soil and surface water acidification in theory and practice

K. Skogs-o. Lantbr.akad. Tidskr. 142:18, 2003

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Kungl. Skogs- ochLantbruksakademiensÅrg. 142 • Nr 18 • År 2003

Soil and surface water acidificationin theory and practice


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Ansvarig utgivare: Akademiens sekreterare och VD: Bruno NilssonRedaktör: Gunilla Agerlid


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Soil and surface water acidificationin theory and practice

Workshop November 11–12, 2002

Respektive författare ansvarar för sitt inlägg

Redovisningen sammanställd under medverkan avakademijägmästare Bo Carlestål


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Contents

IntroductionJan Nilsson ........................................................................................................................ 7

SummaryStefan Löfgren ................................................................................................................... 9

Implications of anthropogenic acidification on forest soil processes in SwedenUlla S Lundström and Patrick A W van Hees ................................................................. 15

Flow paths of water in Swedish forestsAllan Rodhe .................................................................................................................... 23

Acid-base status and changes in Swedish forest soilsErik Karltun, Johan Stendahl and Lars Lundin .............................................................. 31

Modelling acidification and recovery of soils and surface watersFilip Moldan and Veronika Kronnäs .............................................................................. 37

Processes affecting surface water acidity: Natural acid or anthropogenicallyacidified watwers?

Hjalmar Laudon .............................................................................................................. 43

Recovery from acidification in Swedish lakes and streamsAnders Wilander and Stefan Löfgren ............................................................................. 49

List of participants ................................................................................................................... 57

Tidigare utgivna nummer finns uppräknade på omslagets tredje sida


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Introduction

JAN NILSSONProgramme DirectorMISTRAStockholm

To start with, I would like to give you a fewperspectives on questions that we will be dis-cussing during the next two days. As you arewell aware of, Svante Oden initiated the acid-ification discussion in 1967 through his intel-ligent way of linking knowledge from differentenvironments: air, soil and water. I was bornin the most acidified areas of southwesternSmåland and I can remember how the farmersdrove out onto the ice-covered lakes to spreadlime. That was in the early 1950s. This leadsme to believe that they must have noticedthat the fishing had become poorer. Their rea-soning was presumably that if they limedtheir arable fields in order to improve produc-tion, then they could do the same with thelakes.

In my work I am accustomed to look at en-vironmental questions through the eyes ofthe users. Then it is natural to think in differ-ent decision-making arenas, where formula-tions are made of applied needs of know-ledge. In the present context we can distin-guish three such important arenas:1. The LRTAP Convention (Long-Range

Transboundary Air Pollution. This is han-dled by UN-ECE. A decisive agreement was

reached in Göteborg in 1999. Revision ofthis agreement will be made in 2005/2006.If research is to be involved and be able toinfluence the decisions then processingand reporting of results must be adaptedto this time plan. Otherwise we will haveto wait another 10 years.

2. The EU with the so-called “ceiling direc-tive” and the Clean Air for Europe (CAFE)programme. Proposals on measures willbe processed until 2005 and subsequentlya political process will continue until 2005–2006. We have good opportunities to influ-ence the direction of the decisions thatwill be reached if we act in close contactwith the process within EU.

3. National requirements, mainly concerningwork dealing with environmental goals,where a revision will take place in 2004, to-gether with strategies and measures con-cerning forest- and energy policy (bioener-gy, etc.).

Acidification is an exciting field as regards thelinks between research and environmentalmonitoring in this sector. I believe that admin-istrators and researchers in Europe are in


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agreement that this field is the best exampleof how research results and researcher com-petence have made a break-through with re-gard to decisions on direction and extent oflong-term measures in the environmental sec-tor.

I would also like to say a few words aboutongoing research and environmental moni-toring in this sector. During the 1980s therewas a research programme into acidificationin most countries in northern Europe. Today,only Sweden has an all-embracing programme(ASTA). Naturally, individual projects on acid-ification and eutrophication are in progress inother countries, e.g., a nitrogen programme inEngland.

I have chosen to report on the ongoingR&D work in Sweden in four blocks:

Environmental monitoringMonitoring of acidification is included as anintegrated part of environmental monitoring.Soil surveys concentrate on soil sampling,where about 1800 test plots are sampled an-nually. Integrated monitoring is ongoing with-in small catchment areas, where the flux ofdifferent substances are followed in the sys-tem from the atmosphere to the water. Lakesand waterways are covered by a national in-ventory (2000–4000 lakes) every fifth year.Studies are also made of reference waters(about 200 annually).

Research at universities,individual projectsHere there is a relatively limited extent andthe work is directed at individual processes,such as natural acidification, sulphur dynam-ics in the soil, podsol processes and nitrifica-tion.

The ASTA programmeMISTRA funds a research programme for 8years with a total budget of 59 million SEK.This programme is directed at feeding inknowledge into the above-mentioned arenasand is adapted to their respective time plans.The programme organised a workshop atSaltsjöbaden in 2000 where guidelines weredrawn up for the above-mentioned negotia-tions within LRTAP and EU.

Research into liming and returnof ashesThe National Board of Forestry finances a fol-low-up programme in a number of catchmentareas, where the links between soil and waterare studied. In addition, a number of dosingexperiments are being studied. The NationalEnergy Board also has projects in this sector.

Before I hand over the microphone tothose who have more facts to talk about, Iwould like to mention a few of my personalreflections on what we will be facing duringthe next couple of days. I am looking for aconstructive and open discussion, where wetry to respect each others views.

I have not fully understood the wording inthe invitation to this workshop: “The resultsthus are in conflict with the previously pre-vailing theory that surface water chemistryreflects the soil chemistry status”. In my opin-ion, there is good agreement between themap and the terrain. It will be interesting tosee the result of your deliberations. With re-gard to the group work programmes that willbe done, I have two messages: 1) It is theprocesses, not the status, that are most deci-sive for what happens; 2) The spatial varia-tion is large. Water moves in different direc-tions. Thus, we cannot make simple compar-isons between the situation in the soil andwhat is happening in the surface water. Wemust have a dynamic approach.

J. Nilsson


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Summary

STEFAN LÖFGRENDepartment of Environmental AssessmentSLUUppsala

Soil and surface water acidification intheory and practice – conclusions from aKSLA-workshop

Background and aims of theworkshopOne of the scientific theories within the fieldof limnology states that water quality mirrorsthe soil status in the drainage basin, if thewater is not affected by direct discharge ofany substance. According to this soil and sur-face water linkage theory, generally acceptedby the scientific society, soils acidified by acidprecipitation would cause more acidic sur-face waters. The reverse would be true if aciddeposition decreases and the surface watersexhibit recovery.

Since the middle of the 1980’s, the deposi-tion of acidifying compounds has decreasedsubstantially and it is today at the same levelas in the early 1950’s in Central Sweden. Thedecreased deposition of sulphur can be ob-

served in many streams and lakes in the for-ested landscape, demonstrated by reducedsulfate concentrations, increased buffer ca-pacity (ANC and alkalinity) and increased pH(SEPA 2000). In Norway, reduced concentra-tions of inorganic aluminium are documentedas well (Skjelkvåle et al. 1996). Unfortunately,long-term time series on inorganic aluminiumare not available from Sweden.

According to the theory, the acid status ofthe soils should also have improved parallelto the surface water recovery. However, re-cently published (SEPA 2000) soil data andmodel simulations indicated a continuoussoil acidification during the 1990’s down tothe B-horizon (increased exchangeable Al)and that the acid soil status should not beexpected to improve (base saturation andANC) during the forthcoming decades in the


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most acid sensitive areas of Southwest Swe-den, respectively. In the perspective of onedecade, the results from the soil and surfacewater assessments were obviously in conflictwith the theory of surface waters acting as amirror of the soil status. Questions arosewhether the theory is too simple, if our con-clusions have been based on different defini-tions of acidification/recovery of soil andwater or if data and/or mathematical modelsare non-representative and not comparablewith each other.

This scientific workshop was initiated inorder to answer those questions and to de-fine important issues for future research relat-ed to acidity transfer from soils into surfacewaters in forested, Swedish catchments dom-inated by podzolic soils.

Organization of the workshopThe workshop was opened with six state ofthe art presentations focussing on processesimportant for the soil acidity status (UllaLundström), flow paths of water in forestsoils (Allan Rodhe), measured soil acidity sta-tus (Erik Karltun), MAGIC modeled soil andsurface water status (Filip Moldan), process-es important for the surface water acidity sta-tus (Hjalmar Laudon) and measured surfacewater acidity status (Anders Wilander). Sum-maries of these presentations are publishedin this volume.

Thereafter, the participants were split intofour groups for the discussions. The chair-man of each group (Allan Rodhe, Jan Seibert,Kevin Bishop and Gunnar Jacks) presentedtheir conclusions before a final discussiontook place. Jan Nilsson acted as chairmanthroughout the workshop.

The most important conclusions present-ed below have been formulated together withthe participants. Therefore, the conclusionsof the workshop are expressed in consensus.

Results and conclusions fromthe workshopThe relevance of the soil and surface waterlinkage theoryBased on time series from the Swedish sur-face water monitoring, which comprise datafrom through June 2002, Anders Wilander(this volume) showed that the recovery fromsurface water acidification is proceeding. Itcan be measured as reduced sulfate concen-trations and increased concentrations of ANCand alkalinity as well as an increased pH (Wi-lander and Löfgren this volume).

Erik Karltun (this volume) presented anassessment of changes in soil status betweenthe last two Swedish Forest Soil Surveys,which mainly represent trends from 1983through 1998. The assessment was based onalmost twice as many soil samples as wereused in the SEPA evaluation (SEPA 2000). Thelarger data set shows that the changes in soilacidity have been less pronounced than de-scribed in the SEPA report. No statisticallysignificant trends can be observed concern-ing pHH2O in the O-horizon, while a significant,but low increase is indicated for pHH2O in theB-horizon. Exchangeable base cations (BC)have remained fairly constant in the O- and B-horizons. The total acidity as well as ex-changeable Ca and Mg have increased in theO-horizon in the whole country, while therehas been a significant increase of exchanga-ble Al and tendencies of reduced Mg and in-creased Ca concentrations in the B-horizon.Organic carbon (C) shows a net accumulationin O horizons in Southwest Sweden, while nosuch trend can be detected for the rest of thecountry.

The presentations by Wilander and Karl-tun gave valuable up to date informationabout the soil and surface water status inSweden, and modified the current view estab-lished before the workshop (c.f. Backgroundchapter). The current trends are only partlyconsistent with the soil and surface water

S. Löfgren


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linkage theory. One main discrepancy is forinstance a reduced surface water acidity com-bined with a less uniform or less significantsoil improvement. This problem was thor-oughly discussed at the workshop and threemain explanations were brought forward.

Firstly, Filip Moldan (this volume) showed,based on data from the Swedish referencelakes, the Swedish Forest Soil Survey and theestimated acid deposition during the period1850–2040, that the MAGIC model could sim-ulate the surface water acidity in fairly goodagreement with measured values. He alsostressed that the simulations for all objects(132 of which 64 are considered acid sensi-tive) gave similar trends in the future regard-less of original acid status and location in thecountry. The main explanation to this wasmainly the long time needed for rebuildingthe exchangeable BC pools in the soils. Hetherefore concluded that one should expect amuch slower response in soils compared tosurface waters. He also pointed out, that eventhough the lakes are currently improving,without a soil recovery the lakes would nev-er return to their pre-acidification status. Theaccumulation of BC is highly dependent onthe mass balance including BC weatheringrates (c.f. Lundström and Hees this volume),BC deposition, BC uptake by the vegetationand BC leaching.

