Microplastics (MPs) in freshwater environments, such as lakes, have become a significant issue in recent years. However, studies on the lakes of the Yunnan Plateau have been limited. To understand the pollution status and sources of MPs in Lake Chenghai (LCH), 36 sampling sites were selected for the surface water and sediment samples. Morphological identification, compositional analysis, abundance measurement, and spatial distribution mapping of the MPs were carried out. We also performed correlation analyses with hydrological parameters and physicochemical indexes of water and sediments. We aimed to uncover the spatial distribution patterns of the MPs in LCH, along with potential sources. Our findings revealed that all samples contained MPs and all of them were fibers. The abundance of MPs ranged from 90 to 770 n/m³ (329.44 rms) in the water and from 10 to 115 n/kg (43.19 rms) in the sediments, with particle sizes of 1-3 mm and less than 1 mm, respectively. Transparent MPs were prevalent, comprising 68% of the MPs found in the water and 63% in the sediments. The primary components of the MPs were polypropylene (PP), polyethylene terephthalate (PET), and man-made fibers (rayon). The spatial distribution showed an increasing concentration of MPs from south to north in the surface water, whereas the opposite trend was found in the sediments. Human activities, prevailing winds, and the river flowing into the lake influenced the spatial distribution pattern of the MPs. The abundance and assemblage characteristics of the MPs were directly correlated with the factors of nitrogen, phosphorus, and particle size in the water and sediments, but the correlation was not significant. The main source of MPs was the production and livelihoods of the neighboring residents, especially the use of fishing gears and nets. Since LCH shows significant pollution from MPs, there is an urgent need to control and manage the watershed in order to reduce the input of MPs in the future.

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 (COD_Mn) and total nitrogen (TN) increased after 2016, demonstrating that the pollution control measures have had little effect on the improvement of COD_Mn 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.

Algal blooms caused by eutrophication are a major global problem, and the monitoring and prediction of algal densities in lakes are important indicators of eutrophication management. However, the reliability of the commonly used chlorophyll-a (Chl-a) to characterize phytoplankton density in lake environments needs to be further investigated. In this paper, we sampled and analyzed 365 samples from nine plateau lakes in Yunnan Province during the dry and rainy seasons. The Chl-a data measured by the laboratory spectrophotometric method and the portable YSI multi-parameter water quality meter (YSI) directly used in the field were compared, and regression analysis and correlation analysis with phytoplankton density were performed. Most of the Chl-a values measured by the laboratory instrument were greater than those measured by the YSI, and the correlation between the two methods was weak (0.492, p < 0.001). The correlation between Chl-a and phytoplankton density measured by the YSI reached 0.67 (p < 0.001) in the dry season, while the laboratory methods used to measure Chl-a to characterize phytoplankton density may have led to an overestimation of phytoplankton density due to nonspecific sources of Chl-a. However, both methods are relatively inaccurate for characterizing phytoplankton density. For different trophic states of lakes, nutrient concentration changes affect the Chl-a concentration of phytoplankton. During different seasons, changes in the fluorescence intensity of phytoplankton in response to environmental conditions prevent the YSI results from reflecting the authentic phytoplankton density. Furthermore, high species diversity can lead to inconsistent changes in Chl-a and phytoplankton because the content of Chl-a in individual cells of different phytoplankton is different. The relationship between Chl-a and phytoplankton density was species specific. Therefore, when applying Chl-a to characterize phytoplankton density in lakes, it is necessary to consider environmental conditions, phytoplankton community structure and other practical conditions. In addition, laboratory analytical methods and instrumental techniques and instruments need to be improved.

