Effects of simulated throughfall pH and sulfate concentration on a deciduous forest soil

A model deciduous forest soil (Schaffenaker loamy sand) was treated for 8 mo in the greenhouse in 25 cm reconstructed columns with simulated throughfall at pH 6.0 or 4.0, and SO₄ ^2? levels of 12.8 or 24.8 mg L^?1. Red oak seedlings grown in the microcosms showed no growth or foliar element response to the treatments. Sulfate loading had a greater impact on soil and leachate chemistry than pH. Higher available soil P in the A, horizon was associated with the pH 6.0 and high SO₄ ^2?2 treatment combination. High SO₄ ^2? loading also reduced exchangeable K⁺ in the A_1?. Other soil horizons were unaffected by either treatment. Leachate chemistry was not significantly altered by througfall pH, but significantly greater export of Na⁺, Ca²⁺, Mg²⁺, Al³⁺, and NO₃ ^?, and lower SO₄ ^2? loss, occurred with low SO₄ ^? input. Comparatively half as much NO₃ ^? loss was associated with high SO₄ ^2? deposition. The high rate of NO₃ ^? leaching appeared responsible for greater equivalent mass loss of cations from the low SO₄ ^2? treatment. Leachate removal of SO₄ ^2? approximated input after 8 mo. The capacity of this soil to adsorb SO₄ ^2? appeared relatively limited in the absence of normal element cycling. The sulfate component of simulated deciduous forest throughfall was shown to have a potentially greater impact than pH on ion leaching from forest soil. Additional consideration of the role of SO^2? ₄ deposition, in the context of throughfall rather than incident precipitation, is warranted in studies of acidic deposition effects on internal forest soil processes.     

Ion leaching from a sugar maple forest in response to acidic deposition and nitrification

Year-to-year variation in acidic deposition within a mature sugar maple-dominated forest and in leaching of ions from the associated podzolic soil were examined at the Turkey Lakes Watershed between 1981 and 1986. Below-canopy inputs to the soil of SO₄ ^2? and NO₃ ^? in throughfall averaged 640 and 295 eq. ha^?1 yr^?1; the corresponding ranges were 493–917 and 261–443 eq. ha^?1 yr^?1. The contribution of atmospheric deposition to SO₄ ^2? NO₃ ^? and Ca²⁺ leaching decreased over the six years. During the study period, the mean annual volume-weighted NO₃ ^? concentration decreased in throughfall and forest-floor percolate and increased in the mineral-soil solution collected below the effective rooting zone. A substantial shift in the balance between SO₄ ^2? and NO₃ ^?leaching from the mineral soil was observed; leaching of SO₄ ^2?decreased and NO₃ ^? leaching increased with time. Leaching of Ca²⁺ and Mg²⁺ from the soil was increased as a result of excess NO₃ ^? production in the soil. The calculated output of NO₃ ^? from the soil, which averaged 1505 eq. ha^?1 yr^?1, considerably exceeded the atmospheric deposition of NO₃ ^?, whereas SO₄ ^2? outputs were only moderately greater than inputs.     

Nutrient balance in Scots pine (Pinus sylvestris L.) forest. 2. Effects of plant growth and N-deposition on soil solution and leachate chemistry in a lysimeter experiment

Three years of N application to a Cambic arenosol (Typic Udorthent) in two lysimeter series, one with and one without young saplings of Pinus sylvestris L. have produced significant changes in soil solution and leachate chemistry. An application of 30 kg N/ha^*yr^?1 significantly increased NO₃ ^? leaching from the soil. This N load was also sufficient to significantly increase the mobility of the phyto-toxic elements Al³⁺ and Mn²⁺, likewise to increase leaching of the important plant nutrients Ca²⁺, Mg²⁺ and K⁺. At a N load of 90 kg N/ha^*yr^?1 significant increase in NH₄ ⁺ leaching was observed, but total leaching of NH₄ ⁺ was still very low compared to NO₃ ^? leaching. No significant treatment effects were found for SO₄ ^2?, Fe²⁺ and Cl^? in the leachate. Trees grown in the lysimeters buffered the acidifying effect of N application and increased the leachate pH by 0.2 pH units compared to lysimeters without trees.     

