The contribution of Scirpus mariqueter to sediment carbon storage of Chongming East Tidal Flat wetland in Yangtze River Estuary

Marsh plants capture the carbon from atmosphere by photosynthesis to create carbohydrates which could be imported into the soil as organic matter. Assessment of carbon stocks in marsh plant and allochthonous terrigenous particle settlements is a basic step in evaluating the carbon sequestration potential of the wetland ecosystem. By using the feldspar marker horizons and pipe bury method, the contribution of Scirpus mariqueter to the organic carbon storage of Chongming east tidal flat wetland sediment was calculated. Results show that buried plants decomposition and sediments respiration in different temperatures are the key factors which cause the significant difference in the sediment organic carbon contents in summer and winter. In buried pipe, organic carbon accumulated in winter, and its' content reached 5.72 mg·g^-1. Winter is the “carbon accumulating” period of the sediment organic carbon pool. However, in summer, sediment carbon content decreased to 4.89 mg·g^-1 in the buried pipe, which is a “carbon losing” period. The organic carbon content in the buried pipe sediment profiles showed significant variation due to the decomposing of dead and buried S. mariqueter and the microbe respiration in sediment. The internal distance between the organic carbon accumulation layer is about 10 cm, which was corresponding to the short-term (≤1 year) marsh accumulation rate (11.6 cm·a^-1, from August 28th, 2012 to September 2th, 2013) measured by feldspar marker horizons. The significant negative correlation (p<0.01) between the buried pipe sediment organic carbon and the δ¹³C contents suggests that the organic carbon dynamic in sediment, accumulation and degradation, was affected by the plant inputs, and the organic carbon from S. mariqueter decomposition is the main portion of the sediment carbon pool change. Ignoring the carbon fractionation during the process of organiccarbon degradation, contribution of S. mariqueter input to the Chongming east tidal flat sediment organic carbon pool was estimated by using the reference on a simple two component mixing equation. Net input of organic carbon from S. mariqueter into the sediments was about 0.65 mg·g^-1 in half summer year and 2.06 mg·g^-1 in half winter year, account for 7.35% and 31.20% to the sediments carbon pool respectively.