Long-term development of element budgets in a Norway spruce (Picea abies (L.) Karst.) forest of the German solling area

To evaluate ecosystem response to changing atmospheric deposition, element budgets were established over the period from 1973 to 1991 for a Norway Spruce (Picea abies (L.) Karst.) site. Budgets for Na⁺, Cl^?, Ca²⁺, Mg²⁺, N, S and H⁺ were based on total deposition and seepage water fluxes. The deposition of Ca²⁺, Mg²⁺, particularly, of S and H⁺ decreased with time, while calculated N deposition remained constant at a high level. The decrease in Ca²⁺ deposition led to a reduction of Ca²⁺ fluxes with seepage water. The decrease of Mg²⁺ deposition did not have an effect on the output fluxes of Mg²⁺. The reversibility of soil and seepage water acidification by reduced S deposition was delayed by the release of previously accumulated soil SO ₄ ^2? . The highest NO ₃ ^? fluxes were observed during the period of 1986 to 1988; NO ₃ ^? fluxes in general demonstrated a considerable annual and periodic variation. Total N accumulation in the ecosystem amounted to nearly 590 kg ha^?1 yr^?1 during the observation period. The major sink of N in the spruce site is the aggrading humus layer. The results emphasize the need for measurements over several years to make conclusions regarding the function of ecosystems in response to atmospheric deposition.     

Acid deposition and lake chemistry in southwest China

A water quality survey has been performed on selected lakes and streams in southwest China. The purpose of the study was to measure the concentrations of acidic deposition and surface water chemistry in a region of severe air pollution, forest decline, and relatively sensitive geology to acidic deposition. We show that, although there are some high elevation lakes of low acid neutralizing capacity (ANC<150μeq L^?1, acidification of lakes has not occurred in southwest China due to production of base cations in soil and dry deposition of dust that serves to neutralize acidic deposition. Water chemistry is buffered by high base cation concentrations (Ca²⁺, Mg²⁺, Na⁺, and K⁺ greater than 300μeq L^?1, and pH values are always greater than 6.5.     

Trends in Soil Water Composition at a Heavily Polluted Site - Effects of Decreased S-Deposition and Variations in Precipitation

Precipitation, soils and soil water in a forested catchment in western Poland have been studied during the period 1992 – 96 (see also Vogt et al., this conf.). The S-deposition in the area during the study period was 2 – 3g S m^?2 yr^?1. In spite of decreasing anthropogenic emissions the S-deposition in the area did not change much during the study period mainly because the first years were exceptionally dry. However, the S-deposition was considerably higher during the previous decade. Based on soil water sulphate concentration, pH, acid neutralising capacity and the ratio of Al³⁺/(Ca²⁺ + Mg²⁺), there is apparently an amelioration in the conditions. A study using inter alia principal component analysis, indicates that this improvement is mainly due to more precipitation in the later part of the study period. Variations in precipitation amount have a pronounced effect on the soil-water chemistry, which makes it difficult to establish trends caused by changes in anthropogenic deposition. Long time series are therefore necessary to establish recovery due to reduced S-emissions.     

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.     

Simulated effects of climate change and acid deposition on soil chemical conditions in a Masson Pine forest of SW China

In SW China, acid deposition has been associated with forest damage such as defoliation and mortality due to serious soil acidification. These effects may be exacerbated by ongoing climate change. Understanding the integrated effects of climate change and acid deposition on soil chemistry of forest ecosystems is the key to alleviate forest damage and recover forest health. In particular, the long‐term development of integrated effects is unclear and, thus, prevents setting up cost‐effective controls of atmospheric deposition for improved forest‐health management. We employed the Nutrient Cycling Model (NuCM) to predict the changes of soil chemistry in a Masson pine (Pinus massoniana) forest at Tie‐Shan‐Ping (nearby Chongqing, the biggest city in SW China) under two scenarios of climate change and five scenarios of atmospheric deposition. Field‐monitoring data were used to calibrate and validate the NuCM model. It is shown that the maintaining of current acid deposition both in its quantity and composition would not enhance soil acidification although it would take further 20 years to reach a steady state with higher SO$ _4^{2-} $ and Ca²⁺ concentrations in soil solution. This simulated trend is in contradiction to the decrease of soil pH observed in field during last several decades. The possible reason of this may be the obviously elevated deposition of Ca²⁺, which may help to raise the pH of soil solution but occurred only in recent several years following the rapid increase of local construction industry. However, this enhanced Ca²⁺ input may not be maintained for long time. A decreased S input would lead to some positive effects on soil chemistry such as the increase of soil base saturation. A high N deposition has implicated the forest ecosystem to be saturated with N, and increased N input will further aggravate soil acidification and nutrient imbalances. The future climate change projected by IPCC, i.e., the increase of temperature and rainfall may slightly enhance the negative effect of increased N input. The integrated effect of climate change and N‐deposition increase may counteract the positive effects of decreased S input to a considerable degree. This supports the need for a rigorous implementation of new technology to decrease the emission of both S and N.     

