Groundwater Quality Evolution Of Weibei Loess Tableland Irrigation District

This paper is based on loess tableland irrigation area’s unique natural and geographical,hydrogeological and socio-economic status etc. By investigating the current situation on thestudy area irrigation’ water quality, hydrogeological data and groundwater dynamicmonitoring data, we research the hydrochemical characteristics of groundwater, mainpollutants and their spatial distribution rule, groundwater dynamic characteristics（includingground water level and water quality ‘dynamic characteristics）,correlation analysis of waterquality factors and prediction of water quality.We select Baojixia-Yangmaowan irrigation district as the typical area. Baojixia-Wool bayirrigation district （referred as Bao-yang irrigation district） is located Shaanxi provinceXianyang city, which belongs to the loess plateau and is an important part of loess tablelandand agricultural production area. In accordance with the hydrogeological conditions, the studyarea is divided into9regions, then, each of the regional selects a typical well.（1） Study of hydrochemical characteristics: Groundwater salinity is less than1mg/l,belonging to freshwater, the total hardness is less than450mg/l, belonging to the softwater district; Water chemistry mostly is HCO₃-Na and HCO₃-Na.Mg, in recent years, ittransformed into HCO₃.SO4-Na and HCO₃.Cl-Na, manifested as the significant fertilizer.（2） Water quality investigation and evaluation: we implemented water quality survey andsampling and analyzed the contents of CODMn, Cr⁶⁺and NO₃^--N. Using the single factorindex method, the Nemerow index method and the fuzzy comprehensive evaluation, weevaluated water quality, the results show that the major threat of pollution of groundwater isCr⁶⁺and NO₃^--N, also, we get the main pollutants’ spatial distribution. The conclusions is thatthe groundwater quality mainly is Ⅲ,the eastern part of the water quality is worse than thewest, the major threat of pollution is Cr⁶⁺, its distribution area is tilt piedmont plain area’central and southern platform area’ triangle regional （Qiandong-Xingping-Xianyang）.（3） Groundwater level dynamic analysis: The dynamic type of the year, the tilt piedmontplain area and the central plains of depression are Irrigation·rainfall supply-Mining·runoffexcretion type, the southern ploskogorye region is rainfall supply-mining·runoff excretiontype; Inter-annual dynamic type, the tilt piedmont plain area and the central plains ofdepression transform from steady irrigation supply-runoff type to continuous decline infiltration of precipitation-mining dynamic type, the southern ploskogorye region transformsfrom turbulent descent to continued increase irrigation infiltration-mining dynamic type.（4）Groundwater chemical dynamics and correlation analysis: Based on the waterchemistry data of1982-2009, we analyzed the variations of salinity,total hardness and waterchemistry’ type, the tilt piedmont plain area is irrigation rainfall desalination-evaporationconcentrated, the central depression region is irrigation rainfall desalination-evaporationconcentrated, the southern tableland is irrigation dilute dynamic..We use person index andstepwise regression to analyze correlation analysis between salinity and other water qualityfactors and the conclusion is that salinity’ changes controlled by anion(HCO₃^-、SO₄^2-、Cl^-).（5）Groundwater quality prediction: We make use of the time series analysis and BPneural network to establish water quality prediction model base on water quality data of1998-2009, then, we get the salinity （or Cl^-） predictive value of2010,2011and2012, but thepredictive results of the two models are different, moreover, the prediction accuracy of BPartificial neural network is higher than the three time exponential smoothing model.（6）Facing the water resources and water environmental problems, we proposed the waterresources and ecological environment conservation measures for groundwater resources andprotect on loess tableland irrigation district...