湘江流域岳麓山周边地区地表水体水化学特征及灌溉适宜性

[目的] 对湘江流域岳麓山地区地表水体进行水化学特征分析及灌溉适宜性评价,为该地区的生态环境保护及水资源综合管理的科学决策提供理论支持。[方法] 以岳麓山周边地区为研究区,从2020年12月至2021年11月采集降水、山涧溪水和湘江河水水样,利用Piper图、Gibbs图、端元图等方法,分析各水体水化学特征以及影响因素。[结果] 降水主要阴阳离子为Ca²⁺,K⁺,SO^2-₄和NO^-₃,无明显水化学类型;山涧溪水主要阴阳离子为Ca²⁺和NO^-₃,主要水化学类型为Cl-Ca·Mg型和Cl-Ca型;湘江河水主要阴阳离子为Ca²⁺和HCO^-₃,主要水化学类型为HCO₃-Ca型。山涧溪水主要受大气降水输入和碳酸盐岩风化控制;湘江河水受碳酸盐岩风化作用影响较大。[结论] Na⁺离子含量,SAR和RSC指标以及其绘制USSL图和Wilcox图分析结果较好,山涧溪水和湘江河水适合用于灌,不易引起盐害或碱害。     

Trends of Major Inorganic Species at the Small Watershed Ecosystem in Northern Tama Hills, the Western Tokyo Metropolitan Area, Japan

Acid rain impacts on the small forested watershed in northern Tama Hills in the western Tokyo metropolitan area Japan were investigated by surveying the trends of major inorganic species in rain and spring water during the years from 1991 to 1997. The ecosystem had been stressed by the annual H⁺-deposition of around 0.43 kmol/ha. The spring water outflow corresponded to ca. 27% of the precipitation. Budgets for the precipitation input and spring water output gave good balance for Cl^?,?0.01 ±0.09 kmol/ha, net gains for H⁺, NO₃ ^? and SO₄ ^2?, and to the contrary, relatively large net losses for Na⁺, Mg²⁺, Ca²⁺, Si(as H₄SiO₄) and HCO₃ ^?, thus suggesting the dissolution of chemical weathered products of silicate minerals. Further, in spring water, some concentration relationships were found: CNa⁺ = 376.5?2.05CCl^? (R²=0.748), CNa⁺=12.69+0.5556CHCO₃ ^? (R²=0.872) and CH₄SiO₄=130.0 + 1.108CHCO₃ ^? (R²=0.816). Evidently, the spring water chemistry reflected probable geochemical changes in the soil layer of the watershed. Mass balance in the ecosystem and estimation of the spring water output of chemical weathered products were investigated     

Using Organic Matter with Chemical Amendments to Improve Calcareous Sodic Soil

Abstract

Kangping soil in northeast China is a sodic soil characterized by a high pH and excessive sodium. The high pH and excessive sodium in sodic soils generally cause loss of soil structure, reduce hydraulic conductivity (HC), increase soil hardness, and make the soil unproductive land. After we mixed organic matter (rice straw) and chemical amendments (H₂SO₄, CaSO₄, and FeSO₄), a column experiment was conducted to evaluate the physical and chemical properties of the soil influenced by the changes in HC, penetrability of soil s`urface, pH, electrical conductivity, CO₃ ^2‐, HCO₃ ^?, Ca²⁺, Na⁺, sodium adsorption rate (SAR), available phosphorus (P) and iron (Fe), and leached P.

Organic matter decreased the concentrations of CO₃ ^2‐, HCO₃ ^?, and Na⁺ in soil solution and increased the total volume of the leachate. Organic matter also reduced the amount of available Fe and increased the available P. However, organic matter did not affect the penetrability of the soil surface as much as soil hardness, HC, and SAR within the short period of this experiment. Among the chemical amendments, H₂SO₄ and FeSO₄ were more effective than CaSO₄ to restore HC, electrical conductivity, Na⁺, and SAR. The chemical amendments, compared with organic matter, significantly leached P from the soil in this study, but the leaching was independent of the concentration of available P in the soil. The CaSO₄ had the strongest effect in increasing leached P from the soil without changing the concentration of available P in the soil. Organic matter with added CaSO₄ leached P from the soil more than all other treatments.     

