rates of acid deposition and their interaction with forest canopy and soil in two beech forest...

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This article was downloaded by: [UQ Library] On: 17 November 2014, At: 19:09 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Environmental Technology Letters Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/tent19 Rates of acid deposition and their interaction with forest canopy and soil in two beech forest ecosystems on limestone and Triassic sandstone soils in N. Germany S. P. Sah a & K. J. Meiwes a a Institute for Soil Science & Forest Nutrition , Büsgen Weg 2, Göttingen, 3400, F.R.G. Published online: 17 Dec 2008. To cite this article: S. P. Sah & K. J. Meiwes (1989) Rates of acid deposition and their interaction with forest canopy and soil in two beech forest ecosystems on limestone and Triassic sandstone soils in N. Germany, Environmental Technology Letters, 10:11, 995-1002, DOI: 10.1080/09593338909384821 To link to this article: http://dx.doi.org/10.1080/09593338909384821 PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform. However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content. Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information. Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content. This article may be used for research, teaching, and private study purposes. Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http:// www.tandfonline.com/page/terms-and-conditions

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Page 1: Rates of acid deposition and their interaction with forest canopy and soil in two beech forest ecosystems on limestone and Triassic sandstone soils in N. Germany

This article was downloaded by: [UQ Library]On: 17 November 2014, At: 19:09Publisher: Taylor & FrancisInforma Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House,37-41 Mortimer Street, London W1T 3JH, UK

Environmental Technology LettersPublication details, including instructions for authors and subscription information:http://www.tandfonline.com/loi/tent19

Rates of acid deposition and their interaction withforest canopy and soil in two beech forest ecosystemson limestone and Triassic sandstone soils in N. GermanyS. P. Sah a & K. J. Meiwes aa Institute for Soil Science & Forest Nutrition , Büsgen Weg 2, Göttingen, 3400, F.R.G.Published online: 17 Dec 2008.

To cite this article: S. P. Sah & K. J. Meiwes (1989) Rates of acid deposition and their interaction with forest canopy and soilin two beech forest ecosystems on limestone and Triassic sandstone soils in N. Germany, Environmental Technology Letters,10:11, 995-1002, DOI: 10.1080/09593338909384821

To link to this article: http://dx.doi.org/10.1080/09593338909384821

PLEASE SCROLL DOWN FOR ARTICLE

Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) containedin the publications on our platform. However, Taylor & Francis, our agents, and our licensors make norepresentations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of theContent. Any opinions and views expressed in this publication are the opinions and views of the authors, andare not the views of or endorsed by Taylor & Francis. The accuracy of the Content should not be relied upon andshould be independently verified with primary sources of information. Taylor and Francis shall not be liable forany losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoeveror howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use ofthe Content.

This article may be used for research, teaching, and private study purposes. Any substantial or systematicreproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in anyform to anyone is expressly forbidden. Terms & Conditions of access and use can be found at http://www.tandfonline.com/page/terms-and-conditions

Page 2: Rates of acid deposition and their interaction with forest canopy and soil in two beech forest ecosystems on limestone and Triassic sandstone soils in N. Germany

Environmental Technology Letters, Vol. 10, pp. 995-1002© Publications Division Selper Ltd., 1989

RATES OF ACID DEPOSITION AND THEIR INTERACTIONWITH FOREST CANOPY AND SOIL IN TWO BEECH FOREST

ECOSYSTEMS ON LIMESTONE AND TRIASSICSANDSTONE SOILS IN N. GERMANY

S. P. Sah* and K. J. Meiwes

Institute for Soil Science & Forest Nutrition,Büsgen Weg 2, 3400 GÖTTINGEN, F.R.G.

(Received 17 July 1989; in final form 14 August 1989)

ABSTRACT

From deposition measurements, for the beech forest on limestone soil, it wascalculated that about 60 % of deposited H + ions from the atmosphere werebuffered through the forest canopy prior to leaching on to the soil surface,compared to only 33% for the acid soil ecosystem. Soil internal protonproduction, as expected, was lower (1.5 keq. ha . a"^) in the acid soil thanthe calcareous soil ecosystem (15.3 keq. ha .a"^ ). Two aspects of soilacidification are discussed; leaching of base cations from soil and release oftoxins.

