Chinese scientists: Technology-driven and law-based system key to lake ecosystems, biodiversity protection by Zhang Weilan, June 25, 2023 “We should integrate our technological resources and build up a sound technological support system, accelerating the building of relevant law & regulation systems for lake protection and management,” Zhang Ganlin, director and researcher of the Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences(CAS), notes in an article released by the Bulletin of Chinese Academy of Sciences (BCAS, in Chinese), a think tank journal supervised and sponsored by the CAS, which focuses on strategic and decision-making research. Among important land resources and as key geographical units of land surface systems, lakes(including artificial reservoirs) are important surface water resources, and they are also an important part of the earth surface system consisting of “mountains,rivers, forests, farmland, lakes, grassland and sand,” as Zhang points out in his article “Ecological and Environmental Changes and Protection Measures of Lakes in China.” The article also notes that lakes play an irreplaceable role in water resource supply, flood control and drought alleviation, water quality purification, and biodiversity protection. Given the important roles and significance of lakes in socio-economic development, the article, based on long-term lake research and monitoring data, proposes the strategies for the protection, management, and restoration in response to the problems faced by lake ecosystems in China. In recent years, the overall condition of the ecological environment of lakes in our country has been becoming better, and the protection to lakes has achieved remarkable results. For example, the water quality of Poyang Lake, which is located in the eastern plains of China has shown a trend of improvement in recent years, and the annual average concentration of total phosphorus, the main pollutant, has declined slightly. From 2012 to 2020, the inter-annual variation of wetland vegetation biomass in Poyang Lake was flat, and the variation range was relatively small. Since 2012, the importance value of the dominant species of the typical plant communities in Poyang Lake wetland have remained above 0.6, showing a relatively stable community structure and playing an important supporting role in the stability of the ecosystem structure and the maintenance of ecological functions in the lake. The paper also reveals that for the past decades, China has strengthened ecological conservation and environment protection at all times and in all dimensions and regions. Since 2021, China has achieved initial success in the critical battle against water pollution. Major action plans on addressing water pollution have been fully implemented. Also, the country has redoubled efforts to preserve and restore lake ecosystems and protect biodiversity, with the integrated protection and restoration of various ecosystems and implementation of a series of fundamental, pioneering, and long-term programs. First, a significant increase can be seen in the total amount of available freshwater resources in lakes. There are 2,670 natural lakes over 1 km2 of area in China, and 98,600 reservoirs with an increase of 10,100 over 2011. Thanks to the lake protection and water quality improvement, the proportion of centralized drinking water sources from lakes and reservoirs across China has increased from 33% to 40% in the past five years, which serves nearly 50% of the population of the country. Second, the lakes under priority control have reported steady improvement of water quality. For instance, the “three lakes” (the Taihu Lake, Chaohu Lake and Dianchi Lake), have registered significantly checked eutrophication trend. With the increase in the transparency of about 70% of large and medium-sized lakes in China in the past 10 years, the lakes have become clearer overall. Third, with the restoration of the aquatic vegetation in lakes and the steady rise in the biodiversity of major lakes, the lakes have reported improvement of ecological service functions. This has been approved by the fact that about 43% and 40% showed a significant improvement of aquatic vegetation between 2010-2014 and between 2015-2019, respectively. However, China still needs to continue with science and technological innovation in lake ecological environment management and protection. There are significant rooms for development of higher level processing materials, key technologies, and equipment, and relevant basic and applied research. Therefore, Chinese scientists have put forward several key approaches to exploring the paths to high-quality development for lake watersheds with low resource consumption and environmental costs. Among all the suggestions, the article attaches great importance to building a technology-driven and law-based system, in an effort to protect lake ecosystems and biodiversity in China. More efforts should be made to set up sound systems in the following areas: performance evaluation and accountability for ecological conservation, compensation for ecological conservation, designation of river and lake managing chiefs. Meanwhile, corresponding laws and regulations should be further formulated or revised. The article further explains that it is necessary to strengthen the role of technology in supporting the lake-type ecological environment protection, that is to say, to integrate all possible technological resources and build up a sound technological support system, and vigorously promote the technology-based lake manager system to further enhance the scientific management and protection of lakes. National legislation for lake protection should also be promoted, accelerating the building of relevant law & regulation systems for lake protection and management and improve the mechanism for the alignment between administrative law enforcement and criminal justice in lake watershed protection. On the institutional level, it is advised to adopt an “ecological bank” model and improve the compensation system for the ecological benefits of lakes.

