Search

To address ongoing threats from human pressures and climate changes, water managers and users require a visual tool that provides accurate information about the health of waterbodies for decision making. However, there is a lack of less sophisticated methods, such as biotic scoring, to assess the health of rivers in West Africa. To bridge this gap, we have developed a macroinvertebrate-based scoring system for monitoring the health of rivers in the Sahelian regions. We adopted a multi-habitat sampling approach to collect macroinvertebrates using hand nets, and these specimens were identified mostly to family taxonomic level using keys. We recorded more than 75 taxa of macroinvertebrates, each assigned relative sensitivity scores to human disturbances ranging from 1 (very tolerant) to 10 (highly sensitive). The Burkina Biotic Score System (BBIOSS) and the Average Score Per Taxa (ASPT) demonstrated a strong and significant correlation with environmental variables, including anthropogenic pressures types (r = 0.6; p < 0.01) making it a robust tool for monitoring rivers. Here, our findings revealed that all taxa scored are expected to be those reported in Western African freshwater. This study has produced an effective tool that can be used or adapted to monitor other riverine ecosystems in West Africa, potentially contributing to the preservation of water and biological resources. [ABSTRACT FROM AUTHOR]

In Australia the impacts of climate change are resulting in considerable water scarcity, a scenario affecting the green and blue spaces that provide well-recognized individual health benefits. However, far less is known about the social health benefits of these spaces, particularly for those residing in rural Australian river communities. In this geographic context, water issues are compounded by a dominant culture that privileges the commodification of water for agricultural purposes over other interests. Using an environmental justice perspective consistent with a green social work approach, this proof-of-concept study contributes a critical element to water debates by examining the cultural, recreational, and environmental meanings of water for the rural river community of Mildura. Results from an online mixed-methods questionnaire (N = 33) show that people privileged cultural meanings of water as fundamental to life, were concerned for river health, and felt marginalized in water debates. Findings suggest that understanding communities' hydrosocial relationships is key to environmentally and socially just water management and to individual, community, and environmental health. Social work can contribute to such environmental issues by working collaboratively to enable communities to exercise their voices and to advocate to decision makers to include consideration of environmental, social, and cultural impact. [ABSTRACT FROM AUTHOR]

This article explores continuities and changes in the damming of rivers in the global South. By the 2000s, the infrastructural promises of large dams seemed exhausted. Yet, currently dams are making a strong comeback with new justifications highlighting their capacity to produce low-carbon energy and climate-proofed waterscapes, while the harms they generate are being presented as fixable. Through cases from the Mekong (Laos and Cambodia), and the Grijalva (Mexico) River Basins, we problematize these claims. Despite changes in the aspirations and agencies that foster damming, obdurate dam materialities and the new profit-maximizing operation modes provoke violent continuities of infrastructural harms and hinder the repurposing of dams to serve climate combat. Neoliberalised dams even augment climate vulnerabilities, as the more volatile rivers increasingly exceed their ordering capacities. We also show how the new dam assemblages continue dispossessing riverine residents while divergently strengthening corporate and state powers and obscuring relations of responsibility. [ABSTRACT FROM AUTHOR]

The migratory life history of anadromous salmonids requires successful migration between nursery, feeding, and spawning habitats. Smolting is the major transformation anadromous salmonids undergo before migration to feeding areas. It prepares juvenile fish for downstream migration and their entry to seawater. We reviewed the effects of climate change on smolt ecology from the growth of juveniles in fresh water to early post-smolts in the sea to identify the potential effects of climate change on migratory salmonid populations during this period in their life history. The focus was especially on Atlantic salmon. The shift in suitable thermal conditions caused by climate change results in Atlantic salmon expanding their range northward, while at the southern edge of their distribution, populations struggle with high temperatures and occasional droughts. Climatic conditions, particularly warmer temperatures, affect growth during the freshwater river phase. Better growth in northern latitudes leads to earlier smolting. Thermal refuges, the areas of cooler water in the river, are important for salmonids impacted by climate change. Restoring and maintaining connectivity and a suitably diverse mosaic habitat in rivers are important for survival and growth throughout the range. The start of the smolt migration has shifted earlier as a response to rising water temperatures, which has led to concerns about a mismatch with optimal conditions for post-smolts in the sea, decreasing their survival. A wide smolt window allowing all migrating phenotypes from early to late migrants' safe access to the sea is important in changing environmental conditions. This is also true for regulated rivers, where flow regulation practices cause selection pressures on migrating salmonid phenotypes. The freshwater life history also affects marine survival, and better collaboration across life stages and habitats is necessary among researchers and managers to boost smolt production in rivers. Proactive measures are recommended against population declines, including sustainable land use in the catchment, maintaining a diverse mosaic of habitats for salmonids, restoring flow and connectivity, and conserving key habitats. [ABSTRACT FROM AUTHOR]

Climate change is altering hydrological cycles globally, and in Mediterranean (med‐) climate regions it is causing the drying of river flow regimes, including the loss of perennial flows. Water regime exerts a strong influence over stream assemblages, which have developed over geological timeframes with the extant flow regime. Consequently, sudden drying in formerly perennial streams is expected to have large, negative impacts on stream fauna. We compared contemporary (2016/17) macroinvertebrate assemblages of formerly perennial streams that became intermittently flowing (since the early 2000s) to assemblages recorded in the same streams by a study conducted pre‐drying (1981/82) in the med‐climate region of southwestern Australia (the Wungong Brook catchment, SWA), using a multiple before‐after, control‐impact design. Assemblage composition in the stream reaches that remained perennial changed very little between the studies. In contrast, recent intermittency had a profound effect on species composition in streams impacted by drying, including the extirpation of nearly all Gondwanan relictual insect species. New species arriving at intermittent streams tended to be widespread, resilient species including desert‐adapted taxa. Intermittent streams also had distinct species assemblages, due in part to differences in their hydroperiods, allowing the establishment of distinct winter and summer assemblages in streams with longer‐lived pools. The remaining perennial stream is the only refuge for ancient Gondwanan relict species and the only place in the Wungong Brook catchment where many of these species still persist. The fauna of SWA upland streams is becoming homogenised with that of the wider Western Australian landscape, as drought‐tolerant, widespread species replace local endemics. Flow regime drying caused large, in situ alterations to stream assemblage composition and demonstrates the threat posed to relictual stream faunas in regions where climates are drying. [ABSTRACT FROM AUTHOR]

Mass mortality of Unionidae from the genera Middendorffinaia, Buldowskia, and Sinanodonta was observed in the plain rivers of the south of Primorsky Krai (south of the Russian Far East) in the abnormally hot and low-water summer–autumn season of 2021. Nodularia douglasiae (Griffith et Pidgeon, 1833) was the most resistant and thus least affected species, the species from the genera Sinanodonta and Middendorffinaia, the least resistant and the most affected. [ABSTRACT FROM AUTHOR]