Secondly, the decreasing sulphur deposi-tion has caused a decline in the ionic strengthin the soil solution. This might have changedthe ion exchange equilibria favoring an in-creased accumulation of exchangeable Al3+

combined with an excess loss of BC to sur-face waters, resulting in a maintenance ofhigh soil acidity but an improved surfacewater quality. The question was raised wheth-er the high and variable marine salt (Na+ andCl- ions) deposition determines the ionicstrength variability in the soil solution inSouthwest Sweden, overshadowing the influ-ence by the anthropogenic sulphur deposi-tion. This region exhibits the same recovery

trends in surface waters as the rest of thecountry, indicating that the ionic strength assuch might be of less importance. However,the relatively higher contribution of sulfate toionic strength compared to Cl- and the factthat sulfate deposition has decreased overtime, while the Cl- deposition is assumed tohave remained at the same level, makes theionic strength effect to an open question thatshould be analyzed further. The leaching ofmobile anions, expressed as the sum of sul-fate, nitrate, chloride and organic anions, wasput forward as the most important factor forthe BC losses.

Finally, the soils sampled by the SwedishNational Forest Soil Survey mainly representdry and mesic sites situated in groundwaterrecharge areas. However, soil properties andwater flow paths in the groundwater dis-charge areas (Fig 1, Rodhe this volume), to avery great extent influence the water chem-istry (c.f. Laudon this volume). Hence, theacid trends in surface waters do not neces-sarily have to be the same as shown by theSwedish National Forest Soil Survey. Thetemporal variation might be disparate be-tween the two media due to unequal kineticsin different compartments of the catchment.The heterogeneous properties of soil andhydraulic activity, with important acid-baseprocesses occurring in moist dischargeareas, might create the observed discrepan-cies.

The most important conclusion on thisissue was that the acid trends observed inthe Swedish soil and surface water surveysare consistent with the prevailing soil andsurface water linkage theory. However, theresults from the soil and surface water sur-veys are not fully comparable due to differ-ent spatial and temporal scales caused bydisparate hydraulic and soil properties indifferent compartments of the catchment.There are theoretical explanations for whythe soils should have a slower recovery ratein terms of increased pools of exchangeable

Summery


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base cations than should the surface watersin terms of increased ANC.

Key issues for future researchThroughout the workshop a large number ofquestions were put forward as being of scien-tific interest for the understanding of the rela-tions between soil and surface water acidifi-cation. Many questions were of an appliednature, e.g. coupled to the planned forest soilliming program or to improvements of themodels used as political decision supporttools, while other questions were of a moretheoretical nature. However, the participantsclearly defined two scientific key issues thatwere important from both theoretical andpractical points of views.

Firstly, the horizontal and vertical hetero-geneity in groundwater flow paths in forestedcatchments, described by Allan Rodhe (Fig. 1,this volume), demonstrates that differentparts of a catchment are unequally involvedin the stream water generation. Hjalmar Lau-

don (this volume) complemented this pictureby showing the importance of BC and there-by ANC dilution and TOC leakage from dis-charge areas for generating stream wateracidity in Northern Sweden. The acid-baseproperties of surface waters are obviouslygreatly influenced by the groundwater flowpaths in the catchment and by the soil prop-erties in the discharge areas. However, inte-grated, scientific studies of acid-base process-es in the different compartments in forestedcatchments are extremely rare both national-ly and internationally. Generally, informationis lacking on either hydraulic, soil physicaland/or soil chemical properties in the dis-charge areas characterized by upward ground-water flow components in the deeper soil lay-ers and mainly lateral groundwater flowpaths near the soil surface. The best availableinformation in Sweden is from 4 forested ref-erence catchments (Integrated Monitoring)and some few (<5) forestry influenced catch-ments.

S. Löfgren

Figure 1. Hypothetical slope in a drainage basin.

Stream

Recharge area

Discharge area,high flow

Waterdivide

Discharge area,low flow

Groundwaterlevels

Bedrock

Mineral soil

Organic soil


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We therefore recommend that a compre-hensive research program should be initiat-ed directed towards detailed studies ofprocesses in discharge areas being expect-ed to have significant influence on the acid-base status of surface waters. The researchprogram should include intensive hydrolog-ical and biogeochemical studies of water-sheds and development of catchment basedmathematical models, taking into accounthydraulic and chemical processes in boththe recharge and discharge areas. It wouldbe advantageous if the studies were locatedat monitoring and research areas already inuse and partly mapped and equipped forthese purposes.

By improving the knowledge about proc-esses in discharge areas we expect the re-search program to generate results impor-tant for the implementation of the EU waterframework directive (acid reference condi-tions), for the development of acidificationremedial measures (silviculture practices,liming etc.) and for improving the estimatesof future surface water acidity.

Examples of research issues of special in-terest for the acid-base status in dischargeareas are:• catchment based three dimensional quan-

tification and simulation of groundwaterflow and stream water generation,

• the effects of soil physics and soil chemis-try in discharge areas on groundwater andstream water acidity,

• processes controlling DOC generation indischarge areas,

• the effects of redox processes in dischargeareas, e.g. S(-II)/(VI), N(-III)/(V), Fe(II)/F(III)and Mn(II)/M(IV), on groundwater andstream water acidity,

• assessments of the Al-chemistry in dis-charge areas, including effects of ionicstrength and development of Al-fractiona-tion techniques suitable for dilute and hu-mic surface waters,

• the influence of groundwater quality inrecharge areas on the groundwater quali-ty in discharge areas,

• the effects of mixing of groundwater orig-inating from discharge areas of differentcharacter, e.g. organic or minerogenicsoils, on stream water acidity (generationof permanent or episodic acid events),

• the effects of climatic variation (drought,flood etc.) on riparian processes,

• the effects of vegetation (tree species com-position, buffer strips etc.) on riparianprocesses,

• the effects of microbial activity on impor-tant redox processes, e.g. mineralizationand oxidation of organically bound sul-phur, nitrogen etc.,

• development of three dimensional dynam-ic models linking hydrology and chemis-try,

• catchment based three dimensional quan-tification and model simulation of acid-base fluxes in groundwater and stream wa-ter.

At a national level, we also recommend in-tensive monitoring of the soil status in dis-charge areas, allowing coordinated and im-proved assessments of forest soil and sur-face water surveys. Long-term monitoringdata on soil and water are of utmost impor-tance for future assessments.

Secondly, the historical, large-scale envi-ronmental changes related to land-use, firefrequency, tree species composition etc. haveobviously influenced the acid-base status ofmany forested catchments in Sweden. Proc-esses such as weathering and carbon accu-mulation, potentially influencing the BC- andTOC-leakage to surface waters, might havechanged tangibly during the past centuries.An improved knowledge about the relationsbetween past large-scale environmental chang-es and acid-base status in soil and surfacewater may help us to identify complementaryremedial measures within silviculture, be-

Summery


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sides reduced emissions of acidifying sub-stances, reduced biomass harvesting, or lim-ing for achieving efficient soil and surfacewater acidity recovery.

We therefore recommend that a compre-hensive research program should be initiat-ed directed towards (i), assessing the effectsof historical, large-scale environmentalchanges on the acid-base status in soil andsurface water and (ii) identification and de-velopment of remedial silviculture practic-es. The research program should includehistorical, paleolimnological, hydrologicaland biogeochemical studies as well as devel-opment of mathematical models, taking intoaccount the quantitatively most importanteffects of these historical changes.

Examples on research issues of special in-terest related to land-use and silviculturepractices are:• in representative catchments, perform

detailed historical reconstruction of land-use change (land-use practices in dry andmoist areas, drainage and burning tech-niques etc.), with special emphasize onforestry and agricultural developmentduring the 20th century,

• in the above catchments, perform pale-olimnological studies, reconstructing veg-etation, land-use, fire regimes, surface wa-ter pH, color etc. since the last glaciation,with special emphasize on forestry andagricultural development during the 20th

century,• based on the above information develop

catchment based proton budgets for thenatural state without human influence(“baseline”) and the most important timeperiods with different land-use,

• based on the above information developcatchment based model simulations ofacid-base fluxes in stream water,

• identification of land-use key factors forthe acid-base status in surface waters,

• experimental testing of land-use key factorsof relevance for development of remedialforestry practices,

• evaluate ongoing and establish new fieldexperiments concerning silviculture meas-ures affecting soil and surface water acid-ity.

AcknowledgementFORMAS, MISTRA, KSLA and SLU financedthis workshop. Bo Carlestål and Ann-MarieAschan at KSLA organized the practical ar-rangements.

ReferencesSEPA (2000). Recovery from acidification in

the natural environment – present know-ledge and future scenarios. Swedish En-vironmental Protection Agency report5034, 96 pp.

Skjelkvåle, B.L., Henriksen, A., Faafeng, B.,Fjeld, E., Traaen, T.S., Lien, L., Lydersen, E.,Buan, A.K. (1996) Regional lake survey1995. A water chemical survey of 1500Norwegian lakes. The national monitoringprogramme for long-range transported airpollutants. Norwegian State Pollution Con-trol Authority, Report 677/96, 73 pp.

S. Löfgren


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Implications of anthropogenicacidification on forest soil processesin Sweden

ULLA S LUNDSTRÖMPATRICK A W VAN HEESMid Sweden UniversitySundsvall

AbstractBy anthropogenic acidification the soil form-ing process, podzolisation, will be perturbed.The organic acids in soil solution will formcomplexes with aluminium to a less degreeand inorganic aluminium will be leached fromthe illuvial horizon. The soil acidification hasnot resulted in declined coniferous forestgrowth, which might be explained by mycor-rhizal activity promoting nutrient uptake di-rect from minerals. Liming and wood ash ap-plications on forest soil might enhance CO2

evolution, increase DOC concentrations andmight also initially decrease pH and increaseAl concentrations in soil solution.

Soil forming processesIn northern Europe and N. America, wherethe climate is humid and the soil is of medium

to coarse texture, coniferous forest soils areoften podzolic. Weathering in these soils ispromoted by organic compounds formingcomplexes primarily with the trivalent ionsFe and Al released from primary minerals.Thereby the nutrients Ca, Mg and K are re-leased mainly as free ions. It has been shownin laboratory experiments that soil solutionscontaining organics and solutions of synthet-ic organic acids enhance the dissolution rateof primary minerals by a factor of 2–4 timescompared to water with the same inorganiccontent of ions (Lundström and Öhman,1990; van Hees et al., 2002). Formation of complexes generally had agreater impact on the dissolution rate thanpH (van Hees et al., 2002). Citrate (50–250µM), acetate (50–175 µM), formate (0–200µM), fumarate (1–5 µM) and oxalate (3–15µM) were found in soil solution from the morlayer of a coniferous forest in north Sweden(van Hees et al., 2000a) (Fig. 1). In the deeper


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horizons these concentrations decreased.Many of these acids have high complex form-ing ability with Al. It has been shown by sizeexclusion chromatography and equilibriumcalculations that these compounds bindabout 30% of the Al in soil solutions of forestsoils (van Hees et al., 1996, 2000b), whileabout 50–60% is bound to high molecularweight compounds and the rest is inorganicAl. This suggests that complex-formation isimportant during the process of mineralweathering.

From observations on thin-section micro-photographs and scanning electron micro-graphs of soil mineral particles, Jongmans etal. (1997) found that fungal hyphae are able toetch weatherable minerals in the upper soil.Mycorrhizal fungi have been shown to pro-duce organic acids (Ahonen-Jonart et al., 2000;Leyval and Berthelin, 1991) and siderophores(Holmström et al., unpubl; Watteau and Ber-thelin, 1994). Siderophores are much strong-er complex-formers than the acids and haverecently been found in the mor soil solution

from a coniferous forest (Holmström et al.,unpublished). The concentrations of organicacids and siderophores surrounding hyphaltips are likely to be much higher than those inthe bulk soil solution. Thus weathering maybe greatly enhanced and a significant propor-tion of the released Al may be bound by thesecomplex-formers. These low molecular weightorganics will be easily decomposed in the soilsolution (van Hees et al., 2003), and thus Almight be complexed by high molecular weightorganic substances to a higher extent.

The main immobilization process in theuppermost B horizon for Al and Fe, beingtransported as organic complexes, might bemicrobial decomposition of the organic li-gand in solution releasing ionic Al and Fe toprecipitate as imogolite type material andferrihydrite, which could also form followingdegradation of adsorbed organic Al and Fecomplexes (Lundström et al., 2000). Rapidevolution of CO2 from the soil is evidence forhigh microbial activity.