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Greening land significantly reduced suspended sediment flux in China’s major rivers

  Sediment in rivers plays an essential role in the river and watershed ecosystems. A recent paper (Science, 24 June 2022, p. 1447-1452) reported widespread decreases in river sediment fluxes for major rivers in the North Hemisphere and concluded that these decreases mainly resulted from dam construction. 
   Generally, the spatial and temporal variations in river sediment are regulated by climate change and human activities, including precipitation, land cover and land use, damming, and dredging activities. In addition to dams, what is the contribution of changes in land cover to the decrease in sediment flux in rivers? 
   Recently, a research team led by Dr. CAO Zhigang and Prof. DUAN Hongtao (Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, China) and Prof. YANG Hong (University of Reading, the UK), collected long-term in-situ sediment flux data from seven major rivers in China. The team found that large dams on the Yangtze River, Zhu River, and Yellow River significantly reduced the sediment fluxes in the first 5-10 years following dam construction. However, the sediment fluxes in these rivers did not continue to decrease as before but even increased. 
   Their findings were published in Science Bulletin on October 30, 2023. 
   “Besides dams, there must be other factors that continuously reduce sediment fluxes after dams have been operational for many years,” said Prof. DUAN. 
   The researchers further used satellites to obtain a long-term dataset of vegetation coverage and suspended sediment concentration in China’s major rivers. The team found that vegetation cover in river catchments significantly increased in the 1980s and correlated well with the variations in sediment concentration. 
   “The variations in sediment fluxes in estuaries resulted from the combined effects of dams and land cover change in the watershed,” said Dr. CAO. 
   “Undoubtedly, anthropogenic activities have altered the landscape in the watershed in various ways. Our analysis demonstrated a significant relationship between vegetation cover in the watershed and river sediment, suggesting that the greening of Chinese land mainly induced by afforestation in the watersheds significantly reduces sediments in rivers,” said Prof. YANG. 
   This study illustrates that greener land exerted essential controls on reducing soil erosion and sediment loads into China's rivers. To a certain extent, while the influence of dam construction on river sediment was dramatic, the impact of land use change was even more profound. 
  In the past two decades, China has implemented several massive ecological restoration programs, including afforestation and the “Grain for Green” project, which significantly increased terrestrial vegetation. Greening land is another crucial strategy to reduce sediments in rivers, and it can also increase carbon sequestration and enhance other ecological services. 
   See the article: 
  Remarkable effects of greening watershed on reducing suspended sediment flux in China major rivers
   TAN Lei 
   Nanjing Institute of Geography and Limnology 
How do temperate lakes respond to atmospheric warming?

  As the atmosphere warms up, so do most freshwater lakes. But this isn’t always the case, and little is known about why. 
  Now, an international team led by the Nanjing Institute of Geography and Limnology of the Chinese Academy of Sciences, sampled 345 lakes distributed across twelve countries, primarily in the United States and Europe, for the controls of thermal response of temperate lakes to atmospheric warming study. 
  This study was published in the leading journal Nature Communications on October, 16. 
  The team found that the rate of lake heating slows as air warms. The differences in local climate, land cover, geomorphology, and water transparency can help explain why the rate of lake heating doesn’t necessarily match the rate of air warming. 
  Especially, lakes with more nutrient pollution – lakes that have layers of green on top of them – are less sensitive to global warming than lakes that are clear, and less polluted. The green lakes are already damaged by human activities in the surrounding landscape. Too many nutrients from land results in green surface waters that act as a shade, keeping the deep waters cool. But greener lakes also lose more oxygen from deep water which results in more fish dying. 
  There is some good news. As lakes warm up, they start to lose water by evaporation and this acts to cool them off. “Just like we sweat to cool off, lakes ‘sweat’ by evaporating water to get rid of excess heat,” says Dr. ZHOU Jian, the first author on the study. 
  “While the good news is that lakes can cool themselves for a period of time by sweating – which protects biodiversity in lakes, recreational fishing, and some aspects of water quality – it’s a short-term measure because those same lakes are losing water. Unfortunately, just like we can become dehydrated if we don’t drink, lakes can’t cool off by evaporation forever, because they will eventually dry out and disappear,” says Dr. Peter Leavitt, the co-author from University of Regina. 
  The researchers also discovered that despite what we may think, remote, deep lakes, especially those at high elevation and far from human activity, are actually more sensitive to atmospheric warming. 
  “Clear lakes aren’t already damaged by human activities, so they more readily respond to human-caused atmospheric warming,” says Prof. SHI Kun, the co-author on the study. 
  Therefore, one-size-fits-all responses to global warming and land-use change won’t work. “Instead, our lake management practices need to consider where lakes are, what they are surrounded by, and how sensitive they might be to unique and interactive effects of climate change and human activities,” says Prof. QIN Boqiang, the co-author on the study.
   TAN Lei 
   Nanjing Institute of Geography and Limnology 
Satellite Helps Monitor Microcystin Risk in Lakes at Large Scale