Anthropogenic climate change is affecting rivers worldwide, threatening water availability and altering the risk of natural hazards. Understanding the pattern of regional streamflow trends can help to inform region-specific policies to mitigate and adapt to any negative impacts on society and the environment. We present a benchmark dataset of long, near-natural streamflow records across Aotearoa New Zealand (NZ) and the first nationwide analysis of observed spatiotemporal streamflow trends. Individual records rarely have significant trends, but when aggregated within homogenous hydrologic regions (determined through cluster analyses), significant regional trends emerge. A multitemporal approach that uses all available data for each region and considers trend significance over time reveals the influence of decadal variability in some seasons and regions, and consistent trends in others. Over the last 50+ years, winter streamflow has significantly increased in the west South Island and has significantly decreased in the north North Island; summer streamflow has significantly decreased for most of the North Island; autumn streamflow has generally dried nationwide; and spring streamflow has increased along the west coast and decreased along the east coast. Correlations between streamflow and dynamic and thermodynamic climate indices reveal the dominant drivers of hydrologic behavior across NZ. Consistencies between the observed near-natural streamflow trends and observed changes in circulation and thermodynamic processes suggest possible climate change impacts on NZ hydrology. [ABSTRACT FROM AUTHOR]

Brook trout (Salvelinus fontinalis) are an iconic freshwater salmonid native to northeastern North America. They prefer cold, clean rivers and lakes, and have been culturally, socially and economically valued for decades. Overharvest and deforestation associated with European settlement in southern Ontario, Canada led to notable declines in brook trout abundance in rivers and streams by the late 1800s. Today, they are threatened by further habitat degradation, non‐native species, and climate change. In this study, we document brook trout occupancy in rivers and streams of the Mixedwood Plains Ecozone in southern Ontario, between 1970–1980 and 2000–2010. We used generalised linear models to determine occupancy variation between the two time periods at five spatial scales spanning multiple watershed levels. We detected a decline in occupancy between time periods for the tertiary (from 23% to 17%) and quaternary (from 35% to 22%) watershed scales. In the Credit River‐Sixteen Mile Creek watershed, mean occupancy decreased to a third of past estimate (from 31% to 10%). For a subset of 86 sites with overlapping sampling in both periods no temporal trend was detected, but a post‐hoc analysis indicated low statistical power (0.07), which suggested that more intensive sampling would be needed to better quantify brook trout occupancy changes at this scale. The occupancies quantified for the past period in our study may serve as benchmarks for brook trout restoration efforts. [ABSTRACT FROM AUTHOR]

River microbiome influenced by increasing extreme events in the Anthropocene. Ensemble model predicts adaptation type of microbiome under heatwave. [ABSTRACT FROM AUTHOR]

In summer, salmonids can experience thermal stress during extreme weather conditions. This may affect their growth and even threaten their survival. Cool water zones in rivers constitute thermal refuges, allowing fish to be more comfortable to grow and survive in extreme events. Therefore, identifying and understanding the spatiotemporal variability of discrete thermal refuges and larger scale cooling zones in rivers is of fundamental interest. This study analyzes thermal refuges as well as cooling zones in two salmonid rivers in a subarctic climate by use of thermal infrared (TIR) imagery. The two studied rivers are the Koroc and Berard Rivers, in Nunavik, Quebec, Canada. On the 17 km studied section of the Berard River, four thermal refuges and five cooling zones were detected, covering 46% of the surveyed section of the river. On the 41 km section studied for the Koroc River, 67 thermal refuges and five cooling zones were identified which represent 32% of the studied section of the river. 89% of identified thermal refuges and about 60% of cooling zones are groundwater-controlled. Continuity of permafrost and shape of the river valley were found to be the main parameters controlling the distribution of refuges and cooling zones. These data provide important insights into planning and conservation measures for the salmonid population of subarctic Nunavik rivers. [ABSTRACT FROM AUTHOR]

• River water quality tends to deteriorate during droughts and heatwaves. • Water quality data are analysed at 314,046 locations worldwide. • Climate type, land use and wastewater treatment affect water quality responses under extremes. Droughts and heatwaves have a major impact on river water quality worldwide. However, previous studies of river water quality under these climate extremes are limited to a small number of river basins and regions, mainly located in North America, Europe or Australia. In this study, we estimate the large-scale effects of droughts, heatwaves and compound drought-heatwave events on river water quality for a total of 314,046 water quality monitoring stations worldwide over the period 1980–2021. We focus on 16 water quality constituents grouped into physical (e.g., temperature, salinity), chemical (e.g., pharmaceuticals, pesticides) and biological constituents (e.g., biochemical oxygen demand, faecal coliform). Further, we analyse the response of each constituent to droughts and heatwaves in relation to climate type, land use and level of wastewater treatment. We find a general deterioration in river water quality under droughts and heatwaves globally for most rivers and water quality constituents considered. For example, there is on average a 27 % increase in river water temperature, 17 % decrease in dissolved oxygen and 24 % increase in salinity under droughts and heatwaves. In addition, we find that climate type, land use and level of wastewater treatment have a significant effect on the magnitude of response in each water quality constituent during these extreme events. The median increase in river water temperature under compound drought-heatwaves is strongly driven by climate zone with higher warming rates at the polar climate zone (+4.5 °C) compared to the tropical zone (+2.1 °C). Increases in salinity under droughts are on average two times larger in irrigated regions compared to non-irrigated regions. The concentrations of nutrients (P and N) in rivers can either increase or decrease under droughts, depending on the nutrient form (dissolved vs. particulate) and land use (urban vs. rural). Higher levels of wastewater treatment contributed to a greater decrease in pathogenic concentrations under droughts and heatwaves (as indicated by faecal coliform). Pharmaceuticals show mixed responses mainly depending on the persistence of the constituent in surface waters, with for instance declines in diclofenac concentrations under droughts and heatwaves due to increased decay under higher water temperatures. The results of this study provide a broader understanding of how droughts and heatwaves affect river water quality compared to previous local and regional-scale analyses. In addition, this study could form the basis for large-scale modelling of river water quality under droughts and heatwaves. [ABSTRACT FROM AUTHOR]

Rivers originating in High Mountain Asia are crucial lifelines for one-third of the world’s population. These fragile headwaters are now experiencing amplified climate change, glacier melt, and permafrost thaw. Observational data from 28 headwater basins demonstrate substantial increases in both annual runoff and annual sediment fluxes across the past six decades. The increases are accelerating from the mid-1990s in response to a warmer and wetter climate. The total sediment flux from High Mountain Asia is projected to more than double by 2050 under an extreme climate change scenario. These findings have far-reaching implications for the region’s hydropower, food, and environmental security. [ABSTRACT FROM AUTHOR]

Understanding the observed temperature dependence of decomposition (i.e., its "apparent" activation energy) requires separation of direct effects of temperature on consumer metabolism (i.e., the "inherent" activation energy) from those driven by indirect seasonal patterns in phenology and biomass, and by longer‐term, climate‐driven shifts in acclimation, adaptation, and community assembly. Such parsing is important because studies that relate temperature to decomposition usually involve multi‐season data and/or spatial proxies for long‐term shifts, and so incorporate these indirect factors. The various effects of such factors can obscure the inherent temperature dependence of detrital processing. Separating the inherent temperature dependence of decomposition from other drivers is important for accurate prediction of the contribution of detritus‐sourced greenhouse gases to climate warming and requires novel approaches to data collection and analysis. Here, we present breakdown rates of red maple litter incubated in coarse‐ and fine‐mesh litterbags (the latter excluding macroinvertebrates) for serial approximately one‐month increments over one year in nine streams along a natural temperature gradient (mean annual: 12.8°–16.4°C) from north Georgia to central Alabama, USA. We analyzed these data using distance‐based redundancy analysis and generalized additive mixed models to parse the dependence of decomposition rates on temperature, seasonality, and shredding macroinvertebrate biomass. Microbial decomposition in fine‐mesh bags was significantly influenced by both temperature and seasonality. Accounting for seasonality corrected the temperature dependence of decomposition rate from 0.25 to 0.08 eV. Shredder assemblage structure in coarse‐mesh bags was related to temperature across both sites and seasons, shifting from "cold" stonefly‐dominated communities to "warm" communities dominated by snails or crayfish. Shredder biomass was not a significant predictor of either coarse‐mesh or macroinvertebrate‐mediated (i.e., coarse‐ minus fine‐mesh) breakdown rates, which were also jointly influenced by temperature and seasonality. Unlike fine‐mesh bags, however, temperature dependence of litter breakdown did not differ between models with and without seasonality for either coarse‐mesh (0.36 eV) or macroinvertebrate‐mediated (0.13 eV) rates. We conclude that indirect (non‐thermal) seasonal and site‐level effects play a variable and potentially strong role in shaping the apparent temperature dependence of detrital breakdown. Such effects should be incorporated into studies designed to estimate inherent temperature dependence of slow ecological processes. [ABSTRACT FROM AUTHOR]