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.     

Assessment of Critical Loads in Tropical Sal (Shorea robusta Gaertn. F.) Forests of Doon Valley Himalayas, India

The present study was conducted in tropical Sal forest ecosystem of the Doon valley in the Indian Himalayas to assess the critical load of sulfur and nitrogen and their exceedances. The observed pattern of throughfall ionic composition in the study are Ca²⁺>K⁺>Mg²⁺>Cl^?>?HCO3^?>?Na⁺>NO ₃ ^? >?SO ₃ ^2? ???NH ₄ ⁺ >F^?. The sum of cation studied is 412.29 ??eq l^?1 and that of anions is 196.98 ??eq l^?1, showing cation excess of 215.31 ??eq l^?1. The cations, namely Ca²⁺, Mg²⁺, K⁺, Na⁺, and NH ₄ ⁺ , made a contribution of about 67% of the total ion strength, where as anion comprising of SO ₄ ^2? , Cl^?, NO ₃ ^? , and HCO ₃ ^? contributed 33%. The chief acidic components were Cl^?C (12%) and HCO ₃ ^? (8%), while the presence of SO ₄ ^2? (5%) and NO ₃ ^? (6%), respectively. Percentage contribution of bole to total aboveground biomass was ??72.38% in comparison to 2.24?C2.93% of leaf biomass, 10.34?C10.96% of branch biomass and 13.21?C17.07% of bark biomass. There was high and significant variation (P?<?0.001) in the total aboveground biomass produced at different sites. The aboveground net primary productivity (ANPP) in these sites ranged between 2.09 and 9.22 t ha^?1 year^?1. The base cations and nitrogen immobilization was found to be maximum in bole. The net annual uptake of the base cations varied from 306.85 to 1,311.46 eq ha^?1 year^?1 and of nitrogen from 68.27 to 263.51 eq ha^?1 year^?1. The critical appraisal of soil showed that cation exchange capacity lied between 18.37 and 10.30 Cmol (p+) kg^?1. The base saturation percentage of soil was as high as 82.43% in Senkot, whereas in Kalusidh it was just 44.28%. The local temperature corrected base cation weathering rates based on soil mineralogy, parent material class, and texture class varied from 484.15 to 627.25 eq ha^?1 year^?1, showing a weak potentiality of the system to buffer any incoming acidity and thus providing restricted acid neutralizing capacity to keep the ecosystem stable under increased future deposition scenarios in near future. The appreciable BS of the soil indicates the presence of intense nutrient phytorecycling forces within this climate and atmospheric deposition in replenishing base cations in the soil, which includes intrinsic soil-forming processes, i.e., weathering. The highest value of critical load for acidity was 2,896.50 eq ha^?1 year^?1 and the lowest was 2,792.45 eq ha^?1 year^?1. The calculated value of the minimum critical loads for nitrogen varied from 69.77 to 265.01 eq ha^?1 year^?1, whereas the maximum nitrogen critical load ranged between 2,992.63 and 4,394.45 eq ha^?1 year^?1. The minimum and the maximum critical loads of sulfur ranged between 2,130.49 and 3,261.64 eq ha^?1 year^?1 and 2,250.58 and 3,381.73 eq ha^?1 year^?1, respectively. The values of exceedance of sulfur and nitrogen were negative, implying that in the current scenario Sal forests of the Doon valley are well protected from acidification.     

