The objective of this thesis is to provide a detailed investigation of phosphorus transformations in constructed wetlands. Five replicate Wetland Units were constructed adjacent the wastewater treatment plant in Richmond, Australia. Each wetland was supplied with secondary or tertiary sewage effluent and planted identically with species of schoenoplectus, Phragmites, and Triglochin. Detention times for each Unit were established at 5 or 15 days. Phosphorus concentrations were monitored routinely at the inlet and outlet of each Unit, with a number of specific studies conducted to investigate internal transformations. These studies, undertaken in 1994 and 1995, determined that plants were the dominant phosphorus store in the short term, during wetland establishment and that sediments were the dominant long-term phosphorus storage compartment. Laboratory investigations indicated that there was no significant role for bacteria or algae in the water column relating to phosphorus sequestering, although microorganisms appeared to have some role in the translocation of phosphorus to soil binding sites. After phosphorus contacted the soil surface, transpiration related entrainment of surface water and direct phosphorus uptake by plants were the dominant mechanisms for causing phosphorus to move deeper through the soil substrate. Removal of phosphorus from the interstitial water was by incorporation to biomass or direct sorption to soil binding sites / Doctor of Philosophy (PhD)