Recent Atmospheric Deposition and its Effects on Sandstone Cliffs in Bohemian Switzerland National Park, Czech Republic

The protected area ??Bohemian Switzerland National Park?? with its characteristic sandstone landscape was influenced by the long-term air pollution and acidic deposition within the area known as Black Triangle (located where Germany, Poland, and the Czech Republic meet, is one of the Europe??s most polluted areas). The local Upper Cretaceous sandstone is subhorizontally stratified, fine- to coarse-grained, quartz dominated, with low content of clay minerals. One of the significant negative effects of the intensive acidic deposition on sandstone outcrops has been identified as chemical (salt) weathering, i.e., a process when the porous sandstone rock is except of chemical influence attacked also by force of crystallization of growing salts crystals. Anions NO ₃ ^? together with SO ₄ ^2? and cation NH ₄ ⁺ were the most abundant solutes in bulk precipitation samples. Current (2002 to 2009) bulk deposition fluxes of SO ₄ ^2? determined at three sites directly in the National Park indicate decline from 23 to 16 kg^?1 ha^?1 year^?1. Infiltration of bulk precipitation solutes into the sandstone mediates the weathering processes. Natural outflow of sandstone pore-water (sandstone percolates) can be sampled only during certain days of year when the sandstone becomes saturated with water and percolates drip out on small number of sites from roofs of overhangs. Under usual conditions percolation water evaporates at the sandstone surface producing salt efflorescences??the typical example is Prav?ická brána Arch locality. The average pH of the dripping sandstone percolates was 3.76. Concentration of SO ₄ ^2? and Al in sandstone percolates reached up to 46 and 10 mg L^?1. The concentration of Al in percolates has been 160-fold greater the one in the precipitation samples suggesting the sandstone as a source. The water O and H isotopic composition of percolates has been virtually identical to precipitation samples, indicating thus relatively short residence time of the solutions within the sandstone pore-spaces. Evaporation experiments with bulk precipitation and percolate samples proved possible origin of some Ca in bulk precipitation and the sandstone rock as the source of Al and possibly of K for the salt efflorescence identified on Rock Arch body.     

Greenhouse gas diffusive fluxes at the sediment–water interface of sewage-draining rivers

Purpose

The purposes of this study were to analyse the spatiotemporal variations in greenhouse gas diffusive fluxes at the sediment–water interface of sewage-draining rivers and natural rivers, and investigate the factors responsible for the changes in greenhouse gas diffusive fluxes.

Materials and methods

Greenhouse gas diffusive fluxes at the sediment–water interface of rivers in Tianjin city (Haihe watershed) were investigated during July and October 2014, and January and April 2015 by laboratory incubation experiments. The influence of environmental variables on greenhouse gas diffusive fluxes was evaluated by Spearman’s correlation analysis and a multiple stepwise regression analysis.

Results and discussion

Sewage-draining rivers were more seriously polluted by human sewage discharge than natural rivers. The greenhouse gas diffusive fluxes at the sediment–water interface exhibited obvious spatiotemporal variations. The mean absolute value of the CO₂ diffusive fluxes was seasonally variable with spring>winter>fall>summer, while the mean absolute values of the CH₄ and N₂O diffusive fluxes were both higher in summer and winter, and lower in fall and spring. The annual mean values of the CO₂, CH₄ and N₂O diffusive fluxes at the sewage-draining river sediment–water interface were ??123.26?±?233.78 μmol m^?2 h^?1, 1.88?±?6.89 μmol m^?2 h^?1 and 1505.03?±?2388.46 nmol m^?2 h^?1, respectively, which were 1.22, 4.37 and 134.50 times those at the natural river sediment–water interface, respectively. The spatial variation of the N₂O diffusive fluxes in the sewage-draining rivers and the natural rivers was the most significant. As a general rule, the more serious the river pollution was, the greater the diffusive fluxes of the greenhouse gases were. On average for the whole year, the river sediment was the sink of CO₂ and the source of CH₄ and N₂O. There were positive correlations among the CO₂, CH₄ and N₂O diffusive fluxes. The main influencing factor for CO₂ and N₂O diffusive fluxes was the water temperature of the overlying water; however, the key factors for CH₄ diffusive fluxes were the Eh of the sediment and the NH₄⁺-N of the overlying water.

