Determine condition of Iowa’s natural lakes from pre-settlement (1850) to present

(mean depth 9ft)

Objectives

• Insight to changes in nutrient concentrations over time (specifically total phosphorus)

• Realistic restoration goals

Average in filling rate of one-tenth of an inch per year

Iowa Results

• 1900’s required more than 20 years to accumulate an inch of sediment, now only 4 years

• 70% of the sediment loading to our lakes originates from 10% of the watershed – targeted approach

Currently 70% of sedimentation to our lakes is derived from the watershed, with remaining 30% from organics and algal production in the lake

Summary

• Historic total phosphorus levels of 26 ppb to 147 ppb

• Current average of 161 ppb

• Trend since pre-settlement for increased rates of sedimentation, nutrient levels and decreased clarity

limnology.eeob.iastate.edu/Publications.aspx