Role of Hydraulic Conductivity on Surface and Groundwater Interaction in Wetlands

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There has been a growing interest in understanding the mechanisms involved in surface and groundwater interactions since these interactions play a crucial role in the behavior of hydrology and contaminant transport in streams, lakes, wetlands, and groundwater (Hakenkamp et al, 1993; Winter, 1995; Packman & Bencala, 2000; Bencala, 2000; Medina et al, 2002). Wetlands are an important part of water resources since they control peak flow of surface runoff and clean polluted water as downstream receiving water bodies and therefore have been recognized as one of the best management practices (Mitsch & Gosselink, 2000; Moore et al., 2002; Mitchell et al., 2002). Wetlands are located in transitional zones between uplands and downstream flooded systems. Surface and groundwater interactions, which occur in these critical zones, result in a change in surface and groundwater depth. Moreover, pollutants in either surface water or groundwater are mixed and the quality of both sources is affected by each other. Therefore, it is important to understand the role of surface and groundwater interactions on wetland sites and incorporate them into the wetland models in order to obtain accurate solutions. The definition of a wetland is difficult since there is no definite boundary for wetlands over the landscape and wetland characteristics change. Different definitions have resulted from government agencies that take either legal or ecological criteria as a basis for wetlands within their jurisdiction. In Section 404 of the Clean Water Act of Environmental Protection Agency (EPA), wetlands are defined as “areas that are inundated or saturated by surface or groundwater at a frequency and duration sufficient to support a prevalence of vegetation typically adapted for life in saturated soil conditions”. From a hydrologic point of view, the change of surface water level or subsurface water table level through time is important. Usually, areas where the depth of standing water is less than 2 m are considered as wetlands. The amount of water present in wetlands is important to support water supply and water quality. It also affects the type of animals and plants living in these areas. Wetlands are classified according to their ecological and hydrological similarities (Mitsch & Gosselink, 2000). The type of interaction between groundwater and wetlands depends on the geomorphological location of the wetland. Wetlands gain water if they are located on seepage faces where there is an abrupt change in landscape slope (Figure 1A), or if there is a stream near the wetland location (Figure 1B). Water level in wetlands is changed usually by direct precipitation or runoff. Especially in riverine wetlands, water level changes