Fuxian Lake Research Articles

Light Bridge and Magnetic Field in a Solar Active Region

Observational data from the Helioseismic and Magnetic Imager on board the Solar Dynamics Observatory and the multiwavelength simultaneous imaging system attached to the New Vacuum Solar Telescope located at Fuxian Lake, China are employed for the study of light bridges and magnetic fields in the active region NOAA 12529. Coronal fields in this active region are computed with a boundary integration model and the field line connectivity in the dominant spot is investigated with the squashing factor Q. Quasi separatrix layer intersections in the CCD coordinate plane are determined according to values of Q. It is found that weak field lanes (WFLs) appear in the umbra and penumbra; open and closed flux systems are separated by QSLs in the dominant spot; and WFLs and QSLs look quite different from each other in the dominant spot but partially overlap in the umbra. Our study demonstrates that WFLs cannot be attributed to topological evolution of magnetic fields and might be regarded as rifts among splitting flux systems.

Geochemical characteristics of n-alkanes in sediments from oligotrophic and eutrophic phases of five lakes and potential use as paleoenvironmental proxies

Profiles of n-alkane proxies in sediment cores have been frequently used to detect historical trends in the nutrient status of lakes. However, the results obtained from these proxies are occasionally confusing because the situations in which a given n-alkane proxy might make a valid indication have tended thus far to be elusive. The current study compared geochemical characteristics of n-alkanes in sediments from the oligotrophic (before 1950) and relatively eutrophic phases (after 1980) of five representative lakes in order to assess their suitability and reliability as proxies for lake trophic state. The results from Lakes Liangzi, Changdang, Taibai and Erhai demonstrated that short-chain odd carbon n-alkane abundances were significantly higher (P < 0.05) in sediments deposited after 1980 than in those dating to before 1950, whereas TAR (terrigenous: aquatic ratios) and ACL15–33 (average chain length of C15–C33n-alkanes) were significantly lower (P < 0.05) in the more recent sediments. These results are compatible with generally accepted variation seen in lakes that have undergone eutrophication. In Lake Fuxian, however, short-chain odd carbon n-alkane abundances, TAR and ACL15–33 were all higher in sediments after 1980 than in sediments before 1950, although the variation was only significant (P < 0.05) for ACL15–33. These results, especially the unexpected trends in TAR and ACL15–33, mean these cannot be relied upon as proxies for eutrophication in this lake. The anomaly is likely to be related to the predominantly low phytoplankton productivity and OM input in Lake Fuxian, coupled with the availability of OM from submerged macrophytes in the relatively eutrophic phase. Interestingly and importantly, two new proxies CPI15–20 ((n-C15 + n-C17 + n-C19)/(n-C16 + n-C18 + n-C20) alkanes) and n-C17/n-C16 alkane, which are indicative of OM input from phytoplankton over non-photosynthetic bacteria, were significantly higher (P < 0.05) in post-1980 sediments than in those dating to before 1950 in all five studied lakes. These two are thus shown to be widely applicable for recording lake eutrophication. Their presence in Lake Fuxian can be explicitly attributed to the absence of influence from submerged macrophytes. Moreover, as ratio results of n-alkanes with similar carbon number, these two proxies are less influenced by processes of OM diagenesis due to comparable degradation of n-alkanes in sediments. The combined results suggest that these previously overlooked proxies may be of considerable value to studies of lake trophic history.

Characteristic study of microplastics distribution and response to human activities in nine highland lakes in Yunnan province

Nine highland lakes in Yunnan Province—Dian Lake, Erhai Lake, Fuxian Lake, Qilu Lake, Yilong Lake, Xingyun Lake, Yangzonghai Lake, Chenghai Lake, and Lugu Lake—were the principal objects of this study. To investigate the microplastic pollution patterns in highland lakes and to identify the most effective microplastic monitoring techniques, the distribution characteristics, abundance, and species of microplastics in the water bodies and sediments of nine highland lakes were scientifically sampled and analyzed in this study. To better understand the relationship between the level of economic development, the intensity of human activity and the level of governmental attention to environmental protection, the strength of the general public's environmental awareness, and the level of microplastic pollution in the Yunnan region, this study also looked into the areas surrounding nine highland lakes. To analyze and study the relationship between the distribution characteristics of microplastics in water bodies and sediments in the nine lakes and external natural conditions, additional external factors, such as geographic location and climatic conditions of the study area of the nine highland lakes, were collected and collated.

