Soil CO2 Concentration Research Articles

皆伐火烧对亚热带森林不同深度土壤CO2通量的影响

PDF HTML阅读 XML下载 导出引用 引用提醒 皆伐火烧对亚热带森林不同深度土壤CO2通量的影响 DOI: 10.5846/stxb201606241245 作者: 作者单位: 福建师范大学地理科学学院;湿润亚热带山地生态国家重点实验室培育基地,福建师范大学地理科学学院;湿润亚热带山地生态国家重点实验室培育基地,福建师范大学地理科学学院;湿润亚热带山地生态国家重点实验室培育基地,福建师范大学地理科学学院;湿润亚热带山地生态国家重点实验室培育基地,福建师范大学地理科学学院;湿润亚热带山地生态国家重点实验室培育基地,福建师范大学地理科学学院;湿润亚热带山地生态国家重点实验室培育基地 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金重点项目（31130013）；国家重点研发计划（2016YFD0600304） The impact of clear-cutting and slash burning on soil CO2 flux at different soil depths in a subtropical forest Author: Affiliation: College of Geograthy Science, Fujian Normal University;State Key Laboratory of Subtropical Mountain Ecology(Funded by Ministry of Science and Technology and Fujian Province),College of Geograthy Science, Fujian Normal University;State Key Laboratory of Subtropical Mountain Ecology(Funded by Ministry of Science and Technology and Fujian Province),College of Geograthy Science, Fujian Normal University;State Key Laboratory of Subtropical Mountain Ecology(Funded by Ministry of Science and Technology and Fujian Province),College of Geograthy Science, Fujian Normal University;State Key Laboratory of Subtropical Mountain Ecology(Funded by Ministry of Science and Technology and Fujian Province),College of Geograthy Science, Fujian Normal University;State Key Laboratory of Subtropical Mountain Ecology(Funded by Ministry of Science and Technology and Fujian Province),College of Geograthy Science, Fujian Normal University;State Key Laboratory of Subtropical Mountain Ecology(Funded by Ministry of Science and Technology and Fujian Province) Fund Project: Key Projects of National Natural Science Foundation of China (31130013) and National Key Research and Development Program of China （2016YFD0600304） 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:评估不同深度土壤的CO2通量是研究土壤碳动态的重要手段。目前有关皆伐火烧对森林土壤碳排放的影响研究仅局限于表层土壤，而对不同深度土壤碳排放影响鲜见报道。以米槠（Castanopsis carlesii）次生林（对照）及其皆伐火烧后林地为研究对象，利用非红外散射CO2探头测定土壤CO2浓度，并结合Fick第一扩散法则估算不同深度（0-80 cm）土壤CO2通量。结果表明：（1）皆伐火烧改变土壤向大气排放的表观CO2通量，在皆伐火烧后的2个月内土壤表观CO2通量显著高于对照68%；2个月后，土壤表观CO2通量低于对照37%。（2）皆伐火烧后，除10-20 cm的CO2通量提高外，其余各深度（0-10、20-40、40-60 cm和60-80 cm）的CO2通量均降低。同时，皆伐火烧改变不同土层对土壤呼吸的贡献率，降低0-10 cm土层的贡献率，提高10-20 cm土层的贡献率。（3）对照样地仅0-10 cm土壤CO2通量与温度呈显著指数相关，10-40 cm深度CO2通量则与土壤含水率呈显著线性相关。皆伐火烧后0-10 cm和10-20 cm处土壤的CO2通量均与温度呈指数相关。说明皆伐火烧改变了不同深度土壤CO2通量对于环境因子的响应。因此为准确评估和预测皆伐火烧对土壤与大气间碳交换的影响，应考虑皆伐火烧后不同时期土壤CO2通量的变化，以及不同深度土壤CO2通量对皆伐火烧的响应。 Abstract:Soil CO2 flux at different depths is an important means of researching the soil carbon dynamics. At present, the impacts of clear-cutting and slash burning on forest soil carbon emissions focus on surface soil, while their impacts on soil carbon emissions at different depths are not well known. In this study, CO2 flux along a soil profile (0-80 cm) was measured in an uncut secondary Castanopsis carlesii forest (CT) and a clear-cut, slash burnt (SB) stand of Castanopsis carlesii located in Sanming, Fujian. A scattered infrared CO2 detector was used to measure soil CO2 concentration, combined with Fick's laws of diffusion to estimate soil CO2 flux at different depths. Results showed that, (1) SB changed the apparent CO2 flux significantly. Within two months after SB, the soil surface CO2 flux increased by 68%. However, the soil surface CO2 flux decreased by 37% two months later. (2) After SB, soil CO2 fluxes at depths of 0-10, 20-40, 40-60 cm and 60-80 cm decreased with the exception of an increase at a depth of 10-20 cm. In the meantime, SB decreased the contribution rate of CO2 flux in the 0-10 cm soil layer, and increased the contribution rate of CO2 flux in the 10-20 cm soil layer. (3) There was an exponential relationship between soil CO2 flux at 0-10 cm and temperature, and the soil CO2 fluxes at other soil depths were linearly correlated with soil moisture in the control plot. After SB, soil CO2 fluxes at depths of 0-10 cm and 10-20 cm were exponentially correlated with soil temperature, which illustrated that SB changed the soil CO2 flux response at different depths due to environmental factors. Thus, in order to estimate and predict the impact of clear-cutting and SB on carbon exchange between soil and the atmosphere accurately, it is necessary to consider the changes in soil CO2 flux during different periods after SB and the response of soil CO2 flux to SB at different depths. 参考文献 相似文献 引证文献

