levels and characteristics of toc in throughfall, forest floor leachate and soil solution in...

LEVELS AND CHARACTERISTICS OF TOC IN THROUGHFALL,FOREST FLOOR LEACHATE AND SOIL SOLUTION IN

UNDISTURBED BOREAL FOREST ECOSYSTEMS

MICHAEL STARR∗ and LIISA UKONMAANAHOFinnish Forest Research Institute, Vantaa Research Centre, P.O. Box 18, FIN-01301 Helsinki,

Finland(∗ author for correspondence, e-mail: [email protected]; phone: +358 102112450;

fax: +358 102112206)

(Received 20 August 2002; accepted 23 May 2003)

Abstract. Total organic carbon (TOC) concentrations and fluxes in throughfall, forest floor leachate,soil solution (15 and 35 cm depths), and groundwater for coniferous forest sites in the boreal zonethroughout Finland are described. Eight upland forest stands and one peatland forest stand are in-cluded in the study and the samples were collected during 1991–1997. Carbon (C) pools in theliving tree biomass and soil compartments are presented, and the hydrophobic/hydrophilic and acidiccomponents of dissolved organic carbon (DOC) in samples collected in autumn 1999 and spring 2000from two of the sites are compared. Biomass (aboveground and belowground) pools of C averaged88 Mg ha−1 and soil (humus layer + 20 cm soil layer) averaged 55 Mg ha−1. Stand throughfall TOCmonthly mean concentrations ranged from 4.0 to 18.6 mg L−1 and annual fluxes averaged 4.0 g m−2

yr−1. TOC concentrations in the water passing through the forest floor and soil decreased with depth.Plot mean concentrations at 35 cm depth values ranged from 4.1 to 21.2 mg L−1 and fluxes averaged3.7 g m−2 yr−1. Throughfall TOC concentrations were lowest during the winter, snowfall periodand highest during the growing season. No monotonic trends in throughfall TOC concentrationsover the 1991–1997 period were found. Soil solution TOC concentrations varied considerably, bothwithin and between years. DOC in throughfall, forest floor, and soil solutions and in both autumnand spring seasons was dominated by hydrophobic fractions, particularly acids. Spruce canopies andlitter appear to be important sources of soluble organic carbon, particularly acidic and hydrophobiccompounds. Further studies on the nature and dynamics of organic carbon fluxing through coniferous,boreal forest ecosystems are needed.

Keywords: boreal, dissolved organic carbon, DOC fractionation, soil solution, throughfall

1. Introduction

Boreal coniferous forest ecosystems contain large amounts of carbon in the bio-mass and soil (Kauppi et al., 1997; Finér et al., 2003) and leach considerableamounts of organic carbon to surface waters (Kortelainen and Saukkonen, 1998).Total organic carbon (TOC) concentrations in Norwegian and Swedish lake andstream waters reportedly have increased during the 1990s. These increases havebeen attributed to climate change, although this trend has not been clearly found inFinland (Skjelkvåle et al., 2001). However, knowledge about the fluxes of organic

Water, Air, and Soil Pollution: Focus 4: 715–729, 2004.© 2004 Kluwer Academic Publishers. Printed in the Netherlands.

716 M. STARR AND L. UKONMAANAHO

carbon (C) associated with throughfall and soil solution in boreal forest ecosystemsis limited compared to that known about forests in the temperate zone (Michalziket al., 2001; Piirainen et al., 2002).

In this paper we report on the levels and trends in TOC concentrations in through-fall and soil solution collected at nine boreal, forest stands over a seven-year period.The hydrophobic and acidic character of the dissolved organic carbon (DOC) inthroughfall and soil solution samples collected in autumn and spring at two of thestands also is described. But first we describe the pools of C in the tree biomassand soil at the stands. One of the stands is on peatland (histosols) and TOC con-centrations at the top of the water table are reported rather than those in water fromthe unsaturated zone. The nine stands are unmanaged, old stands have differingspecies composition and are located throughout Finland. The study is unique inthat it deals with C in undisturbed forests in the boreal zone and because it isa multiple site, long-term and integrated study in which the same sampling andanalytical procedures have been used (Bergström et al., 1995).