Assessing the role of internal phosphorus recycling on eutrophication in four lakes in China and Malaysia

Internal phosphorus recycling (IPR) is an important nutrient source driving algal growth and eutrophication in lakes. The complexity of eutrophication behaviours caused by high IPR complicates lake management and undermines restoration efforts. Hence, knowledge about the possible types of bifurcation behaviours caused by high IPR is essential for effective and sustainable lake eutrophication management. For this purpose, numerical bifurcation analysis is performed on an algae‑phosphorus model to investigate how IPR drives complex and rich eutrophication behaviours in two tropical and two subtropical lakes. The two tropical lakes are Tasik Harapan and Sunway Lagoon in Malaysia, while the two subtropical lakes are Lake Fuxian and Lake Taihu in China. For each specified level of IPR, co-dimension one bifurcation analysis is performed by means of XPPAUT. Co-dimension two bifurcation analysis is then carried out by means of MatCont. At low IPR, Lake Fuxian exhibits reversible behaviour, accompanied by higher external phosphorus loading (EPL) thresholds. Lake Fuxian is also more conducive to stable equilibrium and its lake dynamics are easily predictable. At moderate IPR, Sunway Lagoon is likely to exhibit stable equilibrium, accompanied by possible shifting between two stable steady states (hysteresis behaviour) and oscillations. With higher IPR, Lake Taihu and Tasik Harapan are prone to irreversibility, accompanied by lower EPL thresholds. Because of increased complexity in lake dynamics in Lake Taihu and Tasik Harapan, small changes in EPL or in algal mortality rates could trigger various transitions in lake dynamics. Overall, high IPR can trigger unexpected sharp increases in algal concentration and can reduce the resilience of an oligotrophic lake. For shallow lakes, high IPR would cause unexpected sharp increases in algal concentrations, undermine resilience of lakes, complicate lake management, and delay lake recovery process.

In-lake processing counteracts the effect of allochthonous input on the composition of color dissolved organic matter in a deep lake

Color dissolved organic matter (CDOM) plays a key role in lacustrine ecosystems and its composition is commonly mediated by the allochthonous input and autochthonous production. Deep lakes have a strong in-lake processing, which highly affects the sources, composition and cycle of CDOM. Here, the second deepest lake (Lake Fuxian) in China was selected to investigate the effects of allochthonous input and in-lake processing on lacustrine CDOM in deep lakes. Firstly, a detailed survey on CDOM composition across Lake Fuxian in the top water layer and inflowing rivers was carried out in the wet season representing the allochthonous input. In addition, CDOM in Lake Fuxian was compared with those in other lakes with distinct catchment characteristics and lake morphology. The results showed that compared to lacustrine CDOM in Lake Fuxian, the riverine CDOM contained much more humic-like substances, resulting in the humic-like fluorescence intensity peaked at the confluence of rivers into Lake Fuxian. In contrast, CDOM in Lake Fuxian was dominated by the protein-like substance. Comparison of CDOM composition among Lake Fuxian (well-vegetated catchment, deep lakes) with other diverse lakes in China (shallow/deep lakes with poor-vegetated catchment, and shallow lakes with well-vegetated catchment) showed similar CDOM quality in all type lakes, which were dominated by non-humified and autochthonous CDOM. Yet, CDOM quantity increased as the orders of deep lakes within poor-vegetated (Tibetan deep lakes) < the deep lake within well-vegetated catchment (Lake Fuxian) < shallow lakes within poorly-vegetated catchment (Tibetan shallow lakes) < shallow lakes within well-vegetated catchment (lakes along the middle and lower reaches of Yangtze River). Our results evidenced that the effect of allochthonous input on CDOM composition could be counteracted by in-lake processing in deep lakes. For deep lakes, a comprehensive understanding of in-lake processing of CDOM is critical for predicting lacustrine DOM composition and cycle.

Ecological Assessment Based on Remote Sensing Ecological Index: A Case Study of the “Three-Lake” Basin in Yuxi City, Yunnan Province, China

