Ecological Research

(2003)

18

, 587–597

Blackwell Science, LtdOxford, UKEREEcological Research0912-38142003 Ecological Society of JapanSeptember 2003185587597Original Article

Effect of fog on nutrition of bogsT. Iyobe

et al.

*Author to whom correspondence should beaddressed. Email: sphagnummire@hotmail.com

Received 31 October 2002. Accepted 17 March 2003.

Effect of fog on sea salt deposition on peat soil in boreal

Picea glehnii

forests in Ochiishi, eastern Hokkaido, Japan

Tsutomu

Iyobe

,

1

Akira

Haraguchi

,

2

* Hiroki

Nishijima

,

1

Hideo

Tomizawa

3

and Fumihiko

Nishio

4

1

Graduate School of Science and Technology, Niigata University, Ikarashi 2-8050, Niigata 950-2181, Japan,

2

Faculty of Environmental Engineering, The University of Kitakyushu, Hibikino 1-1, Wakamatsu, Kitakyushu 808-0135, Japan,

3

Kiritapp Mire Research Center, Biwase 103-19, Hamanaka 088-1360, Japan and

4

Center for Environmental Remote Sensing, Chiba University, Yayoi 1-33, Inage, Chiba 263-8522, Japan

We investigated seasonal changes in the chemical properties of precipitation (bulk deposition,throughfall and stem flow) in

Picea glehnii

forests and neighboring

Sphagnum

communities in threeombrotrophic mires in Ochiishi district, northern Japan, to clarify the contribution of fog to nutrientaddition to mires. Na

+

and Cl

–

dominated the bulk deposition, followed by Mg

2

+

, Ca

2

+

and SO

42–

,implying an oceanic influence on mire chemistry. Differences in chemical properties among bulkdeposition, throughfall and stem flow increased with proximity to the coastline. There was little dif-ference in electrical conductivity (EC) among bulk deposition, throughfall and stem flow during theperiod of high fog frequency, which was approximately 17 fog days per month from June to August,but there were large differences in EC during the period of low fog frequency, which was approxi-mately 5 fog days per month from September to November. In general, throughfall and stem flowwere enriched with Na

+

, Mg

2

+

, Ca

2

+

, Cl

–

and SO

42–

at the

P. glehnii

canopy, and seasonal trends inionic concentration showed almost the same trend as EC. This seasonal pattern of atmospheric dep-osition chemistry showed that sea salt deposition on mires depends on fog occurrence. Sea salt iswashed out of the atmosphere by fog when fog covers the forest canopy and, hence, throughfall andstem flow did not lead to the enrichment of chemical constituents during passage through the can-opy in these mires during the season of high fog occurrence.

INTRODUCTION

Several authors have discussed the importance ofrain in the cycling of nutrients within ecosystems(e.g. Bormann & Likens 1967). Both throughfalland stem flow, the major pathways of atmosphericdeposition in forests, are important for nutrition inforest ecosystems (Cronan & Reiners 1983; Parker1983; Lindberg

et al

. 1986). Throughfall and stemflow chemistry are used as parameters for evaluat-ing the influxes of atmospheric deposition to the

forest floor and to soils under vegetation (Neary &Gizyn 1994). Several factors affect throughfall andstem flow chemistry. The wash-off process fromleaf and bark surfaces as the precipitated waterpasses through the canopy can raise the concentra-tion of dissolved substances in precipitation water,relative to that in open-field bulk precipitation,because a forest canopy’s large surface area is anefficient scavenger of atmospheric dry deposition.Hence, throughfall and stem flow chemistry in for-ests can be sensitive to the quantity of dry-deposited particles in the forest canopy, whichrelates to the length of the preceding dry periodbefore each precipitation event.

Precipitation is an important process in hydro-logical and mineral cycles in ecosystems. Fog dripconstitutes an important fraction of the total

588 T. Iyobe

et al.

hydrologic input to an ecosystem, particularly insome coastal or mountainous regions. In tallcoastal redwood (

Sequoia sempervirens

(Lamb.)Endl.) forests in a coastal fog belt in a San Fran-cisco watershed, which are exposed to wind blast-ing, seedlings of Douglas fir, Monterey cypress andeucalyptus grow beneath the redwoods that scav-enge fog (Oberlander 1956). Fog maintains a cooland moist environment, reducing evapotranspira-tion losses from soil and vegetation. Blanket bogsdominate in the coastal zone of the Avalon andBurin peninsulas in southern Newfoundland,where fog frequency is high. Fog alters the micro-climate (e.g. high humidity and low temperature)and makes the ground water table high, enablingthe establishment of blanket bogs (Price 1992).

