Highlights:
- Delaware watersheds show high microbial impairment.
- Researchers collected samples from Delaware waters over 2 years and identified microbial DNA signatures present in the water.
- The findings suggest that both treated and untreated human waste are the culprit, likely due to infrastructural issues.
Washington, D.C.-Delaware has numerous inland waterways with high microbial impairment from unknown sources. Now, a new study suggests that human waste, both treated and untreated, is responsible for the waterway impairment in these Delaware watersheds. The study was published in Applied and Environmental Microbiology, a journal of the American Society for Microbiology.
According to the Clean Water Act, when water is contaminated by pollutants and doesn't meet the standards of clean water, the water bodies are considered impaired. In the new study, researchers worked with state water quality monitoring staff to collect water across many different locations from 3 different inland watersheds in the southern part of Delaware. By examining the DNA in the water, the scientists could see microbial communities that were present. "The nice thing about this study is that the sampling happened on a monthly basis across 2 different years, 2020 and 2021. We were able to capture a lot of different seasonal, tidal and geographic location differences to look at this in a very comprehensive manner," said study coauthor Jennifer Biddle, Ph.D., a professor in the School of Marine Science and Policy at the University of Delaware.
The researchers compared the DNA signatures in the water to those from a library containing signatures from different organisms that live across Delaware, including domestic animals and livestock, as well as humans. The researchers found that the majority of the microbial signatures in the water were comparable to a human waste signature and did not match an animal signature, either domestic or agricultural.
"This idea that you live downstream from a cow farm and thus your water is impaired…we never found that being any sort of signature in the water. It was a majority human signature," Biddle said. The study suggests that the way the microbes are present in the environment are most similar to what is seen in treated and untreated human waste. "With a library of over 10,000 signatures from different microbes, we were able to say that this looks like a human signature instead of a goose signature or some other animal. We don't have a massive issue with animal inputs in the waterway," Biddle added. "People might have concerns about migratory geese or agricultural animals, but it seems like that waste isn't a concern."
The study indicates that infrastructural problems may be the cause of water impairment. "We saw a septic system signature in the water," Biddle said. "We need to look into infrastructure issues and systems that might have been installed a long time ago." Currently, septic systems in Delaware don't need to be replaced until a property is sold, but the study suggests that property owners should more frequently make sure their septic systems are up to code.
"Our ability right now to look at the microbiology of an environment with a massive sequencing approach is very useful and has increased in its utility, beyond just examining what the EPA regulations regularly require," Biddle said.
