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1.
Fluxes of nitrous oxide (N2O) from different land use patterns (matured forest, secondary forest, grassland and cropland) in a subtropical karst region of Guizhou Province, Southwest China, were measured for one year with a closed static chamber technique and by gas chromatography. The results showed that soil under different land uses was a source of atmospheric N2O. The cropland was a source with relatively high N2O as compared to forest and grassland, but no significant differences were observed. N2O emissions from soils varied with land use change and fertilizer application. There were two peaks of N2O flux occurred following the combination of two obvious precipitation and fertilizer events in the cultivated land. Converting from the matured forest to secondary forest tended to increase annual emissions of N2O (from 1.40 to 1.65 kg N ha -1 a -1 ), while changing land use from secondary forest to scattered grassland tended to decrease annual emissions of N2O slightly (from 1.65 to 1.45 kg N ha -1 a -1 ). Our range of cumulative annual N2O emission across different land uses (1.40-1.91 kg N ha -1 a -1 ) in a karst region is in general agreement with previously published data in a non-karst region. However, in the maize field, N2O emission factor (EF) was 0.34% for fertilizer application, which is about 71.2% lower than the IPCC default value. It is suggested that current IPCC (Intergovernmental Panel on Climate Change) EF methodology could overestimate N2O emission from the karstic cropland. Anyway, the N2O emission from cropland in the karst region would contribute significantly to the global N2O budget, so reducing fertilization frequency during the crop growing season could lead to a decrease in N2O emission in the whole year.  相似文献   

2.
Nitrogen and phosphorus are the major nutrients to cause eutrophication to degrade water quality of the Miyun Reservoir,a very important drinking water source of Bijing,China,and they are mainly from non-point sources.The watershed in Miyun County was selected as the study region with a totoal area of 1400km^2.Four typical monitoring catchments and two experimental units were used to monitor the precipitation,runoff,sediment yield and pollutant loading related to various land uses in the meantime.The results show that the total nutrient loss amounts of TN and TP are 898.07t/a,and 40.70t/a,respectively,in which nutrients N and P carried by runoff are 91.3% and 77.3%,respectively.There is relatively heavier soil eroson in the northern mountain area whereas the main nutrient loss occurs near the northeast edge of the reservoir.Different land uses would influence the loss amounts of non-point source pollutants.The amount of nutrient loss from the agricultural land per unit is highest,that from forestry comes next that from grassland is lowest.However,due to the variability of land use areas,agricultural land contributes a lot to TP and forestry lands to TN.  相似文献   

3.
The bacteria used in the experiment are Thiobacillus Ferrooxidans separated from acidic mine water in sulphide deposits. The chemoautotrophic bacteria can act directly on sulphides and accelerate the oxidation of sulphides. The experiment shows that the bacteria, as an important microbial factor of gold's supergenous enrichment within the oxidized zones of sulphide deposits, are helpful to dissolve gold and silver in ferric sulphate. In the bacterial oxidation process, the precipitation of goethite is concerned both with the lower activity of ferric ions and with the existence of carbonates in solution. Meanwhile, the acid-resisting and oxidizing ability of the bacteria will certainly lead up to a microbial way of treating the acidic mine water.  相似文献   

4.
Studies on rain-runoff process in the peripheral mountainous area of the Sichuan Basin, which is regarded as a key ecological shelter, will contribute to flood control and environmental protection for the Upper Yangtze River Basin. In two typical catchments--the Fujiang River Catchment and the Wujiang River Catchment, rainfall simulations have been conducted to study the rain-runoff processes of yellow soil and limestone soil in three types of land use--forestland, farmland and grassland. Results showed that （1） within the same rainfall process, overland flow occurs first on farmland, then on grassland, and finally on forestland; （2） soil surface coverage has a great impact on the occurrence and amount of overland flow. The runoff amount can increase 2-4 times after the coverage is removed; （3） the infiltration before the occurrence of overland flow will decrease because of higher gravel contents of soil, but it takes no effect on infiltration once overland flow becomes stable; （4） the runoff coefficient of the limestone soil forestland is greater than that of the yellow soil forest land, but less than that of the farmland; （5） three empirical infiltration models, including Horton＇ model, Kostiakov＇ model, and modified Kostiakov＇ model, were compared by using the observed results under rainfall simulation. The results showed that the Kostiakov＇ model performed better than both the Horton＇ model and modified Kostiakov model. According to the results of this research, the Kostiakov＇s model can be used to simulate rainfall infiltration when water erosion is modeled in the peripheral mountainous area of the Sichuan Basin.  相似文献   

