Biogeosciences, 7, 1715–1727, 2010
www.biogeosciences.ne /7/1715/2010/
doi:10.5194/bg-7-1715-2010
© Au ho (s) 2010. CC A ibu ion 3.0 License.
Biogeosciences
G eenhouse gas luxes in a d ained pea land o es du ing sp ing
os - haw e en
M. K. Pihla ie1, R. Kiese2, N. B ¨
uggemann2, K. Bu e bach-Bahl2, A.-J. Kieloaho1, T. Lau ila3, A. Lohila3,
I. Mamma ella1, K. Minkkinen4, T. Pen il¨
a5, J. Sch¨
onbo n2,6, and T. Vesala1
1Depa men o Physics, Uni e si y o Helsinki, P. O. Box 48, Uni e si y o Helsinki, 00014, Helsinki, Finland
2Ins i u e o Me eo ology and Clima e Resea ch, A mosphe ic En i onmen al Resea ch (IMK-IFU), Ka ls uhe Ins i u e o
Technology, Ga misch-Pa enki chen, Ge many
3Finnish Me eo ological Ins i u e, P. O. Box 503, 00101, Helsinki, Finland
4Depa men o Fo es Ecology, Uni e si y o Helsinki, P. O. Box 27, Uni e si y o Helsinki, 00014, Helsinki, Finland
5Finnish Fo es Resea ch Ins i u e, Van aa Uni , Finland
6Me eo ological Ins i u e, Albe -Ludwigs-Uni e si y F eibu g, F eibu g, Ge many
Recei ed: 29 May 2009 – Published in Biogeosciences Discuss.: 23 June 2009
Re ised: 8 Ap il 2010 – Accep ed: 28 Ap il 2010 – Published: 25 May 2010
Abs ac . Fluxes o g eenhouse gases (GHG) ca bon diox-
ide (CO2), me hane (CH4) and ni ous oxide (N2O) we e
measu ed du ing a wo mon h campaign a a d ained pea -
land o es in Finland by he eddy co a iance (EC) echnique
(CO2and N2O), and au oma ic and manual chambe s (CO2,
CH4and N2O). In addi ion, GHG concen a ions and soil pa-
ame e s (mine al ni ogen, empe a u e, mois u e con en ) in
he pea p o ile we e measu ed. The aim o he measu emen
campaign was o quan i y he GHG luxes du ing eezing
and hawing o he op-soil, a ime pe iod wi h po en ially
high GHG luxes, and o compa e di e en lux measu e-
men me hods. The o es was a ne CO2sink du ing he
wo mon hs and he luxes o CO2domina ed he GHG ex-
change. The pea soil was a small sink o a mosphe ic CH4
and a small sou ce o N2O. Bo h CH4oxida ion and N2O
p oduc ion ook place in he op-soil whe eas CH4was p o-
duced in he deepe laye s o he pea , which we e un ozen
h oughou he measu emen pe iod. Du ing he os - haw
e en s o he li e laye dis inc peaks in CO2and N2O emis-
sions we e obse ed. The CO2peak ollowed igh ly he in-
c ease in soil empe a u e, whe eas he N2O peak occu ed
wi h a delay a e he hawing o he li e laye . CH4 luxes
Co espondence o: M. K. Pihla ie
([email p o ec ed])
did no espond o he hawing o he pea soil. The CO2
and N2O emission peaks we e no cap u ed by he manual
chambe s and hence we conclude ha high ime- esolu ion
measu emen s wi h au oma ic chambe s o EC a e neces-
sa y o quan i y luxes du ing peak emission pe iods. Sub-
canopy EC measu emen s and chambe -based luxes o CO2
and N2O we e compa able, al hough he luxes o N2O mea-
su ed by EC we e close o he de ec ion limi o he sys em.
We conclude ha i luxes a e high enough, i.e. g ea e han
5–10µgNm−2h−1, he EC me hod is a good al e na i e o
measu e N2O and CO2 luxes a ecosys em scale, he eby
minimizing p oblems wi h chambe enclosu es and spa ial
ep esen a i eness o he measu emen s.
1 In oduc ion
D ainage o pea lands o o es y has been a common p ac-
ice in Fennoscandia du ing he pas 100 yea s. In Fin-
land, mo e han hal o he o iginal pea land a ea has been
d ained o o es y o ag icul u al use since he 1920s (Paa -
ilainen and P¨
ai ¨
anen, 1995; Joos en and Claa ke, 2002).
D ainage lowe s he g oundwa e able and imp o es he
ae a ion o he pea , which inc eases he g ow h o ees.
The eby, d ainage also changes g eenhouse gas dynamics o
he pea land, as a la ge pa o he decomposi ion o he pea
Published by Cope nicus Publica ions on behal o he Eu opean Geosciences Union.
1716 M. K. Pihla ie e al.: G eenhouse gas luxes in a d ained pea land o es du ing sp ing os - haw e en
swi ches om anae obic o ae obic condi ions wi h a shi
om me hane (CH4) o ca bon dioxide (CO2) as he end-
p oduc o decomposi ion (Moo e and Dal a, 1993; Sil ola
e al., 1996; Minkkinen e al., 2002; Roule e al., 1993, Ma -
ikainen e al., 1995; Nyk¨
anen e al., 1998). S imula ed ae -
obic decomposi ion o he pea eleases nu ien s, especially
ni ogen, o he soil, which may lead o ele a ed emissions
o ni ous oxide (N2O) (Ma ikainen e al., 1993; Sil ola e
al., 1996; Laine e al., 1996). Howe e , he changes in N2O
emissions a e d ainage seem o depend on he e ili y o
he o iginal pea land, i.e. i s ni ogen con en o he C:N a io
o he pea , and he le el o he wa e able a e he d ainage
( on A nold e al., 2005a, b).
