Seasonal Hydrochemical Characteristics, Geochemical Evolution, and Pollution Sources of Lake Sha in an Arid and Semiarid Region of Northwest China

Lakes are important water sources and significantly support the local ecological and environmental balance, especially in arid and semiarid regions. For this study, the seasonal hydrochemical characteristics of Lake Sha, which are used for recreation and aquaculture, were analyzed using statistical analysis. Ionic ratio analyses, Pearson correlation analysis, saturation index (SI), and PHREEQC hydrogeochemical simulations were applied to reveal its evolution and pollution sources. Some parameters (chlorophyll-a, CODMn, TP, TN, petroleum, F−, and As) showed seasonal variations, with higher levels in summer and/or autumn due to higher temperatures, more intense human activity during the tourist season, and surface runoff during the rainy season. However, the levels of K+, Hg, and Cr6+ were not impacted by temperature and human activities, showing only slight seasonal variations. The lake water chemistry was mainly controlled by evaporation. The high concentrations of CODMn, TP, TN, and F− are mainly a result of the release of pollutants from sediment, intense evaporation, human activities, the input of Yellow River water, and surface runoff. The simulation results showed that TN increased from 8.61E-05 to 1.06E-04 mol/L, and TP increased from 1.49E-06 to 2.20E-06 mol/L due to the recharge of the Yellow River. Evaporation caused an increase in TP, TN, and F from 1.49E-06, 8.61E-05, and 4.76E-05 mol/L to 2.71E-06, 1.57E-04, and 8.66E-05 mol/L, respectively. This study provides a scientific basis for the sustainable management of Lake Sha and similar inland dry lakes.