Determination of atrazine isotherms on agricultural soils

For determination of atrazine isotherms in agricultural soils of Fars Province, composite soil samples from 0 to 5 cm depth with textures of silty clay loam, clay loam and loam were collected. In order to form the atrazine isotherms, 10, 50 and 100 µg atrazine g^?1 soil was added to the soil samples. Soluble atrazine in water:soil ratios of 10:1, 50:1 and 200:1 was measured after 3-h shaking. Finally, for each cases of applied atrazine, water extractable atrazine was determined and quantified using gas chromatography instrument. The results indicated that there was a linear relationship between the logarithms of water extractable atrazine and added atrazine for different water:soil ratios. A general equation of WEA = K(WS) ^α (AA) ^β is obtained experimentally between water extractable atrazine, µg g^?1(WEA), and added atrazine, µg g^?1 (AA), where K, α and β are absorption constants; WS is the water:soil ratio, g g^?1. For the loam, silty clay loam and clay loam soil textures, the α were 0.49, 0.23 and 0.13, respectively, the β were 0.55, 0.806 and 0.21, respectively, and the K were 1.44, 0.78 and 25.38, respectively.     

Impact of parent rock and topography aspect on the distribution of soil trace metals in natural ecosystems

The concentration and dynamic of soil trace metals in natural ecosystems, in particularly, is dependent on the lithology of parent rock as well as topography and geopedological processes. To ascertain more knowledge for this dependency, soils on three parent rocks involving peridotite, pegmatite, and dolerite in two contrasting topography aspects were investigated. The total values of Fe, Mn, Zn, Cu, and Ni were determined and compared for different soil pedons. The concentration of Fe, Mn, and Ni were highest in soils developed from peridotite (127, 1.8 g kg^?1, and 218 mg kg^?1, respectively), intermediate in soils derived from dolerite (81, 1.3 g kg^?1, and 166 mg kg^?1, respectively), and least in soil developed from pegmatite (50, 0.23 g kg^?1, and 20 mg kg^?1, respectively). The values of Zn and Cu, originated from different parent rocks, were in order of dolerite (78 mg kg^?1) > peridotite (77 mg kg^?1) > pegmatite (28 mg kg^?1) and pegmatite (121 mg kg^?1) > peridotite (111 mg kg^?1) > dolerite (28 mg kg^?1), respectively. For most of the studied pedons, profile metals distribution differed among the soils: The values of Fe, Cu, and Ni were enriched in the cambic horizons mainly as result of release, mobilization, and redistribution of the studied metals during geopedological processes, whereas those of Zn and Mn were concentrated in the surface horizons. Probably due to greater weathering rate of trace metal-bearing rocks on north-facing slope, the content of the trace metals along with the geoaccumulation index (I _geo) and the degree of soil contamination (C _d) were higher than on south-facing slope. Based on assessment of soil pollution indices, the soils were categorized as unpolluted [I _geo ≤ 0 (class 0)], unpolluted to moderately polluted levels [0 < I _geo < 1 (class 1)], and very low [C _d < 1.5 (class 0)] to low degree of contamination [1.5 < C _d < 2 (class 1)].     

Phosphorus release kinetics in a soil amended with biosolids and vermicompost

Wastewater biosolids are large potential sources of macronutrients for agriculture, conservation and restoration of soils; there are, however, few studies on phosphorus (P) release in soils amended with biosolids. Biosolids and vermicomposted biosolids were tested in concentrations (5–30 g amendment kg^?1 soil) equivalent to 18–100 Mg ha^?1. Desorption of P was determined by successive extractions for 65 days. Soil P was low, and biosolid and vermicompost addition released 8 and 6 times more P, respectively, than soil alone. To describe the release of P, zero-, first- and second-order equations, simple Elovich and power functions and the parabolic diffusion law were compared based on their coefficient of determination (r ²) and standard error (SE). In all treatments, the power function and especially the parabolic diffusion law were the best fit, with 0.898–0.996 r ² and 0.022–0.732 SE. The general behavior of the kinetic parameters mostly depended on the amendment doses. Eutrophication posited to start beyond 16 mg P kg^?1 soil was more likely allayed by a maximum vermicompost dose of 50 Mg ha^?1, higher than the 36 Mg ha^?1 maximum biosolid dose. The higher vermicompost P addition and lower P release could favor gradual and longer-term P absorption by plants and may reduce leaching or runoff P losses.     

