Spring and fall bloom
Simple model of the spring bloom in coastal temperate coastal waters. Nitrogen is assumed to be the limiting nutrient, so the model is based on N only. The model represents one liter of water. Dissolved inorganic nitrogen (DIN) accumulates in the water column during winter and has reached 250 µmol/L on March 1st where the model starts. At this time the light intensity have just reached the level necessary to initiate the bloom.
N uptake: Michaelis Menten kinetics with a maximum growth rate that doubles the population each day. Km=5µM.
Grazing: Michaelis Menten kinetics with a maximum daily uptake equal to the N in the population. Km=50µM.
Sloppy eating: 60% of the grazing is wasted to PON
Death: 5% of the zooplankton dies each day
Mineralization: 1% of the PON is mineralized to DIN each day
For the first 6 days the phytoplankton grows exponentially and depletes
the DIN pool. The peak in phytoplankton is followed by a delayed peak in
zooplankton due to its slower growth rate. Slowly the zooplankton graze
down the spring bloom and the nitrogen is transformed to the pool of
particulate dead organic nitrogen (PON). While this happens the
phytoplankton is kept low by the still high zooplankton which allow the
DIN pool to increase from day 25 to day 55. Eventually the phytoplankton
escapes the top down control and we see a secondary bloom based on