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Gas transport in soils is usually assumed to be purely diffusive, although several studies have shown that non‐diffusive processes can significantly enhance soil gas transport. These processes include barometric air pressure changes, wind‐induced pressure pumping and static air pressure fields generated by wind interacting with obstacles. The associated pressure gradients in the soil can cause advective gas fluxes that are much larger than diffusive fluxes. However, the contributions of the respective transport processes are difficult to separate. We developed a large chamber system to simulate pressure fields and investigate their influence on soil gas transport. The chamber consists of four subspaces in which pressure is regulated by fans that blow air in or out of the chamber. With this setup, we conducted experiments with oscillating and static pressure fields. CO2 concentrations were measured along two soil profiles beneath the chamber. We found a significant relationship between static lateral pressure gradients and the change in the CO2 profiles (R2 = 0.53; p‐value <2e‐16). Even small pressure gradients between −1 and 1 Pa relative to ambient pressure resulted in an increase or decrease in CO2 concentrations of 8% on average in the upper soil, indicating advective flow of air in the pore space. Positive pressure gradients resulted in decreasing, negative pressure gradients in increasing CO2 concentrations. The concentration changes were probably caused by an advective flow field in the soil beneath the chamber generated by the pressure gradients. No effect of oscillating pressure fields was observed in this study. The results indicate that static lateral pressure gradients have a substantial impact on soil gas transport and therefore are an important driver of gas exchange between soil and atmosphere. Lateral pressure gradients in a comparable range can be induced under windy conditions when wind interacts with terrain features. They can also be caused by chambers used for flux measurements at high wind speed or by fans used for head‐space mixing within the chambers, which yields biased flux estimates. [ABSTRACT FROM AUTHOR]

Chamber carbon flux measurements are routinely used to assess ecosystem carbon sink/source dynamics. Often these point measurements enclose considerable vegetation biomass, with fluxes upscaled in space and time for each vegetation type. Here we assess the importance of including the volume of peatland dwarf shrub vegetation in chamber flux calculations and outline a simple but effective method of assessing plant volumes. We show that inclusion of plant volumes significantly affects fluxes and that this effect becomes greater as the proportion of chamber volume occupied by plants increases. Moreover, we demonstrate that, with an initial destructive laboratory assessment for each plant species and a little practice at volume estimation, plant volumes can be accurately assessed non-destructively in the field. [ABSTRACT FROM AUTHOR]

Organic soils are important carbon stocks. The conventional (dry) cultivation of these soils turns them into strong sources of greenhouse gas (GHG) emissions. For situations where restoration of natural land cover is not possible, solutions to this problem include the wet cultivation of these soils, reducing CO 2 and N 2 O emissions. One option, paddy rice cultivation, has begun in the Swiss Central Plateau, which hitherto did not provide a suitable climate for wet rice. Wet rice is however associated with high CH 4 emissions. These need to be quantified for this region, as the increased CH 4 fluxes might negate the expected reductions in CO 2 and N 2 O. Here, we quantify CH 4 and N 2 O emissions from wet rice on organic soil with chamber measurements, in an outdoor mesocosm experiment in the Swiss Central Plateau, located in the cool temperate moist zone. We apply two water treatments (a high water table (WT) treatment, − 6 cm with mid-season drainage, and two medium WT treatments, − 11 and − 17 cm without mid-season drainage) and additionally test the use of a mineral cover layer to reduce N 2 O emissions. Additionally, a deeply-drained grassland treatment is used as a reference treatment. Annual CH 4 emissions from rice cultivation are 6.2 g CH 4.m-2.a-1 for the higher WT treatment, 6.4 g CH 4.m-2.a-1 for the medium WT treatment and 2.4 g CH 4.m-2.a-1 for the medium WT treatment with mineral cover. The corresponding N 2 O emissions are 203, 190 and 56 mg N 2 O-N.m-2.a-1, respectively. These results show that adding a mineral cover layer reduces annual emissions from both GHGs substantially. In total, the maximum increase in CH 4 and N 2 O emissions resulting from rice cultivation, compared to the drained grassland treatment, is 2.3 t CO 2 -eq.ha-1.a-1. Expected CO 2 emissions savings (derived from a literature-based model) due to a higher WT are a factor of 5–9 greater than this. We thus conclude that the cultivation of these organic soils in this region with wet rice could reduce their induced warming compared to their cultivation with (deeply drained) grassland. • Annual methane and nitrous oxide fluxes measured from wet rice on organic soils. • First flux measurements from wet rice cultivation in Europe N of the Alps. • A mineral soil cover reduced both nitrous oxide and methane emissions. [ABSTRACT FROM AUTHOR]

Abstract: Soil greenhouse gas emissions from cattle grazed and un-grazed temperate upper salt marsh were measured using dark static chambers, monthly for one year. Below-ground gas sampling tubes were also used to measure soil methane (CH4) concentrations. CH4 efflux from grazed and un-grazed salt marsh did not differ significantly although grazing did lead to ‘hotspots’ of underground CH4 (up to 6% of total air volume) and CH4 efflux (peak of 9 mg m−2 h−1) significantly linked to high soil moisture content, low soil temperatures and the presence of Juncus gerardii. Carbon dioxide (CO2) efflux was greater from the un-grazed marsh (mean of 420 mg m−2 h−1) than the grazed marsh (mean of 333 mg m−2 h−1) throughout most of the year and was positively correlated with the deeper water table and greater soil temperatures. Grazing was not a significant predictor of nitrous oxide (N2O) soil emissions. Global Warming Potential (GWP; over 100 years), calculated from mean yearly chamber fluxes for CH4 and CO2, did not differ significantly with grazing treatment. Seasonal variation in the key drivers of soil greenhouse gas efflux; soil temperature, moisture and water table, plus the presence or absence of aerenchymatous plants such as J. gerardii were more important to the magnitude of greenhouse gas emissions than grazing management per se. [Copyright &y& Elsevier]

Abstract: The Arcachon lagoon is a 156 km2 temperate mesotidal lagoon dominated by tidal flats (66% of the surface area). The methane (CH4) sources, sinks and fluxes were estimated from water and pore water concentrations, from chamber flux measurements at the sediment–air (low tide), sediment–water and water–air (high tide) interfaces, and from potential oxidation and production rate measurements in sediments. CH4 concentrations in waters were maximal (500–1000 nmol l−1) in river waters and in tidal creeks at low tide, and minimal in the lagoon at high tide (<50 nmol l−1). The major CH4 sources are continental waters and the tidal pumping of sediment pore waters at low tide. Methanogenesis occurred in the tidal flat sediments, in which pore water concentrations were relatively high (2.5–8.0 μmol l−1). Nevertheless, the sediment was a minor CH4 source for the water column and the atmosphere because of a high degree of anaerobic and aerobic CH4 oxidation in sediments. Atmospheric CH4 fluxes at high and low tide were low compared to freshwater wetlands. Temperate tidal lagoons appear to be very minor contributor of CH4 to global atmosphere and to open ocean. [Copyright &y& Elsevier]