OPUS MCS: Developing a mechanistic understanding of methane production from small agricultural reservoirs in the Amazon-Cerrado frontier

Woodwell Climate Research Center, Inc., Falmouth MA

Investigators

Abstract

Damming small tropical streams has created hundreds of thousands of artificial reservoirs across Brazil’s agricultural frontier, a lasting legacy of the country’s long history of cattle ranching. The low-oxygen conditions in these water bodies favors production of methane – a potent greenhouse gas that is twenty-five times more powerful than carbon dioxide. Although these water bodies are widespread and can persist for decades, we know little about the factors controlling methane production in reservoirs, or their collective contribution to the global carbon budget. This OPUS award addresses that knowledge gap by supporting new research, relevant training, and mentorship opportunities for the principal investigator. Exposure to cutting-edge lab techniques will allow her to examine the mechanisms underlying methane production in reservoirs and expand the scope of her future research. Resulting datasets will be useful for scientists modeling the global carbon cycle, as well as national agencies tasked with monitoring sources and sinks of greenhouse gases. They also have practical applications for the management of reservoirs in Brazil and other tropical regions. Ultimately, results will improve understanding of which pathways dominate methane fluxes and help identify potential management strategies to reduce greenhouse gas emissions in agricultural landscapes. By facilitating the synthesis of data collected with this award with datasets from over a decade of research in the southeastern Amazon, this project will address several key research objectives. First, it will help clarify the pathways of methane production and consumption through analyses of stable isotopes (13C, D) and the dynamics of sediment accumulation and organic carbon burial in reservoirs. Second, it will shed light on the relative importance of different sources of organic matter driving microbial methane production using a combination of radiocarbon (14C) and stable isotope analyses. Carbon isotopes in sediments may also yield insights into the relative importance of external sources of organic matter (i.e. carbon derived from forest, pasture grasses, or soybeans) versus internal production (i.e. algae or macrophytes stimulated by recent nutrient deposition). Lastly, this work will inform global modeling efforts by characterizing the isotopic fingerprint of biogenic reservoir emissions in the atmosphere and evaluating their relative importance as a methane source. Ultimately, carbon isotopes may provide important clues about whether reservoirs act as a global source or sink of carbon in the landscape. 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.