Dissolved organic matter in aquatic systems: factors affecting its role in greenhouse gas formation

溶解有机物质(DOM)是一种复杂的物质混合物，对水生生态系统的物理和化学环境有很大的影响。DOM控制或影响许多生物过程，如对许多痕量金属的吸收。尽管DOM同时产生于流域的陆地和水生部分，但在营养贫乏的北方湖泊中，DOM大多起源于系统的陆地部分。当这种物质在生态系统中运输时，它经历了影响其数量和质量的变化。这些变化主要是由光化学和微生物过程引起的，它们既改变了DOM的化学结构，也改变了DOM的命运。DOM在水环境中有两种主要的损失机制。输入湖泊的DOM中的一些转化为颗粒物，其中一些最终进入湖泊沉积物，另一些最终成为二氧化碳，这是一种重要的温室气体。因此，DOM对温室气体排放的潜在贡献是巨大的。了解这一来源有多大是很重要的。随着湖泊pH的降低，导致温室气体的光化学途径的相对重要性增加，而且还受到其他外部因素的影响。我们将量化这些因素的重要性。此外，涉及DOM化学性质的内在因素会影响分解途径；我们将再次量化这些关系。后一项调查结果对《京都议定书》要求的影响将是本研究的重点。

Dissolved organic matter (DOM) is a complex mixture of substances that affects the physical and chemical environment of aquatic ecosystems very substantially.  DOM controls or influences many biological processes, e.g. the uptake of many trace metals.  Although DOM is produced in both the terrestrial and aquatic components of catchments, most of the DOM in nutrient-poor Boreal lakes originates in the terrestrial part of the system.  As this material is transported through the ecosystem, it undergoes transformations that affect its quantity and quality.  These changes are largely caused by photochemical and microbial processes, and they result in both altered chemical structure of the DOM and altered fate of the DOM.   There are two major loss mechanisms for DOM in the aquatic environment.  Some of the DOM that is input to lakes is transformed into particulate matter, some of which ends up in lake sediments, while some ends up as carbon dioxide, an important greenhouse gas.  The potential contribution of DOM to greenhouse gas emissions is large. It is important to understand how large this source is.  The relative importance of the photochemical pathway which leads to greenhouse gases increases as lake pH decreases, and is also affected by other external factors.  We will quantify the importance of these factors.  In addition, intrinsic factors concerning the chemical nature of the DOM affect the breakdown pathway; again, we will quantify these relationships. The implications of the latter finding to requirements of the Kyoto accord will be the focus of this study.