Photosynthesis‐driven methane production in oxic lake water as an important contributor to methane emission

Marco Günthel,Mina Bižić,Isabell Klawonn,Hans‐Peter Grossart,Steffen Kümmel,Kam W Tang,Danny Ionescu,Ivonne Nijenhuis,Lars Ganzert,Luca Zoccarato,Jason Woodhouse

doi:10.1002/lno.11557

Abstract

AbstractRecent discovery of methane (CH4) production in oxic waters challenges the conventional understanding of strict anoxic requirement for biological CH4 production. High‐resolution field measurements in Lake Stechlin, as well as incubation experiments, suggested that oxic‐water CH4 production occurred throughout much of the water column and was associated with phytoplankton especially diatoms, cyanobacteria, green algae, and cryptophytes. In situ concentrations and δ13C values of CH4 in oxic water were negatively correlated with soluble reactive phosphorus concentrations. Using 13C‐labeling techniques, we showed that bicarbonate was converted to CH4, and the production exceeded oxidation at day, but was comparable at night. These experimental data, along with complementary field observations, indicate a clear link between photosynthesis and the CH4 production‐consumption balance in phosphorus‐limited epilimnic waters. Comparison between surface CH4 emission data and experimental CH4 production rates suggested that the oxic CH4 source significantly contributed to surface emission in Lake Stechlin. These findings call for re‐examination of the aquatic CH4 cycle and climate predictions.

Highlights

We investigated oxic-water CH4 production in Lake Stechlin (Northeast Germany), an oligo-mesotrophic glacial lake in the temperate region that has been intensively monitored for decades (Casper 1985)
We conducted a comprehensive study of the CH4 dynamics in the oxic water of Lake Stechlin in order to address these questions: Which environmental factors promote oxic CH4 production? How is oxic CH4 production connected to phytoplankton? What is the contribution of this production to water-to-air CH4 flux? To investigate the environmental parameters that promote oxic CH4 production, we statistically analyzed the temporal and spatial CH4 distributions and its isotopic signatures and different biotic and abiotic factors in the lake on seasonal, weekly, and diurnal time scales
The contribution of oxic CH4 production to the water-to-air CH4 flux was examined by comparing oxic production rates from incubation experiments with CH4 emission rates to the atmosphere

Summary

Introduction

We conducted a comprehensive study of the CH4 dynamics in the oxic water of Lake Stechlin in order to address these questions: Which environmental factors promote oxic CH4 production? To investigate the environmental parameters that promote oxic CH4 production, we statistically analyzed the temporal and spatial CH4 distributions and its isotopic signatures and different biotic and abiotic factors in the lake on seasonal, weekly, and diurnal time scales. The contribution of oxic CH4 production to the water-to-air CH4 flux was examined by comparing oxic production rates from incubation experiments with CH4 emission rates to the atmosphere

Methods

Results

Conclusion