POLLUTION AND REMEDIATION

Contents

Acidification

Aquatic Ecosystems and Human Health

Bioassessment of Aquatic Ecosystems

Deforestation and Nutrient Loading to Fresh Waters

Distribution and Abundance of Aqautic Plants – Human Impacts

Effects of Climate Change on Lakes

Eutrophication

Fires

Floods

Invasive Species

Mercury Pollution in Remote Freshwaters

Pollution of Aquatic Ecosystems I

Pollution of Aquatic Ecosystems II: Hydrocarbons, Synthetic Organics, Radionuclides, Heavy Metals, Acids, and

Thermal Pollution

Vector-Borne Diseases of Freshwater Habitats

AcidificationW Geller and M Schultze, UFZ – Helmholtz Center for Environmental Research, Magdeburg, Germany

ã 2009 Elsevier Inc. All rights reserved.

Introduction

Natural rain is weakly acidic by atmospheric carbondioxide, reacting to carbonic acid in water. Therefore,the chemical characteristic of natural waters is domi-nated by dissolved carbonates, since these are the onlyminerals in rock and sediments that can easily bedissolved by rain water. The composition of freshwaters, in both soft and hard waters, is differing bythe concentrations of the components of the system(eqns. [5c–e]), which together are buffering standardfresh waters to about pH 7.Acidification is the additional input of acids to

waters – from natural and anthropogenic sources(Plate 1) – shifting the pH to lower values and usuallyeliminating the carbonate buffering system. The twomost important mineral acids in this respect are sul-furic and nitric acid. Industrial acid emissions havealtered lakes and rivers because of wind transportaway from the source areas and lack of neutralizingmaterials in the geology of the receiving regions, e.g.,in North America and Scandinavia.Accompanying the acidification, further problems

arise beyond low pH and aciditiy:

. rising concentrations of dissolved solids, particu-larly of sulfate in the drainage waters,

. mobilization of potentially toxic metals, and

. loss of biologic diversity.

The adverse factors prohibit the use of theimpacted water for irrigation, fishery and aquacul-tures, and its use as drinking water.

Following, the sources, distribution pathways, reac-tive modifications, effects on soils and biota, andthe importance of the different kinds of acidificationare described. The approaches how to mitigate or toremediate acidifications are presented elsewherewithinthis encyclopedia.

Chemistry of Acidified Waters andBuffering Mechanisms

Carbonic Acid and Fresh Water

Natural fresh waters contain mainly carbonates,HCO�

3 and CO2�3 , and most fresh waters show

nearly identical chemical compositions with pH7and the carbonate buffering system dominating.Carbonate-poor geological regions have soft waterswith low mineral content, and carbonate-rich areasshow higher mineralized hard waters.

Definitions and Dimensions

The capacity to neutralize additions of acids or basesdepends on the respective concentrations of base

1

Plate 1 Anthropogenic and natural acid waters: Upper left panel – Acid Sulfate Soil: Bottle Bend Lagoon, Australia, acidified after

lowering of water level by drought, with aeration of sulfidic sediments. (Image by courtesy of CSIRO 2004, Land and water Technical

Report 28/04: http://www.clw.csiro.au/scientific_reports.html). Upper right – Acid Rio Tinto draining the Pyrite Belt in Southern Spain(Photograph: M. Koschorreck). Lower panels – Acid lignite pit lake (pH 2.3) in Lusatia, East Germany (Photograph: G. Packroff). See

also view of acid volcanic Lake Voui – http://www.altitude-photo.com/fiche-photo.php?id photo=11994/, http://www.

volcanodiscovery.com/volcano-tours/typo3temp/pics/15e7421124.jpg

2 Pollution and Remediation _ Acidification

cations, of strong acid anions, and the concentrationsof two- or three-valent weak acids that function asbuffering systems by stepwise dissociation of theirprotons. The relationship between base cations andstrong acid anions determine whether the water isalkaline, neutral, or acidic.

Alkalinity and acidity The term alkalinity is equiva-lent to the acid-neutralizing capacity (ANC). Nega-tive values of alkalinity are termed acidity, equivalentto the base-neutralizing capacity (BNC).

ANC ¼ ðsum of base cation concentrations :

Ca2þ; Mg2þ; Naþ; Kþ; NHþ4

� ðsum of strong acid anion concentrations :

SO2�4 ; NO�

3 ; Cl�Þ½concentrations inmilliequivalents per litre : meq L�1� ½1�

ANC¼�BNC thus.The BNC of acid waters can be measured directly

by titration, usually with a solution 0.01N sodiumhydroxide till pH 8.2, resulting in a measure of (mmolL�1), or (meq L�1). The acidity of acid water alsocan be calculated from the pH-value and from themajor weakly acid components of water (Fe, Al, Mn;

metal concentrations given in mg L�1) by eqn. [2](if the concentrations of carbon dioxide, dissolvedsilicate, humic acids, and other heavy metals aresmall compared to the sum of iron, aluminum, andmanganese):

Acidcalc½meqL�1� ¼ 2Fe2þ

56þ 3Fe3þ

56þ 3Al

27þ 2Mn

55

þ 1000� 10�pH

½2�

The pH-value is a bulk measure comprising thestrong mineral acids, which are completely disso-ciated into their anions and protons, and the disso-ciated part of the weak acids. The non-dissociatedprotons of the weak acids are set free stepwise duringthe titration process, thereby functioning as bufferingsystems.

