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1.
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2.
In situ analysis of mineral nitrogen dynamics by means of the isotopic tracer method was conducted in a subalpine meadow of the Pyrenees during summer. The observed isotope dilution curves were interpreted by both compartment and stochastic analysis. Only stochastic analysis gave reliable results although the net mean output of ammonium was high (124 mg NH+4-N m?2day?1). This high mineralization rate is accounted for by the great size of the labile fraction of organic matter present in the top layer. The released ammonium is quickly taken up by vascular plants, thus reducing nitrogen loss from the ecosystem. Unfortunately, direct foliar labelling during tracer injection does not allow the exploitation of the isotope dilution curve of the plant compartment. This considerably reduces the data supplied by this type of experiment.  相似文献   

3.
14C-labelled glucose and 15N-labelled KNO3 were added to soil and the microbial biomass during 42 days' incubation was estimated using the chloroform fumigation-incubation method (CFIM). By day 1, most of the glucose (1577 μgCg?1 soil) was metabolized and 110 μg NO?3-Ng?1 soil were immobilized. In situ values for the proportions of biomass C (kC) and biomass N (kN) mineralized during the 10 days after CHCl3 fumigation were determined on the basis that the immobilized labelled C and N remaining in the soil at this time were present as living microbial cells and their associated metabolites. The tracer data indicated that biomass C could be calculated by applying a kc value of 0.41 to the CO2-C evolved from the fumigated sample without subtraction of an unfumigated “control”. Biomass N was estimated from the net NH4?-N accumulation during the fumigation-incubation. The problem of reimmobilization of NH+4-N where organisms of wide C:N ratio occur was overcome by adjusting the value of kN according to the ratio of CO2-C evolved: net NH4+-N accumulated during the fumigation-incubation (CF:NF).A CF:NF ratio of 6:1 resulted in a kN of 0.30 whereas a ratio of 13:1 indicated a kN of 0.20.  相似文献   

4.
Limnologists have modeled solute retention (% of input) in lake sediments using the parameter: 100 k s {(z:t w +k s}?1, wherek s is an empirical mass transfer coefficient or ‘sedimentation velocity’ (m yr?1), z is lake mean depth (m), andt w is lake hydraulic residence time (yr). This flushing or residence time model was tested against sulfate and silica concentrations in lakes of the northeastern and northcentral U.S.A., using data collected during the U.S. EPA's Eastern Lake Survey. This parameter failed to predict intra-regional variations in lake sulfate at fall turnover, but was consistently negatively correlated with silica in each of the regional lake populations. However, except in the western section of the Upper Peninsula of Michigan, lake sulfate was everywhere inversely dependent on DOC [mean slope=?0.020(SE=0.03) meq mM?1]. Sulfur retention in aquatic environments appears more closely coupled to organic carbon and trophic state, than to variations in hydraulic residence time.  相似文献   

5.
Many studies have shown that the characteristic parameters of an aquifer, specifically the hydraulic conductivity, increase with an increase in the portion of the aquifer tested. The main cause of this behavior is the heterogeneity within the aquifer. Sets of measurements performed on an artificial aquifer by different methods are utilized here, because it was verified that the scale dependence of hydraulic conductivity does not depend on the specific method of measurement. The unconfined aquifer in question was created in the laboratory utilizing sandy porous medium with a well-known grain-size distribution. An experimental scaling law of the power type was obtained for the hydraulic conductivity, utilizing values measured at different scales by different methods (on undisturbed soil samples by flux cells, on the artificial aquifer by slug tests and aquifer tests). Similarly, porosity measurements of a direct and indirect type were carried out: the former performed in the laboratory and the latter utilizing a relation between k and ? based on the particle size analysis of the porous media considered. Successively, a new empirical relationship is proposed here, to derive ?, since the k values and vice versa, are well-known, the validity of which is limited to the sands with effective grain size between 0.059 mm and 0.82 mm and for volumes of aquifer not higher than those investigated here.  相似文献   