In general, water influx and soil moisture arehigher under tree canopies or in forest stands inwhich the fog is ‘stripped’ from the air mass (Ober-lander 1956; Azevedo & Morgan 1974). In north-eastern Japan, the prevention of advection fogs byforests, which reduce precipitation over inlandareas, has been discussed by some investigators(e.g. Fukutomi 1953). Tree canopies capture fogon the leaves and branches and diffuse the eddies ofair above the forests. However, the compositionand annual fluxes or seasonal fluctuation of atmo-spheric deposition in these forests have not yetbeen reported in detail. Azevedo and Morgan(1974) suggested that additions of ample amountsof elements in fog water captured by forest cano-pies are as significant as additions from rainthroughout the growing season.

Fog water, as occult deposition, is significantlymore acidic and concentrated with chemicals thanrainwater collected in the open field (e.g. Wald-man

et al

. 1982). Nishio

et al

. (1995) reported thatthe fog in northeastern Japan was highly acidicand that acid fog affects natural ecosystems in asimilar way to acid rain. Erisman (1993) alsopointed out that the concentrations of pollutantsin fog and clouds are, in general, much higher thanin rain. These reports demonstrate that fog is abetter scavenger and transporter of atmosphericsubstances than rain or snow. Fog particles have avery small volume and a very large total surfacearea and can form stable suspensions by mixingwith horizontal wind (Paoletti

et al

. 1989).The southeastern coast of Hokkaido, northern

Japan, is often shrouded in advection fogs in

spring and summer, which come in from thePacific Ocean south of Hokkaido. Advection fogsin this region arise in areas of the ocean wherewarm, high-humidity air moves over the coldOyashio current. These advection fogs occur withremarkable seasonality. The present study wasdesigned to evaluate patterns of seasonal varia-tion in the chemical properties of bulk deposi-tion, throughfall and stem flow inside andoutside forests with reference to fog frequency.When we compare the precipitation chemistrybetween the high and low frequency seasons offog occurrence, we can evaluate the contributionof fog to sea salt loading in coastal ecosystems.We investigated the chemical properties of pre-cipitation in both foggy and non-foggy seasonsin three forested mires with the same communitystructure to examine the relationship betweenfog appearance and precipitation chemistry inforest mire ecosystems. We discuss the transpor-tation process of sea salts by fog and rain in thecoastal, ombrotrophic forest mire ecosystems inOchiishi district.

METHODS

Study site

The study area in Ochiishi (43

∞

10

¢

N, 145

∞

30

¢

E) islocated on the Nemuro Peninsula, northeasternJapan, facing the Pacific Ocean (Fig. 1). The aver-age annual temperature, rainfall and humidity ofthe area from 1961 to 1990 were 5.9

∞

C, 1035 mmand 80%, respectively (unpubl. reports from themeteorological observatory in Nemuro city). From

Fig. 1.

The study sites in Ochiishi district, easternHokkaido, northern Japan.

Effect of fog on nutrition of bogs 589

June to August, this area is covered with sea fog byprevailing winds from the south (Fig. 2).

There are several

Sphagnum

mires on the coastalterrace, which has an elevation of approximately50 m a.s.l. We selected three mires as study sites:Cape Ochiishi Mire, East Ochiishi Mire and Bet-toga Mire (Fig. 1). Cape Ochiishi Mire is the near-est to the coastline (ca. 500 m), followed by EastOchiishi Mire (1000 m) and Bettoga Mire(3000 m). The dominant plants at the three miresare

Sphagnum

spp. and

Picea glehnii

(Fr. Schmidt)Mast. The bog surface exhibits well-developedhummock–hollow microtopography.

Picea glehnii

forests surround the

Sphagnum

communities and

P. glehnii

plants on the community boundary arestunted and distorted. The

Sphagnum

bogs aredominated by

Sphagnum fuscum

(Schimp.) Klinggr.,

Empetrum nigrum

L. var.

japonicum

K. Koch and

Vac-cinium oxycoccus

L. In the

P. glehnii

peat forest,

Lysi-chiton camtschatcense

(L) Schott,

Ledum palustre

L. spp.

diversipilosum

(Nakai) Hara and

Sphagnum

spp. (mainly

Sphagnum girgensohnii

Russ. and

Sph-agnum squarrosum

Crome) dominate the understory(Haraguchi 1996). The densities (stands ha

-

1

) of

P. glehnii

individuals (diameter at stem base

>

1.0 cm) were 8364 in Cape Ochiishi Mire,11 440 in East Ochiishi Mire and 6560 in BettogaMire. The cumulative stem basal areas of

P. glehnii

were 92.9, 98.9 and 54.0 m

2

ha

-

1

, respectively.

Precipitation sampling

Bulk deposition (wet and dry), throughfall andstem flow samples were collected every 2 weeksfrom 13 June to 29 November 1997 (i.e. on 13occasions). The bulk deposition collector was con-structed from an 18 l polyethylene bottleequipped with a PVC gutter (1 m long and 10 cmwide) that was cut in half lengthwise. The bottleswere shielded with a net to exclude debris. Onecollector was placed above the

Sphagnum

commu-nity at each mire. Throughfall samples were alsocollected using this apparatus and one collectorwas placed under a

P. glehnii

forest at each mire.Stem flow collectors were made of PVC tube (2 mlong and 1 cm in diameter) cut in half lengthwise.The tubes were fixed on boles of

P. glehnii

, encir-cling the stem. The stem flow samples flowed into5 l polyethylene bottles. Samples were collectedfrom two

P. glehnii

trees (6–7 m in height and 20–25 cm in basal diameter) in each mire.

