Long‐term changes of macroinvertebrate communities in relation to flow variations: The river Glen, Lincolnshire, England

Taxa and community relationships with flow were investigated using National Rivers Authority macroinvertebrate sampling records from a total of 45 sites in the River Glen catchment and daily flow records, taken over the period 1976–1994. Four sites (two upstream and two downstream of an interbasin transfer outflow) were studied in detail. Community analyses of summer samples (41 records from 1977 to 1994) showed April mean flow and low flows in the same summer as sampling to be the best predictors of macroinvertebrate community type. Comparison of the frequency of individual taxa in summers when flows were above or below the flow sustained by the inter‐basin transfer (0.107 m3 s−1) showed a relatively high number of taxa, including Sailidae, Molannidae, Planorbis spp. and Haliplidae, to be more frequent in low‐flow summers, whereas other taxa, including Rhyacophilidae and Leptophlebidae, were more frequent in high‐flow summers, differences apparently related to position in the catchment and variability in the development of marginal macrophytes. The implications of altering flow regime on habitat and macroinvertebrate communities are discussed, and the suitability of National Rivers Authority biological records for developing long‐term flow‐preference relationships for individual taxa are considered.