John Davy-Bowker

European river plant communities: the importance of organic pollution and the usefulness of existing macrophyte metrics

The macrophyte surveys undertaken as part of the EU-funded STAR project are a unique resource allowing aquatic plant communities to be studied at a Pan-European scale (211 stream sites with macrophytes in 14 countries). Using this dataset, we examined the influence of organic pollution in relation to other environmental correlates of river plant community variation across Europe. We examined the relationships between several existing macrophyte metrics and nutrient enrichment, and we also explored the possibility of developing a pan-European macrophyte-based assessment system. We showed that trophic (nutrient) status is an important driver of aquatic plant communities in European rivers. We found that while most existing macrophyte metrics are useful, none can be applied at a pan-European scale in their current form. Our attempt to redesign the Mean Trophic Rank (MTR) index by the addition of further species, and the re-scoring of existing species, resulted in a considerable improvement in the relationship between MTR scores and nutrient variables. We conclude that an enlarged core group of macrophyte species can form part of an improved pan-European macrophyte-based bioassessment system, although regional modifications may be required to adequately describe the nutrient status of certain stream types.

The development and testing of a macroinvertebrate biotic index for detecting the impact of acidity on streams

A new macroinvertebrate biotic index for assessing the impact of acidity on streams and rivers in England and Wales is presented, the Acid Waters Indicator Community index (AWIC). Using a 1042 sample training dataset, the AWIC index was derived by firstly using canonical correspondence analysis (CCA) to identify independent physical variables that best accounted for the observed macroinvertebrate communities. Secondly, partial CCA was used to factor out the confounding influence of physical variables other than mean pH. Thirdly, the ranking of taxa along the first axis of the pCCA (strongly correlated with mean pH) was the basis for assignment of index scores. Ephemeridae and Physidae were among the most acid sensitive taxa (AWIC score of 6), while Chloroperlidae and Nemouridae were the most tolerant of low pH conditions (AWIC score of 1). Within the training dataset, AWIC was strongly correlated with mean pH (r s = 0.814, P <0.001). Testing on an independent dataset of 2710 samples, AWIC was also more effective at discriminating between samples of differing mean pH and gave rise to fewer Type I errors (false positives) than an existing biotic index derived by a classification approach. Our analysis suggests that at family level, macroinvertebrate communities are not characterised by a specific obligate acid-waters assemblage so that while most acidic sites primarily support families that are acid tolerant, these families are also commonly found in circum-neutral waters. The AWIC index distinguishes acid sites by the absence of any of a large number of acid sensitive families, any of which can shift the overall AWIC index towards one indicative of higher pH. The AWIC index should compliment existing family and species level acidity indices and should be of use to regulatory authorities charged with assessing the biological consequences of acidity in streams and rivers.

A comparison of the European Water Framework Directive physical typology and RIVPACS-type models as alternative methods of establishing reference conditions for benthic macroinvertebrates

The EU Water Framework Directive requires European Union Member States to establish ‘type-specific biological reference conditions’ for streams and rivers. Types can be defined by using either a fixed typology (System-A), defined by ecoregions and categories of altitude, catchment area and geology, or by means of an alternative characterisation (System-B) that can use a variety of physical and chemical factors. Several European countries also have existing RIVPACS-type models that give site (rather than stream type) specific predictions of benthic macroinvertebrate communities. In this paper we compare the Water Framework Directive (WFD) System-A physical typology and three existing European multivariate RIVPACS-type models as alternative methods of establishing reference conditions. This work is carried out in Great Britain – using RIVPACS, Sweden – using SWEPACSRI and the Czech Republic – using PERLA. We found that in all three countries, all seasons and season combinations, and for all biotic indices tested, RIVPACS-type models were more effective (lower standard deviations of O/E ratios) than models based solely on the WFD System-A variables or null models (based on a single expectation for all sites). We also investigated the explanatory power of whole groups of WFD System-A variables and RIVPACS-type model variables, and the explanatory power of individual variables. We found that variables used in the RIVPACS-type models were often better correlates of macroinvertebrate community variation than the WFD System-A variables. We conclude that this is primarily because while the latter use very broad categories of map-derived variables, the former are based on continuous variables selected for their ecological significance.

