19
Hydrobiologia 348: 19–38, 1997.
I. P. Muniz (ed.), The Høylandet Reference Area.
c 1997 Kluwer Academic Publishers. Printed in Belgium.
Soil and stream water chemistry in a pristine and boggy site in mid-Norway
Rolf D. Vogt1 & Ivar P. Muniz2
1
2
Department of Chemistry, University of Oslo, POB 1033, Blindern, N-0315 Oslo, Norway
NINA, POB 736 Sentrum, N-0105 Oslo, Norway
Key words: bog chemistry, pristine stream water chemistry, water flowpath, PCA, salt episode
Abstract
Stream- and soilwater at the 18.7 ha pristine Ingabekken catchment, on gneiss bedrock at Høylandet, have been
studied for three years, including intensive episode studies in spring and autumn. The site mainly consists of blanket
bogs which are typical for these marine west coast climates. Water drains through the blanket peats by means of
two major flowpaths. Each flowpath contributes to the stream with a distinct chemical fingerprint rendered by the
soil/soil water interactions along the flowpath, i.e. they may be regarded as end-members. The soil water from
the upper peat layers is the end-member representative of stormflow discharge whereas baseflow originates mainly
from seepage of the other end-member, which is the mineral soil water from beneath the peat. The pHBaCl2 of the
soils that control the runoff chemistry during highflow conditions was as low as 2.6, allowing for a substantial
pH drop in streamwater in the case of a seasalt episode. pH in the stream varied from more than 7 at baseflow
to 5 or slightly below at stormflow. The lowest pH (4.8) was observed during early snowmelt due to release of
meltwater highly enriched in seasalts. The fraction of exchangeable aluminum (AlS) was much higher in the surface
layers of the lower reaches of the catchment than close to the water divide. This suggests a transport of Al, much
like podzolisation, though downslope by a lateral flowpath. A Principal Component Analysis on the stream water
chemical data shows the importance of water flowpaths in addition to dilution or ionic strength and antecedent
conditions as a factor in determining the water quality. On the plane of the two major principal components the
base cations (Ca2+ , Mg2+ , Na+ , K+ ) were negatively related to [H+ ], and the total organic carbon (TOC) was
negatively related to strong acid anions (Cl , SO4 2 , NO3 ). These relationships between the parameter loadings
along the two main principal components remained indifferent to the effects of both dilution and flowpaths.
Under the present conditions of low acid deposition, this sensitive system is effectively buffered by its weak
acids and all released Al is complexed by natural organic acids. Similar boggy areas located in regions with heavy
anthropogenic acid deposition may not be able to neutralize the mineral acids. A shallow water flowpath and a high
H+ saturation of the ion exchanger in the soils controlling the highflow chemistry may lead to discharge episodes
where strong mineral acids are allowed to pass through the system releasing elevated levels of toxic aluminum in
the stream.
Introduction
Surface water acidification is the result of complex
interactions between the naturally occurring biogeochemical processes and anthropogenic impacts on
these processes. To better understand the effects of this
anthropogenic deposition, we therefore need to first
understand the naturally occurring processes. Integrated catchment studies (including monitoring of precipi-
*138807
tation, soil- and stream water, as well as measurements
of soil chemical characteristics) are important tools in
assessing the dominant natural processes controlling
stream water chemistry. However, most such integrated field studies have been conducted in areas that have
been anthropogenically acidified. Furthermore, to put
data from acidified sites into perspective, there is a
need for reference data from pristine but ‘mineral acid
sensitive’ areas.
Article: hydr 3972 GSB: Pips nr 138807 BIO2KAP
hydr3972.tex; 10/09/1997; 17:02; v.7; p.1
20
Despite recent decreases in emission of SO2 in
Europe and North America, ‘the acid rain still reigns’
(Rodhe et al., 1995), and large, still pristine regions in
the northern hemisphere are receiving loadings of acidifying compounds that enhance the mobility of base
cations out of the soil.
Blanket Histosols are common throughout a considerable part of a wide belt that runs through northern
Europe and central Canada. Peat and Hydromor soils
(i.e. permanently- and temporarily waterlogged superposed humus, respectively) possess unique characteristics concerning both hydrology and soil chemistry
demanding special concern when attempting to delineate their hydogeochemical response factors. The Histosol peat profile is by its nature generally waterlogged
since they develop in areas where the groundwater level reaches the ground surface. The waterlogged conditions reduce the vertical hydrological conductivity so
that the infiltration capacity is often less than the rain
intensity, leading to frequent sublateral- and overland
flow. Large amounts of excess precipitation combined
with a distinct shallow sub-lateral water pathway ‘short
circuits’ the geochemical buffering by bypassing the
deeper soils, often possessing greater bufferring capacities. These conditions render watersheds with a coastal
boreal climate susceptible to acid episodes as these
watersheds often comprise downslope and thin blanket
bogs. Despite this, the Histosol soil type has received
little attention in scientific literature (FitzPatric, 1983).
Enhanced knowledge and understanding of the dominant processes controlling runoff chemistry in such
acid sensitive systems are required to determine credible critical load estimates. This study is also particularly relevant for the further testing and development
of the conceptual chemical relationships used in acidification models such as the Birkenes model (Christophersen et al., 1982; Seip et al., 1995), ILWAS (Gherini
et al., 1985), MAGIC (Cosby et al., 1985), PROFILE
(Warfvinge and Sverdrup, 1992) and RAINS (Hordijk,
1991).
This report summarizes the research on soil and
stream water chemistry carried out at the 18.7 ha
Ingabekken boggy catchment, situated within the
broader pristine Høylandet area (Figure 1). A more
comprehensive site description is found in the papers
by Christophersen et al. (1990a, b), Mulder et al.
(1995), Pijpers and Mulder (1990) and Fjeldal (1992).
Effort is made to synthesize the data and findings presented in these papers as well as information from other studies in the Høylandet area (e.g. Anderson et al.,
1996; Muniz, 1996; Blakar & Hongve, 1997). Based
on present understanding, new interpretations are made
on previous findings. Emphasis is placed on studying relationships between the chemical parameters, in
general, by means of advanced and simple statistics
as well as of detailed studies of episodic changes in
stream water chemistry. The chemical relationships are
assessed in the context of water flowpaths and conceptual soil/soil water chemical interactions (e.g. cation
exchange, calcium over magnesium ratio (Ca/Mg) and
aluminum (Al) solubility). The focus is set on highflow
conditions, since the most adverse biological effects in
acidified streams occur associated with peak discharge
(Leivestad & Muniz, 1975).
Site description
The Ingabekken catchment, at an elevation of 280 to
370 m (64 390 N, 12 60 E), is in the subalpine zone
of the greater Høylandet watershed in Mid Norway
(Figure 1). This small subcatchment, situated on the
southeastern slope facing Lake Storgrönningen has a
suboceanic climate. The Ingabekken catchment represents a Histosol system being comprised mainly of
blanket bogs.
The discussion over the last decades regarding the
causes for soil and freshwater acidification has, aside
from acid deposition, also involved land use changes
in combination with naturally occurring organic acids
and seasalts (Rosenqvist, 1978; Overrein et al., 1980;
Krug & Frink, 1983). The studied site has not been utilized for harvesting of animal fodder nor timber during
the last century due to its inconvenient location, steep
topography and marginal productivity. Local effects of
land use changes have therefore not been considered.
Palaeolimnological studies of sediments from the
nearby lake Røyrtjønna indicated that the pH has been
remarkably stable (5.6–5.9) since about AD 650 (Berge
et al., 1990). Muniz (1997) conducted a regional survey
of the lake Storgrönningen drainage area during high
and low discharge periods and concluded that this area
(Figure 1) may serve as a pristine reference to more
antropogenically acidified regions. The chemical quality of the stream ‘Ingabekken’ generally spans over
the 95% interval of the spatial variation found in the
regional survey. This great span in chemistry is mainly due to the difference between temporal and spatial
variation and that the regional sites include fewer firstorder streams and instead several lakes and ponds with
very different hydrological regimes. The large temporal variability found in Ingabekken stresses the great
hydr3972.tex; 10/09/1997; 17:02; v.7; p.2
21
Figure 1. Location of study site and soil map of the Ingabekken catchment including stations for soil and soil water sampling.
hydr3972.tex; 10/09/1997; 17:02; v.7; p.3
22
Table 1. Volume weighted bulk precipitation chemistry (as eq l 1 )
from the various monitoring sites in the Høylandet area. The amount
of deposition collected during the study periods (PRE) are presented
in mm
IngabekkenA Stor GrønningenB HøylandetC
Monitoring Fall
period
1986
Summer
1987
Summer
1988
19871988
PRE
H+
NH+
4
Na+
Mg2+
Ca2+
K+
1001
10
3
90
2
5
4
370
6
13
50
9
9
6
270
9
22
38
13
6
6
2115
10,2
17
66
16
8
3
19
4
100
38
41
66
59
24
9
75
SO24
NO3
Cl
A Semb, 1987.
