Physical and Chemical Properties of Soils in Wetlands of Caizi Lake Different in Restoration History in Anqing, Anhui Province

Returning farmland to lake (RFL) is an important strategy in China for the restoreation of wetland ecology in the middle and lower reaches of the Yangtze River. Soil physical and chemical properties are important indices for evaluation of the restoration of wetland ecology. Plots of wetland different in restoration history (2, 5, 8, 10 and 20a) in the Caizi Lake were selected for comparison with their adjoining rapeseed fields and natural wetland in soil physical and chemical properties, i.e. soil bulk density, clay content, water content, pH, organic matter, total nitrogen, hydrolysable nitrogen, total phosphorus and available phosphorus, to expose law of the variation of ecological features of the soils after RFL. Results show that the variation of soil physical and chemical properties differed in trend between plots different in restoration history. Soil organic matter content increased with the age of restoration; soil total nitrogen and alkalyzable nitrogen increased significantly 5 years after restoration, and gradually leveled off in the later years; soil total phosphorus and available phosphorus decreased first and then increased; soil clay content increased gradually; soil bulk density rose first and then declined; soil water content went up steadily; and soil pH lowered gradually and slowly. The 2-year wetland soil was still similar to the adjoining rapeseed land soil in soil ecological feature. The second year seemed to be the turning point, after which the soil began to evolve towards natural wetland soil in ecological feature. During the 20 years soil physical and chemical properties changed more significantly in the surface layer than in the subsurface layer. Regression analysis shows that recovery of clay content, bulk density, water content, organic matter, total phosphorus and available phosphorus in the restored wetland to the respective level in the natural wetland may take 19, 23, 31, 26, 27 and 22 years in the surface layer, and 20, 31, 51, 40, 30 and 23 years in the subsurface layer.