巢湖水体二氧化碳浓度时空分布特征及其水-气交换通量

为揭示巢湖水体二氧化碳浓度（cCO₂）时空变化特征及其影响因素,2017年2、4、8和11月分别采集巢湖表层水样,测定水样的理化、生物学参数以及cCO₂,并以此计算其水-气界面交换通量.结果表明：巢湖表层水体cCO₂的变化范围为13.31~55.47 μmol/L,年平均值为26.27 μmol/L,在空间上呈现出西高东低的分布趋势;在季节上表现为暖季（夏季）低、冷季（春、秋和冬季）高的规律.巢湖表层水体cCO₂与溶解性有机碳浓度呈显著正相关,与叶绿素a浓度呈显著负相关,说明有机质分解和光合作用在巢湖CO₂生物化学循环过程中占重要作用;同时,南淝河等入湖河流污染严重,输入大量有机和无机碳,对西巢湖水体CO₂贡献较大.总体上,巢湖CO₂排放量相对较低,巢湖部分区域在冷季（2、11月）表现为CO₂的汇.本研究对于明晰富营养化湖泊CO₂排放特征以及准确估算全球内陆湖泊碳通量等都具有参考价值.     

Annual variation of carbon flux and impact factors in the tropical seasonal rain forest of Xishuangbanna, SW China

Two years of eddy covariance measurements of above- and below-canopy carbon fluxes and static opaque chamber and gas chromatography technique measurements of soil respiration for three treatments (bare soil, soil litterfall, soil litterfall seedling) were carried out in a tropical seasonal rain forest. In addition, data of photosynthesis of dominant tree species and seedlings, leaf area index, litter production and decomposing speed, soil moisture, soil temperature and photosynthetic photon flux density within the forest were all measured concurrently. Data from January 2003 to December 2004 are used to present annual variability of carbon flux and relationships between carbon flux and impact factors. The results show that carbon flux of this forest presented unusual tendency of annual variation; above-canopy carbon fluxes were negative in the dry season (November-April) and mainly positive in the rainy season, but overall the forest is a carbon sink. Carbon flux has obviously diurnal variation in this tropical seasonal rain forest. Above-canopy carbon fluxes were negative in the daytime and absolute values were larger in the dry season than that in the rainy season, causing the forest to act as a carbon sink; at night, carbon fluxes were mainly positive, causing the forest to act as a carbon source. Dominant tree species have greater photosynthesis capability than that of seedlings, which have a great effect on above-canopy carbon flux. There was a significant correlation between above-canopy carbon flux and rate of photosynthesis of tree species. There was also a significant correlation between above-canopy carbon flux and rate of photosynthesis of seedlings; however, the below-canopy carbon flux was only significantly correlated with rate of photosynthesis of seedlings during the hot-dry season. Soil respiration of the three treatments displayed a markedly seasonal dynamic; in addition, above-canopy carbon fluxes correlated well with soil respiration, litterfall production, litterfall decomposition rate, precipitation, and soil moisture and temperature. A primary statistical result of this study showed that above-canopy carbon flux in this forest presented carbon source or sink effects in different seasons, and it is a carbon sink at the scale of a year.     

Interrill soil erosion processes and their interaction on low slopes

Soil erosion by water is mostly the result of rainfall‐driven and runoff‐driven processes taking place simultaneously during a storm event. However, the effect of interaction between these two erosion processes has received limited attention. Most laboratory experiments indicate that the rate of erosion in a rain‐impacted flow is greater than for un‐impacted flows of similar depth and velocity; however, negative interaction between the two processes has also been reported. There is no provision for any such interaction in any of the current erosion models. This paper reports on the results of a number of exact experiments on three soil types carried out in the flume of Griffith University's large rainfall simulator to study interaction between rain and runoff processes. The results show that interaction is generally positive under approximately steady state condition and there is very limited sign of negative interaction reported by others. Results provide strong evidence that raindrops continuously peel fine sediment from larger stable aggregates. This mechanism could be the reason for positive interaction during simultaneous rainfall and flow driven erosion in well aggregated soils as a result of increased fine particles in the eroded sediment. Strong positive interaction between rain and runoff erosion also occurs for medium to large aggregates. This strongly suggests that mechanisms that are not well understood are operational. It is quite possible that particle movement can be stimulated by rolling or creeping in a size‐selective manner. Indeed, such additional mechanisms may well be largely responsible for the positive interaction observed between rain and surface flow. Copyright © 2006 John Wiley & Sons, Ltd.     

