PARENT SESSION
Oral Session # 54: Coastal Ecosystems: Salt Marshes.
Presiding: P Ringold
Wednesday, August 6. 1:30 PM to 5:00 PM, SITCC Meeting Room 105.

Modeling the past 500 years of organic matter accumulation in a Chesapeake Bay salt marsh.

Saunders, Colin^*,1, Reynolds, James¹, Megonigal, J², Drake, Bert², ¹ Department of Biology, Durham, NC, USA² Smithsonian Environmental Research Center, Edgewater, MD, USA

ABSTRACT- Evidence from salt marshes along the Atlantic Coast indicates the composition of plant species has changed in the last century, attributed to changes in land use, sea-level, and salinity. Ecosystem models are needed to explore the consequences of changes in species composition on ecosystem structure and function. The goal of this study is to determine whether changes in species composition improve predictions of soil accumulation in a Chesapeake Bay salt marsh. We developed five alternate ecosystem models, ranging from simple to highly mechanistic, that incorporate changes in C3/C4 plant composition but differ in their assumptions about plant growth, plant chemistry and belowground structure that accompany changes in species composition. We use two data sets, including soil cores and elevation change measured in a 13-year CO₂ enrichment study, to calibrate and validate the models. We found the simplest model, in which species changes are ignored, generated the highest overall likelihood to the observed soil profiles. However, we also found that excluding species-specific root profiles, associated with changes in species composition, generated the highest likelihood to observed soil profiles of the specific organic chemistry types. Finally, models that included species-specific root profiles matched observed changes in elevation better than models that did not. In summary, while a simple model that excludes changes in species composition (and species-specific root profiles in particular) may be useful as a baseline predictor of soil accumulation, the importance of root profiles in successfully predicting elevation change suggests important feedbacks between elevation change and species composition. Given that the relationship between sea-level rise and elevation change may control processes such as erosion, saltwater intrusion, and potential habitat loss, understanding the links between species changes, belowground structure, and elevation change will be crucial for successfully predicting long-term dynamics of marshes in the Chesapeake Bay.

Key words: SOM, modeling, marshes, vegetation