气候和人类活动对典型岩溶地下河系统径流年际变化的影响

为揭示气候变化与人类活动对岩溶地下河系统年径流量的影响,以南洞地下河为研究对象,利用其1972-2014年的径流量、降水量和蒸散量数据,分析其年际变化特征。研究结果表明：研究期内径流、降水和蒸散均呈现波动减少的趋势。其中流域内径流整体以0.014亿m³/a的速度减少,降水整体以3.14 mm/a的速度减少,蒸散整体以7.94 mm/a的速度减少。通过有序聚类法和Mann-Kendall法综合确定出径流、降水的突变年份为2002年、2008年。通过累积量斜率变化率比较法,定量分解了不同时期气候与人类活动对径流变化影响的贡献率：综合考虑降水和蒸散因素,以人类活动轻微的T₁（1972-2002年）阶段为基准期,气候变化对径流减少的贡献率在T₂（2003-2008年）、T₃（2009-2014年）时期分别为-86.68%、35.92%,人类活动对径流减少的贡献率在T₂、T₃阶段分别为186.68%、64.08%。可见,人类活动是南洞地下河流域径流量年际变化的主导因素,其中生活、生产的直接耗水和土地利用/土地覆被变化影响下径流过程的变化,共同影响着径流年际变化。     

Natural and anthropogenic factors affecting the groundwater quality in the Nandong karst underground river system in Yunan, China

The Nandong Underground River System (NURS) is located in a typical karst agriculture dominated area in the southeast Yunnan Province, China. Groundwater plays an important role for social and economical development in the area. However, with the rapid increase in population and expansion of farm land, groundwater quality has degraded. 42 groundwater samples collected from springs in the NURS showed great variation of chemical compositions across the study basin. With increased anthropogenic contamination in the area, the groundwater chemistry has changed from the typical Ca–HCO₃ or Ca (Mg)–HCO₃ type in karst groundwater to the Ca–Cl (+ NO₃) or Ca (Mg)–Cl (+ NO₃), and Ca–Cl (+ NO₃ + SO₄) or Ca (Mg)–Cl (+ NO₃ + SO₄) type, indicating increases in NO₃⁻, Cl⁻ and SO₄²⁻ concentrations that were caused most likely by human activities in the region. This study implemented the R-mode factor analysis to investigate the chemical characteristics of groundwater and to distinguish the natural and anthropogenic processes affecting groundwater quality in the system. The R-mode factor analysis together with geology and land uses revealed that: (a) contamination from human activities such as sewage effluents and agricultural fertilizers; (b) water–rock interaction in the limestone-dominated system; and (c) water–rock interaction in the dolomite-dominated system were the three major factors contributing to groundwater quality. Natural dissolution of carbonate rock (water–rock interaction) was the primary source of Ca²⁺ and HCO₃⁻ in groundwater, water–rock interaction in dolomite-dominated system resulted in higher Mg²⁺ in the groundwater, and human activities were likely others sources. Sewage effluents and fertilizers could be the main contributor of Cl⁻, NO₃⁻, SO₄²⁻, Na⁺ and K⁺ to the groundwater system in the area. This study suggested that both natural and anthropogenic processes contributed to chemical composition of groundwater in the NURS, human activities played the most important role, however.