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Finnish rivers exported annually on average 1.2 M t carbon, and total organic carbon (TOC) comprised the major share (nearly 80 %) of this export. The mean area specific carbon export was 4.5 g C m year. The highest organic carbon export originated from peat dominated catchments, whereas rivers draining agricultural catchments had the highest area-specific inorganic carbon fluxes. Between 1975 and 2014 total inorganic carbon (TIC) concentrations rose more steadily than the respective TOC concentrations. There was an overall decrease in TOC concentrations between 1975 and the mid-1990s. Decreased point source loading contributed to this pattern, although decreases were also detected in rivers without any major pollution sources. From the mid-1990s TOC concentrations started to rise and the increase was even more pronounced than the earlier decrease. The upward trend was ubiquitous, both in time and space, and it was not possible to link the changes to any specific catchment characteristics or another single driver. Warming climate, changes in hydrology and decreases in acidic deposition were the major driving factors although their contribution varied geographically. At the same time both TOC and TIC export increased slightly, but the strong upward trends in TOC concentrations were not reflected as clearly in TOC export trends. This was because changes in water flow had a dominant influence on TOC export to the sea and any changes in concentrations were masked behind the variation in flow. [ABSTRACT FROM AUTHOR]

This article presents a review of previous studies on the impacts of climate change and the operation of dam reservoirs on the characteristics of river ice cover. Based on a review of the existing literature, the spatial and temporal variability of trends in individual river ice cover conditions and their relationship to both climate change and the operation of dam reservoirs is explored. From this analysis, climate change is identified as the main determinant of the river ice cover disturbances observed since the start of the twentieth century. The study found that in the twentieth century, climate change contributed to a decrease in the duration of ice cover on rivers. The shortening of ice cover duration occurs primarily through earlier breakup rather than later formation. The trends in ice cover freeze-up and breakup are less spatially variable across Eurasia than in North America. The analysis indicates that dam reservoirs can exert a significant control on the spatiotemporal distribution of ice cover occurrence on rivers, even on a global scale. The first quantitative estimate of the number of dam reservoirs in river ice cover areas was also presented based on climatological and reservoir location data. The obtained results highlight the need to research river ice cover changes based on remote sensing data; such studies will make it possible to recognize the temporal–spatial distribution of trends in river ice cover parameters and the strength and extent of the influence of dam reservoirs. [ABSTRACT FROM AUTHOR]

Extreme temperatures have increased in intensity, duration and frequency in the last century, with potential consequences on key ecological processes such as organic matter breakdown. Many stream ecosystems are fueled by the breakdown of terrestrial leaf litter, which is exposed to atmospheric conditions for certain periods of time before entering the stream. Thus, extreme warming or freezing events may affect the litter physicochemical structure, which could translate into altered breakdown within the stream. The above prediction was tested by exposing litter of common riparian tree species in southern Chile to freezing (−20 ºC; dry or wet litter) or heating (40 ºC) and comparing breakdown with control litter exposed to room temperature (20 ºC), separating the effects of different breakdown agents (i.e., leaching, microorganisms and detritivores). The greatest effects were found in wet litter subjected to freezing; this treatment significantly increased leaching in the short term (48 h) and slowed down breakdown in the long term (30 days), mostly due to the inhibition of microbial breakdown. Heating also retarded microbial breakdown, but the effect was smaller. Our results suggest that short-term extreme temperatures—particularly cold ones—have the potential to slow down litter breakdown in streams, which will most likely impact global biogeochemical cycles where streams play a key role. [ABSTRACT FROM AUTHOR]

Intermittent streams comprise the majority of stream length in many parts of the world, particularly dry regions. Many dry regions are expected to experience longer and more intense dry periods as the global climate changes. The response of benthic macroinvertebrate communities in intermittent streams to current variability in dry-period duration and intensity may predict their future response to climate change, but such responses require quantification in different stream types and climate zones. I compared the macroinvertebrate community among drier and wetter years from 2008 to 2012 in intermittent forested and pasture streams in a relatively warm, dry region of New Zealand. I predicted that macroinvertebrate communities would decline in density and taxonomic richness with increasing dryness, and that drought-sensitive Ephemeroptera, Plecoptera and Trichoptera (EPT) taxa would show a stronger response than Diptera and non-insects. EPT richness and density did decline with increasing dry period duration, whereas total macroinvertebrate density and richness, and Diptera richness, showed weak and/or non-significant relationships. I predicted that loss of remnant pools (a potential dry-season refuge) would cause a decline in macroinvertebrate richness and density, but found no significant difference between years with and without pools. I predicted that years when flow resumed late in the autumn (when temperatures are too cool for insect flight) would have lower EPT richness and density than years when flow resumed early, and results confirmed this. Intermittent pasture stream communities showed a weaker response to dry period duration than communities in intermittent forested streams, as taxa relatively tolerant of agricultural stressors are also relatively tolerant of drying. Results suggest that global climate change will cause a loss of drought-sensitive species from intermittent streams in this region. [ABSTRACT FROM AUTHOR]

Hydrological alterations in Alpine rivers have been largely increasing due to the combined effects of global climate change and local impacts. Water flow intermittency starts with a process called lentification, which leads to the transformation of the aquatic ecosystem with severe consequences on biotic communities. These consequences have a greater impact in Alpine headwater streams, which are considered important and fragile hotspots of biodiversity and a source of threatened species; the new regime creates conditions to which native biota are poorly adapted. The main aim of our work was to evaluate taxonomical, functional and structural changes of diatom communities in Alpine rivers during the lentification process that precedes a supra-seasonal drought. Contrary to what was expected, communities exposed to river shrinking showed a level of homogeneity comparable to those collected in permanent sections. We therefore hypothesized that lentification created an intermediate disturbance that favoured heterogeneity of assemblages. Conversely, ecological guilds, growth forms and eco-morphological groups varied along temporal and spatial gradients driven by the lentification process. Small, motile and medium-sized low profile species were more abundant during summer, as well as adnate and stalked ones. Lentification limited the presence of high profile guilds and mucous-forming colonies. Droughts in Alpine streams are fairly recent processes, and the dynamics of aquatic communities facing water scarcity are largely unknown. The results we obtained provide important insights towards a more refined functional classification of diatoms for evaluating hydrological alterations. [ABSTRACT FROM AUTHOR]

Temporary streams on the island of Mallorca support unique fauna that differ from other temporary streams on the mainland. It comprises many poor-dispersing endemics as well as more ubiquitous species with better dispersal abilities. To determine the importance of spatial and temporal drivers, this study assesses on the composition and biological traits of macroinvertebrate assemblages, and their variation among 26 non impaired streams corresponding to 3 temporary stream types (mountain, canyon and lowland) during two hydrological phases (flow and disconnected pools) sampled seasonally between 2005 and 2008. Mountain and canyon streams showed longer water permanence, and higher biodiversity than lowland streams, which were characterized by higher drying impact. Significant differences (PERMANOVA and PERMDIST) in species and biological traits composition were found among hydrological phases and stream types, indicating the high spatial and temporal heterogeneity of these temporary systems. The lack of desiccation-resistant forms was dominant in the temporary streams community, suggesting that taxa may survive and persist over the summer in other refugia, such as the hyporheic zone and/or groundwater springs. The environmental variables (physico-chemical, hydromorphological and basin land uses) explained only 40% of the distribution of macroinvertebrate composition (dbRDA analysis), leaving spatial characteristics and temporal variables the highest percentages of variance. Moreover, a significant influence of distance on the macroinvertebrate dispersion (within the surrounding 5 km) was found. Therefore, both neutral (dispersal processes) and niche explanations (local environmental conditions) contribute to patterns of local diversity. Our study highlights the importance of determining the spatio-temporal drivers which influence the ecology and composition of aquatic communities of temporary streams. Such improvement on our knowledge is highly needed for the appropriate design of monitoring programs, being urgently required in the lowlands streams, as they are the most vulnerable to climate change (longer seasonal and supra-seasonal droughts) and human impacts. [ABSTRACT FROM AUTHOR]

