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1. Previous studies investigating community-level relationships between plant functional trait characteristics and stream environmental characteristics remain scarce. Here, we used community-weighted means to identify how plant traits link to lowland stream typology and how agricultural intensity in the catchment affects trait composition. 2. We analysed plant trait characteristics in 772 European lowland streams to test the following two hypotheses: (i) trait characteristics differ between plant communities in small and medium-sized streams, reflecting adaptations to different habitat characteristics, and (ii) trait characteristics vary with the intensity of agricultural land use in the stream catchment, mediated either directly by an increase in productive species or indirectly by an increase in species that efficiently intercept and utilize light. 3. We found that the communities in small streams were characterized by a higher abundance of light-demanding species growing from single apical meristems, reproducing by seeds and rooted to the bottom with floating and/or heterophyllous leaves, whereas the community in medium-sized streams was characterized by a higher abundance of productive species growing from multi-apical and basal growth meristems forming large canopies. 4. We also found indications that community trait characteristics were affected by eutrophication. We did not find enhanced abundance of productive species with an increasing proportion of agriculture in the catchments. Instead, we found an increase in the abundance of species growing from apical and multi-apical growth meristems as well as in the abundance of species tolerant of low light availability. The increase in the abundance of species possessing these traits likely reflects different strategies to obtain greater efficiency in light interception and utilization in nutrient-enriched environments. 5. Synthesis and applications. Our findings challenge the general assumption of the EU Water Framework Directive compliant assessment systems that plant community patterns in streams reflect the nutrient preference of the community. Instead, light availability and the ability to improve interception and utilization appeared to be of key importance for community composition in agricultural lowland streams. We therefore suggest moving from existing approaches building on species-specific preference values for nutrients to determine the level of nutrient impairment to trait-based approaches that provide insight into the biological mechanisms underlying the changes. We recommend that existing systems are critically appraised in the context of the findings of this study. [ABSTRACT FROM AUTHOR]

Abstract: Restorations have been conducted in Danish lowland streams for almost 30 years to combat the poor physical conditions resulting from decades of channelisation, flood plain drainage and other impacts. Despite this effort, the recently drafted River Basin Management Plans show that physical improvements are still required in more than 7000km of stream in order to comply with the Water Framework Directive. In this study we used published studies and expert knowledge to describe the restoration approaches most likely to achieve the environmental goals. In addition, we collected information about the economic costs of the different restoration approaches based on Danish experiences. For heavily impacted lowland streams (channelised and deeply incised streams) we described only two different restoration methods, both of which are relatively expensive. For lesser impacted streams (channelised but not deeply incised streams) we described six different options for improving ecological quality, varying significantly in cost. Our analysis showed that the cost may increase dramatically if several remedial actions are required or if land owners are entitled to large monetary compensations. Consequently, stream managers face an important challenge in the future prioritisation of restoration efforts aimed to obtain ecological improvements within tight budgets. The information presented in this paper can help the decision-making of managers. [Copyright &y& Elsevier]

1. The articles in this Special Issue on pressure-response relationships in stream ecology cover a range of pressures including acidification, excess loading of metals, nutrients and organic matter to stream ecosystems and changes in riparian and catchment land use. Impacts on the biota (macroinvertebrates), ranging from single species to community responses, are addressed over a multitude of spatial scales using large data sets. 2. The majority of articles are based on monitoring data compiled as part of the EU-funded project REBECCA, but the Special Issue also includes articles from outside Europe (US and New Zealand) as well of studies using other data sources. 3. Results from the six articles gave new insights of relevance to water managers and documented that large-scale monitoring can be an asset to freshwater science. The large data sets enable a range of analytical approaches that single out important patterns in highly variable data.: importance of humic substances in reducing the negative impact of low pH; impact of very low levels of BOD (<2 mg L−1); higher sensitivity of trait-based metrics compared with identity-based metrics and importance of catchment and riparian vegetation for the ecological quality of streams. 3. We advocate an increased use of monitoring and survey data in addressing questions relevant to scientist and end-users, but issues relating to especially data quality should be considered. In future, the use of these data could increase knowledge exchange between the scientific community and managers with the ultimate aim of improving our freshwater resources. [ABSTRACT FROM AUTHOR]

An extensive amount of literature on linkages between the in-stream physical environment and river benthic macroinvertebrates reports a number of relationships across multiple spatial scales. We analyzed data on different spatial scales to elucidate the linkages between different measurements of hydromorphological degradation and commonly used macroinvertebrate indices. A regression analysis of 1049 sites from 3 countries revealed that the strongest relationship between a biotic metric-average score per taxon-and physiochemical variables ( R = 0.61) was obtained with a multiple regression model that included concentration of total phosphorus and percent arable land in the catchment, as well as hydromorphological quality variables. Analyses of 3 data sets from streams primarily affected by hydromorphological degradation showed an overall weak relationship (max R = 0.25) with the River Habitat Survey data of 28 Swedish streams, whereas moderate ( R ≈︁ 0.43) relationships with more detailed measurements of morphology were found in 2 Danish studies (39 and 6 streams, respectively). Although evidence exists in the literature on the importance of physical features for in-stream biota in general and macroinvertebrates specifically, we found only relatively weak relationships between various measures of hydromorphological stress and commonly used macroinvertebrate assessment tools. We attribute this to a combination of factors, including 1) the mixed nature of pressures acting on the majority of river reaches, 2) scaling issues (spatial and temporal) when relating habitat surveys to macroinvertebrate assessments, and 3) the scope of commonly used macroinvertebrate assessment systems (mainly focusing on water chemistry perturbation, such as eutrophication and acidification). The need is urgent to develop refined and updated biological assessment systems targeting hydromorphological stress for the use of the European Water Framework Directive (WFD) and national water-related policies. [ABSTRACT FROM AUTHOR]

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 P samp 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 Saprobic-based 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. [ABSTRACT FROM AUTHOR]