Spatial and temporal variations in temperate forest soil carbon dioxide during the non-growing season

In the Whitehall Forest of Georgia during the 1985-86 non-growing season soil CO₂ varied with soil depth, varied spatially at constant depth, and varied temporally with changing environmental conditions. Variations with depth in the upper 1.4 m of the soil were of greater magnitude than temporal variations and spatial differences at 30 cm depth were of lesser magnitude. Mean soil CO₂ in evergreen forest was higher (0.207 per cent) than in deciduous and mixed forest (0.157 per cent). There were no trends in soil CO₂ along hillslopes or with changes in soil texture, bulk density, moisture content, or temperature. Soil CO₂ did increase near trees possibly due to increased root densities and/or more numerous pockets of microbial activity. For CO₂ at 30 cm depth, two variables–the mean daily temperature range in the month before measurement and actual evapotranspiration in the week before measurement (AET7)–explained 76 per cent of the variation in mean soil CO₂. At the profile site, where soil CO₂ was measured at five depths, 66 per cent of the variability in CO₂ was explained by soil depth, AET7, and the average daily temperature range in the two months before measurement.     

A world model of soil carbon dioxide

Mean growing season soil PCO₂ data were obtained for 19 regions of the world in nine countries. Bivariate and multiple linear regression analysis with soil log(PCO₂) as the dependent variable and TEMP, PRECIP, log(AET), and log(PET) as the four climatic independent variables demonstrated that AET was the best independent predictor of soil PCO₂. An improved soil PCO₂-AET model was developed by assuming (1) that as AET approaches zero, soil PCO₂ approaches the atmospheric value and (2) that there is an upper limit to soil PCO₂ at very high AET. This model has the form log(PCO₂) = ?3·47 + 2·09 (1 ?e^{?0·0172 AET}) where AET is in mm. It explains 67 per cent of the initial variation in the soil PCO₂ data, predicts a soil log(PCO₂) of ? 3·47 at AET = 0, and an upper limit of 3·5 per cent (log(PCO₂) = ? 1·45) for mean growing season soil PCO₂ at AET values of 2000 mm and above. The results of this study suggest that soil PCO₂ levels in tropical areas are, on average, higher than those in temperate, alpine, and arctic regions.     

Helium and CO2 soil gas emission from Santorini (Greece)

Soil gas investigation is a useful tool to detect active faults. The sudden appearance of soil gas anomalies in zones of deep-reaching faults represents a promising potential precursor of earthquakes and volcanic eruptions. In volcanic areas the development of soil gas monitoring techniques is particularly important, as they can represent, together with remote sensing techniques, the only geochemical methods that can be safely applied during volcanic unrest, when it becomes impossible or too dangerous to sample crater fumaroles. A soil gas survey was carried out in June 1993 at the main island of Thera, in the Santorini volcanic complex. CO₂ flux and CO₂ and helium concentrations were measured at 50 cm depth for 76 points covering the entire island, with a spacing of 500 m or less. Several anomalous soil degassing sites have been detected. The main anomalies correspond to the Kolumbos line and to the Kameni line, two volcano-tectonic fault systems that controlled all the historic volcanic activity of Santorini. A third anomaly is related to a gas-leaking fault cutting the geothermal field of southern Thera. Soil gas data, together with geovolcanological and seismological evidence, indicate that the Kolumbos and Kameni lines are the most probable sites for future volcanic or seismic reactivation, and provide the basis for the establishment of a new geochemical monitoring technique at Thera.     

