STREAM CHANNEL, RIPARIAN CORRIDOR, AND WETLAND RESTORATION FOR WATER QUALITY AND HABITAT IMPROVEMENT

Water quality and aquatic/riparian habitats were historically degraded by deforestation, wetland drainage, and stream channel straightening within an 8.5-hectare floodplain site along Burd Run in south-central Pennsylvania. Stream banks were actively eroding and contributing high sediment loads to the stream. Water quality was further degraded by high nutrient loads delivered via surface flows, shallow (alluvial) groundwater flows, and deeper groundwater discharging at a limestone spring. Water quality monitoring illustrates that these separate pathways are an important influence on the transport and fate of nutrients. Most significant, deeper groundwater delivers elevated concentrations of nitrate (mean NO₃-N=7.4 mg/L) to a wetland that drains directly into the stream, which has lower nitrate concentrations (mean NO₃-N=3.8 mg/L). Artificial drainage had greatly reduced water retention within the wetland and thus limited denitrification and other processes of water quality remediation.

During 2001-2002 restoration strategies were applied to improve fluvial geomorphic stability and diversity and to lower nutrient concentrations delivered to the stream. The stream was restored to a meandering course lined by over 1500 riparian tree and shrub plantings. Nutrient concentrations in groundwater discharged into the stream were addressed through both the riparian plantings (to treat shallow groundwater) and improving wetland water retention behind a constructed berm.

Channel geomorphology is monitored at 19 monumented transects and 9 bank erosion pins as well as through repeat surveying of the longitudinal profile and repeat photography of key features. Stream planform has adjusted only slightly as a result of two bankfull flow events in six months since flow was introduced into the newly constructed channel. Bedforms have shown greater development, with incipient point bars, riffles, and pools developing. Nutrient concentrations are measured weekly at three sites. Results indicate that nitrate-nitrogen concentrations are lower as a result of the wetland restoration, although variable hydrologic conditions hamper comparison of pre- and post-restoration water quality data.