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Abstract Fiddler crabs, as coastal ecosystem engineers, play a crucial role in enhancing biodiversity and accelerating the flow of material and energy. Here we show how widespread crab burrows modify the carbon sequestration capacity of different habitats across a large climatic gradient. The process of crab burrowing results in the reallocation of sediment organic carbon and humus. Crab burrows can increase more greenhouse gases emissions compared to the sediment matrix (CO2: by 17–30%; CH4: by 49–141%). Straightforward calculations indicate that these increased emissions could offset 35–134% of sediment carbon burial in these two ecosystems. This research highlights the complex interactions between crab burrows, habitat type, and climate which reveal a potential lower carbon sink function of blue carbon ecosystems than previously expected without considering crab burrows.

Abstract Global impervious surface area (ISA) has more than doubled over the last three decades, but the associated carbon emissions resulting from the depletion of pre-existing land carbon stores remain unknown. Here, we report that the carbon losses from biomass and top soil (0–30 cm) due to global ISA expansion reached 46–75 Tg C per year over 1993–2018, accounting for 3.7–6.0% of the concurrent human land-use change emissions. For the Annex I countries of UNFCCC, our estimated emissions are comparable to the carbon emissions arising from settlement expansion as reported by the national greenhouse gas inventories, providing independent validation of this kind. The contrast between growing emissions in non-Annex I countries and declining ones in Annex I countries over the study period can be explained by an observed emerging pattern of emissions evolution dependent on the economic development stage. Our study has implications for international carbon accounting and climate mitigation as it reveals previously ignored but substantial contributions of ISA expansion to anthropogenic carbon emissions through land-use effects.

The COVID-19 pandemic has posed severe threats to global sustainable development. However, a comprehensive quantitative assessment of the impacts of COVID-19 on Sustainable Development Goals (SDGs) is still lacking. This research quantified the post-COVID-19 SDG progress from 2020 to 2024 using projected GDP growth and population and machine learning models including support vector machine, random forest, and extreme gradient boosting. The results show that the overall SDG performance declined by 7.7% in 2020 at the global scale, with 12 socioeconomic SDG performance decreasing by 3.0%–22.3% and 4 environmental SDG performance increasing by 1.6%–9.2%. By 2024, the progress of 12 SDGs will lag behind for one to eight years compared to their pre-COVID-19 trajectories, while extra time will be gained for 4 environment-related SDGs. Furthermore, the pandemic will cause more impacts on countries in emerging markets and developing economies than those on advanced economies, and the latter will recover more quickly to be closer to their pre-COVID-19 trajectories by 2024. Post-COVID-19 economic recovery should emphasize in areas that can help decouple economic growth from negative environmental impacts. The results can help government and non-state stakeholders identify critical areas for targeted policy to resume and speed up the progress to achieve SDGs by 2030.

Study region: The Yarlung Zangbo Basin (YZB) on the Tibetan Plateau, the world's highest river basin, features a significant cryosphere with glaciers and seasonal snow cover crucial to its hydrology. The study focuses on the region between the Nuxia and Dexing river gauging stations, where glaciers cover 15.4 % of the area. Study focus: The research quantifies the contributions of snow melt (SM) runoff, glacier melt (GM) runoff, rainfall runoff, and baseflow to the total runoff in the YZB. The Spatial Processes in Hydrology (SPHY) model, enhanced with a cryosphere module, was utilized, calibrated with runoff data from the Nuxia station and evapotranspiration data from 2003 to 2014. New hydrological insights: The study found rainfall runoff to be the primary contributor to annual runoff (66.3 %), followed by snow melt runoff (19.7 %), glacier melt runoff (6.2 %), and baseflow (7.8 %). Snow melt runoff is dominant in early spring, while baseflow prevails in winter. Glacier melt runoff contributes directly to river flow (90.1 %) and replenishes groundwater (9.9 %), which then drains as baseflow. In glacier-rich areas, percolated glacier meltwater significantly recharges groundwater, underscoring its vital role in sustaining river flow in the YZB. This research enhances the understanding of hydrological processes in large alpine river basins and highlights the crucial role of glacier and snow melt in maintaining the Tibetan Plateau's water resources.

Abstract High-quality regional development requires coupling of socioeconomic and natural domains, but it remains unclear how to effectively integrate the regional economy with river basin ecosystems. Here we establish a developmental perspective of 65 river economic belts, formed through history along the main stems of the world’s great rivers, covering initial, developing, and developed stages. We find that river economic belts characterized by basin-based regional integration can substantially upgrade their eco-efficiency through the harmonization of enhanced regional economic growth and efficient utilization of basin resources, once key prerequisites (e.g., gross domestic product per capita, de-industrialization status, and human development index) are met for river economic belts entering the developed stage. Importantly, primary concerns such as resource stress, environmental pollution, and biodiversity loss are also inherently addressed. Under representative scenarios of regional development planning and climate change (2015–2050), the basin-based regional integration strategy would provide river economic belts with new opportunities and pathways towards sustainability in emerging regions worldwide.

Abstract The hydrological and biogeochemical properties of the hyporheic zone in stream and riverine ecosystems have been extensively studied over the past two decades. Although it is widely acknowledged that sediment heterogeneity can influence biogeochemical reactions, little effort has been made to understand the role of heterogeneity on the spatiotemporal variability of riverbed redox conditions under changing flow dynamics at different timescales. Here we integrate a mechanistic model and field data to demonstrate that heterogeneity in permeability plays a vital role in modulating sediment redox conditions at both seasonal (annual) and event (daily‐to‐weekly) timescales, whereas heterogeneity in particulate organic carbon (POC) content only has a comparable influence on redox conditions at the seasonal timescale. These findings underscore the importance of accurately characterizing sediment heterogeneity, in terms of permeability and POC content, in quantifying biogeochemical dynamics in the riverbed and hyporheic zones of riverine ecosystems.

Abstract Mantle‐derived volatile degassing lacks quantitative evaluation in continental regions without active magmatism, such as the Tibetan Plateau. Ten new gas abundance and helium isotope data points combined with 286 hydrothermal volatile literature data points in India–Asia continental collision settings demonstrate widespread mantle‐derived volatiles across the thick (∼70 km) crust. The mantle‐derived 3He is best explained by direct mantle volatile input from subcontinental lithospheric mantle (1%–36.5%) or the asthenospheric wedge (1%–27.8%) instead of fossil residual magmatic fluids or Quaternary mantle‐derived melt intrusion into crustal depth. Mantle‐derived 3He is transported from the deep mantle to the surface at an upflow rate of 30–11,700 mm/year based on a newly developed steady‐state one‐dimensional flow model, corresponding to a mantle‐derived 3He flux of 17 to 1.5 × 107 atoms m−2 s−1 (81.7%–99.4% of the total 3He flux) and a mantle‐derived 4He flux from 2.0 × 106 to 1.8 × 1012 atoms m−2 s−1 (1.4%–36.5% of the total 4He flux). The mantle‐derived helium fluxes in the study area are comparable to those of other nonvolcanic hydrothermal systems in the tectonically active regions but lower than those of volcanic fields. The helium transit time ranges from 5.3 ka to 2.3 Ma, indicating that the spatial pattern of 3He/4He ratios in the India‐Asia continental collision settings can provide a snapshot of the state of the Indian mantle lithosphere between those revealed by potassic‐rich mafic rocks (25–8 Ma) and seismic methods (present).

