What are the Potential Implications of Sea Level Rise on Carbon Stored in Coastal Freshwater Peatlands?

Abstract:

Freshwater peatlands can be dense carbon stores and are ecologically diverse with many specialised organisms. Climate-related threats to carbon storage include increases in rates of oxidation and methanogenesis, increases in drainage and dissolved organic carbon export from run off. Due to their lowland locations, coastal freshwater peatlands are at increasing risk from sea level rise and is expected to result in ecosystem shifts with impacts on carbon stores and species diversity. Fed by a network of rivers and lakes in close proximity to the coast, the Broads, UK, is a series of freshwater peatlands at risk of increased incursion of saline water coupled with increased frequency and intensity of flooding events due to an anticipated sea level rise of 3–5 cm decade^-1 compounded by a predicted isotactic sinking of 0.055 cm yr^-1. This study attempts to unravel the risks posed by sea level rise to carbon stored in coastal freshwater peatlands. Near surface cores (~50 cm long) collected from three sites were analysed for bulk density and carbon content, and dated radiometrically (lead-210, cesium-137) to ascertain carbon accumulation. To understand loss by leaching and microbial decomposition, mass loss from litterbags was measured over one year. Results indicated that recent carbon accumulation rate (since 1964) was significantly higher (p < 0.001) at the site inundated for the longest period throughout the year (94 ± 0.17 g C m^-2 yr^-1) and lowest at the least inundated site (79 ± 0.17 g C m^-2 yr^-1). Accretion rates over the last two years were highest in the site with the most fluctuating water table (0.55 ± 0.13 cm yr^-1) and lowest at the driest site (0.25 ± 0.04 cm yr^-1). Proportion of mass loss was significantly different between sites for both leaves (p < 0.001) and stems (p < 0.001). Overall, this research has shown that extent of inundation can influence recent accumulation rate and proportion of mass loss.