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

Research Progress

More

Upcoming Events

More

News & Updates

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
  
Urbanization in developing countries overrides catchment productivity in fueling inland water CO2 emissions
2022-10-17

  Carbon emissions from rivers, lakes, and reservoirs comprise a large proportion of the global carbon cycle and have attracted extensive attention from scholars worldwide. In recent years, studies on the carbon emission from inland waters in China have been focused on single lakes or rivers, and the influences of anthropogenic disturbances on inland water carbon emissions have received continuous attention. Several studies have investigated the emission fluxes of carbon dioxide (CO2) from inland waters in China, but to date none of them have unraveled the underlying factors driving CO2 emissions.
  Recently, the research group led by Prof. Yunlin Zhang from the Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences compiled meta data from the literatures with measured data on efflux of CO2 from inland waters and obtained a total of 1405 measurements, including 658 river sites, 625 lake sites, and 122 reservoir sites sampled primarily between 2010 and 2020, and investigated the effluxes of CO2 and drivers across inland waters in China. This work was published on Global Change Biology.
  Based on a series of data sharing platforms, including the Resource and Environmental Science and Data Center, Chinese Academy of Sciences, and the National Earth Science Data Center of China, etc, the scientists obtained a series of data products including land use and land cover, gross primary productivity (GPP) and net primary productivity (NPP) at spatial resolutions of 30 m and 1 km. The scientists then extracted data on catchment %urban and agricultural land use, gross domestic product (GDP), population density, NPP, topsoil organic carbon, topsoil pH, and precipitation. The driven mechanisms of CO2 efflux from lakes, reservoirs and rivers in China were then unraveled.
  Notably higher CO2 efflux from rivers than from lakes and reservoirs was found and altogether a total of 61.9 ± 55.3 TgC was emitted from Chinese inland waters annually. The effluxes of CO2 from rivers and lakes increased significantly with the increasing catchment %urban land use, and CO2 effluxes of lakes and reservoirs increased significantly with increasing catchment %agricultural land use. The effluxes of CO2 from lakes, reservoirs, and rivers increased with increasing catchment GDP and population density. In comparison, no significant relationships were found between the CO2 efflux and catchment annual NPP, topsoil organic carbon concentration, pH of topsoil, or catchment precipitation.
  Previous studies have found that compared to less populated regions, an increase in population density results primarily in eutrophication of inland waters caused by the discharge of agricultural, industrial, and residential effluents, as well as nonpoint sources of organic carbon. In eutrophic waters, primary production is commonly increased with high amounts of bio-labile organic matter, favoring microbial degradation and thereby strongly enhancing the CO2 production and emission from inland waters.
  These results suggest that anthropogenic disturbances in relation to urbanization and agricultural land use can influence CO2 emissions from inland waters more than catchment productivity, which previously has been identified as the main driver for CO2 emissions from inland waters in less populated regions. This work demonstrated that the presence of anthropogenic disturbances in catchments, represented by urban and agricultural land use, GDP, and population density, were positively related to the emission of CO2.
  This work highlighted the high importance of in situ production of CO2 via the degradation of household effluents, nonpoint source- and algal-organic carbon in catchments draining densely populated areas compared with CO2 being directly delivered through inflowing catchment streams.
  In the foreseeable future, more land will be transformed from natural forest and grassland into residential areas or agricultural land use, especially in developing countries. Such land use alterations will not only change the terrestrial carbon cycle but as shown here, also the inland water carbon cycle.
   Relationships between the efflux of CO2 and the mean catchment %urban land use (b), %agricultural land use (c), gross domestic production (GDP, d), population density (e), net primary productivity (NPP, f), topsoil organic carbon (SOC, g), topsoil pH (h), and precipitation (i) of each sampling site collected from lakes, reservoirs, and rivers.
  Link at https://doi.org/10.1111/gcb.16475.
  
