Inputs of Phosphorus from Precipitation to Lake Michigan

Precipitation samples were collected at six locations around Lake Michigan and analyzed for the concentrations of the different forms of phosphorus present. The concentrations were found to be higher in the southern part of the lake. Precipitation-weighted concentrations of total phosphorus and dissolved reactive phosphates were found to be 0.023 mg/1 and 0.011 mg/1, both higher than the concentrations found in the open lake of 0.009 and 0.002 mg/1. Inputs of total phosphorus to the lake were calculated to be 1.0 × 10 6 & kg/yr or about 18% of the present phosphorus budget of the lake. More than 40% of the phosphorus in precipitation is in the form of dissolved reactive phosphates and it is estimated that about 0.6 × 10 6 & kg/yr of the phosphorus coming into the lake in precipitation becomes available to organisms in the lake.