The 3rd International Symposium on Watershed Geographic Sciences (ISWSGS2020)

  ISWSGS2020 (the 3rd International Symposium on Watershed Geographic Sciences) will be held online from October 17 to 18, 2020. This symposium is organized by the Key Laboratory of Watershed Geographic Sciences, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences. The theme of the symposium is “Watershed geography and interdisciplinary sciences”. This symposium aims to provide a forum for the exchange of the latest research achievements on watershed geography and other related sciences. World leading scientists are invited to present keynotes covering the latest advances in soil and water processes, human geography, remote sensing and watershed management.
  Topics include
  1. Observation and monitoring at multiple scales
  2. Integrated watershed modeling of multi-processes
  3. Watershed soil and water processes and their environmental impacts
  4. Human activities, processes and driving mechanism in watersheds
  5. Sustainable development and watershed planning
  6. Watershed integrated management and spatial optimization
  7. Other topics relevant to watershed geography
  October 17 2020 for local participants’ arrival
  October 18 2020 for keynote speeches online
  Information and contacts
  Tel: +86 25 8688 2083
  Fax: +86 25 5771 4759
  Add: 73 East Beijing Road, Nanjing, China
  General enquiry:

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Satellites Reveal Hotspots of Global River Extent Change

  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)
  TAN Lei 
  Nanjing Institute of Geography and Limnology 
High Tolerance of the Invasive Submersed Plant Cabomba Caroliniana to Underwater Light Attenuation May Facilitate Its Invasiveness

  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
  (online on Jan. 31 2023)
  TAN Lei 
  Nanjing Institute of Geography and Limnology 
Researchers Reveal Quantitative Response of the DOM Composition to Hydrological Processes in the Watershed of the Largest Lake in Tibet

  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)
  TAN Lei 
  Nanjing Institute of Geography and Limnology 

Int’l Cooperation News

Sediment organic matter properties facilitate understanding nitrogen transformation potentials in East African lakes

  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,
A comprehensive evaluation of organic micropollutants (OMPs) pollution and prioritization in equatorial lakes from mainland Tanzania, East Africa

  A lack of understanding the fate of highly toxic organic micropollutants (OMPs) in the equatorial lakes of Tanzania hinders public awareness for protecting these unique aquatic ecosystems, which are precious water resources and stunning wildlife habitats. To address this knowledge gap, the occurrence of 70 anthropogenically-sourced OMPs, including phthalates (PAEs), polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs), was investigated in the water and sediment of 18 lakes in Tanzania. Similar residue concentrations were found in both compartments, showing higher pollution of PAEs ranging from 835.0 to 13,153.1 ng/L in water and 244.6–8691.8 ng/g dw in sediment, followed by PAHs, while OCPs and PCBs were comparatively lower. According to the multi-criteria scoring method for prioritization, the final OMP priority list for the lake environment in Tanzania comprised 25 chemicals, specifically 5 PAEs (DEHP, DIBP, DBP, DCHP and DMPP), 6 PCBs (PCB153, PCB105, PCB28, PCB156, PCB157 and PCB167), 6 PAHs (BaP, BaA, BbF, Pyr, DahA and InP) and 8 OCPs (cis-chlordane, trans-chlordane, p,p’-DDD, p,p’-DDE, p,p’-DDT, endrin, methoxychlor and heptachlor epoxide), suggesting the key substances for conventional monitoring and pollution control in these equatorial lakes, with an emphasis on PAEs, especially DEHP, due to the top priority and endocrine disruptor properties.
  Zhonghua Zhao, Xiaolong Yao, Qiqi Ding, Xionghu Gong, Jianjun Wang, Saadu Tahir, Ishmael Aaron Kimirei, Lu Zhang, A comprehensive evaluation of organic micropollutants (OMPs) pollution and prioritization in equatorial lakes from mainland Tanzania, East Africa, Water Research, Volume 217, 2022, 118400, ISSN 0043-1354,
Re-evaluation of Wetland Carbon Sink Mitigation