According to the US standards, acidity is measuredby the amount of CaCO3 that has to be added toreach neutrality. The dimension (mg CaCO3 L�1)can be converted to (meq L�1) following eqn. [3]:

AcidityðmeqL�1Þ ¼ ðmgCaCO3L�1Þ=50 ½3�

Buffering systems: the weak acids of carbon, alumi-num, and iron Acids may enter aquatic systems

35

30

25

20

15

Num

ber

of la

kes

10

5

02 3

Fe3+ HCO−3AI3+

4 5pH

6 7 8 9

Figure 1 Frequency distribution of the pH values of 159 mining

lakes in Germany (data from Nixdorf et al. (2001) Tagebauseen in

Deutschland. Umweltbundesamt, Berlin. UBA-Texte 01/35

http://www.umweltdaten.de/publikationen/fpdf-l/1996.pdf). Thehatched areas indicate the pH ranges of the buffering system

of ferric iron (Fe3þ), aluminium (Al3þ), and bicarbonate (HCO�3 ).

Pollution and Remediation _ Acidification 3

directly or after passage of soil anddeeper underground.The contacts of the solid phase of soil and undergroundto the passing acids result in buffering, i.e., proton-consuming reactions. Thereby, the dissolution of miner-als is the main source of metal mobilization among thebuffering processes. The relevant processes are:

. Buffering by carbonates and carbonic acid eqns.[5a–d]

Carbonic acid system:

CaCO3 þ 2Hþ , Ca2þ þ CO2 þH2O ½5a�

CaCO3 þHþ , Ca2þ þHCO�3 ½5b�

CO2�3 þHþ , HCO�

3 ½5c�HCO�

3 þHþ , H2CO3 ½5d�H2CO3 , CO2 þH2O ½5e�

. Buffering by silicates, especially aluminosilicatesand aluminum silicates (eqns. [6a–d] give exam-ples). The liberated aluminum and the formedgibbsite behave as described in eqns. [7a–c].

Feldspar dissolution:

KAlSi3O8 þ 7H2OþHþ , AlðOHÞ3 þ 3H4SiO4 þ Kþ

½6a�2KAlSi3O8þ9H2Oþ2Hþ,Al2Si2O5ðOHÞ4þ4H4SiO4þ2Kþ

½6b�KAlSi3O8þ4H2Oþ4Hþ,Al3þþ3H4SiO4þKþ ½6c�

Clay dissolution:

Al2Si2O5ðOHÞ4 þ 6Hþ , 2Al3þ þ 2H4SiO4 þH2O ½6d�

. Buffering by pedogenic oxides and (oxi)hydroxides(eqns. [7a–c] – dissolution of gibbsite which formsthe so-called aluminum buffering system and eqns.[8a–c] – dissolution of ferrihydrite which forms theso-called iron buffering system).

Aluminum system:

AlðOHÞ3 þHþ , AlðOHÞþ2 þH2O ½7a�

AlðOHÞþ2 þHþ , AlOH2þ þH2O ½7b�

AlOHþ2 þHþ , Al3þ þH2O ½7c�

Iron system:

FeðOHÞ3 þHþ , FeðOHÞþ2 þH2O ½8a�

FeðOHÞþ2 þHþ , FeOHþ2 þH2O ½8b�

FeOH2þ þHþ , Fe3þ þH2O ½8c�

. Buffering by ion exchange (eqn. [9] gives an exam-ple;X – active site at the surface of particles or solidmaterial).

Sites of ion exchange:

X � KþHþ , X �Hþ Kþ ½9�

. Buffering by protonation of humic substances

Humic acids:

R� COO� þHþ , RCOOH ½10�

When acids enter aquatic systems directly, the rele-vant buffering systems are in the liquid phase: thecarbonate system eqns. [5b–d], the aluminum buffereqns. [7a–c], the iron buffer eqns. [8a–c], and reac-tions of further weak acids (e.g., humic/fulvic acids,silicate). The chemical equilibrium between sulfateand hydrogensulfate comes into play if pH dropsbelow 2.5 (eqn. [11]).

Formation of hydrogensulfate:

SO2�4 þHþ , HSO�

4 ½11�

The action of the different buffering systems resultsin typical distributions of pH-values obtained fromregional surveys in lakes which are partly acidified.Figure 1 shows the pH-values of German pit lakesresulting from lignite mining forming a three-modaldistribution. Surveys of lakes which are partlyimpacted by atmospheric deposition usually result ina two-modal pH-distribution formed by the alumi-num buffer and by the carbonate buffer.

10

9

8

7

6

pH v

alue

5

4

3

20 2 4

Lake FelixML 117ML 110ML 111

6 8Added alkalinity in meq L−1

10 12 14

AI3+

Fe3+

16

Figure 2 Titration curves of four different mining lakes in theLusatian lignite mining district, Germany (data by courtesy of

O. Totsche). The shaded areas indicate the pH ranges of the

buffering systems of ferric iron (Fe3þ) and aluminum (Al3þ).Depending on the concentrations of ferric iron and aluminum andthe formed minerals in the particular lakes, the extent of the

according plateaus differs in the titration curves. Below pH 2.5,

hydrogensulfate (HSO�4 ) may act as buffer. Ion exchange with

particles, silicates, and the carbonate buffering system are

relevant at pH above 5, depending on the availability of

suspended particles and (bi-)carbonate.

