Encyclopedia of Inland Waters || Acidification

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  • TIm

    thetic Organics, Radionuclides, Heavy Metals, Acids, and

    r E

    . rising concentrations of dissolved solids, particu-

    are described. The approaches how to mitigate or to

    Definitions and Dimensions

    larly of sulfate in the drainage waters,

    . mobilization of potentially toxic metals, and

    . loss of biologic diversity.The capacity to neutralize additions of acids or basesdepends on the respective concentrations of basedissolved by rain water. The composition of freshwaters, in both soft and hard waters, is differing bythe concentrations of the components of the system(eqns. [5ce]), 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:

    remediate acidifications are presented elsewherewithinthis encyclopedia.

    Chemistry of Acidified Waters andBuffering Mechanisms

    Carbonic Acid and Fresh Water

    Natural fresh waters contain mainly carbonates,HCO3 and CO

    23 , 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.minerals in rock and sediments that can easily beNatural 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 only

    impacted 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 acidificationPOLLUTION AND REMEDIA

    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

    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, Syn

    Thermal Pollution

    Vector-Borne Diseases of Freshwater Habitats

    AcidificationW Geller and M Schultze, UFZ Helmholtz Center fo

    2009 Elsevier Inc. All rights reserved.

    Introductionnvironmental Research, Magdeburg, Germany

    The adverse factors prohibit the use of thepactsION1

  • l

    2 Pollution and Remediation _ AcidificationPlate 1 Anthropogenic and natural acid waters: Upper left panecations, 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 sum of base cation concentrations :Ca2; Mg2; Na; K; NH4 sum of strong acid anion concentrations :SO24 ; NO

    3 ; Cl

    concentrations inmilliequivalents per litre : meq L1 1

    ANCBNC 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 (mmolL1), or (meq L1). The acidity of acid water alsocan be calculated from the pH-value and from themajor weakly acid components of water (Fe, Al, Mn;

    lowering of water level by drought, with aeration of sulfidic sediment

    Report 28/04: http://www.clw.csiro.au/scientific_reports.html). Uppe(Photograph: M. Koschorreck). Lower panels Acid lignite pit lake (p

    also view of acid volcanic Lake Voui http://www.altitude-photo.com

    volcanodiscovery.com/volcano-tours/typo3temp/pics/15e7421124.jpAcid Sulfate Soil: Bottle Bend Lagoon, Australia, acidified aftermetal concentrations given in mg L1) 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):

    AcidcalcmeqL1 2Fe2

    56 3Fe

    3

    56 3Al

    27 2Mn

    55

    1000 10pH2

    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 measured

    by the amount of CaCO3 that has to be added toreach neutrality. The dimension (mg CaCO3 L

    1)can be converted to (meq L1) following eqn. [3]:

    AciditymeqL1 mgCaCO3L1=50 3

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

    s. (Image by courtesy of CSIRO 2004, Land and water Technical

    r right Acid Rio Tinto draining the Pyrite Belt in Southern SpainH 2.3) in Lusatia, East Germany (Photograph: G. Packroff). See

    /fiche-photo.php?id photo=11994/, http://www.

    g

  • . 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 KH , X H K 9

    . Buffering by protonation of humic substances

    Humic acids:

    R COO H , RCOOH 10

    When acids enter aquatic systems directly, the rele-vant buffering systems are in the liquid phase: thecarbonate system eqns. [5bd], the aluminum buffereqns. [7ac], the iron buffer eqns. [8ac], 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:

    Pollution and Remediation _ Acidification 3directly 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.[5ad]

    Carbonic acid system:

    CaCO3 2H , Ca2 CO2 H2O 5a

    CaCO3 H , Ca2 HCO3 5b

    CO23 H , HCO3 5cHCO3 H , H2CO3 5dH2CO3 , CO2 H2O 5e

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

    Feldspar dissolution:

    KAlSi3O8 7H2OH , AlOH3 3H4SiO4 K6a

    2KAlSi3O89H2O2H,Al2Si2O5OH44H4SiO42K6b

    KAlSi3O84H2O4H,Al33H4SiO4K 6c

    Clay dissolution:

    Al2Si2O5OH4 6H , 2Al3 2H4SiO4 H2O 6d

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

    Aluminum system:

    AlOH3 H , AlOH2 H2O 7a

    AlOH2 H , AlOH2 H2O 7b

    AlOH2 H , Al3 H2O 7c

    Iron system:

    FeOH3 H , FeOH2 H2O 8a

    FeOH2 H , FeOH2 H2O 8b

    FeOH2 H , Fe3 H2O 8cSO24 H , HSO4 11

    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.

    35

    30

    25

    20

    15

    Num

    ber o

    f lak

    es

    10

    5

    02 3

    Fe3+ HCO3AI3+

    4 5pH

    6 7 8 9

    Figure 1 Frequency distribution of the pH values of 159 mininglakes 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 (Fe3), aluminium (Al3), and bicarbonate (HCO3 ).

