The Hydro-geochemical Characteristics And The Controlling Factorsin Nansihu-lake Area

Nansihu-Lake is the largest freshwater lake in northern China. And the basin ofNansihu Lake consists of various source rocks, these natural sources alwayscontrolled the chemical compositions in the water.At the same time, theanthropogenic inputs displayed a significant impact on the major ion concentrationand distribution in the area, due to the rapid local development of industry andurbanization and the intensive agriculture activities. The sampling of river watersand groundwater and the analysis of measured major ions allowed thehydro-geochemical research in the basin of NansihuLake.43groundwater samples and20river water samples were collected, and theirparameter were measured, including pH,K+,Na+,Ca2+,Mg2+,Cl-,SO42-,HCO3-,NO3-,F-,the hardness and TDS, and As,Hg,Cr6+,Pb2+,Cd2+.The results of SingleFactor Evaluation and Comprehensive Evaluation showed that the concentration ofHg and Cd in some samples of the surface water was higher than the limits and thesulfate and chloride data wassome abnormal, and the concentration Pb of somesamples in the groundwater was higher than the limits and the nitrate data was alsoabnormal.The variation of the distribution and concentration of the chemicalcomposition could be caused by anthropogenic inputs, including industrial andagricultural activities.Through stoichiometricanalyses of major ions in the waters, the contribution ofdifferent sources was determined for each tributary, includingatmospheric inputs(0.6-2.0%), anthropogenic inputs (1.0-70.1%) and weathering of rocks (29.3-97.0%).The average contribution from weathering of rocks in the basin was approximately61.1%, including32.0%evaporites,21.0%carbonate and8.1%silicate. Combinedwith information about runoff and drainage area, the annual contribution of totaldissolved solid (TDS) to waters was estimated to be2.35ton/km2from silicate,10.43ton/km2from carbonate and35.53ton/km2from evaporites. Associated with weathering of silicate and carbonate, the consumption of CO2was approximately7.02×10~9mol/a in whole basin.