Removing filterable reactive phosphorus from highly coloured stormwater using constructed wetlands

Area of Science:

• Environmental Engineering
• Water Quality Management
• Wetland Ecosystems

Background:

• Urban stormwater runoff often contains high levels of phosphorus, contributing to eutrophication.
• Constructed wetlands are a promising nature-based solution for treating urban runoff.
• Optimizing phosphorus removal from urban stormwater is critical for protecting receiving water bodies.

Purpose of the Study:

• To evaluate the effectiveness of a novel constructed wetland design for removing filterable reactive phosphorus (FRP) from urban stormwater.
• To quantify phosphorus pools and key removal processes within the experimental wetland cells.
• To assess the role of plants, sediment, and biofilms in FRP removal.

Main Methods:

• Construction of three 1:1 scale experimental wetland ponds representing a cell from a larger design.
• Intensive sampling of inflow and outflow waters for FRP and Total Phosphorus (TP) over two years (1998/99).
• Quantification of phosphorus in plants and sediment, and measurement of benthic flux, biofilm, and Schoenoplectus validus uptake.

Main Results:

• Achieved FRP removal efficiencies of 5% in 1998 and 10% in 1999.
• Initial FRP uptake primarily occurred in plant biomass, with sediment becoming a significant sink over time.
• Anoxia did not induce phosphorus release from sediments, suggesting apatite binding. Low biofilm biomass (<1 g x m(-2)) was observed, potentially due to highly colored water.

Conclusions:

• The constructed wetland design demonstrated immediate effectiveness in removing FRP from urban stormwater post-construction.
• Sediment and Schoenoplectus validus play crucial roles in phosphorus sequestration.
• Further research is necessary to determine the long-term phosphorus removal capacity and performance of this wetland design.