Effect of beaver dam analogs (BDAs) on waterborne protozoal pathogens <i>Giardia duodenalis</i> and <i>Cryptosporidium parvum</i>

Beaver dam analogs (BDAs) are a cost-effective, low-environmental impact technique for stream and riparian meadow restoration that provide a variety of beneficial ecosystem services; however, their impact on waterborne fecal protozoal pathogens has not been evaluated. This study used an <i>in situ</i> protozoal release trial to quantify the effect of BDAs on the load of <i>Giardia duodenalis</i> and <i>Cryptosporidium parvum</i> in streams in California. Results showed that <i>G. duodenalis</i> concentrations below BDAs were significantly reduced by 81%. The median percent decrease in load-based recovery rates below a BDA for <i>G. duodenalis</i> and <i>C. parvum</i> was 78% and 80%, respectively. This finding indicates that BDAs may promote passive filtration of waterborne pathogens, thereby improving water quality in downstream reaches and adding to the beneficial outcomes associated with using BDAs in stream and meadow restoration efforts. The potential benefit to resource managers and communities is immense.