2. Materials and Methods

2.1. STUDY SITES

The data presented in this paper have been collected from four catchments (Fig-ure 1). These headwater catchments belong to the network of UN-ECE Interna-tional Co-operative Programme on Integrated Monitoring (Bergström et al., 1995)and, nowadays, also to the network of UN-ECE ICP-Forests/EU Intensive Monit-oring sites set up under the 1979 Convention on Long-Range Transboundary AirPollution. They are located in extensive areas of protected forest (national parks)having semi-natural, undisturbed old-growth forests. The terrain in each catchmentwas formed by the last glaciation and the landscape is characterised by areas ofupland coniferous or mixed forest, peatland, seepage lakes and ponds, and a dis-charge lake with stream. No agriculture is carried out in the vicinity and there are nosources of air pollution emissions nearby. The annual mean temperature (◦C) is 3.1at Valkea-Kotinen, 2.0 at Hietajärvi, –0.5 at Pesosjärvi, and –1.9 at Vuoskojärvi.In the same order, the annual precipitation (mm) is 618, 592, 571 and 395. Thenumber of days per year with snow cover (in the open) increases from about 130at Valkea-Kotinen to about 210 at Vuoskojärvi.

In each catchment, a number (7–9) of permanent monitoring plots, varying insize from 25 × 25 to 40 × 40 m, have been established (1988–1989) in the mainhabitat types (stands). In this paper only those plots at which throughfall and soilsolution have been monitored are included. The stands are composed of varyingproportions of Scots pine, Norway spruce, and deciduous (mainly birch) trees(Table I). For further a description and details about the catchments and plots, seeBergström et al. (1995).

TOC IN BOREAL FOREST ECOSYSTEMS 717

TAB

LE

I

Soi

ltyp

ean

dst

and

(199

1–19

92)

char

acte

rist

ics

ofth

eni

nest

udy

plot

s

Cat

chm

ent

Plo

tE

leva

tion

Soi

ltyp

eS

tem

volu

me

Age

ma.

s.l.

m3

ha−1

Sco

tspi

neN

orw

aysp

ruce

Dec

iduo

usa

Sta

ndin

gde

addo

min

ant

%%

%%

tree

s,ye

ars

Val

kea-

Kot

inen

VK

215

6Te

rric

His

toso

l43

38

857

219

0

VK

316

1D

ystr

icC

ambi

sol

579

454

412

155

Hie

tajä

rvi

HJ1

168

Hap

lic

Pod

zol

201

860

141

100

HJ4

167

Hap

lic

Pod

zol

232

910

90

230

Pes

osjä

rvi

PJ1

263

Car

bic

Pod

zol

154

269

291

320

PJ2

270

Hap

lic

Pod

zol

184

4836

166

240

PJ3

293

Hap

lic

Pod

zol

144

2451

251

240

Vuo

skoj

ärvi

VJ2

146

Hap

lic

Pod

zol

163

097

–15

0

VJ3

158

Hap

lic

Pod

zol

5098

02

118

0

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ainl

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irch

,Bet

ula

spp.

,but

also

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,Mou

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(B.p

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czer

epan

ovii

).


Figure 1. Map showing location of the four study catchments.

2.2. BIOMASS AND SOIL C POOLS

All trees (living and dead, both snags and fallen) on the plots have been mappedmeasured for breast height diameter, top height, canopy height, and crown pro-jection. Forest stand C pools were calculated from estimates of biomass fractionsof all the living trees on the plot (kg ha−1) and assuming a C content of 52%for all fractions. The biomass fractions for Scots pine, Norway spruce, and birch(Betula pendula and B. pubescens) were calculated using the allometric functions


developed by Marklund (1988) and for mountain birch (B. pubescens ssp. czere-panovii) at Vuoskojärvi using those developed by Starr et al. (1998). Marklund’sfunctions provide estimates of stem (over bark), needles (but not birch leaves),living and dead branches, and stump and coarse roots, while the functions formountain birch provide estimates of stem (over bark), living and dead branches,and foliage (at full development) but not stump and roots.

With the exception of plot 2 at Valkea-Kotinen (VK2), which is on peat, fourparallel composite soil samples of the organic (humus) layer (Of + Oh), 0–5 and5–20 cm layers were taken systematically at each plot. At plot VK2, the 0–5, 5–10and 10–20 cm layers were sampled. Carbon concentrations in the air-dried humuslayer, peat (milled) and mineral soil (<2 mm) samples were determined using aLECO-CHN analyser. The soil C pools for each sampled layer were calculatedfrom the mean soil sample C concentration, layer thickness, bulk density, and stonecontent values. For further details, see Starr and Ukonmaanaho (2001).