U. S. Lundström, P.A.W. van Hees

Figur 1. a) Average concentration of citric acid (µM, n=6)) in soil solution of Nyänget profile.b) Average concentration of DOC (DOC<1000D, DOC 1000-3000D, DOC>3000D) (mM, n=6)) in soilsolution of Nyänget profile.c) Average Al (QR Al (inorg), orgAl<1000D, Al<3000D-(orgAl<1000D)- QRAl (µM, n=6)) in soil solu-tion of Nyänget profile.


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Soil acidification processesAs a result of increasing acidification the pro-portion of organically complexed Al in soilsolution will decrease due to equilibrium con-ditions: the complex-forming acids becomeprotonated at low pH. In addition, as a resultof lower pH inorganic Al will be released fromthe illuvial horizon where it was formerlybound. Combined these indirect effects ofacidification may disrupt the processes ofweathering and soil formation.

The sites Svartberget, Gårdsjön, and Tisaare exposed to different acidic load (Lund-ström et al., 1995). From Svartberget beingalmost unaffected to Tisa being in the mostaffected area in Europe. The different degreesof perturbation of the soil forming processare demonstrated by the aluminium specia-tion in soil solution in the profiles (Fig. 2). AtSvartberget there are low concentrations oftotal aluminium (<40 µM) mainly present inthe upper soil. About 80% of the aluminum isorganically bound. These relations show thata normal soil forming process is going on,

where the organic acids promote weathering,aluminium is complexed and immobilized inthe illuvial horizon. At Gårdsjön these proc-esses are affected. The total concentration ofaluminium is higher, the part being organical-ly bound is lower and obviously inorganic,mainly trivalent aluminium, is leached fromthe illuvial horizon but seems to be immobi-lized deeper down. At Tisa the total concen-tration of aluminium is high (>600 µM) in thedeep soil and almost all is as inorganic alu-minium, mainly trivalent and aluminium sul-fate complex. This aluminium distributionshows that the soil forming process is per-turbed with a great leakage of inorganic alu-minium. The pH and sulfate concentrations inthese profiles support this conception. ThepH in the profile of Svartberget is about onepH unit higher than at Gårdsjön, which in turnis about a half pH unit higher than at Tisa. Thesulphate concentrations in the profiles,which relate to the deposition was muchhigher at Tisa.

At high concentrations of trivalent Al andhydrogen ions, a large proportion of the pool

Implications of anthropogenic acidification on forest soil …

Figur 2. Aluminium speciation with depth at Svartberget (Umeå), Gårdsjön (Göteborg) and Tisa (CzechRepublic).


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of exchangeable cations will be comprised ofthese ions and the part composed of the basecations will be less, resulting in low base sat-uration.

Soil acidification and treegrowthIn laboratory experiments inorganic Al in soilsolution has been shown to interfere with thegrowth of the roots of young seedlings (Rost-Siebert 1983, 1985). Increased concentrationsof inorganic Al, resulting from acidification,have been assumed to affect tree growth par-ticularly if the concentrations of Ca are low.The molar ratio (Ca+Mg)/Alinorg, has beenused to estimate critical loads. It has beensuggested that where this ratio is less than 1,tree growth will be reduced (Sverdrup et al.,1992). In addition, the lower base saturationresulting from acidification has been suggest-ed to decrease tree growth as a result of nutri-ent deficiencies leading to a non-sustainableforest. However, there is little field evidencethat soil acidification leads to a decline in for-est growth.

An extensive investigation was made in thecounty Värmland on soil chemistry and treegrowth (Lundström et al., 1998; Nyberg et al.2001). The depostion of sulphate in the southof the county is 2.5 times higher than in thenorth. In Värmland pH in soil solution in theupper B-horizon was about 5.5 in the northand about 4.7 in the south of the county. Inthe deeper horizons the pH´s were about 0.8lower throughout the profiles in the south-west of the Värmland than in the north ofVärmland.

In the southwest of Värmland the concen-trations of total aluminium and inorganic alu-minium were generally higher than in thenorth of Värmland (Fig. 3). Also the part oftotal Al being inorganic was higher in theseareas, sometimes as high as 50% in the upperB-horizon and on average 30%. In the north,

inorganic Al made up a smaller part. Alumin-ium concentrations in the north of Värmlandwere comparable to those found in Svart-berget, while the concentrations in the southof Värmland were lower than in Gårdsjön.

The base saturation in the mor layer washigh (>60%) and no distribution pattern forVärmland could be recognized. In the illuvialhorizon the base saturation was lower, withthe lowest values in the southwest of Värm-land.

Principal Component Analyses made onsoil solution composition and exchangeablecations and additional parameters demon-strated the availability of pH and the concen-trations of total aluminium and inorganic alu-minium in soil solution as indicative parame-ters.

An evaluation on the tree growth including80 sites, did not suggest any correlation be-tween soil acidification and forest growth(Nyberg et al., 2001). All over Europe forestbiomass production is greater than ever be-fore (Kauppi, 1992).

Mycorrhizal activity has important impli-cations for the weathering process. The po-tential direct access by the trees, via theirmycorrhizal fungi, to Ca, Mg and K in soil min-erals means that the base saturation of theexchangeable pool may be less importantthan previously thought for the nutrient sup-ply of the tree. This may explain the failedimpact of acidification on forest growth andmay have implications for the treatment offorest soils.

Ash and lime applicationsIn the south of Sweden two ash/lime treatedsites were investigated (Lundström et al.,2003a). At Horröd 3.3 ton/ha of dolomite and4.3 ton/ha of wood ash and at Hasslöv twodoses of dolomite, 3.5 ton/ha and 8.8 ton/hawere applied. The exchangeable pool as wellas the base saturation in the mor layer were



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increased after treatment. Also the concen-tration of base cations in the mor layer solu-tion was enhanced after treatment.

At Horröd 4 years after treatment therewere tendencies of lower pH and increasedconcentration of inorg Al in soil solution(Geibe et al., 2003). This might have been in-duced by the increased exchangeable pooland the exchange of H+ for Ca and Mg. AtHasslöv 15 years after treatment on the otherhand the pH was higher and the Al concentra-tion in soil solution lower than in the control.At both sites DOC concentrations were in-creased and at Hasslöv the respiration wasup to 37% higher at treated areas, whichmight be due to higher microbial activity de-

pleting the C storage (Holmström et al., 2003;van Hees et al., 2003). The increased respira-tion may play a role for the forest as a sink orsource for carbon. At Hasslöv after applica-tion of the high dose of dolomite the concen-tration of NO3 was high and leached from theprofile, which might eutrophicate surface wa-ters. All these findings are in accordance withother studies on lime and ash treatments asreviewed by Lundström et al.(2003b). In addi-tion most studies report declined or un-changed forest growth. Liming and ash appli-cation on forest soils have been proposedwith the aim to remediate soil processes, pro-mote forest growth, protect surface waters,and for wood ash for recycling. However, at


Figur 3. Inorganic aluminium concentration in soil solution from the upper illuvial horizons and treegrowth ratio (expected growth/ measured growth).


20

present acid surface waters in Sweden arelimed directly, and this might be preferable.To recognize processes involved in the inter-action between soil, ground and surface wa-ter further studies are needed.

ConclusionsThe soil forming process, podzolisation, isperturbed by acidification resulting in low pHand leaching of inorganic aluminium to soilsolution and surface waters. These effects ofacidification, in addition to low base satura-tion, do not imply declined forest growthprobably because the weathering process isinduced by mycorrhizal activity deliveringmineral nutrients. Treatments with lime andwood ash of forest soils may induce negativeeffects as increased CO2 evolution, higherDOC concentrations, initially lower pH andhigher Al concentrations in soil solution. Theinteraction between soil, ground and surfacewater is not well recognized.

ReferencesAhonen-Jonnarth, van Hees, P.A.W., Lund-

ström, U.S. and Finlay, R.D. 2000. Produc-tion of organic acids by mycorrhizal andnon-mycorrhizal Pinus sylvestris L. Seed-lings exposed to elevated concentrationsof aluminium and heavy metals. New Phy-tologist 146, 557–567.

Geibe, C., Holmström, S., van Hees P.A.W., andLundström U.S. 2003. Impact of lime andash applications on soil solution chemistryof acidified podzolic soils. Water, Air andSoil Pollution, Focus

van Hees, P.A.W., Andersson, A-M. & Lund-ström U.S. 1996. Separation of organic alu-minium complexes in soil solution by sizeexclusion chromatogrphy in combinationwith HPLC determination of low molecular

weight organic acids. Chemoshpere 1951–1966.

van Hees, P.A.W., Lundström, U.S. and Giesler,R. 2000a. Low molecular weight acids andtheir Al-complexes in soil solution – Com-position, distribution and seasonal varia-tion in three podzolized soils. Geoderma94, 173–200.

van Hees, P.A.W. and Lundström, U. 2000b.Equilibrium models of aluminium and ironcomplexation with different organic acidsin soil solution. Geoderma 94, 201–221.

van Hees, P.A.W., Lundström, U.S and Mörth,C-M. 2002. Dissolution of microcline andlabradorite in a forest O horizon extract:the effect of naturally occurring organicacids. Chemical Geology 189, 199–211.

van Hees, P.A.W., Jones, D.L., Lundström U.S.and Godbold D.L. 2003. Biodegradation oflow molecular weight organic acids inlimed forest soils. Accepted Water, Air andSoil Pollution, Focus.

Holmström, S.J.M., Lundström, U.S., Finlay,R.D. and van Hees, P.A.W. Siderophores insoil solution and their production by anectomycorrhizal fungus. Submitted.

Holmström, S., Riise, G., Tau Strand L., Geibe,C., van Hees P.A.W and Lundström U.S.2003. Effects of lime and ash treatments onDOC fractions and low molecular weightorganic acids in soil solutions of acidifiedpodzolic soils. Water, Air and Soil Pollution,Focus.

Jongmans, A.G., van Breemen, N., Lundström,U., van Hees, P.A.W., Finlay, R.D., Srinivas-an, M., Unestam, T., Giesler, R., Melkerud,P.A., and Olsson, M. 1997. Rock-eating fun-gi. Nature 682–683.

Kauppi, P.E., Mielikainen, K. and Kuusela, K.:1992, ‘Biomass and carbon budget of Euro-pean forests, 1971 to 1990, Science 256, 70–74.

Leyval, C. and Berthelin, J., 1991. Weatheringof mica by roots and microorganisms ofpine. Soil Sci. Soc. Am. J., 55: 1009–1016.



21


Lundström, U. & Öhman, L-O. 1990. Dissolu-tion of feldspars in the presence of natural,organic solutes. J. Soil Sci. 41, 359–369.

Lundström, U.S & Giesler, R. 1995. Use of alu-minium species composition in soil solu-tion as an indicator of acidification. Ecolog-ical Bulletins 44, 114–122.

Lundström, U.S., Nyberg, L., Danielsson, R.,and van Hees, P.A.W. 1998. Forest soil acid-ification: Monitoring on the regional scaleexeplified by Värmland, Sweden. Ambio27, 551–556.

Lundström, U.S., van Breemen, N., Bain, D.C.,van Hees, P.A.W., Giesler, R., Gustafsson, J.P., Ilvesniemi, H., Karltun, E., Melkerud, P.-A., Olsson, M., Riise, G., Wahlberg, O.,Bergelin, A., Bishop, K., Finlay, R., Jong-mans, A.G., Magnusson, T., Mannerkoski,H., Nordgren, A., Nyberg, L., Starr M., andTau Strand, L. 2000. Advances in under-standing the podzolization process result-ing from a multidisciplinary study of threeconiferous forest soils in the Nordic Coun-tries. Geoderma. 94, 335–353.

Lundström, U.S., Bain, D.C., Taylor, A.F.S., vanHees, P.A.W., Geibe, Ch.E., Holmström,S.J.M., Melkerud, P.-A., Finlay, R., Jones,D.L., Nyberg, L,. Gustafsson, J.P., Riise, G.and Tau Strand L 2003a. Effects of acidifica-tion and its mitigation with lime and woodash on forest soil processes in southernSweden. A joint multidisciplinary study.Accepted Water, Air and Soil Pollution,Focus.