The southeastern part of the Tibetan Plateau (TP), one of the regions with the largest glacier distribution on the plateau, has been experiencing a significant loss in glacier mass balance (GMB) in recent decades due to climate warming. In this study, we used the Spatial Processes in Hydrology (SPHY) model and satellite data from LANDSAT to reconstruct the runoff components and glacier mass balance in the Niyang River basin (NRB). The measured river discharge data in the basin during 2000–2008 were used for model calibration and validation. Then, the validated model was applied to reconstruct the runoff components and GMB in the Niyang River basin for the period 1969–2013. Results showed that rainfall runoff (67%) was the dominant contributor to total runoff, followed by snowmelt runoff (14%), glacier melt runoff (10%), and baseflow (9%). The NRB experienced a severe loss in GMB, with a mean value of −1.26 m w. e./a (corresponding to a cumulative glacier mass loss of −56.72 m w. e.) during 1969–2013. During periods Ⅰ (1969–1983), Ⅱ (1984–1998), and Ⅲ (1999–2013) glacier mass loss was simulated at rates of −1.27 m w. e./a, −1.18 m w. e./a, and −1.33 m w. e./a, respectively. The annual loss of glacier mass in the northern region of the NRB (−1.43 m w. e./a) was significantly greater than that of the southern region (−0.53 m w. e./a) from 1969 to 2013, largely due to temperature variations, especially in summer months. These findings enhance our understanding of how different hydrological processes respond to climate change and provide a potential method to study runoff components and GMB in other glacierized catchments worldwide.

Both iodine deficiency and excess could cause thyroid disorders. By creating a national map of groundwater iodine throughout China, the authors reveal the spatial responses of diverse health risks to iodine in continental groundwater.

Lakes are essential components of the hydrological and biogeochemical cycles. Here, Pi et al develop a global lake dataset called GLAKES via high-resolution satellite images and deep learning to examine global lake changes over four decades.

Study region: Jiemayangzong Glacier basin, source of the Yarlung Zangbo, Tibetan Plateau. Study focus: Mountain groundwater is an important water source to recharge rivers. However, there is still a lack of a suitable “climate-glacier-groundwater” modeling framework to project future changes of glacier and the consequent impacts on evolution of groundwater in the Tibetan Plateau (TP). The groundwater model HydroGeoSphere (HGS) is coupled with the glacier retreat method Δh - parameterization to simulate subglacial meltwater recharge to groundwater (SMRG), precipitation recharge to groundwater (PRG), and total groundwater recharge (TGR) in the Jiemayangzong Glacier basin, source of the Yarlung Zangbo. New hydrological insights for the region: Results show that the volume of the Jiemayangzong Glacier would continuously retreat from 2021 to 2100. For the SSP126 and SSP585 climate change scenarios, the glacier volume would maximum decrease to 26.1% and 14.7% in 2100 (reference ∼ 2021), respectively. The simulated rate of annual SMRG is 24 mm/yr, which accounts for 63% of TGR. SMRG and TGR would decrease to 26% and 73% in 2100 under SSP585 climate change scenarios. Although PRG would continuously increase to 151% for SSP585 in 2100, it could not counteract the loss of SMRG. The change in hydraulic head is significant in the glacier terminus and the aquifer shallow zones (elevation above 4000 m). Glacier retreat results from increasing temperature will seriously affect local groundwater resources, particularly for the SSP585 scenario.

Little information is available on how the types, concentrations, and distribution of chemicals have evolved over the years. The objective of the present study is therefore to review the spatial and temporal distribution profile of emerging contaminants with limited toxicology data in the pearl river basin over the years to build up the emerging contaminants database in this region for risk assessment and regulatory purposes. The result revealed that seven groups of emerging contaminants were abundant in this region, and many emerging contaminants had been detected at much higher concentrations before 2011. Specifically, antibiotics, phenolic compounds, and acidic pharmaceuticals were the most abundant emerging contaminants detected in the aquatic compartment, while phenolic compounds were of the most profound concern in soil. Flame retardants and plastics were the most frequently studied chemicals in organisms. The abundance of the field concentrations and frequencies varied considerably over the years, and currently available data can hardly be used for regulation purposes. It is suggested that watershed management should establish a regular monitoring scheme and comprehensive database to monitor the distribution of emerging contaminants considering the highly condensed population in this region. The priority monitoring list should be formed in consideration of historical abundance, potential toxic effects of emerging contaminants as well as the distribution of heavily polluting industries in the region.

The Himalayan and Tibetan Plateau (TP) region serves as the “Asian water tower”. Yarlung Zangbo basin (YZB) is one of most important major rivers originating from TP sustaining billions of lives in the downstream alluvial plain. Climate change has impacted the hydrological cycle in this alpine region; however, the temporal and spatial trends of runoff and the water balance has not been quantified adequately. Here, we have optimized the snowmelt module of the Soil and Water Assessment Tool (SWAT) for the YZB to quantify the historical and future variability in the runoff, snowmelt water, and water balance components. According to the results of the Coupled Model Intercomparison Project Five and Six (CMIP5 and CMIP6) the future precipitation (2020–2099) projected by the CMIP6 will increase by 2.7% when compared to historical reference (1980–2019), while the precipitation will increase by 10.2% when projected by the CMIP5. The increase in average air temperature (2.4°C) projected by CMIP6 exceeds that of CMIP5 (1.9°C). The runoff between 2020 and 2050 will decrease by −12.7% compared with historical reference, and it will further decline by −9.2% during 2060 and 2099. Based on the average results of CMIP5 and CMIP6, the water balance deficit will increase primarily due to an increase in evaporation of 42.4%, whereas snowmelt (−32.1%), water yield (−9.4%), soil water (−19.8%), and groundwater recharge (−17.8%) will decrease. Long-term water balance evaluation implicates that middle and upper reaches will face a higher risk of drought, implying a potential threat to the sustainability of grassland ecosystems upstream.

Study region: Calabar, Cross River State, Nigeria Study focus: Urban groundwater is a strategic water resource in Africa that offers a buffer against climate variability. Increasing population, extensive pollution, and climate change threaten the contribution of urban groundwater in compensating increasing freshwater demand. Modern urban areas are often established on productive alluvial aquifers because of the proximity between shallow water bodies and historical settlements. Groundwater dynamics in urban aquifers are complex. Impervious surfaces impede water infiltration, and leakage from water infrastructure contributes to groundwater recharge. In this study, groundwater dynamics of an African metropolis are assessed, and insights into aquifer protection are provided through detailed hydrogeological analysis and numerical models. New hydrogeological insights for the region: The Calabar metropolis (area of 166 km2 and 570,000 inhabitants) is characterized by a tropical climate, with annual rainfall of over 3000 mm/y and large groundwater resources enabling supply for 69% of the population. A simplified three-dimensional hydrogeological model of the metropolis was proposed using USGS-MODFLOW to assess groundwater resources and recharge rates. Recharge decreased to 46% from water-rich rural areas to disadvantaged and highly urbanized communities. Aquifer recharge driven by huge rainfall dilutes the nitrogen content and pathogens, contributing to an acceptable drinking water quality during the prolonged wet season.

