O sis,
6:
215-229 (1991)
Red ains as majo con ibu o s o nu ien s
and alkalini y o e es ial ecosys ems
a Mon seny
(NE
Spain)
Anna Á ila and Fe an Roda
Cen e de Rece ca Ecolbgica i Aplicacions Fo es als. Uni e si a Au bnoma de Ba celona.
08193 Bella e a. Spain.
Keywo ds: acid ain, a mosphe ic deposi ion, calcium, elemen inpu s, Saha an dus .
Abs ac . Du ing wo yea s (1983-1985), 8 ed ains we e collec ed in he Mon seny moun ains.
The suspended ma e con ained in ed ains has i s sou ce in he Saha a dese and co esponds
o ine sil s. Due o he calci e con en o dus esponsible o he ed ains, hese ains a e
alkaline wi h a olume weigh ed mean pH o 7.7 e sus 4.7 o non- ed ains. Es ima ed HCO;
alkalini y inpu due o ed ains is 0.21 keqlhaly and o al annual HCO; alkalini y inpu is 0.24
keqlhaly . To ha igu e, one has o add a leas 0.24 keqlhaly due o he alkalini y o calci e
con ained in ed dus . Fo he same pe iod, hyd ogen inpu in bulk deposi ion amoun s o 0.19
keqlhaly . These esul s indica e ha acidi y due o non- ed ain espisodes is neu alized on an
annual basis, wi h ed ains being he majo neu alizing agen . Ion concen a ions in ed ains
a e high, which makes hem an impo an sou ce o nu ien s e en hough hey only accoun
o 5.4% o annual p eci i a ion. Red ains a e pa icula ly en iched wi h ca2+ ha ing a
P+
olume-weigh ed mean Ca concen a ion 14 imes highe han non- ed ains and deli e ing
46% o he annual inpu s o soluble ca2+ in bulk p ecipi a ion a Mon seny.
Resum.
Pape de les pluges de ang en I'apo a mos e ic de nu ien s i d'alcalini a al Mon seny.
Du an dos anys (1983-1985) es a en ecolli 8 pluges de ang a La Cas anya (Mon seny). La
ma k ia pa iculada de les pluges de ang s'o igina al dese del Saha a, i co espon a llims ins.
Degu al con ingu de calci a d'aques s llims, les pluges de ang són alcalines, amb un pH mig
de 7.7, en on de 4.7 pe la es a de les pluges. L'en ada anual es imada d'alcalini a en o ma
de bica bona dissol a les pluges de ang és de 0.21 keqlhalany, d'un o al es ima de 0.24
keqlhalany pe o es les pluges. A aques a xi a cal a egi almenys 0.24 keqlhalany degu al con-
ingu de calci a a la ase sblida de les pluges de ang. Du an el ma eix pe iode, I'en ada d'hi-
d ogenions a la deposició global és de 0.19 keqlhalany. Aques s esul a s indiquen que, a escala
anual, les pluges de ang apo en su icien alcalini a com pe neu ali za I'acidesa de la es a
de les pluges. Les concen acions ibniques són ele ades a les pluges de ang, i aques es s6n pe
an , un ac o impo an en la deposició a mos k ica de nu ien s, enca a que ep esen en en
p omig només un 5.4% de la p ecipi ació anual. Les pluges de ang són pa icula men iques
en calci: la se a concen ació mi jana ponde ada d'aques elemen és 14 egades més g an que
la de la es a de les pluges, i con ibueixen amb un 46% a les en ades anuals de calci en la
deposició global del Mon seny.
In oduc ion
Acid ain has been he subjec o a as esea ch e o a emp ing o cla i y
he ole o incoming a mosphe ic acidi y in he al e a ion o biogeochemical
cycles in e es ial and aqua ic ecosys ems (Ad iano
&
Ha as 1989, D ablos
&
Tollan 1980, Hu chinson
&
Ha as 1980, Reuss
&
Johnson 1986).
Ne e heless, he e a e ela i ely ew s udies s essing he ac ha pa icula
a eas equen ly ecei e ain e en s o high
pH
(PH well abo e 5.6, he pH
alue o pu e wa e equilib a ed wi h a mosphe ic CO*).
