Activation of soil pyrophosphatase by metal ions

Inorganic pyrophosphatase activity in three soils decreased when exchangeable and soluble metals were removed by leaching with in NH₄OAc (pH 8). The effect of added metal ions at various concentrations in the leached soils showed that, at certain concentrations, Ba²⁺, Ca²⁺, Co²⁺, Mg²⁺, Mn²⁺, Ni²⁺ and Zn²⁺ promoted, K⁺ and Na⁺ had no effect, and Fc²⁺ and Cu²⁺ decreased pyrophosphatase activity. At high concentrations (>50 mM). Co²⁺, Mn²⁺, Ni²⁺ and Zn²⁺ inhibited pyrophosphatase activity in two soils. The concentration of metal ion needed for optimum activity of pyrophosphatase varied among the soils. The efficiency of the metal ions at optimum concentrations (average percentage increase for three soils in parentheses) in promoting pyrophosphatase was Ca²⁺ (47) > Mg²⁺ (42) > Ba²⁺ = Co²⁺ (29) > Ni²⁺ (27) > Zn²⁺ (20) > Mn²⁺(16). Pyrophosphatase activity in two leached soils adjusted to 50, 75, 100 or 150 mM PPi and Ca²⁺ or Mg²⁺ concentrations from 0 to 250 mM was at an optimum when the metal ion: PPi ratio was 1:1. Soil pyrophosphatase in the presence of 200 mM CaCl₂ or MgCl₂ was protected against inactivation by heat (90 C for up to 30 min).     

Evidence of Long-Range Transport of Pollutants from the Size-Fractionated Ionic Composition of Aerosols in the Jeju Island of Korea

The ionic composition of total suspended particulate (TSP) and fine (PM_2.5) fractions was investigated from an 1,100 site in the middle of Mt. Halla in Jeju Island, Korea from March to November 2006. The sum concentrations of cation and anion species in TSP fraction were 205 ± 170 and 183 ± 164 neq m^?3, respectively, while those for PM_2.5 as 118 ± 129 and 88.5 ± 89.3 neq m^?3, respectively. In TSP, the concentration of the major ions changed in the order of SO₄ ^2? > NH₄ ⁺ > Ca²⁺ > Na⁺ > NO₃ ^? > Mg²⁺ > K⁺ > Cl^?, while its PM_2.5 counterpart as NH₄ ⁺ > SO₄ ^2? > Ca²⁺ > NO₃ ^? > Na⁺ > Mg²⁺ > K⁺ > Cl^?. Inspection of the temporal variabilities of ionic components indicated that most ions peaked in spring or fall months. The back trajectory analysis showed that the atmospheric composition of the major ionic species was affected fairly sensitively by long-range transport from China under the favorable meteorological conditions. In contrast, the lowest ionic concentration levels were seen most abundantly, when air masses passed from South Sea. Hence, the analysis of ionic concentration data suggests that their distributions are controlled by the combined effects of various source processes including the most prominent Chinese origin and the meteorological condition favorable for such transport.     

不同白榆品系对滨海盐碱地的改良效果及盐分离子的分布与吸收

为揭示不同白榆(Ulmus pumila L.)品系对滨海盐碱地土壤盐分的改良作用及盐分离子在土壤-白榆系统中的分布与吸收特征,筛选适宜在滨海盐碱地造林的耐盐白榆品系,以中度盐渍化生境下4年生的6种白榆品系(1,5,28,30,46,105号)为试验材料,采用野外取样与室内测试相结合的方法,研究了Na+、K+、Ca2+、Mg2+等盐离子在土壤及白榆品系各器官(根、茎、叶)中的分布特征。结果表明:(1)白榆可降低滨海盐碱地土壤中盐离子及全盐含量,不同白榆品系较对照的土壤全盐含量降低了55.0%～63.1%,30号白榆降幅最大。(2)不同白榆品系将Na+、K+、Ca2+、Mg2+优先积累到叶中,且叶中维持较高的K+/Na+、Ca2+/Na+、Mg2+/Na+比值,不同白榆品系通过建立新的离子平衡以适应盐胁迫环境。(3)不同白榆品系的离子吸收选择性系数均为SK,NaSCa,NaSMg,Na,其对K+的吸收选择性大于对Ca2+、Mg2+吸收选择性;种内差异导致不同白榆品系对Na+、K+、Ca2+、Mg2+吸收选择能力不同,28号白榆根系对K+的吸收性最强,5号白榆根系对Ca2+、Mg2+的吸收性最强。     

