Soil moisture control over autumn season methane flux, Arctic Coastal Plain of Alaska

Abstract. Two shortfalls in estimating current and future seasonal budgets of methane efflux in Arctic regions are the paucity of non-summer measurements and an incomplete understanding of the sensitivity of methane emissions to changes in tundra moisture. A recent study in one Arctic region highlighted the former by observing a previously unknown large methane pulse during the onset of autumn soil freeze. This study addresses these research gaps by presenting an analysis of eddy covariance measurements of methane efflux and supporting environmental variables during the autumn season of 2009 and associated soil freeze-in period at our large-scale water manipulation site near Barrow, Alaska (the Biocomplexity Experiment). We found that methane emissions during the autumn were closely tied to liquid soil moisture in the top 30 cm of soil. Declines in soil moisture between manipulated wet, intermediate, and dry conditions as well as through time during the soil freeze-in period led to corresponding declines in methane efflux. During the period of soil freeze-in (from 23 September to 28 October), we estimate that our wet section emitted 623 mg CH4 m−2 while the dry section emitted only 253 mg CH4 m−2, the average of which represents 18 % of net emissions from the typically measured growing season. We did not find evidence for a pulse in methane emissions during soil freeze at this site. Results from this study imply that future changes in tundra moisture will have a large effect on methane emissions in this region, and changes which span the saturation point are likely to have the largest effect. We speculate that changes in autumn soil moisture are also likely to affect winter emissions via the insulative effects of ice on winter soil temperature and liquid soil moisture availability after bulk soil freeze. Further research should expand the use of eddy covariance methane flux measurements to investigate ecosystem-level effects of tundra moisture on autumn and winter methane emissions in this and other Arctic regions.

Download Full-text

Soil moisture control over autumn season methane flux, Arctic Coastal Plain of Alaska

Biogeosciences ◽

10.5194/bg-9-1423-2012 ◽

2012 ◽

Vol 9 (4) ◽

pp. 1423-1440 ◽

Cited By ~ 57

Author(s):

C. S. Sturtevant ◽

W. C. Oechel ◽

D. Zona ◽

Y. Kim ◽

C. E. Emerson

Keyword(s):

Large Scale ◽

Winter Season ◽

Methane Flux ◽

Soil Freezing ◽

The Arctic ◽

Freezing Process ◽

Unfrozen Water ◽

Ch4 Emission ◽

Ch4 Emissions ◽

Autumn Season

Abstract. Accurate estimates of annual budgets of methane (CH4) efflux in arctic regions are severely constrained by the paucity of non-summer measurements. Moreover, the incomplete understanding of the ecosystem-level sensitivity of CH4 emissions to changes in tundra moisture makes prediction of future CH4 release from the Arctic extremely difficult. This study addresses some of these research gaps by presenting an analysis of eddy covariance and chamber measurements of CH4 efflux and supporting environmental variables during the autumn season and associated beginning of soil freeze-up at our large-scale water manipulation site near Barrow, Alaska (the Biocomplexity Experiment). We found that the autumn season CH4 emission is significant (accounting for 21–25% of the average growing season emission), and that this emission is mostly controlled by the fraction of inundated landscape, atmospheric turbulence, and the decline in unfrozen water during the period of soil freezing. Drainage decreased autumn CH4 emission by a factor of 2.4 compared to our flooded treatment. Flooding slowed the soil freezing process which has implications for extending elevated CH4 emissions longer into the winter season.

Download Full-text

Representativeness assessment of the pan-Arctic eddy-covariance site network, and optimized future enhancements

10.5194/bg-2021-133 ◽

2021 ◽

Author(s):

Martijn Pallandt ◽

Jitendra Kumar ◽

Marguerite Mauritz ◽

Edward Schuur ◽

Anna-Maria Virkkala ◽

...