4 Pollution and Remediation _ Acidification

The buffering systems govern not only the decreaseof pH as the result of impact of acids. The progressof neutralization is shown by typical titration curvesof water from acid German pit lakes in Figure 2. Theplateaus indicate the action of the iron and the alumi-num buffering systems, respectively. The extent of theplateaus depends on the concentration of the respec-tive metals in the lake water.

Pyrite weathering Acids of geogenic origin can beset free by natural weathering or by processes inducedby mining or by agriculture. The most importantprocess is the oxidation of pyrite or similar sulfides(eqns. [12–15]). These oxidation processes are accel-erated by sulfur and iron oxidizing bacteria. Theoverall products of the multi-step reaction are sulfuricacid and ferric iron hydroxide.

FeS2 þ 7=2O2 þH2O , Fe2þ þ 2SO2�4 þ 2Hþ ½12�

Fe2þ þ 1=4O2 þHþ , Fe3þ þ 1=2H2O ½13�

Fe3þ þ 3H2O , FeðOHÞ3 þ 3Hþ ½14�

FeS2 þ 14Fe3þ þ 8H2O , 15Fe2þ þ 2SO2�4 þ 16Hþ ½15�

In the case of mining-induced pyrite oxidation,dewatering operations bring pyrite in contactwith air. Before, the pyrite had been stable in the

water-saturated anoxic underground. Once in con-tact with air, the oxidation goes on rapidly andforms acid mine drainage (AMD). Pyrite is not onlyone of the most important iron ores but also occurs asan accompanying mineral in many sulfidic ores ofother metals, in lignite and coal deposits, in shales,or in marine sediments, such as mined clay deposits.

Outcrops of natural pyrite deposits provide naturalconditions for pyrite oxidation. Such natural acidicwaters are known from the Iberian Pyrite Belt insouthern Spain, mountainous regions in New Mex-ico, or the lakes of the Tyrell Basin and the YilgarnBlock in southern Australia.

Concentrations of dissolved substances in acid watersThe concentrations of total dissolved solids in acidwaters increase from about 50mg L�1 at pH5 in softwaters, which result from atmospheric deposition, to100g L�1 at pH0 in extremely acidic brines of volcanicsprings. The spectrum of dissolved elements originatesfrom the involved mineral acids and from the composi-tion of the thereby dissolved minerals in soils and rocks.

We show in Figure 3, the concentration of someconstituents of acid waters resulting from thedescribed types of acidification. For all types, datafrom ground water, springs, streams and lakes areincluded. However, these data comprise only waterswith pH< 6.

The occurring concentrations of sulfate and metalsresult from sulfide oxidation as well as from bufferingprocesses in soil and water (eqns. [5–9,12,15]). ThepH-values of these acid waters range from 6 to valuesbelow zero under extreme conditions in abandonedmine workings in California. We show in Figure 4,the pH-values of the waters comprised in Figure 3.

Types and Extent of Acid Waters

Atmospheric Deposition and Acid Rain

The atmospheric pathway distributes acidic gaseousSO2, NH3, and NOx over large areas of land. Thesources of SO2 and NOX are combustion of coal, lig-nite, and oil in power plants and in households, wastegases ofmotor cars, and various industrial waste gases,e.g., resulting from roasting of sulfidic ores. NH3 emis-sions often result from stock farming, especially whendone in large-scale units. The acidity ofNH3 emissionsresults from oxidation/nitrification during atmos-pheric transport or after deposition in the top soil.

Although the term acid rain is commonly used,this kind of acidification usually includes the

7

6

Acy SO42− Ca Mg Na Fe AI Mn Zn Cu Ni

nd

nd nd nd nd

Ore mining

Acidic sulfate soils

Coal and lignite mining

nd

As Cd Pb Co Cr SiK

Acy SO42− Ca Mg

Log 10

of a

cidi

ty (

Acy

) in

meq

L−1

or

conc

entr

atio

n in

mg

L−1

Na Fe AI Mn Zn Cu Ni As Cd Pb Co Cr SiK

Acy(a) SO42− Ca Mg Na Fe AI Mn Zn Cu Ni As Cd Pb Co Cr SiK

5

4

3

2

1

−1

−2

−3

−4

0

7

6

5

4

3

2

1

−1

−2

−3

−4

0

7

6

5

4

3

2

1

−1

−2

−3

−4

0

Figure 3 (Continued)

Pollution and Remediation _ Acidification 5

Acy SO42− Ca Mg Na Fe AI Mn Zn

Waters acidified by atmospheric deposition(by acid rain)

Acid volcanic waters

Cu Ni As

nd nd nd

Cd Pb Co Cr SiK

Acy(b) SO42− Ca Mg Na Fe AI Mn Zn Cu Ni As Cd Pb Co Cr SiK

7

6

5

4

3

2

1

−1

−2

−3

−4

0

7

6

5

4

3

2

1

−1

−2

−3

−4

0

Log 10

of a

cidi

ty (

Acy

) in

meq

L−1

or

conc

entr

atio

n in

mg

L−1

Figure 3 Characteristics of acid drainage by the concentrations of chemical constituents. Lines within the boxes are median values,

box limits are 25 and 75 percentiles, and whiskers show the 10- and 90-percentile values. Single dots indicate data below 10 percentileor above 90 percentile, respectively (nd – not detected).

