Catchment conceptualisation for examining applicability of chloride mass balance method in an area with historical forest clearance
Catchment conceptualisation for examining applicability of chloride mass balance method in an area with historical forest clearance
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DOI：
10.5194/hess-14-1233-2010
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发表时间：
2009-11
影响因子：
6.3
通讯作者：
H. Guan;A. Love;C. Simmons;J. Hutson;Z. Ding
中科院分区：
文献类型：
--
作者：
H. Guan;A. Love;C. Simmons;J. Hutson;Z. Ding
抽象的。在估算地下水补给量的各种方法中，氯化物质量平衡法（CMB）是最常用的方法之一，尤其适用于干旱和半干旱地区。广泛的原生植被清除，在全球许多地区都很常见，改变了地表边界条件，提出了一个问题，即目前的系统是否已经达到新的氯化物平衡，需要一个CMB应用。虽然一维CMB可以应用于水和氯离子通量局部处于稳定状态的点，但CMB方法通常应用于流域尺度，因为山区存在显著的横向流动。CMB方法的适用性，各种氯平衡条件下的几个概念集水区类型进行了研究。的概念，结合当地的气候条件，被证明是有用的，在评估是否集水区已达到新的氯化物平衡。六个概念集水区类型进行了测试与11个选定的集水区在山高山脉（MLR），沿海丘陵地区在南澳经历了广泛的历史森林清除。结果表明，11个集水区中有6个符合VI型氯平衡条件（氯不平衡与增益流），与流氯输出（O）的比例超过大气氯输入（I），或集水氯O/I比，范围从2到4。两个集水区符合V型氯平衡条件（氯不平衡与流失流），集水区氯O/I比约为0.5。对于这些V类和VI类集水区，CMB方法不适用。结果还表明，无论是氯O/I比小于1，也不是一个低的季节性波动的径流氯离子浓度（低于4的因素）保证在研究区域的氯离子平衡条件。大的氯O/I值（大于1）和水流氯浓度的大波动（系数为10及以上）通常表明氯不平衡或跨流域水转移，或两者兼而有之，CMB方法不适用。基于VI类集水区的氯O/I值与年降水量之间的回归，MLR中年降水量为900 mm的集水区最有可能达到新的氯平衡，如果没有跨集水区水转移发生，则可以应用CMB方法。CMB适用于一个集水区在氯化物平衡，建议地下水净补给27毫米/年，约3%的年降水量。
Abstract. Of the various approaches for estimating groundwater recharge, the chloride mass balance (CMB) method is one of the most frequently used, especially for arid and semiarid regions. Widespread native vegetation clearance, common in many areas globally, has changed the land surface boundary condition, posing the question as to whether the current system has reached new chloride equilibrium, required for a CMB application. Although a one-dimensional CMB can be applied at a point where the water and chloride fluxes are locally in steady state, the CMB method is usually applied at a catchment scale owing to significant lateral flows in mountains. The applicability of the CMB method to several conceptual catchment types of various chloride equilibrium conditions is examined. The conceptualisation, combined with some local climate conditions, is shown to be useful in assessing whether or not a catchment has reached new chloride equilibrium. The six conceptual catchment types are tested with eleven selected catchments in the Mount Lofty Ranges (MLR), a coastal hilly area in South Australia having experienced widespread historical forest clearance. The results show that six of the eleven catchments match a type VI chloride balance condition (chloride non-equilibrium with a gaining stream), with the ratios of stream chloride output (O) over atmospheric chloride input (I), or catchment chloride O/I ratios, ranging from 2 to 4. Two catchments match a type V chloride balance condition (chloride non-equilibrium with a losing stream), with catchment chloride O/I ratios about 0.5. For these type V and type VI catchments, the CMB method is not applicable. The results also suggest that neither a chloride O/I ratio less than one nor a low seasonal fluctuation of streamflow chloride concentration (a factor below 4) guarantees a chloride equilibrium condition in the study area. A large chloride O/I value (above one) and a large fluctuation of streamflow chloride concentration (a factor of 10 and above) generally indicates either a chloride disequilibrium, or cross-catchment water transfer, or both, for which the CMB method is not applicable. Based on regression between chloride O/I values and annual precipitation for type VI catchments, a catchment with annual precipitation of 900 mm in MLR has most likely reached new chloride equilibrium, and the CMB method can be applied if no cross-catchment water transfer occurs. CMB is applied to one catchment at chloride equilibrium, suggesting a net groundwater recharge of 27 mm/yr, about 3% of annual precipitation.