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Acidification and Arctic Haze

The road eastward from Finnish Lapland to the Kola Peninsulaof Russia is a testimony to the severe local effects of pollution inthe Arctic. At the border, the coniferous forest appears healthywith a thick mat of reindeer lichen covering the ground. Then,as one approaches the nickel-copper smelters of Zapolyarnyyand Nikel, the scenery changes drastically. Dead tree trunkswithout any needles left at all. The ground bare and eroded. Oneof the major culprits in this forest death is emissions of acidify-ing sulfur dioxide. Effects on nearby streams and lakes are notas immediately visible, but nevertheless real. Mayflies and otheracid-sensitive animals, including fish, are threatened.

This chapter describes local as well as regional emissions of acid-ifying air contaminants, along with pathways and effects on theArctic environment. It also explores the future impact on north-ern soils and waterways if the current emissions are not reduced.

Contaminants that cause acidification are also involved in thephenomenon of Arctic haze, which obscures visibility when thesun finally returns to the Arctic after the long polar winter. Thischapter addresses the causes of the haze and its impact on theenvironment.

Acidification – a short historyAwareness of acidification as an environmentalproblem has a long history. Fish kills connect-ed to acidification were observed in Norwe-gian rivers as early as 1911. However, the prob-lem did not receive international attention un-til the late 1960s, when similar observationswere made in Sweden, Canada, and the UnitedStates. At that time, suspicions that rain wasthe cause were confirmed with observations ofhigh levels of sulfuric acid in rainwater.

The surprise was the source of the acid in therain over southern Scandinavia: most of it camefrom continental Europe and Great Britain. Itwas one of the first documented cases showingthat pollutants can create havoc in ecosystemsfar from their sources. Scandinavia’s waterssuffered because its soils could not buffer theacid as effectively as soils closer to the pollu-tants’ sources. This new scientific understand-ing had immediate political implications, serv-ing as the starting point for international nego-tiations about controlling substances thatundergo long-range transport. Pollution hadbecome a regional rather than a local problem.

Since the 1960s, the acidification questionhas widened. Today, the focus is not only onstreams and lakes but also on vegetation and

on interactions between acidifying contami-nants and other factors, such as ground-levelozone, eutrophication, and climate change. Asa result of the intense scientific and environ-mental policy work on acidification, thesources of acidifying contaminants are fairlywell understood, as are the atmosphericprocesses that govern their transport.

SourcesOxides of sulfur are the major acidifying com-pounds in the Arctic. They are formed whenfossils fuels burn and when sulfide ores aresmelted. Release of sulfur dioxide to the envi-ronment has risen with the growth in energydemand and industrial activity.

Industrial areas farther southcontribute to Arctic air pollution

Most sulfur in Arctic air comes from industrialareas further south. Eurasia (40 percent) andeastern North America (20 percent) are themajor global sources. A large part of theremaining global emissions occur in the FarEast, particularly China. The map above indi-cates the geographical distribution of sources.

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Emission of sulfur in theNorthern Hemisphere,gigagrams (1000 tonnes)in 1985.

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Emissions of sulfur dioxide have decreasedconsiderably in North America and Europeafter a peak in the late 1970s and early 1980s.This results from an interplay of political deci-sions to cut emissions, the replacement of‘dirty’ fuels, and new technologies for remov-ing sulfur from fossil fuel and for cleaning fluegases in power plants. Nonetheless, powergeneration and smelting remain major sources.

Metal smelters have the largest emissionswithin the Arctic

Production of copper, nickel and other non-ferrous metals from sulfur-bearing ores createthe largest emissions of acidifying substanceswithin the Arctic. The traditional smeltingmethod roasts the ore to remove the sulfur assulfur dioxide and to oxidize the iron in theore before further smelting and refining. Thesulfur dioxide can be recovered in modernsmelters and used as a raw material for pro-ducing sulfuric acid, gypsum, and some otherinorganic chemicals. However, this is economi-cally feasible only when the smelters are closeto other industries.

Most smelter emissions come from theNikel, Zapolyarnyy, and Monchegorsk com-plexes on the Kola Peninsula and from Norilskin northwestern Siberia. Compared with simi-lar industries in other areas, emissions fromthese smelters are extremely high. Norilsk isthe largest source, spewing out more than amillion tonnes of sulfur every year.

Sulfur emission from thesmelters on the KolaPeninsula and Norilsk,Russia in 1992, giga-grams (1000 tonnes).

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The old nickel smelter,Norilsk.

Local energy production is a small source

Emissions from energy production in theArctic are generally low because the popula-tion is sparse. There are coal-fired powerplants in Vorkuta and Inta in Russia, servinglocal settlements around coal mines and gasfields in the area. The mining settlements onSpitsbergen also have coal-fired power plants.

Shipping and fishing fleets are also sourcesof sulfur. The extensive fishing fleet in theBarents Sea uses large amounts of diesel fuel.Marine transport, particularly of timber andtimber products, is important along theSiberian coast and on Siberian rivers.

Algae and volcanoes are natural sulfur emitters

Oceans are a source of sulfur to the atmos-phere in the form of dimethyl sulfide (DMS)produced by algae. Globally, they contribute15-30 million tonnes of sulfur per year, most

of it during the peak productive season. This isof the same magnitude as anthropogenic emis-sions from Europe. In the Arctic, the peak inDMS production is between June and August.Marine sulfur may account for as much as halfof the sulfur in the air over Spitsbergen duringthe summer peak. On a yearly basis, however,the marine share is only 2 percent of the total.

