The compositional heterogeneity of biotic assemblages among sites, or β‐diversity, regulates the relationship between local and regional species diversity across scales. Recent work has suggested that increased harshness of environmental conditions tends to reduce β‐diversity by decreasing the importance of stochastic processes in structuring assemblages. We investigated the effect of nutrient enrichment on the compositional heterogeneity of lake benthic invertebrate assemblages in Ireland at both local (within‐lake) and regional (among‐lake) scales. At local scales, we found that the compositional heterogeneity of benthic assemblages was related inversely to the extent of nutrient enrichment (as indicated by measurements of water column total phosphorus, total nitrogen, and chlorophyll a), after effects of lake morphology (i.e., surface area, connectivity, and depth of sampling) and alkalinity were accounted for. At regional scales, we found that nutrient‐rich lakes had significantly more homogenous benthic assemblages than nutrient‐poor lakes, over and above the effect of alkalinity and across a similar range of lake morphologies. These findings have profound implications for global aquatic biodiversity, as the homogenization of benthic assemblages at both local and regional scales may have important and unpredictable effects on whole aquatic ecosystems, with potentially considerable ecological and evolutionary consequences.
We analyzed data from 81 shallow European lakes, which were sampled with standardized methods, for combined effects of climatic, physical, and chemical features of food‐web interactions, with a specific focus on zooplankton biomass and community structure. multiple‐regression analysis showed that total phosphorus (TP) generally was the most important predictor of zooplankton biomass and community structure. Climate was the next most important predictor and acted mainly through its effect on pelagic zooplankton taxa. Benthic and plant‐associated taxa (typically almost half the total zooplankton biomass) were, however, affected mainly by macrophyte coverage. Neither climate nor TP affected the relation between small and large taxa, and we found only a weak trend with increasing TP of increasing mean crustacean body mass. Dividing the data set into three climate zones revealed a pronounced difference in response to lake productivity between cold lakes, with long periods of ice cover, and the two warmer lake types. These ÂÂice lakes differed from the others with respect to the effect of TP on chlorophyll a, the zooplankton : chlorophyll a ratio, the chlorophyll a :TP ratio, and the proportion of cyclopoids in the copepod community. Our data suggest that bottom‐up forces, such as nutrient concentration, are the most important predictors of zooplankton biomass. In addition, climate contributes significantly—possibly by affecting top‐down regulation by fish—and may interact with productivity in determining the zooplankton standing biomass and community composition. Hence, the present study suggests that food‐web dynamics are closely linked to climatic features.
The European Union (EU) Water Framework Directive (WFD) requires EU member states to produce and implement river basin management plans, which are to be designed and updated via participatory processes that inform, consult with, and actively involve all interested stakeholders. The assumption of the European Commission is that stakeholder participation, and institutional adaptation and procedural innovation to facilitate it, are essential to the effectiveness of river basin planning and, ultimately, the environmental impact of the Directive. We analyzed official documents and the WFD literature to compare implementation of the Directive in EU member states in the initial WFD planning phase (2000–2009). Examining the development of participatory approaches to river basin management planning, we consider the extent of transformation in EU water governance over the period. Employing a mixed quantitative and qualitative approach, we map the implementation “trajectories” of 13 member states, and then provide a detailed examination of shifts in river basin planning and participation in four member states (Germany, Sweden, Poland and France) to illustrate the diversity of institutional approaches observed. We identify a general tendency towards increased, yet circumscribed, stakeholder participation in river basin management in the member states examined, alongside clear continuities in terms of their respective pre-WFD institutional and procedural arrangements. Overall, the WFD has driven a highly uneven shift to river basin-level planning among the member states, and instigated a range of efforts to institutionalize stakeholder involvement—often through the establishment of advisory groups to bring organized stakeholders into the planning process.