Dynamics of plankton blooms: lessons from an epidemiological model

Background/Question/Methods

Data on time-varying nitrate and phytoplankton levels are available from diverse aquatic environments, and the dynamics vary in different environments and conditions.  To explain these observations, we use a modeling approach that is based only on the interaction between nitrogen and phytoplankton, assuming that zooplankton dynamics are on a longer time scale.  In this case, the dynamics are mathematically equivalent to well studied dynamics of epidemiological models like the SIR model.

Results/Conclusions

In our initial exploration of the SIR model approach, we confine examples to a scenarios where the uptake of nitrogen is much faster than exchange processes, so that one can make the assumption of no new nitrogen influx as in the SIR assumption of a closed population.  Specifically, we think of a high-nitrate water parcel upwelling into the euphotic zone and developing an algal bloom as it is transported offshore.  In contrast, we consider the spring bloom in the North Atlantic, where onset of stratification isolates a parcel of surface water with moderate nitrate levels.  In both cases, blooms appear which look like epidemics, but the post-bloom nitrate level differs markedly as a result of the initial bloom concentration in accord with the qualitative behavior