Analysis on temporal and spatial variation characteristics of karst groundwater hydrochemistry in Jinci spring area based on EOF and M-K Models

In order to study the temporal and spatial variation of karst groundwater hydrochemistry in Jinci spring area, based on the water quality data of representative monitoring points of karst groundwater in the study area from 2001 to 2014, pH, the seven major ions (K+、Na+、Ca2+、Mg2+、HCO3-、SO42-、Cl-)and TDS were selected as the factors for the water quality assessment. The methods combing Empirical Orthogonal Function (EOF) decomposition with MannKendall(M-K) mutation analysis were used to separate the temporal and spatial structure of 14 years’ hydrochemistry fields in Jinci spring area. The results show that,(1) In terms of spatial distribution, pH decrease from north to south in Jinci spring area, the low value region appears in the south of middle reaches of Fenhe River. The spatial variation trends of Ca2+、Mg2+、HCO3-、SO42-and TDS are similar to that of the pH values, which gradually increase from north to south, and the contour line of high value appears in Gujiao region. Although the contents of K++ Na+ and Cl- are generally low in the whole spring area, the contents of K++ Na+ are relative high in Wangfeng and Xizhai areas at the boundary of the spring area, and the content of Cl-increase in Gujiao and Xihuayuan area. (2) In terms of temporal evolution, from 2001 to 2014, the contents of pH, Mg2+, K++ Na+, HCO3- and Cl- fluctuated in the mean value. The contents of Ca2+ and SO42- decreased yearly, and showed a obviously downward trend after 2008 and 2009. TDS showed a significant downtrend from 2005 to 2007 ,while the downward trend was not remarkable at other periods.