Biotransformation potential of hexavalent chromium by Bacillus pumilus-S4, Pseudomonas doudoroffii-S5 and Exiguobacterium-S8 in association with hydrophytes

Three chromium-resistant bacteria Bacillus pumilus-S4, Pseudomonas doudoroffii-S5 and Exiguobacterium-S8 were isolated from chromium-contaminated wastewater/soil and could resist very high concentrations of potassium chromate in Luria agar (up to 25 mg ml^?1) and acetate minimal medium (2 mg ml^?1). The strains showed growth at diverse pH and temperatures and could resist multiple heavy metals. Pseudomonas doudoroffii-S5 reduced (8.27 mg hexavalent chromium 24 h^?1) at a lower initial potassium chromate concentration (100 μg ml^?1), but overall more chromate (28.4 mg hexavalent chromium 24 h^?1) was reduced at a higher initial concentration (1,000 μg ml^?1). The addition of various heavy metals (zinc sulphate, copper sulphate, and manganese sulphate at 50 μg ml^?1) in the chromium reduction media did not significantly affect the hexavalent chromium reduction potential of these isolates. The chromium removal/detoxification potential of these strains increased when used in conjunction with hydrophytes Eichornia crassipes and Pistia stratiotes. Interestingly, the whole process runs automatically with less energy input, that is, the bacterial strains support the growth of plant while in turn the plant releases exudates that help bacterial growth.     

Effects of sheet flow rate and slope gradient on sediment load

Sheet erosion is known as one of the most important forms of erosion, particularly in agricultural land. The purpose of this study was to investigate the effect of flow rate and slope gradient on runoff and sediment discharges in two different soils. Experiments were conducted using a tilting flume facility with the test area of 0.2?×?1.0 m. Overall, 24 experiments on two soils (clay loam and sandy clay loam textures) including six flow rates (75, 100, 125, 150, 175, and 200 ml/s) and two slope gradients (1.5 and 2 %) were performed. The selected flow rates and flume slopes were generated to simulate sheet erosion. The results showed that for both soils and slopes, unit flow discharge (q) and sediment concentration increased with increasing flow rate; however, the effect of slope gradient on flow discharge depends on soil type. In addition, sandy clay loam exhibited higher values of q and sediment concentration and consequently, it showed greater amounts of sediment load. At the start of event, sediment concentration was high but it decreased to approach a steady state. In addition, the time needed to reach a steady state condition was shorter for sandy clay loam than that for clay loam soil and in lower flow rates than higher flow rates. For each soil and slope, there was a direct relationship between sediment load and flow rate. The result implied that the effect of slope gradient on sediment load was almost greater in sandy clay loam soil than clay loam soil. Moreover, the differences between sediment loads of two soils are enlarged at slope 2 %.     

Flux of nutrients and heavy metals from the Melai River sub-catchment into Lake Chini, Pekan, Pahang, Malaysia