Keyword(s):

Eddy Covariance ◽

Active Sites ◽

Arctic Region ◽

Methane Flux ◽

The Arctic ◽

Network Coverage ◽

Mountainous Regions ◽

Flux Data ◽

Spatio Temporal ◽

Edaphic Variables

Abstract. Large changes in the Arctic carbon balance are expected as warming linked to climate change threatens to destabilize ancient permafrost carbon stocks. The eddy covariance (EC) method is an established technique to quantify net losses and gains of carbon between the biosphere and atmosphere at high spatio-temporal resolution. Over the past decades, a growing network of terrestrial EC tower sites has been established across the Arctic, but a comprehensive assessment of the network’s representativeness within the heterogeneous Arctic region is still lacking. This creates additional uncertainties when integrating flux data across sites, for example when upscaling fluxes to constrain pan-Arctic carbon budgets, and changes therein. This study provides an inventory of Arctic (here >= 60° N) EC sites, which has also been made available online (https://cosima.nceas.ucsb.edu/carbon-flux-sites/). Our database currently comprises 120 EC sites, but only 83 are listed as active, and just 25 of these active sites remain operational throughout the winter. To map the representativeness of this EC network, based on 18 bioclimatic and edaphic variables, we evaluated the similarity between environmental conditions observed at the tower locations and those within the larger Arctic study domain. With the majority of sites located in Fennoscandia and Alaska, these regions were assigned the highest level of network representativeness, while large parts of Siberia and patches of Canada were classified as under-represented. This division between regions is further emphasized for wintertime and methane flux data coverage. Across the Arctic, particularly mountainous regions were poorly represented by the current EC observation network. We tested three different strategies to identify new site locations, or upgrades of existing sites, that optimally enhance the representativeness of the current EC network. While 15 new sites can improve the representativeness of the pan-Arctic network by 20 percent, upgrading as few as 10 existing sites to capture methane fluxes, or remain active during wintertime, can improve their respective network coverage by 28 to 33 percent. This targeted network improvement could be shown to be clearly superior to an unguided selection of new sites, therefore leading to substantial improvements in network coverage based on relatively small investments.

Download Full-text

Quantifying the impact of emission outbursts and non-stationary flow on eddy-covariance CH4 flux measurements using wavelet techniques

Biogeosciences ◽

10.5194/bg-16-3113-2019 ◽

2019 ◽

Vol 16 (16) ◽

pp. 3113-3131 ◽

Cited By ~ 3

Author(s):

Mathias Göckede ◽

Fanny Kittler ◽

Carsten Schaller

Keyword(s):

Eddy Covariance ◽

Methane Flux ◽

Stationary Flow ◽

Methane Emissions ◽

Gap Filling ◽

Short Term ◽

Flux Measurements ◽

Systematic Biases ◽

The Impact ◽

Short Term Variability

Abstract. Methane flux measurements by the eddy-covariance technique are subject to large uncertainties, particularly linked to the partly highly intermittent nature of methane emissions. Outbursts of high methane emissions, termed event fluxes, hold the potential to introduce systematic biases into derived methane budgets, since under such conditions the assumption of stationarity of the flow is violated. In this study, we investigate the net impact of this effect by comparing eddy-covariance fluxes against a wavelet-derived reference that is not negatively influenced by non-stationarity. Our results demonstrate that methane emission events influenced 3 %–4 % of the flux measurements and did not lead to systematic biases in methane budgets for the analyzed summer season; however, the presence of events substantially increased uncertainties in short-term flux rates. The wavelet results provided an excellent reference to evaluate the performance of three different gap-filling approaches for eddy-covariance methane fluxes, and we show that none of them could reproduce the range of observed flux rates. The integrated performance of the gap-filling methods for the longer-term dataset varied between the two eddy-covariance towers involved in this study, and we show that gap-filling remains a large source of uncertainty linked to limited insights into the mechanisms governing the short-term variability in methane emissions. With the capability for broadening our observational methane flux database to a wider range of conditions, including the direct resolution of short-term variability on the order of minutes, wavelet-derived fluxes hold the potential to generate new insight into methane exchange processes with the atmosphere and therefore also improve our understanding of the underlying processes.

