MODELING FLOW REGIMES FOR A CYCLICAL WETLAND USING GROUNDWATER TEMPERATURES IN MCLEAN COUNTY, IL

Wetlands act as a sink in reducing excess nutrients through plant uptake and denitrification before entering into lakes, rivers, and streams. Additionally, seepage into the subsurface and the subsequent migration also serves as a sink for nutrients. Variation in the flow regime of the wetland may influence the fate of nutrients in the subsurface. In order to assess water quality of the wetland system, a groundwater model was used to determine fluid flow and the velocity of solutes within the system. The constructed wetland has a flaw, and during the late summer, it goes dry. A bromide tracer test was completed in May 2013 to evaluate the wetland’s capacity to retain water. By the sixth day, the Br^- concentrations within the wells approached the mean concentration within the wetland, suggesting that the wetland is leaking. The similar concentrations between the water in the wells and in the wetland suggest there is limited dilution by groundwater. Also temperature data indicate different flow regimes associated with a filled wetland and the dry wetland. To assess the role of the conditions within the wetland on the groundwater flow regimes, a model was created using SEAWAT. The observed temperatures are used in SEAWAT. Preliminary data suggests that the presence of water within the wetland alters the local groundwater flow direction. While the underlying groundwater flow direction does not change, the presence of water within the wetland creates an area of recharge from which water appears to radiate in all directions.