Limnology (2007) 8:175–182
DOI 10.1007/s10201-007-0206-4
© The Japanese Society of Limnology 2007
ASIA/OCEANIA REPORT
Akira Haraguchi
Effect of sulfuric acid discharge on river water chemistry in peat swamp
forests in central Kalimantan, Indonesia
Received: January 5, 2007 / Accepted: February 8, 2007 / Published online: July 7, 2007
Abstract To estimate the range of area that is affected by
sulfuric acid pollution after pyrite oxidation, the surface
water chemistry of two rivers in peat swamp forests in central Kalimantan, Indonesia, was surveyed at 1.0- to 3.0-km
intervals in September 2003 and 2004 (dry season) and
March 2004 and 2005 (rainy season). Water discharged
from canals into the main stream of the Sebangau River and
the Kahayan River showed lower pH compared to the
mainstream water of the rivers, implying sulfuric acid loading from the canal to the main stream of the rivers. The ratio
of concentrations of sulfate ion/chloride ion, which was
used as a parameter for estimating the contribution of pyritic sulfate to river water chemistry, showed that sulfuric
acid loading from pyrite oxidation occurred from the river
mouth up to 150 km upstream in both rivers. Water of the
main stream of the rivers as well as water discharged from
artificial canals into the main stream in the rainy season
showed much higher acidity and a higher ratio of sulfate
ion/chloride ion than that in the dry season. This result implies that the discharge of pyritic sulfate from peat swamp
forests to the limnological system is much higher in
the rainy (high water table) season than the dry (low water
table) season. Water in the canal in the rainy season was
found to be highly acidic (pH = 2.0–3.0). Pyrite oxidation
after peatland development causes not only acidification of
soil but also acidification of the limnological ecosystem.
Key words Acid sulfate soil · Basin · Canal · Mire ·
Pyrite · River · Sulfate · Tropical peat swamp
A. Haraguchi
Faculty of Environmental Engineering, The University of
Kitakyushu, Wakamatsu, Kitakyushu 808-0135, Japan
Tel. +81-93-695-3291; Fax +81-93-695-3383
e-mail [email protected]
Introduction
Peatlands are regarded as important carbon pools that regulate the concentration of atmospheric carbon and the consequent global environment (Hadi et al. 2000; Haraguchi et
al. 2000; Shimada et al. 2001; Nakagawa et al. 2002). Tropical areas have large expanses of peat lands (Anderson
1983), and the tropical peat, especially in Kalimantan,
makes up a large carbon pool (RePPProT 1990). Maltby
and Immirzi (1993) estimated that 3%–4% of global
peat and carbon (329–525 Pg) is in the Indonesian peat
swamp forest. Recent agricultural utilization of peat swamp
forest in Kalimantan has led to the disappearance of peat
in huge areas of the district. Peat swamp forests in central
Kalimantan have very high precipitation in the rainy season, which impedes plant decomposition as a result of the
high water table and the consequent anoxicity in the peat
layer.
Human activity affecting tropical peat swamp forest, especially destruction of peat soil for reasons of agricultural
land development (e.g., Mega-rice project in central Kalimantan Indonesia), leads not only to emission of greenhouse gases but also to various serious regional environmental
problems. One of the regional environmental problems
caused by the destruction of tropical peat is the oxidation
of pyrite (FeS2) within the sediment underneath the peat
layer in the coastal area of the tropical region, an effect
much like sulfuric acid pollution in coal mining areas of
Europe (Monterroso and Macias 1998; Balkenhol et al.
2001).
Pyrite is distributed widely in the sediments and bedrock
around the world. One of the serious environmental problems caused by pyrite oxidation is the generation of acid
mine drainage (AMD) from mine site spoils. Mining operations produce large amounts of waste tailings, which are
usually deposited in open-air impoundments. Waste tailings
containing metal sulfates such as pyrite lead to the production of acid rock drainage, which contaminates the environment with heavy metals and sulfuric acid. Many reports
describe the effect of sulfuric acid from mine wastes on
176
vegetation destruction and ecosystems (Meyer et al. 1999;
Bachmann et al. 2001; Werner et al. 2001).
