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

水环境中的溶解有机物(DOM)是全球碳循环的基本组成部分，支持多种生态系统服务。DOM在操作上被定义为不被过滤保留的有机物质(孔径从0.2到0.7微米不等)，是一种富含酚酸、羧酸的复杂混合物，通常统称为腐殖质(Hawkes等人，2019年)。然而，DOM的浓度、组成和化学高度依赖于来源(例如，异地与本地)，也存在各种其他重要的DOM化合物，包括生物聚合物、酸和中性物质(Pereira等人，2014年)。各种因素可以影响水中DOM的组成，包括温度、离子强度、pH、主要阳离子组成以及共输送沉积物的表面化学(例如Leenheer等人，2003年)。通过光化学和微生物活动进一步转化DOM增加了其组成的可变性(例如Battin等人，2009年；以及Benner和Kaiser，2011年)。锰(锰)氧化物是DOM反应活性的重要媒介，参与氧化和还原过程，在某些条件下可以改变组成(Johnson等人，2015)。例如，向DOM的腐殖质池中添加锰可以产生支持微生物活动和更广泛的河流生态系统功能的低分子量(LMW)有机底物(Sunda&Kieber，1994)。细菌对锰的氧化也被证明是二氧化碳转化为生物质的重要过程(Yu&LeadBetter，2020)。然而，尽管已经确定了一些关键途径，具体着眼于腐殖质的作用，但关于锰如何在更广泛的DOM池内相互作用以及在什么条件下有利于这些反应在水生连续体中发生存在关键的知识缺口(Allard等人，2017年)。这个博士生将首次研究在温带(英国)和热带(圭亚那)水域的陆地-海洋横断面上，锰氧化物影响DOM反应的不确定性。一个关键的重点将是在莱尔中心气候控制设施中调查土壤、淡水和河口/海洋水域在不断变化的物理条件下DOM-Mn相互作用的分配情况，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.