Erupting volcanoes can emit considerableamounts of sulfur. For example, Mount Pina-tubo in the Philippines released 7.8 milliontonnes when it erupted in 1991. On averagehowever, volcanoes contribute an order ofmagnitude less sulfur to the global atmospherethan do the oceans. While the Arctic has sev-eral active volcanoes, in the North Atlantic, inthe Bering Sea, and in southern Alaska, volca-noes generally emit to the upper atmosphereand do not contribute to local acidification.

An interesting local source of sulfur is theSmoking Hills in Canada, where emissionsfrom natural combustion of shale are highenough to damage vegetation up to 500 metersfrom the source. However, compared with therest of the Arctic, the quantity of sulfur is neg-ligible.

Nitrogen emissions are less important

Burning of fossils fuels also creates nitrogenoxides. In more densely populated areas, traf-fic and power production are the most impor-tant sources. Emissions increased rapidly fromthe 1950s to 1975. In North America andEurope, they have remained fairly constantsince 1980. Nitrogen oxides contribute toacidification in non-Arctic parts of Europe andNorth America, but are less important in theArctic context.

Atmospheric processesThe fate of sulfur and nitrogen emissionsdepends on what happens in the atmosphere.Light, moisture, and reactive chemical com-pounds in the air act together to transform sul-fur dioxide and nitrogen oxides into acid pre-cipitation and into particles that can settle onsurfaces they encounter. The box to the leftdescribes the air chemistry of sulfur.

When air from mid-latitudes moves north-ward with its load of contaminants, it rises,forming layers of dirty air at higher altitudes.However, pollution released into the Arctic air-mass tends to remain within a couple of kilo-meters of the ground because of temperatureinversions that create a lid of cold air.

In the spring and winter, lack of precipita-tion in the High Arctic keeps acidifying conta-minants suspended in the air. Sparse vegetationalso provides for low deposition rates of par-ticulate matter. During summer, two mecha-nisms keep the air cleaner: first, the northwardshift of the Arctic front, away from major

132Acidificationand Arctic haze

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Fossil fuels with high sulfur content produce sulfur dioxide when they burn. In theatmosphere, the gas reacts with hydroxyl radicals (OH), ozone, and peroxide (H2O2),creating sulfuric acid (H2SO4).

In the cold air of the High Arctic, sulfuric acid takes the form of sub-micrometerparticles, which are the main components of Arctic haze. Sulfate particles can adheredirectly to surfaces as dry deposition.

Sulfuric acid can also react with water in rain, snow, and fog, dissociating intohydrogen and sulfate ions, which get washed out as wet deposition.

Biogenic sulfur compounds, such as dimethyl sulfide (DMS) from plankton andhydrogen sulfide (H2S) from volcanoes, enter the same chemical cycle in the atmos-phere via a reaction with hydroxyl radicals (OH).

The rates of different chemical reactions in the sulfur cycle depend on energy fromthe sun. In the Arctic, lack of sunlight during the polar winter limits production of thehydroxyl radical, which in turn slows production of sulfuric acid from sulfur dioxide.When the sun returns in the early spring, there is a load of sulfur dioxide in the air,ready to be converted into sulfate aerosols. This photochemical mechanism explainswhy Arctic haze is most pronounced in March and April, after the Arctic sunrise.

source regions, reduces contaminant inputs,and second, increased precipitation washesacid contaminants out of the air.

Air concentrations are highest aroundKola and northern Fennoscandia

Measurements of air concentrations of sulfurdioxide show that the Kola Peninsula andnorthern Fennoscandia bear the brunt ofEuropean emissions that find their way to theArctic; see the map to the right. Moreover,large local emissions in this region add to theburden, causing episodes of extremely pollutedair. Peak levels are comparable to pollutedregions in central Europe.

By combining detailed meteorological infor-mation with data on emissions, it is possible tomake computer models of the transport, trans-formation, and removal of acidifying gases andaerosols. The models suggest that all sourcescontribute to high levels of sulfur dioxide dur-ing winter months. Only in the Kola andNorilsk regions are local sources dominant.

Long-term trends in emissions show up in air concentrations and glacier ice

Emissions of sulfur dioxide from Eurasia havedecreased significantly since the mid-1980s. Atthe monitoring station in Ny-Ålesund, Sval-bard, this shows up as a decreasing trend insulfate concentration; see the graph below.However, in the Canadian High Arctic, sulfateconcentrations in air have remained almostconstant. A series of measurements from Alertshows a peak every March and April, but nosignificant trends. This indicates that emissionswithin the subregions of Eurasia that affectAlert and Svalbard have changed differently.

Another important source of informationfor assessing the development of Arctic air pol-lution is glacial ice. The accumulated snow,which can be analyzed in ice cores, reflects thechemistry of the atmosphere at the time ofdeposition. Such measurements of snow andice composition have been made in Greenland,on northern Ellesmere Island, Canada, and onMount Logan in northwestern Canada.

