The purposes of this paper are to investigate the geochemical characteristics of rare earth elements (REEs) in the surface sediments of Jiulong River, southeast China, to probe the provenance compositions of the sediments, and to analyze the potential anthropogenic influence on REEs in the sediments. REEs and Sr-Nd isotopes were selected as the tools because REEs can be used to identify the anthropogenic effects on sediments and Sr-Nd isotopes have been widely known as powerful tracers for provenance analysis.
Materials and methodsFifty-three samples of surface sediments (0~5 cm) were collected from Jiulong River. The concentrations of REEs and Sr-Nd isotopic compositions in the surface sediments were determined by inductively coupled plasma mass spectrometry (ICP-MS) and thermal ionization mass spectrometry (TIMS), respectively. The chondrite-normalized and WRAS-normalized REEs patterns, enrichment factor, plots of La-Th-Sc and La/Yb-∑REE, and plots of εNd(0) vs 87Sr/86Sr and εNd(0) vs δEu are presented.
Results and discussionThe mean concentration of ΣREEs in the surface sediments of Jiulong River was 254.25 mg kg?1. The mean values of ΣLREEs (227.6 mg kg?1), ΣHREEs (26.64 mg kg?1), and (La/Yb)N ratios (9.24) suggested an enrichment of LREEs compared to HREEs. Negative Eu anomalies were observed in the surface sediments. The distribution patterns of REEs in the surface sediments from different areas of Jiulong River were remarkably similar. The values of 87Sr/86Sr, 143Nd/144Nd, and εNd(0) were 0.714091~0.733476, 0.511875~0.512271, and ??14.88~??7.16, respectively. The plots of εNd(0) vs 87Sr/86Sr, εNd(0) vs 1/[Nd], and εNd(0) vs δEu indicated that the sediments in Jiulong River were mainly derived from natural geological processes and the REEs might be also influenced by anthropogenic activities such as Fujian Pb-Zn deposit, coal ash, and industrial sludge.
ConclusionsThe REEs in the surface sediments at different sites are similar in geochemical characteristics, with a right-inclined distribution pattern and higher enrichment of light REEs (LREEs) compared to heavy REEs (HREEs), and a negative Eu anomaly but no evidence of Ce anomaly. The sediments in Jiulong River were mainly derived from natural geological processes (granite and magmatic rocks), and the REEs in the sediments were also influenced by anthropogenic activities (Fujian Pb-Zn deposit, coal ash, and industrial sludge).
相似文献Imidacloprid is a widely used seed dressing insecticide in Brazil. However, the effects of this pesticide on non-target organisms such as soil fauna still present some knowledge gaps in tropical soils. This study aimed to assess the toxicity and risk of imidacloprid to earthworms Eisenia andrei and collembolans Folsomia candida in three contrasting Brazilian tropical soils.
Materials and methodsAcute and chronic toxicity assays were performed in the laboratory with both species in a tropical artificial soil (TAS) and in two natural soils (Oxisol and Entisol), at room temperature of 25 °C. The ecological risk was calculated for each species and soil by using the toxicity exposure ratio (TER) and hazard quotient (HQ) approaches.
Results and discussionAcute toxicity for collembolans and earthworms was higher in Entisol (LC50?=?4.68 and 0.55 mg kg?1, respectively) when compared with TAS (LC50?=?10.8 and 9.18 mg kg?1, respectively) and Oxisol (LC50collembolans?=?25.1 mg kg?1). Chronic toxicity for collembolans was similar in TAS and Oxisol (EC50 TAS?=?0.80 mg kg?1; EC50 OXISOL?=?0.83 mg kg?1), whereas higher toxicity was observed in Entisol (EC50?=?0.09 mg kg?1). In chronic assays with earthworms, imidacloprid was also more toxic in Entisol (EC50?=?0.21 mg kg?1) when compared to TAS (EC50?=?1.89 mg kg?1). TER and HQ values indicated a significant risk of exposure of the species to imidacloprid in all soils tested, and the risk in Entisol was at least six times higher than in Oxisol or TAS.
