Date of Graduation

Spring 5-18-2024

Document Access

Project/Capstone - Global access

Degree Name

Master of Science in Environmental Management (MSEM)

College/School

College of Arts and Sciences

Department/Program

Environmental Management

First Advisor

Aviva Rossi

Abstract

Blue carbon ecosystems like tidal marshes, mangroves, and seagrass are efficient carbon sinks that release minimal methane under saline conditions. However, coastal wetlands globally are under threat, and on the U.S. West Coast some 85% of historic tidal wetlands have been lost. As such, there is increasing interest in their restoration as a necessary climate mitigation strategy. This GIS analysis identifies potential tidal marsh restoration sites in Humboldt Bay, California, and estimates the post-restoration greenhouse gas benefits. An elevation-based model of Humboldt Bay’s full estuary extent developed by West Coast researchers was combined with data from the California Aquatic Resources Inventory and a digital elevation model. These datasets were used to identify land around Humboldt Bay that could potentially restore to tidal marsh if reconnected to the tides. This area was refined using land use and planning datasets to derive a pool of permissible and ecologically feasible potential restoration sites. Pre- and post-restoration emission factors derived from Intergovernmental Panel on Climate Change defaults and California datasets were applied to each potential site to estimate the impact restoration would have on greenhouse gas emissions. There are 3,933 acres (15.9 km2) of land around Humboldt Bay that could restore to brackish or saline tidal marsh if reconnected to the tides. This land consists mostly of former tidelands that were diked and drained for agriculture in the 19th Century and are now used as pasture. Most restoration opportunities are around Humboldt Bay’s north embayment. Total current greenhouse gas emissions from the 3,933 acres (15.9 km2) of potential restoration sites are 20,427 t CO2e/year (20,427 Mg CO2e/year). Total emissions would be -5,438 t CO2e/year (-5,438 Mg CO2e/year) if all sites were restored. This represents a change of -25,865 t CO2e/year (-25,865 Mg CO2e/year), or the equivalent of removing more than 6,000 cars from the road. Restoring pasture generates the biggest per-acre emissions change: -7.74 t CO2e/acre/year (-1,913 g CO2e/m2/year) if post-restoration salinity is brackish, -7.27 t CO2e/acre/year (-1,796 g CO2e/m2/year) if saline. Restoring palustrine non-vegetated wetlands is also impactful, but few such sites were identified. Overall, most of the greenhouse gas benefits stem from avoided emissions. Detailed groundtruthing of potential restoration sites is required, as is regional coordination and the development of a blue carbon action plan. Acquiring local and regional greenhouse gas emissions data should be prioritized.

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