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The historical record from Greenland indi-cates that there has been an increase in theconcentrations of strong acid anions in thiscentury, starting in the 1930s or 1950sdepending on where the ice core was taken.The historical record for conductivity, whichis closely correlated with acidity, indicates anincrease of about 75% between 1956 and1977. This trend mirrors European sulfurdioxide and nitrogen oxide emissions.

Measurements of recently accumulated icelayers indicate that the peak in sulfates andfine particles occurred at the beginning of1980s. There were no major changes duringthe 1980s, but decreases were detected atsome stations at the end of the decade. Theserecent trends can be attributed partially todocumented reductions in sulfur emissions inEurope, and partially to the replacement ofcoal by natural gas to produce heat and elec-tricity, particularly in the former Soviet Union.

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Annual average air con-centrations of sulfurdioxide.

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Highest deposition is around the smelters

While air concentrations are important forunderstanding transport of acidifying contami-nants and direct impacts of sulfur dioxide onforests, data on deposition gives a better pic-ture of the acid load on vegetation, soil, andwater. Deposition depends not only on air con-centration, but also on how effectively precipi-tation washes out acidifying substances, andon how effectively acid particles adhere to sur-faces such as snow and vegetation.

The general picture is that the sulfur deposi-tion in northern Canada, Alaska, and Green-land is low, whereas the load in the Barentsand Taimyr regions is relatively high; see themap above. The levels range from slightlyabove background in the low-deposition areasto several grams of sulfur per square meter inareas close to Russian smelters, which is ashigh as in the polluted areas of central Europe.

The most detailed information on deposi-tion patterns comes from northern Fennoscan-dia and the Kola Peninsula because of concernover the fate of the large sulfur dioxide emis-sions from Russian smelters in the region.Emissions seem to have only a moderate influ-ence on precipitation in areas farther than 20-50 kilometers from the smelters. Surprisinglylittle information is available from Norilsk,which has the largest smelters in the Arctic.

Acidifying particles can also deposit directlyon vegetation, on rock surfaces, or on snowand ice rather than through precipitation. Suchdry deposition is low in the Arctic because sur-faces of snow and ice are relatively inefficientin gathering acidic particles and gases com-pared to vegetation-covered surfaces or water.However, it accounts for a high proportion ofthe total deposition in areas close to thesources. For example, approximately 75 per-cent of acid deposition on the Kola Peninsulais through dry deposition. Research into thefate of contaminants when they encounter treecanopies supports the idea that dry depositionof sulfur is the dominant pathway of acidifyingpollutants into ecosystems around smelters.Beyond 150 kilometers, dry deposition con-tributes much less to total deposition.

Arctic hazeThe term Arctic haze was coined in the 1950sto describe an unusual reduction in visibilitythat the crews of North American weatherreconnaissance planes observed during theirflights in the High Arctic. After further studyof visibility data in the mid 1970s, it becameclear that the haze was seasonal, with a peakin the spring, and that it originated from

134Acidificationand Arctic haze

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anthropogenic sources outside the Arctic. Themost severe episodes occur when stable high-pressure systems produce clear, calm weather.Visibility can be reduced to 30 kilometers, inspite of the otherwise clear weather. MatthewBean, a Yupik Eskimo elder from Bethel,Alaska, describes the changes he has seen inthe sky: ‘Sometime back, the skies on a clearday used to be deep blue all over, even at thehorizon. Now you hardly ever see that any-more, especially on the horizon. It is alwayspale blue, almost white or even dirty gray. Itmakes me sad to see what future generationsare going to have to put up with.’

Haze aerosols are mainly sulfate

The haze has been thoroughly analyzed. It con-sists of sulfate (up to 90 percent), soot, andsometimes dust. The particles are about thesame size as the wavelength of visible light,which explains why the haze is so apparent tothe naked eye. The composition of haze hasbeen used as a chemical fingerprint to identifyits sources. The presence of black carbon and aparticular relationship between the metalsvanadium and manganese indicate coal burn-ing. Most of the particles originate in Eurasia.

The transport routes for the haze are wellunderstood. Eurasian emissions are much moreimportant than those from North America, inpart because the Eurasian sources are 5o to 10o

further north than those in North America.Moreover, the Arctic air mass stretches rela-tively far south over the Eurasian landmassduring the winter. The contaminants are thuspicked up by the airmass that moves north-ward and over the pole in winter months.

Winter blocking favors transpolar transport

Why is Arctic haze important? First, it com-pletely changed the earlier notion that aerosolpollution could only be local or regional. Thecold, dry air in the polar regions allows parti-cles to remain windborne for weeks rather thandays, which in turn allows sulfur contaminantsto spread from industrial sources in Eurasiaacross the entire Arctic and into North America.

Second, haze particles might give metals andother contaminants a free ride to and withinthe polar region. Metals as well as some persis-tent organic compounds adhere to aerosolsand could be deposited along with the aerosolsSubstantial amounts of industrial contami-nants may thus be washed out by precipitationoccurring over major ocean areas surroundingthe Arctic.

Arctic haze often appears in distinct bandsat different heights because the warm dirty airis forced upward until it reaches the dome ofcold air that sits over the North Pole in winter.The clear, cold winter weather is one impor-tant reason why Arctic haze occurs in winterand spring and not in summer and fall.

The most apparent effect of the haze is thatit reduces visibility. The figure above showshow severe the situation can be in differentparts of Canada, but the phenomenon occursthroughout the High Arctic. The haze has pre-viously been considered a hazard to air traffic,but today’s automated navigation systems havemade poor visibility less of a problem.

