Urban nitrogen biogeochemistry

城市化是全球变化最显著的组成部分之一。在加拿大，城市人口超过80%，而安大略省的这一比例更高(85%)，预计未来几乎所有的人口增长都将主要发生在城市地区，主要是通过“郊区化”的过程，即在其边缘扩张。虽然从自然土地利用转变为农业土地利用的生物地球化学影响已经得到了很好的研究，但城市土地利用转变为城市土地利用的影响受到的研究相对较少。特别值得关注的是城市土地利用变化对N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，城市溪流中的氮素保留量通常会减少，因为它们的水文条件更鲜艳，水力停留时间减少，河岸地带的连接也发生了变化。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、雨水滞留池塘和路边沟渠。这项研究计划的长期目标是评估土地利用变化对加拿大人口最多的安大略省南部城市化流域内生物地球化学循环的影响。这项为期5年的研究计划将重点研究土地利用变化对安大略省南部大都市区氮素循环的影响。具体地说，这项建议的短期目标是：(A)调查沿城市-郊区-农村边缘坡度的氮循环；(B)确定氮循环的热点(即雨水池、草坪和路边沟渠)的特征；以及(C)量化沿坡度的炎热时刻(风暴和春季融化)期间的氮素释放。这些短期目标将通过1个博士和3个硕士来实现。4个结合城市梯度、斑块动态和小流域(质量平衡)方法的本科生荣誉论文项目。

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.