With continuous urbanization, human activities have left considerable impacts on the ecology. Therefore, it is necessary to perform timely and objective monitoring and evaluation of the ecology. With the basin of three highland lakes (Fuxian Lake, Xinyun Lake, and Qilu Lake) in Yunnan Province as the study case, four indices, i.e., the Normalized Difference Vegetation Index (NDVI), the Wet Index (WET), the Normalized Differential Build-Up And Bare Soil Index (NDBSI), and the Land Surface Temperature (LST), which indicate, respectively, greenness, humidity, dryness, and heat of the study area, were extracted. On the basis of five sets of terrestrial images of the areas around the three lakes from 2001 to 2021, principal component analysis (PCA) was performed on these four indices; the more informative principal component contribution was selected as the weight to establish a remote sensing ecological index (RSEI) evaluation model to evaluate the ecological environment quality of the study area; the Mann–Kendall test combined with Sen’s slope (Sen + MK) and the Hurst exponent were employed to explore the ecological conditions and development trends of the “three-lake” basin. The results showed that the ecological quality of the study area improved and then deteriorated from 2001 to 2021. The ecological quality classes in the study area were fair, medium, and good. The ecological quality has been greatly improved, but poor ecological quality was still observed in some regions such as Chengjiang. Eighty-eight percent of the study area witnessed a stable trend in the ecological quality over the 20 years; in 2021, the area of built-up land with fair and poor ecological quality reached 140.97 km2, which occupies 68.1% of the total area under the same land use type. Analysis shows that urban area expansion and human activities have exacerbated ecological problems of towns and built-up land in the study area. In the selected indicators, both greenness and humidity are positive indicators to ecological quality, and the R2 value of the two in 5-year regression was both greater than 0.99, which validated the reliability of the selected model indicators. The research findings are expected to provide a basis for scientific ecological planning and restoration of lake basins.

Sedimentary records and stable lead isotopes reveal increasing anthropogenic impacts on heavy metal accumulation in a plateau lake of China over the last 100 years

Plateau lakes in China are faced with heavy metal contamination. The present study investigated the concentrations, sources, and ecological risks of 11 heavy metals in sediments of Lake Fuxian over the last 100 years. The concentrations of V (124–244 mg/kg), Cr (69.3–127 mg/kg), Cu (59.4–105 mg/kg), Ni (36.0–66.3 mg/kg), and Co (15.4–25.5 mg/kg) significantly decreased in the last 100 years while Cd, Sb, Pb, and Zn had contrary trends. In the last 100 years, correlations between the heavy metals changed in reverse due to the combined influences of lithogenic and anthropogenic sources. In the last 40 years, the lithogenic sources mainly contributed to the concentrations of As, Hg, V, Cr, Co, Ni, and Cu, with the rates of 55 %− 85 %. Moreover, Cd, Sb, Pb, and Zn were mainly affected by anthropogenic sources (e.g., mining activities and human settlement change), with the contribution rates of 53 %− 80 %. The change of stable Pb isotope in the sediment cores indicated that galena mining was the main source of Pb. With increasing anthropogenic activities, there was a possibility of 90 % that a moderate ecological risk might appear in the last 40 years. Among the heavy metals, Cd should attract attention because it contributed 96 % to the combined ecological risk.

Dissolved oxygen concentrations influence the distribution of isoGDGTs in a deep Lake Fuxian in China: Implications for the use of TEX86 in stratified lakes

The TEX86 (tetraether index of 86 carbon atoms) temperature proxy has been widely applied to marine settings. The application of TEX86 in lakes, however, is more complicated, as many other factors, such as dissolved oxygen (DO), also appear to influence the lacustrine TEX86 signal. In order to better understand how DO content affects TEX86, we analyzed an annual cycle of isoGDGT distributions and abundances in the water column (0–100 m) of Lake Fuxian, in southwest China. It appears that isoGDGTs in suspended particulate matter (SPM) of the water column are mainly produced by aquatic Group I.1a Thaumarchaeota. The peak concentration of total isoGDGTs occurs mainly in June and December, which is probably driven by release of nutrients during phytoplankton blooms with a lag of about one month. About 95% of isoGDGTs occurred in the bottom water layer (hypolimnion) of this thermally stratified lake, indicating that Thaumarchaeota prefer to live in suboxic water conditions in Lake Fuxian. IsoGDGT-2 is the most sensitive component to monthly variations in DO contents. This relationship leads to a similar negative correlation between TEX86 and DO. When TEX86 values, especially at the hypolimnion, are lower than anticipated, this is caused by %isoGDGT-2 falling below 45%. Conversely, a warm bias of TEX86 arising from a %isoGDGT-2 greater than 45% appears to be associated with lower DO contents. Therefore, this threshold of %isoGDGT-2 could be used in future paleoclimate reconstructions (of Lake Fuxian, and possibly similar lakes), especially since Thaumarchaeota typically reside at suboxic water layers.