Sea water intrusion is an important environmental issue that plagues the economic and social development in coastal areas. The implementation of quantitative simulation, prediction and visual management of sea water intrusion is a cost-effective means for monitoring and mechanism analysis of sea water intrusion, which can provide important theoretical and technical supports for the formulation of sea water intrusion control measures. VFT3D was proposed to model the sea water intrusion processes and predict the impacts on groundwater, which can comprehensively consider the effects of surface water and groundwater, simulate variable-density groundwater flow, and solve complex reactive migration problems. This article provides an introduction to the VFT3D model and presents an application of VFT3D to modeling seawater intrusion process. The simulated results are compared with those of the SEAWAT. The results show that the simulated water heads with VFT3D are close to the SEAWAT simulation results. The SEAWAT is unable to simulate complex chemical reactions during the sea water intrusion. The results indicate that geochemical processes (cation adsorption and exchange) have a significant effect on the movement of cations (Na+, K+, Mg2+ and Ca2+). Geochemical process leads to the concentration change in the transition zone, whose influence on the process of sea water intrusion can not be ignored. Therefore, the variable density and complex reaction process should be involved to more accurately describe the sea water intrusion, which can benefit the implementation of the underground saltwater remediation and management.

Abstract Background Long-read sequencing has shown its tremendous potential to address genome assembly challenges, e.g., achieving the first telomere-to-telomere assembly of a gapless human chromosome. However, many issues remain unresolved when leveraging error-prone long reads to characterize high-complexity metagenomes, for instance, complete/high-quality genome reconstruction from highly complex systems. Results Here, we developed an iterative haplotype-resolved hierarchical clustering-based hybrid assembly (HCBHA) approach that capitalizes on a hybrid (error-prone long reads and high-accuracy short reads) sequencing strategy to reconstruct (near-) complete genomes from highly complex metagenomes. Using the HCBHA approach, we first phase short and long reads from the highly complex metagenomic dataset into different candidate bacterial haplotypes, then perform hybrid assembly of each bacterial genome individually. We reconstructed 557 metagenome-assembled genomes (MAGs) with an average N50 of 574 Kb from a deeply sequenced, highly complex activated sludge (AS) metagenome. These high-contiguity MAGs contained 14 closed genomes and 111 high-quality (HQ) MAGs including full-length rRNA operons, which accounted for 61.1% of the microbial community. Leveraging the near-complete genomes, we also profiled the metabolic potential of the AS microbiome and identified 2153 biosynthetic gene clusters (BGCs) encoded within the recovered AS MAGs. Conclusion Our results established the feasibility of an iterative haplotype-resolved HCBHA approach to reconstruct (near-) complete genomes from highly complex ecosystems, providing new insights into “complete metagenomics”. The retrieved high-contiguity MAGs illustrated that various biosynthetic gene clusters (BGCs) were harbored in the AS microbiome. The high diversity of BGCs highlights the potential to discover new natural products biosynthesized by the AS microbial community, aside from the traditional function (e.g., organic carbon and nitrogen removal) in wastewater treatment. Video Abstract

Abstract Watersheds are the basic unit of Earth's terrestrial systems and are therefore ideal units for the study of critical zones (CZs). However, grand challenges remain regarding the observation, modeling, and management of CZs and watershed systems. We synthesize the progress and breakthroughs associated with watershed science and CZ research in the Heihe River basin (HRB), a large‐scale endorheic river basin with unique mountain cryosphere‐oasis‐desert landscapes and prominent human‐nature competition for water resources. The HRB observation system consists of mountain cryosphere, agricultural oasis, and natural oasis observatories and is promoted by large‐scale comprehensive experiments to achieve multiscale observations. A watershed system model that couples ecohydrological models with socioeconomic models is developed to investigate the complex interactions among water, ecology, and socioeconomics in the HRB. The model is embedded in a decision support system to bridge science and decision‐making and to better serve river basin sustainability. Significant progress and breakthroughs have been made in CZ and watershed process research (e.g., cryospheric hydrological processes, ecological and hydrological interactions, and surface‐groundwater interactions) in the HRB. Nevertheless, observation and modeling of geochemical and geomorphological processes in the CZ have not been well addressed in integrated watershed studies of the HRB. In the future, new observation technologies, agent‐based models, machine learning, and data assimilation will benefit both watershed science and CZ science and help to address complexity and dynamics in the CZ at the river basin scale. Overall, the HRB has successfully demonstrated how an experimental river basin can link CZ science with watershed science.

Extensive human activities and climate change in recent decades have triggered severe eutrophication problems in the coastal oceans in the Greater Bay Area (GBA) of China. However, a comprehensive characterization of the spatial and temporal patterns of chlorophyll-a (Chl-a, a major indicator of phytoplankton biomass) in this region is not available. Our study attempts to fill this gap by using long-term satellite observations. With massive in situ datasets from underway sampling systems, we developed a novel hybrid Chl-a retrieval algorithm combining the recalibrated OC3 and line-height-based (BL443) algorithms for waters with different turbidity levels. Satellite-retrieved Chl-a values with the hybrid algorithm agreed well with in situ measurements, with an uncertainty level of 33.8 %. Long-term analysis revealed significant decreasing trends over the inner Pearl River Estuary (averaged at 0.054 μg/L yr−1), while significant increasing trends were found in eastern Daya Bay (averaged at 0.035 μg/L yr−1). The developed algorithm is expected to aid routine Chl-a monitoring in the adjacent oceans of the GBA, and the long-term datasets here can serve as critical information for further coastal conservation and management efforts.

Summary: Perfluoroalkyl and polyfluoroalkyl substances (PFASs) are persistent in the environment and have been detected in a variety of plants such as vegetables, cereals, and fruits. Increasing evidence shows that plants are at a risk of being adversely affected by PFASs. This review concludes that PFASs are predominantly absorbed by roots from sources in the soil; besides, the review also discusses several factors such as soil properties and the species of PFASs and plants. In addition, following uptake by root, long-chain PFASs (C ≥ 7 for PFCA and C ≥ 6 for PFSA) were preferentially retained within the root, whereas the short-chain PFASs were distributed across tissues above the ground — according to the studies. The bioaccumulation potential of PFASs within various plant structures are further expressed by calculating bioaccumulation factor (BAF) across various plant species. The results show that PFASs have a wide range of BAF values within root tissue, followed by straw, and then grain. Furthermore, owing to its high water solubility than other PFASs, PFOA is the predominant compound accumulated in both the soil itself and within the plant tissues. Among different plant groups, the potential BAF values rank from highest to lowest as follows: leaf vegetables > root vegetables > flower vegetables > shoot vegetables. Several PFAS groups such as PFOA, PFBA, and PFOS, may have an increased public health risk based on the daily intake rate (ID). Finally, future research is suggested on the possible PFASs degradation occurring in plant tissues and the explanations at genetic-level for the metabolite changes that occur under PFASs stress.

