Denitrification and nitrous oxide production in aquatic systems

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The goal of my research program is to better understand major elemental cycles in aquatic systems.  Nitrogen loading to aquatic systems is the most pervasive form of chemical pollution in these ecosystems.  Some fraction of this nitrogen can be removed by denitrification (reduction of nitrate to N2), thus denitrification has the potential to improve water quality. However, a byproduct of denitrification, N2O, is a potent greenhouse gas.  Aquatic systems are already a significant source of nitrous oxide and this source is projected to increase as global use of nitrogen fertilizers, and therefore nitrogen pollution of aquatic systems, increases.  The end-products of denitrification are gases, making it challenging to measure rates of production in the field. As a result, most research on denitrification and N2O production is bench-top scale, lacking the ecological complexity of natural systems.  At this scale, it is not possible to determine the importance of higher-level physical, biological, or chemical factors that affect denitrification. We, therefore, know little about how important lakes are as sinks for nitrogen and sources for N2O.  This makes it difficult to devise effective watershed management plans for nutrients, or to constrain the global budget for greenhouse gas production in global warming models.I propose an approach to measure denitrification and N2O production in lakes at the whole-system scale. This approach is based on high-precision measurements of dissolved gases (N2 and N2O), lake mixing models, and modeled atmospheric flux. This approach should make possible construction of very accurate budgets for annual production and emissions of these gases from lakes. Students in my laboratory will use this approach to study the roles of various biological (community structure), chemical (elemental ratios), and physical attributes of lakes as potential determinants of denitrification and N2O production rates.