Abstract: Soil active organic carbon is the most important carbon pool in soil, due to its active characters and fast turnover. It has great significance in the study of soil carbon cycling and carbon interception, and is a good indicator in ecosystem management. Generally, it originates from litter decomposition, plant root secretion, soil organic matter hydrolysis, microbes themselves and their metabolic products, and is affected by season, humidity, land use/ land management pattern , and soil pH, etc. It greatly affects the solution, adsorption, desorption, translocation, and biotoxicity of soil chemical substances, and thus, has strong influences on soil nutrients flux, heavy metals mobility, metal complexes formation, and inherent productivity. In addition, the content of this carbon directly affects the quantity and activity of soil microbes, and accordingly, affects the greenhouse gases emission and its regulation, the quality of aquatic ecosystem, and the erosion process of lithosphere. To further study the dynamics of soil active organic carbon is of significance for environmental protection and nutrients cycling.

Key words: Outer Changjiang estuary, Red tide, Plume front, Changjiang River diluted water, Upwelling