Phosphorus Loading to Milwaukee Harbor from Rivers, Storm Water, and Wastewater Treatment

Abstract

Recent concerns about excessive algal (Cladophora) growth in the nearshore area have prompted a comprehensive study of phosphorus concentrations and loads in the Milwaukee watershed (2000–2008). During this period, total phosphorus (TP) decreased slightly for Outer Harbor water monitoring Station 1 (OH-1) representing the confluence of the three rivers into the Outer Harbor; whereas TP remained the same or slightly increased for Outer Harbor water monitoring Station 2 (OH-2) near the Jones Island Water Reclamation Facility (WRF) outfall. Concentrations of TP at OH-2 (0.095±0.005 mg/L) are higher than at OH-1 (0.073±0.006 mg/L). Years with high rainfall and river discharge during May through June produce high daily and annual average TP loads. This appears to be caused by resuspension and erosion of sediments containing TP in the river beds. Jones Island WRF contributes 39,500 kg/year or less than 34% of the total load to the Harbor. An estimate of TP load to Lake Michigan from rivers is 76,500 kg/year (65.7%). Stepwise regression results show that total soluble phosphorus (TSP), total suspended solids (TSS), and biochemical oxygen demand (BOD), in that order, are important predictors of TP except for Station OH-2.