Determining trajectory using ecological indicators at the Cogmagun River salt marsh nine-years post restoration

Abstract

The Cogmagun River salt marsh was a Ducks Unlimited impoundment that CB Wetlands and Environmental Specialists restored by reintroducing tidal flow in 2009 by removing part of the dyke embankment. Since the initial restorative actions, ecological indicators; vegetation, hydrology, soils and sediments have been monitored for five-years. In order for marsh systems to protect against sea level rise, they must be able to build vertically via trapping and deposition of sediment between shoots of salt marsh vegetation. This study monitored the ecological indicators nine-years post restoration. The aim was to discover how characteristics vary spatially, in the years following the restoration and when compared to reference conditions of a natural undisturbed salt marsh. The results showed that nine years after the re-introduction of tidal flow, the Cogmagun salt marsh displayed environmental characteristics similar to those at the reference site. The marsh exhibited a positive trajectory from the last measurements taken in 2014. The vegetation characteristics such as species richness and halophytic composition demonstrated a typical salt marsh, and was supported by the presence of zonation. Rod surface elevation tables (RSETs) and maker horizons indicate that there is compaction occurring below-ground at most sites, which was supported with the presence of anoxic layers in the soil characteristics. Net sediment accretion remains greater than compaction, contributing to a positive net change in the surface elevation, indicating vertical growth of the marsh surface.