The role of river biogeochemical function in the watershed eutrophication cascade

富营养化（公害和有害藻华的扩散）是由农业和废水中过量的营养物质（磷和氮）引起的。这是全球水质受损的一个主要来源，也是对加拿大水安全的一个紧迫和普遍的威胁。仅加拿大五大湖流域的富营养化成本就高达83亿美元/年。这项研究的长期目标是对从地方到全球范围内淡水富营养化的驱动因素进行新的定量了解。需要进行这项研究，以指导具有成本效益的水质管理，并改善水环境健康，因为水环境健康也日益受到气候和土地使用变化的威胁。这个为期5年的研究计划的重点是了解通过流域控制营养物质循环，运输和级联的瞬时过程。河道内生物地球化学过程可以通过调节磷和氮的下游输送并降低湖泊和其他受纳水体的富营养化风险，保留营养物质并发挥重要的“自我清洁”服务的作用。然而，我们对这些瞬时过程的理解主要限于低流量条件下的小型可涉流。预计较大的较深的河流在较高流量下更有效地保留营养物质（这是大多数流域营养物质输出发生的时候），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。该计划将通过原位传感器和高分辨率水化学监测（可在大型河流和高流量下安全进行）的新应用来解决这一重要不足，以量化溪流和河流在整个水流状态下保留P和N的功能能力。该计划将为两名博士生和两名硕士生提供培训，结合现场和实验室地球化学，在现场水化学传感器的使用和应用方面具有尖端技能，沿着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通量传输和富营养化风险方面的作用。该方案将审查半连续排放到河流中的废水和其他“点”源（可能造成河流水质长期基线损害）是否降低了河流的“自我净化”能力。如果是这样的话，减少点源营养素投入可以通过提高河流的“自我清洁”能力，保留在高流量下输送的更广泛的农业来源的营养素，从而产生重大的额外共同效益。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.