ConclusionsThe toxicity and risk of imidacloprid varied significantly between tropical soils, being the species exposure to this pesticide particularly hazardous in very sandy natural soils such as Entisol.
相似文献This study investigated the concentrations of cadmium (Cd), chromium (Cr), copper (Cu), lead (Pb), nickel (Ni), zinc (Zn), and polycyclic aromatic hydrocarbons (PAHs) in sediments collected from gully pots for road drainage in Hong Kong. The presence and intensity of anthropogenic contamination of road gully sediments were assessed. Identifications of potential sources of trace elements and PAHs were performed to help understand the situation for future control of pollution to the land and aquatic environments.
Materials and methodsGully sediment samples were collected from gully pots of 18 roads that are potentially exposed to different pollution sources in Hong Kong. The selection of roads considered different road features, adjacent land uses, and traffic volumes. Composite samples were collected for the analysis of trace elements (Cd, Cr, Cu, Pb, Ni, and Zn) and PAHs by an accredited environmental testing laboratory. Geo-accumulation index (Igeo), contamination factor (Cf), modified degree of contamination (mCd), ecological risk factor (Er), and pollution load index (PLI) were used to assess the level of ecological risk of trace element contamination. Positive matrix factorization (PMF) and PAH diagnostic ratios were applied to identify the sources of trace elements and PAHs.
Results and discussionElevated trace element concentrations were commonly found in gully sediments. The concentrations of Zn (267–3700 mg kg?1) were the highest compared to the other trace elements. Noticeable high concentrations of Cu (27–1020 mg kg?1), Pb (21–332 mg kg?1), and Cr (14–439 mg kg?1) were found in all samples. The PAH contents were moderate to high (0.6 to 24.7 mg kg?1). Commercial/industrial emissions and road features that cause frequent acceleration-deceleration and turning events showed important influences on the contaminant levels. Strong correlations between the concentrations of Cd, Cr, Pb, and Zn were identified, implying that these trace elements are likely from common sources. The contamination assessment indices reflect significant sediment pollution. The ecological risk ranges from the considerable/moderate-risk class to over the high-risk class.
ConclusionsThe collected gully sediments are identified as highly contaminated and need to be isolated from the environment upon final disposal. Through the comprehensive analysis of the collected data, this study provides a detailed insight into the contaminant levels of road gully sediments and potential sources of contamination. Disposal of gully sediments and potential impacts due to release of contaminants into the downstream aquatic environment during rainstorm events should receive attention and need further investigation.
相似文献Identification of phosphorus (P) species is essential to understand the transformation and availability of P in soil. However, P species as affected by land use change along with fertilization has received little attention in a sub-alpine humid soil of Tibet plateau.
Materials and methodsIn this study, we investigated the changes in P species using Hedley sequential fractionation and liquid-state 31P-NMR spectroscopy in soils under meadow (M) and under cropland with (CF) or without (CNF) long-term fertilization for 26 years in a sub-alpine cold-humid region in Qinghai–Tibet plateau.
Results and discussionLand-use change and long-term fertilization affected the status and fractions of P. A strong mineralization of organic P (OP) was induced by losing protection of soil organic matter (SOM) and Fe and Al oxides during land-use change and resulted in an increase of orthophosphate (from 56.49 mg kg?1 in M soils to 130.07 mg kg?1 in CNF soils) and great decreases of orthophosphate diesters (diester-P, from 23.35 mg kg?1 in M soils to 10.68 mg kg?1 in CNF soils) and monoesters (from 336.04 mg kg?1 in M soils to 73.26 mg kg?1 in CNF soils). Long-term fertilization boosted P supply but failed to reclaim soil diester-P (from 10.68 mg kg?1 in CNF soils to 7.79 mg kg?1 in CF soils). This may be due to the fragile protection from the combination of SOM with diester-P when long-term fertilization had only improved SOM in a slight extent.
