Assessing magnitudes and directions of CO2 fluxes within a karst landscape

2021 ◽  
Author(s):  
Taryn Thompson ◽  
Ryan Stewart ◽  
Daniel McLaughlin ◽  
Madeline Schreiber
Keyword(s):  
Unsaturated Soils ◽  
Growing Season ◽  
Gas Diffusion ◽  
Upward Movement ◽  
Measured Concentration ◽  
Cave System ◽  
Hourly Data ◽  
Primary Driver ◽  
Karst Landscapes ◽  
Zero Flux Plane

<p>Gas diffusion is a primary driver of carbon dioxide (CO<sub>2</sub>) movement through unsaturated soils. In typical soils, high soil concentrations of CO<sub>2</sub> caused by autotrophic and heterotrophic respiration cause the gas to primarily diffuse upward. However, karst landscapes can have subsurface CO<sub>2</sub> sinks, both due to CaCO<sub>3</sub> weathering and losses via underlying caves and fracture networks. In this study our objective was to quantify the magnitude and direction of CO<sub>2</sub> fluxes in a pastured karst system located in Southwest Virginia (James Cave). Our hypotheses were: 1) the zero-flux plane, or location of maximum CO<sub>2</sub> concentration within the soil profile, is located at deeper depths, ≥60 cm depth during warmer months of the year and located at shallower depths, ≤60 cm, during the colder months of the year, 2) the zero-flux plane will exist ˂60 cm depth at the sinkhole location more often than at the upslope locations, and 3) CO<sub>2</sub> fluxes will be primarily upward during the growing season and primarily downward during the colder months of the year. We installed paired CO<sub>2</sub> and soil moisture sensors at 20 cm, 40 cm, and 60 cm depths, with profiles installed in the shoulder, midslope, and bottom (i.e., sinkhole) of a hillslope adjacent to the cave entrance. The sensors recorded hourly data between 7 February 2017 and 13 September 2019. The depth of the zero-flux plane was identified by the depth of maximum CO<sub>2</sub> concentration for each profile, while the measured concentration gradient from 20 to 60 cm was used to estimate CO<sub>2</sub> flux with Fick’s Law. Our findings support our hypotheses that the relative location of the zero-flux plane was located more often at deeper depths during warmer months of the year and located at shallower depths, i.e. ˂60 cm, during colder months of the year. The zero-flux plane was more frequently shallow (i.e., ˂60 cm) at the sinkhole location compared to the upslope profiles. The CO<sub>2</sub> fluxes reflected upward movement during the growing season and downward movement during the colder months of the year. We speculate that these processes reflect the influence of the underlying cave system, which may serve as a CO<sub>2</sub> sink during colder months, when the cave becomes vented via natural convection. Altogether, these findings suggest that downward diffusion may be an important yet oft-overlooked component of carbon fluxes in karst landscapes.</p>

scholarly journals Evaluation of Evapotranspiration from Eddy Covariance Using Large Weighing Lysimeters

Agronomy ◽  
2019 ◽  
Vol 9 (2) ◽  
pp. 99 ◽  
Author(s):  
Jerry Moorhead ◽  
Gary Marek ◽  
Prasanna Gowda ◽  
Xiaomao Lin ◽  
Paul Colaizzi ◽  
...  
Keyword(s):  
Energy Balance ◽  
Eddy Covariance ◽  
Water Use ◽  
Growing Season ◽  
Irrigation Scheduling ◽  
Error Rates ◽  
Energy Balance Closure ◽  
Crop Water ◽  
Crop Water Use ◽  
Hourly Data

