Modeling the relations between riverine DIC and environmental factors in the lower Xijiang of the Pearl River, China

Abstract

The Zhujiang River (the Pearl River) is a major contributor of riverine discharge to South China Sea and has received great attention in carbon cycling study for recent years. To explore the relations between riverine carbon and impacting factors for the Xijiang drainage basin, the major subsystem of the Zhujiang River, this study employed a partial least square (PLS) regression model with Geographic Information System (GIS) and Matlab techniques. In this model, specific spatial relations of the factors respecting the processes of riverine dissolved inorganic carbon (DIC) are addressed, including the effects of upper river on the lower river, tributaries on the stem river, and the effects of spatial accumulation and hysteresis. Modeling results indicate that the lithologic type of the exposed bedrocks defined by their easiness for chemical weathering is the dominant factor that is positively correlated with riverine DIC in all the three tributaries, the Gujiang, Hejiang and Xijiang Rivers. Relative altitude is the second important positive factor. Human activity (represented by per capita GDP and population density) is negatively related to riverine DIC, with a moderate importance in the Guijiang and Xijiang, and a least importance in the Hejiang River. Land use (net primary production, NPP) and soil type (defined by carbon content) show relatively small influences on DIC, with a positive correlation in Hejiang and Xijiang, and a negative correlation in Guijiang. Rainfall is negatively correlated to DIC in the whole Xijiang, but has no significant influence on DIC in the Guijiang and Hejiang. These results may provide important clues for understanding the geochemical processes of the riverine DIC associated with the environmental factors. © 2007 Elsevier Ltd and INQUA.