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

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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.