Acoustic emission and volumetric strain induced in coal by the displacement sorption of methane and carbone dioxide

The aim of this study was to assess whether acoustic emission (AE) could carry information on preferential sorption/desorption of CH₄ or CO₂ in coal. AE and expansion/contraction of two nearly identical cylindrical coal samples were continuously monitored during displacement sorption experiments. One sample was subjected to presorption of CH₄, followed by sorption of CH₄/CO₂ mixture. With the other one, presorption of CO₂ preceded sorption of the mixture. The results obtained are the following: first, AE and stain kinetics show that the affinity of the coal tested is higher for CO₂ than for CH₄; second, methane is preferentially desorbed after presorption of CH₄ — sorption of mixture of CH₄ and CO₂; third, during displacement sorption, kinetics of AE and sample swelling/shrinkage bring out the importance of presorption and the sorbate used. It matters whether the coal is first exposed to CH₄ or to CO₂. The present study has demonstrated that injection of CO₂ into the coal previously exposed to CH₄ causes considerable swelling of the coal. On desorption after CH₄/CO₂ exchange sorption, initial shrinkage is followed by swelling of the coal. These results could have implications for the sequestration of CO₂ in coal seams and CH₄ recovery from coalbeds (ECBM). Swelling/shrinkage of the coal matrix should be included in models used to predict coal permeability and gas flow rates. They also show that the AE technique can give more insights into coal matrix-gas interactions.     

Effects of frozen soil and snow cover on cold‐season soil water dynamics in Tokachi,Japan

Despite the potential impact of winter soil water movements in cold regions, relatively few field studies have investigated cold‐season hydrological processes that occur before spring‐onset of snowmelt infiltration. The contribution of soil water fluxes in winter to the annual water balance was evaluated over 5 years of field observations at an agricultural field in Tokachi, Hokkaido, Japan. In two of the winters, soil frost reached a maximum depth of 0·2 m (‘frozen’ winters), whereas soil frost was mostly absent during the remaining three winters (‘unfrozen’ winters). Significant infiltration of winter snowmelt water, to a depth exceeding 1·0 m, occurred during both frozen and unfrozen winters. Such infiltration ranged between 126 and 255 mm, representing 28–51% of total annual soil water fluxes. During frozen winters, a substantial quantity of water (ca 40 mm) was drawn from deeper layers into the 0–0·2 m topsoil layer when this froze. Under such conditions, the progression and regression of the freezing front, regulated by the thickness of snow cover, controlled the quantity of soil water flux below the frozen layer. During unfrozen winters, 13–62 mm of water infiltrated to a depth of 0·2 m, before the spring snowmelt. These results indicate the importance of correctly evaluating winter soil water movement in cold regions. Copyright © 2010 John Wiley & Sons, Ltd.     

The response of CO2 flux to rain pulses at a saline desert

As the substantial component of the ecosystem respiration, soil CO₂ flux is strongly influenced by infrequent and unpredictable precipitation in arid region. In the current study, we investigated the response of soil CO₂ flux to rain pulses at a saline desert in western China. Soil CO₂ flux was measured continuously during the whole growing season of 2009 at six sites. We found that there were remarkable changes in amplitude or diurnal patterns of soil CO₂ flux induced by rainfall events: from bimodal before rain to a single peak after that. Further analysis indicated that there is a significant linear relationship (P < 0.001) between soil CO₂ flux and soil temperature (T_soil). However, a hysteresis between the waveform of diurnal course of CO₂ flux and T_soil was observed: with soil CO₂ flux always peaked earlier than T_soil. Furthermore, a double exponential decay function was fitted to the soil CO₂ flux after rainfall, and total carbon (C) releases were estimated by numerical integration for rainfall events. The relative enhancement and total C release, in association with the rain pulses, was linearly related to the amount of precipitation. According to the size and frequency of rainfall events, the total amount of C release induced by rain pulses was computed as much as 7.88 g C·m^–2 in 2009, equivalent to 10.25% of gross primary production. These results indicated that rain pulses played a significant role in the carbon budget of this saline desert ecosystem, and the size of them was a good indicator of rain‐induced flux enhancement. Copyright © 2012 John Wiley & Sons, Ltd.     

Downslope soil detachment–transport on steep slopes via rain splash

This study developed a one‐dimensional model of downslope rain splash transport based on field experiments and previous studies. The developed model considers soil detachment processes, ground cover, probability densities, and the effect of overland run‐off in preventing detachment. Field monitoring was conducted to observe precipitation run‐off, ground cover, and sediment production on steep hillslopes. Field‐observed data were used to develop the splash detachment rate equation, probability densities for splash transport, and the maximum splash transport distance. Observed and estimated splash transport showed overall agreement, with some differences for small storm events or events with relatively low intensity, probably caused by variation of overland run‐off depth and connectivity as well as differences in soil surface cohesion at various degrees of wetness. Our model can provide insights on the interactions among rainfall intensity, soil surface condition, soil wetness, and splash transport on forested hillslopes. Copyright © 2011 John Wiley & Sons, Ltd.     

