Melanie A. Bickerton

The effects of water abstractions on invertebrate communities in U.K. streams

There are increasing concerns about the ecological effects of water abstraction and in the UK, these concerns have been hightened by the 1976, 1984 and 1988-92 droughts. This paper assesses macroinvertebrate and environmental changes induced by surface and groundwater abstractions on 22 streams throughout the UK.The approach involved comparative research to assess differences between reference and impacted sites.Using a database comprising 204 sets of biological and environmental data (89 taxa and 16 environmental variables) a preliminary ordination using principle components analysis clearly differentiated three types of sites: upland, lowland and an intermediate type. At this scale, any effects of abstractions on invertebrate communities are shown to be insignificant relative to regional controls. A simultaneous ordination of the environmental and faunal differences between pairs of sites was undertaken separately for each of the three regional groups. Differences are considered as vectors having both direction and amplitude and the analysis elucidates common patterns in the faunal and environmental data. Important changes were observed in two situations: upland streams affected by major diversions as part of hydro-power schemes in Scotland and lowland rivers impacted by groundwater abstractions.No strong patterns of change (either in amplitude or orientation) were demonstrated within any of the taxonomic groups. However, within the upland type some rheophilous taxa were shown typically to be reduced in abundance at impacted sites. Within the lowland type, a consistent pattern in the dataset is demonstrated by a group of taxa that are reduced in abundance at the impacted sites.

Assessing stream quality using information on mesohabitat distribution and character

1. The purpose of this paper is to demonstrate: (i) how mesohabitats—medium-scale habitats which arise through the interactions of hydrological and geomorphological forces—can be used as a basis for assessing instream habitat diversity; (ii) how combining data on mesohabitat distribution with those from macroinvertebrate sampling can produce an index for assessing stream quality; and (iii) how, when nested with River Habitat Survey (RHS), mesohabitat information can provide a comprehensive assessment of stream quality. 2. A survey of a small chalk stream in southern England showed that the distribution of mesohabitats varied considerably between reaches. However, a mesohabitat quality index, derived from data on mesohabitat distribution and faunal communities, indicated that there was relatively little longitudinal variation in stream quality as defined by mesohabitat diversity and macroinvertebrate community. Heavy modification of the channel banks, as indicated by RHS, suggested significant habitat impoverishment. 3. Simulations, using different environmental conditions, suggested that the mesohabitat quality index was a potentially useful measure of stream quality. 4. The combination of mesohabitat survey and RHS provided a more comprehensive view of the stream channel and banks than either technique used alone. The study indicated that management efforts to rehabilitate impoverished reaches should be directed towards maximizing instream mesohabitat diversity and mitigating human impacts on the river margin. Copyright

Flow management to sustain groundwater-dominated stream ecosystems

Groundwater is an important resource, not least in south-eastern areas of England, where chalk is the dominant aquifer. Such chalk-fed stream ecosystems are rich and highly productive, they have particularly important springhead wetlands, and are characterised by fast-growing trout populations. The legislative framework, founded on the Minimum Acceptable Flow concept, is in place to protect these stream ecosystems. In surface water dominated catchments, normal operational rules use prescribed (usually hands-off) flows to protect in-river needs. Such rules are inappropriate for most groundwater-dominated catchments because of the slow response between change in groundwater abstraction and river flow. This paper illustrates the use of an Ecologically Acceptable Flow Regime (i) to determine a MAF based on the annual volume of flow, described as a flow duration curve, to protect the riverine ecosystem at the catchment scale, and (ii) to set a prescribed flow that must be maintained locally by river support.

Geographical cline in breeding systems and ploidy levels in European populations of Daphnia pulex

Ninety populations of Daphnia pulex from sites throughout the UK and Scandinavia were assayed for genetic variation at 11 variable enzyme loci. A latitudinally-related cline in both breeding system and ploidy level was observed. Southern populations (latitudes 52–59°N) comprised only diploid cyclic parthenogens. Northern populations (latitudes 68–71°N) were dominated by polyploid obligate parthenogens and diploid cyclic parthenogens were absent. An assemblage of populations from a site of intermediate latitude (61°N) included both diploid cyclic parthenogens and diploid obligate parthenogens. This cline parallels one previously described from temperate to arctic North America. The obligately parthenogenetic (asexual) clones were generally heterozygous at one or more loci for a common D. pulex allele plus an allele not found in cyclically parthenogenetic (sexual) populations of D. pulex: it is argued that these asexual clones arose polyphyletically following several independent hybridizations between D. pulex and an unrecognized but closely related taxon. Fifteen different asexual clones were detected and 25 of 28 asexual populations were uniclonal: the mean number of asexual clones per population was 1.21.

Channel changes and invertebrate faunas below Nant‐Y‐Môch Dam, River Rheidol, Wales, UK: 35 Years On

River regulation initiates a succession of changes within lotic ecosystems driven by the adjustment of channel form to the imposed flow and sediment transport regimes. One typical sequence of channel changes involves channel adjustment to reduced flows. This temporal succession of channel changes is also found as a spatial sequence of channel forms, in different stages of adjustment during the relaxation period. This paper describes channel changes within a short reach of the River Rheidol, Wales, which was regulated in 1961. The ecological implications of channel change are assessed by examination of the benthic macroinvertebrate communities. Survey data from 1996 are compared with data from the early 1980s. A model of ecological change is presented comprising two main stages: (i) an accommodation phase, during which flows are accommodated within the pre-existing channel form and (ii) an adjusting phase, the period of channel change. Thirty-five years after dam closure, most of the River Rheidol is experiencing an accommodation response and changes of the macroinvertebrate community are related to stable flows and local siltation in the pre-regulation channel. Channel change is limited to a 200 m reach below a tributary confluence, i.e. below a sediment source. In terms of the number of taxa, more were found in the regulated river than in unregulated sites and the greatest number occurred in the short reach that was in a late stage of channel change.

Morphological and ecological change on a meander bend: the role of hydrological processes and the application of GIS

Environmental change induced by hydrological processes can often be quite small. This paper illustrates subtle changes in river planform on a single meander bend of the lower River Dee, Wales, and the significance of those changes for the ecology of the present riparian zone. Geographical information systems (GIS) are shown to provide an excellent framework for integrating historical and contemporary information from different sources, and for quantifying possible transcription errors so that true environmental associations and relatively small changes, in the context of the spatial scales of the sources, can be identified with confidence. As a result, functional units within the riparian zone of a regulated river can be defined and mapped.