Sand Hill River Watershed Biotic Stressor Identification Report

The Minnesota Pollution Control Agency (MPCA) utilizes biological (i.e., fish and macroinvertebrate) monitoring to assess stream health as part of its Intensive Watershed Monitoring strategy. In 2011, the MPCA conducted biological monitoring at several sites throughout the Sand Hill River Watershed (SHRW). The resulting data, along with previously collected data, was used to produce an Index of Biological Integrity (IBI) score for the fish (F-IBI) and macroinvertebrate (M-IBI) communities of each site. The biological monitoring results for the watershed were formally assessed as part of the development of the Sand Hill River Watershed Monitoring and Assessment Report (MPCA, 2014) to determine if individual stream reaches met applicable aquatic life standards; each reach has one or more associated monitoring sites. A stream segment with a low IBI score (i.e., below an established threshold) is considered "impaired" (i.e., unable to support its designated beneficial use) for aquatic life. Three stream reaches in the SHRW were determined to be biologically impaired, while two reaches were found to be supporting a healthy fish and macroinvertebrate community. In addition, five stream reaches were not assessed, primarily due to extensive channel alteration. The purpose of this report is to identify the causes, or "stressors," that are likely contributing to the biological impairments in the SHRW. A comprehensive review of available data (e.g., plans and reports) for the watershed was initially performed to identify the six candidate causes examined in this report. Further analysis was performed to determine potential connections between each candidate cause and the biological impairments. The results of the stressor identification process point to several probable stressors in each of the biologically impaired reaches of the watershed. The following summarizes the probable stressors per impaired reach: Reach 541 - Sand Hill River (Headwaters to County Ditch 17/AUID #09020301-541) F-IBI Impairment Stressors: · Loss of Connectivity · Flow Regime Alteration · Lack of Instream Habitat · Low Dissolved Oxygen M-IBI Impairment Stressors: · Flow Regime Alteration · Excess Suspended Sediment · Low Dissolved Oxygen Reach 542 - Sand Hill River (County Ditch 17 to Kittleson Creek/AUID #09020301-542) F-IBI Impairment Stressors: · Loss of Connectivity · Flow Regime Alteration · Lack of Instream Habitat Reach 515 - County Ditch 17 (Garden Slough to Sand Hill River/AUID #09020301-515) M-IBI Impairment Stressors: · Flow Regime Alteration