  • water-saturated anoxic underground. Once in con-tact with air, the oxidation goes on rapidly and

    waters increase from about 50mg L at pH5 in softwaters, which result from atmospheric deposition, to

    10

    9 Lake Felix

    4 Pollution and Remediation _ AcidificationThe 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 the

    8

    7

    6

    pH v

    alue

    5

    4

    3

    20 2 4

    ML 117ML 110ML 111

    6 8Added alkalinity in meq L1

    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 (Fe3) and aluminum (Al3).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 (HSO4 ) may act as buffer. Ion exchange withparticles, silicates, and the carbonate buffering system are

    relevant at pH above 5, depending on the availability of

    suspended particles and (bi-)carbonate.plateaus 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. [1215]). 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 7=2O2 H2O , Fe2 2SO24 2H 12

    Fe2 1=4O2 H , Fe3 1=2H2O 13

    Fe3 3H2O , FeOH3 3H 14

    FeS2 14Fe3 8H2O, 15Fe2 2SO24 16H 15

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

    The atmospheric pathway distributes acidic gaseous

    SO2, 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 the100g L1 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 some

    constituents 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 metals

    result from sulfide oxidation as well as from bufferingprocesses in soil and water (eqns. [59,12,15]). 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 Rainforms 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 natural

    conditions 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 acid

    1

  • 76

    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 1

    0 of a

    cidity

    (Acy

    ) in m

    eq L

    1 or

    conce

    ntra

    tion

    in m

    g 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

  • 6 Pollution and Remediation _ Acidification765deposition 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

    Acy SO42 Ca Mg Na Fe AI MK

    Acy(b) SO42 Ca Mg Na Fe AI MK

    4

    321

    1234

    0

    7654321

    1234

    0

    Log 1

    0 of a

    cidity

    (Acy

    ) in m

    eq L

    1 or

    conce

    ntra

    tion

    in m

    g L

    1

    Figure 3 Characteristics of acid drainage by the concentrations ofbox limits are 25 and 75 percentiles, and whiskers show the 10- and 9or 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

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

    Figure 4 pH values of the waters comprised in Figure 3. Lines witpercentiles, and whiskers show the 10- and 90-percentile values. Sin

    respectively (nd not detected).Waters acidified by atmospheric deposition(by acid rain)waters seeping through the soils dissolve furtherminerals, especially Al-silicates. These waterscause the acidification of ground water and surfacewaters.

    n Zn

    Acid volcanic waters

    Cu Ni As

    nd nd nd

    Cd Pb Co Cr Si

    n Zn Cu Ni As Cd Pb Co Cr Si

    chemical constituents. Lines within the boxes are median values,

    0-percentile values. Single dots indicate data below 10 percentile

    0 1 2 3pH-value

    4 5 6

    hin the boxes are median values, box limits are 25 and 75gle dots indicate data below 10 percentile or above 90 percentile,

  • ate-free, and the affected waters are enriched in

    Belt, the worlds largest deposit of pyrite and other

    Pollution and Remediation _ Acidification 7sulfate 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 cationsCa2, Mg2, and K is lower than 20% of the totalcation exchange capacity, or the acid neutralizationcapacity (ANC) is below 025 meq L1. Estimationsof the critical loads in geologically sensitive areasshowed a range of annual sulfur depositions between300 and 800mg m2.After the emissions of sulfur dioxide and nitrogen

    oxides, transport times of 1521 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 occursBeyond 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 Ca2 and Mg2

    cations by H and Al3. After a large-scale process oftitration, the impacted soils and waters are carbon-sulfidic 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 across

    an 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-Eastafter 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 was

    estimated 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 Rio

    Odiel are natural drainages of the Iberian Pyrite

  • affected rivers, e.g., Murray, Darling. The total area

    brates disappeared with pH below 4.8. In a survey of

    8 Pollution and Remediation _ Acidificationextent 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 100 g/kg, SO2470 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 SO24 , 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 theAsia, 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 (60007000yearsBP) 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 theneutral 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 heavy

    metals 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 miningPatuha 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 Argentina

    at Copahue Volcano, supplying the 13km-long RioAgrio, an extremely acidic river with pH0.61.6.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

  • Ac

    In

    p

    ifie

    od

    Pollution and Remediation _ Acidification 9Success 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-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.

