Quantifying Methane Ebullition in a Freshwater Lake with Passive Acoustic Monitoring and Digital Signal Processing 41 views

Methane is a potent greenhouse gas with a disproportionate impact on global warming. The majority of natural methane emissions are produced by aquatic ecosystems, with lakes representing the largest aquatic source. However, quantifying aquatic methane remains expensive, labor-intensive, and prone to error. These measurement limitations lead to underrepresentation of aquatic emissions in global methane budgets and climate models and, consequently, to misinformed climate policy and carbon credit valuation. This study sought to advance passive acoustic monitoring, a promising alternative to traditional ebullition quantification techniques, by developing a digital signal processing (DSP) program that automates bubble event and frequency detection and calculates the total methane volume to estimate flux. The program and methodology were calibrated and tested in controlled laboratory experiments before being applied to a northern Wisconsin lake. Laboratory trials revealed a strong negative relationship between bubble volume and frequency for uniform bubbles released directly into the water column, but this relationship weakened for inconsistent bubbles that travelled through sediment before reaching the water. The DSP program produced accurate volume estimates for all exposed tube sizes, but overestimated bubble counts and volume for smaller buried tubes. Although the program successfully identified natural bubble events and produced annual flux estimates for field recordings, these values varied widely and were much lower than a previous gas trap estimate. Overall, this study demonstrates that passive acoustic monitoring is a promising and efficient method for quantifying methane ebullition, but the method must be further refined and validated before it can reliably characterize entire ecosystems.

BS (Bachelor of Science)

methane ebullition; passive acoustic monitoring; digital signal processing; lake methane emissions; blue carbon

English

2026-10-02