Phosphorus Sorption by Sediments from Wetlands in the Cedar River Watershed

Abstract

Excess phosphorus can lead to eutrophication of aquatic ecosystems, which can indirectly cause many species to suffer due to lower oxygen levels. The intent of this project was to determine if wetlands draining agricultural soil in the Cedar River watershed are removing phosphorus prior to empting into a tributary of the Cedar River. To determine the fate and transport of phosphorus in the wetlands, the total phosphorus (TP) of both the water and sediments was measured, and the ability for sediments to remove phosphate was also determined. The TP in the water column in the wetlands varied temporally from 700 to 1700 μg/L. Dissolved inorganic phosphate (SRP) totals were usually less than 10% of the total P, with a modest spike observed after a rainfall event. The low levels of SRP in the water led to testing of the TP levels in sediments and TP sorption capabilities. The TP of the sediment varied spatially from 500-700 μg/gdw. Sediments from the tributary (Beaver Creek) had total phosphorus levels of about 500 μg/gdw and the inlet to the wetlands varied from 300-400 μg/gdw. Depending on sampling locations, maximum sorption for sediments from the main body of the wetland ranged from 2-9 mg/gdw. Sediments from both the tributary (Beaver Creek) and the inlet to the wetlands sorbed about 7 mg/gdw. The results suggest that sediments in the wetlands are not yet saturated with phosphorus and therefore, when aerobic, can prevent phosphorus transport to rivers and streams.