Application of WASP5E to Model Phosphorus Removal Dynamics in a Stormwater Wetland
Water pollution abatement has received considerable attention from the research community over the recent years. Treatment of urban stormwater runoff has likewise been the focus of sizeable amounts of research. Phosphorous is a key indicator parameter for eutrophication problems and was therefore the parameter of focus in this research. Urban activities create sources of phosphate such as fertilizers, animal waste, detergents, etc. Phosphate loads in urban runoff vary greatly due to variations in rainfall characteristics, watershed features and urban activities (EPA, 1993). Reported ranges of total phosphate loads vary from 0.2 to 2.0 kg/ha for residential areas, and from 0.9 to 6.0 kg/ha for industrial areas (Novotny and Olem, 1994). Constructed wetlands have been widely promoted for urban stormwater management because of their inherent capacity for water rage and water quality improvement.
The Ontario Land Use Planning Act (1990) defines wetlands as: lands that are seasonally or permanently covered by shallow water, as well as lands where the water table is close to or at the surface. In either case the presence of abundant water has caused the formation of hydric soils and has favoured the dominance of either hydrophytic plants or water tolerant plants. This research, conducted at the School of Engineering, University of Guelph, studied the feasibility of modelling phosphorus assimilative capacity by stormwater wetlands in cold climates. The over-riding aim of this research was the application of computer simulation in evaluating water quality improvement efficiency of constructed wetlands in an effort to enhance their proficiency and promote their utilization.
For this research, a vast amount of background data relating to urban stormwater, wetlands and modelling was collected and examined. Previous studies and field data were reviewed to find useful and adequate data modelling purposes. Due to the lack of data from a constructed wetland system a data set for the Hidden Valley wetland, a natural stormwater wetland (Typha marsh), was chosen and adopted to test the selected water quality model.
A number of water quality models were scrutinized to establish their adequacy for modelling phosphorus dynamics in wetland systems. The US EPA’s WASP5 simulation program and the vegetation growth/phosphorus uptake model ECOL1 were selected. The linked phosphorus cycle kinetics of WASP5 to ECOL1 developed here is called WASP5E. The two primary objectives of the study were to assemble into a computer simulation process the main components of phosphorous dynamics in stormwater wetlands and to test the utility of the process in simulating those phosphorous dynamics.
Phosphorus dynamics in wetlands systems have been widely describe analyzed in literature. Phosphorus wetland processes are schematically illustrated in Figure 23. 1. The dynamics of phosphorus removal in wetlands is an interaction of mechanisms such as sedimentation, chemical precipitation and incorporation to biomass, plants and algae. For a description of P cycle in wetland systems, refer to Tchobanoglous and Schroeder (1987), Vymazal (1995), Kadlec and Knight (1996), Strecker et al. (1992), Shaver (1995), Kadlec and Kadlec (1978), Bayley (1985), Kadlec (1987), Reddy and DeBusk (1987), Good and Patrick (1987), Hossner and Baker (1988), and Davis et al. (1978).
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