In spite of their impact on visibility, the lev-els of sulfur compounds are much lower thanthose found in heavily polluted cities. Duelargely to low deposition rates, the haze causesneither adverse effects on plants and animals,nor direct health problems in people.

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Arctic haze overGreenland

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The haze absorbs and scatters solar energy

Recently, Arctic haze has also been broughtinto discussions on global climate change.Unlike regions with low surface reflectivity,acidic and soot-laden aerosols over highlyreflective snow tend to warm rather than coolthe spring Arctic atmosphere. At certain timesof the year, a viewer from space would see theNorth Pole as orange-brown rather than whitebecause of the soot in the haze. The conse-quences for global climate are poorly under-stood and climate models are just starting totake the haze into account. They suggest smallbut measurable effects.

Levels in soil and waterThe impact of acid deposition on soils andfreshwater ecosystems depends to a largeextent on whether acid precipitation has anopportunity to percolate through the soil, andif so, on the type of soil in that area. Soil chem-istry has been extensively studied during pastdecades, and the emerging picture explains whythe same acid deposition has little effect in someareas and severe consequences in others.

Poorly buffered soils are sensitive to acidification

In waterlogged areas of the tundra and inmany areas with permafrost, the soil consists

mainly of peat. These soils are naturally acidic.The high content of organic matter means thatthey are strongly buffered and therefore resis-tant to acidification by airborne contaminants,at least at moderate levels of deposition.

Mineral soils are low in organic matter andcan be much more sensitive. Their reaction toacids depends to a large extent on the weather-ing rate of the parent material. In many areasof the Arctic, glaciers removed all the soil andmost of the weathered material, leaving onlyrelatively inert silicate-rich rocks, many ofwhich have a low capacity to supply base ions.

Locally, however, carbonate minerals createsoils that are fairly resistant to acidification,because they supply base ions at a high enoughrate to neutralize the acid.

Clay content of soil is also important. Thefine particles of which clay is composed have alarge surface area, which increases the soil’scapacity to buffer acidic water. A high contentof organic material can have the same effect.Coarse soils, on the other hand, often let thewater through too fast for effective buffering.

The figure on the opposite page highlightsthe areas that are sensitive to acidification.They include most of northern Fennoscandia,the northern Kola Peninsula, and non-carbon-ate rocks and coarse-textured shallow soils onthe Canadian Shield. The area around theSeveronickel and Pechanganikel smelters onthe Kola Peninsula have basic or ultrabasicrocks, with a high buffering capacity. Many ofthe islands of the Canadian Archipelago alsohave acid-resistant soils.

The rate at which the acidic water percolatesthrough the soil will determine whether the buf-fering capacity will be fully used. If most of thewater comes during a short period, as is commonduring the snowmelt season, it will run directlyinto streams and lakes rather than through thesoil. In the Arctic, percolation through the soilcan also be inhibited by permafrost.

Soil damage is limited to vicinity of smelters

The only evidence for soil acidification in theAMAP area comes from the immediate vicinity(0 to 30 kilometers) of the nickel-copper smel-ters on the Kola Peninsula. In these areas, basesaturation levels, i.e. the amount of basiccations available for buffering, can be as lowas 15 percent. The base cations in the soil haveprobably been replaced by high loads ofhydrogen ions and heavy metals.

In northern Fennoscandia and other parts ofnorthwest Russia, base saturation levels rangefrom 15 to 80 percent. Theoretical calculationssuggest that the sulfur deposition load in someparts of northern Fennoscandia exceeds thecritical load for forest soils. However, the ac-tual sulfur concentration in the humus is onlyslightly elevated, and there are no signs ofaccelerated soil damage due to acidification inthe northernmost parts of Finland, Norway,and Sweden.

A major concern with acidified soil is thatthe low pH will allow aluminum to leach out,but the maximum reported total aluminum con-centration in ground water, 2 milligrams per li-ter, is well below the threshold value for the onsetof aluminum damage to roots. The high organicmatter content of the podzol soils of this areaalso means that a large portion of the availablealuminum is in a form that is not toxic to plants.

There is no information about the soilaround Norilsk. In Chukotka and on WrangelIsland, base saturation levels are very high.

136Acidificationand Arctic haze

pH and buffering capacity

Acidity is measured as pH, which indicates the concentration of hydrogen ions (H+)in a solution. At pH 7, a solution is neutral, meaning that the concentration of H+ isequal to the concentration of hydroxyl anion (OH-). Below pH 7, H + dominates anda solution is acidic.

pH is a logarithmic function, and each step in the scale is a tenfold change in acid-ity. If the pH in a lake has decreased from 7 to 6, the acidity has increased ten times,if the pH has changed from 7 to 5, the acidity is one hundred times higher, and so on.

The sensitivity of soils and lakes to acid precipitation depends to a large degree onprocesses that resist acidification. Weathering of basic minerals neutralizes incomingacidity and provides base cations for buffering cation exchange. Over time this buf-fering capacity can be exhausted if the rate of acid deposition is higher than the geo-logical production of new base cations, resulting in a very rapid drop in pH. Measur-ing the share of base cations from the overall cation exchange capacity, i.e. base satu-ration, gives an estimate of the present status of soil acidification and sensitivity tofurther acidification.

