Effect of Simulated Acid Rain on Sulfate Movement in Acid Forest Soils1

B. R. SINGH, G. ABRAHAMSEN, AND A. SiUANEs2

ABSTRACTThe effect of simulated acid rain on sulfate mobility in iron-

podzol and semipodzol (Typic Udipsamments) forest soils ofsouthern Norway was studied. The study was carried out withlysimeters with undisturbed soil. The lysimeters were wateredwith 'rain" having pH 5.6 and 4.3. It was found that sulfatemobility was higher in the semipodzol than in the iron-podzoland it was dependent on their sulfate adsorption capacitieswhich in their turn were dependent on Al contents of thesesoils. Sulfate losses from applied MS increased with increasingvolume and decreasing pH of the 'rain". The element losseswere also higher in the semipodzol reflecting further highermobility of sulfate in this soil.

The total sums of cations, on equivalent basis, in the leach-ate from the semipodzol were nearly equal at pH 5.6 and 4.3(0.480 and 0.485 meq liter-1, respectively). In the iron-podzol,however, total sums of cations at pH 5.6 and 4.3 differedslightly (0.314 and 0.387 meq liter-1, respectively).

Additional Index Words: acid precipitation, lysimeters, MS,element budgets.

Singh, B. R., G. Abrahamsen, and A. Stuanes. 1980. Effect ofsimulated acid rain on sulfate movement in acid forest soils.Soil Sci. Soc. Am. J. 44:75-80.

CONCERN FOR THE POSSIBLE effects of acid precipita-tion on cation removal from terrestrial ecosystems

has stimulated interest in the movement of sulfate insoils and especially in natural forest soils not exposedto liming and fertilization. The increased leachingof nutrients from these soils may have deleterious ef-fects on forest production. A number of investigators

have reported that acid leaching reduced the contentsof exchangeable cations and base saturation of soils(Abrahamsen et al., 1976b; Teigen et al., 1976; Haug-botn, 1976; Tamm et al., 1977). Haugbotn (1976)working with 85S found that nearly 60% of the originalexchangeable quantities of Ca, Mg, Na, and K wereleached from a clay free sand with acidified water ofpH 3.0. Cole and Johnson (1977) reported that acidprecipitation and associated SO4

2~ ions accountedfor 25% of the yearly cation removal from a forestsite in Washington. In Hubbard Brook watershed inNew Hampshire (Likens et al., 1977) and Thompsonsite in Washington (Cole and Johnson, 1977), theannual output of sulfate from the ecosystem exceededthe input. In contrast to these sites, a net accumu-lation of sulfate in the Soiling site in central Ger-many (Heinrichs and Mayer, 1977), Walker Branchsite in eastern Tennessee (Shriner and Henderson,1978), and LaSelva site in Costa Rica (Johnson et al.,1979) was reported.

If sulfate is adsorbed by specific adsorption mechan-ism, as is reported (Kingston, 1967), it can be im-mobilized within the soil, but in the process other non-specifically adsorbed anions such as Cl~ and NOs~will be released. Therefore, cation loss may still occuras a result of acid rainfall because released anions willcarry with them cations in order to maintain theelectroneutrality in the leachate. If, however, sulfate

Contribution from SNSF-project FA 38/79 (Sur nedb0rsvirkning pS skog og fisk, "Acid precipitation — Effects on for-est and fish"). Received 9 Apr. 1979. Approved 5 Oct. 1979.

3 Soil Scientists, The Norwegian Forest Research Inst., 1432Aas-NLH, Norway.

76 SOIL SCI. SOC. AM. J., VOL. 44, 1980

is added in heavy amounts, little cation loss will occurdespite the possibility of "anion exchange" with Cl~or NOs", probably because of low initial levels ofadsorbed Cl~ and NO3~ relative to incoming sulfate.It has also been reported that the specific adsorptionof sulfate causes the displacement of zero point ofcharge to lower pH values and the net effect is theincrease in cation exchange capacity, a phenomenonoften observed in the specific adsorption of phosphate(Sawhney, 1974; Rajan, 1978).

Although sulfate is considered mobile in many soils,its mobility, however, depends upon soil characteris-tics, fertilizer practices, and rainfall distribution, thussulfate movement in soils varies greatly (Chao et al.,1962; Hogg and Toxopeus, 1966; Barrow et al., 1969;Williams, 1972; Haque and Walsley, 1974; and" Tilland McCabe, 1976).