Chemical properties of water

Water samples were stored in 150 ml polyethylenebottles in the field and brought to the laboratorywithin 6 h after sampling. The pH and electricalconductivity (EC) were measured in the laboratoryon the unfiltered samples using pH and EC meters(TOA Co., Tokyo, Japan, models HM-10P andCM-50AT, respectively). Samples were then fil-tered through cellulose nitrate membrane filters(0.45

m

m, Advantec Toyo Co., Tokyo, Japan) andrefrigerated. Concentrations of NH

4

+

, K

+

, Ca

2

+

,Na

+

, Mg

2

+

, Cl

–

, SO

42–

and NO

3–

were determinedby using a capillary electrophoresis system (modelQuanta 400, Waters Japan Co., Tokyo, Japan).

HCO

3–

was determined by titration with0.1 mol l

-

1

HCl until the sample pH reached 4.3(Patnaik 1997).

Fig. 2.

(a) Monthly fog days and (b) daily precipita-tion observed at Nemuro Meteorological Observatoryfrom June to November 1997.

30

20

10

0

120

100

80

60

40

20

0

J J A S O N

1997

(a)

(b)

Pre

cipl

tatio

n(m

m d

ay–1

)D

ays

of fo

g ap

pear

anc

(day

s m

onth

–1)

590 T. Iyobe

et al.

Data analysis

The chemical parameters of bulk deposition andthroughfall in each mire were used directly, andthose of stem flow were represented as the averageof duplicate samples. A Kruskal–Wallis test wasconducted for the chemical data on bulk deposi-tion, throughfall and stem flow to test for differ-ences among the three sites. Friedman’s test wasconducted for the precipitation chemistry at eachmire to test for differences among bulk deposition,throughfall and stem flow.

RESULTS

Chemical characteristics of precipitation

Mean EC of throughfall and stem flow were sig-nificantly higher than that of bulk deposition ineach mire (Table 1, Fig. 3), and the mean EC ofstem flow was much higher than that of through-fall. There were significant differences in mean ECof throughfall and stem flow among the threemires; EC of throughfall and stem flow increasedin the order Bettoga Mire

<

East OchiishiMire

<

Cape Ochiishi Mire (Table 1). Mean pH ofbulk deposition, throughfall and stem flow werenot significantly different among the mires(Table 1). Mean pH of throughfall showed littledifference from bulk deposition, but mean pH ofstem flow were much lower than those of through-fall and bulk deposition (Table 1), significantly soat Cape Ochiishi Mire and Bettoga Mire (Fig. 4).

Na

+

was the dominant cation in precipitation,followed by Mg

2

+

, Ca

2

+

and K

+

(Table 1). MeanNa

+

and Mg

2

+

concentrations in throughfall andstem flow were significantly higher than those inbulk deposition (Table 1, Fig. 5). The mean Na

+

and Mg

2

+ concentrations in bulk deposition,throughfall and stem flow increased in the orderBettoga Mire < East Ochiishi Mire < Cape Ochi-ishi Mire. Ca2+ concentrations in throughfall andstem flow were significantly higher than those inbulk deposition (Table 1, Fig. 5). Except for Ca2+

concentration in stem flow, the mean Ca2+ of bulkdeposition, throughfall and stem flow tended to behigher in the order Bettoga Mire < East OchiishiMire < Cape Ochiishi Mire. K+ was a minor cationin precipitation (Table 1). The mean K+ concentra-tions in throughfall and stem flow were higher

than that in bulk deposition in each mire(Table 1). There was a significant difference in K+

concentration of stem flow among the three mires(Table 1). K+ concentrations of stem flow in CapeOchiishi Mire were much higher than those in theother two mires. The mean NH4

+ concentrationsamong the three mires did not show significantdifferences, although NH4

+ concentration inthroughfall in Cape Ochiishi Mire and stem flowin East Ochiishi Mire were exceptionally high(Table 1).

Cl– was the dominant anion in precipitation, fol-lowed by SO4

2–, HCO3– and NO3

–. Mean Cl– con-centrations in throughfall and stem flow weresignificantly higher than those of bulk deposition(Table 1, Fig. 6). The mean Cl– concentrations inbulk deposition, throughfall and stem flow tendedto be higher in the order Bettoga Mire < EastOchiishi Mire < Cape Ochiishi Mire. The meanSO4

2– concentrations of throughfall and stem flowwere significantly higher than the concentration inbulk deposition in each mire (Table 1, Fig. 6).There were significant differences in mean SO4

2–

concentrations of stem flow among the three mires(Table 1). The SO4

2– concentration in stem flow inBettoga Mire was significantly lower than that inCape Ochiishi Mire and East Ochiishi Mire. Themean NO3

– concentrations in precipitation werenot significantly different among the three mires;mean values were <0.01 mmolc L-1 (Table 1);however, the differences among bulk deposition,throughfall and stem flow were significant (Fig. 6).Site differences in mean HCO3

– concentrations ofprecipitation were not significantly different inbulk deposition and throughfall (Table 1). HCO3

–

in stem flow increased in the order Cape OchiishiMire < Bettoga Mire < East Ochiishi Mire(Table 1).

