首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 187 毫秒
1.
Phosphorus is an essential and common limiting element for plants. Phosphorus losses from agricultural production systems are known to contribute to accelerated eutrophication of natural waters. In this study, soil available phosphorus (SAP) content and SAP density were estimated based on a soil survey of a small watershed in the Dan River, China, and the spatial heterogeneity of SAP distribution and the impacts of land-use types, elevation, slope and aspect on SAP were assessed. Field sampling was carried out based on a 100 m × 100 m grid system overlaid on the topographic map of the study area, and samples were collected in three soil layers to a depth of 40 cm. A total of 190 sites were sampled, and 539 soil samples were collected. The results showed that classical kriging could successfully interpolate SAP content in the watershed. SAP content showed a downward trend with the increase in soil depth and the extent of SAP variability in the three soil layer is moderate. There were significant differences among the three soil layers (P < 0.01). The land use had a great impact on the SAP content. ANOVA indicated that the spatial variation of SAP contents under different land-use types was significant (P < 0.01). The SAP density of different land-use types followed the order of cropland > forestland > grassland. The mean SAP density of cropland, forestland and grassland at a depth of 0–40 cm was 4.28, 3.74 and 2.81 g/m2, respectively. SAP and topographic factors showed that SAP content increased with decreasing altitude and slope gradient. The soil bulk density played a very important role in the assessment of SAP density. In conclusion, the soils in the source area of the middle Dan River would reduce SAP with conversions from cropland to forest or grassland.  相似文献   

2.
Intensive soil tillage is a significant factor in soil organic matter decline in cultivated soils. Both cultivation abandonment and foregoing tillage have been encouraged in the past 30 years to reduce greenhouse gas emissions and soil erosion. However, the dynamic processes of soil organic carbon (SOC) in areas of either continuous cultivation or abandonment remain unclear and inconsistent. Our aims were to assess and model the dynamic processes of SOC under continuous tillage and after cultivation abandonment in the black soil of Northeast China. Soil profiles were collected of cultivated or abandoned land with cultivation history of 0–100 years. An isotope mass balance equation was used to calculate the proportion of SOC derived from corn debris (C4) and from natural vegetation (C3) to deduce the dynamic process. Approximately 40% of SOC in the natural surface soil (0–10 cm) was eroded in the first 5 years of cultivation, increasing to about 75% within 40 years, before a slow recovery. C4 above 30 cm soil depth increased by 4.5%–5% or 0.11–0.12 g·kg?1 on average per year under continuous cultivation, while it decreased by approximately 0.34% annually in the surface soil after cultivation abandonment. The increase in the percentage of C4 was fitted to a linear equation with given intercepts in the upper 30 cm of soil in cultivated land. A significant relationship between the change of C4 and time was found only in the surface soil after abandonment of cultivation. These results demonstrate the loss and accumulation of corn-derived SOC in surface black soil of Northeast China under continuous tillage or cultivation abandonment.  相似文献   

3.
The spatial heterogeneity of soil nutrients influences crop yield and the environment. Previous research has focused mainly on the surface layer, with little research being carried out on the deep soil layers, where high root density is highly related to crop growth. In the study, 610 soil samples were collected from 122 soil profiles (0–60 cm) in a random-sample method. Both geostatistics and traditional statistics were used to describe the spatial variability of soil organic matter (SOM) and total nitrogen (TN) deeper in the soil profile (0–60 cm) with high root density from a typical Mollisol watershed of Northeast China. Also, the SOM and TN in farmland and forest (field returned to forest over 10 years) areas was compared. The spatial autocorrelations of SOM at 0–50 cm depth and TN at 30–60 cm depth were strong, and were mainly influenced by structural factors. Compared to farmland, SOM and TN were typically lower in the 0–30 cm depth of the forest areas, while they were higher in the 30–60 cm depth. As well, both SOM and TN decreased from the 0–20 cm layer to the 30–40 cm layer, and then discontinues, while they continuously decreased with increasing soil depth in the farmland. SOM and TN were typically higher at the gently sloped summit of the watershed and part of the bottom of the slope than at mid-slope positions at the 0–30 cm depth. SOM and TN were lower on the back slope at the 30–60 cm depth, but were higher at the bottom of the slope. Also, the spatial distribution of the carbon storage and nitrogen storage were all highest at the bottom of the slope and part of the summit, while they were lowest in most of back slope in depth of 0–60 cm, and mainly caused by soil loss and deposition. SOM at 0–60 cm and TN at 0–40 cm greater than the sufficiency level for crop growth (3.7–79.2 and 0.09–3.09 g kg?1, respectively) covered 99 % of the total area, yet for TN, over 35 % of the total area was less than the insufficiency level at the 40–60 cm depth. Generally, accurately predicting SOM and TN is nearly impossible when based only on soil loss by water, although the fact that variability is influenced by elevation, soil loss, deposition and steepness, was shown in this research. Nitrogen fertilizer and manure application were needed, especially in conjunction with conservation tillage in special conditions and specific areas such as the back slope, where soil loss was severe and the deep soil that lacked TN was exposed at the surface.  相似文献   

