湘西喀斯特区植烟土壤有效磷时空变异及风险评估

Temporal and Spatial Variability Risk Assessment of Soil Phosphorous in Karst Tobacco-planting Region of Xiangxi, Hunan

为揭示典型喀斯特烟区土壤有效磷的时空变异特征,为喀斯特地貌烟区合理施磷和控制磷素面源污染提供依据,以湘西州2000年和2014年耕地土壤有效磷含量为研究对象,利用空间自相关、半方差函数及分形维数等方法,对县域内土壤速效养分时空变异特征和环境风险进行了评价。结果表明,2014年土壤有效磷平均含量增加了30.89 mg/kg,增幅达425.48%;土壤有效磷Moran’s I指数标准化Z值下降,分形维数和块金效应增加,说明土壤有效磷空间结构减弱,随机变异性增强;土壤有效磷"极高"、"很高"和"高"等级面积显著增加,分别增加了28.36%、26.89%和25.94%;而"低"和"极低"等级面积分别下降了57.45%和27.12%;土壤有效磷含量与海拔、成土母质、土地利用类型、轮作模式及有机质含量关系密切;2014年湘西州有效磷含量超过风险临界值的概率大幅增加,很高风险(概率>80%)、高风险(概率60%~80%)和中等风险(概率40%~60%)区域分别占研究区域面积的1.77%、5.40%和13.96%。其中,龙山县北部和永顺县东部应作为农业面源磷污染的重点控制区。

Based on methods of spatial autocorrelation, semi-variance function and the fractal dimension as well as the data of soil available phosphorus in 2000 and 2014, the spatiotemporal variation and environmental risks of soil available phosphorus in Karst tobacco-planting region in Xiangxi of Hunan were studied. The results showed that, during the 14 years, soil available phosphorus content increased by 30.89 mg/kg; the Z scores of soil available phosphorus index decreased, fractal dimension and the nugget effect increased, indicating a weaker spatial structure and stronger stochastic variability; the areas of ‘extremely high＇, ‘very high＇ and ‘high＇ levels were increased by 28.36%, 26.89% and 25.94%, while the areas of ‘low＇ and ‘very low＇ levels decreased by 57.45% and 27.12%, respectively; There were significant correlation between soil available phosphorus and elevation, soil parent material, land use type, rotation mode and SOM content; Probability of soil available phosphorus content exceed the risk critical value increased greatly, the total areas of very high risk（probability 80%）, high risk（probability 60%–80%） and medium risk（probability 40%–60%） accounted for 1.77%, 5.40% and 13.96% of the total study area, respectively. North of Longshan and east of Yongshun are the key regions to control agricultural non-point pollution of phosphorus.