Spatial structure in lotic macroinvertebrate communities in England and Wales: relationship with physical, chemical and anthropogenic stress variables

We describe the relationship between macroinvertebrate community composition, the physicochemical environment and anthropogenic impacts, in running water sites across a range of water qualities in England and Wales. We have also investigated the degree of spatial structure present in both the macroinvertebrate community and the measured environment. Selected explanatory variables could account for 26% of the variation in lotic macroinvertebrate assemblage composition across England and Wales. The explanatory power of the CCA model was based predominantly on a combination of local scale variables (substrate, alkalinity, urban run-off) and regional scale variables (discharge category, northing). The physicochemical gradient associated with changes in stream type from headwaters to estuary dominated assemblage composition. The influence of pollution and habitat modification were of secondary importance. There was a substantial level of spatial structure to both the physicochemical (47% of its explanatory power spatially structured) and anthropogenic stress data (63% of its explanatory power spatially structured), which resulted in a high level of predictable spatial structuring in macroinvertebrate assemblages. Almost 40% of the variation in assemblage composition accounted for by the explanatory model exhibited spatial structure. Positive spatial autocorrelation in macroinvertebrate community composition extended to sites up to 150km apart. As a consequence, community composition could be described from northing and easting with 75% of the explanatory power of the eight physicochemical variables. Our study has confirmed the importance of the longitudinal gradient within catchments, as well as the geographical position of the catchment to macroinvertebrate communities. We have also demonstrated how quantifying the spatial structure in the dataset can improve our understanding of the factors influencing macroinvertebrate community structure.

Occurrence and variability of River Habitat Survey features across Europe and the consequences for data collection and evaluation

River Habitat Survey (RHS) data collected for the EU-funded STAR project was used to identify hydromorphological characteristic features of rivers in four European regions namely: lowlands; mountain; the Alps; and the Mediterranean. Using RHS attributes, Habitat Quality Assessment (HQA) – a measure of natural habitat diversity, and Habitat Modification Score (HMS) – a measure of anthropogenic modification, we identified considerable differences in frequency, diversity and evenness of features between the regions. A relatively small subset of features clearly distinguish the hydromorphological characters of lowland, Alpine and southern European rivers. It was more difficult to distinguish mountain rivers from Alpine rivers. The highest statistical differences are observed between Lowland and Mountain region. Within the four regions studied the RHS attributes that most strongly influence the HQA and HMS indices were identified. We conclude that specific effort should be made to ensure these are recorded properly as part of the quality control of RHS data.

Estimates and comparisons of the effects of sampling variation using ‘national’ macroinvertebrate sampling protocols on the precision of metrics used to assess ecological status

The Water Framework Directive (WFD) of the European Union requires all member countries to provide information on the level of confidence and precision of results in their river monitoring programmes to assess the ecological status class of river sites. As part of the European Union project STAR, the overall effects of sampling variation for a wide range of commonly used metrics and sampling methods were assessed. Replicate samples were taken in each of two seasons at 2-6 sites of varying ecological status class within each of 18 stream types spread over 12 countries, using both the STAR-AQEM method and a national sampling method or, where unavailable, the RIVPACS sampling protocol. The sampling precision of a combination of sampling method and metric was estimated by expressing the replicate sampling variance as a percentage P samp of the total variance in metric values with a stream type; low values of Psamp indicate high precision. Most metrics had percentage sampling variances less than 20% for all or most stream types and methods. Most national methods including RIVPACS had sampling precisions at least as good as those for the STAR-AQEM method as used in their country at the same sites; the main exceptions were the national methods used in Latvia and Sweden. The national methods used in the Czech Republic, Denmark, France, Poland and the RIVPACS method used in the UK and Austria all had percentage sampling variances of less than 10% for the majority of metrics assessed. In contrast, none of the metrics had percentage sampling variances less than 10% when based on either the Italian (IBE) method, which used bank-side sorting, or the Latvian national method which identifies only a limited set of taxa. P samp was lowest on average for the two stream types sampled in the Czech Republic using either the PERLA national method or the STAR-AQEM method. Averaged over all stream types and methods, the three Saprobicbased metrics had the lowest average percentage sampling variances (3–6%) amongst the 26 metrics assessed. These estimates of sampling standard deviation can be used to help assess the uncertainty in single or multi-metric systems for estimating site ecological status using the general STAR Bioassessment Guidance Software (STARBUGS) developed within the STAR project.

