海水中腐殖质对溶解态铁的络合及其影响因素

Fe complexation by humic substances in seawater and its influencing factors

腐殖质(humic substances,简称HS)是地表普遍存在的天然有机物,对海洋中重要的微量营养元素-铁(Fe)的分布及生物地球化学循环具有重要的影响作用。本文对腐殖质的来源、分布及对海水中溶解态铁的迁移转化的影响做了总结,特别论述了其在河口及沿岸水域的行为。大量研究表明河口、沿岸及开放海水中溶解态铁分布的变化可以用腐殖质的浓度及其铁结合能力的变化来解释。腐殖质的络合作用不仅能够阻止溶解态铁(DFe)在河口、沿岸等水域被去除,而且能够通过洋流将DFe迁移至外海及大洋区域,此外还能增加铁的溶解度及对海水中浮游植物的生物可利用性,并且促进铁的氧化还原循环。研究还发现两者之间的络合强度受到盐度、pH等理化因素的影响。盐度是影响HS与DFe配合能力的重要影响因素,盐度增加,导致HS中可以与Fe配合的位点数量降低,配合总量呈现指数降低,而pH的增加可以增加HS与DFe的配合量。另外HS还能影响海水中DFe的氧化还原,并以此影响浮游植物对DFe的吸收利用。因此腐殖质对溶解态铁的有机络合作用是影响其海洋生物地球化学循环的一个重要参数,对进一步研究海水中腐殖质的浓度和分布具有重要的意义。

Humic substances(HS)are ubiquitous components of natural organic matter on the earth's surface.They substantially influence the distribution and biogeochemical cycle of iron(Fe),a critical micro-nutrient in marine systems.This study summarizes the origin and distribution of HS and their effects on the migration,transformation,and bioavailability of Fe in seawater,particularly estuaries and coastal waters.Numerous studies have demonstrated that the variation in the concentration and Fe binding capacity of HS can explain the variation in the distribution of dissolved iron(DFe).HS complexation not only prevents the removal of DFe in estuaries and coastal waters but also allows DFe to be transported to the open ocean by ocean currents.Furthermore,it can also increase the solubility of Fe in seawater and its bioavailability to phytoplankton and promote its redox cycle.The complexation of Fe and HS is influenced by physicochemical factors,such as salinity and pH.Salinity is a vital factor influencing the Fe binding ability of HS.A higher salinity results in fewer sites that can coordinate with Fe and an exponential decrease in the total coordination amount,whereas a higher pH can increase the HS-DFe complexation.HS can also influence the redox reaction of DFe in seawater,thereby affecting the absorption of DFe and its utilization by phytoplankton.Therefore,the organic complexation of Fe and HS plays a vital role in the marine biogeochemical cycle of Fe,and it is crucial to further study the HS concentration and distribution in seawater.