Aquatic ecosystems, including lakes and wetlands, are responsible for approximately 80% of global natural methane (CH4) emissions. Scientists long believed that CH4 production occurs exclusively under anoxic conditions. However, CH4 supersaturation has been frequently observed in oxygenated water bodies, and after excluding CH4 transport processes, oxic CH4 production has been confirmed. This supersaturation phenomenon, referred to as the “methane paradox”, has drawn significant scientific interest, yet direct empirical evidence and mechanistic understanding remain limited.Detecting this methane production was a major challenge. Traditional methods struggled because oxygen in water creates false signals. Given that oxic CH4 production often involves rapid, subtle concentration fluctuations—particularly in algal-driven processes—a high-sensitivity, real-time monitoring method is indispensable.Led by Prof. Lu ZHANG from the Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, the researchers developed new tracking technology to reveal that algal (especially cyanobacterial) metabolism is a key player in CH4 production in oxic environments of cold-temperate mountainous lakes. This study was recently published in Water Research.“The research enhances our understanding of the aquatic CH4 cycle by providing valuable insights into the role of algae in CH4 production,” said Prof. ZHANG, “It also highlights the importance of preserving environmental balance in freshwater ecosystems, with minimal human disturbance.”

Understanding how Earth’s climate naturally fluctuated during the Holocene—the current geological epoch spanning the last 11,700 years—is vital for contextualizing modern human-driven warming and improving future climate projections. Yet, tropical Australasia’s climate history has remained enigmatic, with scientists divided over interpretations of paleoclimate records.Published in CATENA, the research led by Prof. ZHANG Enlou from the Nanjing Institute of Geography and Limnology analyzed remarkable "molecular fossils"—branched glycerol dialkyl glycerol tetraethers (brGDGTs)—preserved in Girraween Lagoon’s sediments. These organic compounds function as precise paleothermometers when properly calibrated.Using a specific calibration for tropical lakes, the research team reconstructed mean annual air temperatures over the past 10,400 years. The results reveal a steady warming trend of 2 °C throughout the Holocene. This warming aligns with other land temperature records, alkenone-derived ocean temperature data, and climate models for the region. Intriguingly, it diverges from estimates using magnesium-to-calcium ratios in planktonic fossils, highlighting ongoing debates about proxy reliability.More than just temperature, the sediments recorded an environmental transformation. The lagoon grew increasingly acidic over millennia. This acidification stemmed from two key factors. First, declining rainfall in northern Australia reduced the inflow of alkaline groundwater from limestone sinkholes beneath the lake. Second, decaying organic matter in the sediments boosted acid production. Together, these processes transformed the lagoon’s chemistry.By correlating their data with regional climate archives, researchers traced these changes to intensifying El Niño-Southern Oscillation (ENSO) activity. As ENSO variability grew, tropical Australasia shifted from cool/wet conditions to today’s warmer, drier climate with stark seasonal contrasts.This dual reconstruction of temperature and pH not only resolves long-standing scientific contradictions but also provides a holistic framework for understanding how ocean-atmosphere interactions, hydrology, and biogeochemical cycles jointly shaped the region’s climate history. Such insights are critical for refining models to predict how tropical climates may respond to future global warming."Lake sediments are like nature’s history books," said Prof. ZHANG, "By reading their chemical signatures, we’re better preparing for climate challenges ahead."

　　Social-ecological systems (SES) are complex, dynamic systems with interdependencies between their ecological components and social actors. Studying the transient (e.g., nonlinear) dynamics of interlinked SES can provide valuable insights into achieving the UN Sustainable Development Goals for a more desirable future. 
　　However, identifying critical transitions in real-world SES remains a major challenge. A significant knowledge gap exists in index framework for characterizing dynamic behaviors within SES changes. This issue is also compounded by the scarcity of long-term datasets spanning entire transition periods, which together limits our comprehension of the Anthropocene landscape changes. 
　　Recently, an international research team led by Dr. LIN Qi and Prof. ZHANG Ke from the Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences made some progresses by advancing an evolutionary framework that utilizes a dynamic metric based on Rate of Change (RoC) derived from multidecadal socioeconomic and geobiophysical (lake sediment) records. These researchers from China, France, Netherlands, Sweden, Italy, United Kingdom, and South Africa worked together, and applied the co-evolutionary framework to Lake Taihu watershed from China’s Yangtze River Delta region. 
　　The study was published in Proceedings of the National Academy of Sciences of the United States of America. 
　　By integrating sedimentary ancient DNA (sedaDNA) metabarcoding, multi-proxy paleoenvironmental analyses, and socioeconomic data, the researchers elucidated the temporal dynamics of regional SES over several centuries. Starting in the 1950s, the SES underwent a shift towards an interconnected and ecologically unsustainable state, driven by a series of deleterious positive feedbacks. These process exacerbated water eutrophication, soil erosion, air pollution, and ecosystem resilience loss under human stressors. More interestingly, the study revealed a decoupling of socioeconomic development from eco-environmental degradation since the early 2000s, signifying a potentially more sustainable reconfiguration of the regional SES. 
　　“Thanks to the wide-ranging environmental laws and policies, conservation and ecological engineering projects, and institutional innovations, the recent decoupling signal discloses a sustainable development pattern not observed over the past millennium in this iconic region”, said Dr. LIN Qi, first author of the study. The signal highlights the crucial role of adaptive management and policy intervention in fostering positive transformations. 
　　This case study also provides insights into the resilience and adaptability of regional SES facing similar ecological and environmental stressors. It demonstrates potential strategies for transformative action as outlined under the UN Sustainable Development Goals. “Adopting the co-evolutionary framework to address the complexities of SES dynamics, just like in Lake Taihu case, can offer a blueprint for where and how transformative steps can be taken to achieve a good Anthropocene”, said Prof. ZHANG Ke, corresponding author of the study.
　　 
　　IMAGE: Dynamic changes of intertwined SES from a historical evolutionary perspective. 
　　CREDIT by ZHANG KE  
　　Website linkage: https://www.pnas.org/doi/10.1073/pnas.2321303121 
　　Contact Information 
　　Ke Zhang at the Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences
　　Email: kzhang@niglas.ac.cn