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[Display omitted] • Radionuclides and models show soil erosion dynamics over decades to century. • Soil-erosion trend is increasing over past decades on the southeastern TP. • Increasing temperature and human activities are main triggers of recent soil erosion. • Accelerating soil erosion is particularly strong for permafrost-dominant regions. Soil erosion has created landscape problems in many parts of the world and in particular in cold regions where the sensitive permafrost conditions have changed due to climate warming. Such a case occurred in the Tibetan Plateau (TP), which has been strongly affected by global warming and human activities. Monitoring technologies, like remote sensing and field surveys were used to explore soil erosion rates in the TP, but they were limited by the resolution and meteorological disturbance factors or the spatial and time scales. Here, we present for the first time 210Pb ex (excess lead-210) and 137Cs (caesium-137) data of soils from the southeastern TP (SETP) covering an area of 640,000 km2. In the permafrost-dominant areas, the results show mean soil-erosion rates in the last 56–100 years that were relatively higher (1891 t·km−2·a-1) based on 210Pb ex than those based on 137Cs (1623 t·km−2·a-1). Modelling results from the Revised Universal Soil Loss Equation (RUSLE) indicate relatively high mean soil erosion rates of 4363 and 4394 t·km−2·a-1 using a period covering the last 40 or 10 years respectively. Our data suggest accelerating erosion rates on the SETP that are linked to permafrost degradation, and glacier and snow melting due to accelerating global climate warming. The increase in ground surface temperature of ∼2 °C in the last four decades has further shifted the regional hydrology, affecting the degeneration of vegetation cover and a further increase in soil-erosion rates. However, our radionuclides data also expose low erosion rates in the seasonally frozen ground at some sampling sites which indicates the complex nature of erosion trends in cold regions that require careful adaptation of soil management. [ABSTRACT FROM AUTHOR]

• Estimated permafrost degradation using coupled hydro-thermal dynamics model WaSiM. • Permafrost degraded from DPT increasing, bottom rising and ended with decreasing MFD. • PA decreased at a rate of −7105 km2/decade (-5.8 %/decade) and DPT 31.76 cm/decade. • AMFD decreased at −14.47 cm/decade, TD −5.56 days/decade and NFD −9.97 days/decade. • Changing rates of ADPT and AMFD close to 0 when AT trend smaller than 0.55 °C/decade. Global warming has aggravated the problem of permafrost degradation, the long-term variation of which is not well estimated. In this study, a fully coupled hydrothermal dynamics cold region hydrologic model was used to quantify the historical spatial–temporal characteristics of permafrost degradation by estimating the depth to permafrost table (DPT), taliks in different subbasins, maximum frozen depth (MFD) for seasonally frozen ground (SFG), thaw date (TD), and annual number of frozen days (NFD) in the headwaters of the Yellow River (HWYR) in eastern High Mountain Asia. The model considered the taliks and successfully estimated four historical fine-scale permafrost maps. Permafrost degradation began with the enlargement of active layer thickness (ALT), formation of taliks, rise in the permafrost bottom, and merging of the permafrost table and bottom, and ended with a decrease in MFD. From 1980 to 2014, the permafrost area (PA) in the study area decreased by a total of 17,849 km2 at a rate of more than −7100 km2/decade (−5.8 %/decade). The mean DPT increased by 0.8 m at 31.76 cm/decade and more than 100 cm/decade at the grid scale. The absolute MFD (AMFD) decreased by 0.11 m at −14.47 cm/decade. The mean TD decreased by 14.28 days at −5.56 days/decade and more than −20 days/decade at the grid scale. The mean NFD decreased by 25.51 days at −9.97 days/decade. The lowland area had a smaller NFD and an earlier TD than the mountainous area. Basins with a large air temperature (AT) and small elevation had a small DPT, MFD, TD, NFD, a large rate of decrease in TD and NFD, and increase in absolute DPT (ADPT), and a small rate of decrease in AMFD. The rates of increase in ADPT and decrease in AMFD were close to 0 when the change in AT was lower than 0.55 °C/decade. [ABSTRACT FROM AUTHOR]

Macrophyte rhizosphere microbes, as crucial components of the wetland ecosystem, play an important role in maintaining the function and stability of natural and constructed wetlands. Distinct environmental conditions and management practices between natural and constructed wetlands would affect macrophytes rhizosphere microbial communities and their associated functions. Nevertheless, the understanding of the diversity, composition, and co-occurrence patterns of the rhizosphere bacterial communities in natural and constructed wetlands remains unclear. Here, we used 16S rRNA gene high-throughput sequencing to characterize the bacterial community of the rhizosphere and bulk sediments of macrophyte Phragmites australis in representative natural and constructed wetlands. We observed higher alpha diversity of the bacterial community in the constructed wetland than that of the natural wetland. Additionally, the similarity of bacterial community composition between rhizosphere and bulk sediments in the constructed wetland was increased compared to that of the natural wetland. We also found that plants recruit specific taxa with adaptive functions in the rhizosphere of different wetland types. Rhizosphere samples of the natural wetland significantly enriched the functional bacterial groups that mainly related to nutrient cycling and plant-growth-promoting, while those of the constructed wetland-enriched bacterial taxa with potentials for biodegradation. Co-occurrence network analysis showed that the interactions among rhizosphere bacterial taxa in the constructed wetland were more complex than those of the natural wetland. This study broadens our understanding of the distinct selection processes of the macrophytes rhizosphere-associated microbes and the co-occurrence network patterns in different wetland types. Furthermore, our findings emphasize the importance of plant–microbe interactions in wetlands and further suggest P. australis rhizosphere enriched diverse functional bacteria that might enhance the wetland performance through biodegradation, nutrient cycling, and supporting plant growth. [ABSTRACT FROM AUTHOR]

Understanding the hydrologic processes of inland lake basins in the Tibetan Plateau (TP) could provide insights into the responses of Tibetan lake dynamics to climate change. An efficient approach for this purpose is to represent complex hydrologic behaviors of such Tibetan lake watersheds with plausible hydrologic models. In this study, water level fluctuations of Lake Nam Co, an inland lake in the central TP, were investigated using a lumped lake-watershed model. The degree-day factor method was introduced to improve the model applicability in glacier-covered basins. The model simulated the hydrologic processes as well as the lake water budget. Remote sensing images (Landsat MSS, TM, ETM + and OLI) from 1972 to 2015 were used to identify the glacier and lake boundaries. Multisource climate data (e.g., ground point observation, 0.25 o gridded APHRODITE and TRMM 3B42 v7 precipitation products) were used to drive the hydrologic model at a monthly time step. Results of trend analysis showed that basin-wide annual air temperature increased by the rate 0.04 °C/yr from 1961 to 2015. Mean annual precipitation slowly increased from 1961 to the mid-1990s, and then rapidly increased from the late-1990s to the mid-2000s, and finally obviously decreased after the mid-2000s. As a response to climate change, glaciers decreased by 62.69 km 2 (29%) and lake area increased by 91.83 km 2 (4.7%) from 1972 to 2015. The analysis of lake water budget suggested that, the total basin runoff and on-lake precipitation contributed 1.36 km 3 /yr (66%) and 0.7 km 3 /yr (34%), respectively, to mean annual water gain of the lake. Glacier runoff was 14% of the basin runoff and 10% of the total water gain of the lake. The percentages of lake evaporation, water seepage and water surplus were 65%, 20% and 15%, respectively. Lake level increased with the rate of 0.14 m/yr for the study period 1961–2015. It could be concluded that precipitation was the dominant controlling factor for the different magnitudes of lake level rising rates of 0.10, 0.41 and 0.06 m/yr for the periods of 1961–1998, 1999–2008 and 2009–2015, respectively. [ABSTRACT FROM AUTHOR]

The issue of growing water scarcity has been increasingly perceived as a global systemic risk. To solve it, an integrated approach considering different perspectives of water scarcity is at a premise. In this study, we developed an approach to calculate the blue water scarcity (BWS) and integrated the production, consumption, and water transfer perspectives into a single framework. The results are as follows: The average BWS in the Hetao irrigation district was 0.491 during the 2001–2010 year period, which was much larger than the threshold of 0.30, indicating a high water stress level. From the production perspective, the agricultural sector was the largest contributor to regional water scarcity and the average BWS was as high as 0.479. From the consumption perspective, BWS related to virtual water export was much larger than that related to water consumption for making products to be consumed locally and the values were 0.422 and 0.069, respectively. Under the influence of physical and virtual water transfer, BWS changed from 0.242 (medium to high water stress level) to 0.491 (high water stress level). Strategies for reducing agricultural water consumption, such as increasing crop water productivity, improving irrigation efficiency, and promoting more reasonable irrigation water price, could be adopted in the Hetao irrigation district to alleviate regional BWS. Compared with physical and virtual water import, the virtual water export played a more important role in influencing the regional water scarcity, and the increase in crop water productivity, decrease in crop export volume, or adjustment of trade pattern from water-intensive crops to water-extensive ones could be feasible measures to decrease virtual water export for lower water stress, while the trade-offs in the product-consuming regions should be considered. [ABSTRACT FROM AUTHOR]