ConclusionsThese results suggest that SOM plays an important role in the soil P cycling and prevents OP mineralization and losses from soil. It is recommended that optimization of soil nutrient management integrated with SOM was required to improve the P use efficiency for the development of sustainable agriculture.
相似文献In contaminated streams, understanding the role of streambank and streambed source contributions is essential to developing robust remedial solutions. However, identifying relationships can be difficult because of the lack of identifying signatures in source and receptor pools. East Fork Poplar Creek (EFPC) in Oak Ridge, TN, USA received historical industrial releases of mercury that contaminated streambank soils and sediments. Here, we determined relationships between the contaminated streambank soils and sand-sized streambed sediments.
Materials and methodsField surveys revealed the spatial trends of the concentrations of inorganic total mercury (Hg) and methyl mercury (MeHg), Hg lability as inferred by sequential extraction, particle size distribution, and total organic carbon. Statistical tests were applied to determine relationships between streambank soil and streambed sediment properties.
Results and discussionConcentrations of Hg in streambank soils in the upper reaches averaged 206 mg kg?1 (all as dry weight) (n?=?457), and 13 mg kg?1 in lower reaches (n?=?321), while sand-sized streambed sediments were approximately 16 mg kg?1 (n?=?57). Two areas of much higher Hg and MeHg concentrations in streambank soils were identified and related to localized higher Hg concentrations in the streambed sediments; however, most of the streambank soils have similar Hg concentrations to the streambed sediments. The molar ratio of Hg to organic carbon, correlation between MeHg and Hg, and particle size distributions suggested similarity between the streambank soils and the fine sand-sized fraction (125–250 μm) collected from the streambed sediments. Mercury in the fine sand-sized streambed sediments, however, was more labile than Hg in the streambank soils, suggesting an in-stream environment that altered the geochemistry of sediment-bound Hg.
ConclusionsThis study revealed major source areas of Hg in streambank soils, identified possible depositional locations in streambed sediments, and highlighted potential differences in the stability of Hg bound to streambank soils and sediments. This work will guide future remedial decision making in EFPC and will aid other researchers in identifying source–sink linkages in contaminated fluvial systems.
相似文献Calcareous soils are characterized by high pH and phosphorus (P) fixation capacity. Increasing application of P fertilizer recently has significantly improved soil P concentration, especially available P (Olsen-P) and inorganic phosphate (Pi) fractions. However, there are few data available on the ability of soils with different initial Olsen-P levels to continuously supply P (i.e., P desorption capacity) to crops without additional P fertilization and on which Pi fraction exerts the greatest influence on P desorption capacity.
Materials and methodsFive soils with different initial Olsen-P levels (0.5, 14.3, 38.4, 55.4, 72.3 mg kg?1, hereafter refer as OP1, OP2, OP3, OP4, and OP5) but similar other soil properties were selected to evaluate the capacity of P desorption and its relationship with Pi fractions. Soil P was sequentially extracted once daily for 16 consecutive days using Olsen solution.
Results and discussionThe content and proportions of dicalcium phosphate fraction (Ca2-P), octacalcium phosphate fraction (Ca8-P), aluminum phosphorus fraction (Al-P), and iron phosphorus fraction (Fe-P) in Pi increased significantly with the increase of initial Olsen-P (P?<?0.01). Applied P fertilizer was mostly stored as Ca8-P in the soil. Soil P desorbed reached an equilibrium after 16 extractions for all soils, and P desorption capacity (12–358 mg kg?1) showed a significant linear relationship with initial Olsen-P (P?<?0.01), with an increase of 4.2 mg kg?1 desorbed P per 1 mg kg?1 increase of initial Olsen-P. Ca2-P exerted the conclusive effect on P desorption in the first four extractions, but Ca8-P played a more important role in the 16 extractions.
ConclusionsCa8-P was the greatest potential pool for P desorption after Ca2-P was depleted. P desorption capacity was significantly linearly related to initial Olsen-P (P?<?0.01). Different fertilizer use strategies were developed based on P desorption capacity for soils with different initial Olsen-P levels. The present study provided basic data on how to reduce effectively the application amount of chemical P fertilizer.
