Drivers and stressors of freshwater biodiversity patterns across different ecosystems and scales : a review

The present review with focus on the last decade (2000-2010) aims to (i) collecting the major hypotheses explaining freshwater biodiversity patterns, (ii) identifying the main stressors affecting freshwater biodiversity, and (iii) revealing information gaps regarding ecosystem types, organism groups, spatial and temporal scales to highlight research needs to better propose sound conservation measures. The comparative analysis addresses six organism groups ranging from microorganisms to fish in basins, rivers, lakes, wetlands, ponds and groundwater. Short-term studies at ecoregion and catchment scale focusing on invertebrates, macrophytes and fish in Palaearctic and Nearctic regions dominated. The most frequent hypotheses tested were the landscape filter concept, the species-area relationship, the metacommunity concept. Dominating natural drivers were area, heterogeneity and disturbance. Land use, eutrophication and habitat destruction were identified as most important stressors. Generally, freshwater biodiversity declined in response to these stressors in contrast to increasing biodiversity determined by natural drivers across all ecosystems. Preferred organism groups were fish and invertebrates, most frequently studied in rivers, in contrast to smaller organisms (e.g. bacteria) and, e.g. groundwater being underrepresented. Hypotheses originating from the last century are still tested in freshwater research, while novel concepts are either missing or untested. Protection of freshwater biodiversity is the ultimate challenge since it supports valuable ecosystems services ensuring perpetuation of mankind. For that, comprehensive large-scale studies with holistic approaches are urgently needed

Delivrable D5.1-3: EQBs sensibilité au changement global/climatique dans les cours d'eau Européens : implication pour les conditions de référence et pour les chaînes pression-impact-récupération

[Departement_IRSTEA]Eaux [TR1_IRSTEA]QUASAREThis report, comprising four studies, attempts to assess the consequences of climate change on the distribution of 23 fish species, as well as the effects of climate change on functional assemblages. The first study aimed to estimate the ecological requirements of these species, by modelling the occurrences of fish species with environmental factors, including temperature and precipitation. The confidence intervals around the occurrence–environment relationships were also computed, to identify in which environmental conditions the predictions are more uncertain. The second aim of this study was to compare two approaches so as to compute the expected metric values. The results showed that metrics computed from the species distribution models or from models related to functional trait variability or environmental conditions give relatively similar results. The first aim of the second study was to assess the consequences of climate change on the distribution of the 23 fish species. The logistic regressions computed in the first study were used to compute the probability of species presence under different climatic scenarios. These results demonstrated that cold- or cool-water species will be greatly and negatively affected by climate change, while warm-water species will be favoured. The uncertainty of the predicted probabilities reveal that for some species the effect of global change remains unclear, while for others only the magnitude of the response to climate change differs. These results were discussed from the perspective of river restoration and species conservation. The second aim of this study was to use the models developed to predict functional traits, so as to assess the expected drift of reference conditions. The results suggest that metrics based on species tolerance will be less represented in fish assemblages in the future, which will have important consequences on the use of current bio-assessment tools. The third part of this report is a case study on the Traun River in central Austria. A long-term survey of more than 30 years has been conducted in a station downstream of a lake outlet flow. Owing to climate warming, the water temperature in August has increased on average by 2.2°C. In reaction to this warming, a shift of species dominance and a large decline of the grayling population were observed. This study is a good illustration of the consequences of climate change on fish assemblages and of the necessity for water managers to take into account the effect of climate change when planning restoration measures. The fourth part of this report is a case study on the Seine basin in France. Species projections were made for the whole catchment area and demonstrate that cold-water species would be highly affected by climate change, especially in the decade of 2050–2060. Several species are predicted to be extinct up to this period, while some warm-water species are expected to expand their distributions throughout the catchment area. Human pressures were also included in the species distribution models to assess the potential effect of restoration scenarios on species distributions. The results highlight the potential benefits from these restoration measures, but mostly show that climate change will be the major factor driving species distributions, overcoming restoration measures

Chapter Three - From Natural to Degraded Rivers and Back Again: A Test of Restoration Ecology Theory and Practice

Extensive degradation of ecosystems, combined with the increasing demands placed on the goods and services they provide, is a major driver of biodiversity loss on a global scale. In particular, the severe degradation of large rivers, their catchments, floodplains and lower estuarine reaches has been ongoing for many centuries, and the consequences are evident across Europe. River restoration is a relatively recent tool that has been brought to bear in attempts to reverse the effects of habitat simplification and ecosystem degradation, with a surge of projects undertaken in the 1990s in Europe and elsewhere, mainly North America. Here, we focus on restoration of the physical properties (e.g. substrate composition, bank and bed structure) of river ecosystems to ascertain what has, and what has not, been learned over the last 20 years. First, we focus on three common types of restoration measures—riparian buffer management, instream mesohabitat enhancement and the removal of weirs and small dams—to provide a structured overview of the literature. We distinguish between abiotic effects of restoration (e.g. increasing habitat diversity) and biological recovery (e.g. responses of algae, macrophytes, macroinvertebrates and fishes). We then addressed four major questions: (i) Which organisms show clear recovery after restoration? (ii) Is there evidence for qualitative linkages between restoration and recovery? (iii) What is the timescale of recovery? and (iv) What are the reasons, if restoration fails? Overall, riparian buffer zones reduced fine sediment entry, and nutrient and pesticide inflows, and positive effects on stream organisms were evident. Buffer width and length were key: 5–30 m width and > 1 km length were most effective. The introduction of large woody debris, boulders and gravel were the most commonly used restoration measures, but the potential positive effects of such local habitat enhancement schemes were often likely to be swamped by larger-scale geomorphological and physico-chemical effects. Studies demonstrating long-term biological recovery due to habitat enhancement were notable by their absence. In contrast, weir removal can have clear beneficial effects, although biological recovery might lag behind for several years, as huge amounts of fine sediment may have accumulated upstream of the former barrier. Three Danish restoration schemes are provided as focal case studies to supplement the literature review and largely supported our findings. While the large-scale re-meandering and re-establishment of water levels at River Skjern resulted in significant recovery of riverine biota, habitat enhancement schemes at smaller-scales in other rivers were largely ineffective and failed to show long-term recovery. The general lack of knowledge derived from integrated, well-designed and long-term restoration schemes is striking, and we present a conceptual framework to help address this problem. The framework was applied to the three restoration types included in our study and highlights recurrent cause–effect chains, that is, commonly observed relationships of restoration measures (cause) and their effects on abiotic and biotic conditions (effect). Such conceptual models can provide useful new tools for devising more effective river restoration, and for identifying avenues for future research in restoration ecology in general

International perspectives on the effects of climate change on inland fisheries

A range of perspectives is presented from the International Fisheries Section of the American Fisheries Society on climate change effects on inland fisheries from standing and flowing waters in Africa, Asia, Australia, Europe, and Latin America