Soil Organic Carbon Loss In The Wujiang River And Yuanjiang River Catchments

Karst is one of the most important ecosystems on the earth, which supports the living of one fourth population. However, its stone sesertification has become a regional environmetal issue due to the combined impacts of human and natural activities. China owns the largest karst ecosystem over the world, which is located in its southwest part. This ecosystem includes the small part of Chongqing, Guangxi, Yunnan and Sichuan as well as the most part of Guizhou. The latter is the center of this ecosystem. During the past decades, a lot of measures have been taken by the local and central governments in order to hold back theecosystem degradation, however the tendency of the stone desertification has not mediated. This indicated the mechanism responsible for the stone desertification has to be approached in terms of the relationship between the soil carbon cycle and the health of the kasrt ecosystems.A river is a collector and integrater of informations pertaining to carbon cycling in its catchment. Moreover, it is simpler to collect river samples than soil samples. Biogeochemistry of riverine organic carbon species (POC and DOC) can efficiently indicate the status of carbon cycling in related catchments. The Wujiang and Yuanjiang River catchments in Guizhou are two different ecosystems with different stone desertification strength, different soil depth, different vegetation coverage, different soil organic matter content, and different human activity strength. They can be used as prime objects to approach on the carbon cycling during the stone desertification processes.Water samples were collected during the low water stage (Jan. 18 - Feb. 8,2002) and high water stage (July 15 - Aug. 4,2002) for the Wujiang and Yuanjiang River (including the Wuyanghe River and Qingshuijiang River). The total samples were up to 49 for each sampling period. The dissolved organic carbon (DOC) and particulate organic carbon (POC) were classified with the Whatman glassfiber filter (GF/F, 0.65μm). The terrestrial plant samples were randomly collected, and their carbon isotope composition was determined .