Simple Metrics Predict Salt-Marsh Sediment Fluxes

Abstract

The growth (or decay) of salt marshes depends on suspended-sediment flux into and out of the marsh. Suspended-sediment concentration (SSC) is a key element of the flux, and SSC-based metrics reflect the long-term sediment-flux trajectories of a variety of salt marshes. One metric, the flood-ebb SSC differential, correlates with area-normalized sediment flux and can indicate salt-marsh resilience over months to years. We hypothesize that these metrics may be relevant over shorter time periods. With data from 13 salt-marsh channels, we show that sediment flux direction and magnitude can be inferred from SSC differential over a wide range of timescales. Furthermore, in settings characterized by a standing tidal wave, the water-level gradient can be used instead of velocity to compute the SSC differential, enabling less-intensive measurements that capture fundamental sediment-flux parameters. Distilling the sediment-flux trajectory into simple metrics improves sediment-budget assessment, drives geomorphic model development, and clarifies field observations.