B Anderson et al., 1997.
C From 18.02.87 - 1.1.89; Tørseth, 1995.
importance of considering the prevailing hydrological
regime during sampling of spot samples. Questioning
how representative the Ingabekken site is to the broader area, we note that the site is generally more pristine
and is more strongly buffered with lower concentration of mineral acids and higher concentrations of both
weak organic and inorganic acidity and base cations
than most sites in the regional survey.
Other streams, including the main brook, Skifteså,
have been monitored for shorter intervals in order
to further test the temporal representativeness of
Ingabekken. Stream water chemical composition was
similar in all the studied streams, though the pH range
observed at Ingabekken (4.8–7.2) exceeded the range
at the other streams. This was mainly due to its thinner soils, smaller catchment and lower stream order
making Ingabekken a good reference site for mineral
acid sensitive areas virtually un-impacted by anthropogenic activity. The similarity of the highflow chemistry at Ingabekken compared with the earlier pristine composition at currently acidified catchments like
Birkenes in southernmost Norway can, of course, never
be ascertained. However, if the highflow end-member
at Ingabekken is assumed representative for preindustrial stream water chemistry in southern Norway, this
catchment has the potential for contributing to the
understanding of the acidification processes.
Deposition
Chemical data on bulk deposition are sparse. Precipitation chemistry was measured on-site only during four
months in the most stormy season in the fall of 1986 and
1987 (cf. Semb, 1987). These data may be somewhat
biased towards more seasalts and less of local pollutants. Additional data are available from a site close to
the shore of lake Storgrönningen, only 0.75 km from
Ingabekken – but at a lower elevation (165 m). Here
the deposition was monitored during the snowfree seasons in 1987 and 1988 (Anderson et al., 1997). The
closest station with permanent monitoring exists since
1987 at Høylandet, the local village 5 km from the
site (Tørseth, 1995). Data from these stations are comprised in Table 1.
Precipitation at Høylandet is normally generated
from unpolluted air masses over the North Atlantic
ocean. Generally we see that the precipitation at
Høylandet is dominated by seasalts, especially during the fall and winter months. Excess sulphate concentration was only about 9 eq l 1 . Total annual sulphate deposition (assuming an insignificant dry
deposition) during the monitored period was estimated to be approximately 1.3 g SO4 2 m 2 of which
30% can be classified as excess sulphate. These estimates agree well with long term measurements (1987–
1995) of precipitation chemistry at Høylandet (Tørseth,
1995). Based on precipitation chemistry at lake Storgrönningen (assuming that snow chemistry approximates to autumn deposition chemistry) Anderson et al.
(1997) determined the excess deposition to 0.7 g SO24
m 2 . The excess sulphur and the nitrogen deposition
at Storgrönningen reflect some contribution from local
sources with relatively high excess sulphate during
the snowfree periods being associated with ammonium
(Anderson et al., 1997). In the following the summer
rainfall quality from Storgrönningen was used instead
of on site rain chemistry since this was a more comprehensive dataset collected reasonably close to the site
and therefore still beleved to be representative for the
in site rainfall quality.
As the amount of precipitation increases and evapotranspiration decreases with elevation, the amount
of precipitation at the site is assumed to be around
2200 mm yr 1 (cf. Blakar & Hongve, 1997 and references therein).
hydr3972.tex; 10/09/1997; 17:02; v.7; p.4
23
Table 2. Soil density and content of soil organic matter of composite samples (each of 75 sub samples)
collected in a 300 m2 grid of the hydromor Histosol
in the Ingabekken catchment.
Horizon
Volume weight
kg l 1
Organic matter
%
Hi Histic
He Hemic
Ha Sapric
0.451
0.517
0.533
95.8
91.4
91.2
Edaphic conditions and hydrology
Ingabekken is drained by small streams, which converge only 50 m above the weir (Figure 1). The catchment lies above the marine limit on bedrock of gneiss.
During the glacial retreat the drainage was towards
the west, leaving a thin layer of glacifluvial material
in the area (cf. Blakar & Hongve, 1997). At relatively high elevations in the landscape a small section of
the Ingabekken catchment consists of orthic Podzols
(Figure 1) which due to the high drainage and a coarse
sandy soil texture are well developed with sharp boundaries between the different genetic horizons. About
half the catchment (primarily the upper northwestern part) consists of rock outcrops with shallow soil
pockets developed into rankers. The remaining catchment – the lower parts adjacent to the streams, and the
less steep northwestern facing slope – consists largely
of blanket peats. The peat areas are generally underlain by gley (Bg) mineral soils directly on the solid
bedrock. Although the bedrock is gneiss, these mineral
deposits contain some easy weatherable amphibolitic
minerals (cf. Anderson et al., 1989). These peatlands
are either of minerothrophic or ombrothrophic character. The minerothrophic bogs, as fens and swamps,
are found in flat downslope areas or in topographic
depressions receiving drainage from above. Isolated
from the influence of groundwater the ombrothrophic
(rain-fed) hydromor bogs, are found in the infiltration
zone close to the water divide. Blanket bogs are associated with cold climate, low evapotranspiration and
an evenly distributed precipitation over time, causing
low organic decomposition rates. The organic matter
may thereby accumulate and dystric blanket Histosols
are thus formed.
Once established the hydromor Histosols become
more mature and saprist (i.e. more decomposed) than
their peat counterparts since enhanced humification is
favored by continuous seepage of fresh precipitation,
saturated with oxygen (FitzPatrick, 1983). The densities of these ombrothrophic saprist hydromor soils are
therefore particularly high (cf. Table 2; common values
for organic material are between 0.04 and 0.2 kg l 1 ;
Grip & Rodhe, 1991). The high soil density allows for
less hydrological permeability leading to even greater
overland flow during periods of high rain intensities.
Previous studies of the water flowpaths at
Ingabekken, by Mulder et al. (1995), using an end
member mixing technique (EMMA; Christophersen
et al., 1990c), concluded that baseflow discharge is
dominated by seepage from the mineral soils beneath
the bogs. This is likely to be the case considering
the generally waterlogged conditions and a greater
hydraulic conductivity of the glacifluvial sand deposits
than in the overlying mature compact hydromor material. During highflow, the EMMA technique showed
that the runoff chemistry becomes controlled by the
surface hydromor soils in the bog close to the water
divide. This is also likely to be the case since the lower
reaches of the bogs are saturated with water.
As a first approximation one might therefore consider the stream water chemistry as a mixture of two
types of soil water: Groundwater- and Surfacewater
runoff (cf. Seip & Rustad, 1984; Neal & Christophersen 1989; Christophersen et al., 1990c). The
groundwater end-member will be representative for
baseflow whereas stormflow is originating from the
upper, more acidic soil zones. Hydrogeochemical
mechanisms controlling runoff chemistry can then be
revealed by considering each end-member separately
with special emphasis on the acidic surface hydromor
soils as they determine the chemical quality of runoff
during periods of stormflow; i.e. acid episodes.
Methods
From October 1986 until August 1988 routine sampling of the brook was conducted on a weekly/two
weekly basis, combined with intensive sampling during episode studies. Campaigns of soil solutions sampling within the catchment were conducted by several
research groups by means of different types of tension lysimeters (Christophersen et al., 1990b; Fjeldal,
1992; Mulder et al., 1995). The lysimeters in the bog
were located either close to the main stream (streambank) or close to the water divide. Lysimeters were
also installed in all genetic horizons of a Podzol profile
located on a small mound (Figure 1).
hydr3972.tex; 10/09/1997; 17:02; v.7; p.5
24
pH was measured in all samples. Subsets of samples were selected for fractionation of aluminum (into
inorganic monomeric Al (Ali ) as well as monomeric organic complexed Al (Alo )), and for analysis of
[Ca2+ ], [Mg2+ ], [Na+ ], [K+ ], [NH4 + ], [SO4 2 ],
[Cl ], [NO3 ], total fluoride, total organic carbon
(TOC) and total inorganic carbon (TIC). An acidimetric titration to pH 4.5 was also undertaken to give an
estimate of the partial acid buffering capacity of the
waters (PBC4:5 ).