An understanding of the propagation process from meteorological to hydrological drought contributes to accurate prediction of hydrological drought. However, the comprehensive influence of direct human activities involved in drought propagation is not well understood. In this study, an identification framework for drought propagation time was constructed to quantify the effects of direct human activities (i.e., reservoir storage, irrigation, industrial, domestic, and agricultural water consumption) on drought propagation. Subsequently, the effects of meteorological and underlying surface factors on the drought propagation process were clarified based on random forest method, and the driving effect of teleconnection factors was investigated from top to bottom. The Wei River basin (WRB), the largest tributary of the Yellow River basin, was selected as the case study. Results disclosed that the propagation time from meteorological to hydrological drought was short in summer (approximately 2 months) and autumn (approximately 3 months), while long in spring (approximately 3–5 months) and winter (approximately 3–8 months), exhibiting noticeable spatial variability. In a changing environment, the propagation time generally showed a decreasing trend in spring and winter, while increasing propagation time was observed in summer and autumn. The dynamic drought propagation time of each season was all jointly controlled by the different extent variation of meteorological and underlying surface conditions, and the basic flow is all relatively significant throughout the period. Direct human activities had an effect on the seasonal dynamics of drought propagation, especially during the winter of the nonflood season, which alleviated the severity of winter hydrological drought to some extent, thus delaying the transmission of meteorological signals to hydrological systems. Sunspots, the dominant direct teleconnection driving force in the WRB, could indirectly affect the local precipitation and base flow in spring, autumn, and winter and interfere with the drought propagation process. This study sheds new insights into the attribution of drought propagation dynamics in a changing environment. [ABSTRACT FROM AUTHOR]

Recent climate change is altering the timing, duration and volume of river and stream flows globally, and in many regions, perennially flowing rivers and streams are drying and switching to intermittent flows. Profound impacts on aquatic biota are becoming apparent, due in part to the strong influence of flow regime on the evolution of life history. We made predictions of life‐history responses for 13 common aquatic invertebrate species (four caddisflies, five mayflies, two stoneflies, a dragonfly and an amphipod), to recent flow regime change in Australian mediterranean climate streams, based on historic studies in the same streams. Size distributions, phenology, voltinism and synchrony were compared, revealing five main responses. More than half of the species were restricted to perennially flowing streams and were absent from those that had switched to intermittent flows (including all four caddisfly species). These formerly common species are at risk of extinction as climate change progresses. Two mayfly species had divergent responses in voltinism and synchrony, and one relied on drought micro‐refuges to persist. One stonefly species changed development timing to suit the new flow regime, and the amphipod species retreated to subterranean refuges. Two formerly common species were not detected at all during 2016–2017. In addition, a new mayfly species and a caddisfly species proliferated under new flow regimes, because they had life histories suited to brief hydroperiods. Importantly, previous life history rarely predicted species' actual responses to climate‐driven flow regime change, raising doubts about the veracity of predictions based on species traits. This is because a species' potential for flexible phenology or growth rate is not necessarily indicated by life‐history traits. [ABSTRACT FROM AUTHOR]

Wzrost temperatury globalnej, drastyczny w ostatnich dziesięcioleciach, niesie ze sobą szereg skutków ubocznych, takich jak zwiększone zagrożenie suszą i powodzią, wydłużenie okresu wegetacyjnego, wzrost częstotliwości ekstremalnych zdarzeń pogodowych, nasilenie procesów erozyjnych i wzrost ładunku zanieczyszczeń dostających się do wód ze źródeł obszarowych czy nasilenie występowania nowych chorób i szkodników. Artykuł zawiera przegląd literatury naukowej dotyczącej funkcji pełnionych przez ekosystemy nadrzeczne w krajobrazie rolniczym i ich znaczenia dla łagodzenia skutków współczesnych zmian klimatu. Ekosystemy nadrzeczne jako bufory stanowią filtry i bioreaktory dla związków biogennych i pestycydów, pełnią rolę stabilizującą w utrzymaniu różnorodności biologicznej i powiązań ekologicznych w krajobrazie, poprzez zacienienie ograniczają rozprzestrzenianie się światłożądnych gatunków obcych, łagodzą wzrost temperatury wody, asymilują dwutlenek węgla, poprawiają retencję dolinową i ograniczają erozję brzegów. Przeprowadzona kwerenda w bazach Web of Science Core Collection i Scopus pokazuje, że w ostatnich kilkunastu latach rośnie zainteresowanie modelowaniem wpływu użytkowania ziemi w skali zlewni na procesy fizyczne, biogeochemiczne i biologiczne w kontekście zmian klimatycznych. Stosowanie buforów nadrzecznych jako jednego z elementów dobrych (najlepszych) praktyk gospodarowania przyczynia się do poprawy stanu środowiska. Zwraca się też uwagę na specyficzne usługi ekosystemowe świadczone przez bufory nadrzeczne. Badania koncentrują się na obszarze Ameryki Północnej, skąd pochodzi koncepcja buforów (riparian buffer) i w Europie. [ABSTRACT FROM AUTHOR]

Monitoring changes in river runoff at the Third Pole (TP) is important because rivers in this region support millions of inhabitants in Asia and are very sensitive to climate change. Under the influence of climate change and intensified cryospheric melt, river runoff has changed markedly at the TP, with significant effects on the spatial and temporal water resource distribution that threaten water supply and food security for people living downstream. Despite some in situ observations and discharge estimates from state-of-the-art remote sensing technology, the total river runoff (TRR) for the TP has never been reliably quantified, and its response to climate change remains unclear. As part of the Chinese Academy of Sciences' "Pan-Third Pole Environment Study for a Green Silk Road," the TP-River project aims to construct a comprehensive runoff observation network at mountain outlets (where rivers leave the mountains and enter the plains) for 13 major rivers in the TP region, thereby enabling TRR to be accurately quantified. The project also integrates discharge estimates from remote sensing and cryosphere–hydrology modeling to investigate long-term changes in TRR and the relationship between the TRR variations and westerly/monsoon. Based on recent efforts, the project provides the first estimate (656 ± 23 billion m3) of annual TRR for the 13 TP rivers in 2018. The annual river runoff at the mountain outlets varies widely between the different TP rivers, ranging from 2 to 176 billion m3, with higher values mainly corresponding to rivers in the Indian monsoon domain, rather than in the westerly domain. [ABSTRACT FROM AUTHOR]

