江西省鄱阳湖流域农田生态系统土壤Se元素含量变化研究

The changes of selenium element content in soils of the agroecosystem in Poyang Lake Basin,Jiangxi Province

以江西省鄱阳湖流域农田生态系统中Se元素为研究对象,以大气干湿沉降、灌溉、施肥、喷施农药为输入途径,以农作物收割、地表径流以及Se升华为输出途径对Se的生物地球化学循环规律进行研究。结果表明,鄱阳湖流域Se元素的大气干湿沉降通量密度平均值为6.90g/(hm2.a),灌溉、施肥、喷施农药通量密度明显较低,它们对土壤Se元素的富集贡献率分别为77%、20%、1%和2%。Se通过升华输出通量密度相对较小,土壤Se年净增量主要受大气干湿沉降的制约。以20cm厚的耕作土体为研究介质,经估算,当前的Se年平均通量密度可引起土壤Se质量分数升高0.007mg/kg。20a后研究区富硒土壤将由目前5 960km2增加至6 672km2。研究中未考虑天降水下渗问题,这对中国南方土壤中元素的地球化学行为有非常重要的影响。

In order to study the biological and geochemical laws of Se element, we made use of Se element in the farmland ecosystem of Poyang Lake Basin, Jiangxi Province as the main subject studied, using atmospheric bulk deposition, irrigation, fertilization and pesticide spray as input parameter, and crop harvest, surface runoff and sublimation of Se element as output parameter. The study shows that the average value of atmospheric bulk deposition flux density of Se element in Poyang Lake Basin is 6.90 g/（hm2 · a）, while the values of irrigation flux density, fertilization flux density and pesticide spray flux density are obviously low, and their corresponding contribution rates to the enrichment of edaphic Se element are 77 %, 20%, 1% and 2%, respectively. The sublimation of Se element flux density output value is relatively small and the annual net increment values of edaphic Se element are majorly affected by the constraints of atmospheric bulk deposition. It is estimated that the current average annual Se element flux density can cause edaphic Se concentration increased by 0. 007 mg/kg, and accordingly, the enriched Se element soil of the study area will increase from 5960 km2 to 6672 km2 in 20 years. This study does not take the infiltration of rain water into consideration, which has a vital influence on the geochemical behavior of elements in southern China soil.