  Safe and clean drinking water is a fundamental human right. Lakes are the most important drinking water sources. /p>
   However, under the combined impact of climate changes and human activities, many lakes around the world are experiencing eutrophication and cyanobacterial blooms, which in turn pose a serious threat to drinking water safety by microcystins (MCs) produced by the cyanobacteria. 
  Recently, researchers led by Prof. DUAN Hongtao from the Nanjing Institute of Geography and Limnology of the Chinese Academy of Sciences have developed an assessment scheme for human health risks of MCs in lakes from space. 
  The research findings were published in Water Research on October 15, 2023. 
  " MCs do not absorb or scatter light, making them undetectable by optical sensors directly," said Prof. DUAN. "Therefore, the key to monitoring MCs from satellites is to find a surrogate optical water quality parameter that links them to remote sensing signals." 
  "MCs are secondary metabolites of cyanobacteria, so they have good relationships with pigment concentrations such as chlorophyll-a and phycocyanin," said Dr. SHEN Ming, first author of the study. "In particular, phycocyanin is a unique pigment of cyanobacteria and responds to environmental factors similar to MCs." 
  Utilizing this relationship, the research group developed a "two-stage" remote sensing assessment scheme for MCs health risks: an enhanced random forest regression model for phycocyanin concentration was developed, and the MCs were estimated from derived phycocyanin concentrations. Subsequently, the hazard quotient (HQ) method was used to evaluate the health risks of MCs.
  The analysis showed that in eastern China, most large lakes have experienced high risks exceeding one pixel (300m×300m) at least once, but the frequency of high risks is only around 1% in most water areas.This indicates that from the perspective of MCs, most water bodies can still be designated as water sources for drinking water, but management authorities need to take measures against cyanobacterial blooms.
  "Our study emphasizes the potential of satellite remote sensing in monitoring and assessing MCs risks and ensuring drinking water safety. It provides a technical reference for advancing the implementation of the sustainable development goal 6.1 (safe and affordable drinking water)." said Prof. DUAN.
  Figure: remote sensing assessment scheme for microcystin health risks (by SHEN Min) Link: 
   TAN Lei 
   Nanjing Institute of Geography and Limnology 

Int’l Cooperation News

Synergistic effects of warming and internal nutrient loading interfere with the long-term stability of lake restoration and induce sudden re-eutrophication

