Improving habitat: periphyton and macroinvertebrate colonization on large wood in Pool 8 of the Upper Mississippi River

Abstract

Large wood is an important restoration tool in aquatic ecosystems as it has a variety of geomorphological and ecological benefits. We have limited knowledge regarding the role of large wood in large rivers as most research focuses on streams and small rivers. This research aims to understand the characteristics and dynamics of large wood in Pool 8 of the Upper Mississippi River while examining environmental conditions that influence periphyton accrual and macroinvertebrate colonization on wood. We surveyed naturally occurring large wood along shorelines of reconstructed islands between September and July and deployed wood substrate samplers across varying flow habitats in June that were sampled biweekly until September. The positive net change in wood abundance (+3.2 pieces) and shift in wood characteristics (unattached, dry, and bare without bark) along this flow gradient suggests that flow dynamic is a primary factor influencing wood abundance and mobilization. Arthropod dry mass (1.1 mg/cm2), abundance (73 individuals), and richness (3 order taxa) were greatest in higher flow habitats where additional habitat substrate was limited, whereas periphyton accrual was similar across flows. The information we provide on use of wood substrates by periphyton and macroinvertebrates across habitat conditions may be further used to link higher trophic level interactions with large wood. Overall, this study supports that large wood is an effective tool in restoration efforts aimed at improving habitat heterogeneity by increasing available substrate.