Rock weathering and nutrient cycling along an erodosequence

IF 1.9 3区 地球科学 Q3 GEOSCIENCES, MULTIDISCIPLINARY
F. von Blanckenburg, J. Schuessler, J. Bouchez, P. Frings, D. Uhlig, M. Oelze, D. Frick, T. Hewawasam, Jean L. Dixon, K. Norton
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引用次数: 10

Abstract

How flowing water and organisms can shape Earth's surface, the Critical Zone, depends on how fast this layer is turned over by erosion. To quantify the dependence of rock weathering and the cycling of elements through ecosystems on erosion we have used existing and new metrics that quantify the partitioning and cycling of elements between rock, saprolite, soil, plants, and river dissolved and solid loads. We demonstrate their utility at three sites along a global transect of mountain landscapes that differ in erosion rates – an “erodosequence”. These sites are the Swiss Central Alps, a rapidly-eroding, post-glacial mountain belt; the Southern Sierra Nevada, USA, eroding at moderate rates; and the slowly-eroding tropical Highlands of Sri Lanka. The backbone of this analysis is an extensive data set of rock, saprolite, soil, water, and plant geochemical and isotopic data. This set of material properties is converted into process rates by using regolith production and weathering rates from cosmogenic nuclides and river loads, and estimates of biomass growth. Combined, these metrics allow us to derive elemental fluxes through regolith and vegetation. The main findings are: 1) the rates of weathering are set locally in regolith, and not by the rate at which entire landscapes erode; 2) the degree of weathering is mainly controlled by regolith residence time. This results in supply-limited weathering in Sri Lanka where weathering runs to completion in the regolith, and kinetically-limited weathering in the Alps and Sierra Nevada where soluble primary minerals persist; 3) these weathering characteristics are reflected in the sites' ecosystem processes, namely in that nutritive elements are intensely recycled in the supply-limited setting, and directly taken up from soil and rock in the kinetically settings; 4) the weathering rates are not controlled by biomass growth; 5) at all sites we find a deficit in river solute export when compared to solute production in regolith, the extent of which differs between elements. Plant uptake followed by litter export might explain this deficit for biologically utilized elements of high solubility, and rare, high-discharge flushing events for colloidal-bound elements of low solubility. Our data and new metrics have begun to serve for calibrating metal isotope systems in the weathering zone, the isotope ratios of which depend on the flux partitioning between the compartments of the Critical Zone. We demonstrate this application in several isotope geochemical companion papers.
沿侵蚀层序的岩石风化和营养循环
流动的水和生物如何塑造地球表面,即关键地带,取决于这一层因侵蚀而翻转的速度。为了量化岩石风化和生态系统中元素循环对侵蚀的依赖,我们使用了现有的和新的指标来量化岩石、腐生岩、土壤、植物、河流溶解和固体负荷之间元素的分配和循环。我们在全球山脉景观样带的三个地点展示了它们的效用,这些地点的侵蚀速率不同-一个“侵蚀序列”。这些地点是瑞士中部阿尔卑斯山脉,一个快速侵蚀的后冰川山脉带;南内华达山脉,美国,以中等速度侵蚀;以及斯里兰卡缓慢侵蚀的热带高地。这种分析的主干是一个广泛的数据集,包括岩石、腐岩、土壤、水和植物的地球化学和同位素数据。这组材料特性通过使用宇宙核素和河流负荷产生的风化速率和风化速率,以及生物量增长的估计,转化为过程速率。这些指标结合起来,使我们能够推导出通过风化层和植被的元素通量。主要发现有:1)风化速率是由局部风化层决定的,而不是由整个景观的侵蚀速率决定的;2)风化程度主要受风化层停留时间控制。这导致了斯里兰卡的供应有限的风化作用,那里的风化作用在风化层中完成,而阿尔卑斯山和内华达山脉的动力有限的风化作用,那里的可溶性原生矿物持续存在;3)这些风化特征反映在遗址区生态系统过程中,即在供应受限的环境中,营养元素被强烈地循环利用,在动力环境中,营养元素直接从土壤和岩石中吸收;4)风化速率不受生物量增长的控制;5)在所有地点,我们都发现河流溶质输出与风化层溶质产生相比存在缺陷,其程度因元素而异。植物吸收之后的凋落物输出可能解释了高溶解度的生物利用元素的不足,以及低溶解度的胶体结合元素罕见的高流量冲洗事件。我们的数据和新指标已经开始用于校准风化带的金属同位素系统,其同位素比率取决于临界带各隔室之间的通量分配。我们在几篇同位素地球化学论文中论证了这一应用。
本文章由计算机程序翻译,如有差异,请以英文原文为准。
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来源期刊
American Journal of Science
American Journal of Science 地学-地球科学综合
CiteScore
5.80
自引率
3.40%
发文量
17
审稿时长
>12 weeks
期刊介绍: The American Journal of Science (AJS), founded in 1818 by Benjamin Silliman, is the oldest scientific journal in the United States that has been published continuously. The Journal is devoted to geology and related sciences and publishes articles from around the world presenting results of major research from all earth sciences. Readers are primarily earth scientists in academia and government institutions.
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