Evapotranspiration (ET) is an important component in the water budget and used extensively in water resources management such as water planning and irrigation scheduling. In semi-arid regions, irrigation is used to supplement limited and erratic growing season rainfall to meet crop water demand. Although lysimetery is considered the most accurate method for crop water use measurements, high-precision weighing lysimeters are expensive to build and operate. Alternatively, other measurement systems such as eddy covariance (EC) are being used to estimate crop water use. However, due to numerous explicit and implicit assumptions in the EC method, an energy balance closure problem is widely acknowledged. In this study, three EC systems were installed in a field containing a large weighing lysimeter at heights of 2.5, 4.5, and 8.5 m. Sensible heat flux (H) and ET from each EC system were evaluated against the lysimeter. Energy balance closure ranged from 64% to 67% for the three sensor heights. Results showed that all three EC systems underestimated H and consequently overestimated ET; however, the underestimation of H was greater in magnitude than the overestimation of ET. Analysis showed accuracy of ET was greater than energy balance closure with error rates of 20%–30% for half-hourly values. Further analysis of error rates throughout the growing season showed that energy balance closure and ET accuracy were greatest early in the season and larger error was found after plants reached their maximum height. Therefore, large errors associated with increased biomass may indicate unaccounted-for energy stored in the plant canopy as one source of error. Summing the half-hourly data to a daily time-step drastically reduced error in ET to 10%–15%, indicating that EC has potential for use in agricultural water management.

Dissipation of Norflurazon and Other Persistent Herbicides in Soil

Weed Science ◽  
1990 ◽  
Vol 38 (1) ◽  
pp. 81-88 ◽  
Author(s):  
Craig W. Hubbs ◽  
Terry L. Lavy
Keyword(s):  
Clay Content ◽  
Soil Surface ◽  
Growing Season ◽  
Upward Movement ◽  
Silt Loam ◽  
Relative Mobility ◽  
Laboratory Studies ◽  
Capillary Water ◽  
Layer Chromatography ◽  
Dissipation Losses

Norflurazon applied for weed control in cotton, as well as some other herbicides, sometimes persists in soil from one growing season to the next at levels phytotoxic to the following crop. Dissipation modes of norflurazon were characterized by using14C-labeled herbicides for adsorption, mobility, photolysis, and volatility studies to aid in the prediction of conditions influencing herbicide carryover problems. A direct soil-counting technique modified for use in these studies yielded a norflurazon recovery as high as 83% of the applied radioactivity. Relative mobility of the herbicides on soil thin-layer chromatography plates was fluometuron ≥ atrazine > norflurazon. Norflurazon adsorption increased and mobility decreased as soil organic matter and clay content increased. Considerable upward movement of norflurazon and atrazine occurred in subirrigated columns containing herbicide-treated Hebert silt loam. Upward movement in excess of 5 cm occurred in 10 days and 8 weeks for atrazine and norflurazon, respectively. Photolysis and volatilization studies with norflurazon and atrazine revealed low volatilization but significant photolytic losses for norflurazon when herbicide-treated soil-coated slides were exposed to ultraviolet or sunlight. After 98 h atrazine volatilization was greater and photolysis in sunlight less than that observed for norflurazon. Laboratory studies showing upward movement of norflurazon and atrazine, in conjunction with dissipation losses occurring at the soil surface, suggested that losses of norflurazon and atrazine are facilitated by movement in capillary water referred to as the “wick” effect.

scholarly journals The contribution of soil biogenic NO and HONO emissions from a managed hyperarid ecosystem to the regional NO<sub><i>x</i></sub> emissions during growing season

2016 ◽  
Vol 16 (15) ◽  
pp. 10175-10194 ◽  
Author(s):  
Buhalqem Mamtimin ◽  
Franz X. Meixner ◽  
Thomas Behrendt ◽  
Moawad Badawy ◽  
Thomas Wagner
Keyword(s):  
Growing Season ◽  
Secondary Peak ◽  
Biogenic Emissions ◽  
Nox Emissions ◽  
Top Down ◽  
Monthly Basis ◽  
Bottom Up ◽  
Strong Peak ◽  
Hourly Data ◽  
No Emissions

