Post-fire carbon dioxide emissions from a peatland undergoing restoration

<p>In May 2019, a major wildfire event affected >60 km2 within the 4000 km2 Flow Country in Northern Scotland, UK, a flagship blanket bog peatland that is being considered for UNESCO World Heritage Status. While the fire itself created significant damage, it also led to an extraordinary and unique opportunity to compare burned and unburned landscape scale greenhouse gas flux and surface energy dynamics using sites that, crucially, have otherwise identical biophysical characteristics (slope, aspect, peat depth) and land management histories. Since September 2019, carbon dioxide and methane flux data have been collected alongside other micrometeorological variables. Due to the COVID-19 lockdown in the UK, the team had severe difficulties in maintaining the equipment and hence, only partial and preliminary data will be reported here to showcase the findings from this project to date. The data obtained so far suggest a post-fire reduction in net CO2 emissions for a period of one year since the beginning of our monitoring campaign.</p>

Different responses of CO₂, CH₄, and N₂O fluxes to seasonally asymmetric warming in an alpine grassland of Tianshan Mountains

An experiment was conducted to investigate the effect of seasonally asymmetric warming on CO2, CH4, and N2O fluxes in alpine grassland of Tianshan Mountains of Central Asia, from October 2016 to September 2019. Our results indicated that the CO2, CH4 and N2O fluxes varied in the range 0.56–98.03 mg C m−2 h−1, −94.30–0.23 μg C m−2 h−1, and −1.28–10.09 μg N m−2 h−1, respectively. The CO2 and N2O fluxes were negatively correlated with soil temperature, but the CH4 fluxes decreased with the increase in temperature. Furthermore, the variation in greenhouse gas flux under seasonally asymmetric warming was different between the growing season (June to September) and the non-growing season (October to May). In addition, the response rates of CO2 and N2O fluxes to temperature increases was significantly reduced due to warming throughout the year. Warming during the growing season led to a significant decrease in the response rate of CO2 flux to temperature increases. However, warming during the non-growing season caused a significant increase in the response rate of CO2 flux to temperature increases. The response rate of CH4 flux was insensitive to temperature increase under seasonally asymmetric warming. Thus, the main finding of our results was that seasonally asymmetric warming resulted in different responses in the fluxes of individual greenhouse gases to rising temperatures in the alpine grassland.

Climate change and the carbon cycle of frozen floodplains.

<p>Permafrost-affected river plains are highly diverse in discharge regime, floodplain morphology, channel forms, channel mobility and ecosystems. Frozen floodplains range from almost barren systems with high channel mobility, to extensive wetland areas with low channel mobility, abundant abandoned channels, back-swamps and shallow floodplain lakes. Floodplain processes are increasingly affected by climate-induced changes in river discharge and temperature regime: changes in the dates of freeze-up, break-up and spring floods, and changes in the discharge distribution throughout the year.</p><p>In permafrost floodplains, changes in flooding frequency, flood height and water temperature affect active layer thickness, subsidence and erosion processes. Data from the Northeast Siberian Berelegh river floodplain (a tributary to the Indigirka river) demonstrate that increasing spring flood height potentially causes permafrost thaw, soil subsidence and increase of the floodplain area. INSAR (interferometric synthetic aperture radar) data indicate that poorly drained areas in this region are affected by soil subsidence. Morphological evidence for subsidence of the river floodplain is abundant, and river-connected lakes show expansion features also seen in thaw lakes.</p><p>These floodplain wetland ecosystems are also affected by changes in the discharge regime and permafrost. On the one hand, floodplains are sites of active sedimentation of organic matter-rich sediments and sequestration of carbon. This carbon is derived from upstream erosion of permafrost and vegetation, and from autochthonous primary production. Nutrient supply by flood waters supports highly productive ecosystems with a comparatively large biomass.</p><p>On the other hand, these ecosystems also emit high amounts of CH<sub>4</sub>, which may be affected by flooding regime. In the example presented here, the CH<sub>4 </sub>emission from floodplain wetlands is about seven times higher that the emission from similar tundra wetlands outside the floodplain.</p><p>The dynamic nature of floodplains hinders carbon and greenhouse gas flux measurements. Better quantification of greenhouse gas fluxes from these floodplains, and their relation with river regime changes, is highly important to understand future emissions from thawing permafrost. Given the difficulties of surface greenhouse gas flux measurements, recent remote sensing material could play an important role here.</p>

Spatial soil respiration measurements under varying environmental conditions in a dry grassland

<p>Spatial variability of ecosystem processes constitutes significant uncertainty source in greenhouse gas flux measurements and estimations. The major disadvantage of the chamber-based flux measurements is the poor spatial representativeness, but eddy-covariance measurements also have an uncertainty due to the unequal and not constant footprint area. One way to overcome these difficulties is the spatial sampling improving the field-scale data coverage.</p><p>The aim of this study was to describe the spatial variability of grassland soil CO<sub>2</sub> efflux under varying environmental conditions. For this reason, we conducted spatial measurements on a range of variables including soil respiration, above-ground biomass, greenness index of the vegetation, soil water content and soil temperature during a seven-year study in a dry grassland site in Hungary. Altitude and soil organic carbon (SOC) content of the measuring positions were also used as background factors. Measurements were repeated 19 times at 78 positions during the study, in the main phenological stages of the grassland vegetation: spring growth, summer drought, autumn regrowth. The sampling scheme was based on 80×60 m grid of 10 m resolution. SOC content was highly variable among the positions due to the exposure differences and their environmental constrains. We analyzed the effect of the drivers on soil respiration grouping the measuring positions by the SOC content of the soil.</p>

Low-cost methane (CH4) sensors for use in in flux chambers

<p>The lack of reliable low-cost greenhouse gas flux measurement approaches limit our ability quantify regulation and verify mitigation efforts at the local level.   Methane (CH4), one of the most important greenhouse gases, is particularly dependent on local measurements because levels are regulated by a complex combination of sources, sinks and environmental conditions. There are still major gaps in the global methane budget and the reasons for the irregular development over time remains unclear. Facilitation of local flux measurements in all parts of the world therefore seem important to constrain large-scale assessments. As the high cost of gas analysers is a limiting factor for flux measurements, we here present how low-cost CH4 sensors can be used outside their specified range to yield reasonably accurate chamber-based flux measurements. By using a two-step calibration approach, testing multiple alternatives on how to model interference from temperature and humidity, an R2 ≥ 0.99 was achieved over a CH4 concentration range of 2 – 700 ppm under variable temperature and relative humidity. We also demonstrate ways to reach such calibration results without complicated calibration experiments and instead using in the order of 20 in situ reference measurements at different environmental conditions. Finally we, constructed and described a make-it-yourself Arduino based logger with the tested sensors for CH<sub>4</sub>, temperature, humidity and carbon dioxide (CO<sub>2</sub>) intended for flux chamber use with a material cost of approximately 200 Euro. We hope that this can contribute to more widespread greenhouse gas flux measurements in many environments and countries.</p>