Alkalini y esponsible o his pH inc ease is mainly due o dissolu ion
o alkaline componen s o aeolian soil dus . Khemani e al. (1987) ound in
India ha highly alkaline pH alues in cloud and ainwa e we e associa ed
o high concen a ions o dus pa icula es in he a mosphe e. Bua -Ména d
e al. (1974) epo ed obse a ions o Ca2' en ichmen in ma ine ae osols
o e he A lan ic wich we e a ibu ed o soil dus om he Saha a and he
Kalaha i dese s. Loye-Pilo e al. (1986) obse ed in Co sica ha ain wi h
high concen a ions o dus had an impo an Ca2' en ichmen and Gigh pH
alues. Dus collec ed in Co sica was aced back o o igina e in he Saha a
dese . As a consequence, geog aphic a eas in he icini y o a id o
denuda ed egions a e subjec o occasional episodes in which he
a mosphe e is loaded wi h Ca2+-MgZ ae osols o high neu alizing capaci y.
The Medi e anean is a pa icula example o such an a ea, being
in luenced by dus anspo om No h A ica, as has been widely epo ed
(Büche
&
Lucas 1984, Ches e e al. 1984, Loye-Pilo e al. 1986,
Ma in-Vide
&
Mo eno 1985). Be game i e al. (1989) ha e iden i ied
se e a1 seasonal pa e ns o a mosphe ic ci cula ion ha p oduce anspo
o A ican dus o e he Medi e anean. Saha an dus anspo o sou he n
Eu ope is e ealed by he occasional occu ence o episodes o so-called ed
ain o ed snow. A Ba celona, he a e age annual equency o ed ain
e en s was 2.8 o he pe iod 1944-1974, being concen a ed mos ly in sp ing
and summe (Ma in-Vide
&
Mo eno 1985). Red ain episodes ha e been
s udied om a me eo ological o mine alogical poin o iew (Büche e al.
1983, Büche
&
Lucas 1972, 1975, Clemen e al. 1972), bu he chemis y
o ed ains is poo ly documen ed.
The pu pose o his pape is o desc ibe he chemis y o ed- ains
collec ed in a u al a ea o NE Spain and o e alua e hei con ibu ion o
he annual inpu o nu ien s and in he neu aliza ion o acidic deposi ion.
To ha pu pose we p esen da a o a wo-yea pe iod o weekly sampling
o bulk p ecipi a ion in he Mon seny moun ains, dis inguishing ain e en s
con aining ed dus om e en s wi hou ed dus .
S udy a ea
The s udy si e is loca ed wi hin he Es ació Biolbgica de La Cas anya
I
RED RAINS AS CONTRIBUTORS OF NUTRIENTS AND ALKALINITY
217
(41°46'N, 2'21'E) in he Mon seny moun ains, a p edominan ly o es ed
massi which lies 25-30 km om he Medi e anean coas in no heas Spain.
Ag icul u a1 land lie o he eas and wes o he moun ain, i s nea es indus
ial conu ba ion being ha o Ba celona, 40 km o he SSW. The li hology
o Mon seny is mainly o med by low g ade me omo phic schis s and
g anodio i es.
The si e o p ecipi a ion sampling is loca ed in a o es clea ing nea he
ou le o a small expe imen al wa e shed (TM9) wich is ou inely moni o ed
o chemis y by ou labo a o y wi hin he scope o a b oade s udy o
nu ien cycling in holm-oak (Que cus ilex L.) o es s (A ila 1988, A ila
&
Rodi 1988, Fe és e al. 1984, Roda 1983, Roda e al. 1990). The al i ude
a he si e o p ecipi a ion sampling is 700 m a.s.1. Mean annual p ecipi a ion
measu ed o 7 yea s a he si e is 873 mm. Mean annual ai empe a u e is
es ima ed o be a ound 9°C. Vege a ion o he wa e shed and on su ounding
slopes is a dense, undis u bed o es o holm oak.
