Is manganese(III) a ubiquitous part of the total dissolved manganese in soil solutions?

锰(III) 是土壤溶液中溶解锰总量中普遍存在的部分吗？

• 批准号: 426549767
• 负责人: Professor Dr. Tim Mansfeldt
• 金额: --
• 依托单位: Geographisches Institut
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2019
• 资助国家: 德国
• 起止时间: 2018-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/426549767?language=en
• 关键词: manganese; III; ubiquitous; part; total

The number of possible valence states of manganese (Mn) renders the environmental behavior of this essential trace element complex. Until recently, it was assumed that natural waters are dominated by the divalent form, Mn(II), and its related aqueous species, whereas the trivalent, Mn(III), and tetravalent, Mn(IV), forms occur exclusively as colloids. The latest field studies of marine and estuarine environments, however, revealed that Mn(III) is a major part of the total dissolved Mn pool. Mn(III), which is generated by both oxidative and reductive pathways, is stabilized by natural organic ligands in these waters. We postulate that Mn(III) is a ubiquitous component, even in the aqueous phase of soils, because both pathways take place in soils and the omnipresent dissolved organic matter (DOM) can act as a ligand for Mn(III). However, knowledge concerning dissolved Mn(III) in soils is extremely limited. The objectives of this proposal are: (i) to clarify the influence of different reduction-oxidation (redox) conditions on Mn speciation in soils with different properties; (ii) to reveal the effects of various natural organic ligands on the dissolution of synthetic Mn oxides and the subsequent speciation of released Mn; and (iii) to prove the existence of Mn(III) in soil solutions and forest floor leachates in field conditions. Speciation of Mn will be achieved using a spectrophotometric kinetic method which differentiates Mn(II), as well as weak and strong organic complexes of Mn(III). The speciation of Mn under different redox regimes will be studied using microcosm experiments with controlled redox potential in the laboratory. Each of two soil horizons from three soils (one Stagnosol and two Gleysols) which differ in their water regime, land use and physicochemical properties will be investigated. Soil suspensions will be incubated in a bioreactor using representative redox cycles. The influence of DOM obtained from moder and mor on the dissolution of birnessite and manganite and the speciation of the released Mn will be determined in batch experiments, with special focus on the reaction kinetics and the effects of pH. To determine whether Mn(III) is a component of soil in field conditions, soil solutions and forest floor leachates will be investigated in four mineral soils (two Gleysols, a Stagnosol and a Cambisol) and one organic soil (Histosol). Our findings will provide the first insight into the occurrence and behavior of Mn(III) in soil solutions. Neglecting the intermediate Mn species would underestimate the redox capacity of the soluble Mn pool in soil solutions. The environmental significance of the strong oxidant, Mn(III), is attributed to, among other factors, its critical involvement in the breakdown of soil organic matter, oxidation of particulate organic carbon to the greenhouse gas carbon dioxide, and degradation of organic contaminants.

锰（MN）可能的价态数量使这种基本痕量元素复合物的环境行为。直到最近，假定天然水是由Mn（II）及其相关水物种主导的，而三价，Mn（III）和MN（IV）的三价（III）（IV）形式仅作为胶体出现。然而，对海洋和河口环境的最新现场研究表明，MN（III）是溶解的MN池的主要部分。由氧化和还原途径产生的Mn（III）被这些水中的天然有机配体稳定。我们假设MN（III）是一种无处不在的成分，即使在土壤的水相中，这两种途径都在土壤中发生，并且无所不在的溶解有机物（DOM）可以充当MN（III）的配体。但是，关于土壤中溶解的Mn（III）的知识极为有限。该提案的目标是：（i）阐明不同还原氧化（氧化还原）条件对具有不同特性的土壤中MN物种形成的影响； （ii）揭示各种天然有机配体对合成Mn氧化物溶解的影响以及随后释放的MN的物种； （iii）证明在土壤溶液和森林地板中存在Mn（iii）在田间条件下渗出。将使用分光光度动力学方法来实现MN的形态，该方法将Mn（III）和弱和强的有机络合物（III）区分开来。将使用在实验室中具有控制的氧化还原电位的微观实验来研究MN在不同氧化还原方面的物种形成。将研究来自三个土壤（一种stagnosol和两个gleysols）的两个土壤层中的每一个，它们的水状态，土地使用和物理化学特性不同。土壤悬浮液将使用代表性的氧化还原周期在生物反应器中孵育。从Moder和MOR获得的DOM对Birnese和锰矿的溶解以及已释放的MN的物种形成的影响将在批处理实验中确定，特别关注反应动力学和pH的影响。为了确定Mn（III）是否是土壤条件下土壤的组成部分，将在四个矿物质土壤（两个gleysols，stagnosol和casbisol）和一个有机土壤（Hamposol）中研究土壤溶液和森林地板渗滤液。我们的发现将为MN（III）在土壤溶液中的发生和行为提供首次见解。忽略中间MN物种会低估土壤溶液中可溶性MN池的氧化还原能力。强氧化剂MN（III）的环境意义归因于其在土壤有机物分解的关键参与，颗粒有机碳对温室气二氧化碳碳氧化的氧化以及有机污染物的降解。