6.
This paper describes the use of dry free hanging filters, as passive samplers to determine ozone in the ambient air. The filters, with a diameter of 25?mm, were impregnated with 5,5??-disodium indigo disulphonate (IDS), a reagent for ozone. From the amount of reacted indigo compound, found on the filter, and the ozone concentration in the ambient air, a pseudo rate constant k 1, of the reaction between ozone (O3) and IDS on the filter, is calculated. The range of measurement is between 9 and 205???g/m3 ambient ozone. The dry filter method is specific for ozone, while the Dutch standard method NEN2789, based on an aqueous solution of IDS, has to be corrected for the presence of NO x . From wind tunnel and field experiments, k 1 proved to vary between 0.7 and 1.5?×?10?6?m3?s?1 (??g O3)?1 at wind velocities between 1 and 3?m/s and at an exposure time of 60?min. Within these conditions, ozone concentrations have been determined with free hanging filters in four busy streets in Yogyakarta, Indonesia and at two background sites using an average value of k 1 of 1.2?×?10?6. Subsequently, the traffic NO emission was estimated from the difference of the O3 concentrations at both sides of a road. For an arbitrary situation, an NO emission of 255???g/s per metre road length was calculated. The filter method is inexpensive and practical, needs no electricity, is easily assembled and can be used to perform measurements in remote areas. It is shown here that this simple measurement technique may support air quality studies, e.g., in developing countries.  相似文献   

7.
In this work, the influence of solute concentration of two types of electrolyte solutions single-ion (Na) and mixed-ion (Na–Ca) systems on hydraulic and some physical properties of a clay soil was investigated. Saturated hydraulic conductivity (HC) declined noticeably using lower solute concentration in single ion system. The highest reduction in HC was observed at 250 molec m?3 solute concentration. Application of high solute concentration of single-ion system reduced meanweight diameter (MWD) to less than half of the control treatment (0.16 mm compared with 0.33 mm). Resistance to penetrometer increased with decreasing solute concentration. In mixed-ion system the MWD was increased whereas the resistance to penetrometer was decreased. HC values ranged from 6.5?×?10?4 to 9.0?×?10?4 mm s?1 in mixed ion system compared with 7.2?×?10?4 to 13.0?×?10?4 mm s?1 in single-ion system. The improvement of some physical properties in mixed-ion solution treatment is attributed to the presence of calcium ion that usually acts as amendment to sodium-affected soil. Soil HC showed lower values at low solute concentrations.  相似文献   

8.
Aqueous 2-chloronapthalene was contacted with cast iron in batch systems, resulting in an initial rapid increase in the sorbed 2-chloronapthalene concentration (C s ) followed by a slow decline, and an initial rapid decline in the aqueous 2-chloronapthalene concentration (C a ) followed by a slower decline. The initial rapid partitioning of 2-chloronapthalene to the solid phase was due to its adsorption on elemental carbon present on the cast iron surface, while the residual aqueous phase 2-chloronapthalene underwent reductive dehalogenation at a slower rate through interaction with the metallic iron surface. The overall rate of change of total 2-chloronapthalene concentration (C T = C s +C a ) with time, i.e., (d/C T }{{d}t}) could be described by the expression,?k 1 ?M? (C a ) n , where M is the concentration of cast iron. The values of k 1 and n were determined to be 1.576 × 10?5 hr?1 g?1 iron L and 1.945 respectively. Equilibrium partitioning of 2-chloronapthalene between solid and aqueous phases could be described by a Freundlich isotherm, C s = K? [C a ] m , where m and K were determined to be 0.55 and 4.92 × 10?3 L g?1. Considering K to be the ratio of the adsorption (k 2) and desorption (k 3) rate constants, expressions were developed for describing the evolution of C s and C a with time. Putting k 3 = 1 hr?1 in these expressions resulted in adequate model fit to the experimental data. Napthalene was identified as the major dehalogenation by-product, with greater than 99 percent of the naphthalene produced partitioning to carbon present on the cast iron surface. No competition between 2-chloronapthalene and naphthalene for adsorption on the carbon surface was observed, suggesting non-specific adsorption of these compounds restricted only by the physical size of the molecules and the available carbon surface area.  相似文献   

