我国南方地区桉树叶浸泡对水库沉积物致黑元素分布及迁移转化的影响

Effects of soaking Eucalyptus leaves on melanogenic elements distribution,migration and transformation in reservoir sediments of Southern China

我国南方地区桉树种植区周边水库冬季水体泛黑现象频发,桉树砍伐残体(尤其是叶)浸出液中富含的溶解性有机碳(DOC)、单宁酸与铁、锰、硫化物等一系列反应是其主要致黑原因,然而目前致黑物质对水库泛黑的贡献程度和途径仍不清楚.为了模拟桉树叶浸泡对水库黑水形成的影响机制,研究选取夏季水体未泛黑期(水体热分层稳定)进行室内浸泡实验,测定每6 h上覆水体溶解氧(DO)、氧化还原电位(Eh)、透光度等理化指标,分析DGT有效态铁、锰、硫和DOC、单宁酸浓度分布规律及迁移转化特征,计算沉积物水界面处Fe^(2+)、Mn^(2+)、S^(2-)表观扩散通量.结果表明:桉树叶浸泡明显消耗水体中的DO,且显著影响水体Eh与透光度.此外,透光度与DO浓度呈显著正相关(相关系数为0.618~0.978).桉树叶浸泡释放大量DOC和单宁酸,其中单宁酸浓度远超有氧马尾松组,其上覆水中浓度分别达到23.9、26.0和34.0 mg/L,说明桉树浸泡为黑水形成提供了重要的DOC和单宁酸来源.桉树叶浸泡后上覆水和表层沉积物中DGT有效态Fe浓度均明显增加,深层沉积物间隙水中DGT有效态Fe浓度明显下降,且其表观扩散通量均为正值,说明深层沉积物中Fe向沉积物水界面迁移,为黑水形成提供了重要的Fe来源.研究结果可为解决我国南方地区桉树人工林区水库水体突发性泛黑问题提供科学依据.

Water blackening occurs frequently in reservoirs around Eucalyptus planting areas in Southern China in winter.A series of reactions of dissolved organic carbon(DOC)and tannic acid in the leaching solution of Eucalyptus cutting residues(especially leaves)with iron,manganese,and sulfide are the main reasons for blackening.However,the contributions of black substances to reservoir blackening are still unclear.To simulate the influence mechanism of Eucalyptus leaves immersion on the formation of black water in the reservoir,the indoor immersion experiment was carried out in the summer non-black period(stable thermal stratification).Dissolved oxygen(DO),oxidation-reduction potential(Eh)and transmittance of overlying water were measured every 6 hours.The concentration distribution,migration and transformation characteristics of DGT-labile iron,manganese,sulfur,DOC,and tannic acid were analyzed.The apparent diffusion fluxes of Fe^(2+),Mn^(2+),S^(2-)at the sediment-water interface were calculated.The results showed that:The process of Eucalyptus leaves immersion significantly consumed DO in water,and affected water Eh and transmittance.In addition,there was a significant positive correlation between water transmittance and DO(correlation coefficient was 0.618-0.978).A large amount of DOC and tannic acid were released by Eucalyptus leaves immersion,where tannic acid concentration was much higher than that under Pinus massoniana leaves immersion.The concentrations in overlying water were 23.9 mg/L,26.0 mg/L and 34.0 mg/L,respectively,indicating that Eucalyptus leaves immersion provides an important source of DOC and tannic acid for black water formation.The concentration of DGT-labile Fe increased significantly in overlying water and surface sediments and decreased significantly in deep sediment interstitial water under Eucalyptus leaves immersion.The apparent diffusion flux under Eucalyptus leaves immersion was positive,indicating that Fe in deep sediments migrated to the sediment-water interface,which provided an important source of Fe for the formation of black water.The research results provide a scientific basis for solving the sudden blackening problem of reservoir water in Eucalyptus artificial forest area.