In former open-cut brown coal mining areas dating from
the early 20th century, for example, in the Lower Lusatian
lignite mining district in Germany, there still remain many
open mining casting lakes with high concentrations of sulfuric acid and extremely high acidity (pH = 1.5–2.5). Sulfuric
acid comes from the mine spoils surrounding the lakes, and
the continuous supply of sulfuric acid to the lake accelerates
the acidification of the lake water. Furthermore, at this
point most of the areas have not been reclaimed. An advanced method of open-cut mining of brown coal using a
conveyer bridge dump can prevent pyrite oxidation by retaining the stratigraphy of the Tertiary strata to the greatest
degree possible (Wisotzky and Obermann 2001). However,
rehabilitation of the vegetation after open mining in such
areas is difficult because of the contamination of the topsoil
by pyrite.
After destruction of the peat layer over pyrite-containing sediment, pyrite is biologically oxidized by atmospheric
oxygen and sulfuric acid is produced. Then, sulfuric acid
concentration increases in the soil, and a large proportion
of the nutrients is lost. Discharged sulfuric acid from the
soil causes the acidification of river water and subsequent
effects on the littoral zone. Indonesia has large areas of
tropical peatlands, and Kalimantan has about 6.7 Mha of
peatlands. The 1 million ha “Mega Rice Field Project, Central Kalimantan” started in 1995, and the project aimed to
establish irrigated rice fields on 1 million ha of peat swamp
forest. The project, however, stopped in 1997, and most of
the fields have been abandoned.
Among such abandoned fields, peat in the lower basin
of Sebangau River in Central Kalimantan was affected by
the pyrite in the mineral layer underneath the peat layer
(Haraguchi et al. 2000). The pH of the peat pore water in
Paduran, the lower basin of the Sebangau River, was 3.6
from the surface layer to the bottom layer (100 cm depth),
whereas that of peat in Lahei, the middle basin of Kapuas
River, increased from 3.5 to 6.0 from the surface to the bottom (500–550 cm depth). This observation implies acidification by pyrite oxidation in the lower basin of the river,
because pyrite is formed in a reducing environment in salt
marsh or shallow coastal sediments with a continuous supply of sulfur and iron in the presence of easily decomposable organic matter (Howarth and Merkel 1984; King 1983).
However, insufficient data are available for clarifying the
range of pyrite distribution and the extent to which peat soil
and discharged water are polluted by sulfuric acid after pyrite oxidation.
A major objective of this study is to estimate the area of
the basin that is chemically affected by the sulfate produced
by pyrite oxidation under the peat layer. We collected
surface water from Sebangau River and Kahayan River,
including discharged water from canals and tributaries, at
1.0- to 3.0-km intervals and analyzed the chemical components in the water. The surveyed area ranged from the
river mouth to the uppermost stream of the Sebangau River
(about 176 km from the river mouth) and Kahayan
River (about 224 km from the river mouth to Palangkaraya
City). From the analytical data for dissolved dominant cations and anions, we estimated the range over which the
river water is affected by sulfuric acid produced by pyrite
oxidation.
Study sites and methods
The study area belongs to a tropical peat swamp forest in
Central Kalimantan, Indonesia. Palangkaraya City (1°35′–
2°25′ S, 113°29′–114°07′ E, 15–20 m a.s.l.) is the capital of
Central Kalimantan Province. The population density of
Central Kalimantan is low except for Palangkaraya City
(population about 170 000). About 56% of the land of
Palangkaraya City is covered by forest. Forestry and agriculture are the main industries of Palangkaraya City and
Central Kalimantan Province, and heavy industries are
rare. Averaged air temperature between 1978 and 2000 in
Palangkaraya City was 26.7°C, and monthly averaged temperature shows two maximums in May (27.2°C) and October (26.9°C) and two minimums in January (26.3°C) and
June (26.3°C; data from Hayasaka et al. 2003 and Usup et
al. 2003). Mean annual precipitation between 1978 and 2000
in Palangkaraya City was 3400 mm, and monthly precipitation shows a maximum in November (348.1 mm) and a minimum in August (113.5 mm). Monthly precipitation is less
than 200 mm from July to October whereas it exceeds
300 mm from November to April, although fluctuation between years is very large. Forest fire breaks out widely in
the dry season with low annual precipitation (e.g., 1997 or
2007), and fire causes serious problem of haze. The water
resource in Palangkaraya City depends mostly on groundwater, and wastewater is discharged to the Kahayan River.
