Carbon-water cycle, inland waters, organic-inorganic interactions, manganese, organic matter

水环境中的溶解有机物（DOM）是全球碳循环的重要组成部分，支持着各种生态系统服务。DOM在操作上被定义为不被过滤保留的有机物质（孔径范围为0.2至0.7 μ m），并且是富含酚、羧酸的材料的复杂混合物，其通常被统称为腐殖物质（Hawkes等人，2019年）。然而，DOM的浓度、组成和化学性质取决于来源（例如，外来的与本地的）而高度可变，还存在各种其他重要的DOM化合物，包括生物聚合物、酸和中性物（佩雷拉等人，2014）。各种因素可以影响水中DOM的组成，包括温度、离子强度、pH、主要阳离子组成和共运输沉积物的表面化学（例如，Leenheer等人，2003年）。DOM通过光化学和微生物活性的进一步转化增加了其组成的可变性（例如，Battin等人，二○ ○九年;和Benner和Kaiser，2011）。锰（Mn）氧化物是DOM反应性的重要介质，其参与氧化和还原过程，在某些条件下可以改变组成（约翰逊等人，2015）。例如，Mn添加到DOM的腐殖物质池中可以产生低分子量（LMW）有机基质，支持微生物活性和更广泛的河流生态系统功能（Sunda & Kieber，1994）。细菌对锰的氧化也被证明是将二氧化碳转化为生物质的重要过程（Yu & Leadbetter，2020）。然而，虽然已经确定了一些关键途径，特别是着眼于腐殖物质的作用，但关于Mn如何在更广泛的DOM池中相互作用以及在何种条件下有利于这些反应在水生连续体中发生，存在着关键的知识空白（Allard等人，2017年）。这个博士研究生将首次调查锰氧化物影响DOM反应性的不确定性，沿着从温带（英国）和热带（圭亚那）沃茨的陆地-海洋横断面。一个关键的重点将是调查分区的DOM-Mn相互作用从土壤，淡水，河口/海洋沃茨在不断变化的物理条件下，在莱尔中心气候控制设施，并检查微生物的反应。

Dissolved organic matter (DOM) in aquatic environments is a fundamental part of the global carbon cycle supporting a variety of ecosystem services. DOM is operationally defined as organic matter that is not retained by filtration (pore sizes ranging from 0.2 to 0.7 um) and is a complex mixture of phenolic, carboxylic acid rich material that is often collectively referred to a humic substances (Hawkes et al., 2019). However, DOM concentration, composition, and chemistry are highly variable dependant on the source (e.g. allochthonous vs autochthonous) with a variety of other important DOM compounds also present including biopolymers, acids, and neutrals (Pereira et al., 2014). Various factors can influence the composition of DOM in water including temperature, ionic strength, pH, major cation composition, and the surface chemistry of co-transported sediments (e.g. Leenheer et al., 2003). Further transformations of DOM by photochemical and microbial activity increase its compositional variability (e.g. Battin et al., 2009; and Benner and Kaiser, 2011).Manganese (Mn)-oxides are important mediators of DOM reactivity involved in both oxidation and reduction processes that under certain conditions can modify the composition (Johnson et al., 2015). For example, Mn additions to the humic substances pool of DOM can produce lower molecular weight (LMW) organic substrates that support microbial activity and wider river ecosystem functions (Sunda & Kieber, 1994). Mn oxidation by bacteria has also been shown to be an important process to CO2 into biomass (Yu & Leadbetter, 2020). However, while some key pathways have been identified looking specifically at the role of humic substances, there is a critical knowledge gap on how Mn interacts within the wider DOM pool and under which conditions are favourable for these reactions to occur in the aquatic continuum (Allard et al., 2017). This PhD studentship will investigate for the first time the uncertainties in which Mn oxides impact DOM reactivity along a land-ocean transect from temperate (UK) and tropical (Guyana) waters. A key focus will be to investigate the partitioning of DOM-Mn interactions from soil, fresh, and estuarine/marine waters under changing physical conditions in the Lyell Centre climate-controlled facilities and examine the microbial response.