Heifer International has honed its approach over more than 60 years in the sustainable community development field. Integral components of Heifer's approach include:
Heifer's Cornerstones—a set of values which includes the principle “Passing on the Gift,” and guides all of Heifer's work.
Transformation—the process of community and individual transformation resulting in significant lasting improvements in the community and the lives of the families involved.
Measurement of progress at three levels: below the ground (values, knowledge, behavior), on the ground (basic needs), and above the ground (the community is able to affect policy and systems levels).
The bioavailability of potassium (K) depends on its speciation distribution in the soil. Different methods are commonly used to estimate K speciation including traditional single leaching (TSL) and sequential extraction process (SEP). However, K speciation is largely affected by soil pretreatment methods. The effects of both TSL and SEP soil pretreatment methods were evaluated.
Materials and methods
The TSL method classifies K speciation content based on bioavailability, while the SEP classifies the metal speciation based on the effects of environmental conditions. These two methods, together with a modified sequential single leaching (SSL) scheme, were used to evaluate five types of soil including soil without potassium fertilization, soil with long-term K fertilization, alkaline soil, red soil, and forest soil. The soil samples were gathered randomly at depths varying up to 30 cm before being dried in air at room temperature. The samples were then ground and mixed before passing through a sieve (10 mesh or 100 mesh) in order to perform K speciation analysis via the modified SSL technique, the TSL method, and the four schemes of SEP.
Results and discussion
Soil pretreatment influenced K speciation, with higher concentration in soil samples sieved through 100 mesh than through 10 mesh. In alkaline soil, potassium was observed to be associated with carbonate. For the various SEP schemes, K speciation was found to be greatest in the residual fraction, with only 3% observed in the carbonate, exchangeable, metal organic complex, or amorphous hydroxides of Fe or Mn. After following the first two steps of the SEP schemes, the available K was similar to that of the TSL method. Distribution of non-exchangeable K using the TSL method was comparable with the five combined SEP extraction steps which were all affected by environmental conditions.
Conclusions
Pretreatment affected K speciation distribution and total amount of metal in the soil. The 100 mesh sieve was more effective in estimating K soil speciation. The SEP method was acceptable for estimating K speciation, with the Krishnamurti et al. (Analyst 120:659–665, 1995) scheme as a useful appraisal of K bioavailability. Combination analyses using both TSL and SEP methods are useful techniques to enable a better understanding of K speciation transformation in soil.
Based on the fact that the clostridia isolated from paddy field soil were mostlyproteolytic and that they produced some branched-chain volatile fatty acids on peptone media, the occurrence and the substrates for the production of such acids in paddy soil were investigated. The results obtained are as follows:
1) It was revealed that two branched-chain volatile fatty acids, iso-valeric and iso-butyric acids, were detected In fresh paddy field soil.
2) The paddy soil supplemented with peptone solution produced significant amounts of branched-chain volatile fatty acids-iso-butyric and iso-valeric acidsin addition to straight-chain volatile fatty acids-acetic, propionic, and butyric acids. When glucose was added instead of peptone, not branched-chain fatty and propionic acids were detected but only acetic and butyric acids. These facts indicate that the branched-chain fatty acids may originate from amino acids.
3) When a pair of amino acids, such as proline and leucine or proline-and valine, were supplemented in addition to peptone, the production of iso-valeric or iso-butyric acids was increased, respectively. Even In the case of glucose, the supplementation of a pair of amino acids supported the production of branched-chain fatty acids. These facts indicate that the Stickland reaction may take place in paddy field soil.
4) All the strains of strict anaerobes isolated from the soil and supplemented with peptone formed iso-valeric and iso-butyric acids in addition to two or three kinds of volatile fatty acids when they were cultured in medium containing peptone. All of them were classified as belonging to genus Clostridium. No strains of facultative anaerobes isolated from the same soil produced any branched-chain fatty acids, but produced only acetic acid.
5) In conclusion, these results reveal that the branched-chain fatty acid in paddy field soil is produced only by clostridia through the Stickland reaction.