Seasonal changes in precipitation chemistry

The number of foggy days in Nemuro city peakedin July and decreased from August to November(Fig. 2). The mean number of foggy days fromJune to August was 17 days month-1. In July,cumulative precipitation was 35 mm and thenumber of days with precipitation <1.0 mm day-1

was 19 (Fig. 2). In October, cumulative precipita-tion was 43 mm, and the number of days with pre-cipitation <1.0 mm day-1 was 7. Except for July

Effect of fog on nutrition of bogs 591

and October, monthly precipitation was>100 mm.

The pH of precipitation did not show seasonaldifferences at each mire. The pH of precipitationin Cape Ochiishi Mire fluctuated erratically, andthroughfall pH showed remarkable peaks in July(Fig. 4). Electrical conductivity, Na+, Cl–, Ca2+,

Mg2+ and SO42– concentrations in precipitation

showed remarkable peaks in July and October(Figs 3,5,6), although the peaks in July weresmaller than those in October for each chemicalparameter. The value of EC and concentration ofthese ions in mid July and October increased in theorder Bettoga Mire < East Ochiishi Mire < Cape

Table 1 Mean electrical conductivity (EC; mS m-1), pH and concentrations (mmolc L-1) of ions in bulk deposition,throughfall and stem flow. Samples were collected once biweekly from June to November 1997 at three mires inOchiishi, northern Japan (SD in parentheses)

Cape Ochiishi East Ochiishi Bettoga Significance

Bulk depositionEC 5.21 (3.9) 3.3 (1.8) 2.7 (1.7) NSpH 4.79 (0.53) 4.62 (0.35) 4.63 (0.43) NSNa+ 1.12 (1.02) 0.51 (0.40) 0.40 (0.29) *Mg2+ 0.27 (0.28) 0.12 (0.11) 0.08 (0.08) **Ca2+ 0.13 (0.10) 0.07 (0.06) 0.06 (0.05) *K+ 0.07 (0.07) 0.06 (0.09) 0.04 (0.05) NSNH4

+ 0.11 (0.18) 0.05 (0.10) 0.08 (0.14) NSCl- 0.56 (0.55) 0.38 (0.47) 0.32 (0.38) NSSO4

2- 0.04 (0.03) 0.03 (0.03) 0.02 (0.01) NSNO3

- 0.00 (0.00) 0.00 (0.00) 0.00 (0.01) NSHCO3

- 0.09 (0.20) 0.07 (0.14) 0.05 (0.12) NSThroughfall

EC 27.8 (28.5) 15.4 (12.5) 7.0 (5.5) **pH 5.22 (1.05) 4.62 (0.35) 4.66 (0.45) NSNa+ 3.65 (4.23) 2.66 (2.83) 1.00 (0.72) **Mg2+ 1.12 (1.53) 0.75 (0.88) 0.27 (0.24) *Ca2+ 0.89 (1.78) 0.40 (0.59) 0.21 (0.14) NSK+ 0.28 (0.34) 0.26 (0.34) 0.17 (0.11) NSNH4

+ 0.90 (2.87) 0.05 (0.15) 0.05 (0.09) NSCl- 1.86 (3.18) 1.23 (1.76) 0.57 (0.59) NSSO4

2- 0.11 (0.20) 0.08 (0.10) 0.04 (0.04) NSNO3

- 0.00 (0.01) 0.00 (0.00) 0.00 (0.00) NSHCO3

- 0.12 (0.21) 0.03 (0.05) 0.08 (0.22) NSStemflow

EC 63.3 (53.6) 29.9 (21.9) 14.6 (10.8) **pH 4.27 (0.57) 4.38 (0.66) 4.43 (0.32) NSNa+ 5.76 (5.22) 3.09 (2.84) 1.86 (1.47) **Mg2+ 2.66 (3.80) 1.01 (1.32) 0.55 (0.58) **Ca2+ 2.66 (5.47) 0.71 (1.18) 2.13 (1.68) **K+ 0.49 (0.38) 0.23 (0.17) 0.25 (0.12) *NH4

+ 0.08 (0.16) 0.52 (1.65) 0.09 (0.12) NSCl- 2.30 (2.87) 2.17 (4.02) 0.85 (0.78) NSSO4

2- 0.11 (0.11) 0.11 (0.21) 0.05 (0.04) *NO3

- 0.00 (0.00) 0.00 (0.00) 0.00 (0.00) NSHCO3

- 0.03 (0.08) 0.09 (0.17) 0.05 (0.12) **

Significance level for Kruskal–Wallis test (P > c2) comparing three mires in the Ochiishi region for chemical parameters of pre-cipitation are given by the following symbols: *P < 0.05; **P < 0.01; NS: not significant P > 0.05.

