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The water quality of Lake Erhai has deteriorated in recent decades due to socioeconomic development in the lake basin. After the massive implementation of water environmental protection measures in Lake Erhai in 2016, the trend of water quality deterioration has been curbed and the intensity and frequency of algal blooms has decreased. However, water quality monitoring data show that pollutant concentrations in Lake Erhai still exceed acceptable values, and there is a risk of water quality standard limits being further exceeded in the future. Therefore, it is urgent to systematically study the variability characteristics of water quality in Lake Erhai to provide practical methods to predict the future evolution of water quality. Based on water quality monitoring data from 2009 to 2019, the current water quality characteristics of Lake Erhai were analyzed, and a two-dimensional hydrodynamic and water quality mathematical model was built to predict the water quality in 2025. The results showed that the total phosphorus (TP) concentration declined after 2016, mainly due to the significant reduction of TP entering the lake due to pollution interception. However, the concentrations of the potassium permanganate index (CODMn) and total nitrogen (TN) increased after 2016, demonstrating that the pollution control measures have had little effect on the improvement of CODMn and TN. The spatial and temporal distribution of pollutants showed that the water quality in winter and spring was better than in summer and autumn, and the water quality in the southern lake was better than in the northern lake. This analysis indicates that non-point source pollution remains the main source of pollution in Lake Erhai, and that rainfall is the main driving force of pollutants exceeding the water quality standard. According to the water quality predictions, without additional pollution control measures, pollutant concentrations in Lake Erhai will exceed the Class II water quality standard by 2025. This study analyzes the water quality characteristics, predicts the direction of future water quality changes, and provides a theoretical basis for the future water quality protection of Lake Erhai. [ABSTRACT FROM AUTHOR]

FengYun-3E (FY3E) is the world's first dust-dawn orbiting meteorological satellite for civil use, which has filled the vacancy of global early-morning-orbit satellite observation by working together with FengYun-3C and FengYun-3D satellites. The Medium Resolution Spectral Imager-Low Light (MERSI-LL) sensor carried by FY3E can detect surface temperature variation. The radiometric calibration conditions of MERSI-LL thermal infrared bands were evaluated using the collected field measurements and atmospheric transfer simulations during 5–23 December, 2022, at Lake Erhai. A thermal infrared radiometer equipped on an unmanned surface vehicle was used to continuously collect surface-emitted radiance and water temperature. Atmospheric conditions, surface emissivity, and aerosol optical depth measured near-field experiment site were adopted by atmospheric radiative transfer code to calculate the influence of atmosphere on long-wave radiation during the propagation from land surface to satellite aperture. The good in-orbit operational status could be detected according to our calibration experiments, and the calibration analysis suggested that the differences between the simulated brightness temperature and satellite-based brightness temperature are 0.71 K with an RMSE of 0.79 K and 0.11 K with an RMSE of 0.47 K for channels 6 and 7, respectively, which achieved better or similar calibration accuracy by comparing with TIR channels of other FengYun satellites.

A thermal infrared spectrometer is an important sensor onboard the SDGSAT-1 dedicated to serving the 2030 Agenda for Sustainable Development of the United Nations. Field campaigns were conducted from January to December 2022 to evaluate its radiometric calibrations. A radiance-based calibration method was used to derive the spectral radiance of the lake surface around the satellite overpass using a boat-deployed TIR spectrometer or radiometer. The radiometric calibration conditions were quantified by examining the temperature bias between the satellite-based brightness temperature and the predicted at-sensor brightness temperature. Our results indicated that the average brightness temperature bias reached 0.772 K, −1.032 K, and −0.300 K, with RMSEs of 1.00, 1.10, and 0.43 K in bands 1, 2 and 3, respectively. Eighty percent of the field experiments achieved a high calibration accuracy with temperature biases of less than 1 K, and the calibration accuracy of band 3 was better than that of other bands. Atmospheric conditions and surface characterization play important roles in determining the calibration accuracy through surface observations and atmospheric transfer simulations. With the increasing need for SDGSAT-1 products, periodic field experiments are needed to monitor and improve the operational radiometric calibration of satellite instruments to create high-resolution and reasonable scientific datasets.

Excessive nutrient loss from farmland located on the west bank of Erhai Lake has resulted in significant non-point source pollution within the Lake Erhai basin. However, mitigating this issue proves challenging due to the intricate nature of soil properties and environmental factors. Here, during the rainy season in the Lake Erhai basin, we collected and analyzed soil profile samples, 35 topsoil (0–20 cm) samples, and more than 300 field baseflow samples. Our objective was to explore the influences of soil properties, field baseflow, and agricultural management measures on the spatiotemporal migration of nutrients. The results indicated that the concentration of soil organic matter (SOM) has a significant impact on the spatial patterns of nutrient distribution in sandy soil. Consequently, this leads to a substantial reduction in the potential for nutrient loss in the Lake Erhai basin. The vegetable-field baseflow exhibited the highest concentrations of nitrogen and phosphorus when subjected to high fertilization and flood irrigation. The concentrations of TN and TP in baseflow increase by a factor of 2 and 7.7, respectively, during rainfall compared to periods of no rainfall. Optimizing agricultural measures, such as replacing chemical fertilizers with organic fertilizers and modifying irrigation methods to enhance the organic content of sandy soil and minimize baseflow elution, has a beneficial impact on mitigating agricultural non-point source pollution in the Erhai Lake basin. The research results can enable us to have a more systematic understanding of the problem of non-point source pollution in the Erhai River Basin, and provide a theoretical basis for developing targeted agricultural non-point source pollution mitigation plans. Simultaneously, optimizing agricultural management models to strike a balance between agricultural economic development and ecological protection issues holds significant practical significance for managers. [ABSTRACT FROM AUTHOR]

Climate change and its impact on plateau lakes are of wide concern in China owing to their diverse yet fragile ecosystems. The three largest and most concerning plateau lakes (Dianchi, Erhai, and Fuxian lakes) in southwestern China were selected as case studies to demonstrate their different hydrological responses attributing to the local climatic and watershed characteristics. We processed 27 climate change scenarios according to the local climate characteristics and simulated the daily runoff of each lake basin under the historical and the 27 climate change scenarios. Then we analyzed the change of mean annual and seasonal runoff, and hydrological extremes of each lake basin. The results indicate a great risk of socio-economic and ecological for these plateau lakes as climate change will significantly alter the horological regimes of each lake basin. The mean annual runoff of the three lake basins will change from–65.24 to 54.17 %, when the air temperature increases by 1–2 °C and precipitation changes from –20 to + 20 %. Climatic and topographic heterogeneities caused each lake basin responded differently to climate change. Among them, the LFB was more sensitive to climate change than the LDB and LEB. Changes in the annual and seasonal runoff for the LFB were approximately 1.5-fold higher than that of the LDB and LEB. The hydrological extremes in the LFB also had the most significant changes. To cope with future climate change, each lake requires reasonable and effective mitigation measures.

