Distribution And Sources Of Sedimentary Organic Matters In Typical Intertidal Zone?Eastern China

This study investigates the source and distribution of sedimentary organic matter at 12 typical inter tidal zone,Eastern China.The content of total organic carbon?TOC?and total nitrogen?TN?and their vertical and spatial distribution in sediments are compared and analyzed.The sediment organic matter is qualitatively analyzed with?¹³C and C/N as source index.And quantitative analysis of the source of organic matter is made by using three-end member mixing model combined?¹³C and C/N values.The main conclusions are as following:?1?TOC concentrations in the sediment are between 0.16%and 1.41%while TN contents are from 0.005%to 0.056%.The highest values of TOC and TN appear in the Dagu Estuary and Jiulongjiang Estuary,respectively.The lowest values both appear in Yellow River Estuary.Except DaLiaohe Estuary and Jiulongjiang Estuary,there is a significant positive correlation between TOC and TN in other inter tidal sediments.?2?Sedimentary C/N ratios show a range from 17.28 to 75.23,which indicates that terrestrial source is the main source of organic matter in the sediments.The vertical distribution shows:Sedimentary C/N ratios increase with depth at Daliaohe Estuary,Yellow River Estuary,Jiulongjiang Estuary,Pearl River Estuary,Yingluo bay and Dongzhan Bay.The C/N ratios of sediments in Jianhe Estuary and Yancheng shoal decrease as the depth increases.The C/N ratios of sediments in the Dagu Estuary,Yangtze River Estuary and Qiantangjiang Estuary fluctuate within a certain range with depth.In terms of spatial distribution,the C/N values decrease first and then increase with decreasing latitude.?3?Variation range of?¹³C in the inter tidal sediments is from-27.5‰to-21.0‰,with an average value of-24.0‰,indicating marine and terrestrial mixed sources.The?¹³C of sediments in the Yangtze Estuary and Pearl River mouth of Chongming Island increases with depth,while the?¹³C of other inter tidal sediments decreased with the increase of depth.The overall trend of?¹³C at the inter tidal zone is the lower the latitude,the smaller the sediment is.?4?Based on two-member mixing model with index?¹³C,we get the result that marine source is main source of sediment organic matter at Daliaohe Estuary,Jianhe Estuary,Dagu Estuary and Jiulongjiag Estuary and terrestrial source is the major source of other estuaries.However,with C/N as an indicator,the preliminary inference is that organic matter of all estuaries is mainly partial to terrestrial source.The contradiction between the traces of?¹³C and C/N indicates that there are other input sources of sediment organic matter.?5?Local vegetation input and marine input account for most organic matter in non-estuary wetland.Therefore,we use two-member mixing model for preliminary quantitative calculation.The result shows that the contribution of local vegetation to sediment at Yancheng Shoal is 18.43%while marine source accounts for 81.57%;the organic matter of Yingluo bay is contributed by 65.37%of mangrove plant,and 34.63%marine contribution;the mangrove plant contribution to the sediment at Dongzhai Bay is 80.68%,and marine source is 19.32%.The highest local vegetation input appears at Dongzhai Bay and highest marine input appears at Yancheng Shoal.?6?Using three-member mixing model with both index C/N and?¹³C,we derive the contribution ratio of organic sources.Marine source varies from 9.56%to75.42%.The highest and lowest values appear in Dagu estuary and Minjiang Estuary,respectively.The source of organic matter has a bias towards marine input in Daliaohe Estuary and Jianhe Estuary whose marine contribution both exceeds 60%.The contribution of terrestrial source to sediment organic matter is at range from14.50%to77.11%,and the maximum value occurs in Minjiang Estuary which indicates that terrestrial source is main source to its sediment organic matter.What's more,terrestrial sources of sediment organic matter in Yellow River Estuary,Yangtze River Estuary and Qiantangjiang Estuary are also the major sources.Contribution of local vegetation source is from 7.35%to 35.82%.The local mangrove in Pearl Estuary,Jiulongjiang Estuary and local Scirpus mariqueter in Yangtze river Estuary account for more than20%organic matter in the sediment.Not only accumulating terrestrial and marine organic matter,buried local vegetation itself is also an important source of organic matter in the sediment at inter tidal zone.So,when we calculate the source of organic matter in the inter tidal zone,we cannot ignore the input of local vegetation.