4.
Drastically disturbed soils caused by opencast mining can result in the severe loss of soil structure and increase in soil compactness. To assess the effects of mining activities on reconstructed soils and to track the changes in reclaimed soil properties, the variability of soil properties (soil particle distribution, penetration resistance (PR), pH, and total dissolved salt (TDS)) in the Shanxi Pingshuo Antaibao opencast coal-mine inner dump after dumping and before reclamation was analyzed using a geostatistics method, and the number of soil monitoring points after mined land reclamation was determined. Soil samples were equally collected at 78 sampling sites in the study area with an area of 0.44 km2. Soil particle distribution had moderate variability, except for silt content at the depth of 0–20 cm with a low variability and sand content at the depth of 20–40 cm with a high variability. The pH showed a low variability, and TDS had moderate variability at all depths. The variability of PR was high at the depth of 0–20 cm and moderate at the depth of 20–40 cm. There was no clear trend in the variance with increasing depth for the soil properties. Interpolation using kriging displayed a high heterogeneity of the reconstructed soil properties, and the spatial structure of the original landform was partially or completely destroyed. The root-mean-square error (RMSE) can be used to determine the number of sampling points for soil properties, and 40 is the ideal sampling number for the study site based on cross-validation.  相似文献   

5.
In order to investigate changes caused in clay mineralogy and potassium (K) status by different land-use types, 42 soils samples (0–30 cm) were monitored and analyzed. Soil samples belonging to Reference Soil Groups of Cambisols and Vertisols were collected from three neighboring land uses involving cropland (under long-term continuous cultivation), grassland, and forestland. The soils reflected an alkaline and calcareous aspect as were characterized by high pH (mean of 7.1 to 7.5) and calcium carbonate equivalent (mean of 35 to 97 g?kg?1) in the three land-use types. X-ray diffraction patterns of the clay fraction showed that the soils were mainly composed of illite, smectite, chlorite, and kaolinite. Chlorite and kaolinite remained unweathered irrespective of land use and soil types, soil processes, and physicochemical attributes assessed. Some changes in the XRD diffractograms of illite and smectite (the intensity or the position of peaks) were observed in the cultivated soils compared to those of the adjoining grassland that may explain the dynamics of the K trapped in illite interlayer sites. Potassium issues reflected a heterogeneous response to changes in land-use types. In light of this, a pronounced variation in soluble K (4–22 mg?kg?1), exchangeable K (140–558 mg?kg?1), and non-exchangeable K (135–742 mg?kg?1) appeared among the land-use types for both Cambisols and Vertisols, corresponding to variability in clay content, nature and type of clay mineral (mainly illite and smectite), cation exchange capacity (CEC), and soil organic carbon (SOC). In general, the largest amounts of soluble K and exchangeable K were recorded in the forestland, whereas the highest contents of non-exchangeable K were found in the grassland for both Cambisols and Vertisols. Exchangeable K, available K, CEC, and clay contents in the soils with higher smectite values (25–50 %) were significantly different (P?≤?0.05) compared to those of the lower smectite values (10–25 %). This suggests that smectite is a major source for surface sorption of K in the studied soils.  相似文献   