The temporal dynamic of riverine ecosystems and their fish communities and populations has been addressed in ecological theory and management for several decades. A growing number of case studies on the historic development especially of European and North American rivers have been published. Nonetheless, a theoretical debate about the contributions and limits of historical approaches and interdisciplinary co-operation is lacking. This article presents a brief overview of the role of history in river and fish ecology and suggests historical ecology as a scientific field that can offer a framework for future research. Based on case studies compiled in this special issue on the 'Historical ecology of riverine fish in Europe', we draw conclusions on long-term changes of fish communities, on fisheries, aquatic ecosystem management and past habitat alterations and the potential of archaeological remains and written sources to study them. We discuss how modelling of historical fish data can help elucidate the effects of climate change and human influences on rivers and fish. Finally, we account for the necessity to consider appropriate spatial and temporal scales. In conclusion we call for future comparative studies on continental and global scales and methodological development, which can benefit especially from recent advances in marine historical ecology. We suggest that future interdisciplinary studies of ecologists, hydrologists, historians and archaeologists can reveal the history of riverine ecosystems as socio-ecological systems, addressing both their natural dynamics and human dimension. Such an endeavor can also support developing management plans for habitat restoration and conservation against the background of global change. [ABSTRACT FROM AUTHOR]

Water temperature (Tw) plays a critical role in the aquatic ecosystem of rivers. Studying the response process and mechanisms of Tw to climate change and human activities is crucial for assessing the sustainable development of river ecological environments. In this study, we conducted a multi-time scale analysis of Tw using mathematical and statistical models and a vector autoregressive model. We analyzed hydrometeorological data collected from 1961 to 2019 to understand the evolutionary characteristics of Tw under different meteorological conditions and reservoir operation stages. Our findings reveal a significant mutation in Tw in 1994, with the warming rate changing from 0.007 to 0.032 °C/year. Among the various meteorological factors examined [runoff, evapotranspiration, air temperature (Ta), rainfall, duration of sunshine, wind speed, air pressure, and solar radiation], Ta and runoff were found to have the greatest influence on Tw, accounting for > 30% of the observed changes. Conversely, the wind speed had the weakest impact. Furthermore, the Three Gorges Dam (TGD) exerted a substantial influence on Tw. The presence of the TGD elevated winter Tw compared to the non-impoundment condition. Additionally, the completion of the TGD significantly weakened the correlation between runoff, Ta, and Tw, resulting in a 25–34 day delay in the Chinese sturgeon's target spawning time. This delay could have negative ecological implications for the lower reaches of the TGD. These findings offer essential support for guiding water resource management, protecting river eco-hydrological processes, and understanding the impact on aquatic ecology in the Yangtze River. [ABSTRACT FROM AUTHOR]

Rivers in Mediterranean high mountains are especially vulnerable to climate change because these areas are characterized by extreme climatic conditions of snowy winters and relatively frequent summer droughts. Climate induced alterations in temperature and the magnitude of high and low river flows are expected to have significant effects on aquatic fauna. Here, we analysed changes in the caddisfly communities of the Sierra Nevada during a 20-year period on an altitudinal gradient range of 952-3050 m. Furthermore, we related these changes to an observed increase in air temperature and decrease in river flow over the last 40 years. Overall, caddisfly species richness increased but patterns varied depending on altitude in a non-linear shape. Richness increased in altitude with maximum values at sites of intermediate-high altitude (1800-2000 m). The effects of the observed climate change may be explained by the colonization of headwaters and middle reaches from mid-lowland species or by those from streams and rivers in nearby mountain chains at lower altitude. The observed richness increase and its association with environmental conditions suggest that mountains with a considerable altitudinal gradient may function as refuges for species and populations during periods of climatic change, which strength the importance of the conservation of mountainous habitat. [ABSTRACT FROM AUTHOR]

Tropical and subtropical Asia differs from other tropical regions in its monsoonal climate and the dominant influence of the Hindukush and Himalayan mountain ranges which result in extremes of spatial and temporal variability in precipitation. However, several major rivers and their tributaries arise in the Himalayan ranges and are fed by thousands of glaciers. Huge sediment loads carried by these rivers result in important deltas at their mouths. The climatic and physiographic diversity have endowed the region with many kinds of wetlands. Of these, the peatswamps of southeast Asia constitute about 56% of the world's tropical peatlands, and more than 42% of the world's mangroves occur in South and southeast Asia. Among other wetlands, riverine swamps are rather restricted whereas the seasonal marshes are a dominant feature. Another characteristic feature of tropical Asia are the innumerable human-made and intensively managed wetlands of which the paddy fields and aquaculture ponds are the most extensive. Throughout tropical Asia, wetlands have been a part of the socio-cultural ethos of the people and many communities have lived in wetlands. However, the pressures of high population and the economic development have extensively impacted upon wetlands which have been transformed for paddy cultivation and aquaculture, drained and converted to other land uses for economic gains (e.g., conversion to oil palm), and degraded by discharge of domestic and industrial wastes. Invasive plant and animal species have also played a significant role. The climate change is already being felt in the rapid retreat of Himalayan glaciers, increased temperature and variability in precipitation as well as the frequency of extreme events. Sea level rise is seen as a major threat to the coastal wetlands, particularly the mangroves. Increasing droughts have caused frequent fires in Indonesian peat swamps that have further feedback impacts on regional climate. However, the actual threat to wetlands in this region arises from the extensive hydrological alterations being caused by storage, abstraction and diversion of river flows for agriculture, industry and hydropower. Currently, the state of our understanding wetlands in general, and the efforts and infrastructure for research and training in wetlands are very poor. Although a few wetlands have been designated as Ramsar sites, the policies aimed at wetland conservation are either non-existent or very weak. Human responses to greater uncertainty and variability in the available water resources in different parts of Asia will be crucial to the conservation of wetlands in the future. [ABSTRACT FROM AUTHOR]

Species distributions models (SDM) that rely on estimated relationships between present environmental conditions and species presence-absence are widely used to forecast changes of species distributions caused by global warming but far less to reconstruct historical assemblages. By compiling historical fish data from the turn to the middle of the twentieth century in a similar way for several European catchments (Rhône, Danube), and using already published SDMs based on current observations, we: (1) tested the predictive accuracy of such models for past climatic conditions, (2) compared observed and expected cumulated historical species occurrences at sub-catchment level, and (3) compared the annual variability in the predictions within one sub-catchment (Salzach) under a future climate scenario to the long-term variability of occurrences reconstructed during an extended historical period (1800-2000). We finally discuss the potential of these SDMs to define a 'reference condition', the possibility of a shift in baseline condition in relation with anthropogenic pressures, and past and future climate variability. The results of this study clearly highlight the potential of SDM to reconstruct the past composition of European fish assemblages and to analyze the historical ecological status of European rivers. Assessing the uncertainty associated with species distribution projections is of primary importance before evaluating and comparing the past and future distribution of species within a given catchment. [ABSTRACT FROM AUTHOR]

Dry river beds are common worldwide and are rapidly increasing in extent due to the effects of water management and prolonged drought periods due to climate change. While attention has been given to the responses of aquatic invertebrates to drying rivers, few studies exist on the terrestrial invertebrates colonizing dry river beds. Dry river beds are physically harsh and they often differ substantially in substrate, topography, microclimate and inundation frequency from adjacent riparian zones. Given these differences, we predicted that dry river beds provide a unique habitat for terrestrial invertebrates, and that their assemblage composition differs from that in adjacent riparian zones. Dry river beds and riparian zones in Australia and Italy were sampled for terrestrial invertebrates with pitfall traps. Sites differed in substrate type, climate and flow regime. Dry river beds contained diverse invertebrate assemblages and their composition was consistently different from adjacent riparian zones, irrespective of substrate, climate or hydrology. Although some taxa were shared between dry river beds and riparian zones, 66 of 320 taxa occurred only in dry river beds. Differences were due to species turnover, rather than shifts in abundance, indicating that dry river bed assemblages are not simply subsets of riparian assemblages. Some spatial patterns in invertebrate assemblages were associated with environmental variables (irrespective of habitat type), but these associations were statistically weak. We suggest that dry river beds are unique habitats in their own right. We discuss potential human stressors and management issues regarding dry river beds and provide recommendations for future research. [ABSTRACT FROM AUTHOR]

