393761 - Stormwater Ponds Can Release Phosphorus
Tuesday, June 5
10:30 AM - 12:00 PM
Location: Mirage Room
University of Minnesota - St. Anthony Falls Laboratory
Tyler Olsen, Minneapolis, MN – University of Minnesota - St. Anthony Falls Laboratory; Poornima Natarajan, Minneapolis, MN – University of Minnesota - St. Anthony Falls Laboratory; John Gulliver, Minneapolis, MN – University of Minnesota - St. Anthony Falls Laboratory
Aging urban stormwater retention ponds may become net sources of phosphorus to receiving waters during high flow events. Wet retention ponds are typically designed to settle out suspended particulate phosphorus and adsorb soluble reactive phosphorus to cations in sediments. However, certain internal loading mechanisms release bound phosphorus from sediments and into the water column under different physio- and bio- chemical conditions. This is problematic because released phosphorus is typically labile and can create toxic algal blooms. In order to identify and better understand these mechanisms, intact sediment and water cores were extracted from various stormwater ponds in Minnesota. Each mesocosm is subjected to different redox conditions to simulate oxygen depletion and is flushed with synthetic stormwater to simulate precipitation events. Water column phosphorus concentrations are measured over a monitoring period to obtain an overall sediment phosphorus flux rate. At the conclusion of the monitoring period for each mesocosm, a sequential extraction of the sediments illustrates the phosphorus speciation and reveals the primary dynamics within the water column. Continuous in-situ monitoring of the stormwater pond conditions, as well as a phosphorus mass-balance, informs observed correlations between different physio- and bio- chemical conditions and phosphorus release. This understanding is crucial to guiding the remediation of aging stormwater ponds and controlling the release of captured phosphorus.