Me hods
Bulk p ecipi a ion o analysis was sampled wi h 4 collec o s, each consis ing
o a polye hylene unnel
19
cm in diame e connec ed by a loop o a 10 L
polye hylene bo le, ollowing he Hubba d B ook design (Likens e al.,
1977). Collec o s a e pe manen ly open o he a mosphe e, so he measu ed
lux is bulk deposi ion which includes we deposi ion and g a i a o y
sedimen a ion o pa icles. Weekly, ainwa e samples (and occasionally
snow collec ed by a 63-cm diame e bucke ) we e collec ed, and collec o s
we e eplaced by labo a o y cleaned ones. The cleaning p ocedu e consis ed
o a de e gen wash o he disassembled pa s o he collec o , a inse wi h
abundan ap wa e ollowed by soaking in 10% dilu ed comme cial HCl,
and a inse wi h abundan dis illed wa e . Final conduc i i y o dis illed wa e
un h ough he assembled collec o was checked o ensu e ha no
con amina ion o HCl ocu ed.
A
plug o nylon mesh, also washed wi h
dis illed wa e and checked o conduc i i y, was placed in he unnel neck
o p e en insec s and la ge deb is om eaching he collec ing essel.
In equen samples wi h insec s o deb is we e disca ded. Usually, collec o s
we e bulked by pai s o gi e wo eplica es o analysis, bu o small ains
(up o
5
mm) all collec o s we e bulked o gi e a single sample. Occasionally,
he samples o he ou collec o s we e analyzed. The amoun o p ecipi a ion
was measu ed by a s anda d ain-gauge a weekly in e als.
The day o collec ion, samples we e aken o he labo a o y, whe e pH
and conduc i i y we e measu ed a e equilib a ing he sample o he
labo a o y empe a u e. pH was measu ed po en iome ically using a
combined elec ode which was calib a ed wi h pH bu e s o 7 and 9, o 4
and
7
depending on he sample PH. Conduc i i y was measu ed a e
calib a ion o he conduc ime e wi h a 100 pS/cm (a 20°C) solu ion. All ed
ains we e il e ed excep o one (sample collec ed on 2 May 1985). Majo
ions we e analyzed on ozen aliquo s. Sodium and po assium we e measu ed
by a omic emission spec ome y, calcium and magnesium by a omic
abso p ion spec ome y, and C1-, NO;, So; and NH4
'
by ion
ch oma og aphy. Di e ences be ween collec o eplica es we e nea ly
always less han 10%. In cases o highe di e ences, incohe en alues could
be easily iden i ied and we e disca ded. P ecission and accu acy we e es ed
in all analy ical uns and we e ound o be sa is ac o y (A ila 1988). Mean
pH was calcula ed by ans o ming indi idual pH alues o hyd ogen
concen a ion, weigh ing hese by p ecipi a ion olume and econ e ing o
PH.
We ha e no alkalini y da a o he s udy pe iod, so o ob ain a en a i e
igu e we ha e es ima ed he HCO; concen a ions om he equilib ium
eac ions o he ca bonic acid-ca bona e sys em:
and me ging he wo equa ions,
Knowing he pH o indi idual ain samples, HCO; can be ound om
he abo e ela ionship. We ha e aken an a mosphe ic pC02 o 340 ppm as
e lec ing ha o he ainwa e samples, and alues o kh and kl a labo a o y
empe a u e (20°C): kh=10-'.41 and kl= 10-638 (D e e 1982). F om ha we
ob ain:
[HCO;] =5.13/[H'] (concen a ions in peq
L-')
This ela ionship was applied o he
H'
concen a ion o each sample, and
HCOJ es ima ed alues we e hus ob ained. These we e hen weigh ed by
olume o ob ain a HCO; olume-weigh ed mean concen a ion.
