The influence of drought on chalk stream macroinvertebrates

Chalk streams are characterised by naturally regulated flow regimes but their headwaters (winterbourne streams), are typified by periods of desiccation alternating with periods of high flow. This paper describes the impacts of drought on the macroinvertebrate community of the Little Stour River, Kent. Following the 1988-1992 drought, riverine habitats were severely degraded and some dewatering of previously perennial reaches occurred. Large volumes of fine sediment were deposited at the channel margins and on the river bed. In the summer of 1992 the relative abundance of macroinvertebrates was low. However, recovery was dramatic in the following three years. In 1995 a severe summer rainfall deficit had no detectable deleterious impact on the macroinvertebrate community, reflecting the importance of winter groundwater recharge in sustaining summer flows in chalk streams. Few taxa were eliminated as a result of the drought, suggesting the presence of refugia from which recolonisation of taxa could take place. The results are discussed in relation to the reported impact of drought on other groundwater fed rivers