Microbially-driven nitrous oxide transformations and fluxes in organic-poor sediments from a tropical lagoon

Area of Science:

• Environmental microbiology
• Biogeochemistry
• Coastal ecosystem science

Background:

• Nitrous oxide (N₂O) fluxes in organic-poor tropical sediments are understudied.
• Understanding N₂O cycling in these environments is crucial for global biogeochemical models.

Purpose of the Study:

• To investigate microbially-driven nitrous oxide (N₂O) transformations and fluxes in organic-poor tropical coastal sediments.
• To identify the key drivers and microbial communities involved in N₂O cycling.
• To determine if these sediments act as a source or sink for N₂O.

Main Methods:

• Intact sediment core incubations with acetylene inhibitors to quantify gas fluxes.
• Analysis of dissolved gases and nutrients at the sediment-water interface.
• 16S rRNA (V3-V4) gene sequencing to identify bacterial communities.
• Seasonal sampling to assess temperature and salinity influences.

Main Results:

• N₂O consumption was significant, driven by high oxygen uptake rates.
• Nitrate concentration at the sediment-water interface was the primary control on N₂O consumption.
• Bacterial families Neisseriaceae, Burkholderiaceae, Desulfovibrionaceae, and Clostridiaceae were key players.
• Chemoheterotrophic and chemolithotrophic pathways were vital for microbial metabolism.

Conclusions:

• Organic-poor inlet sediments in Pulicat lagoon function as a net sink for N₂O.
• These findings highlight the importance of considering organic-poor sediments in global N₂O budgets.
• Similar ecosystems may also represent significant, yet overlooked, N₂O sinks.