The Sundarban, covering about one million ha in the delta of the rivers Ganga, Brahmaputra and Meghna is shared between Bangladesh (~60%) and India (~40%), and is the world’s largest coastal wetland. The area experiences a subtropical monsoonal climate with an annual rainfall of 1,600–1,800 mm and severe cyclonic storms. Enormous amounts of sediments carried by the rivers contribute to its expansion and dynamics. Salinity gradients change over a wide range of spatial and temporal scales. The biodiversity includes about 350 species of vascular plants, 250 fishes and 300 birds, besides numerous species of phytoplankton, fungi, bacteria, zooplankton, benthic invertebrates, molluscs, reptiles, amphibians and mammals. Species composition and community structure vary east to west, and along the hydrological and salinity gradients. Sundarban is the habitat of many rare and endangered animals ( Batagur baska, Pelochelys bibroni, Chelonia mydas), especially the Royal Bengal tiger ( Panthera tigris). Javan rhino, wild buffalo, hog deer, and barking deer are now extinct from the area. Large areas of the Sundarban mangroves have been converted into paddy fields over the past two centuries, and more recently into shrimp farms. The Sundarban has been extensively exploited for timber, fish, prawns and fodder. The regulation of river flows by a series of dams, barrages and embankments for diverting water upstream for various human needs and for flood control has caused large reduction in freshwater inflow and seriously affected the biodiversity because of an increase in salinity and changes in sedimentation. Heritiera fomes (locally called Sundari, from which Sundarban derives its name), Nypa fruticans and Phoenix paludosa are declining rapidly. During the past three decades, large parts of the remaining Sundarban have been protected for wildlife, particularly tiger, through the creation of several sanctuaries and a biosphere reserve. Parts of the Sundarban in both India and Bangladesh have been declared World Heritage sites. However, its biodiversity continues to be threatened by a growing human population that not only places pressure on its biological resources, but also impacts on the freshwater inflows from upstream areas. Oil exploration in coastal areas is also emerging as a new threat. Further threats arise from global climate change, especially sea level rise. The future of the Sundarban will depend upon the management of freshwater resources as much as on the conservation of its biological resources. [ABSTRACT FROM AUTHOR]

Human population growth, economic development, climate change, and the need to close the electricity access gap have stimulated the search for new sources of renewable energy. In response to this need, major new initiatives in hydropower development are now under way. At least 3,700 major dams, each with a capacity of more than 1 MW, are either planned or under construction, primarily in countries with emerging economies. These dams are predicted to increase the present global hydroelectricity capacity by 73 % to about 1,700 GW. Even such a dramatic expansion in hydropower capacity will be insufficient to compensate for the increasing electricity demand. Furthermore, it will only partially close the electricity gap, may not substantially reduce greenhouse gas emission (carbon dioxide and methane), and may not erase interdependencies and social conflicts. At the same time, it is certain to reduce the number of our planet's remaining free-flowing large rivers by about 21 %. Clearly, there is an urgent need to evaluate and to mitigate the social, economic, and ecological ramifications of the current boom in global dam construction. [ABSTRACT FROM AUTHOR]

Wetlands cover at least 6 % of the Earth's surface. They play a key role in hydrological and biogeochemical cycles, harbour a large part of the world's biodiversity, and provide multiple services to humankind. However, pressure in the form of land reclamation, intense resource exploitation, changes in hydrology, and pollution threaten wetlands on all continents. Depending on the region, 30-90 % of the world's wetlands have already been destroyed or strongly modified in many countries with no sign of abatement. Climate change scenarios predict additional stresses on wetlands, mainly because of changes in hydrology, temperature increases, and a rise in sea level. Yet, intact wetlands play a key role as buffers in the hydrological cycle and as sinks for organic carbon, counteracting the effects of the increase in atmospheric CO. Eight chapters comprising this volume of Aquatic Sciences analyze the current ecological situation and the use of the wetlands in major regions of the world in the context of global climate change. This final chapter provides a synthesis of the findings and recommendations for the sustainable use and protection of these important ecosystems. [ABSTRACT FROM AUTHOR]

The present area of European wetlands is only a fraction of their area before the start of large-scale human colonization of Europe. Many European wetlands have been exploited and managed for various purposes. Large wetland areas have been drained and reclaimed mainly for agriculture and establishment of human settlements. These threats to European wetlands persist. The main responses of European wetlands to ongoing climate change will vary according to wetland type and geographical location. Sea level rise will probably be the decisive factor affecting coastal wetlands, especially along the Atlantic coast. In the boreal part of Europe, increased temperatures will probably lead to increased annual evapotranspiration and lower organic matter accumulation in soil. The role of vast boreal wetlands as carbon sinks may thus be suppressed. In central and western Europe, the risk of floods may support the political will for ecosystem-unfriendly flood defence measures, which may threaten the hydrology of existing wetlands. Southern Europe will probably suffer most from water shortage, which may strengthen the competition for water resources between agriculture, industry and settlements on the one hand and nature conservancy, including wetland conservation, on the other. [ABSTRACT FROM AUTHOR]

Sediment deposition in water reservoirs has major implications for storage capacity, reservoir lifetime, and water quality. Changes in rainfall patterns and land use will consequently alter the rate of erosion and therefore have a direct effect on sedimentation rates. This literature review employed a systematic mapping approach to collate and describe evidence of contemporary sedimentation trends for impounded reservoirs and natural lakes with emphasis on studies which analysed impacts on water storage capacity. Fourteen studies determined an overall increase in sedimentation rate, 13 identified a recent decline and another 5 reported mixed results. Interestingly, 83.3% of the articles that studied natural lakes found an increase in recent contemporary sedimentation, while 54.5% of the articles on impounded reservoirs indicated recent declines in sediment deposition. Land use change was the main causative factor responsible for sedimentation rate increase followed by the combined effects of land activities and climate change. Soil and sediment management strategies, implemented in and upstream of some impounded reservoirs, have proved to be effective in mitigating and remediating reservoir sedimentation. From the 147 papers preselected, only 33 contain sufficient sedimentation data to infer recent rate trends with only about 45% of these articles reporting quantities of storage capacity loss caused by sedimentation. Across these 33 studies, assessments of sedimentation and associated storage capacity loss are compromised by the limited spatiotemporal resolution of current measurement methods, reinforcing the requirement to develop new, more robust techniques to monitor sedimentation and storage capacity changes. [ABSTRACT FROM AUTHOR]

Dissolved oxygen (DO) concentration is a fundamental metric to describe climate-related alterations in deep lakes. Increasing water temperatures enhance thermal stratification, leading in temperate basins to a growing isolation of deep waters. This leads to the depletion of hypolimnetic DO, which adds up to limited nutrient circulation and restricted replenishment of the trophogenic layers. With vanishing convective mixing, it is commonly believed that the only source of hypolimnetic DO replenishment will be represented by deep intrusions of cold oxygenated waters from the tributaries. In this study, we first analyse the 1993–2020 long-term observed trends of DO concentrations in the subalpine deep oligomictic Lake Maggiore (Italy/Switzerland). Then, through an algorithm calculating daily intrusion depths and mass discharges of DO for the major tributaries, we show that deep insertions are suppressed for increasing winter water temperatures and residual thermal stratification. Turbulent entrainment is proved fundamental for DO replenishment, leading to mass discharges of DO released into the deep hypolimnion up to more than two orders of magnitude larger than the original ones from the tributaries. Last, we discuss the results of simulations made through a one-dimensional coupled ecological–hydrodynamic model about the possible effects of a full turnover on DO concentrations in the deep hypolimnion. Two cases are displayed, with the turnover taking place either now or with an anoxic hypolimnion deriving from decades of isolation due to severe climate warming. Through this study, climate warming is shown to be a fundamental driver of DO in Lake Maggiore, its depletion harming both water quality and the ecosystem. [ABSTRACT FROM AUTHOR]

