Study On The Distribution And Adsorption Behaviors Of The Soil DOC From Wetlands Of Subtropical Monsoon Climate Zone Of China

In the process of wetland carbon cycle, the soil organic carbon can not only be converted into gases (CO2, CH4) and releases into the atmosphere, but also can be carried into the water as the form of dissolved organic carbon, being another important part of the wetland carbon cycle. At present, studies about wetland carbon cycle mainly focused on CO2 and CH4 emissions, while migration and transformation of DOC were mentioned rarely. In this article, three kinds of wetland ecosystems in the subtropical monsoon climate zone of China were selected as the objects. The distribution and adsorption behaviors of DOC of the wetland soil were studied. The results obtained are as follows:1. The DOC content was in the range of 125.72～512.92 mg·kg-1, and the average content was 269.72±119.01 mg·kg-1, accounting for about 2% of the TOC average content. It presented a trend that the DOC content decreased with the soil depth increased. And the order of different wetlands was:paddy field>urban wetland>lake wetland. The DOC content was correlated with the soil physical and chemical properties. It was positively correlated with the content of soil TOC, moisture, TN and available nitrogen. Additional, the path analysis results showed that TOC and available nitrogen were the most important factors, and TOC played a more direct role.2. When the initial concentration of the adsorbate was between 0 and 45 mg·1-1, all of the adsorption models IM isotherm, Freundlich and Temkin could simulate the adsorption process properly. Among them, IM isotherm was the most suitable one. The partition coefficient m showed that the bottom soils owned the largest adsorption capacity. The soil adsorption capacity was positively correlated with the soil pH value, the physical clay and the active Al content. While the other properties like TOC and moisture didn’t exhibit a significant effect.3. It was observed that the particles with larger specific surface area, pore diameter and pore volume tended to adsorb and store more DOC. And part of the DOC adsorbed by the particles gathered in the pore structure. Thus, it could be deduced that physical absorption was one of the absorption mechanism. In addition, the ligand exchange of hydroxyl was proved to be the chemical adsorption mechanism.