Original Papers (pp. 805–810) K2Ca2Si2O7, the major component of fused potassium silicate fertilizer, released potassium (K), calcium (Ca) and silicon (Si) in a slow manner. The 10% of K in K2Ca2Si2O7 was quickly solubilized in water. Further K dissolution was very slow. The amounts of dissolved Ca and Si in water were much smaller than that of K. The decrease of the Ca and Si concentration in water indicated the occurrence of a re-deposit of Ca and Si at a later stage. The surface imaging method was used in order to study the slow-release process of K2Ca2Si2O7 in water. The surface analysis of K2Ca2Si2O7 particles after dissolution in water for 30 min showed that there were Ca- and Si-rich particles stuck on the fertilizer surface. The results of the analysis of the cross section of K2Ca2Si2O7 particles showed that the K content was lower than those of Ca and Si in the surface boundary layer. On the other hand, the mole ratio of K, Ca and Si was same inside the fertilizer particle. In the portion between the inside and the surface of the fertilizer particle, the content of K and Ca was lower than that of Si. These results indicated that the order of dissolution of fertilizer components from K2Ca2Si2O7 particle was first K, then Ca, and Si last. From the results mentioned above, the process of slow-release K was speculated to be as follows: 1) K on the particle surface was released quickly by an ion exchange reaction with hydrogen ions in water. 2) K inside the particle was released slowly because of dissolution through Si-O-Si bonds. 相似文献
Abstract A routine soil test that accurately predicts soil nitrogen (N) mineralization has long eluded researchers. Soil incubations, which are not practical for routine soil testing, are the only methods that have proven successful. Although several quick analytical methods have been proposed, no one method has correlated consistently enough to be implemented into a soil‐testing program. The objective of this study was to compare proposed quick analytical procedures with the amount of ammonium (NH4)‐N mineralized after a 14‐d anaerobic incubation. The analytical methods of interest were
applying a mild acid oxidation to the soil using acidified permanganate;
analyzing a 1 M potassium chloride (KCl) soil extract in the ultraviolet (UV) spectrophotometric range before and after nitrate (NO3) removal with Devarda's alloy; and
quantifying soil amino sugar‐N content using the Illinois soil N test (ISNT) diffusion method.
Fifty agricultural soils with different physical and chemical properties were utilized in this study. All methods displayed significant relationships with the anaerobic incubation procedure; however, some methods displayed higher, more acceptable, coefficients of determination. The ISNT and UV spectrophotometry measurement at 210 nm after NO3 removal failed to accurately estimate N mineralization (R2=0.45 and 0.31, respectively). The acid oxidation procedure and UV measurement at 260 nm of soil extracts before NO3 removal produced better results with coefficients of determination of 0.58 and 0.56, respectively. We suspect the ability of some methods to predict N mineralization was hindered because of the wide variety of geographic locations from which the soils were collected. Additional analyses were conducted on a subset of 16 silt‐loam soils from Arkansas. The coefficient of determinations increased for each method: acid oxidation procedure increased to 0.83, the ISNT increased to 0.71, and the UV method (at 260 nm before NO3 removal) increased to 0.63. If anaerobic incubation is a true indication of N mineralization in the field, the aforementioned methods display promise to correlate with N uptake by field‐grown plant studies when adapted to a specific geographic location and/or soil series. 相似文献
Determining potassium supply of soil plays an important role in intensive crop production, since it is the basis for balancing nutrients and issuing fertilizer recommendations for achieving high and stable yields within economic feasibility. The aim of this study was to compare the different extraction methods of soil potassium from arable horizon of different types of soils with ammonium lactate method (KAL), which is frequently used as analytical method for determining the accessibility of nutrients and it is a common method used for issuing fertilizer recommendations in many Europe countries. In addition to the ammonium lactate method (KAL, pH 3.75), potassium was extracted with ammonium acetate (KAA, pH 7), ammonium acetate ethylenediaminetetraacetic acid (KAAEDTA, pH 4.6), Bray (KBRAY, pH 2.6) and with barium chloride (\(K_{BaCl_2 }\), pH 8.1). The analyzed soils were extremely heterogeneous