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On Saturday June 10th, a group met for the ongoing,  'Bugs in Brooks' community survey. Their mission is to collect and identify the bugs in the rivers, streams, brooks and ponds around Eynsham as a means of assessing the health of our wqter courses. NRN also have a long-term project of monthly chemical testing of water for chemical pollutants like phosphate and nitrate. Now quantifying the different species of invertebrates that inhbit these water courses adds another important dimension to our knowledge of our local water quality.

 

On this occasion we combed through samples from the Chilbrook, the Limb brook and the Fish Ponds, careful not to miss a single dragonfly larva, freshwater shrimp, or diving water beetle. Does this leech have 8 or 10 eye spots? Is this snail right- or left-coiled? Are you sure those gills on the mayfly larva are feathery and not plate-like? Who could have guessed there is such a diversity hidden in the mud and between stones and water plants?

 

 

Fifteen invertebrate families live in the Chilbrook, seventeen in the Limb Brook, and twelve in the Fish Ponds. Ah…OK…but is that all, you might think? Yes, that was all. The numbers in the brooks have been slowly decreasing since measurements began by the Environment Agency in the late 1980s. Unfortunately, many sampling points have not been sampled regularly in the last decade as the Environment Agency reduced its remit due to budget cuts. But with the Nature Recovery Network’s  “Bugs in Brooks” team, the invertebrate sampling around Eynsham is back. And with the increase in sewage spillage in our water courses, this project is increasingly relevant for recording how pollution is impacting our streams.

 

Why bother with invertebrates in the first place? Well, this very diverse group of small animals is sensitive to (organic) pollution from sewage and other nutrient inputs (e.g. agricultural fertiliser), and it is possible to calculate a water quality score, the WHPT index, named after the people who developed this water quality index: Whalley Hawkes Paisley and Trigg. After two detailed surveys in March and June this year, we can begin to see the state of our Eynsham brooks for the first time in a decade. So what did we find? The WHPT index has either remained stable or declined in the Chilbrook, Limb Brook, and Wharf Stream over the recent decades - that’s not good news. It’s also hardly a surprise, because we knew the water chemistry of many streams wasn’t fantastic. Not terrible, but certainly not great.

 

That the water courses are polluted with eutrophic chemicals like phosphate and nitrate is clear from the results from the Water Quality Team led by by Dr. Lucy D. Over the past 3 years they have have  collected monthly water samples at ten sites in and around Eynsham over the last three years and chemically analysed the samples using state-or-art lab methods - that’s dedication! By combining the water chemistry data with the invertebrate WHPT values, a clearer picture is merging, but its not good news, however - biodiversity and water quality is gradually decreasing.

 

 

 

In addition to invertebrates, Anna Rowlands is leading a team to monitor the water vole  population that inhabit our water coursers. These shy mammals are also under threat as their numbers have diminshed greatily in living memory.

 

If the state of the water courses and ponds in and around Eynsham worries you too and you want to help, what can you do? Well, we can always use an extra pair of hands and eyes to identify invertebrates - no prior knowledge required, so neophytes very welcome. The next survey will be on 9th September 2023, in late summer, which completes our sampling for 2023. You can register your interest here.

 

We’ll then be back at it in March, June and September 2024. It would be great to see you for a (half) day of bug hunting. 

 

Maarten van Hardenbroek