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
  Schedule
  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: wsgs@niglas.ac.cn ltan@niglas.ac.cn

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News & Updates

Researchers conclude the critical controls for spatial patterns of soil δ15N in different climate zones of the globe
2023-01-12

  The natural abundance of soil nitrogen (N) stable isotope (δ15N) is a good proxy indicating the integrative soil N cycling processes and fluxes over long time scale. 
  However, its spatial pattern in the globe is not well understood, mostly due to the inconsistent relationships between soil δ15N and the relevant environmental variables found in different regions. In addition, the association with soil water content (SWC), which is a critical factor regulating soil N cycling process, has drawn less attention. 
  Therefore, researchers led by Prof. ZHU Qing from Nanjing Institute of Geography and Limnology of the Chinese Academy of Sciences investigated the relationship between soil δ15N and SWC at global scale, and accordingly explored the key controls of soil δ15N in different climate zones. 
  The hypothesis is that investigating the relationship between soil δ15N and SWC can help to explain the controls of the spatial pattern of soil δ15N across regions, as SWC was also controlled by interactions among climate, soil and vegetation. 
  This work was recently published on Catena. 
  Results revealed an upward-concave relationship between soil δ15N and SWC based on the soil δ15N and SWC data in 910 grids of the globe. Higher soil δ15N existed at both the dry and wet ends of the SWC. In addition, inconsistent relationships in five Koppen-Geiger climate zones constituted this upward-concave relationship. “Our findings are expected to deepen understandings on the spatial pattern of soil δ15N and the indicated N cycle at the global scale,” said Prof. ZHU. 
  Positive relationship between soil δ15N and SWC in the Tropical zone determined the increasing trend of soil δ15N at the wet end in the globe. It was mainly casued by the hydrologically regulated soil N losses. Increased SWC under the warm and moist condition would promote the denitrification and thus a lot of N gaseous losses as N2O and N2, and also trigger surface runoff and subsurface flow, and thus drive dissolved and particulate N losses.
  Negative relationship in the Arid zone determined the decreasing trend at the dry end in the globe. Increased proportions of abiotic N losses like ammonia volatilization and N supplement through bedrock weathering (higher δ15N) with the decrease of SWC under the dry, hot and infertile soil condition may be the main reasons. 
  Poor relationships between soil δ15N and SWC in the Temperate, Cold and Polar zones constituted the transition range of the upward-concave relationship in the globe. Not hydrologically regulated but climatically limited determined the low soil N losses and thus low soil δ15N in these zones.
  (a) Global distributions of five Koppen-Geiger climate zones and the classifications of soil δ15N according to the climate zones. (b) Boxplots of the soil δ15N and SWC in five climate zones. (c) Biplot of the standardized soil δ15N and SWC. (Image by LAI Xiaoming) Links: https://www.sciencedirect.com/science/article/pii/S0341816222008657 Contact TAN Lei Nanjing Institute of Geography and Limnology E-mail: ltan@niglas.ac.cn
China Daily: Reports underscore better environment
2022-12-29

