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)含量提高了近200%，并创造了农业土壤经常充满磷的条件，并将在几个世纪内保持这种状态，并向淡水提供过量的磷。在这些条件下，氮(N)的供应可能会调节湖泊产量，降低水质，并有利于有毒藻华。不幸的是，由于氮肥自1970年以来也增加了15倍，并且由于其中一半以上的氮以尿素的形式添加，尿素是氮的一种化学形式，可以促进有毒的蓝藻，因此农业的持续发展可能会导致大陆范围内有毒和致癌藻类的爆发。此外，城市中心不成比例的增长增加了化学还原氮（如NH4+）的供应，在许多海洋和淡水系统中造成水华。鉴于约有10亿人缺乏干净的水，我们寻求开发和应用对加拿大和世界淡水氮污染后果的预测性理解。