Landscape effects of nitrogen on aquatic ecosystems: Achieving a new paradigm for freshwater eutrophication

自1950年以来，人口增加了一倍，部分原因是农业施肥增加了10倍，粮食产量几乎翻了一番。然而，农业实践也使土壤磷（P）含量增加了200%以上，并创造了农业土壤经常被P饱和的条件，并将持续几个世纪，并为淡水提供过量的P。 不幸的是，由于自1970年以来，氮肥也增加了15倍，而且其中一半以上的氮是以尿素的形式加入的，尿素是一种促进有毒蓝细菌生长的氮的化学形式，因此存在着继续农业发展将导致有毒和致癌藻类在大陆范围内爆发的可能性。 此外，城市中心的不成比例的增长增加了化学还原氮（如NH 4+）的供应，在许多海洋和淡水系统中造成水华。鉴于约10亿人缺乏清洁的水，我们寻求开发和应用的N污染在加拿大和世界淡水的后果的预测性理解。该计划将结合联合收割机生态系统操作，长期生态研究（LTER），并在3个组成项目的创新古生态学，以量化如何N通量调节草原淡水的结构和功能。首先，我们将进行一个独特的全流域施肥实验，以量化尿素如何调节生产，食物网的组成，草原湿地和土壤地球化学。尿素占全球氮肥总量的50%，但其对地表沃茨生态系统规模的影响却知之甚少。其次，我们将在52,000平方公里的Qu'Appelle河流域应用我们的数十年LTER研究，以首次量化减少氮流入对富磷湖泊的影响。 在这里，我们利用2016年里贾纳污水处理厂的升级，减少了总氮流入量>50%（NH 4 +>95%），但没有P（约5%下降），三个富含P的下游湖泊。 综合湖沼学分析将结合全湖质量平衡的N，P和C的LTER研究的一部分，在7个参考和污水影响的网站，以测试的假设，仅转移N可以改善水质在富磷湖泊。最后，我们将应用我们先进的统计方法（例如，广义加性模型;条件概率分析）到新的和旧的古湖泊时间序列，以确定营养施肥是否在N-限制（Qu'Appelle湖）和P-限制湖（Yahara湖链，麦迪逊，WI）中引发不同类型的灾难性状态变化。这些项目将为管理人员、科学家、政府和公众提供对不同发展情景下富磷湖泊水质退化控制的变革性理解。

Human population has doubled since 1950, in part due to a 10-fold increase in agricultural fertilization that has nearly doubled food production. However, farming practices have also raised soil phosphorus (P) content by >200% and created conditions in which agricultural soils are often saturated with P, will remain so for centuries, and supply freshwaters with excess P. Under these conditions, supplies of nitrogen (N) may regulate lake production, degrade water quality, and favour toxic algal blooms. Unfortunately, because N fertilization has also increased 15-fold since 1970, and because more than half of this N is added as urea, a chemical form of N which promotes toxic cyanobacteria, there exists the possibility that continued agricultural development will lead to continental-scale outbreaks of toxic and carcinogenic algae. Furthermore, disproportionate growth of urban centres has increased supplies of chemically-reduced N (as NH4+) creating blooms in many marine and freshwater systems. Given that ~1 billion people lack clean water, we seek to develop and apply a predictive understanding of the consequences of N pollution for freshwaters in Canada and the world. This program will combine ecosystem manipulation, long-term ecological research (LTER), and innovative paleoecology within 3 component projects to quantify how N fluxes regulate the structure and function of prairie freshwaters. First, we will conduct a unique whole-basin fertilization experiment to quantify how urea regulates production, food-web composition, and biogeochemistry of prairie wetlands. Urea represents 50% of all global N fertilizer, yet little is known of its ecosystem-scale impacts on surface waters. Second, we will apply our multi-decadal LTER research in the 52,000 km2 Qu'Appelle River catchment to quantify for the first time the effects on P-rich lakes of reducing the influx of N alone. Here we take advantage of the 2016 upgrade of the Regina sewage treatment plant which has reduced total N influx >50% (>95% of NH4+), but not P (~5% decline), to three P-rich downstream lakes. Comprehensive limnological analysis will be combined with whole-lake mass balances of N, P and C as part of LTER studies at 7 reference and sewage-impacted sites to test the hypothesis that diversion of N alone can improve water quality in P-rich lakes. Finally, we will apply our advanced statistical approaches (e.g., generalized additive models; conditional probability analysis) to new and older paleolimnological time series to determine whether nutrient fertilization initiates different types of catastrophic state change in N-limited (Qu'Appelle lakes) and P-limited lakes (Yahara lakes chain, Madison, WI). Together these projects will provide managers, scientists, governments, and the public with a transformative understanding of the controls of water-quality degradation in P-rich lakes under diverse development scenarios.