The analogous sensitivity of water to acid deposition is expressed as alkalinity.A lake with high alkalinity has a high ability to resist changes in pH.

The predominance of high base saturationlevels in Arctic and subarctic soils means thatat present deposition rates, it will take sometime before the buffering capacity of mostareas is exhausted and the effects of acid depo-sition become apparent.

Running water is vulnerable to acid pulses

The effects of acid deposition on lakes andstreams depends on whether the runoff haspercolated through buffering soils and on thetime allowed for buffering reactions to occurin the lakes and streams themselves.

Similar to soils, lakes have a bufferingcapacity that can be depleted by excess acidinputs. Whether and how quickly such deple-tion occurs depends on the size of the reserve(alkalinity) and how long the water stays inthe lake. Acidification can thus also bedescribed as a loss of alkalinity, similar to theloss of base cations in soils. Lakes have someability to counteract the loss of alkalinity.Microorganisms that process sulfates andnitrogen also release calcium, magnesium, andpotassium from lake sediments, restoring somealkalinity. This repair potential depends on therate at which sulfates, nitrates, or other anionsare available.

During snowmelt, streams can be more sen-sitive to acidification than lakes, because therunoff water filling the streams carries the acidload gathered in the snow throughout winter.This situation is exacerbated because mostacids in the snow are released at the beginningof the spring melt. Often, the first 20 percentof the meltwater contains up to 80 percent ofthe major acidic cations, increasing the averageconcentration by a factor of four. Early melt-water seldom percolates through the soil, sincethe ground is still frozen, but flows directlyinto the streams in the catchment area. Even inlow deposition areas, such acid pulses canhave a pH below 5.5. During later snowmelt,the quality of the meltwater usually improvesas most acidifying compounds have alreadywashed out.

137Acidification

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Critical loads tell about sensitivity

How much acid deposition can the soil and water in a catchment area handle beforeacidification will affect plants and animals in the long run? The answer to this ques-tion is summarized as the ‘critical load’. The critical load depends on how effectivelyand how fast the soil and water chemistry can resupply the base ions that neutralizethe deposited acid. If the input of sulfuric acid is faster than the regenerating proces-ses, the soil and water will slowly but surely become more acidic. The critical load ofacidity is exceeded when the calculations show that the pH will eventually drop farenough to affect plants and animals.

Critical loads have been calculated and mapped for Europe and are used as a basisfor political negotiations about reducing acidifying emissions under the auspices ofthe Convention on Long-range Transboundary Air Pollution (LRTAP).

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Sensitivity of terrestrialecosystems to acid depo-sition.

Streams and rivers reflect proximity to smelters

The figure above shows some of the time trendsin acidification of the waterways in northernFennoscandia and the Kola Peninsula.

In northern Norway one might expect acidi-fication of rivers close to the nickel-coppersmelter at Nikel. In the river Jakobselva, sul-fate concentrations are indeed high with amarked decrease in alkalinity in the spring, butnot elevated enough to cause acid water. Theriver Dalelva, on the other hand, clearly suffersfrom acidic pulses during the spring flood. Forinstance, during the spring of 1990, its pHdropped from 6.2 to 5.0 in just one day whenthe snow started melting. A comparison ofannual average values shows that the qualityof water here has improved during the pastfew years.

The rivers of the Kola Peninsula have suf-fered a significant decrease in alkalinity, andsome streams have had severe acid pulses. Onan annual basis, there is some indication of aslight recovery of alkalinity in recent years.

The results of Finnish monitoring of riverwater chemistry show that acidification of thewater has leveled out. Since the 1970s, therehas been no decrease in pH. Moreover, thebuffering capacity has remained high, andalkalinity has increased between 1980 and1995.

Measuring sulfate content provides anotherindication of how waterways respond to chang-ing deposition. In the western parts of FinnishLapland, which are influenced more by emis-sions from outside the Arctic than from the KolaPeninsula, there is a slight decrease, reflectingthe decline in emissions. In northeastern Lap-land, the concentrations are more stable.

The rivers in northern Sweden mirror thedecrease in European emissions, with sulfateconcentrations decreasing since the late 1970s.The buffering capacity is largely unchanged.

However, in many small streams there is adecline in animals that are sensitive to low pH.The annual average pH of these streams isabove 6, but the damage may be caused by thebrief acid pulse from the first days of snowmelt.

Many lakes are acidified or susceptible

Small lakes are sensitive to changes in waterchemistry and are therefore used for monitor-ing acidification. One of the hardest-hit areasin the Arctic appears to be Sør-Varanger,Norway. Some of the lakes have no alkalinityleft, and almost half the lakes have a pH of lessthan 6.0. Since 1986, however, there has notbeen any further acidification. Recently, theconcentrations of some buffering ions in lakeseast of Kirkenes and in the Jarfjord regionhave even increased, which could be a first signof recovery from acidification.

There are acidified lakes throughout thenorthern Kola Peninsula, and strongly acidi-fied lakes in the mountains of the Kiopukas,Chuna, Volchii, and Monche regions. North-ward from Pechenga along the Barents Seacoast, the condition of the lakes is critical.

