Sulphur constraints on peatland carbon cycle

<p>The reduction of sulphate  (SO ) represents an alternative terminal electron acceptor for the oxidation of organic matter in peat soils. The greenhouse gas budget in peatlands will be constrained by how much a peatland can utilise SO<sub>4</sub> reduction and provide an alternative to methanogenesis. This study used records of atmospheric deposition and stream chemistry coupled with elemental analysis of peat soil, vegetation and dissolved organic matter (DOM) from streams and soil porewater, to estimate a 23-year long sulphur (S) budget for a blanket bog-covered catchment in the North Pennines, England. The study showed that:</p><ul><li>1) Atmospheric deposition of total S significantly declined over the study period from 2.4 to 0.5 t S/km<sup>2</sup>/yr.</li> <li>2) Long term accumulation of S into deep peat at 1 m depth averaged 127 kg S/km<sup>2</sup>/yr.</li> <li>3) Based upon shallow soil water concentrations the total S fluvial flux peaked as 4.5 t S/km<sup>2</sup>/yr with an average of 0.7 t S/km<sup>2</sup>/yr. The flux of total S increased over the catchment suggesting a groundwater source of oxidised S.</li> <li>4) Over the 23 years of monitoring, 0.25 t S/km<sup>2</sup>/yr were reduced to either mineral sulphides or hydrogen sulphide; however, in 8 out of the 23 years the catchment was a net producer of S to the streams of the catchment.</li> </ul><p>At maximum observed S reduction capacity the peatland was capable of a net removal of 71% of atmospheric S deposition. Allowing for the efficiency of energy transfer in the redox process and the oxidation state of peat organic matter means that for every mole of SO<sub>4</sub> reduced, 1.69 moles of CO<sub>2</sub> were produced and not the 2 moles normally assumed. In this catchment an average of 0.47 t C/km<sup>2</sup>/yr are diverted from methanogenesis.</p>

Evaluation and optimization of ICOS atmosphere station data as part of the labeling process

The Integrated Carbon Observation System (ICOS) is a pan-European research infrastructure which provides harmonized and high-precision scientific data on the carbon cycle and the greenhouse gas budget. All stations have to undergo a rigorous assessment before being labeled, i.e., receiving approval to join the network. In this paper, we present the labeling process for the ICOS atmosphere network through the 23 stations that were labeled between November 2017 and November 2019. We describe the labeling steps, as well as the quality controls, used to verify that the ICOS data (CO2, CH4, CO and meteorological measurements) attain the expected quality level defined within ICOS. To ensure the quality of the greenhouse gas data, three to four calibration gases and two target gases are measured: one target two to three times a day, the other gases twice a month. The data are verified on a weekly basis, and tests on the station sampling lines are performed twice a year. From these high-quality data, we conclude that regular calibrations of the CO2, CH4 and CO analyzers used here (twice a month) are important in particular for carbon monoxide (CO) due to the analyzer's variability and that reducing the number of calibration injections (from four to three) in a calibration sequence is possible, saving gas and extending the calibration gas lifespan. We also show that currently, the on-site water vapor correction test does not deliver quantitative results possibly due to environmental factors. Thus the use of a drying system is strongly recommended. Finally, the mandatory regular intake line tests are shown to be useful in detecting artifacts and leaks, as shown here via three different examples at the stations.

Extracellular Electron Transfer May Be an Overlooked Contribution to Pelagic Respiration in Humic-Rich Freshwater Lakes

ABSTRACTHumic lakes and ponds receive large amounts of terrestrial carbon and are important components of the global carbon cycle, yet how their redox cycling influences the carbon budget is not fully understood. Here we compared metagenomes obtained from a humic bog and a clear-water eutrophic lake and found a much larger number of genes that might be involved in extracellular electron transfer (EET) for iron redox reactions and humic substance (HS) reduction in the bog than in the clear-water lake, consistent with the much higher iron and HS levels in the bog. These genes were particularly rich in the bog’s anoxic hypolimnion and were found in diverse bacterial lineages, some of which are relatives of known iron oxidizers or iron-HS reducers. We hypothesize that HS may be a previously overlooked electron acceptor and that EET-enabled redox cycling may be important in pelagic respiration and greenhouse gas budget in humic-rich freshwater lakes.

Extracellular electron transfer may be an overlooked contribution to pelagic respiration in humic-rich freshwater lakes

ABSTRACTHumic lakes and ponds receive large amounts of terrestrial carbon and are important components of the global carbon cycle, yet how their redox cycling influences the carbon budget is not fully understood. Here we compared metagenomes obtained from a humic bog and a clearwater eutrophic lake, and found a much larger number of genes that might be involved in extracellular electron transfer (EET) for iron redox reactions and humic substance (HS) reduction in the bog than in the clearwater lake, consistent with the much higher iron and HS levels in the bog. These genes were particularly rich in the bog’s anoxic hypolimnion, and were found in diverse bacterial lineages, some of which are relatives of known iron oxidizers or iron/HS reducers. We hypothesize that HS may be a previously overlooked electron acceptor and EET-enabled redox cycling may be important in pelagic respiration and greenhouse gas budget in humic-rich freshwater lakes.