Factors Influencing Carbon Stocks and Accumulation Rates in Eelgrass Meadows Across New England, USA

A B Novak,M Charpentier,M N Gutierrez,M C Pelletier,P Vella,J Simpson,A Arias-Ortiz,P Colarusso,P Masque

doi:10.1007/s12237-020-00754-9

Abstract

Increasing the protection of coastal vegetated ecosystems has been suggested as one strategy to compensate for increasing carbon dioxide (CO2) in the atmosphere as the capacity of these habitats to sequester and store carbon exceeds that of terrestrial habitats. Seagrasses are a group of foundation species that grow in shallow coastal and estuarine systems and have an exceptional ability to sequester and store large quantities of carbon in biomass and, particularly, in sediments. However, carbon stocks (Corg stocks) and carbon accumulation rates (Corg accumulation) in seagrass meadows are highly variable both spatially and temporally, making it difficult to extrapolate this strategy to areas where information is lacking. In this study, Corg stocks and Corg accumulation were determined at 11 eelgrass meadows across New England, representing a range of eutrophication and exposure conditions. In addition, the environmental factors and structural characteristics of meadows related to variation in Corg stocks were identified. The objectives were accomplished by assessing stable isotopes of δ13C and δ15N as well as %C and %N in plant tissues and sediments, measuring grain size and 210Pb of sediment cores, and through assessing site exposure. Variability in Corg stocks in seagrass meadows is well predicted using commonly measured environmental variables such as grain size distribution. This study allows incorporation of data and insights for the northwest Atlantic, where few studies on carbon sequestration by seagrasses have been conducted.

Highlights

The concentration of carbon dioxide (CO2) in the atmosphere has increased from 280 to 410 ppm since pre-industrial times and is expected to increase to 990 ppm by the end of this century
Seagrasses are a group of foundation species that grow in shallow coastal and estuarine systems
Sediments in seagrass meadows are considered a long-term carbon sink with large amounts of Corg deposits formed by refractory belowground biomass, seagrass detritus, as well as allochthonous Corg materials

Summary

Introduction

The concentration of carbon dioxide (CO2) in the atmosphere has increased from 280 to 410 ppm since pre-industrial times and is expected to increase to 990 ppm by the end of this century. While coastal vegetated ecosystems comprise only 0.05% of the plant biomass on land, they store a comparable amount of carbon per year, making them one of the most important carbon sinks and mitigators of excess of CO2 on the planet (Smith 1981; Duarte et al 2005; Nellemann et al 2009; Mcleod et al 2011). Like other vegetated coastal ecosystems, seagrasses sequester and store large quantities of carbon in biomass and in sediments (Smith 1981; Duarte et al 2005; Fourqurean et al 2012; Röhr et al 2018). Recent assessments suggest that 300,000–600,000 km of the ocean is covered in seagrass habitats (0.1% of ocean surface), potentially storing between 4.2 and 8.4 Pg C, contributing to 10% of the annual carbon burial in the ocean (Duarte et al 2005; Fourqurean et al 2012)

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Conclusion