Leaching Characteristics Of Dissolved Organic Carbon In Coastal Wetland Of Jiaozhou Bay

As the most active part of soil organic carbon, dissolved organic carbon(DOC) was adsorbed by soils, or moved into water body with water transport, and further participated in a larger range of C cycle. As an important "mobile carbon pool", the leaching process was an important way for the loss of soil organic carbon. Therefore, it was theoretical and practical significance to study the characteristics(the determination of soil organic carbon pool, the capacity and the dynamic change of soil active organic carbon pool and so on) of soil DOC leaching.In the present research, the experimental soils were sampled in four different ecological environments of Jiaozhou Bay Coastal Wetland. Firstly, the physical and chemical properties of the tested soil were analyzed. Secondly,based on the research results of the spatial distribution of TOC and DOC content in soil and their relationship, the leaching characteristics under different ecological environment of soil DOC were explored through the method of indoor soil column simulated leaching,. It revealed the characteristics of soil leaching migration and main factors of different ecological environment. Besides, it provided more comprehensive base data for the researching of coastal wetlands. The results of present study were as follows:(1) The soil water and salt in different sample plot had obvious change of gradient, and the soil water and salt content nearer the sea had a higher value than that further away. The content of water and salt in the rice straw wetland was the highest, owing to double effects of submerged plants and tidal action. Light beach wetland was the second due to the strong influence of tide. Soil water and salinity of the salt tolerant plant Suaeda wetlands and reed wetland were obviously low. The character of salt content of Jiaozhou Bay coastal wetland soil is mainly chloride saline soil and a little Sulfate saline soil. The high chloride content in the area was due to the frequent sea water erosion and the severe sea water intrusion. Soil bulk density and soil moisture content were significantly affected by the same factors. The higher the water content, soil bulk density was smaller. The measuring result showed that the soil p H was not affected by hydrology and vegetation.(2) The TOC and DOC contents in soil showed the opposite trend in distance from the sea, and its content was positively correlated with the overall performance. In the vertical direction, the comparison of the effect of hydrology, vegetation and tidal on distribution of TOC and DOC contents indicated different response existed between TOC and DOC, and DOC was more sensitive than TOC. There were some differences between the distribution of DOC and TOC in soil. The correlation analysis of DOC and TOC content and physical and chemical properties of soil shows that DOC was different from TOC in physical and chemical properties. But the overall result showed that the DOC and TOC were significantly positively correlated with the soil salinity content and moisture content, and negatively associated with soil pH and bulk density.(3) The leaching characteristics of different tested soil DOC was different. However,the content of DOC in soil leaching solution increased with the increasing of soil depth and gradually decreased with the increase of time. Leaching DOC was trapped firstly and then adsorbed in the process of leaching. In the absence of exogenous carbon, the loss amount of soil organic carbon in the upper layer obviously increased due to the long leaching. The content of TOC in soil showed a decreasing trend after leaching and the loss of TOC decreased obviously with the increase of soil depth. It was because that each layer of soil had the adsorption and retention capabilities in the process of leaching, whereas the upper soil always in a state of leaching.(4) The structure characteristics of DOC in soil leaching solution were different. Soil showed poor adsorption capacity for small molecules with smaller aggregation. The component would always give priority to leaching and the content of carbonyl, hydroxyl and ester in the aromatic ring of DOC in leaching solution was higher than that of the other groups during the leaching process. The aggregation and molecular weight of DOC in leaching solution increased gradually, because more and more macromolecular substance with comp lex structure of soil DOC desorbed and were leached into the subsoil during the leaching process. The influence factors of structure characteristics of DOC in leaching solution were more complicated than that of the content. The present research found that the structure characteristics of DOC in soil leaching solution in light beach wetland and rice straw wetland closer to the sea were similar, and that in salsa wetlands and reed wetland were similar.