In early July 2013 the River Kennet – a Site of Special Scientific Interest - was exposed to a pesticide spill that triggered a catastrophic loss of its invertebrate fauna on an unprecedented scale: extinctions occurred over 15km of the river after Chlorpyrifos was accidentally discharged into the river via a sewage treatment works (see news reports; Initial reports came from citizen scientists involved in the Action for the River Kennet (ARK) monthly riverfly monitoring scheme. The immediate impacts and longer-term repercussions for the whole ecosystem are enormous, as the spill has effectively ripped out the middle of the food web. Thus the fish assemblages, although seemingly not directly affected, have been left without food, and the microbes at the base of the web are blooming after losing their consumers. These profound changes to the river’s biota are being manifested over large spatial and temporal scales. 
We are currently measuring the impact across the whole food web, including the microbial drivers of ecosystem functioning at its base, and to track its recovery. This unfortunate accident provides a uniquely valuable case study because we know very little of the impacts of modern pesticides on riverine ecosystems, and even less about their effects across multiple biological levels of organisation.   

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AboveThe River Kennet with map showing ARK study sites, Stonebridge lane and Elcot Mill, upstream and downstream respectively of the point at which pesticide entered the River Kennet in July 2013.

Above: ARK riverfly monitoring data collected during 2013 from Stonebridge Lane, and Elcot Mill, upstream and downstream of the point of pollution respectively. The red arrow indicates the timing of the pollution.

Murray Thompson,
May 9, 2014, 3:43 AM