黄河中下游及小浪底水库溶解态锰的分布、季节变化及影响因素

Distribution,Seasonal Variations and Influence Factors of Dissolved Manganese in the Middle and Lower Reaches of the Yellow River and Xiaolangdi Reservoir

本文利用催化动力学分光光度法对2017年6月、12月和2018年5月、9月黄河中下游及小浪底水库溶解态锰(DMn)的含量进行测定。结果表明,黄河中下游沿程DMn的含量在2.1~63.5 nmol·L^(-1)范围之间波动,四个季节的平均浓度分别为(13.8±14.5)、(31.3±18.8)、(15.6±15.4)和(6.5±5.5)nmol·L^(-1),存在显著的季节性差异,冬季DMn的浓度要显著高于其他季节,秋季浓度最低。黄河中下游沿程DMn的空间分布表现为小浪底水库浓度显著低于水库上、下河段。沿程DMn的变化在一定程度上会受到径流量变化、水沙调控、地貌改变、支流汇入及水库大坝的影响。小浪底水库四个季节DMn的平均浓度分别为(17.2±16.4)、(10.1±4.9)、(10.8±4.1)和(9.6±5.4)nmol·L^(-1),DMn的空间分布差异较大,但整体都表现为在底层存在DMn的高值,除冬季外,小浪底水库底层水体中库首DMn的浓度高于库尾。通过探讨影响小浪底水库DMn分布的主要因素发现,DMn在悬浮颗粒物-水界面的吸附解吸作用是会对DMn的分布产生一定影响。在夏季和春季底层低氧区存在有机质降解释放DMn的现象,表明氧化还原环境改变是影响DMn分布的重要因素;夏季和秋季水库表层叶绿素a浓度较高的区域浮游植物对DMn存在显著的清除现象,表明表层水体中的DMn被浮游植物吸收。

Manganese is a redox sensitive element and one of the key micronutrients for the growth of phytoplankton.Understanding the distributions and major influencing factors of dissolved manganese(DMn)is important to study its biogeochemical cycles in the large riverine drainage basin.The distributions of DMn in the middle and lower reaches of the Yellow River and Xiaolangdi Reservoir(XLDR)were investigated in June,December 2017,and May,September 2018.The concentrations of DMn were measured by the catalytic-kinetic spectrophotometric method.The results showed that the DMn content along the middle and lower reaches of the Yellow River ranged from 2.1 to 63.5 nmol·L^(-1),with the averages of(15.6±15.4)nmol·L^(-1)in spring,(13.8±14.5)nmol·L^(-1)in summer,(6.5±5.5)nmol·L^(-1)in autumn and(31.8±18.8)nmol·L^(-1)in winter,respectively.There existed significant seasonal variation for concentrations of DMn,with the highest value in winter and the lowest in autumn.DMn concentrations was affected by the variations of runoff in different seasons.The spatial distributions of DMn along the middle and lower reaches of the Yellow River in different seasons showed that the concentrations of DMn in the XLDR were significantly lower than the upper and lower reaches of the reservoir.The distributions of DMn along the middle and lower reaches were affected by geomorphic change,tributary inflow and reservoir dam to a certain extent.The average concentrations of DMn in the XLDR were(10.8±4.1)nmol·L^(-1)in spring,(17.2±16.4)nmol·L^(-1)in summer,(9.6±5.4)nmol·L^(-1)in autumn,and(10.1±4.9)nmol·L^(-1)in winter,respectively.The spatial distributions of DMn in the XLDR during four seasons were quite different.Overall,the concentrations of DMn were higher in the near bottom layer,corresponding to the high SPM or low DO content.In addition to winter,the distributions of the DMn in the bottom water of XLDR showed an increase downstream towards the dam.The main factors affecting DMn distributions in XLDR are discussed.The adsorption and desorption of DMn at the suspended particulate matter(SPM)-water interface is an important factor affecting the distributions of DMn in the XLDR.In summer and spring,degradation of organic matter can release DMn in the near bottom layer with relatively low dissolved oxygen.In summer and autumn,DMn is significantly removed in the surface,corresponding to higher concentrations of chlorophyll A(Chl a),which indicate that the DMn in the surface water is removed by phytoplankton.