The Al-fractionation followed the operationally
defined Barnes/Driscoll procedure (Sullivan et al.,
1986). Major cations and anions were determined
according to standard procedures using atomic absorption spectroscopy and ion chromatography, respectively. Total fluoride was measured potentiometrically after
addition of TISAB buffer. TOC was calibrated from
E254nm absorbency, based on the optical densities of
34 samples determined for carbon (mg C l 1 ). Sampling and transport routines were optimized to minimize degassing of CO2 prior to analysis. Samples
for TIC determination were taken in air tight glass
bottles. The organic anion contribution to the PBC4:5
(PBC(org)4:5) is calculated as the difference between
the PBC4:5 and the sum of [HCO3 ] + H+ , where H+
denote the increase of [H+ ] in solution from the original pH to 4.5. See Christophersen et al. (1990a) and
Mulder et al. (1995) for more detailed analytical and
computational protocol.
Fjeldal (1992), Pijpers & Mulder (1990) and Mulder et al. (1995) collected soil samples along two parallel soil transects (Figure 1). Both transects were
perpendicular to the stream with sampling points
at 20 m intervals. These air dried soils were analyzed for the Effective Cation Exchange Capacity
(CECE ), including Al, Fe, H+ and base cations
(BC = Ca + Mg + Na + K), according to an exchange
method developed for forest soils by Hendershot &
Duquette (1986) using an unbuffered solution of 0.1 M
BaCl2 . A thorough method protocol is given in the
referred papers. Composite samples (each of 75 samples) of the Histosol profile were collected from a
300 m2 grid of the peat. CECE and exchangeable
cations in these air dried samples were determined by
extraction with 1M NH4 NO3 . These data have not been
previously published. Soil samples were also collected
in the peat close to the water divide by Christophersen
et al. (1990a) and approximately halfway up the bog
slope by Anderson et al. (1997). These air dried samples were determined for Potential Cation Exchange
Capacity (CECP ); i.e. using an buffered extractant. For
exchangeable base cations (BC), one obtains approximately the same value using either unbuffered or
buffered extraction, but the total CEC, including H+
and Al, will be larger in the latter case, implying a lower base saturation (BS, i.e.% BC of CEC). The content
of organic matter of the soil was determined by loss on
ignition at 500 C.
A multivariate Principal Component Analysis
(PCA) (see, e.g. Esbensen et al., 1987) was conducted (using correlation matrix) with statistical software
c (1993).
from Minitab
Results and discussion
Soil chemistry
Despite its ombrothrophic nature the hydromor at
the water divide is found to have large amounts of
both effective and potential exchangeable bivalent base
cations (Table 3). This is due to a large deposition of
seasalts (rich in magnesium, Table 1) augmented by
biological cycling (of especially calcium) by a heather
vegetation through the rather shallow soils (20 cm deep
organic layer overlying a 20 cm thick mineral soil; cf.
Pijpers & Mulder, 1990). Furthermore, these organic
soils suffer seasonal drying. This desiccation causes
polymerization and stabilization of stable humic compounds with high exchange capacity and marked affinity for bivalent cations (Duchaufour, 1982).
An even more striking feature of these soils was a
very low pHBaCl2 . Values down to 2.6 were common,
suggesting a strong ability to cause acid pulses during
salt episodes, despite their high base saturation (see
below). The high amount of effective exchangeable
H+ is possible due to the lack of source for exchangeable aluminum. A high potentially exchangeable acidity (i.e. total acidity) was also found when determining
the potential CEC (CECP ) on the same soil samples
(Table 3); an average of 818 meq OH kg 1 was needed to bring the extractant to pH 7.
The upper peat soil layers were found to have
decreasing BS downslope, though with less exchangeable H+ , while instead the amount of exchangeable Al
(AlS, i.e.% Al on the CEC) increased. Similar spatial
trends in BS and AlS has also been found elsewhere
(e.g. Birkenes in southernmost Norway; Mulder et al.,
1991) in regions with poorly weatherable bedrock
(Vogt et al., 1994). Downslope the deep and constantly
waterlogged sphagnum peat lack the biological cycling
but receive some minerogenic seepage. This seepage
hydr3972.tex; 10/09/1997; 17:02; v.7; p.6
25
Table 3. Effective and potential cation exchange capacity and the composition of the soil exchanger in
different samples collected from the surface horizons of the hydromor soils. The samples were collected
from the water divide (top), midslope (mid) and adjecent to the stream (streambank). CEC denotes
total cation exchange capacity; H+ and BC denotes exchangeable amount of protons and base cations
respectively - all in meq/kg; HS, BS and AlS denote the fraction (in%) of the cation exchanger occupied
by H+ , base cations and Al3+ , respectively
Comments
Method
Top1
Mid1
Streambank1
Top2
CECE
CECE
CECE
CECP
0.1M BaCl2
0.1M BaCl2
0.1M BaCl2
1M NH4 OAc
pH in
BaCl2
CEC
H+
meq kg 1
BC
HS
%
BS
AlS
2.7
3.3
3.6
–
283
134
113
1025
224
64
29
206
15
8
4
80
79
49
24
20
6
43
71
–
41
11
5
818
1
Average values from Pijpers & Mulder (1990); Top: stations A & AB, Mid: stations B, C and AC,
Streambank: stations D & AD (Figure 1).
2 Average values from stations A & AB (Figure 1).
allows Alo from the gley mineral soil layers below the
peat in the upper reaches to be transported to the upper
peat layers in the lower returnflow regions and become
immobilized there. The elevated levels of AlS in the
surface peats close to the streams (Table 3) were therefore associated with elevated levels of Alo in the soil
water. Although lateral flow, this process has much
in common with podzolization (Mulder et al., 1991,
1995). High flow at Ingabekken becomes increasingly
dominated by solutions originating in the surface peat
bog close to the water divide (Mulder et al., 1995). This
implies that the rainwater during peak discharge only
have contact with the soil in these upper regions before
entering the stream. The shallow stormflow flowpath
and the great acidity of this soil (i.e. the low pHBaC l2
surface Histosol layers at the water divide) suggest that
this site may be susceptible to episodic pH depressions.
Such a pH depression in the stream can in turn cause
a mobilization of labile forms of Al from the surface
layers of the streambank peat being high in AlS, as
well as the streambed proper (see Norton & Henriksen, 1983; Henriksen et al., 1988). The large stores
of readily available organically bound and exchangeable Al (AlS) in surface peat close to the brook may
therefore be a potential future source of Al if exposed
to strong mineral acids or acid surges caused by salt
episodes; analogous to the leaching of the Bhs layer
in regions with acid deposition (Mulder et al., 1989).
Focusing on the low AlS values of the surface Hydromor layers close to the water divide and that these soils
are the main contributors to runoff during highflow
periods, Mulder et al. (1995) concluded nevertheless,
that acid deposition at current levels is unlikely to result
in increased Ali levels in the stream at highflow. This is
likely the case when considering the low anthropogenic
acid loading at Høylandet. But it should, however, be
noted that the existence of bicarbonate-rich groundwater is no guarantee against acidification of the highflow
end-member; the Plynlimon catchments in mid-Wales
providing a good example (Neal et al., 1986).
Early findings by Christophersen et al. (1990a)
were based only on soil samples collected from the
peat profile close to the water divide. As presented by
Pijpers & Mulder (1990) and Mulder et al. (1995) these
locations show relatively low levels of exchangeable Al
relative to regions further downslope. This lack of Al
(only approx. 4 meq kg 1 , or about 5% of the CECP ) in
these pristine soils led the authors to hypothesize that,
because of acid deposition, the exchange sites undergo
a transition under which exchangeable H+ is replaced
by aluminum. Clearly, the new information concerning
the spatial distribution of AlS does not support such a
hypothesis. This example stresses the importance of
insight into the spatial structure of soil data, particularly in case of modelling or comparative studies.
The gleyed mineral soil layers beneath the bog were
also sampled and theire exchange characteristics were
determined by several research groups for either potential or effective CEC (Table 4). The pH values, both in
water and salt (BaCl2 ) extract, were relatively similar
and the span in spatial variation was only between 4.5
and 4.9. The amounts of effective exchangeable base
cations along the transects were generally low (from
1.0 to 13 meq kg 1 ), though since the CEC also was
low the BSE differs considerably (from 5.6 to 52%).
Also in samples determined by extraction with 1M
NH4 OAc/NaClAl (i.e. CECP ), the BSP range from 2 to
30% (n = 6; Christophersen et al., 1990b). The cause
hydr3972.tex; 10/09/1997; 17:02; v.7; p.7
26
Table 4. Effective and potential cation exchange capacity and composition of deep mineral
horizons beneath the peat soils. CEC denotes total cation exchange capacity; H+ and BC
denotes exchangeable amount of protons and base cations respectively - all in meq/kg; HS, BS
and AlS denote the fraction (in %) of the cation exchanger occupied by H+ , base cations and
Al3+ , respectively.