This study was carried out to determine the flux of nutrients and heavy metals from the Melai sub-catchment into Lake Chini through the process of erosion. Melai River is one of the seven feeder rivers that contributed to the present water level of Lake Chini. Three properties of soils, such as particle size, organic matter content, and soil hydraulic conductivity and three chemical soil properties, such as available nutrients, dissolved nutrients, and heavy metals, were analyzed and interpreted. Potential soil loss was estimated using the revised universal soil loss equation model. The results show that the soil textures in the study area consist of clay, silty clay, clay loam, and sandy silt loam. The organic matter content ranges from 3.40 to 9.92 %, while the hydraulic conductivity ranges from 5.2 to 25.3 cm/h. Mean values of available P, K, and Mg amount was 8.5 ± 3.7 μg/g, 24.5 ± 3.4 μg/g, and 20.7 ± 18.6 μg/g, respectively. The highest concentration of soluble nutrients was SO ₄ ^?2 (815.8 ± 624.1 μg/g), followed by NO₃ ^?-N (295.5 ± 372.7 μg/g), NH₄ ⁺-N (24.5 ± 22.1 μg/g) and PO₄ ^3? (2.0 ± 0.8 μg/g). The rainfall erosivity value was 1658.7 MJ mm/ha/h/year. The soil erodibility and slope factor ranges from 0.06 to 0.26 ton h/MJ/mm and 7.63 to 18.33, respectively. The rate of soil loss from the Melai sub-catchment in the present condition is very low (0.0028 ton/ha/year) to low (18.93 ton/ha/year), and low level flow of nutrients and heavy metals, indicating that the Melai River was not the contaminant source of sediments, nutrients, and heavy metals to the lake.     

The effects of petroleum-contaminated soil on photosynthesis of <Emphasis Type="Italic">Amorpha fruticosa</Emphasis> seedlings

A pot experiment was conducted to monitor the dynamic response of photosynthesis of Amorpha fruticosa seedlings to different concentrations of petroleum-contaminated soils from April to September. The results showed that the photosynthetic rates, stomatal conductance and transpiration rate of seedlings significantly decreased in 5–20 g kg^?1 petroleum-contaminated soil during the three given sampling period of July 31 (early), August 30 (mid-term) and September 29 (late). However, the intercellular CO₂ concentration significantly increased in 10 g kg^?1 contaminated soil, while declined in 20 g kg^?1 contaminated soil during the early sampling period as well as in 20 g kg^?1 contaminated soil during the late sampling period. The leaf relative water content of seedlings significantly increased in 20 g kg^?1 contaminated soil during the early sampling period, while it dropped dramatically in 15–20 g kg^?1 contaminated soil during the late sampling period. The contents of chlorophyll a, chlorophyll b and the total chlorophyll of seedlings showed a sharp decline during the three sampling periods in contaminated soil. Comprehensively, considering the negative effects of petroleum on the photosynthesis, growth performance and remediation effect on petroleum of A. fruticosa seedlings, this plant was tolerant of petroleum-contaminated soil and was potentially useful for the phytoremediation of petroleum-contaminated sites in northern Shaanxi, China.     

Fluoride sorption and desorption on soils located in the surroundings of an aluminium smelter in Galicia (NW Spain)

Aluminium smelters are major sources of F emission to the environment. We studied, in laboratory experiments, the sorption and desorption of fluoride on organic and mineral horizons of soils located within 2 km from one of these factories, situated in the northern coast of Galicia (NW Spain). The soils, developed from granite, are acid (pH H₂O 3.9–5.5), rich in organic matter (4–16 % C in the A horizon) and most A horizons have high Al saturation in the exchange complex. All samples showed a notable F sorption, between 1,066 and 1,589 mg kg^?1, after adding 200 mg F L^?1, which accounts for 53–80 % of F added. The sorption was slightly higher in the A horizons than in the respective organic horizons (differences of up to 194 mg kg^?1). The fluoride sorption upon addition of 200 mg F L^?1 correlated significantly (p < 0.05) with soil pH in water (r = ?0.77), iron extracted by acid ammonium oxalate (r = 0.68), aluminium plus iron extracted by acid ammonium oxalate (r = 0.63), exchange aluminium (r = 0.52) and clay percentage in soil (r = 0.76). The F sorption fitted to both Langmuir and Freundlich models. Desorbed F accounted for only 12–22 % of sorbed fluoride and correlated (p < 0.05) negatively with non-crystalline (extracted by acid ammonium oxalate) Fe (r = ?0.51) and clay content (r = ?0.74) and positively with organic matter (r = 0.69) and with the effective cation exchange capacity of the soil (r = 0.50).     