Over recent decades, many Mediterranean and Ponto-Caspian aquatic invertebrate species have dispersed northwards and established as non-native species in colder regions. We hypothesized that these species have cold-tolerant traits, which facilitate dispersal into colder climates. Thanks to these traits, Southern European aquatic species are able to cross biogeographic boundaries. We downloaded the list of all alien invertebrate species that were fully aquatic (i.e. lacking terrestrial adults) from the GRIIS database and picked out those Mediterranean and Ponto-Caspian species that have undergone northwards range expansion. We identified traits that may facilitate dispersal to colder climates including the following: small size; capacity for behavioural thermoregulation; feeding habit (omnivorous, filter-feeders, food generalists); quiescence and dormancy (or diapause); freezing avoidance (presence of cryoprotectants); tolerance to low temperatures or eurythermicity; active dispersal; and enhanced reproduction. We statistically tested the null hypotheses that Mediterranean and Ponto-Caspian alien aquatic invertebrate species that dispersed into the north have all of these traits. We used contingency tables populated with raw frequency data with χ2—tests and assessed statistical significance at α of 0.05. We identified 95 Mediterranean and Ponto-Caspian alien aquatic invertebrate species that have shown northwards range extension, 10 (10%) of which were of Mediterranean origin and 85 (90%) of Ponto-Caspian origin. We found that this northwards dispersal from Southern Europe is mainly limited to a few following groups of aquatic invertebrates: small crustaceans, molluscs, cnidarians and annelids. Ability to go to diapause, hibernation or resting period, temperature tolerance and small size were the traits most commonly shared by these organisms. We conclude that Mediterranean and Ponto-Caspian aquatic invertebrate species showing northwards range expansion have cold-tolerant strategies. The traits analysed can favour the establishment of the species. [ABSTRACT FROM AUTHOR]

The condition of many wetlands across Australia has deteriorated due to increased water regulation and the expansion and intensification of agriculture and increased urban and industrial expansion. Despite this situation, a comprehensive overview of the distribution and condition of wetlands across Australia is not available. Regional analyses exist and several exemplary mapping and monitoring exercises have been maintained to complement the more general information sets. It is expected that global climate change will exacerbate the pressures on inland wetlands, while sea level rises will adversely affect coastal wetlands. It is also expected that the exacerbation of these pressures will increase the potential for near-irreversible changes in the ecological state of some wetlands. Concerted institutional responses to such pressures have in the past proven difficult to sustain, although there is some evidence that a more balanced approach to water use and agriculture is being developed with the provision of increasing funds to purchase water for environmental flows being one example. We identify examples from around Australia that illustrate the impacts on wetlands of long-term climate change from palaeoecological records (south-eastern Australia); water allocation (Murray-Darling Basin); dryland salinisation (south-western Australia); and coastal salinisation (northern Australia). These are provided to illustrate both the extent of change in wetlands and the complexity of differentiating the specific effects of climate change. An appraisal of the main policy responses by government to climate change is provided as a basis for further considering the opportunities for mitigation and adaptation to climate change. [ABSTRACT FROM AUTHOR]

About two-thirds of Russia's land area are flat lands, which contributes to the development of conditions favouring wetland formation. Wetlands cover vast areas, especially in the north. Wetlands in the former Soviet Union were not recognized as separate or distinct ecosystems and this is still the situation in Russia today. Bogs are one of the most abundant and typical wetlands and were treated as worthless wastelands. Beginning in the 17th century and continuing under the Soviet government there was an enforced policy to drain wetlands and reclaim the land, mainly for farming. After the collapse of the USSR, this practice was discontinued along with the Soviet model of agriculture and an end to the forced and unnecessary use of pesticides and fertilizers with the result that the toxic load on Russian aquatic systems decreased drastically. Industrial production was also greatly curtailed. While it is now recovering, many of these are turning to environmentally-friendly technologies. The intensity of land-use related impacts upon Russian wetlands is negligible compared to that in more densely populated countries and therefore the environmental conservation of wetlands in Russia may not currently be an urgent problem. There is currently no consensus on what the overall direct and indirect impacts of climate change on the number of Russian wetlands will be-in some areas they may increase but decrease in others. In Russia, the most urgent issue is not the preservation of wetlands but the development of proper wetland management practices. For effective plans, data and information on wetland status, trends and characteristics are required that are not currently available. [ABSTRACT FROM AUTHOR]

The exact size of the wetland area of South America is not known but may comprise as much as 20% of the sub-continent, with river floodplains and intermittent interfluvial wetlands as the most prominent types. A few wetland areas have been well studied, whereas little is known about others, including some that are very large. Despite the fact that most South American countries have signed the Ramsar convention, efforts to elaborate basic data have been insufficient, thereby hindering the formulation of a wetland-friendly policy allowing the sustainable management of these areas. Until now, the low population density in many wetland areas has provided a high level of protection; however, the pressure on wetland integrity is increasing, mainly as a result of land reclamation for agriculture and animal ranching, infrastructure building, pollution, mining activities, and the construction of hydroelectric power plants. The Intergovernmental Panel on Climate Change has predicted increasing temperatures, accelerated melting of the glaciers in Patagonia and the Andes, a rise in sea level of 20-60 cm, and an increase in extreme multiannual and short-term climate events (El Niño and La Niña, heavy rains and droughts, heat waves). Precipitation may decrease slightly near the Caribbean coast as well as over large parts of Brazil, Chile, and Patagonia, but increase in Colombia, Ecuador, and Peru, around the equator, and in southeastern South America. Of even greater impact may be a change in rainfall distribution, with precipitation increasing during the rainy season and decreasing during the dry season. There is no doubt that the predicted changes in global climate will strongly affect South American wetlands, mainly those with a low hydrologic buffer capacity. However, for the coming decades, wetland destruction by wetland-unfriendly development planning will by far outweigh the negative impacts of global climate change. South American governments must bear in mind that there are many benefits that wetlands bring about for the landscape and biodiversity as well as for humans. While water availability will be the key problem for the continent's cities and agroindustries, intact wetlands can play a major role in storing water, buffering river and stream discharges, and recharging subterranean aquifers. [ABSTRACT FROM AUTHOR]

The larger wetlands of Sub-Saharan Africa, cover 2,072,775 km (9.01 %) of the landmass. This paper reviews the major threats, including climate change, to these wetlands, a number of which lie in semi-arid regions. Climate change predictions are that the arid or semi-arid regions of Africa in the latitudes around the Tropics of Capricorn and Cancer will become drier. The future of wetlands is allied to human well-being, and the effects of climate change cannot be de-linked from human activities occurring in and around wetlands. The high productivity of wetlands supports substantial populations of poor people dependent on ecosystem services for at least part of their livelihood. This is particularly so in the semi-arid Sahel in the North and equivalent latitudes in the south, which are seen as vulnerable to climate change largely due to high levels of poverty and low adaptive capacity. While sustainable ecosystem management is a long-term goal, survival is more immediate to poor people depending on ecosystem services for their livelihoods. Population increase and a decrease in the resource base due to predicted decreased rainfall will lead to over exploitation of the resource base. Certain engineering interventions redistribute ecosystem services to the benefit of those upstream or away from the river system. Governance systems play a key role in the sustainable management of resources. Breakdown of governance systems through civil war is seen as a driver of poverty and a major cause of breakdown in resource conservation, increasing the dependence of poor people on ecosystems. [ABSTRACT FROM AUTHOR]

Winter stream temperatures, though infrequently studied, exert important influences on aquatic communities. To quantify effects of watershed physical characteristics on stream winter thermal regime, 54 streams (watershed area = 0.2–7.9 km2; altitude < 1300 m) on the Olympic Peninsula, Washington, USA were monitored hourly for 4 years. During the study, an exceptionally warm winter (2015) was used to evaluate influences of watershed characteristics under climatic conditions similar to those projected for mid-twenty-first century. Four watershed characteristics were hypothesized to influence winter stream temperature: stream size, elevation, solar exposure, and presence of glacial materials overlying bedrock. Larger streams were associated with colder winter water temperatures and higher thermal sensitivity to atmospheric conditions. Elevation—the strongest driver of winter stream temperatures—was negatively correlated to stream temperature, except on the coldest 15 days of winter when it had no influence. Watershed solar exposure had only a marginal influence on how cold streams were in winter but was positively correlated to diel stream temperature variation and thermal sensitivity. Streams in watersheds with glacial material overlying the sedimentary bedrock were colder and had less diel variation and lower thermal sensitivity than streams in watersheds where glacial material was not present. During the warm 2015 winter, the influences of watershed characteristics on temperature tended to be weaker compared with the other years. These insights improve our understanding of how watershed physical characteristics influence stream winter thermal regimes and how these winter thermal regimes vary across landscapes, facilitating development of predictive models, a first step in designing management plans that account for winter thermal habitat needs. [ABSTRACT FROM AUTHOR]

