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 Nat ional 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 downstrea m of an interbasin transfer outflow) were studied in detail. Community analyses of summer samples (41 records from 1977 to 1994) showed Apri l mean flow and low flows in the same summer as sampling to be the bes t predictors of macroinvertebrate community type. Comparison of the fr equency of individual taxa in summers when flows were above or below t he flow sustained by the inter-basin transfer (0.107 m(3) s(-1)) showe d a relatively high number of taxa, including Sailidae, Molannidae, Pl anorbis 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 margin al macrophytes. The implications of altering flow regime on habitat an d 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.