The lakes of northeast Finland have lostmuch of their buffering capacity. In the mostsensitive areas, northeast of Lake Inari, somelakes have no alkalinity left. Map ‘A’ oppositeshows the status of lake acidification in theFennoscandian Arctic and the Kola Peninsula.

The lakes in the AMAP region of Canadahave not been acidified to any significantextent. Some lakes with extremely low pHseem to have been unproductive throughouttheir existence because of natural acidification.Data from Prudhoe Bay in Arctic Alaska alsodo not indicate any acidification. However,some small ponds in the Arctic NationalWildlife Refuge have low alkalinity and poorbuffering capacity and would therefore be sus-ceptible to acidification.

Map ‘B’ opposite shows the critical load ofsulfur for Arctic lakes. The critical load varies

Time trends for alkalinityin some rivers andstreams in northernFennoscandia and theKola Peninsula, micro-equivalents per liter.

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geographically, with values ranging from 300to 1300 milligrams sulfur per square meter peryear.

The largest area where the critical load iscurrently exceeded is in northern Finland,Norway, and the Kola Peninsula. In Sør-Varanger, 70 percent of the area cannot buffercurrent depositions, most of which come fromemissions on the Kola Peninsula. On the KolaPeninsula itself, the critical load is exceeded inalmost half of the area.

The groundwater has not suffered yet

Groundwater benefits from the capacity of soilto buffer acidic surface water. In Finland, thereare no signs that acidification is taking place.At a groundwater station near the Finnish-Russian border, at Nellim, there has been noappreciable change in alkalinity or pH duringthe 15-year monitoring period.

Also, in inland Norway and northernSweden, the groundwater has not beenaffected by strong acids, nor has there beenany continuous groundwater acidification.

Effects on plants and animalsWhen the levels of sulfur dioxide in the air arehigh enough or when soil and water have beenseverely acidified, plants and animals will suf-fer. Such visible deterioration of the environ-ment is well documented in the vicinity oflarge smelters.

Loss of soil fertility contributes to tree death

Soil fertility depends on the availability ofnutrients. In upland soils, nitrogen is often alimiting factor for tree growth, and on peat-land, phosphorus and potassium are usually inshort supply. Acid deposition in the form ofnitrogen compounds can increase soil fertilityin the short term, but acidification will eventu-ally deplete soils of many of their nutrients.

Neither soil-chemistry analysis nor investi-gation of the nutrients in tree needles indicateany loss of soil fertility in northern Fenno-scandia.

Close to the smelters at Monchegorsk andNikel on the Kola Peninsula, there is a severedecrease in soil fertility caused by high inputsof nickel and copper, which have replacednutrient ions. The levels of several macronutri-ents and trace elements are extremely low,both in the soil and in tree needles, and thepoverty of the soil has undoubtedly con-tributed to tree death in the area.

Fungi and microorganisms help maintainsoil fertility by breaking down plant matterinto humus. Studies of areas close to thePechenga nickel-copper smelter show that thenumber of species has decreased and that these

decomposer communities are now dominatedby acid-resistant species. While it is difficult toseparate the effects of acidification from theeffects of heavy metals, the result of the com-bined stress is dramatic. In the area closest tothe smelters, the humus layer has completelydisappeared.

Sulfur dioxide has damaged the forest

Aside from its acidifying effect on the soil, sul-fur dioxide can harm plants directly. If the lev-els in the air are high enough, needles andleaves are damaged. At lower levels, acid depo-sition stresses plants, making them more vul-nerable to diseases and harsh weather.

The critical level of sulfur dioxide for forestecosystems at low temperatures is an annualaverage of 15 micrograms of sulfur dioxide per

300200100

No data

Base cations,µeq / liter

300150

500700

No data

Critical load,5th percentilemg S/m2/year

200 km

A

B

8

7

6

5

4

3

pH

Carbonate buffering

Cation exchange

Aluminumbuffering

Ironbuffering

Ca2+

HCO3–

Ca2+

Mg2+

K+

Al3+

Fe3+

Box: Acidification depletes nutrients

Most Arctic mineral soils are naturally acidic,because slow weathering limits the rate at whichthey can replace the base ions that trees use fornutrients. Acid deposition amplifies this naturalacidification process when hydrogen ions replacebase ions, causing the base ions to leach furtherdown into the soil or to be washed away in runoff.As a result, the pool of nutrients in the soildecreases. Moreover, once the easily available baseions such as calcium and magnesium are used up,another buffering process starts freeing previouslybound aluminum ions, which are toxic to plants.Tree damage from acidification has many causes,but the lack of nutrients and the excess of aluminumions are two important culprits. The figure showsthe pH at which different base ions become mobile.

A: Base cation concen-trations in lakes innorthern Fennoscandiaand the Kola Peninsula,microequivalents perliter.B: Critical load of acid-ity reflecting the load ofsulfur deposition thelakes can tolerate with-out harmful effects.

cubic meter of air. The vegetation can with-stand higher levels for short periods, and thecritical level for a one-hour exposure is 150micrograms of sulfur dioxide per cubic meterof air.

Both long-term and short-term critical val-ues are exceeded over large areas of the KolaPeninsula and on the Norwegian side of theNorway–Russia border. At Viksjøfjell inNorway, there have been hourly mean concen-trations of 3000 micrograms per cubic meter.The concentrations are occasionally higherthan 1000 micrograms per cubic meter as faras 50 kilometers from the Nikel smelter.