Abstract Increased concentration of airborne particulate matter (PM) in the atmosphere alters the degree of polarization of skylight which is used by honeybees for navigation during their foraging trips. However, little has empirically shown whether poor air quality indeed affects foraging performance (foraging trip duration) of honeybee. Here, we show apparent increases in the average duration of honeybee foraging during and after a heavy air pollution event compared with that of the pre‐event period. The average foraging duration of honeybees during the event increased by 32 min compared with the pre‐event conditions, indicating that 71% more time was spent on foraging. Moreover, the average foraging duration measured after the event did not recover to its pre‐event level. We further investigated whether an optical property (Depolarization Ratio, DR) of dominant PM in the atmosphere and level of air pollution (fine PM mass concentration) affect foraging trip duration. The result demonstrates the DR and fine PM mass concentration have significant effects on honeybee foraging trip duration. Foraging trip duration increases with decreasing DR while it increases with increasing fine PM mass concentration. In addition, the effects of fine PM mass concentration are synergistic with overcast skies. Our study implies that poor air quality could pose a new threat to bee foraging.

The study describes the hydrogeological setting of the Pearl River Delta, a sub-tropical area of southern China encompassing the metropolises of Guangzhou, Shenzhen, Hong Kong and Macau. In the last 40 years, a booming economy and a population of about 60 million has increased water demand satisfied by a huge system of dams and reservoirs. Aquifers in the studied area are underutilized and only a few recent studies have addressed hydrogeological characterization at a local scale. Understanding groundwater dynamics of the Pearl River Delta is important for developing additional water supplies, understanding and mitigating groundwater pollution, and for implementing ‘Sponge City' concepts. Via a collection of data from literature and field surveys, the hydrogeological setting of the area is synthetized and represented through thematic maps, cross sections and a hydro-stratigraphic column. Hydrogeological conceptual models are developed that describe the groundwater dynamics in urban and rural areas within the Pearl River Delta.

Abstract Background Genome-centric approaches are widely used to investigate microbial compositions, dynamics, ecology, and interactions within various environmental systems. Hundreds or even thousands of genomes could be retrieved in a single study contributed by the cost-effective short-read sequencing and developed assembly/binning pipelines. However, conventional binning methods usually yield highly fragmented draft genomes that limit our ability to comprehensively understand these microbial communities. Thus, to leverage advantage of both the long and short reads to retrieve more complete genomes from environmental samples is a must-do task to move this direction forward. Results Here, we used an iterative hybrid assembly (IHA) approach to reconstruct 49 metagenome-assembled genomes (MAGs), including 27 high-quality (HQ) and high-contiguity (HC) genomes with contig number ≤ 5, eight of which were circular finished genomes from a partial-nitritation anammox (PNA) reactor. These 49 recovered MAGs (43 MAGs encoding full-length rRNA, average N50 of 2.2 Mbp), represented the majority (92.3%) of the bacterial community. Moreover, the workflow retrieved HQ and HC MAGs even with an extremely low coverage (relative abundance < 0.1%). Among them, 34 MAGs could not be assigned to the genus level, indicating the novelty of the genomes retrieved using the IHA method proposed in this study. Comparative analysis of HQ MAG pairs reconstructed using two methods, i.e., hybrid and short reads only, revealed that identical genes in the MAG pairs represented 87.5% and 95.5% of the total gene inventory of hybrid and short reads only assembled MAGs, respectively. In addition, the first finished anammox genome of the genus Ca. Brocadia reconstructed revealed that there were two identical hydrazine synthase (hzs) genes, providing the exact gene copy number of this crucial phylomarker of anammox at the genome level. Conclusions Our results showcased the high-quality and high-contiguity genome retrieval performance and demonstrated the feasibility of complete genome reconstruction using the IHA workflow from the enrichment system. These (near-) complete genomes provided a high resolution of the microbial community, which might help to understand the bacterial repertoire of anammox-associated systems. Combined with other validation experiments, the workflow can enable a detailed view of the anammox or other similar enrichment systems. Video Abstract

The exploitation of rivers has been at the detriment of river ecosystems. Here the authors propose a concept of Golden Inland Waterways (GIWs) to represent large waterways and find that the exploitation ratio threshold around the turning point for most GIWs appear to be less than 80%, subject to ecological constraints.

Summary Human intestinal microbiota is important to host health and is associated with various diseases. It is a challenge to identify the functions and metabolic activity of microorganisms at the single‐cell level in gut microbial community. In this study, we applied Raman microspectroscopy and deuterium isotope probing (Raman–DIP) to quantitatively measure the metabolic activities of intestinal bacteria from two individuals and analysed lipids and phenylalanine metabolic pathways of functional microorganisms in situ. After anaerobically incubating the human faeces with heavy water (D2O), D2O with specific substrates (glucose, tyrosine, tryptophan and oleic acid) and deuterated glucose, the C–D band in single‐cell Raman spectra appeared in some bacteria in faeces, due to the Raman shift from the C–H band. Such Raman shift was used to indicate the general metabolic activity and the activities in response to the specific substrates. In the two individuals' intestinal microbiota, the structures of the microbial communities were different and the general metabolic activities were 76 ± 1.0% and 30 ± 2.0%. We found that glucose, but not tyrosine, tryptophan and oleic acid, significantly stimulated metabolic activity of the intestinal bacteria. We also demonstrated that the bacteria within microbiota preferably used glucose to synthesize fatty acids in faeces environment, whilst they used glucose to synthesize phenylalanine in laboratory growth environment (e.g. LB medium). Our work provides a useful approach for investigating the metabolic activity in situ and revealing different pathways of human intestinal microbiota at the single‐cell level.

Riverine carbon flux to the ocean has been considered in estimating coastal carbon budgets, but submarine groundwater discharge (SGD) has long been ignored. In this paper, the effects of both SGD and river discharges on the carbon cycle were investigated in the Guangdong-HongKong-Macao Greater Bay Area (GBA), a highly urbanized and river-dominated coastal area in China. SGD-derived nitrate (NO3–), dissolved organic carbon (DOC), and dissolved inorganic carbon (DIC) fluxes were estimated using a radium model to be (0.73–16.4) × 108 g/d, (0.60–9.94) × 109 g/d, and (0.77–3.29) × 1010 g/d, respectively. SGD-derived DOC and DIC fluxes are ∼2 times as great as riverine inputs, but SGD-derived NO3– flux is one-fourth of the riverine input. The additional nitrate and carbon inputs can stimulate new primary production, enhance biological pump efficiency, and affect the balance of the carbonate system in marine water. We found that SGD in the studied system is a potential net source of atmospheric CO2 with a flux of 1.46 × 109 g C/d, and river, however, is a potential net sink of atmospheric CO2 with a flux of 3.75 × 109 g C/d during the dry winter season. Two conceptual models were proposed illustrating the major potential processes of the carbon cycle induced by SGD and river discharges. These findings from this study suggested that SGD, as important as rivers, plays a significant role in the carbon cycle and should be considered in carbon budget estimations at regional and global scales future.