Comm.
Method
1
2
3
4
CECP
CECP
CECE
CECE
1M NH4 OAc/NaClAl
1M BaOAc/NaClAl
0.1M BaCl2
1M NH4 NO3
CEC H
meq kg 1
BC
HS
%
BS
AlS
35
22
28
75
6
6
4
7
77
68
9
45
17
27
20
10
6
5
73
45
27
15
2
33
1
Median values from 6 samples (Christophersen et al., 1990 a,b).
Bg-horizon of a midslope Histo-dystric glaysol from Anderson et al. (1996 this volume).
3 Median values of 9 samples from the soil transects (stations A, D, H, J, L, AA, AB, AC, AI;
Figure 1) from Fjeldal (1992).
4 Average data on composite sample (of 75 sub samples from a 300 m2 grid).
2
for this spatial variation may lie in an uneven distribution of more base rich minerals (e.g. Hornblende) as
found by Bain et al. (1990) in the C-horizon of glacial
mineral deposits in the area.
Soil water chemistry
The soil water at 5 cm depth (H-horizon) in the hydromor bog at the water divide corresponds closely to a
slightly more concentrated precipitation (30% in terms
of [Cl ]) (Figure 2). The [H+ ], [Na+ ], [Mg2+ ]and
[K+ ] remain practically constant relative to chloride,
while [Ca2+ ] was further enriched by a factor of 4.
At the streambank the soil water from the same depth
(5 cm H-horizon) was less concentrated by evapotranspiration (20%; using the [Cl ] as a proxy) though
greatly enriched in base cations, for [Ca2+ ] by a factor
of 11.5, and for [K+ ] by 6, and for [Mg2+ ] 2, as well
as [Na+ ] by 1.5. Even though concumption of H+ in
exchange for Ca2+ may be an important process (see
next chapter) the relative small loss of [H+ ] compared
to precipitation does not contribute significantly to the
observed release of base cations. This leaching must
therefore mainly be due to the organic acids, providing
both protons for ion exchange and an anionic charge
for cation co-transport.
The chemical composition of the soil solution
remains stable down through the peat, except in the
Histic (Hi) layer at the streambank (‘bog at streambank’ in Figure 2). Due to the watersaturated conditions and low hydrological conductivity of the Hihorizon (see above) carbon dioxide from decomposition processes accumulated in this soil water. The
resulting high pCO2 and an average pH of 6.1 caused
high bicarbonate levels, allowing for elevated release
of calcium into solution. In the deeper sapric organic
and gleyic mineral layers (Ha/Bg) of the peat bogs the
concentrations of Ca2+ , Mg2+ , and to a lesser extent
also K+ , generally reach high levels. The samples had
frequently pH values above 7, with Ca + Mg accounting for more than 50% of the cationic charge, and the
weak acid anions accounting for 75% of the anionic charge. This corroborates reasonably well with the
runoff chemistry during baseflow (Figure 2).
The bog soil water concentrations of Alo are
between 4 and 10 M. The [Alo ] is highest in the upper
H-horizons, especially in the streambank bog, and lowest in the middle Hi-horizons, especially at the water
divide. Vogt and Taugbøl (1994), studying soil water
in anthropogenically acidified sites, found that [Alo ] in
soil water may be modelled by a simple model using
the [DOC], [H+ ] and [Ali ] in solution, along with the
complexation and protolysation constant for the DOC
material and the number of organic binding sites. The
mobilization of Alo is therefore best studied using a
multivariable approach. A principal component analysis (PCA) of the [Alo ], [DOC], [H+ ] and [Ali ] was
conducted on all bog soil water data irrespective of the
sampling location. Along the first principal component (PC1), explaining 42% of the data variation, the
Alo was negatively related to the DOC (i.e. loadings
of 0.458 and 0.257 respectively), and positive related to H+ and Ali ( 0.541 and 0.657 respectively).
In the second principal component (PC2), explaining
26% of the variance, the DOC showed high loading
( 0.889) along with Alo ( 0.429). The third principal
hydr3972.tex; 10/09/1997; 17:02; v.7; p.8
27
Figure 2. Chemical composition of precipitation, soil water and stream water. Weak acids comprise both organic anions and bicarbonate.
Top graph shows absolute concentrations, bottom graph shows relative composition. Letters in bars denote soilwater datasets: data from
(a) Christophersen et al. (1990b); (b) Fjeldal (1992), Pijpers and Mulder (1990) and Mulder et al. (1995).
hydr3972.tex; 10/09/1997; 17:02; v.7; p.9
28
Table 5. Volume-weighted average as well as median highflow and baseflow values for stream water chemistry (sea
salt episode data excluded). Note that the volume-weighted
stream water values will be biased towards the highflow
situation due to an over representation of samples during
episodes. Sum(cat.-an.) does only include inorganic species
All samples
volume
Highflow Baseflow
weighted
(> 8 l/s) (< 8 l/s)
H+
Na+
K+
Ca2+
Mg2+
NH+
4
NO3
SO24
Exc. SO24
Cl
HCO3
Alo
Ali
eq l
1
M
TOC
mg l
TIC
M
PBC4:5
PBC(org)4:5 meq l
Sum (cat.-an.)
8.0
97
6
19
28
<1
2
25
12
124
3
1.7
<1
1
4,7
76
1
0.05
0.02
0.01
6.0
86
5
22
25
<1
<1
20
9
96
3
2.0
<1
5,9
72
0.04
0.00
0.02
0.4
159
6
69
51
3
1
29
13
144
51
1.7
<1
6,0
136
0.15
0.02
0.04
component (PC3) explained only 20% of the variation,
though had a strong Alo loading (0.707) which was
negative related to all the other variables, especially H+ ( 0.675). From this we may speculate that the
mobilization of Alo appears primarily controlled by the
mobilization of Ali in these acid soil waters (cf. PC1),
and secondly by the (production and leaching of) DOC
(cf. PC2), especially when pH is high (cf. PC3). Any
released Ali was complexed in solution by organic ligands on DOC so that Ali in solution remained low.
Also at the pristine HUMEX site in mid-western Norway, with only minor [Ali ], Vogt et al. (1994) found
that the variation of [Alo ] in the peat soil water was
poorly determined by the [DOC]. Here including the
[H+ ] into a linear model improved the correlation at
only some locations.
A puzzeling feature in our data was that there was
practically no sulphate found in all soil water samples from the organic bog layers. This is a paradox
considering that in the runoff, the sulphate although
low never decreased below 4 eq l 1 during highflow and 6 eq l 1 during baseflow. In fact, usually
the sulphate concentrations were about 20 and 29 eq
l 1 during highflow and baseflow respectively (median
values; Table 5). A sink of sulphate in the soils may be
envisaged through (bio)chemical reduction processes
where the S becomes bound to the organic matter or
reduced to sulphide. In its reduced form the sulphur
may have been lost from the sample by volatilization
as H2 S, especially in samples with low pH. In samples
with high pH the oxidation to sulphur is more likely
to be a dominating process in the sample vessel. Significant amounts of sulphate were in fact found where
the pH was high; i.e. in the mineral layers beneath
the peat close to the streambank (average pH was 6.2).
A low amount of iron in the peat (as inferred by low
amounts of exchangeable Fe on the soil ion exchanger;
see Pijpers & Mulder, 1990) could permit such a transport of sulphur in reduced form, either as sulphide or as
bound to dissolved organic matter, through the deeper soil layers. Upon entering the stream, the mixing
with aerobic water would serve to rapidly oxidize the
sulphide compounds to sulphate so that hydrogensulphide is not remitted to the atmosphere. It is currently
not possible to assess the amount of sulphur being reemitted from the catchment to the atmosphere.
Stream water chemistry – a general picture
When studying stream water chemistry in general,
the results from a seasalt episode (i.e. samples with
[Na+ ]>200 eq l 1 ) during the snowmelt of 1987 are
excluded and discussed separately below in the seasalt
snowmelt section. Volume-weighted average as well
as median highflow and baseflow concentrations of
stream water chemistry are presented in Table 5 and in
Figure 2. While the highflow resembles the precipitation in terms of ionic strength and chemical composition, except for higher [Ca2+ ] and [TOC], the baseflow
is twice as concentrated due to weathering, production
of bicarbonate, and evapotranspiration. The solute level during highflow lies between the low concentration
in precipitation and the greater levels found for soilwater. This may only be explained by a strong dilution of the soilwater by rainwater. The leaking of ions
to streamwater or accumulation in the catchment is
reflected by a change in the concentration ratio with
respect to rainwater (summer rainfall; Table 1) and
is expressed by the median fractionation factor (i.e.
