Study On Dissolved Organic Carbon Content And Structure Characteristics Of Soil In Typical Estuary Wetland Of Jiaozhou Bay

In order to reveal the key factors for soil dissolved organic carbon in the estuary wetland and provide basic reference data for estuary or coastal wetland carbon cycle research, the typical Jiaozhou Bay estuary wetland as the research object in this paper, the temporal and spatial distribution of soil DOC content and characteristics were studied,and the impact of tidal effects on soil DOC were analyzed. The results showed that:(1) The soil DOC content decreased from sea to land, but the variation laws of soil profile at different sites were quite different. The seasonal variation showed that the soil DOC content was highest in April, followed in July, the lowest in October. Hydrology,vegetation and soil physicochemical properties were the main reasons for the difference of DOC content distribution in the soil. In summer, soil porewater DOC content did not show significant variation from sea to land like soil DOC content. In soil profile, the coefficient of variation of bare flat soil porewater DOC was higher than the wetlands with vegetation whose maximum contents located in the rhizosphere. The distribution of soil water DOC was influenced by the vegetation cover and salt content of soil.(2) The aromatic compounds of soil DOC were increased but not significant from sea to land and wetland soil DOC, and humification degree of the wetland with vegetation is higher than bare flat. Due to the small molecule decomposition and root secretion, the vertical aromatic compounds in the surface soil is relatively high. The seasonal variation in the first plot showed the humification degree was highest in October, followed in July,the lowest in April; however, in the other plot the lowest appeared in July. Ground vegetation, the root system and soil physicochemical properties were the main reasons for the difference of DOC humification degree in the soil. In summer, the aromatic compounds of soil porewater DOC also did not show significant variation from sea to land. In soil profile, the humification degree of the rhizosphere DOC was low and bare flat had not significant variation like the soil porewater DOC content.(3) In tidal process, DOC was transported from porewater to tidewater. In different soil layers the aromatic compounds variation laws of bare flat soil porewater DOC were consistent, while the aromatic compounds variation laws of wetland with Suaeda salsa were significantly different, which showed vegetation influenced the response of soil DOC to tidal action. The soil porewater salt of coastal wetland response to tidal stronger than that of the upstream wetlands, meanwhlie the p H and ORP change laws of the two soil porewater were opposite wtih soil porewater salt. The soil porewater salt was the key factor for DOC and the humification degree was mainly affected by the p H and ORP.