D ained pea lands which ha e been used o ag icul u e
i s and hen plan ed wi h ees (a o es ed pea soils) a e
s ong poin sou ces o N2O. These N2O emissions a e o
he same o de o magni ude as he emissions om d ained
pea lands which a e s ill used o ag icul u e (Maljanen e al.,
2001; Regina e al., 2004; M¨
aki an a e al., 2007). D ained
o es ed pea lands co e 25% o o es a ea in Finland mak-
ing hese ecosys ems po en ially impo an sou ces o g een-
house gases. Du ing he las wo decades he e has been de-
ba e whe he he d ainage o pea lands o o es y u ns hem
om ne sinks o ca bon in o ne sou ces, and whe he N2O
makes up an impo an pa o he o al g eenhouse gas bal-
ance.
In ensi e measu emen s o GHG emissions om d ained
pea land o es s a e sca ce. Also, compa isons o di e en
measu emen echniques in hese ecosys ems a e almos non-
exis en . Mos o hes udies ha ebeen conduc edwi h cham-
be echniques using weekly o mon hly measu ing in e als.
This measu emen equency may se e ely miss impo an
emission e en s, so called “ho momen s”, ela ed especially
o N2O emissions om soils (see e.g. Ma zne and Bo ken,
2008; Papen and Bu e bach-Bahl, 1999), such as os - haw
pe iods which could be subs an ial in bo eal en i onmen s
(see e.g. Koponen e al., 2004, 2006). As a esul , calcula-
ions o seasonal o annual budge s o g eenhouse gases may
be biased and po en ially unde es ima ed i he equency o
measu emen s o spa ial co e age is no su icien o co e
a ia ions.
We epo esul s o g eenhouse gas emissions (CO2, CH4
and N2O) om a d ained pea land o es in Kale ansuo,
sou he n Finland. The measu emen campaign las ed wo
mon hs om he end o Ap il un il he end o June 2007, and
was un unde he Ni oEu ope IP EU-p ojec . The main aim
was o quan i y he o al GHG balance du ing a po en ially
high peak season in he sp ing, when he pea is mel ing and
os - haw d i en N2O luxes a e likely o occu . We mea-
su ed ne CO2exchange abo e and below he o es canopy
and N2O exchange below he o es canopy by he eddy co-
a iance (EC) me hod and compa ed hese luxes o soil CO2,
CH4, and N2O luxes measu ed simul aneously wi h au o-
ma ed and manual chambe echniques.
Ou aim was o es ima e he ne GHG exchange and he
impo ance o di e en C and N lux componen s on he o-
al GHG balance du ing he wo-mon h measu ing pe iod.
We hypo hesise ha N2O is an impo an componen o he
ecosys em g eenhouse gas exchange due o “ho momen ”
emissions such as os - haw e en s. Ou second aim was o
e alua e he sui abili y o sub-canopy EC-based N2O mea-
su emen s as a sophis ica ed al e na i e o adi ionally used
chambe me hods in his en i onmen . The quali y con ol
and lux e o analysis o he EC N2O measu emen s a he
si e a e p esen ed in his issue in Mamma ella e al. (2010).
2 Ma e ials and me hods
2.1 Si e desc ip ion
The measu emen s we e conduc ed a a Kale ansuo d ained
pea land o es classi ied as an omb o ophic dwa -sh ub
pine bog. The si e is loca ed in sou he n Finland (60◦390N,
24◦220E), whe e he mean annual p ecipi a ion is 606mm
and he mean annual empe a u e is 4.3◦C. The bog was
d ained o o es y in 1971 by open, abou 1m deep di ches
dug wi h app oxima ely 40m spacing be ween he pa allel
di ches. In 1973 he si e was e ilised wi h phospho us and
po assium, ollowing he guidelinep ac ises o d ained pea -
lands. D ainage esul ed in a lowe ed wa e able down o
app ox. 40cm om he pea su ace, and a changed compo-
si ion o g ound ege a ion om ypical bog ege a ion o-
wa ds mo e o a o es unde s o ey. Howe e , some ea u es
such as he abundance o pea land dwa sh ubs and ai ly
high co e age o Sphagnum species s ill dis inguish he si e
om upland o es s. Cu en ly he heigh o he ee s and is
15–18m, a e age basal a ea is 18m2ha−1, and a e age s em
densi ies a e 900, 750, and 40 s ems pe ha o he dominan
Sco s pine (Pinus syl es is L.) ees and he smalle unde -
s o ey downy bi ch (Be ula pubescens) and No way sp uce
(Picea abies L.) ees, espec i ely. The o al LAI in he si e
is app oxima ely 2m2m−2(Mamma ella e al., 2010).
Fo es loo ege a ion consis ed mainly o hummock
dwa sh ubs (Vaccinium i is-idaea, Vaccinium my illus,
Empe um nig um, Vaccinium uliginosum, Ledum palus e
and Be ula nana), sedges like E iopho um agina um and
mosses (Pleu ozium sch ebe i,Dic anum polyse um, Sphag-
num ussowii, Spagnum capilli olium and Sphagnum angus-
i olium).
The dep h o he well decomposed Sphagnum pea a he
si e is app oxima ely 2.5m wi h pea a pH o 5.0 and C/N a-
io o 41 in he li e laye and 45 in he op 10cm o he pea
soil.
2.2 Flux measu emen s
In ensi e GHG measu emen s we e ca ied ou om 25 Ap il
o 27 June 2007 wi hin a homogenous and ep esen a i e ap-
p ox. 1ha plo o he o es ( o al a ea o app ox. 60ha). The
Biogeosciences, 7, 1715–1727, 2010 www.biogeosciences.ne /7/1715/2010/
M. K. Pihla ie e al.: G eenhouse gas luxes in a d ained pea land o es du ing sp ing os - haw e en 1717
main measu emen s included mic ome eo ological eddy co-
a iance (EC) measu emen s o CO2abo e and below he
o es canopy and N2O luxes below he canopy, au oma ed
as well as manual chambe -based measu emen s o CO2,
CH4and N2O luxes. The loca ions o he di e en mea-
su emen sys ems a e shown in Fig. 1.
