Internal loading in stormwater ponds as a phosphorus source to downstream waters
Vinicius J. Taguchi, Tyler Olsen, Poornima Natarajan, Ben Janke, John S. Gulliver, Jacques C. Finlay, Heinz G. Stefan
Abstract
Abstract We assessed the prevalence and causes of sediment phosphorus (P) release within urban stormwater ponds, a process that may reduce P removal by sedimentation. Data collected from surface water of 98 urban stormwater ponds in Minnesota showed that nearly 40% had median summer total P concentrations in excess of average stormwater runoff (0.38 mg L −1 ), implying effects of internal loading. We sampled seven ponds more intensively and found four were strongly stratified with persistent hypolimnetic anoxia, despite mean depths <2 m. Sediment core incubations revealed that, unlike in most lakes, both labile organic P (NaOH minus persulfate extractions) and redox‐sensitive P (NH 4 Cl and Na 2 S 2 O 4 extractions) contribute to P release. Together, these analyses suggest P accumulated in stormwater ponds is highly susceptible to internal release and potentially contributes to downstream eutrophication. Understanding how frequently these conditions occur and how they affect different P forms is vital to improving pond design and management.