Tidal dissipation morphodynamic feedback triggers loss of microtidal marshes

Abstract

Coastal marsh loss is commonly attributed to changes in external forcings, such as an increase in sea-level rise rate or a reduction in sediment supply. Here we show that extensive marsh loss can be caused by internal mechanisms alone, and specifically by autogenic tidal choking. This occurs when the marsh fills in, increasing tidal dissipation by bed friction and eventually decreasing the tidal range in its landward section. The reduced tidal range decreases sediment import on the marsh platform and increases ponding, both of which lead to interior marsh loss even with modest sea-level rise rates. This process is predicted to occur in dissipative microtidal marshes, which are experiencing some of the fastest rates of marsh loss worldwide. Considering this mechanism is essential to understanding the relationship between marsh loss, sea-level rise, and sediment supply and to eventually predicting future marsh evolution.