    50

    40

    30

    20

    10

    01 2 3 4

    Acidic pit lakesN

    umbe

    r of b

    enth

    ic in

    verte

    brat

    es ta

    xa

    Lakes acid

    Figure 5 Macrozoobenthos in acidic lakes. (By courtesy of G. Rtion 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

    miis aofbypoacme(c)biotra

    trethi

    anThcothetion preceding biological response. Biologicalrecovery is emerging along the given generationlengths, zooplankton and macroinvertebrates need310 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.

    id Mine Drainage and Acid Sulfate Soils

    areas exposed to geogenic acidification from acidsuspended limestone. Thereby, 6000 lakes and halfof the acidified area could be treated. Remediationappears as a two-step process, chemical remedia-

    5H-value

    d by acid rain

    6 7 8

    rigues, Diss. Techn. Univ. Braunschweig 2001).ne drainage, a broad spectrum of countermeasuresvailable and under development. The acidificationlakes and rivers by acid drainages can be preventedpreclusive measures and direct treatment of thelluting waters as (a) restrictions on running miningtivities, (b) neutralizing the waters by active treat-nt of the AMD by addition of alkaline chemicals,passive treatment using natural geochemical andlogical reactions to reduce acidity, and ion concen-tions, and (d) the in situ treatment of acidic lakes.The different approaches for remediation andatment are described in a separate article withins encyclopedia.The problems of acid sulfate soils are complex,d the approaches for countermeasures are limited.e primary option appears as reducing andntrolling the artificial drainage, thereby decliningaccess of oxygen to the sulfidic layers. Acid

  • n = 3 n = 42 n = 119

    eg

    n = 105

    E

    s f

    ario

    souws

    alu

    ns.ker

    tur

    10 Pollution and Remediation _ Acidificationdrainage water from sulfate soils can be treated with

    4.0

    RELA ONTW ONTC ONT

    Figure 6 Distribution of modeled andmeasured pH values of lakeArea, western Ontario; ONTW region east of Lake Superior, Ont

    ONTE region east of Georgian Bay of Lake Huron, Ontario; QC NF Newfoundland). Within each regional block, the first box sho

    shows 1975 (worst case) distribution, the third shows year 2000 v

    agreed-to Canadian and currently proposed US emission reductioare median values, box limits are 25 and 75 percentiles, and whis

    Environment Canada 2007). Source: Clair et al. (2007) Past and fu

    modeling approach. Applied Geochemistry 22: 11891195.7.5

    7.0

    6.5

    6.0pH

    5.5

    5.0

    4.5the 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 11.5m, 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 3.94.5) by oxidation of the loadof 3000 tons of ammonium-N per year. After stop-ping the input of industrial wastewaters, the lake wastreated 19891990 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.7.5

    7.0

    6.5

    6.0

    5.5

    5.0

    4.5

    4.0n = 9

    ion

    n = 23 n = 63 n = 22

    QC NB NS NF

    rom different regions of Eastern Canada (ELA Experimental Lake

    ; ONTC region north of the central part of Lake Huron, Ontario;

    thern Quebec; NB southern New Brunswick; NS Nova Scotia;the distribution of modeled pre-acidification values, the second

    es, while the fourth box describes expected values under further

    The number of sites in each region is given. Lines within the boxess show the 10 and 90 percentile values. (By courtesy of e changes to acidified eastern Canadian lakes: A geochemicalConclusions

    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

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

    Persson G (2008) Zooplankton response to long-term liming: Com-

    Pollution and Remediation _ Acidification 11sources, 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.parison of 15 limed and 15 reference lakes in Sweden. Limnolo-gica 38: 113.

    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-1999000021: 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: 149157.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 Earths 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 141:349382.

    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: IWAPublishing.

    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: 180198.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: 180.

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

    in Sweden Effects and countermeasures.Ambio 22(5): 257337.Folster J and Wilander A (2002) Recovery from acidification in

    Swedish forest streams. Environmental Pollution 117: 379389.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 338:314.

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

    nism of acid mine drainage in wetlands: A critical review.Miner-als Engineering 19: 105116.

    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. 15491561. Philadelphia: Lippincott-RavenPublishers.

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

    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

    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.

    12 Pollution and Remediation _ AcidificationTransboundary 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

    AcidificationIntroductionChemistry of Acidified Waters and Buffering MechanismsCarbonic Acid and Fresh WaterDefinitions and DimensionsAlkalinity and acidityBuffering systems: the weak acids of carbon, aluminum, and ironPyrite weatheringConcentrations of dissolved substances in acid waters

    Types and Extent of Acid WatersAtmospheric Deposition and Acid RainAcid Mine Drainage (AMD)Drainage from Acid Sulfate SoilsThe case of western FinlandThe case of Australia

    Volcanic Waters and Crater Lakes

    Biological Effects of AcidificationSuccess of Countermeasures and Long-Term DevelopmentsRain-Acidified WatersAcid Mine Drainage and Acid Sulfate SoilsLake Orta: Acidified by Industrial Waste and Remediated by Liming

    ConclusionsGlossaryFurther ReadingOutline placeholderOutline placeholderOutline placeholderfigfigfigfigfigfigfigfigfigfigfigfigfigfigfigfigfigfigfigfigfig

    Relevant WebsitesOutline placeholderOutline placeholderOutline placeholderfigfigfigfigfigfigfigfigfigfigfigfigfigfigfigfigfigfigfigfigfigfigfigfigfig

    Glossary