Inorganic arsenic sorption by drinking-water treatment residual-amended sandy soil: effect of soil solution chemistry

Previous studies in our laboratory have demonstrated that drinking-water treatment residuals are effective sorbents of arsenic V. However, the effect of soil solution chemistry on arsenic V sorption by drinking-water treatment residuals-amended soils remains to be explored. The current study uses a batch incubation experimental set up to evaluate the effect of soil solution pH, competing ligands, and complexing metal on arsenic V sorption by a sandy soil (Immokalee series) amended with two rates (25 and 50 g kg^?1) of aluminum and iron-based drinking-water treatment residuals. Experiments were conducted at three initial arsenic loads (125, 1,875, 3,750 mg kg^?1) and a constant solid: solution ratio of 200 g L^?1. An optimum equilibration time of 8 days, obtained from kinetic studies, was utilized for sorption experiments with both aluminum and iron drinking-water treatment residual-amended soil. Presence of phosphate decreased arsenic V sorption by both aluminum and iron drinking-water treatment residual amended soils, with a strong dependence on pH, drinking-water treatment residual types, drinking-water treatment residual application rates, and phosphate concentrations. Addition of sulfate had no effect on arsenic V sorption by aluminum or iron drinking-water treatment residual-amended soil. A complementing effect of calcium on arsenic V sorption was observed at higher pH. Results elucidating the effect of soil solution chemistry on the arsenic V sorption will be helpful in calibrating drinking-water treatment residual as a sorbent for remediation of arsenic-contaminated soils.     

Biodegradation of diazinon by the <Emphasis Type="Italic">Stenotrophomonas maltophilia</Emphasis> PS: pesticide dissipation kinetics and breakdown characterization using FTIR

A diazinon-degrading bacterium was isolated from paddy soils under flooded conditions. Biochemical characterization and 16S rRNA sequencing showed the isolate was an oxidase-positive Stenotrophomonas maltophilia. The isolate could grow on a mineral salt medium (MSM) supplemented with diazinon as the main carbon source (50 µg ml^?1) and dissipate the pesticide in a simple first-order manner with DT₅₀ and DT₉₀ of 4.54 and 15.09 days, respectively. The addition of glucose favored the bacterial growth and reduced the pesticide’s DT₅₀ and DT₉₀ to 3.39 and 11.27 days, respectively. The dissipation of diazinon in MSM was accompanied by a slight reduction of the pH which was more significant in the glucose-treated media. FTIR analysis proved the separation of the heterocyclic leaving group by hydrolyzing the ester bond and aerobic cleavage of the aromatic ring as the main pathways of diazinon degradation in the MSM. The dissipation of diazinon (150 µg g^?1) in the inoculated sterilized flooded paddy soils was biphasic, and based on this, only 31.55 µg g^?1 of the initial concentration declined with a faster rate while the rest of the residue dissipated slowly as the adsorbed phase. In the non-inoculated non-sterilized soils, diazinon dissipated more slowly with an initial lag phase.     

Chelate enhanced phytoremediation of soil containing a mixed contaminant

Greenhouse tests were conducted to study the effect of chelates on the phytoextraction of cadmium and lead, and the rhizodegradation of used engine oil present as a mixed contaminant in a sandy soil. Indian mustard plants were grown in test pot soil for 30 days and chelates ethylenediamine tetraacetic acid (EDTA) and ethylenediaminedisuccinic acid (EDDS) were individually applied to the test soil. The soil was spiked earlier with 50 mg kg^?1 of CdCl₂, 500 mg kg^?1 of PbCl₂ and 500 mg kg^?1 of used engine oil to form the mixed soil contaminant. At the same concentration of chelates, EDTA was found to be more effective than EDDS in increasing the concentration of metal contaminants Cd and Pb in the plant. Compared to EDDS, EDTA was also more effective in promoting rhizodegradation of the organic contaminant formed by used engine oil. The study demonstrated that the application of chelates to soils containing mixed contaminants such as heavy metals (Cd and Pb) and organics (used engine oil) can simultaneously assist metal accumulation at higher concentrations in the biomass of Indian mustard plant and also reduce the amount of used engine oil in the soil through rhizodegradation.     