with a wide range of determined values. Soil pH reaction \(\left( {pH_{H_2 O} } \right)\) ranged from 4.77 to 8.75, organic matter content ranged from 1.87 to 4.94% and clay content from 8.03 to 37.07%. In relation to KAL method as the standard method, \(K_{BaCl_2 }\) method extracts 12.9% more on average of soil potassium, while in relation to standard method, on average KAA extracts 5.3%, KAAEDTA 10.3%, and KBRAY 27.5% less of potassium. Comparison of analyzed extraction methods of potassium from the soil is of high precision, and most reliable comparison was KAL method with KAAEDTA, followed by a: KAA, \(K_{BaCl_2 }\) and KBRAY method. Extremely significant statistical correlation between different extractive methods for determining potassium in the soil indicates that any of the methods can be used to accurately predict the concentration of potassium in the soil, and that carried out research can be used to create prediction model for concentration of potassium based on different methods of extraction. 相似文献
ABSTRACT Nutrient uptake over a 72 h culture period by clonal micropropagules of Phalaenopsis Tanigawa × Yukimai Dream ‘KS 370’ and ‘KS 352’ were surveyed by Ichihashi's (1997)Ichihashi, S.1997. “Orchid production and research in Japan”. In Orchid Biology, Reviews and Prospectives, Edited by: Arditti, J. and Pridgeon, A. M.171–212. Dordrecht, , The Netherlands: Kluwer. [Google Scholar] nutrient solution at the original ion strength and its half and quarter. Uptake of major anions [nitrate (NO3?), phosphate (H2PO4?), and sulfate (SO42?)] and cations [ammonium (NH4+), potassium (K+), calcium (Ca2+), and magnesium (Mg2+)] measured with an ion chromatograph increased as the ionic strength of the solution increased in both cultivars. The final uptake rates of nutrients were 0.8, 2.0, 2.1, 1.2, 3.0, 2.0, and 1.6 me L?1, respectively in the order of ions mentioned above. The ratios of the uptake rates between cations (mono or bivalent) were almost in proportion to the ratio of their initial ion strength. Therefore, no antagonistical absorption of cations was found in that ion strength. Leaf content of phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg), and copper (Cu) increased as the ionic strength of the solution increased, but concentrations of iron (Fe), manganese (Mn), and zinc (Zn) were not affected significantly. Nitrogen (N) content of leaves in ‘KS 370’ after 72 h culture increased significantly by increasing the ionic strength of the solution. Root concentrations of P, K, Ca, Mg, and Fe increased as the ionic strength of the solution increased in both cultivars. The N concentrations of roots in either ‘KS 370’ or ‘KS 352’ had positive correlations with an increasing ionic strength of the solution, although they were constantly greater in ‘KS 370’ than in ‘KS 352’. The greatest fresh weight was obtained when the plants were cultured in a half strength solution. Whereas dry weight decreased in all treatments as the ionic strength of the solution decreased. These findings show that increased ion absorption affected plant dry weight. The obtained findings provide fundamental information for the closed hydroponic system of phalaenopsis cultivation. 相似文献
Abstract Evaluation of nutrient status in soil is important for nutritional, environmental, and economical aspects. This research was carried out to determine the potassium (K) available to corn (Zea mays) in 15 soils from the Hamedan province in the west of Iran. The treatments included two K levels [0 and 200 mg K kg?1 as potassium sulfate (K2So4)] and 15 soils in a factorial experiment in a randomized block design with three replications. The results indicated that K application increased yield, K concentration, and K uptake of corn. According to the mechanism of the extraction, these extractants can be classified into four groups. The first group of extractants, acidic extractants, includes 0.02 M strontium chloride (SrCl2)+0.05 M citric acid, 0.1 M hydrochloric acid (HCl), and Mehlich 1. The second group includes 0.1 M barium chloride (BaCl2), 0.01 M calcium chloride (CaCl2), and 1 M sodium acetate (NaOAc). The third group includes 1 M ammonium acetate (NH4OAc), ammonium bicarbonate–diethylenetriamine tetraacetic acid (AB‐DTPA), and finally distilled water. The results showed that correlation between extractants in each groups were significantly high. Correlation studies showed that NH4OAc and AB‐DTPA cannot be used as available K extractants. The correlation of other extractants with relative yield, plant response, and K uptake were significantly high. Therefore, these extracting solutions can be used as available K extractants. Potassium critical levels by extractants were also determined using the method by Cate and Nelson (1971)Cate, R. B. and Nelson, L. A.1971. A simple statistical procedure for partitioning soil test correlation into two classes. Soil Science Society of America Proceeding, 35: 658–660. [Crossref], [Web of Science ®], [Google Scholar]. Potassium critical levels for 90% relative yield were 29, 27, 82, 84, 45, 145, and 272 mg kg?1 for 0.002 M SrCl2, distilled water, 0.02 M SrCl2+0.05 M citric acid, 0.1 M HCl, Mehlich 1, 1 M NaOAC, and 0.1 M BaCl2, respectively. 相似文献
