Global Water Research Articles

Enhanced solar desalination with photothermal hydrophobic carbon nanotube-infused PVDF membranes in air-gap membrane distillation

This work aims to increase the efficiency of the solar powered-air gap membrane distillation (SP-AGMD) process; a desalination method driven by solar energy, providing an eco-friendly and sustainable approach to addressing global water shortages. The innovation lies in integrating photothermal hydrophobic multiwalled carbon nanotubes (h-MWCNTs), in varying weight percentages from 5 % to 60 %, into polyvinylidene fluoride (PVDF) membranes using the phase inversion membrane fabrication technique. The h-MWCNTs were synthesized through oxidation and functionalization with oleylamine (OL) to improve their photothermal properties. Their successful integration was confirmed via scanning electron microscopy (SEM), thermogravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and Raman spectroscopy. The h-MWCNTs-based SP-AGMD membranes were further evaluated for wettability, liquid entry pressure (LEP), surface temperature, and solar absorbance, demonstrating significant solar light absorption and localized surface heating. This generated the necessary driving force for the AGMD process. Performance metrics such as vapor flux, salt rejection, specific thermal energy consumption, photothermal efficiency, and temperature polarization (TP) coefficient were significantly improved, especially with a 20 % h-MWCNTs addition, which tripled the solar-energy-driven flux and increased photothermal efficiency by 326 % under standard solar conditions, compared to unmodified membranes. All h-MWCNTs-based SP-AGMD membranes achieved over 99 % salt rejection. Lastly, the membranes were tested with real seawater to confirm their applicability for desalination. This photothermal approach offers a scalable, sustainable solution for water purification, making a significant advancement in membrane distillation technology.

Pharmaceutical and personal care products in recycled water for edible crop irrigation: Understanding the occurrence, crop uptake, and water quantity effects

Global water scarcity poses a great challenge to agriculture productivity. Recycled water offers a promising alternative for agricultural irrigation, yet residual pharmaceutical and personal care products (PPCPs) in recycled water can transfer to edible crops during irrigation, and adversely affect food safety. Furthermore, irrigation water quantity can influence the accumulation of PPCPs in edible crops. This study comprehensively investigates the use of recycled water for agricultural irrigation by critically reviewing three key components: PPCPs occurrence in recycled water, their accumulation in edible crops, and the impact of water quantity on PPCPs accumulation. Literature analysis showed that PPCPs were present from 130 to 1400 ng/L in secondary effluent and 25–400 ng/L in tertiary effluent, with sulfamethoxazole being the most prevalent in both effluents. PPCPs uptake and accumulation varied between leafy and fruity vegetables, with diclofenac accumulating highest in leafy vegetables and fluoxetine in fruity vegetables. Furthermore, the water requirement of leafy and fruity crops vary throughout the growing season. In leafy vegetables, PPCPs accumulation in leaves is influenced by transpiration rate, with reduced accumulation occurring under limited water availability due to slower transpiration. In fruity vegetables, osmotic adjustment drives the water transport in fruits, leading to increased PPCPs accumulation under limited water conditions. This study contributes insights into PPCPs occurrence, accumulation, and irrigation water quantity, aiding in the development of effective strategies for recycled water use in agriculture.

Nitrate sources and transformation in surface water and groundwater in Huazhou District, Shaanxi, China: Integrated research using hydrochemistry, isotopes and MixSIAR model

