Macroinvertebrate communities, organic matter, and physical habitat conditions across headwater streams of the Otter River, in Michigan's Upper Peninsula

Headwater streams in forested watersheds are strongly tied to the landscapes from which they flow. Local and watershed-scale land use practices can have a strong impact on the physical, chemical and biological functioning of these headwater drainages. This research examined relationships between adjacent land use, organic matter standing stocks and macroinvertebrate composition across headwater streams with a range of 3-11 years since adjacent forests were last selection logged. Results suggest that logging is impacting physical habitat conditions and organic matter standing stocks in these study streams. Riparian canopy cover, streambed substrate size and fall, coarse benthic organic matter densities were all significantly lower in study streams adjacent to forests more recently logged, while stream discharge was higher.;In contrast, overall macroinvertebrate composition (total biomass, Hillsenhoff tolerance index, Shannon Diversity index and Ephemeroptera, Plecoptera, Trichoptera index) was not significantly correlated with logging across study sites. We did not detect a direct relationship between detritivore (collector-gatherers or shredders) community biomass and logging history, local physical habitat or organic matter standing stocks. However, the taxonomic composition of detritivore communities as well as individual biomass did vary significantly with local and landscape factors and organic matter standing stocks. Gatherer community composition across these sites appears to be associated with the presence or absence of key traits providing physical tolerance and/or trophic flexibility to disturbances generated across the watershed, while taxa individual condition was more strongly determined by trophic conditions influenced by reach-scale land use activities. Our ability to discern relationships was limited by natural variation in watershed and stream channel geomorphology across sampling sites, however overall trends seem to clearly suggest that disturbances associated with selective logging are having a detectable short-term (3-11years) impact on physical habitat and organic matter dynamics. The physical and trophic impacts associated with logging appear to be in turn influencing the composition and individual condition of local detritivore communities, possibly altering the biological and physical dynamics within these headwater streams as well as their critical links to downstream biota.