Soil types differentiated their responses of aggregate stability to hydrological stresses at the riparian zones of the Three Gorges Reservoir

Abstract

The aim of this study was to investigate the resistance of aggregates to flooding stresses for different soil types and present implications for the restoration of eroded soils. Twelve field sites for three soil types were selected and separated into four hydrological stress levels at the riparian zones of the Three Gorges Reservoir. Soil samples were collected randomly, followed by lab analysis of soil mechanical composition, soil aggregate and stability, and soil carbon and nitrogen contents in the bulk soil and different sizes of aggregates. Clay and silt migrated from the upper water level sites to lower water level sites for Regosols under hydrological stresses; however, the mechanical compositions were not changed for Anthrosols and Luvisols. Total carbon content (TC), total nitrogen content (TN), and carbon and nitrogen ratio (C/N) were highest under strong hydrological stress for all-sized aggregates and bulk soils. Aggregate disintegration under hydrological stresses made organic matter exposed, but the anaerobic environment created by flood avoided organic matter from being decomposed. Most TC and TN in aggregates and bulk soils were negatively correlated with stability. Compared with Anthrosols and Luvisols, Regosols had lower aggregate stability due to its low large macro-aggregate proportions for each stress level. Therefore, much attention should be given to Regosols which has a high potential for erosion. Resistances of aggregates to strong and intermediate hydrological stress were higher for Anthrosols than other tested soils. However, Luvisols had the highest resistance to hydrological stresses because of its higher stability above the elevation of 165 m, due to its highest small macro-aggregate proportion. Therefore, anthropogenic restorations are recommended to stabilize the structure of Anthrosols and Luvisols under weak and strong hydrological stress, respectively. The operation of the Three Gorges Reservoir forced the riparian ecosystem to undergo periodical flooding stresses. The resistance of soil aggregates to hydrological stresses was lowest for Regosols, which should be concerned urgently to reduce soil losses. Under strong and intermediate hydrological stresses, Anthrosols had greater stability to maintain its original structure. However, the aggregate stability of Luvisols was higher for weak and none hydrological stress levels. Hence, anthropogenic restorations are recommended to take priorities for Anthrosols and Luvisols to reduce soil erosion under weak and strong hydrological stress, respectively.