δ¹⁵N And Trace (Macro) Elements In Groundwater In Jinfo Mountains

Due to special hydrogeological structure,groundwater in karst areas is easy to mixt with rainwater and surface water.This leads to its geochemical properties sensitive to reflecting environmental changes.Jinfo Mountains represent a typical karst region. its research work on geochemistry is just in underway stage,and water resource and hydrochemistry data are limited;besides,drought and excessive rain weather occurred in Chongqing municipal(including Jinfo Mountains)during summer of 2006 and 2007, many towns and villages were suffered.From July 2006 to July 2007,and the author had ever five-times collected data in a large-scale in Jinfo Mountains.By field sampling and laboratorial analysis,and main selecting the carriers ofδ¹⁵N and trace elements, works over the difference of karst spring water quality within different geological backgrounds.Hereby,it can reveal the main controlling and influencing factors of the groundwater quality,and evaluate the groundwater resource in Jinfo Mountains area.It can offer the villager instructions for seeking drinkable groundwater if the drought or excessive rain weather occurs again,meanwhile,provide scientific support for the rural safe drinking in the karst region of southwest china.Sample analysis methods:titration for testing the contents of HCO₃^-,CO₃^2-,Cl^-; ultraviolet spectrophotometer for testing the concentrations of SO₄^2-,NO₃^-;TOC analysis for testing the content of total organic carbon;ICP-OES for testing macro elements(K,Na,Ca,Mg)and trace elements(Fe,Mn,Ba,Sr,Cu,Zn,Al etc.); anion exchange colophony for enriching NO₃^-,and Flash EA1112-Conflo-IRMS online for testing the value ofδ¹⁵N.This study proof-tests the measured data by comparing the field data and the laboratorial data,balance verifying cations and anions,and checking relative standard deviation.According to the data analysis,conclusions are made as below:(1)The groundwater hydro-geochemical types of the study zone are Ca-HCO₃ and Ca,Mg-HCO₃.Based on the spatial distribution characteristics of 6 spring groups,it educes that ground water mainly roots in atmospheric precipitation,and its chemical components are mainly controlled by formation lithology,landform and transmit time of groundwater.(2)The drought and excessive rain weather caused deterioration of groundwater quality in Jinfo Mountains.Discussed the space-time distribution characteristics and influence factors of the trace(macro)elements of the groundwater in Jinfo Mountains area.The contents of five elements include As,Cr,Cu,Zn,Hg are comparative low, most of which are lower than equipment limit;In spatial scale,it has a trend that the element content increase from the top(protected zone)to the piedmont(nonprotected zone),separate ones are exceptionally high;In time scale,different elements change quite differently within the alternation of summer and winter.The distribution are related to lithologic and chemical nature of water-bearing media,the pH value of groundwater,runoff conditions,oxidation-Reduction environment,the impact of human activities,etc.(3)Discussed the NO₃^- contamination status of the groundwater in Jinfo Mountains area in particular.No.1,No.16,No.19 springs have the highest content of nitrate, 57.85mg/L in average,which could influence production and living.Derive from analyzingδ¹⁵N,the change range is -8.615‰～+11.27‰in this area.The NO₃^- roots in manure,fertilizer,natural soil,industrial castoff and sewage.It's a caution for people to protect own water source.And there's little disturbance from bacteria alike organism in this study area.(4)Most of the groundwater is controlled by the geological background,all the contents of evaluation index are low,water quality is fine.But it's influenced by human activities in a certain extent,which represents the increment of Ca²⁺,Cl^-,NO₃^-,SO₄^2- contents,especially NO₃^-,has already exceed the gradeâ…¢water limit defined in Quality standards of groundwater,which has become the main contaminated factor of groundwater in Jinfo Mountains area.Therefore,it's an urgent need to notify the residents about the condition,and take action to protect the groundwater resource.