Coastal wetland soils accumulate carbon at rates higher than any other ecosystem and carbon transport, cycling, and storage are among the most fundamental processes that support estuarine ecosystem services, such as wildlife habitat and foodweb support. The restoration of the Nisqually River Delta (NRD) culminated in 2009 and resulted in 360 ha restored to tidal processes in Puget Sound, WA, USA. The restoration goal is to increase the capacity of the estuary to support a diversity of wildlife, waterbirds, and native fish such as the Nisqually Fall Chinook (Oncorhynchus tshawytscha), a vital cultural resource and threatened population under the Endangered Species Act. Here USGS works with land management agencies (US Fish and Wildlife Service and Nisqually Indian Tribe) to assess the carbon sources that support wildlife foodwebs and to quantify carbon sinks and fluxes. Carbon sources from primary producers, invertebrates, and fish were collected across five main habitat types across the estuarine gradient (tidal forest, transition, tidal marsh, mudflat, and eelgrass). We used remote sensing techniques and algorithms to map vegetation biomass and distinguish C3 from C4 producers. We also measured carbon sources and storage in the tidal marsh sediments in a marsh restored in 2009 and a reference site.
Soil bulk density profiles in the 2009 restoration site reflect a historical agricultural land use with low bulk density pasture grasses situated below currently accreted marsh sediments. The reference marsh soil had an overall lower bulk density that increased gradually with depth. Vegetation biomass was similar across habitat types (excluding eelgrass), and predominately ranged from 250-750g/m2. Stable C, N, S isotope analyses indicated notable movement of carbon throughout the estuary. For instance, particulate organic matter originating from the nearshore, was assimilated within invertebrate prey from all habitat types, but rooted vegetation contributed locally to invertebrate production. The timing of invertebrate productivity also varied by site, season, and strata (terrestrial, aquatic, benthic), which illustrate the capacity for the restoring estuary to provide food resources throughout the outmigration season. By integrating carbon foodweb functions we hope to link traditional objectives of protecting, restoring, and managing diverse wetlands to support a broad array of habitats and species with carbon sequestration initiatives.