1

Bulletin of Glaciological Research ,- (,**0) +ῌ+,῍Japanese Society of Snow and Ice

ArticleRelationship between seasonal trends in stream water chemistry and forest typein a snowy temperate region of northwestern Honshu, Japan
Makoto NAKATA
Graduate School of Science and Technology, Niigata University, Niigata 3/*ῌ,+2+, Japan(Received June ,3, ,**/; Revised manuscript accepted November 1, ,**/)

Abstract
Stream water chemistry was compared between neighboring Cryptomeria japonica evergreen
coniferous (CFs) and deciduous broad-leaved forests (BFs) in a snowy temperate region of northwestern Honshu, Japan. The stream water chemistry of the study area was characterized by extremely
high concentrations of Cl῍ and Naῌ, which were thought to be mostly derived from sea salts. There
were negative correlations between runo# and the concentrations of many ions, especially Cl῍, Naῌ,and Mg,ῌ, from spring to mid-autumn. However, these correlations became weak in late autumn andwinter due to the high inﬂux of sea salt components transported by the northwest monsoon, as wellas the acid shock phenomenon. As the runo# increased from late February to mid-March, the electricalconductivity (EC) of stream water rose abruptly, reached a maximum in early March, and then fell
abruptly. The ﬂuctuations during this period were extremely sharp in BFs. The pH of stream water in
BFs (0.-ῌ0.2) was signiﬁcantly higher than in CFs (0.+ῌ0./) from spring to mid-autumn. The pH in lateautumn and winter was lower than that from spring to mid-autumn, especially in BFs (/./ῌ0.-). Thismay be induced by the decline in the acid-neutralizing capacity (ANC), the supply of sea salts causedby the northwest monsoon, and the increase in NO-῍ concentration in late autumn and winter. Boththe snow depth and total of chemical components in snow were greater in BFs than in CFs due to thedi#erence in the accumulation pattern of snow on tree crowns and the ground. Approximately 2*ῌ ofthe chemical components in the snow were estimated to originate from sea salt. These chemicalcomponents in the snow dissolved more rapidly in BFs than in CFs from late winter to early spring
due to the di#erence in the quantity of sunlight received at the snow surface and the density of thesnowpack. Two patterns of pH drop (as low as /..ῌ/.0) in stream water were recognized from late
winter to early spring: one induced by an early snowmelt in BFs, and the other by the dilution of the
ANC during the peak ﬂow in the snowmelt season in both BFs and CFs. Acid shock was evident when
the weather improved following cold snowy days in this snowy temperate region of Japan. Thistendency was clearer in BFs than in CFs due to the di#erent snowmelt patterns between the twoforest types.

+.

Introduction

Stream water chemistry is a#ected by the naturalenvironment, e.g., geology, climate (or weather), vegetation (or biology), and soil, as well as human impacts
such as acid deposition, forest management, and landuse (Kato, +333). Several studies on the e#ect of vegetation on stream water chemistry have been conducted outside Japan. In the northeastern and eastern
United States, Johnson et al. (,***) reported a higherorganic acidity in stream water in a spruce-ﬁr-whitebirch catchment than in a broad-leaved forest, while

the broad-leaved forest had higher net production
rates of basic cations. Johnson and Swank (+31-) studied the input-output budgets in catchments coveredby di#erent vegetation types, and smaller losses ofbasic cations were recognized for broad-leaved oryoung forests than non-forest vegetation types. In
France, Lelong et al. (+33*) also recognized smaller
losses of basic cations in an old beech forest than inother vegetation types (young spruce forest and grassland). Lower stream water pH was observed duringstormﬂow in a forested catchment than in grasslandin the UK, although the pH was almost the same
during baseﬂow (Neal et al., +323). Grieve (+33*) re-2

Bulletin of Glaciological Researchported higher concentrations of mean dissolved organic carbon (DOC) and sulfate (SO.,῍) in a forested
catchment than in moorland catchments in southwestern Scotland. Edberg et al. (,**+) reported thatboth the basic cation concentration and pH of stream
water during the peak snowmelt ﬂow were lower inwatersheds above the tree line than in those of wetlands and forests in Sweden.
In Japan, Ishiguro et al. (+32,) reported that thechemistry of stream water ﬂowing from a forested
watershed was more stable than that from a reclaimed
watershed. Satoh et al. (+33.) reported a higher totalorganic carbon (TOC) concentration of stream water
during a rain event in watersheds covered by naturalforests than those covered by Sasa kurilensis Makino
et Shibata and/or Sasa senanensis Rehder (dwarf bamboo). The inﬂuences of forest management, such as
harvesting (Kato, +333; Hamabata, ,***) and forest age(Hirose et al., +322; Ohrui et al., +33.; Asano et al.,+330), have been well studied with reference to nitrate(NO-῍) dynamics. Some studies have compared thestream water chemistry of broad-leaved and planted
coniferous forests (Hirose et al., +322; Tokuchi et al.,+33+; Morisada and Hirai, +33/). However, they foundno distinct correlations between stream water chemistry and forest type. This may be attributable to an
insu$cient sampling frequency, such as once amonth, or a restricted study period, such as less than
one year. No studies have examined the e#ect offorest type on stream water chemistry all the year
around in Japan.
The emissions of air pollutants, especially sulfur
emissions from Asian countries, have increased rapidly since the +3/*s, in contrast to North Americanand European countries, where emissions have beenleveling o# since the +32*s (Lefohn et al., +333). Air
pollution emissions from East Asian countries andchemical components originating from sea salt aretransported to Japan by westerly winds and the northwest monsoon, especially in the regions of northwestern Honshu adjacent to the Sea of Japan(Ohizumi et al., +331). Of the total sulfur deposition in
Japan, an estimated .*ῌ had an East Asian continental source (Ichikawa et al., +332). Fukuzaki et al. (,**+)
observed greater deposition of non-sea-salt SO.,῍ andhydrogen (Hῌ) ions in winter precipitation in the regions along the coast of the Sea of Japan. The e#ects
of snowmelt water on the freshwater and aquaticbiota, the so-called acid shock phenomenon, in northern Europe and eastern Canada have been reported
since the +31*s (e.g., Hagen and Langeland, +31-;
Je#ries et al., +313). In central to northwestern Japan,
Shimizu and Tsuboyama (+33*) and Sakurai (+332)
reported a decrease in ion concentration due to snowmelt water and the absence of the acid shock phenomenon. Fukuzaki and Ohizumi (+33/) predicted thatthe phenomenon of acid shock might be milder in thesnowy temperate regions of Japan than in northern
Europe and that it would appear from late winter toearly spring. However, an increased ion concentration
and a drop in the pH of stream water were recognizedin mid-winter as well as in the snowmelt season in asnowy temperate watershed in northeastern Japan(Suzuki, +33/). Suzuki (+330, ,**-) also reported seasonal trends in the stream water chemistry in thesame watershed.
The purpose of this study is to clarify the e#ect offorest type on the seasonal trends in stream waterchemistry by comparing the neighboring small watersheds covered by a Cryptomeria japonica D. Don evergreen coniferous forest and a deciduous broad-leaved
forest in the snowy temperate region of northwestern
Honshu, Japan. The inﬂuence of the northwest monsoon and snowmelt on stream water chemistry is also
discussed. In central to northern Japan, most mountainous areas are covered by deciduous broad-leaved
forests or planted coniferous forests, especially thoseof C. japonica. Therefore, a study to clarify the inﬂuence of forest types on the stream water chemistry isimportant for sound forest management given theincreasing air pollutant emissions from East Asian
countries and their consequent long-distance transport to Japan.