9.
Understanding wetland hydrogeology is important as it is coupled to internal geochemical and biotic processes that ultimately determine the fate of potential contaminant inputs. Therefore, there is a need to quantitatively understand the complex hydrogeology of wetlands. The main objective of this study was to improve understanding of saturated groundwater flow in a forested riparian wetland located on a golf course in the Lower Pee Dee River Basin in South Carolina, USA. Field observations that characterize subsurface wetland flow critical to solute transport originating from storm-generated runoff are presented. Monitoring wells were installed, and slug tests were performed to measure permeabilities of the wetland soil. A field-scale bromide tracer experiment was conducted to mimic the periodic loading of nutrients caused by storm runoff. This experiment provided spatial and temporal data on solute transport that were analyzed to determine travel times in the wetland. Furthermore, a 3-D numerical, steady-state flow model (MODFLOW) was developed to simulate subsurface flow in the wetland. A particle tracking model was subsequently used to calculate solute travel times from the wetland inlet to the outlet based on flow modeling results. It was evident that observed tracer breakthrough times were not typical of these measured wetland soil matrix conductivity values. Based on surface water sampling results at the wetland outlet, tracer arrival time was about 9 h after the injection of the tracer. These results implied an apparent mean K value of 2,050 m/day, which is 152 times larger than the mean of the measured values using slug tests (13.4 m/day). Modeling efforts clearly demonstrated this implied preferential flow behavior; particle travel times resulting from the calibrated flow model were in the order of hundreds of days, while actual travel times in the wetland were in the order of hours to a few days. This significant difference in travel times was attributed to the presence of macropores in the form of dead root channels and cavities forming a pipe-flow network. The analyses presented in this study resulted in an estimate of the ratio of matrix permeability to matrix plus macropore permeability of approximately 1/150. Eventually, the tracer test and resulting travel times between various points in the wetland were critical to understanding the true wetland flow dynamics. The final conceptual model of the hydraulic properties of the wetland soils comprised a low permeability matrix containing a web of high K macropores. Simulation of tracer transport in this system was possible using a flow model with significantly elevated K values.  相似文献   

10.
The kinetics of cadmium uptake by Selenastrum capricornutum Printz was studied at 21 °C and 0 °C and at four different concentrations of free cadmium (10?9, 10?8, 10?7 and 10?3 M). The free cadmium concentrations in the medium were kept constant through buffering by a chelating agent (NTA). Initial uptake occurred within 10 min at both temperatures, indicating a fast process. At 21 °C, the cadmium uptake increased during the experimental sampling times from 0.12 to 50 h, whereas at 0 °C, the cadmium uptake remained constant after the first sampling time. Apparently, two different processes were involved in cadmium uptake, a first fast, probably passive process and a second slower, possibly physiological process. The cadmium uptake processes are described with a generalized metalligand complex formation model. The experimental dissociation constants for the fast (K R,F ) and the slow process (K R,S ) were reproducible for different experiments and they were both in the order of 5 10?6 mol L?1. For the slow process, the uptake- and release rate constants (k1 and k2) were quantified; for two experiments, the mean value for ki was 111±28 L mol?1 h?1 and the mean value for k 2 was (5.1±1.8) 10?4 h?1. These values were calculated using the fitted value of the cadmium uptake in the fast process.  相似文献   