Sulfur dioxide has damaged a vast areaaround the smelters. The figure to the left indi-cates the extent of the damage around Nikeland Monchegorsk and the accompanying lev-els of sulfur dioxide in the air. Close to thesmelters, the forest is completely dead. TheMonchegorsk forest-death area, caused byemissions of sulfur and heavy metals, covers400-500 square kilometers and extends 10kilometers south and 15 kilometers north ofthe smelter complex. This zone is expanding ata rate of half a kilometer per year. The areasseverely affected by air pollution aroundNikel-Pechenga and Varanger increased from400 square kilometers in 1973 to 5000 squarekilometers in 1988.

The prevailing winds carry most pollutantsfrom the Nikel and Zapolyarnyy smelters tothe northeast and east. The forest-death areacaused by these smelters is greater in size thanthe one near Monchegorsk.

The outer visible-damage zone extends intothe eastern parts of Inari in Finland, which isthe only Finnish area under immediate threatfrom air pollution from the smelters. On theNorwegian side of the border with Russia, themain problem seems to be episodes of high airconcentrations of sulfur dioxide. On severaloccasions, this has damaged trees and othervegetation, causing leaves and needles to turnbrown. The most severe vegetation damage onthe Norwegian side of the border is aroundJarfjord Mountain.

The figure at the bottom of the page showsthe area around Norilsk that has been dam-aged by sulfur and heavy metals from thenickel-copper smelters. This zone extendsabout 80 kilometers south of the city.

Kola emissions have killed lichens and some shrubs

Most vegetation in northern Norway and theKola Peninsula is lichens and dwarf shrubs.Lichens, in particular, are very sensitive to airpollution, and the high sulfur dioxide load hashad a devastating effect. Between 1973 and1988, the lichen-dominated area aroundNikel-Pechenga and Varanger decreased from2783 square kilometers to 538 square kilome-ters. Lichens growing on birch trunks are

140Acidificationand Arctic haze

0

10

20

30

40

50

60

SO2 in air, monthly average, Viksjøfjell, Norway, 1992µg/m3

Jan Mar May July Sep Nov

100 km

F I N L A N D

R U S S I A

N O R W A Y

Monchegorsk

Nikel

Viksjøfjell

Minor damage:microscopic changes in structure of pine needles and lichens

Moderate damage:also changes in species composition of lichens

Intermediate damage:also damage on needles and leaves, shrub composition change

Severe damage:also marked loss of needles in conifers, no epiphytic lichen

Total damage:vegetation dead

Not included in survey

Minor

Moderate

Intermediate

Severe

Total

Vegetation damage

100 km

Norilsk

Taymyr

Dudinka

reviR

yesi

ne

Y

Sulfur dioxide concen-tration in air, monthlyaverages, Viksjöfjäll,Norway, 1992, andextent of vegetationdamage on the KolaPeninsula.

Extent of vegetation dam-age around Norilsk, Russia.

absent in large parts of the Norwegian forestclose to the Russian border.

The growth of reindeer lichen is especiallyimportant as it provides reindeer populationswith winter fodder. In fact, the carrying capa-city of the most important ranges of reindeer isdetermined by the growth of this lichen. Closeto the smelters, reindeer lichen has completelydisappeared. Only 50 to 60 kilometers awayfrom the smelters, lichens continue to grow attheir normal rates.

Dwarf shrubs have an important ecologicalrole in protecting the ground from erosion. Inareas with forest death, they are often the onlyremaining field vegetation. The proportion ofblueberry shrubs has decreased near the emis-sion sources, whereas another shrub, crow-berry, has increased. Some species of moss canalso benefit from high sulfur dioxide concen-trations.

141Acidification

and Arctic haze

90 km from Norilsk,Russia.

Cemetary, Norilsk.

Near Monchegorsk,Kola Peninsula, Russia.

KN

UT

BR

YK

NU

T B

RY

KN

UT

BR

Y

Sensitive invertebrates have disappeared

Streams and small lakes are more sensitive toacidification than larger water bodies, andtheir plants and animals are thus likely to suf-fer the consequences sooner. The diagram onthe opposite page shows the pH at which vari-ous aquatic animals will disappear. On theKola Peninsula, there has been a decline in thediversity of plankton as acid-sensitive specieshave disappeared. In small acidified lakes, thenumber of species and the abundance ofphyto- and zooplankton are as low as in lakescontaminated by heavy metals. In the Jarfjordregion of Norway, a number of acid-sensitivedaphnids, a group of small crustacean plank-ton, have disappeared.

The bottom fauna of streams have also suf-fered in this region. A study of the Sør-Varangerand Varanger areas showed that sensitive spe-cies were missing and the total number of spe-cies was low. In the Jarfjord region, acid-sensi-tive mayflies have disappeared from acidifiedlakes, and in the Dalelva watershed the bottomfauna are damaged because of low pH andhigh aluminum concentrations.

Also in the Murmansk region, many acid-sensitive species have been lost, and the num-ber and diversity of animals in the bottom sed-iments are low. The worst effects are seen inremote lakes on base-poor bedrock.

In northeastern Finland, bottom-dwellingfauna have fared better. No clear indication ofacidification effects in streams and rivers hasbeen detected so far, and even acid-sensitive

species, such as mayflies and caddis flies, arestill present. Since acidification increases fromwest to east, it is possible that the lakes closestto the Russian border might be affected.