There are many gold mining activities upstream of the
Kahayan River, and hence river water has the likelihood of
contamination by mercury.
To estimate the range of the area that is affected by sulfuric acid pollution, the water chemistry of the two rivers
was surveyed in September 2003 and 2004 (dry season) and
March 2004 and 2005 (rainy season). The Sebangau River
(Fig. 1) originates at Kya, 6 km upstream from Kerengbangkirai (the southern part of Palangkaraya City), and flows
west of Palangkaraya City. Whole catchments of the Sebangau River are covered by peatlands, and hence river water
contains a high concentration of humic substances (dark
brown color) and background pH is 3.5–4.0. Tachibana et
al. (2003) reported that maximum water flux of Sebangau
River is 50 m3/s from December to February and the minimum is 5 m3/s from June to September at Kya. Water flux
of the lower basin of the Sebangau River is not reported.
Six main tributaries flow into the main stream of the Sebangau River. Six main canals have been constructed and connected to the Sebangau River from the eastern part of the
main stream. Water samples were collected from the river
mouth to Kya, including the Paduran canal (artificial) and
four natural tributaries (Paduran River, Bangah, Rasau,
Bakung). Data on Paduran canal, Bangah, Rasau, and
Bakung were missing in September 2003.
177
2.00 S
i
K at B
an
a
ng
Kanu pa
ti n
Ka
Bakung
Ak
ng
a
l
B ulan
Bu
ng
Rana ng
M
usa
a
n
sa
2.50 S
Rasau
n
Ba
S
e
b
a
n
g
a
u
ah
y
nu
san
T er u
n
ga
a
as
Kapu
Palangkaraya
Kya
Kerengbangkirai
h
p
g
in
Kat
u tu
ngk
K
R
Ma
ng
an
a lahasi
n
ga
un
Fig. 1. Map showing the study
area in central Kalimantan, Indonesia. Data were collected from
two rivers, Sebangau River and
Kahayan River. The surveyed
area of the two rivers is indicated
by the bold line. Data were collected also from tributaries
(Bakung, Rasau, Bangah, and
Paduran Rivers) and canals (Paduran canal, Pulangpisau canal,
Basarang canal, Kanamit canal,
Pangkoh canal). Closed circles
denote cities, villages, or research
stations
gah
Pulangpisau
0
10
Kanamit
3.00 S
Pangkoh
ya
Ra
u
Tar
r un g
n
ba
Se
K
a
h
a
y
a
n
san
Seban
gau K e
cil
gau
Kaki
Paduran
Basarang
K a puas
un
K etimp
Pad
ura
n
mu
as
pu
a
K
20km
3.50 S
113.50 E
The Kahayan River originates at Kahukung Mountain
(about 200 km upstream from Palangkaraya) and flows east
of Palangkaraya City. Most of the peatlands are distributed
downstream of the Kahayan River from Palangkaraya City,
and hence the concentration of humic substances in the
river water is much lower than in the Sebangau River. Because of the intensive activity of gold mining upstream of
the Kahayan River from Palangkaraya City, the turbidity
114.00 E
of river water is quite high, and the pH of water around
Palangkaraya City is 5.5–7.0, higher than in the Sebangau
River. Water flux of the Kahayan River is not reported.