6.
Soil–water characteristics are necessary for water quality monitoring, solute migration and plant growth. Soil–water characteristic curve (SWCC) is a relationship between suction and water content or degree of saturation. However, little information is available concerning the impacts of grazing exclusion management on soil–water characteristics. Here, the soil–water characteristics of grasslands, which were excluded grazing for 5 (GE5) and 15 years (GE15), were studied. The saturated hydraulic conductivity (K s), SWCC, particle composition, field capacity and some other indexes were determined. Results showed that the clay content and K s of grassland soil were higher for GE15 than GE5. For both treatments, in low suction condition (≤100 kPa), the water holding capacity of 0–10 cm soil was the best. Water holding capacity of topsoil decreased gradually with the increasing of suction, and it reached the strongest when the suction reached 600 kPa. In all soil water suction, the water holding capacity of subsoil was the weakest. The van Genuchten expression was applicable for most of the samples, except 20–30 cm of GE5 and 10–20 cm of GE15. Dual porosity equation was applicable for all the samples. The soil–water capability and soil structure of which was fenced for 15 years is superior to that of 5 years. This study suggests that the enclosure management improved the soil structure and soil–water capability.  相似文献   

7.
Soil aggregate stability has been known as one of the most important soil properties which is influenced by cultivation system. This study investigates the effect of different cultivation systems on aggregate stability indices in two statuses of dry (DSA?>?0.25 mm) and wet (WSA?>?0.25 mm). The study was done in six cultivation systems consisting wheat, barley, maize, alfalfa, fallow, and plowed farms. The results showed that aggregate stability indices affected significantly by the type of cultivation system. In contrast, no meaningful effect of soil depth (0–10 and 10–20 cm) on selected soil properties was observed. In addition, soil primary particles as well as organic carbon differed significantly between the cultivation systems. Wheat and alfalfa farms consisted of larger aggregates, while water-stable aggregate for wheat found to be in a greater degree. Moreover, wheat and barley showed the highest contents of organic carbon. The results of WSA?>?0.25 mm indicated that the correlation coefficients for sand, silt, clay, and organic carbon contents were ?0.67, 0.74, 0.12, and 0.70, respectively. Compared to the DSA?>?0.25 mm, the effect of soil organic carbon on the WSA?>?0.25 mm was arisen while the influence of clay fraction reduced.  相似文献   

8.
A study was made to determine the influence of pasture degradation on soil quality indicators that included physical, chemical, biological and micromorphological attributes, along the hillslope positions in Chaharmahal and Bakhtiari province, western Iran. Soil samples from different slope positions were collected from 0 to 30 cm depth for physical and chemical properties and from 0 to 15 cm depth for biological properties at two adjacent sites in the two ecosystems: natural pasture and cultivated land. Soil quality indicators including bulk density, mean weight diameter, soil organic carbon (SOC), particulate organic material (POM) in aggregate fractions, total nitrogen, available potassium, available phosphorus, cation exchange capacity, soil microbial respiration (SMR) and microbial biomass C and N were determined. The results showed that SOC decreased cultivation from 1.09 to 0.77 % following pasture degradation. The POM decreased by about 19.35 % in cultivated soils when compared to natural pasture; also, SMR and microbial biomass C and N decreased significantly following pasture degradation. Furthermore, aggregate stability and pore spaces decreased, and bulk density increased in the cultivated soils. Overall, our results showed that long-term cultivation following pasture degradation led to a decline in soil quality in all selected slope positions at the site studied in the semiarid region.  相似文献   

9.
Preliminary geochemical mapping was carried out within urban areas in Tampere Central Region, Finland, to gain a better understanding of element concentrations in urban soil and to provide information on baselines in soil within urban centres for soil contamination assessment purposes. The soil samples were taken from central city parks, day-care centres and school yards, and residential areas. Various sampling depths have generally been used in urban geochemical surveys. The aim of this study was to compare the results from two commonly used sample types taken from the same sites in urban soil: single samples of minerogenic topsoil from the 0–25 cm layer and composite samples of minerogenic topsoil from a depth of 0–2 cm. The concentrations of most of the studied trace elements showed a significant correlation between samples from 0 to 2 and 0 to 25 cm, but element concentrations differed between the two studied sample depths. For most of the studied elements, the median concentrations were higher in the 0–25 cm samples, but anomalous concentrations were more often found in the 0–2 cm samples. Some elements had elevated concentrations when compared with the Finnish guideline values for soil contamination assessment. This study did not conclusively establish whether a sampling depth of 0–2 or 0–25 cm should be recommended for similar studies in the future. Selection of the sampling depth in geochemical studies greatly depends on the aim of the project. In order to determine the upper limits of geochemical baseline variation, the deeper sampling depth appears to be more feasible. However, for the preliminary health risk assessment of areas with sensitive land uses, e.g. children’s playgrounds, samples from 0–2 cm depth are considered informative. Such samples may also be used to indicate local sources of dusting creating site-specific hotspots of potentially harmful elements in urban topsoil.  相似文献   