A thermal infrared spectrometer is an important sensor onboard the SDGSAT-1 dedicated to serving the 2030 Agenda for Sustainable Development of the United Nations. Field campaigns were conducted from January to December 2022 to evaluate its radiometric calibrations. A radiance-based calibration method was used to derive the spectral radiance of the lake surface around the satellite overpass using a boat-deployed TIR spectrometer or radiometer. The radiometric calibration conditions were quantified by examining the temperature bias between the satellite-based brightness temperature and the predicted at-sensor brightness temperature. Our results indicated that the average brightness temperature bias reached 0.772 K, −1.032 K, and −0.300 K, with RMSEs of 1.00, 1.10, and 0.43 K in bands 1, 2 and 3, respectively. Eighty percent of the field experiments achieved a high calibration accuracy with temperature biases of less than 1 K, and the calibration accuracy of band 3 was better than that of other bands. Atmospheric conditions and surface characterization play important roles in determining the calibration accuracy through surface observations and atmospheric transfer simulations. With the increasing need for SDGSAT-1 products, periodic field experiments are needed to monitor and improve the operational radiometric calibration of satellite instruments to create high-resolution and reasonable scientific datasets. [ABSTRACT FROM AUTHOR]

Introduction of planktivorous fish or eutrophication can alter lake food webs, especially the zooplankton communities are susceptible to changes in top–down and bottom-up controls, and eventually lead to the dominance of harmful cyanobacteria. Hence, for the recovery of large-size zooplankton abundance that graze on cyanobacteria, there is an urgency to understand the relative roles of top–down and bottom-up effects. Although much is known about these two effects in temperate lakes, little knowledge about their relative importance in subtropical highland lakes exists, where eutrophication and stocked planktivorous fish are of particular concern. Thus, we conducted research in Lake Erhai in Yunnan plateau, China, to examine the drivers affecting the dynamics of crustacean zooplankton. Redundancy analysis (RDA) was used to analyze the effects of environmental variables, phytoplankton biomass, and planktivorous fish on the biomass and body weight of zooplankton taxa in the lake, and variance decomposition analysis was applied to examine the relative roles of the bottom–up and top–down controlling factors on zooplankton biomass. The results of RDA and Pearson correction analysis showed that total nitrogen (TN) in the water column affected phytoplankton and altered the biomass of cladocerans, while water temperature directly affects the biomass of cladocerans. These findings indicate a pronounced bottom–up control link exists from nutrients to phytoplankton, and then to zooplankton. The abundance of Japanese smelt was negatively correlated both with the biomass and body weight of cladocerans. This finding suggests the pronounced top–down control link exists from fish to zooplankton. The results of variance decomposition analysis showed that TN and zooplanktivorous predation were more important in driving total zooplankton biomass, while TN, water temperature and fish predation were more essential in the variation of zooplankton biomass. Our study provides a reference for the recovery of large-size zooplankton populations in eutrophicated lakes. [ABSTRACT FROM AUTHOR]

The preservation of biodiversity is crucial for sustaining ecosystem functioning, and recently the ongoing loss of biodiversity in lake ecosystems due to human activities has raised significant concerns. This study aimed to assess the impact of human activities on the biodiversity of aquatic plants through long-term empirical evidence. By comparing species composition and genetic diversity of submerged macrophyte within last decade, this research focused on the long-term changes of submerged macrophyte biodiversity resulting from human disturbances and restoration efforts. Three plateau lakes - Lake Erhai, Lake Fuxianhu, and Lake Jianhu - were selected as study sites, exhibiting varying biodiversity alterations in response to different levels of human disturbance and restoration activities. The oligotrophic Lake Fuxianhu demonstrated a stable level of both biodiversity levels, and the eutrophic Lake Jianhu exhibited a significant reduction in species diversity and genetic diversity. Meanwhile, the strong restoration measures in Lake Erhai between the 2010s and the 2020s effectively safeguard species diversity and alleviate declines in genetic diversity due to eutrophication during the last decade. We also found that improper use of alien species and the transplantation of clones of aquatic plant may pose ecological risks to biodiversity. Given the importance of aquatic plant re-establishment for the long-term recovery of plateau lakes, conservation strategies could prioritize large-scale propagation of aquatic plant materials through local seed banks. • This research focused on the alterations in biodiversity of submerged macrophyte in three plateau lakes over the last decade. • Lake Erhai have experienced well-preserved biodiversity and reduced losses in genetic variation. • Introducing exotic species inappropriately could lead to ecological consequences. • The use of local seed banks to propagate aquatic plants in targeted lakes to conserve biodiversity was suggested. [ABSTRACT FROM AUTHOR]

To understand the lake status and reasons of eutrophication at Lake Erhai in recent years, water quality, including water temperature (T), pH, dissolved oxygen (DO), total nitrogen (TN), total phosphorus (TP) and chlorophyll-a (Chl-a) from 2016 to 2020 was monitored and analyzed. The results showed no obvious thermocline in the vertical direction at Lake Erhai, while Chl-a demonstrated obvious spatiotemporal distribution characteristics in Lake Erhai. Chl-a concentrations increased to a maximum in summer in August with the low TN:TP value, leading to algal blooms, most notably in the southern lakes. Low pH and DO appeared due to the thermocline of Erhai Lake (August 2016). A large area of algae distribution due to the increase of total phosphorus appeared in the northern lake area of Lake Erhai in December 2016, with a tendency of mesotrophic to light eutrophic in summer by the nutritional evaluation of Lake Erhai, especially in the central lake area and the northern lake area. Pearson's correlation coefficient and principal component analysis showed a significant positive correlation between Chl-a and T (r = 0.34, p ≤ 0.01) and TP (r = 0.31 p ≤ 0.01) in the mesotrophic Lake Erhai, indicating that TP content was one of the triggering factors for the algal blooming. Based on the spatiotemporal changes in water quality parameters and their relationship with eutrophication, scientific agencies should implement management strategies to protect Lake Erhai, supplemental to the costly engineering measurements. [ABSTRACT FROM AUTHOR]

Excessive nutrient loss from farmland located on the west bank of Erhai Lake has resulted in significant non-point source pollution within the Lake Erhai basin. However, mitigating this issue proves challenging due to the intricate nature of soil properties and environmental factors. Here, during the rainy season in the Lake Erhai basin, we collected and analyzed soil profile samples, 35 topsoil (0–20 cm) samples, and more than 300 field baseflow samples. Our objective was to explore the influences of soil properties, field baseflow, and agricultural management measures on the spatiotemporal migration of nutrients. The results indicated that the concentration of soil organic matter (SOM) has a significant impact on the spatial patterns of nutrient distribution in sandy soil. Consequently, this leads to a substantial reduction in the potential for nutrient loss in the Lake Erhai basin. The vegetable-field baseflow exhibited the highest concentrations of nitrogen and phosphorus when subjected to high fertilization and flood irrigation. The concentrations of TN and TP in baseflow increase by a factor of 2 and 7.7, respectively, during rainfall compared to periods of no rainfall. Optimizing agricultural measures, such as replacing chemical fertilizers with organic fertilizers and modifying irrigation methods to enhance the organic content of sandy soil and minimize baseflow elution, has a beneficial impact on mitigating agricultural non-point source pollution in the Erhai Lake basin. The research results can enable us to have a more systematic understanding of the problem of non-point source pollution in the Erhai River Basin, and provide a theoretical basis for developing targeted agricultural non-point source pollution mitigation plans. Simultaneously, optimizing agricultural management models to strike a balance between agricultural economic development and ecological protection issues holds significant practical significance for managers.