INTRODUCTION

The increasing consumption of fossil fuels has resulted in the increasingflow of noxious substances into the atmosphere. These changed chemicalproperties of the atmosphere have influenced the flows of elements from theatmosphere to the forests and into the forest soils. Therefore, it is necessaryto investigate the amount of deposition of noxious substances (i.e. pollutants)and their effect upon the forest ecosystem. This study is concerned with thosepollutants which deposit protons or have the potential to produce acids in theforest ecosystem, immediately or later. This means that the elements to beconsidered are H, N- and S-compounds because it has been hypothesised that S0£and NO (NO and NO£) produced from the combustion of fossil fuels are precursorsof strong acids in the precipitation (1,2). It is based on the fact that pH ofincident rainfall can not decrease by weak acid (carbonic acid) in eqillibriumwith atmospheric CO2 less than 5.6.

It is important to recognise that there are large variations in thepotential effects of these pollutants upon forest ecosystems due to differencesin soil characteristics and in the amount of pollutants deposited. The objectiveof this paper is to demonstrate the effect of acid deposition on two beechforest ecosystems, which are opposite in respect of the chemical condition ofthe soil; one system with soil derived from limestone and the other systemderived from loess on triassic sandstone.

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It is also observed that the forest canopy may react with the depositedacids as a sink, by buffering H-ions; a process which may depend on soilchemical properties.

The effect of acid deposition on the soil internal proton production isdescribed, which may also be influenced by soil chemical conditions.Furthermore, the effects of soil chemical states on leaching of ions from thesoil are also studied.

METHODS AND SITE DESCRIPTIONS

The two beech forests, situated in N.Germany, were at Gottingen (calcareoussoil, 350 m above sea level, annual precipitation 600 mm) and Soiling (acidsoil, 500 m above sea level, and annual precipitation 1000 mm).

For the deposition measurement of elements, precipitation above and belowthe forest canopy was collected (3). For assessing dry deposition from theatmosphere (interception deposition), the Interception-Model (4) was used. TheSoil Internal Net Proton Production was determined by following H+-producing andH+-consuming processes in the forest ecosystems - 1. accumulation of "excesscation" in biomass increment; 2. accumulation of "excess cation" in humuslayer; 3. H -production by the production of organic acids; 4. Reproduction byinorganic acids ( like HCO3") in the soil; 5. H -production by the retention ofNH-+/NO3" in the soil, deposited from the atmosphere; 6. H+-production by thebuffering of deposited H + ions on the canopy surface.

RESULTS AND DISCUSSIONS

1. The rate of deposition H. S- and N-compounds

The long-term mean values of the rate of precipitation deposition, totaldeposition, and throughfall deposition of the elements H, S- and N-compounds aregiven in Table 1 for both stands. The results presented in this table showdistinctly that Soiling receives more acid formers than Gottingen. The bulkprecipitation contains more acidity in the acid soil ecosystem - 0.82 keq.ha"j".a"j" ( i.e pH — 4.1) - than in the calcareous soil ecosystem - 0.41 keq.ha"1.a'1 ( i.e pH - 4.3). The rates of deposition of S, NH4, N0 3 and total N arealso a little bit more in Soiling.

However, the precipitation deposition does not include complete input fromthe atmosphere. The vegetation will intercept fog, sea-spray, dry salts, soilpollution-derived minerals and gases; a process, which has been suggested asinterception deposition (4). Therefore, a distinction is made betweenprecipitation deposition (wet fall) and interception deposition (dry fall). Theimportance of dry deposition (interception deposition), as compared to wetdeposition, may well increase for the areas where fog or low clouds arefrequent. The investigated areas receive around 1-2 times more interceptiondeposition than precipitation deposition. As compared to other elements, it isdifficult to determine the interception deposition of N due to its variousconvertible forms e.g. NH^-N, NO3-N and N Q and its assimilation by the forestcanopy surface. However, the total deposition of N is estimated here as the rateequivalent to the rate of throughfall deposition, under the assumption thatthere is no considereble assimilation of N by the leaves. In this way, thecalculated rate of total deposition of H, S and N shows that the ecosystemSoiling receives about 30-40 % more input of these elements than Gottingen. Thisappears typical of high elevation forest, where the interception of acidifiedfogs and cloud-droplets are rather higher. Both stands show that 50-70 % oftotal deposition exists in the form of interception deposition.

