Geomorphic and Greenhouse Gas Dynamics of Restoration and Flood Events in Streams in a Karst Agricultural Landscape

In agricultural landscapes, alterations in river flow and channel geometry, increased sediment and nutrient loads, and invasive species degrade lotic ecosystems and are now being exacerbated by climate change. Stream restoration efforts respond to these pressures, but important questions remain about restoration impacts in landscapes undergoing rapid hydrologic change. Examining the relationship of stream restoration and flooding to channel geomorphology and greenhouse gas (CO2, CH4) diffusive fluxes on restored and reference reaches, we hypothesized that flood flows through restored reaches would increase cross-sectional area and floodplain connectivity while decreasing soft sediment depth, and they would increase CO2 and CH4 diffusive fluxes change in response to restoration-driven changes in channel form, floodplain reconnection, and floods. Through elevation profiles, geomorphic surveys, and greenhouse gas sampling, we compared channel form and CO2 and CH4 fluxes in a reach before and after restoration to four unrestored reference reaches in two streams in Wisconsin’s Driftless Area over a period that included multiple floods. Restoration activities were constrained by flood events and did little to enhance potential floodplain reconnection, yet they were related to increased emissions of CO2 and CH4 despite limited changes in channel form; meanwhile, flooding was related to short-term increases in emissions. These results highlight that legacies of agricultural practices are continuing to impact stream systems in subtle and compounding ways, despite and maybe even because of restoration interventions.