Lake Erhai is a potentially phosphorus (P)-limited lake and its water quality may have been affected by atmospheric P deposition. However, there have been few studies on atmospheric P deposition in this lake. In this study, we established five wet deposition monitoring sites and two dry deposition monitoring sites around Lake Erhai to quantify the wet and dry deposition of total phosphorus (TP), including dissolved inorganic phosphorus (DIP), dissolved organic phosphorus (DOP) and particulate phosphorus (PP) from July 2022 to June 2023. Wet deposition fluxes of P species were collected by automatic rainfall collection instrument, and dry deposition fluxes were estimated using airborne concentration measurements and inferential models. The results reveal that among the different P components, DOP had the highest contribution (50%) to wet TP deposition (average all sites 12.7 ± 0.7 mg P m2/yr), followed by PP (40%) and DIP (10%). Similarly, DOP (51%) was the major contributor to dry TP deposition (average two sites 2.4 ± 0.9 mg P m2/yr), followed by DIP (35%) and PP (14%). Wet deposition dominated the annual total TP deposition (wet plus dry), accounting for approximately 83%. The key seasons for dry deposition were spring and autumn, which accounted for 64% of the annual total dry TP deposition. In comparison, wet deposition was significantly higher in the summer, accounting for 73% of the annual total wet TP deposition. The results of the potential source contribution function and concentration-weighted trajectories analysis indicate that local source emission and long-range transport from surrounding cities jointly exerted a substantial influence on aerosol P concentrations, particularly in the eastern and northwestern regions of the lake. These findings provide a comprehensive understanding of the different P components in atmospheric deposition, which is beneficial for developing effective strategies to manage the P cycle in Lake Erhai. [Display omitted] • Wet and dry fluxes of P were 12.7 and 2.4 mg P/m2/yr in Lake Erhai, respectively. • DOP contributed 50% and 51% of total wet and dry P deposition fluxes, respectively. • Wet deposition peaked in summer, while dry deposition peaked in autumn or spring. • Total TDP deposition flux accounted for approximately 7% of the riverine TDP inputs. • Local emission sources and regional transport jointly affected P deposition. [ABSTRACT FROM AUTHOR]

Trapanatans is one of the main species causing the swamping in the littoral zones of Erhai Lake. It commonly forms a dense canopy on the water surface in the growing season (June–September), which hampers the local water quality and habitat of submerged macrophytes, and releases nutrients to the water after death in autumn and winter, resulting in the deterioration of local water quality. At present, there are many and positive research studies on the short-term effects of harvesting water chestnut on water quality and aquatic plants, but long-term observation results are lacking. In response to the above problems, we studied responses of water quality and aquatic plant community to the removal of Trapa in littoral zone of a northern bay in Erhai from August 2014 to January 2017. This could be the first attempt to discover the long-term effects of floating-leaved vegetation management in the freshwater ecosystem. The results showed that the artificial removal of Trapa significantly improved the local water quality in the growing season, for example, the concentrations of total nitrogen (TN), dissolved nitrogen (DN), total phosphorus (TP), and dissolved phosphorus (DP) in the non-Trapa zone (NTZ) were much lower than the concentrations of those in the adjacent Trapa zone (TZ). And the biomass of aquatic macrophyte community (BAMC) was significantly increased in the NTZ, up to the maximum value of about 21 kg/m2 in fresh weight. However, the diversity indexes of the community in the NTZ declined. Therefore, we suggested that although the removal of Trapa improved the water quality and increased the productivity of the submerged aquatic plant community, it reduced the species diversity of the aquatic plant community in the long run. This is another issue that we need to pay attention to in the later management in Erhai Lake.

Understanding social-ecological interactions is a major research priority for sustainable management. However, the scarcity in multi-decadal records represents a big gap in information that hinders the development of above research. In this paper, we propose a framework to explore the long-term dynamic mechanisms between social and ecological systems, and present a case study in the Erhai basin, southwest China. Using paleolimnological proxies to reconstruct the long-term trends of ecological changes, the social-ecological system (SES) framework links the variations of ecosystem services (ESs) and ecosystem functions with social policies. According to the results of the Erhai basin, there were increasing social demands and wanted provisioning ESs but degraded ecosystem functions over the last 70 years. Typically, the introduction of four major Chinese carps since the 1950s, the construction of hydropower stations on the Xi'er river since the 1970s, and the development of tourism since the 1990s, have been implemented to meet the social demands for wanted fish provisioning, hydroelectricity provisioning, and culture services respectively. Although there were temporary benefits in above desired services, improper strategies have gradually impaired the functions of native fish diversity, hydrodynamic forces, and nutrient cycling. Degraded ecosystem functions threatened the sustainable provision of wanted ESs, which motivated the implementation of subsequent social policies, such as the fishing ban after the 1950s, water level control after the 1970s and restoration projects after the 1990s. By rounds of renewed social drivers/policies, the social system and ecosystem in the Erhai basin are tightly connected in the form of a feedback loop in the SES, rendering dynamic changes in wanted ESs. The current social-ecological trap in the Erhai basin emphasizes the significance of SES framework and advantages of a paleolimnological approach in revealing the long-term SES dynamics, which can help tailor proper management measures in the future. [ABSTRACT FROM AUTHOR]

Over the past decades, faece and sewage pollution from agricultural and industrial activities has induced severe eutrophication and ecosystem deterioration of Lake Erhai in southwestern China. Investigations on the anthropogenic faece and sewage input from both spatial and historical viewpoints are of great values for recovery strategies. In this study, we investigated fecal steroids in surface sediments from Lake Erhai collected in 2018, and found that the faece and sewage contamination is mainly from the southern region due to urban development, while the raw sewage contributes more in the northern region due to agriculture activities. We further applied fecal steroids to reconstruction of faece and sewage contamination to Lake Erhai over the past ∼200 years. The concentrations in fecal steroids remained low during ∼1820–1970, started to increase since the 1970s, and further increased after the 1990s, indicating a cumulative effect of contamination on the lake ecosystem by agricultural activities and urbanization practices. Diagnostic ratios of faece and sewage contamination over in-situ productivity remained stable or even decreased slightly during ∼1970–1980, and significantly increased during ∼1980–2008, suggesting that the contamination in Lake Erhai began at the 1980s. The fecal steroid records also demonstrated that even though anaerobic sewage treatment was in process, production of raw sewage still exceeded sewage treatment after the 1980s. Considerable faece and sewage contamination in the Lake Erhai catchment from anthropogenic industrialization and urbanization, which has also been observed from various environments throughout the world, asks for further efforts on regulations to protect water quality and human life. Fortunately, governmental regulations have significantly reduced the anthropogenic faece and sewage contamination to Lake Erhai over the past decades, highlighting a crucial role of sustainable management on lake ecosystem. • Faece and sewage contamination to Lake Erhai are mainly from urban practices. • Cumulative effect of faece and sewage contaminations since the 1970s. • More serious faece and sewage contaminations issue began at the 1980s. • Increased input of raw sewage exceeded anaerobic sewage treatment after the 1980s. • Governmental regulations effectively reduced contamination over the past decade. [ABSTRACT FROM AUTHOR]