The estuary-bay system is a common and complex coastal environment. However, quantifying submarine groundwater discharge (SGD) and associated nutrient fluxes in the complex coastal environment is challenging due to more dynamic and complicated riverine discharge, ocean processes and human activities. In this study, SGD and SFGD (submarine fresh groundwater discharge) fluxes were evaluated by combining stable and radium isotopes in the Guangdong-Hong Kong-Macau Greater Bay Area (GBA), a typical estuary-bay system. We first built a spatially distributed radium mass balance model to quantify SGD fluxes in coastal areas of GBA integrating the Pearl River Estuary (PRE), bays and shelf. We then used the stable water isotope (δ2H and δ18O) end-member mixing model to distinguish submarine fresh groundwater discharge (SFGD) from SGD. Based on the 228Ra mass balance, the estimated SGD fluxes in the PRE, adjacent bay, and shelf areas were (6.14 ± 2.74) × 108 m3 d-1, (3.00 ± 1.11) × 107 m3 d-1, and (5.00 ± 5.64) × 108 m3 d-1, respectively. Results showed that the largest area-averaged SGD was in the PRE, followed by that in the adjacent shelf and the bay. These differences may be mainly influenced by ocean forces, urbanization and benthic topographies controlling the variability of groundwater pathways. Further, the three end-member mixing model of 228Ra and salinity was developed to confirm the validity of the estimated SGD using the Ra mass balance model. In the two models, groundwater end-member and water apparent age estimation were the main sources of uncertainty in SGD. The estimated SFGD flux was (1.39 ± 0.76) × 108 m3 d-1, which accounted for approximately 12% of the total SGD. Combining stable and radium isotopes was a useful method to estimate groundwater discharge. Moreover, the estimated SGD associated dissolved inorganic nitrogen (DIN) flux was one order of magnitude higher than other DIN sources. SGD was considered to be a significant contributor to the DIN loading to the GBA. The findings of this study are expected to provide valuable information on coastal groundwater management and environmental protection of the GBA and similar coastal areas elsewhere.

Study region: Lhasa River Basin (LRB) on the Tibetan Plateau, China. Study focus: Tibetan Plateau has been undergoing climate warming in the past five decades. The hydrological processes in the LRB, a representative alpine headwater region basin on the Tibetan Plateau, are changing in response to climate warming. However, characteristics of groundwater recharge and discharge and response of the groundwater flow system to future climate change in this region remain unclear. This study constructed a three-dimensional numerical model to simulate the groundwater flow variations under different future climate change scenarios. New hydrological insights for the region: Approximately 13.6 % (∼71.6 mm/yr) of annual precipitation recharges groundwater. Glacier meltwater recharge is 10 % of the total groundwater recharge across the entire LRB, and this proportion increases to 34.8 % in the Yangbajing subbasin. More than 80 % of the groundwater circulates within 0∼0.3 km below ground surface. The groundwater flow system is dominated by travel times between 10–100 years and flow path distances less than 10 km. The baseflow shows an increasing trend in response to future climate change, and the increasing trends range from 0.07 to 0.21 m3/s per year under different future climate change scenarios. The baseflow variation indicates that wet year will become wetter and dry year will become drier in the future.

China is facing frequent waterlogging and an increasing water scarcity that mirrors the fast urban and economic expansion of the last 4 decades. To mitigate these issues, the government promulgated the “Sponge City” strategy; a concept rooted in practices in western countries aimed at collecting and reusing 65–90% of urban rainfall. The application consists of absorbent infrastructures such as green roofs and rain gardens combined with the pre-existing urban environment. However, due to climate heterogeneities and the different urbanization contexts in China, these goals may seem overly ambitious in many areas of the country. Compact urbanization, together with heavy rainfall concentrated in short events, puts dramatic stresses on these infrastructures. At the same time, overdesigned infrastructures are expensive and may not be practical to retrofit in existing urban areas. In this paper, the role of urban aquifers as natural Sponge City elements are investigated throughout China. The method of implementation is inexpensive and easy to apply, favoring the direct infiltration to the subsoil after the conversion of the urban surfaces from impervious to permeable. Infiltration to urban aquifers alleviates the pressure on sewers, urban streams, as well as waste-water treatment plants. Considering urban aquifers with different hydraulic characteristics, water table dynamics after large infiltration events from rainfall are simulated via numerical analysis. Hydrogeological and geomorphological analyses are carried out to individuate criteria for the mapping of high absorbance areas at the regional and local scales. A Sponge City approach involving the urban aquifers can represent a winning formula for the success of this ambitious but compelling plan.

Water scarcity threatens food security in arid areas, highlighting the importance of water-saving agriculture for food production. Agricultural management practices are developed to improve water-use efficiency, and their water-saving effects are generally evaluated at the field scale rather than the regional scale. To figure out the regional water-saving potential of irrigation methods and mulching practices, the FAO AquaCrop model was first calibrated and validated at the three experimental stations. With aggregating spatial information, a distributed model was constructed and validated in a typical arid river basin of northwest China. Twelve combinations of soil mulching (plastic and straw) and irrigation methods (basin, furrow, drip, and subsurface drip) were simulated using the model to evaluate the effect of agricultural management practices on crop evapotranspiration (ET), crop water productivity, and regional water consumption. The results showed that soil mulching, advanced irrigation methods, and their combinations reduced noneffective soil evaporation (E) and the E/ET ratios and improved crop water productivity. Plastic mulching combined with subsurface drip irrigation is the most promising practice, increasing the crop water productivity of seed maize and spring wheat by 18.2% and 11.1% on average and reducing regional crop water consumption by 7.7% (75.0 million m3) and 7.4% (72.7 million m3), respectively. The reduction in irrigation water extraction ranged from 20.6% under furrow irrigation with straw mulching to 68.7% under subsurface drip irrigation with plastic mulching. This study quantitatively assessed the water-saving potential of soil mulching, irrigation methods, and their combinations to reduce agricultural water use, offering practical implications for the management and development of water-saving agriculture in arid areas.

Study area: Venafro Mts., southern-central Italy, Mediterranean basin. Study focus: Via a collection of geological and hydrogeological data, a flow conceptual model of a carbonate aquifer has been coupled with a numerical model via MODFLOW code and Unsaturated Zone Flow (UZF) package in steady state and transient conditions. Simulation is further implemented with different management scenarios, for facing possible emergencies due to recharge decrease, also simulating a drastic water abstraction cut-off. New hydrological insights for the region: Carbonate fractured aquifers are a strategic water resource in the whole Mediterranean area, supplying major metropolitan areas. Despite these huge extensions, such groundwater systems are threatened by increasing drought occurrence and significant human water abstraction. A characterization of a carbonate fractured aquifer (370 km2) located in central-southern Italy has been performed. Venafro Mts. Aquifer (VMA) hosts a strategic resource for the Western Campania Waterworks (WCW) that supplies the populous metropolitan area of Naples, with 3.8 million inhabitants. VMA shows a slow response, with recovery time estimated at the decennial scale, testifying its limited resilience to natural and human pressures. A shift is proposed from passive management to a more comprehensive concept of smart-water monitoring, applied not only to waterworks and pipelines, but also to groundwater resources in the environment.