Global water resources affected by excessive nitrate (NO3−) have caused a series of human health and ecological problems. Therefore, identification of NO3− sources and transformations is of pivotal significance in the strategic governance of widespread NO3− contaminant. In this investigation, a combination of statistical analysis, chemical indicators, isotopes, and MixSIAR model approaches was adopted to reveal the hydrochemical factors affecting NO3− concentrations and quantify the contribution of each source to NO3− concentrations in surface water and groundwater. The findings revealed that high groundwater NO3− concentration is concentrated in the southwestern region, peaking at 271 mg/L. NO3− concentration in the Wei River and Yuxian River exhibited an increase from upstream to downstream, but in the Shidi River and Luowen River, its concentration was highest in the upstream. Groundwater NO3− has noticeable correlation with Na+, Ca2+, Mg2+, Cl−, HCO3−, TDS, EC, and ORP. In surface water, NO3− level is significantly correlated with NH4+ and ORP. Major sources of NO3− in surface and groundwater comprise manure & sewage and soil nitrogen. Source contribution for surface water was calculated by MixSIAR model to obtain soil nitrogen (57.7%), manure & sewage (23.8%), chemical fertilizer (12%), and atmospheric deposition (6.4%). In groundwater, soil nitrogen and manure & sewage accounted for 19% and 63.8% of nitrate sources, respectively. Both surface water and groundwater exhibited strong oxidation, with nitrification the primary process. It is expected that this study will provide insights into the dynamics of NO3− and contribute to the development of effective strategies for mitigating NO3− contaminant, leading to sustainable management of water resources.

Domestic wastewater treatment towards reuse by “self-supplied” microbial electrochemical system assisted UV/H2O2 process

Domestic wastewater is a potential source of water for non-potable reuse that may help address the global water, energy, and resource challenges. Herein, a “self-supplied” process through integrating microbial electrochemical system (MES) with UV/H2O2 was developed and investigated for wastewater treatment. H2O2 was “self-supplied” from MES while the MES catholyte was “self-supplied” from the final effluent of UV/H2O2. It was found that the MES accomplished > 80 % degradation of chemical oxygen demand (COD) through bioanode degradation, and produced 18 - 20 mg L−1 H2O2 via oxygen reduction reaction in the gas diffusion cathode. The MES effluent was further treated by the UV/H2O2 process, which achieved the complete removal of recalcitrant diclofenac and > 6 log inactivation of Escherichia coli. The enhanced treatment performance of UV/H2O2 was demonstrated via a comparison with the control experiments (UV or H2O2 treatment) and benefited from ·OH generation and sulfide removal. When treating the actual wastewater, the proposed system exhibited consistent treatment performance for the organic compounds and recalcitrant contaminants, and the quality of the treated water would meet the non-potable water reuse guidelines. The results of this study encourage the further exploration of emerging contaminant removal, system coordination, and use of renewable energy by the cooperation between MES and UV/H2O2.

A globally sampled high-resolution hand-labeled validation dataset for evaluating surface water extent maps

Abstract. Effective monitoring of global water resources is increasingly critical due to climate change and population growth. Advancements in remote sensing technology, specifically in spatial, spectral, and temporal resolutions, are revolutionizing water resource monitoring, leading to more frequent and high-quality surface water extent maps using various techniques such as traditional image processing and machine learning algorithms. However, satellite imagery datasets contain trade-offs that result in inconsistencies in performance, such as disparities in measurement principles between optical (e.g., Sentinel-2) and radar (e.g., Sentinel-1) sensors and differences in spatial and spectral resolutions among optical sensors. Therefore, developing accurate and robust surface water mapping solutions requires independent validations from multiple datasets to identify potential biases within the imagery and algorithms. However, high-quality validation datasets are expensive to build, and few contain information on water resources. For this purpose, we introduce a globally sampled, high-spatial-resolution dataset labeled using 3 m PlanetScope imagery (Planet Team, 2017). Our surface water extent dataset comprises 100 images, each with a size of 1024×1024 pixels, which were sampled using a stratified random sampling strategy covering all 14 biomes. We highlighted urban and rural regions, lakes, and rivers, including braided rivers and coastal regions. We evaluated two surface water extent mapping methods using our dataset – Dynamic World (Brown et al., 2022), based on Sentinel-2, and the NASA IMPACT model (Paul and Ganju, 2021), based on Sentinel-1. Dynamic World achieved a mean intersection over union (IoU) of 72.16 % and F1 score of 79.70 %, while the NASA IMPACT model had a mean IoU of 57.61 % and F1 score of 65.79 %. Performance varied substantially across biomes, highlighting the importance of evaluating models on diverse landscapes to assess their generalizability and robustness. Our dataset can be used to analyze satellite products and methods, providing insights into their advantages and drawbacks. Our dataset offers a unique tool for analyzing satellite products, aiding the development of more accurate and robust surface water monitoring solutions. The dataset can be accessed via https://doi.org/10.25739/03nt-4f29 (Mukherjee et al., 2024).

