Abstract: The purpose of this study is to investigate geochemical process and driving forces of soil major chemical elements in the forest-dominated Jinshui River basin, tributary of the upper Hanjiang River. We carry out investigations on soil major chemical elements distribution and transport patterns and driving forces by integrated analysis of natural environmental factors and human activities. In order to achieve these goals, we further employ efficient approaches including field investigation, laboratory testing and GIS spatial simulation. Through this research work, following findings are achieved. Firstly, general soil weathering process of Jinshui River Basin basically evolves from Ca, Na stages to K stage. Ca, Na decreased rapidly, and silicate weathering process evolved gradually. Major ions of water are subject to carbonate dissolution, about 2 / 3 of the soil in the basin are alkaline (pH>7) which provide good condition for mineralization of organic nitrogen. Chemical index of alteration (CIA) gradually increase from south to north, initially decrease from east to west and increase eventually. Predominant major elements in the upper stratum of soil are oxides of Si, Al, Fe and Ca, which account for about 78.1% of the total. Secondly, specific soil weathering process differs in spatial patterns and elements transport which is driven by integrated interior forces (e.g., mineral materials) and external forces (e.g., temperature, precipitation, wind and the gravity). Original mineral materials are changed into soils with different physical properties (soil texture, mechanical composition) and chemical components (organic matter). Upstream original mineral materials have been transported, accumulated and deposited in the downstream, which are driven by forces of gravity, water transport, glacial effects, and wind. Key ecological factors of plant growth change greatly which are caused by integrated environmental effects such as climatic conditions, sunlight, nutrients and soil biological characteristics. Organic matters accumulate in forest covered belts of Jinshui River while inorganic weathering processes are dominated by decomposition and eluviation of silicate minerals. In the vertical section, within all vegetation types, soil moisture storage capacity and saturation decrease with an increase in depth. Forest soil has better conditions of physical properties and chemical characteristics than those of wasteland and farmland. Mixed coniferous soil reserves the most water than other vegetation types, followed by coniferous forest, chestnut forest and shrub. Thirdly, land use and cover is one of key contributors to determine geochemical patterns of soil organic matters. Land use and cover types greatly impact on volumes of standing deadwood, particulate organic carbon content and Na / K value. Soil particulate organic carbon and Na / K are in good correlation, especially in dry land and bamboo areas. Intensity of mineral weathering process decreases with the decrease of biomass which follows the sequences, dry land> bamboo> paddy soil> shrub> coniferous forest> mixed forest> deciduous forest. Improper human activities decreased soil organic matters, and thus had negative impacts on agriculture. However, it helps to prevent the loss of N, P if effective countermeasures are adopted to develop a vegetation buffer zone along riversides, especially in residential areas. The overall investigation of this study suggests that protection of forestry ecosystem and proper human activities are important for improvement of water quality and soil erosion.

Key words: Geochemical transport of soil chemical elements; soil weathering; forestry ecosystem; Hanjiang River Basin; Jinshui River