11.
The concern for groundwater pollution by agrichemicals through solute movement within the soil is widespread. Zeolite is a type of soil amendment that is utilized to improve physical properties of soil and ameliorate polluted soil. The high negative charge of the zeolite and its open space structure allows adsorption and access of heavy metals and other cations and anions. The objectives of this research were (i) to determine the effects of different application rates of zeolite (0, 2, 4, and 8 g kg?1) on the immobile water content and mass exchange coefficient in a loam soil and then (ii) to determine the effects of optimum application rate of zeolite on the immobile water content and mass exchange coefficient of sandy loam and clay loam soils in saturated conditions by a mobile and immobile (MIM) model. In a disturbed soil column, a method was proposed for determination of MIM model parameters, that is, immobile water content (θim), mass exchange coefficient (α), and hydrodynamic dispersion coefficient (Dh). Breakthrough curves were obtained for different soil textures with different zeolite applications in three replicates, by miscible displacement of chloride (Cl?1) in disturbed soil column. Cl?1 breakthrough curves were evaluated in terms of the MIM model. The results showed that the pore water velocity calculated based on the total soil volumetric water content (θim+ θm) and real pore water velocity calculated based on the mobile water content (θm) increased in the loam soil with an increase in zeolite application rate, so that, between these different rates of zeolite application, the maximum value of pore water velocity and real pore water velocity occurred at zeolite application rates of 8.6 and 11.5 g kg?1, which are indicated as the optimum application rates. However, the comparison between different soils showed that the zeolite application rate of 8 g kg?1 could increase pore water velocity of sandy loam and loam soils by 31% more than that of clay loam soil. The immobile water content and mass exchange coefficient of loam soil were correlated with the zeolite application rate and reduced with an increase in the rate of applied zeolite. In a comparison between different soils at zeolite application rate of 8 g kg?1, the immobile water contents of the zeolite-treated soil decreased by 57%, 60%, and 39% on sandy loam, loam, and clay loam soils, respectively, compared with the untreated soil. Furthermore, zeolite application could reduce mass exchange coefficient by 9%, 43%, and 21% on sandy loam, loam, and clay loam soils, respectively. A positive linear relationship was found between θim and α. Zeolite application increased real pore water velocity of sandy loam soil by 39% and 46% compared with loam and clay loam soils, respectively. In other studies there was a decrease in ammonium and nitrate leaching due to the zeolite application, and therefore, an increase in real pore water velocity due to zeolite application in sandy loam soil, as compared with the loam and clay loam soils, may not show more rapid movement of solute and agrichemicals to the groundwater.  相似文献   

12.
《Geoderma》2005,124(3-4):399-413
Relative to montmorillonitic or kaolinitic soils, volcanic soils have atypical dielectric characteristics that interfere with the applicability of the Time Domain Reflectometry (TDR) technique for soil moisture (θ) determination when common, empirical calibration equations are used. This particular dielectric response affects estimation of salinity in volcanic soils. Six TDR-based methods to estimate bulk electrical conductivity (σa) on a range of KCl saline reference solutions were compared, with Nadler's method giving the best results (R1:12=0.988). Three models (linear, non-linear and empirical) for predicting soil solution electrical conductivity (σw) based on σa and θ, were experimentally tested on 24 hand-packed soil columns varying in salinity (Br−) from 0.2 to 4.0 dS m−1, each in four θ levels (36–58%). Rhoades' linear model performed better, especially for large water contents, than the other two (R1:12=0.986 vs. 0.976 and 0.983, respectively). An interpretation in terms of mobile vs. immobile volumetric fractions of water present in volcanic soils is suggested as a possible explanation for these results. The empirical model resulted over-parameterized and an alternative equation with fewer non-correlated parameters, σa=(aθ2+bθ)σw+cθ2, is proposed and tested with good results in volcanic soils from the Canary Islands and New Zealand. The equation encompasses both the relative dielectric dominance of the mobile water fraction at high water content typical of volcanic soils, and of the immobile fraction at low water contents. Simultaneous measurements made with a standard four-electrode probe and TDR gave good correlation (R2=0.964). A good linear correlation was also found between tracer concentration in the soil solution and σw (R2=0.960). Nadler's and the new empirical model also tested with good results under dynamic (flow) conditions during a miscible displacement experiment in a large monolith using bromide as a tracer. The method reveals itself as a robust tool for solute transport studies under controlled salinity conditions in a volcanic soil.  相似文献   