Biogeochemistry of two Appalachian deciduous forest sites in relation to episodic stream acidification

Bulk precipitation, throughfall, and soil water chemistry were studied from November 1983 to November 1984 at two ridge-top Appalachian deciduous forest sites to isolate causes of differing episodic stream acidification. The Fork Mountain site in West Virginia, which exhibited little episodic stream acidification, had lower deposition of H⁺ and SO _inf4 ^sup2? and greater reductions of H⁺ in the water circulating through the forest canopy, forest floor, and mineral soil than the Peavine Hill site in Pennsylvania. Greater neutralization at Fork Mountain was linked to higher Ca and Mg carbonate contents in the sandstone and shale soil parent materials. Fork Mountain had greater amounts of exchangeable bases in the organic and mineral soil horizons. Neither site appeared to be accumulating SO _inf4 ^sup2? in the soil, with Peavine Hill losing 56% more than was received in bulk deposition. Anions in soil leachate at Fork Mountain were largely balanced by Ca²⁺ and Mg²⁺, while at the Peavine Hill site A1" was the dominant cation. Results suggest that the typically-low carbonate content of sandstone and shale soil parent materials commonly found in Appalachian forests may be a key parameter controlling soil and stream acidification. Data for the one-year period also suggest bulk deposition of H⁺ was 63% greater at Peavine Hill than Fork Mountain.     

Elevational Patterns of Acid Deposition into a Forest and Nitrogen Saturation on Mt. Oyama, Japan

Virgin fir trees have been dying on Mt. Oyama, which is located in the southwestern part of Kanto Plain, although the frequency of death seems to be reducing recently. We report elevational patterns of acid deposition in precipitation and throughfall under fir and cedar canopies and nitrogen saturation in the forest ecosystem on Mt. Oyama. The deposition fluxes of major inorganic ions in precipitation were nearly constant regardless of elevation except for hydrogen and ammonium ions, whereas the deposition fluxes of all major inorganic ions in throughfall among cedar increased. The 5-year average of annual nitrate deposition in precipitation from 1994 to 1998 showed 19.3 – 23.5 kg ha^?1 yr^?1 (annual inorganic total N deposition: 9.6 – 10.7 kgN ha^?1 yr^?1) at four sites ranging in elevation from 500 to 1252 m, whereas the deposition in both cedar and fir throughfall was over 6 times greater than that in precipitation. The average soil surface nitrate concentration in 1998 was 140 µg g^?1 (the range: 21.1 – 429 µg g^?1, n=80) and the 7-year average of nitrate concentration in stream water from 1992 to 1998 was 4.81 mg L^?1 (the range: 2.38 – 20.6 mg L^?1, n=317). Our results indicate that nitrogen saturation is occurring in the forest ecosystem because of high N deposition, probably via acid fog, on Mt. Oyama.     

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.     

Concentrations and depositions of SO2, SO4 2− etc. in a Chongqing suburban forested area

During the period from 25 May 1991 to 30 May 1992 the atmospheric concentrations and depositions of oxides of sulfur were continuously measured in a suburban masson pine forest which is currently experiencing severe dieback, in Chongqing, China. The annual mean concentrations of SO₂ and particulate SO₄ ^2? were 220 μ g/m³ (77 ppbv) and 32 μ g/m³ respectively. The atmospheric concentrations of these sulfur compounds were high in late autumn and winter. The annual wet and dry depositions of sulfur to the forest as measured by throughfall and stemflow were 93.1 and 46.6 kgSha^?1a^?1 respectively. These depositions are among the highest level ever reported in the world. Althogh the cause of the dieback of the masson pine trees has not been unequivocally determined, it is probable that the direct impact of SO₂ is more likely the cause than acid deposition.     

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.     