The abo e canopy EC CO2 lux measu emen sys em
(ECabo e) included a METEK USA-1 ul a sonic anemome-
e (METEK GmbH, Elmsho n, Ge many) moun ed on he
op o a 21.5m elescopic mas and a LI-7000 CO2/H2O
analyze (Li-Co , Inc., Lincoln, NE, USA) moun ed a 6m
heigh in he owe . Ai was d awn om he p oximi y o
he sonic o he LI-7000 CO2/H2O analyze using a Be -A-
Line IV ubing (The moplas ic p ocesses, S i ling, NJ) wi h
an inne diame e o 3.1mm. The s o age lux o CO2was
calcula ed om he concen a ion da a measu ed a heigh s o
21.5m and 6m, he la e being measu ed wi h a LI-820 CO2
analyze (Li-Co Inc., Lincoln, NE, USA). The s o age lux
was added o he measu ed ne ecosys em exchange (NEE),
he ea e NEE e e ing o he sum o u bulen and s o age
luxes. The mas was loca ed in he cen e o he measu e-
men si e (Fig. 1).
The sub-canopy EC measu emen s (ECsub) we e con-
duc ed a 4m heigh . The sub-canopy mas was loca ed ap-
p oxima ely 100m sou hwes o he all mas , and app oxi-
ma ely hal way be ween he all mas and he au oma ic soil
chambe s (see Fig. 1). The CO2 luxes we e measu ed wi h
a Li-7500 Open-Pa h In a ed CO2/H2O Gas Analyze (Li-
Co , Inc., Lincoln, NE, USA) and a CSAT3 Sonic Anemome-
e (Campbell Scien i ic Inc., Logan, UT, USA). EC mea-
su emen s o N2O luxes we e conduc ed a he same mas
using he same CSAT3 anemome e and a unable diode lase
spec ome e (TGA-100A, Campbell Scien i ic Inc., Logan,
UT, USA).
Fo es loo (soil and g ound ege a ion) luxes o CO2,
N2O and CH4we e measu ed wi h he enclosu e me hod
using au oma ic ( anspa en ) and manual (opaque) cham-
be s. The au oma ic chambe sys em consis ed o a
al e-d i en sampling sys em (cus om-made by IMK-IFU)
o nine soil chambe s wi h dimensions o 50×50×15cm
(leng h ×wid h ×heigh ). The au oma ic chambe s we e
loca ed app ox. 170m sou hwes o he all EC mas , and ap-
p ox.100msou hwes om hesub-canopyEC mas (Fig. 1).
The chambe s we e connec ed o a gas ch oma og aph (SRI
Ins umen s, To ance, CA, USA) equipped wi h an elec on
cap u e de ec o (ECD) o N2O and a lame ioniza ion de-
ec o (FID) o CH4, and a GMD20D in a ed CO2analyze
(Vaisala, Van aa, Finland). The nine chambe s we e spli in o
3 se s o 3 chambe s. One measu emen cycle included clo-
su es o 3 chambe s and a simul aneous calib a ion wi h a
e e ence gas. Each chambe was closed o 48min, and he
mean sampling in e als we e 6, 18, 30, and 42min a e
he closu e. The measu emen sys em is desc ibed in mo e
de ail in Kiese and Bu e bach-Bahl (2002) and We ne e
al. (2007). The ege a ion inside he au oma ic chambe s was
Fig. 1. Map o he measu emen si e showing he loca ions o
abo e canopy eddy co a iance (EC) mas (ECabo e), sub-canopy
EC mas (ECsub), manual chambe s (MC, squa e) and au oma ic
chambe s (AC, ci cle). Do ed line nex o one o he manual cham-
be g oups show he place o soil gas concen a ion pi s, and g ey
line a ound he sub-canopy EC mas show he oo p in a ea om
which 85% (a 30m) o he sub-canopy N2O luxes o igina e (see
Mamma ella e al., 2010).
simila han in he pea land gene ally, howe e , all dwa
sh ubs we e no p esen . De ailed ege a ion su ey was no
conduc ed o he au oma ic chambe s.
Manual chambe measu emen s we e conduc ed once a
week du ing Ap il o June 2007, and o nigh ly du ing July
o Sep embe 2007. In o al 16 ci cula me al colla s we e
loca ed in g oups o ou app ox. 30–60m om he all EC
mas in he ou main di ec ions, and 10–150m no h-eas
om he sub-canopy EC mas (Fig. 1). The colla s we e in-
s alled in 2004 a soil dep h o 3–5cm, on op o he oo
laye . Du ing chambe measu emen s, a 30cm high ci -
cula me al chambe was placed on he colla . Volume o
he chambe was app ox. 27L. Ai inside he chambe was
mixed wi h a an, and he empe a u e inside he chambe
was moni o ed wi h a he mome e in o de o co ec he
luxes. Gas samples (100ml) we e collec ed wi h a sy inge
a 2, 15, 25 and 35min in e als and ans e ed immedi-
a ely in o 12-ml glass ials (Labco Exe aine ®, Labco Lim-
i ed, Buckinghamshi e, UK). Nine y ml o he gas sample
was used o lush he ai in he ial wi h wo needles. The
es 10ml o he gas sample was used o o e -p essu ize
he ial a e emo ing he lushing needle. Gas samples
we e analyzed wi hin one week o N2O and CH4by a
www.biogeosciences.ne /7/1715/2010/ Biogeosciences, 7, 1715–1727, 2010
1718 M. K. Pihla ie e al.: G eenhouse gas luxes in a d ained pea land o es du ing sp ing os - haw e en
gas ch oma og aph (Agilen 6890 GC, Agilen Technologies
Finland, Espoo, Finland) equipped wi h an ECD o N2O and
an FID o CH4.
2.3 Soil measu emen s
Concen a ions o N2O and CH4in he pea p o ile we e mea-
su ed a wo pi s loca ed app oxima ely 40m sou hwes o
he abo e-canopy EC mas . The concen a ions we e mea-
su ed in he pea a 5cm, 22 and 45cm below he li e laye .
