Tropical wetlands have numerous natural functions, one of which is the filtration of wastewater for water quality improvement. The aim of this paper is to investigate the performance of constructed wetlands in Universiti Sains Malaysia for water quality treatment of stormwater runoff. A total of 17 sampling stations were selected from different sections of possessing different compositions, characteristics and plant species. Weekly physico-chemical and biological parameters were analysed during the one year period starting from December 2010 to December 2011. The results exhibited significant improvement of water quality as the concentration of nitrate, nitrite, ammoniacal-nitrogen, orthophosphate, TSS, BOD and COD decreased after the water passed through the macrophyte and micropool zones before being discharged to the wetland outlet. The concentration of nitrite was significantly reduced (80%);nitrate (61.56%), ammoniacal-nitrogen (51.49%), orthophosphate (60.98%), TSS (67.86%), BOD (27.7%) and COD (46.43%). The decrease in the concentrations of the above pollutants showed that the improvement of water quality was performed in the wetland. Most of the concentrations fall in Class IIA and IIB based on National Water Quality Standards for Malaysia and Department of Environment (DOE) Water Quality Index Classification. Biological measurement showed high diversity of species. Based on the results obtained, the macrophyte zone showed a high number of species and percentage distribution of phytoplankton and zooplankton, starting from the Wetland 1and 2 until the outlet wetland (14.6% - 14.9% until 3.5%). While for fish distribution, Oreochromis niloticus was the dominant fish species from the others seven species found in the constructed wetland. Overall, the results from this study demonstrate that constructed wetlands significantly improve water quality of stormwater runoff, and that they are a good natural resource for the sustenance and maintenance of biodiversity.
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