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 dine 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 (6 1°N) included both diploid cyclic parthenogens and diploid obligate parthenogens. This dine 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.

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

1. Water abstraction from gladal rivers is an important characteristic of hydroelectric power schemes in Alpine regions. Streams in the Valais region of Switzerland have been particularly affected. 2. Invertebrate distributions are described in La Borgne d'Arolla, a gladal stream with icemelt-, snowmelt-and ground water-dominated tributaries. The icemelt-dominated streams have been affected by abstractions for more than 30 years. 3. The gladal streams contain only Chironomidae {Diamesa), and are devoid of fauna for between 200 and 500 m below the glader snouts. 4. Immediately below the water intakes the streams are intermittent, flowing only during system purges and high floods, and are devoid of fauna for short distances 5. Further downstream, abstraction of gladal meltwater increases the importance of snownmelt and groundwater, increasing water temperatures, improving water clarity and increasing the length of krenal/rhithral streams at the expense of kryal streams. 6. A community including Chironomidae, Simuliidae, Baetidae, Nemouridae, Limnephilidae and Chloroperlidae occurs as soon as a permanent flow is maintained by tributary runoff, and the channel becomes stable. 7. A wide range of taxa inhabit snowmelt-and groundwater-dominated tributary streams with stable channels, often at much higher altitudes than the main river. The tributaries provide sources for rapid colonization of the main channel following ice retreat or physical disturbance.

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 © 2000 John Wiley & Sons, Ltd.

The invertebrate communities and environmental characteristics of three English chalk streams; the rivers Wissey, Rhee and Pang, were investigated to determine the effects of groundwater abstraction. The data were collected as part of a larger study of 21 UK rivers subject to a variety of types of abstraction. A variety of analytical techniques, including a novel multivariate analysis (co-structure analysis), and the use of species profiles, showed significant physical and biotic differences between the three rivers and between impacted and natural sites on each river. The observed faunal differences are discussed in relation to existing data on the impact of natural droughts on chalk streams, and the problems associated with determining the effects of non-point source abstractions (such as from groundwater) are considered