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Study: Climate Warming Drives Sustained Oxygen Loss in Global Rivers

According to a study published in Science Advances on May 15, global rivers are undergoing widespread and sustained deoxygenation driven by climate warming, among which tropical rivers are the most vulnerable ecosystems, with an urgent need to combat oxygen loss.A research team led by Prof. SHI Kun from the Nanjing Institute of Geography and Limnology (NIGLAS) of the Chinese Academy of Sciences conducted this study, with Dr. GUAN Qi serving as the first author, in collaboration with a researcher from Tongji University.Oxygen is a fundamental foundation of river ecosystems, sustaining ecological health, supporting aquatic organisms, and regulating biogeochemical cycles. Its decline poses threats to river biodiversity.To investigate long-term trends in river dissolved oxygen, the team employed a machine-learning stacking algorithm to analyze data from 21,439 river reaches across the globe over a nearly 40-year period (1985–2023).Key findings from the study indicated that river ecosystems are losing oxygen at a rate of -0.045 mg L-1 decade-1, with 78.8% of the studied rivers experiencing deoxygenation.The most severe deoxygenation occurred in tropical rivers (between 20°S and 20°N), such as those in India. This contradicts prior expectations that high-latitude rivers, which face amplified climate warming, would be the primary deoxygenation hotspots. The study found that low oxygen levels coupled with faster deoxygenation make tropical rivers more vulnerable to hypoxia events.The researchers further quantified the impacts of flow regimes and dam impoundment on river deoxygenation. Results indicate that both low- and high-flow conditions can partially mitigate river deoxygenation, leading to an 18.6% lower deoxygenation rate in low-flow conditions compared with normal conditions. On the other hand, high-flow conditions led to a 7.0% lower deoxygenation rate compared with normal-flow conditions. Furthermore, dam impoundment also altered deoxygenation in its impoundment area: negative in shallow reservoirs but positive in deep reservoirs. That is to say, dam impoundment can accelerate deoxygenation in shallow reservoirs, but mitigate deoxygenation in deep reservoirs.Further analysis identified climate-driven declines in oxygen solubility as the major cause of river deoxygenation, accounting for 62.7% of the observed decline. Ecosystem metabolism—reflected by factors such as temperature, light, and flow—was responsible for 12% of the deoxygenation.Heatwave events were also specifically analyzed, with their impacts on river deoxygenation quantitatively assessed. The results show that heatwaves were responsible for 22.7% of global river deoxygenation, with an increase of 0.01 mg L-1 decade-1 in the deoxygenation rate, relative to conditions under average climatological temperatures.These findings underscore the negative consequences of climate warming on lotic ecosystems and identify tropical rivers as the ecosystems in greatest need of effective action and mitigation strategies to combat deoxygenation crises. The study provides a systematic baseline for policymakers in formulating measures to mitigate river deoxygenation worldwide.