10.
Urban soils, although crucial to defining urban vegetation types and strengthening the resilience of urban ecosystems, can be severely modified by human activities. Yet understanding of these modifications and their implications for soil properties is limited. This study examined the vertical and spatial variability of selected soil physicochemical properties (pH, SOM, OC, TN, and bulk density) in Kumasi, Ghana, using a stratified random sampling technique. Soil samples were collected at three depths (0–15, 15–30, and 30–60 cm) from 161 plots in eight green space types within two urban zones. Mean topsoil pH ranged between 5.0 in the natural forest and 6.5 in home gardens. Mean bulk density, nitrogen, and carbon concentrations differed among green space types and depths (p?<?0.0001). Soil nitrogen and carbon concentrations in the 0–15 cm depth were two times greater than those of the 30–60 cm depth. Soil pH and organic matter concentrations were higher in the core urban soils than in the peri-urban while the reverse was true for total soil N and bulk density. Canonical discriminant analysis showed considerable separation of green space types based on the soil physicochemical properties. Higher total nitrogen and C:N ratios separated natural forest and cemetery from the other UGS types, whereas higher pH and bulk densities separated plantations and home gardens from the rest of the UGS types. Furthermore, the subsoil layers were laden with undecomposed cloths, plastics, concrete, and metal parts which can obstruct root growth and water movement. Results generally demonstrate considerable variability in soil properties among urban green spaces and highlight the need for a better understanding of these patterns to ensure continued support for plant growth, green space sustenance and maintenance, and the ecosystem services derived from them.  相似文献   

11.
Soil samples from 0 to 100 cm depth were collected in four sampling sites (Sites A, B, C and D) along a 250-m length of sampling zone from the Yellow River channel to a tidal creek in a seasonal flooding wetland of the Yellow River Delta of China in fall of 2007 and spring of 2008 to investigate spatial and seasonal distribution patterns of total phosphorous (TP) and available phosphorus (AP) and their influencing factors. Our results showed that TP contents in spring and AP contents in both seasons in surface soils increased with increasing distances away from the Yellow River channel. TP contents in surface soils (0–10 cm) followed the order Site A (698.6 mg/kg) > Site B (688.0 mg/kg) > Site C (638.8 mg/kg) > Site D (599.2 mg/kg) in fall, while Site C (699.6 mg/kg) > Site D (651.7 mg/kg) > Site B (593.6 mg/kg) > Site A (577.5 mg/kg) in spring. Generally, lower TP content (630.6 mg/kg) and higher AP level (6.2 mg/kg) in surface soils were observed in spring compared to fall (656.2 mg/kg for TP and 5.2 mg/kg for AP). Both TP and AP exhibited similar profile distribution patterns and decreased with depth along soil profiles with one or two accumulation peaks at the depth of 40–80 cm. Although the mean TP content in soil profiles was slightly higher in spring (635.7 mg/kg) than that in fall (628.0 mg/kg), the mean TP stock was obviously lower in spring (959.9 g/m2) with an obvious accumulation at the 60–80 cm soil depth compared to fall (1124.6 g/m2). Topsoil concentration factors also indicated that TP and AP had shallower distribution in soil profiles. Correlation analysis showed that AP had significant and positive correlation with these soil properties such as soil organic matter, salinity, total nitrogen and Al (p < 0.01), but TP was just significantly correlated with TN and Al (p < 0.05).  相似文献   

