The role of river biogeochemical function in the watershed eutrophication cascade

富营养化(公害和有害藻类水华的扩散)是由农业和废水中过量的营养物质磷、磷和氮引起的。这是全球水质受损的主要来源，也是对加拿大水安全的紧迫和普遍威胁。仅在加拿大五大湖流域，富营养化的成本就约为83亿美元/年。这项研究的长期目标是形成对淡水富营养化驱动因素的新的量化理解，从局部到全球。这项研究需要指导具有成本效益的水质管理和改善水生环境健康，水生环境健康也日益受到气候和土地利用变化的威胁。这项为期5年的研究计划侧重于了解河流过程，这些过程控制着营养物质在流域中的循环、运输和级联。Instream生物地球化学过程可以保留营养，并通过调节P和N的下游输送，减少湖泊和其他接收水体的富营养化风险，发挥重要的“自我净化”服务的作用。然而，我们对这些内流过程的了解大多局限于在低流量条件下的可波动的小河流。据预测，较大的较深河流在较高流量(这是大多数分水岭营养物质输出发生的时候)下更有效地保留营养物质，因此可能在减少下游富营养化风险方面发挥关键作用。然而，目前缺乏证实这一点的数据。该计划将通过现场传感器和高分辨率水化学监测(可在大河和大流量下安全地进行)的新应用，来解决这一重要不足，以量化溪流和河流在整个流态中保留P和N的功能能力。该计划将为两名博士生和两名硕士学生提供培训，将野外和实验室生物地球化学结合起来，掌握使用和应用现场水化学传感器的尖端技能，以及复杂的数据分析技术。这些技能越来越受到研究、环境机构和水务公司雇主的追捧。博士和硕士学员将使用这些工具和技术来探索河流生物地球化学功能在减少或放大下游营养物质通量传输和富营养化风险方面的作用。该方案将审查废水流出物和其他半连续排放到河流中的“点”源(并可能导致河流水质长期基线受损)是否会降低河流的“自我净化”能力。如果是这样的话，减少点源养分投入可以通过加强河流的“自我净化”能力来保留在高流量下输送的更广泛农业来源的养分，从而产生重大的额外惠益。这将对加拿大和国际上的富营养化管理产生深远的影响。

Eutrophication (proliferation of nuisance and harmful algal blooms) is caused by excess nutrients, phosphorus, P, and nitrogen, N, from agriculture and wastewater. This is a major global source of water-quality impairment, and an urgent and pervasive threat to Canada's water security. Eutrophication costs ~$8.3billion/year in the Canadian Great Lakes basin alone. The long-term goal of this research is to forge novel quantitative understanding of the drivers of freshwater eutrophication, from local to global scales. This research is needed to guide cost-effective water-quality management and to improve aquatic environmental health, which is also increasingly threatened by climate and land-use change. This 5-year research program focuses on understanding the instream processes that control the cycling, transport and cascade of nutrients through watersheds. Instream biogeochemical processes can retain nutrients and function as an important `self-cleansing' service, by regulating downstream delivery of P and N, and reducing eutrophication risk in lakes and other receiving water bodies. However, our understanding of these instream processes is mostly limited to small wadeable streams during low-flow conditions. Larger deeper rivers are predicted to be more efficient at retaining nutrients under higher flows (which is when most watershed nutrient export occurs) and may therefore play an pivotal role in reducing downstream eutrophication risk. However, data to verify this are currently lacking. This program will address this important shortfall, through novel applications of in-situ sensors and high-resolution hydrochemical monitoring (which can be safely undertaken in large rivers and under high flows) to quantify the functional capacity of streams and rivers to retain P and N across the entire flow regime. The program will provide training for two PhD students and two MSc students, combining field and laboratory biogeochemistry, with cutting-edge skills in the use and application of in-situ hydrochemical sensors, along with sophisticated data-analysis techniques. These skillsets are increasingly sought-after by employers in research, environmental agencies and water utilities. The PhD and MSc trainees will use these tools and technologies to explore the role of river biogeochemical function in diminishing or amplifying downstream nutrient flux transmission and eutrophication risk. The program will examine whether wastewater effluent and other `point' sources that discharge into rivers semi-continuously (and can cause chronic baseline river water-quality impairment) degrade river `self-cleansing' capacity. If so, reducing point-source nutrient inputs could have major additional co-benefits by enhancing the `self-cleansing' capacity of rivers to retain nutrients from wider agricultural sources, delivered under high-flows. This would have profound implications for eutrophication management in Canada and internationally.