Sulfate is generally a dominant anion in acid pre-cipitation of southern Norway where relatively largeamounts of SC>4 (3 to 4 g/m2) are added annually tothe soils through dry and wet deposition. The annualweighted mean H+ concentration of this precipitationcorresponds to pH 4.3 (Dovland et al., 1976). Keep-ing the above points in view it is essential thatstudies on the movement, adsorption and desorptionof sulfate in different soils in relation to the acidityof precipitation be conducted. This may help in eval-uating the potential losses of nutrients in the percolat-ing water as a result of acid precipitation.

The present study, which is a part of a series ofinvestigations on the effects of acid precipitation onthe movement, adsorption and desorption of sulfatein acid forest soils, aims to determine the effect ofsimulated acid rain on sulfate movements and leach-ing of other nutrients in two acid forest soils.

MATERIAL AND METHODSSoil lysimeters from two acid forest soils, viz. an iron-podzol

and a semipodzol, both classified as Typic Udipsamment ac-cording to Soil Taxonomy (Soil Survey Staff 1975), were usedfor this study. The vegetation cover and some of the chemi-cal characteristics of these soils are presented in Table 1, but thedetailed description of these soils is given elsewhere (Abraham-sen et al., 1976a; and Stuanes and Sveistrup, 1979). The lysi-meters were 50-cm long grey PVC tubes with an inside diam-eter of 16 cm. The lysimeters were pressed vertically into thesoil without disturbing the vegetation, and the soil was removedfrom around the cylinders which were then pressed furtheruntil they were filled to a depth of 40 cm. The bottom of the

soil columns was cut using a sharp knife and the columnswere upturned and polyethylene pellets were filled in beforea PVC plate with an outlet for percolating water was weldedat the bottom of the lysimeter. The lysimeters were transportedto the laboratory without the natural profile of the soil beingdisturbed.

The experiment was carried out in the laboratory at roomtemperature. The lysimeters were saturated with distilled water,before the initiation of the experiment, in order to avoid mois-tur variations in the lysimeters. When drainage ceased, 100 mlof solution containing 100 mg of S as K2SO4 labelled with 100,uCi of ^S was spread uniformally on the soil surface. Abovethe lysimeters a funnel with a perforated bottom, composed ofan almost cylindrical PVC vessel, was installed. Artificial rainwater of the same composition as that of natural rain water fromthe southern part of Norway (Table 2) was used. Two pH lev-els of the artificial rain water, viz. 5.6 and 4.3, were used. ThepH was adjusted with H2SO, in order to stimulate H+ and SCV"concentration of the natural rain water and the extra amount ofS added for this purpose in columns with pH 4.3 treatmentwas 14.9 mg.

There were two replications for each treatment. One literof artificial rain water per day was applied for 18 days. About90% of this volume percolated through the lysimeters withinan hour, but at the time of sampling, there was no significantdifference between the volumes of applied rain water and theleachate. The data reported in Fig. 4 are, therefore, based onthe total amount of water applied. After a volume of 2, 6, 10,14, and 18 liters of water corresponding to 100, 300, 500, 700,and 900 mm of precipitation, respectively, had percolatedthe lysimeter, the leachate was analyzed for ^S. One milliliterof leachate was mixed with 10 ml of scintillation liquid andthe activity was measured by liquid scintillation. The activityin the samples was compared with a standard of known specificactivity, determined simultaneously, to calculate the amount of^S present in the solution. For analysis of total contents ofcations and anions in the leachate, samples taken at differentinterval were pooled. The data reported are the total contentsof the pooled samples.

After drainage ceased, soil lysimeters were frozen and cutinto 5-cm sections and each section was then air-dried andthoroughly mixed. The soil samples were extracted with 0.01Mcalcium dihydrogen phosphate for ^S and extractable sulfates.The activity in the extracted solution was measured by themethod mentioned above. Sulfate was determined by auto-analyzer as per procedure developed by Sinclair (1973) and

Table 2—Ionic composition of the simulated rain(from Gjessing et al., 1976).

Cations

Ca2*Mg!*K*NH4*Na*

rag/liter

0.240.180.120.541.29

Anions

so«2-NCVci-

mg/liter

3.031.862.73

Table 1—Vegetation cover and chemical properties of the soils used in the lysimeters.