Microcystins (MCs) have seriously polluted drinking water supplies and have caused great harm to aquatic organisms and humans. Understanding the dynamics of MC concentrations and its influencing factors is necessary for drinking water safety. Many previous studies on MC pollution focused on intracellular MCs rather than on extracellular MCs, which are more difficult to remove by water treatment. So far, the release characteristics of MCs and the relationships between intracellular and extracellular MCs are still unclear. To explore these questions, a survey was conducted at 18 sites across Lake Erhai from May 2014 to April 2015 as in Lake Erhai the frequency and coverage area of cyanobacterial blooms have been increasing. Variation of extracellular MCs lagged behind that of intracellular MCs. The highest value of intracellular MCs was 1.07 μg L−1 in October 2014 and the highest extracellular MC concentration was 0.035 μg L−1 in November 2014. Intracellular MCs were positively influenced by MC-producing cyanobacterial biomass, water temperature (WT), pH, and conductivity (Cond). The extracellular MCs showed little correlation with cyanobacterial abundances and intracellular MC concentrations, but showed significant negative correlations with WT, pH, and Cond. These results indicated that high biomass and high intracellular MC concentrations did not quickly lead to large releases of MCs, and that when cyanobacterial cells died and blooms disappeared, MCs were intensively released into the water, posing the greatest threat to drinking water supply. [ABSTRACT FROM AUTHOR]

In Lake Erhai, water quality was affected by the basin nutrient discharge and climate change. To analyze the relationships between the water quality (total nitrogen [TN], total phosphorus [TP], chemical oxygen demand [CODmn], ammonia [NH4], and trophic level index [TLI]) and basin nutrient discharge (TNd, TPd, and CODd) combined with climate changes (air temperature [AT], precipitation [pre], wind speed [wind], and sunshine hours [SHs]), the generalized additive model (GAM) was employed to explore the nonlinear relationships with their interactions using data sets ranging from 1999 to 2012. Our findings revealed that the water quality in Lake Erhai deteriorated in the early twentieth century, and the basin discharge and AT appeared significant (p < 0.05) rising trends in a long time, while the precipitation decreased significantly (p < 0.05) in the study period. Single-factor GAM results indicated that the basin nutrient discharge was the main explanatory factor for the variations of TN and TP in lake, while precipitation was the main driver for CODmn and NH4. Besides, the water quality displayed nonlinear responses to the basin discharge, but all of the water quality variables went up as the emission levels increased in the lower range. The results showed that the water quality deteriorated in the lower rainfall, and TN rose as the AT increases, while TP was elevated accompanied by the ascending SHs there. The GAM interaction results suggested that the increase of AT and TPd had a promoting effect on TP in Lake Erhai. Stricter nutrient management measures should be implemented when the impacts of climate change are taken into account. [ABSTRACT FROM AUTHOR]

Temporal and spatial variations of phytoplankton community in Lake Erhai were investigated from May 2010 to April 2011. A total of 124 species belonging to 8 phyla and 72 genera were recorded, among which Chlorophyta (74) ranked the first, followed by Bacillariophyta (24) and Cyanophyta (17). Total phytoplankton density ranged from 27.7 × 105 to 442.1 × 105 cells/L, with annual average value of 196.3 × 105 cells/L. The range of total phytoplankton biomass was between 0.68 mg/L and 3.25 mg/L, with annual average value of 2.31mg/L. In winter and spring, the dominant species were Fragilaria capucina and Aulacoseira granulata, while it changed into Cyclotella meneghiniana, Microcystis (M. aeruginosa, M. wesenbergii and M. viridis) and Psephonema aenigmaticum in summer and autumn. Phytoplankton biomass in the southern zone of the lake was significantly higher than those in the northern and middle zones of the lake. Two-way ANOVA showed that the influences of temporal (F = 43.75, P < 0.001), spatial variability (F = 14.85, P < 0.001), and their interaction (F = 2.74, P < 0.001) on phytoplankton biomass in Lake Erhai were all significant. Redundancy analysis revealed that water temperature, transparency, nutrient concentration and crustacean zooplankton were main environmental factors affecting phytoplankton community structure. [ABSTRACT FROM AUTHOR]

Abstract Denitrification plays an important role in nitrogen (N) removal in freshwater ecosystems. This internal process regulates the fluctuations of N concentration, especially for lakes with high nutrients concentrations and long residence time. Lakes in Yunnan plateau (southwestern China) provide typical cases, while studies in this region have been rare. Therefore, we studied denitrification of two lakes (Lake Dianchi in hypereutrophic state and Lake Erhai in mesotrophic) in this region. We used acetylene inhibition technique to quantify potential denitrification rate (PDR) of these lakes in April and August, 2015 and 2016. PDR of the sediments ranged 0–1.21 μmol/(N·m2·hr), and that of overlying water ranged 0–0.24 μmol/(N·L·hr). Then, we used Least Angle Regression to determine the controlling factors for denitrification. Nutrients controlled PDR from two aspects: providing essential nitrogen sources; and affecting the richness and metabolism of denitrifying bacteria. In April, both aspects limited PDR; while only nitrogen sources limited PDR in August, due to depleted nitrate and enhanced denitrifying bacteria activity. Ammonia was most significant to denitrification, indicating that nitrate from nitrification transported to the bottom of well-mixed lake provide major N source by denitrification. The high PDR and low nitrate concentrate in August were evidence of an enhanced internal N cycling by algal blooms. Graphical abstract Unlabelled Image [ABSTRACT FROM AUTHOR]

Effects of climate change and nutrient load caused by human activities on lake phytoplankton blooms have attracted much attention globally. However, their roles and synergistic effects on phytoplankton biomass and community historical succession are not well understood, especially for meso-eutrophic plateau lakes. In this study, a multi-year (1997–2022) monthly dataset including hydro-chemical and meteorological indicators of the meso-eutrophic plateau lake Erhai in China, was used to explore the contributions of climate change and nutrients on phytoplankton biomass variation and community succession. Phytoplankton biomass increased from 1997 to 2006, slowly decreased from 2006 to 2015, then increased again from 2015 to 2022, according to a generalised additive model (GAM). Alongside warming, nitrogen, phosphorus and organic matter are key drivers of long-term interannual variation in phytoplankton biomass and historical succession of the phytoplankton community. The extensive blooms in recent years were strongly associated with both organic matter accumulation and global warming. Phytoplankton biomass in northern and southern districts was greater than in central areas, with Cyanophyta and Pyrrophyta dominating in the north and Chlorophyta prevalent in the south. Since 2015, phytoplankton diversity has increased significantly, and biomass has declined in the southern district but increased markedly in the northern district. Spatial heterogeneity was caused by the spatial distribution of nutrients and the buoyancy regulation capacity of cyanobacteria. The results demonstrate that bloom mitigation responds strongly to nitrogen and phosphorus control in meso-eutrophic lakes, therefore preventing and controlling blooms through nitrogen and phosphorus reduction is still an effective measure. Given the accumulation of organic matter in recent years, synergistic control of organic matter and total nitrogen and phosphorus could effectively reduce the risk of cyanobacterial and dinoflagellate blooms. [Display omitted] • Phytoplankton was investigated in a meso-eutrophic plateau lake • Phytoplankton biomass displayed temporal and spatial heterogeneity • Warming and nutrient levels affected phytoplankton biomass • Organic matter and warming influenced phytoplankton community succession • Pollution heterogeneity and buoyancy caused spatial variation in phytoplankton [ABSTRACT FROM AUTHOR]

