Use of stable isotopes in the studies on cycling of water and ions in ecosystem.

为了解决土壤中氚水(HDO)示踪的问题，进行了以下研究：1)TCD-GC测定纯净水中HDO浓度的准确性；2)分析水样的分离和净化方法；3)海洋和陆地水域中HDO的自然丰度及其波动。1)用电解轻水得到的低HD载气(HDO浓度=11ppm)，用TCD-GC测定HDO浓度的标准误差小于2ppm。2)采用张力式蒸渗仪采集土壤溶液样品，用于田间DHO测定。当土壤吸力小于250cmH20时，提取过程中的同位素效应较小。结果表明，当土壤吸力大于300cmH20时，用张力式蒸渗仪进行抽提是不适用的。3)土壤中HDO的天然丰度在135~150ppm之间，通过田间试验进一步了解HDO在田间条件下作为水分示踪剂的应用。在用双环入渗仪测定入渗量时，发现入渗水量分布极不均匀。与土壤大孔隙系统的尺度相比，圆柱体尺度还不够大。在田间试验中，添加的HDO被迅速稀释，很难追踪到，特别是在土壤湿度较高的情况下，如泥炭土壤。

To solve the problems concerning to the tracer use of deuterium water(HDO) in soils, following studies were conducted : 1) Accuracy of the determination of HDO concentration in purified water samples by using a TCD-gaschromatography, 2) methods to separate and purify the water samples for the analysis, 3)natural abundance of HDO and its fluctuation in marine and terrestrial waters, including soil water.1) The standard error of the determination of HDO concentration by the TCD-gaschromatography was less than +2 ppm when the low HD carrier gas obtained by electrolysis of light water(HDO conc.=11 ppm) was used. 2) A tension lysimeter method was developed to collect the samples of soil solution for the DHO determination in the field. The isotope effect during the extraction was slight when soil water suction was less than 250cmH20. It is concluded that the extraction by the tension lysimeter method is hardly applicable when soil water suction is higher than 300cmH20. 3) Natural abundance of HDO in soils was in the range from 135 to 150 ppm.Some field experiments were conducted to obtain additional information on the application of HDO as a tracer of water under the field condition. During the determination of infiltration capacity by using the double ring infiltrometer, extremely uneven distribution of infiltrated water was noticed. It was concluded that the scale of cylinder was not sufficiently large in comparison with the scale of macropore systems in soils. In field experiments the added HDO was diluted rapidly and was hardly traceable, especially when the soil wetness was high, as in the case of peat soils.