Armin W. Lorenz

A New Method for Assessing the Impact of Hydromorphological Degradation on the Macroinvertebrate Fauna of Five German Stream Types

We developed a new Multimetric Index for stream assessment, which is mainly focussed on the impact of hydromorphological degradation on the macroinvertebrate fauna. The index was developed for five German stream types, three of which are located in the lowlands of Northern Germany and two in the lower mountainous areas. For each stream type sites representing different stages of hydromorphological degradation were investigated; the macroinvertebrate fauna of each site was sampled two or three times in 2000 (83 sites and 174 samples altogether). In addition, more than 200 parameters describing the hydromorphology of the sites have been recorded.

The impact of hydromorphological restoration on river ecological status: a comparison of fish, benthic invertebrates, and macrophytes

The European Water Framework Directive (WFD) has led to an increase in hydromorphological restoration attempts in European rivers, but data on the ecological responses of rivers to these restoration attempts are scarce. We investigated the effects of 24 hydromorphological river restoration projects in Germany. We compared hydromorphological parameters and biological diversity of macroinvertebrates, fish, and macrophytes in restored reaches to nearby unrestored sections. We applied, for the first time, the WFD to assess the results of these restoration projects. While hydromorphology changed significantly in the restored sections, differences between restored and unrestored sections in terms of biological parameters were lower. Positive restoration effects were observed for fish (11 of 24 cases) only. Based on the synthesis of results from the different organism groups, only one of the 24 restored sections reached a “good” Ecological Quality Class as demanded by the WFD. Our results indicate that stressors other than hydromorphological degradation still affect the biota in restored sections. We emphasize the need for advanced restoration strategies based on catchment analyses considering water pollution, source populations, and dispersal capacities of sensitive species, and recommend the inclusion of additional parameters, including societal and stakeholder perspectives, in assessing the initial success of restoration projects.

Vulnerable taxa of European Plecoptera (Insecta) in the context of climate change

We evaluated 516 species and/or subspecies of European stoneflies for vulnerability to climate change according to autoecological data. The variables considered were stream zonation preference, altitude preference, current preference, temperature range preference, endemism and rare species. Presence in ecoregions was used to analyse the vulnerability of taxa in relation to their distribution. We selected the variables that provided information on vulnerability to change in climate. Thus, we chose strictly crenal taxa, high-altitude taxa, rheobionts, cold stenotherm taxa, micro-endemic taxa and rare taxa. Our analysis showed that at least 324 taxa (62.79%) can be included in one or more categories of vulnerability to climate change. Of these, 43 taxa would be included in three or more vulnerability categories, representing the most threatened taxa. The most threatened species and the main factors affecting their distribution are discussed. Endangered potamal species, with populations that have decreased mainly as a consequence of habitat alteration, also could suffer from the effects of climate change. Thus, the total number of taxa at risk is particularly high. Not only are a great diversity of European stoneflies concentrated in the Alps, Pyrenees and Iberian Peninsula, but so are the most vulnerable taxa. These places are likely to be greatly affected by climate change according to climate models. In general, an impoverishment of European Plecoptera taxa will probably occur as a consequence of climate change, and only taxa with wide tolerance ranges will increase in abundance, resulting in lower overall faunal diversity.

Effects of sampling and sub-sampling variation using the STAR-AQEM sampling protocol on the precision of macroinvertebrate metrics

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 one-sixth 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.

Typology of streams in Germany based on benthic invertebrates: Ecoregions, zonation, geology and substrate

Abstract Based on 390 benthic invertebrate samples from near-natural streams in Germany we defined eight stream type groups by Non-metric multidimensional scaling (NMS). The taxa lists were restricted to Mollusca, Ephemeroptera, Odonata, Plecoptera, Coleoptera and Trichoptera species and evaluated on presence/absence level. At genus level, streams located in the lowlands differ from streams in lower mountainous areas and the Alps, while the two latter groups were undistinguishable. At species level, a clear separation of different stream size classes is visible in the lowlands; a second gradient is related to the bottom substrate. Streams in the Alps can be distinguished from streams in lower mountainous areas at species level. Within the lower mountainous regions a size gradient is detectable, a less obvious gradient indicates catchment geology. The resulting “bottom-up” stream typology is compared to other stream typological systems in Germany.

