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.

SUMMARY 1. Temporal changes in a series of habitats and their macroinvertebrate assemblages were examined on a 50‐m section of a chalk stream in Berkshire, England between June 1975–79 and June 1997–2001. 2. The site was part of a trout fishery in 1975–79, when river management included instream weed cutting together with control of bankside trees and riparian vegetation. Management ceased in the 1980s and by 1997–2001, the site was heavily shaded by trees and riparian vegetation. 3. The mean area of instream macrophytes decreased by 50% between the first and second sampling period. In contrast, gravel and silt increased and invading marginal vegetation formed a new habitat. 4. Changes in macroinvertebrate family richness between sampling periods were scale dependant. Although there were, on average, significantly more families in individual replicates in 1975–79 than in 1997–2001, total family richness for the site in each year did not differ significantly between sampling periods. 5. Sixty families of macroinvertebrates were recorded during the study, 50 in both sampling periods, 53 in 1975–79 and 57 in 1997–2001. This small increase in site family richness may be due to the invading marginal plants. 6. Total macroinvertebrate abundance was significantly lower in the second sampling period. A major drought in 1976 resulted in significantly higher densities of macroinvertebrates, partly through the exploitation of epiphytic diatoms by chironomid larvae. A drought in 1997 failed to elicit a similar response because of the limited macrophytes and diatoms under heavy shading by trees and marginal vegetation. 7. Significant increases in important shredders and decreases in some scrapers between the early and later sampling years largely reflected changes in available food resources. 8. Whereas macroinvertebrate family richness has been conserved under the recent ‘no management’ regime, the site is now less attractive as a fishery because of poor access and lower densities of some macroinvertebrates taken by brown trout.

Management and restoration procedures in rivers frequently have a major influence on the bank and marginal zone, depending on the timing of disturbance and the eventual structure of the bank. This study examines changes in macroinvertebrate communities in four different bank types at 3-weekly intervals throughout a year. The banks differed in their profile and in their structure: shallow sloping and vegetated, stepped shallow profile, steep profile (eroded soil bank), and iron revetments. Velocity patterns over the year showed much variability, both between and within bank types ranging from standing water in the summer to velocities in excess of 0.9 m s − 1 in the winter. The shallow-sloping vegetated site supported a total of 115 taxa, in contrast to the artificial iron revetment, on which only 32 taxa were recorded. Total abundances were five to six times greater in the shallow vegetated sites compared with the steeply sloped and artificial banks. Highest abundances were recorded in the late spring (May/June) and most taxa were found in August and September. Fluctuations in both abundance and number of taxa were least on the reveted bank. Ordination of the fauna/site matrix revealed a seasonal separation with specific winter and summer communities. The results suggest that the bankside is a dynamic environment where communities change in relation to growth of bankside vegetation and its concomitant effect on flow. The implications of these findings to management activities and restoration procedures are discussed.

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As part of the extensive field sampling programme within the European Union STAR project, replicate macroinvertebrate samples were taken using the STAR-AQEM sampling method at each of 2-13 sites of varying ecological quality within each of 15 stream types spread over 12 countries throughout Europe. The STAR-AQEM method requires the sub-sampling and taxonomic identification of at least onesixth of the sample and at least 700 individuals. Replicate sub-samples were also taken at most of these sites. Sub-sampling effects caused more than 50% of the overall variance between replicate samples values for 12 of the 27 macroinvertebrate metrics analysed and was generally greatest for metrics that depend on the number of taxa present. The sampling precision of each metric was estimated by the overall replicate sampling variance as a percentage P samp of the total variance in metric values within a stream type. Average over all stream types, the three Saprobic indices had the lowest percentage sampling variances with median values of only 3-6%. Most of the metrics had typical replicate sampling variances of 8-18% of the total variability within a stream type; this gives rise to estimated rates of mis-classifying sites to ecological status class of between 22 and 55% with an average of about 40%. This suggests that the precision of such metrics based on the STAR-AQEM method is only sufficient to indicate gross changes in the ecological status of sites, but there will be considerable uncertainty in the assignment of sites to adjacent status classes. These estimates can be used to provide information on the effects of STAR-AQEM sampling variation on the expected uncertainty in multi-metric assessments of the ecological status of sites in the same or similar stream types, where only one sample has been taken at a point in time and thus there is no replication.

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