Resul s and discussion
Resul s epo ed he e e e o he wo-yea pe iod om
1
Augus 1983 o
31 July 1985. Du ing his pe iod 87 bulk p ecipi a ion weekly samples we e
collec ed, 8 o which we e iden i ied as ed ains by isual obse a ion o a
colou ed solid esidue on unnel walls. O he 8 ed ains, 3 occu ed in he
i s yea ( hose collec ed on 16 Ap il 1984, 6 May 1984 and 25 June 1984),
and 5 in he second (collec ed on 12 No embe 1984, 25 Ap il 1985, 2 May
1985, 21 June 1985 and 19 July 1985). The ed ain on 19 July 1985 was e y
RED RAINS AS CONTRIBUTORS OF NUTRIENTS AND ALKALINITY
219
small (0.1 mm) gi ing no enough olume o chemical analyses, and ha o
16 Ap il 1984 (1.3 mm) was disca ded because o p obable con amina ion;
he e o e, only he chemis y o he emaining 6 pe iods o ed ain will be
conside ed he e (Table 1). As hey we e weekly samples, hey may ha e
included mo e han one indi idual ed ain because ed ains end o be
con iguous (Ma in-Vide and Mo eno 1985). The di e ences in p ecipi a ion
chemis y ound in his s udy be ween ed and non- ed ains a e hus
conse a i e es ima es.
Amoun o p ecipi a ion
The annual amoun o p ecipi a ion a TM9 was 1052.5 mm and 873.0 mm
o 1983-1984 and 1984-1985 espec i ely. The wo yea mean was 962.8 mm.
The 8 weekly samples con aining ed ains deli e ed a o al o 103.9 mm, o
52.0 mm y -l. This amoun s o 5.4% o he mean p ecipi a ion ecei ed a
he si e in his pe iod. The e was a nine old di e ence in he amoun o ed
Table
1.
Volume-weigh ed mean concen a ion in ed ains and non- ed ains o he
wo-yea pe iod
1983-1985
a Mon seny. Conduc i i y in yS cm-I a
20
OC; concen-
a ions in yeq L-'; p ecipi a ion in mm y -l.
Non- ed Red non- ed
Ion Red ain ain ain
Conduc i i y
73.3 18.5 4.0
PH
7.76 4.68
-
H+
0.02 21.1
10-~
Na'
98.6 21.6 4.6
K+
12.3 2.43 5.1
CaZc
549 38.5 14.3
Mg2'
47.7 9.5 5.0
Mg*
26.7 4.6 5.8
NH:
19.7 26.6 0.7
NO3-
36.1 19.0 1.9
SO:-
140 50.5 2.8
SO:
128 47.9 2.7
C1-
126 26.0 4.8
HCO~-"
416 3.3 126
P ecipi a ion
51.2~ 908' 0.06
n
6 72
-
*
M~~'
and SO:- concen a ions a e co ec ing o sea-sal ae osol wi h Na' as e-
e ence ion.
"
es ima ed om equilib iuin eac ions o he ca bona e sys em, ha ing conside ed
a cons an pCOz
a
340
ppm and kl and kh alues a
20
"C.
non-analyzed and non-conside ed e en s o alled a u he
1.4
mm y -I.
non-analyzed e en s o alled a u he
3
mm y -l.

ains be ween he wo yea s: 10.6 mm in 1983-1984 s. 93.3 mm in 1984-1985,
accoun ing espec i ely o 1% and 10% o he annual p ecipi a ion. The
g ea e amoun o ed ain eco ded in he second yea esul ed om wo
la ge- olume e en s (50 mm collec ed on 12 No embe 1984 and 31 mm
collec ed on 25 Ap il 1985). These wo s o ms accoun oge he o 88% o
he o al p ecipi a ion o ed ains in he second yea . The e o e, he e is a
hgh in e annual a iabili y in ed ain amoun o p ecipi a ion depending
on he p ecipi a ion deli e ed by pa icula e en s. The amoun o
p ecipi a ion pe pe iod does no di e signi ican ly be ween pe iods o ed
ain and pe iods o non- ed ain ( es a e loga i hmic ans o ma ion,
P>0.05).
Solu es
in
ed
ain
The olume weigh ed mean concen a ions o majo ionic componen s in ed
ain and non- ed ain samples collec ed a TM9 a e gi en in Table
1.
