Collaborative Research: Influence of phosphorus deficiency on enigmatic biological methane production in oxic freshwater lakes

Montana State University, Bozeman MT

Investigators

Abstract

Atmospheric levels of methane have risen 150% since the Industrial Revolution, and continue to increase. Although energy sector and agricultural sources are major contributors, natural microbiological sources account for roughly half of total global methane emissions. Microbial methane production has long been assumed to be an anoxic process, carried out only under conditions of extremely low to zero oxygen. Recent research has demonstrated the potential for microbial methane production to occur in oxygenated upper waters of lakes and oceans through a previously unappreciated metabolic pathway present in microorganisms. Under conditions of phosphorus deficiency, certain bacteria can utilize otherwise unreactive organic molecules known as methylphosphonates to meet their phosphorus requirements, releasing methane in the process. The extent to which this mechanism supports the out-gassing of methane from lakes to the atmosphere is unknown, as are the consequences of changing environmental conditions upon it. This project will address this knowledge gap by investigating the distributions, rates of and controls on aerobic methane production in Flathead Lake and 18 other Montana lakes of varying phosphorus deficiency status. Because atmospheric deposition of pollutant nitrogen and deliberate measures to curtail phosphorus inputs to lakes can both lead to phosphorus deficiency, it is crucial that we know whether these factors may have the unexpected consequence of enhancing methane emissions. This research will also directly support the education, field and laboratory experiences of graduate and undergraduate students and will provide training to local high school teachers from Native American (Kootenai and Salish) tribal lands. This project will evaluate temporal and spatial variability in microbially-mediated, oxic methane production across lakes with varying phosphorus availability in western Montana. It is guided by the overarching hypothesis: diffusive effluxes of methane from oxic freshwater lakes are directly influenced by the nature and severity of ecosystem nutrient (nitrogen, phosphorus) deficiencies. A combination of observational and experimental approaches employing chemical, stable isotopic, metagenomic and PCR-based gene analyses will be used to examine: 1) time and space variability in the concentration, stable isotope composition, and net production of methane in freshwater lakes in Montana, focusing on Flathead Lake; 2) The extent to which microbial methylphosphonate degradation results in net production of methane in these lakes; 3) The functional diversity, abundances, and transcriptional activities of microorganisms involved in both phosphonate and methane cycling; and 4) How the stoichiometry (specifically nitrogen:phosphorus ratios) of aquatic nutrient (inorganic and total) pools influences oxic methane production and expression of methane cycling functional genes. The study will provide a systematic evaluation of microbial methane sources and the potential contribution of methylphosphonate degradation as a source of methane in oxic freshwater lakes. Results from this project will provide new insights and advance current understanding of coupled interactions between carbon and phosphorus cycling in freshwater lake habitats. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.