At short notice but taking advantage of the glowing autumn weather yesterday, volunteers established the first two FIN sampling points on Thimblemill Brook. The sampling point we had chosen in July (when thunderstorms stopped play) has since been subjected to widening as part of a series of channel modifications along the brook so we set up a new sampling point in Section 3 – a lot further downstream by Stanhope Road.
The channel looked idyllic with dappled sunshine and autumn colours on the trees and scrub. Did not hold out much hope for the water creatures, given the presence of sewage debris, but was proved wrong – the water was teeming with shrimp and also found water slaters, plume midge larvae, flatworms and olive mayfly. A nice find was freshwater limpet – which appeared to favour only the smoother cobblestones.
Then a 2 km dash (not so quick in wellies) to establish a sampling point in section 1 upstream (so many changes have been carried out upstream and also parts are concrete bottomed so we will have to revisit to find a good sampling point here). They spotted grey water coming from a recently cleared outfall on the way, which Vivien will report to the EA hotline. A new bridge has been put in over the channel linking Broadmoor ave and Norman Road. As the channel appeared undisturbed, they chose this as the sampling point. Not a single shrimp here. A few Water Slaters and the highly pollution tolerant Bladder snail. Interestingly, some cranefly larvae were found (one of which was monstrous in size – pictures to follow), and these are said to be more tolerant of organic pollution than shrimp. Can they burrow in the mud to avoid a pollution incident which would kill the shrimp ?
A very good start to monitoring and improving Thimblemill Brook.