Iron: Studies on the speciation and bioavailavility in the Baltic Sea

波罗的海受到大气和河流输入的人为和自然微量金属的影响。海洋生物地球化学循环和食物网对向海洋环境中添加微量营养素作出反应。微量金属进入地表水的运输与生物生产和修饰过程的季节变化密切相关。在海水中，铁是最重要的微量元素。它主要以有机络合的形式存在，以不溶性铁（III）的形式存在（氧/羟基），在海洋表层水中以溶解性铁（II）的形式存在较少。这些铁络合物主要通过吸附或掺入颗粒并通过水柱运输而从光带中去除。众所周知，由于下沉速率缓慢，它们聚集在水平界面/边界，如斜斜，OMZ（氧最小带）或氧化还原边界。氧化还原界面与停滞的深水水体是波罗的海中部的典型特征。铁属于氧化还原敏感元素，这意味着在缺氧条件下，不溶的铁（III）种被还原为溶解的铁（II）种。铁（II）与磷一起形成了一种动力学上方便的可溶化合物。这就是氧化多西斜以下波罗的海溶解铁（II）浓度增加的原因。在较深的缺氧层中，由于形成了热力学上更稳定的化合物Fe （II）硫化物，从而平衡了可溶性物质，溶解铁浓度下降。与不溶性Fe在底部沉积物中富集平行的是，在150m深度，溶解Fe（II）种在redox斜上存在扩散输运通量。铁催化固氮蓝藻对氮的吸收。在这种情况下，已经假设，溶解的铁（II）是蓝藻生长过程中吸收的更生物可利用的物种。这就引出了一个主要问题：“铁是波罗的海蓝藻繁殖的限制因素还是促进因素？”因此，这个项目应该结合深水停滞的形成到缺氧的程度，由此导致的铁形态的变化（还原为铁（II））和扩散的铁（II）运输到绿化带是施肥和蓝藻华增加的原因。

The Baltic Sea is affected by anthropogenic and natural trace metals via atmospheric- and riverine input. The marine biogeochemical cycles and food webs respond to the addition of micronutrients to the marine environment. Entering the surface waters, the transport of trace metals is closely linked to the seasonal variation of the biological production and modification processes. In seawater Fe (Iron) belongs to the most important micronutrients. It mainly exists as organically complexed species, as insoluble Fe (III) species (oxy / hydroxyl) and to a lesser extent as dissolved Fe (II) species in ocean surface waters These Fe complexes are mostly removed from the euphotic zone by adsorption on or incorporation into particles and the transport through the water column. They are known to accumulated at horizontal interfaces / boundaries such as the pycnocline, the OMZ (oxygen minimum zone) or the redox boundary because of slow sinking rates. Redox interfaces with stagnant deep water bodies are typical for the central Baltic. Fe belongs to the redox-sensitive elements, which means that under anoxic conditions insoluble Fe(III) species are reduced to dissolved Fe(II) species. Together with phosphorus the Fe (II) species built up a soluble compound which is kinetically convenient. This is the reason for the increasing dissolved Fe(II) concentrations in the Baltic below the redoxcline. In the deeper anoxic layers dissolved Fe concentrations are decreasing because of the formation of the thermodynamically more stable compound Fe (II) sulphide, which equilibrates the soluble species. Parallel to the enrichment of insoluble FeS in the bottom sediments, there is a diffusive transport flux of dissolved Fe(II) spezies across the redoxcline in 150m depth. Fe catalyses the uptake of nitrogen in nitrogen fixing cyanobacteria. In this context it has been assumed, that dissolved Fe(II) is the more bioavailable species for the uptake during cyanobacteria growth. This leads to the main question: “Is Iron a limiting or a promoting factor of cyanobacteria blooms in the Baltic Sea?” Therefore this project should combine how far the formation of stagnant deepwater up to anoxic conditions, the resulting change of Fe Speciation (reduction to Fe(II)) and the diffusive Fe(II) transport to the euphotic zone are responsible for the fertilisation and the increase of cyanobacteria blooms?