Suppose that the average residence time ignoring respiratory

Suppose that the average residence time (ignoring respiratory pathways) of carbon in the phytoplankton in a lake is 2 weeks. Zooplankton in the lake, grazing upon the phytoplankton, consume 40% of the net primary production and have an incorporation efficiency of 25% (i.e., 25% of the phytoplankton biomass they eat is incorporated into the zooplankton biomass). In other words, the net productivity of the zooplankton is .25 x .40 or 10% of the npp of the algae. If the average residence time (ignoring respiratory pathways) of carbon in zooplankton biomass is 6 months, estimate the ratio of the average biomass of the zooplankton population to that of the phytoplankton population in the lake.

Solution

In 6 months, there is 6 x30 days = 180 days. In addition, carbon in phytoplankton resides for 2 weeks or 14 days.

So net primary production for phytoplanktonin 6 months is = 180/14 =12.85 times from week 1

The 12.85 factors for net biomass production of phytoplankton too

Now, the zooplankton has 10% or 0.1 of NPP of phytoplankton so the net biomass is 180/180 = 1 factor but this is only 10% or 0.1 factor of phytoplankton biomass

So

Net biomass production phytoplankton/ Net biomass production zooplankton = 12.85 / 0.1= 128.5 factors

Net biomass production phytoplankton= 128.5 x Net biomass production zooplankton