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1.
B. Kluge G. Wessolek M. Facklam M. Lorenz K. Schwärzel 《European Journal of Soil Science》2008,59(6):1076-1086
Peatlands are common in many parts of the world. Draining and other changes in the use of peatlands increase atmospheric CO2 concentration. If we are to make reliable quantitative predictions of that effect, we need good information on the CO2 emission rates from peatlands. The present study uses two different methods for predicting CO2‐C release of peatland soils: (i) a 40‐year field investigation of balancing organic carbon stocks and (ii) short‐term CO2‐C release rates from laboratory experiments. To estimate long‐term losses of peat, and its resulting C input to the atmosphere, we combined highly detailed maps of surface topography and its changes, and the organic C contents and bulk densities of a drained peatland from different years. Short‐term CO2‐C release rates were measured in the laboratory by incubating soil samples from several soil horizons at various temperatures and soil moistures. We then derived nonlinear CO2‐C production functions, which we incorporated into a numerical simulation model (HYDRUS). Using HYDRUS, we calculated daily soil water components and CO2‐release for (i) real‐climate data from 1950 to 2003 and (ii) a climate scenario extending to 2050, including an increase in temperature of 2°C and 20% less rainfall during the summer half year, i.e. from April to September inclusive. From our field measurements, we found a mean annual decrease of 0.7 cm in the thickness of the peat. Large losses (> 1.5 cm year?1) occurred only during periods when groundwater levels were low (i.e. a deep water‐table). The annual CO2‐C release results in a mean loss from the peat of about 700 g CO2‐C m?2, mostly as a direct contribution to the atmosphere. Both methods produced very similar results. The model scenarios demonstrated that CO2‐C loss is mainly controlled by the groundwater (i.e. water‐table) depth, which controls subsurface aeration. A local climate scenario estimated a c. 5% increase of CO2‐C losses within the next 50 years. 相似文献
2.
Gerd Wessolek Kai Schwrzel Manfred Renger Robert Sauerbrey Christian Siewert 《植物养料与土壤学杂志》2002,165(4):494-500
A simple model to predict soil water components and the CO2 release for peat soils is presented. It can be used to determine plant water uptake and the CO2 release as a result of peat mineralization for different types of peat soils, various climate conditions, and groundwater levels. The model considers the thickness of the root zone, its hydraulic characteristics (pF, Ku), the groundwater depth and a soil‐specific function to predict the CO2 release as a result of peat mineralization. The latter is a mathematical function considering soil temperature and soil matric potential. It is based on measurements from soil cores at varying temperatures and soil water contents using a respiricond equipment. Data was analyzed using nonlinear multiple regression analysis. As a result, CO2 release equations were gained and incorporated into a soil water simulation model. Groundwater lysimeter measurements were used for model calibration of soil water components, CO2 release was adapted according long‐term lysimeter data of Mundel (1976). Peat soils have a negative water balance for groundwater depth conditions up to 80—100 cm below surface. Results demonstrate the necessity of a high soil water content i.e. shallow groundwater to avoid peat mineralization and soil degradation. CO2 losses increase with the thickness of the rooted soil zone and decreases with the degree of soil degradation. Especially the combination of deep groundwater level and high water balance deficits during the vegetation period leads to tremendous CO2 losses. 相似文献
3.
C. Kechavarzi Q. Dawson P. B. Leeds-Harrison J. Szatyowicz & T. Gnatowski 《Soil Use and Management》2007,23(4):359-367
The rate of oxidation of peat soils is highly seasonal and varies with temperature and soil moisture content. Large variations in soil moisture content result in wet–dry cycles that can enhance peat degradation. Water‐table management plays a crucial role in controlling and damping the effect of these environmental factors. However, maintaining high ditch water levels in fields bounded by ditches does not guarantee a high field groundwater level. The effect of installing subsurface irrigation at different spacings on water table elevation was studied in a low‐lying peat grassland. The water table elevation data were compared against values predicted with a water balance model. In addition, greenhouse experiments were carried out on undisturbed soil core samples collected from the peat grassland as well as a low‐lying peatland under intensive arable faming to measure CO2 evolution under different water regimes. The field data from the peat grassland suggest that sub‐irrigation spacing as low as 10 m is necessary during summer periods to maintain groundwater levels similar to those in the ditches. Over the same period of observation, the difference in water level between the ditches and the non‐irrigated fields is as high as 0.7 m. Modelled outputs are in good correlation with the field observations, and demonstrate that simple water balance models can provide an effective tool to study the effect of water management practices and potential changes in subsurface conditions, climate and land use on water‐table levels. The measurement of CO2 emission from undisturbed peat soil columns shows that the rate of oxidation of soil organic matter from peat soils is highly seasonal and that drainage exacerbates the rate of peat mineralization. 相似文献
4.