Gas collec o cups we e 100ml in olume and made o s ain-
lesss eel. Thecupswe eins alledho izon allyapp ox.20cm
apa om each o he , upside down wi h an open end a he
bo om in he soil and connec ed o he a mosphe e ia a
1/800 s ainless s eel ube. Gas samples we e collec ed weekly
du ing Ap il o June om he dep hs 5 and 25cm and o -
nigh ly du ing July o Sep embe om all dep hs (5, 22 and
45cm). A he ime o gas sampling, he 5–10ml gas ol-
ume inside he ubing was disca ded a e which a 100ml gas
sample was aken and ans e ed in o 12-ml glass ials as de-
sc ibed abo e. When a gas collec o was below he g ound-
wa e able, a wa e sample o 50ml was aken wi h he sy-
inge. Then he gas dissol ed in he wa e was equilib a ed
wi h 50ml o ambien ai by shaking he sy inge igo ously
o 10min. A e shaking, 20ml o he gas sample was in-
jec ed in o a p e-e acua ed 12-ml glass ial.
Soil empe a u e and olume ic wa e con en s we e mea-
su ed adjacen o he au oma ic chambe s in he li e laye
and a 5 and 10cm dep hs o he pea (T ime®TDR IMKO
and P -100, IMKO GmbH, E lingen, Ge many). In addi-
ion, soil empe a u es in he li e laye , and a 5 and 30cm
dep hs o he pea we e measu ed close o he all EC mas by
FMI (Finnish Me eo ogical Ins i u e). The a ia ion o he
g ound wa e le el nea he main EC mas was moni o ed by
a PDCR 1830 le el p essu e senso (D uck Inc., New Fai -
ield, CT, USA).
Soil ammonium (NH4-N), ni a e (NO3-N) and o al dis-
sol ed ni ogen con en s we e analysed om samples col-
lec ed weekly du ing Ap il o June 2007, and mon hly du -
ing July o Sep embe 2007. Soil samples om he li e laye
and pea (0–10cm) we e collec ed in 5 eplica es: ou om
close incini y o he manual chambe s (4 g oups) and one
om close incini y o he au oma ic chambe s. F esh soil
samples we e s o ed a +4◦C and ex ac ed wi h 1MKCl
he nex day a e he sampling. The ex ac s we e ozen a
−18◦C un il analysis by a low injec ion analyze (FIA 5012,
Teca o ) a he Finnish Fo es Resea ch Ins i u e. To al ca -
bon and ni ogen con en s we e analyzed om d ied (40◦C)
soil samples using a a io MAX CN elemen al analyse .
2.4 Da a analysis
Flux a es o manual and au oma ed chambe measu emen s
we e calcula ed wi h he ollowing equa ion
Fc=dC
d h, (1)
whe e Fcis he lux o he a ge gas (gm−2s−1), Cis he gas
concen a ion in he chambe ai (gm−3) a s anda d p essu e
(101325Pa) and empe a u e measu ed in he headspace, is
closu e ime (s) and h he heigh o he chambe (m). The de-
elopmen o he gas concen a ion inside he chambe s was
linea o he majo i y o he measu emen s. Fo he man-
ual chambe da a we compa ed luxes calcula ed based on
quad a ic i and linea eg ession. The use o a quad a ic i
esul ed in up o 30% highe luxes o CH4and 20% smalle
luxes o N2O as compa ed o he linea eg ession. Due o
only ou da a poin s and luxes close o ze o, we conside ed
ha he linea eg ession me hod was mo e eliable o his
da a and hence we calcula ed all he luxes by a linea e-
g ession analysis (n=4). We il e ed ou bad quali y da a by
emo ing da a wi h R2- alue 0.7 o less.
EC luxes we e calcula ed as 30min a e age co a iances
be ween he scala s (CO2and N2O) concen a ion and he
e ical wind eloci y acco ding o he commonly accep ed
p ocedu es (Aubine e al., 2000). The abo e canopy EC da a
acquisi ion was done wi h a modi ied e sion o a p og am by
McMillen (1986). Coo dina e o a ion and da a de ending
by an au o eg essi e unning-mean il e wi h a 200-s ime
cons an we e pe o med acco ding o McMillen (1988).
The lag be ween he ime se ies esul ing om he anspo
h ough he inle ube was aken in o accoun in he on-line
calcula ion. An ai densi y co ec ion ela ed o he sensible
hea lux is no necessa y, bu he co esponding co ec ion
ela ed o he la en hea lux was made (Webb e al., 1980).
Co ec ions o he sys ema ic high- equency lux loss ow-
ing o he impe ec p ope ies and se up o he senso s we e
ca ied ou o -line using ans e unc ions wi h empi ically-
de e mined ime cons an s. The da a p ocessing p ocedu es
ha e been p esen ed in mo e de ail by Lohila e al. (2007)
and Au ela e al. (2009).
The sub-canopy luxes we e calcula ed using so wa e de-
eloped by he Mic ome eo ology g oup a he Uni e si y o
Helsinki, Depa men o Physics. The so wa e is ou inely
used o pos -p ocessing EC da a measu ed in se e al pe -
manen si es and ield campaigns. I con ains all he upda e
me hods and co ec ions acco ding o he Eu o lux me hod-
ology (Aubine e al., 2000; Lee e al., 2004). Fo he p esen
s udy, he so wa e was sligh ly modi ied in o de o handle
wi h he lase da a, as epo ed by Mamma ella e al. (2010).
All signals we e de ended o emo ing he a e age alues
and ends. A simple linea de ending p ocedu e was used
o calcula ing he CO2 lux. The N2O signal measu ed by
he TDL gas analyze was cha ac e ized by s onge ends,
caused mainly by ins umen al d i , which can gi e an ex a
Biogeosciences, 7, 1715–1727, 2010 www.biogeosciences.ne /7/1715/2010/
M. K. Pihla ie e al.: G eenhouse gas luxes in a d ained pea land o es du ing sp ing os - haw e en 1719
con ibu ion o he es ima ed lux in he case ha he luc ua-
ions o he concen a ion a e co ela ed wi h he luc ua ions
o he e ical wind eloci y. In o de o emo e he ins u-
men al d i e ec and o educe he andom lux a iabili y,
a unning mean il e (McMillen, 1988) was pe o med p io
o calcula ion o he N2O lux. A mo e de ailed desc ip ion
o he da a p ocessing o N2O EC signal is gi en in Mam-
ma ella e al. (2010).