12.
Monitoring general variability of soil attributes is a fundamental requirement from the point of view of understanding and predicting how ecosystems yield. In order to monitor impact of different land use types on the combination of morphological, clay mineralogical and physicochemical characterizes, 42 soil samples (0–30 cm) were described and analyzed. Soil samples belonging to Cambisols and Vertisols reference soil groups collected from three neighboring land use types included cropland (under long-term continuous cultivation), grassland, and forestland. The soils were characterized by high pH (mean of 7.1–7.5) and calcium carbonate equivalent (CCE) (mean of 35–97 g kg?1) in the three land use types. The weakening in soil structure, hardening of consistency, and lighting of soil color occurred for the cropland under comparable condition with grassland and forest. Changes in land use types produced a remarkable change in the XRD patterns of clay minerals containing illite and smectite due the dynamic and removal of potassium. Continuous cultivation resulted in an increase in sand content up to 35 % while silt and clay content decreased up to 22 and 18 %, respectively, as compared to the adjoining grassland and forest mainly as a result of the difference of dynamic alterational and erosional process in the different land use. Long-term cultivation caused a negative and degradative aspects on soil heath as is manifested by the increasing in soil pH (a rise of 0.3–0.46 unit), electrical conductivity (EC) (a rise of 1.78–5.5 times), sodium absorption ration (SAR) (a rise of 10–51 %), exchangeable sodium percentage (ESP) (a rise of 3–46 %), and the decrease in soil organic C (a drop of 12–41 %), along with soil fertility attributes. Overall, the general distribution of soil organic C, total N, available P and K, cation exchange capacity (CEC), and exchangeable cations (Ca, Mg, and K) followed the order: forestland > grassland > cropland. The general distribution of EC, SAR, ESP, and exchangeable Na, however, followed the order: cropland > grassland > forestland. Soil quality index (SQI), calculated based on some physicochemical properties, specified that cultivation led to a negative effect in SQI for both Cambisols (a drop of 10–17 %) and Vertisols (a drop of 17 %) as compared to those of under grassland and forestland.  相似文献   

13.
The distribution and bioavailability of Hg in vegetable-growing soils collected from the estuary areas of Jiulong River, China, were studied. Concentrations of Hg in top-soils, soil profiles and plant samples were measured with the method of hydride generation atomic fluorescence spectrometry after microwave digestion. Mercury species in soils were determined with the sequential extraction procedures based on Kingston method. Results showed that Hg concentrations in top-soils ranged from 49.8 to 1,685 ng g?1, with an average of 510 ng g?1 which was more than twice higher than the mercury limit (250 ng g?1 at pH < 6.5) of soil quality set for edible agricultural products in China (HJ 332-2006). High levels of Hg were found to mainly distribute in the top-soils from the northern, western and southern part of the estuary areas. Hg concentrations decreased with the increases of profile depths, except for one sample (S15) in which Hg level in the depth of 0–20 cm was found lower than that in the 20–40 cm. Hg in most of soil samples in non-mobile forms accounted for 46–82 % of total Hg in soils, while Hg in the mobile forms only 0.6–8.7 %. No significant correlation of Hg concentrations between the vegetables and the soils was observed in the studied areas, which indicates that the transfer factors could only reflect the abilities of Hg uptake and accumulation in a specific plant, but they are unsuitable to be used as the general indexes for the mobility and bioavailability of Hg in soils.  相似文献   

14.
Unsafe lead (Pb) concentrations in leafy vegetables raised in urban and peri-urban agricultural production systems have been reported across cities in Northern Nigeria, even though Pb concentrations in soils are within regulatory safe levels. This study examined the soil enrichment, adsorption and chemical species of Pb in urban garden fields irrigated with untreated wastewater at three industrial locations in Kano, northern Nigeria. Total Pb in the soil profiles ranged from 9 to 91 mg kg?1 and decreased rapidly from the surface to the subsurface layer, but attaining nearly constant concentration at depth ≥1.2 m in the profiles. The potentially labile Pb maintained fairly constant concentration with depth up to 0.9 m, but decreased fairly rapidly with depth thereafter. There was a significant Pb enrichment of the soils, extending up to 30–60 cm depth in the soil profiles. The adsorption of Pb by the soils increased drastically with pH, and attained maximum adsorption at pH ≥ 7.0 in the surface layer, and at pH ≥ 6 in the subsurface layer. The surface soils adsorbed between 85 and 97 % of added Pb at pH ≤ 5. Free Pb2+ activities in soil solution accounted for between 46 and 87 % at pH 5–7 of total dissolved Pb (PbT). The quantifiable chemical species of Pb in solution consisted mainly of PbOH+, PbSO 4 · , PbCl+ and PbOH 2 · which accounted for between 0.9 and 26 % of PbT in soil solution at pH ≥ 5.0, but declining to between 0.1 and 2.1 % at pH ≥ 7.5. There was no apparent equilibrium between Pb2+ activities and known Pb-compounds in the soils. It was concluded from the data that reports of excess Pb concentrations in leafy vegetables raised in these soils are consistent with high free Pb2+ activities maintained in soil solution by these predominantly sandy-textured soils.  相似文献   

