Characteristics of local groundwater recharge cycles in South African semi-arid hard rock terrains - rainwater input
Characteristics of local groundwater recharge cycles in South African semi-arid hard rock terrains - rainwater input
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南非半干旱硬岩地形当地地下水补给循环特征——雨水输入
DOI：
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发表时间：
2011
期刊：
影响因子：
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通讯作者：
D. Vermeulen
中科院分区：
文献类型：
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作者：
E. V. Wyk;G. V. Tonder;D. Vermeulen
南非半干旱地区的降雨事件在深度和复发率方面具有典型的反复无常的特点。对循环雨水的化学评估已识别出3个间隔，间隔在水文循环上，报告了冬季和夏季降雨区雨水的不同水化学成分。冬季雨水产生于南大西洋海域。与热带辐合带/赤道西印度洋产生的夏季雨水相比，这些雨水含有明显更高的海洋气溶胶(氯化钠)浓度。大陆上产生的陆源尘埃的零星增加大大提高了夏季雨水中非海洋含氮和含硫气溶胶的浓度。雨水水化学特征的显著季节变化与半干旱气候的特征--周期性降雨深度相吻合。夏季旱期(4月至9月)的常量元素浓度与湿季(10月至3月)的浓度相比相对较高。然而，后一个时期报告说，在降雨高峰期(1月至3月)，进入当地地下水收支的水化学雨水明显耗尽。10月至12月(初)是一个介于尘土飞扬、干燥的冬季大气和12月相对湿润的大气之间的阶段，9月中旬前后出现了第一次区域性降雨。个别早期降雨的水化学浓度甚至比前一个干旱时期更高，随后随着空气中水分含量的增加而扩散，接近1月份开始的降雨高峰期。夏季半干旱地区的连续降雨事件监测发现，短期湿循环包含异常高的降雨事件，称为间歇性事件。这些湿循环在时间上非常不稳定，可能持续3至8天，5年复发率为1。雨水的水化学特征与正常的降雨成分有很大的不同，为追踪渗透的雨水提供了独特的机会。例如，个别高降雨事件(40至150 mm)的氯离子浓度可能低至0.4 mg·L-1，而背景值在0.8 mg·L-1左右。环境氯是估计雨水和地下水补给之间迁移的一种保守示踪剂。浓度水平在一年中不是恒定的，在使用累积的雨水样本和不受控制的地下水采样技术进行地下水补给估计时，可能会导致错误的假设。
Rainfall events in semi-arid regions of South Africa are characteristically erratic in terms of depths and recurrence rates. Chemical assessment of cyclic rainwater has recognised 3 intervals, spaced over the hydrological cycle, reporting diverse hydrochemical compositions of rainwater in winter and summer rainfall regions. Winter rainwater is generated over the south Atlantic maritime waters. This rainwater contains noticeably higher concentrations of oceanic aerosols (NaCl) than the summer rainwater generated in the Intertropical Convergence Zone/equatorial western Indian Ocean. Sporadic addition of terrigenous dust generated over the continent substantially elevates concentrations of non-oceanic nitrogenous and sulphurous aerosols in the summer rainwater. Prominent seasonal variations in the rainwater hydrochemistry signature coincide with cyclic rainfall depths, characteristic of the semi-arid climate. Macro-element concentrations during the summer dry period, April to September, are relatively high in relation to those recorded for the wet cycle, October to March. However, the latter period reports a noticeably depleted hydrochemical rainwater input into the local groundwater budget during the peak rainfall period (January to March). The October-December (early) period represents a phase between a dusty, dry winter atmosphere and a relatively flushed atmosphere in December, after the first regional rainfall manifests around middle September. Individual early rainfalls contain even higher hydrochemical concentrations than the previous dry period, which subsequently diffuses as the airborne moisture content increases towards the peak rainfall period starting in January. Continuous rainfall event monitoring in the summer semi-arid regions identified short-term wet cycles contain ing extraordinary high rainfall events, referred to as episodic events. These wet cycles are highly erratic in time and may last from 3 to 8 consecutive days with a recurrence rate of 1 in 5 years. The rainwater hydrochemistry signature differs significantly from the normal rainfall composition and represents a unique opportunity for tracing the infiltrating rain water. For example, chloride concentrations from individual, high rainfall events (40 to 150 mm) may be as low as 0.4 mg·l-1, whereas the background value varies around 0.8 mg·l -1 . Environmental chloride represents a conservative tracer for estimating the migration between rainwater and groundwater recharge. The concentration levels are not constant throughout the year and may lead to erroneous assumptions when performing groundwater recharge estimations using accumulated rainwater samples and uncontrolled groundwater sampling techniques.