Coal and lignite mining(n = 80)

Ore mining(n = 57)

Acidic sulfate soils(n = 36)

Acid volcanic waters(n = 36)

−1 0 1 2 3pH-value

4 5 6

Waters acidified by atmospheric deposition(by acid rain; n = 36)

Figure 4 pH values of the waters comprised in Figure 3. Lines within the boxes are median values, box limits are 25 and 75percentiles, and whiskers show the 10- and 90-percentile values. Single dots indicate data below 10 percentile or above 90 percentile,

respectively (nd – not detected).

6 Pollution and Remediation _ Acidification

deposition of aerosols, of fog, the dry depositionof the mentioned gases, and of dust. In a two-stepprocess, the soils first become acidic after com-plete loss of carbonate minerals, then, acidic

waters seeping through the soils dissolve furtherminerals, especially Al-silicates. These waterscause the acidification of ground water and surfacewaters.

Pollution and Remediation _ Acidification 7

Beyond the critical limits, the interaction betweensoil and trickling water leads to accumulation ofacidity (N and S content) in soils. The carbonateand hydrogen carbonate anions in soil and surfacewaters are replaced by sulfate, and Ca2þ and Mg2þ

cations by Hþ and Al3þ. After a large-scale process oftitration, the impacted soils and waters are carbon-ate-free, and the affected waters are enriched insulfate and aluminum, with pH-values in a rangebetween 4.5 and 5.5.Under certain conditions, this kind of acidification

occurs episodically. If the reaction time betweenintroduced acidity and soil is long enough the men-tioned buffering processes are able to neutralize thetrickling water. Elevated precipitation rates or the sud-den liberation of accumulated acidity, e.g., from melt-ing snow covers, however, may cause temporarilyelevated acidity.Soft waters of carbonate-poor geological regions

are more affected by acidic inputs because of the lowcontents of ions and low buffering capacities. They aresensitive to acid depositions. The critical load limitsare reached where the percentage of the base cationsCa2þ, Mg2þ, and Kþ is lower than 20% of the totalcation exchange capacity, or the acid neutralizationcapacity (ANC) is below 0–25 meq L�1. Estimationsof the critical loads in geologically sensitive areasshowed a range of annual sulfur depositions between300 and 800mg m�2.After the emissions of sulfur dioxide and nitrogen

oxides, transport times of 15–21 h were observedfrom the states in the midwestern United States,where the emissions occurred, to the northeasternstates in New England and Canada, where the acidrain was precipitating. Similar transport times anddistances are known from England and from centralEurope to southern Scandinavia. The percentages ofacidified lakes were 27% in Norway. In Sweden,17 000 (20%) of 85 000 surveyed lakes were affecteduntil 1992. The trend of atmospheric acidificationwas reversed during the 1980s and 1990s by counter-measures in the western industrial countries. Thepresent global problem areas with risk of surfacewater acidification are in mid- and northeasternNorth America, in eastern Canada, in western, cen-tral and northern Europe, in the eastern parts ofChina, in India, and in northwestern Russia.

Acid Mine Drainage (AMD)

Acidification of inland waters by acid mine drainageis common in many mining areas where we findacidic open pit lakes, acidic streams or acid minedrainages from shafts, adits, waste rock or overbur-den dumps, and tailings. If the acid drainage occurs

after cessation of ore-mining operations or if it origi-nates from the naturally outcropping deposits, theterm acid rock drainage (ARD) is used.

The impact of acid mine drainage on rivers wasestimated to 19 300 km in the United States. AvocaRiver in southeastern Ireland is affected from an aban-doned copper and sulfur mine area by AMD of pH2.7. The annual load amounts to 300 tons of metals:108 tons Zn, 276 tons Fe, 6 tons Cu, 0.3 tons Cd.In Germany, about 500 lakes result from open castlignitemining. Surface coalmining left hundreds of pitvoids and lakes in the Appalachians and the USMidwest during the first half of the last century. Inthis area, new post-mining lakes will appear from 86major ore mining plants, and in Nevada 30 pit lakeswill emerge within 20 years.Many surface-mine voidswill become future lakes, largely acidic and contami-nated with toxic metals, from 19 metal mines inCanada, 74 in Australia, 37 in Chile, 75 in Kazakh-stan, and in several other countries.

In southern Spain, the rivers Rio Tinto and RioOdiel are natural drainages of the Iberian PyriteBelt, the world’s largest deposit of pyrite and othersulfidic ores. Rio Tinto is a naturally extreme envi-ronment with mean pH-values of 2.2 and high con-centrations of heavy metals (Fe 2.3 g/L, Zn 0.22 g/L,Cu 0.11 g/L). The metals are deposited in estuarineand near-shore marine sediments containing 11.2%Fe, 0.93 g/kg Cu, 1.15 g/kg Zn, 0.73 g/kg Pb, and0.66 g/kg Ba. These loads are caused by natural pro-cesses since 300000 years and, additionally, by miningactivities since about 4000 years.

