Hydrological and biogeochemical resilience of human-dominated watersheds

目前，世界上50%以上的人口居住在城市地区，预计到2030年这一比例将增加到60%。在各个尺度上，城市化的特征是不透水表面积的增加、水入渗率的减少和地表径流的增加。这些对自然景观的改变极大地改变了河流水文响应降水输入的时间和幅度。当雨水或融水冲刷不透水的表面时，它会收集污染物并将它们带入雨水流系统，导致水质下降。为了减缓水流速度和防止过量物质到达水体，通常采用雨水控制措施。尽管做出了这些努力，但城市发展对河流健康的负面影响仍然存在，而且现在因更频繁的极端天气事件而加剧。本研究计划的总体目标是促进我们对气候和土地利用变化对人类主导（即城市和城市化）流域水文和生物地球化学的累积影响的理解。研究的短期目标包括：(1)研究土地利用方式对人类主导流域水文-生物地球化学行为的影响；(2)量化雨水控制措施对人类主导流域水文-生物地球化学行为的影响；(3)评估和比较不同人类主导流域对极端事件的水文和生物地球化学恢复能力。这些目标将通过在安大略省中南部的四个中尺度流域及其子集水区采用各种时间和空间密集的水文-生物地球化学场采样方法来实现。研究的流域跨越了从高度城市化到以农业为主的面积和土地利用梯度。将对每个流域进行有效或水力连接的不透水区域的地理空间确定，并对土地利用空间分布的多种指标进行量化。流域水文功能，特别是在风暴事件期间离开流域的“新”事件水的比例，以及在多个时间尺度上离开每个流域的水龄分布，将使用稳定的水同位素进行估计。流域生物地球化学功能将通过对研究流域内多个水源集水区（有或没有雨水管理池）的天气性纵向调查期间季节性收集的关键水质数据进行空间分析来评估。最后，对流域尺度上的降水-径流和溶质浓度-排放关系进行统计分析，以评估不同土地利用模式对极端天气事件的恢复能力。这项研究将为加拿大城市水资源的可持续管理提供信息。

More than 50% of the world's population now lives in urban areas and this is projected to increase to 60% by 2030. Across scales, urbanization is characterized by increases in impervious surface area, reductions in water infiltration rates, and increases in surface runoff. These alterations to the natural landscape drastically alter the timing and magnitude of stream hydrological responses to precipitation inputs. When rain- or melt-water washes over impervious surfaces it collects pollutants and carries them into the stormwater-stream system leading to degraded water quality. To slow water down and prevent excess materials from reaching water bodies, stormwater control measures are often employed. Despite these efforts, the negative impacts of urban development on stream health remain and are now exacerbated by more frequent extreme weather events. The overall goal of this research program is to advance our understanding of the cumulative impacts of climate and land use changes on the hydrology and biogeochemistry of human-dominated (i.e. urban and urbanizing) watersheds. The short-term objectives of the research include: (1) Examining the influence of land use patterns on the hydro-biogeochemical behaviour of human-dominated watersheds, (2) Quantifying the impact of stormwater control measures on the hydro-biogeochemical behaviour of human-dominated watersheds, and (3) Assessing and comparing the hydrological and biogeochemical resilience of different human-dominated watersheds to extreme events. These objectives will be addressed through a variety of temporally and spatially intensive hydro-biogeochemical field sampling approaches in four meso-scale watersheds and their sub-catchments located in south-central Ontario. The study watersheds span a gradient of size and land use from highly urbanized to dominantly agricultural. Geospatial determination of effective, or hydraulically connected, impervious area and the quantification of multiple metrics of the spatial distribution of land use will be carried out for each watershed. Catchment hydrological functioning, specifically the proportion of 'new', event water leaving the catchment during storm events and the distribution of water ages leaving each watershed on multiple time scales, will be estimated using stable water isotopes. Catchment biogeochemical functioning will be assessed through the spatial analysis of key water quality data collected seasonally during synoptic longitudinal surveys of multiple headwater catchments (with and without stormwater management ponds) in the study watersheds. Lastly, statistical analyses of precipitation-runoff and solute concentration-discharge relations at the watershed-scale will be used to evaluate the resilience of different land use patterns to extreme weather events. This research will inform sustainable management of urban water resources in Canada.