The study, carried out by Dr Ian Vaughan and Professor Steve Ormerod, investigated more than 2,300 rivers, measuring changes in the occurrence and spread of insects, snails and other invertebrates between 1991 and 2011. Of the 78 types of organisms examined, 40 have become more prevalent in English and Welsh rivers, and 19 have declined.
Using data supplied by the Environment Agency and Natural Resources Wales, the pair also attempted to determine whether water quality, temperature or river flow best explained the changes in invertebrate abundance that they observed. The results indicated that reductions in gross pollution were the most significant factor.
The water in British rivers has warmed by about 1–2°C in recent decades, but the findings suggest that improvements in the control of pollution entering the rivers has offset any damage this may have done to the aquatic ecosystems. ‘Our analysis showed clearly that many British river invertebrates are sensitive to climate,’ Vaughn said. ‘However, it seems that efforts over the past two to three decades to clean up pollution from sewage and other sources have allowed many of these sensitive organisms to expand their range, despite 1–2°C warming trends and several periods of drought.’
‘These results reveal part of a larger pattern in which organisms dependent on cleaner waters, faster flows and high oxygen concentrations have been progressively recolonising Britain’s urban rivers,’ Ormerod added. ‘We need to protect river organisms against climate change effects – and solving other problems such as pollution clearly helps.’
This story was published in the July 2014 edition of Geographical Magazine