Responses of Aquatic Macroinvertebrates to Stream Channel Reconstruction in a Degraded Rangeland Creek in the Sierra Nevada

摘要

Streams on western rangelands are sometimes degraded to the point that reestablishing lost ecological values requiresrebuilding their physical structure, shape, and form. We evaluated the biological response to reconstruction of a smallrangeland stream channel through comparisons of aquatic invertebrate communities before and after engineering activi-ties and in relation to local and regional reference stream conditions. We measured geomorphic and riparian habitatfeatures along with benthic macroinvertebrates for two years prior to restoration actions and for two years afterward.Stream restoration activities included the construction of a new channel to replace an incised meadow stream reach(including addition of coarse rock substrate, erosion control fabric, and willow planting) and the rehabilitation of gul-lies and roads in the meadow and its watershed. In postproject monitoring, we found statistically significant changes inthe macroinvertebrate community and trophic structure at the restored site. These were exhibited as increases in EPTtaxa (mayflies, stoneflies, caddisflies) and the proportion and diversity of sensitive taxa, decreased tolerant taxa, and anincrease in consumers of riparian organic matter (shredders) and decrease in fine organic particle filter-feeders. A sitemonitored downstream of the restoration activities exhibited increased deposition of fines and sand one year after projectconstruction, but was similar to preproject conditions in the second year, and the macroinvertebrate community wasunchanged. Improved biological integrity at the restored site showed that rapid recovery can occur in rebuilt streamswithin rehabilitated watersheds, but neither degraded nor enhanced conditions were transferred to downstream habitat,at least over the initial postproject period.