Phosphorus comes from soil minerals. As Hatch explains, when those minerals wash into Tahoe s streams, some of the phosphorus dissolves into the water, becoming phosphate ions. The amount depends on chemical equilibrium established between mineral particles containing phosphorus and dissolved phosphate ions. That equilibrium varies from time to time and place to place. But when that mix of mineral phosphorus and dissolved phosphate gets to the lake, it separates.
Larger particles sink to the bottom of the lake.
Dissolved phosphate and tiny particles hang around for awhile in the water layer that s home to algae. Phosphate is what algae use. And the tiny mineral particles that float will slowly release more phosphates that help nourish algae. Stimulation of Tahoe s algal growth by tiny particles and dissolved phosphorus was confirmed by Hatch s studies. Phosphorus at the bottom of the lake is locked up by reactions with iron and oxygen.