Impact of major changes in flow regime on the macroinvertebrate assemblages of four chalk stream sites, 1997–2001

Abstract

The macroinvertebrate assemblages of three unshaded sites on the River Kennet and one shaded site on the River Lambourn in Berkshire, England, were sampled in summer 1997-2001. Quantitative samples were taken on gravel and on the dominant macrophyte at each site in each year and abundance data were recorded for 57 families of macroinvertebrates. The study commenced during a major drought (1997), but in subsequent years discharge prior to sampling was much higher, culminating in the exceptionally high flows of spring 2001. Both family richness and abundance varied significantly in relation to site, habitat and year. Multidimensional scaling ordination, based on Bray-Curtis dissimilarities, also displayed significant differences between sites, habitats and years. Differences in composition between the Kennet sites were partly due to longitudinal zonation whilst on the Lambourn, faunal differences resulted from shading and the addition of families from nearby habitats, including marginal vegetation. Major changes took place in family composition and abundance between the drought year of 1997 and 1998, indicating that faunal recovery from drought was rapid. Thereafter, faunal changes between 1998 and 2000 were relatively limited. In 2001, following the prolonged period of exceptionally high discharge, overall family richness peaked on both habitats at the three Kennet sites and family abundance reached peak or second highest values on all four sites and both habitats. Thus, the recent high discharge regimes experienced by these perennial chalk stream sites have had no immediate detrimental consequences for the macroinvertebrate assemblages.

Macroinvertebrate community response to inter‐annual and regional river flow regime dynamics

“…These events correspond to major droughts and constitute 'supra-seasonal events' (Lake, 2003), extending over more than one season or year, and resulted in significant impacts on river flows (e.g. Burt et al, 1998;Peters et al, 2006) and instream ecology (Wood and Armitage, 2004;Wright et al, 2004). Years associated with higher regime magnitudes can also be clearly identified (1994 -1995 and 1999 -2000) (Figure 3).…”

“…Hynes, 1958;Extence 1981;Ledger and Hildrew 2001;Lake, 2003). However, the recovery pattern associated with supra-seasonal droughts has not been widely reported (Lake 2003) and data demonstrating the extended duration of faunal recovery over two years were limited to a small number of sites until now (e.g., Wood et al, 2000;Wood and Armitage 2004;Wright et al, 2004).…”

Effects of bottom sediment restoration on interstitial habitat characteristics and benthic macroinvertebrate assemblages in a headwater stream

“…Hydrological disturbance predominantly consists of spates and droughts, which generate an alteration of the habitats (Smock et al, 1994), changes in biotic processes (Williams, 1987;Smock et al, 1994;Wright et al, 2004) and aquatic communities (McElravy et al, 1989;Boulton and Lake, 1992b;Wright, 1992;Smock et al, 1994;Miller and Golladay, 1996). Droughts generally induce decrease in densities, species richness of invertebrate assemblages (Cowx et al, 1984;Wood and Petts, 1999;Meyer and Meyer, 2000;Boulton, 2003) and changes in the size or age structure of populations (Lake, 2003).…”

The long-term effects of invasive signal crayfish (Pacifastacus leniusculus) on instream macroinvertebrate communities

“…During the study period, England experienced highly variable hydro-climatological conditions with a series of high magnitude droughts and prolonged periods of low flows in 1989-1992, 1995-1997 and 2004-2006, with the latter years focussed in the South East of England (Marsh et al, 2007;Hannaford and Buys, 2012). With the exception of one site, the River Ver in South East region, the invasion by P. leniusculus occurred during or directly after one of these high magnitude low flow periods known to have resulted in community changes across England (Wright et al, 2004;Monk et al, 2008;Worrall et al, 2014). These periods resulted in changes to community composition at all of the sites examined and provides evidence to explain the longterm changes observed at control sites in addition to those at sites invaded by P.…”