Greenhouse gas (GHG) emissions from freshwater streams are poorly quantified in sub-tropical climates, especially in the southern hemisphere where land use is rapidly changing. Here, we examined the distribution, potential drivers, and emissions of carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) from eleven Australian freshwater streams with varying catchment land uses yet similar hydrology, geomorphology, and climate. These sub-tropical streams were a source of CO2 (74 ± 39 mmol m−2 day−1), CH4 (0.04 ± 0.06 mmol m−2 day−1), and N2O (4.01 ± 5.98 µmol m−2 day−1) to the atmosphere. CO2 accounted for ~ 97% of all CO2-equivalent emissions with CH4 (~ 1.5%) and N2O (~ 1.5%) playing a minor role. Episodic rainfall events drove changes in stream GHG due to the release of soil NOx (nitrate + nitrite) and dissolved organic carbon (DOC). Groundwater discharge as traced by radon (222Rn, a natural groundwater tracer) was not an apparent source of CO2 and CH4, but was a source of N2O in both agricultural and forest catchments. Land use played a subtle role on greenhouse gas dynamics. CO2 and CH4 increased with catchment forest cover during the wet period, while N2O and CH4 increased with agricultural catchment area during the dry period. Overall, this study showed how DOC and NOx, land use, and rainfall events interact to drive spatial and temporal dynamics of GHG emissions in sub-tropical streams using multiple linear regression modelling. Increasing intensive agricultural land use will likely decrease regional CO2 and CH4 emissions, but increase N2O. [ABSTRACT FROM AUTHOR]

Lake browning—the increase in catchment-derived (allochthonous) dissolved organic matter (DOM) to lakes—is altering lake physicochemical environments, with consequences for phytoplankton biomass and community composition. We hypothesized that as lakes brown, there will be an increase in phytoplankton biomass and a shift to cyanobacteria-dominated phytoplankton communities as a result of the reduced light availability and increased DOM-bound nutrients (e.g., nitrogen, phosphorus, iron). We tested this hypothesis by sampling temperate lakes in central Ontario (Canada) spanning DOM quantity and quality gradients. We found that lake browning results in larger concentrations of more refractory (i.e., aromatic, high molecular weight) DOM and greater concentrations of nutrients; however, internal nutrient loading was also an important nutrient source in these lakes. We also found that these changes were related to the predominant species in the phytoplankton community. Diatoms dominated in clear oligotrophic lakes. Low levels of lake browning, with concentrations of dissolved organic carbon (DOC) between 4 and 8 mg L− 1, resulted in a shift from diatoms to cyanobacteria. Higher levels of lake browning, with concentrations of DOC between 8 and 12 mg L− 1, resulted in a replacement of cyanobacteria with mixotrophic species. Lake browning appears to fuel phytoplankton chlorophyll-a concentrations while triggering shifts to phytoplankton able to survive if not thrive in progressively browner waters. Lake browning may therefore have consequences on energy transfer through the lower food web. [ABSTRACT FROM AUTHOR]

Elevational gradients are ideal ecological venues for testing how communities respond to environmental changes associated with global warming. Recent warming rates have been shown to increase with elevation, hypothetically translating into heat waves that more adversely affect cold-adapted alpine communities than lower montane communities exposed to cold waves. We tested this hypothesis by conducting a replicated two-factor (source × elevation) experiment involving a reciprocal transplant of regional alpine and montane pond communities across two elevational sites (2345 m versus 1390 m asl). At each elevation, half of the mesocosms were inoculated with zooplankton and sedimentary egg-banks collected from alpine ponds while the other mesocosms were similarly seeded with zooplankton and sediment collected from montane ponds in 2016. After overwintering, the mesocosms were sampled for temperature and plankton during the ice-free periods of 2017 and 2018. The mesocosms at the low elevation were 8.0 ± 1.2 °C °C warmer than those at the high elevation. Elevation significantly affected total zooplankton biomass, whereas source effects were not significant. Elevation effects revealed that the temperature difference between sites affected the phenology of species within the assembled communities, but not their total biomass. Functional trait analysis revealed that the warmer environment selected for smaller body size and asexual reproduction as a warmer thermal regime stimulated several small parthenogenetic herbivores while suppressing larger, obligate sexual omnivores. Nevertheless, thermal regime shifts did not substantially affect the abundance-weighted mean functional identities of either transferred pond community, highlighting ponds as potential sources of functional insurance against increasingly extreme climate events. [ABSTRACT FROM AUTHOR]

Many studies have examined the effects of climate warming on lake stability, but few have addressed environmental changes concomitant with climate change, such as alterations in water clarity and lake inflow. Although air temperature rise is a predominant factor linked to lake thermal characteristics, climate-driven changes at watershed scales can substantially alter lake clarity and inflow, exacerbating the effects of future air warming on lake thermal conditions. Without accounting for potential changes in clarity and inflow, future thermal predictions could be inaccurate. We employed the General Lake Model to simulate future thermal conditions (relative thermal resistance to mixing; RTRM) of small (< 12 ha) mountain lakes of the western United States by calibrating the model to a set of lakes in the Southern Rocky Mountains, USA. We found that after air temperature, alterations in inflow had the largest effect on lake thermal conditions, changes in wind had the least effect, and larger lakes experienced more than double the increase in lake stability than smaller lakes. Generally, clear, high inflow lakes had the lowest stability now, and in the future, while the largest overall increase in thermal stability occurred in larger lakes with low inflows and high turbidity. Assuming air temperature rise alone, summer stability of mountain lakes of the western United States was predicted to increase by 15–23% at + 2 °C air temperatures, and by 39–62% at + 5 °C air temperatures. When accounting for associated changes in clarity and inflow, lake stability was predicted to increase by 208% with + 2 °C air warming and 318% with at 5 °C air warming. Thus, ignoring the multivariate effects of climate change can substantially underestimate changes to mountain lake thermal and stratification regimes. Dimictic lakes may become more strongly stratified and polymictic lakes will experience more prolonged stratification. While predicted changes to lake temperatures may not be harmful to trout species that currently inhabit mountain lakes, longer and more intense stratification could cause indirect effects, such as hypoxia, that could reduce growth and survival of these organisms. [ABSTRACT FROM AUTHOR]

Dam removal is analyzed as a conservation strategy for the Formosan landlocked salmon Oncorhynchus masou formosanus, a critically endangered species whose last refuge is the Wuling basin in central Taiwan. In a previous study, a stochastic age-structured simulation model was developed and used to assess the effectiveness of removing four dams in increasing salmon abundance in Kaoshan Stream in the context of climate change. Three check dams remain intact in Chichiawan Stream and one of its tributaries. In this study, the model is recalibrated for these regions and simulates the removal of each of these dams. Model analysis suggests that the combined effect of dam removal and climate change decreases the effectiveness of dam removal while increasing the negative impact of climate change on abundance. A simple graphing technique is presented for comparing the predicted impact of the removal of each dam under consideration. The model predicts that removing the dam in Chichiawan Stream has the largest potential for increasing the 2035 abundance, but only under narrow conditions of climate change and effectiveness of dam removal. The potential benefit from removing one of the tributary dams is smaller, but the conditions for reaching closer to its potential are less restrictive. This type of analysis is useful for dam removal management decisions regarding habitat restoration. [ABSTRACT FROM AUTHOR]

Climate change is predicted to increase average temperatures and the frequency of extreme weather events, and thus might alter the composition of freshwater communities through effects on climate-sensitive taxa, with uncertain outcomes for the ecosystem processes they regulate. Here we investigated how loses of more environmentally sensitive detritivores alter the key ecosystem process of leaf litter decomposition in a field experiment in two pristine streams with different local shredder assemblages in the Palatinate forest, south-western Germany. We compared bulk leaf decomposition rate and the leaf processing efficiency of shredders in enclosures containing three shredder diversity treatments, where species loss was simulated based on their climate sensitivity. Litter decomposition rates contrasted markedly between survey sites, with a 33% increase and 41% decrease in decomposition following species loss at the first and second site, respectively. Results for the first site suggest that the least sensitive taxa, which were also larger in biomass, contributed most to leaf mass loss, and these were able to compensate for losses of sensitive species, ultimately increasing bulk leaf processing. By contrast, at the second site sensitive species played a more important role in litter decomposition and their loss was not compensated when accounting for detritivore biomass. Our findings demonstrate the importance of the species trait composition of local species pools in regulating the potential effects of changes in assemblage composition caused by climate change. [ABSTRACT FROM AUTHOR]

