Habitat value considerations for sediment caps
Type:
Presented during:
WODCON XVII: "Dredging in a Sensitive Environment" - 2004, Hamburg, Germany
Authors:
D. Ludwig, C. Barnes, S. Garbaciak, Jr., T. Iannuzzi, and R. Mohan
Abstract: Among the most compelling issues in aquatic environments are habitat losses and chemical pollution. In general, management tools for pollution abatement and ecosystem restoration within waterways are quite different. An exception to this pattern is active sediment remediation where benthic substrate is frequently altered by removal (dredging) or emplacement (capping) of materials. This paper presents one conceptual approach to integrated pollution/habitat management design for sediment environments, develops some specifics regarding the implementation of such designs and the associated benefits, and discusses some project examples that take advantage of integrated design principles. The basic premise is that an upper module (EpiCap), based on specific habitat considerations, can be laid over an engineered subcap designed to control contaminant migration. Conceptual designs of four potential EpiCap modules (emergent wetland, submerged aquatic vegetation, hard bottom, and soft bottom) are discussed. The value of the habitat modules is presented in terms of one potential measure of restoration "success"--fish production. Other measurable benefits include food web support, shelter, foraging substrate, and cover for a great variety of resources, ranging from invertebrates to forage fish, amphibians and reptiles, through birds and mammals. Costs can vary significantly reflecting the degree to which the habitat modules can be effectively integrated into the overall cap design.
Where more intense intervention is required, such as active planting of wetland vegetation or submerged aquatic vegetation, costs can rise precipitously. A successful example of habitat integration into a sediment capping project is the St. Paul Waterway in Washington State, USA, constructed a decade ago. This illustrated that restoration of sediment environments can be designed into sediment management projects. The habitat components enhance biological recovery from intrusive effects of dredging or capping and, if carefully designed, contribute to the control of contaminant transport or exposure as an integral component of the project.
Keywords: ecology, ecosystem, remediation, restoration, waterways, harbors