Alag- imeo 2.3s was ob ained o he abo e-canopy CO2
signal, maximizing he c oss-co a iance unc ion be ween
he CO2concen a ion and he e ical wind eloci y. The
same p ocedu e was applied o he sub-canopy N2O signal,
bu because he N2O emissions we e e y close o de ec ion
limi o he sys em, i was no possible o clea ly de e mine
expe imen ally he N2O lag ime. Then using a p ocedu e
simila o Pihla ie e al. (2005), we used a ix lag ime o
1s. The same alue was ob ained by using he sample low
and olumes o he inle ubing and he sample cell, o es i-
ma ing he heo e ical N2O lag ime. The CO2 lux was co -
ec ed o densi y luc ua ions e ec (WPL co ec ion; Webb
e al., 1980), while such co ec ion was unnecessa y o N2O
luxes, because o he p esence o high low sample d ye
in he sys em (PD1000 Na ion®d ye , Campbell Scien i ic,
Inc., Logan, UT, USA). Tempe a u e luc ua ions do no need
o be co ec ed because hey can be assumed o be damped in
he sampling ube (Rannik e al., 1997). No Bu ba co ec ion
was used o he eddy co a iance da a om open pa h CO2
analyze e en hough he co ec ion may sligh ly inc ease he
lux le els (Bu ba e al., 2008). The EC luxes we e co -
ec ed o he high equency lux unde es ima ion acco ding
o Mamma ella e al. (2010). Fo ypical mean wind eloci y
in he sub-canopy laye , he lux loss was abou 5% and less
han 10% o CO2and N2O, espec i ely.
S a is ical es s (pai ed - es ) o he lux and soil mea-
su emen da a was done wi h SPSS s a is ical p og am (SPSS
Inc., Chicago, IL, USA).
3 Resul s
3.1 En i onmen al condi ions
A he s a o he measu emen campaign pa o he pea
was s ill ozen. The ai empe a u es a ied om below
0◦C in he end o Ap il o a maximum o 27◦C in he begin-
ning o June (Fig. 2). P io o he s a o he measu emen
campaign he soil had mel ed and ozen se e al imes. The
i s p onounced eeze- haw cycle was eco ded in he end o
Ma ch, one mon h p io o he measu emen campaign (da a
no shown). Howe e , as indica ed by empe a u e measu e-
men s o ai and li e laye , he pea su ace laye was s ill
eezing and hawing du ing he measu ing campaign in he
end o Ap il (Fig. 2). Du ing he in ensi e measu emen pe-
iod (25 Ap il–27 June) he soil empe a u e inc eased om
a ound 0◦C up o app ox. 16◦C in he uppe pa (5cm
dep h) o he pea soil. Rain all du ing Ap il–June was low
wi h low in ensi ies excep o wo e en s in mid Ap il and in
he end o May, esul ing in sho inc eases in he soil wa e
con en (Max. 22 ol%) and wa e able (see Fig. 2). De-
spi e hese sho inc eases, he wa e able and soil mois u e
dec eased (−25cm o −40cm; 16 o <10 ol%) du ing he
in ensi e measu emen pe iod.
3.2 Concen a ion o soil ammonium, ni a e and o al
dissol ed ni ogen
Soil ni a e (NO−
3-N) concen a ions we e close o ze o
h oughou he whole measu ing pe iod, whe eas soil am-
monium (NH+
4-N) and o al ni ogen ( o -N) concen a ions
we e ele a ed a he beginning o he measu emen pe iod
wi h a maximum du ing he os - haw e en in May, and de-
c eased owa ds he end o he measu ing campaign (Fig. 6).
The concen a ions o NO−
3-N, NH+
4-N and o -N we e al-
ways highe in he li e laye han in he pea a 0–10cm
dep h (da a no shown). To al dissol ed ni ogen concen a-
ions in he soil a ied be ween 50–230mgNkg−1d y soil,
and we e app oxima ely one o de o magni ude highe han
he concen a ions o NH+
4-N in he soil.
3.3 CO2 luxes
EC measu emen s abo e he o es canopy e ealed ha he
si e was on a e age a ne sink o CO2du ing he mea-
su ing campaign, om la e Ap il o la e June 2007 (see
Fig. 3). The daily ne ecosys em exchange (NEE) o CO2
inc eased om app oxima ely −0.014mgCm−2s−1du ing
Ap il o maximum o −0.064mgCm−2s−1in he middle o
June. The d ained pea land o es was a weak sou ce o ca -
bon (0.02mgCm−2s−1) on ew ainy days du ing he mea-
su emen pe iod. O e all, he CO2exchange ollowed he
changes in ai and soil empe a u es being highe (up ake) in
wa m and lowe (up o emission) in cold days (see Figs. 2
and 3).
In con as o he ne CO2up ake o he whole o es
ecosys em, soil and g ound ege a ion oge he u ned ou o
be a sou ce o CO2 o he a mosphe e. Bo h, CO2 luxes be-
low he o es canopy measu ed by he EC and by au oma ic
chambe s on he soil su ace showed an inc easing emission
end om Ap il o June (Fig. 3). Fo es loo CO2 luxes
(au oma ic chambe s) and sub-canopy luxes (sub-canopy
EC) inc eased om a minimum o 0.001mgCm−2s−1in
he end o Ap il o a maximum o 0.013mgCm−2s−1and
0.03mgCm−2s−1, espec i ely, in he end o May when
also soil and ai empe a u es eached hei maximum. In
June a dec ease in empe a u e was ollowed by a dec ease
in CO2 luxes, howe e , his was mo e p onounced in he
sub-canopy EC luxes. In he end o June o es loo and
sub-canopy luxes le eled a ound 0.01mgCm−2s−1, how-
e e s ill ollowing changes in he ai and soil empe a u es
(Figs. 2 and 3). Mean o es loo (0.008mgCm−2s−1)
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1720 M. K. Pihla ie e al.: G eenhouse gas luxes in a d ained pea land o es du ing sp ing os - haw e en
Fig. 2. (a) Ai empe a u e, (b) soil empe a u es in li e laye (hummock and hollow) and in pea , and (c) soil mois u e ( ol/ ol), g ound
wa e able dep h (WT) and p ecipi a ion a he d ained pea land pine o es du ing Ap il–Sep embe 2007 (in ensi e measu emen s 25 Ap il–