Five main canals from the western part and also five canals
from the eastern part have been connected to the main
stream of the Kahayan River downstream from Palangkaraya. The Rungan River merges 12 km upstream of
Palangkaraya City. Data on the Kahayan River and the
178
(a) Sebangau pH (dry season)
8.0
7.0
pH
6.0
5.0
4.0
3.0
0
50
100
150
Distance from the river mouth (km)
200
(b) Sebangau pH (rainy season)
4.4
4.2
4.0
3.8
pH
Rungan River were obtained up to 326 km and 333 km from
the river mouth, respectively, but this article presents data
of the Kahayan River from the river mouth to Palangkaraya
City (224 km from the river mouth), including four artificial
canals (Pangkoh, Kanamit, Basarang, Pulangpisau). Data
from the river mouth to 45.1 km as well as Kanamit canal
were missing for September 2003.
Water samples were collected at the center of the river
at intervals of every 1.0–3.0 km along the rivers. Each water
sample was directly collected from a boat by using a plastic
tub of about 1000 ml at each sampling point. The position
of each sampling point was determined by GPS (Poke Navi
map 21EX; Empex, Tokyo, Japan). The ITRF94 unit was
used for coordination. Water temperature, pH, and EC
(electrical conductivity) of the collected water were measured just after water sampling by using a portable pH meter (D-25; Horiba, Kyoto, Japan) and an EC meter (ES-12;
Horiba). Water samples were filtered within 12 h after
sampling using a 0.45-µm cellulose acetate membrane filter
(Advantec, Tokyo, Japan) and stored in 2.0-ml plastic tubes
at room temperature before chemical analysis. Major cations (ammonium, sodium, potassium, magnesium, calcium
ions) and anions (nitrite, nitrate, chloride, sulfate, phosphate ions) were determined using an ion chromatograph
(Dionex Model DX-120; Japan Dionex, Tokyo, Japan).
3.6
3.4
3.2
Results and discussion
In the Sebangau River, the pH of the surface river water in
the dry season tended to decrease from Kya (uppermost
stream of the Sebangau River) to a point 60–80 km from the
river mouth (Fig. 2a), and then the pH increased downstream to the river mouth in the dry season. Although pH
at 40–60 km and 135–150 km from the river mouth was different between September 2003 and September 2004, the
profile along the river was similar between the two measurements. Water at the river mouth was affected by seawater, and the effect of seawater on the surface river water
chemistry appeared up to at least 60–80 km from the river
mouth in the Sebangau River in the dry season. Surface
river water of the Sebangau River in the rainy season
showed lower pH than during the dry season, ranging between 3.4 and 4.2. Although pH at 0–70 km from the river
mouth in March 2004 was lower than in March 2005 and the
position of the minimum differed ∼30 km between 2004 and
2005, the range of pH was limited, between 3.4 and 4.2. This
difference could be caused by the tidal range rather than
difference between years. The pH of the surface river water
did not show an increasing tendency to the river mouth at
the lower basin in the rainy season (Fig. 2b). Inundation of
seawater to the Sebangau River was not obvious in the
rainy season, probably because of the high water level of
the river caused by high precipitation. Water depth at the
river mouth was strongly affected by tides, but averaged
depth (roughly estimated at 5.0 m) did not show a difference
between dry and rainy seasons (Haraguchi, unpublished
data). On the other hand, water depth at Kya in September
3.0
0
50
100
150
Distance from the river mouth (km)
Paduran canal
Bangah
Paduran river
200
Rasau Bakung
Fig. 2. Surface water pH of the Sebangau River in central Kalimantan,
Indonesia, in (a) the dry season (closed symbols, September 2003; open
symbols, September 2004), and (b) the rainy season (closed symbols,
March 2004; open symbols, March 2005). Data on the main stream of
the Sebangau River are presented as circles. Data on canals and tributaries are represented by triangles; each arrow (shown below the xaxis) shows the position of the junction with the main stream of each
canal or tributary
2004 and March 2005 was 2.5 m and 5.5 m, respectively.
Considering the difference of altitude of 15–20 m between
the river mouth and Kya, inundation of seawater to the
river is possible in the dry season. Partial minimum of pH
at 50 km (March 2004) and 20 km (March 2005) showed the
acidification of water in the main stream of Sebangau in the
rainy season, whereas acidification of the main stream was
not observed in the dry season.
