Abstract Title

Session S-07H: Assessing, Planning and Adapting to Climate Change Impacts in Skagit River Watershed

Keywords

Shorelines

Start Date

1-5-2014 3:30 PM

End Date

1-5-2014 5:00 PM

Description

Estuaries worldwide are facing the possibility of conversion to open water if accretion cannot keep pace with increasing rates of eustatic sea level rise (ESLR). Recent research into sediment elevation dynamics in Padilla Bay, a National Estuarine Research Reserve in Puget Sound, has revealed a mean bay-wide elevation deficit of -0.39 cm/year since 2002. However, a more mechanistic prediction of the estuary’s response to future ESLR should also incorporate non-linear feedback mechanisms between water depth, plant biomass, and sediment deposition. Therefore, we used the field data collected as part of this research (measurements of sediment accretion rates, suspended sediment concentrations, eelgrass stem density, and above- and belowground eelgrass biomass) to build and calibrate a marsh equilibrium model (MEM), developed elsewhere but applied here for the first time to this eelgrass-dominated intertidal habitat. We then coupled the MEM with a relative elevation model (REM) which has previously been applied here, to create a hybrid model that combines each model’s strengths in mechanistically simulating above- and belowground processes, respectively. The model predicts elevation change under various ESLR and suspended sediment scenarios. We used an 11-year elevation change dataset obtained from an extensive surface elevation table (SET) network in Padilla Bay for model validation. Here we present preliminary results suggesting sediment accretion rates to be primarily determined by stem density instead of plant biomass or water depth. Because the non-native eelgrass, Zostera japonica, grows in higher densities than the native Z. marina, Z. japonica may provide a disproportionate contribution toward maintaining elevation in the face of sea level rise in this sediment-starved estuary.

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May 1st, 3:30 PM May 1st, 5:00 PM

Assessing Padilla Bay’s response to sea level rise with a hybrid ecogeomorphic model

Room 607

Estuaries worldwide are facing the possibility of conversion to open water if accretion cannot keep pace with increasing rates of eustatic sea level rise (ESLR). Recent research into sediment elevation dynamics in Padilla Bay, a National Estuarine Research Reserve in Puget Sound, has revealed a mean bay-wide elevation deficit of -0.39 cm/year since 2002. However, a more mechanistic prediction of the estuary’s response to future ESLR should also incorporate non-linear feedback mechanisms between water depth, plant biomass, and sediment deposition. Therefore, we used the field data collected as part of this research (measurements of sediment accretion rates, suspended sediment concentrations, eelgrass stem density, and above- and belowground eelgrass biomass) to build and calibrate a marsh equilibrium model (MEM), developed elsewhere but applied here for the first time to this eelgrass-dominated intertidal habitat. We then coupled the MEM with a relative elevation model (REM) which has previously been applied here, to create a hybrid model that combines each model’s strengths in mechanistically simulating above- and belowground processes, respectively. The model predicts elevation change under various ESLR and suspended sediment scenarios. We used an 11-year elevation change dataset obtained from an extensive surface elevation table (SET) network in Padilla Bay for model validation. Here we present preliminary results suggesting sediment accretion rates to be primarily determined by stem density instead of plant biomass or water depth. Because the non-native eelgrass, Zostera japonica, grows in higher densities than the native Z. marina, Z. japonica may provide a disproportionate contribution toward maintaining elevation in the face of sea level rise in this sediment-starved estuary.