  Visitors walk through the East Lake National Wetland Park in Wuhan, Hubei province, in February. [Photo by Zhang Liewen/For China Daily]
  Data, surveys display improvement in quality of lakes, wetlands, air over decade
  China's ecology and environment have undergone historic and profound improvement over the last decade, according to a series of reports published by the Chinese Academy of Sciences on Tuesday.
  The five reports feature the latest data and survey results of national freshwater resources, wetlands, mountains, water conservation in arid northwest areas, and environmental conditions in the country's three major urban clusters: Beijing-Tianjin-Hebei, the Yangtze River Delta, and Guangdong-Hong Kong-Macao Greater Bay Area.
  According to the reports, China had 2,670 natural lakes over 1 square kilometer in size in 2020, totaling 80,662 sq km. The water quality of 70 percent of mid-size to large lakes has improved over the decade.
  This has also led to the gradual increase of biodiversity in lake systems. In Poyang Lake, China's largest freshwater lake, the number of wintering waterfowl rose from 357,000 to 689,000, from some 50 species of birds.
  Wetlands are a major ecosystem rich in biodiversity and also regulate water and filter waste from the landscape, hence their nickname of the "kidneys of the Earth".
  China has one of the world's largest and most diversified wetland ecosystems, the reports said. In 2020, it had 412,000 sq km of wetlands, the most in Asia.
  Chinese wetlands currently hold over 55.5 billion metric tons of fresh water, and each hectare of wetland can remove 1,000 kilograms of nitrogen and 130 kg of phosphorus on average per year.
  From 2015 to 2020, the total area of wetlands underwent a net increase of 903 sq km. By the end of 2020, there were nearly 1,200 artificial wetlands, 750 more compared to a decade ago.
  China's wetlands are rich in biodiversity, hosting over 1,691 species of flora and 296 wetland bird species. About 73 of these plants and 91 of the bird species are rare and protected.
  "The role of wetlands in safeguarding water and ecological security is becoming more prominent. They also play an important role in addressing global climate change," the reports said.
  With nearly two-thirds of its land covered by mountains and plateaus, these ecosystems play a crucial role in providing natural resources, biodiversity, and safeguarding environmental security, the reports said.
  Over the past decade, natural mountain conservation areas have increased by 14.4 percent to around 1.17 million sq km. As for water conservation in the northwest, the surface water area has increased by 161 sq km on average annually for nearly a decade. Water use in agriculture has also decreased from 95.8 percent in 2012 to 90.9 percent in 2021.
  Beijing-Tianjin-Hebei, the Yangtze River Delta, and the Guangdong-Hong Kong-Macao Greater Bay Area urban clusters account for around 5 percent of China's land area, but are home to 25 percent of its population and contribute nearly 40 percent of its GDP.
  "They are the core engines of economic growth, but intense levels of human activity have placed enormous stress on the ecology and environment," the reports said.
  Over the last decade, environments in the three regions have steadily improved, most notably in terms of air quality.
  From 2012 to 2021, the annual PM2.5 density decreased by 53.1 percent in Beijing-Tianjin-Hebei, 54.2 percent in the Yangtze River Delta, and 47.2 percent in the Guangdong-Hong Kong-Macao Greater Bay Area.
What water color parameters could be mapped using MODIS land reflectance products?
2022-11-18

  Satellite ocean color instruments have been used to characterize physical, chemical, and biological variabilities in oceanic, coastal, and inland waters. However, the massive loss and large uncertainty results of remote sensing reflectance data in difficulty in monitoring nearshore coastal and inland waters. The ocean color community has been pursuing easy-access and reliable reflectance products for observing nearshore coastal and inland waters.
  Most of the coastal and inland waters are generally turbid; in these areas, the contribution of water to the signals of the top of the atmosphere is raised, suggesting the possibility reality for oceanographers and limnologists to use land reflectance products for water monitoring. MODIS surface reflectance product (R_land) has been used to monitor water clarity and suspended solids in waters yet the applications to retrieve phytoplankton pigments and colored dissolved organic carbon has rarely been addressed. To date, its applicability in aquatic remote sensing has not been sufficiently assessed. Some fundamental questions such as the following need to be addressed: How does the R_land product perform in global inland and coastal waters? What water color parameters can be mapped using R_land?
  Recently, a research group led by Prof. Hongtao Duan and Ronghua Ma from the Nanjing Institute of Geography and Limnology of the Chinese Academy of Sciences provided a comprehensive evaluation of the performance of MODIS R_land products against a field optical dataset containing 4143 reflectance spectra, 2320 chlorophyll-a samples, and 1467 suspended particulate matter samples across global nearshore coastal and inland waters.
  This work was published in Earth-Science Reviews.
  "Despite the ease of using this product and its higher spatial resolution than the MODIS ocean bands, according to our assessment, R_land might not be an optimal data source for monitoring inland and coastal waters," said Prof. Duan.
  The results showed that R_land significantly overestimated remote sensing reflectance, particularly in 469 nm and 859 nm bands. Such a global assessment was consistent with the results published in Lake Taihu and Chesapeake Bay before. In addition, land reflectance showed evident overestimations compared to the ocean color products derived using SeaDAS software in the east China Sea.
  The study also reported noticeable negative values and patchiness in the R_land imagery. The proportion of R_land at 555 nm is even beyond 5% in the coastal area of Australia and Africa. R_land was frequently negative in the pixels covered by cyanobacterial scums, e.g., >20% negatives in Lake Taihu. "The negatives and patchiness in R_land possibly resulted from the unsuitable mechanism to remove aerosols in generating R_land over waters, " said Prof. Ma.
  Existing algorithms did not estimate satisfactory Chla and suspended solids from R_land across the global inland and coastal waters. Machine learning models outperformed the state-of-the-art algorithms for SPM retrievals in global turbid waters from R_land. But, all models, including machine learning models, cannot retrieve reliable chlorophyll-a from R_land with approximately 55% uncertainty due to the limited spectral information and uncertainty of R_land products. This implicated that R_land might be able to quantify the parameters closely related to suspended solids (e.g., water clarity and extinction coefficients) in most waters; however, it is challenging to quantify pigments like Chla in waters from R_land.
  This study comprehensively evaluated the accuracy of R_land for the first time in global inland and coastal waters. MODIS R_land does not contain sufficient information that makes these existing algorithms usable. Consequently, various water color parameters from R_land are difficult to retrieve except for several parameters, such as SPM, turbidity, and water clarity. The results are anticipated to provide a benchmark of R_land in various waters worldwide.
   
