Sea level rise and sediment elevation dynamics in a hydrologically altered Puget Sound estuary

Abstract

As sea level rise (SLR) accelerates in response to climate change, coastal wetlands must accrete vertically to prevent submergence and habitat loss. Padilla Bay, an estuary in the Puget Sound containing an expansive eelgrass meadow, has been hydrologically altered such that insufficient sedimentation may now prevent vertical accretion, potentially affecting the long-term survival of the eelgrass meadow. The objective of this study was to quantify trends in surface elevation change throughout Padilla Bay. To this end, our research group monitored surface elevation change at 19 sites from 2002-2010 using sediment elevation tables (SET’s). Additionally, I explored potential ecogeomorphic relationships between surface elevation change and selected physical (elevation, sediment characteristics) and biological (eelgrass biomass) variables. Only 1 of 19 study sites exhibited significant surface elevation gain, whereas, 9 sites exhibited significant elevation loss. The mean rate of surface elevation change throughout Padilla Bay was -0.22 ± 0.27 cm yrˉ1, values ranged from -0.80 cm yrˉ1 to 0.22 cm yrˉ1. Accounting for surface elevation change, eustatic SLR (0.33 cm yrˉ1), and regional geologic uplift (0.09 cm yrˉ1), I calculated a mean surface elevation deficit of -0.46 ± 0.27 cm yrˉ1. These findings indicate that surface elevation change in Padilla Bay is not keeping pace with the current rate of SLR. A negative relationship between surface elevation change and elevation, and a positive relationship between surface elevation change and eelgrass biomass were apparent, although correlations were non-significant. There was a significant negative correlation between elevation and eelgrass biomass. Surface elevation change did not correlate with the sediment properties measured (bulk density, mineral matter,