Stability of Ionic Components in Precipitation Samples — A Case Study in Taipei

The changes in ionic contents were studied in acidic precipitation samples collected for precipitation events in Taipei, which is near the sea. The storage cases under investigation include filtration, refrigeration, and light. Thus the experimental design leads all precipitation samples collected in the same rain event stored under different conditions. They were then analyzed six times successively within two months to provide the information containing potential ionic composition change. The measured constituents are H⁺, K⁺, Na⁺, Ca²⁺, Mg²⁺, NH₄ ⁺, NO₃ ^?, SO₄ ^2?, and Cl^?. The comparison of measured ionic concentrations corresponding to different storage methods yield no significant difference. The increases of NO₃ ^? and decreases of NH₄ ⁺ with time were observed to be of similar magnitude, while the variation of pH values is significant. The presented study indicated the important role played by sample storage in determining the ionic composition of precipitation samples.     

Exploring the effect of organic matter on the interactions between mineral particles and cations with Wien effect measurements

Purpose

Understanding of the interactions between cations, mineral particles, and organic matter (OM) in soils is of paramount importance in plant nutrition and environmental science, and thus, these phenomena have been studied extensively. At present, an effective and simple tool to investigate these interactions does not exist. Based on previous studies of Wien effect in suspensions, the interactions of cations with soil mineral particles, complicated by the presence of organic matter, can be easily determined by means of Wien effect measurements, which was the objective of this study.

Materials and methods

A paddy soil originating from a yellow-brown soil, rich in organic matter, served as a test sample, from which the clay fraction of less than 2 μm in diameter was separated. Organic matter of aliquots of the clay fraction was removed by the oxidation with hot H₂O₂, and the natural and OM-free samples were saturated with various cations: Na⁺, K⁺, Ca²⁺, and Cd²⁺. The effects of OM present in the paddy soil on the interactions between the cations and the soil mineral particles were investigated by measuring the suspension Wien effect with a homemade apparatus, SHP-2.

Results and discussion

The weak electrical field electrical conductivities (EC₀) of suspensions of the natural soils saturated with various cations were higher than those of the OM-free soils. The rate of increase in electrical conductivity of suspensions of the OM-free soil, except that of suspensions saturated with Na⁺, at electrical field strengths >50～100 kV?cm^?1 was higher than those of the natural soil suspensions. The presence of OM increased the mean free binding energies of cations other than Na⁺. The increasing binding energies for K⁺ and Ca²⁺ were 0.56 and 0.57 kJ?mol^?1, respectively, which were significantly larger than the increase for Cd²⁺ as only 0.03 kJ?mol^?1. The binding energies of various cations on both natural and OM-free soils were all in the order: Na⁺?<?K⁺?<?Ca²⁺≈Cd²⁺. As opposed to its effect on the binding energies, the presence of OM reduced the mean free adsorption energies of the cations. Except for Na⁺, the adsorption energies of K⁺, Ca²⁺, and Cd²⁺ at field strengths >50 kV?cm^?1 were lower in the natural soil as compared with the OM-free soil, and the differences between the adsorption energies became larger with increasing field strengths. The presence of OM made the zeta potential of the soil particles saturated with Na⁺ and K⁺ positive, and the particles saturated with Ca²⁺ and Cd²⁺ negative.

