Accumulated Organic Carbon in the Sediments of Shallow Bights of the Peter the Great Bay, Sea of Japan.

Content of accumulated carbon (Cdep, which is referred to as blue carbon, BC) was calculated for the uppermost 1-m thicknesses of sediments in bights of the Peter the Great Bay of the Sea of Japan in 2014–2020. In the absence of Zostera Marina (ZM) meadows in Voevoda, Novgorodskaya and Uglovoy bights, BC contents were 140, 99, and 55 tC/ha, respectively. The presence of sea grass significantly increases these values, which were 180 and 126 tC/ha for Voevoda and Novgorodskaya bights, respectively. Using the measured radioactivity of the 137Cs isotope, the rate of BC accumulation in the bights without meadows ZM was estimated at 17, 69, and 98 gC/(m2 year) in Uglovoj, Novgorodskaya, and Voevoda bights, respectively, and at 101 and 144 gC/(m2 year) at sites covered by ZM meadows in Novgorodskaya and Voevoda bights, respectively. Using data of chlorophyll a measurements in sediments of the basins in 2018 through 2020, the bioturbation coefficients (62.7–5.3 cm2/day) and the constants of apparent organic carbon degradation in sediments (0.003–0.068 day–1) were estimated. The maximum BC degradation rates were found in the upper horizons: 550, 39, 6, and 4 gC/(m2 year) at sites with ZM in Voevoda, and without ZM in Voevoda, Novgorodskaya, and Uglovoy bights, respectively. It was found out that ZM meadows cause the maximum concentration of refractory organic carbon ( in sediments of Voevoda bight). [ABSTRACT FROM AUTHOR]