G. Sun, H. Riekerk, L. V. Korhnak2
The hydrology of three wetland/upland ecosystems, which were embedded in a 42 ha slash pine flatwoods landscape, were studied for 3 years to evaluate environmental effects of upland silvicultural practices (harvesting and fertilization) on cypress wetlands. This study emphasized the interactions between wetlands and surrounding uplands, such as the surface water and groundwater continuum in the wetland-upland systems. Wetlands water balance principles were used for data collection and analysis.
It was found that surface runoff was dictated by the annual rainfall patterns and normally occurred during the wet seasons (Summer and Winter) when the groundwater tables were high. Surface flows from one wetland to the adjacent represented the emergence of groundwater flow from the shallow surficial aquifer. Although it was found that most of the wetlands in the research site were groundwater flow-through types, a few showed temporary outflow patterns during the dry season (Spring), caused by the difference in soil properties or/and evapotranspiration between wetlands and their surrounding uplands. The areas showing outflow were associated with flatter landscapes. Groundwater flow velocity in the surrounding uplands was in the range of 0.5-13.0 cm/day with hydraulic conductivity in the range of 40-1480 cm/day and hydraulic gradient of less than 1.0%. This low gradient and velocity were the reasons for the low magnitude of groundwater flow in the overall water balance of cypress wetlands. Water balances showed that rainfall and evapotranspiration were the major water input (91.3%) and output (76.4%) pathways.
This study suggested that surface flow in pine flatwoods was the major pathway of potential pollutants for wetland contamination during wet seasons. Wetland margin and inter-wetland areas may be more sensitive to upland forest management practices. Forest harvesting in wetlands or surrounding uplands may change the water balance of wetlands and alter the hydroperiod of wetlands by reducing evapotranspiration and by raising groundwater tables.
