The effect of delivering influent water to a wetland as seasonal pulses or as a continuous steady-flow on hydroperiod, water chemistry, avian use, plant primary production, and plant community structure was investigated in a whole-ecosystem study involving a 3-ha created riparian wetland at the Schiermeier Olentangy River Wetland Research Park at The Ohio State University in Columbus, Ohio USA during 2003 through 2006. A simulation model was then developed using short-term measurements of river and wetland stage to predict long-term patterns of succession within the wetland.
The natural hydroperiod of the riparian wetland was varied in 2005; its natural flood-pulses were removed and replaced with an artificial steady-flow supplied by submersed pumps. In 2004 the wetland received 27 m of inflow followed by 20 of inflow in the steady-flow year 2005. The nutrient removal rate was higher for nitrate-nitrogen, total nitrogen, and total phosphorus during the year with flood-pulsing than during the steady-flow year. A greater removal of NO 3 -and TP occurred in the emergent marsh section of the wetland than the open water section. Conversely TN increased through the emergent marsh and decreased through the open water. There was greater avian use of the wetland during pulsing than steady-flow conditions. The guild of bird species most affected was shorebirds. Peak observed shorebird use corresponded to dry conditions in the wetland in the later part of the growing season during migration. Primary productivity of macrophytes was compared among the 2004 pulsing hydroperiod year, the 2005 steady-flow year, and in 2006 when natural pulsing was again restored. The wetland was significantly more productive (α = 0.05) during pulsing compared to steady-flow conditions. The simulation model predicted water depth (based on precipitation, potential evapotranspiration, river stage, and overland outflows), calculated the growth of trees and emergent macrophytes (based on water depth and the duration and timing of flooding), and also predicted the annual state of the ecosystem (open water, mudflat, marsh, or forested wetland). Overall, the oxbow design appeared to be successful in ecological terms and similar diversion wetlands are recommended for other locations to examine their function under different climates and hydroperiods.