Complexity, Variance, and Nonlinearity: A Multisite, Multiseasonal Study of Tidal Marsh Sedimentation Processes in the St. Lawrence Estuary, Canada

Abstract

A review of the international literature demonstrates the high potential of intertidal marshes for sediment sequestration and growth over time. Surprisingly few studies, however, discuss the sediment pathways that occur both seasonally and annually or the magnitude of such transits. Using a multifactorial approach that accounts for asymptotic evolution, this study examines and compares four marsh sites in the maximum turbidity zone of the St. Lawrence Estuary. The aim is to determine the role of intrinsic and extrinsic factors, ecogeomorphologic feedbacks, and coastal configuration on sediment dynamics. The hypothesis is that multiagency results in nonlinear evolution trends that are site specific. The methodology comprises interannual and intersite surface-height measures, sediment concentration values, tidal inundation frequency, relative sea-level data, and a weather activity index. The results reveal variable sediment deposition rates and surface-height evolution across the marsh profile over multiple seasons and between sites. They also conform with the understanding of asymptotic evolution and illustrate a multifactorial agency driving current dynamics. As hypothesized, the evolution of the studied marshes was highly variable and nonlinear across time and space, demonstrating complex sediment pathways. Recognition of this variability brings into question the generalizability of tidal marsh dynamics in large systems. Ultimately, modelling the trajectories and predictability of future marsh evolution in large systems such as the St. Lawrence Estuary requires a multifactorial approach over multiple seasons and at multiple sites.