Phosphorus Recycling in Five Shallow Lakes

Abstract

Phosphorus recycled from lake sediments is a most important nutrient source for midsummer algae blooms in very shallow northcentral lakes with depths from 2 to 7 meters. A study of the Fairmont Lakes in southern Minnesota conducted over a period of several years has produced extensive data on phosphorus budgets and time-series measurements of phosphorus concentrations which infer or prove that extensive release of phosphorus from the sediments occurs in midsummer. The in-situ evidence presented herein includes measurements of: (1) Phosphorus content in a major storm runoff event; (2) phosphorus depletion after spring snowmelt runoff; (3) phosphorus content in midsummer runoff compared to lake phosphorus content; (4) midsummer phosphorus stratification in the lake; and (5) relationship between temperature stratification and phosphorus stratification dynamics.