13.
Factors controlling the acidity of running waters between the coast of the Gulf of Bothnia and the Caledonian mountain range in central-northern Sweden were studied intensively in 8 large streams and in two synoptic surveys of 179 small streams. The bulk deposition of SO4 2? was between 11–22 μeq m?2 y?1, of which 93% was nonmarine, with the highest values in the coastal region. Organic anions were the most frequent acid anions in the whole investigation area followed by sulfate. The major portion of SO4 2? was from natural sources in the whole investigation area. The most acidic streams occurred in the hilly wave-washed terrain of the coastal region, because of a high terrestrial export of organic acids and very low neutralizing capacity. It is concluded that most of the acidity in the investigated streams is due to natural sources.  相似文献   

14.
We studied the dynamics of Cd uptake and depuration in epilithic periphyton and in the grazing amphipod Hyalella azteca. Both stable Cd, sufficient to achieve an aqueous concentration of 90 ng L?1, and its radiotracer 109Cd, were added during 1987 to the epilimnion of oligotrophic Lake 382 of the Experimental Lakes Area in northwestern Ontario. Cadmium dynamics within both periphyton and Hyalella were rapid, with equilibrium being approached within two weeks. For periphyton, the Cd uptake rate constant (K uw ) was 3.8×104 d?1 with a depuration rate of 0.29 d?1. For Hyalella the depuration rate was 0.36 d?1, 10% due to growth dilution and 90% to excretion or desorption. The total Cd uptake rate (k ut ) by Hyalella was 6.1×104 d?1, with more of the uptake (58%) derived from food (periphyton) than from water. Hyalella assimilated 80% of ingested Cd. Steady-state bioconcentration factors (BCF) were at least 10-fold higher than previously published values for Amphipoda. In periphyton and Hyalella the BCF were 1.2×105 and 3.2×105, respectively.  相似文献   

15.
A multiple-antibiotic resistantE. coli was applied to rye-grass covered field mini-plots to simulate point-source contamination. Using three mini-plots for testing and a fourth as a control, the ability of the tracer bacterium to survive under field conditions was studied. Three test plots each received separately 107, 108, or 1010 cfu mL?1 E. coli grown for 24 h. in 5 L one-third strength Tryptic soy broth. In Phase I of the study, it was determined that the tracer disappeared from leaf surfaces of rye-grass covering the plots after 41 days. In Phase II, determination of the presence of the tracer in the top 2″ (5 cm) of soil after two months elapsed time indicated that tracer cfu/g dry wt. of soil had declined five, three, and three-logs for test plots 1,2, and 3. In Phase III, subsurface soil sampling using a soil auger on the three test minei-plots indicated the tracer had penetrated through the top-soil and into the underlying B horizon (20 to 50 cm down). In Phase IV, detailed sampling by excavation of the subsurface soil Horizons of the third test mini-plot showed that the tracer had also penetrated through the hardpan (C Horizon) located 0.6 m below the surface to enter the groundwater (1.06 m deep) (Phase V).E. coli counts fell precipitously to 103 cfu g?1 in soil and then, in the groundwater at the groundwater-soil interface, persisted at a concentration of 103 cfu 100 mL?1 for 2 yr. As time past, tracer counts fell to 145 cfu/100 mL in 6 yr. rose to 820 cfu 100 mL?1 in 1986 (8 yr elapsed time), and then fell to 25 cfu 100 mL?1 in 1991 after 13 yr. Serotyping of 1986E. coli isolates indicated that 62% were of the original tracer serotype (0.128:B12) while only 43% of the 1991 isolates were of the same serotype. The penetration rate of the tracer down through the mini-plot soil into the groundwater was 0.02 m day?1 while downslope dispersion occurred at an estimated rate of 1.0 m day?1. The implications of the above findings are discussed.  相似文献   

16.