Drainage from Acid Sulfate Soils

The acidification of sulfate soils originates from sedi-mentary deposits where sulfate-rich waters previouslywere mixed with organic loads. The decay of organicmatter reduced sulfate and iron, resulting in pyrite asfinal product. Where these layers are disturbed, forexample, by agriculture, or by lowered water tablesafter drought or drainage, the contact with air givesthe same results as in oxidized sulfidic mining areas,and the sulfate soils turn to acid sulfate soils (ASS).

Acid sulfate soils are distributed worldwide acrossan area estimated at 170000km2. Sulfidic deposits canform in sedimentary basins where organic loads meetwith sulfate waters, both in coastal areas, where thesulfate source is marine water, and in river basins withnon-marine saline loads. Examples are coastal man-grove forests, coastal lagoons, estuaries, flood-plainsof inland rivers in semi-arid regions, and agriculturalland after long-term irrigation with gypsiferous water.Reports are given from the Carribean region, Guyana,Surinam, Trinidad, Venezuela, Africa, South-East

8 Pollution and Remediation _ Acidification

Asia, Thailand, Vietnam, The Netherlands, England,Wales, Scotland, Russia, Finland, and from Australia.

The case of western Finland The coastal area ofwestern Finland between Helsinki in the south andOulu in the north previously was covered by the seaand, after post-glacial isostatic land uplift, is now up to100m a.s.l. across a total area of 3360km2. The sedi-ments containing metal sulfides, usually pyrite, weredeposited during the Litorina period (6000–7000yearsBP) and emerged above the sea about 4000 years ago.Fifty to eighty years ago these areaswere cultivated anddrained. The artificial draining lowered the groundwater table and gave access to atmospheric oxygen.After oxygenation the drain water became highlyacidic, contaminating the receiving rivers.

The case of Australia Acid soils are found in Aus-tralia in both coastal areas and river floodplains, andare a general problem after draining the land foragriculture. The unprecedented drought of 2007 ledto an additional drop in inland water levels, and moresulfidic sediment may become exposed along theaffected rivers, e.g., Murray, Darling. The total areaextent in Australia is estimated to be 40000km2 ofASS. A national strategy for the management of coastaland inland acid sulfate soils was developed to identifysuitable countermeasures. These, however, are lim-ited to only a few options, such as tidal flushing ofcoastal areas, better control of drainage, reforesta-tion, or liming campaigns.

Volcanic Waters and Crater Lakes

Volcanic activities are a natural geogenic source ofacidity. Volatile mineral acids are thermally set free asgaseous SO2, HCl, and HF. After mixing with meteoricwaters, strongacids are formed thatdissolve the volcanicrock, causing leaching and weathering. The outflowingwater is extremely acidic, emerging as highly minera-lized brines in geothermal hot springs at flanks and topof the volcanoes, or collect in crater lakes.Rivers which receive acidic and toxic volcanic inputs

are heavily affected. The crater lake of the volcanoKawah Ijen, East Java, contains 32Miom3 of hot andacidic brine water (pH<0.4, TDS> 100 g/kg, SO2�

4

70 g/kg, Cl� 21g/kg, F� 1.5 g/kg). The outflowingbrine is contaminating the Banyupahit River. Since theacidic inflow is only incompletely neutralized, the riverbiota has disappeared. Downstream rice fields are irri-gated with 4m3/s of the river water, containing daily-loads of 150 tons SO2�

4 , 2.8 tons F�, 50 tons Cl�,10 tons Al, 35kg Ti, and 4kg Cu. The crater lake andits environmental impacts are estimated to be morethan 200 years old. A similar situation is found at the

Patuha volcano in West Java, where an acidic craterlake, Kawah Putih, and springs of acid brines withpH< 1 drain into the Citarum River. The river is con-taminated by the toxic elements and, also, is used forirrigation.

Lago Copahue is an acid crater lake in Argentinaat Copahue Volcano, supplying the 13km-long RioAgrio, an extremely acidic river with pH0.6–1.6.The river discharges into the glacial Lake Caviahue,diluting the water to pH2.5. The outflow of the lake,Lower Rio Agrio, is further diluted in its course reach-ing neutrality after ca. 50km in downstream stretches.

Biological Effects of Acidification

With increasing acidity and decreasing pH inlandwaters lose all species of sensitive groups, fish, mol-lusks, and cyanobacteria. Species richness and di-versity of phyto- and zooplankton, and of benthicinvertebrates decrease to low levels. Herbivorousinsects decrease, whereas carnivorous groups increasein numbers. Some groups become more abundant,the dinoflagellates become the dominant phyto-plankton, fungi increase in number and diversity,and sulfate reducing bacteria in anaerobic zones. Inthe littoral zone Sphagnum moss or mats of filamen-tous green algae grow to masses. The food webs inrain-acidic lakes became simpler. The rates of systemmetabolism and productivity are reduced to lowlevels, and, thereby, detritus and dead woody debriscan accumulate.

With lower pH, an increase is observed of acidity,toxic species of aluminum, and more intensive anddeeper reaching UV irradiation. Most fish speciesdisappeared at pH below 5.7 in the acidic lakes ofthe La Cloche Mountains (Canada), and no speciessurvived <pH 4.3. The area of Norway was affectedto 25%. By 1975 in southern Norway, 50% of thepopulations of brown trout were lost. Finally, 9630fish populations disappeared up until 1990, and 5405populations did not reproduce. In several thousandacidified lakes in southern Norway the macroinverte-brates disappeared with pH below 4.8. In a survey ofneutral and rain-acidified streams, and in acidic lig-nite mining lakes in Germany, the number of benthicmacroinvertebrates decreased from about 50 speciesat pH8 to zero at pH2 (Figure 5).