27 June).
and sub-canopy CO2exchange (0.009mgCm−2s−1) o e
he measu ing pe iod we e almos iden ical and a pai ed -
es analysis did no e eal any s a is ical di e ences (Ta-
ble 1). Fo es loo CO2and sub-canopy exchange co ela ed
posi i ely wi h ai and soil empe a u es. The soil empe -
a u e a 5cm dep h explained mos o he a iabili y in o -
es loo CO2 lux a es ( =0.96, p<0.01). The co ela ion
was less p onounced o sub-canopy EC based luxes due o
a mo e sca e ed empo al emission pa e n also e lec ed in
highe alues o CV% (Table 1, Fig. 3). Fu he mo e, we
ound a nega i e co ela ion o o es loo CO2 luxes wi h
soil mois u e (−0.60, p<0.01) and wa e able dep h (−0.76,
p<0.01). These co ela ions we e no signi ican o he EC-
based sub-canopy measu emen s.
The measu emen campaign can be di ided in o wo dis-
inc pe iods: a cold and a wa m pe iod. Du ing he cold
pe iod (30 Ap il–10 May) he ne o es loo CO2 luxes, he
sum o soil espi a ion and CO2pho osyn hesis o g ound
ege a ion, and he CO2ne ecosys em exchange (NEE)
abo e he o es canopywe esmall(Fig.4). Du ing hewa m
pe iod (5 June–15 June) bo h he ne CO2emissions o he
o es loo (Fig. 4c) and he ne CO2up ake o he o es
canopy (Fig. 4d) inc eased. Du ing bo h cold and wa m pe-
iods, he sub-canopy CO2 luxes ollowed a small bu clea
diu nal end when he ne CO2emission dec eased du ing
day- ime and inc eased du ing nigh - ime (Fig. 4a and c).
The compa ison o he mean and median GHG exchange
measu ed by abo e canopy EC and sub-canopy EC and by
au oma ic o es loo chambe s du ing he en i e wo-mon hs
measu emen pe iod is shown in Table 1, and he cumula i e
luxes a e shown in Table 2. Du ing he pe iod o 25 Ap il–
21 June he cumula i e CO2 luxes measu ed by sub-canopy
EC (42.5gCm−2) and o es loo chambe s (37.7gCm−2)
did no s a is ically di e om each o he , and accoun ed o
Biogeosciences, 7, 1715–1727, 2010 www.biogeosciences.ne /7/1715/2010/
M. K. Pihla ie e al.: G eenhouse gas luxes in a d ained pea land o es du ing sp ing os - haw e en 1721
Table 1. Mean and median luxes o CO2, CH4and N2O and coe icien o a ia ion (CV%1) measu ed by eddy co a iance, and au oma ic
and manual chambe s in Kale ansuo pea land o es du ing 25 Ap il–27 June 2007. ECaand ECss and o eddy co a iance abo e and below
he canopy, espec i ely, and AC and MC s and o au oma ic and manual chambe s, espec i ely.
mgCO2-Cm−2s−1µgCH4-Cm−2h−1µgN2O-Nm−2h−1
CO2ECaCO2ECsCO2AC CH4AC CH4MC2N2O ECsN2O AC N2O MC2
Mean3−0.031a0.009b0.008b−37.1a−18.5b3.2a4.5b6.8c
Median −0.026 0.008 0.008 −35.6 −15.2 2.5 3.9 6.8
CV% 180 75.7 45.3 40.2 144 123 62.3 42.8
1Coe icien o Va ia ion was calcula ed as CV% = s de o he lux/mean lux×100.
2Measu emen pe iod 25 Ap il–18 June 2007.
3Di e en supe sc ip s indica e signi ican di e ences be ween lux a es o one componen measu ed wi h di e en me hods.
Fig. 3. (a) Daily mean CO2exchange measu ed wi h eddy co a i-
ance abo e he o es canopy (EC abo e) and inside he canopy (EC
sub) and au oma ic chambe s (AC) a he d ained pea land pine o -
es . E o ba s s and o s anda d de ia ions.
42 and 37% o he o al NEE (−102gCm−2), espec i ely
(Table 2).
3.4 CH4 luxes
Kale ansuo pea land o es was a small sink o CH4du ing
he measu emen campaign (Fig. 5a). The CH4up ake mea-
su ed wi h he au oma ic chambe s inc eased om a ound
−30µgCm−2h−1 o a app oxima ely o −60µgCm−2h−1
in June. The CH4 luxes measu ed wi h manual chambe s
we e cons an ly by a leas a ac o o wo smalle han he
CH4 luxes measu ed wi h he au oma ic chambe s (Fig. 5).
The luxes o CH4we e no a ec ed by hawing o he soil
bu ollowed mo e closely he g oundwa e able and soil
mois u e con en in he pea . CH4up ake co ela ed posi-
i ely wi h soil wa e con en ( =0.38, p<0.01) and wa e
able dep h ( =0.44, p<0.01), and nega i ely wi h soil em-
pe a u es a 5cm and a 30cm dep h ( =−0.50, p<0.01;
=−0.62, p<0.01), espec i ely, and CO2 luxes measu ed
by he au oma ic chambe s ( =−0.50, p<0.01).
