Dissertation Research: The Effects of Nitrogen Deposition on Ecosystem Function in the Forest-Alpine Tundra Ecotone

论文研究：氮沉降对森林-高寒冻土带生态系统功能的影响。摘要大气和水体中的氮污染对生态系统和人类健康都是一个日益严重的问题。在人为氮沉降水平较低的情况下，氮能使植物和土壤肥沃。一旦达到沉积的临界阈值，生态系统就不能再保留氮，从而可能导致饮用水供应受到污染。科罗拉多州的高海拔生态系统被认为处于失去利用这些人类活动增加的氮的能力的边缘。我建议测试一个概念模型，该模型假设亚高山森林和高山苔原之间的过渡可能对氮沉积特别敏感。在冬季，强烈的西风以一种可预测的模式在树木周围和整个过渡区重新分配雪，并伴随着氮污染。因为树木倾向于捕获雪，树木和风之间的这种相互作用可能会在景观中形成氮沉积的热点。我的实验将研究在森林-苔原过渡过程中氮沉积和土壤养分的变化，以测试可预测的沉积模式是否转化为对生态系统和氮保留的可预测影响。这项研究的更广泛的影响是解决氮富集正在影响有价值的生态系统服务（例如，水净化）以及改变相对原始环境的问题。它还将确定森林-冻土带边界是否是监测生态系统氮状况的良好指标。

Dissertation Research: The Effects of Nitrogen Deposition on Ecosystem Function in the Forest-Alpine Tundra Ecotone.Timothy Seastedt and Daniel LiptzinProposal #: 0508769 AbstractNitrogen pollution in the air and water is a growing problem for both ecosystem and human health. At low levels of nitrogen deposition from human sources, nitrogen fertilizes plants and soils. Once a critical threshold of deposition is reached, ecosystems can no longer retain nitrogen potentially leading to contamination of drinking water supplies. High elevation ecosystems in Colorado are thought to be on the verge of losing their ability to utilize these nitrogen additions from human activities. I propose to test a conceptual model which posits that the transition between the subalpine forest and the alpine tundra may be particularly sensitive to nitrogen deposition. During the winter strong westerly winds redistribute snow, and concomitantly, nitrogen pollution, in a predictable pattern around trees and across this transition zone. Because trees tend to capture snow, this interaction between trees and wind may create hot-spots of nitrogen deposition in the landscape. My experiments will examine the variation in nitrogen deposition and soil nutrients across the forest-tundra transition to test whether the predictable pattern of deposition translates into predictable effects on ecosystems and nitrogen retention. The broader impact of this research is to address concerns that nitrogen enrichment is affecting valuable ecosystem services (e.g., water purification) as well as altering relatively pristine environments. It will also determine if the forest-tundra boundary is a good indicator to monitor the nitrogen status of ecosystems.