Flow hydrodynamic condition impacts the deposition process on vegetation and removal of colloid and colloid‐associated contaminants in saturated vegetative filter strips (VFSs) under rainfall. A 9.6‐m‐long flume was constructed to investigate the retention of colloids through VFSs, with saturated soil and simulated rainfall. Colloidal filtration theory was applied to calculate the colloid deposition rate coefficient (kd) on vegetation surface. The result showed that removal efficiencies (η) of the single‐stem decreased, but colloid kd on the flume scale vegetation increased with increased Reynolds number (Re). Flume experiment found that the colloid retention rate in VFSs decreased as the Re increased. Since deposition on vegetation surface and diffusion into saturated soil are two main removal mechanisms, the discrepancy between kd and retention rate suggests that colloid diffusion into the soil was the dominant process of colloid removal in saturate VFSs. The research deepens the understanding of colloid transport mechanism in VFSs, and provides theoretical basis for the design of VFSs. [ABSTRACT FROM AUTHOR]

Summary This paper examines the combination of support vector machines (SVM) and the dual ensemble Kalman filter (EnKF) technique to estimate root zone soil moisture at different soil layers up to 100 cm depth. Multiple experiments are conducted in a data rich environment to construct and validate the SVM model and to explore the effectiveness and robustness of the EnKF technique. It was observed that the performance of SVM relies more on the initial length of training set than other factors (e.g., cost function, regularization parameter, and kernel parameters). The dual EnKF technique proved to be efficient to improve SVM with observed data either at each time step or at a flexible time steps. The EnKF technique can reach its maximum efficiency when the updating ensemble size approaches a certain threshold. It was observed that the SVM model performance for the multi-layer soil moisture estimation can be influenced by the rainfall magnitude (e.g., dry and wet spells). [ABSTRACT FROM AUTHOR]

Most glaciers in the Tibetan Plateau ( TP) are not closely monitored for mass balance (MB) due to their inaccessibility, which makes it difficult to better understand the dynamics of glacial advancement or retreat. Surface energy budget, MB, and the resulting melt runoff were calculated for Zhadang glacier (5,710 m above sea level) of the central TP. Energy balance was calculated on 30-m square grids for the summers of 2007 and 2008. On average, net radiation dominated the total energy source (66%) while the residual was supplied by sensible heat flux. More than 67% of the energy sink was available for melting on the glacier. Thus, less than 33% of the total energy was consumed by latent heat flux. A large and a slightly negative summer MB were calculated for the 2007 and 2008 summers, respectively. The high sensitivity of the glacier to air temperature may indicate that the lower than average seasonal temperature was more important than the increased precipitation for the slightly negative MB in the summer of 2008. Comparisons of glacial melt runoff indicated that rainfall and snowmelt were the dominant contribution to total runoff in the glacierized basin and the ice melting is also very important. Glacial melt calculation provides a basis for quantifying glacial melt-runoff contribution to the river streamflow in the TP. [ABSTRACT FROM AUTHOR]

• Hyporheic flow under rough ice cover conditions was addressed for the first time through numerical models. • Compared to open channel flow, the rough underside of ice cover increases hyporheic flux through shallower zones. • Parsimonious models are provided for predicting ice cover roughness-affected hyporheic flow. Many rivers are subject to ice-covered flow conditions in cold climate regions or during the winter months. The presence of ice cover can change stream flow hydrodynamics and thus affect the hyporheic exchange involved in many biogeochemical processes in aquatic environments. Among the various features of ice cover, its underside roughness is a main factor modifying the surface–subsurface flow hydrodynamics. To date, there has been little research on how ice cover affects the hyporheic exchange, even less on the effect of the ice cover roughness. This leaves open questions on the mechanical changes initiated at the ice-water interface and transferred to the water–sediment interface. In this study, a coupled surface–subsurface computational approach was used to model conjunctively the channel flow over dune bed and the underlying porous flow under different ice cover conditions. The results show that ice cover can enhance the hyporheic flux and reduce the hyporheic zone depth when compared to open channel flow at equivalent discharge. As the river flow depth increases to 4 times the height of the dune, the effect of the ice cover on the hyporheic flow becomes negligible. Within this effective range, the hyporheic flux via the channel water depth follows a power-law function. Ice cover roughness greatly augments the exchange rate while compresses the exchange space, therefore reduces flow residence time in the hyporheic zone. Based on the modeling results, prediction models were proposed for evaluating the impacts of ice cover roughness on the hyporheic exchange flux and depth. Our study indicates that hyporheic flow exchange is significantly impacted by the roughness of the ice cover which in turn the hyporheic exchange is likely to affect the river ice processes as well as the water quality and ecological functions throughout the river corridors. [ABSTRACT FROM AUTHOR]

Wetlands are the largest natural sources of methane (CH 4) emissions worldwide. Littoral wetlands of urban lakes represent an ecotone between aquatic and terrestrial ecosystems and are strongly influenced by water levels, environmental conditions, and anthropogenic activities. Despite these littoral zones being potential "hotspots" of CH 4 emissions, the status of CH 4 emissions therein and the role of physicochemical properties and microbial communities regulating these emissions remain unclear. This study compared the CH 4 fluxes, physicochemical properties, and CH 4 -cycling microbial communities (methanogens and methanotrophs) of three zones (a non-flooded supralittoral zone, a semi-flooded eulittoral zone, and a flooded infralittoral zone) in the littoral wetlands of Lake Pipa, Jiangsu Province, China, for two seasons (summer and winter). The eulittoral zone was a CH 4 source (median: 11.49 and 0.02 mg m−2 h−1 in summer and winter, respectively), whereas the supralittoral zone acted as a CH 4 sink (median: −0.78 and −0.09 mg m−2 h−1 in summer and winter, respectively). The infralittoral zone shifted from CH 4 sink to source between the summer (median: −10.65 mg m−2 h−1) and winter (median: 0.11 mg m−2 h−1). The analysis of the functional genes of methanogenesis (mcrA) and methanotrophy (pmoA) and path analysis showed that CH 4 fluxes were strongly regulated by biotic factors (abundance of the mcrA gene and alpha diversity of CH 4 -cycling microbial communities) and abiotic factors (ammonia nitrogen, moisture, and soil organic carbon). In particular, biotic factors had a major influence on the variation in the CH 4 flux, whereas abiotic factors had a minor influence. Our findings provide novel insights into the spatial and seasonal variations in CH 4 -cycling microbial communities and identify the key factors influencing CH 4 fluxes in littoral wetlands. These results are important for managing nutrient inputs and regulating the hydrological regimes of urban lakes. [Display omitted] • Methane flux varied greatly in spatial and seasonal scales. • Flooding condition overwhelmed season in determining the microbial community. • Biotic rather than abiotic factors explained the larger variations of methane flux. • Abiotic factors affected methane flux by mediating the microbial community. [ABSTRACT FROM AUTHOR]

• Biome-BGC model was improved by modifying the ET and canopy multilayers modules. • The increasing trends of GPP, ET and WUE were more pronounced during 1999–2018. • Increasing NDVI mitigated the negative effect of precipitation. Extreme climate occurred frequently in subtropical region, which seriously affects carbon and water fluxes such as evapotranspiration (ET) and gross primary productivity (GPP) of terrestrial ecosystems. The process-based biome biogeochemical cycles (Biome-BGC) model is widely used for simulating carbon and water fluxes of forest ecosystems. However, the lack of the interaction information of climate, vegetation and soil, such as the hysteresis effect, canopy stratification on photosynthesis, impedes better simulations of the ecohydrological processes. Here, we tended to improve the simulation accuracy of Biome-BGC model at a subtropical forest on the Xin'an River in Southeastern China by reconstructing the precipitation series, modifying the ET and canopy multilayers modules, and optimizing the parameters. The spatiotemporal patterns of GPP, ET, water use efficiency (WUE) and their response to environmental factors across the Xin'an River Basin from 1982 to 2018 were further explored. The results showed that the improved model performed well, with the determination coefficient, root means square error and mean absolute error being 0.730, 1.522 gC/m2/d and 1.218 gC/m2/d for GPP, 0.857, 1.082 mm/d and 0.838 mm/d for ET, respectively. Basin-averaged GPP, ET and WUE increased during 1982–2018 and these increasing trends were more pronounced during 1999–2018. Significant positive trends of WUE occurred in the northeast corner. The increasing air temperature and precipitation respectively dominated the increase in GPP and ET, the increasing CO 2 concentration and NDVI mitigated the negative effect of extreme precipitation on WUE. Given that human activities such as afforestation have effectively reduced the extent of damage to forest ecosystems from extreme precipitation, we highlight an urgent need to formulate adaptation strategies aimed at reducing the risk of extreme climate in humid regions. [ABSTRACT FROM AUTHOR]

