found that in polymictic Lake Xolotlan, Nicaragua, the major factor influencing the net growth of phytoplankton is the ratio of photic to mixed depth; net growth was reduced in winter coincident with increased winter season winds and greater sediment re-suspension. East and Sharfstein (East and Sharfstein, 2006) developed a hierarchical decision model that predicted light limitation versus nitrogen limitation in Lake Okeechobee with 70–85% accuracy, the major determinant being the ratio of Secchi to total depth.