相似文献This study aims to explore the effects of antimony (Sb) on the nutrient composition of green leafy vegetables.
Materials and methodsRed beets (Beta vulgaris L.), mallow (Malva sinensis Cavan.), and Chinese cabbage (Brassicacampestris L.) were planted by pouring antimony solution in flowerpot, then the protein content of plants and the changes of seven nutrient elements such as Ca, Mg, Fe, Mn, Zn, Cu, and I under Sb stress were studied.
Results and discussionThe results showed that the red beet had the highest protein content when the concentration was 20 mg L?1, which was 0.2856 gprot L?1. With an increase in the antimony concentration, the protein content decreased gradually, and the protein content of mallow and Chinese cabbage did not change significantly. For nutrient elements, except for Ca and I, other nutrients in red beets increased with the increase in antimony concentration, and Mn and Zn contents in mallow were reduced to the lowest when Sb was treated with 100 mg L?1, while content of I element was the highest at 100 mg·L?1, and the content of nutrients in Chinese cabbage changed in a small range.
ConclusionsThe research showed that the antimony pollution had a great influence on the protein content of red beet. The nutrient content of mallow was fluctuated greatly when Sb was treated with 100 mg L?1. The content of Mn, Zn, and Cu in Chinese cabbage almost did not change due to the antimony concentration.
相似文献Combining biodegradable chelating agents with phytoextraction is an efficient technique to amend metal-contaminated soils, but most studies have addressed remediation efficiency rather than a comprehensive understanding of the interactions among plant stress, metal accumulation, and metal bioavailability. This study aimed to investigate the effects of biodegradable chelating agents on improving the efficiency of phytoextraction for cobalt (Co)-contaminated soil by sweet alyssum (Lobularia maritima (L.)) and to explore the interrelationships among plant stress, Co accumulation, and Co bioavailability.
Materials and methodsSweet alyssum (three plants per pot) was grown in pots containing soil with Co added at 0, 40, and 60 mg kg?1, respectively. After 70 days of growth, we added four biodegradable chelating agents (EDDS, NTA, CA, and OA) at various concentrations (0, 2.5, 5.0, and 7.5 mmol kg?1). The plants were harvested after 7 days, and the biomass, reactive oxygen species (ROS) parameters, Co concentrations of the shoot and root, and available Co content in the soil were analyzed.
Results and discussionThe results demonstrate that chelating agents significantly (p?<?0.05) improved the phytoextraction capability of sweet alyssum and influenced plant growth and stress. The capability of EDDS to activate Co was higher than that of other chelating agents at identical concentrations in Co-contaminated soils. Furthermore, we observed that a moderate concentration (40 mg kg?1) of Co could promote plant growth and that high concentrations of Co (60 mg kg?1) and EDDS (7.5 mmol kg?1) cause enhanced stress to plant growth, even resulting in lower shoot Co accumulation than that in the moderate EDDS treatment (5.0 mmol kg?1).
ConclusionsThe present study demonstrates that the application of EDDS may be a better choice for Co phytoextraction than NTA, CA, and OA; nevertheless, a high concentration of EDDS may enhance the negative effects on plant growth, physiological traits, and Co accumulation.
相似文献Soil pollution indices are an effective tool in the computation of metal contamination in soil. They monitor soil quality and ensure future sustainability in agricultural systems. However, calculating a soil pollution index requires laboratory measurements of multiple soil heavy metals, which increases the cost and complexity of evaluating soil heavy metal pollution. Visible and near-infrared spectroscopy (VNIR, 350–2500 nm) has been widely used in predicting soil properties due to its advantages of a rapid analysis, non-destructiveness, and a low cost.
MethodsIn this study, we evaluated the ability of the VNIR to predict soil heavy metals (As, Cu, Pb, Zn, and Cr) and two commonly used soil pollution indices (Nemerow integrated pollution index, NIPI; potential ecological risk index, RI). Three nonlinear machine learning techniques, including cubist regression tree (Cubist), Gaussian process regression (GPR), and support vector machine (SVM), were compared with partial least squares regression (PLSR) to determine the most suitable model for predicting the soil heavy metals and pollution indices.
