IN THE ABSENCE OF BEAVER: CHARACTERIZING CHANGES IN WATER, SEDIMENT AND ORGANIC CARBON STORAGE IN ACTIVE AND ABANDONED BEAVER MEADOWS

Beaver (Castor canadensis) are ecosystem engineers that shape the environment around them to better suit their habitat needs. Through dam building, beaver alter valley and stream morphology, trap sediment and nutrients, change the riparian vegetation and raise the riparian water table. Dams cause frequent overbank flow, leading to fine sediment deposition and a complex valley bottom with multi-thread channels, ponds and high biodiversity: this is known as a beaver meadow. Beaver alter carbon and nitrogen dynamics by trapping organic carbon with fine sediment behind dams and altering the storage and retention time of nitrogen. Human removal of beaver dams alters the stream geomorphology and hydrology, which in turn changes the riparian community structure. Much is known about how beavers alter the environment to their advantage when they move into a valley, but little has been studied about what occurs in these valleys when the beaver disappear, especially where dams have not been directly removed by humans. Quantifying changes in the morphology, sediment and organic carbon dynamics after the disappearance of beaver could be a helpful tool for assessing the restoration potential of these valley bottoms, and assessing the potential resilience of these ecosystems to changing climate. Rocky Mountain National Park in north central Colorado provides an opportunity to examine the differences between active and naturally abandoned beaver meadows. We quantify surface and stratigraphic complexity, organic carbon storage, and inflow and outflow stream hydrographs for 10 beaver meadows in northern Colorado that range from currently active to sites abandoned by beaver across a range from the 1980s to 2013. Preliminary results from our study indicate greater morphologic complexity, greater surface water storage and greater surface water retention time in active beaver meadows. Beaver meadows become progressively geomorphically and hydrologically simpler following abandonment.