Vertical and seasonal variations in soil CO2 production in a 55-year-old oriental arborvitae (Platycladus orientalis) plantation in China

The aim of this work was to explore the vertical and seasonal variations of CO2 within the soil profile based on Fick’s law of diffusion in an oriental arborvitae plantation. We continuously measured the soil CO2 concentration profile using CO2 sensors buried at different depths in a coniferous forest in northern China and calculated the CO2 flux based on the profile measurements using a dynamic model. The diurnal pattern of CO2 concentration and flux fluctuated during the day and varied less at night. The CO2 profile had a vertical gradient, with the highest concentrations in the deepest soil layers. The CO2 flux had a clear seasonal pattern with a maximum in summer and a minimum in winter. The contributions of the H, A, B, and C horizons to the total CO2 flux were 75.38, 13.52, 7.61, and 3.49%, respectively. Q10 was 2.668, 4.469, 1.175, and 3.333 in the H, A, B, and C horizons, respectively. The CO2 flux determined from the concentration profiles agreed well with the CO2 flux measured by open dynamic chambers, suggesting that this model could be used to successfully measure soil CO2 emissions and to describe the processes underlying CO2 efflux.

Carbon dioxide fluxes in soil profiles as affected by maize phenology and nitrogen fertilization in the semiarid Loess Plateau

To better understand the responses of subsoil CO2 to maize (Zea mays L.) phenology and N fertilization, a field experiment was conducted from 2014 to 2015 in the Changwu Agri-Ecological Station, Shaanxi, China. The experiment included four treatments: unplanted and N-unfertilized soil (C0), unplanted soil amended with 225kgNha−1 (CN), maize planted and N-unfertilized soil (P0), and maize planted soil fertilized with 225kgNha−1 (PN). Soil CO2 concentration at 0–50cm soil depth, at a resolution of 10cm, was measured, and the CO2 effluxes were calculated using the gradient method. Soil CO2 concentrations and fluxes in the planted treatments corresponded with maize growth; they rapidly increased from the jointing stage, peaked around the milk stage, and then slowly decreased with plant maturity. CO2 concentrations and fluxes in the planted soil were significantly higher compared to those in the unplanted soil. N inputs significantly decreased (P<0.05) the CO2 concentrations of the planted soil at depths of 10, 20, and 30cm in 2015 and increased total CO2 fluxes of the 0–50cm soil layers during the maize growing season by 6% (P=0.29) in 2014 and by 18% (P<0.01) in 2015, with the cumulative plant-derived CO2 fluxes enhanced by 20% (P=0.05) and 29% (P=0.07), respectively. In unplanted soil, the CO2 concentrations and fluxes of the 10cm soil layer were slightly (P>0.05) decreased with N inputs in both years. The contributions of the plant-derived CO2 effluxes to the total CO2 effluxes of the 0–50cm soil layers were affected by maize growth, with two year mean values of 0.49 for the P0 treatment and 0.55 for the PN treatment, respectively. The results indicated that subsoil CO2 fluxes were affected by maize phenology and that application of N fertilizer enhanced subsoil CO2 effluxes mainly by increasing plant-derived CO2 effluxes during the late growing season.

