Towards closing the watershed nitrogen budget: Spatial and temporal scaling of denitrification
Towards closing the watershed nitrogen budget: Spatial and temporal scaling of denitrification
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关闭流域氮预算：反硝化的空间和时间尺度
DOI：
10.1002/jgrg.20090
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发表时间：
2013
期刊：
影响因子：
--
通讯作者：
L. Band
中科院分区：
文献类型：
--
作者：
J. Duncan;P. Groffman;L. Band
加强对流域水文地貌模板的考虑对于理解流域氮收支至关重要。本文以美国马里兰州的一个森林流域（池塘分支）为研究对象，建立了一个估算表层土壤中土壤水分和土壤氧的空间分布和时间动态的框架。我们采样土壤芯在不同季节的高地，山坡空心，河岸空心，河岸丘景观位置的生态地球化学通量，包括测量通过反硝化产生的N2气体。我们外推这些利率在空间和时间上的信息来自于原位土壤氧和土壤水分探头规模通量从地块到集水区的水平。我们解决了三个问题：（1）如何重要的是季节性的，每日和风暴事件的变化，土壤中的氧反硝化？(2)反硝化作用在整个流域的空间分布情况如何？(3)反硝化作用对流域氮收支有多重要？我们发现，河岸带内的微地形是一个显着的影响土壤氧动力学，因此氧化还原敏感的生物地球化学过程，如反硝化作用。河岸带洼地（较低的地形位置）占汇水面积的0.5%-1.0%，但占总反硝化量的99%以上。有趣的是，地形是一个更强大的控制器比降雨，这对土壤氧水平的时间变化影响不大的氧气。空间和时间外推的测量速率表明，至少有16%-27%的大气氮沉降损失的反硝化作用。这些结果表明，在森林流域的氮预算的反硝化作用的重要性，从根本上取决于存在的景观元素，如河岸洼地的功能作为“热点”的活动。
Enhanced consideration of the hydrogeomorphic template of watersheds is critical to understanding watershed nitrogen budgets. We developed a framework to estimate the spatial distribution and temporal dynamics of soil moisture and soil oxygen in surficial soils to scale nitrogen transformations for a forested watershed (Pond Branch) in Maryland, USA. We sampled soil cores in upland, hillslope hollow, riparian hollow, and riparian hummock landscape positions in different seasons for biogeochemical fluxes including measurement of N2 gas produced via denitrification. We extrapolated these rates in space and time with information derived from in situ soil oxygen and soil moisture probes to scale fluxes from plots to the catchment level. We addressed three questions: (1) How important are seasonal, daily, and storm event variations in soil oxygen for denitrification? (2) How is denitrification spatially distributed through the watershed? (3) How important is denitrification to the watershed nitrogen budget? We found that microtopography within the riparian zone is a significant influence on soil oxygen dynamics and therefore redox‐sensitive biogeochemical processes such as denitrification. Riparian zone hollows (lower topographic positions) represented 0.5%–1.0% of the catchment area, but accounted for >99% of total denitrification. Interestingly, topography was a much stronger controller of oxygen than rainfall, which had little influence on temporal variation in soil oxygen levels. Spatial and temporal extrapolations of measured rates suggest that a minimum of 16%–27% of atmospheric nitrogen deposition is lost to denitrification. These results suggest that the importance of denitrification in the nitrogen budget of forested watersheds depends fundamentally on the presence of landscape elements, such as riparian hollows that function as “hot spots” of activity.