,.

Materials and methods

Study area
The study area was located in Niigata Prefecture,northwestern Honshu, Japan, -/ km southeast of thecoast of the Sea of Japan (-1῎.+῍N, +-3῎+2῍E; Fig. +).
The elevation of the watersheds ranged from ,3* to.2* m. The aspect and average inclination of the slopes were W to WNW and ,-ῌ-*῎, respectively. The
study watersheds were dominated by planted C. japonica forests and natural secondary forests composed of deciduous broad-leaved trees, including Quercus mongolica Fischer ex Turcz. var. grosseserrata Rehder et Wilson, Sorbus alnifolia C. Koch, and Acer mono
Maxim. The parent rock in the study area was chert(Niigata Prefectural Government, +32-). The annual
mean temperature in the study area estimated using
data from the nearby Niitsu weather station (-1῎.1῍N,+-3῎*/῍E; - m elev.) was +*.*῏ at .2* m elevation and++.,῏ at ,3* m from +313 to ,***. Similarly, the monthly mean temperature of the coldest month (February) was ῍+..῏ (.2* m elev.) and ῍*.,῏ (,3* m). The
annual mean precipitation from +313 to ,*** was +,2,2
mm at the Niitsu weather station. No meteorologicalsnow depth data were available for the study area.
Although the mean maximum snow depths at theNiitsu and Tsugawa (-1῎.*῍N, +-3῎,1῍E; +** m elev.)
weather stations from +32- to ,*** were 02 and +++ cm,
respectively, the author observed maximum snow
depths in the study area to be +0. and +33 cm in +331
,.+.

3

NakataFig. +.

Location of the study area.

and +332, respectively.
Methods
Four small neighboring watersheds were chosen
as study sites (Fig. +); two were covered by C. japonica
evergreen coniferous forests (CF+ and CF,) and two
were covered by deciduous broad-leaved forests (BF+
and BF,). The areas of the four watersheds were ,.+(CF+), *.0. (CF,), +.3* (BF+), and *./1 (BF,) ha. Stream
ﬂow (runo#) was measured and water samples werecollected weekly in each stream for one year (June+330ῌMay +331). Stream water was collected completely at a cascade in each stream using a large
plastic bag. The runo# was calculated by dividing thevolume of the collected water by the collecting time.
Stream water was measured and sampled roughly
between ++ : ** and +- : ** on each sampling day. The
daily ﬂuctuation in runo# with temperature has beenreported for the snowmelt season (Ikeda, +333). Since
the ﬁeld survey in this study during the snowmelt
season was conducted on a day with a rather low
temperature, the inﬂuence of the daily runo# ﬂuctuation was considered to be small. A snow survey was
carried out weekly from +3 January to +1 April in +331.
Snow depth was measured and snow samples werecollected in CF+ (--* m elev.; N1/ῐW) and BF+ (-.* melev.; N1*ῐW). Two replicate snow core samples werecollected by inserting a PVC pipe (, m long, /./ cm
diameter) into the snow vertically to the ground surface. The collected snow samples were weighed, andallowed to melt at room temperature.
The following chemical properties of the collected
stream water and snowmelt water samples were measured. The pH was measured using a pH meter with aglass electrode (N-2F; Horiba, Japan). Electrical conductivity (EC) was measured with a conductivity meter (ES-+.; Horiba). The inorganic ions (i.e., anions:chloride (Cl῍), NO-῍, and SO.,῍; cations: sodium (Naῌ),
ammonium (NH.ῌ), potassium (Kῌ), calcium (Ca,ῌ),and magnesium (Mg,ῌ)) were measured using ion chromatography (LC-+*A; Shimadzu, Japan) after each,.,.

sample was ﬁltered through a membrane ﬁlter (poresize, *../ mm). The acid-neutralizing capacity (ANC) of
stream water was calculated as the di#erence between
the sums of anions (Cl῍, SO.,῍, and NO-῍) and basic
cations (Naῌ, Kῌ, Ca,ῌ, and Mg,ῌ) (Inoue and Satake,,***).
The temperature in the study area was estimatedusing data from the Niitsu weather station. The precipitation data during the study period were from the
Muramatsu weather station (-1ῐ.,ῌN, +-3ῐ++ῌE; ,/ melev.), the station nearest the study area. The maximum snow depth referred to data for both the Niitsu
and Tsugawa weather stations.
Statistical analyses were performed using SPSS
2.* (SPSS, USA). The signiﬁcance of di#erences wastested using the Mann-Whitney U-test or Wilcoxon’s
signed-ranks test, and Spearman’s coe$cient of rankcorrelation was used to test correlations. Cluster analysis for the ion species of stream water was carriedout using the Community Analysis Package (Pisces
Conservation, UK). The concentrations of each ion
species were standardized and dissimilarity among
the ion species was calculated using the Euclidean
distance in this cluster analysis.