Retention and Leaching of Elevated N Deposition in a Forest Ecosystem with Gleysols

The responses of nitrogen transformations and nitrate (NO_{_3} ^-) leaching to experimentally increased N deposition were studied in forested sub-catchments (1500 m²) with Gleysols in Central Switzerland. The aim was toinvestigate whether the increase in NO₃ ^- leaching,due to elevated N deposition, was hydrologically driven orresulted from N saturation of the forest ecosystem.Three years of continuous N addition at a rate of 30 kgNH₄NO₃-N ha^-1 yr^-1 had no effects on bulksoil N, on microbial biomass N, on K₂SO₄-extractableN concentrations in the soil, and on net nitrification rates.In contrast, N losses from the ecosystem through denitrification and NO₃ ^- leaching increased significantly. Nitrate leaching was 4 kg N ha^-1yr^-1at an ambient N deposition of 18 kg N ha^-1 yr^-1.Leaching of NO₃ ^- at elevated N deposition was 8 kg Nha^-1 yr^-1. Highest NO₃ ^- leaching occurredduring snowmelt. Ammonium was effectively retained within theuppermost centimetres of the soil as shown by the absence ofNH₄ ⁺ in the soil solution collected with microsuction cups. Quantifying the N fluxes indicated that 80% ofthe added N were retained in the forest ecosystem.Discharge and NO₃ ^- concentrations of the outflow from the sub-catchments responded to rainfall within 30 min. The water chemistry of the sub-catchment outflow showed thatduring storms, a large part of the runoff from this Gleysol derived from precipitation and from water which had interactedonly with the topsoil. This suggests a dominance of near-surface flow and/or preferential transport through this soil. The contact time of the water with the soil matrix wassufficient to retain NH₄ ⁺, but insufficient for a complete retention of NO₃ ^-. At this site with soilsclose to water saturation, the increase in NO₃ ^- leaching by 4 kg N ha^-1 yr^-1 through elevated N inputsappeared to be due to the bypassing of the soil and the rootsystem rather than to a soil-internal N surplus.     

Relationships between microbial biomass nitrogen,nitrate leaching and nitrogen uptake by corn in a compost and chemical fertilizer-amended regosol

Abstract

To determine the relationships between microbial biomass nitrogen (N), nitrate–nitrogen leaching (NO₃-N leaching) and N uptake by plants, a field experiment and a soil column experiment were conducted. In the field experiment, microbial biomass N, 0.5 mol L^?1 K₂SO₄ extractable N (extractable N), NO₃-N leaching and N uptake by corn were monitored in sawdust compost (SDC: 20 Mg ha^?1 containing 158 kg N ha^?1 of total N [approximately 50% is easily decomposable organic N]), chemical fertilizer (CF) and no fertilizer (NF) treatments from May 2000 to September 2002. In the soil column experiment, microbial biomass N, extractable N and NO₃-N leaching were monitored in soil treated with SDC (20 Mg ha^?1) + rice straw (RS) at five different application rates (0, 2.5, 5, 7.5 and 10 Mg ha^?1 containing 0, 15, 29, 44 and 59 kg N ha^?1) and in soil treated with CF in 2001. Nitrogen was applied as (NH₄)₂SO₄ at rates of 220 kg N ha^?1 for SDC and SDC + RS treatments and at a rate of 300 kg N ha^?1 for the CF treatment in both experiments. In the field experiment, microbial biomass N in the SDC treatment increased to 147 kg N ha^?1 at 7 days after treatment (DAT) and was maintained at 60–70 kg N ha^?1 after 30 days. Conversely, microbial biomass N in the CF treatment did not increase significantly. Extractable N in the surface soil increased immediately after treatment, but was found at lower levels in the SDC treatment compared to the CF treatment until 7 DAT. A small amount of NO₃-N leaching was observed until 21 DAT and increased markedly from 27 to 42 DAT in the SDC and CF treatments. Cumulative NO₃-N leaching in the CF treatment was 146 kg N ha^?1, which was equal to half of the applied N, but only 53 kg N ha^?1 in the SDC treatment. In contrast, there was no significant difference between N uptake by corn in the SDC and CF treatments. In the soil column experiment, microbial biomass N in the SDC + RS treatment at 7 DAT increased with increased RS application. Conversely, extractable N at 7 DAT and cumulative NO₃-N leaching until 42 DAT decreased with increased RS application. In both experiments, microbial biomass N was negatively correlated with extractable N at 7 DAT and cumulative NO₃-N leaching until 42 DAT, and extractable N was positively correlated with cumulative NO₃-N leaching. We concluded that microbial biomass N formation in the surface soil decreased extractable N and, consequently, contributed to decreasing NO₃-N leaching without impacting negatively on N uptake by plants.     

