Volunteers take a dip to find out which creatures call Keynsham river home

Published on: 06 Nov 2015

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November 2015

Wearing wellies and waterproofs, a record number of people waded into the River Chew to help the Keynsham branch of the Avon Wildlife Trust carry out a health check. Dave Sage, chairman of the group, shares the volunteers’ findings.

Stream dipping took place again in the River Chew at Dapp’s Hill on October 11. A record turnout of 43 people took part, a nice mixture of older and younger people, some from Wellsway School’s Green Team, some Avon Wildlife Trust members and some locals who had heard about the event in local publications.

Seventeen kick samples were taken, the most since 2008. The river level was low and the flow rate slow, reflecting quite low rainfall in September (though wetter than last year). A total of 15 major invertebrate indicator groups were represented, one up on 2014. 

Much discussion ensued about whether a yellow and black-striped fly larva was that of a horsefly, a cranefly or a soldierfly. I can categorically state that I am not sure! 

Each sample had relatively low numbers (with the exception of bloodworms) and low biodiversity, possibly reflecting the low flow rate.

Decreases

None, apart from a small decrease in burrowing mayfly nymphs and leeches.
Increases

Stonefly nymphs, swimming mayfly nymphs, cased caddis larva, snails.

Overall, the main indicator groups and species were all present and sufficient to suggest that the quality of water remains good. Certainly there is still no obvious sign of poor water quality, such as increased sediment, sludge, or a bad smell. 

Local fishermen showed us numerous chubb and minnows, a few of which they caught – and returned. 

I also saw a kingfisher here three weeks ago, a sighting backed up by a passer-by. 

However, a marked increase in the numbers of bloodworms in some samples might suggest some reduction in water quality.

Hence, as in 2014 the evidence is slightly conflicting this year. As last year, it is quite possible that the slow flow rate could decrease the oxygenation of the water and account for some of the observed changes in the invertebrate distribution here.

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