Satellite remote sensing provides a powerful tool for assessing lake water surface temperature (LWST) variations, particularly for large water bodies that reside in remote areas. In this study, the MODIS land surface temperature (LST) product level 3 (MOD11A2) was used to investigate the spatiotemporal variation of LWST for 56 large lakes across the Tibetan Plateau and examine the factors affecting the LWST variations during 2000–2015. The results show that the annual cycles of LWST across the Tibetan Plateau ranged from −19.5 °C in early February to 25.1 °C in late July. Obvious diurnal temperature differences (DTDs) were observed for various lakes, ranging from 1.3 to 8.9 °C in summer, and large and deep lakes show less DTDs variations. Overall, a LWST trend cannot be detected for the 56 lakes in the plateau over the past 15 years. However, 38 (68%) lakes show a temperature decrease trend with a mean rate of −0.06 °C/year, and 18 (32%) lakes show a warming rate of (0.04 °C/year) based on daytime MODIS measurements. With respect to nighttime measurements, 27 (48%) lakes demonstrate a temperature increase with a mean rate of 0.051 °C/year, and 29 (52%) lakes exhibit a temperature decrease trend with a mean rate of −0.062 °C/year. The rate of LWST change was statistically significant for 19 (21) lakes, including three (eight) warming and 17 (13) cooling lakes for daytime (nighttime) measurements, respectively. This investigation indicates that lake depth and area (volume), attitude, geographical location and water supply sources affect the spatiotemporal variations of LWST across the Tibetan Plateau.

A municipal wastewater treatment plant plays an important role in treating urban sewage and reducing the quantity of pollutants discharged into rivers. However, the energy consumption of the municipal wastewater treatment industry is large. High energy consumption indirectly produces ecological damage, accelerates the energy crisis, and increases carbon emissions. For energy conservation and emission reduction in wastewater treatment plants, it is first necessary to identify the main factors influencing energy consumption. Electricity consumption accounts for more than 80% of the energy consumption of wastewater treatment plants. Wastewater quantity and wastewater quality have become the key influencing factors of energy conservation and consumption reduction in wastewater treatment plants. In this study, a municipal wastewater treatment plant in Northeast China was selected as the research object, and the measured data, such as air temperature, wastewater quantity, wastewater quality, and electricity consumption of the plant from 2017 to 2020 were statistically analyzed to explore the influences of temperature and wastewater quantity and wastewater quality indicators of influent and effluent on energy consumption. Firstly, the range of influent quantity in the wastewater treatment plant was large. The influent quantity in summer was high because some rainwater entered the sewage treatment plant. In winter, average daily electricity consumption (ADEC) was higher than that in summer. The relationship between ADEC and the wastewater quantity showed a positive correlation, and ADEC slowly increased with the increase in wastewater quantity. Electricity consumption per unit of wastewater (UEC) was negatively correlated with the wastewater quantity, but the correction coefficient in winter was larger than that in summer. Secondly, the ranges of chemical oxygen demand (COD_Cr) and ammonia nitrogen in influent were large, and the ranges of COD_Cr and ammonia nitrogen in effluent were small. Influent COD_Cr concentration was negatively correlated with influent ammonia nitrogen concentration. ADEC increased slightly with the increase in influent COD_Cr concentration. In winter, the increasing trend of ADEC with the influent COD_Cr concentration was higher than that in the summer. The increasing trend of UEC with the increase in influent COD concentration in summer was more significant than that in winter. Thirdly, influent COD_Cr in 11.6% of the samples exceeded the corresponding designed value, and influent ammonia nitrogen concentration in 41.4% of the samples exceeded the corresponding designed value. Effluent COD_Cr in 10.6% of the samples exceeded the First Level Class B standard in “Discharge Standard of Pollutants for Municipal Wastewater Treatment Plants (GB18918-2002)”, and unqualified COD_Cr in 94% of the effluent samples was ascribed to the unqualified ammonia nitrogen concentration in the influent samples. The electricity consumption level under abnormal conditions was higher than that under normal conditions. Fourthly, ADEC was positively correlated with the average daily COD_Cr reduction. The correction coefficient of ADEC with average daily COD_Cr reduction was greater in winter than that in summer. Fifthly, the average electricity consumption per unit of wastewater was close to the national average energy consumption, displaying the characteristics of high energy consumption in winter and low energy consumption in summer. The correlation analysis results of unit electricity consumption and temperature showed that when it was below 0 °C, the lower the temperature, the higher the electricity consumption. In Northeast China, the influences of seasons and temperatures on the electricity consumption of sewage plants were obvious. Accordingly, it is necessary to implement the diversion of rainwater and sewage, reduce the discharge of unqualified wastewater from enterprises, and take thermal insulation measures in winter. In addition, activated sludge microorganisms suitable for a low temperature area and the optimal scheduling of sewage pipe networks can also improve the operation and management of sewage treatment plants.

Most studies have concentrated on the distribution of polycyclic aromatic hydrocarbons (PAHs) in air, water, and soil; however, little is known about their behavior during urban wet deposition. During frequent urban rainstorms, surface runoff carries large amounts of organic pollutants into water, which has a significant impact on the quality of the water environment. “Poseidon” made landfall in Jilin Province on 27 August, 3 September, and 7 September 2020, respectively, causing some impact on the surface water. Gas chromatography–mass spectrometry (GC–MS) was used to measure the concentrations of 16 major PAHs in stormwater and water samples from the Yitong River. The PAH concentrations in rainwater runoff gradually decreased with increasing rainfall duration. The PAHs in the Yitong River water samples were mainly composed of two to three rings, with total concentrations ranging 279.19–756.37 ng/L. Ratio characterization and principal component analysis of the sources of PAHs in the water samples revealed that some water bodies had also been contaminated by oil spills in addition to combustion emissions from coal and motor vehicle oil. Health and environmental risks were assessed for PAHs in water bodies from the Yitong River, and health risk assessment showed that exposure to PAHs in the water is not a health risk for human beings; however, the risk for children is higher than that for adults and requires attention. Although the environmental risk is moderate, the risk from Benzo(a)anthracene(BaA) alone is high and requires ongoing attention. In terms of the sustainability of drinking water sources, consideration should be given to taking necessary regulatory and protective measures to prevent further contamination. These results serve as a guide for managing PAHs in urban water bodies and managing water pollution.

Chromophoric dissolved organic matter (CDOM) is a valuable optically active substance. This study examined the seasonal characteristics of fluorescent CDOM components in the Yinma and Songhua rivers, highly polluted watershed tributaries of the Songhua River, and a drinking water source for the city of Changchun, China. Parallel factor analysis (PARAFAC) and excitation-emission matrix (EEM) spectra were used to assess CDOM fluorescence. Four components attributed to CDOM in 51 water samples were identified: three were humic-like (C1, C3, and C4) and one was protein-like (C2). The average fluorescence intensities of the four components showed seasonal variation from May to November 2016. A positive linear correlation was found between components C3 and C4 (R = 0.86, p<0.001). The results from this investigation demonstrated that the frequency of rainfall and human activities may be the main factors influencing the quantity and quality of CDOM in samples collected from the watershed, and that the Yinma and Yitong rivers were polluted by terrestrial and agricultural pollution. Furthermore, the utility of combining EEM fluorescence and PARAFAC to study CDOM dynamics for different seasons and to quantify CDOM components for similar environmental (water quality) conditions was established.