Antarctic Permafrost Degassing Revealed By Extensive Soil Gas and Co2 Flux Survey in Taylor Valley

McMurdo Dry Valleys comprise 10% of the ice-free soil surface areas in Antarctica. Permafrost stability plays an important role in C-cycle as it potentially stores considerable quantities of greenhouse gases. While the geomorphology of the Dry Valleys reflects a long history of changing climate conditions, comparison with the rapidly warming Northern polar region suggests that future climate and ecosystems may change more rapidly from permafrost degradation. In Austral summer 2019/2020 a comprehensive sampling of soil gases and CO2 flux measurements was undertaken in the Taylor Valley, with the aims to identify potential presence of soil gases in the active layer. The results obtained show high concentrations of CH4, CO2, He and an increasing CO2 flux rate. We identify the likely source of the gas to be from dissolved gases in deep brine moving from inland (potentially underneath the Antarctic Ice Sheet) to the coast at depth beneath the permafrost layer.

Role of Air Flow on Changing Soil Properties and Plant Nutrition in Egyptian Alluvial Soil

Study the effect of air flow on changing some soil properties and plant nutrition is highly important to increase crop quality and productivity. The pot experiment was carried out focusing on Agric faba bean C.V. Giza 2 in Egyptian alluvial soil (clay) during 2017-18 seasons. Two soil samples with three replicates were taken. The results revealed that hygroscopic water (HW), saturation percentage (SP) and real density (RD) have not affected by air flow, while organic matter (OM), hydraulic conductivity (HC) and bulk density (BD) have remarkable increase with air flow. The available macro and micronutrients concentrations in soil and plant are also discussed where different results have been obtained depending upon type of nutrient. The total count of bacteria (TCM) is found to be affected with air flow than without aeration techniques. The findings of this study reveal that aeration or air flow promotes healthy levels of soil gases and plays a critical role in plant growth.

Investigating Effects of Landfill Soil Gases on Landfill Elevated Subsurface Temperature

Subsurface temperature is a critical indicator for the identification of the risk associated with subsurface fire hazards in landfills. Most operational landfills in the United States (US) have experienced exothermic reactions in their subsurface. The subsurface landfill area is composed of various gases generated from chemical reactions inside the landfills. Federal laws in the US mandate the monitoring of gases in landfills to prevent hazardous events such as landfill fire breakouts. There are insufficient investigations conducted to identify the causes of landfill fire hazards. The objective of this research is to develop a methodological approach to this issue. In this study, the relationship was investigated between the subsurface elevated temperature (SET) and soil gases (i.e., methane, carbon dioxide, carbon monoxide, nitrogen, and oxygen) with the greatest influence in landfills. The significance level of the effect of soil gases on the SET was assessed using a decision tree approach. A naïve Bayes technique for conditional probability was implemented to investigate how different gas combinations can affect different temperature ranges with respect to the safe and unsafe states of these gases. The results indicate that methane and carbon dioxide gases are strongly associated with SETs. Among sixteen possible gas combinations, three were identified as the most probable predictors of SETs. A three-step risk assessment framework is proposed to identify the risk of landfill fire incidents. The key findings of this research could be beneficial to landfill authorities and better ensure the safety of the community health and environment.

From Sensor to Cloud: An IoT Network of Radon Outdoor Probes to Monitor Active Volcanoes

While radon in soil gases has been identified for decades as a potential precursor of volcanic eruptions, there has been a recent interest for monitoring radon in air on active volcanoes. We present here the first network of outdoor air radon sensors that was installed successfully on Mt. Etna volcano, Sicily, Italy in September 2019. Small radon sensors designed for workers and home dosimetry were tropicalized in order to be operated continuously in harsh volcanic conditions with an autonomy of several months. Two stations have been installed on the south flank of the volcano at ~3000 m of elevation. A private network has been deployed in order to transfer the measurements from the stations directly to a server located in France, using a low-power wide-area transmission technology from Internet of Things (IoT) called LoRaWAN. Data finally feed a data lake, allowing flexibility in data management and sharing. A first analysis of the radon datasets confirms previous observations, while adding temporal information never accessed before. The observed performances confirm IoT solutions are very adapted to active volcano monitoring in terms of range, autonomy, and data loss.

