|Abstract Title:||Beavers as Critical Zone Engineers: Effects on Biogeochemical Processes|
|Presenter Name:||Clifford Adamchak|
|Company/Institution:||University of Colorado, Boulder. Institute of Arctic and Alpine Research (INSTAAR)|
|Session:||Mercury in Freshwater Ecosystems|
Abstract Information :
The Western United States (U.S.) is experiencing severe drought conditions exacerbated by climate change. The American beaver (Castor canadensis) is being reintroduced to restore water resources. Within river systems, beavers create cascades of sequential dams that alter river geomorphology and redox conditions that influence biogeochemical cycling. Importantly, beaver alterations to the environment influence each part of the Critical Zone (CZ), the portion of Earth?s skin that extends from the top of the tree canopy to the active water table and provides the majority of resources to ecosystems and people. Of the many threats to CZ health, atmospheric deposition of mercury (Hg) continues to increase. In anoxic environments, excess sulfate can be reduced by bacteria, which stimulate the production of methylmercury (MeHg), a neurotoxin that can bioaccumulate and biomagnify in the food web, threatening ecosystem and human health. Beavers? ability to reengineer the CZ?through dam construction and abandonment over time?deserves attention. Specifically, how their activity expands anoxic conditions and increases the potential for Hg methylation, as well as changing Hg, S, and carbon storage. Studies show that MeHg concentrations increase downstream of new dams, but decline with dam age, indicating that biogeochemical cycling changes across age gradients. This presentation will describe a new study of the relationships among areas of beaver activity, water residence times, and biogeochemical cycling in Colorado and California. Specifically, I will describe an approach to quantify sources and sinks of MeHg across beaver cascades and its local storage in the CZ, including the locations of elevated process rates (Hg methylation, demethylation, and sulfate reduction), and the ultimate fates of Hg and S. This project will quantify the changes caused to mountain ecosystems based on beaver presence, illuminate how they change water quality, and the timescales over which they change the function of the CZ.