5.
Semi-sealed preservation of soil samples at different moisture of 4% and 23%, respectively, was simulated to observe the variations of soil microbial communities and determine the contents and isotopic compositions of the total organic carbon and total nitrogen on the 7th and 30th day, respectively. The results show that during preservation, the quantity of microbial communities tended to increase first and then decrease, with a wider variation range at higher moisture (23%). At the moisture content of 23%, the microbial communities became more active on the 7th day, but less after 30 days, and their activity was stable with little fluctuation at the moisture content of 4%. However, there were no significant changes in the contents and isotopic compositions of the total organic carbon and total nitrogen. During preservation, the responses of soil microbes to the environment are more sensitive to changes in the total nitrogen and organic carbon contents. It is thus suggested that the variations of microbial communities have not exerted remarkable impacts on the isotope compositions of the total nitrogen and total organic carbon.  相似文献   

6.
Soils contain about twice the amount of carbon presented in the atmosphere, so a small change in the soil carbon will influence atmospheric chemistry and heat balance. The soil carbon ultimately exchanged with the atmospheric CO2 as soil CO2, which mainly exists at the depth of 0-20 cm. The transport of soil CO2 is affected by the sources of soil CO2. Thus, separation of the contributions of sources of soil CO2 is a fundamental need to understand and predict implications of environmental change on soil carbon cycling and sequestration. It is a complicated task, so that a number of different methodological approaches such as component integration, root removal, and gap analyses have been developed. However, these methods could not avoid changing soil characteristics such as air-filled porosity, soil temperature and soil water contents. Consequently, fractional contributions of respiration of living root and decomposition of soil organic matter to the total soil CO2 cannot be estimated correctly. In this study, based on mass balance theory of both concentrations and δ^13C of soil CO2, a trenching method with a stable-isotope technique was used to determine both soil CO2 sources at the depth of 3-13 cm in a Japanese larch forest area during 30 May to 7 October 2005 and fractional contributions of these sources. Experimental results showed that the amount of atmospheric CO2 invaded the soil air was not significantly variable while its percent rate in the total soil CO2 had significantly temporal variations with the lower values between 5 August and 1 September. The litter-layer decomposition was very small. The soil CO2 derived from the respiration of living root and the decomposition of soil organic matter showed significantly temporal variations with increase from 30 May to 5 Aug. and decrease from 1 September to 7 October, 2005; and it accounted for 82%-98% of the total soil CO2 in which the respiration of living root was in the range from 32% to 62%.  相似文献   

7.
We present n-alkane distributions in the soil samples along a transect from Lhasa on the Tibetan Plateau to Bharatpur in Nepal, which covers a large geographical area and a wide range of climatic conditions. These data allow us to assess the significance of n-alkane distributions in different vegetation types and their relationships to temperature and precipitation. In the tropical rainforest and broadleaved forest zones, n-alkanes exhibit a bimodal distribution pattern with dominant homologues around n-C_(31) and n-C_(23). The bimodal distribution of tropical rainforest n-alkanes may be a general pattern because of the presence of many lianas, epiphytic plants, algae and the strong microbial activity and degradation involved in the postdepositional process. In the warm-temperate mixed forest and needle-leaved forest zones, the long-chain alkanes have a pattern of n-C_(31) n-C_(33) n-C_(27). In the alpine shrub and grassland zone, although the most abundant homologue is n-C_(31) , relatively high n-C_(23) concentrations have also been observed in some samples. The statistical results show a good correlation between n-alkane proxies and climatic factors. The average chain length(ACL) values are positively correlated with precipitation and temperature across the transect. The carbon preference index(CPI) values show a negative correlation with temperature and precipitation along a Lhasa–Bharatpur transect. Although there is a positive relationship between ACL and temperature, it is difficult to separate the two climatic variables(temperature and precipitation) because they are well coupled in the monsoon region.  相似文献   