In geogenically acidic drainages, often toxic heavymetals are found as contaminants. Although theseconstituents are diluted, neutralized, and mineralsare precipitated in the receiving rivers, the acids andtoxic metals damage the freshwater biota. In Europe,a typical case is the above-mentioned Avoca River insoutheastern Ireland which is affected by continuousAMD from an abandoned copper and sulfur mining

50

40

30

20

10

01 2 3 4 5

pH-value

Acidic pit lakesN

umbe

r of

ben

thic

inve

rteb

rate

s ta

xa

Lakes acidified by acid rain

6 7 8

Figure 5 Macrozoobenthos in acidic lakes. (By courtesy of G. Rodrigues, Diss. Techn. Univ. Braunschweig 2001).

Pollution and Remediation _ Acidification 9

area. In the contaminated river, the pH of which is5.8, macrophytes and fish are eliminated, and macro-invertebrates survive only for short periods. The dam-age to the indigenous biota is due to the combinationof metal toxicity, sedimentation, acidity, and saliniza-tion. In permanently acidic and metal-rich waters,unexpectedly diverse communities of extremophilescan develop.

Success of Countermeasures andLong-Term Developments

Rain-Acidified Waters

The control of the atmospheric acidification of soils,lakes, and rivers was achieved in two steps:

1. the emissions of acidic smoke could be reducedwith the result of less acidic atmospheric deposi-tion in these regions. In North America and inEurope, the emissions were reduced during thelast two decades by legal regulation and technicalimprovements, as documented by monitoringnetworks and by long-term observations at singlesites (Figure 6). In Europe, the former eastern bloccountries followed with a delay of one decade; thearea of former East Germany could be identifiedby the atmospheric SO2 content till 1992. In othercountries (China, India, Russia, South-America) the trend shows still increasing emis-sions, and improvements are in delay.

2. The remediation of already acidic waters and soilswas successfully reached in a few countries withcampaigns of liming rivers, lakes, and soils of thecatchment areas. In southern Sweden, the world-wide largest liming program was conducted over20 years by spreading annually 200 000 tons of

suspended limestone. Thereby, 6000 lakes and halfof the acidified area could be treated. Remediationappears as a two-step process, chemical remedia-tion preceding biological response. Biologicalrecovery is emerging along the given generationlengths, zooplankton and macroinvertebrates need3–10 years, fish populations will follow. Thechemistry of surface waters is fast responding tolime treatment, but the recovery of soils across thecatchment areas is generally a slow, centennialprocess during which the soil system still remainssensitive. Therefore, continuing programs of limingsurface waters and forest are needed to consolidatethe reached state of neutralization and to increasethe number of remediated watersheds.

Acid Mine Drainage and Acid Sulfate Soils

In areas exposed to geogenic acidification from acidmine drainage, a broad spectrum of countermeasuresis available and under development. The acidificationof lakes and rivers by acid drainages can be preventedby preclusive measures and direct treatment of thepolluting waters as (a) restrictions on running miningactivities, (b) neutralizing the waters by active treat-ment of the AMD by addition of alkaline chemicals,(c) passive treatment using natural geochemical andbiological reactions to reduce acidity, and ion concen-trations, and (d) the in situ treatment of acidic lakes.

The different approaches for remediation andtreatment are described in a separate article withinthis encyclopedia.

The problems of acid sulfate soils are complex,and the approaches for countermeasures are limited.The primary option appears as reducing andcontrolling the artificial drainage, thereby decliningthe access of oxygen to the sulfidic layers. Acid

7.5

7.0

6.5

6.0pH

5.5

5.0

4.5

4.0

7.5

7.0

6.5

6.0

5.5

5.0

4.5

4.0n = 3 n = 42 n = 119 n = 9

Region

n = 23 n = 63 n = 22n = 105

ELA ONTW ONTC ONTE QC NB NS NF

Figure 6 Distribution of modeled andmeasured pH values of lakes from different regions of Eastern Canada (ELA – Experimental Lake

Area, western Ontario; ONTW – region east of Lake Superior, Ontario; ONTC – region north of the central part of Lake Huron, Ontario;

ONTE – region east of Georgian Bay of Lake Huron, Ontario; QC – southern Quebec; NB – southern New Brunswick; NS – Nova Scotia;NF – Newfoundland). Within each regional block, the first box shows the distribution of modeled pre-acidification values, the second

shows 1975 (worst case) distribution, the third shows year 2000 values, while the fourth box describes expected values under further

agreed-to Canadian and currently proposed US emission reductions. The number of sites in each region is given. Lines within the boxesare median values, box limits are 25 and 75 percentiles, and whiskers show the 10 and 90 percentile values. (By courtesy of ãEnvironment Canada 2007). Source: Clair et al. (2007) Past and future changes to acidified eastern Canadian lakes: A geochemical

modeling approach. Applied Geochemistry 22: 1189–1195.

