Self-organization of salt marsh patches on mudflats: Field evidence using the UAV technique

The salt marsh system on the tidal flat is one of the most productively ecological wetlands with high biological productivity and blue carbon sequestration levels. The evolution of salt marshes-bare flats boundaries and the shapes of salt marsh margins are of scientific and engineering prospects due to the capability on indicating the morphodynamic patterns of tidal flats. Previous studies are almost qualitative, so far, quantitative analysis on this issue is scarce. To improve our understandings on the spatio-temporal characteristics of salt marsh margins and the mechanism underpinning, we extracted datasets on Spartina alterniflora using orthoimages derived from the quarterly-surveyed UAV photographs and satellite imagery. Results show that the patch-size distribution corresponded to the power law, indicating the marsh patches are in the state of self-organized criticality and the system is scale-independent. It was observed that the external dynamic conditions (i.e., the sediment erosion and accretion on the tidal flat) imposed negative impacts on the self-organization process. In particular, when the short-term morphological changes were negligible, R2 of the power-law relationship notably increased to nearly 1, indicating the salt marsh patches tended to adhere to a high-order self-organization structure in this process.