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:

Research Progress


Upcoming Events


News & Updates

Why recurring? - Positive feedback of extreme climate anomalies on cyanobacterial bloom in lakes

  Since the drinking water crisis triggered by the cyanobacterial bloom in 2007, extensive and high-intensity pollution control and ecological restoration carried out in the entire Taihu basin. 
  Ten years later, water quality improved according to some variables; however, the cyanobacterial bloom has not been effectively contained in Lake Taihu. Total phosphorus concentrations have even increased in recent years, intense cyanobacterial blooms have persisted through 2017 with a record-setting bloom occurring in May, 2017. 
  The contradiction between water quality and cyanobacteria bloom fluctuations and intensity management in Taihu Basin is confusing. The effectiveness of scientific and precise restoration of Lake Taihu has been widely questioned, further implementation of Lake Taihu management and the formulation of ecological restoration programs were also hindered. 
  Recently, an international research group led by Prof. QIN Boqiang from the Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences (NIGLAS), carried out multidisciplinary research and proposed that regional extreme climatic anomalies could intensify nutrients cycling in the water-sediment interface and promote the cyanobacterial blooms in Lake Taihu. 
  The study was recently published in Water Resources Research.
  Multi-source data analysis showed that the abnormally high rainfall in the Taihu Basin in 2016 led to a sharp increase in external loading. At the same time, the winter temperature of 2016/2017 was the highest value since the 1960s, resulting in a high value of overwintering cyanobacteria biomass. The 2015/2016 super El Nino event, coupled with warm phase of the Atlantic Multidecadal Oscillation (AMO) and Pacific Decadal Oscillation (PDO), jointly induced heavy rainfall in the Taihu Basin in 2016 and the following warm winter. 
  After the severe blooms in 2017, the pH of the water body increased and the concentration of dissolved oxygen at the bottom of the lake decreased due to photosynthesis or organic matter degradation, which promoted the internal loading and further benefit the blooms, i.e., a positive feedback among "nutrient accumulation-heavy blooms-internal loading-eutrophication aggravation”. The enhanced nutrient cycle provides a continuous nutrient for the cyanobacterial bloom persistence. 
  This research interprets that under the big picture of global warming, regional extreme climate anomalies will further deteriorate lake water quality, promote eutrophication and cyanobacterial blooms in eutrophic lakes. 
  This work was funded by the National Natural Science Foundation of China and the Water Pollution Control and Treatment Science and Technology Major Project.
  Extreme Climate Anomalies Enhancing Cyanobacterial Blooms in Eutrophic Lake Taihu, China
  Fig. 1 Long-term trends of AMO, PDO, ENSO, and their relationships related to temperature anomalies and rainfall in Tahu Basin
  Fig. 2 Conceptual diagram of a combination of climate anomalies induced internal phosphorus cycling which led to a positive feedback to ensure cyanobacterial bloom persistence
Monitoring the dissolved organic carbon budget in Taihu Lake from space