Soil response to s and n treatments in a Northern New England low elevation coniferous forest

A field experiment was designed to evaluate the effects of differing forms of acidifying S and N compounds on the chemistry of soils and soil solutions in a low elevation coniferous forest in northern New England. Treatments consisted of O, 1500, 3000, and 6000 eq of SO₄ ^2? or NO₃ ^? ha^?1 for the 1987 growing season applied biweekly as H₂SO₄ or HNO₃, or in a single application as dry] (NH₄)₂SO₄. Acidifying treatments resulted in a significant increase in soil solution SO₄ ^2? (1.2 to 2.6) or NO₃ ^? (12 to 80) in the upper B horizon. Excess strong acid anion leaching was associated with an accelerated loss of base cations, particularly MG²⁺ As solutions passed through the upper 25 cm of the soil profile, mean SO₄ ^2? concentrations decreased by 5 to 50% of the initial values, indicating that much of the applied SO₄ ^2? was immobilized in the upper portion of the pedon. Elevated concentrations of adsorbed and water-soluble SO₄ ^2? indicate that abiotic adsorption of SO₄ ^2? by soils is the dominant mechanism for the initial attenuation of SO₄ ^2? concentrations in these solutions. Other soil properties showed only small or no change due to treatments over the single growing season of this study. These results indicate that H₂SO₄, HNO₃, and (NH₄)₂SO₄ can all effectively increase strong acid anion concentrations in the soil-soil solution system.     

Nitrogen cycling in two Norway spruce (Picea abies) ecosystems and effects of a (NH4)2SO4 addition

Nitrogen cycling in two Norway spruce (Picea abies (L.) Karst.) ecosystems in the ARINUS experimental watershed areas Schluchsee and Villingen (Black Forest, SW Germany) and initial effects of a (NH₄)₂SO₄ treatment are discussed. Although N reserves in the soils are similar and atmospheric N input is the same low to moderate level characteristic for many forested areas in SW Germany, N export by both seepage and streamwater differs considerably. At Villingen, deposited N is almost totally retained in the ecosystem, whereas at Schluchsee N export is the order of the input. This is explained by differences in forest management history. The Villingen site had been subject to excessive biomass export (e.g., litter raking) leading to unfavorable microbial transformations in the soil. In contrast, as a ‘relic’ of the former beech stand, the Schluchsee site is characterized by high biological activity in the soil with vigorous nitrification despite low pH values. Accordingly, the two ecosystems responded differently to the additional N input (150 kg NH₄ ⁺ -N ha^?1 as (NH₄)₂SO₄). Nitrification starting immediately in the Schluchsee soils led to continued Al mobilization and leaching of basic cations and NO₃ ^?. The availability of Mg, already deficient before treatment, further decreased due to Mg leaching and marked N uptake by the stand. In contrast, most of the added N in Villingen was immobilized in the soil. Hence, uptake by the stand and leaching of NO₃ ^? and cations was correspondingly lower than at Schluchsee. The results emphasize the problems associated with the definition of generally applicable values for ‘critical loads’ of N deposition.     

