Nitrite-dependent methane oxidation: an overlooked nitrogen sink in riparian zones

The wetlands

wetland

An area of land that is periodically saturated with water, which influences the types of plants and animals that can live there. Wetlands include swamps, marshes, bogs, and other similar areas.

Source: A student's guide to Global Climate Change Source

adjacent to streams (riparian zones) provide critical services to ecosystems.

ecosystem

A natural community of plants, animals, and other living organisms and the physical environment in which they live and interact.

Source: A student's guide to Global Climate Change Source

These services include supporting diverse microbial communities that break down pollutants and regulate the cycling of carbon and greenhouse gases, such as methane.

methane

A hydrocarbon that is a primary component of natural gas. Methane is also a greenhouse gas (GHG), so its presence in the atmosphere affects the earth’s temperature and climate system

Source: EPA Source

Fertilizer runoff from agriculture can disrupt the services provided by riparian zone microorganisms, for example by shifting the availability of oxygen for microbial metabolism. Current models that predict how excess nitrogen

nitrogen

Nitrogen, represented by the symbol N and atomic number 7, is a colorless, odorless, and tasteless gas that constitutes approximately 78% of Earth's atmosphere. It is vital for all life forms, as it is a fundamental part of amino acids, proteins, and DNA.

Source: Source

from fertilizer influences stream-associated methane cycling are limited by focusing primarily on metabolisms that operate in the presence of oxygen. These models are incomplete if they do not account for methane consumption due to oxygen-independent metabolisms. This project investigates a potentially overlooked contribution by bacteria that thrive in the absence of oxygen and derive energy by linking the consumption of methane to nitrogen supplied by fertilizer or other sources. In preliminary studies, we detected the bacteria associated with this process – termed nitrite-dependent anaerobic methane oxidation (N-DAMO) – at relatively high abundance in agriculturally-influenced riparian zones of the Judith River Watershed

watershed

An area of land that channels rainfall and snowmelt to creeks, streams, and rivers, and eventually flows to the lowest point in a basin.

Source: USGS Source

(JRW), Central Montana. We hypothesize that N-DAMO is an important methane-consuming process sensitive to environmental change in these and other riparian zones. We will test the role of N-DAMO and other oxygen-independent methane-consuming processes using a combination of environmental sampling over temporal and spatial gradients in the JRW, experimental manipulations, and biogeochemical modeling. This work will 1) map the amount and distribution of soil porewater methane, nitrogen, and other important chemicals acted upon by microorganisms, 2) use isotope-labeling to quantify the rates at which microorganisms consume methane and nitrogen under different oxygen regimes, 3) verify how changes in riparian zone chemistry are linked to the metabolic diversity (genomics)

genomic

An interdisciplinary field of science that focuses on the structure, function, evolution, mapping, and editing of genomes.

Source: energy.gov Source

and gene expression of the resident microbial community, and 4) develop a solute transport model that uses knowledge of chemistry and gene distributions to predict the contribution of oxygen-independent microorganisms to methane consumption. Results of this project will help predict the fate of methane and nitrogen in stream-associated wetlands, notably under increasing disturbances associated with human activity.