• Energy Research

Fresh waters are particularly vulnerable to climate change because (i) many species within these fragmented habitats have limited abilities to disperse as the environment changes; (ii) water temperature and availability are climate-dependent; and (iii) many systems are already exposed to numerous anthropogenic stressors. Most climate change studies to date have focused on individuals or species populations, rather than the higher levels of organization (i.e. communities, food webs, ecosystems). We propose that an understanding of the connections between these different levels, which are all ultimately based on individuals, can help to develop a more coherent theoretical framework based on metabolic scaling, foraging theory and ecological stoichiometry, to predict the ecological consequences of climate change. For instance, individual basal metabolic rate scales with body size (which also constrains food web structure and dynamics) and temperature (which determines many ecosystem processes and key aspects of foraging behaviour). In addition, increasing atmospheric CO2is predicted to alter molar CNP ratios of detrital inputs, which could lead to profound shifts in the stoichiometry of elemental fluxes between consumers and resources at the base of the food web. The different components of climate change (e.g. temperature, hydrology and atmospheric composition) not only affect multiple levels of biological organization, but they may also interact with the many other stressors to which fresh waters are exposed, and future research needs to address these potentially important synergies.

Fresh waters are particularly vulnerable to climate change because (i) many species within these fragmented habitats have limited abilities to disperse as the environment changes; (ii) water temperature and availability are climate-dependent; and (iii) many systems are already exposed to numerous anthropogenic stressors. Most climate change studies to date have focused on individuals or species populations, rather than the higher levels of organization (i.e. communities, food webs, ecosystems). We propose that an understanding of the connections between these different levels, which are all ultimately based on individuals, can help to develop a more coherent theoretical framework based on metabolic scaling, foraging theory and ecological stoichiometry, to predict the ecological consequences of climate change. For instance, individual basal metabolic rate scales with body size (which also constrains food web structure and dynamics) and temperature (which determines many ecosystem processes and key aspects of foraging behaviour). In addition, increasing atmospheric CO2is predicted to alter molar CNP ratios of detrital inputs, which could lead to profound shifts in the stoichiometry of elemental fluxes between consumers and resources at the base of the food web. The different components of climate change (e.g. temperature, hydrology and atmospheric composition) not only affect multiple levels of biological organization, but they may also interact with the many other stressors to which fresh waters are exposed, and future research needs to address these potentially important synergies.

AbstractHimalayan glaciers are undergoing rapid mass loss but rates of contemporary change lack long-term (centennial-scale) context. Here, we reconstruct the extent and surfaces of 14,798 Himalayan glaciers during the Little Ice Age (LIA), 400 to 700 years ago. We show that they have lost at least 40 % of their LIA area and between 390 and 586 km3 of ice; 0.92 to 1.38 mm Sea Level Equivalent. The long-term rate of ice mass loss since the LIA has been between − 0.011 and − 0.020 m w.e./year, which is an order of magnitude lower than contemporary rates reported in the literature. Rates of mass loss depend on monsoon influence and orographic effects, with the fastest losses measured in East Nepal and in Bhutan north of the main divide. Locally, rates of loss were enhanced with the presence of surface debris cover (by 2 times vs clean-ice) and/or a proglacial lake (by 2.5 times vs land-terminating). The ten-fold acceleration in ice loss we have observed across the Himalaya far exceeds any centennial-scale rates of change that have been recorded elsewhere in the world.

AbstractHimalayan glaciers are undergoing rapid mass loss but rates of contemporary change lack long-term (centennial-scale) context. Here, we reconstruct the extent and surfaces of 14,798 Himalayan glaciers during the Little Ice Age (LIA), 400 to 700 years ago. We show that they have lost at least 40 % of their LIA area and between 390 and 586 km3 of ice; 0.92 to 1.38 mm Sea Level Equivalent. The long-term rate of ice mass loss since the LIA has been between − 0.011 and − 0.020 m w.e./year, which is an order of magnitude lower than contemporary rates reported in the literature. Rates of mass loss depend on monsoon influence and orographic effects, with the fastest losses measured in East Nepal and in Bhutan north of the main divide. Locally, rates of loss were enhanced with the presence of surface debris cover (by 2 times vs clean-ice) and/or a proglacial lake (by 2.5 times vs land-terminating). The ten-fold acceleration in ice loss we have observed across the Himalaya far exceeds any centennial-scale rates of change that have been recorded elsewhere in the world.

