Spatial and temporal variability of nitrogen cycling in forests

位于加拿大北方森林的溪流和湖泊的水质在很大程度上取决于景观中水和营养物质（如氮）的循环。这些水和氮循环过程在空间和时间上都是非常可变的，这使得很难预测这些循环将如何响应环境变化，例如降水事件的频率或强度的变化。这些事件改变了水流经森林的方式，改变了土壤的性质，如温度和湿度。这些环境条件决定了森林中氮转化过程的速率，而氮转化过程最终决定了排干这些森林的湖泊和溪流的化学成分。我们对森林中氮过程控制的科学理解存在空白，这限制了我们对未来森林水质做出预测的能力。

The water quality of streams and lakes located in Canada’s boreal forests depend in large part on the cycling of water and nutrients [e.g. nitrogen (N)] on the landscape. These water and N cycling processes are extremely variable in both space and time, which makes it hard to predict how these cycles will respond to environmental changes, such as changes in the frequency or intensity of precipitation events. These events change the way water flows through forests and alter soil properties such as temperature and moisture. These environmental conditions determine the rates of N transformation processes in forests which ultimately determine the chemistry of lakes and streams that drain these forests. There are gaps in our scientific understanding of the controls on N processes in forests, and this limits our ability to make predictions about forest water quality into the future. The major objective of this proposal is to investigate hydrological and landscape controls on spatial and temporal variability in N cycling processes in forests, with a particular focus on the impact of increasing frequency and intensity of hydroclimatic events. We will investigate controls on N cycling in soils near the edge of streams which are particularly vulnerable to droughts and freezing. We will assess how flowpaths of water and N vary during events of different magnitudes and frequencies. We will examine where and when N2O, a potent but elusive greenhouse gas, in produced in forest soils. Ultimately, this work will provide critical insights into N cycling in forests, and help refine models of water quality responses to climate change.