Degradation and destablization of lake ecosystems by anthropogenic nitrogen: a new paradigm for future lake eutrophication

自1950年以来，全球人口翻了一番，这主要是由于绿色革命，其中农业化肥使用量增加了10倍，粮食产量翻了一番。这些耕作方法也使土壤磷（P）含量增加了200%或更多，并在许多哨兵生态系统中创造了条件，其中农业土壤现在饱和了P，并将保持数百年，并为淡水提供过量的P。在这些条件下，氮（N）和光能（E）的供应似乎调节湖泊生产，水质退化，以及有毒藻华的发展。 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，尿素是一种选择性促进有毒蓝细菌生长的氮的化学形式，因此，农业的持续发展有可能导致有毒和可能致癌的藻类在大陆范围内爆发。 鉴于约10亿人已经缺乏清洁水，我们寻求大量资金来预测这些变化对加拿大和世界各地的人类和淡水的影响。 我们建议开发一个新的范例，未来湖泊富营养化的基础上，三个组成部分的项目。 首先，我们将添加生长饱和水平的尿素-N的富磷实验湖测试的假设，这种形式的N优先刺激蓝藻的生长和毒性。 其次，我们将调查如何从一个链的富磷，氮有限的湖泊氮转移可能会改善水质，减少有毒藻类的爆发。 最后，我们将结合联合收割机全湖和流域尺度的质量平衡的N和P与高分辨率的古生态分析，以确定如何湖泊的物理结构（热分层）可能会影响N控制富营养化在一个大的景观。 这些组成部分将为管理人员、科学家和公众提供对未来水质退化控制的新认识。

Global human population has doubled since 1950, largely due to the green revolution in which a 10-fold increase in agricultural application of fertilizer has doubled food production. These farming practices have also raised soil phosphorus (P) content by 200% or more and have created conditions in many sentinel ecosystems in which agricultural soils are now saturated with P, will remain so for centuries, and supply freshwaters with excess P.  Under these conditions, supplies of nitrogen (N) and light energy (E) appear to regulate lake production, water quality degradation, and the development of 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 selectively promotes toxic cyanobacteria, there exists the possibility that continued agricultural development will lead to continental-scale outbreaks of toxic and possibly carcinogenic algae.  Given that ~1 billion people already lack clean water, we seek substantial funding to develop a predictive understanding of the consequences of these changes for humans and freshwaters throughout Canada and the world.          We propose to develop a new paradigm for future lake eutrophication based on three component projects.  First, we will add growth-saturating levels of urea-N to a P-rich experimental lake to test the hypothesis that this form of N preferentially stimulates both growth and toxicity of cyanobacteria.  Second, we will investigate how N diversion from a chain of P-rich, N-limited lakes may improve water quality and reduce outbreaks of toxic algae.  Finally, we will combine whole-lake and catchment-scale mass balances of N and P with high-resolution paleoecological analyses to determine how the physical structure of lakes (thermal stratification) may affect N control of eutrophication over a large landscape.  Together these components will provide managers, scientists and the public with a new understanding of the controls of future water-quality degradation.