592 T. Iyobe et al.

Ochiishi Mire, and the values in October showedclear differences among mires, although there weresome exceptions. Electrical conductivity and con-centrations of cations and anions, except for NH4

+

and NO3–, tended to be higher in throughfall and

stem flow than in bulk deposition. Sea salt com-

Fig. 3. Seasonal changes in electrical conductivity(EC) of bulk deposition (BD; �) in open areas, through-fall (TF; �) and stem flow (SF; �) under Picea glehniiforest at (a) Cape Ochiishi Mire, (b) East Ochiishi Mireand (c) Bettoga Mire in the Ochiishi district, easternHokkaido, Japan. Samples were collected once every2 weeks from June to November 1997. Significancelevel of the Friedman’s test among BD, TF and SF was***P < 0.001.

200

100

0

200

100

0

200

100

0

Ele

ctric

al c

ondu

ctiv

ity (m

S m

–1)

(a)

(b)

(c)

J J A S O N

1997

SF

TF

BD

Fig. 4. Seasonal changes in pH of bulk deposition(BD; �) in open areas, throughfall (TF; �) and stemflow (SF; �) under Picea glehnii forest at (a) Cape Ochi-ishi Mire, (b) East Ochiishi Mire and (c) Bettoga Mire inOchiishi district, eastern Hokkaido, Japan. Sampleswere collected once every 2 weeks from June to Novem-ber 1997. Significance levels of Friedman’s test amongBD, TF and SF were **P < 0.01; *P < 0.05; (ns), notsignificant (i.e. P > 0.05).

7

6

5

4

3

7

6

5

4

3

7

6

5

4

3

1997

pH

TF

BD

SF

(a)

(b)

(c)

ns

J J A S O N

Effect of fog on nutrition of bogs 593

ponents, Na+, Mg2+, SO42– and Cl–, in throughfall

and stem flow were significantly higher than inbulk deposition (Figs 5,6); this tendency wasclearly observed in October, although there weresome exceptions.

K+ in throughfall and stem flow showed twopeaks in July–August and late October–Novem-ber (Fig. 5). NH4

+, NO3– and HCO3

– concentra-tions in precipitation showed occasional peaks, butthe concentrations of these ions in July and Octo-ber did not show remarkable peaks (Figs 5,6).NH4

+ concentrations in bulk deposition and stemflow were not significantly different, but NH4+ in

throughfall in Bettoga Mire was lower than that inbulk deposition (Fig. 5). NO3

– concentrations inthroughfall and stem flow were occasionally lowerthan that in bulk deposition (Fig. 6).

DISCUSSION

Precipitation chemistry in the Ochiishi Mires and the determining factors

From a comparison of chemical properties betweenbulk deposition and throughfall (or stem flow), itis clear that P. glehnii forests modify the chemicalproperties of precipitation. The factors importantin this chemical modification are dissolution ofatmospheric deposition in the canopy and theleaching of minerals from leaves, branches and

Fig. 5. Seasonal changes in cation (Na+, Mg2+, Ca2+,K+, NH4

+) concentrations in bulk deposition (BD; �) inopen areas, throughfall (TF; �) and stem flow (SF; �)under Picea glehnii forest at Cape Ochiishi Mire, EastOchiishi Mire and Bettoga Mire in Ochiishi district,eastern Hokkaido, Japan. Samples were collected onceevery 2 weeks from June to November 1997. Signifi-cance levels of Friedman’s test among BD, TF and SFwere ***P < 0.001; **P < 0.01; *P < 0.05; (ns), notsignificant (i.e. P > 0.05).

Fig. 6. Seasonal changes in anion (Cl–, SO42–, NO3

–,HCO3

–) concentrations in bulk deposition (BD; �) inopen areas, throughfall (TF; �) and stem flow (SF; �)under Picea glehnii forest at Cape Ochiishi Mire, EastOchiishi Mire and Bettoga Mire in Ochiishi district,eastern Hokkaido, Japan. Samples were collected onceevery 2 weeks from June to November 1997. Signifi-cance levels of Friedman’s test among BD, TF and SFwere ***P < 0.001; **P < 0.01; *P < 0.05; (ns), notsignificant (i.e. P > 0.05).

