An enhanced bubble size sensor for long‐term ebullition studies

Abstract

Methane ebullition from freshwater sediments is a significant source of greenhouse gas to the atmosphere. Methane bubble size determines the fraction of methane that dissolves into the water column instead of entering the atmosphere, but current methods to measure bubble sizes in situ are limited. Previously, we reported the design for a novel optical bubble size sensor capable of measuring methane bubble sizes in situ. Here, we report sensor enhancements to allow for continuous long‐term sensor deployment, uninterrupted data collection under high ebullition flux, and improved bubble volume measurement accuracy. The enhanced design includes a data and power cable running from the sensor to a custom data buoy housing batteries and an SD memory card. Batteries and SD cards are replaced every 2–4 weeks through the data buoy, allowing for continuous, undisturbed sensor deployment. In addition, sensor parameters have been tuned to reduce error from particle intrusion and fluctuations in raw signals that were observed during transit of some bubbles through the sensor. Field data show that on average the sensor measures cumulative bubble volumes equaling approximately 86% of collected gas volumes. We discuss potential mechanisms of remaining error, some of which may be due to zooplankton intrusion, and suggest directions for future sensor enhancements.

The Magnitude and Drivers of Methane Ebullition and Diffusion Vary on a Longitudinal Gradient in a Small Freshwater Reservoir

“…For example, rapid decreases in barometric pressure and hydrostatic pressure that occur within short time periods (<24 hr) have been shown to substantially increase ebullition rates (Casper et al, 2000). Using alternate methods such as echo sounders (Ostrovsky, 2003;Tušer et al, 2017) and automated bubble traps (Delwiche & Hemond, 2017;Varadharajan et al, 2010) for measuring ebullition may provide insight on the drivers of ebullition rates at shorter time scales.…”

Using Noble Gases to Compare Parameterizations of Air‐Water Gas Exchange and to Constrain Oxygen Losses by Ebullition in a Shallow Aquatic Environment

“…Direct measurements of ebullition are challenging (e.g. Delwiche & Hemond, ) and typically cannot yet be parameterized. However, ebullition has been measured to be a major gas efflux pathway relative to diffusive exchange in some shallow aquatic settings for biologically generated gases including nitrogen (N 2 ; ebullition flux in a pond similar to diffusive fluxes in other settings; Gao et al, ), CH 4 and CO 2 (ebullition 95–97% of CH 4 and 13–35% of CO 2 net fluxes in a rice paddy; Komiya et al, ), and O 2 (10–22% of net fluxes in a lake and reservoir; Koschorreck et al, ).…”

Ebullition of oxygen from seagrasses under supersaturated conditions

“…Although substantial qualitative evidence exists for the formation and ebullition of bubbles in photosynthetic systems, little attention has been applied to quantifying seagrass oxygen ebullition rates and the in situ conditions that promote bubble formation. Acoustic seagrass mapping and detection of free bubbles has been explored as a tool for estimating photosynthesis (Wilson and Dunton ; Wilson et al , ; Felisberto et al ), optical detectors have been used to quantify bubble spatiotemporal distribution and size (Delwiche and Hemond , b ), and models using noble gas concentrations have been developed to estimate ebullition rates (Howard et al ). However, these methods have not conducted direct measurements of bubble O 2 content, which is needed to accurately determine the fraction of total photosynthetic O 2 released as bubbles.…”