Lundström, U.S., Bain, D.C., Taylor A.F.S. andvan Hees P.A.W. 2003b. Effects of acidifiac-tion and its mitigation with lime and woodash on forest soil processes. A review.Water, Air and Soil Pollution, Focus

Nyberg, L., Lundström, U., Söderberg, U., Dan-ielsson, R. and van Hees, P. 2001. Is thereno impact of soil acidificationon on conif-erous needle compsition and tree growth?Water, Air and Soil Pollution, Focus.1, 242–263

Rost-Siebert, K.: 1983, “Aluminium-Toxicitätund – Toleranz an Keimpflanzen von Fich-te (Picea abies Karst.) und Buche (Fagussylvatica L.) ”, Allgemeine ForstZeitung 38,686–689.

Rost-Siebert, K.: 1985, “Untersuchungen zurH- und Al-ionen- toxicotät an Keimpflanzenvon Fichte (Picea abies I.) und Buche (Fa-gus sylvatica L.) in Lösungskultur”, Berich-te der Forschungszentrums Waldökosys-teme/Waldsterben. Univ. Göttingen, Band12.

Sverdrup, H., Warfvinge, H., Frogner, T.,Håoya, A.O. and Johansson, M.: 1992, “Crit-ical loads for forest soils in the Nordiccountries”, Ambio, 21:5, 348–355.

Watteau, F. and Berthelin, J., 1994. Microbialdissolution of iron and aluminium fromsoil minerals: efficiency and specificity ofhydroxamate siderophores compared toaliphatic acids. Eur. J Soil Biol., 30: 1–9.


22


23

Flow paths of water in Swedish forests

ALLAN RODHEDepartment of Earth SciencesUppsala UniversityUppsala

Stream runoff can quite well be calculatedmathematically without a detailed knowledgeof flow processes in the catchment. Thecatchment can be regarded as a black boxwith precipitation as input and runoff (andevapotranspiration) as output. By using datafrom a period with observed precipitationand runoff, a good fitting between observedand calculated runoff dynamics and volumecan be obtained by tuning parameter valuesin a set of more or less complicated mathe-matical transformations. Such a model maygive good results as long as the catchmentremains unchanged with regard to the condi-tions for the water flow. But when we want toestimate the catchment response underchanged conditions we need more knowledgeof the hydrological processes in the catch-ment (or a new calibration period). Further-more, when we want to understand the chem-ical changes taking place in the water wehave to open the black box and look moreclosely at the water fluxes and storages:• Which flow paths does the water follow on

its way through the catchment?

• To what extent has the discharging waterbeen flowing through mineral soil and or-ganic soil respectively?

• How long time is the water remaining invarious biogeochemical environments?

• Are there important effects of by-passmechanisms such as macropore flow oroverland flow?

These questions will be briefly commented inmy presentation.

The medium in which is thewater flowsMost of the Swedish forest area is dominatedby sandy-silty till soils deposited on fracturedgranite or gneiss bedrock. The soil cover iscomparatively thin, in many areas less than afew meters thick and with rock outcrops fre-quently occurring in elevated parts of thelandscape. Mires, i.e., wetlands with organicsoils, are common in low-lying and flat areas.

As is evident from the fact that much of thewater supply in the countryside is based on


24

wells drilled into the bedrock, the fracturesystem in the bedrock may be quite conduc-tive for water. The role of water flowingthrough these fractures in the runoff processis little known. It is probably of minor impor-tance for the runoff dynamics, but it mayaffect the chemical composition of stream-water.

What we know about the waterflowShallow groundwaterThe groundwater table is typically shallow,with a depth of a few meters in elevated are-as and it gradually approaches the groundsurface when going down the hillslopes. Thegroundwater zone is continuous laterally andvertically, with streams and mires represent-ing local low points for the groundwater sur-face. The depth to the groundwater table isdetermined by ability of the ground to con-duct water (the hydraulic conductivity of thesoil and bedrock and the slope of the groundsurface) and the rate of groundwater re-charge. With considerable groundwater re-

charge, a bedrock of fairly low conductivityand a thin soil cover with low conductivity inits deeper parts, the groundwater zone has toreach close to the ground surface in order totransmit all groundwater recharged uphill.

Most rainwater and snowmelt infiltrates intothe soilThe infiltration capacity of the till soil is nor-mally larger than the rainfall or snowmelt in-tensity. Overland flow is therefore of littleimportance on unsaturated areas (rechargeareas for groundwater), but it may be an im-portant flow process on saturated areas (dis-charge areas). The extent of the dischargeareas is dynamic, with the extent increasingwith increasing groundwater level. Overlandflow can of course also occur on rock out-crops, but this water probably infiltrates infractures or in the soil downhill.

The hydraulic conductivity of till soil decreaseswith depthSeveral investigations have shown that thehydraulic conductivity of Nordic till soils de-creases rapidly with depth (Figure 1). Soilprocesses such as biological activity, chemi-

A. Rodhe

Figure 1. Observed hydraulic conductivity in Nordic till soils. From Lundin (1990).


25

cal weathering and soil freezing and thawingall contribute to develop a structure giving ahigh hydraulic conductivity in the upper me-ter of the soil. Soil compaction in the deepertill contributes to the low conductivity atdepth.

Runoff events in streams are dominated bypre-event waterAlthough it is evident that storm runoff in astream is initiated by rainfall or snowmelt justprior to or during the event, a large number ofisotope investigations have shown that thedischarging water is dominated by pre-eventwater, i.e. water that was stored in the catch-ment before the event. A simplified interpre-tation of the isotopic hydrograph separationshown in Figure 2 is that the “pre-event water”is groundwater discharged as a response togroundwater recharge by rainfall infiltration,whereas the “event water” is rainwater thathas reached the stream directly as saturatedoverland flow on saturated discharge areas.

The mean transit time for water in headwatercatchments is on the order of a few months toyearsIsotopic hydrograph separation separatesthe discharging water into two age classes,event and pre-event water. By following theisotopic input and output to a catchmentover a longer time period, a mean transit timefor the discharging water can be estimated. Inthis way mean transit times ranging from afew months to a few years have been estimat-ed for a few Swedish catchments. It should benoted that those numbers are estimated long-term mean transit times. The mean transittime of the water that is discharging at a cer-tain moment is highly variable over time (Fig-ure 3). Each such mean transit time furtherrepresents a mean value of a transit time dis-tribution with transit times ranging from min-utes (water falling directly on the stream) toseveral years (water with the deepest ground-water flow paths towards the stream).

Flow path of water in Swedish forests

The topography gives a general picture of thewetness pattern in the catchmentSoil wetness and depth to the water tableshow large variations within a catchment, giv-ing different pre-conditions for the water flowand storage. The topography gives valuableinformation on the wetness distribution. Fora location with a large local catchment area(large groundwater flow to be transmitteddownhill) and small slope of the ground sur-face (little ability for the ground to transmitthe groundwater downhill) we can expect ashallow water table and wet soil.

What we believe about thewater flowLateral unsaturated flow is of little importanceThe lateral subsurface flow feeding the dis-charge areas and the streams takes place inthe groundwater zone. There are no indica-tions of an important lateral flow in the un-saturated zone.

Preferential flow in macropores is probably oflittle importance in the unsaturated zone belowthe root zoneHigh rates of water input to the ground mayunder certain conditions give rapid flow andtransport in large interconnected pore sys-tems in the surface layer. A pre-condition forsuch a flow is that the rate of water input tothe pores is large as compared with the hy-draulic conductivity of the soil matrix. Other-wise the larger pores will be emptied by suc-tion from the surrounding pores. With the lowrainfall intensities and the comparativelycoarse till soil in Swedish forest areas, prefer-ential flow in unsaturated soil is probably oflittle importance except in the topmost layerof the soil. In the groundwater zone, on theother hand, large pores or coarse soil layerswill, when they exist, greatly contribute to theflow since they are always water filled.


26

Groundwater discharge to streams increasesdrastically when the shallow, highly conduc-tive layers become saturatedThe main mechanism of stream flow re-sponse to infiltration in till soil is that thewater table rises so that superficial layerswith high hydraulic conductivity become sat-urated (Figure 4). In this way the transmissiv-ity of the ground increases drastically and thegroundwater flow feeding the stream can be

multiplied, although the slope of the ground-water table may remain essentially constant.One effect of this event related saturation ofthe shallow layers is that the lateral flow at acertain shallow depth may be intermittent,with lateral flow taking place only during pe-riods of saturation. Such intermittent lateraldisplacement in shallow layers has been ob-served in tracer experiments.

A. Rodhe

Figure 2. Isotopic hydrograph separation of a rainfall generated runoff event. Catchment F2 at Lake Gård-sjön, Sweden, 1980. From Rodhe (1987).


27

On a long-term basis, the largest volumes oflateral flow go through superficial layersAlthough the superficial layers are saturatedonly during a small fraction of the total time,the flow in these layers dominates the totallateral flow in the soil profile. The high hy-draulic conductivity of these layers morethan compensates for the short time of satu-ration with lateral flow. (Figure 5).


Figure 3. Mean transit time of the discharging water as estimated from catchment runoff using informa-tion obtained from a step shift in the 18O input. Catchment G2 at Lake Gårdsjön, Sweden, Octo-ber 1990 to April 1994. From Rodhe et al. (1996).

Figure 4. Large increase of groundwater flow in the soil profile due to saturation of superficial highly con-ductive layers.

Soil frost has little influence on the magnitudeof the spring floodIsotope studies have shown that also springfloods are dominated by pre event water, andattempts to introduce the effects of soil frostin runoff modelling did not improve the mod-elling of the spring flood. These findingsmight be surprising, since we could expectthe infiltration capacity of the soil to be


28

Stream

Recharge area

Discharge area,high flow

Waterdivide

Discharge area,low flow

Groundwaterlevels

Bedrock

Mineral soil

Organic soil

strongly reduced by soil frost. Factors tend-ing to give infiltration excess and overlandflow during snowmelt are high soil moisturecontent when the freezing starts, thick frozenlayer, continuous soil frost over the area andlarge snow pack with rapid melting. One rea-son for the lack of a significant effect of soilfrost on overland flow might be that some ofthese factors are counteracting each other. Alarge snow pack, for instance, reduces sur-face cooling and frost growth. It is also prob-able that the soil frost is laterally discontinu-ous in many forest soils.

We must have a simplifiedconceptual picture of the flowpathsIn order to understand the chemical process-es taking place in the water and to identifyprocesses that need further research wemust have a picture of the flow path of waterthrough the catchment. Obviously for eachindividual catchment, local geological, topo-

Figure 5. Vertical distribution of the annual lateralgroundwater flow calculated from an ob-served hydraulic conductivity profile andthe frequency distribution of ground-water levels. Catchment G1 at Lake Gård-sjön, Sweden. From Seibert (1993).

A. Rodhe

Figure 6. A hypothetical hillslope with groundwater discharge through organic soil. Modified after StefanLöfgren, personal communication 2002.


29

graphical, climatological factors and effectsof land use and man’s activities in the catch-ment, such as forest draining, have to be tak-en into consideration. The above discussedknowledge, however, allows drawing a gener-alized picture, see for instance Figure 6. Sucha picture can help to understand the relationsbetween hydrological and chemical process-es and should guide further model develop-ment.

ReferencesLundin, L., 1990. Saturated hydraulic conduc-

tivity of Nordic till soils. Hydrogeologicalproperties of till soils, NHP Report 25, 51–55.


Rodhe, A. 1987. The origin of streamwatertraced by oxygen-18. Uppsala Univ., DeptPhys. Geogr., Div. Hydrol.,Report Series A41, 290 pp, Appendix 73 pp. (Doctoral the-sis)

Rodhe, A., Nyberg, L. and K. Bishop, 1996.Transit times for water in a small till catch-ment from a step shift in the oxygen-18content of the water input. Water Resourc-es Research, 32(12):3497–3511.

