The Influence of Bioturbation on Iron and Sulphur Cycling in Marine Sediments: A Model Analysis
The Influence of Bioturbation on Iron and Sulphur Cycling in Marine Sediments: A Model Analysis
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DOI：
10.1007/s10498-016-9301-7
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发表时间：
2016-09
影响因子：
1.6
通讯作者：
S. J. van de Velde;F. Meysman
中科院分区：
文献类型：
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作者：
S. J. van de Velde;F. Meysman
海洋沉积物中铁和硫的地球化学循环紧密交织在一起，形成了一个复杂的氧化还原和沉淀反应网络。生物扰动是指由大型生物引起的颗粒和溶质的所有运输方式，在当今的海底，生物扰动是控制铁和硫生物地球化学循环的最重要因素之一。为了更好地理解生物扰动如何控制铁和硫循环，我们建立了受动物活动影响的沿海沉积物反应输运模型。随后，我们进行了模型敏感性分析，分别研究了两种不同的生物扰动传输模式，即生物混合（固体颗粒传输）和生物灌溉（增强溶质传输）。这一分析表明，生物混合和生物灌溉对铁和硫的循环都有明显的、而且在很大程度上是相反的影响。生物混合增强了氧区和亚氧区之间的运输，从而促进氧化物质（如氧化铁）的还原和被还原物质（如硫化铁）的氧化。通过对硫化铁的再氧化，生物混合极大地促进了铁和硫在还原态和氧化态之间的再循环。另一方面，生物灌溉从沉积物孔隙水中去除还原溶质，即亚铁和游离硫化物。然后，这些被还原的物质在上覆的水中再氧化，而不是在沉积物柱中再循环，这导致铁和S的再循环减少。总的来说，我们的研究结果表明，在评估大型动物对沉积物地球化学的影响时，它们的生态学（诱导生物混合或生物灌溉，或两者兼而有之）很重要。这一发现似乎与寒武纪过渡时期的沉积循环特别相关，当时底栖动物开始殖民和改造海底。
The geochemical cycles of iron and sulphur in marine sediments are strongly intertwined and give rise to a complex network of redox and precipitation reactions. Bioturbation refers to all modes of transport of particles and solutes induced by larger organisms, and in the present-day seafloor, bioturbation is one of the most important factors controlling the biogeochemical cycling of iron and sulphur. To better understand how bioturbation controls Fe and S cycling, we developed reactive transport model of a coastal sediment impacted by faunal activity. Subsequently, we performed a model sensitivity analysis, separately investigating the two different transport modes of bioturbation, i.e. bio-mixing (solid particle transport) and bio-irrigation (enhanced solute transport). This analysis reveals that bio-mixing and bio-irrigation have distinct—and largely opposing effects on both the iron and sulphur cycles. Bio-mixing enhances transport between the oxic and suboxic zones, thus promoting the reduction of oxidised species (e.g. iron oxyhydroxides) and the oxidation of reduced species (e.g. iron sulphides). Through the re-oxidation of iron sulphides, bio-mixing strongly enhances the recycling of Fe and S between their reduced and oxidised states. Bio-irrigation on the other hand removes reduced solutes, i.e. ferrous iron and free sulphide, from the sediment pore water. These reduced species are then reoxidised in the overlying water and not recycled within the sediment column, which leads to a decrease in Fe and S recycling. Overall, our results demonstrate that the ecology of the macrofauna (inducing bio-mixing or bio-irrigation, or both) matters when assessing their impact on sediment geochemistry. This finding seems particularly relevant for sedimentary cycling across Cambrian transition, when benthic fauna started colonizing and reworking the seafloor.