Which of the following ecosystems will be more productive in terms of primary productivity? Justify your answer.
A young forest, a natural old forest, a shallow polluted lake, alpine meadow.

Explanation

Primary productivity can be defined as the rate at which primary producers (e.g. green plants) trap and store solar radiation in the form of biomass. This is measured in terms of weight `(g^(-2))` and in terms of energy.(kcal `m^(-2)`) per year in a given time. So, primary productivity varies from ecosystem to ecosystem and the ecosystem which possesses more produccts will be more productive in terms of primary productivity.
So, young forests grow quicker than older mature forests and are more productive in terms of productivity. The shallow polluted lake and alpine meadow will be less productive because of less number of producers and high amount of dead organic matter.