The climate significance of oxygen isotopes from the central Tibetan Plateau (cTP) ice cores is a debated issue because of large scale atmospheric circulation. A high-resolution δ 18 O record was recovered from the Xiao Dongkemadi (XD) ice core, which expanded the spatial coverage of δ 18 O data in this region. Annual average δ 18 O correlated significantly with nearby MJJAS air temperatures, suggesting the δ 18 O can be used as a proxy to reconstruct regional climate change. The reconstructed temperature anomaly is related to the regional and global warming trends, and the greater warming amplitude since 1970s is related to the elevation dependency of the warming signal. The close relationship of the warming to variations in glacier mass balances and discharge reveal that recent warming has led to obvious glacier shrinkage and runoff increase. Correlation analysis suggests that monsoon and westerly moisture substantially influence the cTP ice core records, along with an increase in their level of contribution to the XD core accumulation in recent decades, and confirms a teleconnection of regional climate of the cTP ice cores with climate parameters in the Indian and North Atlantic Oceans. [ABSTRACT FROM AUTHOR]

Summary Improving the predictive capabilities of rainfall-runoff models in ungauged catchments is a challenging task but has important theoretical and practical significance. In this study, we investigated the predictive capabilities of the conceptual Xinanjiang model (XAJ), which is widely used for flood forecasting and simulation in China, in ungauged catchments. We further produced a hybrid rainfall-runoff model (named XAJ-GIUH) by coupling the XAJ model with the geomorphologic instantaneous unit hydrograph (GIUH) to achieve improved flood predictions in ungauged catchments. The flood prediction capabilities of the original XAJ model and the XAJ-GIUH model were investigated and compared at an hourly time scale in a mountainous catchment with six nested catchments located in the south of Anhui province, China. The two models were first calibrated for each individual catchment by comparing with the observed streamflows. Then, the nested catchments were treated as ungauged and modeled using the parameter values regionalized by transposition from the downstream catchments. The results show that the performance of both models is comparable and satisfactory on different catchment scales in the case that model parameters are calibrated in each catchment. However, the models perform differently in the case that model parameters are transposed from the downstream catchments. The XAJ-GIUH model produced markedly improved estimates of peak discharge and peak time as compared to the original XAJ model in the latter case, indicating that the runoff routing is a major uncertainty source for the application of the XAJ model in this case. Coupling XAJ with topography-based GIUH has the potential to substantially improve the flood prediction capability of the XAJ model in ungauged catchments. Our analysis further reveals that the models do not necessarily perform better when the parameter values are transposed from closer donor catchment. Instead, adopting the parameter values from the catchment with more similar topographic characteristics is more likely to produce better model performance. This study implicates the necessity of including remotely sensed geomorphologic characteristics of ungauged catchments to improve flood predictions in these regions. [ABSTRACT FROM AUTHOR]

• Soil moisture estimation is influenced by multi-factor uncertainties • Soil property has little effect on calculating θ sat , K sat , B , ψ sat • UWEnKF is an effective and practical technique for soil moisture assimilation • Model performance can be improved with a decreasing simulation time step • UWEnKF provides a better soil moisture estimation with higher assimilation frequency Accurate quantification of soil moisture contributes significantly to an understanding of land surface processes. In-situ observable soil moisture data are often sparsely distributed, and model performance is influenced by many factors. In this study, 14 numerical experimental schemes about the effects of uncertainties in multiple factors (soil property, time step, assimilation interval, precipitation, soil layer thickness and initial value) on soil moisture estimation were evaluated based on the unscented weighted ensemble Kalman filter (UWEnKF) and a one-dimensional vertical water flow model at the ELBARA field site in the Maqu monitoring network in the upper reaches of the Yellow River, China. The experiments showed that soil properties had little effect on model parameters (e.g., saturated soil moisture content, saturated soil hydraulic conductivity, saturated soil matric potential) in either the horizontal or vertical direction using the model numerical solving scheme adopted, and thus had little effect on soil moisture estimation. Using only the observed K sat may lead to better soil moisture predictions. Reducing the simulation time step has limited impact on soil moisture estimation. The effects of precipitation on soil moisture estimations varied due to overestimation or underestimation of soil moisture content in different soil layers, and differences in soil layer thicknesses led to uncertainty in soil moisture estimation. The model accurately predicted the change trend of soil moisture if the initial values were reasonable. UWEnKF performed well in terms of improving soil moisture estimations despite the uncertainty of many factors in data assimilation system, and performed better with high assimilation frequency (i.e., small assimilation interval). Thus, UWEnKF is an effective and practical technique for soil moisture assimilation whatever the uncertainty of multiple factors is. [ABSTRACT FROM AUTHOR]

• SVMs and SVM-DA models forced with limited climate variables can forecast CGWLs up to 3 months lead time. • Performance of SVM model can be influenced by the local climate variables. • Addition of GRACE information can further improve the prediction of change in groundwater levels based on SVM-DA model. Groundwater (GW) is a vital resource for human consumption, agriculture, environmental sustainability, and socio-economic development in different parts of the world. Besides, GW plays a crucial role in minimizing the impacts during extreme drought events. However, there is a fast decline in groundwater resources due to increased sectoral water demand compounded by reduced rainfall and rising temperature. Therefore, it is essential to develop appropriate tools to study spatio-temporal dynamics and predict groundwater levels to improve water resource management, especially during drought events. In this study, we applied machine learning algorithms based on support vector machines (SVMs), combined with data assimilation (DA) technique to predict the change in groundwater levels (CGWLs) at 1 to 3-month time scales for 46 GW wells located at the northeast United States. The in-situ climate variables and the Gravity Recovery and Climate Experiment (GRACE) mission-informed groundwater anomalies data (GWA) are used to develop the models. The results suggest that SVMs (SVM-DA) models forced with limited climate variables (i.e., precipitation, solar radiation, air temperature, infrared surface temperature) can forecast the CGWLs up to 3-month lead times at most of the locations. The addition of GRACE data as a forcing variable can improve the performance of SVMs at most of the stations, where a strong relationship exists between the CGWLs and the GWA. The SVM-DA model comparatively performed better than SVMs at most of the stations. [ABSTRACT FROM AUTHOR]

The purpose of this study was to evaluate the applicability of medium and long-term satellite rainfall estimation (SRE) precipitation products for drought monitoring over mainland China. Four medium and long-term (19 a) SREs, i.e., the Tropical Rainfall Measuring Mission (TRMM) Multi-Satellite Precipitation Analysis (TMPA) 3B42V7, the Integrated Multi-satellitE Retrievals for Global Precipitation Measurement V06 post-real time Final Run precipitation products (IMF6), Global Rainfall Map in Near-real-time Gauge-calibrated Rainfall Product (GSMaP_Gauge_NRT) for product version 6 (GNRT6) and gauge-adjusted Global Satellite Mapping of Precipitation V6 (GGA6) were considered. The accuracy of the four SREs was first evaluated against ground observation precipitation data. The Standardized Precipitation Evapotranspiration Index (SPEI) based on four SREs was then compared at multiple temporal and spatial scales. Finally, four typical drought-influenced regions, i.e., the Northeast China Plain (NEC), Huang-Huai-Hai Plain (3HP), Yunnan–Guizhou Plateau (YGP) and South China (SC) were chosen as examples to analyze the ability of four SREs to capture the temporal and spatial changes of typical drought events. The results show that compared with GNRT6, the precipitation estimated by GGA6, IMF6 and 3B42V7 are in better agreement with the ground observation results. In the evaluation using SPEI, the four SREs performed well in eastern China but have large uncertainty in western China. GGA6 and IMF6 perform superior to GNRT6 and 3B42V7 in estimating SPEI and identifying typical drought events and behave almost the same. In general, GPM precipitation products have great potential to substitute TRMM precipitation products for drought monitoring. Both GGA6 and IMF6 are suitable for historical drought analysis. Due to the shorter time latency of data release and good performance in the eastern part of mainland China, GNRT6 and GGA6 might play a role for near real-time drought monitoring in the area. The results of this research will provide reference for the application of the SREs for drought monitoring in the GPM era. [ABSTRACT FROM AUTHOR]

