Tidal marsh ecosystems are comprised of microhabitats at different elevations, which support an array of ecosystem services, including carbon sequestration. However, climate-driven sea level rise threatens the ability of tidal marshes to continue providing these services. Evidence shows moderate increases in sea level can allow marshes to maintain their balance of low marsh, high marsh, and upland habitat over time. However, larger increases in sea level may drown marshland and cause marsh habitats to transition to mudflat.
We evaluated changes in marsh habitat distribution and carbon sequestration for low (50 cm), moderate (100 cm) and high (150 cm) sea level rise (SLR) scenarios at the Billy Frank Jr. Nisqually National Wildlife Refuge near Olympia, Washington, USA. We combined LiDAR elevation data, suspended sediment measurements, and field-based vegetation measurements to estimate 100 years of elevation change and carbon sequestration using the Marsh Equilibrium Model. We then predicted spatial patterns of habitat transitions, and annual carbon sequestration in each marsh habitat type.
Results/Conclusions
With low SLR, marsh elevations and habitat distributions remained similar to baseline. With moderate SLR, nearly 50% of high marsh habitat converted to low marsh habitat and upland habitat declined by nearly 80% within the refuge boundaries. With high SLR, most of the original low marsh transitioned to mudflat, while the majority of upland and high marsh areas both converted to low marsh, replacing lost low marsh area in new locations. Total carbon sequestration in marsh habitats within refuge boundaries increased between low and medium SLR scenarios, likely due to a balance between prolonged inundation periods and increased sediment deposition. Sequestration declined between the low and high SLR scenarios due to conversion of marsh to mudflat.
This study demonstrates that upland and high marsh habitat could be lost with sea level rise, but carbon sequestration might increase. These results will benefit refuge managers as they develop climate change adaptation plans. Our approach is transferable to other tidal wetland ecosystems worldwide.