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Study Reveals High Sedimentation Risk of Global Small Reservoirs
2026-06-03
Reservoirs around the world are losing storage capacity at an average rate of 7.3 percent per decade—disproportionately affecting small reservoirs, which together provide water to billions of people.The data come from a study published in Nature Sustainability on June 5, which offers the clearest global assessment of reservoir sedimentation to date.In the study, led by Prof. SONG Chunqiao of the Nanjing Institute of Geography and Limnology (NIGLAS) of the Chinese Academy of Sciences, the researchers developed the Global REservoir Inventory (GREI), combining remote sensing, geospatial data, and engineering records to identify more than 550,000 reservoirs worldwide. Over 95 percent of these reservoirs are smaller than one square kilometer—a category largely absent from previous assessments.“This study provides the first high-resolution global assessment of reservoir sedimentation that fully incorporates small reservoirs,” said LIU Kai, first author of the study and a researcher at NIGLAS.Reservoirs are essential infrastructure for flood control, irrigation, water supply, and hydropower generation. However, sediment trapped behind dams gradually reduces usable storage capacity, weakening reservoir functionality and threatening long-term water security. Reduced downstream sediment transport may also alter river morphology and intensify risks such as delta subsidence, coastal erosion, and ecosystem degradation.Using field-based sedimentation observations from more than 6,000 reservoirs and a physics-guided machine learning framework, the team found that nearly one in five reservoirs already faces rapid storage loss. Small reservoirs are particularly vulnerable, especially in dryland regions such as the southwestern United States, the Middle East, and western Australia.The study also identifies 16 global sedimentation hotspots, many of which overlap with major irrigated agricultural regions and water-scarce drylands.The researchers found that around one-quarter of global irrigated land, affecting more than 2 billion people, is exposed to elevated sedimentation risk, raising concerns for long-term water and food security. Without effective intervention, the study estimates that more than half of global reservoirs could experience functional degradation by 2060.“Reservoir sedimentation deserves greater attention as a growing challenge to long-term water, food, and energy security,” Prof. SONG said. “More sustainable reservoir management will be essential for supporting human well-being and advancing global sustainable development.”
Study maps China’s lake freshwater resources
2026-05-25
A new study has provided the clearest picture yet of how much water is stored in China's lakes, finding that the country's natural lakes contain about 1,174 km3 of water, including around 335 km3 of freshwater, while eastern population centers have direct access to only a limited share of these natural freshwater resources.The study, published in the journal National Science Review, was conducted by a research team led by researchers from the Nanjing Institute of Geography and Limnology under the Chinese Academy of Sciences (NIGLAS).Using nationwide lake survey data collected over the past three decades and advanced spatial statistical methods, the researchers carried out the first systematic nationwide assessment of lake depth and freshwater–saline lake types across China, quantifying water storage in 2,713 natural lakes larger than 1 km2.To strengthen the reliability of the assessment, the team integrated data from nationwide lake surveys, scientific expeditions and water resource investigations. The researchers compiled high-precision depth and bathymetric measurements from hundreds of lakes across the country and combined them with spatial statistical modeling.The findings reveal a striking geographical imbalance in freshwater distribution. Nearly 65% of China's natural freshwater lake storage is concentrated in a small number of deep lakes in western inland basins, particularly on the Tibetan Plateau. This challenges the traditional perception that freshwater lakes are mainly concentrated in eastern China.By contrast, lakes in eastern plains are generally shallower and store far less water. About 81% of China's population lives in eastern regions, yet these areas have direct access to only around 23% of the country's natural freshwater lake storage. Water quality degradation in some eastern lakes further reduces the amount of safely usable freshwater.The study also noted that China's extensive reservoir network plays an important role in supporting water availability and easing regional disparities in natural freshwater resources.“This study provides the most comprehensive assessment to date of China's natural lake freshwater resources,” said Song Chunqiao, a researcher at NIGLAS and first author of the study.“By combining large-scale field investigations with advanced statistical methods, we were able to move beyond traditional surface observations and better understand how much water China's lakes actually store and where freshwater resources are concentrated,” Song said. “The findings provide an important scientific basis for water resource management and long-term water security planning.”
Study: Climate Warming Drives Sustained Oxygen Loss in Global Rivers
2026-05-17
According to a study published in Science Advances on May 15, global rivers are undergoing widespread and sustained deoxygenation driven by climate warming, among which tropical rivers are the most vulnerable ecosystems, with an urgent need to combat oxygen loss.A research team led by Prof. SHI Kun from the Nanjing Institute of Geography and Limnology (NIGLAS) of the Chinese Academy of Sciences conducted this study, with Dr. GUAN Qi serving as the first author, in collaboration with a researcher from Tongji University.Oxygen is a fundamental foundation of river ecosystems, sustaining ecological health, supporting aquatic organisms, and regulating biogeochemical cycles. Its decline poses threats to river biodiversity.To investigate long-term trends in river dissolved oxygen, the team employed a machine-learning stacking algorithm to analyze data from 21,439 river reaches across the globe over a nearly 40-year period (1985–2023).Key findings from the study indicated that river ecosystems are losing oxygen at a rate of -0.045 mg L-1 decade-1, with 78.8% of the studied rivers experiencing deoxygenation.The most severe deoxygenation occurred in tropical rivers (between 20°S and 20°N), such as those in India. This contradicts prior expectations that high-latitude rivers, which face amplified climate warming, would be the primary deoxygenation hotspots. The study found that low oxygen levels coupled with faster deoxygenation make tropical rivers more vulnerable to hypoxia events.The researchers further quantified the impacts of flow regimes and dam impoundment on river deoxygenation. Results indicate that both low- and high-flow conditions can partially mitigate river deoxygenation, leading to an 18.6% lower deoxygenation rate in low-flow conditions compared with normal conditions. On the other hand, high-flow conditions led to a 7.0% lower deoxygenation rate compared with normal-flow conditions. Furthermore, dam impoundment also altered deoxygenation in its impoundment area: negative in shallow reservoirs but positive in deep reservoirs. That is to say, dam impoundment can accelerate deoxygenation in shallow reservoirs, but mitigate deoxygenation in deep reservoirs.Further analysis identified climate-driven declines in oxygen solubility as the major cause of river deoxygenation, accounting for 62.7% of the observed decline. Ecosystem metabolism—reflected by factors such as temperature, light, and flow—was responsible for 12% of the deoxygenation.Heatwave events were also specifically analyzed, with their impacts on river deoxygenation quantitatively assessed. The results show that heatwaves were responsible for 22.7% of global river deoxygenation, with an increase of 0.01 mg L-1 decade-1 in the deoxygenation rate, relative to conditions under average climatological temperatures.These findings underscore the negative consequences of climate warming on lotic ecosystems and identify tropical rivers as the ecosystems in greatest need of effective action and mitigation strategies to combat deoxygenation crises. The study provides a systematic baseline for policymakers in formulating measures to mitigate river deoxygenation worldwide.
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Int’l Cooperation News