Estimation of the Maximum Critical Load for Sulfur in South Korea

The maximum critical load of sulfur and its exceedance by the sulfur deposition of 1994–1997 were mapped for South Korea with a spatial resolution of 11 × 14 km using the steady-state mass balance method. The Korean soil and geological maps were used as basis for the estimations of the critical alkalinity leaching and the weathering rate of base cations. The normalized difference vegetation index data obtained from the Advanced Very High Resolution Radiometer (AVHRR) together with the observed primary productivity of plants were used for the estimation of the critical uptake of base cations. Wet deposition of the non-sea-salt base cations was derived from measured base cation concentrations in precipitation, precipitation rate and air concentration of total suspended particulate while dry deposition of base cations was estimated using the inferential technique using scavenging ratios. The predominant ranges of base cation weathering, uptake and deposition were estimated to be of 200 – 600 eq ha^?1 yr^?1, 200 – 400 eq ha^?1 yr^?1 and 400 – 600 eq ha^?1 yr^?1, respectively. Critical alkalinity leaching was mainly in the range of 1000 – 2000 eq ha^?1 yr^?1 due to relatively high value of precipitation runoff. Exceedance of sulfur critical load was found at 40 % of the ecosystems considered mainly in the southeastern part of Korea, and about 60 % of Korea ecosystems were sustainable against sulfur acidity loadings.     

Simulated Acid Rain Leaching Characteristics of Acid Soil Amended with Bio-Briquette Combustion Ash

In Chongqing City, the rapid growth of the economy has accompanied an increase of sulfur dioxide emissions from coal combustion, bringing about an expansion of acid rain affected areas and acidification of soil. Recently, we reported that coal-biomass briquettes so-called bio-briquettes (BB), which are produced from pulverized raw coal, biomass, and a sulfur fixation agent (Ca (OH)₂) under 3 to 5 tons cm^?2 pressure, have high sulfur-fixation efficiency. The BB ash contains nutritive substances such as Ca and Mg, and has a large acid-neutralizing capacity. Thus, in order to improve the acid soil in the Chongqing area, we analyzed the chemical composition of the original acid soil and the ash-amended soil, and investigated their leaching characteristics under simulated acid rain (SAR). It was found that plants and crops in Chongqing area would be injured if the present acid rain continues. We carried out a SAR leaching experiment and studeid the potential toxic effects of leachate from soil containing added ash. The results indicated that the contents of most toxic elements, with the sole exception of chromium, were below the environment standard for irrigation water. Because the BB ash was highly alkaline, the leaching aluminum (Al) species would be hydroxide rather than free Al³⁺ ion.     

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.     

Calculating critical loads of acid deposition with PROFILE — A steady-state soil chemistry model

A steady state soil chemistry model was used to calculate the critical load of acidity for forest soils and surface waters at Lake GÄrdsjön in S.W. Sweden. The critical load of all acid precursors (potential acidity) for the forest soil is 1.64 kmol_c ha^?1 yr^?1, and 1.225 kmol_c ha^?1 yr^?1 for surface waters. For the most sensitive receptor, the critical load is exceeded by 1.0 kmol_c ha^?1 yr^?1, and a 80% reduction in S deposition is required, if N deposition remains unchanged. The critical load is largely affected by the present immobilization of N in the terrestrial ecosystem which is higher than the base cation uptake. The model, PROFILE, is based on mass balance calculations for the different soil layers. From measurable soil properties, PROFILE reproduces the present stream water composition as well as present soil solution chemistry. The model calculates the weathering rate from independent geophysical properties such as soil texture and mineral composition.     

Effects of Zeolite on Soil Nutrients and Growth of Barley Following Irrigation with Saline Water

ABSTRACT

Soil salinity is a major abiotic factor limiting crop production but an amendment with synthetic zeolite may mitigate effects of salinity stress on plants. The objective of the study was to determine the effects of zeolite on soil properties and growth of barley irrigated with diluted seawater. Barley was raised on a sand dune soil treated with calcium type zeolite at the rate of 1 and 5% and irrigated every alternate day with seawater diluted to electrical conductivity (EC) levels of 3 and 16 dS m^?1. Irrigation with 16 dS m^?1 saline water significantly suppressed plant height by 25%, leaf area by 44% and dry weight by 60%. However, a substantial increase in plant biomass of salt stressed barley was observed in zeolite-amended treatments. The application of zeolite also enhanced water and salt holding capacity of soil. Post-harvest soil analysis showed high concentrations of calcium (Ca^{2 +}), magnesium (Mg^{2 +}), sodium (Na⁺), and potassium (K⁺) due to saline water especially in the upper soil layer but concentrations were lower in soils treated with zeolite. Zeolite application at 5% increased Ca^{2 +} concentration in salt stressed plants; concentrations of trace elements were also increased by 19% for iron (Fe^{2 +}) and 10% for manganese (Mn^{2 +}). The overall results indicated that soil amendment with zeolite could effectively ameliorate salinity stress and improve nutrient balance in a sandy soil.     