Soil CO2 sources above a subterranean cave—Pisani rov (Postojna Cave, Slovenia)

The objective of this research is to detect abiotic sources of soil CO2 above a subterranean cave in the Slovenian karst region. The research was performed in the forest above Pisani rov (Postojna Cave) near the town of Postojna (SW Slovenia) and also in the cave. Soil gas, atmospheric air and cave air carbon stable isotope composition (δ13CCO2) and CO2 concentration were measured. Sampling and measurements were performed bi-monthly at the test and control sites above the cave. The abiotic source of soil CO2 was estimated using a stable isotope mass balance calculation. Similar seasonal patterns of soil CO2 and δ13CCO2 values were observed at both the test and control sites until spring, with higher levels of CO2 observed in summer and lower in winter. The δ13CCO2 showed the opposite trend, i.e. lower values (−26 to −20 ‰) in summer and higher values (up to −17 ‰) in winter and early spring. In spring, the soil CO2 concentration decreases and the δ13CCO2 value increases only at the control site. A time series of a modelled “isotopically light” endmember revealed large shifts in the data values, due to the presence of an abiotic CO2 source. Results suggest that the subterranean CO2 pool and its ventilation is the main source of soil CO2, accounting for up to 80 % of the soil gas during cold periods. Ventilation from subterranean cavities is an important source of soil CO2 in karstic areas and should be taken into account during carbon cycling studies.

Influence of different ecosystems on the soil moisture and karst effect in Luota, West Hunan Province of China

In this paper, we study the soil CO2 concentration, soil respiration rate, dissolution rate and soil water content of different ecosystems in Luota, western Hunan Province, China, using the CO2 gas monitoring tube method, alkali absorption method, standard specimen method and drying method. The results show the following: the soil CO2 concentrations of the different depths have the same change trends in the forest and bush ecosystems. In spring, autumn and winter, the trends increase as the soil layer deepens, while in summer they first reduce and then increase as the soil layer deepens. However, the seasonal change dynamics differ slightly, and the soil CO2 concentrations of the forest ecosystem at the different depths and in the different seasons are greater than those of the bush ecosystem. From the perspective of comparing the full-year soil CO2 concentration, the full-year soil CO2 concentrations of the forest ecosystem at the depths of 10, 20 and 40 cm are, respectively, 1.66, 1.59 and 1.90 times those of the bush ecosystem. From the perspective of the soil respiration rates of the different seasons, the seasonal change trends of the forest and bush ecosystems are the same, both being summer > autumn > spring. The soil respiration rates of the forest ecosystem in the different seasons are higher than those of the bush ecosystem, and in spring, summer and autumn the respective soil respiration rates of the forest ecosystem are 2.09, 3.46 and 3.06 times those of the bush ecosystem. At the different depths, the dissolution rates have the same change trends in the forest and bush ecosystems, and the dissolution rates at the depth of 15 cm are both greater than those on the ground. At the same depth, the dissolution rate of the forest ecosystem is greater than that of the bush ecosystem, and the dissolution rates on the ground and at the depth of 15 cm are, respectively, 1.11 and 2.57 times those of the bush ecosystem. The soil water content of the forest ecosystem is 1.07 times of that of the bush ecosystem, and the soil water content stability of the forest ecosystem is higher, indicating that the forest ecosystem has a better karst effect.

What determines the calcium concentration of speleothem-forming drip waters?

