ASSESSING HYDROLOGIC AND BIOGEOCHEMICAL FUNCTIONS OF AN ACCIDENTAL URBAN WETLAND

Understanding wetland hydrology is critical to assessing the hydrologic and biogeochemical functions they serve. Our study of a 3.3-ac urban riverine wetland, created by a levee breached during historic flooding along Buck Creek in Springfield, OH, illustrates the variable nature of wetland function resulting from seasonal and event-based variations in wetland hydrology. The wetland has an intermittent hydroperiod, flooded throughout the year except late summer and early fall. During stormflow on Buck Creek, the wetland is recharged by overflow or backflow. At bankfull and higher stages, Buck Creek overflows lower elevations along the bank at breaches in the levee and flows through the wetland from the upstream end. Backflow occurs when stormflow stage exceeds the outlet elevation of the wetland and floods the wetland from the downstream end. At intermediate stages on Buck Creek, recharge to the wetland occurs by bank surge from Buck Creek during dry months, but during wet months or at baseflow stages recharge is by subsurface groundwater flow from upland areas. Comparison of hydrograph and turbidity trends between Buck Creek and the wetland indicates that the wetland provides temporary storage of stormflow and retains suspended sediment at bankfull and higher stages. Overflow conditions create the greatest opportunity for storing suspended sediment. Biogeochemical functions depend in part on dissolved oxygen (DO) and oxidation-reduction potential (ORP). Recharge events of intermediate stage and higher are associated with increased dissolved oxygen which decreases to zero in the following days to weeks but varies on a diurnal basis during that time. ORP is less responsive than DO, generally positive during wet months when subsurface flow dominates wetland recharge. Event-based recharge, from stormflow and bank surge, produces periods of negative ORP. Natural system functions are compromised along urban stream corridors because of constraints imposed by urban infrastructure, public health, property and ownership, and flood control. This study illustrates the potential of small wetland areas along urban streams to provide system functions important to stream health.