8.
To assess the effects of single and combined pollution of cadmium (Cd) and mercury (Hg) on soil micro-bial community structural and functional diversities, an incubation experiment was conducted, by employing two soils, namely, the marine sediment silty loam soil and the yellowish-red soil, in which five levels of Cd, Hg and Cd and Hg in combination were added. After being incubated for 56 days, the phospholipid fatty acids (PLFAs) profile and sole carbon source utilization pattern (BIOLOG) of the samples were tested. The results showed that the compo-sition of the microbial communities changed significantly at different levels of metals application. The principal component analyses (PCA) of PLFAs indicated that the structure of the microbial community was also significantly altered with increasing levels of metals, with increasing PLFAs biomarkers for fungi and actinomycetes, and in-creasing ratio of Gram-positive to Gram-negative bacteria. Sole carbon source utilization pattern analysis revealed that single and combined application of Cd and Hg inhibited significantly the functional activity of soil microorgan-isms, the functional diversity indices [Richness (S), Shannon-Wiener indices (H) and Evenness (EH)] were signifi-cantly lower in polluted soils than those in non-polluted soils, which also significantly altered with increasing levels of metals. PCA for the sole carbon source utilization pattern also indicated that the metal contamination could result in a variable soil microbial community. The results revealed that the combination of Cd and Hg had higher toxicity to soil microbial community structural and functional diversities than the individual application of Cd or Hg.  相似文献   

9.
Carbonate rock outcrops cover 9%–16% of the continental area and are the principal source of the dissolved inorganic carbon (DIC) transferred by rivers to the oceans, a consequence their dissolution. Current estimations suggest that the flux falls between 0.1–0.6 PgC/a. Taking the intermediate value (0.3 PgC/a), it is equal to 18% of current estimates of the terrestrial vegetation net carbon sink and 38% of the soil carbon sink. In China, the carbon flux from carbonate rock dissolution is estimated to be 0.016 PgC/a, which accounts for 21%, 87.5%–150% and 2.3 times of the forest, shrub and grassland net carbon sinks respectively, as well as 23%–40% of the soil carbon sink flux. Carbonate dissolution is sensitive to environmental and climatic changes, the rate being closely correlated with precipitation, temperature, also with soil and vegetation cover. HCO3- in the water is affected by hydrophyte photosynthesis, resulting in part of the HCO3? being converted into DOC and POC, which may enhance the potential of carbon sequestration by carbonate rock dissolution. The possible turnover time of this carbon is roughly equal to that of the sea water cycle (2000a). The uptake of atmospheric/soil CO2 by carbonate rock dissolution thus plays an important role in the global carbon cycle, being one of the most important sinks. A major research need is to better evaluate the net effect of this sink in comparison to an oceanic source from carbonate mineral precipitation.  相似文献   

10.
Urban soil research has invoked great interest in recent years.Previous studies were mainly focused on urban soil physics and chemistry,and soil geography to constrain the source,distribution,transport and deposition of pollutants such as heavy metals and health-hazardous organic matter,bu t litte has been done on soil microbiology.In this paper,the authors reported the variation of microbial features in urban soils compared with those from adjacent rual areas.The results show great changes in basal respiration rates microbial biomass and ecophysiological parameters have taken place in urban environment because of the anthropogenic stress, thus activating the microorganisms.As a result,much more energy,carbon is consumed at a low utilization efficiency.So microbial biosensors can be used to indicate urban environmental pollution effectively.  相似文献   

11.
The impact of air pollution is a substantial European and global problem which has been observed even in the most remote areas of our planet. Not only surface water, but also groundwater resources are partly endangered by dry and wet deposition from the air. Karst and other sensitive aquifers contribute up to 90 % to the total drinking water supply in some European regions. However, they are more vulnerable to contamination than other aquifers due to short transfer times from recharge to source. Therefore, the main objective of this paper is to show possibilities to quantify the impact of air pollution on sensitive water resources （e.g. karst）, to develop an innovative surveillance tool based on isotopes and meteorological considerations. Comparisons of lead isotope measurements in precipitation, spring waters, soil profiles and dolomite bedrock in a relatively pristine and remote area at the front-range of the Northern Calcareous Alps in Austria with literature data indicate that radiogenic Australian gasoline-lead still dominates with 60%-80% the composition of the trace lead in the spring waters. In addition to the lead leached from the dolomite bedrock a third source contributes about 5%-10%. This second long distance Pb-contribution may originate from coal burning and/or Ag-Pb-ore smelting in central Europe in the past. The monthly precipitation （May and September 2005） samples show ^18O-rich sulphate ions, whereas the soil sulphates change in the direction to lower ^18O- and higher ^34S values with depth. The spring waters and bedrock dolomites show relatively low delta ^34S values （4‰-9 ‰）. Assuming the precipitation samples and the dolomite bed rocks are end-members the contribution of atmospheric sulphate can estimated to be 20% in the spring waters and between 10% to 45% in the soil samples. The ^87Sr/^86Sr-isotope results in the precipitation （0.7092） support at least a more radiogeradiogenic, far transported source in addition to a possible recycling of local dolomite and limestone （0.7080-0.7083） dust.  相似文献   