Download Full-text

The Effect of the Dry Line and Convective Initiation on Drought Evolution over Oklahoma during the 2011 Drought

Advances in Meteorology ◽

10.1155/2017/8430743 ◽

2017 ◽

Vol 2017 ◽

pp. 1-16 ◽

Cited By ~ 3

Author(s):

Paul X. Flanagan ◽

Jeffrey B. Basara ◽

Bradley G. Illston ◽

Jason A. Otkin

Keyword(s):

Soil Moisture ◽

Large Scale ◽

Warm Season ◽

Convective Initiation ◽

Model Simulations ◽

Variable Surface ◽

Oklahoma Mesonet ◽

Dry Conditions ◽

Moisture Conditions ◽

The Impact

Observations from the Oklahoma Mesonet and high resolution Weather Research and Forecasting model simulations were used to evaluate the effect that the dry line and large-scale atmospheric patterns had on drought evolution during 2011. Mesonet observations showed that a “dry” and “wet” pattern developed across Oklahoma due to anomalous atmospheric patterns. The location of the dry line varied due to this “dry” and “wet” pattern, with the average dry line location around 1.5° longitude further to the east than climatology. Model simulations were used to further quantify the impact of variable surface conditions on dry line evolution and convective initiation (CI) during April and May 2011. Specifically, soil moisture conditions were altered to depict “wet” and “dry” conditions across the domain by replacing the soil moisture values by each soil category’s porosity or wilting point value. Overall, the strength of the dry line boundary, its position, and subsequent CI were dependent on the modification of soil moisture. The simulations demonstrated that modifying soil moisture impacted the nature of the dry line and showed that soil moisture conditions during the first half of the warm season modified the dry line pattern and influenced the evolution and perpetuation of drought over Oklahoma.

Download Full-text

Enhanced CO2 uptake at a shallow Arctic Ocean seep field overwhelms the positive warming potential of emitted methane

Proceedings of the National Academy of Sciences ◽

10.1073/pnas.1618926114 ◽

2017 ◽

Vol 114 (21) ◽

pp. 5355-5360 ◽

Cited By ~ 25

Author(s):

John W. Pohlman ◽

Jens Greinert ◽

Carolyn Ruppel ◽

Anna Silyakova ◽

Lisa Vielstädte ◽

...

Keyword(s):

Arctic Ocean ◽

Radiative Forcing ◽

Methane Flux ◽

Methane Emissions ◽

The Arctic ◽

Co2 Uptake ◽

Water Characteristics ◽

Continental Shelves ◽

Uptake Rates ◽

Methane Efflux

Continued warming of the Arctic Ocean in coming decades is projected to trigger the release of teragrams (1 Tg = 106 tons) of methane from thawing subsea permafrost on shallow continental shelves and dissociation of methane hydrate on upper continental slopes. On the shallow shelves (<100 m water depth), methane released from the seafloor may reach the atmosphere and potentially amplify global warming. On the other hand, biological uptake of carbon dioxide (CO2) has the potential to offset the positive warming potential of emitted methane, a process that has not received detailed consideration for these settings. Continuous sea−air gas flux data collected over a shallow ebullitive methane seep field on the Svalbard margin reveal atmospheric CO2 uptake rates (−33,300 ± 7,900 μmol m−2⋅d−1) twice that of surrounding waters and ∼1,900 times greater than the diffusive sea−air methane efflux (17.3 ± 4.8 μmol m−2⋅d−1). The negative radiative forcing expected from this CO2 uptake is up to 231 times greater than the positive radiative forcing from the methane emissions. Surface water characteristics (e.g., high dissolved oxygen, high pH, and enrichment of 13C in CO2) indicate that upwelling of cold, nutrient-rich water from near the seafloor accompanies methane emissions and stimulates CO2 consumption by photosynthesizing phytoplankton. These findings challenge the widely held perception that areas characterized by shallow-water methane seeps and/or strongly elevated sea−air methane flux always increase the global atmospheric greenhouse gas burden.

