Interagency Partnership to Assess and Restore a Degraded Urban Riverine Wetland: Dyke Marsh Wildlife Preserve, Virginia

Introduction The narrow-leaved cattail wetland (Hopfensperger and Engelhardt 2007) known as Dyke Marsh formally became a land holding of George Washington Memorial Parkway (GWMP, a unit of the national park system) in 1959, along with a congressional directive to honor a newly-let 30-year commercial sand and gravel dredge-mining lease at the site (Litwin et al. 2013; Figure 1). Dredging continued until 1974 when Public Law 93-251 called for the National Park Service and the United States Army Corps of Engineers to “implement restoration of the historical and ecological values of Dyke Marsh.” By that time, about 83 acres of the marsh remained, and no congressional funding accompanied the passage of the law to effect any immediate conservation or restoration. Decades of dredge mining had severely altered the surface area of Dyke Marsh, the extent of its tidal creek system, and the shallow river bottom of the Potomac River abutting the marsh. Further, mining destabilized the marsh, causing persistent erosion, shoreline retreat, and tidal channel widening after mining ceased (Litwin et al. 2013). Erosion has continued unchecked until the present; approximately 50 acres of the original marsh are now estimated to remain (Figure 2). The specific cause of persistent erosion had been unknown prior to this collaborative study (Litwin et al. 2013) but previously was assumed to be due to flooding by the Potomac River. GWMP needed to (1) quantify the magnitude of acreage loss, (2) determine the most significant causal agents of marsh erosion, and (3) understand the initial environmental conditions in place prior to dredging, in order to comply with Public Law 93-251 and restore Dyke Marsh to a more naturally sustainable geological and biological system. In 2009, the National Park Service (NPS) entered into partnership with the US Geological Survey (USGS) to investigate the causes and rates of unabated marsh erosion; the results of that part-