The pH in the Paduran canal was almost the same as in
the main stream of the Sebangau River in the dry season
(Fig. 2a); however, pH in the Paduran canal measured ∼0.5
units lower than that in the main stream of the Sebangau
River in the rainy season (Fig. 2b). Water in the tributaries
(Paduran River, Bangah, Rasau, Bakung) showed almost
the same pH value or ∼0.2 units lower than the main stream
of the Sebangau River. Acidity of the Paduran canal was
179
(a) Sebangau SO42-/Cl- ratio (dry season)
1.6
1.4
SO42-/Cl- (w/w)
1.2
1.0
0.8
0.6
0.4
0.2
0
0
50
100
150
Distance from the river mouth (km)
200
14
140
12
120
10
100
8
80
6
60
4
40
2
20
0
0
50
100
150
Distance from the river mouth (km)
Paduran canal
Bangah
Paduran river
SO42-/Cl- (w/w)
(b) Sebangau SO42-/Cl- ratio (rainy season)
SO42-/Cl- (w/w)
higher than the main stream in the rainy season, whereas
acidity of the natural tributaries did not show a clear difference from the main stream (Fig. 2b). This result showed
that the water in the artificial canal was highly acidified in
the rainy season.
We estimated the range over which sulfuric acid originating from pyrite oxidation affects the water chemistry of the
river. Sulfate ions come both from seawater and from water
discharged from pyrite-containing soil. Industries releasing
sulfate to the atmosphere are rare in Central Kalimantan,
and hence sulfate originated from industry could be negligible. Automobiles or forest fire could be the origin of atmospheric sulfate. However, pH of bulk deposition is
5.5–6.5 throughout the year (Sulistiyanto et al. 2003), implying deposition of sulfate from the atmosphere to river water
could be negligible in this watershed. Sulfate ion concentration in the water discharged from soils in which pyrite oxidation occurs is usually much higher than the chloride
−
concentration, and so the ratio of SO2−
4 /Cl can be used to
evaluate the effects of sulfuric acid from pyrite oxidation
−
on river water chemistry. In the dry season, the SO2−
4 /Cl
ratio in the Sebangau River decreased from the uppermost
stream of the river to the 135-km point, and it increased
from the 135-km point to the 90-km point (Fig. 3a). Al−
though SO2−
4 /Cl ratio at 70–176 km from the river mouth in
September 2003 was higher than in September 2004, the
profile along the river was similar between the two measurements. The ratio decreased from the 90-km point to the
45-km point and fluctuated around 0.13–0.18, the same
−
value as found in seawater [SO2−
4 /Cl ratio = 0.14 (w/w)],
from the 45-km point to the river mouth. Increases of SO2−
4
/Cl− ratio downstream from the 135-km point implied that
the effect of pyrite on the river water chemistry appeared
downstream from the 135-km point from the river mouth.
In the rainy season, the ratio showed the same tendency as
in the dry season; however, the ratio was much higher than
−
during the dry season (Fig. 3b). Although SO2−
4 /Cl ratio at
0–120 km from the river mouth in March 2004 was higher
than in March 2005, the profile along the river was similar
−
between two measurements. The SO2−
4 /Cl ratio started to
increase from about 140 km from the river mouth, but the
maximum was 45 km from the river mouth, 45 km downstream compared to the location in the dry season. This
observation implies that the effect of seawater on the surface water chemistry of the Sebangau River appeared up to
around 45 km from the river mouth in the rainy season because of the high water level of the river, whereas the effect
of seawater appeared up to around 100 km (maximum of
−
the SO2−
4 /Cl ratio in Fig. 3a) in the dry season. Water of the
main stream of the rivers as well as water from Paduran
canal in the rainy season showed a much higher ratio of
−
SO2−
4 /Cl (Fig. 3b) than the respective results in the dry season (Fig. 3a). This observation implies that discharge of
pyritic sulfate from peat soil to the river system is much
higher in the rainy (high water table) season than in the dry
(low water table) season. Higher acidity and higher ratio of
−
SO2−
4 /Cl in the Paduran canal showed that pyritic sulfate
was discharged from peatlands to the river via the artificial
canal system.