  Dissolved organic matter (DOM) refers to various organic molecules (sugars, fatty acids, and alkanes), is ubiquitous in global lakes, provides food/energy for heterotrophic bacterial growth, and serves as a carbon pool of the global carbon cycle and climate change. Moreover, colored DOM can influence phytoplankton photosynthesis through light absorption, and DOM decomposition consumes dissolved oxygen and deteriorates water quality. 
  Dissolved organic matter content is usually determined by dissolved organic carbon (DOC). With the advantage of having a high spatiotemporal resolution, satellite-based data are optimal for dynamically monitoring DOC dynamics. However, only some empirical band combination algorithms have been proposed for regional lakes, and long-term series DOC satellite products for eutrophic lakes have not been published. 
  Lake DOC has two source types. Autochthonous DOC is mainly derived from phytoplankton through extracellular release and cell degradation. Allochthonous DOC is primarily transported from the terrestrial ecosystem by input rivers. To understand the carbon cycle in a eutrophic lake, it is indeed necessary to know its DOC storage and the DOC exchange fluxes between the lake and surrounding rivers. 
  Globally, lake eutrophication is a common problem, and approximately 63% of lakes with areas > 25 km2 are characterized by eutrophication. Machine learning has achieved exceptionally satisfactory results in remotely retrieving aquatic environmental variables in complex inland waters. Taking the typical eutrophic Lake Taihu as a study area, we realize the observation of lake DOC storage and exchange flux from space. 
  For Lake Taihu, the DOC distributions were spatially consistent with those of phytoplankton content (Chl-a), and high DOC concentrations were observed in the northwestern lake bays. The satellite-derived monthly climatology DOC level displayed spatial distributions similar to those of the annual mean results, with high values in the northwest lake bays. What is noteworthy is that low DOC was observed in the Tiaoxi River estuary in the South Taihu. 
  In Lake Taihu, the annual-monthly mean DOC level increased from 2003–2018. A positive relationship was found between the annual mean DOC level and Chl-a. As with the in-situ data, satellite-derived DOC levels were high in summer July and September, when Chl-a levels were also high. In contrast, the DOC level was low in June, when high basin precipitation diluted riverine input DOC. 
  Annual input and output DOC fluxes by surrounding rivers varied greatly from year to year during 2008-2018. By dividing the lake DOC storage by the total DOC input flux, we obtained that the turnover time for riverine input DOC in Lake Taihu was approximately 24–43 days during 2008–2018. 
  Although the mean net riverine DOC input was approximately 5.2 times the lake DOC storage volume during 2008-2018, DOC variations in Lake Taihu were controlled by phytoplankton growth. Therefore, terrigenous DOC was quickly transformed into other carbon forms after entering Lake Taihu. These indicate that the low dissolved oxygen level in Lake Taihu might be related to the decomposition of the large amount of terrigenous DOC.
  Paper link:
Climate changes of northern China during the “5000-year” Chinese History
The Chinese civilization is the oldest and most enduring in the world. During its long lasting “5000-year” history, China has experienced a series of centennial-scale rise and fall of dynasties, unifications and divisions, war and peace and south-north migration of northern nomads. Climate changes have long been proposed as an important driver of these historical cultural changes through affecting phenology and land productions, especially for China as a traditional farming civilized society. As early as the 1970s, Chu, (1972) first reported the temperature history of China over the past “5000-year” based on phenological documents and pioneered the study of climate and dynasty transitions. Over the past few decades, many efforts have been taken to reconstruct the climate records, but mostly qualitatively. Lack of high-resolution, quantitative climate records, especially for the heartland of ancient Chinese culture, limits a comprehensive examination of the relation between climate and culture changes in Chinese history. A scientific research group, composed of Nanjing Institute of Geography and Limnology, Institute of Tibetan Plateau Research, Nanjing University and other institutions, presents well-dated, high resolution, quantitative warm-season temperature and annual mean precipitation records and provides a high-quality climate background for the entire “5000-year” Chinese history. Results suggest that changes in temperature and precipitation are incomplete coupled in terms of both long-term trend and centennial-scale variability before ~1000 CE (Common era). The temperature displays a slight decrease of ~0.5oC before ~200 CE and a rapid cooling of ~4oC afterwards, superimposed with four 1-2oC centennial-scale cold events. The precipitation shows high value before ~1000 BCE and a gradual decrease of ~250 mm with two distinct ~100 mm centennial scale dry intervals after ~1000 CE. Climate changes in dynastic China indicate that the Three Sovereigns and Five Emperors began in a relatively warm and wet climate, and the moderate conditions lasted until Shang Dynasty followed by a gradually cold and dry climate with large fluctuations afterward. Specifically, we find cold-dry conditions in the late Tang, Five Dynasties and Ten Kingdoms (5D&10K), late Song, Yuan, late Ming Dynasty, and only cold conditions during the period of the Spring and Autumn and Warring States (SAWS), the period of Wei, Jin and Southern and Northern Dynasties (WJSN). It shows the three long-term and large-scale social unrests (5D&10K, SAWS, WJSN) in Chinese history have experienced large climate fluctuations. Comparison of climate changes and other social factors reveals some centennial-scale cold and/or dry oscillations are also accompanied by an increase of war frequency, a sharp decline of population size and a southward migration of northern nomads during three large-scale social unrests of SAWS, WJSN and 5D&10K, and nomadic dynasties (Yuan and Qing Dynasty) when northern nomads ruled the central plains. Thus, climate fluctuations likely played an important role in affecting cultural changes in the “5000-year” Chinese history. Dynasty transitions may also be influenced by other sociocultural factors and administrative efficiency such as class struggle, peasant uprising, economic collapses and misgovernment. For example, the end of some dynasties such as Xia, Shang and Qin Dynasty occurred under a background of stable climate, and ~70 years of cold event at ~750 CE did not lead to the end of the prosperous Tang Dynasty although it likely corresponds to the famous An-Shi Rebellion. Climate change may be not a decisive factor of dynastic transitions, although it has an important impact on Chinese historical cultural changes. Therefore, we must avoid falling into the trap of “geographical determinism” when discussing the relation between both. Our high-resolution quantitative climate records just provide crucial climate context to test the hypothesis of climatic impact on historical culture changes.
  Quantitatively reconstructed temperature (a) and precipitation (b). Frequency of wars in China (c). Population size of China (d). South limit of nomadic national regime with boundary the GreatWall in Inner Mongolia (e). 
  Paper link:

Int’l Cooperation News

Pollution characteristics of persistent and toxic organic substances in lakes of Tanzania

  Due to the inadequate control of Persistent and Toxic Organic Substances (PTOS) in Tanzania, they are still many ways to transport into the lake environment, to threaten the lake ecology safety and human health. 
   To understand the status of PTOS pollution in Tanzanian lakes, Prof. Zhang Lu from the Joint Research Station for East African Great Lakes and Urban Ecology (affiliated to Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences) led a joint group with Tafiri scientiest in early 2020 to conduct a field survey on PTOS pollution in East African lakes. 
   The study of 18 lakes in Tanzania shows that the distribution of PTOS has large spatial variations. Among the lakes, the PTOS level in Lake Jipe, Mabayani Reservoir, Lake Duluti and Lake Hombolo was relatively higher, while was relatively lower in Lake Chala, Lake Small Momela, Lake Babati, Lake Singida and Lake Kindai. Overall, the pollution levels of polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs), and organochlorine pesticides (OCPs) in Tanzania lakes are relatively lighter compared to lakes worldwide. 
   Among the four major types of PTOS pollutants in Tanzania lakes, phthalate esters (PAEs) pollution is the more worthy of attention. Source identification shows that phthalate esters (PAEs), PAHs, HCHs and Methoxychlor have obvious watershed input characteristics. A multi-index comprehensive scoring method based on the measured concentrations of pollutants, the inherent properties of compounds (lipophilicity and hydrophobicity, structure-activity relationship), and lake ecological risks and health risks was proposed. Based on this method, a list of precedent-controlled PTOS pollutants (8PAEs,6 PAHs, 7 OCPs and 5 PCBs) for Tanzania lakes was built. 
   It was concluded that PAEs were the priority pollutants for drinking water safety and ecosystem health for Tanzania lakes. Therefore, Tanzania should control the production, use and emission of PAEs, especially around the lake areas, in order to reduce the impact of PTOS on lake water ecology.
  A list of precedent-controlled PTOS pollutants (8PAEs,6 PAHs, 7 OCPs and 5 PCBs) for Tanzania lakes
Tackling harmful cyanobacterial blooms with Chinese colleagues: we’re all in the same boat

  Harmful cyanobacterial blooms (CyanoHABs) are a rapidly proliferating global problem, threatening the use and sustainability of our freshwater resources. In recent decades, the United States, China, and other developed and developing countries threatened by CyanoHAB expansion have established collaborative efforts aimed at mitigating and managing this environmental and human health problem. However, an escalating negative political climate and restrictive policies on scientific exchange threaten these efforts. In this Perspective, I point to progress that has been made to counter the CyanoHAB problem on U.S.–Chinese fronts through our collaborations, which have been mutually beneficial from research and academic perspectives. Much like global efforts now needed to control pandemics, we are all “in the same boat” when to comes to countering the threat CyanoHABs pose for drinkable, swimmable, and fishable freshwater supplies and human health.
   FIG. (A) Hans Paerl collecting surface algal bloom sample at Lake Taihu, China. (B) Prof. Guangwei Xu and Hans Paerl collecting plankton samples at Lake Erhai, Yunnan Province, China. (C) Prof. Guangwei Xu and Hans Paerl, preparing nutrient addition bioassays near Lake Taihu. (D) Chinese Graduate Students and Hans Paerl filling bioassays with lake Taihu water. (E and F) U.S. and Chinese students working at the experimental mesocosm site located on the shore of Lake Taihu. (G) Hans Paerl and collaborators at the International Society of Limnology (SIL) meetings, held in Nanjing, China, August, 2018. (H) Prof, Yiping Li and Hans Paerl at a Graduate Student Symposium, Hohai University, Nanjing.
  Hans W. Paerl. 2020. JOURNAL OF PHYCOLOGY.DOI: 10.1111/jpy.13058
Radiation dimming and decreasing water clarity fuel underwater darkening in lakes

