Acid rain

There

Acid rain

were therefore

three hypoth-

eses that had been elevated to truths. Apparently

nobody

attempted to in-

vestigate the validities eses by examining

Acid precipitation and acid soil in freshwater lake chemistry

be disproved

of the hypoth-

whether they could

experimentally

practical observations.

or

by

Yet much work

was devoted to illustrating

the hypoth-

eses. The

Professor Rosenqvist outlines Scandinavian research into acid depositions. He challenges the view that precipitation containing industrially produced sulphur emissions is to blame, and explains his theory that the pFoblem is caused by ion exchange between electrolytes.

two

observations,

tive explanation

which does not con-

flict with general geochemical theory and experience.’ lakes

exist

It

or,

more

concentration

correctly.

the

H+

the acidification

in natural Scandinavian

From

this

arise

of precipitation.

series

from

became accepted as a dogma) that it

tration controlled

was the acid precipitation

acidity

acidification

acidity over time. The theless

does

but the increase in word is ncver-

not quite as unambiguous

as it

ment. There

may appear. When it applies to a lake.

in regions

the matter

considerably

is simple:

it then

that the concentration

of H+

means ions

in

the water has increased.

of Jli

collected in the course of a year

has increased. This to the

may be due partly

concentration

precipitation

of

periods

IIt

in

the

having

in-

creased. and partly to the frequency of acid

precipitation

periods

having

risen. When it applies to soil,

acidification

partly

to the so-

called degree of base saturation

Organization tion

and

Sweden. field

known

Coopera-

(OECD)

research

in

in this

in the 1Y7Os and a

as the SNSF

was produced.

in a

Bill

from

tion

Approval

project

of the pro-

proposal

of soil

has be-

the amount

howev-

of acid raw humus,

forest litter and bog soil within an area has increased over time.

steadily

there have been reports increasing

Scandinavia

Measurements that

in

three to four rise of industry

with

to

further

SO2 emission

in

to be the project’s

Report

the

the theory or

hypothesis.

No 6 of 1976.

In

Special

no doubt

mained - acidity in precipitation

in a district occurs

in

(NaOH)

spring.

rewas

the runoff

the previous

year, but contains

Gradually. hypotheses not

SNSF

actually

cipitation sulphur Later

pH

values With

of the

appears to be

across

Europe.

It

seems clear that the consumption

of

fuel is the main reason

behind

surges in streams, due to short-period acid precipitation arise

during

the pollutants

acid

rivers and lakes are episodic inputs of and second,

autumn

highly acid rainfall

first

by

when

these

there

is

and in spring, when

that have been stored in

the snow deposits

melt.

modified

the

the acidity

in

the pre-

that was to blame, but the

pollutants

in the precipitation.

a research group in Bergen was

able to show that heavy precipitation tionally

weak in acid and excep-

low in sulphur,

yet relatively

rich in sodium and chloride,

caused an

acid surge where the river

water was

about

seven

times

two additional

observations:

more

and now states that it was

very

regions,

of 8.5,

in spring is just as acid as in

in the watercourse.’

The

further

hydroxide

melts to water with a pH-value

fied inland freshwater

resources.

sodium

is mixed with snow so that it

statement

extended

It

evident that even if. where acid runoff usually

have

was

but that they are

has also become

Europe

as

and

of the acid-

dependent on its intensity.

particularly

main objective.’ disprove

ity in precipitation,

deemed to be the cause of the acidi-

fauna

after the second world

widely

for

the

that the

in streams

arise independently

more acid.

has occurred.

war, acid precipitation spreading

aim,

and

pattern.

acid surges

precipitation

in central

acid precipitation

of a

number of lakes in

having lost fish

the lakes have become

to limit

a

of the En-

the foundations continues

Protec-

original

types

thus

sodium.’

following

One can only illustrate

Since the final decades of the 19th century,

‘The

negotiations Europe

(1Y73)

by the Minister

establish

(by weight)

the Environmental

Department

quantity

come more acid. More often,

70

Development

began early

project

rivers greatly

of Economic

In Norway,

vironment:

fossil

that had

soil

The

is

It has been demonstrated so-called

In 1Y6Y, the problem was put to the

soil having decreased, that is. a given

shown

runoff

ject wah given in the Parliamentary

may bc attributed

er.

by

hydrological

not become acidified.

that the quantity

and lakes

determined

such as the

and Odenwald)

by soil profiles.

in brooks

streams

more acid precipitation.

in ~~ci.v.s regions

minutes,

cnviron-

however,

which had been subject to

Black Forest

When it applies to the precipitation. the word may signify

(even

were,

(which

that caused

damage to the Scandinavian

which

weathering

After a few seconds or the water has its I-I+ concen-

10000.’

term

in the water

and acid soil.