12.
The sampling method of karst soil is always the one used for non-karst area. However, if the samples can represent the plot, it still needs further investigation due to high degree of spatial variability of karst soil. The study results of soil from the Maolan karst virgin forest in Guizhou Province elucidated that only the surface area-weighted samples could represent plot soils in the karst ecosystem. The remediation of karst rocky desertification has currently become a national issue, but soil degradation research on rocky desertification genesis types and processes is still insufficient. Soil physical, chemical, biological characteristics and enzymes activities from plots of different rocky desertification genesis types and grades in the Cha＇eryan catchment in the Huajiang Gorge area, Guizhou, were studied. The results showed that woodcutting and land reclamation influenced soil biogeochemical characteristics, and the influence of different disturbing ways was huge. The author suggested a soil degradation index system which could illustrate the rocky desertification genesis type and extent. The degraded modes of woodcutting and reclamation sequence were different, both had no synchronism with rocky desertification grades divided by current landscape index. Only soil of serious grade degraded evidently in wood cutting sequence. On the contrary, soils of slight, medium and serious grades degraded evidently in the reclamation sequence.  相似文献   

13.
南亚热带森林凋落物对土壤呼吸的贡献及其影响因素   总被引：9，自引：0，他引：9  
Three main types of Soil respirations(S+L and S) in southern subtropical forests in Dinghushan biosphere reserve were consecutively being monitored over 31 months by the approach of static chamber-gas chromatograph techniques. Research shows that: annual mean contribution rates of litter-fall to soil respiration in the monsoon evergreen broadleaf forest (BF), mixed broadleaf-coniferous forest (MF) and coniferous(pine) forest (PF) reached 27.82%、33.29%和36.35% respectively; Moreover, all three types of forests displayed the same seasonal dynamic features with the peaks contributions of them were from April to September, which accounts for 71.87%、61.89% and 70.39% of annual total contributions of litter fall to soil respiration respectively. Soil respiration(S+L) had an obviously positive relationship with the seasonal changes of litter-fall input（P<0.001; And soil water content had a significant impact on the contribution of litter-fall to soil respiration in the three types of forests (P<0.001); Soil temperature had positive correlativity with soil respiration flux, though it has no distinctive relationship with contribution of litter-fall to soil respiration; the contribution ratios of litter-fall to soil respiration on rainy days were 28.63%、38.20% and 40.12% respectively, which were significantly higher than those in the sunny days in the three types of forests.  相似文献   

14.
Uranium is a redox-sensitive element. While U （Ⅵ）, the oxidized form of uranium, is soluble and thus mobile in groundwater, U （Ⅳ） readily forms UO2（s） and is precipitated. Recent geomicrobiological researches demonstrated that dissimilatory metal reducing bacteria can effectively remove uranium fi＇om contaminated groundwater by reducing soluble U （Ⅵ） to relatively insoluble U （Ⅳ）. This novel form of microbial reduction of U （Ⅵ） is reported to be much faster than abiological reduction. The objective of this work was to investigate U （Ⅵ） reduction by indigenous bacteria in uranium-bearing black shale sediment and to determine whether microbially-precipitated uranium has long-term stability in subsurface. Through this study, fundamental information on the effects of microorganisms on the fate of redox-sensitive elements in natural settings will be provided. Soil and sediment samples were collected from uranium-bearing black shale in the Dukpyung area in Korea. Microbial inoculum was prepared from soil and sediment slurry supernatant. The reactors were purged with N2 ： CO2 gas （80 ; 20） to maintain anaerobic condition. Glucose, acetate or lactate was added as an electron donor at a final concentration of 5 mM.  相似文献   

15.
Based on lead isotope data, it has been shown that lead in the Beishan stratabound sphalerite-pyrite deposit came mainly from the oldland and its underlying basement rocks and, subordinately, the Devonian itself or the seawater at that time. As to its primary source, upper crust lead was predominant. while lower crust lead or upper mantle lead was subordinate. Sulfur was formed mainly through bacterial reduction of marine carbonates. The carbon and oxygen isotopic analyses for carbonate rocks and minerals have demonstrated that carbonate rocks in the Beishan area are normal marine sediments. The isotopic characteristics of the carbonate rocks are intermediate between those of the northern Guangdong and central Hunan, but closer to those of the central Hunan basin. The formation of the Beishan deposit underwent: a depositional-diagenetic mineralization stage and a successive post-diagenetic enrichmentremoulding one.  相似文献   