Atmospheric Deposition and Re-Emission of Mercury Estimated in a Prescribed Forest-Fire Experiment in Florida, USA

Prescribed fires are likely to re-emit atmospherically deposited mercury (Hg), and comparison of soil Hg storage in areas affected by prescribed fire to that in similar unburned areas may provide cross-validating estimates of atmospheric Hg deposition. Prescribed fires are common in the southeastern United States (US), a region of relatively high Hg deposition compared to the rest of the US, and are thus a potentially significant source of re-emitted atmospheric Hg. Accordingly, Hg was determined in soil layers of a prescribed fire experiment in a Florida longleaf pine forest. The Hg deficit in the annually burned forest floor relative to the forest floor unburned for 46 years (0.180 g ha^?1?yr^?1) agreed to within 5% of an independent estimate of Hg deposition for this site based on a regional monitoring network and computer model (0.171 g ha^?1 yr^?1). Consideration of other potential inputs and outputs of Hg suggested that atmospheric deposition was the primary input of Hg to the site. If extrapolated, these results suggest that prescribed fires in the southeastern US mainly re-emit atmospherically deposited Hg and that this re-emission is less than 1% of total US anthropogenic emissions. However, emissions at other sites may vary due to the possible presence of Hg in underlying geological strata and differences in fire regime and levels of atmospheric Hg deposition.     

Cumulative Effect of Soil and Foliar Application of Nitrogen,Phosphorus, and Sulfur on Growth,Physico-Biochemical Parameters,Yield Attributes,and Fatty Acid Composition in Oil of Erucic Acid-Free Rapeseed-Mustard Genotypes

ABSTRACT

The feasibility of split (soil + foliar) applications of nitrogen (N) and phosphorus (P) and addition of a small quantity of sulfur (S) in the spray was tested for improving performance of rapeseed-mustard genotypes in a factorial randomized field experiment. Three genotypes (two erucic acid free, viz. Brassica napus L. cv. ‘Hyola PAC – 401’ and Brassica juncea L. Czern. and Coss. cv. ‘TERI (0E) M 21-Swarna’, and one best performing high yielding Brassica juncea L. cv. ‘Rohini’ as a check) were grown with four soil (B) plus foliar (F) applications of N, P, and S with uniform basal 30 kg potassium (K) ha^{? 1} (K₃₀), viz. (i) the optimum soil-applied treatment supplemented with the spray of deionized water (B_N90P30 + Fw) comprising control, (ii) B_N70P30 + F _N20, (iii) B_N70P28 + F_N20P2, and (iv) B_N70P28 + F_N20P2S2. Soil Plus foliar application of nutrients, particularly B_N70P28 + F_N20P2S2, improved their performance with respect to growth characteristics (shoot length plant^{? 1}, leaf number plant^{? 1}, area leaf^{? 1}, leaf area index, fresh weight plant^{? 1}, and dry weight plant^{? 1}), physico-biochemical parameters (net photosynthetic rate, stomatal conductance, carboxylation efficiency, water use efficiency, carbonic anhydrase activity, leaf NPK content, and N use efficiency), yield attributes (pod number plant^{? 1}, seed number pod^{? 1}, 1000-seed weight, seed yield ha^{? 1}, oil content, and oil yield ha^{? 1}), and fatty acid composition in oil of these genotypes. The cultivar ‘Hyola PAC-401’ performed best particularly with B_N70P28 + F_N20P2S2. The improvement in the response of genotypes to the split application of nutrients may be attributed to their ready availability through foliar application.     