Download Full-text

Quantifying the impact of emission outbursts and non-stationary flow on eddy covariance CH4 flux measurements using wavelet techniques

10.5194/bg-2019-92 ◽

2019 ◽

Author(s):

Mathias Göckede ◽

Fanny Kittler ◽

Carsten Schaller

Keyword(s):

Eddy Covariance ◽

Methane Flux ◽

Stationary Flow ◽

Methane Emissions ◽

Short Term ◽

Flux Measurements ◽

Systematic Biases ◽

Wavelet Techniques ◽

The Impact ◽

Short Term Variability

Abstract. Methane flux measurements by the eddy-covariance technique are subject to large uncertainties, particularly linked to the partly highly intermittent nature of methane emissions. Outbursts of high methane emissions, termed event fluxes, hold the potential to introduce systematic biases into derived methane budgets, since under such conditions the assumption of stationarity of the flow is violated. In this study, we investigate the net impact of this effect by comparing eddy-covariance fluxes against a wavelet-derived reference that is not negatively influenced by non-stationarity. Our results demonstrate that methane emission events influenced 3–4 % of the flux measurements, and did not lead to systematic biases in methane budgets for the analyzed summer season; however, the presence of events substantially increased uncertainties in short-term flux rates. The wavelet results provided an excellent reference to evaluate the performance of three different gapfilling approaches for eddy-covariance methane fluxes, and we show that none of them could reproduce the range of observed flux rates. The integrated performance of the gapfilling methods for the longer-term dataset varied between the two eddy-covariance towers involved in this study, and we show that gapfilling remains a large source of uncertainty linked to limited insights into the mechanisms governing the short-term variability in methane emissions. With the capability to broaden our observational methane flux database to a wider range of conditions, including the direct resolution of short term variability at the order of minutes, wavelet-derived fluxes hold the potential to generate new insight into methane exchange processes with the atmosphere, and therefore also improve our understanding of the underlying processes.

Download Full-text

Year-round simulated methane emissions from a permafrost ecosystem in Northeast Siberia

10.5194/bg-2017-310 ◽

2017 ◽

Author(s):

Karel Castro-Morales ◽

Thomas Kleinen ◽

Sonja Kaiser ◽

Sönke Zaehle ◽

Fanny Kittler ◽

...

Keyword(s):

Eddy Covariance ◽

Land Surface ◽

Large Scale ◽

Molecular Diffusion ◽

Russian Far East ◽

Far East ◽

Methane Emissions ◽

The Arctic ◽

Ch4 Emissions ◽

Permafrost Thaw

Abstract. Methane emissions to the atmosphere from natural wetlands are estimated to be about 25 % of the total global CH4 emissions. In the Arctic, these areas are highly vulnerable to the effects of global warming due to atmospheric warming amplification, leading to soil hydrologic changes involving permafrost thaw, formation of deeper active layers, and rising topsoil temperatures. As a result, projected increase in the degradation of permafrost carbon will likely lead to higher CO2 and CH4 emissions from these areas. Here we evaluate year-round model-simulated CH4 emissions to the atmosphere (for 2014 and 2015) from a region of northeastern Siberia in the Russian Far East. Four CH4 transport pathways are modeled with a revisit-ed version of the process-based JSBACH-methane model: plant-mediated transport, ebullition and molecular diffusion in the presence or absence of snow. This model also simulates the extent of wetlands as the fraction of inundated area in a model grid cell using a TOP-MODEL approach, and these are evaluated against a highly resolved wetland product from remote sensing data. The model CH4 emissions are compared against ground-based CH4 flux measurements using the eddy covariance technique and flux chambers in the same area of study. The magnitude of the summertime modeled CH4 emissions is comparable to those from eddy covariance and flux chamber measurements. However, wintertime modeled CH4 emissions are underestimated by one order of magnitude. The annual CH4 emissions are dominated by plant-mediated transport (61 %), followed by ebullition (~ 35 %). Molecular diffusion of CH4 from the soil into the atmosphere during summer is negligible (0.02 %) compared to the diffusion through the snow during the non-growing season (~ 4 %). We investigate the relationship between temporal changes in the CH4 fluxes, soil temperature, and soil moisture content. Our results highlight the heterogeneity in CH4 emissions at a landscape scale and suggest that further improvements to the representation of large-scale hydrological conditions in the model, especially at regional scales in Arctic ecosystems influenced by permafrost thaw, will allow us to arrive at a more process-oriented land surface scheme and better simulate CH4 emissions under climate change.

