Patrick D. Armitage

The performance of a new biological water quality score system based on macroinvertebrates over a wide range of unpolluted running-water sites

Abstract The occurrence of families of macroinvertebrates has recently been used as the basis for the BMWP (Biological Monitoring Working Party) system of assigning scores to lotic sites. In this study the performance of the system across 268 sites on 41 rivers providing a wide range of physical and chemical features has been appraised. Changes in score and ASPT (average score per taxon) with respect to season and sampling effort have been examined. Seasonal variations were relatively slight and it is concluded that samples taken in any of the three seasons, spring, summer or autumn, were likely to provide consistent estimates of score and particularly ASPT. Sample replication led to substantial accretion of scores but had little effect on ASPT and therefore more information was obtained for less effort when ASPT was used. Data are presented on score and ASPT values for 8 groups of sites derived by multivariate classificatory techniques. Considerable variability in achievable score and ASPT was observed in the different groups of unpolluted sites. In general, scores were highest in the group at the middle of the range of environmental features and lowest in groups at the bottom of the range (lowland areas). ASPT in contrast showed a relatively steady decline in values between groups at the top (mainly upland rivers) and bottom of the range of environmental features. Attempts were made to predict score and ASPT from physical and chemical data, or physical data alone using multiple regression. Equations used to predict ASPT explained on average a higher proportion of the variance (65%) than those predicting scores (22%). It is suggested that predictive equations for ASPT will enable theoretical ASPT to be calculated, thus providing target values against which observed values can be compared. Recommendations to facilitate use and interpretation of the BMWP score system are presented.

Species assemblages as descriptors of mesohabitats

Eight mesohabitats, visually distinct units of habitat withinthestream, were sampled seasonally in a lowland chalkstreamreach. Theaim of the study was to test if mesohabitats defined asstructuralunits were inhabited by particular species assemblages and howthese varied with season. Classification (Bray-Curtisdissimilarityindex and UPGMA) and ordination analyses (DCA) of thedistributionof 258 species in 230 samples, were first used to check theagreement between the subjectively-selected mesohabitat andtheirassociated faunal assemblages. There was a goodcorrespondence, andmesohabitat samples were grouped into 5 major groups (Ranunculusin spring, silt, sand, gravel and macrophytes)whichwere further sub-divided to give a total of 11 groups whenseasonaldifferences were considered. Spearman rank correlation betweenthespatial distribution of mesohabitat groups with environmentalvariables revealed that water velocity and flow dynamicstogetherwith the nature of the substratum, influenced the distributionofthe benthic communities. To evaluate qualitative andquantitativedifferences in taxa composition among mesohabitats,informationstatistics tests and analyses of variance were used incombinationwith the Tukey honestly significant difference test. The 11groupswere characterised by abundance and frequency indicatorspecies.Inverse analysis of dominant species of the community showed agoodequivalence with mesohabitat groups and their indicatorspeciesobtained by direct analysis. The resulting species assemblagesrepresent faunal adaptation to the particular mesohabitats inrelation to natural environmental fluctuations. Themesohabitatscale provides a convenient structural ecological unit toexaminethe functional dynamics of faunal communities inrivers.

Sediment deposition in a small lowland stream—management implications

Fine sediment deposition is a widespread phenomenon encountered in rivers and streams as a result of both natural and anthropogenic activities. The Little Stour (Kent, UK) has a history of low-flow problems owing to drought and groundwater abstraction. Fine sediment deposits were mapped at two sites on the falling limb of the hydrograph at monthly intervals between May and September, 1995. The sampling period coincided with one of the driest periods in England since records began in the 17th century. The area of the channel bed covered by fine sediments increased from approximately 10 to 20% at the upstream site and from 20 to 40% at the downstream site during the study period. The benthic macroinvertebrate communities from different substrate mesohabitats were distinct, with riffle taxa (i.e. Agapetus fuscipes and Simuliidae) confined to areas of clean gravel. This suggests that an expansion of fine sediment deposits may result in impoverishment of the community. The implications of these findings are discussed with particular reference to the timing of management activities within lowland streams. Copyright

An appraisal of pond-net samples for biological monitoring of lotic macro-invertebrates☆

Abstract The use of a pond-net to sample benthic macro-invertebrates is assessed as a technique for use in a national classification scheme for running water sites. In a field trial, 6 pond-net samples of 3 min duration were taken at each of 4 sites on the River Axe in south-west England. Three different people each took 2 samples at each of the sites. A comparison of the number of families and species caught indicated significant differences with respect to sites, operators and site x operator interactions. Significant inter-operator differences in the number of taxa removed from samples were also shown at the sample processing stage, but only at family level. Despite these differences, clustering and ordination procedures showed strong site faithfulness for each series of 6 samples when data were analysed at species level. Similar analyses at family level produced several misclassifications of samples with those from other sites. Most of these misclassifications were eliminated when categories of abundance were applied to the family level data. A 3 min sample collected approx. 62% of families and 50% of species that could be attained at a site by 18 min netting. The results of this field trial provided justification for the use of a pond-net as the principal sampling technique in the classification exercise.