Freshwater ecosystems are often of high conservation value, yet many have been degraded significantly by direct anthropogenic impacts and are further threatened by global environmental change. Traditionally, conservation science and policy has promoted principles based on preservation and restoration paradigms, which are linked to assumptions of stationarity and uniformitarianism. Adaptation requires new approaches based on flexibility, iterativity, non-linearity, and redundancy. Many high alpine river networks represent near natural, pristine river systems and important biodiversity 'hotspots' of European freshwater fauna. However, there remains a lack of guidance on alpine river conservation strategies under a changing climate at EU, regional and local levels. A critical evaluation of current conservation and adaptation principles and governance frameworks was undertaken with relation to predicted climate change impacts on freshwater ecosystems. Case studies are presented from two alpine zones in mainland Europe (the Pyrénées and the Swiss Alps). The complexity of climate change impacts on hydrological regimes, habitat and biota from both case study regions suggests that current legislative and policy mechanisms, which frame conservation approaches, need to be realigned. In particular, a shift in focus from species-centric approaches to more holistic ecosystem functioning conservation is proposed. A methodological approach is set out that may help conservationists and resource managers to both prioritise their efforts, and better predict future habitat and biotic responses to set ecological baseline conditions. Due to the complexity and limited potential for preventative intervention in these systems, conservation strategies should focus on: (i) the maintenance and enhancement of connectivity within and between alpine river basins and (ii) the control and reduction of additional anthropogenic stressors.

Freshwater ecosystems are often of high conservation value, yet many have been degraded significantly by direct anthropogenic impacts and are further threatened by global environmental change. Traditionally, conservation science and policy has promoted principles based on preservation and restoration paradigms, which are linked to assumptions of stationarity and uniformitarianism. Adaptation requires new approaches based on flexibility, iterativity, non-linearity, and redundancy. Many high alpine river networks represent near natural, pristine river systems and important biodiversity 'hotspots' of European freshwater fauna. However, there remains a lack of guidance on alpine river conservation strategies under a changing climate at EU, regional and local levels. A critical evaluation of current conservation and adaptation principles and governance frameworks was undertaken with relation to predicted climate change impacts on freshwater ecosystems. Case studies are presented from two alpine zones in mainland Europe (the Pyrénées and the Swiss Alps). The complexity of climate change impacts on hydrological regimes, habitat and biota from both case study regions suggests that current legislative and policy mechanisms, which frame conservation approaches, need to be realigned. In particular, a shift in focus from species-centric approaches to more holistic ecosystem functioning conservation is proposed. A methodological approach is set out that may help conservationists and resource managers to both prioritise their efforts, and better predict future habitat and biotic responses to set ecological baseline conditions. Due to the complexity and limited potential for preventative intervention in these systems, conservation strategies should focus on: (i) the maintenance and enhancement of connectivity within and between alpine river basins and (ii) the control and reduction of additional anthropogenic stressors.

Most research on the effects of environmental change in freshwaters has focused on incremental changes in average conditions, rather than fluctuations or extreme events such as heatwaves, cold snaps, droughts, floods or wildfires, which may have even more profound consequences. Such events are commonly predicted to increase in frequency, intensity and duration with global climate change, with many systems being exposed to conditions with no recent historical precedent. We propose a mechanistic framework for predicting potential impacts of environmental fluctuations on running-water ecosystems by scaling up effects of fluctuations from individuals to entire ecosystems. This framework requires integration of four key components: effects of the environment on individual metabolism, metabolic and biomechanical constraints on fluctuating species interactions, assembly dynamics of local food webs, and mapping the dynamics of the meta-community onto ecosystem function. We illustrate the framework by developing a mathematical model of environmental fluctuations on dynamically assembling food webs. We highlight (currently limited) empirical evidence for emerging insights and theoretical predictions. For example, widely supported predictions about the effects of environmental fluctuations are: high vulnerability of species with highper capitametabolic demands such as large-bodied ones at the top of food webs; simplification of food web network structure and impaired energetic transfer efficiency; and reduced resilience and top-down relative to bottom-up regulation of food web and ecosystem processes. We conclude by identifying key questions and challenges that need to be addressed to develop more accurate and predictive bio-assessments of the effects of fluctuations, and implications of fluctuations for management practices in an increasingly uncertain world.