Due to the imprecise structure originated from the limitation of knowledge level or lack of information, the inverse problems for identifying the unknown parameter of system will face the challenges in the solving mechanism and the computational cost. Compared with the traditional inverse problems, this kind of inverse problems not only need to identify the unknown parameter, but also need to quantify the uncertainty caused by the imprecise structure. In this paper, a basic solving framework based on evidence theory for this inverse uncertainty quantification is established to inversely estimate the effect of the uncertainties in imprecise structure on the unknown parameters. In order to overcome the computing bottleneck problem caused by the coupling of evidence-based uncertainty propagation and the inverse computation, an efficient similar system analysis method is further proposed. Firstly, the marginal interval analysis method is developed to transform the evidence-based uncertain inverse problem into several deterministic inverse problems at the marginal collocation points. Afterwards, the similar system analysis method is proposed by adequately utilizing the similarity of systems at any two adjacent marginal collocation points to further improve the computational efficiency of several deterministic inverse problems. Because of the coupling effect of the above two strategies, the proposed uncertain inverse method decouples the time-consuming multi-layer nested inverse procedure, and then greatly reduces the computational cost of inverse uncertainty quantification based on evidence theory. Two numerical examples and one engineering application are provided to verify the high efficiency of the proposed uncertain inverse method. [ABSTRACT FROM AUTHOR]

Freshwater lakes are subject to variable degrees of eutrophication. Within lakes, the planktonic bacterial community (PBC) and sediment bacterial community (SBC) are both significant participants in biogeochemical processes of lake ecosystems. However, how the assembly patterns of bacterial communities vary seasonally along a trophic gradient in freshwater lakes is poorly understood.Here, we collected and analysed water and sediment samples from 13 shallow lakes located in an urban region of China during summer and winter, the trophic states of which ranged from mesotrophic to middle eutrophic in summer and oligo‐mesotrophic to light eutrophic in winter. High‐throughput sequencing of 16S ribosomal RNA genes was used to determine the diversity and composition of bacterial communities.Our results indicated that bacterial communities derived from different habitats and seasons did not exhibit a uniform response to lake trophic states. Linear and nonlinear mixed effect models suggested that the α‐diversity of PBC and SBC, respectively, showed a unimodal and monotonically decreasing trend with increasing eutrophication in summer, whereas that of PBC and SBC, respectively, exhibited no obvious trend or an increased pattern along the trophic gradient in winter. In addition, the taxonomic compositional dissimilarity of the PBC was most significantly related to lake trophic differences in summer. Phylogenetic structure analysis revealed that mostly environmental selection regulated the SBC and PBC in both seasons. Moreover, dispersal limitation and homogenising dispersal contributed more to the assembly of SBC and PBC in both seasons, respectively. Water temperature, associated with seasonal variability, was the most important variable driving the PBC assembly, while sediment pH overwhelmed nutrients in regulating the seasonal patterns of SBC assemblages.Overall, we highlighted that the water and sediments, as well as the seasons, differentiated the diversity patterns and assembly processes of bacterial communities along a trophic gradient of freshwater lakes. Our findings provide novel information for understanding the ecological responses of lacustrine bacterial communities to trophic gradients and seasonal variations. This study also contributes an important reference for predicting the changes of microbial community biodiversity under future scenarios of eutrophication. ​ [ABSTRACT FROM AUTHOR]

Groundwater level fluctuations are affected by surface properties due to complex correlations of groundwater‐surface water interaction and/or other surface processes, which are usually hard to be accurately quantified. Previous studies have assessed the relationship between groundwater level fluctuations and specific controlling factors. However, few studies have been conducted to explore the impact of the combination of multiple factors on the groundwater system. Hence, this paper tries to explore the localized and scale‐specific multivariate relationships between the groundwater level and controlling factors (such as hydrologic and meteorological factors) using bivariate wavelet coherence and multiple wavelet coherence. The groundwater level fluctuations of two wells in areas covered by different plant densities (i.e., the riparian zone of the Colorado River, USA) are analyzed. Main findings include three parts. First, barometric pressure and river stage are the best factors to interpret the groundwater level fluctuations at small scales (<1 day) and large scales (>1 day) at the well of low‐density plants stand, respectively. Second, at the well of high‐density plants stand, the best predictors to control the groundwater level fluctuations include barometric pressure (<1 day), the combination of barometric pressure and temperature (1‐7 days), temperature (7‐30 days), and the combination of barometric pressure, temperature, and river stage (>30 days). The best predictor of groundwater head fluctuations depends on the variance of the vegetation coverage and hydrological processes. Third, these results provide a suite of factors to explain the groundwater level variations, which is an important topic in water‐resource prediction and management. Article impact statement: This method note provides a multivariate method to identify multiple factors that can best explain the groundwater level fluctuation. [ABSTRACT FROM AUTHOR]

• Long-term dynamics of permafrost changes on the TP were assessed. • Changes in permafrost distribution and ALT were considered simultaneously. • 15 representative GCMs were used to project permafrost future changes on the TP. • The permafrost stability and the elevation-dependent change of ALT were analyzed. Permafrost degradation on the Tibetan Plateau (TP) will significantly affect local water cycle processes, downstream water ecology, and water security. In this study, we evaluate the long-term interannual dynamics of permafrost distribution and active layer thickness (ALT) on the TP based on historical data from Climatic Research Unit gridded Time Series (CRU TS) downscaling and projected data under four shared socio-economic pathways (SSPs) in Scenario Model Intercomparison Project (ScenarioMIP) of the Coupled Model Intercomparison Project Phase 6 (CMIP 6). To achieve this, we employ a data-driven scheme at 1 km resolution for both historical and future periods (1901–2100) that compares the performance of four machine learning algorithms to select the optimal algorithm for permafrost distribution and ALT simulations. Our results indicate that the permafrost on the TP has been undergoing degradation in both historical and future periods, with a decrease in permafrost area and an increase in ALT. The changing rates of permafrost area and regionally averaged ALT during the historical period (1901–2020) are −1.05 × 104 km2 decade–1 and 0.012 m decade–1, while an accelerated degradation is observed after the 1970 s (with changing rates of permafrost area and regionally average ALT of −3.62 × 104 km2 decade–1 and 0.055 m decade–1). Our results also suggested that permafrost degradation on the TP will continue in the future under the four SSP scenarios. The individual global climate models (GCMs) exhibit a consistent degradation trend but great uncertainty in degradation speed. The ensemble mean of simulations across 15 selected GCMs showed that the degradation percentage of permafrost area on the TP under scenarios SSP1-2.6, SSP2-4.5, SSP3-7.0, and SSP5-8.5 was 26.0 ± 6.8 %, 50.4 ± 5.6 %, 79.2 ± 4.5 %, and 89.0 ± 4.0 % by 2100, and the regionally average ALT increased by 0.301 ± 0.112 m, 0.628 ± 0.113 m, 1.204 ± 0.119 m, and 1.486 ± 0.125 m, respectively. We also analyze permafrost stability and elevation-dependent changes of ALT on the TP. The permafrost stability increases with elevation and latitude, and ALT changes more intensely with increasing elevation. This study will provide valuable data for hydrological and ecological studies related to permafrost on the TP. [ABSTRACT FROM AUTHOR]

A diagram illustrating distribution and evolution model of soil water isotopic differences in the studied catchment. [Display omitted] • The immobile soil water showed high deviation from the LMWL in summer than in spring. • The mobile soil water was controlled by the precipitation input and less influenced by evaporation fractionation. • The mobile/immobile soil waters showed large isotopic differences and different mobility in summer. • Soil thawing provided important soil water sources and influenced the subsurface mixing processes. Recently studies postulate that there are two distinct soil water pools, i.e., mobile and immobile soil water (MSW and IMSW), and different soil waters have different mobility to generate runoff. Evaluating the influences of soil thawing on the subsurface mixing between different soil waters is important for understanding subsurface hydrological processes. In this study, the isotopic differences between different soil waters were evaluated in a permafrost-underlain headwater catchment by comparing the variations of stable isotopes and seasonal origin of MSW and bulk soil water (BSW), including both IMSW and MSW. BSW was sampled using soil augering and cryogenic vacuum distillation in thawed and frozen soil layers, and MSW was collected using a zero-tension lysimeter in thawed soil layers. The results show the following: (1) The average δ2H values of MSW, thawed BSW, and frozen BSW were similar during the spring snowmelt period (SSP), this can be attributed to weak evaporation and their similar origin, which is supported by the high line-conditioned excess values and their similar seasonal origin index values. (2) The enriched MSW collected during the SRP compared to the spring MSW and was associated with enriched summer precipitation, and the IMSW experienced strong evaporation during the period from the SSP to the SRP, both leading to enriched summer BSW compared to the spring BSW. (3) The frozen and thawed BSW had very similar isotopic compositions and seasonal origin, indicating the close hydrological connection between them and the important recharge of the melting frozen soil to soil water or runoff. The different freeze–thaw stages and soil moisture conditions controlled the stable isotope variations and mixing of different soil waters, this results in the different mobility of the mobile/immobile soil waters involved in the runoff generation processes during the SRP and the SSP, and therefore these features are useful to verify the isotopes-aided precipitation–runoff models applied in such catchments. [ABSTRACT FROM AUTHOR]

