PHOSPHORUS DYNAMICS IN STORMWATER PONDS
Tyler Olsen, Masters Candidate in Civil, Environmental, and Geo- Engineering
Advisor: Dr. John Gulliver, Department of Civil, Environmental, and Geo- Engineering and St. Anthony Falls Laboratory, University of Minnesota
Retention ponds are designed to settle particulate phosphorus in the sediments. However, internal loading mechanisms can release bound phosphorus from sediments into the water column, leading to eutrophication conditions in the pond and downstream waterbodies. To understand these mechanisms, twentyone intact sediment and water cores were extracted from four stormwater ponds. Each mesocosm was subjected to different redox conditions and monitored over 30 days. The water column orthophosphate concentrations are used to obtain an overall sediment phosphorus flux rate. Phosphorus fractions in the sediment are analyzed to better understand the role of pond sediment characteristics in phosphorus release. Iron bound phosphorus concentrations correlated with phosphorus release from the sediments, highlighting the important influence of redox conditions in ponds. Four relations were developed to quantify phosphorus release rates in ponds by fitting regressions to oxygen consumption and sediment P fractions versus the measured phosphorus flux in the mesocosms.