ResultsThe results showed that the nonlinear machine learning models performed significantly better than the PLSR model in most cases. Overall, the SVM model showed a higher prediction accuracy and a stronger generalization for Zn (R2V?=?0.95, RMSEV?=?6.75 mg kg?1), Cu (R2V?=?0.95, RMSEV?=?8.04 mg kg?1), Cr (R2V?=?0.90, RMSEV?=?6.57 mg kg?1), Pb (R2V?=?0.86, RMSEV?=?4.14 mg kg?1), NIPI (R2V?=?0.93, RMSEV?=?0.31), and RI (R2V?=?0.90, RMSEV 3.88). In addition, the research results proved that the high prediction accuracy of the three heavy metal elements Cu, Pb, and Zn and their significant positive correlations with the soil pollution indices were the reason for the accurate prediction of NIPI and RI.
ConclusionUsing VNIR to obtain soil pollution indices quickly and accurately is of great significance for the comprehensive evaluation, prevention, and control of soil heavy metal pollution.
相似文献Copper (Cu) is the earliest anthropogenic metal pollutant, but knowledge of Cu soil concentrations at ancient metalworking sites is limited. The objective of this work was to examine the ability of portable X-ray fluorescence to quantify Cu in soils at such sites.
Materials and methodsUsing a Bruker Tracer III-SD pXRF, we examine factory “scan” settings versus simple instrument parameter changes (a reduction in energy settings from 40 to 12 kV) to target analysis for Cu. We apply these to a set of uncontaminated samples (n?=?18, <?92 mg Cu kg?1) from Central Thailand and compare results to standard wet chemistry analysis (aqua regia digestion and ICP-OES analysis). We then apply the optimized method to a set of highly contaminated samples (n?=?86, <?14,200 mg Cu kg?1) from a known ancient smelting site.
Results and discussionWe demonstrate that simple changes to factory recommended “scan” settings can double the sensitivity of Cu determination via pXRF (“optimized limit of determination” of 19.3 mg kg?1 versus an initial value of 39.4 mg kg?1) and dramatically improve the accuracy of analysis. Changes to other results for other elements are variable and depend on concentration ranges, soil matrix effects, and pXRF response for the individual element. We demonstrate that pXRF can accurately determine Cu across a wide concentration range and identify grossly contaminated soil samples.
ConclusionsWe conclude that pXRF is a useful tool to rapidly screen and analyse samples at remote sites and can be applied to ancient metalworking sites. Simple optimization of the pXRF settings greatly improves accuracy and is essential in determining comparative background concentrations and “unaffected” areas. Application to other elements requires further element and matrix specific optimization.
相似文献Determination of the effectiveness of white mustard and oats in immobilising cadmium as a soil contaminant and determining the role of cellulose and urea in restoring homeostasis in soil under pressure from Cd2+.
Materials and methodsSoil samples were contaminated with cadmium (CdCl2·21/2H2O) at 0, 4, 8 and 16 mg Cd2+ kg?1. In order to reduce the negative impact of Cd2+, cellulose was introduced to the soil at the following rates: 0 and 15 g kg?1 and urea at 80 and 160 mg N kg?1. The yield of the above-ground parts and roots was determined on days 40 and 80 of the experiment, along with the cadmium content in the plant material. The enzyme activity was also determined, and the physical and chemical properties of the soil were determined on the day of the oats’ (aftercrop) harvest.
Results and discussionContamination of soil with Cd2+ at 4 to 16 mg kg?1 d.m. of soil reduced the yield of white mustard and oats. The tolerance index (TI) values indicate that oats (aftercrop) is more tolerant than white mustard of soil contamination with Cd2+. Cadmium accumulated more intensely in roots compared with the above-ground parts of the plants. The translocation index (TF) indicates smaller Cd2+ translocation from roots to above-ground parts, as it was below 1 in both plants. An addition of cellulose and nitrogen offsets the adverse impact of cadmium on plants. Arylsulphatase was the most sensitive to soil contamination with Cd2+, followed by dehydrogenases, catalase, β-glucosidase and urease, and alkaline phosphatase and acid phosphatase were the least sensitive. Contamination of soil with Cd2+ changed its physical and chemical properties only slightly.