Soil

Semipodzol(TypicUdipsammentlt

Iron-podzol(TypicUdipsamment) t

1 1*66 Sp€Cl€Sand dominatingground coverspecies

Pinus contortaandDesckampsiaflexuosaPinus abiesandDeschampsiaflexuosa

Chemical properties

Soil texture

Clay: 7.9- 1.2%Silt: 21.1- 3.5%Sand: 71 -95.3%

Clay: 5.0- 2.2%Silt: 22.2- 7.7%Sand: 72.8-90.1 %

Soilhori-zons

AhBs2C

0EBsl

Bs2BeCl

OrganicC

%5.460.750.20

43.302.191.71

0.560.310.16

pH(H,0)

4.65.05.1

4.23.94.3

4.84.95.3

CECUMNH«OAcpH 7.0)

meq/100 g15.85.61.5

102.812.414.8

4.22.31.4

Basesatura-

tion

13.16.67.9

18.85.01.7

3.35.69.1

Dithionite-citrate

extractable

Fe

1.17

1.53

1.170.67

Al

% —

0.33

0.25

0.400.26

Na-pyrophosphate

extractable

Fe

0.26

0.57

0.110.02

Al

0.20

0.24

0.160.09

!

Extract-able SO.

ppm246939

729

36

38122266

t Both the soils were collected from Nordmoen and correspond to profile number 1 and 4 in Stuanes and Sveistrup 1979 and A, and A, in Abrahamsen et al.,1976a.

SINGH ET AL.: EFFECT OF SIMULATED ACID RAIN ON SULFATE MOVEMENT IN ACID FOREST SOILS 77

modified by Ogner and Haugen (1977). Analyses for total con-tents of ions were performed according to methods describedby Ogner et al. (1975). Ammonium was determined by theindophenol method and total nitrogen partly by the samemethod after Kjeldahl digestion or partly by alkaline oxidationwith peroxodisulphate to nitrate (Ogner et al., 1977). Nitratewas reduced to nitrite with subsequent diazotation of sulpha-nilamide and coupling with N-1-naphtyl-ethylendiamine. Po-tassium, magnesium, sodium, manganese, and calcium weremeasured by atomic absorption spectroscopy. Aluminum wasdetermined by autoanalyzer after digestion with potassiumperoxodisulfate (Henriksen 1975).

EXPERIMENTAL RESULTSThe concentrations of extractable SO4 8c 35S at dif-

ferent depths of soil profiles as related to the pH ofartificial rain water are shown in Fig. 1 for the iron-podzol and in Fig. 2 for the semipodzol. The resultswere calculated on a weight basis. In the iron-podzol35S concentration was low in the 0, E, and Bsl horizonsand increased to a relatively high level in the Bs2horizon but dropped further in the Cl horizon to thesame level as that in the 0, E, and Bsl horizons, there-by showing a narrow highest peak in the Bs2 horizon.The distribution patterns under different pH levelsof the leaching rain were slightly different. In thelysimeters leached with "rain" of pH 4.3, higheramounts of 35S were leached to the lower layers ascompared to the lysimeters leached with the "rain"of pH 5.6. The higher application of S (needed toadjust pH) in pH 4.3 treatment seems to be the pos-sible reason for higher mobility of 35S in this treat-ment because specific activity of 35S was decreased.Although the concentration of extractable SO4 wasseveral times higher than that of 35S, the distributionpattern was nearly identical to that of 35S. Leachingof extractable SO4 to deeper soil depths, however,

cm-3-

0

23

30

cm

-3 ~00 E"

23

30

SO4-S CONCENTRATIONmg/kg mg/dm3

20 40 60 80 100 120 200 20 40 60 80 100 120 200—3—————I_____I_____I_____I_____I—t i—I -T.—————'—————I—————I—————I—————'——————LV I——

Extract. 804-6Radioact. SO4-S

mg/kg mg/dm320 40 60 80 100 120 00 20 40 60 80 100 120 200

. -1 _ , . ) , - . . , . 1 ,———I—————I—————\-ff-——I r— r—— ————— ————— —————'—————"—————ty/——

could not be demonstrated. These results also indi-cate that the B horizon of the iron-podzol retainedthe major portion of 35S (80%) as well as that ofnaturally present SO4 (57%).

In the semipodzol, on the other hand, distributionof 35S was different from that in the iron-podzol. Theconcentrations of 35S in the Ah and Bs horizons wererelatively low and increased substantially in the Chorizon. The Bs horizon of the semipodzol containedless than half the amounts of 35S compared to that ofthe Bs horizon of the iron-podzol. The acidity of"rain" appears to have had the same leaching effect onthe 35S as we found in the iron-podzol.

The concentration of 35S in the leachate as well asthe cummulative amounts of 35S leached were cal-culated for different pH levels and after differentvolumes of leaching (Fig. 3). The concentration of35S decreased gradually with increasing volume ofleaching in both the soils. The concentration as wellas percent amounts of 35S leached were higher at pH4.3 than at pH 5.6. They were also higher in the semi-podzol than in the iron-podzol. Total 35S losses inthe iron-podzol and the semipodzol were 5 and 30%,respectively.