Purpose

Nitrous oxide (N2O) production and reduction rates are dependent on the interactions with each other and it is therefore important to evaluate them within the context of simultaneously operating N2O emission and reduction. The objective of this study was to quantify the simultaneously occurring N2O emission and reduction across a range of subtropical soils in China, to gain a mechanistic understanding of potential N2O dynamics under the denitrification condition and their important drivers, and to evaluate the potential role of the subtropical soils as either sources or sinks of N2O through denitrification.

Materials and methods

Soils (45, from a range of different land uses and soil parent materials) were collected from the subtropical region of Jiangxi Province, China, and tested for their potential capacity for N2O emission and N2O reduction to N2 during denitrification. N2O emission and reduction were determined in a closed system under N2 headspace after the soils were treated with 200?mg?kg?1 NO 3 ? -N and incubation at 30?°C for 28?days. The soil physical and chemical properties, the temporal variations in headspace N2O concentration, and NO 3 ? -N and NH 4 + -N concentrations in the soil slurry were measured.

Results and discussion

Variations in N2O concentration (N) over incubation time (t) were consistent with an equation in which average R 2?=?0.84?±?0.11 (p?<?0.05): $ N = A \times \left( {1 - \exp \left( { - {k_1} \times t} \right)} \right) - B \times \exp \left( {{k_2} \times t} \right) $ , where A is the total N2O emission during the incubation, B is a constant, and k 1 and k 2 are the N2O emission constant and reduction constants, respectively. The results of the simulation showed that k 1 was greater than k 2. The reduced amount of NO 3 ? -N in the first 7?days of incubation and the N2O emission rate (the percentage of A value relative to the amount of NO 3 ? -N reduced during the 28-day incubation, R n) were able to explain 82.9?% (p?<?0.01) of the variation in total N2O emission (A) during the incubation for the soil samples studied, indicating that the total amount of N2O emitted was determined predominately by denitrification capacity. Soil organic carbon content and soil nitrogen mineralization are the key factors that determine differences in the amounts of reduced NO 3 ? -N among the soil samples. The R n value decreased with increasing k 2 (p?<?0.01), indicating that soils with higher N2O reduction capacity under these incubation conditions would emit less N2O per unit of denitrified NO 3 ? -N than the other soils. Results are valuable in the evaluation of net N2O emissions in the subtropical soils and the global N budget.

Conclusions

In a closed, anaerobic system, variations in N2O concentration in the headspace over the incubation time were found to be compatible with a nonlinear equation. Soil organic carbon and the amount of NH 4 + -N mineralized from the organic N during the first 7?days of incubation are the key factors that determine differences in the N2O emission constant (k 1), the N2O reduction constant (k 2), the total N2O emission during the incubation (A) and the N2O emission rate (R n).  相似文献   

17.

Purpose

The objective of this study was to evaluate the effect of the physicochemical properties of five dissolved organic matter (DOM) isolates on their reactivity with the hydroxyl radical (HO·) in water.

Materials and methods

Five DOM isolates were purchased from the International Humic Substance Society (IHSS). Weight average molecular weight (M W) of these samples was quantified using size exclusion chromatography based on polyethylene glycols as reference standards. Functional group and elemental composition of the DOM samples were available from the IHSS website. Room temperature rate constants were measured using electron pulse radiolysis.

Results and discussion

Five IHSS standards were examined in this study: two soil organic and three aquatic organic matters. The composition varied from samples that had primarily aliphatic carbon (Pony Lake fulvic acid) to mostly aromatic carbon moieties (Elliot Soil humic acid). The M W values of the five samples ranged from 2,400 to 4,100 Da, with an average value of 3,060 Da. Second-order reaction rate constants between DOM and HO· (k DOM-HO·) were measured using thiocyanate competition kinetics, giving values ranging from 1.21 to 10.36?×?108 MC ?1?s?1. The k DOM-HO· values were not found to correlate with either M W or the aliphatic-aromatic carbon ratio, which is consistent with previous reports looking at natural organic matter (NOM), but is different to reports on size-fractionated (ultrafiltration through 15–1 kDa membranes) effluent organic matter (EfOM). We attribute this difference to the larger molecular weight distributions in size-fractionated EfOM compared to NOM.