Nitrous oxide (N2O) is a potent greenhouse gas, and nitrate () is a water contaminant. In grazed grassland, the major source of both leaching and N2O emissions is nitrogen (N) deposited in animal excreta, particularly in the urine. The objective of this study was to determine the effectiveness of two nitrification inhibitors: (i) a solution of dicyandiamide (DCD) and (ii) a liquid formulation of 3,4‐dimethylpyrazole phosphate (DMPP) for reducing N2O emissions and leaching from urine patch areas in two grazed pasture soils under different environmental conditions. In the Canterbury Templeton soil, the nitrification rate of ammonium from the animal urine applied at 1000 kg N/ha was significantly decreased by the application of DCD (10 kg/ha) and DMPP (5 kg/ha). N2O emissions, measured over a 3‐month period, from dairy cow urine applied to the Canterbury Templeton soil were 1.14 kg N2O‐N/ha, and this was reduced to 0.43 and 0.39 kg N2O‐N/ha by DCD and the liquid DMPP, respectively. These are equivalent to 62–66% reductions in the total N2O emissions. Nitrate leaching losses from dairy cow urine applied to the Waikato Horotiu soil lysimeters were reduced from 628.6 kg ‐N/ha to 400.6 and 451.5 kg ‐N/ha by the application of DCD (10 kg/ha) or DMPP (1 kg/ha), respectively. There was no significant difference between the DCD solution and the liquid DMPP in terms of their effectiveness in reducing N2O emissions or leaching under the experimental conditions of this study. These results suggest that both the liquid formulations of DCD and DMPP have the potential to be used as nitrification inhibitors to reduce N2O emissions and leaching in grazed pasture soils. 相似文献
The extensive application of phosphate fertilizers could produce a series of environmental problems by adsorbing on the surface of soil particle and migrating into water during soil erosion. Therefore, this study is to explore the effects of phosphate on soil aggregate stability and soil erosion and to analyze the mechanisms of phosphate enhancing soil erosion from the scope of soil charge density, electric field, and particle interaction.
Materials and methods
A variable charged soil (0–20 cm) was pre-treated firstly by KCl, K2HPO4, and KH2PO4, respectively. Under the conditions of KCl, K2HPO4, and KH2PO4 solutions with concentrations of 0.0001, 0.001, 0.01, 0.1, and 1 mol L?1, (1) the amounts of soil particle transport and erosion intensities were measured using rainfall simulation with electrolyte solutions instead of rainwater; (2) the aggregate stabilities were measured by weighing the particles and micro-aggregates of <2, 5, and 10 μm after soil aggregate breakdown in electrolyte solutions; and (3) the zeta potentials of soil particles were measured in electrolyte solutions.
Results and discussion
The application of K2HPO4 and KH2PO4 in soil strongly enhanced soil aggregate breakdown and soil erosion, while in KCl application, soil aggregates were stable and erosion did not occur. Moreover, the intensities of soil aggregate breakdown and soil erosion for K2HPO4 application were much stronger than that for KH2PO4 application. Phosphate, especially K2HPO4, strongly increased surface negative charge density of soil particles and thus increased the electrostatic repulsive pressure between adjacent soil particles in aggregates, and as a result, the soil erosion intensity increased. However, the surface charge density was not increased by the increased pH, specific adsorption, and dispersion force adsorption but possibly attributed to a non-classic induction force adsorption arising from the anionic non-classic polarization in the strong electric field around soil particle surface.
Conclusions
The application of phosphate decreased aggregate stability and stimulated soil erosion through increasing charge density of particle surface by a new non-classic induction adsorption of phosphate.
The purpose of the present study is to examine the effect of phosphate on the aggregation kinetics of hematite and goethite nanoparticles.
Materials and methods
The dynamic light scattering method was used to study the aggregation kinetics of hematite and goethite nanoparticles.