Seibert, J., 1993. Water storage and flux in amicr catchment at Gårdsjön, Sweden. The-sis paper (Examensarbete 20 p), Dept ofEarth Sciences, Hydrology, Uppsala Uni-versity.


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31

Acid-base status and changes inSwedish forest soils

ERIK KARLTUNJOHAN STENDAHLLARS LUNDINDepartement of ForestSoilsSLUUppsala

IntroductionIt is now more than fifteen years since Hall-bäcken & Tamm (1986) and Falkengren-Gre-rup et al. (1987) showed an increase in theacidity and a decrease in pH in southern Swe-den. They repeated sampling of previousstudies and could by comparing the acid-base status of the older soil samples with thenewly sampled detect a significant decline inpH of Swedish forest soils over the middlepart of last century. In other studies (Erikssonet al., 1992;Karltun, 1994) the geographicalpattern of acid-base status over Sweden wasrevealed. There was a strong correlation be-tween deposition of acidifying substancesand the acidity of the soil profiles. This con-firmed that the soil acidification showed thesame geographical distribution as the lakeacidification with south-west Sweden as themost acidified area. Just around 1990 the de-position of acidifying substances started todecline quite rapidly. This was a combination

of air-pollution protocols coming into effectand the collapse of the eastern bloc economy.Surface waters have responded positively tothis decrease in deposition with increasingpH and ANC (Stoddard et al., 1999; Skjelkvaleet al., 2001).

Another factor that may have affected theacid-base status of the soil are the growingforests. We have had a continuous increase instanding biomass in the Swedish forests overthe last 20 years. This increase has resulted inan input of acidity to the soils, a process thatmight have counteracted the effect of thedecreased deposition. In this paper we usedata from the Swedish National Survey ofForest Soils and Vegetation (NSFSV) to evalu-ate the present acid-base status of forest soilsto try to answer the following questions.Which role do anthropogenic and biologicalacidification play for the present acid-basestatus of the soil profile? What is the presentacid-base status of Swedish forest soils andhow large areas may be considered as severe-


32

E. Karltun, J. Stendahl, L. Lundin

ly acidified? Do the current tendencies in soilacid-base status correspond with the positivedevelopment in surface waters?

Materials and methodsData materialThe recent status of the forest soils were eval-uated using data from the second inventorysampled between 1993 and 1998. The datasetcontained data for the O horizon from 7535plots, for the B horizon from 2178 plots andfor the C horizon from 1738 plots.

The possible changes in soil status wereevaluated using data from the first inventory1983 to 1987 and the second inventory 1993and 1998. All paired plots where the samehumus form (O horizon) or soil type (B hori-zon) has been recorded in both inventories.For pH there were 3007 paired plots and forbase cations and acidity there were 525 plotsthat fulfilled the selection criteria.

The following variables were used; pH(H2O),total acidity (TA) determined in 1M ammoni-um acetate extract, exchangeable acidity(EA) determined in 1M KCl and exchangeableCa and Mg determined in 1M ammonium ac-etate extract. Base saturation was calculatedusing the sum of exchangeable base cationsplus the total acidity as the cation exchangecapacity.

StatisticsWhen data is presented as a mean it is thearea-weighted mean where each plot is weight-ed by a factor which size is determined by theforest area that the plot represent, i.e. the for-est area of a region divided by the number ofplots in that region. They area-weightedmeans are calculated as

where V is the analyzed variable and AF thearea factor. The area-weighted means areused because the plot density is different indifferent regions. Uncertainty is given as 95%confidence intervals. The changes betweeninventories on paired plots were analysed byANOVA using time as the main factor.

Systematic error compensationAfter re-analyzing samples from the first in-ventory to check for comparability systemat-ic differences between the inventories hasbeen detected for some variables. The differ-ences were compensated for before doing theANOVA analysis. The compensation is de-scribed in Bertills (2003).

Results & discussionBiological contra anthropogenic acidificationThe effect of a growing stand on the acidity ofthe soil is more likely to be most pronouncedin the part of the soil where the uptake ofnutrients is highest. In figure 1 we have plot-ted the pH for O, B and C horizon versus thestand age in 10 year classes. The pH in the Ohorizon shows a strong negative trend withstand age. The negative trend for the B hori-zon is weaker but still significant while thereis no trend for the C horizon. Thus, the standdevelopment affect primarily the acidity ofthe O horizon while the mineral soil is lessaffected. When the same variable is plottedagainst latitude, as in figure 2, there is no re-lationship for the O horizon. In the mineralsoil samples, however, there is a positivecorrelation between latitude and pH. Thispositive correlation is most pronounced inthe C horizon. This observation is consistentwith earlier studies which showed that theregional differences in acid-base status, alleg-edly caused by differences in deposition, aremore pronounced at deeper levels of the soilprofile where the effect of biological acidifica-tion is small (Karltun, 1995).


33

Acid-base status and changes in Swedish forest soils

Figure 1. pH(H2O) in the O, B and C horizons as a function of stand age.

Figure 2. pH(H2O) in the O, B and C horizons as a function of latitude.

Stand age (yr)

pH

(H2O

)

Latitude

pH

(H2O

)


34


Table 1. Area of Swedish forests with a pH(H2O)<4.5 in the B horizon and a pH(H2O)<4.75in the C horizon.

Region Area

ha % of % of region country

northern Norrland 123 000 2.0 0.54southern Norrland 193 000 3.2 0.85Svealand 259 000 4.6 1.10Götaland 838 000 16.4 3.70

Table 2. Results from ANOVA analysis on the change in different variable describing the acidity betweenthe first (1983–1987) and second (1993–1998) inventory of the NFSVS. Signs in brackets are re-sults where the change is relatively large but still not significant

Variable O horizon Average Average B horizon Average Average1983–87 1993–98 1983–87 1993–98

PH (-) +4.10 4.06 *** 4.73 4.85

Base saturation1 no change no change(%) 19.2 19.4 6.41 6.31

Al3+ (+) +(mmol/kg TS) 8.31 10.3 *** 5.81 8.12

Total aciditet +(mmolc /kg TS) *** 566 673 no change 77.3 75.8

Ca2+ + (+)(mmol/kg TS) *** 40.4 50.9 1.18 1.65

Mg2+ + -(mmol/kg TS) *** 11.0 13.2 * 0.61 0.47

1) Base saturation using CECpH 7

Extent of acidification of Swedish forest soilsTo determine how large areas that are severe-ly affected by acidification is of course diffi-cult. Since there are no obvious thresholdsfor soil acidification the determined area willbe very much dependent on the criteria thatis formulated for what is considered to be anacidified soil. In this presentation we used aclassification published by the Swedish Boardof Forestry (Gustafsson et al., 2001) althoughwe slightly modified it. In it’s simplest version

the classification of acidified soils in the re-port from the Forestry Board is based on thepH of the B horizon (<4.5) or the pH of the Chorizon (<4.75). We used a modified versionwere we used the above criteria but requiredboth pH levels to be below the given values toconsider the profile severely acidified. Theserequirements were applied to the NSFSV data-base and the results are presented in table 1.Just above 6% or 1.4 million ha of Swedishforest soils fulfill the acidification criteria andof that area as much as 60% is located in Göta-land, the southernmost geographical region.In Norrland, both the southern and northernpart, the relative proportion of acid soils ismuch smaller and more likely to be the lowertail of the natural, normal variation in acidityamong soil profiles.

Changes in acidification status between1983–1987 and 1993–1998The changes between the first and secondinventories of NSFSV were studied usingANOVA. The results are presented in Table 2.


35

Acid-base status and changes in Swedish forest soils

The results in the O horizon and in the B ho-rizon are quite different. In the O horizon thepH show a tendency to decrease while thetotal acidity is increasing. This may be inter-preted as an increasing biological acidifica-tion. However, exchangeable Ca2+ and Mg2+

are also increasing in the O horizon, whichmake this explanation more unlikely. Thechanges may also be an artifact caused by aslight change in the way the O horizon wassampled between inventories. We know thatthe C concentration of the O horizon has in-creased between the inventories, which indi-cates that a more pure organic part, i.e. lessinclusion of mineral soil in the sample, of theO horizon has been sampled in the secondinventory. Since the total capacity of the sam-ple to hold acidity and base cations, the CEC,is much higher in organic matter than in min-eral soil it can explain why both total acidityand exchangeable cations like Ca2+ and Mg2+

can increase. In the B horizon the pH is in-creasing significantly, in average about onetenth of a pH unit. Despite an increasing pHthe exchangeable Al3+ is also increasing in theB horizon which is difficult to explain. Ex-changeable Ca2+ show a tendency to increasewhile Mg2+ is decreasing so there is no generaltrend among the base cations. Thus, the dis-covered tendencies are neither easily inter-preted nor mutually supportive. Some obser-vations points at an increased acidificationwhile others indicate improvements. Itshould be noted that the base saturation re-mains constant in both the O and B horizonwhich indicates that the changes in the acid-base status of the soils, in any direction, arerather small.

ConclusionsGeographical differences in the acid-base sta-tus of Swedish forest soils are still large withmost of the acidified soils found in the southof Sweden.

The geographical differences in acid-basestatus increase with depth and are most pro-nounced in the C horizon.

Even if some variables show statisticallysignificant changes between the first and sec-ond NFSVS inventory there is no general, uni-form trend towards increased or decreasedacidification.

ReferencesBertills, U. (in press). Fördjupad utvärdering

för Miljömålet Bara naturlig försurning.Rapport,

Eriksson, E., Karltun, E. & Lundmark, J.E. 1992.Acidification of forest soils in Sweden.Ambio 21, 150–154.

Falkengren-Grerup, U., Linnermark, N. & Tyler,G. 1987. Changes in acidity and cationpools of south Swedish soils between 1949and 1985. Chemosphere 16, 2239–2248.

Gustafsson, J.P., Karltun, E., Lundström, U. &Westling, O. 2001. Urvalskriterier för be-dömning av markförsurning. Rapport. 11D,Skogsstyrelsen, Jönköping, 26pp.

Hallbäcken, L. & Tamm, C.O. 1986. Changes insoil acidity from 1927 to 1982–84 in a forestarea of south-west Sweden. Scand.J.For.Res.1, 219–232.

Karltun, E. 1994. Principal geographic varia-tion in the acidification of Swedish forestsoils. Water Air Soil Pollut. 76, 353–362.

Karltun, E. 1995. Acidification of forest soils onglacial till in Sweden. Report 4427, SwedishEnvironmental Protection Agency, Solna,Sweden, 76pp.

Skjelkvale, B.L., Mannio, J., Wilander, A. &Andersen,T. 2001. Recovery from acidifica-tion of lakes in Finland, Norway and Swe-den 1990–1999. Hydrology and Earth SystemSciences 5, 327–337.

Stoddard, J.L., Jeffries, D.S., Lukewille, A.,Clair, T.A., Dillon, P.J., Driscoll, C.T., Forsius,M., Johannessen, M., Kahl, J.S., Kellogg,J.H., Kemp, A., Mannio, J., Monteith, D.T.,


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Murdoch, P.S., Patrick, S., Rebsdorf, A.,Skjelkvale, B.L., Stainton, M.P., Traaen, T.,van Dam, H., Webster, K.E., Wieting, J. &Wilander, A. 1999. Regional trends in

aquatic recovery from acidification inNorth America and Europe. Nature 401,575–578.


37

Modelling acidification and recovery ofsoils and surface waters

IntroductionDeposition of acidifying compounds has beendecreasing in Sweden approximately since1990. In particular the sulphur (S) deposition

is today only a fraction of the deposition inthe late 1980ies. On the Swedish west-coastthe decrease since 1990 was more than 50%(Figure 1).

FILIP MOLDANVERONIKA KRONNÄSIVL Swedish Environmental ResearchInstituteGöteborg

Figure 1. Sulphur deposition measured in throughfall, Gårdsjön, 1980–2000.