A lysimeter method using undisturbed soil columns was used to investigate the effect of water table depth and soil properties on soil organic matter decomposition and greenhouse gas (GHG) emissions from cultivated peat soils. The study was carried out using cultivated organic soils from two locations in Sweden: Örke, a typical cultivated fen peat with low pH and high organic matter content and Majnegården, a more uncommon fen peat type with high pH and low organic matter content. Even though carbon and nitrogen contents differ greatly between the sites, carbon and nitrogen density are quite similar. A drilling method with minimal soil disturbance was used to collect 12 undisturbed soil monoliths (50 cm high, Ø29.5 cm) per site. They were sown with ryegrass (Lolium perenne) after the original vegetation was removed. The lysimeter design allowed the introduction of water at depth so as to maintain a constant water table at either 40 cm or 80 cm below the soil surface. CO2, CH4 and N2O emissions from the lysimeters were measured weekly and complemented with incubation experiments with small undisturbed soil cores subjected to different tensions (5, 40, 80 and 600 cm water column). CO2 emissions were greater from the treatment with the high water table level (40 cm) compared with the low level (80 cm). N2O emissions peaked in springtime and CH4 emissions were very low or negative. Estimated GHG emissions during one year were between 2.70 and 3.55 kg CO2 equivalents m−2. The results from the incubation experiment were in agreement with emissions results from the lysimeter experiments. We attribute the observed differences in GHG emissions between the soils to the contrasting dry matter liability and soil physical properties. The properties of the different soil layers will determine the effect of water table regulation. Lowering the water table without exposing new layers with easily decomposable material would have a limited effect on emission rates. 相似文献
5.
Magdalena Matysek Jonathan Leake Steven Banwart Irene Johnson Susan Page Jorg Kaduk Alan Smalley Alexander Cumming Donatella Zona 《Soil Use and Management》2022,38(1):341-354
Forty percentage of UK peatlands have been drained for agricultural use, which has caused serious peat wastage and associated greenhouse gas emissions (carbon dioxide (CO2) and methane (CH4)). In this study, we evaluated potential trade-offs between water-table management practices for minimizing peat wastage and greenhouse gas emissions, while seeking to sustain romaine lettuce production: one of the most economically relevant crop in the East Anglian Fenlands. In a controlled environment experiment, we measured lettuce yield, CO2, CH4 fluxes and dissolved organic carbon (DOC) released from an agricultural fen soil at two temperatures (ambient and +2°C) and three water-table levels (−30 cm, −40 cm and −50 cm below the surface). We showed that increasing the water table from the currently used field level of −50 cm to −40 cm and −30 cm reduced CO2 emissions, did not affect CH4 fluxes, but significantly reduced yield and increased DOC leaching. Warming of 2°C increased both lettuce yield (fresh leaf biomass) and peat decomposition through the loss of carbon as CO2 and DOC. However, there was no difference in the dry leaf biomass between the intermediate (−40 cm) and the low (−50 cm) water table, suggesting that romaine lettuce grown at this higher water level should have similar energetic value as the crop cultivated at −50 cm, representing a possible compromise to decrease peat oxidation and maintain agricultural production. 相似文献
6.