Community engagement enhances undergraduate civil engineering capstone design projects

Abstract Over the past several decades numerous studies have shown the value of community engagement in global water, sanitation, and hygiene (WASH) programs. Engaging and collaborating with communities through the design process enables wider community acceptance and ownership of WASH interventions, ensures a more functional and impactful design, and opens the door for co-benefits of these systems. Accounting for a range of dimensions within a community is critical to creating WASH designs that provide the most benefits. Undergraduate engineering curriculums focus on design, but often do not explicitly account for the social, environmental, and economic elements that affect the success, efficacy, and sustainability of a design. There is increasing emphasis on educating engineers on sustainability and systems thinking so they are equipped to solve complex, multidisciplinary problems. To understand how social, environmental, and economic elements fit into engineering design and how to create sustainable WASH interventions, undergraduate engineering students benefit from participating in WASH design projects that engage and collaborate with communities. This perspective highlights the value of community engagement with partners in Uganda in teaching water resources and environmental engineering design to undergraduate civil engineering students.

Economic valuation of changes in ecosystem services of 77 Ramsar wetlands in West Asia over 37 years (1984–2021)

Summary In the West Asia region, the vulnerability of Ramsar Convention wetlands due to unsustainable utilization driven by water scarcity continues to grow. Here, a global surface water product generated by the European Joint Research Centre was used to assess changes in surface water in 77 wetlands listed under the Ramsar Convention over a 37-year period (1984–2021). By combining this product with a quantitative valuation model, estimates were made of the economic value of the ecosystem services provided by these wetlands, enabling the determination of the economic losses resulting from any reduction in surface water. We show that 20% (7550 km2) of permanent surface waters in Ramsar sites have disappeared or are no longer classified as permanent. Based on this, USD 106 billion of the economic value of wetlands ecosystem services have been lost. Additionally, 33% (12 100 km2) of seasonal surface waters in these wetlands have experienced a decrease in area. Iran and Iraq account for 90% of water losses, primarily in 34 wetlands (30 in Iran and 4 in Iraq). These findings underscore the urgent need for water management policies and conservation strategies in the West Asia region.

Exploration of laser-assisted chemical bath for enhancing synthesis of undoped and nickel-doped zinc oxide and its potential applications in water purification and mitigating antimicrobial resistance

This study aims to explore the antimicrobial and photocatalytic efficiencies of pure and Ni-doped ZnO nanostructures produced via Laser-assisted Chemical Bath Synthesis (LACBS) to develop sustainable solutions for water treatment and pathogen control amid the global water crisis exacerbated by climate change and environmental pollution. Utilizing zinc acetate dihydrate and hexamethylenetetramine, the nanostructures were synthesized with Ni doping levels of 0.0 %, 1.5 %, 3.0 %, and 4.5 %, targeting their promising photocatalytic and antimicrobial properties to combat contaminants from pharmaceuticals, agriculture, and industries. Morphological analyses using Scanning Electron Microscopy showed a transition from hexagonal particles to nanoflowers, enhancing photocatalytic activity due to increased surface-to-volume ratio. X-ray Diffraction confirmed the hexagonal wurtzite structure, with variations in peak intensities indicating improved crystallinity with Ni doping. Energy Dispersive X-ray analysis verified the purity and successful incorporation of Ni. Photocatalytic assessments indicated up to 99.24 % degradation of Methylene Orange dye under blue laser irradiation within 60 minutes, correlating with Ni content. Antimicrobial tests demonstrated effective inhibition of pathogens such as Escherichia coli, Staphylococcus aureus, and additional strains like Candida albicans and Klebsiella pneumonia, with increasing zones of inhibition corresponding to higher Ni levels, extending up to 37 mm. The results underscore the dual functionality of ZnO nanostructures for applications in sustainable water treatment and antimicrobial controls, highlighting the need for future studies to examine the impacts of further increased doping concentrations on the material properties and efficacy.