Comparison of multimodel simulations of land use and land cover change considering integrated constraints - A case study of the Fuxian Lake basin

The simulation and future prediction of spatial and temporal land use and land cover change (LUCC) have long been the focus (and challenge) of research on land use change and sustainable development. However, the existing research lacks empirical comparisons among different simulation models under the same conditions in the same region; hence, the most accurate simulation results cannot be obtained through the optimal model. In this paper, taking the Fuxian Lake basin as an example, the CA-Markov, FLUS, and PLUS models are adopted to explore the optimal model for simulating LUCC in this basin by integrating restricted areas of LUCC. This study shows the following. (1) The simulation results are more accurate under the joint restrictions of open water, prohibited development zones and ecological protection red lines than under a single restriction. (2) All three models can simulate the LUCC in the Fuxian Lake basin. Among these models, the PLUS model has the highest simulation accuracy in simulating LUCC at the basin scale and offers the best match of land types in terms of their quantity and spatial distribution. (3) The PLUS model can accurately predict the changes of LULC in the Fuxian Lake basin. The results of this study should help decision makers evaluate land use development patterns and provide a reference for the formulation of regional sustainable development policies.

Lake metabolic processes and their effects on the carbonate weathering CO2 sink: Insights from diel variations in the hydrochemistry of a typical karst lake in SW China

The precipitation of carbonate minerals does not invariably result in CO2 emission to the atmosphere, because dissolved inorganic carbon (DIC) can be partially utilized by terrestrial aquatic phototrophs, thus generating an autochthonous organic carbon (AOC) sink. However, little is known about the potential effects of this mechanism on carbon cycles in DIC-rich lakes, mainly due to the lack of detailed documentation of the related processes, which limits our ability to accurately evaluate and predict the magnitude of this carbon sink. We conducted field observations in Fuxian Lake, a large and representative karst lake in the Yunnan-Guizhou Plateau, SW China. Continuous diel monitoring was conducted to quantitatively assess the coupled relationship between lake metabolism and DIC cycling and its influence on the carbonate weathering-related CO2 sink. We found that the diel physicochemical variations and isotopic characteristics were mainly controlled by the metabolism of aquatic phototrophs, evidenced by a significant relationship between net ecosystem production and diel DIC cycling, and demonstrating the significance of DIC fertilization in supporting high primary production in karst lakes. The data showed that a reduction in photosynthesis occurred in the afternoon of almost every day, which can be explained by the lower CO2/O2 ratio that increased the potential for the photorespiration of aquatic plants, thus reducing photosynthesis. We found that a net autotrophic ecosystem prevailed in Fuxian Lake, suggesting that the lake functions more as a sink than a source of atmospheric CO2. Considering carbonate weathering, the estimated AOC sink amounted to 650–704 t C km−2 yr−1, demonstrating both the potentially significant role of metabolism in lacustrine carbon cycling and the potential of the combination of photosynthesis and carbonate weathering for carbon sequestration. Our findings may help to quantitatively estimate the future impact of lake metabolism on carbon cycling, with implications for formulating management policies needed to regulate the magnitude of this carbon sink.

Self-Assembled Supercrystals Enhance the Photothermal Conversion for Solar Evaporation and Water Purification.

Photothermal materials can convert renewable solar energy into thermal energy and have great potential for solar water evaporation. Copper sulfide (Cu2- x S) is an easily available and inexpensive plasmonic material with a high photothermal conversion efficiency and can be applied to solar evaporation and water purification. Monodispersed Cu7 S4 nanoparticles (NPs) and supercrystalline self-assembled superparticles are obtained via wet chemical synthesis and micelle self-assembly. The photothermal properties of the superstructures are investigated using the finite difference time domain method and laser radiation photothermography. The results show that the electromagnetic field intensity and photothermal efficiency of the self-assembly are significantly higher than those of isolated NPs, which is due to the plasmonic coupling of the NPs. The evaporation efficiency of the superstructure is significantly higher than that of isolated NPs, the metal salt ion and total organic carbon concentrations in the waterbody significantly decrease after evaporation, and the water polluted by high salt and organic dye concentrations is purified. The water quality significantly improves after the lake water from Fuxian Lake in the Yunnan-Guizhou Plateau of China is used for solar evaporation. The color changes from pale yellow to colorless and the ion and total organic carbon contents significantly decrease.