Bisphenol AF (BPAF), an alternative to bisphenol A, is widely detected in aquatic environments. Owing to health concerns, the toxic effects of BPAF on organisms are drawing attention. The present study aims to evaluate the toxicity of BPAF, combining the results of omics techniques and experiment. Employing transcriptome sequencing (RNA-seq), we obtained 391, 648, 512, and 545 differentially expressed genes (DEGs) in 0.1, 1, 10, and 100 μg/L BPAF-exposed zebrafish larvae, respectively. Gene ontology (GO) analysis and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment revealed the early development, stimulus-response, and MAPK signaling pathway were significantly affected by BPAF. In addition, five hub genes (fgf3, fgf4, map2k1, myca, and casp3b) were highlighted as the key genes in MAPK signaling pathway using the protein-protein interaction network. Therefore, the RNA-seq results showed that early development and stimulus-response were the main processes affected by BPAF, which was consistent with our morphological and pathological results. The hatching rate of zebrafish embryos in 1 and 10 μg/L BPAF groups was significantly inhibited, and the oxidative stress indexes, including the level of total antioxidant capacity (T-AOC), superoxide dismutase (SOD), and lipid peroxidation (LPO), were significantly increased by the 100 μg/L BPAF treatment. Moreover, the activity of alkaline phosphatase (AKP) was significantly decreased in all BPAF exposure groups. In conclusion, exposure to BPAF at environmental relevant concentrations affected the early development and immune system of zebrafish larvae by modulating MAPK signaling pathway, and our results provide solid evidence for the future studies on the toxicity of bisphenols.

Groundwater is expected to be more vulnerable to water-quality degradation in the future due to rapid urbanization. However, despite knowledge that protecting future groundwater resources is necessary for sustainable groundwater resource development, little is known about the role of groundwater policy in influencing the spatial distribution of urbanization. This study sheds light on how a policy that protects vulnerable groundwater could affect the distribution of urban expansion. Groundwater vulnerability to pollution under future climate change scenarios is used as a factor to generate urban expansion probability maps for China. The results indicate that there will be a significant and uneven urban growth by 2030, if current trends in urban expansion continue. The amount of urban land in 2030 will range from 2.9 to 4.2 times the urban area in 2010. Meanwhile, the urban expansion probability maps for projections with and without consideration of groundwater vulnerability in urban suitability are compared. The comparation shows that consideration of a groundwater policy would significantly alter the future spatial distribution of urban areas. Even with a weight of only 10% for groundwater vulnerability in the urban suitability consideration, the percentage of change area in the urban expansion probability distribution map can be as high as 60%. The probabilities of urban expansion are forecast to gradually transfer from the southeast coastal areas to inland areas as higher weight (from 10% to 50%) of groundwater vulnerability is given to urban suitability consideration. Our study demonstrates that groundwater protection from urbanization pressures can be achieved, provides support for policy and decision makers in evaluating options to modify existing urban expansion policies, and concludes that groundwater protection at the macro-scale is an appropriate policy goal.

Chinese cities and megacities occupy large areas with high population densities. These urban sectors have extensive impervious surfaces and import large amounts of water from pristine sources, putting pressure on the urban drainage systems during storms. To reduce flood risk and tackle water scarcity, the Chinese government promulgated the Sponge City concept: an ensemble of absorbing features, including permeable pavements and green roofs, to reduce urban runoff and increase water storage. We evaluate the benefits of merging the urban aquifer with conventional Sponge City features by simulating stormwater storage in aquifers with a groundwater model (MODFLOW) and a stormwater management model (SWMM). The urban aquifers of an ideal district, characterized by high-density housing and a flat morphology, collect and dissipate extreme rains (200 mm in 6 h) when the hydraulic conductivity of the subsoil is higher than 1·10−5 m/s, roughly corresponding to a medium productive aquifer. Economic and ecological benefits at the catchment scale are also discussed. Suitable shallow aquifers are individuated and discussed throughout China via a hydrogeological and geomorphological approach. The proposed method increases the percentage of water that can be controlled above that obtained through conventional Sponge City features.

The active layer thickness (ALT) in permafrost regions regulates hydrological cycles, water sustainability, and ecosystem functions in the cryosphere and is extremely sensitive to climate change. Previous studies often focused on the impacts of rising temperature on the ALT, while the roles of soil water content and soil granularity have rarely been investigated. Here, we incorporate alterations of soil water contents in soil thermal properties across various soil granularities and assess spatiotemporal ALT dynamics on the Qinghai-Tibet Plateau (QTP). The regional average ALT on the QTP is projected to be nearly 4 m by 2100. Our results indicate that soil wetting decelerates the active layer thickening in response to warming, while latent heat exerts stronger control on ALTs than thermal conductivity does. Under similar warming conditions, active layers thicken faster in coarse soils than in fine soils. An important ramification of this study is that neglecting soil wetting may cause overestimations of active layer thickening on the QTP.

Low doses of antibiotics are ubiquitous in the marine environment and may exert negative effects on non-target aquatic organisms. Using primary macrophages of common carp, we investigated the mechanisms of action following exposure to several common antibiotics; cefotaxime, enrofloxacin, tetracycline, sulfamonomethoxine, and their mixtures, and explored the immunomodulatory effects associated with the nuclear factor-κB (NF-κB) signaling pathway. A KEGG pathway analysis was conducted using the sixty-six differentially expressed genes found in all treatments, and showed that exposure to 100 μg/L of antibiotics could affect regulation of the NF-κB signaling pathway, suggesting that activation of NF-κB is a common response in all four classes of antibiotics. In addition, the four antibiotics induced nf-κb and NF-κB-associated cytokines expression, as verified by qPCR, however, these induction responses by four antibiotics were minor when compared to the same concentration of LPS treatment (100 μg/L). Antagonists of NF-κB blocked many of the immune effects of the antibiotics, providing evidence that NF-κB pathways mediate the actions of all four antibiotics. Moreover, exposure to environmentally relevant, low levels (0.01–100 μg/L) of antibiotics induced a NF-κB-mediated immune response, including endogenous generation of ROS, activity of antioxidant enzymes, as well as expression of cytokine and apoptosis. Moreover, exposure to mixtures of antibiotics presented greater effects on most tested immunological parameters than exposure to a single antibiotic, suggesting additive effects from multiple antibiotics in the environment. This study demonstrates that exposure of fish primary macrophages to low doses of antibiotics activates the NF-kB pathway. Keywords: Antibiotics, Nuclear factor-κB, Immunomodulatory, Macrophages

Study area: Shenzhen Megacity, southern China. Study focus: “Sponge City” is a Chinese concept aimed to mitigate flood risk, tackle chronic water scarcity, and improve the urban environment. It consists of a combination of new storage and infiltration facilities distributed on a large scale. The concept is similar to strategies and developments already adopted in the Western world. In this paper, new constraints on the interactions between the sponge facilities, the landscape and the subsoil are identified for a hilly, sub-tropic terrain. New hydrological insights for the region: Using a geomorphological zonation at the catchment scale, a conceptual model is proposed for southern China to identify areas where groundwater infiltration and storage is feasible. The proposed model is applied to Shenzhen, a megacity in southern China chosen as a pilot site for Sponge City, with 24 project areas already identified. Our zonation approach suggests that project areas on the coastal plain and reclaimed land will only work with above-ground storage, while there is significant potential to enhance many of the other pilot areas with infiltration facilities. The conceptual model improves the Sponge City approach aimed at increasing the managed annual runoff; it also mitigates the waterlogging risk. At the same time, the proposed conceptual model has moderate costs and makes possible the application of the Sponge City concept in other urban areas of southern China. Keywords: Conceptual model, Flood mitigation, Groundwater, Urban planning, Urban waterlogging, Wet climate

