River discharge and local‐scale physical habitat influence macroinvertebrate LIFE scores

Abstract

1. Methods are needed to relate changing river flows to ecological response, particularly those which do not require collection of extensive new data for river segments that lack historical data. Using time-series of river biomonitoring data from wadeable lowland streams in Denmark and the East Midlands of the U.K., we describe how local-scale habitat features (indexed through River Habitat Survey or Danish Habitat Quality Survey) and changing river flow (discharge) influence the response of a macroinvertebrate community index. The approach has broad applicability in developing regional flow-ecological response models. 2. We analysed the data using multilevel linear regression, combining sample-level and site-level characteristics as predictors. We focused on the potential for common responses across sites; hence for each sample, the macroinvertebrate community was summarised into an index, Lotic Invertebrate index for Flow Evaluation (LIFE), an average of abundance-weighted flow groups which indicate the microhabitat preferences of each taxon for higher velocities and clean gravel ⁄ cobble substrata or slow ⁄ still velocities and finer substrata. 3. For the Danish fauna, the LIFE score responded to three predictors in an additive manner: high flows in the preceding 4 months (positive), substratum composition and whether the channel was meandering or straight. The East Midlands fauna responded to three predictors: high and low flows in the preceding 6 months (positive) and the degree of resectioning of the channel (negative). In both cases, LIFE responded negatively to features associated with historical channel modification. We suggest that there are several mechanisms for these relationships, including the narrower tolerances of taxa preferring high velocity habitat; these taxa are also continually recovering from extreme flow events over an inter-annual timescale. 4. At the East Midlands sites, there was an interaction between degree of resectioning and antecedent low flow. At sites with a greater extent of resectioning, the LIFE-discharge relationship was also steeper than at less modified sites. Consideration of the underlying data suggests that there are two mechanisms for this response. Firstly, in less modified sites, refugia are present during low flows for taxa preferring higher velocities such as riffle beetles, caseless caddis, mayflies and Gammarus pulex. Secondly, high flows are associated with decreasing abundances of taxa such as molluscs, flatworms and leeches at more resectioned sites, but with stable or increasing abundances at less modified sites. 5. The LIFE index responded to both antecedent flow and habitat modification in two separate data sets from lowland wadeable streams. This is the first time that the combined importance of these two factors has been demonstrated using routine invertebrate biomonitoring data. These results complement other site-specific studies that have shown how channel structure interacts with flow to create physical habitat, and should assist future work aiming to...

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

“…The assignment of a nominal date allowed a direct comparison between the control and invaded sites over the same time-period and also provided a means of assessing whether there were temporal shifts in invertebrate community composition not associated with crayfish invasion. This approach was taken as previous long-term analyses of UK data sets have revealed changes in community composition associated with drought (Monk et al, 2008), modification of channel morphology (Dunbar et al, 2010) and improvements in water quality (Durance and Ormerod, 2009 To assess changes in individual taxa associated with crayfish invasion, taxon occurrence (presence or absence) amongst the control and invaded rivers both before and after invasion were examined. Nine taxa (3 Mollusca, 2 Ephemeroptera, 2 Hirudinea, 1 Trichoptera and 1 Crustacean) were selected for further analysis on the basis of the following criteria: i) identified as driving community differentiation in a number of regions through application of SIMPER in analyses outlined above and / or ii) widely cited in previous studies of invasive crayfish effects in lotic systems (e.g.…”

The identification of hydrological indices for the characterization of macroinvertebrate community response to flow regime variability

“…However, only a relatively small proportion of the statistical variance within the ecological data could be accounted for by hydrological indices alone. This demonstrates the high level of redundancy associated with hydrological indices and also reinforces the fact that a range of other biotic and abiotic factors (in addition to the flow regime) structure in-stream communities (Durance and Ormerod 2009, Dunbar et al 2010b, Shenton et al 2012, Vaughan and Ormerod 2012. These factors, including riverine habitat, channel structure characteristics and water quality, need to be incorporated in future analysis and environmental flow studies so that they can help inform future management strategies.…”

“…there is a range of other important factors structuring the in-stream community that may include channel morphology and habitat characteristics (Dunbar et al 2010b), biotic interactions (Shenton et al 2012) and water quality (Durance and Ormerod 2009), and these may need to be incorporated into future analyses. However, screening of sites and data in the preliminary stages of this research ensured that sites with known water quality pressures were removed.…”

“…These studies have subsequently been used to help define sustainable ecological/environmental flow regimes in regulated and anthropogenically modified rivers (Acreman et al 2008, Dunbar et al 2010b, Poff et al 2010, Peters et al 2012.…”

“…The LIFE scores for individual families and species are based on the known associations of British benthic macroinvertebrates to flow velocity. The LIFE method and scores have been widely used in the UK to examine and assess macroinvertebrate community response to flow regime variability in a number of studies (Dunbar et al 2006, 2010a, 2010b, Monk et al 2008Dunbar and Mould 2009, Clews et al 2010, Wilby et al 2011, Vaughan and Ormerod 2012.…”