岩溶洞穴系统SO_(4)^(2-)、NO_(3)^(-)来源及其对水岩作用的影响

Sources of SO_(4)^(2-) and NO_(3)^(-) and Their Disturbances to Water Rock Processes in Karst Cave Systems

为揭示洞穴系统中SO_(4)^(2-)和NO_(3)-离子来源及其对洞穴碳酸盐溶解的影响,通过对麻黄洞6个水点自2018年8月至2019年7月进行为期一个完整水文年的系统监测,对于监测结果进行综合分析.结果表明:(1)麻黄洞洞穴水水化学类型为HCO_(3)‐Ca·Mg以及HCO_(3)·SO_(4)‐Ca·Mg型;(2)通过实地调查与元素比值法综合分析可知,麻黄洞NO_(3)^(-)与SO_(4)^(2-)各水点来源存在一定差异,其中麻黄洞NO_(3)^(-)主要源于农业活动和大气N沉降,而SO_(4)^(2-)主要以农业活动、石膏溶解为主要来源,SO_(4)^(2-)和NO_(3)^(-)均参与了岩溶作用,加速了基岩的溶蚀,这一过程主要受离子浓度、径流大小以及补给模式影响;(3)基于水化学计量法和稳定同位素技术估算可知,SO_(4)^(2-)和NO_(3)^(-)洞穴水DIC的贡献为0.05~0.61,释放DIC的同时改变了水中离子浓度,对于岩溶作用形成扰动,总体呈现出旱季>雨季、滴水>裂隙水的特征.同样,由于岩溶区的复杂和不可知,在对其进行系统研究时应当注重多种方法的结合与比较,提高研究精度与可信度.

In order to reveal the source of SO_(4)^(2-) and NO_(3)^(-)in the cave water and their influence on the hydrogeochemical process,a complete hydrological year monitoring was carried out at six monitor points in Mahuang Cave from August 2018 to July 2019.The results showed as follows:(1)The cave waters hydrochemical types are HCO_(3)^(‐) Ca·Mg and HCO_(3)·SO_(4)^(‐) Ca·Mg;(2)SO_(4)^(2-) and NO_(3)^(-) are mainly derived by agricultural activities,atmospheric deposition and gypsum dissolution,and their sources are different at different drip points.NO_(3)^(-) in the Mahuang cave is mainly caused by agricultural activities and atmospheric N deposition,while SO_(4)^(2-) is supplemented by agricultural activities and gypsum dissolution;The SO_(4)^(2-) and NO_(3)^(-) both participate in the karstification and accelerate the dissolution of bedrock;(3)Based on the estimation of hydrochemistry method and stable isotope technique,the contribution of DIC of SO_(4)^(2-) and NO_(3)^(-) cave water ranges from 0.05 to 0.61.The release of DIC also changes the ion concentration in the water,causing disturbance to karstification and presenting a general pattern of Dry season>Rainy season and dripwaters>fissure water.Similarly,due to the complexity and unknowability of karst area,the combination and comparison of various methods should be paid attention to in the systematic study of karst area,so as to improve the accuracy and credibility of the study.