Effects of rainfall intensity and compaction on water transport from opencast coal mine soils: An experimental study

The use of heavy machinery during opencast coal mining can result in soil compaction. Severe soil compaction has a negative impact on the transport of water and gas in the soil. In addition, rainfall intensity has traditionally been related to soil surface sealing affecting water transport. To assess the effects of rainfall intensity and compaction on water infiltration and surface runoff in an opencast coal mining area, the disturbed soils from the Antaibao opencast mine in Shanxi Province, China, were collected. Four soil columns with different bulk densities (i.e., 1.4 g cm^-3, 1.5 g cm^-3, 1.6 g cm^-3, and 1.7 g cm^-3) were designed, and each column received water five times at rainfall intensities of 23.12, 28.91, 38.54, 57.81, and 115.62 mm hr^-1. The total volume of runoff, the time to start runoff, and the volumetric water contents at the depths of 5 cm, 15 cm, 25 cm, 35 cm, 45 cm, 55 cm, and 65 cm were measured. Under the same soil bulk density, high rainfall intensity reduced infiltration, increased surface runoff, and decreased the magnitude of change in the volumetric water contents at different depths. Under the same rainfall intensity, the soil column with a high bulk density showed relatively low water infiltration. Treatments 3 (1.6 g cm^-3) and 4 (1.7 g cm^-3) had very small changes in volumetric water contents of the profiles even under a lower rainfall intensity. Severe soil compaction was highly prone to surface runoff after rainfall. Engineering and revegetation measures are available to improve compacted soil quality in dumps. Our results provide a theoretical basis for the management of land reclamation in opencast coal mine areas.     

Towards constraining the magnitude of global agricultural sediment and soil organic carbon fluxes

Reliable quantitative data on the extent and rates of soil erosion are needed to understand the global significance of soil‐erosion induced carbon exchange and to underpin the development of science‐based mitigation strategies, but large uncertainties remain. Existing estimates of agricultural soil and soil organic carbon (SOC) erosion are very divergent and span two orders of magnitude. The main objective of this study was to test the assumptions underlying existing assessments and to reduce the uncertainty associated with global estimates of agricultural soil and SOC erosion. We parameterized a simplified erosion model driven by coarse global databases using an empirical database that covers the conterminous USA. The good agreement between our model results and empirical estimates indicate that the approach presented here captures the essence of agricultural erosion at the scales of continents and that it may be used to predict the significance of erosion for the global carbon cycle and its impact on soil functions. We obtained a global soil erosion rate of 10.5 Mg ha^‐1 y^‐1 for cropland and 1.7 Mg ha^‐1 y^‐1 for pastures. This corresponds to SOC erosion rates of 193 kg C ha^‐1 y^‐1 for cropland and 40.4 kg C ha^‐1 y^‐1 for eroding pastures and results in a global flux of 20.5 (±10.3) Pg y^‐1 of soil and 403.5 (±201.8) Tg C y^‐1. Although it is difficult to accurately assess the uncertainty associated with our estimates of global agricultural erosion, mainly due to the lack of model testing in (sub‐)tropical regions, our estimates are significantly lower than former assessments based on the extrapolation of plot experiments or global application of erosion models. Our approach has the potential to quantify the rate and spatial signature of the erosion‐induced disturbance at continental and global scales: by linking our model with a global soil profile database, we estimated soil profile modifications induced by agriculture. This showed that erosion‐induced changes in topsoil SOC content are significant at a global scale (an average SOC loss of 22% in 50 years) and agricultural soils should therefore be considered as dynamic systems that can change rapidly. Copyright © 2011 John Wiley & Sons, Ltd.     

