Shallow groundwater recharge mechanism and apparent age in the Ndop plain, northwest Cameroon
Shallow groundwater recharge mechanism and apparent age in the Ndop plain, northwest Cameroon
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DOI：
10.1007/s13201-015-0268-0
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发表时间：
2017-03
影响因子：
5.5
通讯作者：
M. J. Wirmvem;M. E. Mimba;B. T. Kamtchueng;Engome R. Wotany;Tasin Godlove Bafon;A. Asaah;W. Fantong-
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文献类型：
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作者：
M. J. Wirmvem;M. E. Mimba;B. T. Kamtchueng;Engome R. Wotany;Tasin Godlove Bafon;A. Asaah;W. Fantong-
关于地下水补给和表观年龄的知识是可持续管理地下水的宝贵工具。因此，利用氧（18O）、氢（2H或D）和氚（3H）的稳定同位素对Ndop平原浅层地下水（n= 72）进行了研究，确定了补给过程、补给时间和速率以及停留时间。浅层地下水δ18O值（−2.7 ~−4.1‰）和3h含量（2.4 ~ 3.1 TU）变化不大。低变率表明地下水库来源相似，含水层均匀，水混合良好，蓄水能力强。像地表水一样，沿Ndop大气水线（NMWL）和全球大气水线的地下水集群表明了大气的起源/补给。降雨补给发生在低相对湿度条件下，蒸发效应可以忽略不计。大约80%的补给来自Ndop平原低海拔（<1,260 m）的直接非均匀/弥漫性局地降水。大约20%来自高海拔降水（局部补给）或来自高海拔的大量流入的溪流和河流补给。在5月和6月季风降雨期间，NMWL上地下水（和地表水）的δ值呈均匀集群，表明这几个月主要补给。补给量至少占年降雨量（1540毫米）的16%，表明年补给量高；高度足以开发农业用地下水资源。地下水中3h含量（>2.4 TU）表明1952年后补给水，估计停留时间<30年，表明地下循环短，随后是可再生含水层。
Knowledge of groundwater recharge and apparent age constitutes a valuable tool for its sustainable management. Accordingly, shallow groundwater (n= 72) in the Ndop plain has been investigated using the stable isotopes of oxygen (18O) and hydrogen (2H or D) and tritium (3H) to determine the recharge process, timing and rate of recharge, and residence time. The shallow groundwater showed low variability in δ18O values (−2.7 to −4.1 ‰) and3H content (2.4–3.1 TU). The low variability suggests a similar origin, homogenous aquifer, good water mixing and storage capacity of the groundwater reservoir. Like surface water, a cluster of groundwater along the Ndop Meteoric Water Line (NMWL) and Global Meteoric Water Line indicates meteoric origin/recharge. The rainfall recharge occurs under low relative humidity conditions and negligible evaporation effect. About 80 % of the recharge is from direct heterogeneous/diffuse local precipitation at low altitude (<1,260 m) within the Ndop plain. Approximately 20 % is from high altitude precipitation (localised recharge) or is recharged by the numerous inflowing streams and rivers from high elevations. A homogenous cluster ofδ-values in groundwater (and surface water) between May and June monsoon rains on the NMWL suggests dominant recharge during these months. The recharge represents at least 16 % (>251 mm) of the annual rainfall (1,540 mm) indicating high annual recharge; high enough for development of the groundwater resource for agriculture. The3H content (>2.4 TU) in groundwater indicates post-1952 recharged water with an estimated residence time <30 years, suggesting short subsurface circulation, and subsequently a renewable aquifer.