Exploring carbon dioxide sequestration in desalination reject brine via NaOH reaction: A kinetics study

Seawater desalination is one of the most sustainable means of water supply in arid and semi-arid regions. Despite its undeniable potential to meet the global water demands, there are several environmental impacts associated with its operation, including the generation of reject brine and the emission of considerable amounts of CO2. Recently, the mineralization of carbon dioxide using desalination reject brine has emerged as a potential solution for simultaneous brine management and CO2 sequestration. In this study, the reaction kinetics of desalination reject brine with CO2 in the presence of NaOH are evaluated. The effect of various operating parameters, such as the temperature, CO2 concentration, NaOH dosage, brine salinity, CO2 flowrates and inert particles volume percent were investigated by varying them within the range of 15–55 °C, 3–20 %, 6–16 g/L, 5–72 g/L, 1–5 L/min and 0–20 %, respectively. The experimental data showed that the overall rate of CO2 conversion is equal to the sum of the rates observed for Ca2+ and Mg2+ carbonation reactions and increases proportionally with the increase in CO2 concentration. The addition of NaOH improved the Ca2+ carbonation reaction rate but had no effect on Mg2+ carbonation reactions within the investigated reaction conditions. Interestingly, increasing brine salinity had a negative effect on the reaction rate, while the change in temperature and inert particles had minimal effect on the overall reaction rate. Analysis of the solid products showed that Hydromagnesite and Calcite were the two major products obtained. Finally, experimental data were used to develop a rate model representing the CO2-Brine-NaOH system. The developed model will assist in successfully predicting the performance of the process and pave the way for efficient brine management and CO2 sequestration.

GIS-based multi-criteria approach for ranking suitable areas for the implementation of PV-Powered MCDI desalination plants in the Rheris Watershed, Southeast Morocco

In Morocco's oases, which rely heavily on surface water from mountain sources, the threat of decreasing rainfall presents a significant challenge, leading to a decline in surface water availability. This study focuses on the Rheris Watershed in Southeast Morocco, where brackish water desalination emerges as a viable alternative to ensure sustainable water supply for agriculture. Prior to the deployment of a pilot plant integrating a desalination unit, selecting an optimal site for PV-powered MCDI desalination plants was critical. This selection was based on a range of criteria, including Groundwater Quantity, Global Horizontal Irradiation, Temperature, Evaporation, Water Salinity, Water Quantity, Well Density and Slope. These criteria were evaluated using a combination of the Analytical Hierarchy Process (AHP), and geospatial data obtained from Remote Sensing (RS) and Geographic Information System (GIS) techniques.This case study in the Rheris watershed identified potential sites for future Membrane Capacitive Deionization (MCDI) desalination projects, High suitability areas encompass 280.45 km² (30.91 %), located west of Tinejdad, Khettarat Moulay Hachem, north of Goulmima, and south of Tinghir. Low suitability areas cover 63.75 km² (7.02 % of the study area), including regions south of Tadighoust and Tinejdad. Moderate suitability areas span 562.86 km² (62.05 %), involving central regions of Goulmima, Tadighoust, Tinejdad, and Tinghir. Based on the results of the study, the recommendations include focusing on areas identified as highly suitable for MCDI technology for sustainable agriculture, refining selection criteria based on local data, exploring brine management strategies, and adopting integrated water management approaches to ensure sustainable resource use.

Selection and adoption of water purification technologies in the bottled water industry in India

Today, more than sixty per cent of the global bottled water manufacturing takes place in the countries of the global south. Despite being a low-tech sector, the industry is heavily influenced by the advancement and adoption of new water purification technologies and science-based regulations introduced by regulatory agencies. This paper examines the factors and mechanisms through which selection and adoption take place in this sector. The study draws upon firm-level surveys, expert interviews, ethnographic data, and select court cases and policy reports. We find that economic (firm’s size, firm’s age, and ownership structure) and socio-environmental factors (environmental subjectivities of major actors, regulatory (in-) capacity, role of supporting institutions) shape the pattern and combinations of technological adoption and technological changes at the firm level to meet the goals of “safety” and “quality”. However, the use of certain technologies are not devoid of serious environmental and public health concerns. The regulatory actors need to pay closer attention to the direct and indirect impacts of technology use on public health, the economy and the environment to make public policies more just and to meet sustainable development goals.

