• by Karma Loveday

Analysis finds Thames’ investment was “crucial turning point” for river biodiversity


Thames Water’s investment in improved treatment to comply with the EU Urban Wastewater Directive has been identified by academics as “the crucial turning point” in the health of a Wiltshire river.

The Centre for Ecology and Hydrology analysed data from the regular monitoring of both chemicals and invertebrates in the River Ray in Wiltshire by the Environment Agency and its predecessors between 1977 and 2016. This Thames tributary is downstream from Swindon’s large wastewater treatment plant.

The Defra-funded study found that, since 1991, there has been a steady increase in both the diversity and abundance of freshwater invertebrates, which play a vital and varied role in an ecosystem’s food chain. The water is cleaner due to a reduction in ammonia (from sewage) plus an increase in oxygen levels (as a result of less organic matter being discharged into the river).

Professor Andrew Johnson of the Centre for Ecology and Hydrology, who led the study, explained: “There was a marked increase in the diversity and abundance of freshwater invertebrates on the River Ray immediately after 1991 and there has been a steady improvement since then. Therefore, we have identified Thames Water’s investment in improved treatment to comply with the EU Urban Wastewater Directive, which was adopted that year, as the crucial turning point.”

He added: “The fact there has been a continual increase in biodiversity in the Ray despite it being a small river taking the entire treated wastewater of a large town of 200,000 residents is extremely encouraging. It indicates that even for rivers with a very high wastewater content their fortunes can be turned around.”

The centre’s press release linked private investment with higher treatment standards. It pointed out: “The privatisation of the UK water industry in 1989 meant the new water companies could borrow money to invest in their treatment plants to comply with higher standards, overseen by independent regulators. The industry spent £26 billion on various wastewater improvements between 1990 and 2015, according to Defra figures.”

The centre also noted the new findings, published in the journal Environmental Toxicology and Chemistry, echoed other research which indicates there has been an increase in the biodiversity of many rivers across the UK.


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