Conclusions

Organic matter affected the interactions of cations with soil mineral particles significantly. Binding and adsorption energies, which were quantitative measures of the interactions between cations and soil particles, could be determined by Wien effect measurements in suspensions. The binding energies on natural soils were larger than those on the corresponding OM-free soils, and the adsorption energies on the natural soils were lower than those on OM-free soils.     

Proton release by N2‐fixing plant roots: A possible contribution to phytoremediation of calcareous sodic soils

With a world‐wide occurrence on about 560 million hectares, sodic soils are characterized by the occurrence of excess sodium (Na⁺) to levels that can adversely affect crop growth and yield. Amelioration of such soils needs a source of calcium (Ca²⁺) to replace excess Na⁺ from the cation exchange sites. In addition, adequate levels of Ca²⁺ in ameliorated soils play a vital role in improving the structural and functional integrity of plant cell walls and membranes. As a low‐cost and environmentally feasible strategy, phytoremediation of sodic soils — a plant‐based amelioration — has gained increasing interest among scientists and farmers in recent years. Enhanced CO₂ partial pressure (P_CO2) in the root zone is considered as the principal mechanism contributing to phytoremediation of sodic soils. Aqueous CO₂ produces protons (H⁺) and bicarbonate (HCO₃^‐). In a subsequent reaction, H⁺ reacts with native soil calcite (CaCO₃) to provide Ca²⁺ for Na⁺ Ca²⁺ exchange at the cation exchange sites. Another source of H⁺ may occur in such soils if cropped with N₂‐fixing plant species because plants capable of fixing N₂ release H⁺ in the root zone. In a lysimeter experiment on a calcareous sodic soil (pH_s = 7.4, electrical conductivity of soil saturated paste extract (EC_e) = 3.1 dS m^‐1, sodium adsorption ratio (SAR) = 28.4, exchangeable sodium percentage (ESP) = 27.6, CaCO₃ = 50 g kg^‐1), we investigated the phytoremediation ability of alfalfa (Medicago sativa L.). There were two cropped treatments: Alfalfa relying on N₂ fixation and alfalfa receiving NH₄NO₃ as mineral N source, respectively. Other treatments were non‐cropped, including a control (without an amendment or crop), and soil application of gypsum or sulfuric acid. After two months of cropping, all lysimeters were leached by maintaining a water content at 130% waterholding capacity of the soil after every 24±1 h. The treatment efficiency for Na⁺ removal in drainage water was in the order: sulfuric acid > gypsum = N₂‐fixing alfalfa > NH4NO3‐fed alfalfa > control. Both the alfalfa treatments produced statistically similar root and shoot biomass. We attribute better Na+ removal by the N₂‐fixing alfalfa treatment to an additional source of H⁺ in the rhizosphere, which helped to dissolve additional CaCO₃ and soil sodicity amelioration.     

Effect of Environmental Conditions on Chemical Profile of Stream Water in Sanctuary Forest Area

This study reports the evaluation of chemical composition of a Black Vistula and White Vistula streams’ waters taking into consideration both geological conditions of the stream’s catchment area and different water’ level related to seasonal variations in particular catchment ecosystem (high stage: beginning of the vegetation period; medium stage: vegetation period; low stage: final time of vegetation period). The complex data matrix (744 observations), obtained by the determination of major inorganic analytes (Cl^?, NO₃ ^?, SO₄ ^2?, NH₄ ⁺, Na⁺, K⁺, Ca²⁺, Mg²⁺) in water samples by ion chromatography was treated by linear discriminant analysis and non-parametrical testing. In case of both streams obtained results indicate presence of two discriminant functions (DFs). The data variance explained by DFs is as follows: Black Vistula stream—first DF: 93.5%, second DF: 6.5%; White Vistula stream—first DF: 66.3%, second DF: 33.7%. In case of Black Vistula stream first DF allows distinction of medium, high and low waterstage related samples while second DF between high/low and medium water stage related samples. In case of White Vistula stream first DF allowed to distinguish between medium/high and low water stage related samples while second DF between medium and high water level samples. In case of both streams, the most informative DFs were related to geological conditions of investigated catchments (contents of Cl^?, Na⁺, K⁺, Mg²⁺, Ca²⁺, SO₄ ^2?), while the second to nutrient biocycle (mainly NH₄ ⁺ and NO₃ ^?) related to slope’s exposition and inclination.     