-.

Results and discussion-.+. Seasonal trends in the chemical composition of
stream water
The chemical properties for each stream water
are summarized in Table +. The data analysis was
conducted separately for two periods: from spring to
mid-autumn (June-October +330 and April-May +331)
and from late autumn to winter (November +330ῌ
March +331), in order to study the inﬂuence of sea salts
transported by the northwest monsoon, as well as theseasonal trends in the NO-῍ concentration and pH of
the stream water.
The correlation coe$cients for the runo# between each stream (Table ,) were extremely high (r῎*.3,-ῌ*.323, p῎*.***; Spearman’s rho), showing highsynchronization of the four stream ﬂows. The correlation coe$cients were especially high in the same forest types (r῎*.323 between CF+ and CF, and r῎*.3/2
between BF+ and BF,). The average runo# for thefour streams ranged from *.1/ to *.3- L sec῍+ ha῍+ in lateautumn and winter, which were +.,1ῌ+.00 times higher
than those from spring to mid-autumn (*./-ῌ*.0/ L sec῍+ha῍+) for all streams (p῏*.*/; Mann-Whitney), reﬂecting the weather characteristics of northwestern Honshu facing the Sea of Japan. The most abundant ionsin the stream water were Cl῍ and Naῌ (generally ca.
+2*ῌ,,* mmolc L῍+). Ca,ῌ and Mg,ῌ averaged ca. /*ῌ3*mmolc L῍+, and the SO.,῍ levels were ca. /*ῌ0* mmolc L῍+
year-round. Although the average runo# in late autumn and winter was higher than that from spring to
mid-autumn, the average Cl῍, Naῌ, and Mg,ῌ concen-

4Bulletin of Glaciological Research

Table +.
Runo#
Stream (L sec
῎+
ha῎+)

EC
(mS m῎+)Chemical properties for each stream water (average῏standard error).
pH

Cl῎(mmolc L῎+)

NO-῎
SO.,῎
Na῍
K῍
Ca,῍
Mg,῍
ANC
(mmolc L῎+) (mmolc L῎+) (mmolc L῎+) (mmolc L῎+) (mmolc L῎+) (mmolc L῎+) (mmolc L῎+)

From spring to midoautumn (JuneῌOctober +330 and AprilῌMay +331); N ῐ -++0.-῏+./a* .3.2῏+.+a-.2*῏*.*/a* 0.--῏*.*-a ,*0.,῏..0aCF+*./3῏*.+,ab*cdbab*./.῏*.++ *-.-.῏*.*/ * 0.,3῏*.*- * +3,./῏/.+ **.,῏*.+b* /..,῏+.+b*CF,*.0/῏*.+.ac*-.-1῏*.*/b* 0./*῏*.*.b* +1-./῏..*c*2.-῏+.+c* .3.1῏+.+a*
BF+
bd
c
b
b
*./-῏*.+, *-./3῏*.*/
0./-῏*.*- * +2/.0῏../+.1῏*..d* 0*.3῏+..c
BF,
From late autumn to winter (November +330ῌMarch +331); N ῐ ,,CF+
,2.0῏+..a*..*-῏*.*1a* 0.,.῏*.*/a ,+,.-῏/.2a*.1/῏*.*3a*CF,*.13῏*.*3a*-.03῏*.+*b* 0.+*῏*.*/b* ,,,.-῏1./b**.3῏*.-b**.3-῏*.+-a*-.2*῏*.+1b* 0.+2῏*.*0ab* ,*-.0῏3.3a* +/.*῏+./c*
BF+*.22῏*.+,a*-.2-῏*.+.ab 0.+1῏*.*0ab* ,*,.2῏2.+a..+῏+.,d*BF,+20.+῏-.*ab+21.1῏-.2a+2+.,῏..*b+23./῏-.3a/.-῏*.-a,.0῏*.-b../῏*..c,.0῏*.-b*3+.0῏+-.*a* 11./῏+.*a*
0..-῏+*.1b /2.,῏+.,b*
02.0῏ 1.2ab //.*῏+.,c*2..-῏+1.*a 02.*῏+.*d22.+῏+-.3a*0/.2῏++..a*
11.3῏ 2.2ab*
30.-῏+1.-b*/*./῏+.*a +3*.-῏,./a/,..῏*./ab* +3*.2῏-.0a//./῏,./b* +30.1῏1.-a0,.1῏,.-c +3*.3῏/.3a../῏*./ab-.,῏*..c/.-῏*.2a...῏*.0b*/2.+῏,.1a*...1῏,.3b/+.*῏-.1c
0/.*῏+,.2a.0.*῏/.-a*-..*῏../b*././῏/.1a*0-.1῏++.+c*

2..0῏+.1a*
1*.2῏,.,b*00.0῏-.-c*
1,.3῏,.0b

Notes; Di#erent letters indicate signiﬁcant di#erences among the four streams by multiple comparisons with the Friedman test (Wilcoxon’s
signedoranks test, pῑ*.*//0ῐ*.**2-).
“*”indicates a signiﬁcant di#erence between the two separated periods for each stream by MannoWhitney U-test (pῑ*.*/).

