Urban nitrogen biogeochemistry

城市化是全球变化中最显著的组成部分之一。在加拿大，城市人口超过80%，而在安大略省，这一比例甚至更高（85%），几乎所有未来的人口增长预计将主要通过“郊区化”过程发生在城市地区，或在其外部边缘扩张。虽然从原生土地利用到农业土地利用变化的生物地球化学影响已经得到了很好的研究，但转换为城市土地利用的影响却相对较少得到研究关注。特别值得关注的是城市土地利用变化对氮生物地球化学的影响。与自然土地利用类型相比，城市系统中的氮输入和输出发生了很大的变化，由于城市溪流的“闪光”水文、水力停留时间缩短和河岸带连接改变，氮潴留往往减少。相反，城市地区可能存在一些独特的N储存和反硝化热点，包括草坪、雨水滞留池和路边沟渠。本研究计划的长期目标是评估土地利用变化对安大略省南部城市化流域生物地球化学循环的影响，安大略省南部是加拿大人口最多的地区。这个为期5年的研究项目将重点研究安大略省南部大都市地区土地利用变化对氮循环的影响。具体而言，本提案的短期目标是：(a)沿着城市-郊区-城乡边缘梯度调查N循环；(b)表征N循环的热点（即雨水池、草坪和路边沟渠）；(c)量化沿梯度热时刻（风暴和春融）的N释放。这些短期目标将通过1个博士学位，3个硕士学位来实现。4个本科荣誉论文项目，结合城市梯度、斑块动态和小流域（质量平衡）方法。

Urbanization is one of the most conspicuous components of global change. In Canada, the urban population exceeds 80%, whereas the proportion is even higher in Ontario (85%) and virtually all future population growth is expected to occur in urban areas primarily through the process of 'suburbanization', or expansion at their outer margins. While the biogeochemical impacts of changes from native to agricultural land-use have been well studied, the effect of conversion to urban land use has received relatively little research attention. Of particular concern, is the effect of urban land use change on N biogeochemistry. Nitrogen inputs and outputs are greatly modified in urban systems compared with natural land use types and N retention is often reduced in urban streams due to their 'flashier' hydrology, reduced hydraulic residence times and altered riparian zone connections. Conversely, a number of unique hotspots for N storage and denitrification may exist in urban areas, including lawns, storm water detention ponds and roadside ditches. The long-term goal of this research program is to evaluate the impacts of land use change on biogeochemical cycling within urbanizing watersheds in southern Ontario - the most populated region in Canada. This 5-year research program will focus on the impacts of landuse change on nitrogen (N) cycling in a southern Ontario metropolitan area. Specifically, the short-term objectives of this proposal are to (a) investigate N cycling along an urban-suburban-rural edge gradient; (b) characterize the hot spots (i.e. storm water ponds, lawns and roadside ditches) of N cycling and, (c) quantify N release during hot moments (storms and spring melt) along the gradient. These short-term objectives will be met through 1 PhD, 3 MSc. and 4 undergraduate Honours thesis projects that combine the urban gradient, patch dynamic and small catchment (mass balance) approaches.