Best management practices (BMPs) have been widely adopted to mitigate diffuse source pollutants, and the simulated processes of its pollutant reduction effectiveness suffer from manifold uncertainties, such as watershed model parameters and climate change. We presented a novel Bayesian modeling framework for BMPs planning, integrating process-based watershed modeling and Bayesian optimization algorithm to reveal the impact of multiple uncertainties. The proposed framework was applied to a BMPs planning case study in the Erhai watershed, the seventh-largest freshwater lake in China. Firstly, priority management areas (PMAs) were identified for BMPs siting using a simulation-optimization approach. Bayesian networks were subsequently embedded to reveal the multiple uncertainty sources in the optimal planning and the reliability level (RL) is introduced to represent the probability to meet the water quality target with BMPs implementation. The results suggest that E NS of discharge and nutrients concentration simulation by LSPC are both greater than 0.5, which displays satisfactory performance. The identified PMAs account for 0.8% of the total watershed areas while contribute to more than 15% of nutrient loadings reduction. The analysis of multiple uncertainty sources reveals that precipitation is the most influential source of uncertainties in BMP effectiveness. The construction of hedgerows plays an important role in the nutrient reduction. With the improvement of the reliability levels, the cost increases sharply, indicating that the implementation of BMPs has a marginal utility. The study addressed the urgent need for effective and efficient BMPs planning by identifying PMAs and addressing multi-source uncertainties. [Display omitted] • We present an uncertainty optimization framework for BMP planning based on Bayesian networks. • We identify priority management areas for BMP siting using a simulation-optimization approach. • Optimal BMPs strategies are obtained under different reliability levels. • Precipitation is the most influential driver of uncertainties in BMP effectiveness. [ABSTRACT FROM AUTHOR]

• Climate change can pose sever pressure on lakes on the Yunnan–Guizhou Plateau. • Annual, seasonal, and extreme hydrological regimes varied significantly. • Climatic and watershed characteristic shaped the different responses of each lake. • Specific strategies for each plateau lake are urgently required in the future. Climate change and its impact on plateau lakes are of wide concern in China owing to their diverse yet fragile ecosystems. The three largest and most concerning plateau lakes (Dianchi, Erhai, and Fuxian lakes) in southwestern China were selected as case studies to demonstrate their different hydrological responses attributing to the local climatic and watershed characteristics. We processed 27 climate change scenarios according to the local climate characteristics and simulated the daily runoff of each lake basin under the historical and the 27 climate change scenarios. Then we analyzed the change of mean annual and seasonal runoff, and hydrological extremes of each lake basin. The results indicate a great risk of socio-economic and ecological for these plateau lakes as climate change will significantly alter the horological regimes of each lake basin. The mean annual runoff of the three lake basins will change from–65.24 to 54.17 %, when the air temperature increases by 1–2 °C and precipitation changes from –20 to + 20 %. Climatic and topographic heterogeneities caused each lake basin responded differently to climate change. Among them, the LFB was more sensitive to climate change than the LDB and LEB. Changes in the annual and seasonal runoff for the LFB were approximately 1.5-fold higher than that of the LDB and LEB. The hydrological extremes in the LFB also had the most significant changes. To cope with future climate change, each lake requires reasonable and effective mitigation measures. [ABSTRACT FROM AUTHOR]

To quantitatively evaluate the effects on water quality improvement caused by reducing external loadings entering Lake Erhai through inflow rivers, a one-dimensional hydrodynamic and ecological model (DYRESM-CAEDYM) was set up to simulate the water quality and water level variations. The calibrated and validated model was used to conduct six scenarios for evaluating the water quality responses to different amounts of external loading reduction at Lake Erhai. The results show (1) the total nitrogen (TN) concentration of Lake Erhai will be higher than 0.5 mg/L without any watershed pollution control during April-November 2025, which cannot meet Grade II standard of the China Surface Water Environmental Quality Standards (GB3838-2002). (2) External loading reductions can significantly reduce the concentrations of nutrients and Chla at Lake Erhai. The effects of water quality improvement will be proportional to the reduction rate of external loading reductions. (3) Internal release might be an important source of pollution It needs to be seriously considered as well as external loading for mitigating the eutrophication at Lake Erhai in the future.

The previous studies indicated that Tychonema-like strains from Lake Erhai could release geosmin so that the species was listed as the potential harmful cyanobacteria influencing the drinking water safety around Lake Erhai. But, the dynamics and biological information of this species were too limited. In this study, the polyphasic approach was used to reveal its biological characterization and the dynamics in Lake Erhai. The characters of trichomes, including filaments with solitary or bundle state, reddish-brown or blue-green color, planktonic habitat, and presence of keritomized content, were examined by the microscopic method. The 16S rDNA sequences of these strains were used for phylogenetic analysis and molecular identification. The strains were morphologically classified as Tychonema bourrellyi, and geosmin and β-ionone were identified as the major volatile substances using gas chromatography-mass spectrometry (GC-MS) analysis. No strains of T. bourrellyi were found to produce microcystin by the HPLC and mcy gene approaches. Cell numbers at 12 sampling sites in Lake Erhai were shown as an average of 3 × 10 cells L in 2009 and 2010. The obvious peaks occurred in July and August each year. This was the first report on occurrence of T. bourrellyi from outside of Europe, and T. bourrellyi was also a newly recorded species in China. Such a result demonstrated that T. bourrellyi could distribute extending from cold waters in North Europe to the warm waters in subtropical regions. It was interesting to observe the coincidence of the occurrence of T. bourrellyi with slightly eutrophicated waters since Lake Erhai had been regarded as an early phase of eutrophicated lake. [ABSTRACT FROM AUTHOR]

Artificial enhancement of lakes using filter-feeding silver carp is a technique that is widely used to manipulate and/or promote fisheries' production in Chinese lakes. To evaluate the impact of this enhancement on nutrient cycling in the water column, we analyzed two silver carp biomass gradient testing sites by stocking experimental enclosures within Lake Taihu (eutrophic) with 0, 35, 70 and 150 g m − 3 of silver carp biomass and those within Lake Erhai (mesotrophic) with 0, 20, 50 and 100 g m − 3 of silver carp biomass. Total phosphorus and dissolved nitrogen were obviously influenced by the fish density. At relatively low densities, the silver carp were able to graze for particles of food directly, resulting in a decline in phosphorus and chlorophyll- a levels within the Lake Taihu enclosures. When fish were introduced to the Lake Erhai enclosures, chlorophyll- a levels increased. Increased dissolved nitrogen levels were recorded in the Lake Taihu enclosures during the experiment, while the enhanced uptake of nutrients by increased algae resulted in decreased dissolved nitrogen levels in the Lake Erhai enclosures. We hypothesize that although silver carp could potentially reduce cyanobacteria in water bodies with large algal blooms, the relatively small change in fish in Lake Taihu is still too minor to control severe algal blooms. In relatively clean water bodies such as Lake Erhai, artificial ecological enhancement using silver carp should be evaluated carefully before action is taken in order to assess the risk of increasing small algal blooms and nutrients. [ABSTRACT FROM AUTHOR]

To study the proximal factors inducing diel vertical migration (DVM) in large and small zooplankton species in a plateau lake in China, we investigated the DVM of crustacean zooplankton in lake Erhai bimonthly from November 2009 to September 2010. We hypothesized that the factors affecting DVM behaviour in different-sized zooplankton were different. A linear regression was used to assess the relationships between environmental variables and the vertical distribution of zooplankton. All crustacean zooplankton exhibited normal DVM patterns (down during the day, up at night) across sampling months. The weighted mean depth (WMD) of all zooplankton did not show a significant correlation with the WMD of the dominant phytoplankton and chlorophyll-a. However, a negative relationship was observed between the distribution of zooplankton and water temperature in January, March, and July 2010, but the relationship was relatively weak (R2 between 0.1 and 0.4). The vertical distribution of zooplankton was primarily affected by water transparency (P0.05), whereas the factors inducing DVM behaviour differed between large and small zooplankton. Predation avoidance and phototactic behaviour may be the dominant factors influencing DVM of large species, whereas only phototaxis contributed to the migratory behaviour of small species.

