Structures Mimicking Beaver Dams Reduce Waterborne Parasites
Highlights:
- Built structures that mimic beaver dams, called beaver dam analogues (BDAs), slow the flow of water in a creek or stream.
- Previous studies show that these BDAs improve stream and meadow health.
- Researchers recently studied their effect on waterborne pathogenic protozoa and saw that BDAs significantly reduce the load of pathogens that can cause serious diarrheal disease in humans and animals.
This week in researchers report that BDAs significantly reduce the amount of a waterborne protozoal pathogen, Giardia duodenalis, in stream water flowing through a cattle ranch in California.
“We found that slowing down the water in these creeks allowed these pathogens, which can cause disease in animals or people, to be removed by the BDA structures,” said epidemiologist and senior author Woutrina Smith, DVM, MPVM, Ph.D., from the University of California, Davis. “The water that goes through the BDAs becomes cleaner.”
BDAs are built from natural materials, such as river plants woven through vertical wood posts in the stream. When these structures slow down a stream’s flow, water spreads out, increasing the interface between a floodplain and the stream. This can help restore degraded ecosystems, Smith said. Ecologists have been building these structures for more than 2 decades, and previous studies have shown that they can help shift riparian streams from a pulse of water released to slower long-term release of water throughout the year, as well as improving vegetation.
Previous studies have shown that BDAs act as passive filters, generally improving water quality, and Smith’s group has previously studied coastal farm practices that improve water quality. However, the effect of BDAs on waterborne protozoal pathogens in these settings hadn’t been studied before.
G. duodenalis and Cryptosporidium parvum, the parasites at the heart of the new study, have a wide range of animal hosts, including humans, and cause diarrheal disease. They can survive for months to years in the environment and are shed in feces. "Finding practical interventions has a critical and useful application for public health," Smith said.
She and her collaborators conducted experiments on a series of BDAs already installed at a wet meadow restoration ranch site in Plumas County, California. To gauge the filtering effects of the structures, they released inactivated cysts of the 2 pathogens upstream at 3 BDAs. They compared concentrations of the cysts found upstream and downstream of the structures and compared those data to a control stream without a BDA.
They found that BDAs reduced the load of both pathogens, compared to the control site, and their follow up analyses showed that the G. duodenalis reduction was statistically significant. The researchers suspected the BDA would be useful as a barrier filter, but they were surprised at the effectiveness of the structures as a filter for the protozoa. In future work, Smith said, the scientists plan to study the effects of BDAs on waterborne protozoa in other riparian settings as well.
BDAs are easy to build and show how a low-cost strategy can address both ecological and public health issues. “They’re good for wildlife and livestock, but also good for people who come into contact with that stream for hundreds of miles downstream,” Smith said. “It is exciting to think that conservation can help restore an ecosystem and improve water quality at the same time.”
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The American Society for Microbiology is one of the largest professional societies dedicated to the life sciences and is composed of over 37,000 scientists and health practitioners. 91Â鶹ÌìÃÀ's mission is to promote and advance the microbial sciences. 
91Â鶹ÌìÃÀ advances the microbial sciences through conferences, publications, certifications, educational opportunities and advocacy efforts. It enhances laboratory capacity around the globe through training and resources. It provides a network for scientists in academia, industry and clinical settings. Additionally, 91Â鶹ÌìÃÀ promotes a deeper understanding of the microbial sciences to all audiences. 
The American Society for Microbiology is one of the largest professional societies dedicated to the life sciences and is composed of over 37,000 scientists and health practitioners. 91Â鶹ÌìÃÀ's mission is to promote and advance the microbial sciences. 
91Â鶹ÌìÃÀ advances the microbial sciences through conferences, publications, certifications, educational opportunities and advocacy efforts. It enhances laboratory capacity around the globe through training and resources. It provides a network for scientists in academia, industry and clinical settings. Additionally, 91Â鶹ÌìÃÀ promotes a deeper understanding of the microbial sciences to all audiences. 
