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Lake restoration usually focuses on reducing external nutrient sources. However, when sediments contain nutrients accumulated over multiple years, internal nutrient release can delay restoration progress. In lake restoration and management, it is important to understand the dynamic relationship between nutrient concentrations in a lake and internal and external nutrient sources. In this study, we quantified external nutrient inputs through measurements and compared them with internal sediment release from simulation using the PCLake+ model. Additionally, we evaluated alterations in the internal nutrient release, lake nutrient concentrations, and algae biomass (chlorophyll-a) within the lake following varying degrees of reduction in external nutrient loads. The results demonstrate that the PCLake+ effectively simulated the lake's nutrient concentration and algae biomass. Based on the PCLake+ estimates, internal nutrient loads accounted for 51 % of the total nitrogen (N) and 80 % of the total phosphorus (P) loadings in Lake Erhai in 2019. In 2020, the total contributions were 43 % for TN and 72 % for TP. We simulated four scenarios where external nutrient inputs were reduced to 25 %, 50 %, 75 %, and 99.99 % of their original levels. The 40-year simulation showed that the lake's ecological system initially exhibited a fast internal response but reached equilibrium after eight years. P concentrations took longer to reach equilibrium compared to N concentrations, probably due to the stronger binding characteristics of P. To meet the water quality target in the future, it is necessary to reduce external N and P inputs into Lake Erhai by at least 23 % and 15 %, respectively, under current conditions. Although reducing external nutrient loads can indirectly lower internal nutrient loads, water management should address both external and internal loads simultaneously, as internal release cannot be effectively reduced by external reductions alone. Additionally, the lake's internal release may continue for several years, even with reductions in external inputs., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier B.V. All rights reserved.)

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., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

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 m 2 /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 m 2 /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., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 Elsevier Ltd. All rights reserved.)

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., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

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., Competing Interests: Declaration of Competing Interest The authors declare that they have no known competing financial interests’ personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier Ltd. All rights reserved.)

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 [NH 4 ], 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 NH 4 . 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.

Spatial and temporal characteristics of release fluxes of sediment nitrogen (N) and phosphorus (P) were investigated in the high-risk period of algal blooms in Lake Erhai. Moreover, the influence factors were examined. Results show that the release flux of N and P increased in recent years, exhibiting a clear increase in the period from 2009 to 2013, and a slight increase in the period since 2013. The release flux of dissolved total nitrogen (DTN) ranged between 11.71-14.15 mg·(m 2 ·d) -1 , within which the release flux of dissolved organic nitrogen (DON) and dissolved inorganic nitrogen (DIN) were 6.39-8.42 mg·(m 2 ·d) -1 and 5.31-5.73 mg·(m 2 ·d) -1 , accounting for 58% and 42% of the DTN, respectively. The release flux of dissolved total phosphorus (DTP) ranged between 0.11-0.14 mg·(m 2 ·d) -1 , within which the release flux of dissolved organic phosphorus (DOP) and dissolved inorganic phosphorus (DIP) were 0.04-0.05 mg·(m 2 ·d) -1 and 0.07-0.09 mg·(m 2 ·d) -1 , accounting for 34% and 66% of the DTP, respectively. The distribution of release flux of N showed a decreasing order:south > north > middle, while P was north > middle > south. The release flux of N increased by 17%, 13% and 23%, and the release flux of P increased by 19%, 28%, and 29% in north, middle, and south part of Lake Erhai from 2009 to 2018. Comparing the years 2009, 2013 and 2018, although the contents of N and P were stable, the release flux of N and P in the sediment was enhanced due to increasing pH and decreasing DO. Therefore, the increasing release of nitrogen and phosphorus from sediments, caused by changes in the water environment factors, should be paid attention to for the protection of Lake Erhai.

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·m 2 ·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., (Copyright © 2018. Published by Elsevier B.V.)

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.