Hydromorphology — major results and conclusions from the STAR project

The major results and conclusions of the two papers in the hydromorphology section of the Hydrobiologia special issue on the EU STAR project are summarised. Several key findings have emerged from this research. Firstly, the hydromorphological characteristics of rivers between different geographical regions of Europe were found to vary considerably with rivers in each region possessing distinctive hydromorphological characteristics. Secondly, the hydromorphological attributes that most strongly influence two existing hydromorphological indices (the Habitat Quality Assessment and the Habitat Modification Score) were identified and attention was drawn to the accurate definition and recording of these attributes in field surveys and training courses. Thirdly, links between hydromorphological characteristics and macroinvertebrate quality indices were investigated. Two types of bank modification (resectioning and reinforcement) were significantly correlated with two biotic indices (EPT taxa and MTS), while channel modifications were negatively correlated with ASPT. While biotic indices were often strongly correlated with Habitat Quality Assessment they were less strongly related to Habitat Modification Score suggesting that physical habitat diversity may be more important in determining macroinvertebrate community structure than morphological alteration. The papers in this section provide important underpinning research for the implementation of the European Water Framework Directive. In both papers suggestions are made for further research on the hydromorphology of European rivers.

Ecology of Industrial Pollution: Ecological monitoring and assessment of pollution in rivers

Introduction Many organisms respond to pollution in a predictable way, and it has long been realised that the biota can be used to determine the extent of pollution at a site, a technique termed biomonitoring. Much of the science of biomonitoring developed in aquatic systems, driven by concerns about the impact of industrial and domestic pollution on potable water resources. Over the past century, aquatic biomonitoring has travelled a long way from the early methodologies, and much about the pitfalls and benefits of using biota to assess pollution or other stressors has been discovered. Here we describe the history of biomonitoring and how our understanding has developed, with particular focus on RIVPACS (River InVertebrate Prediction And Classification System). This system marked a major advance in biomonitoring techniques, introducing the reference condition approach, where the physical and geographical characteristics of the river were taken into account when determining what taxa would be expected to be present if the site were not polluted. Assessment of a site was then based on a comparison of the observed community and derived scores, to that expected if the site were not polluted. RIVPACS was also the first biomonitoring tool to incorporate a measure of uncertainty; any assessment is based on spatially and temporally variable samples and it is necessary to calculate the confidence associated with the quality class derived using these samples.

Field testing the AWIC index for detecting acidification in British streams

Using data from 132 acid-sensitive streams in Wales and Scotland from two available data sets, we tested a recently proposed indicator system that uses aquatic invertebrates to detect acidification in British rivers, the Acid Water Indicator Community (AWIC). Although many sites held less than a quarter of AWIC scoring taxa, index values at sites in both data sets correlated significantly with acid-base variables including pH, calcium concentration, alkalinity and dissolved aluminium. Relationships with acid-base status during acid episodes were particularly strong in the more comprehensive test set. Strong correlations between the AWIC index and pH in a subset of sites from Scotland indicated potential for some extrapolation beyond the initial calibration regions of England and Wales. Despite considerable pH variability within AWIC classes, measured base-flow pH was within 0.5 pH units of values expected from invertebrates at over 55-70 % of test sites, and within 1 pH unit at 87-100 %. This compares favourably with direct pH measurement, where samples at fortnightly-monthly intervals are typically required to confidently estimate mean pH within 0.7-1.2 pH units. These data, drawn from a realistic application, illustrate the potential accuracy and integrating value of invertebrate bioassessment in acid-sensitive waters. Further developments should involve more specific identification and targeted calibration to i) improve discrimination between sensitive streams of contrasting acidity; ii) further improve the accuracy of pH determination based on invertebrates; iii) avoid the apparent over-estimation of pH in the lower AWIC classes; iv) clearly differentiate between acid-sensitive and acidified streams.