In recent decades, an increase in the number of extreme flood events as well as extreme drought events has been observed in Slovenia. This rise the need for a comprehensive analysis of trends in discharge data series. In the study, statistical trends in seasonal and annual mean, maximum, extreme and low discharge values were investigated using the Mann Kendall test. The results show a temporal and spatial variability of trends in discharge. In general, a decreasing trend in water quantities in the rivers was observed. However, results at some gauging stations indicate statistically significant increasing trends, especially for maximum and extreme discharges. Additional analyses show that the discharge trends depend on the location of the gauging station. [ABSTRACT FROM AUTHOR]

This article explores how changing environmental conditions and practices connect with shifting forms and valuations of sociality in a Ngaju Dayak village in the radically transformed peatlands of southern Borneo. It proposes that the production of values and social relations is indivisible from the production of a livelihood through material means and dwelling in the local environment. The article describes how changing Ngaju orientations to social life and the riverscape have been interlinked with fluctuations in the local valuescape. The focus is on two distinct but overlapping forms of organising sociality and labour in the riverine environment, and how they have influenced and been influenced by the dialectically conjoined Ngaju values of solidarity and autonomy, and, more recently, by emerging economic value. It is argued that the valuation of sociality crucially reflects the changing valuation of land and nature and related politics of value within the local riverscape. Finally, the article shows that the radically transformed riverine environment sets limits on (imagining) environmental practices, forms of sociality, and how they are valued. [ABSTRACT FROM AUTHOR]

Representative samples of biota collected relative to environmental gradients are important for measuring present distributions and predicting shifts in distribution of taxa in response to climate change or reduced river connectivity. Based on river ecology theory and established measures of species diversity, we present a method to identify suitable river segments for sampling and monitoring changes in taxon diversity. Alpha and beta diversities of selected aquatic macroinvertebrates were assessed in seven South African rivers. Data were drawn from historical and field samples and represented longitudinal species patterns down longitudinal river axes. Representative sampling sites were identified using a logistic regression model to predict the probability of site pairs that were more than 50% similar as a function of up-/downstream distance. Alpha diversities peaked in the upper third of river lengths; beta diversities showed predictable exponential decay rates down river axes up to and excluding the start of estuarine conditions. Application of the model to a 370-km long river indicated that 14 sites should be selected for sampling to capture overall biodiversity patterns. Additional factors, such as confluences tributaries, which influence alpha diversity at sites, are identified and incorporated into site selection. [ABSTRACT FROM AUTHOR]

Changes in climate are causing floods to occur more often and more intensely in many parts of the world, including agricultural landscapes of southern Wisconsin (U.S.A.). How flooding and greater flood frequency affect stream carbon dioxide (CO2) and methane (CH4) fluxes and concentrations is not obvious. Thus, we asked how diffusive fluxes of CO2 and CH4 varied over time, particularly in response to floods, in agricultural streams, and what were likely causes for observed flood responses.We measured concentrations and diffusive fluxes of CO2 and CH4 at 10 stream sites in mixed agricultural and suburban catchments in southern Wisconsin (U.S.A.) during the growing season (March–November) in a year that experienced multiple floods. Habitat, hydrologic, and water chemistry attributes were also quantified to determine likely drivers of changes in gas concentrations and fluxes.Habitat and water chemistry, as well as CO2 and CH4 concentrations and fluxes were temporally erratic and lacked any seasonality. Carbon dioxide and CH4 concentrations and fluxes were higher during floods along with increased water velocity, turbidity, and dissolved organic carbon and decreases in dissolved oxygen, soft sediment depth, and macrophyte cover.Increased gas concentrations and fluxes were probably due to flushing of gases from soils, respiration of organic matter in the channel, and increased gas exchange velocities during floods.Flooding alleviated both supply and transfer limits on CO2 and CH4 emissions in these agricultural streams, and frequent and prolonged flooding during the growing season led to sustained high emissions from these streams. We hypothesise that such persistent increases in emissions during floods may be a common response to high precipitation periods for many agricultural streams. [ABSTRACT FROM AUTHOR]

Median timing of reproduction in salmonid populations is generally consistent among years, reflecting long-term patterns of natural selection from characteristics of the local environment. However, altered selection from factors related to climate change or human intervention might shift timing over generations, with implications for the population's persistence. To study these processes, we modeled median timing of redd (nest) counts as an index of spawning timing by natural-origin Chinook salmon (Oncorhynchus tshawytscha) in the Skagit River system in Washington State, USA. Over the last 2–6 decades, natural-origin salmon have been spawning later by 0.03–0.52 days·year–1, while a naturally spawning group that is influenced by strays from a hatchery has been spawning earlier by 0.19 days·year–1. Trends in the spawning timing of hatchery-origin strays may reflect opposing selection from the hatchery, where egg take for propagation has become earlier by 0.58 days·year–1. As mean August river temperatures have risen over the period of record, hatchery timing trends may be moving in the opposite direction from the plastic or adaptive patterns expressed by natural-origin fish. [ABSTRACT FROM AUTHOR]

The Atlantic salmon (Salmo salar) population of the River Minho represents the southern natural distribution edge of the species. In line with the general trend for Atlantic salmon, this population has been declining over the years and is now at a critically low level. With river connectivity compromised by a large dam just 80 km upstream the River Minho's outlet, and an expected deterioration of climatic conditions, it is urgent to increase our knowledge of this population and identify survival bottlenecks that can be addressed. In this study, we used radio and acoustic telemetry to track Atlantic salmon smolts during their migration towards the sea and record both survival rates and possible causes of mortality. The recorded survival for the tagged migrating Atlantic salmon remained below 55% in the three studied years, indicating that the in‐river loss of smolts is likely a strong constraint to this population. From the smolts to which a likely cause of mortality could be attributed (34%), most appear to have been removed from the river (25%), with two confirmed events of bird predation and one of mammal predation. Interestingly, eight tags were recorded moving back upstream, likely indicating predation by larger fish. Increasing predator populations (e.g. cormorants, Phalacrocorax carbo) and invasive predators (e.g. American mink, Neovison vison) lead to elevated predation pressure on this already strained Atlantic salmon population, and further studies quantifying their impact in more detail could prove crucial for future management considerations. [ABSTRACT FROM AUTHOR]

Aim: Biodiversity on Earth is threatened by climate change. Despite the vulnerability of freshwater habitats to human impacts, most climate change projections have focused on terrestrial systems. Here, we examined how the current distributions and biodiversity of stream taxa might change under mitigated, stabilizing and increasing greenhouse gas emissions. Location: Conterminous USA. Time period: Present day to 2070. Major taxa studied: Stream diatoms, insects and fish. Methods: We developed species distribution models for 336 freshwater taxa from 1,227 distinct stream localities using water chemistry, watershed and climatic variables. Models based only on climate were used to project changes in the distributions and biodiversity of cold‐ versus warm‐water taxa under representative concentration pathways (RCPs) ranging from 2.6 to 8.5 W/m2. Results: In all three organismal groups, climate emerged as the strongest predictor of species distributions, providing comparable explanatory power to water chemistry and watershed variables combined. The RCP‐based projections suggested a widespread expansion of warm‐water taxa, outpacing the decline of cold‐water taxa. Consequently, overall species richness would increase, but beta diversity would decrease drastically with the severity of climate change. A closer look at individual taxa and functional guilds revealed that vulnerable cold‐water taxa included: (a) diatom guilds forming the base and bulk of the biofilm; (b) environmentally sensitive insects, characteristic of unimpacted streams; and (c) ecologically and recreationally important salmonids, which were forecast to diminish dramatically in source habitats. Warm‐water fish projected to increase their distributions include bait bucket release minnows and dominant predators. Main conclusions: Our results suggest potentially devastating impacts of climate change on stream ecosystems, with the restructuring of diatom, insect and fish communities, diminished distributions of functionally important taxa and widespread expansion of warm‐water taxa, giving rise to biotic homogenization. Given that the magnitude of these biotic shifts depends on the severity of climate change, appropriate current policy decisions are necessary to preserve freshwater ecosystems. [ABSTRACT FROM AUTHOR]