2.3. THROUGHFALL AND SOIL SOLUTION C CONCENTRATIONS AND FLUXES

Throughfall was collected using permanently open (bulk) collectors (12–16 duringsnow-free period, 6–8 during winter) located systematically round the plots (Ukon-maanaho, 2001). Soil solution at depths of 15 and 35 cm depth in the mineral soilwas sampled using suction cup lysimeters (initially 3 at each depth and then 6)installed along one edge of the plots. A suction of 60 kPa was used to draw thesamples. At the Hietajärvi plots, in addition to the suction lysimeters, three zero-tension lysimeters were installed at 15 and 35 cm depths and also directly under thehumus layer. Of the zero-tension lysimeter data, only those from the humus layer,which collect forest floor leachate, has been used in this paper. Lysimeters werenot installed in the peatland plot at Valkea-Kotinen, VK2, but groundwater wells(5) were.

A weekly sampling interval during the snow-free period (usually May–Novem-ber) was used to collect and analyse all the water samples and monthly volume-weighted mean TOC concentration values were calculated. From winter 1994/1995,monthly snowfall sampling during the winters was initiated. Throughfall TOC con-centration values for the winter months during 1991–1994 were given the mean val-ues calculated from the 1995–1997 data and corresponding hydrologic fluxes (mm)estimated using a regression model based on the strong correlation between bulkdeposition collected in the open (Finnish Meteorological Institute) and throughfall(r = 0.93, n = 593). Monthly throughfall concentration values were multiplied bythe hydrologic flux to give monthly TOC flux values, which were then summedto give annual values. To calculate forest floor leachate and soil solution annualTOC fluxes, the available monthly volume-weighted TOC concentration valueswere averaged and multiplied by a modelled annual hydrologic flux value (Starr,1999). For the peatland plot, VK2, we calculated the mean TOC concentration of


the groundwater from weekly samples, which are only available for May–October1995.

Organic carbon concentrations in the water samples were measured using a Shi-madzu TOC-5000 Analyzer. Prior to analysis, the samples were filtered (Schleicher& Schuell 589/2). Because dissolved organic carbon (DOC) is defined as organiccarbon in water passing through a membrane filter of pore size 0.45 µm, we referto our organic carbon concentrations as total organic carbon (TOC) concentrations.

2.4. THROUGHFALL, FOREST FLOOR AND SOIL SOLUTION DOCFRACTIONATION

As part of a Nordic project (Vogt et al., 2001), the DOC in throughfall, forestfloor, and soil solution samples taken from Valkea-Kotinen (VK3) and Hietajärvi(HJ4) in September–October (Autumn) 1999 and in April–May (Spring) 2000 fol-lowing snowmelt was characterized by fractionation. The fractionation was madeusing adsorption/exchange resins (XAD-8 nonionic, MSC-1 cation exchange andDuolite A-7 anion exchange resins) based on the procedure described by Qualls andHaines (1991) that separates DOC into hydrophilic and hydrophobic acids, basesand neutrals. The samples were collected weekly, but bulked by season and keptrefrigerated until analysed in September 2000, when a subsample of 200–250 mLwas filtered through a membrane filter of pore size 0.45 µm for analysis. Carbonconcentrations in the filtrates were measured using the same Shimadzu TOC-5000Analyzer as for the other water samples.

3. Results and Discussion

3.1. SOIL AND FOREST STAND C POOLS

The size of the soil C pool (humus layer + 0–20 cm layer, corrected for stonecontent) at the plots ranged from 29 to 112 Mg ha−1, and averaged 55 Mg ha−1

(Figure 2). As could be expected, the peat plot (VK2) had the largest soil pool.The smallest pools were associated with the Vuoskojärvi plots, the northernmostcatchment, where the primary production and therefore input of organic matter tothe soil is low. Our values are comparable to those reported by Tamminen (2000),Liski and Westman (1995, 1997), Kauppi et al. (1997), and Finér et al. (2003) forFinnish forest soils. Earlier studies showed that our soil C contents were correlatedto soil pH, exchangeable Ca2+ + Mg2+ contents, exchangeable acidity, and heavymetal contents (Starr and Ukonmaanaho, 2001).

