Simmler Michael, Bommer Jérôme, Frischknecht Sarah, Christl Iso, Kotsev Tsvetan, Kretzschmar Ruben
Institute of Biogeochemistry and Pollutant Dynamics, Department of Environmental Systems Science, CHN, ETH Zurich, Zurich, Switzerland.
Institute of Biogeochemistry and Pollutant Dynamics, Department of Environmental Systems Science, CHN, ETH Zurich, Zurich, Switzerland.
Environ Pollut. 2017 Dec;231(Pt 1):722-731. doi: 10.1016/j.envpol.2017.08.054. Epub 2017 Aug 29.
Mining activities have contaminated many riverine floodplains with arsenic (As). When floodplain soils become anoxic under water-saturated conditions, As can be released from the solid phase. Several microbially-driven As solubilization processes and numerous influential factors were recognized in the past. However, the interplay and relative importance of soil properties and the influence of environmental factors such as temperature remain poorly understood, especially considering the (co)variation of soil properties in a floodplain. We conducted anoxic microcosm experiments at 10, 17.5, and 25 °C using 65 representative soils from the mining-impacted Ogosta River floodplain in Bulgaria. To investigate the processes of As solubilization and its quantitative variation we followed the As and Fe redox dynamics in the solid and the dissolved phase and monitored a range of other solution parameters including pH, Eh, dissolved organic C, and dissolved Mn. We related soil properties to dissolved As observed after 20 days of microcosm incubation to identify key soil properties for As solubilization. Our results evidenced reductive dissolution of As-bearing Fe(III)-oxyhydroxides as the main cause for high solubilization. The availability of nutrients, most likely organic C as the source of energy for microorganisms, was found to limit this process. Following the vertical nutrient gradient common in vegetated soil, we observed several hundred μM dissolved As after 1-2 weeks for some topsoils (0-20 cm), while for subsoils (20-40 cm) with comparable total As levels only minor solubilization was observed. While high Mn contents were found to inhibit As solubilization, the opposite applied for higher temperature (Q 2.3-6.1 for range 10-25 °C). Our results suggest that flooding of nutrient-rich surface layers might be more problematic than water-saturation of nutrient-poor subsoil layers, especially in summer floodings when soil temperature is higher than in winter or spring.
采矿活动已使许多河漫滩受到砷（As）污染。当河漫滩土壤在水饱和条件下缺氧时，砷可从固相释放出来。过去人们认识到了几种微生物驱动的砷溶解过程以及众多影响因素。然而，土壤性质之间的相互作用和相对重要性，以及温度等环境因素的影响，仍然了解甚少，尤其是考虑到河漫滩土壤性质的（共同）变化。我们在10℃、17.5℃和25℃下，使用来自保加利亚受采矿影响的奥戈斯塔河河漫滩的65种代表性土壤进行了缺氧微观实验。为了研究砷的溶解过程及其定量变化，我们跟踪了固相和溶解相中砷和铁的氧化还原动力学，并监测了一系列其他溶液参数，包括pH值、氧化还原电位、溶解有机碳和溶解锰。我们将土壤性质与微观实验培养20天后观察到的溶解砷相关联，以确定砷溶解的关键土壤性质。我们的结果证明，含砷铁（III）氢氧化物的还原溶解是高溶解率的主要原因。发现养分的有效性，最有可能是作为微生物能量来源的有机碳，限制了这一过程。遵循植被土壤中常见的垂直养分梯度，我们在1-2周后观察到一些表层土壤（0-20厘米）中有数百微摩尔的溶解砷，而对于总砷含量相当的下层土壤（20-40厘米），只观察到少量溶解。虽然发现高锰含量会抑制砷的溶解，但温度升高时情况相反（10-25℃范围内的温度系数Q为2.3-6.1）。我们的结果表明，营养丰富的表层土壤被淹没可能比营养贫瘠的下层土壤水饱和问题更大，尤其是在夏季洪水期间，此时土壤温度高于冬季或春季。
