Dam! Impacts of Beaver Dams on Surface and Groundwater Quality
Beaver (Castor canadensis) activity (i.e., damming of streamflow) holds significant potential to impact in-stream nutrient processing, through reduction of streamflow velocity and increase of water residence time within pools, trapping of sediment and organic material, raising of riparian groundwater tables and restoration of channel-floodplain connectivity. Thus, dams may represent a “no-cost in-stream conservation practice” that provides compound benefits beyond water quality and quantity, such as enhanced wildlife habitat and increased riparian vegetation diversity. Few studies have focused exclusively on beaver dam impacts to in-stream nutrient processing and watershed-scale nutrient loading, especially in the agricultural Midwest, where watersheds frequently exhibit elevated nutrient loads, flashy hydrology and stream channel incision.
The overall goals of this project are to identify and quantify key nutrient-removal processes associated with beaver dams and estimate the potential impact of dams on watershed-scale nutrient loading within the agricultural Midwest. To achieve project goals, we will pursue three main objectives:
- quantify hydrologic impacts of beaver dams at the stream reach-scale in select Iowa watersheds;
- quantify in-stream and shallow groundwater nutrient processing impacts of beaver dams at the stream reach-scale in select Iowa watersheds; and
- expand stream reach-scale results to estimate watershed-scale hydrologic and nutrient loading impacts of beaver dams.
Project objectives will be achieved through two years of field data collection and modeling, focused on six beaver dam complexes located within six central Iowa watersheds in the Central Iowa and Minnesota Till Prairies Major Land Resource Area, i.e., Des Moines Lobe.
During this initial reporting period, project team members focused on dam site selection and access acquisition, refinement of field and laboratory standard operating procedures (SOPs), preliminary field data collection, undergraduate training, and graduate student (MS) recruitment.
Project team members scouted, identified and field-verified a number of active dam complex sites within the Des Moines Lobe. Six sites have been selected as primary research and monitoring sites for the project. A number of “reserve” sites will be monitored if primary sites are destroyed or become inactive during the project timeframe. Sites are located within both agriculturally-dominated watersheds (three primary sites) and less-agricultural (three primary sites) watersheds with a greater forest landcover component. Sites are located on both private and public lands. Permission for access and monitoring has been granted for all sites for the project duration.
During the effort to locate and acquire access to dam complex sites, critical relationships have developed between project team members and partners including U.S. Army Corps of Engineers, U.S. Fish and Wildlife Service, Iowa DNR, County Conservation, and a number of private landowners. U.S. Fish and Wildlife Service staff provided project team members with a field tour of constructed beaver dam analogue sites, to allow for observation of long-term water quality and stream geomorphology effects of dams and dam-like structures.
Intensive data collection and graduate student involvement in the project have been delayed due to the COVID-19 pandemic and associated limitations on research activities. However, scaled-back data collection has occurred during the reporting period, and a graduate student (Master’s, Environmental Science) has been successfully recruited for the project.
Scaled-back data collection during the report period included nitrate, total suspended solids, in-channel sediment storage, stream discharge and velocity, dissolved oxygen, pH and temperature measurements associated with dam pools and reference reaches. In addition, data on physical dam and pool dimensions, as well as stream geomorphic surveys have occurred. Field and laboratory SOPs were refined and three undergraduate research assistants were trained on SOPs.