Spawning water are acidified enough to affect brown trout

The rivers in the northern part of the KolaPeninsula and Sør-Varanger are important forfish production, especially for brown trout andAtlantic salmon. The salmonid fishes are espe-cially sensitive to low pH during hatching, asfry, and later on in the life cycle as smolts. Insmall streams, pH values during snowmelt arelow enough to be harmful to the fish, espe-cially if metal levels are high. Brown trout ismost vulnerable and possibly threatened atcurrent spring-time water quality levels.

Salmon have done better, probably becausethey spawn in larger rivers that are not as eas-ily acidified. In addition, salmon egg hatchingalso takes place at a more favorable time.Arctic char also seem to be less affected thanbrown trout, probably because they spawn inlakes rather than streams. Interviews with fish-ermen do not suggest any severe loss of fish inthe fresh waters of the county of Nordland inNorthern Norway.

In small lakes in northeastern Finland, evenacid-sensitive species have not been affected bythe acidification. Burbot, European minnow,and brown trout are still abundant.

The future hinges on reduced emissions

How will Arctic ecosystems fare in the futureif emissions of acidifying compounds con-tinue? One way to answer this question is to

142Acidificationand Arctic haze

Vegetation in the crystal-clear water of an acidi-fied lake.

�Spawners of Atlanticsalmon killed during anautumn episode of toxicacidic waters.

�Smolts of Atlanticsalmon killed during anacidic episode caused bysnowmelt in spring.

BJ

ØR

NO

LA

VR

OS

SE

LA

ND

BJ

ØR

NO

LA

VR

OS

SE

LA

ND

FR

ED

RIK

ED

ST

RA

ND

make models of how soils and water respondto different emission levels. Such models forthe river Dalelva in northern Norway and theChristmas Lakes in northeastern Finland sug-gest that, in the long run, the region is vulnera-ble even to fairly low rates of sulfur deposi-tion. The models indicate that future sulfurdeposition will have to be very low to stop andreverse the acidification now taking place.

If there are no reductions in emissions, themodels predict that the Christmas Lakes willrapidly acidify after 2010. A new steady-statewill be achieved after some 40 years, at a pHof around 4.5. In the river Dalelva, the highemission scenario, which assumes no reduc-tions from current levels, is predicted to resultin water at pH 5.5 or less by 2040.

On the positive side, the soil base saturationlevels remain fairly high. This means that a dras-tic reduction in sulfur deposition to backgroundlevels within 10 to 20 years would allow thesewaters to avoid the predicted damage.

SummaryAcidification of Arctic ecosystems is at presenta local problem around the nickel-coppersmelters on the Kola Peninsula and at Norilskin Russia. The input of sulfur dioxide into theenvironment in these areas is extremely high.The air concentrations and the depositionrates are comparable to heavily polluted areasin central Europe. On the Kola Peninsula, thesoil in some areas is severely acidified. More in-formation is needed about the Norilsk region.

The forest ecosystem close to smelters iscompletely destroyed, and the forest-deatharea is increasing every year. However, onlyrestricted impacts extend into areas of Finlandand Norway that neighbor the Kola Peninsula.

High deposition of sulfur affects water qual-ity on the Kola Peninsula and in eastern Finn-mark in Norway. In particular, it contributesto pulses of very acidic water in some riversand streams during spring snowmelt. Theseacid pulses may be more critical to plants andanimals in these waters than annual averagepH. In some streams and small lakes, acid-sen-sitive invertebrates have disappeared. Browntrout is the most vulnerable fish species.Information from the area around Norilsk isnot available. Models suggest that continuedsulfur dioxide emissions can pose an evengreater threat in the future. In particular, somelakes in northern Fennoscandia are vulnerableeven to fairly low rates of continued sulfurdeposition.

Except for the regions affected directly bythe smelters (within 200 kilometers), there isno evidence for large-scale soil or water acidifi-cation in the Arctic today.

The sources of acidifying contaminants tothe Arctic as a whole are well known. Sulfurdioxide from combustion of fossil fuels andsmelting of sulfuric ores is most important.The major source regions are industrial areasfurther south in Eurasia and North America.Sulfur dioxide reaches the whole Arctic area be-cause unique meteorological conditions allowlong-range transport during the polar winter.

In the atmosphere, sulfur dioxide convertsto sulfate aerosols, which can make the skylook hazy, even on clear days. In late winterand early spring, high concentrations of sulfateaerosols reduce visibility throughout the HighArctic. The aerosols have the potential to carryother contaminants. They might also have animpact on regional and global climate, but thisaspect of the haze is poorly understood at pre-sent. Most of the sulfates that form Arctic hazeoriginate from sources in Eurasia.

143Acidification

and Arctic haze

7.0 6.0 5.0 4.07.5pH 6.5 5.5 4.5

Crustaceans

Snails

Mollusks

Mayflies

Arctic char

Grayling

Brown trout

Healthy Slightly acidified Medium acidified Strongly acidified

Crustaceanreproduction

reduced

Crustaceanswhich are

major food itemsfor salmon die

Fishreproduction

reduced

Fishdying or

disappearing

A fewmolluskspecies

still surviving

All normal lifehas gone

Sensitivity of differentorganisms to decreasingpH.