Studies of Soils, Soil Water and Stream Water at a Small Catchment near Guiyang, China

Acid deposition is considered to be a major environmental problem in China, but information about effects on soils and waters is scarce. To contribute to increased knowledge about the problem a small catchment (about 7 ha) in the outskirts of Guiyang, the provincial capital of Guizhou in south-western China, was instrumented for collection of precipitation, throughfall, soil water and stream water. In addition soil samples have been collected and analyzed for key properties. Median pH in the precipitation is 4.40 (quartiles: 4.19 and 4.77) and the median sulfate concentration 228 µeq/L (quartiles: 147 and 334 µeq/L). The dry deposition of both SO₂ and alkaline dust is considerable. The sum of wet deposition of sulfate and dry deposition of SO₂ has been estimated to about 8.5 gSm^-2yr^-1. The total S-deposition may be somewhat higher due to dry deposition of sulfate and occult deposition. In soil water, SO₄ ^2- is the major anion, generally ranging from 300 to 2500 µeq/L in the different plots. Calcium is an important cation, but there is also a considerable contribution of aluminum from the soil. In some of the plots the concentrations of inorganic monomeric aluminum (Ali) are typically between 200 and 400 µm. Potential harmful levels of aluminum and/or high Ali/(Ca²⁺ + Mg²⁺) molar ratios occur in the catchment, but damages to vegetation have not yet been reported. In most cases exchangeable aluminum accounts for between 75 and 95% of the total effective cation exchange capacity (CEC_E) in the mineral soils. The aluminum chemistry cannot easily be explained by conventional models as the Gaines-Thomas ion-exchange equation or equilibrium with an Al(OH)₃ mineral phase. The stream water is generally less acidic and has considerably lower concentrations of aluminum than the soil water, even though quite acid events have been observed (pH < 4.4). The median pH values are 4.9 and 5.0 in the two first order streams and 6.3 in the dam at the lower boarder of the catchment.     

Long-Term Evaluation of Acidic Atmospheric Deposition on Soils and Soil Solution Chemistry in the Daniel Boone National Forest,USA

Combustion of fossil fuels has contributed to many environmental problems including acid deposition. The Clean Air Act (CAA) was created to reduce ecological problems by cutting emissions of sulfur and nitrogen. Reduced emissions and rainfall concentrations of acidic ions have been observed since the enactment of the CAA, but soils continue to receive some acid inputs. Many soils sensitive to acid deposition are found to have low pH, a loss of base cations, and a shift in the mineral phase controlling the activity of Al³⁺ and/or SO₄ ^2?. If inputs continue, soil may be depleted of base cations and saturated with Al and could cause low forest productivity. Soil samples and soil solutions from pan lysimeters were taken on ridge-tops in the Daniel Boone National Forest to evaluate potential impacts of acid deposition recently and in the future. Sample results were compared to historical data from identical locations. Physicochemical characteristics of the soils revealed that sites were very low in base saturation and pH and high in exchangeable acidity, illustrating change since previously sampled. Soil solution data indicated that sites periodically received high acid inputs leading to saturation of Al in soils and the formation of Al-hydroxy-sulfate minerals. Given these conditions, long-term changes in soil chemistry from acid deposition are acknowledged.     

Soil changes induced by air pollutant deposition and their implication for forests in central Europe

A survey of leaf and needle losses of European forests in 1993 revealed that 23% of the total forested area had defoliation of more than 25%. The focus of this defoliation is in Central Europe, namely in Poland, Slowakia, Czech Republic, and Germany. The annual surveys of leaf losses and discoloration indicated only small changes during the last years for the coniferous forests in Germany. However, the increasing leaf losses of oak and beech during the last years were alarming. Evaluating the potential relation between air pollutant deposition, soil changes and forest damage, we focus here on the recent changes in deposition and soil conditions, and their implication on tree root development and drought susceptability of trees. While deposition of SO₄ ^2?, H⁺ and Ca²⁺ in many Central European forests decreased in the last decade, input of NH₄ ⁺ and NO₃ ^? remained high or even increased. The H⁺ load of many forest soils today is thus still high compared to weathering rates, but the proportion of the H⁺ load resulting from turnover of deposited N has increased. Recent effects of changing depositions on acid forest soils were: depletion of soil Al-pools, release of formerly stored soil SO₄ ^2?, accumulation of N in soil organic matter, increasing N availability to trees and decreasing concentration of Ca²⁺ in the soil solution. We hypothesise that soil acidification and increased N availability will decrease the fine root biomass of trees and shift the rooting zone to upper soil layers. Increased above ground growth, observed in many areas of Europe, will furthermore decrease the root/shoot ratio. This development will finally cause increased drought susceptability of trees and is thus of destabilizing nature. The proposed chain of events might be overlapped by other effects of air pollutants on forest ecosystems, namely direct effects of gases on leaves, nutritional inbalances, and interactions with pests.