Deposition Patterns of SO4 2−, NO3 − and H+ in the Brazilian Territory

SO₄ ^2?, NO₃ ^? and H⁺ depositions are estimated in the Brazilian territory based on the existing rainfall chemical data and on annual rainfall distribution over the whole territory. Local and regional depositions are estimated. Rainfall chemical data over the Braziliian territory shows that the average pH values are usually low (between 4.0 and 5.5). These values are observed in the tropical Amazon forest as well as in urban areas. However, the rainwater acidity in the tropical forests are due to organic acids naturally produced by the vegetation while in urban areas the acidity is mainly due to acidic anion deposition (NO₃ ^? and SO₄ ^2?). In some Amazonian areas, the average input values through rainfall for NO₃ ^? is about 0.06 keq.ha.yr^?1 and for SO₄ ^2? is between 0.23 and 0.54 keq.ha^?1.yr^?1. On the other hand, in some urban centers, such as São Paulo, values of .072 keq.ha^?1.yr^?1 for NO₃ ^? and 1.16 keq.ha^?1.yr^?1 of SO₄ ^2? are found and in sites where sulfate sources (coal mining) are present, as for the area of Florianópolis, values as high as 5.59 keq.ha^?1.yr^?1 for SO₄ ^2? are found.     

Does the potential ammonium fixation of soils have an impact on the optimum nitrogen fertilizer rate?

Field experiments were conducted to determine the effect of nitrogen (N) fertilizer forms and doses on wheat (Triticum aestivum L.) on three soils differing in their ammonium (NH₄) fixation capacity [high = 161 mg fixed NH₄-N kg^?1 soil, medium = 31.5 mg fixed NH₄-N kg^?1 soil and no = nearly no fixed NH₄-N kg^?1 soil]. On high NH₄⁺ fixing soil, 80 kg N ha^?1 Urea+ ammonium nitrate [NH₄NO₃] or 240 kg N ha^?1 ammonium sulfate [(NH₄)₂SO₄]+(NH₄)₂SO₄, was required to obtain the maximum yield. Urea + NH₄NO₃ generally showed the highest significance in respect to the agronomic efficiency of N fertilizers. In the non NH₄⁺ fixing soil, 80 kg N ha^?1 urea+NH₄NO₃ was enough to obtain high grain yield. The agronomic efficiency of N fertilizers was generally higher in the non NH₄⁺ fixing soil than in the others. Grain protein was highly affected by NH₄⁺ fixation capacities and N doses. Harvest index was affected by the NH₄⁺ fixation capacity at the 1% significance level.     

Chemical Composition of Precipitation, Throughfall and Soil Solutions at Two Forested Sites in Guangzhou, South China

Rain water at two forested sites in Guangzhou (south China) show high concentrations of SO₄ ^2?, NO₃ ^? and Ca²⁺ and display a remarkable seasonal variation, with acid rain being more important during the spring and summer than during the autumn and winter. The amount of acid rain represents about 95% of total precipitation. The sources of pollutants from which acid rain developed includes both locally derived and long-middle distance transferred atmosphere pollutants. The seasonal variation in precipitation chemistry was largely related to the increasing neutralizing capacity of base cations in rainwater in winter. Soil acidification is highlighted by high H⁺ and Al³⁺ concentrations in soil solutions. The variation in elemental concentration in soil solution was related to nitrification (H⁺, NH₄ ⁺ and NO₃ ^?) and cation exchange reaction (H⁺, Al³⁺) in soil. The negative effect of soil acidification is partly dampened by substantial deposition of base cations (Ca²⁺, Mg²⁺ and K⁺) in this area.     

The effect of potassium chloride on ion dynamics and – budget in a slightly acidic forest soil

In a laboratory study, KCI- a neutral salt - equivalent to 300kg K/ha and 272 kg CI/ha was applied to the surface of undisturbed columns of a forest soil (Terra Fusca Rendzina) under steady state unsaturated flow conditions (1.0 cm/day). The effluent of the five soil columns was collected daily, and pH, cation- and anion concentrations were measured. Most of the applied K ions were retained in the top 10cm of the soil and moved in decreasing amounts further down the column. Among the cations studied Ca⁺⁺, Mg⁺⁺, and Na⁺ were lost from the system, K⁺, NH₄, Fe⁺⁺⁺, Mn⁺⁺, H⁺, and Al⁺⁺⁺ were retained. Nitrate and sulfate concentrations in the leachates showed a temporary decrease when CI passed through the columns. This decrease was accompanied with a decrease in pH. CI^?, NO₃^?, and SO₄^? exhibited leaching losses. Besides these anions, HCO₃^? played an important role.     

