Sedimentological Response of a Recently Restored Wetland: Preliminary Results Highlighting Changes in Sedimentation and Organic Carbon Burial a Decade Following Restoration

Abstract:

By some estimates, California has lost >90% of its historic wetlands primarily due to human activities. This has led to an increased effort to restore wetlands in the region. While restoration can restore the critical ecosystem services and natural functionality, the time required to achieve a renewed equilibrium post-restoration is often unknown. Therefore, this project aims to investigate physical sedimentary and organic carbon (OC) characteristics of a recently restored (~11 years) wetland in San Francisco Bay to understand 1) the transition in soil properties immediately following restoration, 2) assess the return to functionality (i.e. has the wetland reached a new equilibrium, or remains in a transition phase), and 3) compare mass accumulation rates and OC burial pre- and post-restoration. Here, we present preliminary results from 3 cores collected in 2018 from 3 different habitat types in the wetland: mudflat (unvegetated), cordgrass-dominated, and pickleweed-dominated. At all three sites, there was a change in sediment texture following restoration, however the specific response varied by habitat. While the percentages of sand, silt, and clay were generally consistent across all 3 sites pre-restoration, following restoration the sand fraction increased in the mudflat, the silt fraction increased in the cordgrass, and the clay fraction increased in the pickleweed. For OC, values at all 3 locations increased following restoration, however these values have been steadily increasing at all sites post-restoration suggesting the system remains in a transition phase. Overall, all 3 sites showed an increase in mass accumulation rates post-restoration, most significantly within the mudflat and pickleweed sites. These two sites also showed increases in OC burial rates, while the OC burial rate slightly decreased in the cordgrass. Collectively these results indicate that 1) evidence for restoration is preserved within the sediment, 2) restoration increases mass accumulation rates and OC burial rates at most locations, and 3) the wetland remains in a transition phase 11 years following restoration highlighting that restoration may require multiple decades for functionality to reach a new equilibrium, and this transition may vary across habitat types.