Abstract. A study was carried out to understand the contributions of soil biogenic NO emissions from managed (fertilized and irrigated) hyperarid ecosystems in NW China to the regional NOx emissions during the growing season. Soil biogenic net potential NO fluxes were quantified by laboratory incubation of soil samples from the three dominating ecosystems (desert, cotton, and grape fields). Regional biogenic NO emissions were calculated bottom-up hourly for the entire growing season (April–September 2010) by considering corresponding land use, hourly data of soil temperature, gravimetric soil moisture, and fertilizer enhancement factors. The regional HONO emissions were estimated using the ratio of the optimum condition ((FN,opt(HONO) to FN,opt (NO)). Regional anthropogenic NOx emissions were calculated bottom-up from annual statistical data provided by regional and local government bureaus which have been downscaled to monthly value. Regional top-down emission estimates of NOx were derived on the monthly basis from satellite observations (OMI) of tropospheric vertical NO2 column densities and prescribed values of the tropospheric NOx lifetime. In order to compare the top-down and bottom-up emission estimates, all emission estimates were expressed in terms of mass of atomic nitrogen. Consequently, monthly top-down NOx emissions (total) were compared with monthly bottom-up NOx emissions (biogenic + anthropogenic) for the time of the satellite overpass (around 13:00 LT) with the consideration of the diurnal cycle of bottom-up estimates. Annual variation in total Tohsun Oasis NOx emissions is characterized by a strong peak in winter (December–February) and a secondary peak in summer (June–August). During summer, soil biogenic emissions were from equal to double that of related anthropogenic emissions, and grape soils were the main contributor to soil biogenic emissions, followed by cotton soils, while emissions from the desert were negligible. The top-down and bottom-up emission estimates were shown to be useful methods to estimate the monthly/seasonal cycle of the total regional NOx emissions. The resulting total NOx emissions show a strong peak in winter and a secondary peak in summer, and the second maximum in summer was only found if the soil emissions were taken into account, which provides confidence in both completely independent methods. Despite the regional character of these findings, particularly the second maximum in summer provides substantial evidence to hypothesize that biogenic emissions from soils of managed drylands (irrigated and fertilized) in the growing period may be much more important contributors to regional NOx budgets of dryland regions than thought before.

RELATIONSHIPS BETWEEN NITRATE IN SUMMER-FALLOWED SURFACE SOIL AND SOME ENVIRONMENTAL VARIABLES

1975 ◽  
Vol 55 (2) ◽  
pp. 213-223 ◽  
Author(s):  
C. A. CAMPBELL ◽  
V. O. BIEDERBECK ◽  
W. C. HINMAN
Keyword(s):  
Temperature Effects ◽  
Environmental Variables ◽  
Soil Moisture Content ◽  
Surface Soil ◽  
Growing Season ◽  
Upward Movement ◽  
Moisture Change ◽  
Wetting And Drying ◽  
Total N ◽  
Moisture Conditions

Multiple regression was used to quantify the relationships between NO3 in surface soil versus several selected environmental variables. Measurements were made on summer-fallowed Wood Mountain loam in the field. The temperatures and moisture conditions measured during one growing season were simulated in the laboratory using three soils. The most important factor influencing NO3 change was wetting and drying. The latter's effect was dependent on the soil moisture content just before the change occurred and/or the temperature during the period of change. Nitrification accounted for 12% of the increases in NO3 in the top 2.5 cm of soil; 88% of the increase resulted from upward movement of NO3-salts into the surface layer of soil as a result of evaporation. Of the NO3 produced by nitrification in the Wood Mountain loam, about 17.4% was credited to temperature effects. Thus only about 2.1% of the NO3 increase in the top 2.5 cm of soil in the field was due to temperature. In the simulation study, 19 C appeared to be a critical temperature above which the rate of nitrification was sufficient to counterbalance NO3 losses resulting from leaching and/or denitrification. The effect of moisture change on NO3 change appeared to be directly proportional to the total C and total N content of the three soils.