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2. The interaction between deposited acids and forest canopysurface

Before the rainfall enters the soil, it will pass through the canopy of theforests and experiences a change in acidity during its passage. The followingcan be observed:-

2a. Change in acidity (or pH) in throuphfall

The mean annual rates of total deposition, throughfall deposition andleaching of H+, SO^ , NH^+, NO3" and N from soil are presented in Table 1 foreach investigated site, to observe the changes in acidity caused by canopysurface of forest.

Tab.l The long-term mean rates of deposition (keq. ha" .a" ) of H, N-and S-compounds and their output with percolation water in twobeech forest ecosystems; Gottingen (3? -and Soiling (11), x - 1969-1985, + Sx.

1. Gottingen

1. Precipitation deposition (PD)

2. Interception deposition (ID)

3. Total deposition (TD)( - 1+2)

4. Throughfall deposition (TFD)

5. Output with percolationwater (OP)

2. Soiling

1. Precipitation deposition (PD)

2. Interception deposition (ID)

3. Total deposition (TD)( - 1+2)

4. Throughfall deposition (TFD)

5. Output with percolationwater (OP)

H

0.41(0.02)0.86(0.10)1.27(0.10)0.51(0.04)0.00

0.82(0.05)1.18(0.30)2.00(0.30)1.33(0.05)0.47(0.04)

S

1.16(0.05)1.14(0.13)2.30(0.12)2.30(0.12)2.29

1.45(0.08)1.67(0.19)3.12(0.21)3.12(0.17)2.54(0.24)

NH4-N

0.65(0.03)

-

-

0.86(0.03)0.03

0.85(0.03)-

-

0.96(0.06)0.01(0.006)

NO3-N

0.60(0.02)-

-

0.83(0.02)0.86

0.62(0.02)-

-

0.82(0.04)0.11(0.03)

N

1.(0

-

2.(0

1.

1.(0-

-

2.(00.(0

f

50

• 11)

01.06)04

78.07)

49• 17)04.04)

It is important to recognise that the amount of H + ions is decreasedconsiderably in throughfall of both beech forests. It is also apparent that thethroughfall acidity is higher for the stand on acid soil than those oncalcareous soil. Other studies for mixed hardwood stands (5) confirmed thispattern of throughfall pH. pH-increase in throughfall has been also observedeven for evergreen species, at least in summer (6,7). From these observations,it can be remarked that H ions are taken up by the canopy surface. In otherwords, H + ions are bufferd by the canopy. It has been hypothesized (4) that theH + buffering takes place by a cation exchange process in the leaf tissue, inwhich deposited H-ions from the atmosphere replace the cations in the cell wallof leaves. The mechanisms for this process are discussed below.

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The pH values in stemflow of both beech stands are the smallest incomparison with incident rainfall and canopy drips. The mean pH measured overlongterm, of stemflow for Gottingen amounts to approx. 3.6 and 3.4 for Soiling.Thus, both beech forests show no buffering of H-ions by stemflow. In contrast,it results in the decrease of pH to values even lower than those of incidentrainfall. In the ecosystem on limestone near GSttingen, soil pH around the stembase has been found as low as 3.4, which is suggested to be caused by the directpassage of acidified water of stemflow (9). This points out that stemflow canshift a soil chemical condition up to Al-buffer range even in a calcareous soil.The concentrated acidity in the small area around the base of stem can evencause podzolisation in soil (10). Therefore, it has been suggested (8) that treecorks may even function as sensible indicators of air pollution.

2b. Proton-turnover in canopy

It has already been mentioned that the atmospheric H + ions are buffered bythe forest canopy and to maintain the electroneutrality in plants as well as insoil, plants must either take anions in equal amount from soil or give upcations from the leaves to the soil. It is generally agreed that H+-exchangeoccurs on the leaf surface. The following mechanism of H + bufering has beenhypothesized (4).