The tree stand C pools ranged from 11 to 200 Mg ha−1 and averaged 88 Mgha−1 (Figure 2). The stem compartment accounted for 50% or more of the totalbiomass pool. The coarse root fraction at the mountain birch plot, VJ2, could notbe estimated but the belowground C pool (i.e. soil plus coarse roots) at the othercatchments accounted for half or more of the combined soil and stand C pool. The


Figure 2. Carbon pools in the stand and soil at each study plot (values for the root compartment atVJ2 are not available).

biomass of fine roots, although having a high turnover, is small (Finér et al., 2003).It should be noted that we have not included the C associated with dead trees (snagsand fallen stems). This pool has not yet been calculated for our sites, but the volumeof coarse woody debris (CWD) in Norway spruce dominated old-growth forests inFennoscandia ranges from 50 to 120 m3 ha−1, and accounts for 28% of total standvolume (living + dead) on average (Siitonen, 2001). Corresponding CWD volumesfor Scots pine dominated old-growth stands are 20 to 120 m3 ha−1, which accountsfor 25% of total stand volume. Standing and fallen dead stems and fallen branchesaccounted for 13% of the total (living + dead) above-ground biomass compartmentin a Norway spruce dominated old-growth stand in eastern Finland (Finér et al.,2003).

3.2. THROUGHFALL, FOREST FLOOR AND SOIL SOLUTION TOCCONCENTRATIONS AND FLUXES

Plot average throughfall TOC concentrations collected during the 1991–1997 periodranged from 4.2 to 18.6 mg L−1 (Table II). This range falls within that presentedby Michalzik et al. (2001) for temperate forests in their review of 42 case studies.Our throughfall TOC concentrations generally decreased northwards. This trendmight be related to a similar trend in stand volume (Table I), which would result ina reduced degree of interaction between precipitation and canopy. Rainfall passing


TABLE II

Descriptive statistics (mean, standard deviation and number of samples) of TOC concentrations(mg L−1) in monthly bulk deposition, throughfall, forest floor and soil solution samples collectedfrom each study plot during 1991–1997

Plot

VK2 VK3 HJ1 HJ4 PJ1 PJ2 PJ3 VJ2 VJ3

Bulk depositiona

Mean 3.7 3.7 3.1 3.1 3.8 3.8 3.8 3.6 3.6

St. dev. 1.2 1.2 0.8 0.8 1.8 1.8 1.8 1.9 1.9

n 12 12 12 12 12 12 12 12 12

Throughfall

Mean 18.6 14.0 7.4 8.8 7.9 4.9 n.d. 4.0 8.4

St. dev. 9.5 7.5 5.0 5.5 4.9 4.0 3.7 7.1

n 58 59 53 57 54 54 53 53

Forest floor

Mean 29.1b 45.7 53.1 n.d. n.d. n.d. n.d. n.d.

St. dev. 10.0 17.3 28.4

n 103 29 31

Soil solution 15 cm

Mean n.d. 20.1 11.9 13.6 n.d. 36.0 7.2 17.2 23.3

St. dev. 17.2 12.7 7.4 56.2 4.8 17.3 33.5

n 41 47 38 38 47 15 56

Soil solution 35 cm

Mean n.d. 9.5 8.3 6.4 n.d. 14.0 4.1 8.5 21.2

St. dev. 9.4 22.2 7.9 27.5 3.3 4.4 34.1

n 51 46 37 44 47 17 55

a Monthly samples collected outside the forest during 1997.b Mean weekly groundwater May–September 1995.n.d. = Not determined.


Figure 3. Annual mean (1991–1997) carbon fluxes in throughfall and soil solution (40 cm depth) foreach study plot (See Table I for plot abbreviations). Error bars are standard deviations.

through the canopy is known to dissolve slightly soluble and soluble organic acidsboth from the foliage itself and from dry deposition accumulated on foliar surfaces(Thurman, 1985). Bulk precipitation collected in 1997 at a nearby open area in eachcatchment has been analysed for TOC (Table II). The enrichment of the throughfallin organic C is indicated by the ratio of throughfall to bulk precipitation TOCconcentrations. Plot values of this ratio calculated from the mean concentrationvalues for 1997 ranged from 2 to 7, being the highest for the Valkea-Kotinenplots. But besides having the highest stand volumes, the Valkea Kotinen standsalso have the highest proportion of Norway spruce present (Table I). The higherTOC concentrations at Valkea-Kotinen may therefore reflect a species effect on theleaching of organic C from forest canopies, with spruce being more susceptiblethan other species.

