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

氮（N）是植物生长的必需营养素，作为肥料和粪肥添加到农业流域，以最大限度地提高作物产量并处理动物粪便。N随时间的过度应用被称为N遗留。在许多城市，污水处理厂（WWTPs）直接将高负荷的N排放到河流中。加拿大的人口增长正在增加淡水系统的压力，这是两个基本但截然相反的服务：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，在某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-都高于旨在保护水生生态系统健康的指导方针。数量，释放的时间轨迹和这N遗产的最终命运是未知的。我们将把重点放在加拿大最大的流域喂养伊利湖，格兰德河，在那里的几个机构和监管机构需要信息的科学为基础的管理。该流域是95万人的家园，预计20年内人口增长将超过40%。目前，超过50万人依靠这条河饮用水，而沿河沿着有30个污水处理厂。非点源养分含量也极高，因为农业（包括大型畜牧业）是土地的主要用途。为了适应这一新的增长，已经做出了数十亿美元的废水和饮用水处理以及农业土地管理的决定。2012年，两个主要的污水处理厂进行了改造，以改变氮（N）释放到河流中的形式。因此，河流中的NO3-水平已经上升到使用河流作为饮用水的大城市的关注水平。该研究项目利用了滑铁卢大学最近建立的地球化学和景观尺度建模方面的专业知识。一个全面的，流域规模的N模型将被开发，将转移到加拿大的其他农业流域。我们将使用全年实地采样，我们研究小组开发的新的天然同位素技术，流域氮素应用和水质的历史重建和新的建模方法，以检查关键的氮循环过程和氮遗产的后果，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，以便管理行动可以针对他们将有最大的影响。

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.