Fig. 4. Daily ime cou se o CO2 luxes a he d ained pea -
land pine o es measu ed wi h au oma ic chambe s (AC) and sub-
canopy eddy co a iance (EC sub) (a), (c) and abo e canopy eddy
co a iance (EC abo e) (b), (d) du ing a cold pe iod in 30 Ap il–
10 May 2007 (a), (b) and a wa m pe iod in 5–15 June 2007 (c),
(d). Do s ep esen median alues o each hou (AC, EC sub) o
hal hou (EC abo e) o e he 10-day pe iod. E o ba s ep esen
s anda d de ia ions.
3.5 N2O luxes
Kale ansuo d ained pea land o es was a small sou ce
o N2O du ing he measu emen pe iod om Ap il
o June 2007. Mean emission a es a ied be ween
3.2µgNm−2h−1measu ed by he sub-canopy EC ech-
nique, 4.5µgNm−2h−1by he au oma ic chambe s, and
6.8µgNm−2h−1by he manual chambe echniques (Fig. 6,
Table 1). Independen o he measu ing echnique N2O emis-
sions ha dly exceeded 10µgNm−2h−1excep o a sho pe-
iod a he beginning o he measu ing campaign when ele-
a ed N2O emissions could be de ec ed a leas wi h he em-
po ally highly esol ed EC and au oma ic chambe measu e-
men s (see Fig. 6). The ele a ed N2O emissions coinside
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1722 M. K. Pihla ie e al.: G eenhouse gas luxes in a d ained pea land o es du ing sp ing os - haw e en
Table 2. Cumula i e g eenhouse gas CO2, CH4and N2O luxes
a he Kale ansuo d ained pea land o es measu ed by eddy co-
a iance and au oma ic chambe s du ing he in ensi e measu emen
pe iod 25 Ap il–26 June 2007.
Componen cumula i e lux, cumula i e lux, GWR100 CO2eq .
Cm−2gGHGm−2
CO2ECa(NEE) −102 −373 −373
CO2ECs42.5 156 156
CO2AC 37.7 138 138
CH4AC −0.046 −0.062 −1.30
N2O AC 0.006 0.009 2.77
1Measu emen pe iod 25 Ap il–21 June 2007.
2GWP100 e e s o Global Wa ming Po en ial wi h a 100-yea ime
ho izon.
Fig. 5. (a) Daily mean luxes o CH4measu ed wi h au oma ic (AC,
n=9) and manual (MC, n=16) chambe s, (b) soil concen a ions o
CH4a h ee dep hs and in he ambien ai measu ed a he d ained
pea land. Fi s column o he igu es ep esen he pe iod o in en-
si e measu emen s, he second shows he da a ou side he measu e-
men campaign. E o ba s s and o s anda d e o s o he mean.
wi h he coldes pe iod (ai emp <0◦C) wi hin he mea-
su ing pe iod and a apid inc ease in ai empe a u es up o
15◦C (Fig. 6). A signi ican up ake o a mosphe ic N2O was
ne e de ec ed. In gene al, N2O luxes measu ed wi h he
EC echnique we e mo e a iable han chambe based N2O
luxes which is indica ed by a much highe CV% o 123 as
compa ed o alues o CV% o 62.3 and 42.8 by he au o-
ma ic and manual chambe s, espec i eley (Table 1). N2O
emissions measu ed by he au oma ic chambe s co ela ed
nega i ely wi h ai empe a u e ( =−0.50, p<0.01) and soil
empe a u es in he li e laye , a 5cm and a 30cm dep hs
( =−0.48, p<0.01; =−0.47, p<0.01; =−0.46, p<0.01),
espec i ely, soil mois u e con en ( =−0.46, p<0.01), and
Fig. 6. (a) Mean soil N2O luxes measu ed wi h eddy co a iance,
au oma ic and manual chambe s, (b) soil concen a ions o N2O a
h ee dep hs and in he ambien ai , and (c) mine al ni ogen and o-
alni ogen concen a ions in heli e laye o he soil du ing Ap il–
Sep embe 2007 a he d ained pea land pine o es . Fi s column o
he igu es ep esen he pe iod o in ensi e measu emen s, he sec-
ond shows he da a ou side he measu emen campaign. E o ba s
s and o s anda d e o s o he mean.
CO2 luxes ( =−0.48, p<0.01). Posi i e co ela ions we e
ound wi h wa e able dep h ( =0.40, p<0.01) and CH4up-
ake ( =0.30, p<0.05).
3.6 CH4and N2O concen a ion in pea p o ile
Du ing he in ensi e measu ing campaign om Ap il o
June 2007 CH4and N2O concen a ions in he pea p o ile
we e close o ambien ai concen a ions o ∼1.8ppm and
∼0.35ppm , espec i ely (Figs. 5b and 6b). In gene al, du -
ing he in ensi e measu emen campaign he CH4concen-
a ions dec eased (i.e. consump ion) and N2O concen a ion
sligh ly inc eased (i.e. p oduc ion) wi h pea dep h in he op-
soil. F om July o Sep embe he concen a ions o CH4in
deepe pea laye s (22 and 45cm dep h) inc eased ma kedly.
The highes concen a ion o 1400ppm was measu ed a
45cm dep h in Sep embe . A he same ime he CH4con-
cen a ions in he li e laye we e close o he ambien ai
concen a ions and he ne luxes measu ed by manual cham-
be s showed ha he soil was s ill a sink o CH4(Fig. 5a
and b).
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M. K. Pihla ie e al.: G eenhouse gas luxes in a d ained pea land o es du ing sp ing os - haw e en 1723
Ni ous oxide concen a ions a 22cm dep h we e mos
o he ime highe han he concen a ion jus below he li -
e laye a 5cm (Fig. 6b). Concen a ions a 45cm dep h
measu ed du ing July o Sep embe a ied be ween 0.210–
0.240ppm and we e much lowe han a 5 o 22cm dep hs
and well below he a mosphe ic concen a ion.