ConclusionsWhite mustard and oats have phytostabilisation potential with respect to soil contaminated with cadmium. Cellulose introduced to the soil and fertilisation with urea alleviated the negative impact of cadmium on the growth and development of plants.
相似文献Metallic nanomaterials (MNM) like cobalt oxide (nano-Co3O4) are currently attracting enormous interest owing to their unique size and shape-dependent properties and potential applications in various sectors. The aims of this study were to assess the toxicity of nano-Co3O4 and to propose a risk limit through the estimation of a Predicted No Effect Concentration (PNEC) for this MNM to soil biota.
Materials and methodsFor this purpose, a battery of sub-lethal ecotoxicological tests was performed to assess the influence of this MNM on four plant species (endpoints: germination and growth) and two invertebrate species (endpoints: avoidance and reproduction) following standard protocols. Further, biochemical endpoints (acetylcholinesterase [AChE], catalase [CAT], glutathione-S-transferase [GST] activity, and lipid peroxidation [LPO]) were also assessed in Eisenia andrei, one of the invertebrate species tested, in order to contribute for refining the PNEC value.
Results and discussionThe recorded data showed a significant inhibition in the germination of L. lycopersicum and in the growth of Z. mays, even at the lowest concentration tested (269.3 mg kg?1 soildw of nano-Co3O4). Concerning the soil invertebrates, the results showed only significant avoidance (p?<?0.05) by E. andrei in the soil contaminated with the highest concentration tested (1000 mg kg?1 soildw of nano-Co3O4), while no significant ecotoxicological effect on reproductive outputs of both species was recorded. However, the data reported for AChE, CAT, GST, and LPO showed significant effects at the range of concentrations tested in E. andrei. Thus, we recorded, the occurrence of oxidative stress and the enhancement of lipid peroxidation, on this invertebrate species.
ConclusionsThe data obtained in this study supports the proposal of a PNEC value of 9.1 mg kg?1 soildw for nano-Co3O4 in soil. The integration of data from biochemical endpoints allowed the refinement of the PNEC value and to obtain a more protective threshold.
相似文献The aim of this research was to quantify the effect of plantain (Plantago lanceolata L.) on soil nitrification rate, functional gene abundance of soil ammonia oxidisers, and the concomitant effect on nitrous oxide emissions from urine patches in a shallow, free-draining soil in Canterbury during late autumn/winter season.
Materials and methodsUrine was collected from dairy cows grazing either ryegrass/white clover (RGWC), 30% plantain (P30) mixed in with RGWC or 100% plantain (P100) pasture, and applied at two rates (700 or 450 kg N ha?1) to intact soil blocks growing either RGWC, P30 or P100 pasture.
Results and discussionResults showed that increased plantain content reduced N-concentration in urine from 7.2 in RGWC urine to 4.5 and 3.7 g N L?1 in P30 and P100 urine, respectively. Total N2O emissions and emission factors (EF3) from urine-treated pastures were low, <?2 kg N ha?1 and <?0.22%, respectively. Urine application at the lower urine N-loading rate of 450 kg N ha?1 (i.e. representative of that in a P30 urine patch) resulted in 30% lower N2O emissions (P?<?0.01) and 35% lower soil nitrate concentrations (P?<?0.001) compared to those at the higher urine loading rate of 700 kg N ha?1 (i.e. representative of that in a RGWC urine patch). Increasing plantain content in the pasture sward from 0 to 30% and 100% with urine N applied at the same loading rate did not reduce N2O emissions or nitrification compared to the standard ryegrass-white clover pasture. Cow urine derived from the different pasture diets had no effect on N2O emissions, N transformation or ammonia-oxidiser abundance in soil compared to the RGWC urine applied at the same rate.
