Saltmarsh restoration: the shift from a terrestrial to a marine environment

Over recent decades salt marshes have been restored as a cost-effective response to coastal biodiversity loss and flood management. Previous research on established sites has demonstrated that restored marshes have significantly different sediment properties than natural marshes which appears to broadly impact ecosystem function. A study was conducted to examine the differences in natural and realigned salt marshes in terms of plant biodiversity, sediment characteristics (bulk density, water content, pH and nutrients) and microbial communities in Colchester Essex, UK. We studied three pairs of natural and realigned salt marshes of different ages, 13, 62, 118 years since breaching of the sea wall. Furthermore, we studied monthly changes of sediment characteristics of a newly realigned site from breach to 14 months of tidal inundation. In addition to monthly sediment changes, we placed invertebrate exclusion chambers in the newly realigned marsh to examine the effect of bioturbation in changing sediment characteristics and microbial communities. Sediment characteristics of our realigned marshes were significantly different than those of the natural marshes. In addition, natural marshes displayed higher variability and heterogeneity in nutrient and water content than our realigned marshes. Within our newly realigned salt marsh we observed that despite the different starting sediment characteristics, 14 months after inundation our realigned site was broadly similar to the natural marsh but only on the top 5cm of sediment, indicating the presence of a relic agricultural layer which can affect the hydrology and development of the system. Macro-invertebrate colonization has shown that it can influence the geochemical characteristic and microbial communities of sediment in a newly realigned salt marsh. Microbial communities’ composition and abundances within a newly realigned marsh are significantly different from natural marshes 14 months post inundation.