Download Full-text

Methane and carbon dioxide emissions from two contrasting wetlands in the Okavango Delta, Botswana.

10.5194/egusphere-egu2020-6023 ◽

2020 ◽

Author(s):

Carole Helfter ◽

Mangaliso Gondwe ◽

Mike Murray-Hudson ◽

Ute Skiba

Keyword(s):

Carbon Dioxide ◽

Soil Moisture ◽

Eddy Covariance ◽

Carbon Dioxide Emissions ◽

Methane Emissions ◽

Okavango Delta ◽

Natural Soil ◽

River Channels ◽

Seasonal Wetland ◽

Permanent Wetland

We report on two years of continuous monitoring of methane (CH4) and carbon dioxide (CO2) emissions at two contrasting sites in the Okavango Delta, North-Western Botswana, an inland delta bordered by the Kalahari Desert. Approximately 60% of the annual water influx into the Okavango Delta results from seasonal river discharges originating in the Angolan Highlands, and the remainder comes from direct rainfall. 96-98% of the 16.1 billion m3 entering the Delta annually are lost through evapo-transpiration (1500 mm.year-1). Flooding is gradual and it takes the pulsed influx ca. 4-5 months to travel the 250 km separating the inlet in Mohembo from the main outlet in Maun. The wetlands of the Okavango Delta are in pristine condition and can be separated into three categories: permanently flooded, seasonally flooded (3-6 months per year) and occasionally flooded (typically once per decade).&#160;Two eddy-covariance systems were set up in August 2017, one at Guma Lagoon (18&#176;57'53.01" S;&#160; 22&#176;22'16.20" E) at the edge of an extensive papyrus bed in the permanently-flooded section of the delta, and the second one at Nxaraga on the SW edge of Chief&#8217;s Island (19&#176;32'53'' S; 23&#176;10'45'' E) in the seasonal floodplain. In addition, monthly measurements of methane and carbon dioxide fluxes were taken using a clear dynamic chamber at the Nxaraga site along transects chosen to span the natural soil moisture gradient (very dry to waterlogged soils).The emissions of methane exhibited contrasting spatial and temporal patterns between sites. At the seasonal wetland, very low fluxes of CH4 were typically observed from January to June. Emissions increased abruptly from July-August onwards after flood waters rewetted the flooplain in that area of the Delta. Throughout the year, local emission hotspots of CH4 were observed along the vegetated river channels within the flux footprint of the eddy-covariance system, whereas CH4 oxidation was recorded in persistently dry areas where the soil is sandy and salt-crusted. The chamber measurements corroborated the findings of the eddy-covariance measurements and soil moisture is likely the dominant control of methane fluxes at the seasonal wetland.The methane emissions from the floating papyrus mat in the permanent wetland exhibited a marked seasonal cycle, characterised by relatively high emissions (of the order of 250 nmol.m-2.s-1; 2.5 larger than peak emissions recorded at the seasonal wetland) in the summer months (November-March) and minimum emissions in winter (typically 50 nmol.m-2.s-1 in June-August). At the seasonal timescale, methane emissions were strongly correlated to the phenological cycle of papyrus (lowest emissions during the senescence phase), suggesting that plant-mediated transport is the dominant control. The annual budgets of CH4 and CO2 in the permanent wetland were estimated at 153.4 &#177; 27.9 tons.km-2 (3835.0 &#177; 697.5 CO2-eq) and -874.0 &#177; 200.4 tons.km-2 respectively, making the permanent wetland a potent net source of carbon to the atmosphere.