Water abstraction continues to increase worldwide, causing periods with extreme low-flow in many streams, which will likely intensify in the future due to climate change. Extreme low-flow may have major effects on in-stream habitats, organisms, and consequently ecosystem functions. We investigated the effects of a 2 months experimentally induced extreme low-flow scenario on the physical, biological, and functional characteristics in a macrophyte-rich lowland stream using a before-after, control-impact (BACI) approach. We quantified nutrient dynamics, including inorganic nitrogen and phosphorus concentrations, ammonium uptake, and whole-stream metabolism. We found a significant decline in the stream wetted habitat area, an increase in water temperature, and an increase in the accumulation of fine organic matter with reduced flow, but no significant changes in dissolved oxygen or benthic chlorophyll a concentrations. Furthermore, the relative demand and overall uptake of ammonium was lower in the low-flow reach relative to the control reach, whereas the relative demand and uptake of phosphate were higher at low-flow. Our results demonstrate that low-flow conditions cause resource limitation in stream biota most likely due to increased thickness of the diffusive boundary layers and an enhanced heterotrophic activity in the accumulated fine organic matter. Our results imply that the basal resources for productivity shift from autotrophic towards more heterotrophic resources causing a shift at higher trophic levels towards more detritivore based and less herbivore based food webs with implications for the invertebrate community composition and the distribution of functional feeding groups. Based on the strong links observed between low-flow and nutrient uptake, we suggest that functional metrics are suitable to assess the effects of low-flow conditions in small streams. [ABSTRACT FROM AUTHOR]

Stream flow intermittency and subsequent streambed drying, which already occurs in most biomes worldwide, is expected to increase in many regions due to both climate change and increased water demand. We studied the effects of streambed drying on leaves and epilithic biofilm and their effects on potential consumers. In the field, resources were conditioned according to the following treatments: (i) continuously submerged (PERM), (ii) submerged, exposed to the dry streambed and then submerged again (INT), or (iii) conditioned in the dry streambed and only allowed instream conditioning for 1 week (DRY, only for leaves). The results showed that drying affects resource quality, and the effects on biofilm were more severe than those on leaves. Both DRY leaves and INT biofilm showed lower microbial colonization and nitrogen accrual, whereas INT leaves had similar characteristics to PERM leaves. Drying resulted in decreased shredder and herbivore consumption rates and detritivore growth. Our results suggest that bottom-up effects of drying through changes in resource quality can constrain detritivore growth in temporary streams, potentially affecting stream secondary production and invertebrate-mediated organic matter cycling under a drier climate scenario. [ABSTRACT FROM AUTHOR]

The wide range of ecological goods and services provided by tropical coastal lagoons and wetlands are under considerable pressure due to the synergistic effects of local anthropogenic impact and global climate change. In transitional waters, salinity is a key driver of ecological processes mostly depending on the balance between marine and river inputs, a balance that can be significantly modified by climate change and by anthropogenic alteration of the watershed. Mesoamerica being considered as a climate change hot-spot and as an ecoregion strongly vulnerable to global change, our study aimed at analyzing the relationship between salinity, river runoff, and rainfall variability in a tropical coastal lagoon and to assess the respective influence of climate change and watershed management. The study focusing on the large and shallow coastal lagoon of Laguna de Terminos in south eastern Mexico established: (1) the variability in salinity distribution along the yearly cycle and the occurrence of a high salinity anomaly period during the wet season of 2009; (2) the relationship between lagoon waters salinity and river inputs further underlying the anomalous situation encountered in 2009; (3) a long term increase in river discharge during the past 60 years, indicating potential salinity decrease in the lagoon during that same period; (4) an absence of any change in rainfall linking the increase in runoff to watershed management rather than long term trend in climate change. Additionally, the specific context of the 2009-2010 Central-Equatorial Pacific El Niño is underlined and the potential relationship between river discharge and ENSO is discussed. Those results should be of significant practical value to decision-makers who are often keen to point the finger at global climate change when local environmental management is also and sometime most significantly responsible. [ABSTRACT FROM AUTHOR]

Lakes are sentinels of change in the landscapes in which they are located. Changes in lake function are reflected in whole-system metabolism, which integrates ecosystem processes across spatial and temporal scales. Recent improvements in high-frequency open-water metabolism modeling techniques have enabled estimation of rates of gross primary production (GPP), respiration (R), and net ecosystem production (NEP) at high temporal resolution. However, few studies have examined metabolic rates over daily to multi-year temporal scales, especially in oligotrophic ecosystems. Here, we modified a metabolism modeling technique to reveal substantial intra- and inter-annual variability in metabolic rates in Lake Sunapee, a temperate, oligotrophic lake in New Hampshire, USA. Annual GPP and R increased each summer, paralleling increases in littoral, but not pelagic, total phosphorus concentrations. Storms temporarily decoupled GPP and R, resulting in greater decreases in GPP than R. Daily rates of GPP and R were positively correlated on warm days that had stable water columns, and metabolism model fits were best on warm, sunny days, indicating the importance of lake physics when evaluating metabolic rates. These metabolism data span a range of temporal scales and together suggest that Lake Sunapee may be moving toward mesotrophy. We suggest that functional, integrative metrics, such as metabolic rates, are useful indicators and sentinels of ecosystem change. We also highlight the challenges and opportunities of using high-frequency measurements to elucidate the drivers and consequences of intra- and inter-annual variability in metabolic rates, especially in oligotrophic lakes. [ABSTRACT FROM AUTHOR]

Biological invasion represents one of the major threats to global biodiversity as alien species often displace indigenous species. Knowledge of the mechanisms behind such displacements and the driving factors of the competitive superiority of the alien species remain limited. We combined analysis of field data and laboratory experiments examining species interactions to investigate the impact of temperature in the case of the alien freshwater snail Physa acuta and the indigenous snail Physa fontinalis. From field data, we identified higher temperature as the most important difference between sites populated by P. acuta and P. fontinalis. Results of the species interaction experiment conducted at 15, 20, and 25 °C revealed that the competitive superiority of P. acuta over P. fontinalis increases at warmer temperatures. In single species treatments, increasing temperature stimulated growth rates in both species. Coexistence treatments revealed an asymmetric competitive interaction between the two snail species. In both species, the density of conspecifics did not affect growth rates; however, density of heterospecifics did. This effect of heterospecifics varied with temperature. At 15 °C, the presence of heterospecifics stimulated the growth rates of both species, while at higher temperatures the presence of heterospecifics stimulated the growth rate in P. acuta only, but inhibited the growth rate in P. fontinalis. Our study shows that temperature can be a powerful driver of competitive outcomes between alien and indigenous species and highlight that the environmental context influences species interactions and impacts of alien species. [ABSTRACT FROM AUTHOR]

Seasonal changes in emergence rates of aquatic insects and the relative abundance of volant aquatic and terrestrial insects were monitored using emergence, UV-light and Malaise traps over a 14-month period along two forested streams in Hong Kong. Although the mean annual emergence rates in terms of aquatic insect numbers, ranged from 9399 to 17,127 individuals m and were comparable to studies elsewhere, rates in biomass terms (0.713-1.168 g DW m year) were at the lower end of reported values. The absolute magnitude of the annual aquatic subsidy to terrestrial habitats around the two study streams thus appeared to be rather low. Seasonal patterns of emergence trap catches generally matched yields of aquatic insects from light and Malaise traps, with high emergence and abundance from March to October including the entire wet season, and relatively low dry-season emergence. Inter-stream differences in abundance were detected during this period, when local spate events appeared to cause short-term reductions in the aquatic insect subsidy, although data from multiple years would be needed to confirm this. Seasonal patterns of volant aquatic and terrestrial insects were similar in light- and Malaise-trap samples at both sites, although aquatic insects accounted for 74-87 % of light-trap captures but only 13-14 % of insects in Malaise traps. The relative abundance of aquatic versus terrestrial insects was similar between seasons in both trap types, suggesting that aquatic subsidy may remain important for riparian insectivores during the dry season when all insects are scarce. [ABSTRACT FROM AUTHOR]

