Focus on phosphate not a ‘silver bullet’ for River Wye water quality – study

Water quality in the River Wye catchment will not improve by focusing solely on managing the level of phosphate in the water, a new study shows.

The chemical, which finds its way into the river from a range of sources, has been linked to a perceived increase in frequency and severity of algal blooms, which are harmful to the river’s ecology, wildlife, and those using the river for fishing and swimming.

But the new report, prepared over two years by researchers at Cardiff University, shows current phosphate levels are mostly within Special Areas of Conservation (SAC) targets.

Holistic management

Instead, the researchers found a highly diverse and variable community of diatoms, green algae and blue-green algae.

Variations in levels of phosphorus and nitrogen across the catchment were also reported in the study.

Increased levels of ammonium and nitrate, seasonal changes to the river’s flow, and high summer temperatures are all combining to affect the Wye’s health, the report concludes.

Its authors say a holistic management approach, which addresses the river’s flow rate, water temperature, and reduces all nutrients from all sources is essential to reverse the decline in the river’s health.

The report was prepared for the Wye and Usk Foundation.

Professor Rupert Perkins, from Cardiff University, said: “Phosphate is seen as a ‘low-hanging fruit’, an easy thing to focus on as the cause of poor water quality. But it’s just one piece of the jigsaw puzzle.

“By studying the biology with eDNA, alongside water quality measurements, we get a far better understanding of the range of causes behind the problems in the river.

“We’re not saying we can forget about phosphorous altogether.

“We must look at all nutrients as well as flow rates, temperature and the biology of the Wye, working in the catchment on precautionary and preventative approaches.

“Generating an action plan that deals holistically with the range of causes that affect water quality will help organisations like Natural Resources Wales and the Environment Agency in river management on the Wye and on a much wider scale too.

“It’s a beautiful river with lots of great wildlife but we need to look at the bigger picture and not silver-bullet quick fixes.”

Better understanding

Between June and November in 2022 and 2023, the team collected 365 samples from 14 different sites along the 124-mile (200km) river – the UK’s fifth largest – spanning parts of Wales and England.

The samples were analysed in laboratories at Cardiff University to produce a biological fingerprint known as environmental DNA (eDNA) of the cyanobacteria present in the water.

Simon Evans, chief executive of the Wye and Usk Foundation, said: “While phosphate levels in the Wye have been declining in large part due to investment by Dwr Cymru Welsh Water, we were still receiving reports from members of the public that algal blooms had been spotted and were getting worse in the catchment.

“This didn’t make sense. And so, to better understand what was going on, we instigated and funded this study.

“It shows the current focus on phosphate is misplaced, and we need to manage flow, reduce water temperature, shade our rivers and set science-based thresholds for all nutrients.”