0
200
Rasau Bakung
Fig. 3. Ratio of sulfate and chloride ions (weight-to-weight ratio, w/w)
of the surface water of Sebangau River in central Kalimantan, Indonesia, in (a) the dry season (closed symbols, September 2003, open
symbols, September 2004), and (b) the rainy season (closed symbols,
March 2004; open symbols, March 2005). Data on the main stream of
the Sebangau River are presented as circles; data on canals and tributaries are represented by triangles; each arrow (shown below the xaxis) represents the position of the junction with the main stream of
each canal or tributary. Data on canals and tributaries in the rainy
season (b) are presented on a different scale, which appears on the
right-side axis in b
Although the pH of the surface water of the Kahayan
River showed a little difference between two measurements
in both the dry and rainy seasons, the profile along the river
was similar between two measurements in each season except for the lack of a local minimum at 50 km from the river
mouth in the profile of September 2003. In the Kahayan
River, the pH of the surface water increased from Palangkaraya City (224 km from the river mouth) to 20–30 km downstream from the Palangkaraya City in both the dry and
rainy seasons (Fig. 4a,b). The pH of the Kahayan River at
the middle of Palangkaraya City showed ∼1.0 pH unit lower
than the upper and lower part of the river (only partial data
are presented). Lower pH at the center of Palangkaraya
City could be the result of discharge of wastewater in the
city, and analysis of the effect of wastewater on Kahayan
River water chemistry is now in progress. The pH showed
another local minimum around the 50–70 km point from the
river mouth in the dry season (Fig. 4a), whereas the local
180
8.0
(a) Kahayan pH (dry season)
7.5
pH
7.0
6.5
6.0
5.5
5.0
0
50
100
150
200
Distance from the river mouth (km)
250
(b) Kahayan pH (rainy season)
8.0
7.0
pH
6.0
5.0
4.0
3.0
2.0
0
50
100
150
200
Distance from the river mouth (km)
250
Pulangpisau
Pangkoh Basarang
Kanamit
Fig. 4. Surface water pH of the Kahayan River in central Kalimantan,
Indonesia, in (a) the dry season (closed symbols, September 2003; open
symbols, September 2004), and (b) the rainy season (closed symbols,
March 2004; open symbols, March 2005). Data on the main stream of
the Kahayan River are presented as circles; data on canals are represented by triangles; each arrow (shown below the x-axis) represents the
position of the junction with the main stream of each canal
minimum appeared 30–40 km from the river mouth in the
rainy season (Fig. 4b). In the rainy season, the river water
of Kahayan showed ∼1.0 pH unit lower than during the
dry season in the upper basin, whereas the water showed
∼2.5 units lower pH value in the lower basin (Fig. 4a,b).
This result implies that strong effects of sulfuric acid discharged from pyrite-containing peat appeared in the rainy
season.
Although exact data of water depth of the Kahayan
River are not reported, roughly estimated water depth at
the river mouth was about 8.0 m and did not show a difference between the dry and rainy seasons, whereas water
depth in Sei Gohong (86 km upstream of Palangkaraya
City) in September 2004 and March 2005 was 4.5 m and
7.0 m, respectively (Haraguchi, unpublished data). Inundation of seawater to the river is possible in the dry season as
to the Sebangau River. Although water at the river mouth
showed the effect of seawater in both the dry and rainy
seasons, a local minimum of pH appeared in the lower basin
of the Kahayan River in both dry and rainy seasons. The
local minimum was not observed in the Sebangau River in
the dry season; thus, the effect of discharged acid on the
main stream of Kahayan River was much higher than in the
Sebangau River in the lower basin. This difference could be
caused by the existence of extensive artificial canal systems
around the Kahayan River compared with the Sebangau
River. Surface water in the canals connected to the Kahayan River showed lower pH than that of the main stream of
the Kahayan in both the dry and rainy seasons (Fig. 4a,b).
