三江平原水田灌溉-排水过程中铁形态变化及输出贡献

采集三江平原农田灌溉地下水、稻田积水、渠系排水、土壤侧渗水,并采用切向超滤技术分离水体中不同形态铁,分析在灌溉排水及地下侧渗水中铁的迁移特征,并估算水田排水中铁的输出贡献.结果表明,在灌溉排水过程中,铁主要以低分子量形态和酸性不稳定形态迁移,地下水中Fe2+含量占可溶态铁的80.45%;地下水抽取到稻田后Fe2+含量显著降低,络合态铁含量升高,稻田积水中络合态铁占可溶态铁的75.50%;稻田积水排入渠系后,络合态铁中不稳定弱配位铁含量降低13.58%,其他铁形态变化不大.稻田积水通过地下侧渗进入渠系,随侧渗水体深度加深,Fe2+含量升高,络合态和胶体态铁含量降低,地下侧渗水向渠系水主要提供络合态和胶体态铁.三江平原湿地水田化改变了水体中铁的输出形态,同时,排水过程中铁的输出也对河流形成补给,水田灌溉排水过程可溶态铁的输出通量约为390kg.a-.1km-2,输出系数为0.186,灌溉-排水过程中残留在稻田土壤中铁的量约为1460kg.a-.1km-2,残留在排水渠系土壤中铁的量约为250kg.a-.1km-2,这对三江平原水土环境产生了深远影响.

Iron species and output flux in the agricultural irrigation-drainage system in the Sanjiang Plain

After the conversion of wetland to paddy land, agricultural drainage became an important iron source to the Amur River, which influences the iron content, species and transportation in the Amur valley. In this study, agricultural irrigation groundwater, paddy water, canal water and lateral seepage water were sampled to study iron transportation during the process of irrigation, drainage and lateral seepage in the Sanjiang Plain. The cross-flow filtration technique was employed to separate iron species according to their size fraction. The results showed that iron is primarily transported as low molecular weight and acid-labile iron forms in the process of irrigation and drainage. Ferrous ion accounted for 80.45% of total dissolved iron in groundwater. When groundwater was pumped to surface land, the conversion from Fe2+ to complexed iron occurred immediately. The complexed iron accounted for 75.50% of the iron in paddy water. After paddy water flowed into the canal, the complexed iron content decreased 13.58% but other iron species had no significant change. The Fe2+ concentration increased with the depth of soil in the lateral seepage water, and complexed and colloidal iron did conversely. However, after the lateral seepage water flowed from paddy field into canal, the concentration of complexed and colloidal iron increased. The output flux of total dissolved iron was 390 kg·a-1·km-2 and the output coefficient was 0.186 from agricultural drainage in the Sanjiang Plain. The amount of residual iron reached about 1460 kg·a-1·km-2 in the paddy fields during irrigation and 250 kg·a-1·km-2 in canal soil during drainage.