Groundwater residence time and paleorecharge conditions in the deep confined aquifers of the coastal watershed, South-East Tanzania
Groundwater residence time and paleorecharge conditions in the deep confined aquifers of the coastal watershed, South-East Tanzania
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坦桑尼亚东南部沿海流域深层承压含水层地下水停留时间和古充注条件
DOI：
10.1016/j.jhydrol.2012.08.016
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发表时间：
2012
影响因子：
6.4
通讯作者：
S. Gulliksen
中科院分区：
文献类型：
--
作者：
Said Suleiman Bakari;P. Aagaard;R. Vogt;F. Ruden;M. Brennwald;I. Johansen;S. Gulliksen
通过对坦桑尼亚东南部沿海分水岭地下水样品的放射性碳和碳、氢、氧稳定同位素分析，确定了地下水的年龄和补给时的气候条件。根据稳定的碳同位素比值和水化学数据对放射性碳测年进行了校正。确认了两个主要的补给期：(1)浅层含水层和一些深层地下水的近期补给期，其停留时间小于1.3ka BP；(2)对于下部承压含水层，古补给期发生在晚更新世至全新世过渡期间(6至13ka BP之间)。这项研究确定的气候漂移(干旱和湿润阶段)与坦桑尼亚和东非古气候记录研究确定的气候漂移很好地吻合。氧-18和放射性碳的结果表明，沿海含水层系统中不同年龄的地下水沿流动路径存在潜在的混合。一些深层含水层样品的氧化还原参数也表明了这一点。资料还揭示了深层承压含水层中地下水的侧向流动规律较为简单。这项研究和相关古岩石学研究的同位素证据提高了我们对过去气候的了解。这些数据表明，对承压含水层的古补给是在比现在更潮湿的气候条件下从内陆来的。因此，邻近山区向伊法卡拉、莫罗戈罗和乌德宗瓦山脉等沿海地区的古补给可能是金比吉含水层补给区的重要组成部分。然而，达累斯萨拉姆的腹地山脉(主要是普古、姆库兰加、鲁武和基萨拉韦)也可以在补充金比吉沿海含水层方面发挥重要作用。相比之下，浅层潜水含水层的补给以局部降雨和河水入渗为特征。这项研究是此类研究的第一次，使用深层地下水含水层的同位素组成评估了坦桑尼亚东南沿海古气候的指纹。新近系含水层中的淡水资源包含古地下水含水层，这些含水层与最近重新注入的流动系统混合在一起。因此，这些资源可能是可持续的。这项研究还提供了可能有助于设计沿海含水层地下水资源可持续管理最佳战略的信息，并证明了地下水作为古气候档案的重要性。这些信息对于模型师在试图模拟承压含水层在很长一段时间内的水文地质过程时也是必不可少的。
Analysis of radiocarbon and stable isotopes of C, H and O in groundwater samples from the coastal watershed of Southeastern Tanzania is used to decipher the age of groundwater and the climatic conditions at the time of recharge. Radiocarbon dating was corrected on the basis of stable carbon isotope ratios and hydrochemical data. Two main recharge periods are recognised: (1) a recent recharge period with residence times dated to younger than 1.3ka BP, for the shallow aquifer and some deep groundwater aquifers; and (2) a paleorecharge occurring during the Late Pleistocene to Holocene transition (between 6 and 13ka BP), for the lower confined aquifer. The climatic excursions (arid and humid phases) identified in this study match well with those identified from studies of paleo-climatic records in Tanzania and East Africa. The oxygen-18 and radiocarbon results show that there is a potential mixing of groundwater of varying ages along flow paths in the coastal aquifer system. This has also been shown by redox parameters in some of the deeper aquifer samples. The data also revealed that there is relatively simple pattern of lateral groundwater flow in the deeper confined aquifer. Isotopic evidence from this study and related studies in paleolimnology improves our knowledge of the past climates. The data suggests that the paleorecharge to the confined aquifer was from inland under wetter climatic conditions than present. Therefore, paleorecharge from the adjacent mountain regions to coastal area like Ifakara, Morogoro and Udzungwa mountains could be important parts of recharge area of the Kimbiji aquifer. However, the hinterland mountains of Dar es Salaam (mainly Pugu, Mkuranga, Ruvu and Kisarawe) could also play an important role in replenishing the Kimbiji coastal aquifers. In contrast, recharge in the shallow unconfined aquifer is characterized by local rainfall and river water infiltration. This study is the first of its kind, assessing fingerprinting of paleoclimates in Southeastern coastal Tanzania using the isotopic composition of deep groundwater aquifers. The freshwater resources in the Neogene aquifer contain paleo-groundwater aquifers that have been mixed with recently-recharged flow systems. Hence, the resources may be sustainable. This study also provides information that may be useful for designing optimum strategies for a sustainable management of groundwater resources in the coastal aquifer, and it testifies to the importance of groundwater as a paleoclimatic archive. Such information is also essential for consideration by modellers in their attempts to simulate the hydrogeological processes in confined aquifers over very long time spans.
乞力马扎罗山氧同位素记录揭示了过去25年赤道气候的季节性
影响因子：
5.8
作者：
Barker;Hurrell;Cocquyt;C. Sloane;Verschuren
通讯作者：
Verschuren