  A new review of coastal and inland wetland carbon sink services reveals current mitigation concepts for greenhouse gas emissions and measurements are not what they seem. Accumulation of buried organic carbon is not a measure of carbon sequestration; stable organic carbon inputs require subtraction and are undervalued; and carbon mitigation from wetland restoration is less than their preservation. 
  The study was published in the journal Wetlands as a flagship Mark Brison Review, from Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences (NIGLAS) in collaboration with Borneo Marine Research Institute (BMRI) Universiti Malaysia Sabah (UMS), and lead by the Institute for Marine and Antarctic Studies (IMAS) University of Tasmania (UTAS).  
  Associate Reseacher Dr John Barry Gallagher (IMAS) said that the sediment organic carbon accumulation down inland and coastal wetlands has always been regarded as a convenient means of measuring trends and average rates of sequestration over climatic scales. Wetlands, however, are open to organic inputs from catchments and adjacent water bodies. These can be labile and easily consumed or decomposed, and recalcitrant outside the carbon loop that is not consumed or decomposed. 
  Consequently, what is required from the sediment record is not the total organic burial, but the burial rate of what remains of the wetlands plant production from the amount of the labile organics inputs consumed, and the remains of those recalcitrants inputs, largely black or pyrogenic carbon. To estimate this we modified a general decomposition model to hindcast the original input rate and to project what remains for all organic sources after 100 years of burial. 
  For a mangrove and a seagrass ecosystem, we found that carbon accumulation was on average 33.5 and 7.2 times greater than their respective sequestration rates. We also noted that sequestration relative to its non-canopy replacement or alternative stable state is not included for voluntary or compliance carbon markets, instead, only the rate of loss and gain of organic stocks for wetlands likely be disturbed or restored. This limitation would otherwise undervalue the wetlands systems mitigation potential with one caveat: the rate of gain in sediment stocks for a restored system is similarly constrained as a mitigation service by consumption and decomposition of those external organic inputs. 
  Dr Gallagher says that the review is important from two standpoints. Firstly, natural carbon sequestration solutions require re-evaluation. This is required to avoid GHG emissions above their capacity or indeed reduce the ability to fulfil Nations’emission targets, as set by COP26. Secondly, the model provides a new Paleoecological tool. It has the potential to measure and predict how wetlands' ability to function as a carbon sink can change with both climate and catchment agricultural and industrial development from changes to government policy.
  Paper link: 
Estimating seasonal water budgets in global lakes by using multi-source remote sensing measurements

  The seasonal change in lake water storage (LWSsc) reflect periodic fluctuations of the basin-scale water balance. However, the role of LWSsc in regulating the water budget at the global scale has not yet been investigated based on straight-forward observations. Quantifying LWSsc is necessary, especially under the context of global change. Available in-situ measurements of lake water levels and volumes are still scarce. Therefore, the Global Surface Water datasets of Joint Research Centre and multi-source satellite altimetry datasets through mathematical statistics methods are used in this study to address this issue. We estimate the LWSsc of 463 lakes and reservoirs worldwide with areas greater than 10 km2, which represent nearly 64% of the total global lake area and 93% of the total lake volume capacity. Results show that the global seasonal water storage variation of these examined water bodies is 1390.91 ± 78.91 km3, comprising 869.44 ± 67.35 km3 from lakes and 521.46 ± 41.11 km3 from reservoirs. The relatively large estimates of LWSsc are concentrated in North American and African basins. Among the watersheds, the seasonal fluctuations of lakes in the North American Lawrence basin make up the most substantial magnitude of 10.76% of the global LWSsc. The latitudinal direction zonality of LWSsc is relatively significant. The LWSsc is concentrated between 30° N and 60° N in the northern hemisphere and between the equator and 30° S in the southern hemisphere. Considering the geographic similarity and climatological zonality, the global LWSsc estimates are also extrapolated to other lakes without direct satellite altimetry observations on the basis of the average rate of the examined lakes distributed in the same Koppen-Geiger Climate Classification zones. The LWSsc is calculated with a consequence of 488.23 ± 14.72 km3 for these extrapolated lakes, indicating an estimate of 1357.67 ± 68.94 km3 for the LWSsc of the global natural lakes (>10 km2). This initial estimation of LWSsc at a global scale will greatly help the improvement of our understanding of the seasonal behavior of lakes and reservoirs in regulating global and regional water cycles and the contribution of terrestrial water storage to sea level rise.
  CHEN Tan, SONG Chunqiao, KE Linghong et al. Journal of