The influence of drought on chalk stream macroinvertebrates

Chalk streams are characterised by naturally regulated flow regimes but the ir headwaters (winterbourne streams), are typified by periods of desiccatio n alternating with periods of high flow. This pager describes the impacts o f drought on the macroinvertebrate community of the Little Stour River, Ken t. Following the 1988-1992 drought, riverine habitats were severely degrade d and some dewatering of previously perennial reaches occurred. Large volum es 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 th e macroinvertebrate community, reflecting the importance of winter groundwa ter recharge in sustaining summer Bows in chalk streams. Few taxa were elim inated 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 . Copyright (C) 1999 John Wiley & Sons, Ltd.