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Moisture, temperature and light modualte methane oxidation from dry riverbeds - A mesocosms experiment

In this study, under lab conditions (Jan-Apr 2022) in we examined how three key drivers of methane oxidation in soils also modulate methane oxidation (i.e. methanotrophy) in dry riverbed sediments: gravimetric water content (GWC, as proxy of moisture), temperature, and light quality and intensity. We measured potential methane oxidation rates (PMO) as proxy of methanotrophy across a gradient of GWC, temperature (10, 20 and 30ºC), and under different light conditions (green and growth light) from dry (8% GWC) and wet (100%GWC) sediments collected in early Spring 2022 in the Queich River in Offenbach an der Queich (Germany). We used incubation vials (125mL) with about 10 mL sediment and spiked it with 120uL of pure methane gas following Bodmer et al. (2020). Incubations lasted for a week (until methane concentrations were below detection limit) and we replicated each treatment level four times (except for 10ºC that had just three).

Atmospheric weather data (air and soil temperature, relative humidity, photosynthetic photon flux density) (Table 6)

The weather station was set up in the beginning of the sampling period in August 2019 and ran the entire sampling period with an interruption between 30th January 2020 and 11th June 2020. Air and soil temperatures, relative humidity and photosynthetic flux density were measured on hourly intervals. Please note that the ground temperature sensor was situated 20 above the ground and therefore the measured medium depends on the conditions of the field site. Before rewetting, the medium was air, but after rewetting, when the area was usually inundated with water it indicates water temperatures.

Continuous water level (Table 5)

The water level was continuously measured at 5 stations along the transect during the entire sampling period to monitor changes in hourly intervals. Please note that individual loggers were did experience technical failure and did not measure the entire time.

Brackish water rewetting of a temperate coastal peatland in NE Germany: Effects on Biogeochemistry, Microorganisms and Greenhouse gas emissions

The rewetting of drained peatlands is a promising measure to mitigate carbon dioxide (CO2) emissions by preventing the further mineralization of the peat soil through aeration. While freshwater rewetted peatlands can be significant methane (CH4) sources in the short-term, in coastal ecosystems the input of sulfate-rich seawater could potentially mitigate these emissions. The purpose of the data collection was to examine whether the presence of sulfate, known as an alternative electron acceptor, can cause lower CH4 production and thus, emissions by favoring the growth of sulfate-reducers, which outcompete methanogens for substrate. We therefore investigated underlying variables such as the methane-cycling microbial community along with CH4 fluxes and set them in context with CO2 fluxes along a transect in a coastal peatland before and directly after rewetting. In this way, a conclusion about the short-term greenhouse gas mitigation potential of brackish water rewetting of coastal peatlands could be drawn. This data collection consists of six data sets, with direct comparisons before and after rewetting of CO2 and CH4 fluxes (Tab. 2) and associated microbial communities (Tab. 1) being the main data. Pore water geochemistry (Tab. 1 and 3) and surface water parameters (Tab. 4) were collected simultaneously to provide potential explanatory variables. The sampling of continuous water level (Tab. 5) within wells and atmospheric weather data (air and soil temperature, relative humidity, photosynthetic photon flux density; Tab. 6) from a weather station was done in addition. Measurements started in June/July/August 2019 after field installation was finalized and were conducted on the drained coastal fen "Polder Drammendorf" on the island of Rügen in North-East Germany. On 26th November 2019, the dike was opened and channeled in order to rewet the peatland with brackish water. Before, the dike separated the peatland from the adjacent bay "Kubitzer Bodden", which is part of a brackish lagoon system connected to the Baltic Sea. Therefore, the peatland was nearly completely flooded and now resembles a shallow lagoon with high fluctuating water levels. We measured along a humidity (pre-rewetting)/water level (post-rewetting) gradient (stations 0-8) towards and across the main North-South oriented drainage ditch, including four stations on the Eastern side of the ditch (1–4), two ditch stations (0, 5) and two stations (6, 7) on the Western side of the ditch. Station 8 was chosen as an additional station farther towards the adjacent bay on the Western side, but was only accessible before rewetting. CH4 and CO2 fluxes (stations 0-7) were calculated from online gas concentrations measurements using laser-based analyzers and manual closed chambers (Livingston, G. P., & Hutchinson, G. (1995). Enclosure-based measurement of trace gas exchange: Applications and sources of error. In P.A. Matson, & R.C. Harriss (Eds.). Biogenic trace gases: Measuring emissions from soil and water (pp. 14–51). Blackwell Science Ltd., Oxford, UK). Soil cores for microbial, dissolved gas concentrations and isotopic analysis were taken using a Russian type peat corer (De Vleeschouwer, F., Chambers, F. M., & Swindles, G. T. (2010). Coring and sub-sampling of peatlands for palaeoenvironmental research. Mires and Peat, 7, 1–10) before and after rewetting. Each time, we took duplicates at stations 1-8 for this rather labor-intensive process and divided the core into four depth sections: surface, 5–20, 20–40 and 40–50 cm. Subsamples for dissolved gases and stable carbon isotope analyses were taken with tip-cut syringes with a distinct volume of 3 ml (Omnifix, Braun, Bad Arolsen, Germany) and immediately placed into NaCl-saturated vials (20 ml, Agilent Technologies, 5182-0837, Santa Clara, USA) leaving no headspace and closed gas-tight using rubber stoppers and metal crimpers (both: diameter 20 mm, Glasgerätebau Ochs, Bovenden, Germany). Absolute abundances of specific functional target genes, including methane- and sulfate-cycling microorganisms, were measured with quantitative PCR (qPCR) after DNA was extracted (GeneMATRIX Soil DNA Purification Kit, Roboklon, Berlin, Germany) and quantified (Qubit 2.0 Fluorometer, ThermoFisher Scientific, Darmstadt, Germany). Surface and pore water parameters were measured in parallel to the gas measurements and soil coring for microbial analyses. Most surface water variables (pH, specific conductivity, salinity, nutrients, oxygen, sulfate and chloride concentrations, DOC/DIC) were measured in-situ using a multiparameter digital water quality meter or taken to the laboratory as water samples for further analysis. Likewise, pore water/soil variables (pH, specific conductivity, nutrients, metals, sulfate and chloride concentrations, CNS) were either measured in-situ or taken to the laboratory as soil samples. While surface water analysis was only conducted in the drainage ditch before rewetting, it was done along the entire transect after rewetting. In contrast, pore water/soil analysis was mostly conducted before rewetting and only repeated occasionally after rewetting where possible.

