Study on the Chemical Evolution of Groundwater in the Hydrological Cycle of a Limestone Area

根据地形分异和两个地下水系统的存在，明代高原石灰岩地区(日本西部山口县)的集水盆地被划分为6个地区：广谷(明代洞穴所在地区)、卡诺德、黑河、小野、德鲁塔基和索瓦。在这个石灰岩地区，地下水从高原脚下的4个泉水和5个洞穴中流出。用Tsurumi(1982)提出的自洽最小二乘法估计了地下水中溶解成分的来源。所有泉水中溶解成分的含量只能用三种来源的混合来解释：一种是富含石灰岩成分的，另一种是非碳酸盐岩石成分的，另一种是来自高原土壤中的尘埃和硫氧化作用的硫酸钙。秋吉洞穴的集水盆地面积为18.5平方公里，约占秋吉代高原的一半，那里的年平均降水量…更多的是1,974毫米，从明吉岛洞穴流出的平均径流估计为955毫米。底流中钙离子浓度呈现季节性波动，并随土壤二氧化碳分压的变化而变化。在土壤温度为7.2ﾟC时，腐殖质土壤中测得的土壤CO_2含量在7.2ﾟC时为0.15%，在19.0ﾟC时为1.7%，而在覆盖大部分地区的草甸中，土壤CO_2含量在3.8ﾟC时为0.08%，在20.8ﾟC时为1.2%。在开放系统条件下，秋吉代高原地下水中的钙浓度受水-石灰岩溶解平衡控制，取决于草甸土壤CO_2含量。Akiyoshi-Do洞穴地下水年均溶出2100吨石灰石，其中约5%为酸性沉积溶出，采用离子交换相吸附法流动分析痕量铜。该方法无需任何预浓缩，即可高灵敏度、选择性地测定岩溶地下水样品中的铜。通过测量暴雨后水中铜的浓度响应，估算出该岩溶地下水系统土壤带雨水对地下河流的入渗率约为10~20m/d。另一方面，氚浓度响应表明，在一场大风暴之后，滞留时间很长的地下水(约40年)进入了地下水系统。较少

On the basis of the topographic divide and the existence of two groundwater systems, the catchment basins in the Akiyoshi-dai Plateau limestone area(Yamaguchi Prefecture, Western Japan)are divided into six areas:Hirotani(where Akiyoshi-do Cave is located),Kanoide,Kuroiwa,Ono,Narutaki and Sowa. In this limestone area,groundwater flows out from 4 springs and 5 caves at the foot of the plateau. The origin of the dissolved components in the groundwater was estimated by using the self-consistent least squares method proposed by Tsurumi(1982). The contents of the dissolved components for all spring waters could be explained by the mixing of only three sources: one rich in limestone components,another in non-carbonate rock components,and the other in calcium sulfate probably originating from fallout and sulfur-oxidation in the soil in the plateau.With an area of 18.5km^2, the catchment basin of Akiyoshi-do Cave occupies about half of the Akiyoshi-dai Plateau, where the annual mean precipitati … More on is 1,974mm,and the average run-off from Akiyoshi-do Cave is estimated to be 955 mm. The calcium concentration of the baseflow showed seasonal fluctuations,and followed changes in the soil's CO_2 partial pressure. Measured soil CO_2 in the humus soil varied from 0.15% at a soil temperature of 7.2ﾟC to1.7% at 19.0 ﾟC, whereas in the meadows which cover most of the area,it ranged from 0.08% at 3.8ﾟC to 1.2% at 20.8ﾟC. The calcium concentration in groundwater issuing from the Akiyoshi-dai Plateau is controlled by the water-limestone dissolution equilibrium,under open system conditions depending on the meadow's soil CO_2 contents. A yearly average of 2,100tons of limestone was dissolved in groundwater issuing from Akiyoshi-do Cave,about 5% of which,of 110tons, was dissolved by acidic deposition.Ion-exchanger phase absorptiometry was applied to the flow analysis of trace amounts of copper. This method permitted a highly sensitive,selective determination of copper in karst groundwater samples without any preconcentration. By measuring the copper concentration response in the water after a storm,the infiltration rate of rain water from the soil zone to the underground river of this karst groundwater system could be evaluated to be about 10-20m day^<-1>. On the other hand,the tritium concentration response suggested that the faily long residence groundwater(about 40years)entered the groundwater system after a big storm. Less