Results and discussion
Specific adsorption of phosphates could promote aggregation through charge neutralization at low P concentrations, stabilize the nanoparticle suspensions at medium P concentrations, and induce aggregation through charge screening by accompanying cations at high P concentrations. Two critical coagulation concentration (CCC) values were obtained in each system. In NaH2PO4, the goethite CCC at low phosphate concentrations was smaller than hematite and vice versa at high phosphate concentrations. Stronger phosphate adsorption by goethite rapidly changed the zeta potential from positive to negative at low phosphate concentrations, and the zeta potential became more negative at high phosphate concentrations. The clusters of hematite nanoparticles induced by phosphate adsorption had an open and looser structure. Solution pH and the phosphate adsorption mechanisms in NaH2PO4, KH2PO4, and Na3PO4 solutions affected zeta potential values and controlled the stability of hematite suspensions during aggregation. High pH and preference for non-protonated inner-sphere complexes in Na3PO4 solution decreased the zeta potential of positively charged hematite and promoted aggregation. Activation energies followed the order NaH2PO4 > KH2PO4 > Na3PO4 at low P concentrations. K+ was more effective than Na+ in promoting hematite aggregation due to the non-classical polarization of cations.
Conclusions
Phosphate can enhance or inhibit the aggregation of hematite and goethite nanoparticles in suspensions by changing surface charge due to specific adsorption onto the particles. The phosphate-induced aggregation of the nanoparticles mainly depended on the initial concentration of phosphate.
Developing urbanization, water shortage, watercourse pollution, and demands for more food due to population growth require a more efficient water irrigation and fertilizer application. Retaining nutrients and water in agricultural soils brings about higher crop yields and prevents pollution of water courses. Among different solutions, zeolites, which are environmental friendly, ubiquitous, and inexpensive, have been extensively employed in agricultural activities. These minerals are considered as soil conditioners to improve soil physical and chemical properties including infiltration rate, saturated hydraulic conductivity (Ks), water holding capacity (WHC), and cation exchange capacity (CEC). Natural and surface-modified zeolites can efficiently hold water and nutrients including ammonium (NH4+), nitrate (NO3?) and phosphate (PO43?), potassium (K+), and sulfate (SO42?) in their unique porous structures. Their application as slow-release fertilizers (SRFs) are reported as well. Therefore, zeolite application can improve both water use efficiency (WUE) and nutrient use efficiency (NUE) in agricultural activities and consequently can reduce the potential of surface and groundwater pollution. This review paper summarizes findings in the literature about the impact of zeolite applications on water and nutrient retention in the agriculture. Furthermore, it explores benefits and drawbacks of zeolite applications in this regard.
Methane-oxidizing bacteria (methanotrophs) biologically consume and consequently affect the concentration of atmospheric methane (CH4), the second most prominent greenhouse gas, and therefore play critical roles in the mitigation of global warming effect. Long-term fertilization often affects the methanotrophic community and CH4 oxidation in various soils. Here, the immediate effects of nitrogen (N), phosphorus (P), and potassium (K) amendments on the CH4 oxidation activity and methanotrophic community structure were evaluated.
Materials and methods
Paddy soil samples were collected from the Taoyuan Experimental Station of the Chinese Academy of Sciences in central Hunan Province of China. A laboratory-based incubation experiment was conducted to investigate the immediate effects of N, P, and K amendments on the methanotrophs in soil. The CH4 oxidation rates and methanotrophic activities were determined by measuring the dynamic changes of CH4 concentration in the incubation system. The methanotrophic abundance and community changes in all of the seven treatments with and without nutrients addition were studied using real-time PCR and denaturing gradient gel electrophoresis, respectively.
Results and discussion
All of the N, P, and K treatments significantly decreased the CH4 oxidation activities. Compared with the control, the P and K amendments significantly increased the methanotrophic population size, but the N treatments have no effect on the methanotrophic abundance. A negative correlation was found between methanotrophic activity and methanotrophic abundance. We suggested that methanotrophic activity may not be inferred through the pmoA gene copies, especially in the short-term simulation experiments. Investigation of the methanotrophic population size and diversity is not enough to evaluate the soil CH4 sink accurately.