REACTIONS OF AMMONIA WITH SOIL. I

Heats of adsorption and adsorption isotherms of ammonia gas were measured at 300 K (27 °C) on outgassed soil saturated with Na⁺, K⁺, NH₄⁺, Ca²⁺, or Mg²⁺ ions. The Ca and Mg soils adsorbed apparently one more NH₂ molecule per exchangeable ion than the Na and K soils, mostly in the relative pressure range o to 0.005, but not much more than the NH₄ soil. The initial heat of adsorption was c. 75 kJ mol^-1 on the Ca and Mg soils and c. 60 kJ mol^-1 on the other soils. The results suggest that most NH, is sorbed on these soils through reactions not involving exchangeable cations.     

Evaluation of the Atmospheric Deposition in an Urban Region in South Brazil

The purpose of the present study is to analyse the chemical composition of bulk and wet atmospheric deposition samples in the Guaíba Hydrographic Basin (GHB), in south Brazil. Samples of bulk and wet deposition were analysed during a 1-year's period (January to December 2002) at three different stations, i.e., 8^° Distrito and CEASA stations in the city of Porto Alegre, and Charqueadas station, in Charqueadas city. Conductivity, pH, Cl^?, NO₃ ^?, F^?, SO₄ ^{2 ?}, Na⁺, K⁺, Mg^{2 +}, NH₄ ⁺ and Ca^{2 +} were determined. The pH presented an average value between 4.75 and 7.45. Enrichment factor was characterised based on groups of acid (pH < 5.65) and alkaline (pH > 5.65) samples. For most of the studied ions, EF in bulk deposition was higher in alkaline samples, while in wet deposition there was little difference between acid and alkaline samples. The Multivariate Analysis technique, i.e. the Canonical Correlation Analysis (CCA), determined relationships between the two different data set (chemical and meteorological), identified the source (anthropogenic or natural) of the studied variables.     

Solute Release from Weathering of Spent Mushroom Substrate under Controlled Conditions

Weathering of piled material in the field is a popular method to treat spent mushroom substrate (SMS) before reuse. During the weathering process, rainfall and snowmelt pass through SMS piles and a large amount of solutes is released in the leachate. To investigate solute release patterns, the field weathering process was simulated under controlled conditions in the laboratory. Fresh SMS was packed in an acrylic column (20 cm i.d.) to 150 cm height and leached intermittently with a cumulative total of 230 cm of deionized water over 180 days. Leachate was collected and analyzed for dissolved organic carbon (DOC), dissolved organic nitrogen (DON), electrical conductivity (EC), and inorganic salts. Solute release patterns were described using first order models, and total released solutes were calculated. The SMS leachate had DOC, DON and EC values ranging from 450 to 15,500 mg L^?1, 50 to 1,700 mg L^?1, and 3 to 50 dS m^?1, respectively. The major inorganic cations were K⁺, Na⁺, Ca²⁺, Mg²⁺ and NH₄⁺, and anions were Cl^? and SO₄^2?. Release of DOC, DON, and bivalent cations Ca²⁺ and Mg²⁺ were described by a first order Exponential Rise to Maximum model, while releases of monovalent ions Cl^?, K⁺, Na⁺ and NH₄⁺ were described as a first order Sigmoidal Logistic process, and SO₄^2? release was best modeled by a Sigmoidal Chapman equation. Following six months and 230 cm applied water, 3.1 kg of DOC, 0.58 kg of dissolved N, and 8.6 kg of inorganic salts were leached per cubic meter of bulk SMS (220 kg oven dry mass). Weathering of SMS involves a significant removal of nutrients from the composted material, which can contribute to pollution of soil and groundwater.     

