Understanding the role of aquatic plants in stormwater management pond performance in Oshawa, Ontario, Canada

Abstract

Stormwater Management Ponds (SMPs) are engineered to receive, store, and treat stormwater runoff before it enters receiving waters in urbanizing landscapes. While these systems are not considered natural, they are typically colonized by aquatic plants. Although submergent and emergent vegetation is common in SMPs, not much is known about their potential impacts on SMP performance. The aim of my thesis project was to investigate the effect of aquatic plants on the water treatment capacity of 15 SMPs in Oshawa, Ontario, Canada, over two years (2018-2019). I determined that overall, SMPs serve as sinks for certain water quality parameters including chloride and nitrogen, while being a net source of phosphorus to tributaries. The effect of plants on SMP performance was mixed. Increasing submergent plant biomass was associated with decreasing nitrogen concentrations at outflow locations (p = 0.002, cor = -0.316). Emergent vegetation had no significant impact on stormwater treatment overall, but the invasive species, P. australis was associated with decreasing outflow nitrogen concentrations. Overall, I determined that pond characteristics, including pond size, age, and drainage area are significant drivers of established plant profiles.