• Permafrost extent and ALT changes on the TP were evaluated. • The SOC stocks and storage in TP permafrost areas were estimated. • Thawed and perennially frozen state of SOC in permafrost areas is distinguished. • Dynamics of thawed SOC in TP permafrost areas from 1901−2020 were assessed. Large amounts of frozen carbon stored in the permafrost of the Tibetan Plateau (TP) are gradually thawing due to climate warming. The thaw of frozen carbon allows more active soil organic carbon (SOC) on the TP to participate in the global carbon cycle, which has usually been neglected in previous studies of permafrost carbon. This paper assesses the thawed SOC stock and its historical dynamics in TP permafrost areas based on a data-driven scheme. The results show that the current permafrost area of the TP is 1.14 × 106 km2, and the SOC stock in the top 10 m of permafrost areas is 47.36 Pg. The active layer of the TP permafrost has a regional average thickness of 2.37 m during the baseline period (2000−2020), storing 18.19 Pg of SOC, accounting for about 38.4 % of the total SOC stock in the top 10 m, with the remaining more than 60 % perennially frozen in permafrost. The dynamics of thawed SOC are calculated based on baseline period SOC pools. Despite significant fluctuations, there is a general trend of 0.074 Pg SOC thaw per decade over 1901−2020 as the active layer has deepened. Significantly, the thaw trend of frozen SOC after 1976 is more prominent, reaching 0.420 Pg decade−1. Moreover, this paper reconstructs the SOC pool at the beginning of the last century by incorporating historical deep carbon emissions (1 − 10 m) in the current SOC pool. It recalculates the thaw trend of frozen carbon based on this and finds that the general thaw trend of SOC from 1901−2020 is more significant, with a rate of 0.092 Pg decade−1. Additionally, the dynamics of SOC pools in surface soils (0 − 1 m) of TP permafrost areas are also discussed. Our study highlights the importance of permafrost carbon thaw and provides valuable information for TP carbon studies. [ABSTRACT FROM AUTHOR]

• The t-FADE can upscale transport in rough single-fractured media. • Mass flux is defined for flow through rough-walled single fracture. • Fracture roughness is linked with parameters of the upscaled model. Complex structures in fractures and the rock matrix, which are difficult to map exhaustively at the local scale, can dominate contaminant transport in fractured aquifers. An upscaled model is therefore needed to effectively characterize solute transport in a heterogeneous fracture-matrix system on a large spatiotemporal scale. Most existing upscaling methods, however, do not specifically quantify the influence of matrix diffusion and fracture surface roughness on solute transport, and their upscaling parameters are usually difficult to obtain. To fill this knowledge gap, first, a time fractional advection–dispersion equation (t-FADE) model, which can accurately describe solute transport in straight fractured media, is proposed. Next, the influence of local roughness and tortuosity of fractures on transport is comprehensively considered by introducing trend lines. The t-FADE is used to characterize solute transport in each segment of rough fractures, and an upscaled model describing solute transport in rough fractures is established by averaging the governing equations of each segment. Finally, a time-dependent attenuation function is introduced into the convolutional function of the upscaled model to overcome the error caused by overlapping diffusion regions. Model comparison and analysis reveal that the rough wall of fractures strengthens matrix retention capacity, leading to a delayed peak of the breakthrough curve (BTC) with a lower peak concentration, which can be quantitatively characterized by the ratio of the actual fracture length to its longitudinal length; however, the fracture structure does not affect the solute BTC's trailing concentration at the constant fracture mean flow velocity without considering mechanical dispersion, so the relatively simple straight fracture model can be used to describe the trailing stage of transport in rough-walled fracture media. [ABSTRACT FROM AUTHOR]

Diverse microorganisms perform similar metabolic process in biogeochemical cycles, whereas they are found of highly genomic differentiation. Biotic interactions should be considered in any community survey of these functional groups, as they contribute to community assembly and ultimately alter ecosystem properties. Current knowledge has mainly been achieved based on functional community characterized by a single gene using co-occurrence network analysis. Biotic interactions between functionally equivalent microorganisms, however, have received much less attention. Herein, we propose the nirK- and nirS-type denitrifier communities represented by these two nitrite reductase (nir)–encoding genes, as model communities to investigate the potential interactions of two nir denitrifiers. We evaluated co-occurrence patterns and co-association network structures of nir denitrifier community from an emergent macrophyte-dominated riparian zone of highly active denitrification in Lake Taihu, China. We found a more segregated pattern in combined nir communities than in individual communities. Network analyses revealed a modularized structure of associating nir denitrifiers. An increased proportion of negative associations among combined communities relative to those of individual communities indicated potential interspecific competition between nirK and nirS denitrifiers. pH and NH4+-N were the most important factors driving co-occurrence and mutual exclusion between nirK and nirS denitrifiers. We also showed the topological importance of nirK denitrifiers acting as module hubs for constructing entire association networks. We revealed previously unexplored co-association relationships between nirK and nirS denitrifiers, which were previously neglected in network analyses of individual communities. Using nir denitrifier community as a model, these findings would be helpful for us to understand the biotic interactions and mechanisms underlying how functional groups co-exist in performing biogeochemical cycles. [ABSTRACT FROM AUTHOR]

• A system dynamics simulation approach (SDSA) for reservoir operation is proposed. • Scenario based simulation analyses are performed with the SDSA model. • Impacts of placing environmental priorities over power production are investigated. • Research results can contribute to environmentally friendly operation of reservoir. Multipurpose reservoir operation is a very complex decision-making process because of its multiple and usually conflicting targets. A system view of the interactions between various reservoir purposes (like for example, hydropower production and environmental impacts such as fish habitats, sediment flushing, and landslide stability) is a prerequisite to attain the full benefits from reservoir operations. System dynamics simulation is a well suited approach for dealing with complex time-varying systems and is widely used in water resources management and analyses of global change. This paper presents the development of a generic system dynamics simulation approach (SDSA) for the analyses of interactions between reservoir's various functions. The implementation of SDSA includes two steps. First, the causal diagram of the reservoir system is used to map and analyze the main interactions among reservoir system's different components, identify driving feedback relationships and use the system structure to obtain insights' into system behavior. In the second step, the stock and flow diagraming is used to quantify those feedbacks and interactions by introducing a set of physical and empirical relationships required to simulate the model. The developed SDSA is applied to the Three Gorges Reservoir in China. Scenario based simulation analyses are performed with the SDSA model to increase the understanding of placing different priorities on the interactions between hydropower production and environmental impacts of reservoir operations. Results from model validation and sensitivity analyses suggest that the developed SDSA model is capable of simulating interactions among reservoir's various functions, and the case study application demonstrates the utility of the model for capturing the main characteristics of reservoir system dynamic behavior. The insights gained from model simulations can assist in environmentally friendly operations of the reservoir. [ABSTRACT FROM AUTHOR]

Although aquaculture provides a stable and high-quality source of food, the environmental effects related to large-scale industrial aquacultural activities have raised concern. To identify the influence of aquacultural activities on sedimentary bacterial communities, we collected surface and deeper sediments from a series of sites subjected to varying intensities of aquacultural activities within Eastern Lake Taihu, China. The associated physicochemical properties were measured, and 16S rRNA gene sequencing was applied to determine the related bacterial communities in sediment. The diversity and composition of bacterial communities within the surface sediments differed significantly from those of the deeper sediment samples. Marked differences were also found between the surface sediments of the aquaculture-influenced and non-aquaculturally influenced sites. More importantly, phylogenetic structure analysis indicated that stochastic processes dominated the assembly of the bacterial communities; yet, the relative contribution of deterministic processes to bacterial community assembly was greater in the aquacultural zones than in the non-aquacultural zones. Furthermore, we identified total phosphorus (TP) as the most important factor driving the assembly of bacterial communities influenced by aquaculture in sediment. These findings provide useful information for ecological assessments and remediation strategies for aquaculture-influenced ecosystems. [ABSTRACT FROM AUTHOR]

40 small watersheds in the Source Area of the Yellow River were investigated recently to sample surface waters, groundwater and ground ice, and their water isotopic signatures (2H, 18O, 3H, and 222Rn) have been measured. A novel isotope mass balance approach was developed to estimate annual surface and surface flow discharges in catchment combined water age dating. This approach revealed the changing surface and subsurface runoff patterns were along the hydrological trajectory of progressive permafrost degradation. To build up the linkages between the hydrological indictors and environmental and biological features was recommended, which would benefit a better understanding the significant impacts of permafrost degradation on social, ecological and economic developments in cold regions. [ABSTRACT FROM AUTHOR]