scholarly journals The net exchange of methane with high Arctic landscapes during the summer growing season

2014 ◽  
Vol 11 (12) ◽  
pp. 3095-3106 ◽  
Author(s):  
C. A. Emmerton ◽  
V. L. St. Louis ◽  
I. Lehnherr ◽  
E. R. Humphreys ◽  
E. Rydz ◽  
...  
Keyword(s):  
Soil Temperature ◽  
Stream Water ◽  
Soil Layer ◽  
Growing Season ◽  
Organic Soil ◽  
High Arctic ◽  
Carbon Dioxide Flux ◽  
Gas Diffusion ◽  
Growing Seasons ◽  
Chamber Measurements

Abstract. High Arctic landscapes are essentially vast cold deserts interspersed with streams, ponds and wetlands. These landscapes may be important consumers and sources of the greenhouse gas methane (CH4), though few measurements exist from this region. To quantify the flux of CH4 (FCH4) between the atmosphere and high Arctic landscapes on northern Ellesmere Island, Canada, we made static chamber measurements over five and three growing seasons at a desert and wetland, respectively, and eddy covariance (EC) measurements at a wetland in 2012. Chamber measurements revealed that, during the growing season, desert soils consumed CH4 (−1.37 &amp;pm; 0.06 mg-CH4 m−2 d−1), whereas the wetland margin emitted CH4 (+0.22 ± 0.14 mg-CH4 m−2 d−1). Desert CH4 consumption rates were positively associated with soil temperature among years, and were similar to temperate locations, likely because of suitable landscape conditions for soil gas diffusion. Wetland FCH4 varied closely with stream discharge entering the wetland and hence extent of soil saturation. Landscape-scale FCH4 measured by EC was +1.27 ± 0.18 mg-CH4 m−2 d−1 and varied with soil temperature and carbon dioxide flux. FCH4 measured using EC was higher than using chambers because EC measurements incorporated a larger, more saturated footprint of the wetland. Using EC FCH4 and quantifying the mass of CH4 entering and exiting the wetland in stream water, we determined that methanogenesis within wetland soils was the dominant source of FCH4. Low FCH4 at the wetland was likely due to a shallow organic soil layer, and thus limited carbon resources for methanogens. Considering the prevalence of dry soils in the high Arctic, our results suggest that these landscapes cannot be overlooked as important consumers of atmospheric CH4.

scholarly journals Seepage and Gas Diffusion of Volatile Organic Compounds in Unsaturated Soils.

1999 ◽  
pp. 25-32 ◽  
Author(s):  
Masanori SHIMOMURA ◽  
Satoshi IMAMURA ◽  
Toru SUEOKA ◽  
Tetsuo NAGATOU ◽  
Tatemasa HIRATA
Keyword(s):  
Volatile Organic Compounds ◽  
Organic Compounds ◽  
Unsaturated Soils ◽  
Gas Diffusion ◽  
Volatile Organic

scholarly journals Thermally moderated firefly activity is delayed by precipitation extremes

2016 ◽  
Author(s):  
Sara L. Hermann ◽  
Saisi Xue ◽  
Logan Rowe ◽  
Elizabeth Davidson-Lowe ◽  
Andrew Myers ◽  
...  
Keyword(s):  
Plant Communities ◽  
Weak Interactions ◽  
Growing Season ◽  
Soil Disturbance ◽  
Flight Activity ◽  
Precipitation Extremes ◽  
Herbaceous Plant ◽  
Temperature And Precipitation ◽  
Primary Driver ◽  
History Of