Cave drip water calcium ion concentration is a primary determinant of speleothem deposition and growth rate. The factors that determine drip water calcium ion concentrations are the soil and vadose zone CO2 concentrations, and the hydrogeochemical evolution of the water from soil to cave. Here, we use a systematic literature review of cave drip water calcium concentrations, combined with PHREEQC equilibrium modelling, to investigate the global relationship between calcium concentration and surface climate. Our results are discussed in the context of understanding the climatic and environmental controls on drip water calcium concentration, speleothem growth rates and proxies of past climate and environmental change. We use an empirical, global soil CO2 concentration–temperature relationship to derive PHREEQC modelled cave drip water calcium concentrations. The global mean modelled drip water calcium concentration is close to that observed, but it over-predicts at high and low temperatures, and significantly under-predicts at temperate conditions. We hypothesise that closed system hydrochemical evolution due to water saturation is an important control on carbonate dissolution at colder temperatures. Under warmer conditions, for example temperate climates with a dry and hot or warm summer, seasonally-limited water availability can lead to: <100% soil cover; water-limitations on microbial and root respiration; wildfire; and prior calcite precipitation, all of which limit drip water calcium concentrations. In temperate climates with no dry season, higher CO2 concentrations than modelled from soil values are necessary to explain the observed drip water calcium values, which we propose is from an additional source of CO2 from microbial activity and root respiration in the vadose zone during open system hydrochemical evolution.

Effects of elevated soil CO2 concentration on growth and competition in a grass-clover mix

To investigate potential environmental affects in the context of carbon dioxide (CO2) leakage from Carbon Capture and Storage (CCS) schemes. The ASGARD (Artificial Soil Gassing and Response Detection) facility was established, where CO2 can be injected into the soil in replicated open-air field plots. Eight plots were sown with a grass-clover mix, with four selected for CO2 treatment while four were left as controls. Observations of sward productivity throughout the study allowed three effects to be distinguished: a direct stress response to soil gassing, limiting productivity in both species but with a greater effect on the clover; competition between the grass and clover affected by their differential stress responses; and an overall temporal trend from dominance by clover to dominance by grass in CO2 treatments. The direct effect of soil CO2 (or associated oxygen (O2) deprivation due to the high levels of CO2 in the soil) gave estimated reductions in productivity of 42% and 41% in grass, compared to 66% and 32% for clover in the high and low CO2 gassed zones respectively. Canopy CO2 increased by 70 parts per million (ppm) for every 1% increase in soil CO2 and a significant positive response of stomatal conductance in clover was observed; although carbon acquisition by the plants should not therefore be impeded, the reduction in productivity of the gassed plants is indicative of carbon-based metabolic costs probably related to soil CO2 affecting root physiology. Biomass measurements made after gassing has ceased indicated that recovery of vegetation was close to complete after 12 months.

Plastic mulching increased soil CO2 concentration and emissions from an oasis cotton field in Central Asia

AbstractAlthough previous researchers suggest that carbon dioxide (CO2) emissions are influenced by plastic mulching, the effects of this method on soil CO2 concentration and emissions remain uncertain. Soil CO2 concentration and emissions from ridge and furrow soils under mulched and nonmulched treatments in 2014 and 2015 were measured. The soil CO2 concentration was observed using modified diffusion equilibrium samplers, and the soil CO2 emissions were measured using a closed‐chamber method. In the ridge soil, although the plastic mulching increased the CO2 concentration by 49% (0–40 cm), no significant difference in CO2 emissions was found between the mulched and nonmulched treatments. Accordingly, the relationship between soil CO2 concentration and CO2 emissions was affected by plastic mulching, with a lower slope of the linear equation found in the mulched treatment compared to the nonmulched treatment. In the furrow soil, the plastic mulching increased the CO2 concentration and emissions by 15% and 21%, respectively. In conclusion, plastic mulching significantly increased the CO2 concentration in both the ridge and furrow soils and increased the cumulative CO2 emissions by 8%. The temperature sensitivity of the soil CO2 concentration increased with soil depth, whereas the plastic mulching only influenced the temperature sensitivity of the soil CO2 concentration in both the ridge and furrow soils at a depth of 40 cm. Our results suggest that the temperature sensitivity of the soil CO2 concentration not only reflects the effects of temperature on CO2 production but also indicates poor diffusion in the deep profile.

Winter precipitation and snow accumulation drive the methane sink or source strength of Arctic tussock tundra.

