Are quality and fate of DOM linked in boreal lakes? isotopic and stoichiometric approaches

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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 particularly 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 results in 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. The partitioning of carbon between atmosphere and sediments is likely also a function of DOM quality. In the past 20 years our work on carbon cycling has focused on the production and cycling of DOM using 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 will specifically examine the link between DOM quality and fate in boreal systems. We will use whole lake balances and stream studies of carbon and carbon isotopes in companion with incubations and new measures of DOM quality to address a) DOC quality and cycling in boreal lakes, rivers and streams, b) differences in DOM quality between temperate and boreal DOM, and c) the balance between CO2 production and carbon storage in lakes.