The Application of Mass Balance and Hydrodynamic/Pollutant Transport Models for Wetland Restoration

Abstract

<p> This study deals with the use of mass balance and hydrodynamic/pollutant transport models for wetland restoration. The models were applied to Cootes Paradise marsh, located at the western end of Hamilton Harbour, Lake Ontario. Regulated water levels, excess nutrients and high suspended solids have contributed to declining vegetation and a subsequent change in wildlife in this wetland ecosystem. The Royal Botanical Gardens (RBG), which manages Cootes Paradise, has developed goals for the restoration of this wetland which focus primarily on improving water quality. </p> <p> A mass balance approach was applied to Cootes Paradise in order to gather more information on the inputs of phosphorus and suspended solids to the ecosystem. Although data were not complete for many aspects of the model, the mass balance calculations provided an acceptable agreement with field values. The mass balance models also revealed that more than 50% of the inputs of phosphorus and suspended solids were being contributed by the internal sediments. </p> <p> A two-dimensional depth averaged hydrodynamic/pollutant transport model provided an explanation for the movement of substances through the marsh as a result of wind and inflow generated currents. The resulting pollutant distribution patterns could be explained by environmental conditions in the marsh ecosystem. The computer model predicted phosphorus concentrations reasonably well, both for an overall average of the entire marsh and for individual sites. The model also simulated suspended solids and accounted for contributions of particulate matter due to carp and due to wind resuspension of the bottom sediments. Both overall averages and sample site comparisons for suspended solids were within one standard deviation of field values. According to data generated by the computer model for suspended solids, carp and wind are contributing to the concentrations in Cootes Paradise on an almost equal level; both contribute approximately one third to the overall concentration for suspended solids based on the available data. Further information is needed, however, to improve on the data set for Cootes Paradise in order to better validate the results produced by the mass balance and computer models. </p>