  Urban lakes are globally ubiquitous and are usually highly eutrophic, pointing to an increase in frequency, duration and magnitude of harmful algal blooms as wide-spread threats to ecological and human health. 
  Over half a century, phosphate (P) precipitation is among the most effective treatments to mitigate eutrophication in these lakes. However, after a period of high effectiveness, re-eutrophication would possibly occur leading to the return of harmful algal blooms. While such abrupt ecological changes were presumably attributed to internal P loading, the role of lake warming and its potential synergistic effects with the internal loading, thus far, has been largely understudied. 
  Researchers led by Dr. KONG Xiangzhen and Prof. Dr. XUE Bin from the Nanjing Institute of Geography and Limnology of the Chinese Academy of Sciences, along with their international collaborators, have addressed the question by quantifying the contributions of lake warming and the potential synergistic effects with internal P loading in an urban lake located in central Germany, which suffered from the abrupt re-eutrophication and cyanobacterial blooms in 2016 (30 years after the first P precipitation). 
  Their findings were published in Environmental Science & Technology on Feb. 20. 
  In this study, a process-based lake ecosystem model (GOTM-WET) was established using a high-frequency monitoring dataset covering eutro-/oligo-trophic states over 30 years. 
  Model analyses suggested that, for the abrupt occurrence of cyanobacterial blooms, internal P release accounts for 68% of the biomass proliferation, while lake warming contributed to 32%, including both direct effects via promoting growth (18%) and synergistic effects via intensifying internal P loading (14%). The model further revealed that the synergy was attributed to prolonged lake hypolimnion warming and oxygen depletion. 
  “Our study exemplifies how process-based mechanistic modeling could help to tease apart important drivers of abrupt shifts and cyanobacterial blooms in lakes, particularly in an era of rapid global changes including climate change and human activities.” said Dr. Kong. 
  This study unravels the substantial role of lake warming in promoting cyanobacterial blooms in re-eutrophicated lakes. The indirect effects of warming on cyanobacteria via promoting internal loading need more attention in future lake research and management. 
  “Our findings will have far-reaching consequences for lake restoration and management as the nutrient targets we applied so far to reach or maintain a certain trophic state will not work in a far warmer future and need to be adjusted, i.e. stronger nutrient level reduction and higher efforts in restoration are demanded.” said Dr. Kong.
  TAN Lei 
  Nanjing Institute of Geography and Limnology 
Sediment organic matter properties facilitate understanding nitrogen transformation potentials in East African lakes

  East African lakes include the most productive and alkaline lake group in the world. Yet, they generally receive fewer nutrient inputs than the densely populated subtropical and temperate lakes in the northern hemisphere. In these lakes with insufficient supplies of inorganic nitrogen, the mineralization of benthic organic matter can play an important role in driving the nutrient cycle and nitrogen loss. Using a suite of stable 15N isotope dilution and tracer techniques, we examined five main processes of the sediment nitrogen cycle in 16 lakes and reservoirs of Tanzania and Kenya, East Africa: gross nitrogen mineralization, ammonium immobilization, dissimilatory nitrate reduction to ammonium (DNRA), and the dinitrogen (N2) production via denitrification and anaerobic ammonium oxidation (anammox). Gross nitrogen mineralization and ammonium immobilization showed the maximum values of 9.84 and 12.39 μmol N kg-1 h-1 , respectively. Potential DNRA rates ranged from 0.22 to 8.15 μmol N kg-1 h-1 and accounted for 10 %–74 % (average 25 %) of the total dissimilatory nitrate reduction. Potential nitrate reduction rates in most lakes were dominated by denitrification with a contribution of 26 %–85 % and a mean of 65 %. We further found that the sediment nitrogen transformations were driven mainly by benthic organic matter properties and water column phosphate concentrations, reflecting microbial metabolic responses to the changing carbon and nutrients availability. For instance, autochthonous production of protein-like organic matter attributed to active sediment nitrogen mineralization, DNRA, and denitrification. In contrast, the high degree of humification caused by the inputs of terrestrial humic-like substances slowed down the sediment nitrogen transformations. The contribution of DNRA to total dissimilatory nitrate reduction was significantly positively correlated to sediment C: N ratios. These results indicate that predictions of sediment N supply and loss in East African lakes can be improved by incorporating sediment organic matter properties.
  Xiaolong Yao, Zhonghua Zhao, Jianjun Wang, Qiqi Ding, Minglei Ren, Ismael Aaron Kimirei, Lu Zhang, Sediment organic matter properties facilitate understanding nitrogen transformation potentials in East African lakes, Science of The Total Environment, 841, 2022, 156607,
A comprehensive evaluation of organic micropollutants (OMPs) pollution and prioritization in equatorial lakes from mainland Tanzania, East Africa

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

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