The concentrations of different ions in the pooledleachate at different pH levels are presented in Ta-ble 3. The concentrations of almost all ions werehigher in the leachate from the semipodzol than thatfrom the iron-podzol. Total sums of cations, on equi-valent basis, in the leachate from the semipodzol wereequal at pH 5.6 and pH 4.3 (0.480 meq liter"1 and0.485 meq liter""1, respectively), but the leaching ofCa, Mg, Mn, and Al, was higher at pH 4.3 than at pH5.6 as indicated by the element budgets data (Fig. 4).

SO4-S CONCENTRATIONmg/kg mg/dm3

10 20 3O 40 50 60 70 10 20 30 40 50 60 70cm0 -

Bs

cm0 •

PH4.3

Extract. 804-8Radioact SO4-S

PH4.3

mg/kg1,0 2,0 3,0 4fl 50 60 70

mg/dm310 2,0 30 4,0 50 60 70

Fig. 1—Distribution of ^S and extractable SO4-S in an iron-podzol at different pH of the simulated rain.

Fig. 2—Distribution of S and extractable SO,-S in a semi-podzol at different pH of the simulated rain.

78 SOIL SCI. SOC. AM. J., VOL. 44, 1980

Table 3—Effect of the pH of simulated rain on the contents ofcations and anions in the leachate; pH of the

leachate given in the table.Semipodzol Iron-podzol

Nutrients pH5.6 pH4.3 pH5.6 pH4.3mg/liter

CaMgKNaMnAlNO.-NNH4-NSO.-SpH of leachate

4.500.813.252.130.030.06

<0.02<0.02

6.105.36

5.110.912.131.860.060.090.05

<0.025.905.52

1.770.343.691.290.220.21

<0.02<0.02

3.504.55

1.660.556.021.560.110.080.340.154.304.95

zuoa:

QUJIO<UJ

_ 35S leached1=1 35S concen.

0.9

O.8

0.7

OJ6

0.4 gO

0.3 B

0.1

1OO 3OO 5OO 7OO 9OOCUMULATIVE LEACHING (mm)

3O-

20-

10-O

1J?m

1OO 30O 50O 70OCUMULATIVE LEACHING (mm)

900

Fig. 3—Amount of ""IS released from the soils (percent of ap-plied) and its concentration in the leachate during the courseof leaching as related to the pH of the simulated rain. (A,)Semipodzol; (A2) Iron-podzol.

The net loss of Na was, however, higher at pH 5.6.The net losses of N and SC>4 were least affected byacidity of leaching rain. In the iron-podzol, on theother hand, total sums of cations at pH 5.6 and 4.3differed slightly (0.314 and 0.387 meq liter"1, re-spectively) but effects of the acidity of leaching rainwere not consistent and hence a general statement can-not be made. The net losses of Ca, Mg, and Na werehigher in the semipodzol as compared to that of theiron-podzol. On the other hand, net losses of Mn andAl were higher in the iron-podzol. The leaching lossesof nitrate or ammonium from both the soils were verysmall and nitrogen was retained during the study pe-

mg/m2

590 1000 1500 2000 2500 3000 5000

PH5.6A

PH4.3

pHS.6"

pH 4.3

'A3834 »|

'A4379 y>\

x ca1377 |

'A1274 |

200 400 690 800 1000

PH5.6

PH4.3

PH5.6~

A2pH 4.3

y/Asee |

''/A653 |

m Mg144 1

332 |

200040,00 eqoosopo 10,000 1300014000PH5.6

PH4.3"

DH5.6A2

PH4.3

'/////////////. 9376 '/////A\

'///////////, '0384 '///////A

_JK

'////////////, 8980 '//////A|

'////////////. MK'//////AI

500 10pO 1500 2000 25pO

PH5.6A

PH4.3

pH5.6A2

PH4.3

''////////A.756 1

'////////A513 |

Na'/////////.

/////////.247 ]

10,00 2000 30,00 4000 5000PH5.6

AIpH4.3

pH5.6A2

PH4.3

y////y///A*&&>. '////AI

y/////////,w>. ''////A

^ -fcW////////,™'/////AIV/////////,«m/'///ALi

50 100 150 290 250

5,0 10,0 150 290 250

Al

590 1000 15,002000 25,00

NH4+NO3-N

2000 4000 6000 BOpO 10( 00

SO4

Net gains

inputoutput

INet loss

Fig. 4—Nutrient budgets of two acid forest soils as related tothe pH of simulated rain. (At) Semipodzol; (A3) Iron-podzol.(Input/output data are shown on the scale and the valueswritten on the histograms indicate net gain or net loss.)

riod. It should be emphasized here that there were netgains of extractable 35S and SO4, but the iron-podzolaccumulated more S (both ^S and SO4) than the semi-podzol. To slightly higher pH values of the leachatefrom pH 4.3 treatment compared to that from pH5.6, no significant importance could be atached atthis stage because of limited number of observations.This aspect, however, is being further investigated in adetailed study under progress.

