The P in river pollution may be silent

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

In their report on the findings, scientists at Cardiff University said that current phosphate levels in the River Wye catchment are “mostly within Special Areas of Conservation (SAC) targets; lower than historical records; and unlikely to be the primary cause of algal blooms in the river.”

Furthermore, according to co-author of the report, Thom Bellamy, the level of nitrate over a two-year sampling period was “higher than previously reported”. This, Bellamy said, “demonstrates more than anything else that we must look beyond phosphorous levels and monitor the whole suite of nutrients in the river.”

Chief Executive of the Wye and Usk Foundation, Simon Evans, said: “While phosphate levels in the Wye have been declining in large part due to investment by Dŵr 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.”

With regard to the report's findings, Evans added: “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.”

Co-author, Professor Rupert Perkins of Cardiff University’s School of Earth and Environmental Sciences, 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.”

The researchers concluded that increasing levels of ammonium and nitrate, seasonal changes to the river’s flow and high summer temperatures are all combining to impact the Wye’s health. But Perkins emphasised: “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.”