Arctic winter precipitation is projected to increase with global warming, but some areas will experience decreases in snow accumulation. Although Arctic CH4 emissions may represent a significant climate forcing feedback, long-term impacts of changes in snow accumulation on CH4 fluxes remain uncertain. We measured ecosystem CH4 fluxes and soil CH4 and CO2 concentrations and (13) C composition to investigate the metabolic pathways and transport mechanisms driving moist acidic tundra CH4 flux over the growing season (Jun-Aug) after 18years of experimental snow depth increases and decreases. Deeper snow increased soil wetness and warming, reducing soil %O2 levels and increasing thaw depth. Soil moisture, through changes in soil %O2 saturation, determined predominance of methanotrophy or methanogenesis, with soil temperature regulating the ecosystem CH4 sink or source strength. Reduced snow (RS) increased the fraction of oxidized CH4 (Fox) by 75-120% compared to Ambient, switching the system from a small source to a net CH4 sink (21±2 and -31±1mgCH4 m(-2) season(-1) at Ambient and RS). Deeper snow reduced Fox by 35-40% and 90-100% in medium- (MS) and high- (HS) snow additions relative to Ambient, contributing to increasing the CH4 source strength of moist acidic tundra (464±15 and 3561±97mgCH4 m(-2) season(-1) at MS and HS). Decreases in Fox with deeper snow were partly due to increases in plant-mediated CH4 transport associated with the expansion of tall graminoids. Deeper snow enhanced CH4 production within newly thawed soils, responding mainly to soil warming rather than to increases in acetate fermentation expected from thaw-induced increases in SOC availability. Our results suggest that increased winter precipitation will increase the CH4 source strength of Arctic tundra, but the resulting positive feedback on climate change will depend on the balance between areas with more or less snow accumulation than they are currently facing.

Concentration of soil CO2 as an indicator of the decalcification rate after liming treatment

Abstract This paper presents the results of investigation of decalcification of acid sandy and loamy sand soils by infiltration waters, and potential Ca-leaching after liming treatment. For this purpose, monthly measurements were made of the concentration of CO2 in the soil air, dissolved inorganic carbon in the soil waters, and their ionic composition. The determined dissolved inorganic carbon ranged from 5.9 to 10.6 mg dm−3 and from 9.9 to 16.5 mg dm−3 for the sandy and loamy sand soil, respectively. The Ca concentration in soil waters was determined as 5.9-12.4 mg dm−3 in sandy soil and 14.2-19.8 mg dm−3 in soil loamy sand. The calculated rate of decalcification amounted to 23.0 kg ha−1 year−1 in soil sandy and 19.4 kg ha−1 year−1 in loamy sand soil. The potential Ca-leaching is predicted as 124 kg ha−1 year−1 for S and 87 kg ha−1 year−1 for loamy sand soil. At the treatment level of 3 000 kg ha−1 4 year−1 of CaO, ~20% of the Ca-fertilizer can be leached after the liming treatment. The results of the CO2 concentration in the soil air may be useful in estimation of Ca-leaching from soils developed by slightly clayey sands and clayey sands in zones with a moderate climate.

Effects of experimental warming on soil respiration and biomass in Quercus variabilis Blume and Pinus densiflora Sieb. et Zucc. seedlings

In the open-field warming experiment using infrared heaters, 3 °C warming affected soil respiration more in the deciduous Quercus variabilis Blume plot than in the evergreen Pinus densiflora Sieb. et Zucc. plot, but did not affect the plant biomass in either species. Understanding the species-specific responses of belowground carbon processes to warming is essential for the accurate prediction of forest carbon cycles in ecosystems affected by future climate change. This study aimed to investigate the effect of experimental warming on soil CO2 efflux, soil-air CO2 concentration, and plant biomass for two taxonomically different temperate tree species. Experimental warming was conducted in an open-field planted with Q. variabilis and P. densiflora seedlings. Infrared heaters increased the air temperature by 3 °C in the warmed plots compared with the air temperature in the control plots over a 2-year period. The increase in air and soil temperature stimulated soil CO2 efflux by 29 and 22 % for the Q. variabilis and P. densiflora plots, respectively. Seasonal variation in the warming effect on soil CO2 efflux was species-specific. Soil CO2 efflux was also positively related to both soil temperature and soil water content. The soil moisture deficit decreased the difference in soil CO2 efflux between the control and warmed plots. Warming did not affect soil CO2 concentration and plant biomass in either species; however, the mean soil CO2 concentration was positively correlated with root and total biomass. Warming increased soil CO2 efflux in both Q. variabilis and P. densiflora plots, while the increase showed remarkable seasonal variations and different magnitudes for the two species.

Development of a CO2 -releasing coformulation based on starch, Saccharomyces cerevisiae and Beauveria bassiana attractive towards western corn rootworm larvae.