DISCUSSIONThe results have demonstrated that SO4 mobility

was higher in the semipodzol than in the iron-podzol.

SINGH ET AL.: EFFECT OF SIMULATED ACID RAIN ON SULFATE MOVEMENT IN ACID FOREST SOILS 79

They have also indicated that about 95 and 70% ofthe applied 35S was retained by the iron-podzol andthe semipodzol, respectively. It was found that SO4adsorption in the iron-podzol profile was nearly threetimes as high as that in the semipodzol (B. R. Singh,unpublished data). Therefore, the differences in themobility of SO4 appear to be caused by the differencesin the adsorption characteristics. Sulphate adsorptionhas been shown to be strongly pH dependent, greateramounts being adsorbed at low pH values (Chao etal., 1965; Gebhardt and Colman, 1974). Slightly lowerpH in the iron-podzol than in the semipodzol mayhave contributed to some extent to their differentbehavior in -sulphate mobility. The Bs horizon of theiron-podzol retained 78% of sulphate adsorbed by thewhole profile but the corresponding value for the Bshorizon of the semipodzol was 52%. Sulfate adsorp-tion has been shown to be positively correlated withthe contents of Al and Fe oxides in the soil (Har-ward and Reisenauer, 1966, Haque and Walmsley,1973), it seems to hold true in this study as welldespite the fact that the total amounts of Al andFe did not differ significantly in the B horizon ofthese soils. But the B horizon of iron-podzol containedhigher amounts of Al, which was found to have ahighly significant correlation with sulfate adsorptionin these soils (B. R. Singh, unpublished data), thanthe corresponding horizon of the semipodzol. There-fore, Al content per se was more important for sulfateadsorption in these soils than the absolute amountsof sesquioxides.

In general, higher losses of nutrients occurred inthe semipodzol than in the iron-podzol as indicatedby the nutrient budgets data (Fig. 4). Higher lossesof SO4 from the semipodzol seem responsible for thisdifference because leaching SO4 ions will carry withthem cations in order to maintain the electroneutralityin the leachate. The effect of leaching acidity of rainon the removal of Ca, Mg, Mn, and Al was also morepronounced in the semipodzol than that in the iron-podzol. As cited earlier, SO4 adsorption has beenshown to regulate the cation removal from a soil pro-file and the sulphate adsorption isotherm of a par-ticular soil will determine the amount of cation re-moval. The response time of a soil to acid leachingcan be related to the slope of the sulphate adsorptionisotherm. For example, the sulphate adsorption perunit change in sulphate concentration was higher inthe iron-podzol than that in semipodzol (Singh's un-published data) and therefore the effect of acid leach-ing in the semipodzol was more pronounced. Therewas net accumulation of sulfur (both radioactive andchemical S) in both the profiles and these results con-cur very well with those reported earlier from similartypes of soils (Teigen et al., 1976) as well as with thosereported by other investigators (Heinrichs and Mayer,1977; Shriner and Henderson, 1978, and Johnson et al.1979). Relatively high accumulation of K in this studyseems to have been caused by the high application ofK through K2SO4 salt.

CONCLUSIONS

From the results presented in this study it couldbe concluded that the mobility of sulfate and theleaching losses of elements were higher in the semi-

podzol than in the iron-podzol and they were charac-terized by the capacity of these soils to adsorb sul-fate. The effect of the acidity of "rain" on SO4mobility was also higher in the semipodzol. The datademonstrate the importance of SO4 mobility in regu-lating the leaching of elements. The semipodzol withrelatively low sulfate adsorption capacity seems moresusceptible to leaching. Both the soils were foundto accumulate sulfur and this tendency seems to sug-gest that in the long-term application of acid rain-fall these soils may not loose cations because specificadsorption of sulfate may cause an increase in cationexchange capacity of these soils thereby helping themto retain cations. This aspect, however, needs fur-ther investigation.

ACKNOWLEDGMENTThe authors wish to thank Mr. K. Steenberg and his staff

at the Isotope laboratory, Agricultural University of Norway,for providing working space and for help in the analysis of""S samples. The assistance from Drs. K. Bjor, G. Ogner, andG. Dollard in the preparation of this manuscript is gratefullyacknowledged.

80 SOIL SCI. SOC. AM. J., VOL. 44, 1980