidity regimes would benefit native fish and invertebrate species in the Missouri River. |
