Water-isotope ecohydrology of Mount Kilimanjaro
Water-isotope ecohydrology of Mount Kilimanjaro
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DOI：
10.1002/eco.2171
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发表时间：
2019-11-17
期刊：
影响因子：
2.6
通讯作者：
Boeckx, Pascal
中科院分区：
文献类型：
--
作者：
Bode, Samuel;De Wispelaere, Lien;Boeckx, Pascal
尽管对评估热带山区生态系统对当地人为压力和气候变化的脆弱性至关重要，但对基利曼哈罗山气候、水文和植被之间关系的了解非常零碎。解开水从降水到蒸腾的路径也有助于验证来自植物化合物（如叶蜡）的氢和氧同位素特征的古气候代理。我们测量了三角洲H-2和三角洲O-18在降水，流，土壤水，并在木质部和当地常见的植物叶水，连续四个季节沿着海拔3,000米的样带覆盖低地萨凡纳，较低和较高的山地森林，基利曼哈罗山的亚高山带。在所有四个生物气候带中，降水中的Δ H-2和Δ O-18分别以每100 mm-8 +/- 2 ppm和-1.0 +/- 0.3 ppm的速率随月降水量减少。我们的木质素水同位素数据表明，植物一般采取了表层土壤水分在东北季风季节和短暂的旱季，并逐渐转移到更深的土壤水分在东南季风季节和主要旱季。萨凡纳的树木和灌木从一个水池中取水，水池中的水源水具有相对恒定的同位素特征。这一观察结果符合“两个水世界”的假设，并意味着一个可能的季节性偏差，在植物来源的古水文代理。最后，我们的研究结果表明，木质部叶水同位素富集和环境相对湿度之间的强相关性，尽管在萨凡纳的偏见，我们归因于在这个温暖的半干旱环境中的叶冷却机制。
Notwithstanding its crucial importance for assessing the vulnerability of tropical mountain ecosystems to both local anthropogenic pressure and climate change, knowledge of the relationships between climate, hydrology, and vegetation on Mount Kilimanjaro is highly fragmentary. Unraveling the pathway of water from precipitation to transpiration can also help validate paleoclimate proxies derived from the hydrogen- and oxygen-isotopic signatures of plant compounds, such as leaf waxes. We measured delta H-2 and delta O-18 in precipitation, stream, and soil water, and in xylem and leaf water of locally common plants, for four successive seasons along a 3,000-m altitudinal transect covering lowland savannah, lower and upper montane forest, and the subalpine zone on Mount Kilimanjaro. Across all four bioclimatic zones, delta H-2 and delta O-18 in precipitation decreased with monthly precipitation amount at a rate of -8 +/- 2 parts per thousand and -1.0 +/- 0.3 parts per thousand per 100 mm, respectively. Our xylem-water isotope data indicate that plants in general took up topsoil water during the northeasterly monsoon season and short dry season and gradually shifted to deeper soil water during the southeasterly monsoon season and the main dry season. Savannah trees and shrubs tapped from a water pool recharged by source water with a relatively constant isotopic signature. This observation conforms to the "two water worlds" hypothesis and implies a possible seasonal bias in plant-derived paleohydrological proxies. Finally, our results show strong correlation between xylem-to-leaf water-isotopic enrichment and ambient relative humidity, despite a bias in the savannah that we attribute to a leaf-cooling mechanism in this warm, semi-arid environment.