Päivi Mäkiranta Kari Minkkinen Jyrki Hytönen Jukka Laine 《Soil biology & biochemistry》2008,40(7):1592-1600
Partitioning soil respiration (SR) into its components, heterotrophic and rhizospheric respiration, is an important step for understanding and modelling carbon (C) cycling in organic soils. However, no partitioning studies on afforested organic soil croplands exist. We separated soil respiration originating from the decomposition of peat (SRP), and aboveground litter (SRL) and root respiration (SRR) in six afforested organic soil croplands in Finland with varying tree species and stand ages using the trenching method. Across the sites temporal variation in SR was primarily related to changes in soil surface temperature (?5 cm), which explained 71–96% of variation in SR rates. Decomposition of peat and litter was not related to changes in water table level, whereas a minor increase in root respiration was observed with the increase in water table depth. Temperature sensitivity of SR varied between the different respiration components: SRP was less sensitive to changes in soil surface temperature than SRL or SRR. Factors explaining spatial variation in SR differed between different respiration components. Annual SRP correlated positively with peat ash content while that of SRL was found to correlate positively with the amount of litter on the forest floor, separately for each tree species. Root respiration correlated positively with the biomass of ground vegetation. From the total soil respiration peat decomposition comprised a major share of 42%; the proportion of autotrophic respiration being 41% and aboveground litter 17%. Afforestation lowered peat decomposition rates. Nevertheless the effect of agricultural history can be seen in peat properties for decades and due to high peat decomposition rates these soils still loose carbon to the atmosphere. 相似文献
7.
若尔盖高寒湿地土壤活性有机碳垂直分布特征 总被引:30,自引:0,他引:30
对若尔盖高寒湿地沼泽土和泥炭土的有机碳(TOC)和活性有机碳(LC)沿土壤剖面的分布特征研究表明,沼泽土的有机碳和全氮(TN)古量整体上从表层向下呈现下降趋势.中间在16~18cm处出现一个升高点,与当时的有机质来源和沉积环境有关。泥炭土有机碳沿土壤剖面并没有呈现同样的下降趋势.而是从表层向下至22cm呈现升高趋势,22cm向下才呈现下降趋势。全氮含量与有机碳含量的分布特征不同。在表层o~10cm古量较高,向下含量减小。沼泽土活性有机碳沿土壤剖面整体呈现下降趋势,变化于2.4~13.6mg/g.变异系数较大。达到53.25%。泥炭土活性有机碳沿土壤剖面规律性不明显,变化于30-45mg/g,变异系数只有11.62%。沼泽土的活性有机碳占到总有机碳的3%~17%。变化较大;而泥炭土的活性有机碳占到总有机碳的7%~12%,变化较小。沼泽土和泥炭土的有机碳活度(L)最大值并不是出现在表层,而是在表层稍微向下的部分(8~10cm)。再向下有机碳活度呈现下降的趋势。 相似文献
8.
Gardini F. Antisari L. Vittori Guerzoni M. E. Sequi P. 《Biology and Fertility of Soils》1991,12(1):1-4
Summary We have developed a simple method for the determination of gaseous compounds that reflect microbial activity in soil, as affected by factors such as the presence of an organic amendment (peat) or a variation in soil moisture. The method is based on a gas chromatographic analysis of the headspace of vials containing the soil under examination. A single gas chromatograph can detect up to 10 different gases. As expected, after peat was added to the soil, CO2 evolution and O2 uptake increased significantly. Positive relationships were found between the evolution of N2O, and soil moisture and the amount of peat added to the soil. Both the these variables influenced the CO2:O2 ratio. The results given by this method show high reproducibility. 相似文献
9.