15.
Euphrates Flood Plain sediments are recorded in Barwana city which is 6 km south of Haditha City. Much vegetation and climatic and archaeological evidences in this study pointed to several stages of old human settlements in that area. Palynological evidences show the livelihood of those humans before the great Noah Deluge of the period 10,500 years before present (BP). Their food was gathered by collecting crops and hunting animals in a steppe region along the valleys. As a result of this suffering from deluge and climatic variations that affected the region, humans had taken the search for a new way of living by trying to settle in the areas near the Euphrates river and attempted cultivation of this land, where the study showed the first appearance of field crop (cereals) pollens, such as wheat, barley, corn …, etc., at depth of 475–500 cm of the studies section, which represents a warm–humid climate with summer precipitation during the period of 10,000–5,000 years BP. These environmental conditions helped the ancient humans to settle in the agriculture village of Barwana, living on cultivation of the land and domesticating animals, such as grazing animals, for their main forms of food. Evolving palm cultivation and record of many archaeological ceramic pieces in the sample at a depth of 250 cm emphasized his attempt to establish industrial culture in the region after a period of changing climate to warm and dry which affected the region since 6,000 years BP and changed the Barwana settlements to an industrial village. The grasses and tree exploitation for sheep shepherding, building houses, and fire use, as well as dam building and Naoor manufacture for irrigation added evidences for ancient cities developments such as Hanat (Presently Ana) and Heet since about 5000 Y.BP. The desertification manifestation of that warm and dry climate continued from that time to the present with drought increased and deficiency in the rainfall, as well as the human irresponsible activities, as evidenced by increased pollen and spores of Compositae and Bongardia.  相似文献   

16.
In this study, total heavy metal content of soil and their spatial distribution in Sar?seki-Dörtyol district were analyzed and mapped. Variable distance grids (0.5, 1.0 and 2.0 km) were established, with a total of 102 soil samples collected from two different soil depths (0–5 and 5–20 cm) at intersections of the grids (51 sampling point). Soil samples were analyzed for heavy metals (Cd, Co, Cr, Cu, Pb, Zn, Mn, Fe, and Ni). The most proper variogram models for the contents of all heavy metal were spherical and exponential ones. The ranges of semivariograms were between 1.9 and 31.1 km. According to the calculated geoaccumulation (I geo) values, samples from both soil depths were classified as partly to highly polluted with Cd and Ni and partly polluted with Cr and as partly polluted-to-not polluted with Pb and not polluted with Cu, Fe and Mn. Similar results were also obtained when evaluated by the enrichment factor. The contamination levels of the heavy metals were Ni > Cd > Cr > Pb > Zn > Cu > Co > Fe > Mn in decreasing order. The soils in the study area are contaminated predominantly by Cd and Ni, which may give rise to various health hazards or diseases. Cadmium pollution results primarily from industrial activities and, to a lesser extent, from vehicular traffic, whereas Ni contents in the study area result from parent material, phosphorus fertilizer, industries, and vehicles.  相似文献   

17.
Biological soil crusts (BSCs) are an important cover in arid desert landscapes, and have a profound effect on the CO2 exchange in the desert system. Although a large number of studies have focused on the CO2 flux at the soil–air interface, relatively few studies have examined the soil CO2 concentration in individual layers of the soil profile. In this study, the spatiotemporal dynamics of CO2 concentration throughout the soil profile under two typical BSCs (algae crusts and moss crusts) and its driving factors were examined in a revegetated sandy area of the Tengger Desert from Mar 2010 to Oct 2012. Our results showed that the mean values of the vertical soil CO2 concentrations under algal crusts and moss crusts were 600–1,200 μmol/mol at the 0–40 cm soil profiles and increased linearly with soil depth. Daily CO2 concentrations showed a single-peak curve and often had a 1–2 h time delay after the maximum soil temperature. During the rainy season, the mean soil CO2 concentration profile was 1,200–2,000 μmol/mol, which was 2–5 times higher as compared to the dry season (400–800 μmol/mol). Annually, soil moisture content was the key limiting factor of the soil CO2 concentration, but at the daily time scale, soil temperature was the main limiting factor. Combined with infiltration depth of crusted soils, we predicted that precipitation of 10–15 mm was the most effective driving factor in arid desert regions.  相似文献   