Active pharmaceutical contaminants in drinking water: myth or fact?

Global water availability has been affected by a variety of factors, including climate change, water pollution, urbanization, and population growth. These issues have been particularly acute in many parts of the world, where access to clean water remains a significant challenge. In this context, preserving existing water bodies is a critical priority. Numerous studies have demonstrated the inadequacy of conventional water treatment processes in removing active pharmaceutical ingredients (APIs) from the water. These pharmaceutical active compounds have been detected in treated wastewater, groundwater, and even drinking water sources. The presence of APIs in water resources poses a significant threat not only to aquatic organisms but also to human health. These emerging contaminants have the potential to disrupt endocrine systems, promote the development of antibiotic-resistant bacteria, and bioaccumulate in the food chain, ultimately leading to unacceptable risks to public health. The inability of current conventional treatment methods to effectively remove APIs from water has raised serious concerns about the safety and reliability of water supplies. This issue requires immediate attention and the development of more effective treatment technologies to safeguard the quality of water resources and protect both aquatic ecosystems and human health. Other treatment methods, such as nanotechnology, microalgal treatment, and reverse osmosis, are promising in addressing the issue of API contamination in water resources. These innovative approaches have demonstrated higher removal efficiencies for a wide range of APIs compared to conventional methods, such as activated sludge and chlorination, which have been found to be inadequate in the removal of these emerging contaminants. The potential of these alternative treatment technologies to serve as effective tertiary treatment. To address this critical challenge, governments and policymakers should prioritize investment in research and development to establish effective and scalable solutions for eliminating APIs from various water sources. This should include comprehensive studies to assess the performance, cost-effectiveness, and environmental sustainability of emerging treatment technologies. The emerging contaminants should be included in robust water quality monitoring programs (Aus der Beek et al. in Environ Toxicol Chem 2016;35(4):823-835), with strict regulatory limits enforced to protect public health and the environment. By doing so, the scientific community and regulatory authorities can work together to develop a multi-barrier approach to safeguarding the water resources and ensuring access to safe, clean water for all. This review explores the potential of alternative treatment technologies to serve as viable solutions in the fight against API contamination. Innovative approaches, including nanotechnology, microalgal treatment, and reverse osmosis, have demonstrated remarkable success in addressing this challenge, exhibiting higher removal efficiencies compared to traditional methods.

Innovative integration of sustainable technologies in educational programs: Fostering freshwater production and environmental preservation awareness

This study highlights the integration of sustainable desalination technologies into educational programs to raise awareness of freshwater production and environmental preservation. Through a comprehensive curriculum, students explore innovative methods such as pressure-retarded osmosis, multi-effect desalination, and seawater source heat pumps, all powered by renewable seawater thermal energy. The curriculum emphasizes the importance of reducing greenhouse gas emissions, lowering reliance on fossil fuels, and protecting aquatic ecosystems. Students engage in practical evaluations of energy efficiency, economic viability, and environmental impact. Sensitivity analyses are incorporated to help students identify critical factors affecting system performance and optimize operational conditions for various modes. Through hands-on experiments, students learn that components like the heat pump condenser contribute the most to energy loss (29 %), followed by the expansion valve (12 %), compressor (11 %), and seawater heat exchanger (8 %). Economic analyses reveal that while the heat pump condenser and seawater heat exchanger have the lowest financial impact (0.33 % and 2.48 %, respectively), the pressure-retarded osmosis and compressor units have the highest (100 % and 60.3 %, respectively). The findings demonstrate that an optimally designed desalination system can produce freshwater at 80 % lower costs compared to traditional plants, while also reducing carbon emissions by 15 %. Educational experiments also show that integrating pressure-retarded osmosis downstream of multi-effect desalination significantly reduces brine salinity and temperature, highlighting the system's potential for environmental sustainability. This approach not only fosters a deeper understanding of desalination technologies but also equips students with the tools to address future global water challenges.