Numerous simulation studies have considered the effects of impending climate change on lakes. Predictive models exist for the responses of a multitude of variables to a warmer climate, and potential effects on food webs and ecosystem functions. Although these predictions are numerous, there is a need for manipulative experiments testing for the effects of warming on actual lake systems. We used power plant lakes across the central Midwestern US as a substitute for future climate change effects. These treatment lakes receive heated effluent and are typically 2-6 °C warmer than other regional lakes. We collected data from 1997 to 2010 on a number of abiotic and biotic variables from three of these treatment lakes and six control lakes that were of similar size and location but did not have an artificial thermal regime. Phosphorus and phytoplankton concentrations were similar between treatment groups, although treatment lakes had greater phosphorus and less phytoplankton in September. No differences existed in turbidity (measured as Secchi depth transparency). Zooplankton were less abundant in treatment lakes than in control lakes throughout our sampling period (May-October), with differences in cladocerans driving this disparity. There was evidence of earlier spawning of gizzard shad ( Dorosoma cepedianum) due to the warmer temperature regime, but not for bluegill ( Lepomis macrochirus). Average sizes of juvenile bluegill were larger in warmed systems in July and August. Juvenile largemouth bass ( Micropterus salmoides) were larger in heated systems in June, but no differences existed in July or August. Growth of adult largemouth bass was greater in systems with a warmer thermal regime. Our results provide insights into patterns that can be expected in the future, and may be used to further understand the wide-reaching implications of climate change. [ABSTRACT FROM AUTHOR]

Despite increasing evidence that climate change affects aquatic ecosystems, influences on lake benthic communities are still poorly known. We studied the effects of short-term climatic fluctuation on profundal benthic invertebrates using at least six annual samples (over 6-17 years) from 38 Finnish lake basins. Faunal abundance, species diversity and species composition were related to annual winter and summer North Atlantic Oscillation (NAO) indices as measures of climatic fluctuation. Algal productivity, hypolimnetic oxygen concentration and water temperature weakly increased during the positive NAO periods. Profundal macroinvertebrate abundance and species diversity declined with increasing NAO in summer, but not winter. The main gradient of species compositional overturn (DCA axis 1) was negatively associated with lake productivity and varied independent of NAO, whereas the secondary gradient (DCA axis 2) correlated positively with hypolimnetic temperature and winter NAO. The responses of species diversity and abundance to climatic fluctuation were not related to any measured lake-specific environmental characteristics, but the response of species composition (DCA axis 1) to NAO showed a consistent negative association with lake depth and trophic status, so that size and even direction of compositional response to NAO was related to these two lake characteristics. Our study suggests that local profundal benthic macroinvertebrate communities can respond rapidly to short-term, large-scale climate fluctuation and hence that future global warming can be expected to modify these sensitive communities considerably. [ABSTRACT FROM AUTHOR]

Joint effects of climate warming and other stressors are potentially complex and difficult to predict. In stream ecosystems, exotic riparian species have the potential to alter leaf-shredding detritivorous invertebrate assemblages and leaf litter breakdown due to differences in the quality of litter inputs. This is the case for Eucalyptus plantations, which are widespread, occurring along riparian corridors of streams around the world. We hypothesised that the presence of Eucalyptus globulus (Labill.) litter (1) impairs detritivore fitness both directly (i.e., through leaf consumption) and indirectly (i.e., through leaf leachates in the water) and (2) impairs litter breakdown, (3) with stronger effects at higher temperatures. We tested these hypotheses in microcosm experiments with two detritivore species from two locations: the stonefly Diamphipnosis samali (Illies, 1960) in Chile and the caddisfly Calamoceras marsupus (Brauer 1865) in Spain. Eucalyptus leaves affected detritivore growth mainly by direct consumption, while the presence of both Eucalyptus leaves and leachates inhibited the breakdown of native litter. When both litter types were available, breakdown of Eucalyptus leaves was enhanced, possibly as a means of compensatory feeding. Increased temperature exacerbated the negative effect of Eucalyptus on native litter breakdown, possibly because it reduced detritivore survival. Our results add to the mounting evidence that joint effects of multiple stressors can be non-additive, and suggest that the sole presence of Eucalyptus leaves and leachates in the water may impact stream communities and ecosystem functions even if native litter is available, with further negative effects to be expected under a warmer climate. [ABSTRACT FROM AUTHOR]

Harmful algal blooms depend on several factors linked to climate and catchment conditions. Blooms can show significant daily, monthly, seasonal, inter-annual variability as well as horizontal variation in a lake. In the present study, we use satellite data to explore the sensitivity of different sections of a large eutrophic lake (Lake Taihu) to climate and catchment-related drivers. Bloom coverage in the larger open areas of the lake, historically less eutrophic, has increased over the last 12 years even though extensive efforts were made to improve catchment conditions. Decadal trends in these lake sections were more sensitive to climate conditions and nutrient concentrations compared with the more enclosed eutrophic bays. Bloom coverage was bimodal during the year, with regional differences occurring during the second maximum. Links between climate variability, nutrients, and bloom coverage suggest that major bloom events are likely to continue to occur. [ABSTRACT FROM AUTHOR]

We assessed the effects of rising temperature and presence of a dominant detritivore ( Allogamus laureatus; Trichoptera, Limnephilidae) on the decomposition of submerged oak litter ( Quercus robur L.) and associated detritivore and fungal communities in a mountain stream in central Portugal. It was divided longitudinally, with one half maintained at ambient temperature (mean = 12.4 °C) while the other was warmed ~3 °C above ambient temperature. Oak leaves in litter bags were incubated in both stream halves, with half of the bags containing one A. laureatus larva. Replicate bags were collected over 6 weeks to determine litter mass remaining and the detritivore and fungal communities. A. laureatus stimulated decomposition of oak litter and colonization by other shredders at ambient temperature. It also increased fungal biomass at increased temperature, and changed the community of fungi. Higher temperature inhibited A. laureatus activity, resulting in a substantial change in the strength of interactions within both fungal and detritivore assemblages, with important consequences for leaf litter decomposition. [ABSTRACT FROM AUTHOR]

Among the environmental factors affecting benthic algae and cyanobacteria in streams, the one often producing the largest effects is flow intermittency. This study aimed to characterize the responses of algal assemblages to flow intermittency in a Mediterranean intermittent stream during the drying, non-flow (112 days), and rewetting phases. Algae growing in the epilithic, epipsammic and hyporheic streambed compartments were analyzed for pigment composition, and for the existence of structural changes in cells. Chlorophyll-a concentrations decreased between 60 to 90 % during the non-flow phase, indicating low resistance of algal assemblages to desiccation. In contrast, fast recoveries of Chlorophyll-a when flow resumed indicated high resilience. Pigment composition revealed that the epilithic algal assemblage was considerably different than the epipsammic and hyporheic ones. These differences were mainly attributed to the physical conditions prevailing on each streambed compartment that allowed the growth of different algal assemblages. During the non-flow phase, the synthesis of protective carotenoids (i.e. echinenone and scytonemin) and the occurrence of cell resistance structures (i.e. enlarged membrane thickness and resistant spores) enhanced resistance of the epilithic biofilm. The resistance observed in the epilithic biofilm might also be related to the tightly adhered growth-form of algae on this substratum. Main results suggest that algal assemblages in the epilithic compartment, which were the most exposed to desiccation, were structurally and functionally better adapted to flow interruption than those colonizing other streambed compartments, and that this compartment plays a crucial role in maintaining ecosystem functions under varying flow periods. [ABSTRACT FROM AUTHOR]