三峡库区2种土地利用方式下土壤盐基离子及碳氮含量对氮添加的响应

为探究三峡库区2种土地利用方式下土壤交换性盐基离子及土壤碳氮含量对氮添加的响应,以湖北省秭归县的林地和果园土壤为研究对象,进行室内土柱淋溶模拟试验,研究4种不同氮添加量(0,50,120,200 kg/(hm²·a))下,土壤中交换性Ca²⁺、Mg²⁺、Na⁺、K⁺以及NO₃^--N、DOC的变化。结果表明：随着氮添加量的增加,林地土壤中的交换性盐基离子淋失量显著增加(p<0.05),而果园土壤中的交换性盐基离子淋失量无显著变化,且林地土壤中交换性盐基离子淋失总量与各盐基离子淋失量均高于果园土壤;经N1、N2、N3处理后,与对照组(N0)相比,林地土壤中的交换性盐基离子淋失总量分别增加1.78%,4.45%,8.49%,且NO₃^--N淋失量分别增加89.21%,77.73%,157.25%,说明氮添加通过加剧土壤中NO₃^--N的淋失带走土壤中交...     

Influence of acid deposition on element cycling in mature sugar maple forest,Algoma, Canada

Forestry studies were undertaken within the Turkey Lakes Watershed to determine the impact of long-range transport of air pollutants on biogeochemical processes in old-growth sugar maple forest on shallow Precambrian-derived till soils in the Algoma District of Ontario, Canada. Distributions of organic matter and macroelements were determined in the tree- and field-layer vegetation, the forest floor and the mineral soil of the study site. Annual tree growth was largely offset by mortality, resulting in a relatively stable standing stock of ca. 245 t ha^?1. Annual aboveground litter production averaged 3.7 t ha^?1 yr^?1, chiefly in the form of deciduous leaf fall. The average pH of the precipitation (4.3) was reduced considerably by contact with the forest canopy. Throughfall was enriched with other elements, principally K and, to a lesser extent, Ca and Mg. The cationic composition of the forest-floor percolates, on the other hand, was dominated primarily by Ca and only to a lesser extent by Mg and K. The stand receives moderate acid deposition, mainly from average inputs of 33–36 kg ha^?1 yr^?1 of SO₄ ^2? and 24–29 kg ha^?1 yr^?1 of NO₃ ^? distributed throughout the year. Atmospheric inputs add to substantial natural NO₃ ^? production, notably within the forest floor and upper mineral soil, and contribute to leaching of bases, principally Ca and Mg, from the rooting zone. Active recycling of elements together with weathering of primary minerals should assist in preserving the base status of the site.     

Annual Element Budget of Soil in Snow-Dominated Forested Ecosystem

Seasonal fluctuation of concentration and flux of major inorganic ions in throughfall, stem flow, snowpack and soil solution was investigated at a natural cool temperature mixed forest in Hokkaido, northern Japan, in order to clarify the effect of snowmelt on the solute dynamics in the forest soil in snow-dominated region. Na⁺, Ca²⁺, Mg²⁺, Cl^? and SO₄ ^2? concentrations in soil solution showed a large fluctuation in the snowmelt period. The percentage of output of these elements from soil during the snowmelt period in the annual output was as follows. Mg²⁺: 51%, Na⁺ and Cl^?: 59 and 60%, SO₄ ^2?: 65%, Ca²⁺: 77%. Our results indicated that the snowmelt event was very important to quantify the annual elemental budgets in this region. Although the leaching of base cation from the soil was larger than that of inputs and accumulation into the vegetation, annual decreasing rate of acid neutralization capacity (ANC_(s)) from the soil was mostly affected by the base cation accumulation into the vegetation, related that the base cations weathering accompanied with bicarbonate was slow due to the acidic and weathered soil in the studied site. It is suggested that the weakly acidic soil which has low ANC_(s) in snow-dominated region will be relatively sensitive to the future increase of acidic deposition.     

