Parallel grid ditches were dug in approximately 90% of mid-Atlantic and New England salt marshes in the 1920s through the 1940s. Today, managers must navigate the effects of past actions when making decisions about marsh hydrology and drainage that impact human health, ecosystem services, and marsh sustainability. Managers must also consider how stressors such as sea level rise impact marshes. A collaborative research project helped to address this challenge by working iteratively with end user groups to develop a decision support tool for marsh hydrology management strategies that promote sustainability and delivery of valuable ecosystem services under future sea level scenarios.
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This 2020 article which appeared in Geomorphology describes a model to predict marsh pond dynamics in New England salt marshes that was developed as part of a 2017-2020 collaborative research project .
Ponds are common features on salt marshes, yet it is unclear how they affect large-scale marsh evolution. We developed a spatially explicit model that combines cellular automata for pond formation, expansion, and drainage, and partial differential equations for elevation dynamics. We use the mesotidal Barnstable marsh (MA, USA) as a case study, for which we measured pond expansion rate by remote sensing analysis over a 41-year time span. We estimated pond formation rate by comparing observed and modeled pond size distribution, and predicted pond deepening by comparing modeled and measured pond depth. The Barnstable marsh is currently in the pond recovery regime, i.e.,every pond revegetates and recovers the necessary elevation to support plant growth after re-connecting to the channel network. This pond dynamic creates an equivalent (i.e.,spatially and temporally averaged over the whole marsh) 0.5–2 mm/yr elevation loss that needs to be supplemented by excess vertical accretion. We explore how the pond regime would change with decreased sediment supply and increased relative sea-level rise (RSLR) rate, focusing on the case in which the vegetated marsh keeps pace with RSLR. Because of the spatial and temporal components of marsh evolution, a single RSLR threshold value applied across the entire marsh landscape provides a limited description of the marsh vulnerability to RSLR.
G. Mariotti, A.C. Spivak, S.Y. Luk, G. Ceccherini, M. Tyrrell, M. Eagle Gonneea. 2020. Modeling the spatial dynamics of marsh ponds in New England salt marshes, Geomorphology, 365, doi.org/10.1016/j.geomorph.2020.107262.