Large alpine deep lake as a source of greenhouse gases: A case study on Lake Fuxian in Southwestern China

Freshwater lakes are recognized as potential sources of greenhouse gases (GHGs) that contribute to global warming. However, the spatiotemporal patterns of GHG emissions have not been adequately quantified in large deep lakes, resulting in substantial uncertainties in the estimated GHG budgets in global lakes. In this study, the spatial and seasonal variability of diffusive GHG (CO2, CH4, and N2O) emissions from Lake Fuxian located on a plateau in Southwestern China were quantified. The results showed that the surface lake water was oversaturated with dissolved GHG concentrations, and the average concentrations were 24.25 μM CO2, 0.044 μM CH4, and 14.28 nM N2O, with diffusive emission rates of 8.82 mmol CO2 m−2 d−1, 31.94 μmol CH4 m−2 d−1, and 4.94 μmol N2O m−2 d−1, respectively. Diffusive CH4 flux exhibited high temporal and spatial variability similar to that in most lakes. In contrast, diffusive CO2 and N2O flux showed distinct seasonal variability and similar spatial patterns, emphasizing the necessity for increasing the temporal resolution in GHG flux measurements for integrated assessments. Water temperature and/or oxygen concentrations were crucial in regulating seasonal variability in GHG emissions. However, no limnological parameter was found to govern the spatial GHG patterns. The frequent advection mixing caused by wind-driven currents might be the reason for the low spatial heterogeneity in GHGs, in which the inconspicuous mechanism requires further research. It was recommended that at least 11 locations were needed for representative whole lake flux estimates at each sampling campaign. In addition, the maximum peak of CH4 in the oxycline from Lake Fuxian indicated that low CH4 oxidation occurred in oxic waters. Overall, this study suggests that, compared to other tropical and temperate lakes, this alpine deep lake is a minor CO2 and CH4 source, but a moderate N2O source, which are horizontally uniform.

Navicula fuxianturriformis sp. nov. (Bacillariophyceae), a new species from southwest China

Navicula fuxianturriformis sp. nov., collected from Lake Fuxian, Yunnan Province, China, is described as a new species based on light and scanning electron microscope observations. N. fuxianturriformis sp. nov. has lineolate areolae closed by hymenes internally and a peculiar structure of the raphe system where the raphe is elevated internally on a thin longitudinal rib that is laterally expanded at the central area; features that assign it to the genus Navicula. The key diagnostic features of this new species include: 1) lanceolate valves with the cuneate to apiculate apices, 2) mostly long, slit-like, partly round-rectangular areolae on the valve exterior and round to rectangular areolae internally, 3) external distal raphe fissures that are hooked opposite one another, and 4) the oval-elliptical central area, with two to five pairs of irregularly shortened striae. This combination of features distinguishes N. fuxianturriformis from congers such as N. turriformis, N. turris, N. reinhardtii, N. hoevsgoelreinhardtii, N. mongolreinhardtii, N. apiculatoreinhardtii or N. apiculatoreinhardtii f. biseriata. A discussion of the morphological features of this taxon and morphologically-similar species is presented. These findings increase our understanding about the morphology and distribution of the genus Navicula in China.

The succession of submerged vegetation in the northern part of Lake Fuxian and its ecological indication significance(1987-2020)

抚仙湖有近210亿m³的优质淡水资源，具有重要战略价值，但是近年来出现水质退化的现象.沉水植被是湖泊生态系统功能维持的重要生物门类，其演变过程能反映和影响整个生态系统的变化，目前还缺乏对抚仙湖沉水植被长期连续地观测记录.本文基于Landsat遥感数据分析了抚仙湖北部沉水植被面积的动态变化，结合气候变化和水质水文要素分析发现：抚仙湖北部湖区沉水植物在1987—2020年间存在先减少后增加的变化趋势；1987—1995年，沉水植物分布面积约占北部湖区面积的1.64%；1996—2010年北部湖区沉水植被分布面积缩减，湖泊处于高水位低营养状态，水位上升是此时期沉水植物面积减少的主要原因；2011—2020年，水位降低，营养增加，营养和水位的共同作用导致抚仙湖北部湖区沉水植物面积显著增加.沉水植物覆盖度变化伴随着沉水植被以苦草为优势种群转为以穗花狐尾藻为优势种群，沉水植被结构转向耐污染性更强的属种.通过抚仙湖北部湖区沉水植被发育与营养、水位等驱动因子的关系分析，建议现阶段需要严格限制入湖氮磷排放，强化水生植被的长期动态监测，构建水量、水质、水生态一体化监测体系，并开展抚仙湖生态系统演变的模拟和预测，防止抚仙湖生态系统出现突变，以维持抚仙湖生态系统功能多样性.;Lake Fuxian has nearly 21 billion cubic meters of high-quality freshwater resources which has important strategic value, but the water quality has been degraded in recent years. Submerged vegetation is an important biological category for the function maintenance of the lake ecosystem, and its succession can reflect and influence the changes of the whole ecosystem. At present, there is a lack of long-term continuous observation records of submerged vegetation in Lake Fuxian. Based on Landsat remote sensing data, this paper analyzes the dynamic changes of submerged vegetation in the northern part of Lake Fuxian. Integrating climate change and water quality hydrological elements, submerged vegetation in the northern part of Lake Fuxian showed a decrease followed by an increase from 1987 to 2020. From 1987 to 1995, the distribution area of submerged vegetation accounted for about 1.64% of the northern lake area. From 1996 to 2010, the submerged vegetation in the northern lake area reduced, and the lake was in a state of high water level and low nutrients. The rise of the water level was the main reason for the reduction of submerged vegetation area during this period. From 2011 to 2020, the water level decreased and nutrients increased, and the combined effect of nutrients and water level led to a significant increase in the area of submerged vegetation in the northern lake area of Lake Fuxian. The change in submerged vegetation coverage was accompanied by a shift in submerged vegetation from Vallisneria natans as the dominant population to Myriophyllum spicatum as the dominant population, and the structure of submerged vegetation turns into more pollution-tolerant species. In this study, the analysis of the relationship between the development of submerged vegetation and the driving factors such as nutrients and water level in the north of Lake Fuxian suggests that at this stage, it is necessary to strictly restrict the discharge of nitrogen and phosphorus into the lake, strengthen the long-term dynamic monitoring of aquatic vegetation, build an integrated monitoring system for water quantity, quality and ecology, and carry out simulation and prediction of the Lake Fuxian ecosystem change to prevent Lake Fuxian ecosystem from regime shifts and maintain its functional diversity Lake Fuxian.

