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，作为肥料和粪肥被过量添加到农业流域，以最大限度地提高作物产量和处理动物粪便。随着时间的推移，过量施用N被称为N遗留。在许多城市，污水处理厂（WWTPs）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的两种基本但截然相反的服务的压力；饮用水的供应和废物的吸收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，特别是在冬季和风暴期间。在许多河流中，氨（NH3）和NO3-都高于保护水生生态系统健康的准则。释放的数量、时间轨迹和这一N遗产的最终命运都是未知的。我们将重点关注加拿大最大的伊利湖流域，格兰德河，几个机构和监管机构需要科学管理的信息。该流域居住着95万人口，预计20年内人口将增长40%以上。目前，超过50万人依靠这条河获得饮用水，而沿河有30个污水处理厂。非点源养分负荷也非常高，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，在废水和饮用水处理以及农业用地管理方面已经做出了数十亿美元的决定。2012年，两家主要的污水处理厂进行了改造，以改变排放到河流中的氮(N)的形式。结果，河流的NO3水平已经上升到大城市饮用水的水平。该研究项目利用了最近在滑铁卢大学建立的生物地球化学和景观尺度建模方面的专业知识。将开发一个综合的流域尺度N模型，该模型将可转移到加拿大的其他农业流域。我们将使用全年实地采样、我们的研究小组开发的新的自然同位素技术、对流域N应用和水质的历史重建以及新的建模方法来检查关键的N循环过程和N遗产的后果，并将农业与污水排放计划对河流中高水平硝酸盐和氨的贡献分开，以便管理行动可以定向到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.