The spatial distribution of potassium status and clay mineralogy in relation to different land-use types in a calcareous Mediterranean environment

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.     

Induced degradation of crude oil mediated by microbial augmentation and bulking agents

Different bacterial and fungal strains, isolated from petroleum hydrocarbon-contaminated soil, were tested, in isolation as well as in combination, for their ability to degrade total petroleum hydrocarbon (TPH) in soil samples spiked with crude oil (2, 5 or 10 %, w/w) for 30 days. The selected combination of bacterial and fungal isolates, i.e., Pseudomonas stutzeri BP10 and Aspergillus niger PS9, exhibited the highest efficiency of TPH degradation (46.7 %) in soil spiked with 2 % crude oil under control condition. Further, when this combination was applied under natural condition in soil spiked with 2 % (w/w) crude oil along with inorganic fertilizers (NPK) and different bulking agents such as rice husk, sugarcane, vermicompost or coconut coir, the percent degradation of TPH was found to be maximum (82.3 %) due to the presence of inorganic fertilizers and rice husk as bulking agent. Further, results showed that the presence of NPK and bulking agents induced the activity of degradative enzymes, such as catalase (0.718 m mol H₂O₂ g^?1), laccase (0.77 µmol g^?1), dehydrogenase (37.5 µg g^?1 h^?1), catechol 1, 2 dioxygenase (276.11 µ mol g^?1) and catechol 2, 3 dioxygenase (15.15 µ mol g^?1) as compared to control (without bioaugmentation). It was inferred that the selected combination microbes along with biostimulants could accentuate the crude oil degradation as evident from the biostimulant-induced enhanced activity of degradative enzymes.     

A modified normalized model for predicting effective soil thermal conductivity

Effective soil thermal conductivity (λ _eff) describes the ability of a multiphase soil to transmit heat by conduction under unit temperature gradient. It is a critical parameter for environmental science, earth and planetary science, and engineering applications. Numerous models are available in the literature, but their applicability is generally restricted to certain soil types or water contents (θ). The objective of this study was to develop a new model in the similar form of the Johansen 1975 model to simulate the λ _eff(θ) relationship of soils of various soil textures and water contents. An exponential type model with two parameters is developed and a new function for calculating dry soil thermal conductivity is presented. Performance of the new model and six other normalized models were evaluated with published datasets. The results show that the new model is able to well mimic λ _eff(θ) relationship of soils from sand to silt loam and from oven dry to full saturation. In addition, it has the best performance among the seven models under test (with root-mean-square error of 0.059 W m^?1 °C^?1, average deviations of 0.0009 W m^?1 °C^?1, and Nash–Sutcliffe efficiency of 0.994). The new model has potential to improve the reliability of soil thermal conductivity estimation and be incorporated into numerical modeling for environmental, earth and engineering studies.     

Specific detection of bioavailable phenanthrene and mercury by bacterium reporters in the red soil

Genetically engineered Pseudomonas putida reporters (BMB-PL and BMB-ME), which, respectively, carried phnS-luxCDABE and merR-egfp cassette, were used to determine bioavailable phenanthrene and mercury. Over a spiked range of concentrations and aged for 6 days in red soil samples, the reporters were tested to determine the optimal assay conditions and the bioavailable phenanthrene (0–60 mg kg^?1) and Hg²⁺ (0–240 μg kg^?1) were evaluated by the signal of the relative fluorescent units and relative luminescence units. Single contamination was carried out and good correlations were obtained between signal strength and pollutant concentrations, whereas interference and bioavailability repression were observed in dual-contamination experiments. Other heavy metal ions at nanomolar level did not interfere with BMB-ME measurement while BMB-PL showed some response to other polycyclic aromatic hydrocarbons or their intermediate products during degradation. Comparing high-performance liquid chromatography methods with the bacterial reporters, both BMB-ME and BMB-PL appeared to have a detection limit (mercury <40 μg kg^?1; phenanthrene <24 mg kg ^?1) similar to the instrumental analysis. Although physical parameters may affect the interaction of pollutants with bioreporter cells, advantages include the inherent biological relevance of the response, rapid response time, and potential for field deployment. Our results strongly suggest that the BMB-ME and BMB-PL bioreporters constitute an adaptable system for easily detecting the bioavailability of mercury and phenanthrene in the red soils.     