CO2 is known as an attractant for many soil-dwelling pests. To implement an attract-and-kill strategy for soil pest control, CO2 -emitting formulations need to be developed. The aim of the present work was to develop a slow-release bead system in order to bridge the gap between application and hatching of western corn rootworm larvae. We compared different Ca-alginate beads containing Saccharomyces cerevisiae for their potential to release CO2 over a period of several weeks. The addition of starch improved CO2 release, resulting in significantly higher CO2 concentrations in soil for at least 4 weeks. The missing amylase activity was compensated for either by microorganisms present in the soil or by coencapsulation of Beauveria bassiana. Formulations containing S. cerevisiae, starch and B. bassiana were attractive for western corn rootworm larvae within the first 4 h following exposure; however, when considering the whole testing period, the maize root systems remained more attractive for the larvae. Coencapsulation of S. cerevisiae, starch and B. bassiana is a promising approach for the development of attractive formulations for soil applications. For biological control strategies, the attractiveness needs to be increased by phagostimuli to extend contact between larvae and the entomopathogenic fungus growing out of these formulations. © 2016 Society of Chemical Industry.

Changes of carbon dioxide concentration in soils caused by forestry machine traffic

Abstract Forestry machine traffic causes a number of changes that are not immediately reflected in morphological changes of surface soil. These changes are physical and chemical in nature. The change in subsurface soil CO2 concentration was one of the parameters of interest. The critical CO2 concentration is thought to fluctuate around 0.6%. The primary objective of this paper was to determine the impact of forestry machine traffic on subsurface soil CO2 concentration. We measured CO2 concentration in the areas undisturbed by machinery and in the ruts in skid trails in eight forest stands. The measurements were performed using a Vaisala MI 70 meter. The results confirmed significant differences in gas concentrations between the individual measurement sites. In the ruts of the skid trails, CO2 concentrations fluctuated in a range of 0.5 to 2.81% and significantly exceeded the critical concentration. Moisture content and bulk density had a significant impact on the change in gas concentration beneath the surface, which was confirmed by multivariate analysis of variance that revealed that the values of the coefficient of correlation fluctuated in a range of 0.39 to 0.74.

Effects of wildfire on long-term soil CO2 concentration: implications for karst processes

Wildfires reduce soil CO2 concentration by destroying vegetation and soil-dwelling microbes, thus reducing soil respiration. Post-fire vegetation recovery is primarily determined by vegetation growth forms and modes of regeneration, whereas long-term recovery of soil microbes is largely dependent on vegetation rehabilitation. With previous research focussing on post-fire respiration recovery in the context of CO2 flux between the soil and atmosphere, there is a lack of studies measuring the long-term response of soil CO2 concentration in karst environments. Hence, this study aimed to quantify whether soil CO2 concentration was reduced 5 and 10 years after fires in a karst environment and to consider the implications for karst dissolution processes and speleothem growth rate. Paired sites with burnt and unburnt soil were compared with regards to soil CO2 concentration, soil temperature and soil moisture. Samples were taken from a grassland community and woodland community burnt 5 years prior and a forest community burnt 10 years prior. The results showed that soil respiration was depressed in the burnt site relative to the unburnt control in the woodland 5 years post-fire. A vegetation survey indicated that there substantially less biomass in the burnt site relative to the unburnt site. In the forest site 10 years post-fire there was no significant difference in soil CO2 concentration or vegetation between the burnt and control. This demonstrates that soil CO2 concentration takes >5 years to recover to pre-fire levels in woodlands and <10 years in subalpine forests and is determined by vegetation recovery. This long-term reduction in soil CO2 concentration caused by fire has the potential to affect karst subsurface processes governed by soil CO2 which lead to incorrect interpretation of speleothem proxy climate records.

Attraction to Carbon Dioxide from Feeding Resources and Conspecific Neighbours in Larvae of the Rhinoceros Beetle Trypoxylus dichotomus.

