Landscape-scale effects of nitrogen on lake ecosystems: Accelerating a new paradigm for freshwater eutrophication.

我们假设，到2050年，为养活30亿多人口而增加的农业施肥将使土壤中的磷（P）饱和，并创造条件，使随后流入的氮（N）调节发达地区的水质。 然而，与绿色革命期间不同，未来的氮肥将与尿素一起使用。 尿素在1960年之前很少使用，现在占全球氮肥的50%以上，在世界各地的湖泊中无处不在，对水生生态系统具有潜在的有害影响，但人们对其了解甚少。 鉴于目前约有10亿人缺乏清洁水，我们寻求建立一个严格的理论基础，以了解这些全球变化对人类和淡水的影响。 我们的计划将通过开展3个综合项目，为未来的水质退化开发一个新的范例。 首先，我们将结合联合收割机明确的土地利用模型与湖泊和河流参数的详细测量，以产生一个新的尿素是如何创建，破坏和运输的水生态系统的地球化学模型。 其次，我们将使用~60,000 L的实验和古生态（化石）分析作为整个生态系统施肥的替代品，以确定富磷湖泊的N效应的化学阈值。 在这里，非常大的开放和封闭的底部外壳在湖泊中的对比P含量将施肥与N定义阈值N损害和量化的作用，沉积物在调节表面沃茨的响应。 阈值的相关性，以整个湖泊将被测试的复制化石分析过去之间的关系，氮流入量和藻类丰度在20个湖泊沿着梯度的磷含量。 第三，我们将利用整个流域的氮转移，实验证明如何消除富磷湖泊的氮污染调节生态系统的生产和毒性。 在这里，我们将结合联合收割机的规模质量平衡（N，P，C）与一个独特的20年的生态研究计划，以确定明确的N转移是否可以返回富磷湖泊的基线条件。 这些项目应该解决长达40年的科学争论，并为管理人员、科学家、政府和公众提供避免未来水质损失的方法。

We hypothesize that increases in agricultural fertilization needed to feed 3 billion more people by 2050 will saturate soils with phosphorus (P) and create conditions in which subsequent influx of nitrogen (N) regulates water quality in developed regions. However, unlike during the Green Revolution, future N fertilization will be conducted with urea. Rarely used prior to 1960, urea now accounts for >50% of global N fertilizer, is ubiquitous in lakes worldwide, and has potentially detrimental but poorly understood effects on aquatic ecosystems. Given that ~1 billion people currently lack clean water, we seek to develop a rigorous theoretical basis to understand the consequences of these global changes for humans and freshwaters. Our program will develop a novel paradigm for future water quality degradation by conducting 3 integrated projects. First, we will combine explicit land-use models with detailed measurements of lake and stream parameters to produce a new biogeochemical model of how urea is created, destroyed and transported in aquatic ecosystems. Second, we will use ~60,000-L experiments and paleoecological (fossil) analyses as a surrogate for whole-ecosystem fertilization to identify chemical thresholds for N effects on P-rich lakes. Here, very large open- and closed-bottom enclosures in lakes of contrasting P content will be fertilized with N to define thresholds for N damage and quantify the role of sediments in regulating the response of surface waters. The relevance of thresholds to whole lakes will be tested by replicated fossil analysis of the past relationship between N influx and algal abundance in 20 lakes along a gradient of P content. Third, we will take advantage of a whole-catchment N diversion to demonstrate experimentally how elimination of N pollution from P-rich lakes regulates ecosystem production and toxicity. Here we will combine landscape-scale mass balances (N, P, C) with a unique 20-year ecological research program to determine definitively whether N diversion can return P-rich lakes to baseline conditions. These projects should resolve a 40-yr long scientific debate and provide managers, scientists, governments, and the public with a means to avoid future water-quality loss.