Understanding the successional patterns of microbial communities during a phytoplankton bloom is crucial for predicting the compositional and functional stability of lake ecosystems in response to the disturbance of a bloom. Previous studies on bacterial communities associated with blooms have rarely studied the dynamics of these communities. The successional patterns of bacterial communities within different micro‐habitats (i.e. water column versus particles) and mechanisms that shape these communities that differ in composition and structure remain unclear.We selected a eutrophic urban lake to investigate the succession of bacterial communities during a bloom. We divided the bacterial communities into free‐living (FL) and particle‐attached (PA) groups based on their different lifestyles. The amplicon‐based 16S rRNA gene high‐throughput sequencing technology was used to obtain bacterial community composition and phylogenetic structure.Our study showed distinct successional patterns between FL and PA bacterial communities, and the two bacterial lifestyles showed different responses and resilience to the bloom, in terms of diversity and relative abundance of bacterial taxa. Alpha‐diversity of the PA bacterial community decreased during the bloom, whereas that of the FL bacterial community increased. More taxa in the FL bacterial community showed resilience after the disturbance than in the PA bacterial community.The influence of phytoplankton blooms on the assembly of the bacterial community can be viewed as niche selection that led to the decrease in the relative importance of stochastic processes in shaping both FL and PA bacterial communities. This study shows the ecological significance of the bacterial community response to bloom events in lakes. It also shows that assembly processes differ for bacterial communities that have different lifestyles in lake ecosystems disturbed by phytoplankton blooms. [ABSTRACT FROM AUTHOR]

• The hydrologic impact of existing and alternative reservoir network layouts was investigated. • Few large reservoirs regulate the streamflow more significantly than many small ones with similar inflow. • Locating reservoirs somewhere with similar inflow is unlikely to change the streamflow condition. • Assigning reservoirs higher inflow without changing their location can increase their functionality. Reservoirs have been continuously built in the Poyang Lake Basin (PLB) for the local economy. With pending removal and reconstruction of aging reservoirs and planning of new reservoirs in this area, it is advisable to evaluate the likely impact of the existing and alternative reservoir network layouts on the hydrologic regime for more effective water resources planning and management. In this study, reservoirs of multiple sizes in the PLB were integrated into a coupled land surface-hydrologic model (CLHMS) fully coupled with a reservoir scheme. The extended model was then validated and applied to investigate the impact of existing reservoirs. Seven hypothetical scenarios were additionally set up by removing all the reservoirs, replacing smaller reservoirs with few larger ones, replacing larger reservoirs with many smaller ones, moving all reservoirs downstream or upstream, increasing or decreasing the mean inflow of reservoirs, respectively. In all, eight simulations were conducted and analyzed using the Indictors of Hydrologic Alterations (IHA) for the period of 1981–1999. Results indicate that the existing reservoirs in the PLB are able to effectively displace the excessive streamflow in the wet season to the dry season and mitigate the hydrological extremes. By increasing the mean inflow of reservoirs, the effectiveness of reservoirs in downstream flow regulation can be further enhanced. Similarly, replacing many small reservoirs with a few large ones with a same total capacity can lead to more resiliency against the downstream flow variability and extremes, only if the total mean inflow of the new large reservoirs is not considerably lower than that of the small ones. Relocating reservoirs to a different place with similar mean inflow, however, has a relatively minor and probably case-dependent impact on the hydrologic regime. On the other hand, the ecological analysis on the IHA parameters indicates that the layout preferable for the effective flow regulation may not necessarily be ecologically preferable. In general, this study comprehensively evaluates the hydrological impact of reservoir network layouts, and can provide implications for stakeholders to reach a trade-off between reservoir capacity distribution, locations and mean inflow not only in the PLB but also in different regions worldwide. [ABSTRACT FROM AUTHOR]

Estimating groundwater recharge rate is essential for water sustainability of the arid region of the United Arab Emirates that receives most groundwater recharge from the bordering mountain ranges in Oman. Analyses of major ions, stable isotopes (δ2H and δ18O) and the radioactive isotope (14C) and the HydroGeoSphere (HGS) three-dimensional numerical model approach were applied here to investigate groundwater residence time in the aquifers and the recharge rates in the region. Estimate of groundwater recharge ranges from 1.03 to 36.6 mm/year with an average of 5.8 mm/year based on groundwater ages and ranges from 0.23 to 35.3 mm/year with an average of 6.5 mm/year based on HGS modelling. The data provide vital information for making sustainable plans for natural water resources with expected future reduction in rainfall in this region and other arid areas of the Middle East and the world. [ABSTRACT FROM AUTHOR]

Rhizosphere microbiota has received much attention due to their associations with plant growth and their fundamental importance in terrestrial ecosystems. However, relatively few studies have focused on rhizosphere microbial communities associated with aquatic macrophytes in freshwater lakes. We hypothesized that the rhizosphere microbiome would reflect the presence of macrophyte roots and the concomitant microhabitat conditions the roots create. Here, high‐throughput sequencing and network analysis were employed to compare the composition and structure of bacterial communities in the rhizosphere of two common emergent macrophytes, Zizania latifolia and Phragmites australis, with the surrounding sediments in Lake Taihu (China). Results indicated that bacterial diversity, community composition, and co‐occurrence networks differed between the communities of bulk sediments and the communities of rhizosphere and surface sediments. Richness and phylogenetic diversity were higher and more taxa were enriched in the rhizosphere and surface sediment communities compared with bulk sediment communities. No differences were detected between bacterial communities in rhizosphere and surface sediments, nor between rhizospheres sediment communities of the two macrophyte species. Anaerobic taxa were more abundant in bulk sediment communities. Among the co‐occurrence networks, more nodes (operational taxonomic units) and edges (connections) with higher average degree as well as more topologically important nodes were found in rhizosphere and surface sediment communities relative to bulk communities. These findings suggest that rhizosphere microbiome communities are influenced by the presence of macrophyte roots, with oxygenated rhizosphere and surface sediment communities being more diverse, and organized into more interconnected co‐occurrence networks. [ABSTRACT FROM AUTHOR]

On the Qinghai-Tibet Plateau, permafrost degradation and associated release of permafrost meltwater has undoubtedly modified the annual and seasonal streamflow patterns and influenced groundwater conditions. However, it is still unclear how extensively permafrost degradation has influenced surface and subsurface water systems due to very sparse observations. Isotope mass models combining tritium and 222Rn measurements are developed here to quantify the contributions of groundwater discharge and thawing permafrost to rivers and lakes in the Source Area of the Yellow River. Results demonstrate the spatial variability of permafrost thaw impacts and confirm significant influence on surface and subsurface runoff processes including effects on water yield capacity and water drainage connectivity. While results to date are conclusive, further work to refine the method and extend observations is warranted. [ABSTRACT FROM AUTHOR]

A spatially distributed network of thermokarst lakes undergoing significant environmental changes was sampled in 2014 and 2016 to develop a comprehensive understanding of lake water balances in lakes across a gradient of frozen ground conditions. Frozen ground ranges from seasonally frozen ground (SFG) to sporadic discontinuous permafrost (SDP) to extensive discontinuous permafrost (EDP), and is representative of complex conditions in the Source Area of the Yellow River, northeastern part of Qinghai-Tibet Plateau. Radioactive and stable water isotopes in reference lakes (non-thaw lakes), thermokarst lakes, precipitation, wetlands, ground ice and supra-permafrost groundwater are analyzed to characterize systematic variations and to assess lake water balances using stable isotope mass balance (IMB). IMB, paired with analysis of tritium decay gradients, is shown to be a valid approach for detecting short-term shifts in lake water balance, which allows evaluation of the proportion of precipitation-derived versus permafrost-derived water inputs to lakes. All lakes except EDP thaw lakes are evaporation-dominated (E/ I > 0.5). Negative water balances occurred most frequently in reference lakes due to hydrological connectivity with rivers. Precipitation-derived water inputs result in positive water balances in SFG and SDP thermokarst lakes, but negative-trending water balances are found in SDP thermokarst lakes due to substantial reduction in water yield. Increasing contributions from thawing permafrost in EDP thermokarst lakes result in strong positive water balance. Permafrost degradation may also lead to the changes in hydrological connectivity between precipitation and wetlands or thermokarst lakes. Based on these findings, a conceptual model of the hydrological evolution of thermokarst lakes under the influence of permafrost degradation is proposed. Unlabelled Image • Stable isotopes and tritium gradients applied to assess thaw lake water balances. • Thermokarst lake classes include ground-ice-melt and precipitation fed types. • Thawing permafrost produced increases in water yield from catchments to lakes. • Extensive permafrost zone had high, increasing runoff whereas others were in decline. • Shifting hydrology due to permafrost degradation summarized in new conceptual model. [ABSTRACT FROM AUTHOR]

