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.
Note: Project reports published on the INRC website are often revised from researchers' original reports to increase consistency.
The 2022 sampling season saw several advancements in the overall project goals. Continued biweekly sampling for water quality elements (nitrate, phosphorous, and suspended sediment) and in-channel sediment sampling activity took place in conjunction with stream discharge measurements. Rating curves are being developed in order to generate average daily discharge values for the study streams, allowing for estimations of load for the study analytes. Both primary study sites, Caton Branch and Smeltzer Learning Farm, served as pilot studies an assay seeking to determine in channel sediment nitrate removal rates. This work is planned to be expanded to one-time visits to 20-30 dams across the Des Moines Lobe in order to characterize the range of sediment capture and nutrient processing in a wider diversity of beaver dams. In addition to the continued field sampling efforts, several outreach and informational activities took place.
To date, 41 ISU students have had the opportunity to participate in research activities ranging from water quality and sediment probe sampling to the development of lab-based assays and wet chemistry.
Outreach this period included: Presentations were given at the Iowa Water Conference and Geological Society of America (GSA) annual conferences, resulting in a 1st place poster award for top poster at the GSA event and positive feedback from GSA beaver research peers. Field day presentations were given in person at the Smeltzer Learning Farm and filming took place for an Iowa Learning Farms virtual field day to be presented in February 2023. There were also popular press articles published relating to this project, including a project overview in the Cedar Rapids Gazette titled, “Beaver dams do a good job improving Iowa water quality”.
A blog article, written by a Water Rocks! intern was also published about his experience in assisting with sampling and scouting beaver dams. ISU Integrated Crop Management video on project created: https://www.youtube.com/watch?v=uzrPvrEx_Vo
The characterization, estimations of mass and volume, and N removal potential of the dam captured sediments was carried out at the Caton Branch and Smeltzer Farm sites. Researchers on this project will partner with Dr. Tom Isenhart (ISU-NREM) and Dr. Keith Schilling (U Iowa-IIHR) to understand the potential N removal potential of the impounded beaver dam sediments. This sampling effort will also be expanded to additional sites to better capture the potential contributions of beaver dams, with regards to sediment confinement, processing and transport.
The 2021 sediment samples have been processed for bulk density and general characteristics and archived for further analysis. The next step will be the setup and training of student assistants to analyze particle size of the collected sediments.
A one-year project extension was granted, during spring 2022.
Two presentations were given on the project during this time period. Two non-peer-reviewed publications were also developed 1.) Conservation Learning Group (CLG) blog created on recent project findings. CLG is associated with ISU Extension/Iowa Learning Farms. 2.) The blog was revised to create a popular press article in Wallace’s Farmer magazine.
Andrew Rupiper, the graduate student project lead, was awarded first place in the student poster competition at the 2022 Upper Midwest Stream Restoration Symposium, for his poster related to the project.
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 boards 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.