Intercomparison of snow Sampling and Analysis Within the Alpine-Wide Snowpack Investigation (SNOSP)

In order to investigate the seasonal and geographical distribution of snow concentrations anddeposition fluxes of environmentally relevant ionic species in the Alps, the international programSNOSP was initiated. In the framework of this program, intercomparisons of snow samplingtechniques and analytical methods to determine the ionic species C1^-, NO ₃ ^- ,SO ₄ ^2- , K⁺, Na⁺, NH4 ⁺, Mg²⁺, and Ca²⁺, as well as the pH and the specificconductivity were performed. The concentrations of these species in the snow samples collectedin the SNOSP program varied by orders of magnitude with, e.g., concentrations of NO ₃ ^- , SO ₄ ^2- , and NH4 ⁺ ranging from 0.2-60, 0.2-90, and 0.1-60 µeq L^-1,respectively. The intercomparisons revealed a reasonable agreement of the determinations of thespecies Cl^-, NO ₃ ^- , SO ₄ ^2- , Na⁺, and NH4 ⁺ in snow. Results were less satisfactory for K⁺, Mg²⁺, Ca²⁺,and H⁺, mainly due to the very low concentrations. In conclusion, recommendations areformulated for the reliable derivation of chemical inventories from snow packs.     

Growth and acquisition of Na,K and Ca in some elite sweetpotato [Ipomoea batatas (Lam.) L.] genotypes under salinity stress

Soil salinity is a concern in the wake of climate change challenges due to rising sea levels and coastal salinity in Papua New Guinea. A greenhouse experiment was conducted in Split Plot design, with five elite sweet potato genotypes (main-plot factors) and three levels of sodium chlroide (NaCl) concentrations (sub-plot factors) replicated six times. The vine cuttings of genotype RAB 45 showed very low mortality percentage (33%) at 600 mM NaCl concentration. At salinity level of 200 mM NaCl, aerial dry biomass of the genotypes was inversely but significantly (r = –0.40; p < 0.05) related to the accumulation of sodium (Na⁺) in the tissues. The Na⁺ accumulation in the tissues was antagonistic to the potassium (K⁺) and calcium (Ca²⁺) ions. Among the sweetpotato genotypes, Na⁺/K⁺ ratio decreased in the following order: RAB 45> KAV 11 > Northern Star > DOY 2 > L 46, which was more or less corroborated with the trend in the aerial dry matter.     

Calcium,Magnesium, Sodium,and Potassium Release during Decomposition of Some Organic Residues

The use of organic residues might be appropriate in maintaining long-term nutrient requirements of crops. We investigated under laboratory conditions the dynamics of calcium (Ca²⁺), magnesium (Mg²⁺), sodium (Na⁺), and potassium (K⁺) release during decomposition of eight plant residues and two manures over 12 weeks of incubation at 25 ^○C. During the processes of decomposition, these nutrients were extracted by 0.1 M sulfuric acid (H₂SO₄). The release rate of nutrients for residues was best estimated by the exponential model. There were differences in the rates at which release took place between residues and nutrients. In general, release patterns of nutrients with time for all residues were similar in shape, and two regions could be distinguished: a first one during the first 4 weeks of incubation, corresponding to faster release of nutrients, and a second for longer incubation times (weeks 5–12), when the release of nutrients was slower. A 71% loss of K⁺ was found after 1 week for vegetable waste and only 43% loss of Na⁺ for rape. Generally, based on release rate (% week^–1), nutrient release from residues was in the order K⁺ (–0.363) > Na⁺ (–0.344) > Mg²⁺ (–0.327) > Ca²⁺ (–0.280). The release rate of nutrients was significantly correlated with their residue content. Our results suggest that the use of organic residues as a source for short- and long-term nutrients supply for crops should be encouraged. The quick release of K⁺ and Na⁺ may pose a high risk of K⁺ and Na⁺ losses in sandy soils with low cation exchange capacity.     

