A 21-year study of over 2,300 rivers in Britain measured the presence of clean-river invertebrates - a yardstick for river health –   and found they are the cleanest they've been in over two decades. During the days of heavy industry and poor sewage treatment,
clean-river invertebrates
had declined considerably, but now appear to be making a comeback, say scholars
from Cardiff University 

Dr. Ian Vaughan and Professor Steve Ormerod from the University's School of Biosciences analyzed changes in the occurrence and spread of insects, snails and other mini-beasts from major rivers between 1991 and 2011. The researchers then asked whether water quality, temperature or river flow best explained the biological changes they observed.

Among 78 types of organisms examined, 40 have become more prevalent in English and Welsh rivers while 19 have declined. Overwhelmingly, these trends were explained by reductions in gross pollution.

Credit: Cardiff University

Because it is required in order to get mainstream media coverage when it comes to environmental science, they even invoke climate change, affirming that the pollution reduction was the reason for the upward trend rather than changing water flow that might be caused by global warming. They do, however, say that climate change has warmed British rivers by around up to 2 degrees over recent decades but say that pollution reduction offset those damaging effects on river ecosystems, The lesson: prevent some undesirable climate change effects on the environment by improving habitat quality.

Improving water quality has allowed some clean-water organisms from upland rivers to return to previously polluted lowland rivers, and may even explain some northwards movement previously attributed to climate change.  

The researchers believe these results to be very encouraging in showing how reductions in pollution can help offset climate change impacts. Vaughan said, "Our analysis showed clearly that many British river invertebrates are sensitive to climate - for example; because they require good supplies of oxygen that decline as rivers warm up. However, it seems that efforts over the last 2-3 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."  

Ormerod added, "These results reveal part of a larger pattern in which organisms dependent on cleaner waters, faster flows and high oxygen concentrations have been progressively recolonizing Britain's urban rivers: Atlantic salmon, mayflies, and Dippers are prime examples. We need to protect these and other river organisms against climate change effects – and solving other problems such as pollution clearly helps.  

"Away from Britain's urban areas, some pollution problems are increasing, and our analysis shows some negative trends among sensitive organisms such as stoneflies that are typical for rural hill-streams. It's important that our efforts to protect Britain's rivers against pollution or climate change are extended to the farmed, rural, upland landscape."