Excep
o NH4, which is he sole ion o ha e simila concen a ions in bo h ype o
ains, and o H' which dec eases in ed ains, all ions ha e much g ea e
concen a ions in ed ains. Di e ences a e signi ican o all ions (P<0.005
o conduc i i y, PH, Na',
K',
Ca2', Mg2', SO:' and C1-; P=0.09 o NO;)
excep o NH: (P=0.22) when aplying a co a iance analysis wi h amoun
o p ecipi a ion as a co a ia e. Sodium, K', Mg2' and C1- means in ed ains
a e g ea e by a ac o o 4 o 5 han non- ed ains, while o NO; and SO:-
his ac o is
2
and 3 espec i ely (Table 1). Howe e , he ion wi h he highes
di e ence is Ca2', whose mean concen a ion in ed ains is 14 imes ha o
non- ed ains. The abo e men ioned highe ion concen a ions a e e lec ed
in conduc i i y, which consequen ly is g ea e in ed ains. As s a ed be o e,
H' concen a ion is e y low in ed ains, gi ing a olume-weigh ed mean
pH o 7.76. This alue con as s s ongly wi h he mean pH o non- ed ains
o 4.68 (Table 1). The empo al a ia ion o pH in bulk deposi ion a TM9
is p esen ed in Figu e 1, ed ains di e ing om non- ed ains because o
hei highe pH alues. Red ains a e cha ac e is ically e y concen a ed in
all ions, bu hey show also a high a iabili y in concen a ions, wi h
coe icien s o a ia ion
(%)
o 35.2 o conduc i i y, 56.0 o Na', 56.1 o
K', 42.9 o Ca2', 25.8 o Mg2', 68.1 o NH:, 49.7 o NO;, 55.8 o
SO:-
and 54.0 o C1-, o he 6 ed ain e en s a TM9.
Red ains could be dis inc ly di e en ia ed om non- ed ains by means
o a p incipal componen analysis appyied o he ma ix o he 9 analyzed
a iables (PH, Na',
K',
Ca2', Mg2', NH:, NO'!, S04 and C1-) and 85 alid
weekly samples. The g aphical exp ession o he analysis is show in Figu e
2, whe e he h ee i s componen s accoun o 91.7% o ainwa e ionic
a ia ion. Red- ain samples o m a dis inc g oup when indi idual sco es a e
ep esen ed o he i s componen (iden i ied as mine aliza ion o ichness
in Ca2', Mg2', K', S042- and NO
i)
and he hi d componen (de ined by pH
RED RAINS AS CONTRIBUTORS OF NUTRIENTS AND ALKALINI=
221
Figu e
1.
Tempo al a ia ion o bulk p ecipi a ion pH a
TM9.
Red ains a e ep esen ed by
open ci cles.
Figu e
2.
Resul s o p incipal cqmponen analysis o bulk p ecipi a ion chemis y o all he
weekly samples; de ined by hei pH and majo ion concen a ions. Sco es o indi idual ain
samples de ined by he i s and hi d componen s. Red ains a e ep esen ed by illed ci cles.
and NH4 and iden i ied as acidi y-alkalini y o ain). Red ains a e
di e en ia ed om he es o ains because o hei high mine aliza ion and
high pH alues (Fig. 2) as is e lec ed by esul s in Table 1. A his momen ,
i is wo h s essing ha ed- ains we e de ined by usual ecogni ion o
colou ed ma ks o deposi ed dus . I is possible ha , because o he weekly
sampling schedule, some ed ains alling a he beginning o he pe isd and
ollowed by non- ed ains we e missclassi ied, o con e sely, ed ains a he
end o he pe iod could con ain non- ed ains collec ed a he beginning o
he pe iod. In bo h cases, he mixing would p oduce a dilu ion o he usual
high concen a ions o ed ains, and p obably, a dec ease in he sample PH.
These samples, and o he s in luenced by dus ae osols bu no lea ing isual
ma ks, would all in he icini y o he ed ain g oup in he p incipal
componen analysis, and hey migh be as well some o he poin s o ela i ely
high pH in Figu e
1
which a e no signaled as ed ains.