In the first step, the exchange of Ca* ions for H ions takes place in thecell-wall of the leaf. This exchanged Ca ions are leached off as CaSO4 fromthe leaf. The second step is the recharge of buffer. Ca ions needed for therecharge of buffers are carried from the soil in combination with HCOo" ions (orweak organic acids), by means of transpiration, to the cell wall or the leaf,already occupied by proton. Here, these protons are neutralised by HCO3* ionswith the release of CO.? and f^O. The third step shows the consequences of Ca-uptake as the soil acidifies. Ca 2 + in combination with S0 4

2" are taken up by theplants from the soil.

1. Proton buffering on leaf surface:

>wf tt V +( Leaching )

Cell""V 2+ . o „+ . en 2- -Cell \u+ . r,2+ . cn 2-Wall f& + 2 H + S04 >WallJH + r _ _ . T 4

2. Re-charge of Buffers:

C e H T + Ca + * HC°3" " " " V e i r ? * + 2 H2° + C°2. Recharge of

C e " H " T +

Wa_U__ii+ (with Transpiration)

3. Soil acidification:Ca 2 + + SO-2" + 2H2CO3 > 2H+ + S0 4

z" + Ca z + + 2HCO3"(Soil solution) (plants) (Soil solution) ( Plants )

During Ca -uptake, to maintain the electroneutrality in soil as well as inplants, the plants must give an equal amount of H+, which generates from H^COo-acid of plants. In the plants, Ca^+ ions are accompanied by HCO2" ions and xnthe soil SO4

2" with H+. From this reaction, it can be concluded that trees canbuffer the acids in the canopy, while at the same time giving protons to thesoil. So, inspite of this H+-buffering in the canopy, the soil remains under anacid load.

The rate of H + buffering depends also upon the type of forest ecosystem.Table 2 shows clearly that about 60 % of total deposited H + ions from theatmosphere are buffered by the vegetation canopy on the calcareous soilecosystem, whereas it is only 33 % by the vegetation canopy on the acid soilecosystem. The higher capacity of H-ion buffering by the ecosystem on limestone

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is assumed to be caused by the higher rate of the cation-exchange process,providing more calcium ions (being of higher base status) to buffer more H+

ions in leaf tissue. The ions leaching in considerable amounts are as K+, Ca ,Mg , Mn and organic anions. The leaching rate of organic anions is calculatedas the difference in Cation-Anion-Balance of precipitation deposition andthroughfall deposition (11). The results obtained show that both stands havealmost same rate of leaching of organic anions (see Table 2).

Table 2. H+-Turnover (keq. ha .a ) in canopy of two beechstands at Gottingen, ~x - 1981-1987,(min-max) andSoiling (11), x - 1969-1985,(min-max) .

Gottingen Soiling

1. Total H -deposition(dry + wetfall)

2. H+-buffering by canopy

3. Canopy leaching ofcations as;

Ca2+

Mg2+

2+Mn'

Sum of Cations4. Canopy leaching of

organic anions .5. (2-3+4)

1.27(0.84-1.57)

0.76(0.59-0.88)

0.54(0 .36-0.73)

0.46(0.27-0.63)

0.14(0.11-0.19)

0.01(0.007-0.01)

1.15

0.23- 0.16

2.00(1.13-2

0.66(0.01-1

0.54(0.21-0

0.35(0.0-0.

0.09(0.0-0.

0.12(0.09-0

1.10

0.28- 0.16

.75)

.22)

.80)

80)

17)

• 14)

* — (calculated from the difference in Cation-Anion-Balanceof precipitation deposition and throughfall deposition.)

The leaching rate of K+-ions is the same in both forest-ecosystems. Asexpected, the rates of leaching of Ca Z + and Mg 2 + ions are higher in Gottingenthan in Soiling. The opposite is true for the leaching rate of Mn (approx. 10times more at Soiling than Gottingen), based on the fact that Soiling issituated on acid brown earth soil. The total cation leaching rate from thecanopy is almost the same in both beech forests. The sum of cation leachingrates shows that it is twice the H + buffering (in both stands), but to maintainthe electroneutrality in soil as well as in plants, the amount of protonsbuffered must be balanced by the amounts of ions leaching from the canopy.However, when one considers the organic anions, then only a small differenceremains between the processes of H+-buffering and cation leaching. Thisdifference may be explained by the possible leaching of SCv and Cl" which isassumed to be zero in this work. Thus, it can be concluded that the hypothesizedmechanisms of H-ion buffering may be true; at least the data does not show anycontradictions.