Antibiotics in the aquatic environment are of great concern as novel contaminants. In this study, we investigated the occurrence, distribution, potential sources, and risk assessment of antibiotics in an interconnected river–wetland–lake system. Thirty-three target antibiotics, including sulfonamides (SAs), macrolides (MLs), fluoroquinolones (FQs), tetracyclines (TCs), and chloramphenicol (CLs) belong to five common groups of antibiotics, were tested from water samples collected in the Panlong River, Xinghai Wetland, and Lake Dian (or Dianchi). Mass spectrophotometry was used to detect the target antibiotics, and the water quality parameters were measured in situ. We found four antibiotics, lincomycin (LIN), trimethoprim (TMP), sulfamethoxazole (SMX), and ofloxacin (OFL), with relatively low concentrations at the ng/L level, and detection rates among sample sites ranged from 42.3% to 76.9%, with maximum concentrations of 0.71 ng/L~5.53 ng/L. TMP was not detected in the Panlong River but appeared in the wetlands and Lake Dian. Midstream urban areas of the Panlong River showed the highest pollution among sites. Antibiotic concentrations were positively correlated with total nitrogen (TN) (p < 0.05) and showed some negative correlation with pH, salinity, and DO. According to the risk assessment, antibiotics in water do not pose a threat to human health and aquatic ecosystems, but a potentially harmful combined effect cannot be excluded. Our research offers a geographical summary of the distribution of antibiotics in urban river, wetland, and lake ecosystems in the plateau (PWL), which is important for predicting the distribution characteristics of antibiotics in the plateau water environment and establishing a standardized antibiotic monitoring and management system for the government.

Due to the dual influence of climate change and human activities, the water cycle patterns in the lakesheds of the Yunnan karst plateau are undergoing significant changes, leading to increasingly prominent ecological issues. In the history of Lake Yangzong, an artificial water-diversion channel was excavated, altering the lake basin structure. Human activities have intensified, posing severe challenges to water resource supply and water security in recent decades. To investigate the significant increase in human activities, the temporal and phase changes, and the resulting transformation of the water and carbon cycles in the Lake Yangzong basin, we applied X-ray fluorescence spectroscopy (XRF) to scan elements continuously in a 10.2 m sediment core from this lake. By combining correlation analysis, principal component analysis (PCA), core chronology, and total organic carbon (TOC) content, we reconstructed the historical sequence of geochemical element contents in the Lake Yangzong catchment over the past 13,000 years. The results show that PC1 and PC2 contribute 78.4% and 10.3%, respectively, suggesting that erosion intensity is the main factor influencing the lake sedimentation process. From 13,400 to 680 cal a BP (calibrated years before the present), the sedimentation process in Lake Yangzong was mainly controlled by climatic conditions, with vegetation degradation during cold periods and relatively high erosion intensity in the watershed. During the Yuan dynasty, a province was established by the central government in Yunnan, promoting settlement and attracting a large number of immigrants from other provinces to Yunnan. Human activities in the Lake Yangzong basin began to intensify, surpassing natural changes and becoming the dominant force influencing the sedimentation process. In the Ming and Qing dynasties, the population and cultivated land area in Yunnan further increased, resulting in the significant exacerbation of erosion and soil loss in the watershed due to vegetation destruction. In the year 1388, the Tangchi Canal was excavated, transforming Lake Yangzong to an outflow lake, causing Ca²⁺ to be lost through the Tangchi Canal and preventing the formation of precipitation due to oversaturation. The research results indicate that human activities in the Lake Yangzong area have intensified since the Yuan dynasty, leading to increased erosion intensity. The excavation of the outflow canal transformed Lake Yangzong from an inland lake basin into an outflow state, simultaneously generating a significant transformation in the water and carbon cycling patterns in the watershed.

Habitat quality (HQ) is crucial for assessing biodiversity and serves as a key indicator of ecosystem services and health. However, the spatial and temporal evolution of HQ under varying human activity intensities remains poorly understood. We employed the integrated valuation of ecosystem services and trade-offs model to analyze the spatiotemporal distribution and evolutionary characteristics of HQ in Jiawang District (JWD), an area experiencing resource extraction, depletion, and urban expansion. We utilized Pearson correlation analysis, partial least squares-path modeling, the generalized additive model, and patch-generating land use simulation to explore the impact of human activity on HQ and the mechanisms of multifactorial interactions. Our findings revealed the following: (1) From 2000 to 2030, HQ in JWD generally declined, with high- and low-quality areas in the north and east and the west and south, respectively. (2) The land use intensity index and population density were significantly correlated with HQ, emphasizing the role of human-driven land use changes. (3) Topographic factors were positively correlated with HQ but influenced it indirectly through land use. (4) Land use emerged as a critical intermediary influencing HQ, with climate, topography, population, and economy exerting indirect effects. These results provide insights for biodiversity conservation and sustainable urban development.