4 Discussion
4.1 CO2 luxes
Eddy co a iance (EC) measu emen s abo e he o es canopy
e ealed ha he Kale ansuo d ained pea land pine o es
was a ne sink o CO2du ing he measu ing pe iod om he
end o Ap il o he end o June. The measu emen s below
he o es canopy by sub-canopy EC and au oma ic chambe s
showed ha he o es loo was a ne sou ce o CO2, how-
e e , only a small pa o he ne CO2up ake o he whole
o es ecosys em. Du ing ew ainy days in he campaign (in
o al 5 days) he Kale ansuo pea land o es u ned om a
ne sink o ca bon o a ne sou ce. This inding is in line wi h
he s udy by Lohila e al. (2007) whe e hey ound ha an
a o es ed bo eal pea land u ned om a ne sink o a sou ce
o ca bon du ing ainy days in he summe . To al NEE a
he Kale ansuo d ained pea land o es om sp ing o ea ly
summe (25 Ap il–21 June, −102gCm−2) is compa able o
NEE alues epo ed om bo eal o es s g owing on mine al
o pea soils (Suni e al., 2003; Lohila e al., 2007).
In his s udy he diu nal a ia ion in he CO2exchange o
he soil and o es loo ege a ion was e y small measu ed
by he sub-canopy EC and non-exis en measu ed by he au-
oma ic soil chambe s. Simila ly small diu nal a ia ion in
he o es loo CO2exchange o a bo eal o es ecosys em
has been measu ed ea lie by Launiainen e al. (2005) and
Kulmala e al. (2008). Howe e , much s onge diu nal a i-
a ion in he CO2exchange o soil and o es loo ege a ion
has been measu ed in a empe a e o es ecosys em on min-
e al soil (Subke and Tenhunen, 2004). In ou s udy he lack
o diu nal a ia ion in he CO2exchange o he o es loo
may esul om (1) a small pho osyn he ic ac i i y o he o -
es loo ege a ion as compa ed o he soil and o es loo
espi a ion, o (2) he possibili y o high pho osyn he ic ac-
i i y du ing day- ime and a simul aneous inc ease in he soil
espi a ion due o empe a u e dependency, which hen com-
pensa es o he pho osyn hesis. The ne o es loo CO2
luxes measu ed by sub-canopy EC du ing Ap il–June pe iod
compa e well wi h sub-canopy EC measu emen s ca ied ou
in a bo eal pine o es (Launiainen e al., 2005), and chambe
based measu emen s in o he d ained pea land o es s (Ma -
ikainen e al., 1995; Alm e al., 1999).
Co ela ion o o es loo CO2 luxes was highes wi h
soil empe a u es in 5cm dep h. This shows ha a he
he op-soil, ge ing esh li e inpu om ege a ion, is he
majo sou ce o CO2as compa ed o he pea body i sel ,
hus, s imula ed decomposi ion o he pea due o ae a ion by
d ainage has al eady diminished.
In con as o N2O emissions no inc eases in CO2emis-
sions ollowing hawing o he li e laye could be de ec ed.
The in e mi en inc ease o CO2emissions in he end o
Ap il can be ela ed o a signi ican inc ease in soil and ai
empe a u es, howe e , in a pe iod when empe a u es we e
ne e below 0◦C. As he measu emen s s a ed a e he i s
eeze- haw cycles, i is unclea whe he such eeze- haw
induced CO2peaks occu ed a he si e al hough he absence
o less p onounced e ec o os - haw cycles on in si u CO2
emissions in o es ecosys ems is also epo ed in he e iew
o Ma zne and Bo ken (2008).
4.2 CH4 luxes
Au oma ic and manual chambe based measu emen s e-
ealed ha he pea land o es was a sink o a mosphe ic
CH4du ing he whole measu ing pe iod om end o Ap il
o end o June 2007. This means ha he d ainage was deep
enough o change he ae a ion s a us and, hus, he condi ions
a ou able o me hanogenes o hose a ou able o me han-
o ophs. The high in luence o he wa e able dep h on he
CH4exchange o pea lands has been obse ed in o he s ud-
ies (Ma ikainen e al., 1993, 1995) and is u he e lec ed by
he signi ican posi i e co ela ion o CH4up ake a es wi h
changes in wa e able dep h du ing he obse a ion pe iod.
Maximum up ake a es o >60µgCH4-Cm−2h−1we e sig-
ni ican ly highe han obse ed by Ma ikainen e al. (1995)
o a d ainded en wi h compa able wa e able dep hs. In
a la ge s udy combining da a om d ained and und ained
pea land o es s in Finland Minkkinen e al. (2007) ound
ha in gene al, und ained si es unc ioned as CH4sou ces
whe eas d ained si es unc ioned ei he as CH4sinks o s ill
as small sou ces o CH4. In hei s udy he mean CH4up-
ake a es a ied om 1 up o 90µgCH4-Cm−2h−1. Fo
he Kale ansuo si e Minkkinen e al. (2007) epo ed an an-
nual CH4up ake o 0.2gCm−2. A simple linea ex apo-
la ion om he cumula i e lux o a ull yea esul ed in an
up ake o 0.09gCm−2y −1 o he au oma ic chambe s and
0.06gCm−2y −1 o he manual chambe s. This indica es
ha his d ained pea land o es is a signi ican , bu sli gh ly
smalle CH4sink as compa ed o bo eal o es s in gene al
(−0.15gCm−2y −1) (Du au and Ve cho , 2007).
We ound ha CH4was p oduced h oughou sp ing and
summe a 22and25cm dep h in he pea p o ile. A hesame
ime he ne lux o CH4was nega i e, showing CH4up-
ake. This implies ha he Kale ansuo si e was well d ained
and he oxic op-laye o he pea was su icien no only o
oxidize he CH4p oduced in deepe laye s, bu also o oxi-
dize addi ional a mosphe ic CH4. This obse a ion is in-line
wi h obse a ions a o he si es, whe e also CH4concen a-
ions well abo e a mosphe ic concen a ions we e de ec ed
in deepe soil laye s, while soil was s ill ucn ioning as a
ne sink o a mosphe ic CH4(Bu e bach-Bahl and Papen,
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