Nitrogen cycling in nutrient-rich freshwaters

营养物污染被广泛认为是全球影响水质的最重要压力源。营养物污染可导致藻类高产、鱼类死亡和可能有毒的水华。由于问题的技术、经济和社会方面以及生态系统恢复的潜在滞后，解决营养物污染具有挑战性。淡水中的营养盐管理通常集中在控制磷的输入。然而，越来越多的人呼吁也控制氮的投入，并就氮控制的潜在效益和成本展开辩论。 虽然里贾纳和温尼伯市已经在氮去除方面投入了数百万美元，以帮助对抗营养物污染，但氮控制将如何影响湖泊以及湖泊本身如何调节氮浓度仍存在关键问题。由于蓝藻在固定大气氮，使其生物可利用方面的作用，其在湖泊氮收支中的潜在作用受到了广泛重视。关于沉积物中氮的再循环或去除过程，特别是大草原湖泊中的氮的再循环或去除过程知之甚少，大草原湖泊是一个水资源相对不安全的地区，存在营养污染的重大问题，以及可能影响氮循环的不寻常的湖泊化学。我们的工作将采用示踪剂来评估浅水湖泊氮循环的关键过程，以了解沉积物中的氮循环是否会影响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了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。 大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，这对我们缓解本区域普遍存在的养分污染问题的努力构成了挑战。 这些小池塘可能是养分保留的场所，但由于排水，它们正在迅速流失。 在将湿地建设或恢复视为有益的管理实践之前，我们需要更好地了解湿地在传输，保留或释放营养物质方面的作用。 在大草原内，这意味着我们必须更好地了解寒冷条件下的养分循环，以及融雪期间水分和养分运动的关键时期。 在这里，我们将专注于了解浅池塘如何通过春季融化期改变其氮循环过程，了解冬季冻结是否会阻碍春季的营养保留过程，以及氮循环过程如何在空间中变化。 有了这个，我们将建立一个新的认识，草原流域管理的变化将如何影响氮循环和湖泊中的氮可用性，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.