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1. We studied seasonal changes in the carbon and nitrogen stable isotope ratios of larval Chironomus anthracinus and C. plumosus from the profundal sediments of four contrasting lakes. 2. Pronounced seasonal changes in both δ¹³C and δ¹⁵N values were evident in chironomid larvae of both species from two summer-stratified, eutrophic lakes: Esthwaite Water and Wyresdale Park. Changes were most marked in the larvae of C. plumosus and in larvae from greater depths. In contrast, neither C. anthracinus in summer-stratified but mesotrophic Schöhsee, nor C. plumosus in polymictic Großer Binnensee, showed marked seasonality in larval stable isotope ratios. 3. The particularly strong ¹³C-depletion of larvae from the stratified, eutrophic lakes is attributed to a significant contribution of methane-derived carbon to their diets. Feeding by larvae on isotopically light methanotrophic bacteria appears to occur mainly when autumn overturn of the water column restores oxygenated conditions to the sediment surface. At this time both δ¹³C and δ¹⁵N values of larvae decreased sharply. 4. Changes in the mean stable isotope ratio of the larval populations can also occur when larger, more isotopically light, larvae pupate and emigrate from the population to hatch as imagos. This effect can induce seasonal changes in larval isotope values even in lakes in which there is no evidence of a significant involvement of methane-derived carbon in their diets. Variations in emergence patterns between species and between lakes may generate differences in the seasonal pattern of change in stable isotope ratios in larval populations. 5. Our results emphasise the importance of adequate seasonal sampling if stable isotope ratios are to be used as biomarkers to study the role of key groups, such as chironomid larvae, in the trophic structure of lakes

Global freshwater biodiversity is declining dramatically, and meeting the challenges of this crisis requires bold goals and the mobilisation of substantial resources. While the reasons are varied, investments in both research and conservation of freshwater biodiversity lag far behind those in the terrestrial and marine realms. Inspired by a global consultation, we identify 15 pressing priority needs, grouped into five research areas, in an effort to support informed stewardship of freshwater biodiversity. The proposed agenda aims to advance freshwater biodiversity research globally as a critical step in improving coordinated actions towards its sustainable management and conservation.

Freshwater biodiversity is declining dramatically, and the current biodiversity crisis requires defining bold goals and mobilizing substantial resources to meet the challenges. While the reasons are varied, both research and conservation of freshwater biodiversity lag far behind efforts in the terrestrial and marine realms. We identify fifteen pressing global needs to support informed global freshwater biodiversity stewardship. The proposed agenda aims to advance freshwater biodiversity research globally as a critical step in improving coordinated action towards its sustainable management and conservation.

Transboundary river-basin management is a challenging task emerging from lack of on-site expert knowledge, high administrative and socioeconomic complexity, various stakeholder interests, and difficulties enforcing international and national law. Therefore, an efficient ‘science–policy interface’ is a crucial ingredient for the successful development and implementation of adequate management strategies. The Danube River Basin (DRB) drains areas of 19 countries with different cultural, political, and environmental legacies. The European Water Framework Directive (WFD) has provided the guiding legal instrument for DRB management since 2000, supported by several multilateral agreements. The International Commission for the Protection of the Danube River (ICPDR) is responsible for the implementation of the WFD in the DRB. It stimulates management-oriented research and coordinates the various activities of the contracting parties and observers, including those of many NGOs and stakeholders. The development of the first DRB Management Plan in 2009 constituted a milestone of cooperation among scientific, political, and public organisations. Key stressors and pressures have been identified, a new basin-wide monitoring network has been established, and numerous conservation and restoration sites have been designated. A major challenge in DRB management will be to establish synergies among the competing interests of navigation, hydropower production, flood protection and nature conservation. This paper examines the strengths and weaknesses of DRB science–policy interactions and outlines future strategies for sustainable development of the DRB as a template for transboundary river basin management.