Wetlands play a diverse and important role in the ecosystem. They provide numerous environmental, economic, cultural, recreational, aesthetic and ecological benefits to society. Meanwhile, wetlands are lost at an alarming rate due to human actions such as deforestation, expansion of agricultural land, pollution, and climate change. Quantifying wetland functionality is the first step to protect these valuable and biologically diverse ecosystems. However, current functional assessment techniques only provide a general overview of wetland functions in large and diverse watersheds. In addition, due to the qualitative nature of these techniques, they cannot be used to develop future management and restoration plans, which require solid understanding of hydrological and water quality characteristics of the wetlands. The goal of this research is to address some of these limitations by examining the impacts of wetland size, depth, and placement on flow and sediment transport at subbasin and watershed scales. The Soil and Water Assessment Tool (SWAT), a physically-based watershed model, was used along with the System for Urban Stormwater Treatment and Analysis Integration (SUSTAIN) to examine flow and sediment transport in two watersheds in Michigan, the Shiawassee Watershed (southeastern Michigan) and the River Raisin Watershed (southeastern Michigan and northeastern Ohio). Both watersheds were selected because they have experienced significant conversion of land from wetlands to agriculture since European settlement. Wetland area was found to be more influential in controlling streamflow rate than wetland depth. Meanwhile, wetland implementation has limited impacts of daily peak flow rates and frequency of peak flow events at the watershed outlet. In general, rate of streamflow reduction is higher than sediment reduction at the subbasin level but more comparable at the watershed level. These results reveal the importance of wetland size, depth and placement as part of restoration efforts. This study introduces an alternative approach to the functional assessment of wetlands that is more accurate and quantitative.
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