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

锰（Mn）的可能价态的数量呈现了这种必需微量元素复合物的环境行为。直到最近，人们一直认为天然水中主要是二价形式的Mn（II）及其相关的水相，而三价形式的Mn（III）和四价形式的Mn（IV）只以胶体的形式存在。然而，最近对海洋和河口环境的实地研究表明，Mn（III）是溶解Mn库的主要组成部分。Mn（III）通过氧化和还原两种途径生成，在这些水体中被天然有机配体稳定。我们假设Mn（III）是一种普遍存在的成分，即使在土壤的水相中，因为这两种途径都发生在土壤中，而且无处不在的溶解有机物（DOM）可以作为Mn（III）的配体。然而，关于土壤中溶解的锰（III）的知识是非常有限的。本提案的目的是：(i)阐明不同还原-氧化（氧化还原）条件对不同性质土壤中Mn形态的影响；（ii）揭示各种天然有机配体对合成锰氧化物的溶解和随后释放的锰形态的影响；以及（iii）在野外条件下证明土壤溶液和森林地面渗滤液中Mn（iii）的存在。Mn的形态将通过分光光度动力学方法来实现，该方法可以区分Mn（II）以及Mn（III）的弱和强有机配合物。在实验室中，通过控制氧化还原电位的微观实验，研究了锰在不同氧化还原机制下的形态。将对三种土壤（一种牡藓土和两种gleysol）的两个土壤层中的每一个进行调查，这些土壤层的水分状况、土地利用和物理化学性质都不同。土壤悬浮液将在具有代表性的氧化还原循环的生物反应器中培养。从现代和现代获得的DOM对birnite和锰矿的溶解以及释放的Mn的形态的影响将在批次实验中确定，特别关注反应动力学和ph的影响。为了确定Mn（III）是否在田间条件下是土壤的组成部分，将在四种矿物土壤（两种Gleysols，一种Stagnosol和一种Cambisol）和一种有机土壤（Histosol）中研究土壤溶液和森林地表渗滤液。我们的发现将首次深入了解Mn（III）在土壤溶液中的发生和行为。忽略中间锰种会低估土壤溶液中可溶性锰库的氧化还原能力。强氧化剂Mn（III）的环境意义在于，除其他因素外，它对土壤有机质的分解、颗粒有机碳氧化为温室气体二氧化碳以及有机污染物的降解起着关键作用。

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.