Canada's nitrogen legacy: Combining modeling & isotope approaches for drinking water quality and aquatic ecosystem health of rivers

氮(N)是植物生长所必需的营养物质，它作为肥料和肥料添加到农业流域中，以最大限度地提高作物产量和处理动物排泄物。随着时间的推移，N的过量应用被称为N遗留。在许多城市，污水处理厂(WWTP)将高氮负荷的污水直接排放到河流中。加拿大的人口增长增加了淡水系统在两项基本但截然相反的服务方面的压力：提供饮用水和吸收废物。在加拿大南部的溪流和河流中，河流中的硝酸盐(NO3-)随着时间的推移而增加，在一些地区接近饮用水极限，特别是在冬季和暴风雨期间。在许多河流中，氨(NH3)和NO3-都超过了旨在保护水生态系统健康的指导方针。这N笔遗产的数量、发行的时间轨迹和最终命运都是未知的。我们将把重点放在加拿大最大的伊利湖流域--格兰德河，那里的几个机构和监管机构需要信息来进行基于科学的管理。该分水岭是95万人的家园，预计20年内人口增长将超过40%。目前，有50多万人依靠这条河喝水，而沿河有30个污水处理厂。非点源养分负荷也极高，因为农业(包括大型畜牧业)是主要的土地利用方式。为了适应这种新的增长，已经在废水和饮用水处理以及农业土地管理方面做出了数十亿美元的决定。2012年，对两个主要的污水处理厂进行了改造，以改变向河流排放的氮(N)的形式。因此，3号河的水位已经上升到了大城市的担忧水平，这些城市使用这条河作为饮用水。这一研究项目利用了滑铁卢大学最近建立的生物地球化学和景观尺度模型方面的专业知识。将开发一个全面的分水岭规模的N模型，该模型将可移植到加拿大的其他农业流域。我们将使用全年田间采样、我们的研究小组开发的新的天然同位素技术、流域内氮肥用量和水质的历史重建以及新的建模方法来研究关键的氮素循环过程和氮素遗产的后果，并将农业和污水处理厂对河流中高水平硝酸盐和氨的贡献分开，以便管理行动能够针对它们将产生最大影响的地方。

Nitrogen (N), an essential nutrient for plant growth, is added in excess of requirements to agricultural watersheds as fertilizer and manure to maximize crop yields and to dispose of animal wastes. Excess application of N over time is termed the N legacy. In many cities, wastewater treatment plants (WWTPs) discharge effluent with high loads of N directly into rivers. Population growth in Canada is increasing the pressure on freshwater systems for two essential but diametrically opposed services; the provision of drinking water and the assimilation of wastes. In streams and rivers in southern Canada, nitrate (NO3-) in rivers is increasing with time and in some areas approaches drinking water limits, especially in winter and during storm events. In many rivers, both ammonia (NH3) and NO3- are above guidelines designed to protect aquatic ecosystem health. The quantity, time trajectory for release and the ultimate fate of this N legacy are unknown. We will focus on the largest Canadian watershed feeding Lake Erie, the Grand River, where several agencies and regulators require information for science-based management. The watershed is home to 950,000 people, and the expected population increase is over 40% within 20 years. Currently, more than 500,000 people rely on the river for drinking water while there are 30 WWTPs along the river. Non-point source nutrient loads are also extremely high, as agriculture (including large livestock operations) is the dominant land use. To accommodate this new growth, billion dollar decisions for wastewater and drinking water treatment and agricultural land management have been taken. In 2012, two major wastewater treatment plants were modified to change the form of nitrogen (N) released to the river. As a consequence, river NO3- levels have risen to levels of concern for large cities that use the river for drinking water. This research project capitalizes on expertise in both biogeochemistry and landscape scale modelling that has been established very recently at the University of Waterloo. A comprehensive, watershed-scale N model will be developed that will be transferable to other agricultural watersheds in Canada. We will use year round field sampling, new natural isotopic techniques developed by our research group, historical reconstructions of N application and water quality in the watershed and new modelling approaches to examine the key N cycling processes and the consequences of N legacy and to separate agricultural from WWTP contributions to high levels of nitrate and ammonia in rivers so that management actions can be directed to where they will have the greatest impact.