Anthropogenic eutrophication of shallow lakes: Is it occasional?
2022-06-23

  According to the report of ‘The Fifth Global Environment Outlook’ by the United Nations Environment Program, more than 40% of water bodies all over the world are suffering eutrophication. Lake eutrophication is a great international concern because of its economic and ecological consequences.
  Anthropogenic eutrophication of lake ecosystems is a widely acknowledged, but largely unresolved, especially for some large shallow lakes (Okeechobee, Winnipeg, Erie, Great Salt, and Champlain in North America, Lough Neagh, Peipsi, and Malaren in Europe, and Taihu, Chaohu, and Dianchi in China). It is worth thinking about why shallow lakes appear to be prone to eutrophication and resistant to restoration.
  It is well recognized that the prevalence of lake eutrophication varies with respect to watershed geology, climate, land use, landscape position, connectivity, and lake morphology, each of which varies with lake district or ecoregion. However, most researches studied their effects on lake eutrophication separately, and relatively little is known of how these factors interact. A holistic understanding of lake eutrophication and improved lake management strategies requires freshwaters to be considered as part of an integrated socio-ecological system. There is a profound need to better understand the susceptibility of lakes to eutrophication to safeguard these systems for a sustainable future.
  To protect lake ecosystems and achieve the Sustainable Development Goals identified by the United Nations, a group of Chinese scientists led by Prof. Boqiang Qin from the Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences analyzed 1151 lakes with area ≥ 0.5 km2 located within the Europe and the United States of America to identify how lake morphology and regional social-ecological systems interact to affect the susceptibility of lakes to anthropogenic eutrophication.
  Their findings were published in Water Research.
  The findings demonstrate that lake depth is linked to the ecoregion and land use of lake ecosystems, which largely determines the intensity of human activities and, consequently, lake productivity. Specifically, lakes distributed in agricultural plain and densely populated lowland areas were generally shallow and subjected to intense human activities with high external nutrient inputs. In contrast, deep lakes frequently occurred in upland regions, dominated by natural landscapes with little anthropogenic nutrient input. Moreover, lake depth appeared to not only reflect external nutrient load to the lake, but also acted as an amplifier that increased shallow lake sensitivity to anthropogenic disturbance.
  The susceptibility of lake to anthropogenic eutrophication, and consequently the risk of water quality issues, is not the same for all lakes. The findings suggest that shallow lakes are more susceptible to human forcing and are predisposed to receiving large quantities of nutrients, their eutrophication may be not an occasional occurrence. Special attention should be given to shallow lakes that are at high risk of waters quality degradation and eutrophication, yet may be more resistant to restoration compared to deep lakes.
  In the future, increased agricultural production to meet demands for food and energy will intensify both point and diffuse sources nutrients. Many shallow lakes already exhibit eutrophic conditions, yet lie in watersheds where further eutrophication may be an inevitable rather than an occasional occurrence.
  This information may help clarify why shallow lakes are prone to eutrophication and why some efforts to control eutrophication have resulted in frustratingly slow or modest effects in shallow productive lakes. This study helps set realistic goals and adjusts community expectations to advance the protection and restoration of lakes globally. It may be a challenge that convincing stakeholders continue to invest in nutrient reductions without evidence of rapid improvement, but it is necessary for long-term water quality improvement. The findings are expected to increase understanding for limnologists, stakeholders, and managers.
  Lake depth relates the effects of external nutrient input and in-lake biogeochemical processes to regulate the productivity of lake ecosystems.
  Generally, shallow lakes lie in naturally fertile plain and lowland regions, where they are exposed to strong anthropogenic disturbances (agriculture and urban development) and are predisposed to receiving large quantities of nutrients due to extensive drainage networks. In contrast, deep lakes are frequently concentrated in poor upland regions (mountains and highlands) with mainly natural land cover (e.g., forest and shrubland), low degrees of human disturbance, and limited nutrient input. Compared to deep lakes, shallow basins often have a small volume and weak capacity to dilute input nutrients resulting in high sensitivity to anthropogenic forcing. In addition, strong water-sediment interactions are more common and sediment is more prone to resuspension in shallow lakes, leading to elevated internal nutrient loading and higher productivity. Collectively, shallow lakes in agricultural or populated regions may be particularly susceptible to eutrophication and their eutrophication may be not an occasional occurrence.
  Paper link: https://www.sciencedirect.com/science/article/pii/S0043135422006819
   
   
   
   
   
   
   
   
  
More

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.
More