Dynamic assessment of the impact of compound dry-hot conditions on global terrestrial water storage

Precipitation and temperature are critical factors influencing terrestrial water storage (TWS) can lead to unexpected TWS losses when compounded by dryness and high temperatures. Yet, a dynamic assessment of the individual and combined effects of these conditions on TWS is lacking. This study proposes a framework to assess TWS loss driven by compound dry-hot conditions (CDHC) and dynamically evaluates risk probabilities and thresholds for 2003–2012 and 2013–2022. Results showed that CDHC exert a greater impact on TWS than dry or hot conditions alone. The risk probabilities of global TWS loss are higher in the late period than in the early period, with risk probabilities for light and extreme levels increasing by approximately 9–11 % and 2–7 %, respectively. Although the resilience of water resource systems to CDHC has increased in some regions, it still shows a decreasing trend on a global scale. The decrease in the resilience to TWS in major hyperarid areas is primarily influenced by temperature, whereas that in arid areas is primarily affected by precipitation. These distinct patterns may be the primary factors contributing to the exacerbation of global TWS loss. This study provides a novel approach for the dynamic assessment of global TWS under CDHC. The research findings offer valuable insights for decision-makers developing adaptive strategies to mitigate future CDHC challenges.

Advanced Technologies for Sustainable Water Management: A Comprehensive Review

This review paper provides a comprehensive analysis of the latest advancements in water management technology, focusing on the integration of Internet of Things (IoT), machine learning, blockchain, and other emerging technologies. The study examines 19 key research papers, exploring various methodologies, key outcomes, and the challenges associated with these technologies. While significant progress has been made in improving water resource management through real-time monitoring, predictive analytics, and decentralized data management, several challenges persist, including high implementation costs, integration complexities, and the need for standardized protocols. The review identifies opportunities for future research, particularly in developing cost-effective solutions, enhancing interoperability, and advancing artificial intelligence applications in water management. Additionally, the paper highlights the importance of evolving regulatory frameworks and increasing public awareness to ensure the successful adoption of these technologies. The findings of this review contribute to the ongoing efforts to create more sustainable and efficient water management systems capable of addressing the growing global water demand.

Pure water and resource recovery from municipal wastewater using high-rate activated sludge, reverse osmosis, and mainstream anammox: A pilot scale study

In response to the escalating global water scarcity and the high energy consumption associated with traditional wastewater treatment plants, there is a growing demand for transformative wastewater treatment processes that promise greater efficiency and sustainability. This study presents an innovative approach for municipal wastewater treatment that integrates high-rate activated sludge with membrane bio-reactor (HRAS-MBR), reverse osmosis (RO) and partial nitrification-anammox (PN/A). With an influent of 8.4 m³/d, the HRAS-MBR demonstrated a removal efficiency of approximately 85 % for chemical oxygen demand (COD), with over 70 % of it being recovered for energy production. The RO system achieved a recovery rate of 75 % for the influent, producing pure water with an electrical conductivity of 50 μS/cm. Concurrently, it concentrated ammonia, thereby enhancing the effectiveness of the PN/A process for nitrogen removal in the mainstream, resulting in a removal efficiency exceeding 85 %. Notably, the HRAS-MBR achieved significant phosphorus removal without chemical additives, attributed to the presence of influent calcium and magnesium ions. Overall, this integrated system reduced the net energy consumption for reclaimed water production by about 26 % compared to conventional methods. Additionally, the new process produced a revenue of 0.75 CNY/m³, demonstrating considerable economic and environmental benefits. This pilot-scale study offers a viable alternative for wastewater treatment and water reuse in water-scarce regions, contributing to sustainable water resource management.