Outbreaks of infectious diseases among freshwater fish damage the aquaculture industry. A technique for detecting pathogens in environmental water samples has recently been developed. In the present work, the monitoring of pathogenic viruses in Lake Erhai and Lake Dianchi (Yunnan, China) was performed. Yunnan possesses a rich diversity of cyprinid fish, and the aquaculture of freshwater fish is a highly prosperous industry in this region. Thus, Cyprinid herpesvirus 1, 2, and 3 as well as three rhabdoviruses, Infectious hematopoietic necrosis virus, Viral hemorrhagic septicemia virus, and the Spring viremia of carp virus, all of which have severe impacts on aquaculture, were targeted. Viruses in lake surface water were concentrated and then quantified/detected by real-time PCR/real-time reverse transcription PCR. Five of the six tested viruses were detected in lake water. Although there has been no reported viral outbreak in the survey lakes, our results indicate a potential risk for these viral diseases. [ABSTRACT FROM AUTHOR]

Lake Erhai is the second largest lake of Southwest China and an important drinking water source. The lake is currently defined as the preliminary stage of eutrophic states, but facing a serious threat with transfer into intensive eutrophication. The present study examined the dynamics of Microcystis blooms and toxic Microcystis in Lake Erhai during 2010, based on quantitative real-time PCR method using 16S rRNA gene specific for Microcystis and microcystin systhesis gene ( mcy), and chemical analysis on microcystin (MC) concentrations. Total Microcystis cell abundance at 16 sampling sites were shown as an average of 1.7 × 10 cells l (1.3 × 10-3.8 × 10 cells l). Microcystin LR (MC-LR) and microcystin RR (MC-RR) were the main variants. The strong southwesterly winds, anticlockwise circular flows and geographical characteristics of lake and phytoplankton community succession impacted the distribution patterns of Chl a and MC in the lake. The concentration of Chl a and MC and abundances of total Microsytis and MC-producing Microsystis (MC M) were shown to be positively correlated with pH, DO and TP, negatively correlated with SD, NO-N, TN/Chl a and TN/TP, and not correlated with NH-N, TN, dissolved total nitrogen (DTN) and water temperatures. When TN/TP decrease, Microcystis tended to dominate and MC concentrations tended to increase, suggesting that the 'TN/TP rule' can be partially applied to explain the correlation between the cyanobacterial blooms and nutrients N and P only within a certain nutrient level. It is speculated that N and P nutrients and the associated genes (e.g., mcy) may jointly drive MC concentration and toxigenicity of Microcystis in Lake Erhai. [ABSTRACT FROM AUTHOR]

Lake sediments are important archives of environmental changes and human activities, but the influences of human processes and lake spatial heterogeneity on the sedimentation of trace metals are still poorly understood. Based on 16 sediment cores from Lake Erhai (249 km2), trace metals (including As and Hg) contamination over the past century and the spatial heterogeneity and their response to the in-lake and in-watershed factors were explored. The elements were divided into two groups by cluster analysis: group I included As, Cd, Hg and Pb, and group II included Al, Fe, Ti, Cr, Cu, Ni and Zn. The element concentrations were generally stable in the low section of the cores, and started to increase since the 1980s for elements in group I, while element concentrations in group II generally decreased since the 1990s. Enrichment factor analyses identified group I elements as typical pollutants, and suggested that contamination started from the 1980s and reached maximum in the 2000s. Regional atmospheric deposition from ore mining and smelting was the main source, and anthropogenic As and Cd were also affected by watershed industrial discharges. Multi-core analyses indicated that spatial distributions and accumulation of As, Cd, Hg and Pb in the cores were affected by both human activities and sediment supply. Different from metal contamination pattern in surface sediments, high anthropogenic metal fluxes appeared in the central lake areas due to more sediment accumulation. Our study highlighted that reliable estimation of whole-lake pollutant inventories strongly relied on comprehensive analyses of multiple sediment cores and legacy input from the catchment. [Display omitted] • Spatio-temporal variations of sedimentary metals over the last century were studied. • Each metal showed similar vertical variations in cores from different lake areas. • Metals contamination started from the 1980s and reached maximum in the 2000s. • Source and sediment accumulation rate led to spatial heterogeneity of metals. • Multi-core analysis is recommended in characterising metal accumulation. [ABSTRACT FROM AUTHOR]

A comprehensive 3-dimensional hydrodynamic and eutrophication model, the environmental fluid dynamics code model (EFDC) with three functional phytoplankton groups, was applied to simulate the algal dynamics in a mesotrophic P-limited subtropical plateau lake, Lake Erhai, Southwestern China. Field investigations revealed the seasonal patterns in external total phosphorus (TP) input and TP concentration, as well as the composition of the phytoplankton community. The model was calibrated to reproduce qualitative features and the succession of phytoplankton communities, and the net primary production was calculated. The modeled daily net primary production (NPP) ranged between −16.89 and 15.12 mg C/m2/d and exhibited significant seasonal variation. The competition for phosphorus and temperature was identified as the primary governing factor of NPP by analyzing the parameter sensitivity and limitation factors of the lake. The simulation of four nutrient loading reduction scenarios suggested high phytoplankton biomass and NPP sensitivity to the external TP reduction. A significant positive correlation was found among NPP, total phytoplankton biomass and TP concentration. Overall, this work offers an alternative approach to estimating lake NPP, which has the potential to improve sustainable lake management. [ABSTRACT FROM AUTHOR]

The composition and seasonal variation of the phytoplankton and bacterioplankton community were investigated, and SPSS and redundancy analysis (RDA) were used to explore the relationship between the phytoplankton and bacterioplankton community dynamics in the typical plateau Lake of Lake Erhai from July 2009 to April 2010. Obvious seasonal variation of phytoplankton was observed, and the abundance of phytoplankton ranged from 2.02 × 106 to 57.9 × 106 cells/L. The dominant species in autumn and summer was Microcystis sp., Psephonema aenigmaticum Skuja was dominant in winter, and Microcystis sp., Aphanizonmenon flos-aquae, Asterionella sp., P. aenigmaticum, etc. were dominant in spring. The abundance of bacterioplankton in the whole lake changed between 1.93 × 109 and 4.61 × 109 cells/L showing distinct seasonal variation characteristics. The results of correlation and RDA indicated that the abundance and community diversity of bacterioplankton were significantly correlated with the abundance of phytoplankton, and the group of Bacteroidetes had obvious correlation with Microcystis sp. and other cyanobacteria, which might have some links with the harmful algal blooms in Lake Erhai. Further research is needed to study the mechanisms of interactions between phytoplankton and bacterioplankton communities. [ABSTRACT FROM AUTHOR]

