Distribution and influencing factors of subsoil fluorine forms of the ditch system in Daan Irrigation District
Fluorine is a chemical element widely distributed in nature,which has an important impact on environment and human health.The content of total fluorine and different forms of fluorine in the subsoil of farmland drainage ditches are determined by the sequential extraction procedure,and the effects of farmland planting years,vegetation cover and subsoil physicochemical properties on the distribution of fluorine forms are discussed.The results indicate that the concentration of different forms of fluorine shows an upward trend with the increase of farmland planting years.Under the alkaline environment with subsoil pH between 8.09 and 10.24,the content of Ws-F and Ex-F are significantly positively correlated with pH,and the concentration of Fe/Mn-F and Or-F are significantly negatively correlated with pH;The content of TF is significantly positively correlated with TP and the specific gravity of clay grains,but significantly negatively correlated with the content of TN.In the ditches with vegetation cover,the percentage of subsoil clay particles is higher,and the contents of Ws-F,Ex-F and Or-F are significantly higher than those in the area without vegetation cover,indicating that vegetation cover is an important factor influencing the distribution,migration and transformation of fluorine.Therefore,lowering subsoil pH,reducing phosphorus fertilizer use,and increasing ditch vegetation cover can reduce the bioavailability of fluorine in subsoil-water system,thereby reducing ecological risks.The conclusion can provide theoretical references for farmland management and ecological restoration in irrigation districts.
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