594 T. Iyobe et al.

stems when precipitation water passes through thecanopy (Eaton et al. 1973; Cronan & Reiners 1983;Parker 1983; Edmonds et al. 1991). In coniferousforests, in particular, large amounts of atmosphericdeposition are retained owing to the complexstructure of the needle leaves and the complexityof the canopies. Moreover, the rough bark ofP. glehnii plants provides a large surface area forprecipitation to come into contact with the plants.Therefore, the morphology of P. glehnii forestsleads to the effective accumulation of atmosphericdeposition on the canopy or the bark, and to theconsequent chemical interaction between precipi-tation and P. glehnii plants. Atmospheric deposi-tion in coastal regions is dominated by sea saltparticles from the ocean, which reach the vegeta-tion and land surface through wet, dry and occultdeposition (Farrell 1995). Na+ and Cl– dominatedin precipitation and their concentrations increasedin the order of Bettoga Mire < East OchiishiMire < Cape Ochiishi Mire. The negative correla-tion between distance from the coastline to eachmire and the precipitation concentration of Na+

and Cl– shows that sea salt comes to mires throughatmospheric deposition. Therefore, in mires inOchiishi large amounts of salts dissolved in pre-cipitation are carried to the soil and lead to highsalt concentrations in the peat pore water in themire forests (Haraguchi et al. 2003).

Seawater components, Na+, Mg2+, SO42– and Cl–

, in throughfall and stem flow were significantlyhigher than in bulk deposition (Figs 5,6). Cronanand Reiners (1983) suggested that most of theinorganic anions are transferred to vegetation fromatmospheric sources. This is also the case in Ochi-ishi mires because high Cl– and SO4

2– concentra-tions corresponded to the Na+ enrichment inthroughfall and stem flow. As a result, largeamounts of sea salt accumulated in the peat underP. glehnii canopies would be affected by chemicalmodification from precipitation in the forests. Ca2+

is a minor cation in seawater and is supplied by saltleaching from plant surfaces (Fig. 5; Parker 1983).

Throughfall and stem flow were typicallyenriched with K+ (Fig. 4). Studies on K+ cyclingwithin a forest show the process of K+ leachingfrom the canopy and the following uptake by plantroots (Tukey 1970; Eaton et al. 1973; Wood &Bormann 1975; Jonasson & Chapin 1985). Thus,the correspondence of high K+ concentration with

low pH precipitation results from canopy neutral-ization of acidic precipitation by ion exchange ofH+ on the leaf surfaces (Morton 1977; Hemond1980; Proctor 1994). The correspondence of highK+ concentration in throughfall and stem flowwith low pH of bulk deposition in Ochiishi Mires(Figs 4,5) would represent the K+ leached from thecanopy by precipitated acids reported by theseworkers. NO3

– and NH4+ concentrations in

throughfall and stem flow were occasionally lowerthan in bulk deposition (Figs 5,6). This impliesthat deposited atmospheric nitrate and ammo-nium were absorbed in the P. glehnii canopy asnutrients. This agrees with the report by Nearyand Gizyn (1994) that the exhaustion of NO3

– andNH4

+ in stem flow was the result of uptake by theconiferous canopy.

Seasonal changes in precipitation chemistry

The values of EC and concentrations of Na+, Cl–,Mg2+, SO4

2– and Ca2+ in throughfall and stem flowin October were much higher than those in midJuly, although there were two peaks in the concen-tration of these ions. Most chemical impurities inrainwater result from contamination by atmo-spheric particles (aerosols) of falling raindrops(Attiwill 1966); hence, the difference in ionic con-centrations in precipitation between October andJuly explains the difference in concentration ofaerosols in the atmosphere between October andJuly. During the 21 days in July in which precip-itation was <1.0 mm day-1, there were 13 fogdays. Fog would scavenge the aerosols in the atmo-sphere and the amount of dry deposition on thecanopy would be reduced. Thus, throughfall andstem flow were not enriched with sea salt in thedry deposition on the canopy, although there waslittle precipitation for 21 days. During the 9 daysin October in which precipitation was<1.0 mm day-1, there were only five fog days. Lowfog frequency would accelerate the accumulationof dry deposition on the canopy, resulting in theenrichment of sea salts in throughfall and stemflow in October. Accidental sea salt transport bystrong winds and heavy rain could be one of theprocesses of direct sea salt deposition from seawa-ter to mires. The comparison of precipitationchemistry between July and October, however,implies the contribution of fog to the deposition of

Effect of fog on nutrition of bogs 595

sea salt in mires. Precipitation in a P. glehnii forestin Syunkunitai, on the northern side of the Nem-uro Peninsula (facing the Okhotsk Sea) and justopposite the Ochiishi district, showed the sameseasonal trend as the Ochiishi Mires (Iyobe et al.1997). This implies a minor effect of wind direc-tion on sea salt deposition on the P. glehnii canopy.Scavenging of aerosols by fog particles could beone of the determining factors controlling the fluxof dry deposition on the canopy. Hence, inorganicsalt concentrations in precipitation were low dur-ing the high fog frequency season. In the low fogfrequency season (from October to November),there was no wash-off effect of fog particles in theatmosphere. Therefore, large amounts of aerosolsremained in the atmosphere to be deposited on theforest canopy. This resulted in the enrichment ofinorganic nutrients in bulk deposition, throughfalland stem flow when fog was rare.

