不同地下水位深度条件下地表径流过程中溶质迁移规律研究

Chemical transport from soil into surface runoff under different ground-water tables

【目的】探明不同地下水位深度条件下,地表径流过程中溶质的迁移规律。【方法】采用模拟试验,研究3种地下水位(地下水位与地表持平、低于地表5和10cm)及不同地表径流流速下(90,120,200,250mL/s),土壤溶质迁移到地表径流过程中,其在3种途径(土壤侵蚀、伯努利效应、扩散)下的变化规律。【结果】当地表径流流速小于200mL/s时,随着地表径流流速的增加,土壤溶质流失加剧,伯努利效应和扩散作用是引起土壤溶质流失的主导因素;当地表径流流速大于200mL/s时,土壤侵蚀是引起土壤溶质流失的主导因素。径流60min后,当地下水位低于地表5～10cm时,随着土层深度的增加,土壤剖面中溴化物质量浓度则逐渐增大。当地下水位与地表持平时,混合层深度为0.9～4.6mm;当地下水位低于地表5和10cm时,混合层深度均小于2.5mm。【结论】土壤溶质迁移过程与地表径流流速和地下水位高低有重要关系。

[Objective] The study was conducted to prove chemical transport processes under different soil hydrologic conditions. [Method] We developed a laboratory flow cell and experimental procedure to quantify chemical transport from soil to runoff water by each of the individual process. 1） erosion;2） Bernoulli effect;and 3） diffusion under groundwater table with the same height, 5 cm,and 10 cm beneath the soil surface by 4-kinds of surface runoff flow rates （90,120,200,250 mL/s）. [Result] Our data proved that soil chemical loss aggravated as runoff flow rate increased ; nevertheless , we had additional quantitative data describing the contribution from each individual chemical loading process under different surface runoffs and soil hydrologic conditions. When surface runoff velocity was less than 200 mL/s, Bernoulli effect and diffusion had a great contribution to chemical loss from soil to runoff. On the contrary, erosion was the dominant factor for chemical loss. After 60-min surface runoff,when groundwater table was 5-10 cm lower than soil surface. Bromide concentration increased in soil profile as soil depth increased. According to our data,the mixing zone depth reached between 0.9-4.6 mm when the under groundwater table was of the same height with soil surface,and less than 2.5 mm when the under groundwater was 5-10 cm lower than soil surface. [Result] Chemical transport has a significant relationship with surface runoff flow rate and groundwater table.