Flow variations and macroinvertebrate community responses in a small groundwater-dominated stream in south-east England

Changes in the macroinvertebrate community in response to flow variations i n the Little Stour River, Kent, UK, were examined over a 6 year period (199 2-1997). This period included the final year of the 1988-1992 drought, foll owed by some of the wettest conditions recorded this century and a second p eriod of drought between 1996 and 1997. Each year, samples were collected f rom 15 sites during late-summer base-flow conditions. Correspondence analys is identified clear differences between samples from upstream and downstrea m sites, and between drought and non-drought years. Step-wise multiple regr ession was used to identify hydrological indicators of community variation. Several different indices were used to describe the macroinvertebrate comm unity, including macroinvertebrate community abundance, number of families and species, and individual species. Site characteristics were fundamental in accounting for variation in the unstandardized macroinvertebrate communi ty. However, when differences between sites were controlled, hydrological c onditions were found to play a dominant role in explaining ecological varia tion. Indices of high discharge (or their absence), 4-7 months prior to sam pling (i.e. winter-spring), were found to be the most important variables f or describing the late-summer community. The results are discussed in relat ion to the role of flow variability in shaping instream communities and man agement implications. Copyright (C) 2000 John Wiley & Sons, Ltd.