3. Soil Internal Proton Production (SINP)

The ion cycle in the forest ecosystem is often connected with twoprocesses; biomass production and its mineralisation. In a steady stateecosystem, there must be the same rate of assimilation and respiration according

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to the law of conservation of mass and electroneutrality. Any deviation fromsteady state must result in a net production of protons in the soil. H + producedby all the processes are presented in Table 3. These processes are described asfollows:

Because the pH of calcareous soil is more than 5, there is dissociation ofHoCO-j acid (produced by the respiration of plants and microorganisms) into H +

and HCO2". Soil internal proton production by carbonic acid dissociation, inthe beech forest ecosystem on the limestone, is about 80 % of total soilinternal proton production (14.9 keq.ha .a" 1). As the pH value of the soilsolution of acid soil ecosystem is less than 5, one cannot expect thedissociation of carbonic acids here. In contrast, there is a production andleaching of organic anions from soil, which is calculated from the difference incation-anion-balance of total deposition and output with percolation water. Thisamounts here to about 0.15 keq.ha . a , which is of no importance for thecalcareous soil ecosystem.

Table.3 Total H+-production (TAP) in keq. ha"1.a"1 in twobeech stands: Gottingen (x - 1981-1987) andSoiling (11), x - 1969-1985.

H " * " - p r o d u c t i o n G o t t i n g e n Soiling

1. H~*"-buffering in canopy2. Accumulation of excess base

in the increment of biomass3. Retention of NH4+/or NO3" in

the soil deposited from atmosphere.4. Production of organic acids

in the soil.5. Production of inorganic acids

in the soil.6. Soil internal proton-pro tonproduktion (SINP) (- 1+2+3+4+5)7. Total proton load (TPL)

{SINP + H +( T D ))

:id balance(TAB)

0PJ

( T D )

8. Total acid balance(TAB)[TPL - (H++Al3++Fe3++Mn2+)

0.76

1.26

0.90

0.00

12.0014.92

16.19

+16.17

0.66

0.63

0.24

0.15

0.001.68

3.68

+1.06

OP - Percolation Water

In the calcareous soil ecosystem, soil internal proton production, by excesscation accumulation in biomass, was twice that of Soiling, which can beexplained by the large amount of cation uptake in calcareous soil.

As already mentioned, the considerable amount of N in the form of NH^+-N andNO3-N are transported to the both beech forests. The deposition of N in excessof forest requirement may cause nitrification and N03" leaching. Since,nitrification of NH^ results in the production of proton in the soil, the protonproduction caused by N-deposition can be quantified from the difference ininput-output-balance of NH^ and NOo. It amounts to> 0.9 keq. ha"1.a for thecalcareous soil ecosystem and 0.2 keq. ha .a for the acid soil ecosystem.The higher rate of proton production in the beech forest on calcareous soil iscaused by net output of NOo" i.e. output > input from the soil system (see Table1). In Soiling, on contrary, there is a negligible rate of N-leaching from soilresulting in only a minimum production of proton.

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As earlier mentioned, the H+-buffering in the canopy is connected with theequivalent amount of H+ production in the soil, i.e. the more the H+-bufferingin the canopy, the more the H+- production in the soil. As expected, in thecalcareous soil ecosystem, more H + are produced in the soil by means of thisprocess than in the acid soil ecosystem.

The sum of all the H+-producing processes amounts to approx. 15 keq.ha .ain calcareous soil, whereas it is only 1.7 keq.ha .a"1 in acid soil. In thebeech forest on calcareous soil, 90 % of proton production in the soil is ofinternal origin ( HCO^" leaching and biomass increments) and 10 % by deposition.The opposite is true for the beech forest on acid soil, i.e. 91 % of the protonproduction in the soil results from deposition and only 10 % is of soilinternal origin. Similar results have been reported from Holland (12), where thesoil internal proton production for the forest ecosystem on limestone soilamounts to 16 keq.ha .a and on acid soil up to 5 keq.ha .a . For N«-fixingforest ecosystems from the U.S.A, soil internal proton production by HCOn" -leaching, was found to be up to 24 keq.ha .a (13).