Water level retrieval for the past and prediction for the next 30 years at Lake Fuxian

在极端气候事件频发和人类活动加剧的背景下，抚仙湖水位波动显著，尤其是2009—2012年极端干旱事件的发生，使抚仙湖平均水位（1721.31 m）低于法定最低水位（1721.65 m），给生态环境安全带来严重威胁.因此，找到合适有效的湖泊水位模拟方法，对气候变化影响下的未来水位进行预测，并做好相应的应对准备，对湖泊生态系统的保护至关重要.本文运用DYRESM水动力模型对抚仙湖1959—2050年水位进行了模拟.因抚仙湖流域尚无长时间序列的历史水文观测数据，故利用模型和水量补偿法对抚仙湖入湖水量进行反推，构建了降水量-入湖水量的回归方程，并通过有效的实测入湖水量和水位数据，对回归方程的精度进行了检验.利用全球气候模式BCC-CSM2-MR中SSP245和SSP585两种情景提供的未来气候预估数据，运用DYRESM预测了抚仙湖2021—2050年水位变化趋势.结果表明：（1）构建的DYRESM水动力模型和降水-入湖水量回归方程精度较高，模型结果能很好地反映抚仙湖水位的年际和年内变化趋势，且能有效捕捉到抚仙湖的水位峰值.（2）在SSP245和SSP585两种情景下，抚仙湖2021—2050年多年平均水位分别为1722.98和1723.93 m，较1959—2017年平均水位1721.77 m分别升高1.21和2.16 m.两种情景下抚仙湖未来水位均有部分时段超过法定最高蓄水位（1723.35 m），但均高于法定最低水位.因此，未来气候变化对抚仙湖水量的影响有限，并不会导致水位过低，当水位超过法定最高蓄水位时，可通过控制出流闸门将水位调节在合理范围内.;With frequent extreme climate events and intensive human activities, the water levels at Lake Fuxian have fluctuated significantly in the past especially during 2009-2010 with an extreme drought. The average water level from 2009 to 2012 was (1721.31 m) lower than the minimum required value (1721.65 m), which caused a great threat to the lake ecosystem. So, it is very important to find an effective method or tool for predicting the water levels under the climate change in the future and to make corresponding adaptation. In this paper, a one-dimensional hydrodynamic model (DYRESM) was used to simulate the water levels at Lake Fuxian from 1959 to 2050. Due to lack of observation of inflow volumes, we developed a regression model between inflow and precipitation to produce the missing lake inflows using DYRESM, existing inflow measurements and rainfall. The model was then verified and used to simulate the water levels for 2021-2050 based on rainfall predicted by a global climate model (BCC-CSM2-MR) under Scenario SSP245 and Scenario SSP585. The results show that DYRESM and the regression model had satisfied performance. The average lake water levels from 2021 to 2050 under Scenario SSP245 and Scenario SSP585 were 1722.98 and 1723.93 m respectively, which will be 1.21 and 2.16 m higher than those for 1959 to 2017. The predicted water levels might be intermittently higher than the maximum warning water level (1723.35 m), but will not be lower than the minimum warning water level (1721.65 m). In conclusion, the climate change in the future might have limited impact on the water volume of Lake Fuxian.

