Effects of Forest Cover Change on Streamflow in Low Relief Glaciated Catchments

Abstract

Forest cover disturbance, climate change, and their interaction can alter how catchments store and process water, which has ramifications for all aspects of the hydrologic cycle, including flood risk, channel geomorphology, and water quality. Catchments in the boreal-temperate transition zone may be especially vulnerable to these factors. While streams in this glaciated region have low-topographic relief and may originate from expansive wetlands, much of the past research on forest disturbance-streamflow relationships comes from regions where landscape characteristics and subsequent hydrological function is substantially different, e.g. mountainous regions with bedrock close to the soil surface. Further, most work investigating the forest-streamflow relationship occurs at small spatial scales (< 10 km2). I seek to fill a knowledge gap by 1) creating a new conceptual model for how forest cover change affects sediment yield in managed temperate forested catchments that accounts for how sediment yield responds to altered catchment hydrology, 2) developing a new approach to peak-flow analysis using paired catchment experiments at the Marcell Experimental Forest (MEF) in north-central Minnesota, and 3) investigating how forest cover change and climate affect peak flows and water yield in large (> 10 km2) catchments in Minnesota. My results indicate that in low-relief glaciated regions, glacial geology controls sediment yield response to forest harvesting; forest harvesting may affect large peak flows by altering the occurrence probabilities of large peaks at the small catchment scale; and streamflow in larger catchments is largely controlled by climate variation, with land cover a minor yet discernable driver of peak flows and water yield. These results are framed within a new forest harvesting/water quality framework that holistically accounts for all sources of increased sediment yield after forest harvesting in diverse landscapes. Please note that multiple of these chapters are under peer review in scientific journals as of August 2020, and those versions will supersede this dissertation for purposes of citations.