Rachhpal Jassal Andy Black Mike Novak Kai Morgenstern Zoran Nesic David Gaumont-Guay 《Agricultural and Forest Meteorology》2005,130(3-4):176-192
To better understand the biotic and abiotic factors that control soil CO2 efflux, we compared seasonal and diurnal variations in simultaneously measured forest-floor CO2 effluxes and soil CO2 concentration profiles in a 54-year-old Douglas fir forest on the east coast of Vancouver Island. We used small solid-state infrared CO2 sensors for long-term continuous real-time measurement of CO2 concentrations at different depths, and measured half-hourly soil CO2 effluxes with an automated non-steady-state chamber. We describe a simple steady-state method to measure CO2 diffusivity in undisturbed soil cores. The method accounts for the CO2 production in the soil and uses an analytical solution to the diffusion equation. The diffusivity was related to air-filled porosity by a power law function, which was independent of soil depth. CO2 concentration at all depths increased with increase in soil temperature, likely due to a rise in CO2 production, and with increase in soil water content due to decreased diffusivity or increased CO2 production or both. It also increased with soil depth reaching almost 10 mmol mol−1 at the 50-cm depth. Annually, soil CO2 efflux was best described by an exponential function of soil temperature at the 5-cm depth, with the reference efflux at 10 °C (F10) of 2.6 μmol m−2 s−1 and the Q10 of 3.7. No evidence of displacement of CO2-rich soil air with rain was observed.Effluxes calculated from soil CO2 concentration gradients near the surface closely agreed with the measured effluxes. Calculations indicated that more than 75% of the soil CO2 efflux originated in the top 20 cm soil. Calculated CO2 production varied with soil temperature, soil water content and season, and when scaled to 10 °C also showed some diurnal variation. Soil CO2 efflux and concentrations as well as soil temperature at the 5-cm depth varied in phase. Changes in CO2 storage in the 0–50 cm soil layer were an order of magnitude smaller than measured effluxes. Soil CO2 efflux was proportional to CO2 concentration at the 50-cm depth with the slope determined by soil water content, which was consistent with a simple steady-state analytical model of diffusive transport of CO2 in the soil. The latter proved successful in calculating effluxes during 2004. 相似文献
10.
Agricultural peat soils in the Sacramento-San Joaquin Delta, California have been identified as an important source of dissolved organic carbon (DOC) and trihalomethane precursors in waters exported for drinking. The objectives of this study were to examine the primary sources of DOC from soil profiles (surface vs. subsurface), factors (temperature, soil water content and wet-dry cycles) controlling DOC production, and the relationship between C mineralization and DOC concentration in cultivated peat soils. Surface and subsurface peat soils were incubated for 60 d under a range of temperature (10, 20, and 30 °C) and soil water contents (0.3-10.0 g-water g-soil−1). Both CO2-C and DOC were monitored during the incubation period. Results showed that significant amount of DOC was produced only in the surface soil under constantly flooded conditions or flooding/non-flooding cycles. The DOC production was independent of temperature and soil water content under non-flooded condition, although CO2 evolution was highly correlated with these parameters. Aromatic carbon and hydrophobic acid contents in surface DOC were increased with wetter incubation treatments. In addition, positive linear correlations (r2=0.87) between CO2-C mineralization rate and DOC concentration were observed in the surface soil, but negative linear correlations (r2=0.70) were observed in the subsurface soil. Results imply that mineralization of soil organic carbon by microbes prevailed in the subsurface soil. A conceptual model using a kinetic approach is proposed to describe the relationships between CO2-C mineralization rate and DOC concentration in these soils. 相似文献
11.
Helena Lina Susilawati Prihasto Setyanto Miranti Ariani Anggri Hervani Kazuyuki Inubushi 《Soil Science and Plant Nutrition》2016,62(1):57-68
Recently, large areas of tropical peatland have been converted into agricultural fields. To be used for agricultural activities, peat soils need to be drained, limed and fertilized due to excess water, low nutrient content and high acidity. Water depth and amelioration have significant effects on greenhouse gas (GHG) production. Twenty-seven soil samples were collected from Jabiren, Central Kalimantan, Indonesia, in 2014 to examine the effect of water depth and amelioration on GHG emissions. Soil columns were formed in the peatland using polyvinyl chloride (PVC) pipe with a diameter of 21 cm and a length of 100 cm. The PVC pipe was inserted vertically into the soil to a depth of 100 cm and carefully pulled up with the soil inside after sealing the bottom. The treatments consisting of three static water depths (15, 35 and 55 cm from the soil surface) and three ameliorants (without ameliorant/control, biochar+compost and steel slag+compost) were arranged using a randomized block design with two factors and three replications. Fluxes of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) from the soil columns were measured weekly. There was a linear relationship between water depth and CO2 emissions. No significant difference was observed in the CH4 emissions in response to water depth and amelioration. The ameliorations influenced the CO2 and N2O emissions from the peat soil. The application of biochar+compost enhanced the CO2 and N2O emissions but reduced the CH4 emission. Moreover, the application of steel slag+compost increased the emissions of all three gases. The highest CO2 and N2O emissions occurred in response to the biochar+compost treatment followed by the steel slag-compost treatment and without ameliorant. Soil pH, redox potential (Eh) and temperature influenced the CO2, CH4 and N2O fluxes. Experiments for monitoring water depth and amelioration should be developed using peat soil as well as peat soil–crop systems. 相似文献
12.
