As a recent zoology graduate moving from my place of study in Cornwall back to my home county of Surrey I wanted to re-connect with the local environment, find more like-minded people and help contribute to conservation efforts.
Surrey Wildlife Trust was the obvious place to start and so I signed onto their Riverfly Identification and Monitoring Day. This was run by Glen Skelton (Wetland Projects Manager) as part of Surrey Wildlife Trust’s RiverSearch project. This partners with Thames Water and the Riverfly Partnership to train citizen scientists to help monitor water quality and improve river health in the Wey and Mole catchment areas.
I met Glen alongside other volunteers on a sunny morning in Cranleigh where the day started with a presentation introducing us to riverflies and the importance of monitoring. Riverflies are sensitive to water quality and as such are known as the “canaries” of a river because their absence is an indicator of potential water pollution. Water quality issues include:
- Sewage – bacteria decompose this waste, using up oxygen in the water meaning there’s less oxygen for the riverflies
- Agricultural run off – this is high in nutrients such as phosphates which act as a fertiliser and encourages algae growth. This also reduces oxygen levels in the water
- Physical modification – for example dredging, where the sediment buries the larval riverflies’ gravel habitat
- Climate change – hotter summers dry up the rivers, leaving small pools of water where there’s less oxygen and food for riverflies.
The riverflies in question are split into four groups: caddisflies, upwing flies (aka mayflies), stoneflies and freshwater shrimp. We were given a tray akin to an artist’s large mixing palette with different species from each of these groups to get our identification eye in. Then, with the importance of riverflies ringing in our ears and armed with new identification knowledge we went down to the river to see what we could find. We used a kick-sampling method to disturb the submerged gravel and collect the riverfly larvae in a net. Carefully, we tipped the net’s contents into a plastic tray and separated the different species of riverfly to count them. This land-locked county’s version of rockpooling is not just important for conservation but also very satisfying.
The last, and arguably most vital step, was recording our findings. A score is assigned to each species of riverfly depending on how many you find. For example, if you find fewer than ten cased-caddisflies you assign them the number one. If you consistently get a score lower than a set number, known as a “trigger level”, something is likely to be wrong (eg, high levels of water pollution), so you should alert your local riverfly authority to investigate the issue. We mostly found freshwater shrimp, which are more tolerant to low water quality, suggesting some improvements to the river’s health could be made (which is what the RiverSearch project aims to tackle). Nonetheless, by the end of the afternoon there was a sense of community and achievement, so I encourage you to dip your toe in (quite literally in this case) and join your next local event – you never know what skills you might learn and where it might take you!
You can find Maddy on LinkedIn or on Instagram @nature_nutter