10 Pollution and Remediation _ Acidification

drainage water from sulfate soils can be treated withthe same methods as acid mine drainage. The soiltreatment with lime is more difficult, since the alka-line substances must be introduced into the subsur-face layers in depths of about 1–1.5m, where thesulfidic metals had been accumulated and, afterdrainage, were subsequently oxidized in the past.Coastal sites with acid sulfate soils can be treatedwith tidal flushing. National strategies for theremediation of acid sulfate soils, at coastal and atinland sites, presently are under discussion mainly inAustralia and Finland.

Lake Orta: Acidified by Industrial Waste and

Remediated by Liming

The prealpine Lake Orta in northern Italy is 143mdeep, with a water volume of 1.3 km3. The water washeavily polluted from 1926 to 1982 by industrialwastewater (ammonium sulfate, heavy metals Cu,Cr, Ni, and Zn). Between 1960 and 1980, the lakebecame acidic (pH 3.9–4.5) by oxidation of the loadof 3000 tons of ammonium-N per year. After stop-ping the input of industrial wastewaters, the lake wastreated 1989–1990 with 18 000 tons of powderedlimestone and could be neutralized by this chemicaltreatment. To date, this was the worldwide biggestliming application at a single lake.

Conclusions

Acidification of inland waters affects ground water,streams, rivers and lakes. The reasons may be naturalones, suchas volcanismoroxidationatnatural outcropsof pyrite deposits, or artificial ones, such as atmosphericdeposition of acidity (acid rain) or pyrite oxidationcaused bymining or agriculture. The anthropogenicallyinduced acidification requires both themitigation of thesymptoms and the remediation of the causes. The recov-eryof acidifiedwaters innorthernAmericaand innorth-ern Europe was only possible after removal of theoriginal causes, the major sources of acid waste gases.Usually, the effort for mitigation is high, but smallerthan the costs of loosing aquatic ecosystems by acidifi-cation. Treatment of drainage fromnatural sourcesmayalsobenecessarywhere the impactedwaters areused forirrigation or drinking water supply.

Generally, acidification appears – after eutrophica-tion – as the most important threat and stress factorfor continental water resources and the ecosystemsof lakes and rivers. In many impacted countries thecurrent regulations are not sufficient to reach theremediation targets.

Glossary

Acid drainage (AD) – Drainages with acidic waterboth from anthropogenic and from natural acid

Pollution and Remediation _ Acidification 11

sources, as from mining of coal, sulfidic ores, fromaerated sulfide-containing soils, and from volcanicsources.

Acid mine drainage (AMD) – Mine drainage wateracidified after oxidation of pyrite from mining ofcoal and sulfidic ores.

Acid rain – Rain, snow, sleet, and dry deposition,which are acidified by waste gases from industrialand other anthropogenic sources, often used assimplifying synonym for atmospheric deposition ofacidic substances.

Acid sulfate soil (ASS) – Soils with sulfide content thatrelease acidic and sulfate containing water afteraeration by agriculture and/or lowered groundwater.

Acidification – Change of water chemistry afterinput of acids by acid rain or acids from geogenicsources.

Acid-neutralization capacity (ANC) – The capacity ofwaters to neutralize added acids.

Atmospheric acidification – Impact on soils andwaters by atmospheric transport of acid wastegases, aerosols, and dust from the anthropogenicsources to the affected areas which are impactedby wet and dry deposition of acid substances.

Atmospheric deposition – Sum of wet and dry depo-sition.

Buffering system – The two- or three-valentweak acidswhich keep a system within a certain pH range bytheir ability to change their dissociation state, i.e., toremove protons from the system (protonation of theweak acids’ anions) or to liberate protons into thesystem (by de-protonation of the weak acids).

Dry deposition – Amount of substances deposited asgases, aerosols and dust from the atmosphere ontothe earth surface.

Geogenic acidification – Acidification by natural oranthropogenically induced acid impacts from geo-logical sources via ground water.

Liming – Treament of acid waters or soils by pow-dered limestone or suspended lime to mitigate thesymptoms of acidification.

Remediation – Measures to restore acidified sys-tems by eliminating the cause and the source ofacidification.

Restoration – Treaments and measures to restoreacidified waters and ecosystems from the disturbedstate to reach again the original, natural state.

Volcanic acidification – Acid impact on soils andwaters from active volcanoes via air and volcanicwater.

Wet deposition – Amount of substances deposited asfog, rain, snow and other kinds of wet precipitationfrom the atmosphere onto the Earth’s surface.

See also: Restoration of Acidic Drainage.

Further Reading

Bouwman AF, van Vuuren DP, Derwent RG, and Posch M (2002)

A global analysis of acidification and eutrophication of

terrestrial ecosystems. Water, Air and Soil Pollution 141:349–382.

Brodin YW (ed.) (1992) Critical loads in nordic countries. AmbioSpecial issue, 21.

Brown M, Barley B, and Wood H (2002) MinewaterTreatment: Technology, Application and Policy. London: IWA

Publishing.

Driscoll CT, Lawrence GB, Bulger AJ, Butler TJ, Cronan CS,

Eagar C, Lambert KF, Likens GE, Stoddard JL, and WeathersKC (2001) Acidic deposition in the northeastern United States:

Sources and inputs, ecosystem effects, and management strat-

egies. BioScience 51: 180–198.Eloranta P (ed.) (2004) Inland and Coastal Waters of Finland.

Helsinki: Publ. Univ, ISBN 952-10-1141-6.

EPA – U.S. Environmental Protection Agency (2006) Management

and Treatment of Water from Hard Rock Mines, EPA/625/R-06/014. http://www.epa.gov.