Table ,. Correlation coe$cients (Spearman’s rho) for
the runo#5 EC, and pH between each stream.
Stream

Runo#

EC

pH

CF+ῌCF,
CF+ῌBF+
CF+ῌBF,
CF,ῌBF+
CF,ῌBF,
BF+ῌBF,

*4323
*43-3
*43,*43,2
*43/.
*430*

*422*
*41/*
*4/./
*4203
*402/
*4222

*41**4.1.
*4/*,*40.*40/2*43*2

Note; All correlation coe$cients were pῑ*.*+.

trations for all streams were also higher in late autumn and winter than from spring to mid-autumn (pῑ*.*/ in three and two of the four streams for Mg,῍ andCl῎, respectively). This may have been attributable tothe high inﬂux of chemical components originatingfrom sea salt transported by the northwest monsoon.
An inﬂux of +,.+ kmolc ha῎+ yr῎+ of chemical components originating from sea salt was measured in aforested watershed in Niigata Prefecture, and most of
this was concentrated in late autumn and winter(Nakata et al., unpublished data).
The K῍ concentration was extremely low relative
to the other ions, i.e., ca. ,ῌ/ mmolc L῎+ year-round.
Nevertheless, the K῍ concentration increased to between 2 and +2 mmolc L῎+ in early to mid-November,which may have been a result of leaching from fallen
leaf litter.
The NO-῎ concentration was signiﬁcantly higher
in late autumn and winter (Fig. ,a) than from spring to
mid-autumn for all streams (pῑ*.*/; Mann-Whitney)
indicating a sound forest condition with respect to thenitrogen cycle (Aber et al., +323; Stoddard, +33.). It
di#ered markedly between study sites; the averageNO-῎ concentrations for the four streams throughout
the study period were in the order CF+ῒBF+ῒBF,ῒ
CF, (pῐ*.***; Wilcoxon’s signed-ranks test). This may
reﬂect the di#erent mineralization process of nitrogenin each watershed. However, no mineralization data
were available in this study.

The Cl῎, NO-῎, SO.,῎, Na῍, and Mg,῍ concentrations were highest on / March. Although the Ca,῍ andK῍ concentrations were also high on / March, they
were highest in other seasons. The ANC was signiﬁcantly lower in late autumn and winter (-..*ῌ0-.1
mmolc L῎+ on average) than from spring to midautumn (0/.2ῌ30.- mmolc L῎+ on average) for all streams(pῑ*.*/; Mann-Whitney).
Watershed geology strongly a#ects the concentrations of ions in stream water (Bailey et al., +321).
Table - compares the stream water chemistry for awatershed with the same geology (i.e., chert) in Nagano Prefecture (Sakurai et al., +332; Fukushima et al.,,***), which is located inland on Honshu and is adjacent to Niigata Prefecture. Although the ion concentrations are variable depending on the runo#, therelative proportions of major basic cations are roughly constant (Fukushima et al., ,***). Of the fourbasic cations, the proportion of Ca,῍ was highest (0/ῌ2*ῌ) in both streams in Nagano Prefecture, whereasthat of Na῍ was low (ca. +*ῌ). In contrast, the proportion of Na῍ exceeded /*ῌ in the study area, and Ca,῍
was ca. ,*ῌ, which was comparable to Mg,῍. The
proportions of Na῍ and Mg,῍ were higher in lateautumn and winter than those from spring to midautumn in the study area. The average concentrationof Cl῎ in the study area was ca. ,** mmolc L῎+, which
was more than ten times higher than that in Nagano
Prefecture. The dissolution rate of Cl῎ from the parent
rock is extremely low (Fukushima et al., ,***). Therefore, most of Cl῎ in the stream water was considered
to have originated from precipitation or atmosphericdeposition, and were also estimated to be of sea salt
origin in the regions of northwestern Honshu adjacent to the Sea of Japan (Yasuda et al., +33+; Suzuki
and Endo, +33.). The concentrations of Cl῎ and Na῍increased in the following order: mid- to southern Nagano Prefecture, northern Nagano Prefecture, and Niigata Prefecture. This corresponds to the geographicalgradient from the inland part of Honshu toward the
Sea of Japan, reﬂecting the inﬂuence of sea salts.

5

NakataFig. ,. The ﬂuctuation in (a) NO-῎ concentration, (b) EC, and (c) pH relative to average runo# in the stream water of
di#erent forest types.
Notes: ῌῐῌ, CF+; ῌῒῌ, CF,; ῌ῏ῌ, BF+; ῌῑῌ, BF,; vertical bar, average runo# from the four streams.

