Impacts of global change on two tropical, high mountain lakes in Central Mexico

Relationships between water quality of a long-distance inter-basin water diversion project and air pollution emissions along the canal: Distributions, lag effects, and nonlinear responses

Understanding and quantifying the influences and contributions of air pollution emissions on water quality variations is critically important for surface water quality protection and management. To address this, we created a five-year daily data matrix of six water quality indicators-permanganate index (CODMn), NH3-N, pH, turbidity, conductivity, and dissolved organic matter (DOM)-and six air pollution indicators-O3, CO, NO2, SO2, 2.5 μm particulate matter (PM2.5), and inhalable particles (PM10)-using data from seven national monitoring stations along the world's longest water-diversion project, the Middle Route of the South-to-North Water Diversion Project in China (MR-SNWD). Multivariate techniques (Mann-Kendall, Spearman's correlation, lag correlation, and Generalized Additive Models [GAMs]) were applied to examine the nonlinear relationships and lag effects of air pollution on water quality. Air pollution and water quality exhibited marked spatial heterogeneity along the MR-SNWD, with all water quality parameters meeting Class I or II national standards and the air pollution indicators exceeding those thresholds. Except for CODMn and DOM, the other water quality and air pollution indicators exhibited significant seasonal differences. Air pollution exhibited significant lag effects on water quality at the northern stations, with NO2, SO2, PM2.5, and PM10 being highly correlated with changes in pH, with an average lag of 17 d. Based on the GAMs, lag effects enhanced the significant nonlinear relationships between air pollution and water quality, increasing the average deviance explained for CODMn, NH3-N, and pH by 93%, 24%, and 41%, respectively. These findings provide a scientific basis for protecting water quality along the long-distance inter-basin water-diversion project under anthropogenic air pollution.

Seasonality of hydrogeochemical evolutions and isotopic variabilities (δ18O, δ2H and d-excess) in the surface water as well as groundwater from tropical central-south Mexico

Due to adverse impact of the global warming on hydrological resources, we intended to document the hydrogeochemical evolutions of surface and groundwater at tropical central-south Mexico in terms of seasonality of rock-water interaction, precipitation/evaporation variation and moisture source by evaluating the major ion chemistry in Piper and Gibbs plots, Durov diagram and through estimation of the chloro-alkaline indices as well as assessing the stable isotope compositions (δ18O and δ2H) in samples from different seasons of a year. Surface water of the Lake Coatetelco shifted from mostly Ca-Mg-HCO3 facies in wet summer-autumn to Na-HCO3-Cl facies in the dry spring due to elevated Na, Cl and HCO3. Greater evaporation in spring led to a maximum δ18O enrichment of ca.7‰ compared to the other seasons, and much depleted deuterium excess (-40.92‰ to -39.20‰). Interaction of the lake water with subsurface carbonate lithologies, and comparable isotopic compositions reflected the enhanced interaction between the surface water body and aquifers in the wet autumn. Effect of seasonality, however, was unclear on the groundwater facies, and its heterogenous composition (Ca-Mg-HCO3, Na-HCO3-Cl and Na-HCO3) reflected the interactions with different lithologies. Fractionations in isotope compositions of the groundwater were caused from recharge at different elevations, seasonality of moisture sources and moisture recycling. The water-mineral saturation index was an efficient proxy of seasonality as the lake water and groundwater (avg SIcalcite > 0.5) of the dry autumn were saturated with calcite. This vital information about carbonate precipitation, pCO2 and chemical facies would be useful for the better interpretation of paleoclimate archives in this region.

Comparison of Typical Alpine Lake Surface Elevation Variations and Different Driving Forces by Remote Sensing Altimetry Method

Alpine lakes play a significant role in improving watershed ecology, adjusting water storage, and managing regional water resources. They are also a valuable freshwater reservoir, flood storage, and species gene pool in Central Asia. This article validated the accuracy of the CryoSat-2 footprints altimetry dataset for the Lake Bosten and Lake Issyk-Kul ranges. The time series for the surface elevations of the Central Asian alpine lakes Karakul and Chatyrkul were established, based on footprints altimetry data. The lake hydrological drivers were analyzed using remote sensing meteorological reanalysis data of the lake basins. The following main conclusions were reached. The CryoSat-2 footprints altimetry dataset has high confidence in lake surface elevation monitoring. Compared with Hydroweb monitoring results, the agreement between the monitoring results in the range between Lake Bosten and Lake Issyk-Kul are 0.96 and 0.84. The surface elevation of Lake Karakul shows an overall increasing trend with a variation rate of +7.7 cm/yr from 2010 to 2020, which has a positive correlation with the temperature in the basin. This indicates that the increased temperature, which results in the increased snow and ice meltwater in the basin, is the main driving force of the increased lake evolution. The lake surface elevation of Lake Chatyrkul shows an overall decreasing trend, with a variation rate of -9.9 cm/yr from 2010 to 2020, which has a negative correlation with the temperature in the basin. This suggests that Lake Chatyrkul is poorly recharged by snow and ice meltwater. The main driving force of its evolution is the increased evaporative output of the lake due to the increase in temperature. These conclusions prove that temperature and alpine glacial variability within the lake basin play an important role in lake surface elevation variations in alpine regions of Central Asia.