The purpose of this study was to monitor the dynamics of gases such as CO2 and CH4 in a soil profile with sufficient temporal resolution to observe possible diurnal variations. A computer-controlled device called a membrane probes array (MPA) was developed that consisted of 9-12 individual membrane probes installed at various soil depths. Each probe was made of a stainless steel pipe with a 1 mm orifice covered with a silicone membrane. Soil gases diffuse through the membrane at a rate proportional to the ambient soil gas concentration. To measure diffusion rates, the probes are flushed with N2 one-by-one at regular time intervals and accumulated gas is detected as a spike with IR and FID analyzers. The longer the period between flushings the higher the gas accumulation and the lower the detection limit for a particular soil gas. The developed MPA agreed well with conventional manual gas sampling in West-Siberian mesotrophic fen. In peat cores with intact Carex-Sphagnum vegetation incubated under constant temperature, water level and artificial light:dark (14:10) cycles, regular diurnal oscillations of soil CO2 and CH4 occurred in the upper part of the peat core down to 19 cm. Gas content in the top layer (3 cm) grew during the light phase, and returned back during the dark phase. In layers further down in the soil, the same events were observed but with progressively increased time delay and lower amplitude. The obtained data agreed with the hypothesis that diurnal variations in soil CO2 and CH4 content are caused by periodic changes in intensity of root exudation that provide a major C- and energy source for soil microorganisms including methanogens. At a soil depth of 23 cm, where the peak of gas bubbles occurred, the signal for both gases became chaotic and not related to the light:dark cycle. 相似文献
13.
The climatic changes on earth may have serious implications for the carbon (C) cycle in the terrestrial Arctic throughout the 21st century. Arctic vegetation takes up carbon dioxide (CO2) from the atmosphere producing biomass. In a cold and often moist soil environment, dead organic matter is preferentially preserved as soil organic matter (SOM) due to the inhibition of decomposition processes. However, viable soil microbes exhale huge amounts of CO2 and methane (CH4) annually. Hence, Arctic ecosystems exhibit annual fluxes of both carbon‐based (CO2 and CH4) greenhouse gases (GHGs) that are in an order of magnitude of millions of tons. Rising Arctic temperatures lead to the degradation of much of today's permafrost in the long run. As a result, large quantities of frozen SOM may become available for decomposers, and GHGs that are entrapped in permafrost may be released. At the same time, warming tends to stimulate the growth, development, and reproduction of many Arctic plants, at least transiently. The present northward migration of boreal shrubs and trees into southern tundra areas may be amplified by that, increasing the ecosystems' gross primary production and, thus, their C sequestration. On the other hand, rising temperatures boost SOM decomposition and microbial respiration rates. In general, soil temperature and soil moisture are key environmental variables to control the intensity of aerobic and anaerobic respiration by microbes, and autotrophic respiration by plants. On the basis of published data on Arctic CO2 and CH4 fluxes, the calculations on the terrestrial C‐based Arctic GHG balance made in this review reveal a current annual GHG exchange that ranges between a weak storage of ≤ 225 Tg CO2 equivalent (eq.) y–1 and a huge release of ≤ 1990 Tg CO2 eq. y–1. Hence, the Arctic GHG balance does apparently already contribute positively to the climatic changes at present. Regarding the future, the relative development of the uptake and release of CO2 and CH4 by northern ecosystems is fundamental to the overall GHG status of the Arctic under scenarios of continued climate change. 相似文献
14.
