Lower Windrush Valley Conchological Society Meeting 17 July 2004

Society members met Alison Hopewell, the Project Officer for the Lower Windrush Valley Project, at the Linch Hill Leisure Park (SP 417040) on a pleasant but comfortable day and visited three flooded gravel pit lakes. Gravel extraction here began in the 1960s, which puts an approximate start date on colonisation by plants and animals. The pits were excavated in Pleistocene sands and gravels mainly derived from the Jurassic limestones of the Cotswolds, and rest on impervious Late Jurassic Oxford Clay. The environment is generally calcareous.

All three pits examined - Stoneacres Lake, Willow Lake and Christchurch Lake are used for coarse fishing and also have large waterfowl populations. The pits are open with about two metres of shallow edge followed by a steep drop. There is a narrow wetland fringe with varying heights of vegetation.

Twenty-three species of aquatic molluscs were found (details in table).

The fauna found was diverse, but numbers of animals were generally low, especially species which are associated with aquatic vegetation, rather than bottom sediments. Each pit examined had species not found in the other two. A sample (c.0.5kg) of sand and gravel from a vegetation free bottom at the edge of Stoneacres (in course of examination) had large numbers of Potamopyrgus antipodarum and pea mussels (Pisidium spp).

Willow Lake, which has more trees surrounding it, has more rotting vegetation on the bottom than Stoneacres. It was the only pit where zebra mussels (Dreissena polymorpha) were found submerged wood, stones and other objects; it was also the only pit to produce Swan mussels (Anodonta cygnea) on this occasion.

Christchurch Lake had had barley straw dumped in it to suppress weed growth, and was also receiving water from an adjacent pit which was being landscaped, so the water level was raised. We did not record any bottom-dwelling molluscs from this site. Most of the snails recorded here were among weed or semisubmerged thistles and reed mace. Eighteen species of land molluscs were found (details in table below).

Because we concentrated on the aquatic fauna the search for land molluscs was limited. There were no extensive areas of fen, but there was a narrow wet fringe to the lakes and here some species typical of such habitats were found: Carychium minimum. Oxyloma pfeifferi, Vallonia pulchella, Zonitoides nitidus, and Deroceras laeve, mostly on decaying Juncus stems, but Z. nitidus was also on rotting drifted vegetation at the edge of Stoneacres.

Two species characteristic of short limerich turf were associated with short mossy vegetation containing wild basil (Clinopodium vulgare) at the edge of Christchurch Lake - Pupilla muscorum, and Vallonia excentrica.

With many thanks to Alison Hopewell for organising this interesting visit and for the permission given by the landowners and angling clubs.