Pthe public outrage over river pollution was heartening to see. Over the past few years, stories of sewage contamination in rivers have caught the public eye and sparked campaigns and protests, such as River Action UK’s upcoming clean water march on 26 October in London. It is important to protect our rivers because they are hotbeds of biodiversity and essential for human health. However, as a freshwater ecologist, I know there are more nuances to this story than you might have thought. From my perspective, there is some good news when it comes to our rivers. I would even say that some of England’s rivers are in the best condition they have been in hundreds of years.
Many rivers in England are polluted, but we must recognize that this is not a new problem, but a much longer-standing one that has been largely ignored by the media and politicians for decades. Much of the recent uproar over pollution has to do with increased awareness rather than a sudden increase in pollution itself. We can only make real progress if we understand how these ecosystems have changed over time and reflect on past successes.
It is widely reported that 97% of English rivers were classified as ‘good chemical status’ in 2016 to none in 2019. In England, the Environment Agency monitors water quality by directly measuring some pollutants and characterizing river life. . This data is then used to classify the water quality in our rivers: ‘high’, ‘good’, ‘moderate’, ‘poor’ or ‘poor’. However, rather than water quality declining drastically over this time frame, the way we measure it has changed—this perceived decline is an artifact of the data. Since 2019, new chemicals have been included in the testing, including “persistent, persistent, bioaccumulative, toxic substances”, which accounts for this major change.
The media has also reported an increase in “sewage leaks” – when raw sewage (instead of treated sewage) is pumped into our seas, lakes and rivers. In 2016, data was available for only 862 storm surges, with that number rising to 6,182 in 2018, 12,092 in 2020, and 13,080 in 2022. Of course, the idea of ​​any raw sewage entering water bodies water, is disgusting and we should work to reduce this number. to zero by updating our Victorian wastewater infrastructure. But the point is that the problem may not have gotten worse in recent years – we’re just really looking for it now.
Other measurements of water quality show that some things have actually improved. For example, many invertebrates can only survive when pollution levels are low, so assessing what species are present provides a quick and inexpensive way to measure water quality. Different metrics are calculated from the invertebrate count data – and a higher score means the water is cleaner. Using this data (and related metrics on algae, fish, hydrology and nutrients) only 15% of England’s rivers are currently classified as having ‘good ecological status’, which sounds pretty dire, especially since in 2009 this status dropped from 24%.
However, there are several factors to consider. First, a large-scale analysis of 223,300 invertebrate data points by researchers at the UK’s Center for Ecology and Hydrology, using records from 1989 to 2018, showed that invertebrate biodiversity has increased over time in England, regardless of river size and land cover . While this trend has slowed in some cases over the past 20 years, the headline is that there is more wildlife in our rivers now than three decades ago. For example, families of mayflies, stilts, and caddisflies (which are particularly sensitive to water quality) have increased by 300% over this time period.
Second, the river classification method uses the “one out, all out” rule. This means that rivers only need to fail on one of 20 metrics to be downgraded from “good” to “moderate” ecological status. In other words, the metric with the worst score determines the overall health. The overall water quality can therefore be more positive than it seems at first glance. The increase in river invertebrate biodiversity in England is good news and shows how far we have come in improving water quality in my lifetime.
At least in part this may be due to improvements in wastewater treatment causing nutrient pollution to decline, with research showing a large drop in phosphate concentrations since 1997. This followed the European Union’s 1991 Urban Wastewater Treatment Directive, which tightened laws and forced water companies to improve wastewater treatment. However, nutrient levels are currently still higher than would naturally be caused by wastewater and agricultural practices, so there is still work to be done. Some of my group’s own research has shown that further reducing phosphorus through better wastewater treatment would be the most effective way to further benefit biodiversity.
Water companies need more scrutiny as there is evidence to suggest they are often still in breach of their licences. They are supposed to discharge raw wastewater only when there is high rainfall. If it reaches such a critical level that the wastewater would rise and threaten to go the wrong way, so to speak, water companies can by law discharge untreated waste. With growing public interest, laws are starting to tighten in this regard, and therefore monitoring data is increasing. Only time will tell, as data from a new network of event duration monitoring devices that are on all storm surges (from 2023) are being analyzed. While we must limit the use of storm drains, we cannot say with certainty that they are actually being used more frequently now than in the past. This is not to diminish the problem, just to say that it may not be a recent problem.
There are still reasons to protest at events such as the River Action UK march. I will definitely be there. Despite improvements in nutrient concentrations and biodiversity, chemical pollutants are emerging and we have very little information about their impact. I think this is where the interested public should turn their attention now. These pollutants are usually household and medical products that go down the drain and are not removed in sewage treatment plants, such as cosmetics and pest treatments. Globally, freshwater ecosystems – which act as hotbeds of biodiversity – are one of the most threatened ecosystems on the planet. They are often forgotten in legislation – so don’t stop campaigning, just make sure you get the facts right so we can make real change.
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Michelle Jackson is Associate Professor of Freshwater/Marine Ecology at the University of Oxford. Professor Jackson has previously conducted one study that received funding from a wastewater treatment company and currently has no industry funding.
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