Spatiotemporal variations of the hydrochemical major ions compositions and their controlling factors are essential features of a river basin. However, similar studies in the southern Tibetan Plateau are relatively limited. This study focuses on the chemical compositions of the dissolved loads in the Lhasa River (LR) in the southern Tibetan Plateau. Two sampling campaigns were conducted during the rainy and dry seasons across the LR basin to systematically investigate the spatiotemporal variations of water chemistry and sources of the dissolved loads. The results show that the river water possesses slight alkalinity with an average pH of 8.05 ± 0.04. Total dissolved solids (TDS) and oxidation-reduction potential (ORP) range widely from 39.8 mg/L to 582.6 mg/L with an average value of 165.6 ± 7.7 mg/L and from −9.4 mV to 295 mV with a mean value of 153.7 ± 6.9 mV, respectively. The major cations follow the decreasing order of Ca2+, Mg2+, Na+, and K+ while HCO3−, SO42−, Cl−, and NO3− for anions. Ca2+ and Mg2+ account for 87.8% of the total cations, while HCO3− and SO42− accounts for 93.9% of the total anions. All the major ions show higher concentrations in the dry season. NO3−, HCO3−, and Mg2+ show significant spatial variations due to the influence of basin lithology and anthropogenic activity. Multi-variables statistical analysis reveals that the mechanisms controlling the LR hydrochemistry are mainly carbonate weathering followed by silicate weathering. Geothermal springs and anthropogenic activities also play crucial roles in altering river water ions composition in the middle stream and downstream. The relatively high NO3− value (3 ± 0.2 mg/L) suggests water quality will be under the threat of pollution with the increase of anthropogenic activities.

Evapotranspiration (ET) is one of the important components of the global hydrologic cycle, energy exchange, and carbon cycle. However, basin scale actual ET (hereafter ETa) is difficult to estimate accurately. We present an evaluation of four actual ET products (hereafter ETp) in seven sub-basins in the Tibetan Plateau. The actual ET calculated by the water balance method (hereafter ETref) was used as the reference for correction of the different ETp. The ETref and ETp show obvious seasonal cycles, but the ETp overestimated or underestimated the ET of the sub-basins in the Tibetan Plateau. A simple and effective method was proposed to correct the basin-scale ETp. The method was referred to as ratio bias correction, and it can effectively remove nearly all biases of the ETp. The proposed method is simpler and more effective in correcting the four ETp compared with the gamma distribution bias correction method. The reliability of the ETp is significantly increased after the ratio bias correction. The ratio bias correction method was used to correct the ETp in the seven sub-basins in the Tibetan Plateau, and regional ET was significantly improved. The results may help improve estimation of the ET of the Tibetan Plateau and thereby contribute to a better understanding of the hydrologic cycle of the plateau.

Although there are many existing analytical studies of tidal groundwater level fluctuations in coastal aquifer systems, few of them focus on an offshore submarine aquifer. Here, we consider tidal groundwater head fluctuations in a submarine leaky confined aquifer overlain by a semipermeable seabed. Both the seabed and the confined aquifer are assumed to extend horizontally infinitely. A one-dimensional mathematical model is established to describe the problem, and the analytical solution is derived. The impacts of the tidal loading efficiency, hydraulic conductivity and elastic storage of the semipermeable layer and aquifer on the groundwater head fluctuations in the aquifer system are analyzed and discussed. Solution analyses indicated that tidal loading effects tend to enhance the amplitude of the tidal groundwater fluctuation in the confined aquifer system and to reduce the phase shift between the groundwater head and the sea tide fluctuations.

The production of tea ( Camellia sinensis (L.) Kuntze), the world’s second most consumed beverage, is susceptible to extreme weather events. However, our understanding about the impacts of extreme temperatures and climate change on tea yields remains fairly limited. Here we quantify the historical and predict future fluctuations in tea yield caused by extreme temperatures in China, the largest tea producing country. We found that both heat and cold extremes were associated with significantly reduced tea yields. In the present climate, dominating cold extremes influence more than half of China’s tea production, with a maximum of 56.3% reduced annual production. In the near future, we predict positive net impacts of climate change on tea yield in all study regions at both the 1.5 °C and 2.0 °C global warming levels. Climate warming may diminish the negative impacts of cold extremes to 14%, especially at the current most affected northern tea growing regions (>28° N). However, new areas of yield reduction by intensified heat extremes will emerge, up to 14%–26% yield losses estimated at the Yangtze River (∼30° N) and southern China (

Seasonally frozen ground (SFG) is a critical component of the Earth’s surface that affects energy exchange and the water cycle in cold regions. The estimation of SFG depth has generally required intensive parameterization which has limited estimates in data-scarce regions such as the Qinghai-Tibet Plateau (QTP). We propose a simple yet robust modeling framework employing ground surface temperatures as major model inputs to assess the spatiotemporal patterns of the SFG depth in the Yarlung Zangbo River Basin (YZRB) on the QTP. The model was calibrated using SFG depth measurements throughout the YZRB from 1980 to 2010. Results suggest that the SFG depth in the YZRB has decreased at a rate of 2.50 cm · a ^−1 from 1980 to 2010. Future projections indicate that the SFG depth in the YZRB will continue to decrease in response to future warming. The present SFG may no longer exist by 2180 under the RCP 8.5 scenario (if not considering the transition of permafrost to SFG). The proposed modeling framework provides an important basis for the evaluation of the hydrological cycles (e.g. surface water-groundwater interactions) in cold regions under changing climatic conditions.

Population ageing, an increase in the older age group’s portion of the total population, worsens the heat tolerance of a society. However, impacts of ageing on the social exposure to projected unprecedented hot summers (UHSs) are uncertain. We show that a shifting of the population distribution towards older ages amplifies the vulnerability of a country to the increasing frequency of UHSs as a result of warming during 2040–2070, especially in most populated regions such as China, India, and sub-Saharan countries. The warming scenarios from Representative Concentration Pathway (RCP) 8.5 are combined with population scenarios from three Shared Socio-economic Pathways (SSPs) SSP2, SSP3, and SSP5 together to estimate the exposure to UHSs. The ageing-driven increase in the exposure of elderly to UHSs ranges 51–198, 91–261, and 47–156 million in China, India, and sub-Saharan countries, respectively, between population scenarios. In China, with decreasing total population, the exposure to UHSs will be increased by rapid population ageing. In India and sub-Saharan countries, the potential of ageing to raise the exposure to UHSs will be even larger than that of warming. In contrast, in aged societies with slow ageing trend, e.g. United States and Europe, the warming mainly increases the exposure to UHSs. Our results suggest the changing age structure could exacerbate a country’s heat vulnerability despite limiting warming to a certain level in the future.