The AQEM/STAR taxalist — a pan-European macro-invertebrate ecological database and taxa inventory

The European list of aquatic macro-invertebrate taxa, and its associated ecological database, originated within the context of the AQEM project and have been extended during the STAR project. The AQEM/ STAR taxalist is a product of co-operation between applied freshwater ecologists and scientists from different zoological fields, applied partners and the administration. The basic idea is that a sound understanding of benthic invertebrate ecology is a prerequisite for the implementation of a biological approach to aquatic ecosystem management in Europe. The database has been generated under the management of BOKU (University of Natural Resources and Applied Life Sciences, Vienna) and UDE (University of Duisburg-Essen) and provides an important means of standardisation and unification of ecological classifications in Europe. This paper outlines the aims for setting up the AQEM/STAR macro-invertebrate taxalist and autecological database and provides a current summary of the numbers of aquatic orders, families, species, and species occurrences in 14 European countries. The number of available and applicable assignments of taxa to each ecological parameter is summarised and examples are given for different parameters and taxonomic groups. Gaps in the autecological information are identified and discussed. Besides its ecological relevance, the operational character of this database is underlined by the fact that it provides the associated taxon codes for each of five different European assessment systems for nearly 10,000 European macro-invertebrate taxa.

Re-Meandering German Lowland Streams: Qualitative and Quantitative Effects of Restoration Measures on Hydromorphology and Macroinvertebrates

We investigated the effects of two river restoration projects on hydromorphology and macroinvertebrate fauna in two German lowland rivers, the Schwalm and the Gartroper Mühlenbach. The stream channels were re-meandered and the floodplain levels were lowered to better connect the streams to their floodplains. The restoration was performed 10 years ago in the Schwalm and 2 years ago in the Gartroper Mühlenbach. We compared the restored reaches to nearby anthropogenically straightened reaches. Twenty-five hydromorphological parameters were recorded on twenty transects; between nine and 23 substrate-specific macroinvertebrate samples were taken per reach. Several hydromorphological parameters, such as the number and width of channel features and the number of substrate types, were significantly higher in the restored reaches compared to nearby anthropogenically straightened reaches. Total numbers of invertebrate families, genera, and taxa were also higher in the restored reaches than in the anthropogenically straightened reaches. Biotic substrates like dead wood or macrophytes were more abundant in the restored reaches, and these substrates hosted 28 taxa not found in the straightened reaches. While diversity was high in both restored reaches, overall abundance increased only in the river that was restored 10 years ago. Using NMS-analysis, substrate-specific faunistic samples of the restored reaches were compared to those of the straightened reaches. Our results revealed different invertebrate communities on the same substrates in the recently restored river. In the 10-year-old restoration, however, the same substrates were similarly inhabited. This comparable colonization of substrates may reflect succession in the macroinvertebrate community. The results are discussed according to the re-colonization potentials of the upstream and downstream reaches and the dispersal capacity of taxa.

‘Electronic subsampling’ of macrobenthic samples: how many individuals are needed for a valid assessment result?

We developed and tested an ‘electronic subsampling technique‘ with benthic invertebrate samples taken in three German stream types to investigate, how strongly the number of individuals analysed influences the results. For each of 152 samples (‘reference samples‘) 100 subsamples of the sizes 100, 200, 300, 500 and 700 individuals were generated randomly. To evaluate subsample deviation from the reference sample 45 metrics were calculated. In general, the variability of metric results increases with decreasing subsample size. Individual metrics show different sensitivity to decreasing subsample size. Three of the metrics tested (German Saprobic Index, German Fauna Index and Ecological Quality Index using Macroinvertebrates) are part of the German AQEM assessment system, for which they are transferred into quality classes. More than 40% of the 100-individuals subsamples are classified into a different quality class compared to the reference samples, but less than 20% for 700-individual subsamples. A certainty >20% is obtained with a subsample size of 300 individuals in lowland streams, whereas 700 individuals are needed to achieve the same level of confidence in mountain streams. Metrics, which rely on absolute abundances or abundance classes (e.g. BMWP, number of taxa) show higher sensitivity to a changing number of individuals than metrics, which depend on relative abundances (e.g. [%] Lithal preferences, [%] of Gatherers/collectors). Thus, the reliability of the metrics is related to subsample size, stream type and metric type.