Aluminium release in relation to the determination of cation exchange capacity of some podzolized New Zealand soils

In upper mineral horizons, CEC by compulsive and isotopic exchange methods, using Ba²⁺ as the saturating cation, gave higher values than the effective CEC at natural soil pH, and much higher values than CEC determined with m NH₄OAc at pH 7. Cumulative Al release during leaching was considerably higher using Mg²⁺ and Ba²⁺ chlorides than K⁺ and NH₄⁺ chlorides, and gave a different shape extraction curve. Basal spacing of the dominant dioctahedral vermiculite in the soil clays contracted from 14.5Å to 10.0–10.9 Å when saturated with NH₄⁺ and K⁺, restricting release of interlayer Al. Lower horizons, containing a large proportion of Al-chlorite in the clay fraction, which did not contract with any of the cations, showed more normal exchange behaviour. On leaching, Al release was slightly greater with K⁺ and NH₄⁺, than with Mg²⁺ and Ba²⁺, chlorides. The implication of the results for CEC measurements is discussed.     

Leaching of nutrients and major ions from an arable field with an unfertilized fallow as infield buffer zone

Abstract

Leaching of nutrients and major ions from a tile-drained arable field was evaluated over a 25-year period (1980–2005). The soil, classified as a Gleyic Cambisol, received moderate applications of fertilizers. During later years the soil was more frequently under ley, and since 2002, an area of ravine (29% of the total field) has been managed as a permanent fallow with annual cutting without removing the grass material. A decrease in the concentration of nitrate nitrogen (NO₃?N) in the drainwater was estimated in 1980–2005, based on non-parametric tests on concentrations flow-normalized with a robust fitting curve procedure. The average concentration of soluble reactive phosphorus after pre-filtration (RP_f) of 0.030 mg l^?l corresponded to a calculated degree of phosphorus saturation (DPS) of 6% in acid extract of ammonium lactate from the topsoil. Between 1995 and 2005, concentrations of suspended solids (SS), RP and total organic carbon (TOC) decreased significantly in the drainage water from the entire field. Throughout the entire period, there was a negative net accumulation of the major ions to the soil. The order of decrease in relative terms was calcium (Ca²⁺)>magnesium (Mg²⁺)>sulphate (SO₄ ^2?)>chloride (Cl^?)>potassium (K⁺). In addition, the soil phosphorus (P) balance was negative. A significant reduction in ion concentrations in the drainwater, including sodium (Na⁺) and hydrogen carbonate HCO₃ ^?, was estimated. The order of reduction in relative terms was: SO₄ ^2?>Mg²⁺>Ca²⁺>HCO₃ ^?>Cl^?>NO₃ ^?>Na⁺>HPO₄. Altogether these trends were equal to approximately 0.1 mmol_c l^?1. yr^?1 of positively and negatively charged ions. Based on measured concentrations, decreasing trends in SO₄ ^2? and Ca²⁺ were also observed in the shallow groundwater (3.6 m below the soil surface), while K⁺, Na⁺ and HCO₃ ^? tended to increase. Trends of cations in deeper groundwater (5.8 m below the soil surface) were in some cases the opposite of the trends in the drainwater.     

Niederschlags-Chemismus und atmosphärische Element-Deposition in einem an der Nordseeküste von Schleswig-Holstein gelegenen Agrarökosystem

