金盆水库沉积物铁锰释放规律

Release Mechanisms of Iron and Manganese from Sediments in Jinpen Reservoir

针对分层型水库周期性厌氧问题,金盆水库利用人工强制混合充氧技术补充底部水体溶解氧,抑制沉积物中还原性污染物的释放.但受水库地形地貌的影响,人工强制混合充氧效率存在一定差异性,在曝气系统运行结束后部分较深区域上覆水体溶解氧迅速耗竭,导致污染物的再次释放.为探究铁锰在该条件下的释放规律及扩散强度,选取主库区代表性采样点,对沉积物间隙水及上覆水溶解态铁锰浓度分布进行测定,并计算沉积物-水界面处溶解态铁锰的扩散通量.结果表明,人工强制混合充氧结束后地势较低区域底部水体迅速进入厌氧状态,导致大量溶解态锰释放进入上覆水体,浓度最高达0.42mg·L-1;而地势较高区域底部水体短暂进入缺氧状态,之后溶解氧浓度迅速回升,因此底部溶解态锰浓度升高幅度较小,浓度最高为0.17mg·L-1.沉积物间隙水-上覆水铁锰浓度分布结果表明,由于铁锰氧化还原电位的差异,溶解态锰相较于铁在厌氧条件下更容易释放进入上覆水体,且不断在表层沉积物及上覆水体中积聚,而溶解态铁的释放不仅受溶解氧的抑制,还受锰氧化物等其他氧化剂的抑制.由扩散通量计算可知,人工强制混合充氧结束后溶解态锰的扩散通量有降低趋势.由质量平衡计算可知,溶解态锰在厌氧层中的积聚不仅与扩散通量有关,还与沉降通量、厌氧层厚度有关,因此厌氧层中铁锰的生物地球化学循环作用有待进一步的研究.

In response to the annual hypolimnetic anoxia in stratified reservoirs,water-lifting aerators(WLAs)were used in Jinpen Reservoir to supplement the dissolved oxygen in the bottom water and suppress the release of reduced pollutants from sediment.However,due to the influence of geomorphic characteristics at the bottom of the reservoir,there were some differences in the efficiency of artificial mixing and aeration.After the deactivation of WLAs,the dissolved oxygen in the bottom water of some deeper areas was rapidly depleted,resulting in the re-release of pollutants.To explore the release mechanisms and diffusion intensity of iron and manganese during this period,the representative samples in the main reservoir area were collected to measure the distribution of dissolved iron and manganese in the pore water and overlying water and calculate the diffusive flux of dissolved iron and manganese across the sediment-water interface.The results showed that the bottom water of the lower terrain rapidly entered the anaerobic condition after the system was deactivated,resulting in the release of a large amount of dissolved manganese into the overlying water,the maximum concentration of which was 0.42 mg·L-1.However,the bottom water of the higher terrain briefly entered a state of hypoxia,after which the dissolved oxygen concentration increased rapidly,so the dissolved manganese concentration increased moderately to 0.17 mg·L-1.The distribution of iron and manganese in the pore-water-overlying water showed that the dissolved manganese was released more easily into the overlying water than the iron under anaerobic conditions and constant accumulation in the upper sediments and overlying water.However,the release of dissolved iron was not only suppressed by dissolved oxygen but also by other oxidants such as manganese oxide.The diffusion flux of dissolved manganese declined after the system was deactivated.A mass balance calculation demonstrated that the accumulation of dissolved manganese in the anaerobic layer was not only related to the diffusion flux but also to the sedimentation flux and the thickness of the anaerobic layer.Therefore,the biogeochemical cycle of iron and manganese in the anaerobic layer requires further study.