Spatial distribution of bacterioplankton community composition and their diversity in Lake Fuxian during thermal stratification period

水体垂向分层是深水湖泊一个重要的特征，这不仅影响水体理化环境因子，而且影响水生生物组成的垂向分布，但是对不同水层水体细菌的多样性和群落结构组成的形成与维持机制知之甚少. 本研究以抚仙湖为研究对象，在水体热力分层期间采集不同位点、不同水层水样，借助16S rDNA Illumina Miseq高通量测序技术，探究水体细菌多样性和群落结构组成的空间分布特征及关键影响因子. 研究结果表明：(1)抚仙湖北部湖心在水深15~40 m处出现温跃层，温度由23℃降至15℃，其余理化环境因子也存在明显的垂向分层现象；与垂向差异相比，表层水体各理化因子在水平方向上的差异相对较小. (2)在水平方向上，南部湖心表层水体细菌alpha多样性(Operational Taxonomic Unit数目和Faith's phylogenetic diversity)最高；在垂向上，水体细菌alpha多样性随着采样水深的增加呈现单峰分布，在30和40 m水层最高；水体细菌alpha和beta多样性的垂向差异均显著大于水平方向差异. (3)表层水体细菌主要由Actinomycetales、unidentified Cyanobacteria、Burkholderiales和Sphingobacteriales组成；温跃层中以Pseudomonadales为主；均温层的优势菌群为unidentified Chloroflexi、Actinomycetales和Burkholderiales. 典范对应分析表明溶解性有机碳、溶解氧、硝态氮、氨氮和总磷浓度是影响细菌群落组成的主要环境因子.;Deep lakes are typically characterized by thermal stratification throughout the year, except for a short mixing period in winter. This vertical partitioning has important effects on many biotic, physical and chemical characteristics of the water column. However, at present, little is known about how these changes affect the vertical distribution of bacterioplankton community diversity. In this study, Lake Fuxian with a relatively long thermal stratification period every year, was chosen for the investigation of bacterioplankton distribution, diversity and composition on August 25th, 2013. 16S rDNA Illumina Miseq high-throughput sequencing technology was performed on DNA extracted from water samples collected from different locations and different water depths. The results showed that: (1) A thermocline appeared in the lake center and in the northern part of this lake at the depth of 15-40 m, with the temperature dropping from 23℃ to 15℃. Other physical and chemical factors also showed obvious vertical stratification pattern. Horizontally, there is no significant difference in physicochemical features. (2) In the horizontal direction, the alpha diversities of plankton bacteria (the number of Operational Taxonomic Units and Faith's phylogenetic diversity) in the surface water of the southern lake center was the highest; in the vertical direction, the alpha diversity gradually increased with the increase of the sampling depth, topping at the depths of 30 m or 40 m, and then gradually decreased; the difference of the bacterioplankton alpha and beta diversity in the vertical direction was significantly greater than those in the horizontal direction. (3) The bacterioplankton in the epilimnion were mainly composed of Actinomycetales, unidentified Cyanobacteria, Burkholderiales and Sphingobacteriales; the relative abundance of Pseudomonadales in the thermocline significantly increased and became dominant; unidentified Chloroflexi, Actinomycetales and Burkholderiales were the dominant bacterial taxa in the hypolimnion. The canonical correspondence analysis demonstrated that the concentrations of dissolved organic carbon, dissolved oxygen, nitrate, ammonium and total phosphorus are the significant environmental variables shaping the bacterial community's composition and diversity.

Lake environmental changes over the past 5000 years recorded by multiple proxies of sediments in Lake Fuxian, southwest China

Lake environmental changes over the past 5000 years recorded by multiple proxies of sediments in Lake Fuxian, southwest China

Grain-size characteristics in lake Fuxian sediments: Implication for dry-humid transformation of Indian summer monsoon over the past 150 years