Soil organic carbon storage and soil CO_2 flux in the alpine meadow ecosystem

High-resolution sampling,measurements of organic carbon contents and 14C signatures of selected four soil profiles in the Haibei Station situated on the northeast Tibetan Plateau,and application of 14C tracing technology were conducted in an attempt to investigate the turnover times of soil organic car-bon and the soil-CO2 flux in the alpine meadow ecosystem. The results show that the organic carbon stored in the soils varies from 22.12×104 kg C hm-2 to 30.75×104 kg C hm-2 in the alpine meadow eco-systems,with an average of 26.86×104 kg C hm-2. Turnover times of organic carbon pools increase with depth from 45 a to 73 a in the surface soil horizon to hundreds of years or millennia or even longer at the deep soil horizons in the alpine meadow ecosystems. The soil-CO2 flux ranges from 103.24 g C m-2 a-1 to 254.93 gC m-2 a-1,with an average of 191.23 g C m-2 a-1. The CO2 efflux produced from microbial decomposition of organic matter varies from 73.3 g C m-2 a-1 to 181 g C m-2 a-1. More than 30% of total soil organic carbon resides in the active carbon pool and 72.8%―81.23% of total CO2 emitted from or-ganic matter decomposition results from the topsoil horizon (from 0 cm to 10 cm) for the Kobresia meadow. Responding to global warming,the storage,volume of flow and fate of the soil organic carbon in the alpine meadow ecosystem of the Tibetan Plateau will be changed,which needs further research.     

Vegetation and soil carbon storage in China

This study estimated the current vegetation and soil carbon storage in China using a biogeochemical model driven with climate, soil and vegetation data at 0.5° latitude-longitude grid spatial resolution. The results indicate that the total carbon storage in China's vegetation and soils was 13.33 Gt C and 82.65 Gt C respectively, about 3% and 4% of the global total. The nationally mean vegetation and soil carbon densities were 1.47 kg C/m2 and 9.17 kg C/m2, respectively, differing greatly in various regions affected by climate, vegetation, and soil types. They were generally higher in the warm and wet Southeast China and Southwest China than in the arid Northwest China; whereas vegetation carbon density was the highest in the warm Southeast China and Southwest China, soil carbon density was the highest in the cold Northeast China and southeastern fringe of the Qinghai-Tibetan Plateau. These spatial patterns are clearly correlated with variations in the climate that regulates plant growth and soil organi     

Evaluating the impact of soil redistribution on the in situ mineralization of soil organic carbon

Soil erosion, transport and deposition by water drastically affect the distribution of soil organic carbon (SOC) within a landscape. Moreover, soil redistribution may have a large impact on the exchange of carbon (C) between the pedosphere and the atmosphere. One of the large information gaps within this research domain, concerns the fate of SOC after erosion by water. According to different (mainly laboratory) studies, soil redistribution leads to aggregate breakdown, thereby exposing the contained SOC to mineralization. Our study aims to quantify the extent to which such increased mineralization occurs in a real field situation. Carbon dioxide (CO₂)‐efflux was measured in the field after an important erosion event for a continuous period of 112 days. The specific situation on the field ensured that almost none of eroded SOC was exported from the field. Measurements of CO₂‐efflux were done in areas with sediment deposition, as well as in comparable areas without sedimentation. Comparison of these measurements allowed the net effect of soil deposition on CO₂‐efflux to be assessed. Field data were complemented by measurements on incubated, undisturbed soil core samples, in order to disentangle the contribution of environmental factors (moisture, temperature) from any erosional effect on CO₂‐efflux. Results of these measurements on the field showed that CO₂‐efflux was regulated by a complex interplay of different factors (mostly soil porosity, soil moisture and soil temperature). In combination with the incubation measurements, it could be concluded that the processes of erosion and transport indeed led to an increased mineralization of SOC, as a result of aggregate breakdown and exposure of previously encapsulated SOC. This effect was, however, much smaller than observed in previous laboratory studies. Moreover, it was only important in the first weeks, immediately after the erosion event. The calculated net erosional effect on CO₂‐efflux represented a mere 1·6% of total SOC, originally present in the soil. Copyright © 2010 John Wiley & Sons, Ltd.     

