The role of dissolved gas fluxes on the biogeochemical evolution of nutrient cycles in lakes.

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Biogeochemical pathways, including those of nitrogen (N), oxygen (O), and phosphorus (P) are mediated by microbes. As the two most abundant elements in the Earth’s atmosphere, N (as N2) and O (as O2), are gaseous species that are important for their cycling processes. O2 is a very important component in ecosystem metabolism, which includes photosynthesis and respiration, and N2 is important for N2 fixation and denitrification. P does not have a major gas component in lake ecosystems, but its cycling is very dependent on O2 concentrations. Anthropogenic activities have increased the reactive N and P pools in freshwater, and the increase in reactive N and P is known as eutrophication. Denitrification, the reduction of nitrate (NO3-) and nitrite (NO2-) to N2, biologically removes N from lakes and helps alleviate the effects of eutrophication. Once O2 in the water column is depleted, denitrifiers can use NO3- as their terminal electron acceptor. P, on the other hand, will either bind to metals or be released depending on the surrounding O2 concentrations. The binding of reactive P in oxic conditions can remove it from the water and potentially bury it for long periods of time until it is released when conditions become anoxic. The overall objective of this project was to quantify N, O, and P dynamics at various spatial, temporal, and experimental scales. This included both water column and sediment cycling, as well as seasonal and year-long studies. More specifically, this project aimed to 1) estimate ecosystem O2 metabolism using membrane inlet mass spectrometry, 2) study N2 accumulation and drawdown in a stratified and well-mixed reservoir, and 3) measure sediment N and P dynamics in differing redox conditions. Taken together, these projects have continued adding to the growing literature about the coupling of biogeochemical cycles, as the interactions of dissolved gases between the water column, sediment, and atmosphere are important for determining the dynamics of an ecosystem.

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