Conclusions

River sediment can be either a sink or a source of greenhouse gases, which varies in different levels of pollution and different seasons. Human sewage discharge has greatly affected the carbon and nitrogen cycling of urban rivers.

     

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.     

QUANTIFICATION OF WEATHERING, SOIL GEOCHEMISTRY AND SOIL FERTILITY

Continental chemical weathering is discussed with reference to a diagram, in which the ratio (CaO + Na₂O + K₂O)/(Al₂O₃+ CaO + Na₂O + K₂O) is plotted against the ratio (SiO₂+ CaO + Na₂O + K₂O)/(Al₂O₃+ SiO₂+ Na₂O + K₂O). The former ratio is a measure of the degree of feldspar breakdown, which is accompanied by the formation of secondary minerals (illite, smectite, etc.). The second ratio is a measure of the enrichment during weathering of Al, Si oxide phases such as kaolinite, quartz and gibbsite. The application of the diagram to a series of global examples leads to the statement: 1) Chemical weathering is the principal process by which continental surfaces are modified. 2) The extent of chemical weathering is correlated with the age of continental surfaces. 3) Global agricultural productivity is correlated with geologically recent additions of fresh rock debris by processes of volcanism, glaciation or alluviation.     

Ion mass budgets for small forested catchments in Finland

Ion mass and H⁺ budgets were calculated for three pristine forested catchments using bulk deposition, throughfall and runoff data. The catchments have different soil and forest type characteristics. A forest canopy filtering factor for each catchment was estimated for base cations, H⁺, Cl^? and SO ₄ ^2? by taking into account the specific filtering abilities of different stands based on the throughfall quality and the distribution of forest types. Output fluxes from the catchments were calculated from the quality and quantity of the runoff water. Deposition, weathering, ion exchange, retention and biological accumulation processes were taken into account to calculate catchment H⁺ budgets, and the ratio between external (anthropogenic) and internal H⁺ sources. In general, output exceeded input for Na⁺, K⁺, Ca²⁺, Mg²⁺, HCO ₃ ^? (if present) and A^? (organic anions), whereas retention was observed in the case of H⁺, NH ₄ ⁺ , NO ₃ ^? and SO ₄ ^2? . The range in the annual input of H⁺ was 22.8–26.3 meq m^?2 yr^?1, and in the annual output, 0.3–3.9 meq m^?2 yr^?1. Compared with some forested sites located in high acid deposition areas in southern Scandinavia, Scotland and Canada, the catchments receive rather moderate loads of acidic deposition. The consumption of H⁺ was dominated by base cation exchange plus weathering reactions (41–79 %), and by the retention of SO ₄ ^2? (17–49 %). The maximum net retention of SO ₄ ^2? was 87% in the HietajÄrvi 2 catchment, having the highest proportion of peatlands. Nitrogen transformations played a rather minor role in the H⁺ budgets. The ratio between external and internal H⁺ sources (excluding net base cation uptake by forests) varied between 0.74 and 2.62, depending on catchment characteristics and acidic deposition loads. The impact of the acidic deposition was most evident for the southern Valkeakotinen catchment, where the anthropogenic acidification has been documented also by palaeolimnological methods.     