ConclusionsThe main effect of plantain in this study appears to be related to the reduction in urine N-loading rate, rather than factors related to urine properties or plantain-soil interactions.
相似文献Wetlands in Mu Us Desert have severely been threatened by grasslandification over the past decades. Therefore, we studied the impacts of grasslandification on soil carbon (C):nitrogen (N):phosphorus (P) stoichiometry, soil organic carbon (SOC) stock, and release in wetland-grassland transitional zone in Mu Us Desert.
Materials and methodsFrom wetland to grassland, the transition zone was divided into five different successional stages according to plant communities and soil water conditions. At every stage, soil physical and chemical properties were determined and C:N:P ratios were calculated. SOC stock and soil respirations were also determined to assess soil carbon storage and release.
Results and discussionAfter grasslandification, SOC contents of top soils (0–10 cm) decreased from 100.2 to 31.79 g kg?1 in June and from 103.7 to 32.5 g kg?1 in October; total nitrogen (TN) contents of top soils (0–10 cm) decreased from 3.65 to 1.85 g kg?1 in June and from 6.43 to 3.36 g kg?1 in October; and total phosphorus (TP) contents of top soils (0–10 cm) decreased from 179.4 to 117.4 mg kg?1 in June and from 368.6 to 227.8 mg kg?1 in October. From stages Typha angustifolia wetland (TAW) to Phalaris arundinacea L. (PAL), in the top soil (0–10 cm), C:N ratios decreased from 32.2 to 16.9 in June and from 19.0 to 11.8 in October; C:P ratios decreased from 1519.2 to 580.5 in June and from 19.0 to 11.8 in October; and N:P ratios decreased from 46.9 to 34.8 in June and changed from 34.9 to 34.0 in October. SOC stock decreased and soil respiration increased with grasslandification. The decrease of SOC, TN, and TP contents was attributed to the reduction of aboveground biomass and mineralization of SOM, and the decrease of soil C:N, C:P, and N:P ratios was mainly attributed to the faster decreasing speeds of SOC than TN and TP. The reduction of aboveground biomass and increased SOC release led by enhanced soil respiration were the main reasons of SOC stock decrease.
ConclusionsGrasslandification led to lowers levels of SOC, TN, TP, and soil C:N, C:P, and N:P ratios. Grasslandification also led to higher SOC loss, and increased soil respiration was the main reason. Since it is difficult to restore grassland to original wetland, efficient practices should be conducted to reduce water drainage from wetland to prevent grasslandification.
相似文献Natural organic acids, such as humic acid (HA), play crucial roles in biogeochemistry of anions and cations in soil due to their numerous functional groups on their surfaces. Selenium (Se) and cadmium (Cd) could bind strongly to HA; nevertheless, it is still unclear as to the effects of HA on Se and Cd uptake in rice which will be focused on in this paper.
Materials and methodsPot experiments were carried out at Huazhong Agricultural University, Wuhan City, Hubei Province, China. Agricultural soils were treated with different concentrations of HA (0, 4, and 8 g kg?1 soil) and Se (SeIV or SeVI) (0 and 2 mg kg?1 soil) as well as with base fertilizer 3 days prior to planting. For Cd treatment, experimental soils were treated with Cd (0 and 2 mg kg?1 soil) 1 month before sowing. For element determination, root (after DCB extraction) and shoot samples were digested with a mixed solution of HNO3-HClO4, and the Se and Cd in digest solution were measured by HG-AFS and ICP-MS, respectively. Fe, Se, and Cd in iron plaque were extracted by DCB extraction and measured by AAS, HG-AFS, and ICP-MS, respectively.
