Nitrogen cycling in nutrient-rich freshwaters

营养盐污染被广泛认为是影响全球水质的最重要的压力源。营养物污染可能导致藻类生产力高、鱼类死亡和水华中毒。由于营养物污染问题的技术、经济和社会方面的原因，以及生态系统恢复的潜在滞后，解决这一问题具有挑战性。淡水中的营养管理通常以控制磷的输入为中心。然而，越来越多的人呼吁也控制氮素的投入，并就氮素控制的潜在好处和成本展开辩论。 尽管里贾纳和温尼伯两个城市已经在脱氮方面投入了数百万美元，以帮助对抗营养物质污染，但关于氮素控制将如何影响湖泊，以及湖泊本身可能如何调节其氮浓度，仍存在一些关键问题。由于蓝藻在固定大气氮、使其可生物利用方面的作用，人们非常重视蓝藻在湖泊氮收支中的潜在作用。关于沉积物中氮素的循环或去除过程，尤其是在草原湖泊中，人们所知的要少得多，这是一个水相对不安全的地区，存在严重的营养污染问题，以及可能影响氮循环的异常湖泊化学物质。我们的工作将使用示踪剂来评估浅水湖泊氮循环中的关键过程，以了解沉积物中的氮循环是否影响到生物重要时期的营养供应，包括水华。我们对氮的内部循环的新见解将帮助我们理解氮是否可以在浅水湖泊中控制，以及我们可能看到氮变化的时间尺度。 草原上的湖泊镶嵌在农业景观中。管理农业养分的选择有限，这对我们缓解该地区普遍存在的养分污染问题的努力构成了挑战。景观中的小池塘可能代表着营养物质的保留，但由于排水，它们正在迅速消失。在考虑将湿地建设或恢复作为一种有益的管理实践之前，我们需要更好地了解湿地在传递、保持或释放养分方面的作用。在草原内部，这意味着我们必须更好地了解寒冷条件下的养分循环，以及在融雪期间水分和养分运动的关键时期。在这里，我们将重点了解浅水池在春季融化期如何改变其氮循环过程，了解冬季冰冻是否阻碍春季的养分保持过程，以及氮循环过程在空间上的变化。通过这一点，我们将对草原流域管理的变化如何影响氮循环和湖泊中的氮素有效性建立一个新的理解，为改善水质提供明智的选择。

Nutrient pollution is widely considered the most significant stressor impacting water quality globally. Nutrient pollution can lead to high algal productivity, fish kills, and blooms which can be toxic. Addressing nutrient pollution is challenging due to technical, economic, and social aspects of the problem, and potential lags in ecosystem recovery. Nutrient management in freshwaters is typically centered on controlling inputs of phosphorus. However, there has been growing call to also control inputs of nitrogen and debate about the potential benefits and costs of nitrogen control. Although the cities of Regina and Winnipeg have made multimillion dollar investments in nitrogen removal to help combat nutrient pollution, there are key questions about how nitrogen control will impact lakes, and about how lakes themselves may regulate their nitrogen concentrations. Much emphasis has been placed on the potential role of cyanobacteria in the nitrogen budgets of lakes due to their role in fixing atmospheric nitrogen, making it bioavailable. Much less is known regarding the processes that recycle or remove nitrogen within sediments, particularly within lakes of the prairies a region of relative water insecurity, significant problems of nutrient pollution, and unusual lake chemistry which is likely to affect nitrogen cycling. Our work will employ the use of tracers to assess key processes in the nitrogen cycle of shallow lakes in order to understand whether nitrogen recycling from sediments is affecting nutrient supply in biologically important periods, including blooms. Our new insights into internal cycling of nitrogen will help us understand whether nitrogen can be controlled within shallow lakes, and the timescale upon which we may see changes in nitrogen. Lakes in the prairies are embedded in an agricultural landscape. Options to manage agricultural nutrients are limited, challenging our efforts to mitigate widespread issues of nutrient pollution in the region. The small ponds that riddle the landscape could represent sites of nutrient retention, but they are rapidly being lost due to drainage. Before considering wetland construction or restoration as a beneficial management practice, we need to better understand the role of wetlands in transmitting, retaining, or releasing nutrients. Within the prairies, this means we must better understand nutrient cycling in cold conditions, and during snowmelt the key period of water and nutrient movement. Here we will focus on understanding how shallow ponds alter their nitrogen cycling processes through the spring melt period understanding whether winter freezing impedes nutrient retention processes in spring, and how nitrogen cycling processes vary in space. With this we will build a new understanding of how changes in the management of prairie watersheds will impact nitrogen cycling and nitrogen availability in lakes, informing wise choices to improve water quality.