Fifteen 10-L plastic containers (Cubitainers)being deployed for incubation in Lake Titicaca, Peru. The response of the phytoplankton (algae) were being tested for their response to additions of nitrogen (NH4NO3), phosphorus (PO4), N+P, Fe and micronutrients. After incubating for 5 days, the chlorophyll levels and nitrogen fixation were measured in each container.
In multiple experiments, phytoplankton growth was stimulated primarily by nitrogen, and nitrogen fixation by either iron or phosphorus. See Wurtsbaugh et al. Freshwater Biology 15:185-195 (1985)for details.