HYPORHEIC ZONE DEVELOPMENT AND WATER QUALITY IMPROVEMENT IN A RESTORED RIPARIAN AREA

Research has identified the hyporheic zone as an important part of stream ecosystems. However, our understanding of how this area functions is still poorly understood. The hyporheic zone is the saturated subsurface sediment that lies directly beneath and beside streams where groundwater and surface water mix. Hyporheic linkages between riparian zones and stream channels greatly influence the translocation of dissolved nutrients and carbon that are fundamental to sustaining stream food webs.  As such, subsurface hyporheic linkages are a key component to understanding the structure and function of riparian and stream systems in restoration projects. The degradation of stream systems has been widespread throughout the United States. In Kentucky, for instance, almost all of the large streams have been impounded or channelized. A restoration project was initiated in a channelized section of Wilson Creek (Nelson Co., KY) to return the meandering configuration of the stream to its watershed. Restoration activities aimed at reestablishing a native riparian corridor using giant cane (Arundinaria gigantea), a historic feature of central Kentucky floodplain terraces, and bottomland forest species. The objectives of this study were to develop techniques for the successful restoration of riparian vegetation communities, and to evaluate the rate at which an active hyporheic zone develops. Use of tree shelters in riparian tree establishment significantly increased the growth of seedlings, and provided physical protection especially during heavy flooding events. Also shelters appeared to have accelerated carbon retention by trapping woody debris and litter. Data also showed that although this system is young, the development of the hyporheic zone has begun through carbon and nutrient accumulation (DOC, NO₃^- -N, NH₄⁺ -N) and changes in subsurface redox conditions. Moreover, retention and transformation of carbon and nitrogen within the restored riparian system has begun. Both riparian vegetation communities appeared to be advancing towards conditions exhibited by the undisturbed section of Wilson Creek.