The community composition and seasonal variation of bacterioplankton were investigated using 16S rRNA gene sequence analysis in high mount Lake Erhai, China. Restriction fragment length polymorphism (RFLP) analysis revealed remarkable seasonal fluctuations in bacterioplanktonic composition. A total of 1498 clones were obtained from 16 water samples, and most of clones belonged to the clusters α-Proteobacteria, β-P roteobacteria, γ-Proteobacteria, Actinobacteria, Bacteroidetes, Verrucomicrobia, and Cyanobacteria. Among these groups, α- Proteobacteria was the identified as most dominant group in spring and summer. However, the structure shifted toward a β-Proteobacterium-dominant community in autumn and winter. The clone libraries were found having the greatest diversity in winter, and some species only appeared in their specific seasons. The number of operational taxanomic uints (OTUs) predicted for the Lake Erhai ranged from 42.7 to 98.0, significantly lower than the samples from low-altitude lakes. The results of partial redundancy analysis (RDA) showed that environmental factors associated with nitrogen could play an important role in driving the conversion of two major groups in Lake Erhai. The present study indicated that the bacterioplankton communities of Erhai Lake were similar to other freshwater ecosystems as many sequences showed 93.8% - 100% homology with known sequences found in other freshwater ecosystems, but had many unique characteristics. And also part of communities predicted to be from marine ecosystems. These findings provided fundamental and specific information on the structure of bacterioplankton and the microfood web in Lake Erhai. [ABSTRACT FROM AUTHOR]

Phytoplankton samples were taken weekly from September 2009 to November 2010 in Lake Erhai. The purpose was to obtain detailed information about the composition variations in the phytoplankton community during the serious drought in 2009 - 2010 and to determine the driving force for the succession of the dominant genera. A total of 147 phytoplankton species were identified during our investigation. Among the 7 main divisions, the maximum contribution (69%) belongs to the Chlorophyta division. The alternation of the dominant group was Cyanophyta, Chlorophyta, and Bacillariophyta. The weekly variations in cell abundance and biomass of the dominant phytoplankton genera were examined. A succession characterized by Psephonema and Asterionella (spring )→Melosira (summer) →Microcystis (autumn) →Microcystis and Psephonema (winter) emerged from the monthly average biomass.Weekly variations in the Shannon-Weaver index ranged between 0.269 and 2.183. Redundancy analysis results showed varied effects of environmental factors on the different phytoplankton dominant genera, with water temperature as the driving force for the seasonal succession of the dominant genera. The shift in succession pattern is induced by light intensity variation. In addition, the dominance of Psephonema in winter is the first report in Lake Erhai in recent years. [ABSTRACT FROM AUTHOR]

• Parameters affecting thermal structure were analyzed comprehensively based on a well established 2-D hydrodynamic model to explore the main process that induces the special thermal structure of Lake Erhai. • The model results revealed that the most likely process inducing the holomixis of Lake Erhai is geothermal heat transfer from sediment to water body. • Except the actual energy, approximately an additional 12% heat flux from sediment is required to mix the entire water column of Lake Erhai in summer. The thermal structure of a lake is strongly associated its hydrodynamics and climatic conditions, and is an important basis to understand the physical, chemical, and ecological processes of the lake. Lake Erhai (100°05′–100°17′N and 25°36′–25°58′E) is a large and deep lake in Yunnan Province, located on the Yunnan–Guizhou Plateau of Southwest China. Some deep lakes located in areas adjacent to Lake Erhai with similar climatic conditions and water depths are warm monomictic lakes. However, the historical data of the surface water temperature and bottom water temperature for the past 15 years (2004–2018) showed small differences (<1 °C). However, ours and some other studies on the vertical water temperature profile showed mixing of the entire water column in different seasons. We have applied a well-established hydrodynamics model (CE-QUAL-W2) to explore the main process that induces the particular thermal structure of Lake Erhai. Model calibration was conducted twice, once with the extinction coefficient (K d) and fraction of solar radiation absorbed in the surface layer (BETA) as the main calibrated parameters, and the other considering the process of bottom-water heat exchange, represented by the sediment temperature (TSED) parameter in the CE-QUAL-W2 model. The simulation results showed that the model can reproduce water level and surface water temperature accurately with the first calibration (TSED is 14.8 °C), however, only when the TSED is greater than 24 °C, the RMSE can be less than 2 °C. The model reproduces the bottom water temperature well when the TSED value was 29.6 ± 0.37 °C. Moreover, a series of scenarios were conducted to quantify the effect of wind speed and/or tributary inflows temperature on the thermal structure of Lake Erhai, and two stability indices (Schmidt stability, Birgean work) were calculated to quantify the energy required for stratification and mixing. These results demonstrated that the most likely process to establish the holomixis of Lake Erhai is geothermal heat transfer from sediment to water column, and an additional 12% heat flux from sediment plus the actual external energy supplies from sediment are required to mix the entire water column of Lake Erhai in summer. [ABSTRACT FROM AUTHOR]

Abstract: To improve age models for lake sediment cores without suitable 14C dating materials such as terrestrial plant fossils, we investigated the radiocarbon dating of lake sediment cellulose. The cellulose fraction in the sediments was obtained by a sequential decomposition of other organic matter, and subsequently dated by AMS. In general, 14C ages of the lake sediment cellulose obtained from a 10-m sediment core from Lake Erhai on the Yunnan-Guizhou Plateau are in agreement with 14C dates from terrestrial plant fossils. For the early Holocene, however, differences of up to 1000 14C years are observed between lake sediment cellulose and terrestrial plant fossils. This disagreement is probably caused by the contribution of 14C-depleted cellulose synthesized by aquatic plants/algae in the lake. To obtain a precise and accurate chronology based on 14C ages of lake sediment cellulose, the origin of lake sediment cellulose needs to be established. [Copyright &y& Elsevier]

The article presents abstracts of several studies on environmental geochemistry. Some of the abstracts presented include "Biogeochemical Cycling of Nutrients in Karstic Catchments, Southwestern China: Linkages to Changes of Eco-Environments," by Congqiang Liu and "Emerging Organic Contamination in China," by Guibin Jiang and colleagues.

A pollen diagram from a 6.62 m sediment sequence in Lake Erhai in northwest Yunnan, China was obtained to examine the roles of climate change and human impact on the development of the Erhai lake-catchment system since 12950 cal. yr BP. The record extends back into the Younger Dryas, where the dominance of Betula and deciduous Quercus points to a relatively cold and wet winter climate. After 11 750 cal. yr BP, a warming climate coupled with enhanced summer monsoon precipitation results in the expansion of Tsuga and evergreen broadleaved trees (Cyclobalanopsis, Lithocarpus and Castanopsis). An increase in evergreen oaks and dry-tolerant species after 10 320 cal. yr BP suggests a greater seasonality in rainfall, reflecting a southward shift in the winter front across the region. This trend of increasing temperatures and seasonality is seen to continue through into the mid-Holocene and the onset of the Holocene optimum. A marked decline in arboreal taxa coupled with increased levels of grass (Poaceae) and other disturbance taxa provides the first evidence for human impact in the catchment at c. 6370 cal. yr BP. This early phase of forest clearance leads to the collapse of the natural altitudinal vegetation gradient that existed in the catchment from the Lateglacial. The subsequent expansion of secondary pine forest suggests that these early clearances were part of a sustained period of shifting agriculture. Archaeological and historical records for the region point to a gradual increase in immigration into the region throughout the late Holocene. The increased pressure on the catchment is reflected in the pollen record by a series of clearance phases, which increase in intensity after 2140 cal. yr BP, linked presumably to intensification of agriculture and early urbanization. This trend continues through the last millennium, before a sharp increase in arboreal pollen at the top of the core reflects a phase of reforestation that took place in the catchment over the last 25 years. [ABSTRACT FROM AUTHOR]