Impact of sewage sludge application on zinc desorption kinetics in some calcareous soils

Sewage sludge usually contains significant amount of Zinc (Zn) and is widely used in agricultural lands. A laboratory experiment was performed to determine Zn desorption characteristics in unamended and amended soils with sewage sludge. Ten calcareous soils were amended with 1 % (w/w) sewage sludge. Amended and unamended soils were incubated at field capacity at 25 ± 1 °C for 1 month. After incubation, the kinetics of Zn desorption in amended and unamended soils were determined by successive extraction with DTPA-TEA (diethylenetriaminepentaacetic acid-triethanolamine) in a period of 1–504 h at 25 ± 1 °C. The results of kinetics study showed that extracted Zn and desorption rate constants in the amended soils were significantly (p < 0.01) higher than in the unamended soils. The results showed that Zn desorption increased from 201 to 343 % in amended soil with respect to unamended soils. The amounts of desorbed Zn in the unamended soils ranged from 3.73 to 8.79 mg kg^?1, while the amounts of desorbed Zn in amended soils ranged from 11.47 to 17.66 mg kg^?1. Desorption kinetics of Zn in two soils conformed fairly well to first-order, parabolic diffusion and power function equations. The results of stepwise regression analysis indicated that calcium carbonate equivalent and clay could be used to estimate Zn desorption characteristics in DTPA-TEA solution in the amended and unamended calcareous soils. It can be concluded that sewage sludge applied to calcareous soils may enhance the source of Zn for the plants.     

Influence of insecticides alone and in combination with fungicides on enzyme activities in soils

Two insecticides, monocrotophos and chlorpyrifos alone and in combination with two fungicides, mancozeb and carbendazim, respectively, were assessed for their effects on the activities of arylamidase (as glucose formed from sinigrin), dehydrogenase (in terms of triphenyl formazan formed from triphenyl tetrazolium chloride) and myrosinase (as β-naphthylamine formed from l-leucine β-naphthylamide) in vertisol and laterite soils collected from a fallow groundnut (Arachis hypogaea L.) field. The influence of selected pesticides, alone and in combination on enzyme activities was concentration dependent; the activities increased with increasing concentration of the pesticides up to 2.5 kg ha^?1, whereas application of monocrotophos alone showed maximum enzyme activities up to 5.0 kg ha^?1, in both soils. However, higher concentrations (7.5 and 10 kg ha^?1) of the pesticides were either innocuous or toxic to the enzyme activities. The significant stimulation in the activities of arylamidase, dehydrogenase and myrosinase, was associated with 2.5 kg ha^?1. The maximum stimulation in arylamidase and myrosinase activity was observed at 20-day incubation, and the enzyme activities decreased gradually at 30 and 40 days of incubation. Significant increase in dehydrogenase activity was observed at 21-day incubation, and the enzyme activity decreased gradually at 28 and 35 days of incubation in both vertisol and laterite soils. The results of the present study thus, clearly, indicate that application of the insecticides alone or in combination with fungicides, in cultivation of groundnut, at field application rates improved the activities of arylamidase, dehydrogenase and myrosinase in soils.     