AbstractThe timing of events in the life history of temperate insects is most typically primarily cued by one of two drivers: photoperiod or temperature accumulation over the growing season. However, an insect’s phenology can also be moderated by other drivers like rainfall or the phenology of its host plants. When multiple drivers of phenology interact, there is greater potential for phenological asynchronies to arise between an organism and those with which it interacts. We examined the phenological patterns of a highly seasonal group of fireflies (Photinus spp, predominantly P. pyralis) over a 12-year period (2004–2015) across 10 plant communities to determine if interacting drivers could explain the variability observed in the adult flight activity density (i.e. mating season) of this species. We found that temperature accumulation was the primary driver of phenology, with activity peaks usually occurring at a temperature accumulation of ~800 degree days (base 10°C), however, our model found this peak varied by nearly 180 degree day units among years. This variation could be explained by a quadratic relationship with the accumulation of precipitation in the growing season; in years with either high and low precipitation extremes at our study site, flight activity was delayed. More fireflies were captured in general in herbaceous plant communities with minimal soil disturbance (alfalfa and no-till field crop rotations), but only weak interactions occurred between within-season responses to climatic variables and plant community. The interaction we observed between temperature and precipitation accumulation suggests that, although climate warming has potential to disrupt phenology of many organisms, changes to regional precipitation patterns can magnify these disruptions.

scholarly journals Thermally moderated firefly activity is delayed by precipitation extremes

2016 ◽  
Vol 3 (12) ◽  
pp. 160712 ◽  
Author(s):  
Sara L. Hermann ◽  
Saisi Xue ◽  
Logan Rowe ◽  
Elizabeth Davidson-Lowe ◽  
Andrew Myers ◽  
...  
Keyword(s):  
Plant Communities ◽  
Weak Interactions ◽  
Growing Season ◽  
Soil Disturbance ◽  
Flight Activity ◽  
Precipitation Extremes ◽  
Herbaceous Plant ◽  
Temperature And Precipitation ◽  
Primary Driver ◽  
History Of

The timing of events in the life history of temperate insects is most typically primarily cued by one of two drivers: photoperiod or temperature accumulation over the growing season. However, an insect's phenology can also be moderated by other drivers like rainfall or the phenology of its host plants. When multiple drivers of phenology interact, there is greater potential for phenological asynchronies to arise between an organism and those with which it interacts. We examined the phenological patterns of a highly seasonal group of fireflies ( Photinus spp., predominantly P. pyralis ) over a 12-year period (2004–2015) across 10 plant communities to determine whether interacting drivers could explain the variability observed in the adult flight activity density (i.e. mating season) of this species. We found that temperature accumulation was the primary driver of phenology, with activity peaks usually occurring at a temperature accumulation of approximately 800 degree days (base 10°C); however, our model found this peak varied by nearly 180 degree-day units among years. This variation could be explained by a quadratic relationship with the accumulation of precipitation in the growing season; in years with either high or low precipitation extremes at our study site, flight activity was delayed. More fireflies were captured in general in herbaceous plant communities with minimal soil disturbance (alfalfa and no-till field crop rotations), but only weak interactions occurred between within-season responses to climatic variables and plant community. The interaction we observed between temperature and precipitation accumulation suggests that, although climate warming has the potential to disrupt phenology of many organisms, changes to regional precipitation patterns can magnify these disruptions.

Compact and efficient gas diffusion electrodes based on nanoporous alumina membranes for microfuel cells and gas sensors

The Analyst ◽  
2020 ◽  
Vol 145 (1) ◽  
pp. 122-131 ◽  
Author(s):  
Wanda V. Fernandez ◽  
Rocío T. Tosello ◽  
José L. Fernández
Keyword(s):  
Response Times ◽  
Hydrogen Oxidation ◽  
Fast Response ◽  
Gas Diffusion ◽  
Limiting Current ◽  
Gas Diffusion Electrodes ◽  
Nanoporous Alumina ◽  
Alumina Membranes ◽  
Current Densities ◽  
Microfuel Cells

Gas diffusion electrodes based on nanoporous alumina membranes electrocatalyze hydrogen oxidation at high diffusion-limiting current densities with fast response times.

Growing season

1992 ◽  
Author(s):  
Nicholas Wellington
Keyword(s):  
Growing Season
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