Critical zone properties control the fate of nitrogen during experimental rainfall in montane forests of the Colorado Front Range

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• 作者：Eve-Lyn S. Hinckley ; Brian A. Ebel ; Rebecca T. Barnes ; Sheila F. Murphy…
• 关键词：15N tracer ; Lithium bromide ; Hillslope aspect ; Hydrologic response ; Convective storm ; Critical Zone Observatory
• 刊名：Biogeochemistry
• 出版年：2017
• 出版时间：January 2017
• 年：2017
• 卷：132
• 期：1-2
• 页码：213-231
• 全文大小：
• 刊物类别：Earth and Environmental Science
• 刊物主题：Biogeosciences; Ecosystems; Environmental Chemistry; Life Sciences, general;
• 出版者：Springer International Publishing
• ISSN：1573-515X
• 卷排序：132

文摘

Several decades of research in alpine ecosystems have demonstrated links among the critical zone, hydrologic response, and the fate of elevated atmospheric nitrogen (N) deposition. Less research has occurred in mid-elevation forests, which may be important for retaining atmospheric N deposition. To explore the fate of N in the montane zone, we conducted plot-scale experimental rainfall events across a north–south transect within a catchment of the Boulder Creek Critical Zone Observatory. Rainfall events mimicked relatively common storms (20–50% annual exceedance probability) and were labeled with 15N-nitrate (\( {\text{NO}}_{3}^{ - } \)) and lithium bromide tracers. For 4 weeks, we measured soil–water and leachate concentrations of Br−, \( {}^{15}{\text{NO}}_{3}^{ - } , \) and \( {\text{NO}}_{3}^{ - } \) daily, followed by recoveries of 15N species in bulk soils and microbial biomass. Tracers moved immediately into the subsurface of north-facing slope plots, exhibiting breakthrough at 10 and 30 cm over 22 days. Conversely, little transport of Br− or \( {}^{15}{\text{NO}}_{3}^{ - } \) occurred in south-facing slope plots; tracers remained in soil or were lost via pathways not measured. Hillslope position was a significant determinant of soil 15N-\( {\text{NO}}_{3}^{ - } \) recoveries, while soil depth and time were significant determinants of 15N recovery in microbial biomass. Overall, 15N recovery in microbial biomass and leachate was greater in upper north-facing slope plots than lower north-facing (toeslope) and both south-facing slope plots in August; by October, 15N recovery in microbial N biomass within south-facing slope plots had increased substantially. Our results point to the importance of soil properties in controlling the fate of N in mid-elevation forests during the summer season.