18.
At present, the prior-established threshold values are widely used to classify contaminated agricultural soils with heavy metals under the cultivation of a variety of crops, without considering the different sensitivity of plants to heavy metals. Evaluation of the characteristics of cadmium transfer from a polluted calcareous soil to cultivated wheat crop and assessment of the efficiency of using the threshold values to reflect the soil pollution risk by cadmium in Zanjan Zinc Town area at the northwest of Iran were the goals of this study. Totally, 65 topsoil (0–20 cm) and corresponding wheat samples of an agricultural region in the proximity of a metallurgical factory were collected and analyzed for cadmium concentration. The results revealed that industrial activities strongly control cadmium distribution in the studied soils. Relatively high bioavailable cadmium contents (mean 0.77 mg kg?1) were found in the soils, notwithstanding their alkalinity. It was observed that just 22.5% of the studied area around the Zinc Town is covered by polluted soils with the cadmium concentration exceeding the maximum permissible concentration of 5 mg kg?1, whereas cadmium concentration in wheat grains of 19 sampled plants is higher than the threshold value of 0.2 mg kg?1. Among these polluted plants, a total of eight samples were grown in areas classified as unpolluted soils with cadmium, based on the soil threshold value. It seems that this misclassification of polluted soils is mainly related to the crop sensitivity to heavy metals uptake from the soil which should be considered.  相似文献   

19.
Ma  Bin  Liang  Xing  Liu  Shaohua  Jin  Menggui  Nimmo  John R.  Li  Jing 《Hydrogeology Journal》2017,25(3):675-688

Subsurface-water flow pathways in three different land-use areas (non-irrigated grassland, poplar forest, and irrigated arable land) in the central North China Plain were investigated using oxygen (18O) and hydrogen (2H) isotopes in samples of precipitation, soils, and groundwater. Soil water in the top 10 cm was significantly affected by both evaporation and infiltration. Water at 10–40 cm depth in the grassland and arable land, and 10–60 cm in poplar forest, showed a relatively short residence time, as a substantial proportion of antecedent soil water was mixed with a 92-mm storm infiltration event, whereas below those depths (down to 150 cm), depleted δ18O spikes suggested that some storm water bypassed the shallow soil layers. Significant differences, in soil-water content and δ18O values, within a small area, suggested that the proportion of immobile soil water and water flowing in subsurface pathways varies depending on local vegetation cover, soil characteristics and irrigation applications. Soil-water δ18O values revealed that preferential flow and diffuse flow coexist. Preferential flow was active within the root zone, independent of antecedent soil-water content, in both poplar forest and arable land, whereas diffuse flow was observed in grassland. The depleted δ18O spikes at 20–50 cm depth in the arable land suggested the infiltration of irrigation water during the dry season. Temporal isotopic variations in precipitation were subdued in the shallow groundwater, suggesting more complete mixing of different input waters in the unsaturated zone before reaching the shallow groundwater.

  相似文献   

20.
The concentration and distribution characteristics of toxic elements in soil and plant were investigated in the coal refuse reclaimed areas of Huainan, China. Ninety soil samples from different depth (0–20, 20–40, 40–60 cm) and 120 plant samples were collected based on grid sampling method. The concentrations of the selected toxic elements (As, Cd, Cu, Ni, Pb and Zn) in the soil and plant samples were determined by using inductively coupled plasma mass spectrometry. The elevated concentrations of toxic elements in the soils at the depth of 20–40 and 40–60 cm suggested that the coal refuse reclamation may lead to potential environmental impacts. The toxic element tolerance could be observed in all the selected plant samples. The concentrations of toxic elements in the underground tissues were higher than that of aboveground tissues. Conclusively, the present study provided a comprehensive evaluation of soil and plant toxic element implications from coal refuse reclaimed areas in China and was also helpful for environmental protection and monitoring the safety of plant.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号