Soil organic carbon distribution in relation to terrain & land use-a case study in a small watershed of Danjiangkou reservoir area, China<bold> </bold>

Understanding the responses of soil organic carbon (SOC) distribution to terrain and land use variations is important for making corresponding measures to enhance the soil quality and its carbon storage. The objective of this study was to characterize the spatial distribution of SOC, and analyze the impacts of environment factors on spatial variation of SOC along the Danjiangkou Reservoir area, China. A village size watershed was selected to investigate the SOC distribution under different terrains and land uses. We found that SOC contents followed a log-normal distribution with arithmetic and geometric means of 6.83 g kg(-1) and 6.09 g kg(-1), respectively, which were moderately variable (Coefficient of Variation = 49.6%) and demonstrated a moderate spatial dependence according to the nugget ratio (37.8%). The experimental variogram of SOC was best-fitted by a spherical model after the spatial outliers had been detected and subsequently eliminated. From the spatial distribution map of SOC contents, the highest SOC content occurred in the center of the watershed, which were along the main water channel or tributaries and normally had lower altitude. While,the lower values of SOC contents were located at the edge of the watershed, such as in the northwest, southwest and southeast of the area where citrus were normally planted. This spatial distribution pattern of SOC was generally consistent with the spatial structure of terrain and land use on the unique terrain of the agriculture-based reservoir area. Therefore, taking terrain and land use type into account when estimating the spatial variation of SOC pool would increase the accuracy in prediction and modeling of SOC movement at the watershed scale. (c) 2019 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).