|Full text PDF:||http://researchrepository.murdoch.edu.au/25675/|
This study looked at the problem of constructed wetlands deviating from their initial design parameters to the detriment of treatment performance, in the context of a contemporary storm water treatment wetland in Perth, Western Australia. The study investigated the system components and internal process management of the wetland, and their impact on its capacity to remove nutrients and contaminants from urban stormwater over a seven year period. It found that a designed feature of the wetland, specifically permanent inundation, compromised the ability of the wetland to accommodate inputs of organic material and sulfate, resulting in intensified substrate reduction. Strongly reduced sediments containing dissolved sulfides and other phytotoxins accumulated to concentrations sufficient to cause vegetation dieback; and the cover and health of the emergent macrophytes within the wetland declined dramatically. Loss of emergent macrophytes coincided with changes in nitrogen removal, not in the reduction of nitrate but in the increase of ammonium, consistent with the increasingly reduced conditions. There was not a significant change in phosphorus removal, perhaps suggesting that phosphorus removal was primarily through physical means (sedimentation) rather than chemical. It was considered that the broadscale deoxygenation of the wetland was detrimental both to its nutrient removal capacity and biodiversity attributes. Applying active adaptive management, a trial was conducted involving manipulation of inundation depths, such that redox potentials were increased in a passively aerated treatment. The growth of the emergent macrophyte species Baumea articulata was demonstrated to improve significantly within this treatment, suggesting a similar modification to the hydraulics of the wetland could improve emergent macrophyte growth. The importance of macrophytes to treatment processes is well established and so this modification is expected to improve the water treatment function of the wetland. The study successfully demonstrated that the design of urban constructed wetlands must be site specific and adaptive to ensure specific ecosystem services, such as water treatment, are maintained.