Application of the environmental isotope δ18O to study water flow in unsaturated soils planted with different crops: case study of a weighable lysimeter from the research field in Neuherberg, Germany.
Application of the environmental isotope δ18O to study water flow in unsaturated soils planted with different crops: case study of a weighable lysimeter from the research field in Neuherberg, Germany.
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DOI：
10.1016/j.jhydrol.2009.01.027
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发表时间：
2009-04
影响因子：
6.4
通讯作者：
C. Stumpp;W. Stichler;P. Maloszewski
中科院分区：
文献类型：
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作者：
C. Stumpp;W. Stichler;P. Maloszewski
尝试改进集中参数模型在种植不同作物的非饱和土壤中的应用。 Stumpp 等人展示了这种改进的第一步。 [Stumpp, C.、Maloszewski, P.、Stichler, W.、Fank, J., 2009。应用环境同位素 δ18O 研究种植不同作物的非饱和土壤中的水流：1. 案例研究 – 奥地利瓦格纳蒸渗计站。 《水文学杂志》] 其中，补给水中的示踪剂浓度根据降水率并通过将观测周期分为不同的植被子周期进行加权。然而，在剧烈变化的流动条件下，这种改进仍然不足以产生足够的建模结果。因此，在本文中，我们研究了高度复杂的蒸渗仪装置中的流动过程。蒸渗仪的长度为 2m，表面积为 1m2，可称重，从而得出水含量随时间的变化。这些数据使得集总参数方法能够进一步发展以适应可变流量条件。找到了一种估计补给水中示踪剂浓度（输入函数）的新方法，该方法考虑了实际蒸散率，而实际蒸散率是通过称重蒸渗计的质量间接确定的。因此，可以使用具有这种新估计输入函数的集总色散模型来以相对较高的精度研究轮作土壤中的 δ18O 传输。将集总频散模型获得的结果与更精确的瞬态流数值模拟进行了比较，但这需要更详细的土壤水力数据。两种建模方法的结果都产生了相似的系统参数。集中参数方法得出不同植被时期的含水量为0.14-0.30cm3cm−3，整个观测期间的平均值为0.22cm3cm−3。瞬态流模型得出的平均含水量为 0.21cm3cm−3。两个模型中发现的色散参数处于相同范围内。这项研究表明，即使在具有有关水平衡的附加信息的强烈变化的流量条件下，集总分散模型也适用于非饱和区域。
An attempt was made to improve the application of a lumped parameter model in the unsaturated soils planted with different crops. A first step of such an improvement was shown in Stumpp et al. [Stumpp, C., Maloszewski, P., Stichler, W., Fank, J., 2009. Application of the environmental isotope δ18O to study the water flow in unsaturated soils planted with different crops: 1. Case study – Lysimeter station “Wagna”, Austria. Journal of Hydrology] where the tracer concentrations in the recharging water were weighted according to the precipitation rate and by separating the observation period to different vegetation sub periods. However, during strongly variable flow conditions this improvement was still not sufficient enough to yield adequate modelling results. Therefore, in the present paper we investigated the flow processes in a high sophisticated lysimeter setup. The lysimeter had a length of 2m and a surface area of 1m2and was weighable which yielded water content as a function of time. This data enabled a further development of the lumped parameter approach to variable flow conditions. A new method was found to estimate the tracer concentration in the recharging water (input function) that takes the actual evapotranspiration rates into account which was indirectly determined from weighing the lysimeters’ mass. Thus, it was possible to use a lumped dispersion model with such a new estimated input function to investigate the δ18O transport in soils planted with crop rotation with relatively high accuracy. The results obtained with the lumped dispersion model were compared with more exact numerical transient flow modelling, which however requires more detailed soil hydraulic data. The results of both modelling approaches yielded similar system parameters. The lumped parameter approach resulted in water contents of 0.14–0.30cm3cm−3during the different vegetation periods and a mean value of 0.22cm3cm−3for the whole observation period. The transient flow modelling yielded a mean water content of 0.21cm3cm−3. The dispersion parameter found in both models was in the same range. This study shows that a lumped dispersion model is applicable in the unsaturated zone even under strongly variable flow conditions having additional information about the water balance.