Organic matter dynamics in aquatic environments using bulk, molecular and isotopic methods

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I propose to continue research initiated in the past 5 years on the forms, sources, reactions, and fates of quantitatively important forms of organic matter (OM) in aquatic environments. The central themes of this program are to develop new analytical methods (bulk, molecular and isotopic) that can be applied to organic mixtures, and to use these methods to test hypotheses about processes affecting OM cycling in aquatic systems. Previously centered on recent marine sediments, our program was spatially and temporally diversified during the last funding cycle with the addition of freshwater and paleoceanography components. The following major themes will be addressed in the next 5 years: (1) we will target the interactions between OM and Fe/Mn (oxy)hydroxides in sediments, and their role in OM cycling and preservation; (2) we will use an unique method for the measurement of the d13C signature of marine DOC, in combination with bulk and molecular level analyses, to study the links between OM composition changes and microbial dynamics as assessed by molecular ecology, metagenomic and gene expression approaches (with David Walsh, Concordia) in the perennially hypoxic St. Lawrence Estuary; (3) we will study on the aquatic cycles of C and N in natural and logging-impacted lakes and reservoirs of the boreal forest to better understand the impact of human perturbations and seasonal variations on the emissions of greenhouse gases from these systems; (4) we will revisit molecular-based methods for the analysis of organic biomarkers to take into account the large bias introduced by OM interactions with Fe/Mn hydroxides in solid samples. The molecularly uncharacterized component of aquatic OM represents one of the greatest analytical frontiers remaining in biogeochemistry. Developing new analytical strategies may thus be a fundamental prerequisite for obtaining mechanistic understanding of OM cycling and preservation in lakes, estuaries and the ocean. Our work on OM interactions with Fe/Mn hydroxides, in particular, is very promising.