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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Anthropogenic eutrophication of shallow lakes: Is it occasional?

  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:
  TAN Lei
  Nanjing Institute of Geography and Limnology
With nitrogen use, soil inorganic carbon is significantly lost

  Researchers from Institute of Soil Science Chinese Academy of Sciences (ISSCAS), Nanjing Institute of Geography and Limnology Chinese Academy of Sciences (NIGLAS), and other 25 universities and research institutes have revealed that soil inorganic carbon (SIC) is not temporally stable due to soil acidification, which is different from the traditional viewpoint. The study was published recently in National Science Review.
  Unlike soil organic carbon (SOC), SIC was frequently disregarded, as its cycling is much slow and the mean residence time is about 78,000 years.
  “Environmental changes, including the use of chemical fertilizers, global warming and atmospheric acid deposition, can cause significant global soil acidification, especially in cropland, which may accelerate SIC turnover,” said Dr. ZHANG Gan-Lin from NIGLAS.
  “We didn’t know how much SIC has been lost during last decades at a continental scale like China, due to data limitations.” To quantify these changes, researchers conducted a national resampling campaign in the last decade and collected legacy soil data as much as possible. The national soil data in the 1980s were taken as control plots. By comparing the SIC data in the 1980s and 2010s, they found that approximately half of the pairs exhibited a clear declining trend.
  “It is a clear evidence of SIC loss,” said Dr. Zhang. “This result is consistent with the findings of similar studies conducted at the regional scale and can provide an important observational benchmark.”
  They also performed the modeling to map the spatial distribution of SIC and estimated the total changes in SIC stock over the last 30 years. The machine learning technique was used to combine soil data at different sites with the environmental covariates that control SIC turnover. It is evidenced that soil acidification caused by enhanced nitrogen precipitation, together with nitrogen fertilizer application is accounted for SIC reduction. A mass of SIC was found in the subsoils regardless of the ecosystems. The total SIC has decreased by approximately 1.37±0.37 Pg C. About 19% of current SIC stocks are projected to disappear by 2100.
  Most of the lost SIC is believed to be converted to CO2 and released to the atmosphere. In general, the SIC losses across China and in cropland can offset approximately 18%-24% of the terrestrial biomass organic carbon sink and 57% of the SOC sink in cropland, respectively.
  The study reveals that the consumption of SIC may offset a large portion of the global efforts aimed at ecosystem carbon sequestration, which emphasizes the importance of better understanding the indirect coupling mechanisms of nitrogen and carbon cycling and of effective countermeasures to minimize SIC loss.
  Paper link:
  TAN Lei
  Nanjing Institute of Geography and Limnology
Seasonal imprint of Holocene temperature reconstruction on the Tibetan Plateau

  Quantitative reconstruction of Holocene paleotemperature is crucial for understanding the evolution of the climate system in an ice-free world and assessing the position of recent global warming within the context of natural climate variability. During the Holocene (between 11.5 and 0 ka BP), the initial compilation of reconstructed global temperature records showed a steady cooling trend, conversely, the simulated Holocene temperature exhibited a general warming trend. The discrepancy between model simulations and proxy reconstructions is colloquially referred to as the “Holocene temperature conundrum”.
  The Tibetan Plateau (TP), located in southwest China, is the highest plateau of the Earth and is one of the most sensitive areas to climate changes with twice as much warming as the global average for the past decades. Many efforts have been taken to reconstruct temperature changes using multiple proxies from various types of geological archives on the TP during the Holocene. However, these paleotemperature reconstructions show complex and even contrasting results and the mechanism underlying such contrasting patterns of temperature changes still remains unclear.
  A scientific research group, composed of Nanjing Institute of Geography and Limnology, Nanjing University, Institute of Tibetan Plateau Research and other institutions, presents a well-dated, high resolution, quantitative ice-free-season temperature record over the past 19 ka from a small alpine lake on the southeastern TP based on branched glycerol dialkyl glycerol tetraethers (brGDGTs) proxy. The reconstructed temperature displays a long-term ~4°C warming trend during the past 19 ka with a deglacial increase of ~3°C and Holocene increase of ~1°C.
  This study reviews 16 published quantitative paleotemperature records since the Last Deglaciation, to better understand the pattern and mechanism of postglacial temperature changes on the TP.
  “Results suggest that a general warming pattern without seasonal biases during the Last Deglaciation but divergent trends of seasonal temperatures during the Holocene with a gradual cooling pattern in summer temperature, an overall warming pattern in winter temperature, and a complicated annual temperature,” said ZHANG Can, first author of the study.
  The inconsistence among annual temperature records is mainly attributed to the length of ice-free season by comparing the geographic background of proxy-reconstructed data. For the ice-free lakes at low altitude regions, lake water temperature covaries with local air temperature and proxy-reconstructed temperature can really reflect the annul mean temperature changes. In contrast, for the high-altitude lakes with the frozen nature, proxy-reconstructed temperature mainly records air temperature changes during the ice-free season due to the isolation between lake water temperature and atmospheric temperature during the cold season.
  According the season differences of proxy-reconstructed temperature, the results reveal an overall cooling pattern for summer temperature, a warming trend for winter temperature, annual temperature, and spring-autumn temperature, and a warming-cooling-warming pattern in warming-season temperature. The reconstructed temperature gradually shifts from the “annual temperature-like” pattern to the “summer temperature-like” pattern with decreasing length of ice-free season.
  “In addition, the TraCE-21ka model results show a remarkable similarity with our composite temperature records of proxy reconstructions for all seasons, and further indicate that the Holocene temperature changes are mainly controlled by the coupling of local seasonal insolation and GHGs on the TP,” ZHANG said.
  Their findings were published in Earth-Science Reviews.
  Paper link:
  Location and topographical setting of the Tibetan Plateau. (a) Map showing the location of the Cuoqia Lake (CQ Lake, red circle, No. 1) and other paleotemperature records (No. 2–16) reviewed in this study. Filled circle, triangle, and square denote lake, peatland, and ice core, respectively.
  Comparison of the composite and simulated temperature records for different seasons on the TP. (a) summer temperature, (b) winter temperature, (c) annual temperature, (d) ice-free-season (March–October) temperature (TM-O), and (e) warm-season (May–September) temperature (TMJJAS). (f) Global temperature anomaly from proxy reconstruction and model-simulation. (g) Dome C ice-core record of the atmospheric CO2 concentration.
  Schematic diagram showing the proxy-reconstructed temperature changes and the driving mechanisms. The length of ice-free season decreases with increasing altitude so that proxy-reconstructed temperature is increasingly skewed toward warm-season. Holocene temperature changes for different seasons are mainly controlled by the coupling of local seasonal insolation and GHGs.TS = summer temperature; TMJJAS = temperature from May to September; TM-O = temperature from March to October; TA = annual temperature; ﹢ = positive correlation; ﹣ = negative correlation.
  Contact information
  TAN Lei
  Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences

Int’l Cooperation News

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
Data construction and spatiotemporal trend attribution of runoff over the African Continent (1981–2016)

  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.
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