Saprophagous (feeding on decaying matter) insects often use carbon dioxide (CO2) as a cue for finding food. Humus-feeding larvae of the giant rhinoceros beetle Trypoxylus dichotomus exhibit a clumped distribution in natural microhabitats, but the mechanisms driving the distribution were unknown. Herein, I examined whether larvae use CO2 as a cue for fermented humus and aggregate in the vicinity of the food. I found that (i) larvae of T. dichotomus are strongly attracted to CO2, (ii) larvae orient toward highly fermented humus when given a choice between highly and poorly fermented humus, (iii) the highly fermented humus emits more CO2 than the poorly fermented humus, and (iv) larvae grow larger when fed highly fermented humus rather than poorly fermented humus. The clumped distribution of larvae is probably formed along the concentration gradient of CO2 induced by heterogeneity of fermented organic materials in soil. My laboratory experiments also revealed that larvae are chemically attracted to each other. Moreover, CO2 concentrations in soil were increased by the larval respiration, and small amounts of CO2 (much less than emitted during respiration by a single larva) were sufficient for larval attraction. These results suggest that not only response to fermented food resources, but also respiratory CO2 from conspecifics may lead to aggregation. Enhanced densities resulted in reduced weight gain under experimental conditions. However, exploiting a high-value resource at enhanced densities still led to greater body weight compared to individually exploiting a low-value resource. This demonstrates the adaptive value of the response to CO2 sources in this species.

Bulk electric conductivity response to soil and rock CO2 concentration during controlled CO2 release experiments: Observations and analytic modeling

To develop monitoring technologies for geologic [Formula: see text] storage, controlled [Formula: see text] release experiments at the Zero Emissions Research and Technology (ZERT) site in Bozeman, Montana, USA, were carried out in 2009–2011. To understand the impact on the electric properties of soil and sediment rock due to possible [Formula: see text] leakage, we have developed an analytical model to explain and predict the electric conductivity (EC) for [Formula: see text] impacted soil and sedimentary rock. Results from the model were compared with the measurements at the ZERT site during 2009–2011 and the [Formula: see text]-Vadose Project site in France in 2011–2012 after model calibration at each site. The model was calibrated using the saturation ([Formula: see text]) and cementation ([Formula: see text]) exponents contained in Archie’s equation, and a chemistry coefficient ([Formula: see text]) as tuning parameters that minimized the misfit between observed and modeled soil/rock bulk conductivity data. The calibration resulted in [Formula: see text], [Formula: see text], and [Formula: see text] for the ZERT site, which was within the range of values in the literature. All the ZERT data sets had rms errors of 0.0115–0.0724. For the [Formula: see text]-Vadose site, calibration resulted in [Formula: see text]–9.85 and [Formula: see text]–4.2, [Formula: see text]–5.65, and the rms error of 0.0002–0.0003; the cementation exponents were consistent with the literature. These results found that the model predicted the bulk EC reasonably well in soil and rock once the unmeasurable model parameters ([Formula: see text], [Formula: see text], and [Formula: see text]) were calibrated.

Chapter 14 Mapping of soil CO 2 diffuse degassing at São Miguel Island and its public health implications

Abstract Soil CO 2 diffuse degassing constitutes a permanent risk in quiescent volcanic–hydrothermal areas, as is the case in the Azores archipelago. Since the early 1990s geochemical studies carried out in São Miguel Island showed that some villages are placed in anomalous high degassing areas, and indoor measurements performed in various dwellings highlight the risk to the population. These high indoor CO 2 concentrations are not only measured in areas classified as high degassing areas, but lethal CO 2 concentrations are also registered in buildings located in areas previously defined as low- and medium-risk zones. These lethal values are measured in non-ventilated environments and basements in areas with soil CO 2 concentration above 1.5 vol%. Hazardous CO 2 concentrations are also commonly measured in buildings located in zones where soil CO 2 is higher than 5 vol%. Considering the dangerous values registered and the fact that indoor gas concentration can increase several orders of magnitude owing to peculiar meteorological conditions, updated values are suggested for the correlation between soil gas concentration and CO 2 exposure. This study highlights that both the use of soil degassing maps by land-use planners and appropriate construction rules for buildings placed in degassing areas are necessary.

