5. Conclusions
This study investigated the stable isotope of precipitation and water level, stable isotope and hydrochemistry of groundwater around Qinghai Lake. The LMWL was δ2H = 7.80 δ18O+10.98, indicating that some non-equilibrium evaporation processes occurred as raindrops fell below the cloud base, and some continental moisture recycled to precipitation under low relative humidity conditions. Most of the groundwater points lay close to the LMWL, and the slope of LEL of groundwater was lower than the slope of LMWL, indicating that the groundwater around Qinghai Lake mainly came from the precipitation at different altitude in the basin, which had been undergone variable degrees of evaporation before infiltration. Most of the groundwater was slightly and moderately hard freshwater, and the hydrochemical type of groundwater was Ca-Mg-HCO3. The chemistry of groundwater would be mainly controlled by carbonate dissolution around Qinghai Lake. Meanwhile, the groundwater sources at east and west of Qinghai Lake were relative complex.
Most of the groundwater was slightly and moderately hard freshwater and fell within the standards for drinking water in all indices. However, the groundwater in location G4 (TDS, Cl-, and NO3-), G6 (TDS and Na+), G11 (NO3-), G16 (NO3-), G24 (NO3-) and G25 (TDS, Na+ and NO3-) were all currently exceed the drinking standards and not suitable for drinking. Overall, the impacts of livestock manure and waste water on groundwater quality could not be ignored around the lake. Scientific planning and engineering management of livestock manure and wastewater discharge in animal husbandry regions are very necessary to be carried out urgently, which could not only protect water resources for drinking, but also contribute to human health and sustainable development of the environment of the Qinghai-Tibet Plateau.