([X]/[Cl])streamwater /([X]/[Cl])rainwater ) in Table 6. The
site is leaking base cations, especially calcium during
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29
Table 6. Median fractionation factors for rainwater components in streamwater during highflow and baseflow. Fractionation factors are given relative to Cl , i.e.
([X]/[Cl])streamwater /([X]/[Cl])rainwater ). Less than unit values denote excess leaching,
while values greater than 1 denote accumulation within the catchment
Flow regime
H+
Ca2+
Mg2+
Na+
K+
NH+
4
SO24
NO3
Highflow
Baseflow
0.5
0.0
2.0
5.0
1.7
2.3
1.2
1.4
0.7
0.7
0.0
0.1
0.4
0.4
0.1
0.1
baseflow, and accumulating nitrogen. Despite a large
proton production within the soils by organic- and carbonic acid, there is a net neutralization of the precipitation within the catchment. An apparent accumulation
of sulphur may eather be due to a loss by volatilization
of H2 S and/or the use of summer rain quality, with elevated deposition of sulphate. Using instead the autumn
rainfall chemistry as reference we find a insignificant
accumulation of sulphate.
The great release of calcium within the catchment
causes the Ca/Mg ratio in the stream to remain above
0.6, even during extreme highflow. The ratio between
exchangeable Ca2+ and Mg2+ in the bog, according to
the ammonium acetate method, increases from 1.1 in
the surface H-horizon layers to 3.3 in the Bg mineral
soils horizon beneath. The almost equimolar amounts
of Ca2+ and Mg2+ only in the upper soil layers as also
in streamwater during periods of high runoff (‘H’ in
Figure 3) ([Ca2+ ] = 0.8 [Mg2+ ]; R2 = 0.77, n = 46),
fortifies the postulation that the high discharge chemistry was mainly controlled by these upper bog layers.
Similarly, during baseflow, when discharge water seeps
from the Bg-horizon beneath the bog (i.e. with high
Ca/Mg ratio on the cation exchanger), the increase
in streamwater [Ca2+ ] with increasing [Mg2+ ] was
much greater than unity ([Ca2+ ] = 2.2 [Mg2+ ] 35.1;
R2 = 0.83, n = 38) (‘L’ in Figure 3). This agrees with the
postulation that the discharge chemistry during baseflow is controlled by the Bg-horizon. During highflow
there was also a very good correlation between the
square root of [Ca2+ ] and [Mg2+ ] vs. [Na+ ] (R2 = 0.8
in both cases). Furthermore, the [H+ ] was mainly negatively related to the Ca/Mg ratio (R2 = 0.5) during
highflow, suggesting that the consumption of protons
in the exchange of Ca2+ may be an important process.
As also indicated in the soil water section these relationships suggest that an ion exchange model controll
the mobilization of cations in the soil end-members.
During baseflow the Ca/Mg ratio was also negatively related to the low [H+ ] (R2 = 0.5), while positively co-related with potassium, alkalinity and bicar-
bonate concentrations (R2 of Ca/Mg vs [K+ ] = 0.7;
PBC4:5 = 0.7; HCO3 = 0.6). This is due to all being
dependent on sufficient residence time allowing for
enhanced weathering conditions. Negative, correlations are therefore found with increases in flow (i.e.
decreasing residence time as well as dilution) (R2
of discharge vs. Ca/Mg = 0.5; [K+ ] = 0.3; Alkalinity = 0.4; HCO3 = 0.4).
Examples of the observed variations in pH, concentrations of chloride, sodium, and calcium with discharge, are shown in Figure 4. The pH at Ingabekken
was, as often is the case (Rosenqvist, 1978; Henriksen
et al., 1984; Christophersen et al., 1982), negatively correlated with flow; for the snow free season the
pH ranged from about 5.0 at highflow to 7.2 during
baseflow.
With decreasing flow the pCO2 and charge contribution of bicarbonate increased from about 2 and 2.5%
at highflow, to 7 and 23% at baseflow, respectively
(see Table 5). During baseflow the total concentration
of bivalent base cations was 120 eq l 1 . This high
release of Ca and Mg is likely due to the weathering of the amphibole minerals (Bain et al., 1990) in
the gley soil beneath the bogs by the weak carbonic
acid. A decreasing trend in the amount of excess sodium ([Na] – 0.85 [Cl]) with an increase in discharge
(marked with crosses in Figure 5) is therefore partly explained by decreased contribution of sodium from
weathering. During highflow conditions the runoff also
becomes diluted by rain water through a lateral overland flowpath, and excess Na in runoff does not differ
significantly from zero.
Even though pH values may drop to 5 the Al fractions remain low with Alo around 2 M and Ali not
exceeding 1 M (Table 5). Other studies in pristine
areas show similar features; for instance, the pristine
Kårvatn site, north-western Norway (SFT, 1987, 1988)
and the HUMEX site in western Norway (Vogt et al.,
1994). At these sites the organic anions have only a
modest part of the ionic load while instead the influence
of seasalts dominated. At higher elevations in Jamieson
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30
Figure 3. The relationship between calcium and magnesium in stream water. ‘H’ and ‘L’ denote normal conditions, while discharge was greater
and less than 8 l s 1 (i.e. highflow and baseflow respectively). ‘S’ denote samples collected during the seasalt episode during spring melt.
Creek, British Columbia, a pH of 4.5 was observed,
organic anions dominated and total monomeric Al was
in the range 2–4 M, predominately as Alo (Driscoll
et al., 1988).
Relationship between chemical parameters in stream
water
It has been our intention to focus on the true multivariate relationship in such hydrogeochemical systems
between the hydrophysical factors and the geochemical mechanisms, as well as between the main chemical variables. A PCA was therefore conducted on the
stream water data (seasalt episode data were excluded)
to identify the main forces governing the variability in
the data (45 cases) and the relationship between the
main chemical parameters (8 variables).
The first principal component (PC1) described
more than half (55%) of the variation in the data
(Figure 6). Along this strong component parameters
that were positively related with discharge had positive loadings, while negatively related parameters (e.g.
Cl ) possessed negative loading. TOC had positive
loading along the PC1 (i.e. positive related to flow)
because the major flowpath during periods of highflow was through the surface layers of the bogs of
which the chemical fingerprint is a high concentration
of DOC. High negative loading of base cations coincides with scores of samples collected during baseflow
conditions. This is due to the mineral soils beneath the
peat being the major source of runoff during baseflow.
The chemical fingerprint of this end member is high
concentrations of base cations and sulphate. That the
base cations and sulphate were negatively related to
TOC along the PC1 may therefore be explained by the
shift from the upper bog horizons during highflow to
the deeper mineral soil layers as the main contributor
to runnoff during baseflow. The fact that parameters
which have similar concentrations in both soil water
end-members (i.e. no fingerprint; e.g. chloride) still
have strong negative loading along the PC1 must be
attributed to other factors than flowpaths. A direct contribution of dilute precipitation or meltwater during
highflow may instead be a likely cause for this negative loading. Chemical equilibrium effects of such
dilution (i.e. negative salt effect) would further serve
to fortify the PC1 response of bivalent base cations,
TOC and H+ , by adsorption to the ion exchanger,
dissolution and organic acid protolysation, respectively. This strong component reflects therefore that the
main spread in runoff chemistry is found over a discharge gradient. This chemical variation is a combined
hydrological effect of flowpaths from geochemically
different soil layers (end-members) and dilution by
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31
Figure 4. Variations in pH, concentrations of chloride, sodium, and calcium with discharge, for the late summer of 1987.
Figure 5. Excess sodium (i.e. Na ([Na] 0.85 [Cl])) relative to discharge in stream water. Crosses denote normal conditions, while ‘S’ denotes
samples collected during the seasalt episode during spring melt.
hydr3972.tex; 10/09/1997; 17:02; v.7; p.13
32
Figure 6. The first and second Principal Component (PC1 & PC2) in the stream water data. Letters in graph refer to chemical parameters and
are positioned at theire respective variable loading. Numbers in graph at sample scores denote discharge in l s 1 during sampling.
Figure 7. The first and second Principal Component (PC1Cl & PC2Cl ) in the stream water data corrected for dilution by dividing the concentrations
by the value for chloride prior to running the analysis. Numbers in graph at sample scores denote discharge in l s 1 during sampling.
rain or melt water fortified by the equilibrium response
to changes in ionic strength.