One can deduce the total proton load (TPL) on the soil as the sum of soilinternal proton production (SINP) and total deposition (TD) of H + fromatmosphere on the soil. This results in 16 keq. ha .a for the calcareous soilecosystem, which is mainly caused by weak acids (carbonic acids) due torespiration processes in the soil, and only approx. 4 keq.ha" .a in acid soil,which is here mainly strong acids. This strong acid may lead to the productionof phytotoxins in the soil. The total acid balance (TAB) may be calculated asthe difference between the total proton load (TPL) and the sum of leaching ofcation acids with percolation water from soil. These are discussed below.

4. The effect of acid deposition upon soil

•Acid deposition may lead to soil acidification. The extent of soilacidification is dependent upon the chemical state of the soils. The soil-systemcan pass from one chemical state to another (i.e. "buffer range"), if the protonload of soil exceeds the actual buffer range (14,9), and soil acidification mayoccur. In this course of soil acidificaion, when exchangeable cations of soilsget exhausted, the protons are buffered by reacting with the clay minerallattice and Al-ions are liberated in mineral soil solution. In this way, thesoil acidification has two aspects; leaching of base cations (mainly Ca andMg ) and release of toxins (mainly Al and Mn ).

As expected, total acid balance (TAB) of the beech forest ecosystem oncalcareous soil shows that rates of cation-acid leaching ( < 0.1 keq. ha" .a" )are negligible compared to total proton load (TPL) of the soil (16.2 keq. h a .a " ) . Among base cations, only the rate of leaching of Ca (15 keq. ha" . a )from soil is here extremely high, which is ecologically of less importance,because most of it stems from CaCOj-dissolution by weak acid (such as carbonicacid), causing higher amount of HCO-j" ions production and leaching (12 keq.ha" .a ) from the soil system.

In the case of Soiling (acid soil ecosystem in Al-buffer range), the totalacid balance (TAB) reveals that the difference between cation-acid leaching (2.7keq. ha . a ) and total proton load (TPL) of 3.7 keq. ha .a is only small.This means that about 70 % of the total proton load remains unneutralised, whichcauses Al-dissolution in the soil, and Al-ions are released into the soilsolution (Al3+ - 1.96 keq.ha"1.a"1, Mn - 0.18 keq.ha"1a"1 ). Under the constantincreasing of proton load, the ratio of Al -/Ca -concentration may reachcritical point (15), which may lead to root-injury. More than 50 % of total acidproduction in the acid soil ecosystem of Soiling originates from deposition fromatmosphere. Therefore, it appears that the increase in acid deposition can

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result in production of more cation-acids (or toxins such as Al ), which canlead to destability of the beech forest ecosystem on acid soil (16).

CONCLUSION

From this work, it can be concluded that the rate of H+-buffering by theforest canopy is chiefly dependent upon the soil type. From our studies, it wasobserved that the rate of acid buffering by the forest canopy on the acid soil(lower base status) was distinctly lower as compared to the calcareous soil(higher base status).

The effect of acid deposition upon acid soil can cause 90 % of total acidproduction, whereas it is much lower (10 %) on calcareous soil. In calcareoussoil, 90 % of total acid production is chiefly due to soil internal origin (i.e.mainly due to leaching of HCOo" ions and to some extent "excess cation"accumulation in biomass increment).

The neutralisation of acid load in the soil is dependent upon the characterof the soil, depending upon the base content. In calcareous soil, as expected,the acid neutralisation takes place without the release of considerable amountof acid cations like Al etc., but in acid soil, in contrast, deposited strongacids cause the release of toxins like Al etc., resulting in soilacidification.

REFERENCES

1. G.E. Likens and F.H. Bormann, Science, 184, 1176 (1974).2. L. Granat, Tellus, 24, 551 (1972).3. K.J. Meiwes, M. Haus, H. Gerke, N. Asche, E. Matzner und N. Lamersdorf, Ber.

des Forschzen. Waldökosvstems/Waldsterben des Univ. Göttingen, 7, 68-142,(1984).

4. B. Ulrich, In: Effects of accumulation of air pollutants in forestecosystems, B. Ulrich & J. Pankrath, eds., D.Reidel, Dordrecht, 127-146(1983),

5. D.D. Richter, D.W. Johnson and D.E. Todd, J. Environ. Oual., 12, 263-270(1983).

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