Plans are currently being drafted for the next decade of action on biodiversity—both the post‐2020 Global Biodiversity Framework of the Convention on Biological Diversity (CBD) and Biodiversity Strategy of the European Union (EU). Freshwater biodiversity is disproportionately threatened and underprioritized relative to the marine and terrestrial biota, despite supporting a richness of species and ecosystems with their own intrinsic value and providing multiple essential ecosystem services. Future policies and strategies must have a greater focus on the unique ecology of freshwater life and its multiple threats, and now is a critical time to reflect on how this may be achieved. We identify priority topics including environmental flows, water quality, invasive species, integrated water resources management, strategic conservation planning, and emerging technologies for freshwater ecosystem monitoring. We synthesize these topics with decades of first‐hand experience and recent literature into 14 special recommendations for global freshwater biodiversity conservation based on the successes and setbacks of European policy, management, and research. Applying and following these recommendations will inform and enhance the ability of global and European post‐2020 biodiversity agreements to halt and reverse the rapid global decline of freshwater biodiversity. [ABSTRACT FROM AUTHOR]

Global change is predicted to have a marked impact on freshwater ecosystems in the High Arctic, including temperature increase, enhanced precipitation, permafrost degradation and increased vegetation cover. These changes in river catchments can alter flow regime, solute transport to streams and substantially affect stream ecosystem functioning. The objective of this study was to evaluate changes in stream functioning in a high-Arctic stream in relation to changes in discharge, and runoff flow path. We measured environmental factors, biofilm structure, nutrient uptake rates and metabolism. We studied three reaches in a headwater stream in NE Greenland with different catchment characteristics in early and late summer (during two different years) to evaluate the potential influence of environmental change on Arctic stream ecosystem functioning. Highest nutrient uptake, primary production and ecosystem respiration was found in late summer showing that streams are more efficient at retaining nutrients and have higher autotrophic production, likely due to less impact of snowmelt, and lower discharge increasing the surface to volume ratio between streambed and water column. Nutrient uptake rates in late summer from high-Arctic tundra streams were comparable to uptake rates in temperate pristine streams, likely due to no shading by bank vegetation and longer days in the high-Arctic summer compared to temperate streams. Overall, the results of this study aids in the endeavor of predicting how climate-derived changes will affect in-stream nutrient uptake and metabolism in high-Arctic streams. The results suggest that their capacity to transport, cycle and retain carbon and nutrient may increase if the importance of soil water flow paths for streams also increase, thus with effect to stream trophic relations and solute export to coastal areas. [ABSTRACT FROM AUTHOR]

Importance of evaluation of global hydrological models (gHMs) before doing climate impact assessment was underlined in several studies. The main objective of this study is to evaluate the performance of six gHMs in simulating observed discharge for a set of 57 large catchments applying common metrics with thresholds for the monthly and seasonal dynamics and summarize them estimating an aggregated index of model performance for each model in each basin. One model showed a good performance, and other five showed a weak or poor performance in most of the basins. In 15 catchments, evaluation results of all models were poor. The model evaluation was supplemented by climate impact assessment for a subset of 12 representative catchments using (1) usual ensemble mean approach and (2) weighted mean approach based on model performance, and the outcomes were compared. The comparison of impacts in terms of mean monthly and mean annual discharges using two approaches has shown that in four basins, differences were negligible or small, and in eight catchments, differences in mean monthly, mean annual discharge or both were moderate to large. The spreads were notably decreased in most cases when the second method was applied. It can be concluded that for improving credibility of projections, the model evaluation and application of the weighted mean approach could be recommended, especially if the mean monthly (seasonal) impacts are of interest, whereas the ensemble mean approach could be applied for projecting the mean annual changes. The calibration of gHMs could improve their performance and, consequently, the credibility of projections. [ABSTRACT FROM AUTHOR]

Ecosystems respond to climatic and anthropogenic forcings with regime shifts and reorganizations of their system structures. In river basins, changes in sediment transport can have cascading effects that cause ecosystem regime shifts. The Yellow River, once the world's most sediment-rich river, has experienced dramatic regime shifts. Although recent intervention has returned sediment discharge in the Yellow River to pristine levels, our understanding of previous regime shifts remains inadequate, particularly for the regime shift to a sediment rich period during early historical time. We reanalyzed previous datasets to clarify the first historical sediment transport regime shift in the Yellow River. Our results show that while historical climatic changes (e.g., the Medieval Warm Period, about 900–1100 AD) caused changes in sediment transport, a regime shift occurred only under increased forcing from anthropogenic stresses (started from about 1350 AD, reached the tipping point after 1900 AD). This unique behavior of the Yellow River under increasing anthropogenic forces may provide perspective for sustainable river basin management. [ABSTRACT FROM AUTHOR]

Global change is increasing biotic homogenization globally, which modifies the functioning of ecosystems. While tendencies towards taxonomic homogenization in biological communities have been extensively studied, functional homogenization remains an understudied facet of biodiversity. Here, we tested four hypotheses related to long‐term changes (1991–2016) in the taxonomic and functional arrangement of freshwater macroinvertebrate assemblages across space and possible drivers of these changes. Using data collected annually at 64 river sites in mainland New Zealand, we related temporal changes in taxonomic and functional spatial β‐diversity, and the contribution of individual sites to β‐diversity, to a set of global, regional, catchment and reach‐scale environmental descriptors. We observed long‐term, mostly climate‐induced, temporal trends towards taxonomic homogenization but functional differentiation among macroinvertebrate assemblages. These changes were mainly driven by replacements of species and functional traits among assemblages, rather than nested species loss. In addition, there was no difference between the mean rate of change in the taxonomic and functional facets of β‐diversity. Climatic processes governed overall population and community changes in these freshwater ecosystems, but were amplified by multiple anthropogenic, topographic and biotic drivers of environmental change, acting widely across the landscape. The functional diversification of communities could potentially provide communities with greater stability, resistance and resilience capacity to environmental change, despite ongoing taxonomic homogenization. Therefore, our study highlights a need to further understand temporal trajectories in both taxonomic and functional components of species communities, which could enable a clearer picture of how biodiversity and ecosystems will respond to future global changes. [ABSTRACT FROM AUTHOR]