Precipitation chemistry and atmospheric element-deposition in an agroecosystem at the North-Sea Coast of Schleswig-Holstein The objective of this study was to examine the chemistry of bulk precipitation and atmospheric element inputs in an arable soil near the North Sea coast of Schleswig-Holstein, North Germany. Bulk precipitation was collected at weekly intervals from November 1989 to October 1991. Precipitation amount, pH, electrical conductivity, and concentrations of Na⁺, K⁺, NH₄⁺, Mg²⁺, Ca²⁺, Cl^?, NO₃^?, and SO₄^2? were recorded. The average volume-weighted pH was 5.5 and the average EC was 92 μS cm^?1. Sodium and Cl^? were with 64% and 76% the dominant ions (equivalent concentration) in bulk precipitation indicating the influence of the North Sea. The contribution of marine alkalinity to neutralization reactions of bulk precipitation was negligible (1%). The neutralizing substances NH₃ (63%) and Carbonate (36%) were more important. Deposition rates were in 1990 and 1991 97.0 and 51.7 kg Na⁺ ha^?1, 6.2 and 4.0 kg K⁺ ha^?1, 15.0 and 8.4 kg Mg²⁺ ha^?1, 13.2 and 10.4 kg Ca²⁺ ha^?1, 12.3 and 9.5 kg NH₄⁺-N ha^?1, 8.0 and 5.9 kg NO₃^?-N ha^?1, 168 and 83.1 kg Cl^? ha^?1 and 19.1 and 12.7 kg SO₄^2?-S ha^?1. In 1990 both more westerly winds and stronger wind-forces occurred than in 1991 and resulted in higher inputs of marine origin. Calculated on Cl^? basis 93% of Na⁺, 55% of K⁺, 74% of Mg²⁺, 24% of Ca²⁺, and 36% of SO₄^2? were of marine origin. Atmospheric input of marine origin supplied 39–72% of Mg and 21–37% of S requirement for crop production. The North Sea is an important source providing significant amounts of these elements to agricultural crops.     

Geochemical Distribution of Selected Heavy Metals in Stream Sediments Affected by Tannery Activities

Bayesian regularized back-propagation neural network (BRBPNN) was developed for trend analysis, acidity and chemical composition of precipitation in North Carolina using precipitation chemistry data in NADP. This study included two BRBPNN application problems: (i) the relationship between precipitation acidity (pH) and other ions (NH₄ ⁺, NO₃ ^?, SO₄ ^2?, Ca²⁺, Mg²⁺, K⁺, Cl^? and Na⁺) was performed by BRBPNN and the achieved optimal network structure was 8-15-1. Then the relative importance index, obtained through the sum of square weights between each input neuron and the hidden layer of BRBPNN(8-15-1), indicated that the ions' contribution to the acidity declined in the order of NH₄ ⁺ > SO₄ ^2? > NO₃ ^?; and (ii) investigations were also carried out using BRBPNN with respect to temporal variation of monthly mean NH₄ ⁺, SO₄ ^2? and NO₃ ^? concentrations and their optimal architectures for the 1990–2003 data were 4-6-1, 4-6-1 and 4-4-1, respectively. All the estimated results of the optimal BRBPNNs showed that the relationship between the acidity and other ions or that between NH₄ ⁺, SO₄ ^2?, NO₃ ^? concentrations with regard to precipitation amount and time variable was obviously nonlinear, since in contrast to multiple linear regression (MLR), BRBPNN was clearly better with less error in prediction and of higher correlation coefficients. Meanwhile, results also exhibited that BRBPNN was of automated regularization parameter selection capability and may ensure the excellent fitting and robustness. Thus, this study laid the foundation for the application of BRBPNN in the analysis of acid precipitation.     