  Long-term decreases in the incident total radiation and water clarity might substantially affect the underwater light environment in aquatic ecosystems. However, the underlying mechanism and relative contributions of radiation dimming and decreasing water clarity to the underwater light environment on a national or global scale remains largely unknown. Here, we present a comprehensive dataset of unprecedented scale in China’s lakes to address the combined effects of radiation dimming and decreasing water clarity on underwater darkening. Long-term total radiation and sunshine duration showed 5.8% and 7.9% decreases, respectively, after 2000 compared to 1961–1970, resulting in net radiation dimming. An in situ Secchi disk depth (SDD) dataset in 170 lakes showed that the mean SDD significantly decreased from 1.80 ± 2.19 m before 1995 to 1.28 ± 1.82 m after 2005. SDD remote sensing estimations for 641 lakes with areas ≥ 10 km2 showed that SDD markedly decreased from 1.26 ± 0.62 m during 1985–1990 to 1.14 ± 0.66 m during 2005–2010. Radiation dimming and decreasing water clarity jointly caused an approximately 10% decrease in the average available photosynthetically active radiation (PAR) in the euphotic layer. Our results revealed a more important role of decreasing water clarity in underwater darkening than radiation dimming. A meta-analysis of long-term SDD observation data from 61 various waters further elucidated a global extensive underwater darkening. Underwater darkening implies a decrease in water quality for potable water supplies, recession in macrophytes and benthic algae, and decreases in benthic primary production, fishery production, and biodiversity.
  Spatial distribution of SDD differences during 2005–2016 compared to the 1960s–1995 (a), comparison of SDDs before 1995 to after 2005 according to the five geographic lake zones and the Hu Huanyong Line (b and c) for the dataset of 170 lakes.
  All: all lakes; EPL: Eastern Plain Lake zone; YGPL; Yunnan-Guizhou Plateau Lake zone; NPL: Northeast Plain Lake zone; IMXL: Inner Mongolia-Xinjiang Lake zone; TPL: Tibetan Plateau Lake zone; NW and SE represent results for lakes in the northwestern and southeastern regions of the Hu Huanyong Line.
  Yunlin Zhang, Boqiang Qin, Kun Shi, Yibo Zhang, Jianming Deng, Martin Wild et al., 2020. Science Bulletin. DOI:
Climate mediates continental scale patterns of stream microbial functional diversity

  Understanding the large-scale patterns of microbial functional diversity is essential for anticipating climate change impacts on ecosystems worldwide. However, studies of functional biogeography remain scarce for microorganisms, especially in freshwater ecosystems. Here we study 15,289 functional genes of stream biofilm microbes along three elevational gradients in Norway, Spain and China.
  We find that alpha diversity declines towards high elevations and assemblage composition shows increasing turnover with greater elevational distances. These elevational patterns are highly consistent across mountains, kingdoms and functional categories and exhibit the strongest trends in China due to its largest environmental gradients. Across mountains, functional gene assemblages differ in alpha diversity and composition between the mountains in Europe and Asia. Climate, such as mean temperature of the warmest quarter or mean precipitation of the coldest quarter, is the best predictor of alpha diversity and assemblage composition at both mountain and continental scales, with local non-climatic predictors gaining more importance at mountain scale. Under future climate, we project substantial variations in alpha diversity and assemblage composition across the Eurasian river network, primarily occurring in northern and central regions, respectively.
  We conclude that climate controls microbial functional gene diversity in streams at large spatial scales; therefore, the underlying ecosystem processes are highly sensitive to climate variations, especially at high latitudes. This biogeographical framework for microbial functional diversity serves as a baseline to anticipate ecosystem responses and biogeochemical feedback to ongoing climate change.
  Félix Picazo, Annika Vilmi, Juha Aalto, Janne Soininen, Emilio O. Casamayor, Yongqin Liu, Qinglong Wu, Lijuan Ren, Jizhong Zhou, Ji Shen & Jianjun Wang*. Microbiome. 2020. DOI:10.1186/s40168-020-00873-2