Conclusions
We concluded that the additions of N, P, and K reduce the activity but enhance the abundance of methanotrophs in a Chinese paddy soil through a short-term incubation experiment. Additionally, we found that the CH4 oxidation activity could be completely inhibited by Cl? toxicity. Our results implied that caution should be exercised in the types and amounts of fertilizers, especially KCl in agricultural systems to control the instantaneous increase in CH4 emission from the field. 相似文献
Surface crusts are important features in arid desert areas and are critical to hydrological processes and ecosystem development. This paper aims to understand the effects of crusts on water movement in the soil and the factors that affect this and to provide the soil parameters for estimation of saturated hydraulic conductivity (Ks) in ecohydrological models.
Materials and methods
The study area was located in the middle and lower reaches of the Heihe River Basin, an arid desert area in Northwest China. There were three crust types in this region: physical soil crusts (PSCs, formed by water drop and erosion), biological soil crusts (BSCs, formed by microorganisms, moss, algae, lichen, and soil materials), and salt soil crusts (SSCs, formed by soluble salts). The infiltration rates of different soil and crust types and scalped soils were determined in situ in the field conditions using a disc infiltrometer with three repetitions. Crusts and soils were collected, and their properties were determined in the laboratory.
Results and discussion
The Ks of crust were significantly lower than that of scalped soils with a decrease of 13–70 %. The Ks of crusts were related to the type of crust and the properties of soil beneath the crusts. In this region, the soil textures are similar throughout, due to ubiquitous loess sedimentation, so textural differences had no significant effect on Ks. Soil organic matter (SOM) played a weak negative role on Ks because most crusts had higher SOM than the underlying soil. However, both crust thickness and electrical conductivity (EC, an index of salt concentration) showed significantly negative exponential relationship with Ks. Therefore, the SSC with high EC and thick crust have the lowest Ks among all crust types. Because soil development is related to salt accumulation, structure, and crust formation, the Ks follows the order of Solonchaks < Cambisols < Regosols, from lowest to highest.
Conclusions
Crusts have different characteristics compared with original soils and are the limiting layer of water infiltration in these arid soils. Therefore, the characteristics of crust must be considered in ecohydrological models. The main apparent controlling parameters of water infiltration rate in this area are crust thickness and EC.
Effect of light intensity at varied potassium supply on CO2 assimilation and yield formation of spring wheat .
1 The effect of a varied K+ supply on CO2 assimilation rates and yield formation has been studied at two different light intensities with wheat (Triticum aestivum L.) grown in solution culture. Light intensity was reduced in one treatment by shading the plants with a cloth, which caused a reduction of about 50 % of the light intensity. This shading was applied from the heading stage until grain maturation.
2 Reduced light intensity resulted in remarkably decreased rates of dry matter increments in both K treatments. In the beginning this growth depression, however, was small in the treatment with the higher K supply. At the stage of transition from the vegetative to the reproductive stage the better K+ nutrition obviously could compensate the lacking light to some degree. This favourable K+ effect, however, decreased with the advance of the reproductive phase. Thus at maturation in both K treatments equal quantities of dry matter were harvested. In the treatments with full light the higher K supply resulted in a yield increase at maturation.
3 The CO2 assimilation rates measured at flowering, milk stage and dough stage indicated that rather the K supply than the light intensities influenced the CO2 assimilation. The treatments with the higher K supply showed almost twice as high assimilation rates compared with the treatments with the lower K supply.
4 The reduced light intensity caused a substantial depression in grain yield in both K treatments. The poor grain yield was mainly due to a reduced thousand grain weight and to a less extent to a reduction in the number of ears.
5 As the better K supply resulted in increased CO2 assimilation rates without having an influence on the grain filling of the plants exposed to a lower light intensity, it is concluded that at low light intensities the grain filling is not limited by the supply of grains with photosynthates but probably is affected by other processes.