The high contribution of sea salts to the stream
water chemistry in the study area was also indicatedin a cluster analysis. Figure - shows dendrograms
indicating the a$nity of the ion species in each stream. Cl῎, Mg,῍, and Na῍ were very similar in all four
streams, suggesting that most of these had the same
origin, i.e., sea salt.
Table . shows correlation coe$cients (Spearman’s rho) between runo# levels and chemical properties in each stream. There were signiﬁcant negative
correlations between runo# levels and ion concentrations, except for NO-῎ and K῍, from spring to mid-autumn. This may result from the dilution of ion
concentrations by the runo# water during hydrological events (Kumagae et al., ,***). The correlation coe$cients were especially high for Na῍, Cl῎, and Mg,῍.
However, these correlations weakened in late autumn
and winter, which may have been caused by the highinﬂux of chemicals originating from sea salt brought
in by the northwest monsoon. Another reason for the
weak correlation between ion concentrations and runo# levels in late autumn and winter was the rise in ion
concentrations accompanied by the increase in runo#
induced by snowmelt, resulting in an acid shock phe-6Bulletin of Glaciological Researchuated between - and . mS mῌ+ from spring to midautumn, and fell to ,..ῌ-.* mS mῌ+ at times of highruno#. The relatively low EC and low ANC (averagevalue῎+** mmolc Lῌ+ in all study streams) indicatedthe susceptibility of the study streams to acidiﬁcation(The Committee for Acid Deposition Measures, ,**.).
There were strong negative correlations between EC
and runo# from spring to mid-autumn (p῎*.*+; Spearman’s rho; Table .). However, the negative correlation
weakened in late autumn and winter and there wereno signiﬁcant correlations between EC and runo# in
CF (p῏*.*/). This may have been due to the highinﬂux of chemicals originating from sea salt and theacid shock phenomenon. Although the average runo#
in late autumn and winter was higher than that fromspring to mid-autumn, the runo# decreased graduallyfrom mid-December +330 to mid-February +331, resulting in a gradual increase in EC. As the runo# increased from late February to mid-March, EC rose
abruptly, reached a maximum on / March, with peaksof 0.0-, 0.*/, /.+3, and ..13 mS mῌ+ for BF+, BF,, CF+,and CF,, respectively, and then fell abruptly. The
ﬂuctuations during this period were extremely sharpin the BFs, and the concentrations of all ions varied in
the same manner during this period. Acid shock wasevident, and was clearer in the BFs than in the CFs.
After reaching a maximum on / March, the EC in the
BFs was lower than that in the CFs until the end of
March.

Fig. -. Dendrograms indicating the a$nity of ion
species in each stream.

nomenon. There were strong positive correlations between runo# levels and the NO-ῌ concentration in CF+ and BF+ from spring to mid-autumn (p῍*.***). Thisphenomenon was explained as an e#ect of the washout of NO-ῌ, which was held in the upper soil layers,
with increased water movement near the ground surface during hydrological events (Kumagae et al., ,***).
The ﬂuctuation in EC relative to runo# in thestream water of di#erent forest types is shown in Fig.
,b. The EC of the four streams ﬂuctuated in a similarmanner, especially in the same forest types (r῍*.22*
between CF+ and CF, and r῍*.222 between BF+ and
BF,, p῍*.***; Spearman’s rho; Table ,). The EC ﬂuct--.,. Seasonal trends in stream water pH in di#erent
forest types
The ﬂuctuation in pH relative to runo# in thestream water of di#erent forest types is shown in Fig.
,c. The stream water pH ﬂuctuated in a similar manner in the same forest types (r῍*.1*- between CF+ andCF, and r῍*.3*2 between BF+ and BF,, p῍*.***; Spearman’s rho; Table ,). However, the correlation coe$cients were relatively low between the di#erent
forest types (r῍*..1.ῌ*.0/2). The pH of stream water in
BFs was signiﬁcantly higher than in CFs from spring
to mid-autumn (p῍*.***; Wilcoxon’s signed-ranks
test; Table + and Fig. ,c). The pH in BFs was 0.-ῌ0.2(average 0./* and 0./- for BF+ and BF,, respectively).
The pH in BFs was especially high during the summer
drought (0.1ῌ0.2). In contrast, the pH in CFs was relatively low, ranging from 0.+ to 0./ (average 0.-- and0.,3 for CF+ and CF,, respectively) from spring to
mid-autumn. The soil type in this area was brown
forest soil and did not di#er between the two forest
types (Niigata Prefectural Government, +32-). However, the stemﬂow of C. japonica is extremely low (῎..*; Sassa et al., +33+), and organic acids and SO.,ῌ
leached from its bark tend to acidify its soil (Matsuura,+33,; Sakai, ,**+). This might lower the pH in thestream water of CFs. However, deﬁnite evidence of adi#erence in pH between CFs and BFs from spring to7NakataTable -. Comparison of stream water chemistry of this study to other watersheds with the same geology (i.e., chert) in
Nagano Prefecture.
Cl῎
NO-῎
SO.,῎
(mmolc L῎+) (mmolc L῎+) (mmolc L῎+)

StreamNa῍K῍Ca,῍(mmolc L῎+) (mmolc L῎+) (mmolc L῎+)

From spring to midῌautumn (JuneῌOctober +330 and AprilῌMay +331); N ῏ -+
CF+
,*04,
+04.342
+204+
CF,
+3,4/
*4,
/.4,
+2141
BF+
+1-4/
24.341
+2+4,
BF,
+2/40
+41
0*43
+234/
Average

+234/

040

/-41

From late autumn to winter (November +330ῌMarch +331); N ῏ ,,CF+,+,4,240/*4/CF,,,,4*43
/,4.
BF+
,*-40
+/4*
//4/
BF,
,*,42
.4+
0,41
AverageMg,῍(mmolc L῎+)

/4,40
.4/
,40

3+40
0.40240
2.4-

114/
/24,
//4*
024*

+204+
(/04+)

-42
(+4+)

114,
(,-4-)

0.41(+34/)+3*4+3*42
+3041
+3*43

.4/
-4,
/4.4.

/24+
..41
/+4*
0/4*

2.40
1*42
0040
1,43

,+*4-

+,4,

//4-

+3,4,
(/34+)

.4.
(+4-)

/.41
(+042)

1-41(,,41)

Northern part of Nagano Pref4(Source; Sakurai et al., +332)

+243

24,

+.340

+*/41
(+-4-)

341
(+4,)

/+04/
(0/4+)+0+4(,*4-)Mid- to southern part of Nagano Pref4(Source; Fukushima et al45 ,***)

++42

ῌ

.04*

1340
(34-)

/40
(*41)

02,41
(1343)

204.
(+*4+)

Note; The ﬁgure in parentheses indicates the relative composition (ῌ) of each basic cation to total ones.

