Geelong, VIC is undergoing a significant urban growth project. The loss of greenfield land to urbanization reduces infiltration of rainwater in the region and creates localized stormwater management challenges. In recent years, constructed wetlands (CWs), engineered waterbodies are utilized to regulate quantity and quality of stormwater runoff containing contaminants, naturally.
Current research has overwhelmingly focused on the performance of CWs with respect to traditional contaminants (nitrogen, phosphorous and suspended solids). However, stormwater typically contains a variety of contaminants, including heavy metals. Understanding the capacity for CWs to capture heavy metals from stormwater runoff will assist in identifying whether they are an effective tool to minimize potential impacts from metal toxicity.
A field monitoring campaign (five events) was conducted over spring 2021 on three wetlands in Geelong, representing different ages and physical characteristics to measure the treatment performance for metals. Water and sediment samples were collected (inlet and outlet) and analyzed for traditional contaminants and metals (water and sediment). For metals, results were compared to the Australia & NZ Freshwater guidelines and National Environmental Protection Measure (sediments).
High copper (1.38–54.67 ug/L), zinc (3.90–103.86 ug/L) and chromium (1.17–2.29 ug/L) levels were observed at Ashbury (residential catchment) due to the ongoing construction works. High levels of metals at the commercial (Waurn Ponds) and residential catchment (Warralily) were observed, exceeding ecotoxic levels most times. Typically, lower concentrations were observed at the outlet but under certain climatic conditions, it was the opposite.
The outcomes of this study are anticipated to shed light on how stormwater runoff containing understudied eco-toxins such as heavy metals can be treated by CWs, it also highlights the high temporal variability in water chemistry across wetlands. Recommendations include more long-term studies at higher sampling frequency to assess the heavy metal treatment capacity of CWs across different climatic conditions.