长江口及其邻近海域2012年3月和7月溶解态铝的分布特征分析

分别于2012年3月和7月对长江口及其邻近海域水体中溶解态铝的分布及其影响因素进行了研究,并在2012年3月至2013年11月期间对长江徐六泾进行了连续观测。结果表明,徐六泾溶解态铝在夏季出现最高值,在冬季呈现最低值,平均值分别为(313±130)nmol/L和(140±43)nmol/L,表现出与径流量相似的季节变化规律。受陆源输入变化的影响,长江口溶解态铝的浓度由近岸向外海逐渐降低,且呈现出明显的季节性差异,即7月明显高于3月。3月表、底层海水中溶解态铝的浓度范围分别为21~129 nmol/L和27~146 nmol/L,平均值分别为(49±21)nmol/L和(59±27)nmol/L;7月表、底层溶解态铝的浓度范围分别为6~332 nmol/L和9~252 nmol/L,平均值分别为(66±69)nmol/L和(83±74)nmol/L。在7月,表、底层溶解态铝呈现显著性差异,底层沉积物的再悬浮可能是造成差异的主要原因。调查结果表明,溶解态铝在长江口呈现出清除型行为,清除主要发生在咸淡水混合初期,初步计算出7月份溶解态铝的清除率约为55%。

Distribution characteristics of dissolved aluminum in the Changjiang Estuary and its adjacent marine area in March and July,2012

Distributions of dissolved aluminum in the Changjiang Estuary and its adjacent area were investigated in two cruises carried out in March and July 2012. The monthly variations of dissolved aluminum in the Changjiang were investigated at Xuliujing from March of 2012 to November of 2013. At Xuliujing, the concentration of dissolved aluminum was maximun in the summer and minimum in the winter, corresponding to the seasonal variations of riverine runoff, with averages of (313±130) nmol/L and (140±43) nmol/L, respectively. Terrigenous material played a significant role on this area, dissolved aluminum concentrations in both surface and bottom waters decreased from the river mouth to the open sea. Dissolved aluminum concentrations in the surface and bottom waters ranged from 21 to 129 nmol/L and from 27 to 146 nmol/L in the March, with averages of (49±21) nmol/L and (59±27) nmol/L, respectively. Dissolved aluminum concentrations in the surface and bottom waters ranged from 6 to 332 nmol/L and from 9 to 252 nmol/L in the July, with averages of (66±69) nmol/L and (83±74) nmol/L, respectively. For dissolved aluminum, there were obvious seasonal variations between the spring and summer. The concentrations of dissolved Al in the bottom layer were significantly higher than the surface layer in the summer due to the desorption during the resuspension of bottom sediments, on the contrary in the spring. However, there wasn't significant difference between the surface and bottom layers in the spring. Dissolved aluminum showed a scavenging behavior in the Changjiang Estuary during the preliminary stage of mixing between salt and fresh water, and with a scavenging proportion of up to 55%.