Litter decomposition, a fundamental ecosystem process in woodland streams, is potentially affected by the predicted increase in water temperature. Here, we assessed the effects of experimental and seasonal warming on oak litter decomposition and on the relative contributions of microbes and invertebrates to this process. Experimental warming (~3 °C) stimulated litter decomposition in the coldest, but not in the warmest, months. This may be attributed to (1) higher temperature sensitivity of decomposition at lower ambient temperature due to temperature limitation of enzymatic activity, (2) higher relative temperature increase in winter than in warmer months, (3) existence of a previous warming period in winter, and (4) stronger stimulation of the activity of detritivores by warming in winter due to the prevalence of earlier (smaller) instars than in warmer months. The low response of litter decomposition to warming may have been due to the low nutrient availability in the study stream. The 30-day litter decomposition was stimulated over the seasonal gradient (monthly mean temperature: 6-16 °C), which may be attributed to a stimulation of metabolic activities by warming and to changes in detritivore life history over the seasons. The stimulation of litter decomposition with temperature suggests that the rate of CO release from freshwaters will increase under global warming. However, invertebrate-driven litter decomposition was more responsive to warming than microbial-driven litter decomposition, suggesting that a larger fraction of litter carbon may be converted into secondary production and stored in the system for longer periods. [ABSTRACT FROM AUTHOR]

North and Central America has a combined total of 2.5 million km of wetlands, with 51 % in Canada, 46 % in the USA, and the remainder in subtropical and tropical Mexico and Central America. Loss rates are well known for the conterminous USA and for parts of Canada but poorly understood for Mexico and Central America. Wetlands of North America continue to be threatened due to drainage for agriculture and urban development, extreme coastal and river management, water pollution from upstream watersheds, peat mining, waterfowl management, and more recently climate change. Human use of wetlands in this region are many, including receiving ecosystem services such as water purification, flood regulation, climate regulation, and direct provisioning benefits for many cultures living in and among wetlands, especially in the Louisiana Delta and in Mexico and Central America. Climate change affects will cause wetland impacts on coastal wetlands due to sea level rise and on inland wetlands due to changes in precipitation, air temperature, and river discharges. Wetlands, in turn, have a major role in the storage of carbon in boreal regions of Canada and with carbon sequestration in temperate and tropical wetlands of the Americas. [ABSTRACT FROM AUTHOR]

This review reports background information on wetlands in the Northeast Asia and High Asia areas, including wetland coverage and type, significance for local populations, and threats to their vitality and protection, with particular focus on the relationship of how global change influenced wetlands. Natural wetlands in these areas have been greatly depleted and degraded, largely due to global climate change, drainage and conversion to agriculture and silviculture, hydrologic alterations, exotics invasions, and misguided management policies. Global warming has caused wetland and ice-sheet loss in High Asia and permafrost thawing in tundra wetlands in Northeast Asia, and hence induced enormous reductions in water-storage sources in High Asia and carbon loss in Northeast Asia. This, in the long term, will exacerbate chronic water shortage and positively feed back global warming. Recently, better understanding of the vital role of healthy wetland ecosystems to Asia's sustainable economic development has led to major efforts in wetland conservation and restoration. Nonetheless, collaborative efforts to restore and protect the wetlands must involve not only the countries of Northeast and High Asia but also international agencies. Research has been productive but the results should be more effectively integrated with policy-making and wetland restoration practices under future climatic scenarios. [ABSTRACT FROM AUTHOR]

Wetlands in south-eastern Australia and other arid regions of the world are experiencing increases in salinity due to dryland salinization and climate change. We investigated changes in wetland ecological function, measured as phytoplankton and benthic algal Chl a, over a large salinity gradient (0.047–226 mS cm−1) and in relation to several local water chemistry variables that may be important predictors of algal biomass. We investigated the relative importance of landscape variables that may affect input pollution and hydrology of wetlands at four spatial scales (100, 500, 1,000 and 5000 m). We explored the strength and form of the relationships between algal biomass and local and landscape predictors with emphasis on the effects of local and landscape salinity. We found local variables were more important than landscape variables in influencing algal biomass. We also found salinity of wetlands was not a good predictor of phytoplankton biomass but it did predict benthic algal biomass. [ABSTRACT FROM AUTHOR]

Abstract.  We analysed the sensitivity of European Trichoptera (caddisfly) species to climate change impacts based on their distribution and ecological preferences, and compared the fraction of species potentially endangered by climate change between the European ecoregions. The study covers 23 European ecoregions as defined by Illies (1978). For 1134 Trichoptera species and subspecies, we coded 29 parameters describing biological and ecological preferences and distribution based on the evaluation of more than 1400 literature references. Five parameters served to describe the species’ sensitivity to climate change impacts: endemism, preference for springs, preference for cold water temperatures, short emergence period, and restricted ecological niches in terms of feeding types. Of the European Trichoptera species and subspecies, 47.9% are endemic, 23.1% have a strong preference for springs, 21.9% are cold stenothermic, 35.5% have a short emergence period, and 43.7% are feeding type specialists. The fraction of endemic species meeting at least one of the four other sensitivity criteria mentioned above is highest in the Iberic-Macaronesian Region (30.2% of all species), about 20% in several other south European ecoregions, and about 10% in high mountain ranges. In 15 out of 23 ecoregions (including all northern European and lowland ecoregions) the proportion is less than 3%. The high fraction of potentially endangered species in southern Europe is a result of speciation during the Pleistocene. Species having colonised northern Europe afterwards have generally a large geographical range and are mainly generalists and thus buffered against climate change impacts. [ABSTRACT FROM AUTHOR]

Recently there have been major increases in water colour and dissolved organic carbon (DOC) in many forest lakes that serve as drinking water reservoirs in the southern part of Norway. We studied changes in the physical and chemical properties in (I) a selected group of lakes and (II) raw water from the municipal waterworks of Oslo since 1983 and 1976, respectively. The largest increase in DOC and water colour occurred between 1997 and 2001. Statistically significant correlations are seen between water colour and accumulated amounts of precipitation, while variation in temperature had no apparent effect. Despite significant reduction in sulphate concentrations in precipitation and lake waters since 1980, the lakes were more acidic in 2000 and 2001 than in previous years. Increases in colour and acidity, together with somewhat minor changes in DOC concentrations, indicate changes in the physical and chemical properties of the natural organic matter (NOM). Alteration in properties of NOM is most probably caused by increased precipitation that has changed the water pathways in the catchments and increased the leaching of organic components from the upper forest floor. [ABSTRACT FROM AUTHOR]

Abstract. This paper presents an overview of water resources issues in the context of world population growth, climate change, and variability, and provides examples of how these issues affect local and regional water policy concerns. Also discussed is the associated research of the international scientific community in regard to physically-based modeling of the hydrological cycle, with special focus on the Global Energy and Water cycle EXperiment (GEWEX) Programme. The critical role of precipitation measurements for climate model accuracy is emphasized, with a review of several satellite methods and strategies for improving precipitation measurements. Finally, the impact of semiarid regions on global hydrologic issues is underscored with a review of research conducted by SAHRA, the National Science Foundation Science and Technology Center dedicated to Sustainability of semi-Arid Hydrology and Riparian Areas. [ABSTRACT FROM AUTHOR]

Measures to reduce lake phosphorus concentrations have been encouragingly successful in many parts of the world. After significant eutrophication in the twentieth century, nutrient concentrations have declined in many natural settings. In addition to these direct anthropogenic impacts, however, climate change is also altering various processes in lakes. Its effects on lacustrine nutrient budgets remain poorly understood. Here we investigate the total phosphorus (TP) concentrations in the epilimnion of the meromictic Lake Zug under present and future climatic conditions. Results are compared with those of other deep lakes. Data showed that TP transported from the hypolimnion by convective winter mixing was the most important source of TP for the epilimnion, reaching values more than ten times higher than the external input from the catchment. We found a logarithmic relationship between winter mixing depth (WMD) and epilimnetic TP content in spring. Warming climate affects WMD mainly due to its dependence on autumn stratification. Model simulations predict a reduction of average WMD from 78 (current) to 65 m in 2085 assuming IPCC scenario A2. Other scenarios show similar but smaller changes in the future. In scenario A2, climate change is predicted to reduce epilimnetic TP concentrations by up to 24% during warm winters and may consequently introduce significant year-to-year variability in primary productivity. [ABSTRACT FROM AUTHOR]