Table .. Correlation coe$cients (Spearman’s rho) between runo# levels and chemical properties in eachstream.
Cl῎

NO-῎

K῍

Mg,῍

ANC

From spring to midoautumn (JuneῌOctober +330 and AprilῌMay +331); N ῏ -+CF+
῎*4/00** ῎*4-+0
῎*4-03**41/-** ῎*4.-/* ῎*41-/** ῎*4,*+CF,
῎*410+** ῎*4-30* ῎*400/** *4+*+*4/*,** ῎*4122** ῎*4**+
BF+
῎*422,** ῎*4110** ῎*4/11** *4013***4,/*
῎*41..** ῎*4./3**
BF,
῎*423/** ῎*41-3** ῎*4103** *4,/3
῎*4.+.* ῎*42..***4,/2

῎*4/-1**
῎*4..,*
῎*4.-.*
῎*4-0*

῎*4-+,
῎*400.**
῎*41*3**῎*413***

῎*4/0.**
῎*4.1***῎*4/2/**
῎*4.*,*

From late autumn to winter (November +330ῌMarch +331); N ῏ ,,CF+
῎*4,,.
῎*4-*+
῎*4*/0*4.3,*
῎*4-00῎*4*,3CF,῎*4+.2῎*4+-,
῎*4*01*4+.,*4,-*
῎*4+*2BF+
῎*4.3-* ῎*4*32
῎*4-0+*4,/+῎*4/+.* ῎*4/03**
BF,
῎*4/+2* ῎*4*++῎*4-0/*4*-+῎*4.1-* ῎*4/-.*῎*4,-1῎*4+,2῎*4.,3*῎*4,2*

῎*4*-+
῎*4*01῎*4.*0῎*4/,-*

῎*4,//
῎*4,,/
῎*4,03῎*4,**

EC

pH

SO.,῎

Na῍

Ca,῍

Stream

*4--2
*4+01
*4*1/
*4*11

Notes; * pῐ*.*/, ** pῐ*.*+.

mid-autumn was not obtained in this study. The pH of
stream water was negatively correlated with runo#
from spring to mid-autumn (pῐ*.*/; Spearman’s rho;
Table .), except for CF+. The correlation coe$cient
was extremely high in BFs (r῏῎*.110 and ῎*.1-3 for
BF+ and BF,, respectively, p῏*.***). The acidiﬁcationof freshwater during hydrological events was explained as a depression of alkalinity due to the dilution of basic cations and an increase in strong acidanions (Tranter et al., +33.). Almost all of the basic
cations in the four streams in this study had negative
correlations with the runo# from spring to midautumn. In contrast, of the strong acid anions, Cl῎ hada negative correlation, NO-῎ had a positive correla-tion, and SO.,῎ had both positive and negative correlations with the runo# during this period (Table .). This
resulted in a signiﬁcantly negative correlation (pῐ*.*/; Spearman’s rho) between the ANC and runo# in
all streams from spring to mid-autumn. The ANC
correlated with pH signiﬁcantly and positively (r῏*../0, p῏*.*+* for CF+, r῏*.0-3, *.0,0, and *.0,., p῏*.*** for CF,, BF+, and BF,, respectively). The washout of organic acids from forest soils was proposed asanother cause of the acidiﬁcation of stream water
induced by rainstorms (Jansson and Ivarsson, +33.).
The pH in late autumn and winter was lower thanthat from spring to mid-autumn (Table + and Fig. ,c).
That was especially evident (p῏*.***; Mann-Whitney)