38

There has been documented widespreadsigns of increasing lake water alkalinity (Wi-lander, 1997). The general pattern of lake wa-ter chemistry trends is declining sulphate(SO4

2-) accompanied partly by decreasingconcentrations of base cations, partly by anincrease of alkalinity. While these changes arereadily observable, the development of acid-ified soils is much less well known. Changesin soils are typically slow compared to chang-es in surface waters and detection of trendsin soils is further complicated by factors suchas spatial heterogeneity or year-to-year vari-ability of temperature and precipitation (Karl-tun et al, this volume).

However, long-term acidification of surfacewaters is to a large extent a consequence ofsoil acidification in catchments (Reuss andJohnson, 1986). In this paper we have usedthe acidification model MAGIC (Cosby et al,1985, 2001) and data from several regionalmonitoring programmes in Sweden to esti-mate past, present and future development ofsoils and lake waters acidification. The maindata which has been used were lake waterchemistry at 143 intensively monitored lakes(SLU), data from soil monitoring (Ståndorts-kartering) at 23 500 plots (SLU) and MATCHmodel calculations of deposition on 20x20 kmscale (SMHI/IVL).

MAGIC calibrationThe MAGIC model is a widely used mediumcomplexity dynamic model. MAGIC consistsof two major sections: an equilibrium sectionand a mass balance section, which are linkedtogether.

The equilibrium section, in which the con-centrations of major ions are simulated, aregoverned by:• sulphate adsorption (Langmuir type of iso-

therm),• cation exchange (Gains- Thomas expres-

sions for monovalent and divalent cations),

• dissolution and precipitation of inorganicaluminium (equilibrium with aluminiumhydroxide),

• dissolution of CO2 followed by dissocia-tion of HCO3 and CO3,

• organic anion dissociation (monoprotic,diprotic and triprotic organic anions).

The mass balance section, in which the flux ofmajor ions to and from the soil are simulated,is assumed to be controlled by:• atmospheric inputs,• chemical weathering,• net uptake and loss in biomass,• runoff loss (sedimentation in the lake).

Data treatment, calibration procedure andresults are described in Moldan et al. (submit-ted). The work has been done with the Swed-ish research programme ASTA (AbatementStrategies for Air Pollution).

In 133 cases the model successfully cali-brated to soil and lake water chemistry meas-ured in 1997 provided measured and/or esti-mated deposition and lakes and catchmentscharacteristics. Also modelled and observed(Skjelkvåle et al., 2001) trends in lake waterchemistry were compared and both magni-tude and direction of lake water chemistrywere in a reasonably good agreement (Moldanet al., submitted).

MAGIC simulation resultsThe model predicted a countrywide increasein lake water ANC for a majority of the lakes.We have divided lakes into three categoriesaccording to magnitude of ANC changes. Thelargest increase was more frequent at thelakes in the southern compared to the north-ern part of the country (Figure 2).

The selection of modelled lakes includedmany lakes which were not particularly sen-sitive to acidification or which were in regionshistorically not much affected by acid depo-

F. Moldan, V. Kronnäs


39

sition. According to Swedish EnvironmentalProtection Agency about 20% of all lakes inSweden are classified as acidified or sensitiveto acidification (Wilander, 1999). Using thesame criteria (pH and alkalinity) about 50% ofthe modelled lakes are acidified or acid sensi-tive. Consequently about 50% of the modelledlakes probably never acidified and thereforealso should not be expected to increase their

alkalinity and pH when the acidifying deposi-tion decrease.

For that reason we have divided the mod-elled lakes into two groups; acid sensitive andnon-sensitive, using ANC in 1997 as a criteria.There were 63 lakes in the acid sensitive cat-egory. To present time series of lake water pHand ANC, we have calculated median, quar-tiles and 5% and 95% percentiles for eachyear (Figures 3 and 4).

For the acid sensitive lakes, the modelledpH generally decreased when the acid depo-sition increased in the middle 20th century,and increased sharply between 1990 and 2000when the acid deposition decreased. The in-crease levelled off after 2010, when deposi-tion stabilised on a new much lower level(Figure 3). The change was relatively smalleron lakes with either high or low historical pH.The pattern of ANC was similar to that of pHincluding generally slow increase of ANC after2010 (Figure 4) in average by about 4 µeq/lover 30 years from 2010 to 2040.

The modelled soil base saturation in thesensitive lakes’ catchments declined for mostof the catchments over practically the entiremodelled period 1860–2040. In contrast to pHand ANC there was no increase of soil basesaturation (Figure 5) in response to the aciddeposition decline after 1990.

Generalised European patternof surface water recoveryThe pattern of lake waters chemistry chang-es (both observed and modelled) is consist-ent with a general picture synthesised from amajor European project on surface watersrecovery RECOVER:2010 (Ferrier et al., 2001).Allowing for a certain degree of generalisa-tion, the pattern in surface water across Eu-rope was such that decreasing SO4

2- and NO3-

led to an increasing ANC, but to an equalsized decrease of base cations (Evans et al.,2001), (Figure 6).

Modelling acidification and recovery of soils …

Figure 2. Simulated annual ANC-change 1997–2010(µeq/l, adapted from Munthe et al, 2002).


40


Figure 3. Simulated pH in 64 acid sensitive lakes 1860–2040.

Figure 4. Simulated ANC (µeq/l) in 64 acid sensitive lakes 1860–2040.


41

Modelling acidification and recovery of soils …

Figure 5. Simulated base saturation in the 64 acid sensitive catchments 1860–2040.

Figure 6. Generalised pattern of surface waters recovery from acidification observed across Europe.From: Evans et al, 2001.


42


ConclusionsThe MAGIC simulations indicate that:• decreased deposition has a positive effect

on both soils and surface waters,• chemical recovery of soils takes much

longer time than of lakes,• surface waters can partly recover even if

soils in the catchments continue to acidify,• in many cases the soils will not recover by

2040 and• in many cases the recovery of lakes will

not be complete by 2040 unless depositionwill decrease further.

AcknowledgementErik Karltun (SLU) provided data and helpedus with interpretation and data analysis of thesoil inventory data, Anders Wilander (SLU)provided data and helped us with analysis ofthe lake inventory data and Jack Cosby (Uni-versity of Virginia) has developed the MAGICmodel and helped us with the regional cali-bration.

ReferencesCosby, B.J., Wright, R.F., Hornberger, G.M. and

Galloway, J.N. 1985. Modelling the effectsof acid deposition: assessment of a lumpedparameter model of soil water and stream-water chemistry. Water Resour. Res. 21:51–63.

Cosby, B.J., Ferrier, R.C., Jenkins A. and Wright.R.F. 2001. Modelling the effects of acid dep-

osition: refinements, adjustments and in-clusion of nitrogen dynamics in the MAG-IC model. Hydrol. Earth Syst. Sci. 5: 499–517.

Evans, C., Jenkins, A., Helliwell, R., Ferrier, R.and Collins, R., 2001. Freshwater Acidifica-tion and Recovery in the United Kingdom.Centre for Ecology and Hydrology, Walling-ford, UK

Karltun E., et al., this volume.Moldan, F., Kronnäs, V., Wilander, A, Karltun,

E., and Cosby, B.J., submitted. Modellingacidification and recovery of Swedishlakes. Submitted to WASP.

Munthe, J., Grennfelt, P., Sverdrup, H. and Sun-dqvist, G. 2002. New concepts and meth-ods for effect-based strategies on trans-boundary air pollution. ASTA SynthesisReport. IVL Report B1495.

Reuss, J.O. and Johnson, D.W., 1986. Acid dep-osition and the acidification of soils andwaters. Ecological Studies 59, Springer-Verlag, New York, 119 p.

Skjelkvåle, B.L., Mannio, J., Wilander, A. andAndersen, T., 2001. Recovery from acidifi-cation of lakes in Finland, Norway andSweden 1990–1999. Hydrol. Earth Syst.Sci., 5(3), 327–337.

Wilander, A. 1997. Referenssjöarnas vatten-kemi under 12 år; tillstånd och trender.(Reference lakes water chemistry under 12years; status and trends.) Naturvårdsver-ket Rapport 4652. (in Swedish)

Wilander, A. 1999. Surhet/försurning. In Be-dömningsgrunder för miljökvalitet. Sjöaroch vattendrag. Red Wiederholm, T., Natur-vårdsverket, Rapport 4920. (in Swedish)


43

Processes affecting surface water acidity:Natural acid or anthropogenicallyacidified waters?

HJALMAR LAUDONDepartment of Forest EcologySLUUppsala

The water quality of streams, rivers and lakesis affected by a number of processes in thelandscape. Vegetation, geology, climate andnatural atmospheric input of nutrients createthe natural chemical conditions. Superim-posed on this natural chemistry is the anthro-pogenic, human induced contribution, whichcan cause large perturbation in the naturalchemistry and therefore produce severe con-ditions for many aquatic organisms.

Acidification, resulting from the emissionof acid precursors to the atmosphere causeone of the most concerning anthropogeniceffects on soils and waters in Sweden. Naturalacid water environments are also commonand ecologically important, especially in thenorthern forest ecosystem, called the borealforest. Soils with low weathering capacity andan accumulation of organic material are acommon feature of the boreal forest. Becausethe conditions of the soil environment to alarge extent control the water quality, drain-

age water from these soils are often nutrientpoor and acidic.

The term acidification suggests a develop-ment over time towards more acid condi-tions. Most natural acid ecosystems todayhave acidified over thousands of years sincethe last glaciation. In contrast, surface watersaffected by anthropogenic acidification oftenexperience a much more rapid transforma-tion. Forest production and timber harvest-ing can also influence the acidity of soils, butthe impact on surface waters is probably rel-atively unimportant compared to the role ofacid deposition in most parts of Sweden.

Many lakes and rivers in south-westernSweden demonstrate serious biological dam-age caused by surface water acidification. Inmany of these waters it is clear that acid dep-osition have played a fundamental role in thepH decline the last decades. Acidificationhave in many locations gone so far that a newpermanent acidified condition occurs, with


44

severely reduced base saturation of soils andconstantly low pH values in surface waters.This can be called chronic acidification andimplies low pH values and high concentra-tions of the inorganic (toxic) form of alumi-num during the entire year despite changes inflow. In northern Sweden, with significantlylower levels of acid deposition, the largestrisk of biological damage in aquatic environ-ments, occur during high runoff periods asso-ciated with snow melt and heavy rain periodsduring summer and fall. These episodic pHdeclines often occur during short periods, last-ing from days to weeks, but they can severelydamage fish and other aquatic organisms. Innorthern Sweden the period between epi-sodes during the winter or during dry summerperiods, called base flow, is often not signifi-cantly affected by atmospheric deposition.

What controls pH?Negative effects caused by acidification areoften described in terms of chemical parame-ters, such as low or declining pH values. In re-ality the main concern are the ecological con-sequences on fish and other aquatic organ-isms that are linked to the chemical changes.However, those ecological changes are much

more difficult to measure and predict. The pHof surface water (at a set partial pressure ofcarbon dioxide [pCO2]) is to a large extent de-termined by DOC (dissolved organic carbon)and ANC (Acid Neutralization Capacity). De-spite the fact that the relationship betweenpH, DOC and ANC is mathematically compli-cated it can be described as figure 2.

DOC is a very important component inmost Swedish surface waters. High concen-trations and therefore often naturally low pHvalues are generally found in regions withlarge areal extent of wetlands in the borealforest. The highest levels are found in the in-land and coast of northern Sweden andsouth-central Sweden. The human impact onDOC is relatively marginal although forestryand ditching can have had some influence.The effect of climate on the concentrationand dynamics of DOC in rivers and lakes hasbeen explored in recent years. Today weknow that temperature and precipitation af-fect the DOC export from nearby soils posi-tively. Winter conditions such as temperatureand snow amounts are also expected tostrongly influence the concentration of DOC,especially during snow melt periods.

ANC expresses the capacity to bufferagainst acidifying protons. Surface water witha high ANC has a high ability to neutralize

H. Laudon

Figure 1. Example of a naturally driven pH decline during the spring flood (to the left) and a stream thathas been acidified for over 100 years by acid deposition (to the right).

