Landscape and morphometric controls on water quality in stormwater management ponds

Stormwater management ponds (SWMPs) are used to mitigate the adverse effects of urbanization on water quality, and are increasing in numbers in the urban landscape. Given that these novel urban environments are becoming more ubiquitous and are being used as habitat by myriad flora and fauna, it is important to understand what controls water quality in SWMPs. We sampled 50 SWMPs and associated forebays in Southern Ontario, Canada for water quality to investigate the role of morphometric and landscape characteristics in determining water quality under baseflow conditions. SWMPs were characterized by extremely variable water quality, which was highly degraded compared to natural ponds. We found significant differences in water quality among varying ponds types, including ponds with different forebay designs and those without forebays. Ambient pond water quality was correlated with variables such as watershed imperviousness contributed by roads, sewershed area, and rainfall amount. We found that pond morphometry influenced nutrient concentrations, and that pond length, width, length: width ratio and surface area: perimeter ratio had the highest correlation with water quality. Over 80 % of SWMPs were found to show thermal structure, which often resulted in low dissolved oxygen, particularly at the sediment-water interface. These results will improve understanding of these new urban aquatic systems, including their suitability as habitat, and help managers improve pond nutrient removal efficiency.