Climate change is altering conditions in high‐elevation streams worldwide, with largely unknown effects on resident communities of aquatic insects. Here, we review the challenges of climate change for high‐elevation aquatic insects and how they may respond, focusing on current gaps in knowledge. Understanding current effects and predicting future impacts will depend on progress in three areas. First, we need better descriptions of the multivariate physical challenges and interactions among challenges in high‐elevation streams, which include low but rising temperatures, low oxygen supply and increasing oxygen demand, high and rising exposure to ultraviolet radiation, low ionic strength, and variable but shifting flow regimes. These factors are often studied in isolation even though they covary in nature and interact in space and time. Second, we need a better mechanistic understanding of how physical conditions in streams drive the performance of individual insects. Environment‐performance links are mediated by physiology and behavior, which are poorly known in high‐elevation taxa. Third, we need to define the scope and importance of potential responses across levels of biological organization. Short‐term responses are defined by the tolerances of individuals, their capacities to perform adequately across a range of conditions, and behaviors used to exploit local, fine‐scale variation in abiotic factors. Longer term responses to climate change, however, may include individual plasticity and evolution of populations. Whether high‐elevation aquatic insects can mitigate climatic risks via these pathways is largely unknown. [ABSTRACT FROM AUTHOR]

Potential effects of projected climate variability on base flow and groundwater storage in the North Fork Red River aquifer, Oklahoma (USA), were estimated using downscaled climate model data coupled with a numerical groundwater-flow model. The North Fork Red River aquifer discharges groundwater to the North Fork Red River, which provides inflow to Lake Altus. To approximate future conditions, Coupled Model Intercomparison Project Phase 5 climate data were downscaled to the watershed and a time-series of scaling factors were developed and interpolated for three climate scenarios (central tendency, warmer and drier, and less warm and wetter) representing future climate conditions for the period 2045–2074. These scaling factors were then applied to a soil-water-balance model to produce groundwater recharge and evapotranspiration estimates. A MODFLOW groundwater-flow model of the North Fork Red River aquifer used the scaled recharge and evapotranspiration data to estimate changes in base flow and water-surface elevation of Lake Altus. Compared to a baseline scenario, the mean percent change in annual base flow during 2045–2074 was −10.8 and −15.9% for the central tendency and warmer/drier scenarios, respectively; the mean percent change in annual base flow for the less-warm/wetter scenario was +15.7%. The mean annual percent change in groundwater storage for the central tendency, warmer/drier, and less-warm/wetter climate scenarios and the baseline are −2.7, −3.2, and +3.0%, respectively. The range of outcomes from the climate scenarios may be influenced by variability in the downscaled climate data for precipitation more than for temperature. [ABSTRACT FROM AUTHOR]

Rising global temperatures are changing how energy and materials move through ecosystems, with potential consequences for the role of animals in these processes. We tested a central prediction of the metabolic scaling framework—the temperature independence of animal community production—using a series of geothermally heated streams and a comprehensive empirical analysis. We show that the apparent temperature sensitivity of animal production was consistent with theory for individuals (Epind = 0.64 vs. 0.65 eV), but strongly amplified relative to theoretical expectations for communities, both among (Epamong = 0.67 vs. 0 eV) and within (Epwithin = 1.52 vs. 0 eV) streams. After accounting for spatial and temporal variation in resources, we show that the apparent positive effect of temperature was driven by resource supply, providing strong empirical support for the temperature independence of invertebrate production and the necessary inclusion of resources in metabolic scaling efforts. [ABSTRACT FROM AUTHOR]

Climate change is expected to alter precipitation patterns worldwide, which can have direct effects on streamflow dynamics. In many tropical regions, climate‐driven changes in rainfall are predicted to decrease streamflow and increase flash flooding, but the implications of these changes for stream ecosystem function are poorly understood. We used a rainfall gradient on Hawaii Island that mimics projected changes in rainfall and streamflow in order to estimate how climate change affects nutrient recycling. We measured per‐capita excretion (nitrogen, phosphorus) and egestion rates of three dominant taxa (shrimp, caddisfly, midge) in eight streams along the gradient for 3 years. We scaled these rates to the population and community levels and measured nitrogen and phosphorus demand of the ecosystem to estimate if the relative contribution of nutrients supplied by invertebrates changes along the gradient. Across all three taxa, population egestion and excretion rates declined by 10‐fold in drier streams. These declines were driven by lower population density, rather than differences in per‐capita rates. Under the current climate scenario, community excretion supplied up to 70% of the nitrogen demand, which was 10‐fold lower with projected changes in rainfall. Conversely, community excretion supplied up to 5% of the phosphorus demand, which did not vary across the rainfall gradient. This difference indicates that climate change may exacerbate nitrogen limitations in tropical island streams, and change the balance of nitrogen and phosphorus dynamics. Our study also demonstrates that space‐for‐time substitutions are a valuable tool to examine implications of climate change on ecosystem function in freshwater systems. [ABSTRACT FROM AUTHOR]

Catchments are complex systems containing channel networks and hillslopes. Channel networks interact with hillslopes and are pathways for transporting water, sediment, and nutrients. Understanding the branching and flux transport patterns of channel networks is critical for predicting the response of catchments to external forcing such as climate and tectonics. However, factors creating complexities in catchments are not fully understood. Here, we propose a new framework based on multiscale entropy approach to evaluate complexity of catchments using two different representations of channel networks. First, we investigate the structural complexity using the width‐function, which characterizes the spatial arrangement of channels. Second, we utilize the incremental area‐function along the main channel to study the functional complexity that captures the patterns of transport of fluxes. Our analysis reveals stronger controls of topological connectivity on the functional complexity than on structural complexity, indicating unchannelized surface (hillslope) contribution to the increase of heterogeneity in transport processes. Plain Language Summary: Catchments are complex natural landscape systems that contain hillslopes and channel networks. Understanding and quantifying features and processes that result in catchment complexity is important for predicting their response to changing human and climatic conditions. In this paper, we use an entropy‐based approach to explore the role of channel network and hillslope toward the contribution to catchment's complexity. Based on 40 natural catchments with minimum human impact across the United States in different climatic and geologic conditions, our results show that hillslopes add significant complexity to the catchments and suggest the amount of hillslope information one needs to account for in accurate predictive modeling of hydrologic processes at the catchment scale. Key Points: Topology controls structural and functional complexityFunctional complexity is higher than structural complexity due to contribution from hillslope processesScale of peak difference between the impact of topology on functional and structural complexity indicates the average hillslope length scale [ABSTRACT FROM AUTHOR]

River longitudinal profile, a key morphological characteristic of the river channel, is subject to river mouth progradation. Given the increasing influence of human activities and climate change on this critical downstream control, understanding its effects on the evolution of the longitudinal profile is imperative. A general theoretical framework is proposed to quantify the relevant effects, which is tested by numerical experiment and compared with field, numerical and laboratory data from the literature. The results suggest the existence of a critical ratio of accommodation space to sediment supply of approximately 0.5, above which the typical concave upward profile tends to form. Further analyses show that sea level rise tends to increase the concavity of the longitudinal profile of a river with a relatively low equilibrium bed slope and progradation rate. Plain Language Summary: As a key feature of a river, the bed level along the river, i.e., the river longitudinal profile, affects flooding, navigation, etc., and thus greatly influences human societies and natural ecosystems. However, the effects of the seaward progradation of a river mouth on the evolution of the river longitudinal profile are still unclear. Given the increasing influence of human activities and climate change on this critical downstream control, understanding these effects becomes imperative. A new theoretical framework incorporating the effects of river mouth progradation on the evolution of a river longitudinal profile is developed and tested by numerical experiments, field observations, and numerical and laboratory data from the literature. The results show that the seaward progradation of a river mouth could potentially lead to the formation of a concave river longitudinal profile. Specifically, we found that there exists a critical condition in which the sediment supply is insufficient to balance the seaward progradation of the river mouth, causing the typical concave upward longitudinal profile to form. The proposed theoretical framework further suggests that sea level rise tends to increase the concavity of the longitudinal profile for river with a relatively low equilibrium bed slope and progradation rate. Key Points: A theoretical framework is proposed for predicting the evolution of the longitudinal profile and its concavity of prograding riversNumerical results suggest a critical ratio of accommodation space to sediment supply for the formation of a concave profileSea level rise tends to increase the concavity of river profiles with a relatively low bed slope and progradation rate [ABSTRACT FROM AUTHOR]