Erisman (1993) pointed out the contribution ofoccult deposition to atmospheric deposition onforests by fog originating in high-altitude moun-tainous regions during periods of high fog fre-quency. In contrast, advection fog originates on theocean near the coastline and transports aerosols,including sea salt particles, from the ocean inland.Advection fog disappears owing to the heat supplyfrom the soil surface or forest stands during themovement inland (Yosida 1953). Yosida 1953)summarized this ‘temperature effect’ as one of thefunctions that forests serve in preventing fog inva-sion through the modification of air temperatureby forest evaporation or the condensation of fogparticles. The process of fog movement and disap-pearance causes the dispersion of the sea saltpresent in fog particles. Thus, the role of fog in theatmospheric transportation of sea salts toombrotrophic mires should be an important mech-anism for sea salt supply to the mires.

The bulk deposition pH in the Cape OchiishiMire was 4.3 (i.e. 1.3 units lower than the precip-itation pH equilibrium with atmospheric carbondioxide). Cronan and Reiners (1983) estimatedthat the H+ concentration in cloud water (includ-ing fog) is two- to three-fold higher than that inbulk deposition. Cape Ochiishi Mire, lying nearestthe coastline, experiences longer periods of fogthan the other two mires. The canopy of P. glehniiinteracts with the fog for much longer at the CapeOchiishi Mire than at the other two mires and,

hence, additional free acid derived from fog couldlower the pH of bulk deposition. The average pHof stem flow was occasionally lower than that ofbulk deposition or throughfall (Table 1), althoughthe pH of throughfall in Cape Ochiishi Mire wasexceptionally high in July. Similar observationshave been reported for many other coniferous for-ests (Feller 1977; Ugolini et al. 1977). Edmondset al. (1991) reported a high dissolved organic car-bon concentration in the stem flow of Pacific silverfir. In the Ochiishi mires, the average pH of stemflow was lower than that of bulk deposition,implying leaching of organic acids from plant sur-faces. Consequently, differences in the pH of porewater among communities could result fromleaching of organic acids from the P. glehnii forestitself, rather than to the release of organic com-pounds (e.g. humic and fulvic acids) during thedecomposition of peat sediments (A. Haraguchiet al., unpubl. data, 2003).

Interaction of rain and fog with the forest canopy

Many investigators have clarified the function ofthe forest canopy in capturing fog particles fromthe atmosphere (e.g. Fukutomi 1953). Fogremoves the deposited substances from the canopylayer when the fog particles are captured by thecanopy, and fog transports atmospheric particlesfrom the ocean inland. The interaction betweenatmospheric substances and fog or rain can besummarized in the following four processes: (i)wash-out of atmospheric substances by fog; (ii)atmospheric deposition on the forest canopy; (iii)wash-off of deposited substances from the canopyas throughfall and stem flow; and (iv) wash-off ofdeposited substances from the canopy by fog.While the fog covers the forest canopy, it removesatmospheric substances from the atmosphere(Fig. 7). Continuous fog scavenges salt particlesfrom the atmosphere, and fog drips wash off depos-ited salt before a rain event in the high fog fre-quency season. This aerosol scavenging effect offog decreases the chemical impurity of the subse-quent rain water. In contrast, in the low fog fre-quency season salts accumulate in the atmosphereand on the forest canopy (Fig. 7). Then the wash-out of aerosols in the atmosphere and wash-off ofdeposited chemicals on the forest canopy by rain

596 T. Iyobe et al.

water transfers the salts to the forest floor. As aconsequence, the inorganic salt concentrations inprecipitation are high during the season of low fogfrequency.

ACKNOWLEDGEMENTS

This work was made possible by field assistancefrom Mr K. Iwasawa and Mr H. Takashima fromthe Laboratory of Earth Planetary Science, Hok-kaido University of Education, Kushiro, Japan.Technical support for laboratory and data analysiswas provided by the Laboratory of Soil Science,Faculty of Agriculture, Hokkaido University, Sap-poro, Japan.

REFERENCES

ATTIWILL P. M. (1966) The chemical compositionof rainwater in relation to recycling of nutrients inmature eucalyptus forest. Plant and Soil 24: 390–406.

AZEVEDO J. & MORGAN D. L. (1974) Fog precip-itation in coastal California forests. Ecology 55:1135–1141.

BORMANN F. H. & LIKENS G. E. (1967) Nutrientcycling. Science 155: 424–429.

CRONAN C. S. & REINERS W. A. (1983) Canopyprocessing of acid precipitation by coniferous andhardwood forests in New England. Oecologia 59:216–223.

EATON J. S., LIKENS G. E. & BORMANN F. H.(1973) Throughfall and stem flow chemistry in anorthern hardwood forest. Journal of Ecology 61:495–508.

EDMONDS R. L., THOMAS T. B. & RHODES J. J.(1991) Canopy and soil modification of precipita-tion chemistry in a temperate rain forest. Soil Sci-ence Society America Journal 55: 1685–1693.

