The fingerprints of urban nutrients: dynamics of phosphorus speciation in water flowing through developed landscapes

As urban ecosystems are known to be phosphorus (P)-rich environments, the sources of this nutrient and its biogeochemistry within human-dominated landscapes remain in need of study. Specifically, very little is known about how different P species vary within and among urban aquatic environments. In this study, we examined the phosphorus dynamics in urban stormwater ponds that are embedded in residential landscapes. Water samples were collected from stormwater ponds located in southern Ontario, Canada during the summer of 2012. We measured several P types: total P; TP, particulate P; PP, and dissolved inorganic P; DIP as well as two classes of DOP (phosphomonoesters (MP) and phosphodiesters (DP)) in the surface water samples. In most ponds, PP in outflowing water were found at concentrations higher (up to 12 times) than those measured in incoming stormwater. With respect to DOP, DP increased and became more abundant in outflowing compared to inflowing waters while MP concentrations decreased within ponds. The magnitude of these spatial changes from pond inlets to outlets was strongly linked to recent periods of rainfall and the hydrological condition of pond inflows. Elevated MP was found adjacent to inlets especially during periods of more frequent rainfall, which indicates that MP is derived from terrestrial sources and delivered by stormwater. In contrast, DP production was more related to internal biological activity in ponds as its concentrations increased during relatively dry conditions with low stormwater flow. Our results demonstrate that stormwater ponds have significant influence on the quantity and types of P moving through these highly human-modified environments.