On the Phosphorus Limitation Paradigm for Lakes

Lakes are often said to be primarily phosphorus limited, but this paradigm has been described in numerous ways and there is considerable evidence that algae in lakes are often limited by other elements too. Crucial whole-ecosystem experiments that support the paradigm of the primacy of P limitation are few in number and have been limited to naturally oligotrophic lakes. A large amount of observational and experimental data seems to contradict the phosphorus limitation paradigm and instead indicates that most lakes are co-limited by N and P as well as, perhaps, by Fe and other resources. The biogeochemical theory behind the phosphorus limitation paradigm is that mechanisms can supplement cycles of C and N (and, discussed here, perhaps Fe) so that ultimately it is P that limits production and biomass. However, no mechanism has been proposed for ecosystems to overshoot this endpoint, meaning one might logically expect to see frequent occurrence of co-limitation by P, N and other resources over short, but still ecologically meaningful time scales that influence, for example, biodiversity patterns in lakes. One point of view has been that small-scale experimentation is simply misleading. However, an alternative is that even if P is ultimately limiting over multi-annual time scales, over shorter but still meaningful time scales, co-limitation of multiple nutrients is expected, and indeed is very common.