The effects of mine drainage and organic enrichment on benthos in the river nent system, Northern Pennines

A preliminary survey of the benthic fauna of sites on the Nent system affected by elevated zinc levels, acid water and organic enrichment is described. Data on faunal composition are presented for 17 sites. A clustering technique was applied to the taxa/site matrix to demonstrate the degree of association between sites varying in zinc concentration. Chandler biotic scores were found to be lowest at sites affected by high zinc levels and/or dense growths of the alga Stigeoclonium tenue. The role of elevated zinc levels and algal growth in determining the diversity and abundance of benthos is discussed.

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.

The response of perennial and temporary headwater stream invertebrate communities to hydrological extremes

The headwaters of karst rivers experience considerable hydrological variability, including spates and streambed drying. Extreme summer flooding on the River Lathkill (Derbyshire, UK) provided the opportunity to examine the invertebrate community response to unseasonal spate flows, flow recession and, at temporary sites, streambed drying. Invertebrates were sampled at sites with differing flow permanence regimes during and after the spates. Following streambed drying at temporary sites, dewatered surface sediments were investigated as a refugium for aquatic invertebrates. Experimental rehydration of these dewatered sediments was conducted to promote development of desiccation-tolerant life stages. At perennial sites, spate flows reduced invertebrate abundance and diversity, whilst at temporary sites, flow reactivation facilitated rapid colonisation of the surface channel by a limited number of invertebrate taxa. Following streambed drying, 38 taxa were recorded from the dewatered and rehydrated sediments, with Oligochaeta being the most abundant taxon and Chironomidae (Diptera) the most diverse. Experimental rehydration of dewatered sediments revealed the presence of additional taxa, including Stenophylax sp. (Trichoptera: Limnephilidae) and Nemoura sp. (Plecoptera: Nemouridae). The influence of flow permanence on invertebrate community composition was apparent despite the aseasonal high-magnitude flood events. Flow permanence was also critical in determining the community response to the spate flows. Following streambed drying at temporary sites, the surficial sediments overlying the karstic bedrock functioned as an effective refugium for several taxa. The development of aquatic insects following experimental rehydration indicated that these taxa survived in dewatered sediments as desiccation-resistant eggs.

The response of four lotic macroinvertebrate taxa to burial by sediments

Sedimentation is widely acknowledged as a major.cause of-degradation of instream habitats. However, macroinvertebrate burial by sediment has been poorly studied. Ex situ experiments were undertaken to examine the response of four common and abundant macroinvertebrate taxa (Baetis rhodani, Nemoura cambrica, Hydropsyche pellucidula, and Asellus aquaticus) to burial by six sediment size classes (range = 125 μm - 10mm in size) and two depths of burial (5 mm and 10mm). The nymphs of the ephemeropteran, Baetis rhodani, were unable to excavate themselves from any of the sediments. In contrast, the plecopteran nymphs of Nemoura cambrica were able to excavate themselves from all sediment classes and burial depths. Adults of the isopod, Asellus aquaticus, were able to excavate themselves rapidly from finer sediment classes ( 1 mm in size and became trapped in coarser sediments (>4 mm in size at 5 mm burial depth and > 2 mm at 10mm burial depth). The larvae of the trichopteran, Hydropsyche pellucidula, were able to excavate their heads from all sediment classes and both burial depths, but became trapped in particles <500 μm in size when buried under 10 mm of sediment. The results demonstrate that the response of individual taxa to burial with sediments is highly variable. Consequently, many of the documented changes to benthic macroinvertebrate community composition due to sedimentation probably mask a variety of individual faunal responses.

The response of the macroinvertebrate community to low-flow variability and supra-seasonal drought within a groundwater dominated stream

Information regarding the instream response to long supra-seasonal droughts, extending over more than one season, in largely perennial riverine systems is fragmentary compared to knowledge regarding floods. The macroinvertebrate community of a groundwater dominated river was investigated over an eight-year period which included two supra-seasonal drought events (1992 and 1996-1997). The community responded directly to changes in the discharge regime. Significant differences in the community abundance, the abundance of the amphipod Gammarus pulex, diversity indices (Shannon Wiener and Simpson diversity) and the Berger-Parker dominance index were recorded between drought, flow recovery and other (non-drought) years. Drought conditions resulted in extremely low community abundance, Gammarus pulex abundance and the Berger-Parker dominance index, and extremely high values of the Shannon Wiener and Simpson diversity indices. Recovery of the community extended over a two-year period and reflected recovery of flow associated with recharge of the groundwater aquifer. The results underline the continuing need for medium to long-term data series to investigate the response of instream communities to flow variability so that extreme events can be placed within the context of natural variability.

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