• Compiled a multi-year, multi-layer daily soil moisture record across Anhui Province. • Soil moisture generally increases with depth in Anhui Province. • Soil moisture in the region has large seasonal fluctuations, decaying with depth. • Effects of antecedent accumulated rainfall on soil moisture varies over depth. Little measurement-based soil moisture information is available for the humid to semi-humid transitional zones in China. Anhui Province is a representative area of these zones and spans several hydroclimatic and geomorphological zones. To overcome shortage of observational soil moisture information in this area, we collected and compiled a multi-layer daily soil moisture record from 2012 to 2016 across Anhui Province based on the observations of a soil moisture-observing network composed of 85 sites. We then analyzed the vertical and spatiotemporal variability of soil moisture across this region. Primary findings are: (a) soil moisture in this region has apparent vertical gradients and increases with soil depth; (b) substantial soil moisture spatial variability appears in the shallow soil layers (depth ≤40 cm) with the highest values in the middle part of this region, but soil moisture in the deep layers (depth >40 cm) shows low spatial variability; (c) seasonality of soil moisture across this region is complicated and has fluctuations with July as the wettest month in most of the province; (d) inter-monthly fluctuation of soil moisture is larger in the upper soil layers than in the lower layers; and (e) antecedent accumulated rainfall is a major factor influencing soil moisture throughout this region with soil moisture in the upper layers more sensitive to immediate weather conditions and soil moisture in the lower layers showing lagged responses to the weather conditions. This study can not only reveal the spatiotemporal and vertical characteristics of soil moisture across this region, but also provide a useful reference dataset for the other soil moisture modeling and retrieval studies. [ABSTRACT FROM AUTHOR]

Abstract The magnitude of soil and sediment erosion and accumulation processes can profoundly affect landscape development and hamper efficient management of natural resources. Consequently, estimating the rates and causes of these processes is essential, particularly in remote regions, for prediction of changes in landform and river evolution and protection of local ecosystem. We here present the results of a soil and sediment erosion investigation in the Source Area of the Yellow River (SAYR), northeast Qinghai-Tibet Plateau based on a combined analysis of 10Be cosmogenic isotope and Soil and Water Assessment Tool (SWAT) simulation modelling. The data reveal variable soil erosion trends that range between 103 and 830 t km−2 a−1. The low values occur in the western part of the basin that are associated with low sediment yield, while the high values appear in the dominant sediment export part of the basin along the main stream of the Yellow River in the east. Generally, soil and sediment accumulation is characterized by high 10Be concentration in the western part and the northwest of Ngöring Lake. The style of landform development by the erosion/accumulation processes is closely linked to the distribution and degradation extent of the permafrost in the study region. Soil surface erosion increases with more permafrost degradation from the western to the eastern part of the basin, and surface soil particles are dominantly removed from the surface rather than deeper layers. Highlights • Soil erosion is assessed by isotopes and Soil and Water Assessment Tool. • Different soil erosion types are identified by 10Be isotope. • Surface erosion, instead of gully erosion, is the main process in the region. • Surface erosion is more severe with the decrease of permafrost covering. [ABSTRACT FROM AUTHOR]

Abstract The radioactive isotope 129I, with a half-life of 1.57 × 107 years, is widely used as a tracer to assess nuclear safety, to track environmental and geological events and to figure out the details of the stable iodine geochemical cycle. This work investigated the 129I and 127I distribution in water samples collected from the terrestrial (rivers, lakes and springs) and marine water systems (estuary and sea) in China. The measured 129I concentrations of (1–51) × 106 atoms/L and 129I/127I ratios of (0.03–21) × 10−10 shows the variability of 129I level in the water systems. The local permafrost and seasonal frozen environment play a key role in groundwater recharge in the Qinghai-Tibet region, which is reflected in the 129I distribution in surface water. The depth distribution of 129I in the water column of the South China Sea reflects the effluence of different currents. The results also indicate that the hydrosphere of China contains one to three orders of magnitude less 129I compared to those reported in Europe. Despite the large distance, the European nuclear fuel reprocessing facilities represent the major source of 129I in the hydrosphere of China through atmospheric transport. The contribution of the Fukushima nuclear accident to 129I levels in the hydrosphere of China was negligible. Highlights • Variable 129I concentrations (1–51) × 106 atoms/L occur in the hydrosphere of China. • The range of 129I/127I is (0.03–21) × 10−10 in the hydrosphere of China. • Depth profiles of 129I in the South China Sea water reveal effects of different ocean currents. • Emissions from the Nuclear fuel reprocessing facilities is the major source of 129I in China. [ABSTRACT FROM AUTHOR]

Abstract Understanding hydrological processes in the Source Area of the Yellow River (SAYR), Qinghai-Tibet Plateau, is vital for protection and management of groundwater and surface water resources in the region. In situ water measurements of exchange rates between surface water and groundwater are, however, hard to conduct because of the harsh natural conditions of the SAYR. We here present an indirect method using in situ 222Rn measurements to estimate groundwater discharge into rivers and lakes in the SAYR. 222Rn was measured in rivers, lakes, groundwater and springs during three sampling periods (2014–2016), and the results indicate large variability in the concentration of the isotope. The data also indicate decreasing 222Rn trends in groundwater in the cold season (the Feb-2015 sampling period) which may be linked to frequency of capturing 222Rn in the frozen ground caused by geocryogenic processes. In addition, permafrost spatial extent and freeze-thaw processes have strongly affected the hydrological conditions in the region. Highlights • 222Rn distribution in natural water of the Source Area of the Yellow River (SAYR). • 222Rn-based estimates of groundwater inflow rates to rivers and lakes in the SAYR. • Effects of frozen ground on 222Rn concentration in water. [ABSTRACT FROM AUTHOR]

Free-living (FL) and particle-attached (PA) bacterial communities play critical roles in nutrient cycles, metabolite production, and as a food source in aquatic systems, and while their community composition, diversity, and functions have been well studied, we know little about their community interactions, co-occurrence patterns, and niche occupancy. In the present study, 13 sites in Taihu Lake were selected to study the differences of co-occurrence patterns and niches occupied between the FL and PA bacterial communities using correlation-based network analysis. The results show that both FL and PA bacterial community networks were non-random and significant differences of the network indexes (average path length, clustering coefficient, modularity) were found between the two groups. Furthermore, the PA bacterial community network consisted of more correlations between fewer OTUs, as well as higher average degree, making it more complex. The results of observed (O) to random (R) ratios of intra- or inter-phyla connections indicate more relationships such as cross-feeding, syntrophic, mutualistic, or competitive relationships in the PA bacterial community network. We also found that four OTUs (OTU00074, OTU00755, OTU00079, and OTU00454), which all had important influences on the nutrients cyclings, played different roles in the two networks as connectors or module hubs. Analysis of the relationships between the module eigengenes and environmental variables demonstrated that bacterial groups of the two networks favored quite different environmental conditions. These findings further confirmed the different ecological functions and niches occupied by the FL and PA bacterial communities in the aquatic ecosystem. [ABSTRACT FROM AUTHOR]

Contaminants can co-exist and migrate together in the environment, causing complex (and sometimes unexpected) transport dynamics which challenge the efficient remediation of individual contaminants. The co-transport dynamics, however, remained obscure for some contaminants, such as arsenic and micro/nano-plastics (MNPs). To fill this knowledge gap, this study explored the co-transport dynamics of arsenic and MNP particles in saturated soil by combining laboratory experiments and stochastic model analysis. Isothermal adsorption and sand column transport experiments showed that the adsorption of arsenic by MNP particles followed the Freundlich model, with a maximum adsorption of 2.425 mg/g for the MNP particles with a diameter of 100 nm. In the presence of MNP particles, the efflux concentration of arsenic ions declined due to adsorption, where the decline rate decreased with the increasing MNP size and increased with the increasing adsorption capacity. Experimental results also showed that the 100 nm nano-plastic particles prohibited arsenic transport in saturated sand columns, while the 5 μm microplastics enhanced arsenic transport due to electrostatic adsorption and media pore plugging. A tempered time fractional advective-dispersion equation was then proposed to quantify the observed breakthrough curves of arsenic. The results showed that this model can reliably capture the co-transport behavior of arsenic with MNPs in the saturated soil with all coefficients of determination over 0.97, and particularly, the small MNP particles facilitated anomalous transport of arsenic. This study therefore improved the understanding and quantification of the co-transport of arsenic and MNPs in soil. • Adsorption kinetics of arsenic on polystyrene plastics follows the Freundlich isothermal adsorption model. • Nano-polystyrene plastics inhibit arsenic's transport in porous media, while micro-polystyrene plastics accelerate it. • The tempered fractional model accurately captures anomalous co-transport behavior of arsenic with varying-sized plastics. • Notable anomalous transport of arsenic occurs due to the tiny size of co-transport plastic particles. [ABSTRACT FROM AUTHOR]