Model based analysis of lateral and vertical soil carbon fluxes induced by soil redistribution processes in a small agricultural catchment

Soil redistribution on arable land significantly affects lateral and vertical soil carbon (C) fluxes (caused by C formation and mineralization) and soil organic carbon (SOC) stocks. Whether this serves as a (C) sink or source to the atmosphere is a controversial issue. In this study, the SPEROS‐C model was modified to analyse erosion induced lateral and vertical soil C fluxes and their effects upon SOC stocks in a small agricultural catchment (4·2 ha). The model was applied for the period between 1950 and 2007 covering 30 years of conventional tillage (1950–1979) followed by 28 years of conservation tillage (1980–2007). In general, modelled and measured SOC stocks are in good agreement for three observed soil layers. The overall balance (1950–2007) of erosion induced lateral and vertical C fluxes results in a C loss of ?4·4 g C m^–2 a^–1 at our test site. Land management has a significant impact on the erosion induced C fluxes, leading to a predominance of lateral C export under conventional and of vertical C exchange between soil and atmosphere under conservation agriculture. Overall, the application of the soil conservation practices, with enhanced C inputs by cover crops and decreased erosion, significantly reduced the modelled erosion induced C loss of the test site. Increasing C inputs alone, without a reduction of erosion rates, did not result in a reduction of erosion induced C losses. Moreover, our results show that the potential erosion induced C loss is very sensitive to the representation of erosion rates (long‐term steady state versus event driven). A first estimate suggests that C losses are very sensitive to magnitude and frequency of erosion events. If long‐term averages are dominated by large magnitude events modelled erosion induced C losses in the catchment were significantly reduced. Copyright © 2011 John Wiley & Sons, Ltd.     

Transfer of carbon dioxide and methane through the soil‐water‐atmosphere system at Mer Bleue peatland,Canada

Surface waters associated with peatlands, supersaturated with CO₂ and CH₄ with respect to the atmosphere, act as important pathways linking a large and potentially unstable global repository of C to the atmosphere. Understanding the drivers and mechanisms which control C release from peatland systems to the atmosphere will contribute to better management and modelling of terrestrial C pools. We used non‐dispersive infra‐red (NDIR) CO₂ sensors to continuously measure gas concentrations in a beaver pond at Mer Bleue peatland (Canada); measurements were made between July and August 2007. Concentrations of CO₂ in the surface water (10 cm) reached 13 mg C l^?1 (epCO₂ 72), and 26 mg C l^?1 (epCO₂ 133) at depth (60 cm). The study also showed large diurnal fluctuations in dissolved CO₂ which ranged in amplitude from ～1·6 mg C l^?1 at 10 cm to ～0·2 mg C l^?1 at 60 cm depth. CH₄ concentration and supersaturation (epCH₄) measured using headspace analysis averaged 1·47 mg C l^?1 and 3252, respectively; diurnal cycling was also evident in CH₄ concentrations. Mean estimated evasion rates of CO₂ and CH₄ over the summer period were 44·92 ± 7·86 and 0·44 ± 0·25 µg C m^?2s^?1, respectively. Open water at Mer Bleue is a significant summer hotspot for greenhouse gas emissions within the catchment. Our results suggest that CO₂ concentrations during the summer in beaver ponds at Mer Bleue are strongly influenced by biological processes within the water column involving aquatic plants and algae (in situ photosynthesis and respiration). In terms of carbon cycling, soil‐stream connectivity at this time of year is therefore relatively weak. Copyright © 2008 John Wiley & Sons, Ltd.     

Soil carbon dioxide and weathering potentials in tropical karst terrain,peninsular Malaysia: A preliminary model

CO₂ concentrations at depths of 15,30, and 50 cm were determined over a one-year period in six karst soils in the Malay peninsula. Evidence suggests that the highest single CO₂ value (MAXCO₂, per cent) recorded at each site/depth provides the best estimate of conditions during groundwater recharge events. Soil depth (cm) and bulk density (BDEN) are the best predictors of MAXCO₂, with the equation loglo(MAXCO₂) = 1·146 (BDEN) + 0·00698 (DEPTH) - 1·227 accounting for 86 per cent of the variation. This equation is used to model MAXCO₂ at seven, more remote sites. Soil throughflow patterns and groundwater recharge points are estimated from slope pantometer and soil depth surveys in order to assess the CO₂ concentration with which soil waters ultimately equilibrate before entering the limestone. Limestone weathering seems to be predominantly of the open system type, the overall mean MAXCO₂ of 1·65 per cent corresponding with a weathering potential of 167 ppm CaCO₃. Weathering potentials vary markedly, ranging from 62–82 ppm on rocky hilltops to more than 280 ppm on certain tower karst footslopes in Selangor and the Kinta Valley and on moderate hillslopes developed in impure limestones in the Boundary Range.