2026-05-26

NIGLAS Delegation Attends 2026 ASLO-SIL Joint Conference in Canada
Sino-Tanzania collaboration boosts the improvement of water and air environment in the near-lake area of Lake Victoria
2026-01-30
Some bays of the Lake Victoria are now facing with the severe problem of Lake Eutrophication, which is mainly caused by the nitrogen (N) discharged from crop farming in the lake bay areas. While the farmers' behaviors affect directly on the N discharged from crop farming.The Sino-Tanzania cooperation project, a part of the International Partnership Program of the Chinese Academy of Sciences is led by Dr. XIONG Chuanhe from the Nanjing Institute of Geography & Limnology (NIGLAS). The project is dedicated to addressing the issues and improving the water and air environment in the near-lake area.Recently, the project conducted on-site investigations to three villages in the Mwanza Lake Bay area of Lake Victoria: Sweyavillage, Kisoko, and Kigoto. Through communication with village leaders, reviewing production records, and conducting on-site estimations, the project investigated the land use and input-output conditions.During the on-site investigations, the project team also conducted interviews and questionnaires with farmers, gaining a comprehensive understanding of the household characteristics, main agricultural production behaviors, awareness of agricultural non-point source pollution, and coping abilities of farmers in dealing with non-point source pollution.The project clarified the main farming behaviors of farmers in the Victoria Lake Basin that have an impact on nitrogen discharge in the area, as well as the extent of such impact. It also revealed the specific mechanisms by which farmers' capabilities and cognition play a role in decision-making regarding the main farming behaviors that have an impact on nitrogen discharge."These efforts enhance China's international reputation in environmental conservation, " said by Dr. XIONG. Economically, the research on nitrogen discharge in lake bay area will help improve water and air quality in surrounding regions, supporting agricultural productivity and local farmers' livelihoods. Socially, the project fosters capacity-building for environmental protection and sustainable development across Africa.
National Key Research and Development Program Plan (Sino-Mongolian international cooperation project) Successfully Convoked in Nanjing and Bayannur
2023-09-11

　　On September 4th to 7th, 2023, the symposiums on the establishment and implementation of the National Key Research and Development Program of China, i.e. Sino-Mongolian Intergovernmental Joint Research Program: The impacts of global change on nutrient cycles and ecosystem evolution in shallow lakes in Sino-Mongolian cold-arid area (No. 2023YFE0100500) were successfully held in Nanjing and Bayannur. 
　　Prof. ZHANG Ganlin, the director of Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences (NIGLAS), delivered a welcoming address on behalf of the host institution. Dr. Odsuren, the scientific secretary of the Institute of Geography and Geoecology, Mongolian Academy of Sciences (IGG, MAS) made a detailed introduction of IGG, MAS. 
　　After that, the project leader Dr. HAN Chao, introduced the current state of lake ecosystems in China and presented a comprehensive report on the overall research objectives, content, implementation plan, expected outcomes, innovative aspects, task decomposition, and progress schedule of the joint project. Followed, Dr. Narangerel from IGG, MAS presented a detailed introduction to the research team's prior achievements in the field of lake science in the cold-arid regions of Mongolia and the current ecological environment of Lake Ugii. 
　　During the local coordination symposium held in Bayannur, Inner Mongolia, Director Bao Wei from Wuliangsu Lake Ecological Protection Center extended a warm welcome to the attending experts. He emphasized that this project was a significant decision and deployment for the protection and comprehensive management of Wuliangsu Lake, which would effectively support the ecological environment protection on Wuliangsu Lake. Subsequently, the joint program teams carried out discussions and communications with the local administrators regarding the implementation plan, research platform status and infrastructure, data collection and sharing, preparation of field instruments and equipment, training of young researchers, and fieldwork plans. After the meeting, all members conducted the field surveys on Wuliangsu Lake. 
　　More than 20 experts and major leaders from NIGLAS, IGGMAS, and Wuliangsu Lake Ecological Protection Center participated in the symposiums. It further expanded the researcher exchanges and cooperation, promoted friendly contacts and mutual understanding between the two sides, which played a significant role in facilitating the smooth implementation of the joint project.
　　(photo by NIGLAS)
　　
Synergistic effects of warming and internal nutrient loading interfere with the long-term stability of lake restoration and induce sudden re-eutrophication
2023-02-27