Integrated mass balance of some heavy metals fluxes in Yaakob village,south Sohag,Egypt

The pollution of soil with heavy metals has direct or indirect adverse effect on human health. The present work was conducted to identify all the expected sources and sinks for heavy metals by applying mass balance model to identify the retention rate of metals by soils in Yaakob village, south Sohag Governorate, Egypt. The studied inputs (sources) include P-fertilizers, irrigation water and dustfall, while the main outputs (sinks) are drainage water and harvested plants. The measurements indicate that soil, clover, dustfall and P-fertilizers contain considerable concentration of Cd, Cr, Co, Cu and Pb. The mass balance measurements indicate that the accumulation rate of Cd, Cr and Co in soil was 5.4, 54.6 and 16.3 g ha^?1 year^?1, respectively. However, depletion trend of Pb and Cu was about 1.4 and 5.2 g ha^?1 year^?1, respectively. The main source of Cd, Pb, Cr and Co in the study area is P-fertilizers with input flux 14.9, 89.9, 198.6 and 18.5 g ha^?1 year^?1, while Cu source was dustfall with 19.33 g ha^?1 year^?1. The index of geoaccumulation calculations indicates different degrees of contamination with Cd, Cr, Co and Cu. On the other hand, the main sink for the studied heavy metals was the Egyptian clover (Trifolium alexandrinum) which can be considered a good bioaccumulator of heavy metals.     

Phytoremediation assessment of native plants growing on Pb–Zn mine site in Northern Tunisia

Pollution by heavy metals presents an environmental concern, and their toxicity threats soil, water, animals and human health. Phytoremediation can be used as a solution to remediate contaminated soils. The aim of this study was to identify native plants collected from tailings: material of Pb–Zn mine sites of Fedj Lahdoum and Jebel Ressas (two abandoned mines located, respectively, in the northwest of Tunisia and in the south of Tunis City). The tolerance of plant to heavy metals (lead, zinc and cadmium) is evaluated. Soil samples were collected and analyzed for Pb, Zn and Cd concentration. The total soil Pb, Zn and Cd are, respectively, reached 6132 mg kg^?1, 11,052 mg kg^?1 and it doesn’t exceed 479 mg kg^?1 for Cd. The highest content of Zn in plants was detected in shoots of Rumex bucephalophorus (1048 mg kg^?1), and the highest Pb concentration was detected in roots of Chrysopogon zizanioides (381 mg kg^?1), while for Cd Silene colorata it accumulated the highest content in roots (51 mg kg^?1). From all plants, only 12 have a translocation factor for Pb which is higher than one. Among all plants, only 17 have a translocation factor that is higher than one for Zn, while for Cd only 13 plants indicate TF > 1. As for the biological absorption coefficient, all samples indicate a rate which is lower than one. These plants can be primarily hyper accumulators and useful in remediation of lead- and zinc-contaminated soils after further biochemistry researches in mechanism of accumulation and translocation of heavy metals in plants.     

Effects of nitrogen fertilization on soil labile carbon fractions of freshwater marsh soil in Northeast China

During the past 50 years, the amount of agricultural fertilizer used in Northern China increased from about 7.5 kg ha^?1 in the 1950s to approximately 348 kg ha^?1 in the 1990s. Given that little is known about the effects of nitrogen fertilization on soil labile carbon fraction in Northern China, this paper evaluated such effects in terms of microbial biomass and dissolved organic carbon in the Sanjiang Plain located in Northeast China. Soils with different cultivation time and undisturbed marsh with Deyeuxia angustifolia were selected to study the effects of nitrogen fertilization on the soil labile organic fractions microbial C (biomass C, microbial quotient, and basal respiration) and to estimate the contributions of nitrogen input on the dynamics of soil labile carbon. Continuous nitrogen application decreased total organic and dissolved organic carbon concentrations significantly, leading to the lack of carbon source for microbes. Therefore, continuous nitrogen fertilizer application induced negative effects on measured soil microbiological properties. However, a moderate nitrogen application rate (60 kg N ha^?1) stimulated soil microbial activity in the short term (about 2 months), whereas a high nitrogen application rate (150 kg N ha^?1) inhibited measured soil microbiological properties in the same period.