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

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 (C_org stocks) and carbon accumulation rates (C_org 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, C_org stocks and C_org 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 C_org 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 C_org 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.

Dispersion and fate of ⁹⁰Sr in the Northwestern Pacific and adjacent seas: global fallout and the Fukushima Dai-ichi accident

The 3D compartment model POSEIDON-R was applied to the Northwestern Pacific and adjacent seas to simulate the transport and fate of (90)Sr in the period 1945-2010 and to perform a radiological assessment on the releases of (90)Sr due to the Fukushima Dai-ichi nuclear accident for the period 2011-2040. The contamination due to runoff of (90)Sr from terrestrial surfaces was taken into account using a generic predictive model. A dynamical food-chain model describes the transfer of (90)Sr to phytoplankton, zooplankton, molluscs, crustaceans, piscivorous and non-piscivorous fishes. Results of the simulations were compared with observation data on (90)Sr for the period 1955-2010 and the budget of (90)Sr activity was estimated. It was found that in the East China Sea and Yellow Sea the riverine influx was 1.5% of the ocean influx and it was important only locally. Calculated concentrations of (90)Sr in water, bottom sediment and marine organisms before and after the Fukushima Dai-ichi accident are in good agreement with available experimental measurements. The concentration of (90)Sr in seawater would return to the background levels within one year after leakages were stopped. The model predicts that the concentration of (90)Sr in fish after the Fukushima Dai-ichi accident shall return to the background concentrations only 2 years later due to the delay of the transfer throughout the food web and specific accumulation of (90)Sr. The contribution of (90)Sr to the maximal dose rate due to the FDNPP accident was three orders of magnitude less than that due to (137)Cs, and thus well below the maximum effective dose limits for the public.