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

氮对水生生态系统的景观影响：实现淡水富营养化的新范例

• 批准号: RGPIN-2018-04590
• 负责人: Leavitt, Peter
• 金额: $ 8.52万
• 依托单位: University of Regina
• 依托单位国家: 加拿大
• 项目类别: Discovery Grants Program - Individual
• 财政年份: 2020
• 资助国家: 加拿大
• 起止时间: 2020-01-01 至 2021-12-31
• 项目状态: 已结题
• 来源: https://www.nserc-crsng.gc.ca/ase-oro/Details-Detailles_eng.asp?id=713153
• 关键词: Landscape; effects; nitrogen; aquatic; ecosystems

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.

自1950年以来，人口翻了一番，部分原因是农业化肥增加了10倍，使粮食产量几乎翻了一番。然而，农业实践也将土壤磷(P)含量提高了200%，并创造了农业土壤经常被磷浸透的条件，这种情况将持续几个世纪，并为淡水提供过剩的磷。在这些条件下，氮(N)的供应可能会调节湖泊产量，降低水质，并有利于有毒藻类的繁殖。不幸的是，由于施氮量自1970年以来也增加了15倍，而且其中一半以上是以尿素的形式添加的，尿素是一种促进有毒蓝藻的N的化学形式，因此持续的农业发展可能会导致大陆规模的有毒和致癌藻类的爆发。此外，城市中心不成比例的发展增加了化学还原N(如NH4+)的供应，导致许多海洋和淡水系统出现水华。鉴于约10亿人缺乏清洁水，我们寻求建立和应用对氮污染对加拿大和世界淡水影响的预测性理解。 该计划将在3个组成部分项目中结合生态系统操作、长期生态研究(LTER)和创新的古生态学，以量化N通量如何调节草原淡水的结构和功能。首先，我们将进行一项独特的全流域施肥实验，以量化尿素如何调节草原湿地的产量、食物网组成和生物地球化学。尿素占全球氮肥总量的50%，但人们对其对地表水生态系统规模的影响知之甚少。其次，我们将在52,000平方公里的曲阿佩尔河流域应用我们的数十年LTER研究，首次量化单独减少N的流入对富P湖泊的影响。在这里，我们利用了2016年Regina污水处理厂的升级，该厂将流入下游三个富磷湖泊的总N减少了50%(NH4+的&gt；95%)，但P没有减少(~5%)。综合湖沼学分析将与全湖N、P、C质量平衡相结合，作为LTER研究的一部分，在7个参照点和受污水影响的地点，以检验仅N分流就可以改善富P湖泊水质的假设。最后，我们将把我们的先进的统计方法(例如，广义加性模型；条件概率分析)应用于新的和旧的古湖水时间序列，以确定养分施肥是否会在N受限(Qu‘appelle湖泊)和P受限湖泊(Yahara Lake Chain，Madison，WI)中引发不同类型的灾难性状态变化。这些项目将使管理者、科学家、政府和公众对不同开发情景下富磷湖泊的水质退化控制有一个革命性的了解。