Biogeochemical response of alpine lakes to a recent increase in dust deposition in the Southwestern, US
Biogeochemical response of alpine lakes to a recent increase in dust deposition in the Southwestern, US
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DOI：
10.5194/bg-8-2689-2011
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发表时间：
2011-01-01
期刊：
影响因子：
4.9
通讯作者：
Neff, J. C.
中科院分区：
文献类型：
--
作者：
Ballantyne, A. P.;Brahney, J.;Neff, J. C.
最近，美国西部一些地区的沙尘沉降量显著增加。在这里，我们探讨了粉尘沉积的变化如何影响美国科罗拉多州两个高山流域的生物地球化学。我们首先重建沉积物质量积累率的近期变化，然后我们使用同位素测量与贝叶斯混合模型相结合，推断湖泊沉积物中大约95%的无机部分来自尘埃。现代沙尘元素分析表明，沙尘富集Ca、Cr、Cu、Mg、Ni等元素，其中一个流域相对基岩富集Fe和P元素。粉尘沉降量的增加和某些元素的富集改变了这些系统的生物地球化学特征。两个湖的初级生产力都有所增加，碳同位素区分度降低；但是，初级生产力提高的原因因流域特征的不同而不同。大流域湖泊的大气N负荷较大，基岩P负荷较小，导致N: P通量比较大。与此相反，小流域湖泊大气氮负荷较少，基岩磷负荷较大，导致N: P通量比减小。结果表明，小流域初级生产力受氮有效度的限制更大。在更现代的沉积物中，氮同位素值的降低表明，固氮作用的增加部分改善了小流域中氮限制的初级生产力。该研究表明，高寒流域是大气沉积变化的优秀集成者，但这些流域的生物地球化学响应可能由其物理（即流域面积）和化学（即下伏地质）性质所调节。
The deposition of dust has recently increased significantly over some regions of the western US. Here we explore how changes in dust deposition have affected the biogeochemistry of two alpine watersheds in Colorado, US. We first reconstruct recent changes in the mass accumulation rate of sediments and then we use isotopic measurements in conjunction with a Bayesian mixing model to infer that approximately 95% of the inorganic fraction of lake sediments is derived from dust. Elemental analyses of modern dust indicate that dust is enriched in Ca, Cr, Cu, Mg, Ni, and in one watershed, Fe and P relative to bedrock. The increase in dust deposition combined with its enrichment in certain elements has altered the biogeochemisty of these systems. Both lakes showed an increase in primary productivity as evidenced by a decrease in carbon isotopic discrimination; however, the cause of increased primary productivity varies due to differences in watershed characteristic. The lake in the larger watershed experienced greater atmospheric N loading and less P loading from the bedrock leading to a greater N: P flux ratio. In contrast, the lake in the smaller watershed experienced less atmospheric N loading and greater P loading from the bedrock, leading to a reduced N: P flux ratio. As a result, primary productivity was more constrained by N availability in the smaller watershed. N-limited primary productivity in the smaller watershed was partly ameliorated by an increase in nitrogen fixation as indicated by reduced nitrogen isotopic values in more contemporary sediments. This study illustrates that alpine watersheds are excellent integrators of changes in atmospheric deposition, but that the biogeochemical response of these watersheds may be mediated by their physical (i.e. watershed area) and chemical (i. e. underlying geology) properties.