Results of Pre-Treatment Habitat and Biota Surveys from the Knife River, MN below County Road 11

Abstract

This report follows the same layout and data summaries as reports provided to the Lake Superior Steelhead Association (LSSA) in recent years (Dumke and Wellard-Kelly, 2017, 2018). … The Natural Resources Research Institute (NRRI) was contracted in 2021 by LSSA to conduct pre-treatment stream surveys of habitat, fish, macroinvertebrates, and water chemistry from a segment of the Knife River main stem below County Road 11, which is planned to receive habitat improvement work in the future. We also measured all the same parameters in another reach not expected to undergo any treatment to serve as a reference for later comparisons. This before-after, control-impact (BACI) design is our standard for attributing changes over time to specific treatments applied to the stream and is useful in evaluating changes caused by habitat improvement projects. In total, two river reaches (a treatment and a reference station) were surveyed by NRRI. In September of 2021 NRRI completed surveys of stream habitat, macroinvertebrates, and water chemistry within both reaches, and completed electrofishing within the reference reach. However, the electrofishing of the treatment reach could not be completed in 2021 due to a combination of rain events causing high flows, upstream construction causing muddy water, and a September 15th stop on electrofishing to protect fall-spawning Brook Trout Salvelinus fontinalis. Therefore, NRRI and LSSA agreed to extend the work contract and NRRI would re-survey fish at the end of June 2022 before new stream construction projects would begin again. We found that all reaches had water quality parameters acceptable for all salmonid species present in the Knife River watershed, at least at the times of our sampling. Among all our fish surveys we collected young-of-year (YOY, aka age0) and age1+ Rainbow Trout Oncorhynchus mykiss, Brown Trout Salmo trutta, and Brook Trout. Our September 2021 survey of the reference reach captured 67 age0 Rainbow Trout, so we know Rainbow Trout are using this area for some reproduction. Electrofishing surveys in June 2022 captured only 1 age0 Rainbow Trout, but the low capture during these surveys may be attributable to the early timing when age0 Rainbow Trout were still too small to be effectively sampled. However, both stream reaches were dominated by non-game fishes, and the total count of trout species contributed less than 10% to the fish assemblage. Macroinvertebrate communities were generally similar between the reference and treatment reaches, but the treatment reach had a slightly higher quality macroinvertebrate assemblage. Reference and treatment reaches both had occurrences of bank erosion, fine sediment comprised on average 30-40% of the stream bed, and coarse substrates were, on average, 20-30% embedded by fines. All of these things contribute to loss of living space among the stream rocks for aquatic macroinvertebrates.