Primary production increases with an increase in total phosphorus concentration.

(a) This aerial photograph shows the contrast in water quality of two basins, separated by a plastic curtain, of a lake in the Experimental Lakes Area near Kenora, Ontario. The lower basin received additions of carbon, nitrogen, and phosphorus, while the upper basin received only carbon and nitrogen. The bright green colour is from a surface film of algae that resulted from the added phosphorus. (b) The increase in primary production is measured as an increase in chlorophyll concentration. A higher chlorophyll concentration in the water means more algae are present.