100 years of acidificationNatural pH decline during spring


45

protons but the ability is reduced when acidis added. ANC is affected by a number of nat-ural factors but is also the parameter that ismost affected by acid deposition. ANC is notmeasured directly but is calculated from

standard water chemical analyses using basecations and strong acid anions. In figure 3 thecalculation of ANC is presented along withnatural and anthropogenic processes thataffect ANC.

Processes affecting surface water acidity…

Figur 2. Relationship between ANC, DOC and pH at atmospheric partial pressure of CO2.

Figur 3. Calculation and factors that affect ANC. Arrows downwards indicate a declining concentration ofthe solute, whereas an upward arrow indicates an increasing concentration. White arrows repre-sent a natural source/sink, a black arrow is anthropogenic source/sink and banded arrows indi-cate that an anthropogenic change is partly compensated by a change in uptake or mobilization.

ANC = BC – SO42- – NO3

- – Cl-

pH

(pC

O2

380

pp

m)


46

Two other factors that affect pH are alumi-num concentration and the partial pressureof carbon dioxide (pCO2). In surface watersthe pCO2 is primarily high during the winterand can therefore have a pH decreasing effecton ice covered lakes. The pCO2 influence be-comes important at pH values above 5.5 andhas therefore a relatively unimportant effecton pH in the most acid surface waters. Foraluminum the effect is the opposite. Alumi-num, or rather the fraction of inorganic mon-omeric aluminum (Ali which is the most tox-ic fraction of aluminum) buffers against pHdecline (and at the same time produce high-er concentrations of Ali). The importance ofaluminum buffering for determining pH is ingeneral limited as long as pH exceed pH 4.5.

Acid episodesIn general, it is the same water chemicalmechanisms that drive pH decline associatedwith high runoff episodes as controls pH dur-ing other periods of the year. The largest dif-ference between an acid episode and chron-

H. Laudon

ic acidification is in the importance of thetransient change in hydrology, which influ-ences both the decline and the recovery ofpH during episodes. The two most importantnatural factors that affect the large pH decline(up to two units) during the spring flood innorthern Sweden are an increase in DOC (of-ten two to three times as high during peakflow compared to base flow figure 4) and anatural dilution of ANC (figure 5). Short puls-es of anthropogenic sulfate from snow or rainduring the episode will be superimposed onthe natural decline of ANC and therefore fur-ther depress pH.

Episodic changes in the water quality are anatural feature of most aquatic ecosystems.Natural variation in water chemistry is of fun-damental importance in the establishment ofnatural biodiversity. Organisms that survivethese often toxic conditions gain competitiveadvantages in the ecosystem.

To conclude that a stream, river or lake isacid is rather straightforward, but to deter-mine that anthropogenic acidification duringthe last century is responsible for that low pHis much more difficult. This task becomes

Figure 4. Example of DOC change during the spring flood in a small stream in northern Sweden. Note thatDOC increases from 7 mg L-1 during baseflow to over 20 mg L-1 during peak runoff.

DO

C (m

g L

-1)

Ru

no

ff (m

m h

a-1 d

ay-1

)


47

Processes affecting surface water acidity…

Figure 5. Natural dilution of ANC during an episode. When a base flow with a high ANC is diluted by snowmelt water or rain water with a very low ANC, a dilution of both the base cations and the strongacid anions will occur.

Figure 6. Observed pH decline and natural (preindustrial) pH decline in a small stream in northern Swe-den. The difference between the observed (dark symbols) and the preindustrial pH decline (opensymbols) depends on the anthropogenic deposition. The preindustrial pH decline is driven by acombination of natural increase in DOC and a natural dilution of ANC.

pH

air

Ru

no

ff (L

s-1

)


48

even more difficult when acidification is epi-sodic and long time series of a water chemis-try and aquatic biology is lacking. The biodi-versity of many surface waters in Swedenhave certainly been affected by acidificationduring the 20th century, but also by of de-struction of spawning grounds, forestry prac-tice, migratory restraints, introduction of newspecies and over-fishing. Without a properprocess base understanding of how surfacewater chemistry is controlled we will neverbe able to understand and separate the an-thropogenic influence on surface water acid-ity from natural variability.

ReferencesLaudon, H., Westling, O., Vøllestad, L. A., &

Poléo, A.B.S. (2001). Naturligt sura och för-surade vatten i Norrland.‘ Naturvårdsver-ket Rapport 5144, Stockholm. (In Swedishwith English summary).

Laudon, H., Westling, O., Löfgren, S. & Bishop,K. (2001). Modelling preindustrial ANC andpH during spring flood in Northern Swe-den. Biogeochemistry, 54, 171–195.

Laudon, H. and Hemond, H. F. (2002). Recov-ery of streams from episodic acidificationin northern Sweden. Environmental Sci-ence & Technology, 36, 921–928.

H. Laudon


49

Recovery from acidification in Swedishlakes and streams

ANDERS WILANDERSTEFAN LÖFGRENDept of Environmental AssessmentSLUUppsala

IntroductionIn 1972 the first UN conference on the envi-ronment was held in Stockholm. One Swedishcontribution dealt with air pollution acrossnational boundaries (Bolin et al. 1971) pre-senting data from river monitoring as frightful

examples of effects of acid deposition (Figure1a). Before the opening of the conference ad-ditional data were included. Svante Odén andThorsten Ahl (1972) concluded that the up-ward step (Figure 1b) was caused by meltwater from thawing snow infiltrating the soil,leading to a raised pH. They also wrote, “the

Figure 1. pH-value for River Klarälven as presented at the 1972 UN Conference. A) Data from the Casestudy (Bolin et al. 1971). B) Updated data (Odén and Ahl, 1972).


50

negative trend, if persistent in time, willchange the situation drastically, within some20 years”. Other information such as in-creased acid deposition and observed fishkills supported their conclusion. Their pre-diction, fortunately, did not realise (figure 2).

In the following the recent changes with re-gard to recovery from acidification in Swed-ish lakes and streams will be elucidated.

Material and methodsThe latest national survey of lakes andstreams was conducted in the autumn 2000(Wilander et al. 2003). Only lakes >4 ha wereincluded. The statistical stratification methodused forced lakes in the southern, more aciddeposition affected parts of the country aswell as large lakes to be over-represented inthe sub-sample of a population of about60 000 lakes >4 ha.

In addition two time-series programmeswere initiated in 1983–84, covering about 100forest lakes and about 50 streams. Emphasiswas put on acid sensitive, clear water lakes,which makes the selection non-representa-tive for the entire Swedish lake population.

The lakes are sampled 3–4 times a year, whilethe streams are sampled monthly and occa-sionally more frequently.

Acid status according to thenational lake and streamsurveys in 1995 and 2000Based on the lake survey in 2000 it was esti-mated the 6.2% of the lake population had analkalinity <0.05 meq/l. When ANC is used as ameasure of buffer capacity, the percentage isas low as 1.3%. In 1995, the corresponding fig-ures were 6.2% and 2.4%, respectively. Accord-ing to the ANC trend, a recovery from acidifi-cation occurred between 1995 and 2000. Asmall recovery was also indicated by thestream surveys (Wilander et al. 2003). Sul-phate concentrations were substantially low-er according to RI00 as compared to RI95 (ta-ble 1). This should lead to equivalent increas-es in alkalinity and corresponding raise in pH-values if the concentrations of base cations(BC) and humic substances (TOC) were con-stant. However, the BC concentrations werelower while the TOC concentrations werehigher (table 1). Thus, there are two opposing

Figure 2. pH-values for River Klarälven from 1965 through 2002. Line fitted with LOWESS smoothing.

A. Wilander, S. Löfgren


51

signals on alkalinity and ANC between thetwo surveys, especially in low ANC lakes. Thecontribution of humic acids diminishing thealkalinity without affecting ANC is the causeof the different patterns.

Aluminium (Al) in inorganic form is strong-ly toxic for gill breathing organisms such asfish and many bottom-living invertebrates.More lakes had inorganic Al concentrationshigher than 25 µg/l in 2000 as compared to1995 (table 2). This is a level where damagecan be expected on salmon and roach (Lyder-sen et al 2002). One cause may be the lowerpH-values in 2000 (table 2). The stream sur-vey in 2000 sowed a mean total aluminiumconcentration of 79 µg/l, which is 25 µg/l high-er than for the survey in 1995 (n=216 bothyears). However, the concentrations of inor-ganic Al were equal or 15 µg/l both years. Theconcentrations of organically bound Al ex-plain the difference in total aluminium. In

both lakes and streams, there was a negativerelation between inorganic Al and pH and apositive relation between inorganic Al andTOC.

Acid trends in reference lakesand streamsMonitoring of lakes and streams sensitive toacidification started in the beginning of1980:ies. As a consequence we have little in-formation about the acidification phase but agood coverage of the recovery. The recoveryphase is exemplified with Lake Brunnsjön (fig-ure 3).

Obviously there are no monotonous trendseven though a decrease in sulphate is accom-panied by a decrease in BC (figure 3a). Alka-linity is more or less unaffected by the sul-phate level (figure 3b), but there is a signifi-

Recovery from acidification in Swedish lakes and streams

Table 1. pH-value, buffer capacity (alkalinity och ANC), base cations (BC) total organic carbon (TOC) andsulphate (SO4) calculated for the lake population > 4 ha (about 58 000).

Parameter RI00 RI95

Percentile (%) 10 50 90 10 50 90

pH 5.53 6.57 7.24 6.01 6.79 7.31Alkalinity (µekv/l) 3 105 382 18 131 450ANC (µekv/l) 56 195 498 49 192 598BC (µekv/l) 99 275 795 99 291 950TOC (mg/l) 2.0 8.7 18.7 2.0 8.4 13.2SO4 (µekv/l) 15 35 142 21 47 193

Table 2. The share of sampled lakes with concen-trations of inorganic Al > 25 µg/l (toxic forthe most sensitive species) and >75 µg/l(toxic for less sensitive species). N=535.

Parameter Tolerance Share of sampled value lakes % 1995 2000

Inorganic Al >25 µg/l 17 26>75 µg/l 6 9

pH-value < 6,0 18 32


52

cant increase in ANC with decreasing sul-phate concentration. The difference betweenthe two parameters is partly due to increasedhumus concentrations, but it is also an effectof the BC/sulphate ratio, which increase atlower sulphate levels. This shows the posi-tive effects on BC and ANC of the decreasedacid deposition. The pH-values has increased

as well (figure 4). Similar behaviours are ob-served in most of the reference lakes in south-ern Sweden.

The pH-values increased with a mean of0.2 units in the two groups of reference lakeswith the lowest pH-values (pH<5.0, n=12 and5.0<pH≤5.5, n=16). A proceeding increase ofthat magnitude can not be expected in the


Figure 3: A) Time series for concentrations of non-marine sulphate (SO4*), non-marine base cations (BC*),acid neutralisation capacity (ANC) and alkalinity for Lake Brunnsjön in southern Sweden (Kal-mar county). Lines fitted with LOWESS smoothing.B) Relationship between non-marine sulphate (SO4*) and non-marine base cations (BC*) andANC. The line shows the ratio 1:1.

Figure 3. Changes in pH-value in the acidified reference lake Brunnsjön in southern Sweden (Kalmarcounty). Line fitted with LOWESS smoothing.


53

future. Lakes with higher pH-values exhibitsmaller changes as expected. ANC increasedin all lake groups with the exception of themost acid one, which had the highest ANCduring 1991–94. Model simulations indicatethat the most acid lakes are natural acidic.Thus, they are very much influenced by TOCvariations. The recovery during the period1990–2001, measured as ANC, was as a mean0.003 meq/l,year for lakes in the three highestpH-classes.

The trends for pH and alkalinity were simi-lar for lakes in the entire country regardlessof the very different S deposition. pH in-creased about 0.02 units/year, while alkalini-ty showed very small changes. ANC, howev-er, increased about 0.003 meq/l, year in themost heavily polluted south-west part of Swe-den and with about 0.002 meq /l, year in theremainder of the country. This indicates amore rapid recovery in the most acid deposi-tion affected regions.