　　Urban lakes are globally ubiquitous and are usually highly eutrophic, pointing to an increase in frequency, duration and magnitude of harmful algal blooms as wide-spread threats to ecological and human health. 
　　Over half a century, phosphate (P) precipitation is among the most effective treatments to mitigate eutrophication in these lakes. However, after a period of high effectiveness, re-eutrophication would possibly occur leading to the return of harmful algal blooms. While such abrupt ecological changes were presumably attributed to internal P loading, the role of lake warming and its potential synergistic effects with the internal loading, thus far, has been largely understudied. 
　　Researchers led by Dr. KONG Xiangzhen and Prof. Dr. XUE Bin from the Nanjing Institute of Geography and Limnology of the Chinese Academy of Sciences, along with their international collaborators, have addressed the question by quantifying the contributions of lake warming and the potential synergistic effects with internal P loading in an urban lake located in central Germany, which suffered from the abrupt re-eutrophication and cyanobacterial blooms in 2016 (30 years after the first P precipitation). 
　　Their findings were published in Environmental Science & Technology on Feb. 20. 
　　In this study, a process-based lake ecosystem model (GOTM-WET) was established using a high-frequency monitoring dataset covering eutro-/oligo-trophic states over 30 years. 
　　Model analyses suggested that, for the abrupt occurrence of cyanobacterial blooms, internal P release accounts for 68% of the biomass proliferation, while lake warming contributed to 32%, including both direct effects via promoting growth (18%) and synergistic effects via intensifying internal P loading (14%). The model further revealed that the synergy was attributed to prolonged lake hypolimnion warming and oxygen depletion. 
　　“Our study exemplifies how process-based mechanistic modeling could help to tease apart important drivers of abrupt shifts and cyanobacterial blooms in lakes, particularly in an era of rapid global changes including climate change and human activities.” said Dr. Kong. 
　　This study unravels the substantial role of lake warming in promoting cyanobacterial blooms in re-eutrophicated lakes. The indirect effects of warming on cyanobacteria via promoting internal loading need more attention in future lake research and management. 
　　“Our findings will have far-reaching consequences for lake restoration and management as the nutrient targets we applied so far to reach or maintain a certain trophic state will not work in a far warmer future and need to be adjusted, i.e. stronger nutrient level reduction and higher efforts in restoration are demanded.” said Dr. Kong.
　　 
　　link: https://pubs.acs.org/doi/10.1021/acs.est.2c07181
　　 
　　 
　　Contact 
　　TAN Lei 
　　Nanjing Institute of Geography and Limnology 
　　E-mail: ltan@niglas.ac.cn
Sediment organic matter properties facilitate understanding nitrogen transformation potentials in East African lakes
2022-10-20

　　East African lakes include the most productive and alkaline lake group in the world. Yet, they generally receive fewer nutrient inputs than the densely populated subtropical and temperate lakes in the northern hemisphere. In these lakes with insufficient supplies of inorganic nitrogen, the mineralization of benthic organic matter can play an important role in driving the nutrient cycle and nitrogen loss. Using a suite of stable 15N isotope dilution and tracer techniques, we examined five main processes of the sediment nitrogen cycle in 16 lakes and reservoirs of Tanzania and Kenya, East Africa: gross nitrogen mineralization, ammonium immobilization, dissimilatory nitrate reduction to ammonium (DNRA), and the dinitrogen (N2) production via denitrification and anaerobic ammonium oxidation (anammox). Gross nitrogen mineralization and ammonium immobilization showed the maximum values of 9.84 and 12.39 μmol N kg-1 h-1 , respectively. Potential DNRA rates ranged from 0.22 to 8.15 μmol N kg-1 h-1 and accounted for 10 %–74 % (average 25 %) of the total dissimilatory nitrate reduction. Potential nitrate reduction rates in most lakes were dominated by denitrification with a contribution of 26 %–85 % and a mean of 65 %. We further found that the sediment nitrogen transformations were driven mainly by benthic organic matter properties and water column phosphate concentrations, reflecting microbial metabolic responses to the changing carbon and nutrients availability. For instance, autochthonous production of protein-like organic matter attributed to active sediment nitrogen mineralization, DNRA, and denitrification. In contrast, the high degree of humification caused by the inputs of terrestrial humic-like substances slowed down the sediment nitrogen transformations. The contribution of DNRA to total dissimilatory nitrate reduction was significantly positively correlated to sediment C: N ratios. These results indicate that predictions of sediment N supply and loss in East African lakes can be improved by incorporating sediment organic matter properties.
　　Xiaolong Yao, Zhonghua Zhao, Jianjun Wang, Qiqi Ding, Minglei Ren, Ismael Aaron Kimirei, Lu Zhang, Sediment organic matter properties facilitate understanding nitrogen transformation potentials in East African lakes, Science of The Total Environment, 841, 2022, 156607, https://doi.org/10.1016/j.scitotenv.2022.156607.
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