The second principal component (PC2), describing 18% of the variation, reflects mainly the spread
in chemistry at a given runoff intensity (or PC1) and
may be interpreted mainly as a hysteresis factor, practically indifferent of dilution (i.e. Cl has insignificant
loading). Within the catchment there is a continous
hydr3972.tex; 10/09/1997; 17:02; v.7; p.14
33
Figure 8. The first and second Principal Component (PC1HF & PC2HF ) in the stream water data collected while runoff was greater than 8 l s
Numbers in graph at sample scores denote discharge in l s 1 during sampling.
accumulation or depletion of the different chemical
parameters (Table 6). The intensity of this leaching and
accumulation is enhanced by an increased hydrological
residence time. During a dry period causing enhanced
residence time, variables that are generally depleted
(fractionation factor >1 in Table 6 and TOC) are able
to accumulate causing an enhanced leaching under the
first runoff episodes. Variables that are generally accumulated within the catchment (fractionation factor <1
in Table 6) will on the contrary become less available
as the residence time increases, causing a diminished
leaching during the initial runoff episode stages. I.e.
the PC2 component is found to reflect the intensity of
depletion/accumulation controlled by the antecedent
hydroclimatic conditions in the end-members (see Vogt
et al., 1990). This postulation is fortified by the fact
that the variable loadings along this component are
well correlated (R2 = 0.90, n = 10) with the fractionation factors in both high- and baseflow streamwater
(Table 6) (Figure 9). An important exception is for the
strong leaching of Ca from weathering during baseflow.
An example of the effect of previous hydrological
conditions may be seen in Figures 4 and 10. During the
onset of the storm on august 22, after a fortnight of no
rain, the concentrations of TOC in the stream increase
rapidly. The initial phases of stormflow reach especially high [TOC] (see Figure 10) (due to wash out of accumulated soluble organic matter; see, e.g. Vogt et al.,
1990), while during the succeeding stages of high-
1.
flow with greater direct overland runoff intensities, the
stream commonly experiences higher [H+ ] (see Figure 4). During the following episodes, the [TOC] was
lower despite greater runoff intensities. Similar stream
chemical response patterns have also been found elsewhere, e.g. Birkenes in southernmost Norway (Seip
et al., 1989; Vogt et al., 1990). During baseflow (PC1
is negative) slow seepage of streambank mineral soil
water causes the base cations and sulphate to reach
high concentration in the stream. There is therefore a
tendency for the samples to wander clockwise around
the origo of the Figure 6 through a series of discharge
episode (i.e. hysteresis effect coused by the changes in
antecedent hydrological conditions). This again suggests that organic acidity was most important in providing H+ during the onset of an event, while during
later stages the mineral acidity retains its role as mobile
counter ion to the H+ . The lower pH during successive
episodes is partly due to shorter residence time and a
more shallow flowpath resulting in less base cations,
and partly enhanced protolization of the organic acids
by dilution.
The parameter relationships superimposed on the
PC1 vs. PC2 plane (Figure 6) reveal a general pattern often recognized in natural water samples. The
following parameter pairs: Ca2+ & Mg2+ , NO3 &
SO4 2 and Na+ & Cl were closely juxtaposed, due
to the strong co-variation among these parameters (see
e.g. Muniz, 1997) due to both mutual chemical dependency (especially Ca & Mg) and by originating from
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34
Figure 9. The second Principal Component (PC2) and the fractionation factor in stream water. Squares and crosses denote highflow and baseflow
conditions, respectively. Fractionation factor vs PC2 loading for Ca at baseflow is not shown.
a common source: The base cations were negatively
related to the H+ (in both the PC1 and PC2 dimensions). Furthermore, the acidity was governed either
by TOC (i.e. a proxy for organic acids) (in the PC1)
or by strong mineral acid anions (in the PC2). A negative relationship between TOC and H+ along the PC2
during high flow may partly be due to protonization
of organic acids by protons provided by strong mineral acids and subsequent precipitation. Finally, the
antagonistic relationship between Ca & Mg and H+ is
perpendicular to the antagonistic relationship between
TOC and NO3 & SO4 2 : see arrows in Figure 6. This
pattern reflects in a very simplistic way the combined
effect of variation in present and past discharge on the
runoff chemistry.
In an attempt to make the PC1 a more pure flowpath component the effects of direct dilution was partly
accounted for by simply dividing all sample concentrations by its chloride value prior to running a new
PCA. This approch will also correct for moderate variations in the seasalt loading, though it will not reflect
the equilibrium reactions adjusting to these different
solute levels. The PC1Cl and PC2Cl now accounted for
only 38 and 23% of the variation in the data, respectively. The new PC1Cl became almost an analog to the old
PC2, while the new PC2Cl resembled the old PC1 (cf.
Figures 6 & 7). The main effect was therefore that the
‘PC1’ and ‘PC2’ had swapped positions as the major
component in the data, except for the loadings of H+
and Na+ . This fortifies the postulation of direct dilution by rain or meltwater being an important force on
the former PC1 and thereby on the stream water chemistry. Devoid of the dilution and ionic strength related
effect, the influence of antecedent hydrological conditions appears to become most prominent. Ascribing
the loss in the percentage of the variation described by
the PC1 and PC2Cl (55 23 = 32%) to dilution factors,
suggests that more than half (i.e. 32 being 58% of 55)
of the variation along the PC1 was due to differences
in volume. The lack of concistancy regarding the loading of H+ and Na+ could reflect equilibrium reactions
responding to the different solute levels. That [H+ ]
was found to be less sensitive or even positive related
to dilution is discussed below. A decrease in [Na+] by
dilution will be alleviated by a release of sodium from
the soil ion exchanger (i.e. negative salt effect).
In order to uniquely study the chemical parameter
relationships of the important highflow end-member,
without the influence by the other main flowpath, the
samples collected at discharge less than 8 l s 1 were
omitted from the data set. A PCAHF on the highflow samples (29 cases) gave a PC1HF and a PC2HF
that accounted for 46 and 19%, respectively, of the
total variation in these data. Supposedly devoid of
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35
Figure 10. Variations in [TOC], [Alo ], [SO4 2 ] and [PBCorg:4:5 ] with discharge, for the late summer of 1987.
the effects of water pathways, the interrelationship
between the variables still remained similar to those
found for the original PCA (and the PCACl ), though
the PC1HF became a more unique dilution component.
The [TOC] was thereby diluted along with the [Cl ],
leaving only the H+ with positive PC1HF loading (i.e.
positively correlated to a dilution) (Figure 8). This positive relation with dilution is believed to be partly due
to (1) lack of neutralization by the deeper soil layers,
(2) negative salt effect on the ion exchanger releasing
monovalent cations, (3) the effect of dilution on the
protolyzation equilibria.
The PC2HF also bears a resemblance to the PC2,
with the main exception that Na+ and H+ now swapped
position so that Na+ is no longer juxtapositioned with
Cl . A separate PCA of baseflow samples was not
possible due to lack of sufficient data.
At large the H+ was inversely related to Cl , Na+ ,
2+
Ca , Mg2+ and K+ . Usually perpendicular to this
relationship, SO4 2 and NO3 were negatively related to TOC. Since this pattern persisted irrespectively
of the influence from factors as concentration/dilution
and flowpaths, we believe that this is due to the
ion exchange/weathering (H+ vs. base cations) and
adsorption (sulphate vs. DOC) interactions, respectively, between the soil proper and its soil water as
discussed in the previous sections.
A seasalt snowmelt episode
During the initial parts of the snowmelt in the spring of
1987 this usually dilute water system became enriched
in all major anions and cations. A record low pH (4.8)
was recorded in the early phase of the melting at medium flows but with high [Na+ ] and [Cl ]. The preferential leaching of salts from the snowpack (Johannessen and Henriksen, 1978) resulted in high levels
of [Cl ] (4.5), [Na+ ] (3.7), [Ca2+ ] (2.9), [Mg2+ ]
hydr3972.tex; 10/09/1997; 17:02; v.7; p.17
36
(3.7), [NO3 ] (15); numbers in parenthesis give times
of greater than median concentrations (median melt
cons./median general conc.; cf. Table 5). Relative to
the chemical composition of the summer precipitation
(Table 1) the runoff became depleted in all monovalent cations, especially Na+ , as well as sulphate and
nitrate. Only the relative depletion of SO4 2 and NO3
may partly be due to the usually lower winter deposition for these constituents (cf. Table 1). An apperent
increasing trend in the retention of [Na+ ] with decreasing flow (S in Figure 5), contradictory to the generally observed trend, may instead be attributed to an
increase in the ionic strength. As the solution became
more concentrated during the extreme salt pulse the
ion exchanger would adsorb sodium and desorb calcium and magnesium. In fact, Ca2+ and to lesser extent
Mg2+ as the only cations, showed an increased excess
leaching with an increased retention of Na+ (relative
to Cl ) (Caexcess = 0.8 Naexcess + 10.4, R2 = 0.76;
Mgexcess = 0.2 Naexcess + 4.0, R2 = 0.59). During
general conditions the leaching of excess Ca2+ was
about three times greater than for excess Mg2+ , while
during this salt episode the export of excess Ca2+
became six times greater than that of excess Mg2+ .
