太湖地区农田土壤大孔隙及胶体释放对有效磷下渗的影响

Effects of macropore and colloid release on vertical migration of available phosphorus in farmland soil of Taihu Lake region

为了进一步验证农田土壤中大孔隙流及农业活动引起的胶体释放对磷素下渗污染地下水的影响,采用太湖地区农田土壤进行平行土柱试验。结果显示:模拟土壤胶体(质量浓度约为50 mg/L)释放情况时,土壤水流中胶体物质和有效磷的垂直迁移速度明显加快,土柱底部(100 cm深度)出流中有效磷的渗漏速率达到0.15 kg/(m2·d),比自然状态增大约15.4%;当土壤中存在约5%(体积分数)的大孔隙情况下,土柱底部的有效磷渗漏速率达到29.9 kg/(m2·d),大孔隙引起的优势流对胶体和有效磷的下渗起主导作用,而土壤胶体物质释放引起的辅助作用约占3.2%。土壤胶体释放对土壤p H和电导率等产生影响,进而影响溶质的运移转化过程。太湖地区农田土壤中广泛存在大孔隙引起的优势流及农业耕作活动引起的土壤胶体释放,为有效磷垂直下渗提供了加速途径,对地下水磷污染造成了较大的影响。

To investigate the effects of macropore flow in farmland soil and colloid release caused by agricultural activities on the vertical migration of phosphorus and groundwater pollution, parallel soil column experiments were conducted using agricultural soil from the Taihu Lake Basin. The results show that the release of colloid （with a concentration of about 50mg/L） in soil accelerated the vertical migration of colloid and available phosphorus,and the leaching rate of available phosphorus at the soil column bottom （100 cm in depth） reached 0.15 kg/（ m2 ~ d） ,about 15.4% higher than it was with no obvious release of soil colloid. Furthermore,the existence of macropores （5% in volume） in soil significantly increased the leaching rate of available phosphorus, with a value of 29.9 kg/（ m2 ~ d） at the soil column bottom. The preferential flow caused by macropores played a critical role in the leaching of colloid and available phosphorus. However,the release of soil colloid accounted for 3.2% of the increase of the leaching rate of available phosphorus when macropores existed. Soil colloid release altered the chemical characteristics of soil, such as pH and electric conductivity, and then influenced the transport of solutes in soil. Preferential flow caused by macropores and soil colloid release caused by agricultural activities exist across the agricultural area of the Taihu Lake Basin. Macropores and soil colloid accelerated the vertical infiltration of phosphorus, which increased the risk of groundwater pollution caused by phosphorus.