Soil Biogeochemical Response to Drought Conditions in the Biosphere 2 Rainforest

<p>The direct measurement of soil gases provides insight into the biogeochemical processes responsible for micro- and macro-nutrient cycling, respiration, signaling, and environmental responses.  The concentrations and isotopic signatures of soil gases are effective messengers of the microbial pathways active in the soil.  We have developed and deployed a high frequency sensor consisting of new diffusive soil probes coupled with a Tunable Infrared Laser Direct Absorption Spectrometer (TILDAS) to monitor a range of soil gas species to investigate biogeochemical soil processes.</p><p>An array of soil probes was deployed at the Tropical Rainforest at Biosphere 2 in Arizona as part of the Water Atmosphere and Life Dynamics (WALD) experiment in 2019-2020.  Probes were located in a root zone and nearby control area, and at several depths via a soil pit.  These probes were coupled with a TILDAS to monitor isotopologues of nitrous oxide (N<sub>2</sub>O) including <sup>14</sup>N<sup>15</sup>NO, <sup>15</sup>N<sup>14</sup>NO, N<sub>2</sub><sup>18</sup>O, and methane (<sup>13</sup>CH<sub>4</sub> and <sup>12</sup>CH<sub>4</sub>), as well as CO<sub>2</sub>. During the WALD experiment, the probe-TILDAS system followed the impact on the soil biome of a 2 month induced drought in the rainforest and the subsequent return of rain.  The high temporal resolution of the system allowed us to monitor each probe every 2 hours and thus observe changes in the composition of soil gases that reflect biogeochemical processes and pathways.  CO<sub>2</sub> and thus respiration decreased significantly during the drought and was slow to recover.  Differences in N<sub>2</sub>O mixing ratios and isotopic signatures (both site preference and bulk 15N) in the root zone versus a controlled soil region were observed during both drought and rewetting periods.  Changes in nitrogen and carbon cycles and the microbial pathways during the induced drought and rewetting as reflected in these observations will be discussed.</p>

Integrated monitoring of soil gases, plume SO2 and volcanic tremor to detect impulsive magma transfer at Mt. Etna volcano (Italy)

<p>Magma transfer in an open-conduit volcano is a complex process that is still open to debate and not entirely understood. For this reason, a multidisciplinary monitoring of active volcanoes is not only welcome, but also necessary for a correct comprehension of how volcanoes work. Mt. Etna is probably one of the best test sites for doing this, because of the large multidisciplinary monitoring network setup by the Osservatorio Etneo of Istituto Nazionale di Geofisica e Vulcanologia (INGV-OE), the high frequency of eruptions and the relatively easy access to most of its surface.<br>We present new data on integrated monitoring of volcanic tremor, plume sulphur dioxide (SO<sub>2</sub>) flux and soil hydrogen (H<sub>2</sub>) and carbon dioxide (CO<sub>2</sub>) concentration from Mt. Etna. The RMS amplitude of volcanic tremor was measured by seismic stations at various distances from the summit craters, plume SO<sub>2</sub> flux was measured from nine stations around the volcano and soil gases were measured in a station located in a low-temperature (T ∼ 85 °C) fumarole field on the upper north side of the volcano.<br>During our monitoring period, we observed clear and marked anomalous changes in all parameters, with a nice temporal sequence that started with a soil CO<sub>2</sub> and SO<sub>2</sub> flux increase, followed a few days later by a soil H<sub>2</sub> spike-like increase and finally with sharp spike-like increases in RMS amplitude (about 24 h after the onset of the anomaly in H<sub>2</sub>) at all seismic stations.<br>After the initial spikes, all parameters returned more or less slowly to their background levels. Geochemical data, however, showed persistence of slight anomalous degassing for some more weeks, even in the apparent absence of RMS amplitude triggers. This suggests that the conditions of slight instability in the degassing magma column inside the volcano conduits lasted for a long period, probably until return to some sort of balance with the “normal” pressure conditions.<br>The RMS amplitude increase accompanied the onset of strong Strombolian activity at the Northeast Crater, one of the four summit craters of Mt. Etna, which continued during the following period of moderate geochemical anomalies. This suggests a cause-effect relationship between the anomalies observed in all parameters and magma migration inside the central conduits of the volcano. Volcanic tremor is a well-established key parameter in the assessment of the probability of eruptive activity at Etna and it is actually used as a basis for a multistation system for detection of volcanic anomalies that has been developed by INGV-OE at Etna. Adding the information provided by our geochemical parameters gave us more solid support to this system, helping us understand better the mechanisms of magma migration inside of an active, open-conduit basaltic volcano.</p>

