Urban Leaf Phosphorus

Stormwater carries phosphorous to receiving waterbodies through the storm sewer network. Urban street leaf litter can be a major source of this phosphorous in stormwater. In urban residential watersheds, managing stormwater runoff to safeguard water quality of urban streams and lakes remains a challenge. Understanding the potential for P release from leaves is important for stormwater source control. In a collaboration with the U.S. Geological Survey, we are studying phosphorous leaching dynamics from street leaf litter and creating a model to estimate end-of-pipe phosphorous in stormwater runoff.

Our study characterized Total Dissolved Phosphorus (TDP) leaching dynamics from leaf litter of Norway Maple and Green Ash trees over 48 hours. The leaching dynamics described by a rapid initial TDP release was followed by a gradual plateau after a certain time, depending on tree species, litter quality, and environmental conditions. TDP maximal release was different for Norway Maple and Green Ash. For both species, TDP maximal release was greater for intact leaves than fragmented or crushed leaves. Temperature (20°C and 4 °C) and volume of water had little influence on TDP release (mg g-1) at each sampling time. The event end-of-pipe P loads significantly correlated with three key explanatory parameters: runoff volume, mass of leaf litter on streets and dry days prior to the storm event.