Hydrochemical modelling of a stream dominated by organic acids and organically bound aluminium

An existing hydrogeochemical model, the Birkenes model (BIM), has been extended to include production of dissolved organic carbon (DOC) in the soil/water system and its chemical interactions with H⁺ and A1³⁺. The model has been calibrated and verified using precipitation and runoff data from the Svartberget catchment in northern Sweden. The catchment is impacted by moderate amounts of sulphur deposition (6 kg S ha^?1 a^?1; the stream is high in DOC (7–35 mg L^?1) and experiences episodically low pH-values (～4.0). The refined BIM is able to simulate the main variations in major chemical components of the stream water (H⁺, Ca²⁺, Mg²⁺, Al_i, Al₀, Cl^?, SO₄ ^?2 and DOC), as well as stream discharge and ¹⁸O, while Na⁺ is not well reproduced. Although very simplified relationships are used for the chemical interactions between DOC and H⁺ and aluminium, the model shows that these interactions are essential to stream acidity and aluminiumspecies content. Some of the model parameters are poorly determined by calibration with runoff data only. Soil and soil water investigations may contribute to the evaluation and development of the model structure and the representation of chemical processes. Further improvements of the model should emphasize DOC-production/absorption, detailed studies on DOC chemical behaviour and hydrological structure.     

Comparing Two Extraction Methods to Evaluate the Composition of Substrate Solution of a Burnt Rice Husk Substrate Used for Carnation Crops

Substrates have been increasingly used in recent years for carnation crops. Burnt rice husk (BRH) is widely available and used as a substrate in Colombia. The present work aims to compare the effects of two aqueous extraction methods on the chemical contents. Saturated and 1:1 (v/v) extractions were performed in three replications. Ionic forms of the macronutrients (NO₃^?, NH₄⁺, PO₄H₂^?, K⁺, Ca²⁺, Mg²⁺, and SO₄^2?, in meq L^?1), micronutrients (Fe, Mn, Zn, Cu, and B, in mg L^?1), Cl^?, CO₃ H^? in meq L^?1, electrical conductivity in dS m^?1, and pH were analyzed. Except for NH₄⁺, Cl^?, and B the determination coefficient R² was greater than 95 percent. Average values and standard errors of data have been used to define suitable intervals for 1:1 extractions. Proposed intervals for 1:1 extracts are consistent with the saturated extract and therefore are a good tool to optimize the management of fertigation in those crops.     

Spatio-temporal variations in nutrient concentration in soil solution under greenhouse tomato

The aim of this trial was to study the spatio-temporal variability in solution nutrient concentration under intensive greenhouse tomato production, to determine the number of suction-cups needed to obtain a representative sample and the influence by the position in the greenhouses. Twenty sampling points were selected within the greenhouse with one suction-cup per sampling point. One soil solution were sampled per point at weekly intervals to analyze for pH, electrical conductivity, chloride, nitrate, phosphate, sulfate, sodium, potassium, calcium, and magnesium (EC, Cl^?, NO₃^?, H₂PO₄^?, SO₄^2—, Na⁺, K⁺, Ca²⁺, and Mg²⁺) concentrations. The pH, Cl^?, H₂PO₄^?, and SO₄^2? concentrations showed no spatio-temporal variation but EC, NO₃^?, and K⁺ showed temporal variation. The spatial variability in EC, K⁺_, Na⁺, Mg²⁺, and Ca²⁺ can be influenced by microclimate and topography. The numbers of suction cups required for a representative sample ranged from 1 to 10 depending on nutrient.     

Desalination of sea water by akadama soil and akadama soil-inorganic adsorbents mixtures

(pp. 33–39)

The purpose of this study is to investigate utilization of Akadama soil and evaluate its ion removal efficiency for seawater desalination. The chemical composition of the Akadama soil was Al₂₀₃ 0.334 kg kg^?1, SiO₂ 0.470 kg kg^?1, Fe₂₀₃ 0.157 kg kg^?1 by weight. X-ray powder diffraction pattern, electron diffraction pattern and IR spectrum of Akadama soil showed that allophane was the main phase and low crystallinity kaolin was generated from the allophane. The column method was carried out to evaluate seawater desalination efficiency, the best mixture ratio of the Akadama soil (particle size was less than 250 m), aluminum silicate adsorbent, aluminium magnesium adsorbent, and magnesium oxide adsorbent was 3:1:1:1. Removal percentages of Na⁺, Mg²⁺, Ca²⁺, K⁺ and Cl^? from artificial seawater were 87.7, 84.4, 91.1, 97.3 and 90.7%, respectively. In the batch method, where the mixed adsorbent was used for removal of heavy metals from 20 mg L^?1 solution, the removal percentages of Cu²⁺, Ni²⁺, Mn²⁺, Zn²⁺, Cd²⁺ and Pb²⁺ were higher than 98%. The removal percentage of PO₄ from river water was 100%.     