Download Full-text

Methane efflux from an American bison herd

10.5194/bg-2020-38 ◽

2020 ◽

Author(s):

Paul C. Stoy ◽

Adam A. Cook ◽

John E. Dore ◽

William Kleindl ◽

E. N. Jack Brookshire ◽

...

Keyword(s):

Greenhouse Gas ◽

Eddy Covariance ◽

Methane Emissions ◽

Environmental Benefits ◽

Skewed Distribution ◽

Bison Bison ◽

Past Century ◽

Flux Footprint ◽

Grazing Systems ◽

Methane Efflux

Abstract. American bison (Bison bison L.) have recovered from the brink of extinction over the past century. Bison reintroduction creates multiple environmental benefits, but their impacts on greenhouse gas emissions are poorly understood. Bison are thought to have produced some 2 Tg year−1 of the estimated 9–15 Tg year−1 of pre-industrial enteric methane emissions, but few contemporary measurements have been made due to their mobile grazing habits and safety issues associated with direct measurements. Here, we measure methane and carbon dioxide fluxes from a bison herd on an enclosed pasture during daytime periods in winter using eddy covariance. Methane emissions from the study area were negligible in the absence of bison (mean ± standard deviation = 0.0024 ± 0.042 μmol m−2 s−1) and were significantly greater than zero, 0.048 ± 0.082 μmol m−2 s−1 with a positively skewed distribution, when bison were present. We coupled an eddy covariance flux footprint analysis with bison location estimates from automated camera images to calculate a mean (median) methane flux of 38 μmol s−1 (22 μmol s−1) per animal, or 52 ± 14 g CH4 day−1 (31 g CH4 day−1), less than half of measured emission rates for range cattle. Emission estimates are subject to spatial uncertainty in bison location measurements and the flux footprint, but from our measurements there is no evidence that bison methane emissions exceed those from cattle. We caution however that our measurements were made during winter and that evening measurements of bison distributions were not possible using our approach. Annual measurements are ultimately necessary to determine the greenhouse gas burden of bison grazing systems. Eddy covariance is a promising technique for measuring ruminant methane emissions in conventional and alternate grazing systems and can be used to compare them going forward.

Download Full-text

PROTOTIPE APLIKASI PENYIRAMAN TANAMAN MENGGUNAKAN SENSOR KELEMBABAN TANAH BERBASIS MICRO CONTOLLER ATMEGA 328

Journal CERITA ◽

10.33050/cerita.v5i1.235 ◽

2019 ◽

Vol 5 (1) ◽

pp. 97-106

Author(s):

Rudi Budi Agung ◽

Muhammad Nur ◽

Didi Sukayadi

Keyword(s):

Soil Moisture ◽

Growth And Development ◽

Large Scale ◽

Simple Method ◽

Moisture Sensor ◽

Sensor Development ◽

Soil Moisture Sensor ◽

Application Systems ◽

Harvesting Systems ◽

Working Principle

The Indonesian country which is famous for its tropical climate has now experienced a shift in two seasons (dry season and rainy season). This has an impact on cropping and harvesting systems among farmers. In large scale this is very influential considering that farmers in Indonesia are stilldependent on rainfall which results in soil moisture. Some types of plants that are very dependent on soil moisture will greatly require rainfall or water for growth and development. Through this research, researchers tried to make a prototype application for watering plants using ATMEGA328 microcontroller based soil moisture sensor. Development of application systems using the prototype method as a simple method which is the first step and can be developed again for large scale. The working principle of this prototype is simply that when soil moisture reaches a certainthreshold (above 56%) then the system will work by activating the watering system, if it is below 56% the system does not work or in other words soil moisture is considered sufficient for certain plant needs.

Download Full-text

Soil moisture control over autumn season methane flux, Arctic Coastal Plain of Alaska