A lake has an input of 1 g P m2 yr1 Assuming that all the P

Solution

Answer a:

Redfield molar ratio C : N : P = 106 : 16 : 1

i.e. 106 moles of carbon : 16 moles of nitrogen : 1 mole of phosphorus.

Converting them to a gram ratio:

Carbon weight = 12g / mol Nitrogen weight = 14g / mol phosphorus weight = 31g / mol

Redfield ratio in grams: 106 x 12 : 16 x 14 : 1 x 31

i.e. C : N : P = 41g : 7.2g : 1g

If P input is 1g m^-2 yr^-1 then it will support 41g m^-2 yr^-1 of Carbon. And since we are given that carbon forms 50% of the biomass by weight, the ( 41 x 2 ) g m^-2 yr^-1 = 84g m^-2 yr^-1 of biomass will be supported by an input of 1g P m^-2 yr^-1.

Answer b:

Nitrogen can be a limiting factor in this if not present in the required proportion, as we get from the ratio. So, amount of N that is required to support 84g m^-2 yr^-1 of algal biomass supported by 1g P m^-2 yr^-1 is (7.2 x 1)g = 7.2g N m^-2 yr^-1.