The effect of soil moisture,soil particle size,litter layer and carbonic anhydrase on the oxygen isotopic composition of soil‐released CO2
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Soil respiration and photosynthesis are the two largest carbon dioxide (CO2) fluxes between terrestrial ecosystems and the atmosphere and, therefore, the dominant processes influencing the oxygen isotopic composition of atmospheric CO2. The characterization of temporal and spatial variations of plant and soil‐related fluxes of different oxygen isotopologues of CO2 (12C16O2; 12C16O18O) is relevant to constraining the global carbon budget. The oxygen isotopic composition of soil‐respired CO2 is controlled by its release rate, the degree of isotopic equilibrium with soil water and the diffusional transport of CO2. The hypothesis of this study was that, as well as soil moisture, the soil particle size, the presence of an organic litter layer and the enzyme carbonic anhydrase (CA) would have a significant impact on the oxygen isotopic composition of soil‐released CO2. We tested this hypothesis with soil microcosm experiments on columns of medium and fine sand. Soil water content and soil texture influenced the isotopic composition of soil‐released CO2 significantly. A litter layer had a significant effect on the isotopic composition of water vapour but not on CO2 released from soil. In the absence of CA, oxygen isotope equilibration between the CO2 invasion flux and soil water was insignificant, whereas in the presence of CA about 55% of the CO2 invading the soil exchanged oxygen isotopes with soil water. Our findings highlight the importance of small‐scale variability of soil attributes for the oxygen isotopic composition of soil‐released CO2 as well as the strong impact of CA activity in soils. 相似文献
15.
16.
S.M.L. Hardie M.H. Garnett A.E. Fallick A.P. Rowland N.J. Ostle T.H. Flowers 《Soil biology & biochemistry》2011,43(12):2432-2440
Feedbacks to global warming may cause terrestrial ecosystems to add to anthropogenic CO2 emissions, thus exacerbating climate change. The contribution that soil respiration makes to these terrestrial emissions, particularly from carbon-rich soils such as peatlands, is of significant importance and its response to changing climatic conditions is of considerable debate. We collected intact soil cores from an upland blanket bog situated within the northern Pennines, England, UK and investigated the individual and interactive effects of three primary controls on soil organic matter decomposition: (i) temperature (5, 10 and 15 °C); (ii) moisture (50 and 100% field capacity – FC); and (iii) substrate quality, using increasing depth from the surface (0–10, 10–20 and 20–30 cm) as an analogue for increased recalcitrance of soil organic material. Statistical analysis of the results showed that temperature, moisture and substrate quality all significantly affected rates of peat decomposition. Q10 values indicated that the temperature sensitivity of older/more recalcitrant soil organic matter significantly increased (relative to more labile peat) under reduced soil moisture (50% FC) conditions, but not under 100% FC, suggesting that soil microorganisms decomposing the more recalcitrant soil material preferred more aerated conditions. Radiocarbon analyses revealed that soil decomposers were able to respire older, more recalcitrant soil organic matter and that the source of the material (deduced from the δ13C analyses) subject to decomposition, changed depending on depth in the peat profile. 相似文献
17.
《Soil biology & biochemistry》2012,44(12):2432-2440
Feedbacks to global warming may cause terrestrial ecosystems to add to anthropogenic CO2 emissions, thus exacerbating climate change. The contribution that soil respiration makes to these terrestrial emissions, particularly from carbon-rich soils such as peatlands, is of significant importance and its response to changing climatic conditions is of considerable debate. We collected intact soil cores from an upland blanket bog situated within the northern Pennines, England, UK and investigated the individual and interactive effects of three primary controls on soil organic matter decomposition: (i) temperature (5, 10 and 15 °C); (ii) moisture (50 and 100% field capacity – FC); and (iii) substrate quality, using increasing depth from the surface (0–10, 10–20 and 20–30 cm) as an analogue for increased recalcitrance of soil organic material. Statistical analysis of the results showed that temperature, moisture and substrate quality all significantly affected rates of peat decomposition. Q10 values indicated that the temperature sensitivity of older/more recalcitrant soil organic matter significantly increased (relative to more labile peat) under reduced soil moisture (50% FC) conditions, but not under 100% FC, suggesting that soil microorganisms decomposing the more recalcitrant soil material preferred more aerated conditions. Radiocarbon analyses revealed that soil decomposers were able to respire older, more recalcitrant soil organic matter and that the source of the material (deduced from the δ13C analyses) subject to decomposition, changed depending on depth in the peat profile. 相似文献
18.