16.
Recently, the impacts of increasing atmospheric CO2 level on the terrestrial ecological system have been intensively studied. The higher the CO2 concentration, the higher the risk of destabilizing vulnerable carbon pool on ecological safety. Metabolism, biomass, activity, and diversity of microbial communities in soils can be significantly altered by the CO2 enrichment. For instance, it may accelerate carbonate weathering, vary the rhizospheric exudation, and enhance the amount of available C from the upper soil layer. However, how the CO2 enrichment would influence food safety such as species transformation and bioavailability of heavy metals in soils is remained unanswered. The bioavailability of heavy metals is strongly affected by bio-factors in addition to the physiochemical conditions of soils. Different physiological mechanisms and states control plant uptake of heavy metals. The enrichment of CO2 influences physiological functionalities of plants, and in turn, is expected to have impacts on the bioaccumulation of pollutants and the stress adjustment system of plants. Currently, in China soil is heavily polluted, in most cases, combined by organic pollutants and heavy metals. Studies of the environmental behavior and ecological effect of Cu in soil under elevated CO2 levels were conducted in China FACE （Free Air Carbon Dioxide Enrichment） from June to October 2005 using pot experiments. Results showed that the accumulation of Cu and Cd in leaves, stems, roots, and grains of rice growing in Cu contaminated soils was significantly lowered, indicating that the bioavailability of heavy metals in soils decreases with increasing CO2 concentration.  相似文献   

17.
The bacteria and plants were associated to remove diesel oil pollutants from soil.Three efficiently degrading bacteria(named strains Q10,Q14 and Q18,respectively) were isolated.Two plants(alfalfa and Indian mustard) were selected to form the association.Biodegradation of diesel oil pollutants in soil was accelerated by bacteria-plants association.The main results are summarized as follows.The plants-bacteria association was more effective in biodegradation of diesel oil pollutants in soil than in respective experiments carried out with plants or bacteria alone.Strain Q18-Indian mustard association resulted in the maximum diesel oil reduction(69.18%).The activities of catalase and polyphenol oxidase in soil were enhanced and microbial populations in soil,especially in rhizosphere,were also stimulated in the treatment of bacteria-plant association.Overall,the soil conditions might be improved by alfalfa or Indian mustard to benefit the growth of bacteria,which resulted in degradation of diesel oil pollutants more effective by the bacteria-plant association.The bacteria-plants association may be a better approach to the removal of diesel oil pollutants from soil.  相似文献   

18.
On the basis of different photosynthetic pathways.there is an obvious difference in δ^13C values between C3 and C4 plants,In terms of this characteristic,we analyzed the organic carbon content (forestlands:1.81%-16.00%;farmland:0.45%-2.22%) and δ^13C values(forestlands:-23.86‰--27.12‰;farmland:-19.66‰--23.26‰)of three profile-soil samples either in farmland or in forestland near the Maolan Karst virgin forest,where there were developed plant C3 plants previously and now are C4 plants.Results showed that the deforestation has accelerated the decomposition rate of soil organic matter and reduced the proportion of active components in soil organic matter and thus soil fertility.  相似文献   

19.
Through microscopic and SEM observations and X-ray diffraction and energy spectrum analyses, the oldest sponge spicules and radiolarians have been found in bedded cherts and it is proposed that microbial activity of algae and bacteria played an important role in silica precipitation. The microbial activity resulted in the formation of a series of single crystals and crystal aggregates with peculiar shapes. Biogenic single crystals usually occur in spherical, rod, platy, colloidal and granular forms. The most common aggregates are framboidal aggregates composed of dense spherical quartz crystals, which are considered to be of typical bacterial origin. Other aggregates, such as favositic, double-spherical, chain-spherica'l and coccoid ones, are considered to be probably the result of silicification of algal cells and mainly of primary sedimentary origin. This paper also discusses the ultrastructural features and diagnostic indications of jasper rocks formed in a submarine hydrothermal environment and cher  相似文献   

20.
Semi-sealed preservation of soil samples at different moisture of 4% and 23%,respectively, was simulated to observe the variations of soil microbial communities and determine the contents and isotopic compositions of the total organic carbon and total nitrogen on the 7th and 30th day, respectively.The results show that during preservation,the quantity of microbial communities tended to increase first and then decrease,with a wider variation range at higher moisture (23%).At the moisture content of 23%,th...  相似文献   

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