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

锰（Mn）的可能价态的数目呈现这种必需微量元素络合物的环境行为。直到最近，人们一直认为天然沃茨主要是由二价形式，锰（II），及其相关的水的物种，而三价，锰（III），和四价，锰（IV），形式只出现作为胶体。然而，最新的海洋和河口环境的实地研究表明，锰（III）是总溶解锰池的主要部分。通过氧化和还原途径生成的Mn（III）通过这些沃茨中的天然有机配体稳定。我们假设，Mn（III）是一个无处不在的组件，即使在土壤的水相，因为这两种途径发生在土壤和无所不在的溶解有机质（DOM）可以作为Mn（III）的配体。然而，有关溶解在土壤中的Mn（III）的知识是非常有限的。该提案的目标是：（一）澄清不同的还原-氧化（氧化还原）条件对不同性质的土壤中锰形态的影响;（二）揭示各种天然有机配体对合成锰氧化物溶解和随后释放的锰形态的影响;（三）证明在野外条件下土壤溶液和森林地面沥滤液中存在Mn（III）。Mn的形态将使用分光光度动力学方法来实现，该方法区分Mn（II）以及Mn（III）的弱有机络合物和强有机络合物。在不同氧化还原状态下，锰的形态将在实验室中使用控制氧化还原电位的微观实验进行研究。每两个土层从三个土壤（一个滞育土和两个潜育土），不同的水分状况，土地利用和物理化学性质将进行调查。使用代表性氧化还原循环在生物反应器中孵育土壤悬浮液。将在批量实验中确定从moder和莫尔中获得的DOM对水钠锰矿和锰锰矿溶解的影响以及释放的Mn的形态，特别关注反应动力学和pH的影响。为了确定Mn（III）是否是野外条件下土壤的组分，将在四种矿物土壤中研究土壤溶液和森林地面沥滤液（两种潜育土，一种滞育土和一种形成土）和一种有机土（组织土）。我们的研究结果将提供第一次深入了解Mn（III）在土壤溶液中的发生和行为。忽略中间锰物种将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）的环境重要性归因于其在土壤有机质分解、颗粒有机碳氧化成温室气体二氧化碳和有机污染物降解中的关键参与。

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.