Towards a unifying model of Dissolved Organic Matter quality for reactivity and fate in arctic, boreal and temperate aquatic systems

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Dissolved organic matter (DOM) plays a critical role in aquatic systems. DOM frequently controls light penetration, temperature, mobility and toxicity of trace metals and organic contaminants, and the acid-base balance in acid sensitive waters. DOM is also an important energy source for bacterial metabolism. DOM in drinking water supplies increases the need for disinfection and chlorination, resulting in production of carcinogenic compounds. Unfortunately, DOM is a complex mixture of thousands of compounds that changes spatially and temporally, even from one dip sample to the next. Recent work has shown that measurements of DOC (dissolved organic carbon) concentrations alone do not adequately reflect the important functions of DOM. Measures of DOM quality are needed. In addition, the ultimate fate of DOM governs the loss of greenhouse gases (CO2) to the atmosphere from freshwater systems. DOM can be either converted to CO2 within the lake or stored in the lake sediments. However, the partitioning of carbon between atmosphere and sediments is also a function of DOM quality. In the past 25 years, our work on carbon cycling has focused on the production and cycling of DOM using novel isotopic approaches. In parallel, we have also been developing new isotopic techniques for nitrogen cycling in forested and agricultural catchments. This proposal continues the development of innovative approaches to carbon and nitrogen cycling. In the next phase, we develop and test a nascent model of DOM that is explicitly linked to DOM reactivity and fate. We will use a combination of field studies of carbon and carbon isotopes in companion with incubation experiments and new analytical techniques for DOM quality to address a) DOC quality and cycling in ground waters, lakes, rivers and streams, b) the sources, quality and disinfection by-product formation potential of urban sources of DOM, and c) the quality and fate of DOM from melting of permafrost in Canada’s north, and d) the effect of DOM quality on the balance between CO2 production and carbon storage in lakes.