Methane paradox revisited: Unravelling the impacts of eutrophication on microbial methane cycling in aquatic ecosystems

Introduction

Aquatic ecosystems are a major source of the potent greenhouse gas methane, accounting for half of the global methane emissions. Biogenic methane is microbially produced in anoxic sediments and typically rapidly consumed by methanotrophic microorganisms, largely limiting emissions to the atmosphere.

The Methane Paradox

However, methane concentrations are often elevated in oxic surface waters of oceans and lakes (“methane paradox”). Aerobic methane production in surface waters might constitute a particularly important source of methane, which, due to its proximity to the atmosphere, might escape the aquatic “microbial methane filter”.

Knowledge Gaps

Yet, we currently lack a comprehensive understanding of the involved processes and microorganisms. Moreover, enhanced eutrophication of coastal ocean and lake ecosystems has been linked to increased methane emissions. Despite the immense importance of methane-cycling microorganisms in controlling emissions from these systems, we know remarkably little about how changes in environmental conditions affect their in situ activities.

Project Objectives

The METHANIAQ project addresses these knowledge gaps by:

1. Resolving and quantifying aerobic methane production in surface waters of aquatic ecosystems with different trophic states.
2. Unraveling how eutrophication affects methane-consuming microorganisms in water columns of coastal ocean and lake ecosystems.

Methodology

To tackle these objectives, I will use an innovative combination of approaches, comprising:

• In situ measurements of biogeochemical process rates.
• Manipulation experiments under controlled laboratory conditions.
• Cutting-edge molecular methods to analyze microbial communities.

Expected Outcomes

The proposed approaches will provide an integrated view from the scales of enzymes and microorganisms to ecosystem-level processes spanning marine and freshwater ecosystems. I expect this cross-disciplinary project to generate essential insights into methane cycling dynamics in aquatic ecosystems and their effect on the global climate.