CO2 and CH4 fluxes before and after rewetting (Table 2)

CH4 and CO2 fluxes (stations 0-7) were calculated from online gas concentrations measurements using laser-based analyzers and manual closed chambers (Livingston, GP, & Hutchinson, G, 1995). Blackwell Science Ltd., Oxford, UK).

Pore water and soil variables (pH, specific conductivity, nutrients, metals, sulfate and chloride concentrations, CNS) (Table 3)

Pore water parameters were measured in parallel to the gas measurements and soil coring for microbial analyses. Pore water/soil variables (pH, specific conductivity, nutrients, metals, sulfate and chloride concentrations, CNS) were either measured in-situ or taken to the laboratory as soil samples. Pore water/soil analysis was mostly conducted before rewetting and only repeated occasionally after rewetting where possible.

Surface water parameters (pH, specific conductivity, salinity, nutrients, oxygen, sulfate and chloride concentrations, DOC/DIC) (Table 4)

Surface water parameters were measured in parallel to the gas measurements and soil coring for microbial analyses. Most surface water variables (pH, specific conductivity, salinity, nutrients, oxygen, sulfate and chloride concentrations, DOC/DIC) were measured in-situ using a multiparameter digital water quality meter or taken to the laboratory as water samples for further analysis. While surface water analysis was only conducted in the drainage ditch before rewetting, it was done along the entire transect after rewetting.

Absolute abundances of methane- and sulfate-cycling microorganisms, pore water gas concentrations and stable carbon isotopes (Table 1)

Soil cores for microbial, dissolved gas concentrations and isotopic analysis were taken using a Russian type peat corer (De Vleeschouwer et al. 2010) before and after rewetting. Each time, we took duplicates at stations 1-8 for this rather labor-intensive process and divided the core into four depth sections: surface, 5–20, 20–40 and 40–50 cm. Subsamples for dissolved gases and stable carbon isotope analyses were taken with tip-cut syringes with a distinct volume of 3 ml (Omnifix, Braun, Bad Arolsen, Germany) and immediately placed into NaCl-saturated vials (20 ml, Agilent Technologies, 5182-0837, Santa Clara, USA) leaving no headspace and closed gas-tight using rubber stoppers and metal crimpers (both: diameter 20 mm, Glasgerätebau Ochs, Bovenden, Germany).

Effects of a brackish water inflow on peat pore water variables and methane-cycling microbial community abundances in a freshwater rewetted coastal fen

The rewetting of peatlands is a promising measure to mitigate greenhouse gas (GHG) emissions by preventing the further mineralization of the peat soil through aeration. In coastal peatland, the rewetting with brackish water can increase the GHG mitigation potential by the introduction of sulfate, a terminal electron acceptor (TEA). Sulfate is known to lower the CH4 production and thus, its emission by favoring the growth of sulfate-reducers, which outcompete methanogens for substrate. The data contain porewater variables such as pH, electrical conductivity (EC) and sulfate, chloride, dissolved CO2 and CH4 concentrations, as well as absolute abundances of methane- and sulfate-cycling microbial communities. The data were collected in spring and autumn 2019 after a storm surge with brackish water inflow in January 2019. Field sampling was conducted in the nature reserve Heiligensee and Hütelmoor in North-East Germany, close to the Southern Baltic Sea coast. We took peat cores using a Russian peat corer in addition to pore water diffusion samplers and plastic liners (length: 60cm; inner diameter 10 cm) at four locations along a transect from further inland towards the Baltic Sea. We wanted to compare the soil and pore water geochemistry as well as the microbial communities after the brackish water inflow to the common freshwater rewetting state. Pore water was extracted using pore water suction samplers in the lab and environmental variables were quantified with an ICP. Microbial samples were sampled from the peat core using sterile equipment. We used quantitative polymerase chain reaction (qPCR) to characterize pools of DNA and cDNA targeting total and putatively active bacteria and archaea. qPCR was performed on key functional genes of methane production (mcrA), aerobic methane oxidation (pmoA) and sulfate reduction (dsrB) in addition to the 16S rRNA gene for the absolute abundance of total prokaryotes. Furthermore, we retrieved soil plugs to determine the concentrations and isotopic signatures of dissolved trace gases (CO2/DIC and CH4) in the pore water.

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