8

Bulletin of Glaciological Research

in BFs (average 0.+2 and 0.+1 for BF+ and BF,, respectively). There were no signiﬁcant di#erences in pH
between BFs and CFs (pῐ*.*/; Wilcoxon’s signedranks test) in late autumn and winter. A similar ﬂuctuation pattern of stream water pH between warm andcold seasons was reported in a snowy temperate areaof northeastern Japan (Suzuki, ,**/). The drop in stream water pH in late autumn and winter was attributed to the lower ANC. Almost all strong acid anions
increased in late autumn and winter. Conversely, ofthe basic cations, Naῌ and Mg,ῌ increased slightly, but
Ca,ῌ decreased considerably in those periods. Therefore, the ANC became signiﬁcantly lower in late autumn and winter than from spring to mid-autumn inall four streams (Table +). Another reason for the drop
in stream water pH in late autumn and winter isthought to be the supply of sea salts (Neal et al., +320;
Vogt and Muniz, +331) caused by the northwest monsoon. Winter precipitation or snow in the regions ofnorthwestern Honshu adjacent to the Sea of Japan
contains many sea salt components (Yasuda et al.,+33+; Suzuki and Endo, +33.). Cation exchange withsea salt occurs in the soil and Hῌ is consequently
released (Haraguchi et al., ,**-). There were no signiﬁcant correlations between pH, ANC, and runo# inlate autumn and winter (pῐ*.*/; Spearman’s rho). However, the NO-῍ concentration had a signiﬁcantly negative correlation with pH (r῎῍*..-0, p῎*.*.- for CF+, r῎
῍*.0*3, p῎*.**- for BF+, and r῎῍*.0./, p῎*.**+ for BF,), except for CF,. Furthermore, the NO-῍ concentration was signiﬁcantly higher in late autumn and winterthan from spring to mid-autumn in all four streams (p῏*.*/; Mann-Whitney; Table +). Therefore, the pH ﬂuctuation in late autumn and winter may be regulated
primarily by the NO-῍ concentration (Suzuki, ,**-).
The stream water pH was considerably lower inlate winter and early spring (,1 Februaryῌ++ March),
and was as low as /..ῌ/.0. At that time, the pH in BFs
was lower than in CFs. The pH in BFs had two minima(,1 February and ++ March), whereas there was only
one in CFs (++ March). The ANC was extremely low(/.*ῌ+1.0 mmolc L῍+) when the pH in all streams had thelowest value on ++ March. An experiment demonstrated that the propagation of two Japanese trout
species was reduced at a pH below 0 (Ikuta et al., +333).
Although the streams in this study were too small forsuch freshwater ﬁsh, the lower pH (/..ῌ/.0) in late
winter and early spring may inﬂuence the aquaticbiota. However, there was no faunal or ﬂoral information for these streams. The cause of the episodic pH
drop in late winter and early spring is discussed inrelation to snowmelt in the next section.
-.-. Snow properties of di#erent forest types in relation
to stream water chemistry in winterThe depth, water equivalent, density, EC, and pHof snow for the di#erent forest types (CF+ and BF+) in+331 are shown in Fig. .a-e, respectively. Snow depths(Fig. .a) increased from January (/*ῌ1* cm) to February, reaching a maximum on ,- February (+0/ and +-0
cm for BF+ and CF+, respectively). The period from +to ,- February +331 was the coldest part of the winter,i.e., the estimated daily mean maximum temperature
at the study site was -.*ῑ, and the daily mean minimum temperature was ῍,.2ῑ (Fig. /). Much snow fellduring this period (+*+ mm in terms of precipitation)and snowmelt was at its lowest level. After ,- February, the weather improved and the daily maximum
temperature exceeded +*ῑ periodically. There wereseveral clear days and some rain fell during this period. Consequently, the snow depth decreased after ,February and the snow disappeared in early to midApril. The snow was deeper in BF+ than in CF+ fromJanuary until the end of March (p῎*.**-; Wilcoxon’s
signed-ranks test). The main reason for this was thegreater snowfall interception rate by the crowns in
CFs (evergreen trees) than in BFs (deciduous trees)(Ishibashi and Takizawa, +32-). The snow water equivalent (Fig. .b) changed in almost the same mannerwith the snow depth, reaching a maximum on ,February in CF+ (/,2 mm) and on ,1 February in BF+(0,2 mm). However, the snow water equivalent decreased somewhat rapidly on / March and increasedslightly on ++ March in CF+. This may have been
attributable to the lag in snow accumulation on the
ground due to the interception by the tree crowns in
CFs. Snow density (Fig. .c) increased gradually fromJanuary (ca. *.- g cm῍-) to early April (ca. *./ g cm῍-)
due to snow recrystallization and the gravitational
compression of the snowpack. The snow density in CF+ was higher than in BF+ from January to ,- February(p῎*.*.-; Wilcoxon’s signed-ranks test), while it was
higher in BF+ than in CF+ from ,1 February to ,+March (p῎*.*.-). During the cold snowy period, theaccumulated snow was more compact in CFs than in
BFs, because in CFs the snow ﬁrst accumulated on theevergreen tree crowns and then fell to the ground inblocks. In contrast, most of the snow accumulated on
the ground directly and evenly in BFs. After ,- February, however, the weather improved and the snow
surface in BFs received more sunlight than that in
CFs on sunny days (Ohta et al., +33*). Consequently,
the melted snow may have increased the snow density
in BF+ more than in CF+.
The EC of snow (Fig. .d) rose from January (,.+ῌ,.2 mS m῍+) to February, reaching a maximum on +/February in CF+ (-.1- mS m῍+) and ,- February in BF+(..-0 mS m῍+). The EC in BF+ was higher than that in
CF+ until ,- February (p῎*.*.-, Wilcoxon’s signedranks test), perhaps due to the dissolution of ions fromthe snow on tree crowns in CFs. After ,- February, theweather improved and the EC of snow dropped, reﬂecting the preferential dissolution of ions from the snow
(Johannessen and Henriksen, +312). The EC decreased

9Nakatato between *.1 and +.* mS m῎+ in early April just before the snow disappeared. No signiﬁcant di#erence
was seen between the EC of snow in BF+ and CF+ after,- February (p῏*..33; Wilcoxon’s signed-ranks test).
The pH of snow (Fig. .e) rose gradually from January(..0ῌ..2) to early April (/.,ῌ/./), showing a signiﬁcantly
negative correlation with the EC of snow (r῏῎*./11, p
῏*.*-3 for CF+ and r῏῎*.3-1, p῏*.*** for BF+; Spearman rho). This indicated a preferential dissolution ofions, especially H῍, from the snow (Satoh et al., +330).
However, the lowest pH value was observed on ,February in BF+ (..,+). The pH in BF+ was signiﬁcantly lower than that in CF+ (p῏*.*+,; Wilcoxon’s
signed-ranks test) throughout the snow period. Thatmay also have been attributable to the dissolution ofions, especially H῍, from the snow on the tree crownsof CFs.
The amounts of chemical components in snow for
the di#erent forest types in +331 are shown in Fig. 0.
Of the chemical components in snow, Cl῎ and Na῍
were the dominant ion species, constituting ca. 1*ῌ ofthe totals. Other than Cl῎ and Na῍, SO.,῎ and Ca,῍were rather abundant ion species, constituting ca. ,*ῌof the totals. The total amount of chemical components in snow was greater in BF+ than in CF+, except
on +0 March and +* April, and the maximum total
amount in BF+ (--2.1 mmolc m῎,, ,- February) wasmuch greater than that in CF+ (,*/.. mmolc m῎,, +/February). This may also have been attributable tothe dissolution of ions from the snow on tree crowns
in CFs. Figure 1 shows the amounts of non-sea-saltchemical components in snow for di#erent forest
types calculated using the chemical composition ofseawater provided by the Oceanographic Society ofJapan (+33*). The amounts of non-sea-salt components
in snow corresponded well with the total amounts ofchemical components in snow (r῏*.23*, p῏*.*** for
CF+ and r῏*.0*2, p῏*.*-0 for BF+; Spearman’s rho),and they always constituted ca. ,*ῌ of the totals
throughout the snow period. Therefore, ca. 2*ῌ of thechemical components in snow were estimated as sea
salt origin. SO.,῎ and Ca,῍ were the dominant ion
species among the non-sea-salt components in snow,
occupying more than 2*ῌ of the totals. The di#erenceof dissolution rate among the ions species (Suzuki,+33+) was not clear in this study, with the exception of
H῍. The contribution of dry deposition on the snow
may mask the dissolution trend of each ion species
from the snow (Satoh et al., +330).
From late February to mid-March, a large ion loss
in the snow was observed for both the total and nonsea-salt components (Figs. 0 and 1), e.g., between ,and ,1 February (BF+) and between / and ++ March(both BF+ and CF+). The greatest loss of chemicalcomponents from the snow was seen in BF+ (+//./
mmolc m῎,) between ,- and ,1 February. This was also
the period when the EC decreased rapidly (from ..-0 to

Fig. .. (a) The depth, (b) water equivalent, (c) density,(d) EC, and (e) pH of snow for the di#erent forest
types (CF+ and BF+) in +331.
Notes: ῌῒῌ, CF+; ῌῑῌ, BF+.

