R.J.M. Gunn

The use of prediction to assess macroinvertebrate response to river regulation

A technique, which uses environmental data to predict the macroinvertebrate fauna of running water sites, was used to investigate the response of faunal communities to flow regulation below a set of upland reservoirs in Great Britain. Five variables (total oxidised nitrogen, alkalinity, chloride, substratum type and site distance from stream source) were used to predict family presence and abundance at 30 regulated sites. The predictions were compared with the observed fauna recorded in samples taking in spring, summer and autumn. Of the 37 commonly occurring families 22 showed statistically significant trends. Twelve of these occurred at lower abundances than predicted and the effect was greatest in Heptageniidae, Simuliidae, Elminthidae, Perlodidae and Rhyacophilidae. Ten families were more more abundant than predicted and these included Polycentropodidae, Sphaeriidae, Sialidae and some groups of chironomids and oligochaetes. Fifteen families showed no significant trends. Most families showed little difference in the observed and expected frequency of occurrence in the 30 sites but Taeniopterygidae and Perlidae amongst others occurred at less than the expected number of sites and Hydridae, Prodiamesinae and Muscidae occurred more commonly than expected. These faunal responses are discussed in relation to environmental changes arising from flow regulation. The possible uses of the predictive technique in simulating and assessing the effects of regulation on downstream fauna are outlined.

Assessing the impact of errors in sorting and identifying macroinvertebrate samples

This study assesses the impact of errors in sorting and identifying macroinvertebrate samples collected and analysed using different protocols (e.g. STAR-AQEM, RIVPACS). The study is based on the auditing scheme implemented in the EU-funded project STAR and presents the first attempt at analysing the audit data. Data from 10 participating countries are analysed with regard to the impact of sorting and identification errors. These differences are measured in the form of gains and losses at each level of audit for 120 samples. Based on gains and losses to the primary results, qualitative binary taxa lists were deducted for each level of audit for a subset of 72 data sets. Between these taxa lists the taxonomic similarity and the impact of differences on selected metrics common to stream assessment were analysed. The results of our study indicate that in all methods used, a considerable amount of sorting and identification error could be detected. This total impact is reflected in most functional metrics. In some metrics indicative of taxonomic richness, the total impact of differences is not directly reflected in differences in metric scores. The results stress the importance of implementing quality control mechanisms in macroinvertebrate assessment schemes.

The biology of Brachycentrus subnubilus Curtis (Trichoptera) in the River Frome, Dorset

Aspects of life-history, oviposition and microdistribution within beds of Ranunculus penicillatus var. calcareus (R. W. Butcher) C.D.K. Cook are considered. Brachycentrus subnubilus Curtis has one generation each year, with five larval instars. Larvae favour sites beneath the weedbeds for most of the year, migrating to more exposed areas in the spring to pupate. Pupation, emergence, oviposition and eclosion are completed in just over two months. Eggs are usually laid on submerged marginal vegetation but any semi-submerged object may be utilized. Larvae appear to disperse mainly as first instars; in this they are likely to be seriously affected by weedcutting activities. Initial development is rapid to fourth instar. Larvae overwinter as fifth instars. Sex ratios show a predominance of males.