农业活动对岩溶作用碳汇的影响:以重庆青木关地下河流域为例

以受农业活动影响强烈的重庆青木关地下河流域为研究对象,利用CTDP300多参数水质自动记录仪、WGZ-1型光电数字水位计、HOBO小型气象站在线自动监测电导率、水位以及降雨等数据,并获取流域耕地面积数据,于2010年分月采集地下水样,分析常规水化学和地下水溶解无机碳δ13C,初步探讨流域农业活动对岩溶作用过程和碳汇的影响,发现农业活动对岩溶作用过程产生明显的影响,进而影响到岩溶地质碳汇。地下水水化学以及地下水δ13CDIC值证实了流域地下水DIC是碳酸、硝酸和硫酸共同溶蚀碳酸盐岩的产物;每月碳酸溶蚀碳酸盐岩产生DIC占地下水中总DIC的比例在55.53%～81.25%之间,雨季(62.98%)普遍低于旱季(74.86%);碳酸溶蚀碳酸盐岩产生的DIC的量为14.67×106mol/a,其中岩溶作用产生的净CO2汇量为7.335×106mol/a,而硝酸和硫酸溶蚀碳酸盐岩产生的DIC总量为7.48×106mol/a,约占地下水中总DIC的33.8%,单位面积耕地上硝酸和硫酸溶蚀碳酸盐岩产生DIC的强度为1.89×106mol/(km2.a)。人类活动引入的硝酸和硫酸参与碳酸盐岩的溶解并改变了区域碳循环。

Agricultural Activities and Carbon Cycling in Karst Areas in Southwest China：Dissolving Carbonate Rocks and CO_2 Sink

HOBO automatic weather station,WGZ-1 photoelectric digital water table gauge and CTDP300 on-line water quality analyzer were set up to monitor rainfall,hydrochemistry and water stage at an agriculture dominated karst catchment,which is Qingmuguan underground river systemin Chongqing China.The groundwater were sampled and analyzed monthly for hydrochemistry,Dissolved Inorganic Carbon(DIC) concentration and stable carbon isotopes(δ13CDIC) in 2010.Hydrochemistry and stable carbon isotopes can verify that sulphuric acid and nitric acid take part in dissolving carbonate rocks,and the concentrations of dissolved inorganic carbon in underground river are due to the weathering of carbonate minerals by carbonic acid,sulphuric acid and nitric acid.The contribution rate that carbonic acid dissolving carbonate rocks making DIC largely varies from seasons,showing 62.98% in wet season and 74.86% in dry season,between 55.53% and 81.25%.In Qing Muguan catchment,the flux of DIC due to carbonic acid dissolving carbonate rocks is 14.67×106 mol/a,accumulating carbon sink of 7.335×106 mol/a,the flux of DIC due to carbonate rocks weathering by sulphuric acid and nitric acid is 7.48×106 mol/a,amounting to a third of total DIC of ground water.Sulphuric acid and nitric acid dissolving carbonate rocks contribute to increasing DIC of 1.89×106 mol/a every square kilometers of cultivated land.This result is obviously less than the values calculated by predecessors.This work shows that sulphuric acid and nitric acid derived from human activities involve in dissolving carbonate rocks and changing carbon cycling.