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

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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.