The transfer function mode) (TFM) and convection-dispersion equation (CDE) were compared for predicting Cl ? transport through a calcareous pelosol during steady, nearsaturated water flow. Large, undisturbed soil cores were used at constant irrigation intensities (q0) between 0.3 and 3 cm h?1, with a step-change in Cl? concentration. The assumption of a lognormal distribution of travel times–characterized by the mean (μ) and variance (σ2)–permitted the flux-averaged breakthrough curves (BTCs) to be modelled very accurately by the TFM. The BTCs could be modelled equally well by the CDE when both the mean pore water velocity (v) and dispersion coefficient (D) were optimized simultaneously by the method of least squares, but not when v was put equal to q0/v, where V was the mean volumetric water content. The best estimate of v was consistently > q0/v, which suggested that not all the pore water was effective in chloride transport. An operationally defined transport volume (θst) was calculated from the mean () or median (τm) travel times derived from the TFM. Chloride exclusion was not solely responsible for θst() being <V: immobile water also contributed. The positive skewness of the travel time distributions meant that θst(τm) < θst(), indicating the effectiveness of macropore flow in solute transport. Dαv1.42 (from the CDE), and σ2αv (from the TFM), confirmed that Cl? dispersion increased as flow velocity increased. Flux-averaged concentrations were used to calculate the volume-averaged resident concentrations. They matched the measured Cl? concentrations most closely when there was a gradual decrease in measured Cl ? concentration with depth, but not when Cl ? decreased sharply below c. 10 cm. Calculations assuming that all the water was effective in chloride transport gave less accurate results. Comparison of the measured and predicted concentrations of solute demonstrated that this must be a critical part of the evaluation of any model of solute transport. 相似文献
Distribution of hydrophobic organic contaminants in abiotic compartments is essential for describing their transfer and fate in aquatic ecosystems. Taihu Lake is the third largest freshwater lake in China. Water quality of Taihu Lake has deteriorated greatly during the last decades and has threatened the water supply. The aim of the present study was to investigate the partitioning of polycyclic aromatic hydrocarbons (PAHs) among overlying water, suspended particulate matter (SPM), sediments, and pore water in Meiliang Bay, Taihu Lake and to provide useful information for the ecological engineering in this area.
Materials and Methods
Overlying water and surface sediment were sampled from six sites in Meiliang Bay, Taihu Lake, China. Within 72 h of sampling, sediments were centrifuged to obtain the pore water. Overlying water samples were filtered to separate dissolved and SPM samples. After extraction, samples were purified following a clean-up procedure. PAH fraction was obtained by elution with a mixture of hexane: DCM (7:3, V/V) and analyzed by GC/MS.
Results
PAHs concentrations in overlying water varied from 37.5 ng/L to 183.5 ng/L. Concentrations of PAHs in pore water were higher than those in overlying water. The total concentrations of 16 priority PAHs in sediments ranged from 2091.8 ng/g-dw to 4094.4 ng/g-dw. PAHs concentrations on SPM were decreased with suspended solid concentrations (SSC). Total PAHs concentrations on SPM varied in the range of 3369.6 ng/g-dw to 7531.1 ng/g-dw. The partition coefficients between sediment and overlying water (log Koc) for PAHs with log Kow<5 were positively correlated with their octanol-water partition coefficients (log Kow) (n=39, r=0.79, p<0.0001). Partition coefficients between sediment and pore water (log Koc′) for all PAHs were also significantly correlated with their log Kow values (n=48, r=0.82, p<0.0001).
Discussion
In general, PAHs derived from combustion sources tend to bind strongly to soot particles in natural sediment. Consequentially, Koc values observed in the natural environment could be orders of magnitude higher than those predicted by linear correlation relationships under laboratory conditions. In the present study, the ratio of log Koc values to log Kow values falls consistently above 1, indicating that the sediment soot carbon in the bay was more attractive for PAHs than n-octanol. The log Koc′ was also higher than that predicted under laboratory conditions, suggesting that the measured pore water PAH concentrations were lower than those predicted. That is to say, not all the sediment PAHs can be available to partition rapidly into sediment pore waters. A variation in soot content is a possible reason. Furthermore, concentrations of PAHs on SPM were higher than those in sediments. The compositions of PAHs on SPM and in sediments were similar, indicating the importance of re-suspension process of sediments in the partitioning process of the shallow lake.
Conclusions
The results indicated the equilibrium partitioning model could be used to predict PAHs distribution in various phases of a shallow lake in the stagnation period, but re-suspension processes should be considered to modify the relationship between log Kocs and log Kows.
Recommendations and Perspectives
Concentration, particle size and composition of resuspended particles could affect the relationship between log Kocs and log Kows. Further work should be done under field conditions, especially where a steady thermodynamic equilibrium state could be assumed.