Comparison of the impacts of elevated CO2 soil gas concentrations on selected European terrestrial environments

Selected European studies have illustrated the impacts of elevated CO2 concentrations in shallow soils on pasture. For the first time, general unified conclusions can be made, providing CO2 thresholds where effects on plants and soil microbiology are observed and making recommendations on how this information can be used when planning projects for CO2 storage. The sites include those where CO2 is being naturally released to the atmosphere from deep geological formations; and a non-adapted site, with no previous history of CO2 seepage, where CO2 has been injected into the unsaturated soil horizon. Whilst soil gas concentrations will be influenced by flux rates and other factors, the results suggest that a concentration of between 10% and 15% CO2 soil gas at 20cm depth, which is within the root zone, is an important threshold level for observing changes in plant coverage. Site-specific plant ‘indicators’ are also observed for CO2 concentrations at ≥35%. Microbiological changes are seen where CO2 soil gas concentrations are between 15% and 40%. As part of site characterisation, an evaluation of the risks of leakage and their potential environmental impacts should be undertaken.

Topographic controls on the depth distribution of soil CO2 in a small temperate watershed

Accurate measurements of soil CO2 concentrations (pCO2) are important for understanding carbonic acid reaction pathways for continental weathering and the global carbon (C) cycle. While there have been many studies of soil pCO2, most sample or model only one, or at most a few, landscape positions and therefore do not account for complex topography. Here, we test the hypothesis that soil pCO2 distribution can predictably vary with topographic position. We measured soil pCO2 at the Susquehanna Shale Hills Critical Zone Observatory (SSHCZO), Pennsylvania, where controls on soil pCO2 (e.g., depth, texture, porosity, and moisture) vary from ridge tops down to the valley floor, between planar slopes and slopes with convergent flow (i.e., swales), and between north and south-facing aspects. We quantified pCO2 generally at 0.1–0.2 m depth intervals down to bedrock from 2008 to 2010 and in 2013. Of the variables tested, topographic position along catenas was the best predictor of soil pCO2 because it controls soil depth, texture, porosity, and moisture, which govern soil CO2 diffusive fluxes. The highest pCO2 values were observed in the valley floor and swales where soils are deep (≥0.7 m) and wet, resulting in low CO2 diffusion through soil profiles. In contrast, the ridge top and planar slope soils have lower pCO2 because they are shallower (≤0.6 m) and drier, resulting in high CO2 diffusion through soil profiles. Aspect was a minor predictor of soil pCO2: the north (i.e., south-facing) swale generally had lower soil moisture content and pCO2 than its south (i.e., north-facing) counterpart. Seasonally, we observed that while the timing of peak soil pCO2 was similar across the watershed, the amplitude of the pCO2 peak was higher in the deep soils due to more variable moisture content. The high pCO2 observed in the deeper, wetter topographic positions could lower soil porewater pH by up to 1 pH unit compared to porewaters equilibrated with atmospheric CO2 alone. CO2 is generally the dominant acid driving weathering in soils: based on our observations, models of chemical weathering and CO2 dynamics would be improved by including landscape controls on soil pCO2.

Bare Soil Carbon Dioxide Fluxes with Time and Depth Determined by High‐Resolution Gradient‐Based Measurements and Surface Chambers

Soil CO2 production rates and fluxes vary with time and depth. The shallow near-surface soil layer is important for myriad soil processes, yet knowledge of dynamic CO2 concentrations and fluxes in this complex zone is limited. We used a concentration gradient method (CGM) to determine CO2 production and effluxes with depth in shallow layers of a bare soil. The CO2 concentration was continuously measured at 13 depths in the 0- to 200-mm soil layer. For an 11-d period, 2% of the soil CO2 was produced below a depth of 175 mm, 8% was produced in the 50- to 175-mm soil layer, and 90% was produced in the 0- to 50-mm soil layer. Soil CO2 concentration showed similar diurnal patterns with temperature in deeper soil layers and out-of-phase diurnal patterns in surface soil layers. Soil CO2 flux from most of the soil layers can be described by an exponential function of soil temperature, with temperature sensitivity (Q10) ranging from 1.40 to 2.00 (1.62 ± 0.17). The temperature-normalized CO2 fluxes are related to soil water content with a positive linear relationship in surface soil layers and a negative relationship in deep soil layers. The CO2 fluxes from CGM and chamber methods had good agreement at multiple time scales, which showed that the CGM method was able to estimate near-surface soil CO2 fluxes and production. The contrasting patterns between surface and deep layers of soil CO2 concentration and fluxes suggest the necessity of intensive CO2 concentration measurements in the surface soil layer for accurate determination of soil-atmosphere CO2 flux when using the CGM.