ERMITE consortium, Younger PL and Wolkersdorfer C (eds.)

(2004) Mining impacts on the freshwater environment: technical

and managerial guidelines for catchment scale management.Mine Water and the Environment 23: 1–80.

Fleischer S and Kessler E (eds.) (1993) Acidifcationof surfacewaters

in Sweden – Effects and countermeasures.Ambio 22(5): 257–337.Folster J and Wilander A (2002) Recovery from acidification in

Swedish forest streams. Environmental Pollution 117: 379–389.

Geller W, Klapper H, and Salomons W (eds.) (1998) Acidic MiningLakes. Berlin, Heidelberg, New York: Springer.

Hem JD (1992) Study and interpretation of the chemical character-

istics of natural water. U.S. Geological Survey Water-SupplyPaper 2254, 264 pp. Washington: U.S. Geological Survey.

Henrikson L and Brodin YW (eds.) (1995) Liming of acidifiedsurfacewaters. Berlin, Heidelberg: Springer.

Johnson DB and Hallberg KB (2005) Acid mine drainage remedia-

tion options: A review. Science of the Total Environment 338:3–14.

Olem H (1991) Liming of Surface Waters, 331pp. Chelsea: LevisPublishing.

Persson G (2008) Zooplankton response to long-term liming: Com-parison of 15 limed and 15 reference lakes in Sweden. Limnolo-gica 38: 1–13.

PIRAMID Consortium (2003) Engineering guidelines for the

passive remediation of acidic and/or metalliferous mine drainageand similar wastewaters. European Commission 5th Frame-

work RTD Project no. EVK1-CT-1999–000021: Passive in-situ

remediation of acidic mine/industrial drainage (PIRAMID). Uni-

versity of Newcastle Upon Tyne. http://www.ncl.ac.uk/piramid.Schindler DW (1988) Effects of acid rain on freshwater ecosystems.

Science 239: 149–157.

12 Pollution and Remediation _ Acidification

Sheoran AS and Sheoran V (2006) Heavy metal removal mecha-

nism of acid mine drainage in wetlands: A critical review.Miner-als Engineering 19: 105–116.

Varekamp JC and Rowe GL Jr. (eds.) (2000) Crater Lakes J Volca-nology and geothermal Research. Special Issue, vol. 97.

Weathers KC, Likens GE, Butler TJ, and Elliott A (2006) Acidrain. In: Rom W (ed.) Environmental and Occupational Medi-cine, 4th edn., pp. 1549–1561. Philadelphia: Lippincott-Raven

Publishers.

Younger PL, Banwart SA, and Hedin RS (2002) Mine Water: Hy-drology, Pollution, Remediation. Dordrecht: Kluwer Academic

Publishers.

Relevant Websites

http://www.cciw.ca/gems – Canada Centre of Inland Waters

(CCIW).http://www.ce.cmu.edu/~acidmine/resources.html – Carnegie Mel-

lon University, Pittsburgh, AMD Resources.

http://www.mines.edu/fs_home – Colorado School of Mines,

AMD-homepage.http://www.emep.int – Co-operative Programme on Long-range

Transboundary Air Pollution.

http://www.claire.co.uk/costar.php – CoSTaR research facility,Hydrogeochemical Engineering Research & Outreach (HERO),

Group at Newcastle University, the Coal Authority, Durham and

Northumberland Councils and CLAIRE.

http://themes.eea.eu.int – European Environment Agency (EEA).http://europa.eu.int – European Union (EU).

http://www.apps.fao.org – Food and Agricultural Organisation of

the United Nations (FAO).

http://www.gemswater.org – Global Environmental Monitoring

System on inland water quality.http://www.bafg.de/grdc.htm – Global Runoff Data Centre.

http://www.gwpforum.org – Global Water Partnership.

http://www.inap.com.au – International Network for Acid Preven-

tion (INAP). Includes clear overview of topics and reports onINAP-funded research.

http://www.clw.csito.au/scientific-reports.html.

http://www.mdbc.gov.au – Murray_Darling Basin Commission.

http://www.nrcan.gc.ca/mms/canmet-mtb/mmsl-lmsm/mend –Mine Environment Neutral Drainage (MEND) Program,

Canadian mining companies and provincial/territorial and federal

departments.

http://nadp.sws.uiuc.edu – National Atmospheric DepositionProgram. Illinois State Water Survey.

http://wvwri.nrcce.wvu.edu – National Mine and Reclamation

Center, West Virginia University.http://www.dpie.gov.au/dpie/armcanz/pubsinfo/ASS/ASS.html –

National Strategy for the Management of Coastal Acid Sulfate

Soils, Australia, New Zealand.

http://www.oecd.org – Organisation for Economic Co-operationand Development (OECD).

http://www.nmnh.si.edu/gvp/volcano – Smithsonian Institution.

Global volcanism program.

http://www.acidrain.org – Swedish NGO Secretariat on Acid Rain.http://www.uba.de – Umweltbundesamt, Berlin.

http://toxics.usgs.gov/topics/minelands.html – U.S. Geological Sur-

vey Toxic Substances Hydrology Program section on Hard-RockMining Contamination.

http://www.epa.gov – US Environmental Protection Agency (EPA).

http://www.wmo.ch – World Hydrological Cycle Observing

System.