Rivers are one of the most dynamic water cycle components of the earth surface and hold fundamental economic and ecological significance for the development of human societies, ecosystem sustainability, and regional climate. Their natural balance has been threatened by a wide range of anthropogenic stressors and ongoing climate change. 
　　With increasing demands for social-economic development, human disturbances in the form of dam construction, aquaculture, and irrigation have resulted in large-scale and rapid transformations of river channels. However, characterizing and understanding such changes have been challenging from a long-term and global perspective. 
　　Researchers led by Prof. SONG Chunqiao from the Nanjing Institute of Geography and Limnology and collaborators from multiple institutes in China and the United States, have revealed a global attribution of the recent changes in river regime to morphological dynamics (e.g., channel shifting and anabranching), expansion induced by new dams, and hydrological signals of widening and narrowing, by analyzing water extent variations observed from four-decade Landsat imagery. 
　　The research findings were published in Nature Communications on March 22, 2023. 
　　“Morphological dynamics prevailed in about 20% of the global river area.” said Prof. KE Linghong, a primary author of this research paper. “On this type of river basin, high percentages of narrowing and widening are observed along different banks of river reaches, which are associated with the variations of flow regimes of meandering, braided, anabranching or wandering river channels.” 
　　“Booming reservoir constructions, mostly skewed in Asia and South America, contributed to 32% of the river widening,” said Prof. SONG. 
　　“The remaining hydrological signals were characterized by contrasting hotspots, including prominent river widening in alpine and pan-Arctic regions and narrowing in the arid/semi-arid continental interiors, driven by varying trends in climate forcing, cryospheric response to warming, and human water management,” said by Ms. WU Qianhan, another primary author. 
　　“Our analysis provides a global-scale but spatially-explicit guidance for better prioritizing future river protection and restoration efforts under the United Nations 2030 Agenda for Sustainable Development, which calls on international actions to track the spatial extent and condition of water-related ecosystems,” said Prof. SONG. 
　　The global distribution of different types of river extent changes in the early 21st century: morphological dynamics (Type-M), hydrological signals (Type-H), and new reservoir-type river reaches (Type-R). (Image by Prof. SONG Chunqiao)
　　Link:https://www.nature.com/articles/s41467-023-37061-3.
　　Contact
　　TAN Lei 
　　Nanjing Institute of Geography and Limnology 
　　E-mail: ltan@niglas.ac.cn
　　

　　Invasion by introduced species has been listed as one of the main threats to freshwater biodiversity worldwide. Invasive species have resulted in reduced abundance and diversity of native species in invaded natural habitats and caused harm to human society. However, the mechanisms of plant invasion in natural habitats remain controversial. 
　　In the late 1980s, Carolina fanwort (Cabomba caroliniana) was introduced to China as an aquarium plant because of its beautiful fan-shaped dissected leaves, and soon escaped as a serious invasive threat to freshwater ecosystems. It was listed as an invasive species in the 4th patch of ‘the List of Alien Invasive Species in China's Natural Ecosystem’ by the Ministry of Ecology and Environment of China in 2016. 
　　Researchers, led by Dr. HUANG Xiaolong, from Prof. LI Kuanyi's team from the Nanjing Institute of Geography and Limnology of the Chinese Academy of Sciences, along with their international collaborators, have investigated why C. caroliniana is so successful in invading China through field investigations and a mesocosm experiment. 
　　Their findings were published in the Diversity and Distributions on Mar. 15, 2023. 
　　In the field investigations, seventy-two aquatic plant quadrats dominated by one of three plant species (native Hydrilla verticillata, Myriophyllum spicatum and invasive C. caroliniana) were collected in East China. The field investigations showed that water turbidity and underwater photosynthetically active radiation (PAR) were the main factors affecting the relative coverage and abundance of the three submerged plants. 
　　Subsequently, a mesocosm experiment was conducted to explore the responses of the functional traits of the three species to different levels of underwater PAR. The results showed that the performance of C. caroliniana was superior to that of the two native species at low underwater PAR, indicating a better ability of this species to attenuate light. 
　　“If underwater darkening continues, submerged plants that are not suitable for or sufficiently tolerant of growth under these conditions may vanish, and plants that are suitable for these conditions, typically invasive plants, may prosper,” said Dr. HUANG. 
　　The results also indicate that if water bodies maintain low turbidity and a high underwater PAR after ecological restoration, the dominance of native aquatic plant vegetation will be achieved, thus constraining the growth and spread of invasive plants. 
　　“The ecological restoration of aquatic habitats that relies on the reconstruction of aquatic vegetation is a feasible strategy, but it must be based on habitat transformation. After the ecological restoration is completed, water bodies can maintain low turbidity and a high underwater PAR, and natural restoration of aquatic vegetation can be achieved,” said Dr. HUANG.
　　Cabomba caroliniana in its introduced natural habitats
　　Link: https://doi.org/10.1111/ddi.13678
　　(online on Jan. 31 2023)
　　Contact
　　TAN Lei 
　　Nanjing Institute of Geography and Limnology 
　　E-mail: ltan@niglas.ac.cn

　　Dissolved organic matter (DOM) encompasses organic carbon in aquatic systems. Climate and hydrology, land use, and trophic status can influence DOM properties in aquatic ecosystems at regional or watershed scales. 
　　Alpine river and lake systems on the Tibetan Plateau are highly sensitive indicators and amplifiers of global climate change and important components of the carbon cycle. However, knowledge about the sources and transformations of DOM throughout the aquatic continuum in alpine regions is relatively limited due to the remoteness and heterogeneity of the landscape. Specifically, there is a need to determine the extent to which DOM composition responds to hydrological controls on the Tibetan Plateau.  
　　Researchers led by Prof. ZHANG Yunlin from the Nanjing Institute of Geography and Limnology and Dr. ZHOU Lei from the Institute of Soil Sciences, Chinese Academy of Sciences, have addressed the question by investigating variability in DOM quality and quantity from headwaters and downstream rivers and lakes along the watershed of Selin Co, the largest lake in Tibet, and quantifying the novel linkages between water stable isotopes and DOM composition. 
　　Their findings were published in Environmental Science & Technology on March 9. 
　　The results show an ideal proxy of water isotopes to investigate the effect of hydrological factors, including the extent of hydrological connection, evaporation, and water retention time in this watershed. The DOC concentrations increased, whereas DOM aromaticity decreased along the river-lake continuum. Strong relationships between water isotopes and DOM composition indicate depleted DOM aromaticity and enhanced microbial activity along the flow paths with lengthened ultraviolet exposure and retention time. Glacier meltwater contributed to elevated relative abundances of aliphatic and protein-like compounds in headwater streams, reflecting the short water retention time and close contact with the catchment, and the hydrological controls on DOM composition are more pronounced in lakes than in rivers. 
　　Based on the warming and wetting trend of the climate in the Tibetan Plateau, increases in precipitation and glacier thaw may contribute to greater proportions of surface or groundwater in the rivers and lakes, altering DOM composition and potentially their biogeochemical function in surface waters on the Tibetan Plateau. 
　　“Our findings reveal the quantitative response of the DOM composition of the plateau river-lake continuum to hydrological processes, and provide a theoretical basis for predicting the impact of climate change on the carbon cycle of plateau aquatic ecosystems,” said Dr. Zhou.
　　Diagram showing changes in DOM composition throughout the river-lake continuum (Image by ZHOU Lei)
　　Link: https://pubs.acs.org/doi/full/10.1021/acs.est.2c08257   
　　Contact 
　　TAN Lei 
　　Nanjing Institute of Geography and Limnology 
　　E-mail: ltan@niglas.ac.cn