TSI is a standard measure or means for calculating the trophic status or productivity of a lake.  More specifically, it is the total weight of living algae (algae biomass) in a waterbody at a specific location and time.  Three variables, chlorophyll a, Secchi depth, and total phosphorus, independently estimate algal biomass.

Phosphorus, Chlorophyll-a (algae concentration) and Secchi depth are related.  When phosphorus increases, that means there is more food available for algae, so algal concentrations increase.  When algal concentrations increase, the water becomes less transparent and the Secchi depth decreases. [Read more…]