ASSESSING ECOHYDROLOGICAL SERVICES PROVIDED BY AN URBAN RIVERINE WETLAND IN RESPONSE TO SEASONAL AND EVENT-BASED FLUCTUATIONS IN STREAM STAGE

Publicly-held land along urban stream corridors can provide varied ecosystem services. Fall weekend recreational releases by the U.S. Army Corps of Engineers (USACE) provide a unique set of conditions to assess the ecohydrological services provided by an urban wetland along Buck Creek in Springfield, OH. Water leveloggers and staff gages were installed and calibrated in a 3.3-ac riverine wetland and at an adjacent point on Buck Creek to study the interaction between surface water, ground water, and wetland stage, hydroperiod, and source water. The wetland has an intermittent hydroperiod, inundated throughout the year except late summer and early fall. At bankfull and greater stormflow events, surface water from Buck Creek flows into the wetland and is stored temporarily until Buck Creek recedes. In years when precipitation is near the long-term average, this occurs 6-9 times per year for a total duration of 5-10 days. For stream stages less than bankfull, ground water from upland areas recharges the wetland and flows from there into Buck Creek during most of the year. During late summer and early fall, stream and wetland stages and the hydraulic gradient between them are at their minimum. During this time, the potential for bank and wetland storage of stormflow for events not exceeding baseflow can be studied using upstream USACE releases. USACE releases during the fall drawdown period occur over 11 weekends, last for 2-2.5 days, and are of constant discharge. The stage hydrograph for the flood wave associated with the release is a rectangular function. Downstream deviation in the hydrograph measured by the levelogger on Buck Creek at the wetland is the result of bank storage between the reservoir and the wetland, a distance of 3.3 miles. The difference between stream and wetland stages is used to quantify hydraulic gradient and direction of flow; the difference between hydrographs illustrates ground water recharge and temporary wetland storage. The wetland provides several ecohydrological services such as regulating groundwater recharge and discharge, water quality, erosion, and floods and supporting soil formation and nutrient cycling through sediment and nutrient retention.