Optimal Phosphorus Abatement Redefined: Insights From Coupled Element Cycles

To successfully combat eutrophication caused by agricultural P loads, we need to understand how various forms of P respond to mitigation measures and thus how they contribute to algal growth. Failure to balance mitigation measures targeting dissolved inorganic P (DIP) and P in eroded soil (PP) may lead to economically inefficient measures at best, and to aggravated eutrophication at worst. We model dynamically optimal eutrophication management in a P-limited and SO4-containing water body by taking into account the O2 available and the coupling between the C, Fe, S and P cycles. We show that optimal management would put more weight on mitigating DIP than PP, and that the emphasis on DIP should be particularly strong in eutrophic water bodies. To foster influential and cost-efficient policies, we urge defining water body-specific multipliers to commensurate the main P forms into eutrophying phosphorus, much as greenhouse gases are converted to their CO2 equivalents.