Biotic and abiotic processes controlling water chemistry during snowmelt at rabbit ears pass,Rocky Mountains,Colorado, U.S.A.

The chemical composition of snowmelt, groundwater, and streamwater was monitored during the spring of 1991 and 1992 in a 200-ha subalpine catchment on the western flank of the Rocky Mountains near Steamboat Springs, Colorado. Most of the snowmelt occurred during a one-month period annually that began in mid-May 1991 and mid-April 1992. The average water quality characteristics of individual sampling sites (meltwater, streamwater, and groundwater) were similar in 1991 and 1992. The major ions in meltwater were differentially eluted from the snowpack, and meltwater was dominated by Ca²⁺, SO ₄ ^2? , and NO ₃ ^? . Groundwater and streamwater were dominated by weathering products, including Ca²⁺, HCO ₃ ^? (measured as alkalinity), and SiO₂, and their concentrations decreased as snowmelt progressed. One well had extremely high NO ₃ ^? . concentrations, which were balanced by Ca²⁺ concentrations. For this well, hydrogen ion was hypothesized to be generated from nitrification in overlying soils, and subsequently exchanged with other cations, particularly Ca²⁺. Solute concentrations in streamwater also decreased as snowmelt progressed. Variations in groundwater levels and solute concentrations indicate that most of the meltwater traveled through the surficial materials. A mass balance for 1992 indicated that the watershed retained H⁺, NH ₄ ⁺ , NO ₃ ^? , SO ₄ ^2? and Cl^? and was the primary source of base cations and other weathering products. Proportionally more SO ₄ ^2? was deposited with the unusually high summer rainfall in 1992 compared to that released from snowmelt, whereas NO ₃ ^? was higher in snowmelt and Cl^? was the same. The sum of snowmelt and rainfall could account for greater than 90% of the H⁺ and NH ₄ ⁺ retained by the watershed and greater than 50% of the NO ₃ ^? .     

Soils,surficial geology,and geomicrobiology of saline-sodic wetlands,North Platte River Valley,Nebraska, USA

Saline-sodic wetlands along a 200-km stretch of the North Platte River Valley in western Nebraska, USA lie within an important agricultural region, but their processes, salt mineralogy, and geomicrobiology have not previously been investigated. Putative anthropogenic salinization has long been a concern, yet early historical accounts of widespread surface salts in the area have never been applied as comparative standards. Surface salts in the area originate from soil capillarity and surface evaporation. Thenardite (Na₂SO₄) and/or mirabilite (NaSO₄·10 H₂O) dominate, depending on ambient conditions. Bloedite (Na₂Mg[SO₄]₂·4[H₂O]), halite (NaCl), burkeite (Na₆CO₃[SO₄]₂), and calcite (CaCO₃) are minor constituents. Historical accounts indicate that salts accumulated naturally long before Euramerican settlement, apparently as a result of rock–water interaction in nearby volcaniclastic sediments of the Brule Formation.Ephemeral to permanent water-holding basins in the wetlands contain Na⁺-rich waters that vary widely in electrical conductivity (as high as 159 mS/cm) and in ionic composition, but local spring waters are extremely dilute. Basin floors exhibit a unique type of microrelief, which appears to form by the filling of microlows with water and the dispersal of soil material therein by Na⁺, followed by dewatering and collapse of the soil with drying. Illite dominates basin surface soils, but smectite dominates at depth; high soil pH, available K⁺, and frequent wetting–drying cycles in the wetlands suggest that in-situ illitization may have occurred. Soil crusts and vesicular surface horizons are common as are upward increases in electrical conductivity. The activity of sulfate-reducing microbes forms prominent near-surface horizons of sulfate reduction in saturated soils, which retract or disappear entirely during dry episodes.Saline-sodic wetland soils in the study area change on daily to seasonal scales. Cycles of surface salt development, microbial activity, and microrelief genesis are all controlled by regular wetting–drying cycles and the interaction of ponded surface waters and shallow groundwaters. Relatively unique aspects of microbial ecology and surface processes make the soils important as “geomicrobial reactors” wherein important parts of hydrological and geochemical cycles occur.     