,.01 mS m῎+; Fig. .d) and the pH increased (from ..,+
to ..0-; Fig. .e) in the snow of BF+. From -+ January to,- February in +331, the stream water runo# was extremely low (average valueῐ*.,/ L sec῎+ ha῎+) due tocold snowy weather conditions. However, the weather
turned warm between ,- and ,1 February (Fig. /), and10Bulletin of Glaciological Research

Fig. /. Weather conditions in the study area in February and March in +331.
Notes: ῌ῏ῌ, daily maximum temperature; ῌ῎ῌ,
daily minimum temperature; vertical bar, daily
precipitation.

both the runo# and EC of the stream water began toincrease (Fig. ,b). Consequently, the abrupt drop in
the pH of the stream water of BF (/.0. and /..2 for BF+ and BF,, respectively; Fig. ,c) on ,1 February wasthought to have resulted from the early snowmelt, i.e.,
the abrupt and preferential dissolution of chemicalcomponents from the snowpack, with their transport
near the ground surface to the streams in both BF+
and BF,. The lowest pH of stream water in Norway
was observed during early snowmelt due to the release of snowmelt water highly enriched in sea salts(Vogt and Muniz, +331). In this study, ca. 2*ῌ of the
dissolved ions from the snow were thought to be ofsea salt origin. Therefore, dissolved ions of sea salt
origin from the snow might contribute to the drop in
the pH of the stream water in BFs. However, no suchrapid dissolution of ions from the snow and consequent drop in stream water pH was recognized ineither CF+ or CF,. This may have been because thesnow surface in CFs received less sunlight than thatin BFs on sunny days (Ohta et al., +33*). Consequently,
ions in the snow dissolved more slowly in CFs than in
BFs. Furthermore, the accumulated snow during thecold snowy period was more compact in CFs than in
BFs (Fig. .c), which contributed to the delayed snowmelt relative to that in BFs.
The pH in all of the streams showed episodic acidiﬁcation on ++ March. The ANC was extremely low onthat day (/.*ῌ+1.0 mmolc L῍+). Although large ion loss
from the snow was observed in both BF+ and CF+
between / and ++ March, the peak ion concentration in
the stream water, as expressed by EC (Fig. ,b), wasobserved on the previous sampling day (/ March). In
contrast, the maximum runo# during the snowmelt
season, i.e., from late February to late March, was on++ March. Therefore, the drop in pH on ++ March in all
four streams may have been due to the dilution ofbasic cations in groundwater by the surﬁcial organichorizon/overland ﬂow of snowmelt water, which may
be high in DOC (Kendall et al., +333; Laudon and Bis-

Fig. 0. The amounts of chemical components in snow
for the di#erent forest types (CF+ and BF+) in +331.

Fig. 1. The amounts of non-sea-salt chemical components in snow for the di#erent forest types (CF+and BF+) in +331.

11

Nakatahop, +333).

References..

Conclusion

The stream water chemistry in the study area
was characterized by extremely high concentrationsof Cl῎ and Na῍, most of which was derived from sea
salts. There were negative correlations between runo# and the concentrations of many ions, especiallyCl῎, Na῍, and Mg,῍ from spring to mid-autumn. However, these correlations weakened in late autumn andwinter probably due to the high inﬂux of sea salt
components transported by the northwest monsoon,
as well as the acid shock phenomenon. The pH of
stream water in BFs (0.-ῌ0.2) was signiﬁcantly higher
than in CFs (0.+ῌ0./) from spring to mid-autumn. The
pH in late autumn and winter was lower than thatfrom spring to mid-autumn, especially in BFs (/./ῌ0.-).
This may have resulted from the drop in the ANC, thesupply of sea salts, and the increase in NO-῎ concentration in late autumn and winter.
Both the snow depth and total chemical components in snow were greater in BFs than in CFs due tothe di#erence in the accumulation patterns of snowon the tree crowns and ground. Approximately 2*ῌ ofthe chemical components in the snow were estimatedto be of sea salt origin. These chemical components inthe snow dissolved more rapidly in BFs than in CFs
from late winter to early spring due to the di#erencesin the quantity of sunlight received at the snow surface and the density of the snowpack.
As the runo# increased from late February to
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the pH drop (as low as /..ῌ/.0) in stream water wererecognized from late February to mid-March induced
by an early snowmelt in BFs, and the dilution of the
ANC during the peak ﬂow in the snowmelt season inboth BFs and CFs. Acid shock was evident when theweather improved following cold snowy days in thissnowy temperate region of Japan. This tendency was
clearer in BFs than in CFs due to the di#erence between the snowmelt patterns of the two forest types.

Acknowledgments
I thank Ms. K. Hirata and Ms. K. Kawasaki of
Niigata University for their assistance with the ﬁeld
survey and chemical analysis. This study was supported ﬁnancially by a Subsidy for Research from theJapan Forest Technology Association and a Grant-inAid for Scientiﬁc Research (No. +0/+**,*) from theJapan Society for the Promotion of Science.

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