Sediment cores were collected from Lake Erhai, which is located on the Yunnan–Guizhou Plateau, a landform formed by the uplift of the Himalayas. These sediments were deposited up to about 697±15 years ago based on 210Pbex and 137Cs dating. δ13Cinorg, δ18Oinorg and δ13Corg values and concentrations of Cinorg, Corg, N and P within the sediment cores have been measured. Corg has an average deposition flux of 12.7 g/m2, and an accumulation flux of 7.20 g/m2. The calculated decomposition rate constant is 0.017 a−1 with a half life of 40 a. δ13Cinorg and δ18Oinorg values range from −1.6 to −7.9‰ and −5.7 to −13.6‰, respectively, and show similar trends over the past 700 years, which is interpreted to be controlled mainly by temperature, corresponding to climatic changes of two and half periods of a ‘warm–cold–warm’ cycle. δ13Corg ranges from −25 to −28‰, indicating that the organic matter originated mainly from land-derived plants, with overprinting from anthropogenic activities over the past 460 years (since 1537 ad). N and Porg concentrations show a similar vertical distribution to Corg. Atomic ratios of organic carbon and nitrogen (C/N) are 5.8 and 6.8 for the deposition and accumulation stages, respectively, similar to the Redfield ratio in the ocean. The C/P ratio, however, is higher than that in the ocean. The vertical distribution of carbon in the sediment cores indicates that Lake Erhai has the characteristics of both an inland lake (land-derived organic matter) and the ocean (similar C/N ratio). The lower C/N and C/P ratios in the lake Erhai sediments are characteristic for a lake at high altitude and in a subtropical region. This ‘low latitude–high altitude effect’ is probably related to the uplift of the Himalayas. [Copyright &y& Elsevier]

Some wastewater sources, such as agricultural waste and runoff, and industrial sewage, can degrade water quality. This study summarises the sources and corresponding mechanisms that trigger eutrophication in lakes. Additionally, the trophic status index and water quality index (WQI) which are effective tools for evaluating the degree of eutrophication of lakes, have been discussed. This study also explores the main nutrients (nitrogen and phosphorus) driving transformations in the water body and sediment. Lake Erhai was used as a case study, and it was found to be in a mesotrophic state, with N and P co-limitation before 2006, and only P limitation since 2006. Finally, effective measures to maintain sustainable development in the watershed are proposed, along with a framework for an early warning system adopting the latest technologies (geographic information systems (GIS), remote sensing (RS)) for preventing eutrophication. Unlabelled Image • We summarize the potential factors leading water quality degradation. • Indices for lake trophic status and water quality are summarized. • We describe the nutrients transformation and mechanisms of eutrophication. • Countermeasures to maintain the sustainable development in watershed are provided. • A framework for an early warning system of eutrophication occurrence is present. [ABSTRACT FROM AUTHOR]

• Approach for eutrophication levels evaluation is developed; • Developed approach merges TOPSIS and MCS method; • It can increase the reliability of evaluated result; • Evaluation of eutrophication level in Lake Erhai is performed; • Sensitivity of coefficient P in membership function is conducted. This study presents an approach for eutrophication evaluation based on the technique for order preference by similarity to an ideal solution (TOPSIS) method and Monte Carlo simulation (MCS). The MCS is employed to produce a normally distributed dataset based on the observed data while the TOPSIS method and membership function are used to evaluate the level of eutrophication. Herein, a eutrophication problem in Lake Erhai is evaluated to check the performance of the proposed approach. The evaluation results were consistent with the real situation when the coefficient P in the membership function is equal to 1. Moreover, the developed approach is able to (i) deal with evaluation items with inherent fuzziness and uncertainties, (ii) improve the reliability of evaluation results via MCS, and (iii) raise the tolerance to errors in measured data. A global sensitivity analysis indicated that the potassium permanganate index (COD Mn) and Secchi disc (SD) are the most sensitive factors in the developed approach. Finally, a range for the coefficient P value in the membership function was recommended. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Eutrophication of lakes is an environmental issue that has attracted increasing attention all over the world. This study analyses the monitoring data of the Lake Erhai, Yunnan Province in China with Carlson's TSI, Improving Carlson's TSI (TSI M) and TLI. The results reveal that the eutrophication index for this lake is in the Mesotrophic status. The mechanism of the eutrophication in Lake Erhai is also investigated. The mechanism shows that rate of nutrient transformation is the core issue and the process of eutrophic evolution involves natural, social, and economic factors. The restrictions on sustainable development in Lake Erhai are discussed. To maintain sustainable development, green watershed construction (GWC) and its corresponding effective measures are proposed. Moreover, lessons learned from Lake Erhai watershed management are presented, to provide valuable experiences for alleviating water pollution caused by insufficient environmental management during rapid economic development. Perspective future research works are proposed, including establishment of the early warning system with remote sensing (RS) and geographic information system (GIS) as well as the artificial intelligence (AI) technology. • Three trophic status indexes, e.g. TSI, TSI M , and TLI, are adopted to evaluate the water quality. • We analysed causes of three severe outbreaks of blooms and impacts of eutrophication in Lake Erhai. • Mechanism of eutrophication and restrictions to sustainability of Lake Erhai are demonstrated. • Effective measures to maintain the sustainable development in watershed are provided. • A successful experience of water treatment and management in Lake Erhai is demonstrated. [ABSTRACT FROM AUTHOR]

Increasing algae in Lake Erhai has resulted in frequent blooms that have not only led to water ecosystem degeneration but also seriously influenced the quality of the water supply and caused extensive damage to the local people, as the lake is a water resource for Dali City. Exploring the key factors affecting phytoplankton succession and developing predictive models with easily detectable parameters for phytoplankton have been proven to be practical ways to improve water quality. To this end, a systematic survey focused on phytoplankton succession was conducted over 2 years in Lake Erhai. The data from the first study year were used to develop predictive models, and the data from the second year were used for model verification. The seasonal succession of phytoplankton in Lake Erhai was obvious. The dominant groups were Cyanobacteria in the summer, Chlorophyta in the autumn and Bacillariophyta in the winter. The developments and verification of predictive models indicated that compared to phytoplankton biomass, phytoplankton density is more effective for estimating phytoplankton variation in Lake Erhai. CCA (canonical correlation analysis) indicated that TN (total nitrogen), TP (total phosphorus), DO (dissolved oxygen), SD (Secchi depth), Cond (conductivity), T (water temperature), and ORP (oxidation reduction potential) had significant influences (p < 0.05) on the phytoplankton community. The CCA of the dominant species found that Microcystis was significantly influenced by T. The dominant Chlorophyta, Psephonema aenigmaticum and Mougeotia, were significantly influenced by TN. All results indicated that TN and T were the two key factors driving phytoplankton succession in Lake Erhai.