Substrate-specific macroinvertebrate diversity patterns following stream restoration

Abstract.We examined the effects of stream restoration efforts that re-established multiple-channel sections in otherwise single-channel streams on aquatic habitat diversity and macroinvertebrate assemblages. At seven pairs of sites (single- vs. multiple-channel) we analysed the diversity of aquatic habitat parameters at various spatial scales (e.g. shore length, channel features, substrate diversity, flow variability). We also sampled macroinvertebrates in all available substrates individually and compared alpha- and beta-diversity and nestedness patterns on substrates between single- and multiple-channel sections. Multiple-channel sections showed a considerably more diverse hydromorphology. Taxa number, abundance, and evenness of macroinvertebrate assemblages did not differ significantly. Ten Coleoptera and seven Trichoptera taxa were present exclusively in multiple-channel sections on loam, sand, living parts of terrestrial plants (LPTP), coarse particulate organic matter (CPOM) or large wood. Non-metric Multidimensional Scaling showed that macroinvertebrate assemblages were substrate-specific rather than section-specific. Nestedness did not differ for samples from single- and multiple-channel sections, nor for individual substrates from different sections. We did not observe differences in alpha-diversity from substrates at single- and multiple-channel sections. However, different substrates host different assemblages and the increased substrate diversity in multiple-channel sections might result in higher beta-diversity in these sections. Our results indicate that stream restoration projects aimed at redeveloping near-natural macroinvertebrate diversity should focus on generating several long multiple-channel stretches with large areas of high quality habitats (e.g. large wood), creating stepping stone habitats for re-colonisation, and should allow sufficient time for new assemblages to establish.

Contrasting the roles of section length and instream habitat enhancement for river restoration success: a field study of 20 European restoration projects

Restoration of river hydromorphology often has limited detected effects on river biota. One frequently discussed reason is that the restored river length is insufficient to allow populations to develop and give the room for geomorphological processes to occur. We investigated ten pairs of restored river sections of which one was a large project involving a long, intensively restored river section and one represented a smaller restoration effort. The restoration effect was quantified by comparing each restored river section to an upstream non-restored section. We sampled the following response variables: habitat composition in the river and its floodplain, three aquatic organism groups (aquatic macrophytes, benthic invertebrates and fish), two floodplain-inhabiting organism groups (floodplain vegetation, ground beetles), as well as food web composition and land-water interactions reflected by stable isotopes. For each response variable, we compared the difference in dissimilarity of the restored and nearby non-restored section between the larger and the smaller restoration projects. In a second step, we regrouped the pairs and compared restored sections with large changes in substrate composition to those with small changes. When comparing all restored to all non-restored sections, ground beetles were most strongly responding to restoration, followed by fish, floodplain vegetation, benthic invertebrates and aquatic macrophytes. Aquatic habitats and stable isotope signatures responded less strongly. When grouping the restored sections by project size, there was no difference in the response to restoration between the projects targeting long and short river sections with regard to any of the measured response variables except nitrogen isotopic composition. In contrast, when grouping the restored sections by substrate composition, the responses of fish, benthic invertebrates, aquatic macrophytes, floodplain vegetation and nitrogen isotopic composition were greater in sections with larger changes in substrate composition as compared to those with smaller changes. Synthesis and applications. The effects of hydromorphological restoration measures on aquatic and floodplain biota strongly depend on the creation of habitat for aquatic organisms, which were limited or not present prior to restoration. These positive effects on habitats are not necessarily related to the restored river length. Therefore, we recommend a focus on habitat enhancement in river restoration projects. The effects of hydromorphological restoration measures on aquatic and floodplain biota strongly depend on the creation of habitat for aquatic organisms, which were limited or not present prior to restoration. These positive effects on habitats are not necessarily related to the restored river length. Therefore, we recommend a focus on habitat enhancement in river restoration projects.