The effects of climatic warming on tropical streams have received little attention, and field studies of such changes are generally lacking. Drifting insects from a Hong Kong forest stream were sampled for 36 months between 2013 and 2016, and compared with samples collected using identical methods in 1983–84. Mean air temperatures rose by ~0.5°C (0.17°C per decade) over this period. The stream drained an uninhabited protected area, so no climate‐change effects were confounded by anthropogenic disturbance. In total, 105 taxa and >77,000 individuals were collected. Richness of samples in the historic and contemporary datasets did not differ, but true diversity of drifting insects was highest in 1983–84, and declined between 2013–14 and 2015–16. There was considerable disparity in assemblage composition between 1983–84 and 2013–16, and smaller between‐year changes in the contemporary dataset. Nine indicator species of the historic dataset were identified. Most were mayflies, particularly Baetidae, which were greatly reduced in relative abundance in 2013–16. Diptera became more numerous, and tanypodine chironomids were the sole contemporary indicator taxon. Relative abundance of eight of 19 drifting species (comprising 60% of total insects) was lower in 2013–16, when the dominant baetid mayfly during 1983–84 had declined by almost 90%; only one of the 19 species occurred at higher abundance. Eight species were affected by seasonal temperature variability, but these responses were not correlated with any tendency to exhibit long‐term changes in abundance. Substantial shifts in composition, including declines in mayfly relative abundance and assemblage diversity, occurred after three decades of warming, despite the broad annual range of stream temperatures (~16°C) in Hong Kong. This contradicts the well‐known prediction that organisms from variable climates have evolved wider thermal tolerances that reflect prevailing environmental conditions. The observed compositional reorganization indicates that variability, rather than stability, may be typical of undisturbed tropical stream communities. [ABSTRACT FROM AUTHOR]

The Yellow River has caused suffering to people with its devastating floods throughout human history. Understanding the occurrence of Yellow River floods and their relationship with climate change is crucial for sustainable water governance in North China. Here we synthesize historical and climatic records in the Yellow River basin to investigate their relationship during the past two millennia. Based on historical archives of river floods and levee breaches, we developed a decadally resolved Yellow River flooding frequency record from 221 BCE to 1949 CE, which provides a rare chance to perceive the river's long-term flood dynamics. As revealed, the Yellow River flooding can be divided into two distinct stages: an early stage of low-frequency floods from the 220s BCE to the 890s CE; and a late stage of high-frequency floods during the 900s–1940s CE. A substantial increase in flooding frequency around the 10th century fell within the transition period into the Medieval Climate Anomaly (MCA), during which the Yellow River basin featured warm and wet climate conditions. Coincidentally, human management of the Yellow River intensified as a response to more severe and frequent floods. The intense river management persisted thereafter and resulted in the super-elevation of the riverbed, which made the river more prone to flooding. Consequently, the Yellow River flooding frequency remained high even after entering the Little Ice Age, during which the river basin featured cool temperature and reduced precipitation. Our study suggests that the dramatic transition from a previous cool, dry into a warm, wet climate during the MCA period triggered intense human management of river channels and the establishment of the flood-prone nature of the Yellow River. [ABSTRACT FROM AUTHOR]

There are two contrasting hypotheses on whether fluvial fans need specific climate conditions to form. Deduction of climatic and tectonic signals from landscapes and the sedimentary record is a key aim in geology and geomorphology. It is thus of great interest to obtain recognition criteria for specific climate changes in the sedimentary record in general, and fluvial fans in particular, because they may form the bulk of the continental fluvial record. The hypothesis that links fluvial fan occurrence to climate specifically indicates precipitation variability as a key control, because it promotes streamflow variability, channel instability, and avulsions, which are the key processes involved in fluvial fan formation. Here, we tested this hypothesis by quantitative analyses of discharge patterns from 68 fan-forming rivers that have a global distribution. Using an ensemble of dimensionless metrics, we show that 75% of the fan-forming rivers in this data set have a high discharge variability. We further analyzed down-fan changes in discharge variability and discuss the nature of discharge variability in different hydroclimates as a function of intra- and interannual precipitation fluctuations. We also examined the fan-forming rivers with moderate to low discharge variability and concluded that although river discharge variability strongly promotes fluvial fan formation, fluvial fans may also be formed by rivers with a moderate or low discharge variability if other favorable conditions that promote avulsions occur. [ABSTRACT FROM AUTHOR]

Upstream range shifts of freshwater fishes have been documented in recent years due to ongoing climate change. River fragmentation by dams, presenting physical barriers, can limit the climatically induced spatial redistribution of fishes. Andean freshwater ecosystems in the Neotropical region are expected to be highly affected by these future disturbances. However, proper evaluations are still missing. Combining species distribution models and functional traits of Andean Amazon fishes, coupled with dam locations and climatic projections (2070s), we (a) evaluated the potential impacts of future climate on species ranges, (b) investigated the combined impact of river fragmentation and climate change and (c) tested the relationships between these impacts and species functional traits. Results show that climate change will induce range contraction for most of the Andean Amazon fish species, particularly those inhabiting highlands. Dams are not predicted to greatly limit future range shifts for most species (i.e., the Barrier effect). However, some of these barriers should prevent upstream shifts for a considerable number of species, reducing future potential diversity in some basins. River fragmentation is predicted to act jointly with climate change in promoting a considerable decrease in the probability of species to persist in the long‐term because of splitting species ranges in smaller fragments (i.e., the Isolation effect). Benthic and fast‐flowing water adapted species with hydrodynamic bodies are significantly associated with severe range contractions from climate change. [ABSTRACT FROM AUTHOR]

The objective of this paper is to determine the trend and to estimate the streamflow of the Gökırmak River. The possible trend of the streamflow was forecasted using an autoregressive integrated moving average (ARIMA) model. Time series and trend analyses were performed using monthly streamflow data for the period between 1999 and 2014. Pettitt's change point analysis was employed to detect the time of change for historical streamflow time series. Kendall's tau and Spearman's rho tests were also conducted. The results of the change point analysis determined the change point as 2008. The time series analysis showed that the streamflow of the river had a decreasing trend from the past to the present. Results of the trend analysis forecasted a decreasing trend for the streamflow in the future. The decreasing trend in the streamflow may be related to climate change. This paper provides preliminary knowledge of the streamflow trend for the Gökırmak River. [ABSTRACT FROM AUTHOR]