  Link at https://doi.org/10.1016/j.earscirev.2022.104154
   
  Contact
  TAN Lei
  Nanjing Institute of Geography and Limnology
  E-mail: ltan@niglas.ac.cn
  
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Int’l Cooperation News

A comprehensive evaluation of organic micropollutants (OMPs) pollution and prioritization in equatorial lakes from mainland Tanzania, East Africa
2022-05-17

  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, https://doi.org/10.1016/j.watres.2022.118400.
Re-evaluation of Wetland Carbon Sink Mitigation
2022-03-22

  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: https://link.springer.com/article/10.1007/s13157-022-01539-5 
Estimating seasonal water budgets in global lakes by using multi-source remote sensing measurements
2021-10-14

  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 Hydrology.doi.org/10.1016/j.jhydrol.2020.125781
Data construction and spatiotemporal trend attribution of runoff over the African Continent (1981–2016)
2021-06-25

  Due to global climate change, coupled with the increase in population, growth in water withdrawals, expansion of farmland area and reduction of forest, the surface runoff process in Africa has undergone major changes and extreme hydrological events have been occurred frequently, which has caused greater impact on the production and life of the people. 
  In order to systematically understand the response of runoff trends to climate change and human activities, the research team of Researcher Prof. Liu Yuanbo from the Nanjing Institute of Geography & Limnology, Chinese Academy of Sciences (CAS) constructed improved monthly runoff data for the African continent from 1981 to 2016 based on the river discharge data from 535 gauging stations using a revised runoff curve number, downscaling and interpolation statistical methods. Then, monthly and annual runoff data, climate data (precipitation and temperature) and human activities (farmland expansion and water withdrawal) were used to assess runoff trend responses to climate change and human activities in Africa during 1981–2016. Related results were published in the Journal of Hydrometeorology. 
  Analysis of runoff trend responses to climate change and human activities revealed that land cover changes contributed more (72% a-1) to the observed net runoff change (0.30% a-1) than continental climate change (28% a-1). These contributions were results of cropland expansion rate of 0.46% a-1 and precipitation increase of 0.07% a-1. The annual runoff trends were 0.21% a-1 in the tropical region, 0.16% a-1 in the temperate region and 0.91% a-1 in the arid region. The runoff increase in the tropical region was fully caused by human activities, with a contribution to net runoff increase of 160% a-1 due to cropland expansion by 0.53% a-1. Climate change was responsible for an increased runoff in the temperate and arid regions, with contributions of 102% a-1 and 117% a-1, respectively. 
  Land cover change was the dominant cause of increased annual runoff, with trends ranging from 0.06% a-1 to 1.38 % a-1 in 7 of the 25 major river basins, including the Africa–Indian Ocean Coast, Limpopo, Shebelle–Juba, Volta, Gulf of Guinea, Africa–East Central Coast and Madagascar due to cropland expansion trends (0.02% a-1 – 1.03% a-1). The Orange, Namibia–Coast, Africa–Red Sea–Gulf of Aden Coast and Zambezi basins experienced runoff reduction (-0.15% – -1.88%) due to the increase in water withdrawal (1.80% a-1 – 3.23% a-1). 
  Climate change was the dominant factor that induced annual runoff change in 14 of the 25 major basins, where 11 basins (Africa–South Interior, Africa–West Coast, Nile, Angola–Coast, Rift Valley, Africa–North West Coast, Niger, Mediterranean South Coast, Africa–North Interior, Lake Chad and Senegal) had runoff increase (0.08% a-1 – 1.76% a-1) due to precipitation increase (0.15% a-1 – 0.73% a-1). Three basins (South Africa–West Coast, South Africa–South Coast and Congo) experienced runoff reduction (-0.89% a-1 – -0.02% a-1) due to precipitation decrease (-0.11% a-1 – -0.55% a-1) and temperature rise (0.07% a-1 – 0.17% a-1). 
  The performance and simplicity of the statistical methods used in this study could be useful for improving runoff estimations in other regions with limited streamflow data. The results of the current study could be important to natural resource managers and decision makers in terms of raising awareness of climate change adaptation strategies and agricultural land-use policies in Africa.
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