14C estimation of soil C02 turnover rates in Ultisols with different land use

<p>The CO<sub>2</sub> flux from soil is a large and significant flux in most ecosystems and can account for more than 2/3 of total ecosystem respiration. In many cases, CO<sub>2</sub> flux from soil is estimated by the eddy covariance technique or by classical chamber method with measures of bulk concentration and isotopic composition of carbon dioxide. Whereas most these studies estimated CO<sub>2</sub> flux from the soil surface, we analyzed its concentration and isotope composition directly in soil profiles down to 5m depth.</p><p>This experiment was conducted in Sumter National Forest by NSF Calhoun CZO research program. A 10cm diameter auger was used to core up to 5 m depth and capped PVC pipe segments of 750 cm<sup>3</sup> volume serve as gas reservoirs, each with two gas impermeable tubes that connected the gas reservoirs. Soil gas reservoirs are installed at 5m, 3m, 1.5m, and 0.5m depths from the soil surface. On a three-week interval, soil gases were extracted with a pump and analyzed in the field for CO<sub>2</sub> and O<sub>2</sub> concentration with samples collected in Tedlar bags for analysis. The samples were collected in summer 2016 under 3 different land uses: hardwood stands that are taken to be never cultivated; old-field pine stands, which had been used for growing cotton in 19<sup>th</sup> century and then abandoned; and cultivated sites which were used growing cotton, but for the last 50-60 years for growing corn, wheat, legume, sorghum, and sunflowers.</p><p>The radiocarbon analyses in the soil CO<sub>2</sub> profile were conducted for the first time. It was discovered that concentration of 14C increased with depth and Δ<sup>14</sup>C changed from 40-60%o in the top 0.5m to about 80-140 ‰ at 5m depth depending on land use.</p><p> </p>

Exploring The Birch Effect In The Subsurface Using Diffusive Soil Probes

<p>Soil gases are efficient messengers of the subsurface biogeochemical processes that underlie important nutrient cycles.  Recent advances in subsurface gas sampling techniques can be combined with high precision trace gas instrumentation to yield novel insights into these processes and their mechanisms.</p><p>We present measurements of a wide range of trace gases before, during, and after a simulated rainfall upon northeastern US temperature forest soil in meso-scale columns.  Subsurface concentrations and above-ground fluxes of N<sub>2</sub>O and its isotopes, CH<sub>4</sub> and its isotopes, CO<sub>2</sub>, NO, NO<sub>2</sub>, NH<sub>3</sub>, and a wide range of volatile organic compounds (e.g. monoterpenes, sesquiterpenes, isoprene, acetonitrile, aromatics) were quantified in real time with 30 minute temporal resolution.  Small molecules were measured using Aerodyne TILDAS instruments, while VOCs were measured using a Vocus mass spectrometer.</p><p>Addition of water to the dried soil column produced a classic Birch effect pulse of both C and N species, including for VOCs.  We explore correlations between responses of trace gases above- and below-ground, and relate the small molecule pulses to the larger VOC responses.  In addition, we demonstrate the value of isotopic signatures for these studies, with the observation of fast, large isotopic shifts in the <sup>15</sup>N<sub>2</sub>O isotopomers.  We compare these isotopic signatures to simple kinetic models to provide insight into the mechanisms underlying the nitrogen Birch effect.</p>