The cation denudation rate as a quantitative index of sensitivity of eastern Canadian rivers to acidic atmospheric precipitation

A model has been developed that relates the cation denudation rate (CDR) of a watershed (the rate that cations derived from chemical weathering are carried off by runoff), the atmospheric load of excess SO₄, and the pH of the river. Chemical and discharge data for rivers in Nova Scotia and Newfoundland were used to develop and test the model, which is based upon the common major ion chemistry of soft surface waters, and may be expressed by three statements: (1) CDR (meq m^?2 yr^?1) ? Excess SO₄ ^?? load (meq m^?2 yr^?1) = HCO₃ ^? (meq m^?2 yr^?1), (2) HCO₃ ^? (meq m^?2 yr^?1)/Runoff (m³ m^?2 yr^?1) = HCO₃ ^? (meq m^?3), (3) pH = pK + \(pP_{CO_2 } \) ? pHCO₃ ^?. The model in concentration form applies well to lakes. A detailed analysis of the data for the Isle aux Morts River, Newfoundland, is presented, showing that the CDR varies throughout the year, affected by both discharge and seasonal pattern.     

Acidity neutralization mechanism in a forested watershed in Central Japan

The contributions of cation exchange and mineral weathering to the neutralization of acidity in the Jingahata watershed in central Japan were estimated through a laboratory weathering experiment and runoff chemistry measurements. The laboratory experiment was conducted in a stirred-flow reactor for a whole soil sample collected from the C horizon in the watershed. The concentration ratios of base cations (Ca²⁺, Mg²⁺, K⁺ and Na⁺) to Si (BC/Si) released during the steady-state stage of the laboratory experiment were in good agreement with the ratios of the net flux of base cations to the flux of Si in the streamwater (BC _{N ET}/Si _L).This result suggests that the acidity in the watershed is neutralized primarily by mineral weathering without causing a net loss of base cations from exchange sites. The alkalinity/acidity balance estimated for the watershed shows that the total weathering rate of base cations is approximately 3.26 keq ha^?1 yr^?1. Weathering of plagioclase (An₄₁) contributes 83% of the total weathering rate. The dominant acidity source is CO₂ released within the soil horizons, accounting for roughly 85% of the total acidity flux (3.20 keq ha^?1 yr^?1). This high internal production of acidity suppresses the relative importance of atmospheric acidity inputs (0.3 keq ha^?1 yr^?1).     

Effects of Land Use on Hydrochemistry and Contamination of Karst Groundwater from Nandong Underground River System, China

The Nandong Underground River System (NURS) is located in Southeast Yunnan Province, China. Groundwater in NURS plays a critical role in socio-economical development of the region. However, with the rapid increase of population in recent years, groundwater quality has degraded greatly. In this study, the analysis of 36 groundwater samples collected from springs in both rain and dry seasons shows significant spatial disparities and slight seasonal variations of major element concentrations in the groundwater. In addition, results from factor analysis indicate that NO ₃ ^? , Cl^?, SO ₄ ^2? , Na⁺, K⁺, and EC in the groundwater are mainly from the sources related to human activities while Ca²⁺, Mg²⁺, HCO ₃ ^? , and pH are primarily controlled by water–rock interactions in karst system with Ca²⁺ and HCO ₃ ^? somewhat from anthropogenic inputs. With the increased anthropogenic contaminations, the groundwater chemistry changes widely from Ca-HCO₃ or Ca (Mg)-HCO₃ type to Ca-Cl (+NO₃) or Ca (Mg)-Cl (+NO₃), and Ca-Cl (+NO₃+SO₄) or Ca (Mg)-Cl (+NO₃+SO₄) type. Concentrations of NO ₃ ^? , Cl^?, SO ₄ ^2? , Na⁺, and K⁺ generally show an indistinct grouping with respect to land use types, with very high concentrations observed in the groundwater from residential and agricultural areas. This suggests that those ions are mainly derived from sewage effluents and fertilizers. No specific land use control on the Mg²⁺ ion distribution is observed, suggesting Mg²⁺ is originated from natural dissolution of carbonate rocks. The distribution of Ca²⁺ and HCO ₃ ^? does not show any distinct land use control either, except for the samples from residential zones, suggesting the Ca²⁺ and HCO ₃ ^- mainly come from both natural dissolution of carbonate rocks and sewage effluents.     

