The potential role of Biodegradable Elements for Starting Ecosystems in protecting saltmarsh pioneer vegetation under erosional conditions

Abstract

Rising sea level associated with climate change is placing coastal communities at higher risk to flooding and erosion, so protecting coastal zones from high water events is of high priority for urban and rural coasts alike. Incorporating natural ecosystems into coastal protection strategies is an increasingly popular option because of the resilience of these communities. Outside of the tropics, salt marsh is one of the most common community types being used for protection, but new salt marsh growth can be slow. Aiding growth in the pioneer zone through temporary stabilization of the sediment should accelerate the development of salt marshes. Biodegradable Elements for Starting Ecosystems (BESE) is a temporary structure that may reduce sediment dynamics by reducing flow velocity and shear stress close to the sediment. This study aims to evaluate the possibility for BESE structures to enhance the survival of pioneer vegetation under erosional conditions. Specifically, BESE is evaluated for its ability to: (i) reduce erosion around seedlings, thus increasing their survival rates, (ii) reduce erosion around isolated tussocks, thus reducing gully formation, and (iii) reduce erosion of salt marsh cliffs, maintaining the cliff height and preventing horizontal cliff migration. Pallets of Spartina alterniflora seedlings, tussocks, and 10-cm cliffs were exposed to high-energy waves with low sediment loads in a large flume to evaluate how BESE might retain eroding sediment. BESE reduced localized scour around seedlings (p < 0.001), likely providing protection against seedling dislodgement. BESE also reduced total sediment loss in recently disturbed sediment around tussocks (p < 0.001) preserving a higher likelihood of tussock expansion following an erosional event. Cliff erosion was of such low magnitudes on all treatments that the effect of BESE on cliff migration could not be evaluated. This early evaluation of BESE does not consider all aspects that affect sediment dynamics of natural marsh, but the findings suggest that BESE can aid the survival and subsequent growth of salt marsh pioneer vegetation.