It has become increasingly important to quantify carbon and water fluxes due to their roles in global warming and climate change, particularly for the agroecosystems. However, the dynamics of carbon and water fluxes have not been clearly recognized in rotation croplands with complex and changeable climate. Here, the variations of net ecosystem productivity (NEP), evapotranspiration (ET) and the water use efficiency (WUE, defined as NEP/ET), and their responses to the environmental factors were investigated in a wheat-maize rotation cropland across the Huaibei Plain of China over 2013–2015. The total average NEP, ET and average WUE respectively were 489.1 gC m-2, 315.8 kgH 2 O m-2, 4.4 gC kg-1H 2 O for wheat and 192.5 gC m-2, 249.0 kgH 2 O m-2, 3.6 gC kg-1H 2 O for maize, implying that wheat season sequestered more CO 2 than maize season. Spring drought and summer flood affected WUE of wheat and maize, respectively. Daily wheat WUE seemed to be more sensitive to changes in photosynthetically active radiation (PAR), vapor pressure deficit (VPD), soil water content (SWC) and canopy conductance (G c). PAR was the dominant factor controlling diurnal dynamics of NEP and ET, while the opposite effect of VPD on NEP was recognized. NEP increasing with PAR was limited by high VPD, which obviously when VPD exceeded 2 kPa during the maize season. Maize NEP was limited with VPD under high solar radiation (> 500 μmol m-2 s-1). WUEs of wheat and maize were negatively related to SWC and G c , and the sensitivity of WUE response to SWC and G c increased with the increase of PAR or VPD range. Sub-diurnal NEP against PAR, VPD or temperature showed clockwise hysteresis but ET against PAR or windspeed showed counter-clockwise hysteresis, and these hystereses were mainly caused by the interplay between evaporative demand and moisture supply, photosynthesis and carbon allocation of the agroecosystems. [Display omitted] • The wheat season sequestered more CO2 than the maize season. • Spring drought and summer flood affected WUE of wheat and maize, respectively. • Wheat WUE seemed to be more sensitive to changes in environmental factors. • PAR was the dominant factor controlling diurnal dynamics of NEP and ET. [ABSTRACT FROM AUTHOR]

Better quantification of the spatiotemporal distribution of soil moisture across different spatial scales contributes significantly to the understanding of land surface processes on the Earth as an integrated system. While observational data for root-zone soil moisture (RZSM) often have sparse spatial coverage, model-simulated soil moisture may provide a useful alternative. TOPMODEL-Based Land Surface–Atmosphere Transfer Scheme (TOPLATS) has been widely studied and actively modified in recent years, while a detailed regional application with evaluation currently is still lacking. Thus, TOPLATS was used to generate high-resolution (30 arc s) RZSM based on coarse-scale (0.125°) forcing data over part of the Arkansas–Red River basin. First, the simulated RZSM was resampled to coarse scale to compare with the results of Mosaic, Noah, and VIC from NLDAS. Second, TOPLATS performance was assessed based on the spatial absolute difference among the models. The comparison shows that TOPLATS performance is similar to VIC, but different from Mosaic and Noah. Last, the simulated RZSM was compared with in situ observations of 16 stations in the study area. The results suggest that the simulated spatial distribution of RZSM is largely consistent with the distribution of topographic index (TI) in most instances, as topography was traditionally considered a major, but not the only, factor in horizontal redistribution of soil moisture. In addition, the finer-resolution RZSM can reflect the in situ soil moisture change at most local sites to a certain degree. The evaluation confirms that TOPLATS is a useful tool to estimate high-resolution soil moisture and has great potential to provide regional soil moisture estimates. [ABSTRACT FROM AUTHOR]

Analyses of stable (D and 18O) and radioactive (T) isotopes of different waters were applied to obtain the hydrological information in watersheds with different frozen ground types in the Source Area of the Yellow River, northeastern of Qinghai-Tibet Plateau in 2014 and 2016. Variations of oxygen and hydrogen isotope ratios, statistically higher tritium concentrations and lower water yields in thaw lakes confirm disparate sources of recharges to thaw lakes and other lakes. Thaw lakes at various stages of evolution influence the surface and subsurface water systems differently. [ABSTRACT FROM AUTHOR]

Real-time precipitation data with high spatiotemporal resolutions are crucial for accurate hydrological forecasting. To improve the spatial resolution and quality of satellite precipitation, a three-step satellite and gauge precipitation merging method was formulated in this study: (1) bilinear interpolation is first applied to downscale coarser satellite precipitation to a finer resolution ( P S ); (2) the (mixed) geographically weighted regression methods coupled with a weighting function are then used to estimate biases of P S as functions of gauge observations ( P O ) and P S ; and (3) biases of P S are finally corrected to produce a merged precipitation product. Based on the above framework, eight algorithms, a combination of two geographically weighted regression methods and four weighting functions, are developed to merge CMORPH (CPC MORPHing technique) precipitation with station observations on a daily scale in the Ziwuhe Basin of China. The geographical variables (elevation, slope, aspect, surface roughness, and distance to the coastline) and a meteorological variable (wind speed) were used for merging precipitation to avoid the artificial spatial autocorrelation resulting from traditional interpolation methods. The results show that the combination of the MGWR and BI-square function (MGWR-BI) has the best performance (R = 0.863 and RMSE = 7.273 mm/day) among the eight algorithms. The MGWR-BI algorithm was then applied to produce hourly merged precipitation product. Compared to the original CMORPH product (R = 0.208 and RMSE = 1.208 mm/hr), the quality of the merged data is significantly higher (R = 0.724 and RMSE = 0.706 mm/hr). The developed merging method not only improves the spatial resolution and quality of the satellite product but also is easy to implement, which is valuable for hydrological modeling and other applications. [ABSTRACT FROM AUTHOR]

To investigate the differences in the microbial community composition and assembly process in two lake zones (Meiliang Bay (MLB) and Xukou Bay (XKB) in Taihu Lake, China) with different nutrient loadings, water samples were collected. Both the 16S ribosomal RNA (rRNA) gene for the bacterial community and the 18S rRNA gene for the microeukaryote community were investigated using the Illumina second-generation sequencing platform (2 × 250 paired-end). The results indicated that both the bacterioplankton and microeukaryote community composition derived from the two lake zones were significantly different. Significantly higher operational taxonomic unit (OTU) richness ( P < 0.01) and phylogenetic diversity ( P < 0.05) were found for the bacterioplankton community of MLB. However, a comparable alpha diversity was found between the microeukaryote communities of MLB and XKB ( P > 0.05). Environmental factors significantly affected the community compositions in XKB for both the bacterioplankton and microeukaryotes. However, they did not significantly influence the microbial community composition in MLB, except for a weak correlation between dissolved organic carbon (DOC) and the microeukaryote community. The microbial communities tended to be more phylogenetically clustered than expected by chance in the two lake zones. Moreover, the results of the phylogenetic structure suggest that deterministic processes played overwhelming roles in driving the assembly of both the bacterioplankton and microeukaryote community in XKB. [ABSTRACT FROM AUTHOR]

In recent decades, saltwater intrusion over some low-lying coastal regions was deteriorated by rising sea-level and decreasing streamflow in the context of climate change. Though physically-based hydrodynamic models are the most detailed means to simulate salinity processes, they are commonly restricted by data insufficiency issues both in spatial resolution and temporal lasting. This motivates us to build a statistical model enable simulation and scenario analysis for coastal salinity change with limited observations. A Bayesian neural network (BNN) model is built hereby to simulate salinity. It offers more precise estimation compared with the conventional artificial neural network. Meanwhile, the model gives the uncertainty behaviors of the final salinity simulation which is not available for other methods. Future scenarios of salinity change are constructed and analyzed in different time periods on the basis of the validated BNN model. Results indicate that the water quality over lower Pearl River is degrading along with more significant uncertainties. Further analysis suggests that streamflow alteration has a more direct impact on salinity variations than the sea-level change does. The method allows a profound analysis of the potential influence on water quality degradation in coastal and low-lying regions in support of water management and adaptation toward global climate change. [ABSTRACT FROM AUTHOR]

The differences between δ18O and δ2H in throughfall and open rainfall were studied for a selected typhoon event in a watershed within the Taihu Lake drainage basin, eastern China. In this event, the isotopic composition of precipitation exhibited a strong temporal variation. Comparison results show that an isotopic composition difference existed not only between gross rainfall and average incremental rainfall, but also between different calculation methods used to derive average. The differences between incremental precipitation and throughfall isotopic composition were observed in this study. Considering the temporal variation in rainfall and throughfall during this typhoon event, the incremental value can have an effect on hydrograph separation more accurately in evaluating the importance of ‘new’ water. In addition, isotopic fluctuations of surface water and groundwater differed from those of rainfall and throughfall throughout the event. [ABSTRACT FROM PUBLISHER]