Interactions between biotic and abiotic processes determine biogeomorphology in Yangtze Estuary coastal marshes: Observation with a modeling approach

Coastal salt marshes are biogeomorphic ecosystems with coupled vegetation and hydro-sedimentary processes. A significant biogeomorphic feature with a positive loop between vegetation colonization, sedimentary accretion, and edge scarp progradation can be found in coastal marshes with a highly depositional environment, such as the Yangtze Estuary. Together with field surveys, we used a process-based salt marsh model to characterize the spatiotemporal dynamics of vegetation and geomorphology in a tidal wetland in the Yangtze Estuary from 2014 to 2019. This model incorporated interactions between biotic processes (plant growth, colonization, and hydrological resilience) and abiotic processes (tidal transport of propagules, sediment inputs, and habitat-specific sediment deposition). Comparisons with field measurements showed that the model satisfactorily described the interannual variations in vegetation growth and lateral expansion, sedimentary dynamics and elevation change, and formation of marsh-edge scarps at two investigation sites. In particular, both observation and simulation revealed that the degree of sediment supply regulated the rates of vegetation behavior and geomorphic changes. The rates of plant establishment and growth were higher at the site with high sediment supply, and a higher rate of vegetation expansion and sedimentary accretion drove a faster seaward progradation of marsh-edge scarps, compared to the site with low sediment supply. Our results indicate that the interactions between biotic and abiotic processes, together with sediment supply, strongly determine the heterogeneity of marsh biogeomorphology in a highly depositional system. Thus, there is a vast potential for application of process-based models in formulating tidal wetland management and assessing future system resilience.