Assessing Carolina Bay Wetland Restoration Risks to Downstream Water Quality by Characterizing Land Use and Stream Proximity

Abstract

Carolina Bay wetlands are distinct common components of the Southeastern US Coastal Plain. Many have a history of drainage for agriculture. Restoration of prior-drained Bays can increase P solubility and transport, with potential adverse impacts downstream. To assess risk of off-site P transport, we documented Bay land use, drained area, and proximity to streams and drainageways. We studied Bladen County, NC, where an exhaustive Bay inventory is available. Land-use was documented via classified Landsat decadal images from 1972 through 2010. We compared sequential image pairs to document land-use changes. Phosphorus risk to downstream waters was assessed based on stream proximity, agricultural land use, and arable area. At least 80% of Bays constituting 97% of total Bay area (51,704 ha) exhibited evidence of land-use change. Edges of Bays comprising 80% of Bay coverage were within 15 m of a stream; Bays comprising 13% were isolated. Twenty-one percent of Bay area remained drained in 2010. Prior, 28% of Bay area posed moderate to severe threats to downstream waters; as of 2010, 9%. Considering long-term effects of restoration-induced off-site transport of agrochemicals, land-use history, drained area, and stream/drainageaway proximity should be considered in choosing Bays for restoration.