Nevertheless, a lower absolute Ca/Mg ratio (<0.7)
was generally observed (‘S’ in Figure 3) during this
episode. The increased leaching of excess Ca2+ is
believed to be due to the ion exchanger reacting to
this low Ca/Mg ratio in the salt pulse when releasing
bivalent cations in exchange for Na, while the generally
low Ca/Mg ratio in the streamwater illustrates the mixing of some direct meltwater having bypassed the soils
due to frozen soil layers. The latter explanation was
also argued by Christophersen et al. (1990a) referring
to these samples as outliers from which sodium had
been much less efficiently exchanged than predicted
by a cation exchange relationship.
Rather disturbing from an environmental viewpoint
was the fact that the salt effect caused a record low pH
(4.8) and the Ali to increase more than seven times
(2.0 M) compared with the normal level, while the
[TOC] became half the normal level. Although remaining low, the Ali increase occured despite a constant level of Alo . A constant [Alo ] in spite of a drop in [TOC]
implicates an increased (1.7) Al complexation to the
organic matter (M/mg C). This may be warranted by
the increased Ali and an increase (2.9) in the organic
anion charge density (as inferred from charge balance
over mg C l 1 ).
The role of weak acidity
As the median pH during baseflow was 6.4 both the
bicarbonate system and organic anions contribute to the
buffering of pH. A high median alkalinity (0.15 meq
l 1 titrated to pH 4.5) relative to the bicarbonate
amount (51 eq l 1 , as inferred from total inorganic carbon (TIC) and sample pH) nevertheless suggests
that the 6 mg C l 1 of TOC would be the major alkalinity buffer, i.e. 0.15–0.05 = 0.10 meq l 1 , during baseflow. In fact bicarbonate was the dominating weak acid
only at pH greater than 6.4. The median charge density of the organic matter in the baseflow is more than
twice as large as during highflow (0.07 and 0.03 eq/g C
respectively). Similarly high charge densities were also
found in the more acid (pH 4.9) mineral soil horizons
at the HUMEX site below Terric Histosols (cf. Ytteborg, 1996). The complexation by aluminum or iron is
not great enough to cause a significant loss of organic
charge. The high charge density while passing through
the Bg-mineral soil layers at higher pH may be due
to both foregoing preferential precipitation/adsorption
of lesser charged, more hydrophobic, organic molecules, and the higher pH causing protolyzation of the
phenolic sites on the organic acids.
At highflow the runoff was more acid (pH 5.2) and
the pH buffering was low (median alkalinity 0.04 meq
l 1 ) relative to baseflow conditions. The weak acids are
now less important as thay are dominated by the still
moderate amounts of [TOC] (5.9 mg C l 1 ), accounting for 8 eq l 1 , while bicarbonate only accounted for 3 eq l 1 . Instead strong mineral acid anions
account for more than 90% of the anionic charge. An
observed lack of correlation between the [TOC] and
PBC(org)4:5 is believed to be due to an protonation of
the organic weak acids by the released H+ from the
soil in exchange for sodium. This is seen as a correlation between excess sodium and organic charge density
(R2 = 0.6, n = 33). Note also that [TOC] correlated positively with Alo (R2 = 0.69, n = 92).
The low level of organic anions during highflow
at Ingabekken is noteworthy assuming the highflow
end-member at Ingabekken as representative for preindustrial stream water chemistry in southern Norway.
It has been suggested that fresh waters now acidified
were previously strongly influenced by organic anions
which were then replaced by strong acid anions, pH
not being significantly altered (Krug & Frink, 1983).
This picture does not seem particularly relevant for
Ingabekken.
hydr3972.tex; 10/09/1997; 17:02; v.7; p.18
37
Conclusions
The data show that even in small headwater catchments
the terrestrial part of the catchment exerts a strong influence on chemical species in stream water, even during highflow. Comparing the precipitation chemistry
with the highflow composition in stream, it is seen that
TOC and calcium, in particular, are leached under such
conditions. The five main forces on the runoff chemistry are (1) the geochemical processes occurring in the
end-members (e.g. ion exchange, adsorption, weathering), (2) the soil water pathways determining which
end-member control the runoff, (3) straight dilution by
rain or meltwater by overland flow, (4) the antecedent
hydroclimatic conditions and (5) the effects of ionic
strength on equilibrium reactions (i.e. salt effect). A
simplified cation exchange model is found to explain
qualitatively the observed cation response to changes in
the ionic loading in both soil end-members in addition
to weathering by weak carbonic acid in the baseflow
end-member. In this watershed, mainly covered by a
blanket bog, there are two important water flowpaths.
One is through the mineral soil layer underneath the
organic peat layers, the other is through the surface
layers of the bog. The mineral soil water dominates
during baseflow conditions, while the soil water from
the surface Histosol horizons close to the water divide
predominates during periods of highflow.
Despite the reduced trend in sulphur emissions the
acid deposition levels remain above the critical load
limit for large regions in the northern hemisphere. The
high amount of exchangeable H+ of the highflow endmember and the shallow water flowpath through the
Ingabekken catchment during episodes, render such
catchments with blanket bogs susceptible to acidification. One can merely speculate about the future of this
catchment as it is exposed to prolonged deposition of
low levels of excess strong acid anions. In the discussion on ‘critical loads’ – i.e. the amount of acid deposition an ecosystem can tolerate without adverse effects
– the Ingabekken study at least suggests that 0.5 g SO4
m 2 yr 1 in excess of seasalts (i.e. the present loading)
is acceptable for sensitive systems like our site.
Acknowledgments
The field work and data analysis were funded by the
Surface Water Acidification Programme. R. V. held a
doctor scholarship from the University of Oslo. We
wish to thank H. M. Seip, N. Christophersen, N. Vogt,
J. Mulder, T. Larssen and H. Anderson for valuable
comments and criticism to the paper.
References
Anderson, H. A., R. C. Ferrier & J. D. Miller, 1989. The surface water acidification programme. A comparison between the
pristine Høylandet and the polluted Loch Chon sites, Report
Macaulay Land Use Research Institute, Aberdeen.
Anderson, H. A., J. D. Miller, R. C. Ferrier, T. A. Bruce Walker, D. C. Bain, R. G. McMahon, A. Hepburn, M. Stewart,
B. F. L. Smith & J. S. Anderson, 1997. The effects of boreal
vegetation and the podzolic soils on hydrochemistry at Høylandet
(mid-Norway). Hydrobiologia 348: 5–17.
Bain, D. A., A. Mellor, J. M. Wilson & D. M. C. Duthie, 1990.
Weathering in Scottish and Norwegian catchments. In Mason,
B. J. (ed.), The Surface Water Acidification Programme. Cambridge University Press: 223–236.
Berge, F., Y. W. Brodin, G. Cronberg, F. El-Daoushy, H. I. Høeg,
J. P. Nilssen, I. Renberg, B. Rippey, S. Sandøy, A. Timberlid
& M. Wik, 1990. Palaeolimnological changes related to acid
deposition and land-use in he catchments of two Norwegian softwater lakes. Phil. Trans. r. Soc. Lond. B 327, 385–389.
Blakar, I. & I. Hongve, 1997. On the chemical water quality in
Høylandet, a reference area for acidification research. Hydrobiologia 348: 39–47.
Christophersen, N., H. M. Seip & R. F. Wright, 1982. A model for
stream water chemistry at Birkenes, Norway. Wat. Res. Res. 18:
977–996.
Christophersen, N., R. D. Vogt, C. Neal, H. A. Anderson, R. C. Ferrier, J. D. Miller & H. M. Seip, 1990a. Controlling mechanisms
for stream water chemistry at the pristine Ingabekken site in midNorway: Some implications for acidification models, Wat. Res.
Res., 26: 59–67.
Christophersen, N., C. Neal, R. D. Vogt, J. M. Esser & S. Andersen,
1990b. Aluminum mobilization in soil and stream waters at three
Norwegian catchments with different acid deposition and site
characteristics, Sci. Total Envir. 96: 175–188.