No only do ed ains di e widely om non- ed ains in hei ionic
concen a ions, bu also hei ela i e ionic p opo ions a e qui e dis inc .
Pa icula ly in e es ing is he a io o non-sea sal Ca2' o non-sea sal
M~~+
(also called excess Ca and excess Mg and ep esen ed by Ca* and Mg*). In
ac , as only 2% o Ca2' in bulk p ecipi a ion a Mon seny comes om sea
sal ae osols, we ha e compu ed excess ca2' only o consis ency wi h ~g~+.
A Mon seny, non- ed ains ha e a ema kably cons an Ca*/Mg* a io o
abou 8, on an equi alen basis. This gi es a high linea co ela ion be ween
Ca* and Mg* (Fig. 3). This cons ancy o he Ca*/Mg* a io implies ha
ei he (i) all majo con inen al sou ces o soluble Ca2' and
M~~'
in non- ed
ains a Mon seny yield a Ca*/Mg* a io o abou . 8, o (ii) di e en sou ces
wi h a ying p opo ions o soluble Ca2' and
M~~+
always combine in such
a manne o gi e he obsemed Ca*/Mg* a io. In con as , ed ains a e
clea ly se apa om non- ed ains in a sca e g am o Ca* e sus Mg* (Fig.
3). In p opo ion o Mg*, ed ains a e much iche in ca2' han non- ed
ains, hei Ca*/Mg* a io be ween olume-weig ed means ising o 21 on an
equi alen basis. This sha p di e ence in ionic p opo ions p o ides u he
e idence ha he sou ce a eas o ai -bo ne ma e a e di e en o ed and
non- ed ains.
Two o he s udies o bulk deposi ion in Ca alonia ha e dis inguished
be ween ed and non ed ain e en s. One was ca ied a a nea by s a ion
named TM5 which is loca ed in culmina1 hea hlands in he Mon seny and is
only 1.35 km away om TM9. The o he one was ca ied a P ades
(Ta agona), 120 km o he
WSW
om ou s udy si e. A TM5, en ed ains
we e iden i ied by isual obse a ion o eddish ma ks on collec o s be ween
Janua y 1982 and Decembe 1984. O hese, only he a i hme ic mean
concen a ion is a ailable (Belillas 1989) which is gi en in Table 2. Fo
compa ison, he a i hme ic mean concen a ion o he
6
ed ain e en s
collec ed a TM9 is gi en in Table 2. Red ains in bo h s a ions show simila
ea u es in: 1) basic pH and 2) e y high ionic concen a ions, pa icula y
-
-
--.
.
-
.
.
-
-
-.
.
..
-
-
RED RAINS AS CONTRIBUTORS OF NUTRIENTS AND ALKALINITY
223
1
Excess
Mg
(peq/L)
Figu e
3.
Sca e g am o non-sea sal ('excess') Ca concen a ion e sus non-sea sal Mg
concen a ion in bulk deposi ion a TM9. Red ains a e ep esen ed by illed ci cles. Poin s no
ma ked as ed ains bu wich a e well abo e he eg ession line could be ed ains no iden i ied
as such in he ield. Reg ession has been compu ed only wi h non- ed ains.
Table
2.
A i hme ic mean chemis y o ed ains in h ee locali ies o no heas e n
Spain. Concen a ions in peq
L-'.
Conduc i i y in pS cm-' a
20
OC. P ecipi a ion in
mm.
Mon seny P adesc
Va iable
TM9" TMS~
Bosc Poble
PH
7.66 6.24 7.07
Na
75.3 148 57.7
K'
16.6 26.1 8.9
CaZ
708 750 199
MgZ
53.1 91.2 20.7
NH:
25.3 62.7 24.9
NO;
52.2 110 22.6
SO,'-
21
1
317 67.2
C1-
97.1 178 53.3
HCO;
-
291d 201
P ecipi a ion
102.3 281 312
n
6 10
6
"
This s udy. Augus
1983
o July
1985.
Belillas
1989.
Janua y
1982
o Decembe
1984.
'
Piñol
1990.
Sep embe
1986
o June
1988.
Mean o
5
samples.