Declining soil moisture related to climate change can greatly affect social, economic, environmental, and hydrological processes, as well as extreme weather events. Hence, it is imperative to understand the timing of significant soil moisture drying under future climate change. Compared to spatial variations in soil moisture drying, however, our understanding of temporal variations remain unclear. In the present study, the timing of significant soil moisture depletion (SSD) is predicted using the soil moisture projection (0–50 cm depth) from the 30 Inter-Sectoral Impact Model Intercomparison Project fast-track outputs under the representative concentration pathways (RCPs) 2.6 and 8.5. Under both RCP scenarios, the ensemble medians of the projections show the emergence of the timing of SSD in Western Europe, Eastern United States, South America, Sub-Saharan Africa, Australia, and Southern China over 40 years (

Study Region: The Heihe River Basin (HRB) is the second largest inland river basin of China located in northwest China with a minor portion in Mongolia. Study Focus: With increasing water demands from domestic, agricultural, and industrial sectors, the HRB has been increasingly undergoing water resources shortage and eco-environmental degradation, especially in the lower HRB. Discerning the trends and any abrupt changes in the streamflow over the river basin could help unravel the causes and effects of historical variations of the water resources. Statistical methods for detecting trends, abrupt and gradual changes were applied to the long-term streamflow, precipitation and temperature data over the HRB to analyze and understand annual and seasonal hydroclimatic variations over the past five decades. New Hydrological Insights for the Region: The findings of this study indicated that although the streamflow coming from the upper reaches have risen, those flowing to the lower reaches have declined significantly. Analysis of the correlation between climatic factors and streamflow variations and the assessment of the development of socioeconomics revealed that: (1) rising temperature and precipitation are the main cause to explain the increases in streamflow in the upper HRB; and (2) human activities in the middle reaches of the HRB rather than climate changes were primarily responsible for the water shortage and ecological deterioration of the lower HRB. Keywords: Streamflow changes, Trends test, Abrupt change test, Heihe River Basin, Inland River Basin

River basins around the world face similar issues of water scarcity, deficient infrastructure, and great disparities in water availability between sub-regions, both within and between countries. In this study, different strategies under the Water Evaluation and Planning system (WEAP) were assessed to mitigate water overuse practices under the Current Trend (CT), Economic Growth (EG), and Demand Side Management (DSM) scenarios in relation to current and future statuses of Tanzania’s Wami Ruvu Basin (WRB). The results show that neither domestic nor irrigation water demand will be met based on the current trend. Under the CT scenario, the total water demand is projected to rise from 1050.0 million cubic meters in the year 2015, to 2122.9 million cubic meters by the year 2035, while under the DSM scenario the demand dropped to 990.0 million cubic meters in the year 2015 and to 1715.8 million cubic meters by the year 2035. This study reveals that there is a positive correlation between the highest surface runoff events and the highest unmet demand events in the basin. Terrestrial water demand alters the hydrological cycle of a catchment by modifying parameters such as surface runoff, particularly in small catchments. The results of this study prove that DSM strategies are more amenable to mitigate the impacts and implications of water demand, as they increase water sustainability and ensure ecosystem security by reducing the annual water demands and surface runoff by 15% and 2%, respectively.

Hydrological extremes in the water cycle can significantly affect surface water engineering design, and represents the high-impact response of surface water and groundwater systems to climate change. Statistical analysis of these extreme events provides a convenient way to interpret the nature of, and interaction between, components of the water cycle. This study applies three probability density functions (PDFs), Gumbel, stable, and stretched Gaussian distributions, to capture the distribution of extremes and the full-time series of storm properties (storm duration, intensity, total precipitation, and inter-storm period), stream discharge, lake stage, and groundwater head values observed in the Lake Tuscaloosa watershed, Alabama, USA. To quantify the potentially non-stationary statistics of hydrological extremes, the time-scale local Hurst exponent (TSLHE) was also calculated for the time series data recording both the surface and subsurface hydrological processes. First, results showed that storm duration was most closely related to groundwater recharge compared to the other storm properties, while intensity also had a close relationship with recharge. These relationships were likely due to the effects of oversaturation and overland flow in extreme total precipitation storms. Second, the surface water and groundwater series were persistent according to the TSLHE values, because they were relatively slow evolving systems, while storm properties were anti-persistent since they were rapidly evolving in time. Third, the stretched Gaussian distribution was the most effective PDF to capture the distribution of surface and subsurface hydrological extremes, since this distribution can capture the broad transition from a Gaussian distribution to a power-law one.

Integrated surface water⁻groundwater (SW⁻GW) models could be used to assess the impacts of climate change or variability on the hydrological cycle. However, the damping effects of the hydrological system have rarely been explored via integrated SW⁻GW modeling. This paper presents an integrated modeling study in a typical humid area, the Miho catchment in Korea, using an integrated model called Groundwater and Surface-water FLOW (GSFLOW). The major findings of this study are as follows: (1) The simulated results from 2005 to 2014 indicate that the temporal variability in the streamflow, stream-groundwater interactions and groundwater recharge are dominated by the precipitation, while the temporal variability in the evapotranspiration (ET) is controlled by the energy conditions; (2) Damping effects can affect the hydrological cycle across different temporal and spatial scales. At the catchment scale, the soil zone and aquifer play a dominant role in damping the precipitation on monthly and annual time scales, respectively; (3) Variability in the capacity to buffer earlier precipitation is found at small spatial scales, such as streams, and larger spatial scales, such as the whole catchment. This variability could affect the water balance at larger spatial scales and affect the hydrography recession at smaller spatial scales.

Non-Fickian diffusion has been increasingly documented in hydrology and modeled by promising time nonlocal transport models. While previous studies showed that most of the time nonlocal models are identical with correlated parameters, fundamental challenges remain in real-world applications regarding model selection and parameter definition. This study compared three popular time nonlocal transport models, including the multi-rate mass transfer (MRMT) model, the continuous time random walk (CTRW) framework, and the tempered time fractional advection–dispersion equation (tt-fADE), by focusing on their physical interpretation and feasibility in capturing non-Fickian transport. Mathematical comparison showed that these models have both related parameters defining the memory function and other basic-transport parameters (i.e., velocity v and dispersion coefficient D) with different hydrogeologic interpretations. Laboratory column transport experiments and field tracer tests were then conducted, providing data for model applicability evaluation. Laboratory and field experiments exhibited breakthrough curves with non-Fickian characteristics, which were better represented by the tt-fADE and CTRW models than the traditional advection–dispersion equation. The best-fit velocity and dispersion coefficient, however, differ significantly between the tt-fADE and CTRW. Fitting exercises further revealed that the observed late-time breakthrough curves were heavier than the MRMT solutions with no more than two mass-exchange rates and lighter than the MRMT solutions with power-law distributed mass-exchange rates. Therefore, the time nonlocal models, where some parameters are correlated and exchangeable and the others have different values, differ mainly in their quantification of pre-asymptotic transport dynamics. In all models tested above, the tt-fADE model is attractive, considering its small fitting error and the reasonable velocity close to the measured flow rate.

A modified Water-Table Fluctuation (WTF) method is developed to quantitatively characterize the regional groundwater discharge patterns in stressed aquifers caused by intensive agricultural pumping. Two new parameters are defined to express the secondary information in the observed data. One is infiltration efficiency and the other is discharge modulus (recurring head loss due to aquifer discharge). An optimization procedure is involved to estimate these parameters, based on continuous groundwater head measurements and precipitation records. Using the defined parameters and precipitation time series, water level changes are calculated for individual wells with fidelity. The estimated parameters are then used to further address the characterization of infiltration and to better quantify the discharge at the regional scale. The advantage of this method is that it considers recharge and discharge simultaneously, whereas the general WTF methods mostly focus on recharge. In the case study, the infiltration efficiency reveals that the infiltration is regionally controlled by the intrinsic characteristics of the aquifer, and locally distorted by engineered hydraulic structures that alter surface water-groundwater interactions. The seasonality of groundwater discharge is characterized by the monthly discharge modulus. These results from individual wells are clustered into groups that are consistent with the local land use pattern and cropping structures.