Conclusions

The k DOM-HO· values in this study ranged over a factor of 10, suggesting that hydroxyl radical reactivity does depend on the sample composition; however, no major correlation was found between the measured reactivity and bulk physicochemical properties of DOM.  相似文献   

18.
Quantity–intensity relations of potassium (K) were worked out for guava orchard soils. Equilibrium activity ratio of potassium (ARe k) ranged from 0.46?×?10?3 to 21.30?×?10?3 (mol L?1)0.5. The majority of the samples had less than 1?×?10?3 (mol L?1)0.5, indicating K depletion in these soils due to continuous K mining. ARe k was significantly and positively correlated with available forms of K, K saturation percentage, labile K (KL), and specific-site K (KX) and negatively correlated with free energy of exchange (–ΔG). The potential buffering capacity (PBC0 K) of K varied from 8.8 to 286.2 cmol kg?1/(mol L?1)0.5. PBC0 K was positively and significantly correlated with clay content. Sixty percent of the soils had ΔK0 values of less than 0.1 cmol kg?1. High KG (Gapon selectivity coefficent) indicated high affinity for K in these soils. Leaf K was positively and significantly correlated with ΔK0, KL, and KX and negatively correlated with –ΔG.  相似文献   

19.
Determination of the saturated hydraulic conductivity (ks) is needed in many studies and applications related to irrigation, drainage, water movement and solute transport in the soil. Although many advances are made for direct measurements of ks, they are usually time consuming and costly. Some attempts have been made to indirectly predict the saturated hydraulic conductivity from the more easily or readily available basic soil properties. The objective of this study was to develop and validate Pedotransfer Functions (PTFs) for estimation of saturated hydraulic conductivity using multiple non-linear regression technique. One hundred and one soil samples were collected from agricultural and forest soils at different depths, at different locations in the Pavanje River basin that lies in the southern coastal region of Karnataka, India. Saturated hydraulic conductivity was measured, by variable falling head method through Permeameter in the laboratory. Prediction accuracies were evaluated using coefficient of determination, root mean square error, mean error, geometric mean error ratio and geometric standard deviation of the error ratio between measured and predicted values. The results show that, the PTFs for the estimation of saturated hydraulic conductivity could be used appropriately for the soils with loamy sand and sandy loam textures falling in this area of the coastal region of southern India.  相似文献   

20.
Anaerobic ammonium oxidation (anammox process) widely occurs in paddy soil and may substantially contribute to permanent N removal; however, little is known about the factors controlling this process. Here, effects of temperature, pH, organic C, and substrates on potential rate of anammox and the relative contribution of anammox to total N2 production in a paddy soil were investigated via slurry incubation combined with 15N tracer technique. Anammox occurred over a temperature range from 5 to 35 °C with an optimum rate at 25 °C (1.7 nmol N g?1 h?1) and a pH range from 4.8 to 10.1 with an optimum rate at pH 7.3 (1.7 nmol N g?1 h?1). The presence of glucose and acetate (5–100 mg C L?1) significantly inhibited anammox activities and the ratio of anammox to total N2 production. The response of potential rates of anammox to ammonium concentrations fitted well with Michaelis-Menten relationship showing a maximum rate (Vmax) of 4.4 nmol N g?1 h?1 and an affinity constant (Km) of 6.3 mg NH4+-N L?1. Whereas, nitrate addition (5–15 mg 15NO3?-N L?1) significantly inhibited anammox activities and the ratio of anammox to total N2 production. Our results provide useful information on factors controlling anammox process and its contribution to N loss in the paddy soil.  相似文献   

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