M. Maier H. Schack‐Kirchner E. E. Hildebrand J. Holst 《European Journal of Soil Science》2010,61(6):877-887
Most studies implicitly consider soil carbon dioxide (CO2) efflux as the instantaneous soil respiration and thereby neglect possible changes in the amount of CO2 stored in the soil pore‐space. We measured the CO2 concentration profile of a well‐aerated soil continuously to evaluate the dynamics of the stored CO2 and to analyse the influence of environmental factors. For 25% of the observation period, changes in the amount of stored CO2 accounted for more than 15% of the soil‐CO2 efflux. The following factors were identified to interfere with steady‐state CO2 storage: (i) the fluctuating groundwater table altered the volume of the vadose zone, causing viscous airflow in air‐filled soil pores, (ii) atmospheric turbulence caused pressure‐pumping at the soil–atmosphere interface and (iii) intense rain greatly reduced the diffusivity of the uppermost soil layer. The friction velocity above the canopy was strongly correlated with fluctuations in the differential pressure between soil air and atmosphere, but no static pressure gradient could be detected because of the permeable nature of the soil. Unexpected short‐term declines in the soil CO2 concentration were observed during intense rainfall events. These declines were explained by the intensified CO2 saturation deficit of the infiltrating rainwater caused by the carbonate chemistry of the soil solution. 相似文献
19.
Reductosols: Natural soils and Technosols under reducing conditions without an aquic moisture regime
According to the German soil classification, Reductosols (German: “Reduktosole”) are soils with a redoximorphic color pattern, but without water saturation for lengthy periods. They are formed by reducing conditions due to oxygen deficiency caused by the accumulation of reduct gases such as CH4, CO2, NH3, or H2S in the soil atmosphere. Soil oxygen may have been displaced by the ascent of CO2 from post‐volcanic mofettes or by CH4 from sanitary landfills. Furthermore, a lack of oxygen causing redoximorphism can occur in unsaturated soils if they contain or receive large quantities of easily decomposable organic matter (i.e., organic urban waste or sludge). Under such circumstances, a gleyic color pattern (e.g., an oxidized Bg horizon above a Cr horizon with strongly reducing conditions) forms without the influence of an aquic moisture regime. Waste‐water and petrol infiltration in soil can form a stagnic color pattern without the stagnation of surface water. Such more or less well‐drained but strongly redoximorphic horizons should be named as Yg instead of Bg. In some cases, such soils only exist for a short time due to the loss of reduct gases or termination of infiltration of organic liquids. Reductosols are ecotops with oxygen deficiency. Natural Reductosols dominate in recent and former volcanic areas, whereas Reductic Technosols are formed in urban‐industrial agglomerations. Their morphology, chemistry, dynamics, genesis, and ecology is summarized and discussed in this paper. Natural gas and CO2 gas are deposited in deeper zones of the earth crust since some time. Leakages of these depots let form reductosols as well. 相似文献
20.
Edyta Hewelke Jan Szatyowicz Tomasz Gnatowski Ryszard Oleszczuk 《Land Degradation \u0026amp; Development》2016,27(4):955-964
An understanding of soil moisture content variability is fundamental in hydrological studies of peat soils, whose preservation depend on water‐related processes. Dehydration of fens and adapting them for agricultural production have contributed to the degradation of peat soils. The goal of this study was to determine how the critical soil moisture content (CSMC) and soil water repellency (SWR) affect soil moisture patterns in a degraded peat‐muck soil profile. SWR was measured under laboratory conditions using the water drop penetration time test, and then the CSMC was assessed. An investigation of moisture patterns was based on soil moisture data collected over short distances in a grass‐covered peat‐muck soil profile on seven dates. Observed differences in moisture patterns demonstrate that the CSMC can be used for the prediction of preferential flow occurrences in peat‐muck soils. Lower values of the CSMC and lower levels of SWR persistence in muck layers than in peat layers indicate that degradation of peat soils improves their wettability. The relatively low values of CSMC and the low shrinkage potential in the muck layer suggest that preferential water flow in the degraded organic soils can occur when heavy rains are preceded by long periods of summer drought. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献