The mean annual throughfall TOC fluxes ranged from 1.2 to 8.0 g m−2 yr−1 andaveraged 4.0 g m−2 yr−1 (Figure 3). These values are similar to those reported byPiirainen et al. (2002) for a Norway spruce dominated stand in eastern Finland, butare clearly less than those reported for temperate forests (Michalzik et al., 2001).Because our throughfall mean TOC concentrations were similar to those reportedby Michalzik et al. (2001), the smaller fluxes at our boreal stands compared to thosein the temperate zone must be due to a difference in the amounts of precipitation.The throughfall TOC flux at our sites decreases northwards, as do TOC concentra-


Fig

ure

4.M

onth

lym

ean

thro

ughf

allT

OC

conc

entr

atio

nsby

stan

ddu

ring

1991

–199

7.


tions and amount of precipitation (Table I). Furthermore, a greater proportion of theannual precipitation falls as snow when going northwards, and snow has less leach-ing efficiency than rainfall. Thus throughfall TOC concentrations tended to peakduring the growing season and to be the lowest during the winter months when thestands were dormant and precipitation fell as snow (Figure 4). Seasonal-Kendallslope estimates of the monotonic trend indicated that there was no significant (p >0.123) trend in throughfall TOC concentrations at any of the plots over the period1991–1997.

Monthly soil solution TOC concentrations varied considerably, both within andbetween plots (Table II). The mean of the monthly concentration values availableranged from 7.2 to 36.0 mg L−1 for the soil solution samples collected at 15 cmdepth and from 4.1 to 21.2 mg L−1 for those collected at 35 cm depth. Thesevalues are similar to reported concentrations in soil solutions taken with zero-tension lysimeters for a Podzol soil in eastern Finland (Piirainen et al., 2002), butsomewhat lower than DOC concentrations in soil solution samples extracted bycentrifugation from Nordic Podzol soils (Van Hees et al., 2000a; Riise et al., 2000).At Hietajärvi, forest floor leachates were yellow-coloured, indicating the presenceof humic substances. The TOC concentrations were 6 times higher, on average,than TOC concentrations in throughfall and 4 times those at 15 cm depth and 7times those at 35 cm depth. Soil solution TOC concentrations at 35 cm depth at allplots were generally lower than those at 15 cm depth, indicating a removal of Cfrom soil solution as it moves downwards. Such a removal can take place throughmicrobial decay, adsorption to Fe and Al sesquioxides, which accumulate in theB-horizon of Podzols, and coagulation and precipitation (Thurman, 1985; Riise etal., 2000). Unlike throughfall, there was no relationship between soil solution TOCconcentrations and latitude, indicating that local soil factors were more importantin controlling soil solution TOC concentrations than climate factors.

Plot soil solution fluxes of TOC at 40 cm depth ranged from 2.4 to 4.9 g m−2

yr−1 and averaged 3.7 g m−2 yr−1 (Figure 3). Our highest values were somewhatlower than B-horizon seepage fluxes reported for temperate sites by Michalzik etal. (2001). Our values were also smaller than B-horizon fluxes from a Podzol ineastern Finland reported by Piirainen et al. (2002). But the hydrologic fluxes intheir study by were based on zero-tension lysimeter catches, which were probablyunderestimates of the true hydrologic flux. The relatively high soil solution fluxesat Vuoskojärvi may be the result of modelled hydrologic fluxes that were too high.There were too many missing monthly values to allow reliable Seasonal-Kendalltrend slope estimates to be made for soil solution TOC concentrations. Simplevisual inspection of the data indicates that forest floor leachate TOC concentrationsincreased with the hydrologic flux, which is higher during spring snowmelt and inautumn when lowered evapotranspiration losses result increased inputs to the soil.Soil solution TOC concentrations appeared to be less affected by the amount ofpercolation. However, these observations need further testing.


Figure 5. Distribution of various DOC fractions in Valkea-Kotinen (VK3) and Hietajärvi (HJ4)throughfall and soil solution samples taken in autumn 1999 and spring 2000. Numbers at end ofbars are the total DOC concentrations (mg L−1).

