春季水华对南黄海总溶解态无机砷生物地球化学行为的影响

摘要

利用氢化物发生-原子荧光光谱法（HG-AFS）对2007年3月30日至4月23日南黄海海域总溶解态无机砷（TDIAs，[TDIAs]＝[As5＋]＋[As3＋]）的含量进行了测定，其中针对水华中心区域（BM1站）进行了25 h 的连续观测，以探讨春季水华对有毒类金属元素砷的生物地球化学行为的影响。结果表明，TDIAs 的浓度范围为7．9～22．3 nmol／L，平均值为（17．8±1．9）nmol／L。TDIAs 在南黄海的分布主要表现为由近岸向外海逐渐升高的趋势，最大值出现在南部海域底层海水中。近岸海域表、底层 TDIAs 的含量相当，而中、南部海域由于存在明显的密度跃层，表、底层 TDIAs 的浓度具有显著性差异。2007年3月31日至 4 月 1日研究区域西南部受到沙尘天气和降雨的影响，表层海水中TDIAs 的含量显著升高。研究区域中、南部海域在观测期间暴发了典型的黄海春季水华，通过大面观测和对重点区域的连续观测可以发现，水华期间 TDIAs 的分布和磷酸盐类似，与 Chl a 呈现出较好的负相关关系（r＝0．51，p＜0．05，n＝39）。经初步计算，浮游植物水华对10 m 以上表层水体中 TDIAs的清除量约为2．4 nmol／L，占表层保有量的15％左右。通过箱式模型计算得出黄海 TDIAs 的停留时间约为（15．6±7．3）a，远远低于大洋。通过对该海域砷、磷摩尔比值的计算可以发现，南黄海砷、磷摩尔比值为大洋中的20倍左右，这可能会引起浮游生物对砷酸盐的大量吸收和转化，从而带来潜在的生态危机，需要引起足够的重视。%In order to understand the impact of spring bloom on the biogeochemical behavior of arsenic (a toxic met-alloid element)in the South Yellow Sea (SYS),the field investigation was carried out during March 30th to April 23rd 2007 to study the concentrations and distributions of total dissolved inorganic arsenic (TDIAs,[TDIAs]=[As5+ ]+[As3+ ])in the SYS.In addition,a 25 h anchor station (BM1)was also carried out at the central of SYS,where Chl a concentrations were higher than 4 μg/L.The concentrations of TDIAs were measured by Hy-dride Generation-Atomic Fluorescence Spectrometry (HG-AFS)and showed the range of 7.9-22.3 nmol/L,with the average of (17.8±1.9)nmol/L.The concentrations of TDIAs increased gradually from the coastal area to off-shore,with the maximum values appearing at the near bottom layer of the southern region.The concentrations of TDIAs showed well mixed vertical profile in the coastal area,while was stratified in the middle and southern re-gion.Due to the impact of strong dust storm and followed rainfall in the SYS during the investigation of March 31st to April 1st 2007,the concentrations of TDIAs in the surface waters were significant increased.A large-scale spring bloom occurred in the middle and southern region of study area for 4-5 days after the dust storm.Through the observations it can be found that the vertical profiles of TDIAs was similar to that of phosphate,and showed relatively negative relationships with chlorophyll a(r=0.51,p<0.05,n=39).After primary estimation,the scav-enging of TDIAs by phytoplankton above 10 meters layer can reach up to 2.4 nmol/L,which account for 15% of that in the surface waters.The residence time of TDIAs in the YS was (15.6±7.3)a,which is much lower than the open oceans.The molar ratio of arsenic to phosphorus in the study area was about 20 times higher than the open ocean,which might lead to significant absorption and transformation of arsenate and cause the potential eco-logical crisis.