Chemical and Statistical Analysis of Precipitation in Singapore

The results of chemical analyses of precipitation samples collected in Singapore between August 1997 and July 1998 are presented. Major inorganic and organic ions were determined in 169 rain samples collected using an automated wet-only sampler. The daily sample pH values ranged from 3.49 to 6.54 with a volume-weighted mean of 4.50, and about 88% of the samples had pH values less than 5.0 Nss-SO₄ ^2? accounted for about 53 % of the sum of anions in rain, whereas chloride, nitrate, formate, and acetate accounted for the remainder. Rain chemistry data were analyzed using principal component analysis to find possible sources of the measured chemical species. Three components that accounted for 83.5% of the total variance were extracted: sea-spray (Na⁺, Cl^? and and Mg²⁺) and soil particles (Ca²⁺ and K⁺), acid factor (nss-SO₄ ^2?, NO₃ ^?, NH₄ ⁺, and H⁺), and biomass burning (HCOO^? and CH₃COOO^?).     

Physiological responses and adaptive strategies of wheat seedlings to salt and alkali stresses

Abstract

Effects of salt (NaCl?:?Na₂SO₄) and alkali (NaHCO₃?:?Na₂CO₃) stresses on the contents of inorganic ions and organic solutes in wheat shoots were compared to explore the physiological responses and adaptive strategies of wheat to these stresses. Wheat significantly accumulated Na⁺ and simultaneously accumulated Cl^?, soluble sugars and proline to maintain osmotic and ionic balance under salt stress. Compared with salt stress, the high pH from alkali stress enhanced Na⁺ accumulation and affected the absorption of inorganic anions. To maintain ionic and osmotic balance, wheat accumulated organic acids, soluble sugars and proline. The accumulation of Cl^? and organic acids was the main difference in the physiological responses and adaptive mechanisms to salt and alkali stresses, respectively.     

Analysis of Proton Generation and Consumption of Forest Surface Soils in Hokkaido, Northern Japan

We determined proton budgets of surface soils in a deciduous forest (Df) and a coniferous forest (Cf) of Volcanogenous Regosols in Tomakomai, Hokkaido of northern Japan. The total H⁺ source was 12.9 and 11.6 kmol_c ha^?1 y^?1 at Df and Cf respectively, and the external H⁺ was 1% at Df and 2% at Cf. The primary H⁺ sources were vegetation uptake of base cations and nitrification, while the major H⁺ sinks were release of base cations and NO₃ ⁺ uptake by vegetation. Leaching incubation experiments using A horizon soils including Df and Cf with NH₄ ⁺ solutions (5.3, 15.9 mg N L^?1) showed that H⁺ from nitrification was generally higher in the Df soil than Cf soil, and nitrification of Tomakomai Df soil was the highest in both treatments. Results of multiple regression analyses suggested that pH_kCl and exchangeable Ca²⁺ contributed to the H⁺ generation via nitrification. Leaching experiments with dilute HCl (pH 3.3) revealed that cation release (mainly Ca²⁺) occurred, and the proportion of release by decrease of exchangeable cations was higher than that by mineral weathering. Mineral weathering in the Tomakomai soil was higher than the other soils.