Based on water quality monitoring data of Lake Erhai from 1990 to 2013,the yearly and seasonally response characteristics of algal chlorophyll-a to total nitrogen (TN),total phosphorus (TP) and water temperature was investigated using quantile regression method.It indicated that water temperature was always the primary limiting factor of algal biomass indicated by chlorophyll a (Chl-a) across recent 24 years,but its limiting effect on algal Chl-a content was kept descending sharply and replaced much by nutrients (e.g.P,N) with the increasing eutrophic level.Especially the slope values of TP on Chl-a were kept ascending from -0.3 to 0.8.Since 2002,the positive effect of TN on Chl-a presented slow descending tendency,and P became the most important limiting nutrient factor of algal growth.According to the seasonal variation analysis,water temperature and N had dominant effects on algal Chl-a in spring and autumn,but they were replaced by P in the case of Chl-a>8 mg·m -3 in spring.In summer,N and P had strong interactive impacts on the algal growth,and the positive effect of P was stronger than that of N in the case of Chl-a>3 mg·m -3 .In winter,algal biomass was co-limited by temperature and P.It suggested that P reduction is the prior choice of eutrophication control of Lake Erhai,and simultaneously reducing N load is necessary in the background of global warming.In addition,so far a emergency controlling measure should be taken to monitor algal blooming due to sharp ascending of water temperature within a few days in spring and autumn.

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(4) cells L(-1) 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.

To understand the health status of aquatic ecosystem in Lake Erhai, the community structure of benthic animals was investigated based on 27 samples from 11 typical monitoring sections in March, June, September and December 2021, and the benthic index of biotic integrity (B-IBI) assessment system was also established. The results showed that Lake Erhai contains 56 genera and species of benthic animals, which refers to 4 phyla, 6 classes, 28 families and 54 genera. The assessment system of B-IBI for Lake Erhai consists mainly of the total number of classification units, proportion of chironomid individuals, and BMWP index, which obtained by range test, discriminatory power and Pearson correlation screen. The health status of aquatic ecosystem in Lake Erhai can divide into five grades according to ratio scoring method, i.e., >2.61, 2.10~2.61, 1.82~2.10, 1.42~1.82 and <1.42, representing health, sub-health, fair, poor and very poor health status, respectively. Based on above method and standard, the health of aquatic ecosystem for Lake Erhai in 2021 is fair status. Specifically, five, six, five, nine and two sampling sites were in health, sub-health, fair, poor and very poor health status, accounting for 18.5%, 22.2%, 18.5%, 33.3% and 7.4% of the total sites, respectively. [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]

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]

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]

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 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]

• 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]

Accurately measuring and estimating trends and variations in nutrient levels is a significant part of managing emerging eutrophic lakes in developing countries. This study developed an integrated approach containing Seasonal Trend Decomposition using Loess (STL) and a dynamic nonlinear autoregressive model with exogenous input (NARX) network to decompose and estimate the nutrient concentrations in Lake Erhai, a preliminary eutrophic lake in China. The STL decomposition results indicated that total nitrogen (TN) concentration of Lake Erhai progressively descended from 2006 to 2014, except for some agriculture area. The total phosphorus (TP) concentration showed an increasing trend from 2006 to 2013 and then decreased in 2014, but in the area near the tourist attractions, TP increased continuously from 2011 to 2014. Seasonal variations in TN and TP indicated that the lowest water quality of Lake Erhai occurred from July to October. Based on results obtained with STL, TP was selected as the sensitive parameter, as it showed a significant deterioration trend, and the area near the tourist attractions was selected as the sensitive area. Three variables (DO, pH, and water temperature) were selected as input parameters to estimate TP using the dynamic NARX model. The NARX modeling results demonstrated that it can accurately estimate TP concentrations with low root-mean-square error (0.0071 mg/L). The study establishes a new approach to better understand trends and variations in nutrient levels and to better refine estimates by identifying more easily accessible physical parameters in a preliminary eutrophic lake. [ABSTRACT FROM AUTHOR]