of observations,

there has arisen the hypothesis

The

that acid

precipitation.

surface water varies by 8 factor of over not mean acidity.

states

due to ion exchange be-

tween electrolytes Acidity

however.

for an alterna-

were better illustrations

as acidic as the

that had caused the flood

It is easy to prove the two secondary hypotheses to be faulty. The main hypothesis

which states that increasing

amounts of sulphur of rivers

cause acidification

and lakes, is not equally easy

to refute because only sporadic analyses

of precipitation

before

the

last

world war are available. On the other hand,

there

have

been

important

LAND USE POLICY January 1985

Acid

analyses of river and lake water for the period 1910-1925 in Sweden and throughout the world, which show high levels of sulphur before the second world war.’ On the basis of these analyses, it is possible to estil mate the increase in the sulphur con1925. tent of precipitation since Analyses of inland ice in Greenland back to the year 1300 show that the precipitation on Greenland, both then as now, was composed of sulphate in the form of ‘excess sulphate’.6 From these facts it seems more than doubtful that the increase in the acidity of the sulphur content of precipitation can be the main cause of the undisputed river acidification of Scandinavia. During the ‘contact’ conference in JBnk(iping, 15-17 September 1981 it was repeatedly claimed that individual lakes in south Scandinavia had become up to 2 pH units more acidic, which is equivalent to saying that the hydrogen ion concentration has become 100 times greater.’ Even though SNSF have given ground a little and now assumes that the lakes have dropped in pH by 0.5 to 1 unit,’ it was claimed in Jiinkiiping and by SNSF, that the cause of this acidification was the increased sulphur content in the precipitation. The Norwegian SNSF project has shown that there exists a highly significant correlation between H+ concentration and ‘excess’ sulphate in 471 lakes in Sorland.’ The linear regression for all this data corresponds to: H+ = 0.225 SO4 + 4.67. This implies that if excess sulphate is doubled, eg from 50 to 100 microequivalents per litre, the H+ concentration will increase by only about 20%. But as excess sulphate in the precipitation consists of the anthropogenic sulphate which derives from combustion of fossil energy carriers in Europe and a number of other components, this regression will mean that a halving of the sulphur emission will result in less than a 20% improvement in the acidity. By incorporating data from Wright and Snekvik in a diagram,“’ it is possible to note a reasonable spread in the data, even if the regression is significant (from approximately 0.59).

LAND USE POLICY January

1985

I

rain

H + in run-off water os function of anloncontent

Storgama 2.H+ =0.47, .I onion + 9p eqv/l m Storgama

I .Hf=037-I

Ejugn H+=0.05-I 0

I

I

I

20

50

100

”

n

anion + 6.3~ eqv/l r-_095

anion + 4 3p eqv/l r_O 0

I

I

I

150

200

250

I x)0

I

I

350

400

Z SO4 NO, Cl /.L eqv/l

Figure 1. H+ in runoff water in Norway as a function of the content of ‘mobile’ ions. Source: H.M. Stip, E.T. Gjessing and H. Kamben, ‘Importance of the composition of the precipitation for the pH in runoff - experiments with artificial precipitation on partly soil-covered “mini-catchments” ‘, SNSF project, IR 47149, p 34.

Turning to individual catchment areas, by studying a single stream, the regression in the individual catchment area has a very high significance between the sum of chlorine, sulphate and nitrate, and the H+ in the runoff (Figure 1). This regression depends on the biogeochemical conditions in the catchment area and is completely independent of the acidity in precipitation. In Figure 1 it can be noted that if the sum of chloride, sulphate and nitrate in Bjugn is doubled, this will lead to an increase of around 5% in the H+ concentration. If, however the botanical and hence the biogeochemica1 conditions change from those obtained at Bjugn to those found at Storgamma 2, even with constant electrolyte content in the precipitation, 11 times more acidity in the runoff water is obtained. As it can be shown by pollen analysis that significant changes in vegetation have occurred over the past 200 years, it does not therefore seem unreasonable that the acidity at individual sites should have increased by 10-100 times. Against this, it is completely unreasonable for it to have increased by as much as 3-10 times, if the biogeochemical conditions in the catchment area had remained constant and only the chemistry of the precipitation had changed. The belief that acidity in precipita-

tion is the reason for acid lakes has been discredited. Yet the sulphate theory retains many adherents. In the Birkenes area in Aust-Agder in southern Norway, investigated by the SNSF, there is roughly the opposite correlation between sulphur content in the freshwater lakes and their acidity. Gunnar G. Raddum has listed the chemical conditions for ten lakes in the Birkenes district.” All the lakes lie above the highest marine boundary and all in gneiss regions (Table 1). In a recently published work by D.J.A. Brown and K. Sadler,” attention is drawn to the fact that the state of the fish in lakes in Stirland, Norway, lying more than 200 m above sea level, is independent of sulphate concentrations. There is no trend towards more fish in lakes with a low sulphate content, and the conclusion is that reduction of sulphate will not result in any dramatic improvement in the fisheries.

