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 −2 d −1 ; 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 water‐column CH 4 concentrations (0.39, 0.21–0.87 μ mol L −1 ) 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 −2 d −1 ) 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 −2 d −1 ) 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.