Cation transport during unsaturated flow through two intact soils

In the quest for better understanding of cation movement through undisturbed soils, leaching experiments on 300-mm long undisturbed soil columns of two contrasting soils were carried out. One soil was a weakly-structured alluvial fine sandy loam, the other a well-structured aeolian silt loam. About 2000 mm of solutions of MgCl₂ and Ca(NO₃)₂ of 0·025 M were applied at unsaturated water flow rates of between 3 and 13 mm h^?1. Solute movement was monitored over several weeks by collecting effluent under suction at the base. In the sandy loam anion transport was influenced by exclusion from the double layer, whereas in the Ramiha soil anion adsorption occurred. Cation transport was described by coupling the convection-dispersion equation with cation exchange equations. Good simulations of the Mg²⁺ and Ca²⁺ concentrations in the effluent and on the exchange sites were obtained if 80% of the exchangeable cations, as measured using the 1 M ammonium acetate method, were assumed to be active. Local physical or chemical disequilibrium did not need to be explicitly taken into account. About 400 kg ha^?1 of native potassium was leached from the alluvial soil, but only about 10 kg ha^?1 was leached from the aeolian soil. The convection-dispersion equation coupled with exchange theory was found to describe cation transport under unsaturated flow through undisturbed soil satisfactorily.     

Sources of acidity in forest-floor percolate from a maple-birch ecosystem

Ion concentrations in water collected within a forest of sugar maple and yellow birch at the Turkey Lakes Watershed near Sault Ste. Marie, Ontario were examined from 1982 to 1984 to determine sources of acidity and the extent of cation leaching from forest floor horizons. Volume-weighted concentrations and ion fluxes in throughfall and forest-floor percolate during the growing and dormant seasons were calculated. Hydrogen ion content of the forest-floor percolate decreased in relation to that of throughfall in the dormant season and increased in the growing season. Hydrogen ion deposition in throughfall could account for 100% of the flux of H⁺ through the forest floor in the dormant period, and 40% of the flux during the growing season. In forest-floor percolate, Ca²⁺ concentrations were positively correlated with those of SO₄ ^2-, NO₃ ^- and organic anions during both dormant and growing seasons. Sources of NO₃ ^- and organic anions within the ecosystem and major external inputs of NO₃ ^- and SO₄ ^2- were critical factors that influenced cation mobility in the forest floor.     

Simultaneous nitrification and diffusion in soil. III. The effects of the addition of ammonium sulphate

The simultaneous nitrification and diffusion of NH₄⁺, applied as ammonium sulphate to laboratory columns, was followed experimentally and with a simulation model. Ammonium was applied as a fertilizer band at levels equivalent to 69 kg N ha^?1 to a 1 cm depth. The concentration profiles of NH₄⁺, NO₃^?, SO^2?₄ and pH were measured in two columns for incubation times of 214 and 286 h. The simulation model provided for the precipitation and ion pair formation of CaSO₄, the adsorption equilibria of NH₄⁺ and soil acid with the soil solid phase, and nitrifier growth and activity. In general, good agreement was found between the experimental and simulated concentration profiles. The effect of CaSO₄ precipitation on the diffusion of N was investigated using model simulations of the diffusion of NH₄⁺ in the absence of nitrification. The simulations suggested that the reactions of SO^2?4 in the soil could markedly affect the spread of NH₄⁺ from a band of (NH₄)₂SO₄.     

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.