Evalution of Acid Deposition in Korea

This study was carried out to evaluate acid depositions and to understand their effect. Wet precipitation has been collected at twenty-four sites in Korea for one year of 1999. The ion concentrations such as H⁺, Na⁺, K⁺, Mg²⁺, NH₄ ⁺, Ca²⁺, Cl^?, NO₃ ^? and SO₄ ^2? were chemically analyzed and determined. Precipitation had wide range of pH(3.5～8.5), and volume-weighted average was 5.2. The contribution amounts of Cl^?, SO₄ ^2? and NO₃ ^? in anion were shown to be 54%, 32%, and 14%, respectively and those of Na⁺ and NH₄ ⁺ in cation were 32% and 25%. The ratios of Cl^? and Mg²⁺ to Na⁺ in precipitation were similar to those of seawater, which imply that great amount of Cl^? and Mg²⁺ in precipitation could be originated from seawater. The concentration of H⁺ is little related with SO₄ ^2?, NO₃ ^? and Cl^? ions, whereas nss^?SO₄ ^2? and NO₃ ^? are highly correlated with NH₄ ⁺, which could suggest that great amount of SO₄ ^2? and NO₃ ^? exist in the form of ammonium associated salt. The annual wet deposition amounts (g m^?2year^?1) of SO₄ ^2?, NO₃ ^?, Cl^?, H⁺, NH₄ ⁺, Na⁺, K⁺, Ca²⁺ and Mg²⁺ were estimated as 0.88～4.89, 0.49～4.37, 0.30～9.80, 0.001～0.031, 0.06～2.15, 0.27～4.27, 0.10～3.81, 0.23～1.59 and 0.03～0.63.     

The effects of feeding byOniscus asellus (Isopoda) on nutrient cycling in an incubated hardwood forest soil

Summary Oniscus asellus produced changes in the nutrients leached from Oie and Oa horizons of a hardwood forest soil. Soil with isopods lost more K⁺ (54%) from the Oie horizon and more Ca²⁺ (25%), Mg²⁺ (40%), and water-extractable S (23%) from the Oa horizon than soil without isopods. In contrast, soils with isopods lost less Ca²⁺ (39076) from the Oie horizon and less dissolved C-bonded S (33%) from the Oa horizon than soil without isopods. In addition, the Oia and Oa horizons exhibited different nutrient dynamics. When isopods were present, the Oa horizon leachates accumulated more Na⁺ K⁺, Ca²⁺, Mg²⁺, NO₃ ^– , water-soluble SO₄ ^2–, and dissolved C-bonded S, and the Oie horizon retained more of these nutrients. The type of leaching solution also had a major effect on nutrients. Leaching with a simulated soil solution resulted in smaller nutrient losses for K⁺ and Mg²⁺ in both horizons and for Na⁺, Ca²⁺, and NO₃ ^– in the Oa horizon than leaching with distilled water.     

Calcium-Ammonium Selectivity of Two Benchmark Soils from Botswana as Assessed by Competing Semi-empirical Ion Exchange Equations

The effectiveness of lime-ammonium-nitrate (LAN) as a nitrogen (N) fertilizer in weathered soils depends on the respective selectivity for ammonium (NH₄) and calcium (Ca) by the soils. The study assessed Ca²⁺/NH₄⁺ exchange selectivity of two benchmark soils from Botswana and examined the soil fertility management implications. Surface horizons (0–20 cm) of Pellustert and Haplustalf were equilibrated with 50 ml stock solution containing variable concentrations of Ca²⁺ and NH₄⁺. The Ca²⁺/NH₄⁺ exchange data were fitted into the Vanselow (K_V), Gaines and Thomas (K_GT), Davies (K_D), and the regular solution (K_RS) equations. The selectivity coefficients for the Ca²⁺/NH₄⁺ exchange reactions varied widely with the soil exchanger composition except for the relatively stable K_RS. The selectivity coefficients indicated strong preference for NH₄⁺ to Ca²⁺. The thermodynamic exchange constant, K_ex, was 5.75 ± 1.24 in the Pellustert, indicating preferential adsorption of NH₄⁺, but not in the Haplustalf with K_ex = 0.92 ± 0.27. The free energy for Ca²⁺/NH₄⁺ exchange (ΔG°_ex) was negative (?4.26 ± 0.59 kJ mol^?1) in the Pellustert but slightly positive in the Haplustalf (0.34 ± 0.87 kJ mol^?1). In conclusion, the soil-NH₄ complex was more stable than soil-Ca complex in the Pellustert, indicating LAN as a N fertilizer would have greater potential effectiveness in the Pellustert than in the Haplustalf.