ERISMAN J. W. (1993) Acid deposition onto naturearea in the Netherlands; Part II. Throughfall mea-surements compared to deposition estimates.Water, Air, and Soil Pollution 71: 81–99.

FARRELL E. P. (1995) Atmospheric deposition inmaritime environments and its impact on terres-trial ecosystems. Water, Air, and Soil Pollution 85:123–130.

FELLER M. C. (1977) Nutrient movement throughwestern hemlock-western red cedar ecosystems insouthwestern British Columbia. Ecology 58: 1269–1283.

FUKUTOMI T. (1953) A theoretical study on thechanges of liquid water contents of intruding sta-tionary sea fogs due to the capturing action of a

Fig. 7. Sea salt transportmodel including fog and rainin the coastal Picea glehniimire forest canopy. (a) Duringthe high fog frequency periodfrom June to August and (b)during the low fog frequencyperiod from September toNovember.

Effect of fog on nutrition of bogs 597

forest in the coastal region. In: Study on Fogs inRelation to Fog-Preventing Forest (ed. T. Hori) pp.81–104. Tanne Trading, Sapporo.

HARAGUCHI A. (1996) Effects of pH on photosyn-thesis of five Sphagnum species in mires in Ochi-ishi, northern Japan. Wetlands 16: 10–14.

HARAGUCHI A., IYOBE T., NISHIJIMA H. &TOMIZAWA H. (2003) Acid and sea salt distri-bution in coastal peat mires with Picea glehnii for-est in Ochiishi, eastern Hokkaido, Japan. Wetlands23 229–235.

HEMOND H. H. (1980) Biogeochemistry of Tho-reau’s Bog, Concord, Massachusetts. EcologicalMonograph 50: 507–526.

IYOBE T., NISHIJIMA H., NISHIO F., HARAGUCHI

A. & TOMIZAWA H. (1997) Studies on the sea salttransport in fog and its effect on the chemical envi-ronment of wetland ecosystem in Ochiishi, easternHokkaido, Japan. Kushiro Ronshu 29: 53–75 (in Jap-anese with English summary).

JONASSON S. & CHAPIN F. S. III (1985) Signifi-cance of sequential leaf development for nutrientbalance of the cotton sedge, Eriophorum vaginatumL. Oecologia 67: 511–518.

LINDBERG S. E., LOVETT G. M., RICHTER D. D.& JOHNSON D. W. (1986) Atmospheric deposi-tion and canopy interactions of major ions in a for-est. Science 231: 141–145.

MORTON A. J. (1977) Mineral nutrient pathways ina Molinietum in autumn and winter. Journal ofEcology 65: 993–999.

NEARY A. J. & GIZYN W. I. (1994) Throughfalland stem flow chemistry under deciduous andconiferous forest canopies in south-centralOntario. Canadian Journal of Forest Research 24:1089–1100.

NISHIO F., ODA N. & TOMIZAWA H. (1995) Acidfog in Kiritapp Marsh. Kushiro Ronshyu 27: 169–184 (in Japanese).

OBERLANDER G. T. (1956) Summer fog precipita-tion on the San Francisco peninsula. Ecology 37:851–852.

PAOLETTI E., GELLINI R. & BARBOLANI E.(1989) Effects of acid fog and detergents on foliarleaching of cations. Water, Air, and Soil Pollution45: 49–61.

PARKER G. G. (1983) Throughfall and stem flow inthe forest nutrient cycle. Advances in EcologicalResearch 13: 58–133.

PATNAIK P. (1997) Handbook of Environmental Anal-ysis. Lewis Publisher, Boca Raton.

PRICE J. S. (1992) Blanket bog in Newfoundland.Part 1. The occurrence and accumulation of fog-water deposits. Journal of Hydrology 135: 87–101.

PROCTOR M. C. F. (1994) Seasonal and shorter-term changes in surface-water chemistry on fourEnglish ombrogenous bogs. Journal of Ecology 82:597–610.

TUKEY H. B. (1970) The leaching of substancesfrom plants. Annual Review of Plant Physiology 21:305–324.

UGOLINI F. C., MINDEN R., DAWSON H. &ZACHARA J. (1977) An example of soil processesin the Abies amabilis zone of Central Cascades,Washington. Soil Science 124: 291–302.

WALDMAN J. M., MUNGER J. W., JACOB D. J.,FLANGAN R. C., MORGAN J. J. & HOFFMANN

M. R. (1982) Chemical composition of acid fog.Science 218: 677–679.

WOOD T. & BORMANN F. H. (1975) Increases infoliar leaching caused by acidification of an artifi-cial mist. Ambio 1975: 160–162.

YOSIDA Z. (1953) General survey of the studies onfog-preventing forest. In: Study on Fogs, in Relationto Fog-Preventing Forest (ed. T. Hori) pp. 81–104.Tanne Trading, Sapporo.