Acidification classification ofSwedish lakesBased on data from RI00, the SSWC model(Rapp et al. 2002) and the Swedish quality

criteria for surface waters (SEPA 1999), thenumber of lakes acidified by acid depositionwas estimated. Based on ANC, 3% of the lakeswere acidified, while based on alkalinity, thesame proportion was 10% (Figure 5). Thishighlights the difficulties in separating natu-rally acidic lakes from anthropogenicallyacidified lakes, when using alkalinity. This isbecause the alkalinity expression does nottake the humus acidity into consideration.

Most acidified lakes are situated in south-west Sweden, while liming activities are com-mon also in the central and northeast part ofthe country (Figure 5). This is partly causedby poor liming criteria (alkalinity and pH) andpartly due to liming against acid episodes innorthern Sweden during snowmelt, heavyrains etc. The latter are mainly of natural ori-gin, but become more severe due to acid dep-osition (c.f. Laudon this volume).

ConclusionsSwedish lakes and streams exhibit recoveryfrom acidification since the late 1980’s due tothe decreased sulphur deposition. The recov-ery is shown as slow increases of ANC and pHand has been most pronounced in poorly


Figure 4. Changes in pH-value (mean values) from 1990 through 2001 (n= 67) for four groups of referencelakes with different initial pH-levels.


54

buffered, circumneutral waters. The ANC in-crease has been largest in the most severelypolluted south-west parts of Sweden, corre-sponding to an annual increase of 0.003 mekvANC/l. In central and northern Sweden, theannual increase has been around 0.002 mekvANC/l. Naturally acidic or well buffered lakesand streams exhibits less pronounced recov-ery trends. Alkalinity exhibits no or very smallchanges with time. According to the officiallyused models and quality criteria for ANC,approximately 3% of the Swedish lakes larger

than 4 ha are still acidified by acid deposition.Most of those lakes are situated in south-westSweden.

Turning back to River Klarälven, J.V. Eriks-son (1929) studied the river in the beginningof last century. Fortunately, that time series(figure 6) was not used at the 1972 UN confer-ence. A comparison with present data doesnot reveal any major difference. Extensiveliming activities in the county of Värmlandand in Norway influence the concentrationsfrom 1990 and onwards.


Figure 5. Lakes >4 ha classified as acidified based on ANC (left) and alkalinity (middle) according to Swed-ish Water Quality Guidelines (SEPA 2000) and limed lakes (all size classes, right). Data from thenational lake survey 2000. Maps from Lars Rapp, SLU.


55


ReferencesBolin, B. et al. (eds.) 1971. Air pollution across

national boundaries. The impact on theenvironment of sulfur in air and precipita-tion. Sweden’s case study for the UnitedNations conference on the human environ-ment. Royal Ministry for Foreign Affairs.Royal Ministry for Agriculture.

Eriksson, J.V. 1929. Den kemiska denudatio-nen i Sverige. In Swedish with French sum-mary. Medd. Statens Meteor. Hydrogr. An-stalt Band 5 N:o 3.

Lydersen, E., Löfgren, S. & Arnessen, T. 2002.Metals in Scandinavian surface waters: ef-fects of acidification, liming, and potentialreacidification. Crit. Rev. Environ. Sci.Techn. 32(2&3):73–295.

Odén, S. & Ahl, T. 1972. The long-term chang-es in the pH of lakes and rivers in Sweden.Paper referring to Section 5.2 of Sweden’scase study for the United Nations confer-

ence on the human environment. (mimeo-graphed report).

Rapp, L. Wilander, A. & Bertills, U. 2002. Kri-tisk belastning för försurning av sjöar. InBertills, U. & Lövblad, G. (eds) Kritisk be-lastning för svavel och kväve. Naturvårds-verket Rapport 5174. In Swedish.

SEPA 2000. Environmental quality criteria.Lakes and watercourses. Swedish Environ-mental Protection Agency. Report 5050.

Wilander, A. & Lundin, L. 2000. Recovery ofsurface waters and forest soils in Sweden.In Warfvinge, P. & Bertills, U. (eds.) Recov-ery from acidification in the natural envi-ronment. Present knowledge and futurescenarios. pp 53–66. Swedish Environmen-tal Protection Agency Report 5034.

Wilander, A., Johnson, R.K. & Goedkoop, W.2003. Riksinventering 2000. En synpotiskstudie av vattenkemi och bottenfauna isvenska sjöar och vattendrag. Inst.f. miljö-analys, SLU Rapport 2003:1. In Swedish.

Figure 6. Comparison of present time series for alkalinity with that given by J.V. Eriksson (1929) for RiverKlarälven.


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57

Deltagarlista

Föredragshållare (i den ordning de uppträder)Jan Nilsson Programansvarig MISTRABruno Nilsson * Sekreterare och VD KSLAUlla Lundstöm Professor MitthögskolanErik Karltun AgrD SLU, Inst f skoglig markläraFilip Moldan FD Svenska MiljöinstitutetAllan Rodhe Professor Uppsala universitet, Inst f hydrologiHjalmar Laudon FD SLU, Inst f skogsekologiAnders Wilander FD SLU, Inst f miljöanalys

Övriga deltagareBertils Ulla Dr Naturvårdsverket, miljöanalysavd.Bindler Richard Dr Umeå universitet, Inst f ekologiBishop Kevin Professor SLU, Inst f miljöanalysBringmark Lage Docent SLU, Inst f miljöanalysCarlestål Bo Akademijägmästare KSLAEriksson Hillevi SkogD SkogsstyrelsenFölster Jens Dr SLU, Inst f miljöanalysGustafsson Jon Petter Universitetslektor KTH, Inst f mark- o vattenteknikvan Hees Patrick Forskarassistent Mitthögskolan, Inst f naturvetenskapHultberg Hans Adj. professor IVLHällgren Jan-Erik* Dekanus SLU, SkogsfakultetenHögbom Lars FD SkogForskJacks Gunnar Professor KTHJohannisson Christian SkogD SkogsstyrelsenKronnäs Veronika Forskare IVLLöfgren Stefan Docent SLUMaxe Lena Statsgeolog SGUNilsson Ingvar Professor SLU, Inst f markvetenskapNohrstedt Hans-Örjan Programchef FormasNyström Ulf Forskare Göteborgs universitet, Inst f

geovetenskapOlofsson Hans Avd. dir. Länsstyrelsen DalarnaOlsson Bengt Docent SLU, Inst f ekologi o miljövårdPersson Gunnar FD SLU, Inst f miljöanalysPersson Tryggve Professor SLU, Inst f ekologi och miljövårdRenberg Ingemar Professor Umeå universitet, Inst f ekologiSeibert Jan Docent SLU, Inst f miljöanalys


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Snäll Sven 1:e statsgeolog SGUStendahl Johan FD SLU, Inst f skoglig markläravon Rosen Dietrich Professor SLU, Inst f biostokastikum/biometriWestling Olle Forskare IVLÖrlander Göran Professor Växjö universitet

* = ledamot KSLA

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Förteckning över tidigare utgivna nummer

År 2001; Årgång 140Nr 1 Sälen – resurs eller problemNr 2 Skogliga konsekvensanalyser 1999Nr 3 Framtida möjligheter till ökat utnyttjande av naturresurserNr 4 Verksamhetsberättelse 2000 Kungl. Skogs- och LantbruksakademienNr 5 Landskapet: restprodukt eller medvetet skapat?Nr 6 Ecologically Improved Agriculture – Strategy for SustainabilityNr 7 Sverige i det europeiska samarbetetNr 8 Bekämpningsmedel i vatten – vad vet vi om förekomst och effekter?Nr 9 Odlingssystem, växtnäring och markbördighet – 18 års resultat från en tidigare ej uppgödslad jordNr 10 Svenska fiskets framtid och samhällsnyttaNr 11 Vem sätter värde på den svenska skogen? – Trämekanisk framsynNr 12 Nutrition och folkhälsa i EU-perspektiv OCH Miljöpåverkan och framtidens matvanor OCH

Framtidens mat i framtidens kökNr 13 Konkurrenskraftig virkesförsörjning– ett kraftprov för skogsteknologin!Nr 14 Fritidsodlingens och stadsgrönskans samhällsnyttaNr 15 Debatt – Hur kan marknad och miljö förenas? Exemplet spannmålsproduktion

År 2002; Årgång 141Nr 1 Genteknik – en skymf mot Gud eller nya möjligheter för mänskligheten?Nr 2 Genmodifierade grödor. Varför? Varför inte? – Genetically Modified Crops. Why? Why Not?Nr 3 Skogsfrågor i ”Konventionen om biologisk mångfald”Nr 4 Mindre kväveförluster i foderodling, foderomvandling och gödselhantering!Nr 5 Bondens nya uppdrag OCH Shaping U.S. Agricultural PolicyNr 6 Verksamhetsberättelse 2001Nr 7 Sustainable forestry to protect water quality and aquatic biodiversityNr 8 Foder – en viktig länk i livsmedelskedjan!Nr 9 Fortbildning för landsbygdsutvecklareNr 10 Hållbart jordbruk – kunskapssammanställning och försök till syntesNr 11 Närproducerad mat. Miljövänlig? Affärsmässig? Djurvänlig?Nr 12 Nya kunskaper inom bioteknik och genetik för nya tillämpningar på husdjur SAMT

Fria Varuströmmar – konflikt med djur- och folkhälsa? Vilka möjliga utvägar finns? SAMT

Exempel på verksamhet inom JordbruksverketNr 13 Bland skärgårdsgubbar och abborrar på MöjaNr 14 EU och EMU – broms eller draghjälp för skogen?Nr 15 Hur kan skogsbruk och kulturmiljövård förenas?Nr 16 Vilket kött äter vi om 10 år? Rött, vitt, svenskt, importerat? Vi får det samhälle vi äter oss till!Nr 17 Avsättning av skogsmark

År 2003; Årgång 142Nr 1 Det sydsvenska landskapet, framtidsvisioner och framtidssatsningar SAMT

Idéer för framtidens skogslandskapNr 2 Viltets positiva värdenNr 3 Inför toppmötet i JohannesburgNr 4 Kapital för landsbygdsföretagareNr 5 Kompetensförsörjningen i svenskt jordbrukNr 6 Fiskets miljöeffekter – kan vi nå miljömålen?Nr 7 Verksamhetsberättelse 2002Nr 8 De glesa strukturerna i den globala ekonomin – kunskapsläge och forskningsbehovNr 9 Tro och vetande om husdjurens välfärd (Enbart publicerad på www.ksla.se)Nr 10 Svenska satsningar på ökad träanvändning (Enbart publicerad på www.ksla.se)Nr 11 Kapital för landsbygdsföretagare (Enbart publicerad på www.ksla.se)Nr 12 Feminisering av Moder natur? Östrogener i naturen och i livsmedelNr 13 Crop and Forest Biotechnology for the FutureNr 14 Landskap och vindkraft – i medvind eller motvind (Enbart publicerad på www.ksla.se)Nr 15 Lantbrukskooperationen – Hållbar företagsidé eller historisk parentesNr 16 Utvecklingen i PolenNr 17 Mid Term Review Vad händer i Sverige när Eu ändrar jordbrukspolitik?Nr 18 Soil and surface water acidification in theory and practice


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Kungl. Skogs- och Lantbruksakademiens Tidskrift (KSLAT) har, under olika namn, utkommit sedan1813, då akademien grundades. Från och med 1994 utges KSLAT som en numrerad serie av skrifter

(15–20 häften/år) med egna titlar. Innehållet består huvudsakligen av dokumentering frånakademiens sammankomster och seminarier – även debattnummer förekommer –

och speglar akademiens verksamhetsområde; de areella näringarnaoch till dessa knutna verksamheter.

Prenumerationspris 350 kr/år.

Kungl. Skogs- och LantbruksakademienDrottninggatan 95 B, Box 6806, 113 86 Stockholm

Tel 08-54 54 77 00, Fax 08-54 54 77 10, Postgiro 18 32 80 - 7

ISSN 0023–5350 ISBN 91–89379-61-6

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soil and surface water acidification in theory and practice

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