One of the rivers sampled for the study, located in England, UK. Dania Albini
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Rivers are the lifeblood of the planet. Essential for plants, animals and humans, clean water is increasingly being contaminated with agricultural runoff containing toxic pesticides and other contaminants.
A new study by researchers at the University of Oxford has found an even greater threat to the water quality of rivers, as well as the ecosystems that rely on them: sewage discharge.
In the United Kingdom, water companies’ treated wastewater is allowed to be released into rivers, as is the untreated overflow of wastewater that results from heavy rainfall, according to the University of Oxford.
This practice impacts ecosystems and biodiversity, as well as human health, if the water is used for agriculture, drinking or recreation.
“In the last few decades, pollution of aquatic ecosystems has become an environmental issue of global concern,” the study said. “In particular, wastewater inputs have been recognised as one of the most common threats to water quality in river ecosystems. Despite treatments in wastewater plants (WWPs) to remove some suspended solids and nutrients, these are not entirely removed and other chemical pollutants (e.g. pharmaceuticals) still enter aquatic ecosystems. These substances can drastically affect the rivers[‘] physical and chemical characteristics, with consequences for the survival and abundance of aquatic organisms.”
The researchers looked at the effects of agriculture, urban runoff and treated sewage discharge on various aspects of river systems. Four rivers in England were tested during three different months in locations upstream and downstream of where sewage had been discharged.
The researchers discovered that the most accurate predictor of bottom-dwelling algae, the abundance of sewage fungus and high levels of nutrients — no matter whether the surrounding land was being used for urban or agricultural purposes — was treated sewage discharge.
“Our study highlights the disproportionate impact that sewage discharge has on river quality, presenting an urgent need for a comprehensive action plan targeting the sewage discharge problem. Improvements to waste water plants should be implemented along with more regulations. These efforts are crucial in safeguarding the integrity and safety of our rivers — fundamental elements of both ecosystems and human well-being,” said Dr. Dania Albini of the University of Oxford’s Department of Biology, who studies the effects of climate change on aquatic ecosystems and is a senior author of the study, according to the University of Oxford.
The study, “The combined effects of treated sewage discharge and land use on rivers,” was published in the journal Global Change Biology.
“There is ongoing debate about the cause of the poor ecological state of many rivers in the UK because it is difficult to disentangle different pollution sources. Here, we show that even treated sewage appears to have a stronger influence on river communities than pollution from the surrounding land. This important information should be used to prioritize the management and conservation of our rivers moving forward,” said Dr. Michelle Jackson of the Department of Biology at the University of Oxford, a senior author of the study.
Nutrients in waterways promote the growth of species that are harmful, such as worms and cyanobacteria, while deteriorating other species. Cyanobacteria is known to produce toxic chemicals that are harmful to many aquatic organisms. Thus, pollution from wastewater can degrade and alter important ecosystem processes due to the loss of critical species.
The study found that the only measurement surrounding agricultural land use that was a good predictor was the abundance of stoneflies, caddisflies and mayflies. This finding points to locally treated sewage discharge being more of a threat than pollution to river communities and their water quality.
“This important research demonstrates yet again the damage from unregulated water companies and agriculture. In addition to the catastrophic impact on wildlife from nutrient pollution, the public should be aware that sewage systems do not remove dangerous bacteria such as E.coli and intestinal enterococci from treated sewage. For instance, recent citizen science on the River Thames found that Thames Water’s outflows often have four to five times the safe levels of bacteria, that has likely caused serious illness in swimmers and rowers. When will the government make water companies and farms clean up their act, especially in places where human lives and sensitive protected habitats are threatened?” said James Wallace, CEO of River Action, a UK-based charity, according to the University of Oxford.
The researchers developed a new early detection method for sewage fungus, which is a mixture of algae, bacteria and fungus that forms in the presence of high organic nutrient levels. Sewage fungus greatly reduces water oxygen levels, which can have an adverse effect on fish and all river species, and can lead to mass fish mortality.
The new technique could be used by monitoring agencies and water companies to limit the buildup of pollution and stop the decline of species.
“Rapid identification of sewage fungus pollution events will allow early intervention which would help prevent any potential negative consequences for local wildlife,” Jackson said.
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