Table 1. Chemical conditions Birkenes. Average value The four most acid lakes The five least acid lakes

Ii+ 25 pequll 1.7 pequ/1

of lakes in so4 96 paqu/l 136 pequll

71

It is characteristic to the theory

of those who cling

that sulphur

emissions

are to blame that when an alternative explanation fication not

of freshwater

was proposed.

investigate

whether

possibly be anything own

reasoning.

lake acidi-

the SNSF there

did

could

wrong with their

Instead

they

set in

flowing and

in unburnt An

Hestssen. August

heavy rain in an upland a lint

region,

of 100 m. it is difficult

after along

to find

the H+ concentration

any area where

does not vary by a factor of two, three

and the runoff

will often

of conifers about

content

autumn

in the lakes to

a small extent

if the same biogeoche-

mica1 conditions ment

area.

remain

Pollen

in the catch-

analysis and other

data show that biogeochemical conditions in the studied acidified areas have undergone significant change recently.” An example of a strongly _ acidified area which had seen extensive grazing and had good fish populations in the 19th and beginning of the 20th century, but where fish seriously declined or died off after the second world war. lies west of Notodden in the Telemark county in Norway. Here there is mostly a very thin organogenic acid soil on a quartzitc rock base. In Ad Soil - Acid Water. the change that has taken place in the use of pasture land and in forestry, particularly in those regions where acidification has now been observed is outlined.” It also draws attention to the fact that it was the acid raw humus that arose (especially where there was heather and conifer forest) which acted with the ions in the precipitation and gave acid runoff water. In order to monitor this situation it was proposed at the contact conference in Jiinkiiping. that both Sweden and Norway should investigate the runoff conditions in districts with strongly acidified water. but should place main emphasis on simultaneous analysis of streams flowing from districts where there had been severe forest fires relatively recently (from S-25 years before the investigation). The acidity of water

72

an

area

is

Here

an

the humus The

area

cover lay

burnt

fire region

to

ranged

and early

The

area is now covered

birch

trees,

raspberry

willow

herb.

After

rain

in late

October,

the

three

and

which flow out from the burnt area at fIest&en IYXI,

were sampled as

also

were

on 5 October three

similar

2 km to the east of the burnt area. In the latter area whose height ranged from 375 to 376 m. the subsoil was also quartzite and the vegetation was the same as originally eiisted at Hestisen, namely pine. spruce and heather. The streams from Hest?isen had: T:S”C and pIi 5.X. 7.2 and 6.8. The streams from the unburnt area had: T:S-7°C and pH 3.5, 3.3 and 3.9. The SO4 content in the various streams varied roughly between 4.4 and 7.4 mg/l, but was almost steady. namely 5.X mg/l in the stream with pH 4.3 and 5.1 mg/l in the stream with pH 6.8. There is no question of any difference in precipitation in the two arcas. The whole difference lies in the fact that large parts of the original humus streams,

cover

at

Hestisen

were

oxidized.

while it lies at the back of the regions

that were not burnt. The acidity level is 2000 times higher in one stream than in another (pH 3.9 and 7.2) and both these streams drain quartzitc regioss without basic rocks or limestones, and 5 years 2 months had elapsed since the fire, so that the readily soluble components from the alkaline ash had long since been leached out. It seemed reasonable to conclude, therefore, that the acidity in the precipitation has no great significance, and that it is the acidity in the

grass, moss. After

rain-

1081 two runoff the following:

October

showed

Outside

the

aspen.

the

burnt

area

17 ys/cm 21 ~&cm the

runoff

showed: [I+ 52 pequil;

with

streams

I!,

in

beach,

H+ 3 Itequ/l; conductivity II+ 10 pequil : conductivity

conductivity

H+ 32 pequ/l:

conductivity H+ 52 klequ/l: conductivity

heavy

September

herb.

on

streams

bushes

the

existing

area was mainly

willow fall

on

area was confined

The

70X ha of

jeld in lY75. The rock type was a light

and heather.

scorched

the runoff.

in Aust-Agder,

open pine forest has burnt at Hakkf-

from about 350 m to SO0 m above sea small

prove the pH conditions

In Froland

grwiss. Vegetation such

when

4 km’.

more acid than the precipitation. A reduction in the acid or sulphate will only im-

cover

with that of water

in Norway.

burnt.

soil that characterizes

and had a sparse vegetation

quartzite

level.

of precipitation

I975

The

humus

forest fire occured on 23-28

also

be

or more.

raw

of

Lifjell,

extensive

have not of conifers

regions.

example

was

is collected

with

should be compared

motion a process to find. or construct, If the surface runoff

regions which heavy growth

heather

faults in the alternative

explanation.‘3

from

yet acquired

At

Birkenes

burnt

21 Its/cm

25 p\/cm 23 ~is/cni

in Aust-Agder

at Bellandsvann

130 ha

in l%S.