Polymodal distributions and end-member modeling of grain-size in lacustrine sediments can reveal the changes in sedimentary processes, transportation mechanisms, and climatic changes. The temporal and spatial variation characteristics of grain-size were investigated in six sediment cores of the plateau deep-lake Fuxian, in southwest China, where the climate was driven by Indian Summer Monsoon (ISM). Results indicated that the size of the dominant grain-size exponentially decreased with the declining hydrodynamic condition towards the deep-water zones, with an exception of the maximum grain-size near the outlet of the lake. Measured grain-size distributions were classified into four end-members (EMs) with a basic end-member model algorithm (BasEMMA), of which could be linked to a distinct transport mechanism and source: EM1 (long-term suspended load from atmospheric dust) with the modal size of 0.3–11.2 µm, EM2 (off-shore suspended load from fine riverine input) with 7.9–14.2 µm, EM3 ((near-shore suspended load from coarse riverine input) with 15.9–31.7 µm, and EM4 (near-shore riverbed load from extremely coarse riverine input) with 35.6–70.9 µm, respectively. Temporal variation of EM2 + EM3 components of grain-size in Core F5 are responses to the changes in instrumentally recorded precipitation in Chengjiang (1961–2008) and ISM (1860–2006), which indicates that changes in river flow in response to changes in precipitation is the primary driver of clastic sediment deposition especially in the narrow section of the lake. Our findings indicate grain-size distribution and sediment compositions are significant tools for improving the understanding of the spatiotemporal heterogeneity in dry-humid transformation of ISM over the past 150 years.

Source analysis and influencing factors of historical changes in PAHs in the sediment core of Fuxian Lake, China

In this study, the influencing factors and sources of historical changes in polycyclic aromatic hydrocarbons (PAHs) in the sediment core of Fuxian Lake were analyzed. Before 1970, the Σ16PAH concentration fluctuated widely, with one or more maximum values. During 1971–2004, the Σ16PAH concentration showed a slow growth trend, while during 2005–2017, the concentration increased sharply, reaching a peak value of 821 ng g−1. dw in 2017. The results of a positive matrix factorization (PMF) model demonstrated that before 1970, PAHs were mainly derived from biomass burning in the Fuxian Lake sediment core, with an overall contribution of 40 %. During 1971–2004, the source of PAHs was mainly coal combustion, with an overall contribution of 34 %. During 2005–2017, PAHs primarily originated from traffic, with an overall contribution of 33 %. Population, coal, GDP, motor, and petroleum had a significant influence on low molecular weight (LMW) PAHs in 1980–2004 and 2005–2017. Motor, coal, population, and GDP had a greater impact on high molecular weight (HMW) PAHs. Before 1970 and in 1971–2004, meteorological factors had little effect on PAHs in the sediment core in Fuxian Lake. During 2005–2017, day and rainfall were significantly negatively correlated with HMW PAHs, while temperature and wind were not correlated with PAH concentrations. During 2005–2017, total organic carbon (TOC) and total nitrogen (TN) had greater adsorption effects on HMW PAHs than on LMW PAHs. Before 1970 and in 1971–2004, the adsorption effects of TOC and TN on 3–4-ring PAHs were greater than those of 2-ring and 5–6-ring PAHs. Total phosphorus (TP) had no adsorption effect on PAHs in the entire sedimentary column.

Extraction of plateau lake water bodies based on an improved FCM algorithm

Changes in plateau body lake water are an important indicator of global ecosystem changes, and a timely and accurate grasp of this change information can provide a scientific reference for the formulation of relevant policies. The traditional fuzzy C-means clustering (FCM) algorithm takes into account the ambiguity of the classification of the ground object pixels but does not consider the rich spectral information of the neighboring pixels and is very sensitive to the background noise” of the remote sensing image, resulting in low water extraction accuracy. Aiming to compensate for the shortcomings of the traditional FCM algorithm, this paper proposes an improved FCM algorithm. This algorithm replaces the Euclidean distance of the traditional FCM algorithm with a combination of the Mahalanobis distance and spectral angle matching (SAM) to fully take into account the spectral information of neighboring pixels and improve the clustering accuracy. The study selected Sentinel-2 images of the Fuxian Lake and Xingyun Lake basins during normal, wet, and dry periods as the data source. Under the same conditions, the clustering accuracy was compared with the traditional FCM algorithm, improved FCM algorithm, K-means clustering method and iterative self-organizing data analysis (ISODATA) clustering method. The experimental results show that the improved FCM algorithm has a higher water extraction accuracy than the traditional FCM algorithm, K-means clustering method and ISODATA clustering method. The kappa coefficient and overall accuracy (OA) of the improved FCM algorithm can be increased by 5.56%–9.45% and 2.66%–5.32%, respectively, and the omission error and commission error can be reduced by 1.72%–4.55% and 12.14%–22.10%, respectively. When the improved FCM algorithm is used, the extraction accuracy is higher for plateau deep lakes than for plateau shallow lakes, and the extraction effect for lakes with poor water environments is more significant than that of other methods. The improved FCM algorithm better maintains the integrity of the water boundary and overcomes the influence of a certain number of mountain shadows and urban building pixels on the clustering results.