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Feng Z.X.,Nanjing University | Gao J.H.,Nanjing University | Gao J.H.,State Oceanic Administration | Chen L.,Nanjing University | And 3 more authors.
Shengtai Xuebao/ Acta Ecologica Sinica | Year: 2015

Spartina alterniflora (C4) was introduced to the coastal region of Jiangsu Province as an exotic species in 1982. This perennial grass then gradually invaded regions previously occupied by native C3 plants. Much research has focused on variation of the ecosystem carbon cycle and has demonstrated that this S. alterniflora invasion has increased the carbon accumulation rate. However, the impact of plant biomass (both aboveground and belowground) on the organic carbon content of salt marsh sediments requires further study. To explore the response of organic carbon content to the biomass dynamics in an S. alterniflora marsh, the contents of total organic carbon (TOC), total nitrogen (TN), and stable carbon isotope composition (δ13C) of sediments, in an S. alterniflora marsh as well as the bare flat, were investigated by analysis of coral and surface sediments, together with the biomass variations of S. alterniflora. The sediment water content, grain size, and δ13C of coastal water and S. alterniflora were also determined. The Litterbag method was used to measure the S. alterniflora litter decomposition rate. The results indicate that the organic carbon of newer litter rapidly decomposed in the first 2 months, and then remained stable. The seasonal variation of the TOC content of surface sediments in the S. alterniflora marsh was significant, and a 2-month phase shift was not only observed in the TOC content variations and surface litter mass but was also recorded for the proportion of organic carbon derived from S. alterniflora and surface litter mass. However, this phase-shift phenomenon did not exist on the bare flat, indicating that the litter is a dominant source of the organic carbon in surface sediments. The results show that 60% and 33% of belowground biomass was observed in the top 20 cm and at 20-40 cm depths, respectively. Compared with the bare flat, the vertical changes of TOC content in the S. alterniflora marsh showed a different distribution pattern. That is to say, the TOC content of sediments at depths < 20 cm was significantly higher than those at depths > 20 cm, and had an increasing trend from depth 20 cm to the surface. A similar variation was observed for the proportion of organic carbon derived from S. alterniflora in the top 20 cm of sediments. Furthermore, there was a remarkably positive relationship between the belowground biomass of S. alterniflora and TOC content. This suggests that belowground biomass plays an important role in TOC variation along the profiles. The greatest and least plant organic carbon storages in the S. alterniflora marsh were observed in October and April, respectively. The average carbon fixation of S. alterniflora, with quantity 2274 g•m−2•a−1, was 460% that of terrestrial vegetation in China. Similarly, the burial rate of organic carbon of S. alterniflora marsh sediments, with quantity 470 g•m−2•a−1, was significantly greater than the average value of coastal salt marshes in China. Thus, the S. alterniflorasalt marsh fixed large amounts of carbon dioxide from the air, and enhanced the organic carbon accumulation of the sediment. © 2015, Ecological Society of China. All rights reserved.

Yang C.,Ministry of Land and Resources Qingdao Institute of Marine Geology | Li G.,Ministry of Land and Resources Qingdao Institute of Marine Geology | Gong J.,Ministry of Land and Resources Qingdao Institute of Marine Geology
Jilin Daxue Xuebao (Diqiu Kexue Ban)/Journal of Jilin University (Earth Science Edition) | Year: 2015

Southeast China Sea area is located in the southeast margin of the Eurasian plate, surrounded by the Pacific plate and Indian plate in the Mesozoic stage. The petroleum explorations in the past are more concentrated on the Tertiary in this area. Based on previous studies,We propose the Mesozoic is a noteworthy exploration through the analysis of petroleum geological conditions in the Southeast China Sea and its periphery. The results of our studies have shown that the Mesozoic strata widely distributes in Southeast China Sea. The distributions of Mesozoic in the southern East China Sea, the Taiwan Island and the southwest Taiwan basin were related to Okinawa suture zone and the Philippines Palawan suture zone, and there were deep sea facies siliceous sedimentation, and the distributions of Mesozoic in the northern South China Sea and the adjacent land areas, especially the marine strata were related to the early Ailao Mountain-Red River Indosinian suture zone, and there were the Upper Triassic-Lower Jurassic marine facies and marine-terrigenous facies clastic rocks and Late Jurassic-Cretaceous continental clastic sediments.It can be inferred from the drilling data and land geology that there are two sets of good hydrocarbon source rocks developed and stronger hydrocarbon generating potential in the Southeast China Sea. A series of hydrocarbon source rock is the Upper Triassic-Lower Jurassic marine mud shale, with organic carbon contents between 0.28%-14.96%, the main types of kerogen type dominatedⅡ2 and Ⅲ, and another is the Lower Cretaceous marine mud-shale, with organic carbon content between 0.60%-2.00%, kerogen type Ⅲ, partial type Ⅱ2. And there are two sets of source-reservoir-caprock assemblages. One is composed of the Upper Triassic-Lower Jurassic Marine mud-shale and Lower Cretaceous marine mud-shale as hydrocarbon source rocks, the Middle-Upper Jurassic sandstone as reservoir, together with the Early Cretaceous mud shale as caprock. Another is composed of the Early Cretaceous mud shale as hydrocarbon source rocks, and the Cretaceous sandstone as reservoir, the Upper Cretaceous or later mud-shale as caprocks. It is worth exploring plays formed by combining with the “lower source-upper reservoir” and “self source-self reservoir”. ©, 2015, Jilin University Press. All right reserved.

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