Environmental safety performance dynamics and estimation of the deterioration of leachate containment elements: Implications for the lifespan of hazardous waste landfills

In the coming decades, the failure and expiration of over 100,000 landfills involving billions of tons of waste not only threaten global water security but also lead to a sudden increase in the global demand for solid waste disposal. Therefore, further research is needed on the ways in which landfill performance is degraded, their life expectancy, the factors that influence them and the ways in which they are influenced. A study estimated the performance degradation and expected lifespan of a modern hazardous waste landfill in China. The landfill experienced slow performance degradation in early years (0–12 years). But during mid-term (12–62 years) due to the rapid degradation of the liner material, the rate of leakage from the containment layer will increase by a factor of 4.8–27.1, leading to its earliest failure after about 38 years. This indicates the need for measures to prevent rapid performance degradation in the middle of the landfill's service life and to strengthen monitoring of performance indicators and environmental medium pollution in the later period (after 62 years) to respond to potential scrapping and pollutant leakage problems. Differences in construction quality and regional climate can cause differences in the lifespan of landfill facilities by up to 20 and 30 times, highlighting the importance of scenario-based failure and lifespan prediction for designing reasonable monitoring plans and preparing response measures to prevent potential groundwater pollution and to meet the sudden increase in demand for secondary waste disposal.

Machine Learning and Artificial Intelligence Improve Data Validation

Artificial intelligence (AI) can assist with time‐series data corrections, relieving a bottleneck in a water utility's quality assurance processes. AI's speed and accuracy can help reduce water scarcity and ultimately improve the global water crisis.

Triple oxygen isotope reveals insolation-forced tropical moisture cycles.

Tropical oceans are the main global water vapor and latent heat sources, but their responses to radiative forcing remain unclear. Here, we investigate oceanic moisture dynamics of the western tropical Pacific (WTP) over the past 210,000 years through an approach of planktonic foraminiferal triple oxygen isotope (Δ'17O). The Δ'17O record is dominated by the precession cycles (~23,000 years), with lower values reflecting higher humidity in concert with higher Northern Hemisphere summer insolation. Our empirical and modeling results, combined with other geological archives, suggest that the enhanced moisture convergence over the WTP largely intensifies changes in the meridional and zonal hydrological cycles, affecting rainfall patterns in East Asia and northern South America. We propose that the insolation-driven WTP moisture dynamics play a pivotal role in regulating tropical hydroclimate.

Metabolic processes drive spatio-temporal variations of carbon sink/source in a karst river

Riverine carbon dioxide (CO2) exchange is a crucial component of the global carbon cycle. However, the changes in the CO2 sink/source in karst rivers caused by differences in lithological features and climate, hindered the resolution of the spatio-temporal heterogeneity of global inland water carbon emissions. Here, we use hydrochemical data and CO2 gas isotopic data to reveal the spatio-temporal variations of CO2 sink/source in karst rivers and their controlling mechanisms. Fifty-two monitoring transects were set up in the subtropical Lijiang River in southwest China in June and December 2019. Our results indicated that the CO2 flux across the water-air interface (FCO2) in the Lijiang River basin ranged from −43.77 to 519.67 mmol/(m2·d). In June, the Lijiang River acted as an atmospheric carbon source due to higher water temperatures (Twater). However, driven by hydrodynamic conditions and the metabolism of aquatic photosynthesis, the river shifts from being an atmospheric carbon source in June to an atmospheric carbon sink in December. The stable isotopes of CO2 (δ13C-CO2) show significant differences in the spatio-temporal variations of CO2 sink/source. In December, the transects of the Lijiang River basin with a negative CO2 flux are significantly negatively correlated with dissolved oxygen (DO) and chlorophyll-a (Chl-a) concentration (p < 0.05). This confirms that the enhancement of aquatic photosynthesis efficiency increased water DO concentrations, which resulted in the positive movement of water δ13C-CO2 and a decrease in the partial pressure of CO2 (pCO2) and FCO2. Comparative analysis with global river FCO2 indicates that under the combined driving forces of metabolic processes of aquatic photosynthetic organisms and hydrodynamic conditions, rivers tend to act more frequently as CO2 sinks, particularly in subtropical and temperate rivers. In conclusion, this study represents a new example focusing on CO2 dynamics to address the spatio-temporal heterogeneity of carbon emissions in inland waters on a global scale.