3.3. CHARACTERISATION OF THROUGHFALL AND SOIL SOLUTION DOC

The results of the DOC fractionation of Valkea-Kotinen and Hietajärvi through-fall and soil solution samples are presented in Figure 5. Because the hydrophobicbase fraction was so small it has been combined with the hydrophilic base frac-tion, which consists of proteins and amino acids, and so easily biodegradable. Thephenol fraction consists of weak hydrophobic acids, weak because of the presenceof phenolic rather than carboxylic acid groups, and inhibits microbial activity. Thehydrophobic acid fraction (humic and fluvic acids, i.e. aquatic humic substances)is relatively resistant to decay while easily degradable carbohydrates dominate theneutral fractions (Qualls and Haines, 1991; Thurman, 1985). The hydrophilic acidfraction contains low molecular weight organic acids (Thurman, 1985; Qualls and


Haines, 1991), which are important to the mobilization and transport of Al and Fein Podzol soils (Van Hees et al., 2002b).

Although DOC concentrations in throughfall were less than those in the forestfloor solutions at both sites and in both seasons, the composition of both typesof water was similar, being dominated by hydrophobic acids (>38%) and withbases forming only a minor part (<8%). The combined acids fraction (hydrophobic,phenols and hydrophilic) accounted for 67 to 90% of the DOC in the throughfalland forest floor leachates. The dominance of acid fractions, particularly the hydro-phobic acid fraction, was also found in throughfall and Oa horizon solutions froman oak-hickory stand by Qualls and Haines (1991). The combined hydrophobicfraction dominated (68 to 90%) the DOC of all samples. This contrasts with theresults presented by Kaiser et al. (2001), who found that the DOC in forest floorleachate from both Scots pine and beech stands to be dominated by the hydrophilicfraction. The hydrophilic fraction has been shown to leach in larger amounts fromdeciduous litter than from coniferous litter (Hongve, 1999). The phenol fraction inour study, especially in the samples from Hietajärvi, was clearly more importantthan in the study by Qualls and Haines (1991). These differences are probably dueto the dominance of coniferous tree species in our stands. Thus, while DOC intemperate deciduous forests is dominated by hydrophilic and neutral compoundsthe DOC in boreal, coniferous forests is dominated by less easily decomposableacidic and hydrophobic compounds. The dominance of hydrophobic and acidicfractions in the samples from Valkea-Kotinen in particular indicates that spruceneedles are an important source of these fractions.

Throughfall DOC concentrations were greater in spring than in autumn, aswas also seen in our main throughfall TOC data (Figure 4), while the forest floorleachate and soil solution DOC concentrations showed the opposite. There was noclear seasonal difference in the composition of DOC, except that the hydrophobicneutrals fraction, for an unknown reason, was absent from the forest floor Valkea-Kotinen spring sample and appeared to dominate the composition of springtimeDOC in the 15 cm soil solution.

4. Conclusions

Below-ground (soil+roots) C pools accounted for half or more of the ecosystemC pool (aboveground and belowground forest stand biomass, humus layer, and0–20 cm soil layer) in these undisturbed, boreal, old-growth forest ecosystems.Precipitation passing through the canopy was enriched in organic carbon, withannual TOC fluxes being 2–7 times greater than corresponding bulk depositioncollected in the open. Although throughfall TOC concentrations were similar tothose reported for temperate zone forests, annual fluxes were smaller, as werealso soil solution TOC fluxes, reflecting lower precipitation amounts in the borealzone. TOC concentrations are substantially increased as throughfall passed through


the forest floor, but then decline as the water continues to percolate downwardsthrough the soil. At 35 cm depth, soil solution TOC concentrations approachedthose in throughfall. Monthly throughfall TOC concentrations were higher dur-ing the growing season but no long-term (1991–1997) trends could be discerned.Hydrophobic compounds, particularly hydrophobic acids, dominated the DOC inthroughfall, forest floor leachate and soil solution. The fraction of phenols appearsto be more important in boreal, coniferous forest ecosystems than in temperate,deciduous forests. Spruce canopies and litter appear to be important sources ofsoluble organic carbon, particularly acidic and hydrophobic compounds. Furtherstudies on the nature and dynamics of organic carbon fluxing through coniferous,boreal forest ecosystems are needed.

Acknowledgements

We wish to thank Dr. Veikko Kitunen, Central Laboratory, Vantaa Research Centre,for performing the DOC fractionation analysis and Mr. Markus Hartman, VantaaResearch Centre, for applying Marklund’s biomass functions.

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levels and characteristics of toc in throughfall, forest floor leachate and soil solution in...

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