Pond methane dynamics, from microbial communities to ecosystem budget, during summer in Alaska

Abstract

Ponds play a larger role in the global freshwater methane (CH 4 ) budget than predicted from surface area alone. To improve our understanding of pond CH 4 dynamics, we measured summer CH 4 production, concentrations, and emissions to the atmosphere in nine Alaskan wetland ponds along with potential physical, chemical, and biological regulators. Pond CH 4 production (0.64, 0.086-1.3 mmol m À2 d À1 ; median, interquartile range), as assessed with slurry incubations, was positively related to water-column temperature and chlorophyll a (Chl a), negatively influenced by oxygen levels, and varied with microbial community structure. Average watercolumn CH 4 concentrations (0.39, 0.21-0.87 μmol L À1 ) were lower in deeper ponds and at higher oxygen levels, and as expected, they were correlated with diffusive emissions (0.055, 0.024-0.20 mmol m À2 d À1 ) assessed with flux chambers. Based on a mass balance approach, 39-99% of CH 4 produced in ponds was oxidized. Pond ebullition (3.7, 0.60-24 mmol m À2 d À1 ) was higher and more variable than diffusive emissions. Additionally, pond ebullition rates were better correlated with production rates from the previous month. We also systematically compared the ratio of ebullition to diffusive CH 4 emissions in our ponds and other northern lakes, which was negatively related to water depth (n = 71), but positively related to Chl a (n = 28). Our study sheds light on the factors that influence pond CH 4 dynamics and demonstrates that pond ebullition is a significant CH 4 source worthy of continued study.

Particulate organic carbon sedimentation triggers lagged methane emissions in a eutrophic reservoir

“…5f). Recently, Vizza et al (2022) reported the existence of a 4-week time lag between CH 4 production in sediments and CH 4 ebullition in temperate ponds at high latitudes in North America. These results indicate that POC might not be readily available as a substrate for the prokaryotic communities.…”

Persistent hot spots of CO2 and CH4 in coastal nearshore environments

“…CH 4 hot spots were observed in two distinct environments, in comparably deep depositional locations and in shallower semi-enclosed embayments. Both environments are characterized by relatively high accumulation of organic material, sustaining high methanogenesis (Wallenius et al 2021;Vizza et al 2022). Locations without hot spots showed significantly lower chl a concentrations and humic-like organic matter compared to CH 4 and CO 2 hot spots (Fig.…”