典型岩溶地下河系统不同水体中硝酸盐时空分布规律及其影响因素分析

Temporal and spatial distribution characteristics and factors influencing nitrate level in waters of a typical karst underground river system

岩溶地下河在西南地区分布极广,作为当地重要的生活和生产水源,近年来遭受了不同程度的污染,其中硝酸盐污染是岩溶地下河面临的最突出最普遍的问题之一。且由于岩溶地区含水层的高度非均质性,使得硝酸盐的分布及其形成规律很难通过模拟手段揭示。本文选取广西柳州市大良镇官村的典型岩溶地下河系统作为研究对象,分别于丰水期和枯水期系统采集不同水体样品。通过水化学及氢氧同位素示踪和统计分析等方法,分析硝酸盐浓度及稳定同位素的变化特征。结果表明,该岩溶地下河系统中,丰水期和枯水期硝酸盐浓度变化趋势一致,上湖洞到下湖洞段硝酸盐浓度逐渐升高,下湖洞到地下河出口硝酸盐浓度呈降低趋势;水体明显受到人为活动的影响,水体中的硝酸盐主要来自农业源和生活源,农业源的输入对水体中硝酸盐浓度的影响较强;由于不同季节地下河系统硝酸盐来源的差异及补给水的不同,使地下河系统不同水体的氢氧同位素特征和硝酸盐浓度分布呈现明显的季节性差异,丰水期水体中硝酸盐平均浓度大于枯水期硝酸盐平均浓度;受外源硝酸盐输入、不同补给水的混合作用及还原作用的影响,岩溶地下河系统中不同水体的硝酸盐浓度分布亦呈现明显的空间差异性。本研究通过示踪的方法分析了硝酸盐在岩溶地下河系统中的时空分布规律及其影响因素,对岩溶地区面源污染防治策略的形成具有重要意义。

Karst underground rivers, which are widely distributed in karst areas in Southwest China, are important water resources. In recent years, with the continuous economic development, karst underground rivers have been rendered polluted to variable proportions. Nitrate pollution is a prominent and common problem in karst underground rivers. The high heterogeneity of karst aquifers makes it difficult to decipher the formation and distribution process of nitrate by simulation. The typical karst underground river system in Guancun Village, Daliang Town, Liuzhou City, Guangxi was selected as the study area. The land use was dominated by agriculture and the primary pollutant was nitrate. Multiple water samples were collected during the wet and dry seasons. The nitrate concentration and stable isotope variation characteristics were analyzed employing tracing and statistical methods. The results indicated that in the Guancun karst underground river system the trending of nitrate concentration during the wet and dry periods were consistent. The nitrate levels gradually increased from the Shanghu Cave to Xiahu Cave. On the contrary, the nitrate levels decreased from the Xiahu Cave to the underground river outlet. The waters of study area were obviously affected by human activities. The nitrates in the water primarily originated from agricultural and living sources. The input from the agricultural source had a profound influence on the nitrate concentration in the water. Due to the different sources of nitrate in the recharge water in different seasons, the distribution of nitrate concentration and stable water isotopes showed significant seasonal characteristics of the underground river system with the average nitrate concentration during wet season being greater than that during the dry season. As a result of the input of exogenous nitrate, mixing waters, and reduction processes, the distribution of nitrate concentration in karst underground river system also exhibit obvious spatial distribution characteristics. In this study, tracing method was employed to analyze the spatial and temporal distribution characteristics and the factors influencing nitrate levels in the karst underground river system. The conclusions arrived at would be significant in formulating non-point source pollution prevention strategies in karst areas.