Image description: A landscape photo of a section of the River Thames at sunrise. Photo by Paul Macallan on Unsplash

The Environment Agency and the University of Stirling have published a new report on the links between phosphorus concentrations and ecology in English rivers.

While phosphorus is an essential nutrient for the growth of aquatic plants, too much phosphorus is detrimental to the health of freshwater ecosystems. Excess phosphorus in rivers is a significant factor in failure to meet Good Ecological Status under the Water Framework Directive (WFD).

Investments in phosphorus removal technology at sewage treatment works (STWs) have reduced inputs of phosphorus into England’s rivers since the 1980s. However, the extent to which these reductions in phosphorus have resulted in ecological improvements in aquatic ecosystems nationally, has long been unclear.

What did the report find?

The report concluded that ecological responses to reduced phosphate concentrations are complex and often confounded by multiple site-specific factors such as river flow and the presence of other pollutants. The results show that:

• The magnitude of change in phosphate concentration influences the response of aquatic organisms
• Biological responses to reducing phosphate concentrations are delayed
• Aquatic organisms and communities respond differently to reducing phosphate concentrations.

The report did observe ecological improvements in aquatic plant communities in response to reductions in phosphorus pollution. These findings may help the Environment Agency to understand why ecological recovery is not yet evident in some rivers, despite significant reductions in phosphate. The report recommends that continued investment in phosphorus management is needed to drive progress towards achieving good ecological status in rivers under the WFD.