Originating in the Tianshan Mountains in arid Central Asia, the natural discharge change of the Naryn River is strongly affected by climate change. As the main source of water for the region, this river is crucial to both the natural environment and the socio-economic development. To extend the discharge record and better understand past and future changes in Naryn River discharge, we developed four tree-ring width chronologies and analyzed the relationship between tree growth and discharge. The resulting reconstruction dates back to 1753 and has an R2 of 0.374 (1939–2017). Interannual discharge variations of the Naryn River indicate that 1917 was the driest year of the past 265 years, while 1956 was the wettest. The record also indicates that the majority of extreme flood years occurred in the past century; prior to about 1900 C.E., the discharge of the Naryn River was relatively stable. Since 1900 C.E., discharge volume has gradually increased, as has discharge variability. At decadal time scales, the 2010s are notable for the frequency of major floods, whereas the 1910s were the driest. Between the 1870s and the 1910s, the Naryn River experienced a period of low discharge that continued for nearly half a century. The discharge of the Naryn River over the past 265 years appears to vary over quasi-periods of 60, 21, 11, and 2-4 years, which are driven by large-scale climate systems. [ABSTRACT FROM AUTHOR]

In the eastern United States, existing paleo-reconstructions in fluvial environments consist primarily of site-specific investigations of climate and human impacts on riverine processes. This paper presents the first meta-analysis of fluvial reconstructions focused on regional watersheds of the eastern United States, including the Lower Mississippi, Tennessee, South Atlantic–Gulf Coast, Ohio, Mid-Atlantic, and New England regional watersheds. Chronologies of fluvial activity (i.e. alluvial deposition) and stability (i.e. landscape stability) were developed by synthesizing data from existing, published, and site-specific fluvial reconstruction studies conducted across the eastern United States. Overall, regional watersheds show variable patterns of synchronicity across watersheds and did not demonstrate cyclic behavior through the Holocene. During the last millennium, only the Lower Mississippi and Ohio regional watersheds exhibit high rates of fluvial activity active during the 'Medieval Climate Anomaly' (650–1050 yr BP), while nearly all other regional watersheds in the eastern United States were active during the 'Little Ice Age' (100–500 yr BP). These findings imply that fluvial activity may be more spatially restricted during warmer/drier climatic conditions than during cooler/wetter periods. We find an increase in fluvial activity during the era of Euro-American colonization (400 yr BP to present) in the southeastern United States but not the northeastern United States, implying a heterogeneous response of fluvial systems to human activities in the eastern United States related to climatic, cultural, and/or physiographic variability. These new insights gained from fluvial chronologies in the eastern United States demonstrate the utility of regionally synthesized paleo-records to understand large-scale climate variation effect on rivers. [ABSTRACT FROM AUTHOR]

Arctic terrestrial ecosystems near the treeline in river lowlands are vulnerable to the changing climate and seasonal extreme events, including flooding. We set up a simple camera monitoring system to record the timings and durations of the leafy period and the spring flush of river water at three observation sites (Boydom [B]: 70.64°N, 148.15°E; Kodac [K]:70.56°N, 148.26°E; Verkhny‐Khatistakh [VK]:70.25°N,147.47°E) in the Indigirka lowland, in Northeastern Siberia. Time‐lapse digital cameras were located at seven points across the three sites. The time intervals were 1–4 or 24 hours. The minimum and maximum monitoring periods were 2 years (July 2016 to August 2018) at B and 5 years (August 2013 to July 2018) at K. One camera documented the timings of river ice melt and open water periods from the riverbank of the Kryvaya River, one of the small tributaries of the Indigirka River. The other six cameras recorded several types of ground cover typical of the area, including larch trees (Larix cajanderi), shrubs (including Salix spp. and Betula nana), forbs, mosses and graminoids in an ecosystem of sparsely forested shrublands, wetlands and riversides. The data consists of 45,617 JPEG‐format images. This dataset can be used to detect the onset and offset of the growing season and to capture the ice melt timing and water cover periods in wetlands and riversides. It may be useful in validating satellite data such as the vegetation remote sensing index for remote and little‐known areas. These data may contribute to the study of the role of high‐latitude ecosystems in global climate changes. The complete data set for this abstract published in the Data Paper section of the journal is available in electronic format in MetaCat in JaLTER at http://db.cger.nies.go.jp/JaLTER/metacat/metacat/ERDP-2020-02.1/jalter-en. [Correction added on 7 September 2020, after first online publication: JaLTER URL has been updated.] [ABSTRACT FROM AUTHOR]

When in 1852 Frederick Douglass hailed whaling in the Pacific Ocean as labor that black and white men did together, and in 1851 when Herman Melville cited Thomas Jefferson's "Observations on the Whale Fishery" in the opening extracts of Moby-Dick, both Douglass and Melville alluded to a history of the entanglements of whaling, national identity, and slavery that had been a long time in the making. When Jefferson wrote his "Observations" in 1788, he was putting his thinking about a warming climate, the rivers and coasts that connected the American interior to the Atlantic Ocean, and the political transformations of a revolutionary Atlantic world to work in the service of a very particular vision of the future. He was certainly doing much more than representing the interests of Nantucket whalers, the purported goal of the report. Indeed, he was attempting to graft his vision of republicanism onto an oceanic world of contested geopolitics and natural history. The issue of whaling implicated Jefferson's entire body of thought and with it the Jeffersonian project of continental expansion and agrarian political economy, the viability of American empire, and the legal and environmental security of white supremacy and planter enlightenment. [ABSTRACT FROM AUTHOR]

We present the first observational evidence of changing patterns of extreme streamflows at multiple locations across Western Himalayan (WH) rivers. We find that the frequency of extreme flow events during the period 1980–2003 has doubled with a statistically significant increasing trend in annual maximum streamflow. We postulate that this streamflow change is due to the increased precipitation extremes occurring during both the summer monsoon and the winter seasons. We further found a stepwise increase of "chi‐gradient" in Bhagirathi and Sutlej Rivers, indicative of a landscape that facilitates rapid flow of water generating severe floods downstream. Our results highlight the severity of hydroclimatic changes underway in the WH region and the critical need for a hydro‐infrastructure for flood forecasting to benefit more than 17 million inhabitants and for ecosystem services to mitigate increasing flood hazards. Plain Language Summary: Flooding in the Western Himalayan rivers has caused colossal loss of life and property in the recent decades. We present a first analysis of changing patterns of observed peak streamflow in Western Himalayan rivers at multiple locations, using high‐quality in situ data. With a high degree of confidence, we conclude that the occurrence of extreme flow events during the period of 1980–2003 has doubled with an increasing trend in annual maximum streamflow. Our analysis shows that this streamflow change is due to the increased precipitation extremes during both the summer monsoon and the winter seasons. We also found that the profiles of two Western Himalayan rivers (Bhagirathi and Sutlej) exhibit steep slopes in a stepwise manner, indicative of a landscape that rapidly responds to extreme precipitation by contributing to severe floods. Our results contextualize the severity of hydroclimatic changes underway in the WH region. Results also highlight the critical need for a hydro‐infrastructure and an operational flood forecasting system to benefit more than 17 million inhabitants and for ecosystem services to mitigate increasing flood hazards. Key Points: First evidence from observations shows that occurrences of extreme streamflow in Western Himalayan rivers have doubled during 1980–2003Increasing trends of rainfall extremes and the geomorphology of the rivers have driven the dramatic increase in extreme streamflowThere is a critical need for a dedicated, high‐resolution, real‐time flood forecasting system for the Western Himalayan region [ABSTRACT FROM AUTHOR]