Agriculture affects small aquatic life more than wastewater
Substances from agriculture influence life in rivers and streams. Treated wastewater, on the other hand, plays a lesser role in the species composition of small organisms. This is shown by a new study conducted by an interdisciplinary team at Eawag.
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Municipal wastewater treatment plants and agriculture are among the main sources of pollution in rivers and streams, affecting aquatic communities. About the Wastewater treatment plants drug residues, nutrients, biocides, resistant bacteria and heavy metals, for example, are released into the Waters. Agriculture, for its part, is primarily responsible for the input of pesticides, fine sediments and nutrients. However, little was previously known about the relative influence of these two sources. That's why Christian Stamm and his team from the EcoImpact project investigated this knowledge gap in a new study that recently appeared in the journal Science of the Total Environment.
Between 2013 and 2014, he and his team took water samples every two months at 23 wastewater treatment plant sites, both upstream and downstream of the wastewater discharges, and determined the water quality and the substances present. In the spring of each year, they determined the small organisms found upstream and downstream in the streams.
Worms love sewage
The results show that agriculture drowns out the influence of organic contaminants from wastewater treatment plants. Thus, the occurrence of insects and other small organisms below wastewater outfalls changed only slightly. The exception is worm-like organisms: These seem to feel comfortable with the mixed treated wastewater and occur significantly more frequently below sewage treatment plants than above.
Agricultural inputs, on the other hand, have a noticeable impact on overall species diversity: "Sensitive species in particular were scarce in areas with intensive arable farming," says Stamm. These include, for example, various mayflies or stoneflies. In addition, the researchers found that especially Pesticides seem to be the culprits - increased nutrient inputs, on the other hand, are hardly reflected in the species composition. "The results underline the need to substantially reduce the pesticide load from agriculture," emphasizes Christian Stamm.
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