Results and discussionHA reduced Se (or Cd)-induced growth stimulation and Se and Cd uptake in rice seedlings, whereas iron plaque formation varied little with different treatments. HA inhibited SeIV (or SeVI) uptake in rice seedlings by reducing Se translocations from soil to iron plaque (or by increasing Se adsorption capacity of iron plaque and decreasing Se transport from iron plaque to root). HA reduced Cd uptake in rice seedlings by reducing Cd transport from soil to iron plaque and from iron plaque to root. Compared with single addition of SeIV or SeVI or HA, adding HA combined with SeIV or SeVI could further reduce Cd uptake in rice seedlings, whereas Se contents of aerial tissues did not change obviously.
ConclusionsHA inhibited the accumulation of Se (SeIV or SeVI) and Cd in rice seedlings; nevertheless, the mechanism was different. Compared with adding Se (or HA) alone, application of Se mixed with HA might be a more effective way to produce Se-enriched and Cd-deficient crop in Cd-contaminated soil.
相似文献Grazing livestock has strong impact on global nitrous oxide (N2O) emissions by providing N sources through excreta. The scarcity of information on factors influencing N2O emissions from sheep excreta in subtropical ecosystems such as those of Southern Brazil led us to conduct field trials in three different winter pasture seasons on an integrated crop–livestock system (ICL) in order to assess N2O emission factors (EF-N2O) in response to variable rates of urine and dung.
Materials and methodsThe equivalent urine-N loading rates for the three winter seasons (2009, 2010, and 2013) ranged from 96 to 478 kg ha?1, and the dung-N rates applied in 2009 and 2010 were 81 and 76 kg ha?1, respectively. Air was sampled from closed static chambers (0.20 m in diameter) for approximately 40 days after excreta application and analyzed for N2O by gas chromatography.
Results and discussionSoil N2O-N fluxes spanned the ranges 4 to 353 μg m?2 h?1 in 2009, ??47 to 976 μg m?2 h?1 in 2010, and 46 to 339 μg m?2 h?1 in 2013. Urine addition resulted in N2O-N peaks within for up to 20–30 days after application in the 3 years, and the strength of the peaks was linearly related to the N rate used. Emission factors of N2O (EF-N2O, % of N applied that is emitted as N2O) of urine ranged from 0.06 to 0.34% and were essentially independent of N rate applied. By considering a ratio of N excreted by urine and dung of 60:40, a single combined excretal EF-N2O of 0.14% was estimated.
ConclusionsOur findings showed higher mean EF-N2O for sheep urine than that for dung (0.21% vs 0.03%), irrespective of the occurrence or not of urine patches overlap. This value is much lower than default value of 1% of IPCC’s Tier 1 and reinforces the needs of its revision.
相似文献Based on two consecutive years of field-scale trials, under different water managements, we illustrated the persistence of remediation effect of palygorskite on a Cd-polluted rice field.
Materials and methodsThe Cd uptake by a plant, pH and Cd chemical extractability, available P/K, and extractable Zn/Cu in paddy soils were used to evaluate the influence of palygorskite on Cd immobilization and soil fertility index.
Results and discussionIn contrast to the 1st year, at 0–1.5% palygorskite applied dose in soils, 0.025 M HCl–extractable Cd in continuous flooding reduced by 12.1–19.0%, and that in wetting irrigation increased by 10.9–18.9% in the 2nd year (p?<?0.05). The toxicity characteristic leaching procedure Cd reduction of 3.0–11.4% and increase of 8.9–12.0% were obtained under above-mentioned water managements (p?<?0.05). Compared with the 1st year, at different clay additional concentrations, grain Cd in continuous flooding reduced by 7.0–11.3%, and that in wetting irrigation increased by 6.5–10.8% in the 2nd year (p?<?0.05). Although trace elements in clay treated soils declined, they had no influence on the grain yield due to a minimum value higher than the critical value of 1.5 mg kg?1 for Zn and 2.0 mg kg?1 for Cu. The available P in continuous flooding took on a maximum increase of 8.2% in the 2nd year (p?<?0.05).
ConclusionsTwo consecutive years of field-scale in situ demonstration tests revealed that continuous flooding was a preferable water management regime for Cd immobilization using palygorskite in the rice field. There were no remarkable differences in extractable Zn/Cu between 2 years.
相似文献