Rock

type was light grwi.ss. Existing tion was mainly small pine, moss, grass. After rainfall on ber 10X1, two runoff streams

heather. I9 Octoshowed:

Hf 32 pequil ; conductivity H+ IS pequil; conductivity

21 psicm 22 Its/cm

Outside

vegeta-

the area:

II+ 126 pequ/l:

conductivity

cm Hf 63 pequil ; conductivity

28 ysi 26 ps/cm

Another point is the degree to which the acidity in the soil is a secondary effect of acidity in the precipitation. This point has been hardly studied at all by soil scientists. It does not help here to point to a recent correlation. There are many interacting factors. and a correlation is not identical with causality. In southern Norway and in Sweden. natural biogeochemical processes often produce 2-3 kmol H+ per haiyr. In parts of central Germany, the amount of atmospherically supplied II+ is three to four times as high as in southern Norway, while natural H ’ production is calculated as 2.Y to 5.5 kmol per ha/yr.‘” In Sudbury, Canada the H+ of the precipitation is IO-10 times higher than in southern Norway.” Analyses of a large number of weathering profiles at Numcdal indicated that since the ice age I .3 kmol II’ per ha have percolated per year through the profiles. The majority of the organic acids produced, break down again to CO?

LAND USE POLICY

January

1985

and water, but some are accumulated in the soil. The total amount of exchangeable Hf ions in an acid podsol profile, or bog, can be determined and usually this quantity corresponds to several hundred or several thousand years of prevailing acid precipitation. This cannot be attributed to the acid precipitation, as the H+ cannot both remain in the soil profile and at the same time flow out into the streams and kill the fish. There is obviously a great need for the preservation of natural resources and the environment, but to do this, it is important to distinguish between aims and means.

Professor 1. Th. Rosenqvist Department of Geology University of Oslo Oslo, Norway

LAND USE POLICY January 1985

‘RF. Wright and Sorensen, Vann, Nos 1,2 and 3. *I. Th. Rosenqvist, Acid Soil - Acid Wafer, Ingenior for laget, Oslo, Norway, 1977. %.M. Seip, S: Andersen and B. Halsvik, Snowmelt Sfudied in a Mini Catchment with Neutralized Snow, SNSF JR 65/80, 1980. 4A. Skartveit, B. Halsvik and E. Meisingset, The input of Sea Salts from Precipitation and the Runoff of ions in the Vest/and Catchment Area, SNSF JR 63180, 1980. 5J.V. Erikson, ‘Chemical Denudation in Sweden. Med fr& Statens Meteor’, AnHalt, Vol 5, No 3, pp l-96. 6M. Koide and E.D. Goldberg, ‘Atmospheric sulphur and fossil fuel combustion’, Journal of Geophysical Research, pp 6589-6596. 7H.M. Seip and A. Tollan, ‘Acid precipitation and other possible sources of acidification of rivers and lakes’, Science and Environment, pp 2X3-270. ‘SNSF, Acid Precipitation - Effects on Forest and Fish, Final report FR 19/l 980, 1980. ‘D.J.A. Brown and K. Sadler, ‘The chemistry and fishery status of acid lakes in Norway and their relationship to European

sulphur emission’, Journal of Applied Ecology, 1981. ‘OR F Wright and E. Snekvik, ‘Acid precipitation - chemistry and fish population in 700 lakes in Southernmost Norway’, Verh lntem Verein f. Limnologie 20, pp 76577.5. _.

“G.G. Raddum, Physical-Chemical Data from Selecfed Freshwater Lakes, in Southem Norway, SNSF TN 55180, 1980. “Op tit, Ref 9. ‘%NSF, Acid Precipitafion and Some Alternative Sources as the cause of Acidification of Watercourses, ISB IV, 82901 5304505, 1977. 14H.J. Heeg, A Pollen Analysis Investigation in the Sforgama Field in Nissedal, SNSF JR 57/81, 1980. 150p tit, Ref 2. 16B. Ulrich, R. Mayer and P.K. Khanna, ‘Chemical changes due to acid precipitation in a loessderived soil in Central Europe’, Soil Science 7980, Vol 130. pp 193-199. “P J Dillon et al, ‘Acid lakes in Ontario, Canada. Their extent and response to base and nutrient addition’, Jubilee Symposium on Lake Metabolism and Lake Management, Uppsala, 1977.