Christophersen, N., C. Neal, R. P. Hooper, R. D. Vogt, & S. Andersen, 1990c. Modelling stream water chemistry as a mixture of
soil-water endmember – a step towards second generation acidification models, J. Hydrol. 116: 307–320.
Cosby, B. J., G. M. Hornberger, J. N. Galloway & R. F. Wright,
1985. Modelling the effects of acid deposition: Assessment of
a lumped parameter model of soil and stream water chemistry,
Wat. Res. Res. 21: 51–63.
Driscoll, C. T., N. M. Johnson, G. E. Likens & M. C. Feller,
1988. Effects of acidic deposition on the chemistry of headwater
streams: A comparison between Hubbard Brook, New Hampshire, and Jamieson Creek, British Columbia, Wat. Res. Res. 24:
195–200.
Duchaufour, P., 1982. Pedology, Pedogenesis and classification.
Georg Allen & Unwin, London: 448.
Esbensen, K., P. Galadi & S. Wold, 1987. Principal component
analysis. Chemometrics and Intelligent Laboratory Systems 2:
37–52.
FitzPatrick, E. A., 1983. Soils: their formation, classification and
distribution. London, Longman: 353.
Fjeldal, P. H., 1992. Jordkjemiens betydning for bekkevannskvaliteten ved tre nedbørsfelt i Norge. (The effect of soil
chemistry on stream water quality at three catchments in Norway)
Thesis, Dept. of Chemistry, University of Oslo.
hydr3972.tex; 10/09/1997; 17:02; v.7; p.19
38
Gherini, S., L. Mok, R. J. M. Hudson, G. F. Davis, C. Chen &
R. Goldstein, 1985. The ILWAS model: Formulation and application, Wat. Air Soil Pollut. 26: 95–113.
Grip, H. & A. Rodhe, 1991. Water pathways – from rain to stream
(In Swedish). Hallgren & Fallgren Studieförlag AB, Uppsala,
Sweden, 156 pp.
Hendershot, W. H. & M. Duquette, 1986. A simple barium chloride
method for determining cation exchange capacity and exchangeable cations, Soil Sci. Soc. Am. J. 50: 605–608.
Henriksen, A., O. K. Skogheim & B. O. Rosseland, 1984. Episodic
changes in pH and aluminium-speciation kill fish in a Norwegian
salmon river. Vatten 40: 225–260.
Henriksen, A., B. M. Wathne, E. J. S.Røgeberg, S. A. Norton &
D. F. Brakke, 1988. The role of stream substrates in aluminium
mobility and acid neutralization. Wat. Res. 22: 1069–1073.
Hordijk, L., 1991. Use of the RAINS model in acid rain negotiations
in Europe. Envir. Sci. Technol. 25: 596–604.
Johannessen, M. & A. Henriksen, 1978. Chemistry of snow melt
water. Changes in concentration during melting, Wat. Res. Res.
14: 615–619.
Krug, E. C. & C. R. Frink, 1983. Acid rain and acid soil: A new
perspective, Science 221: 520–525.
Leivestad, H., I. P. Muniz, 1975. Fish kill at low pH in a Norwegian
river. Nature 259: 391–392.
Minitab, 1993. Minitab statistical software package, Release 9.2.
Minitab Inc. State College, PA, USA.
Mulder, J., M. Pijpers & N. Christophersen, 1995. Water flow paths
and the spatial distribution of soils as a key to understanding
differences in stream water chemistry between three catchments
(Norway). Wat. Air Soil Pollut. 81: 76–91.
Mulder, J., M. Pijpers & N. Christophersen, 1991. Water flow paths
and the spatial distribution of soils and the exchangeable cations
in the acid rain-impacted and pristine catchment. Wat. Res. Res.
27: 2919–2928.
Mulder, J., N. van Breemen & H. C. Eijck, 1989. Depletion of soil
aluminium by acid deposition and implications for acid neutralization. Nature 337: 247–249.
Muniz, I., 1997. Surface water chemistry characteristics in the Lake
Stor Grønningen drainage area, Høylandet, during periods of high
and low discharge. Hydrobiologia.
Neal, C., C. J. Smith, C. J. Walls & C. S. Dunn, 1986. Major,
minor and trace element mobility in the acidic upland forested
catchment of the upper River Severn, Mid Wales, J. Geol. Soc.
London: 143: 635–648.
Neal, C. & N. Christophersen, 1989. Inorganic aluminum – hydrogen
ion relationships for streams; the role of water mixing processes,
Sci. Tot. Envir. 80: 195–203.
Norton, S. A. & A. Henriksen, 1983. The importance of CO2 in
evaluation of effects of acid deposition. Vatten 39: 346–354.
Overrein, L. N., H. M. Seip & A. Tollan, 1980. Acid precipitation –
effects on forest and fish, Final report SNSF project, Norwegian
Institute for Water Research, 175 pp.
Pijpers, M. & J. Mulder, 1990. The spatial variability of the exchange
complex composition in the O horizon of an acid rain impacted
and pristine catchment in Norway. Report to NTNF/NILU. Senter
for Industrial research (SI) report # 87 0406-1; 51 pp.
Rodhe, H., P. I. Grennfelt, J. Wisniewski, C. Ågren, G. Bengtsson,
H. Hultberg, K. Johansson, P. Kauppi, V. Kucera, H. Oskarsson, G. Pihl Karlsson, L. Rasmussen, B. Rosseland, L. Schotte,
G. Selldén & E. Thörnlöf, 1995. Acid Reign’ 95, Conference
summary statement. In proceedings from The 5th int. Conf. on
acid deposition. Gothenburg, Sweden. In special issue of Wat.
Air Soil Pollut. 85: 1–14.
Rosenqvist, I. Th., 1978. Acid precipitation and other possible
sources for acidification of rivers and lakes, Sci. Total Envir.
10: 39–49.
Seip, H. M., D. O. Andersen, N. Christophersen, T. J. Sullivan &
R. D. Vogt, 1989. Variations in concentrations of aqueous aluminum and other chemical species during hydrological episodes
at Birkenes southernmost Norway. J. Hydrol. 108: 387–405.
Seip, H. M., N. Christophersen, J. Mulder & G. Taugbøl. 1995. Integrating field work and modelling. The Birkenes case. In Trudgill,
S. T. (ed.), Solute Modelling in Catchment Systems. John Wiley
& Sons Ltd., 387–415.
Seip, H. M. & S. Rustad, 1984. Variations in surface water pH with
changes in sulphur deposition. Wat. Air Soil Pollut. 21: 217–223.
Semb, A., 1987. A comparison between precipitation quality at
Tustervatn and Høylandet, Norwegian Institute for Air Research,
10 pp. (in Norwegian)
SFT, 1987. Norwegian State Pollution Authority, Monitoring long
range transported air and precipitation, Annual report 1986,
Report 296/87, 199 pp. (in Norwegian).
SFT, 1988. Norwegian State Pollution Control Authority, 1000 lake
survey 1986, Report 313/88, 35 pp.
Sullivan, T. J., N. Christophersen, I. P. Muniz, H. M. Seip & P. D. Sullivan, 1986. Aqueous aluminum chemistry response to episodic
increases in discharge, Nature 323: 324–327.
Tørseth, K., 1995. Monitoring of long range transported air pollutants, Annual report for 1995. Report 663/96, NILU, 2007 Kjeller,
Norway, 189 pp.
Vogt, R. D., D. O. Andersen, S. Andersen, N. Christophersen &
J. Mulder, 1990. Stream water, Soil water chemistry, and water
flowpaths at Birkenes during a dry-wet hydrological cycle. In
Mason, B. J. (ed.), The Surface Waters Acidification Programme
(SWAP). Cambridge University Press: 149-154.
Vogt, R. D., S. Godzik, M. Kotowski, M. Niklinska, L. Pawtowski,
H. M. Seip, J. Sienkiewicz, G. Skotte, T. Staszewski, G. Szarek,
J. Tyszka & P. Aagaard, 1994. Soil, soil water and stream water
chemistry at some Polish sites with varying acid deposition. In
Warfvinge, P. & H. Sverdrup, 1992. Calculating critical loads
of acid deposition with PROFILE, a steady-state soil chemistry
model. Wat. Air Soil Pollut. 63: 119–143.
Ytteborg, G., 1996. Changes in HUMEX soil water chemistry. Treatment induced effects or natural variations. Thesis, University of
Oslo, Dept. of Chemistry, Norway.
hydr3972.tex; 10/09/1997; 17:02; v.7; p.20