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

锰(Mn)的可能价态的数量决定了这种必需的微量元素络合物的环境行为。直到最近，人们一直认为天然水主要是二价态的Mn(II)及其相关的水相物种，而三价态的Mn(III)和四价态的Mn(IV)只以胶体形式存在。然而，对海洋和河口环境的最新野外研究表明，锰(III)是总溶解锰池的主要组成部分。锰(III)由氧化和还原两种途径生成，在这些水域中被天然有机配体稳定。我们推测，即使在土壤的水相中，Mn(III)也是一种普遍存在的组分，因为这两种途径都发生在土壤中，而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Mn(III)的认识是极其有限的。这项建议的目的是：(I)阐明不同还原-氧化(Redox)条件对不同性质土壤中锰形态的影响；(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的形态的影响；(Iii)在田间条件下证明土壤溶液和森林地面淋洗液中锰(III)的存在。用分光光度动力学方法区分锰(II)，以及锰(III)的弱有机络合物和强有机络合物，以实现锰的形态形成。在实验室中，利用氧化还原电位可控的微观实验，研究了不同氧化还原条件下锰的形态分布。将对三种不同水分状况、土地利用和理化性质不同的土壤(一种潮土和两种潮土)的两个土层进行调查。土壤悬浮液将在生物反应器中培养，使用典型的氧化还原循环。从MODER和MOR中得到的DOM对水钠锰矿和锰矿的溶解以及释放出的锰的形态的影响将在间歇实验中确定，特别是反应动力学和pH的影响。为了确定在田间条件下，Mn(III)是否是土壤中的一种成分，将在四种矿物土壤(两种灰壤、一种棕壤和一种风化土)和一种有机土壤(组织土)上进行土壤溶液和林地渗滤液的研究。我们的发现将对土壤溶液中Mn(III)的存在和行为提供第一个洞察力。忽略中间态锰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)的环境意义被归因于除其他因素外，它在土壤有机质的分解、颗粒有机碳被氧化为温室气体二氧化碳以及有机污染物的降解等方面具有关键作用。

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.