−
Although the SO2−
ratio of the surface water of
4 /Cl
Kahayan River showed a little difference between two measurements in both dry and rainy seasons, the profile along
the river was similar between two measurements in each
season, except for lacking of convergence to the value of
seawater at the river mouth in the profile of September
−
2003. In the dry season, the SO2−
4 /Cl ratio in the Kahayan
River was consistently much higher than the ratio in sea−
water (Fig. 5a). The SO2−
4 /Cl ratio decreased from the upper stream to the 150- to 170-km point, and then the ratio
increased moving downstream, showing a local maximum
around the 70- to 130-km point from the river mouth. The
water in the two canals directly connected to the Kahayan
River showed extremely high values in the dry season for
−
the SO2−
4 /Cl ratio, implying that the canal water contained
greater amounts of pyritic sulfate than the main stream of
the Kahayan River (Fig. 5a).In the rainy season, the SO2−
4 /
Cl− ratio in the lower basin (between 30 and 130 km from
the river mouth) of the Kahayan River as well as in canals
showed extremely higher values, implying the loading of
large amounts of sulfuric acid to the river system in the
rainy season (Fig. 5b).
Thus, we estimated the area of sulfuric acid pollution in
the limnological system in Central Kalimantan, Indonesia.
The area actually polluted by sulfuric acid is the area with
a lower pH, and the area ranged up to 70 km and 100 km
from the river mouth in Sebangau River and Kahayan
River, respectively. The area of the threat of sulfuric acid
−
pollution, which is the area with a higher SO2−
4 /Cl ratio but
not with lower pH, ranged 150 km from the river mouth
both in the Sebangau River and in the Kahayan River.
Conclusion
Problems of sulfuric acid pollution after pyrite oxidation
mostly appear in the coastal peat swamp. Estimation of the
range of the area polluted by sulfuric acid after pyrite oxidation in the freshwater ecosystem was successfully achieved
by analyzing the surface river water chemistry at approximately 1.0- to 3.0-km intervals in the peat swamp forests in
both dry and rainy seasons. The effect of pyrite oxidation
on the freshwater system appeared from the river mouth to
150 km upstream from the river mouth. Sulfuric acid discharges from soil to river occurred mostly in the rainy season. Artificial canals are the main source of sulfuric acid to
the main stream of the river. The impact of sulfuric acid on
181
10
laboratory work. This work was financially supported by the Core
University Program of the JSPS, the Sumitomo Foundation for Environmental Research, the Showa Shell Sekiyu Foundation for Promotion of Environmental Research, and the research project fund from
the Ministry of Education, Culture, Sports, Science and Technology of
Japan (Nos. 16658031 & 16405039). Part of the chemical analysis was
done at the Instrumentation Center, The University of Kitakyushu.
(a) Kahayan SO42-/Cl- ratio (dry season)
SO42-/Cl- (w/w)
8
6
4
2
0
References
0
50
100
150
200
Distance from the river mouth (km)
250
150
12
120
9
90
6
60
3
30
0
0
50
100
150
200
Distance from the river mouth (km)
SO42-/Cl- (w/w)
SO42-/Cl- (w/w)
(b) Kahayan SO42-/Cl- ratio (rainy season)
15
0
250
Pulangpisau
Pangkoh Basarang
Kanamit
Fig. 5. Ratio of sulfate and chloride ions (weight-to-weight ratio, w/w)
of the surface water of the Kahayan River in central Kalimantan, Indonesia in (a) the dry season (closed symbols, September 2003; open
symbols, September 2004), and (b) the rainy season (closed symbols,
March 2004; open symbols, March 2005). Data on the main stream of
the Kahayan River are presented as circles; data on canals are represented by triangles; each arrow (shown below the x-axis) indicates the
position of the junction with the main stream of each canal. Data on
canals and tributaries in the rainy season (b) are presented on different
scales (see right-side axis in b)
the river water chemistry in the Kahayan River appeared
much more clearly than in the Sebangau River, probably
because of the extensive canal systems around the Kahayan
River. Research on seasonal differences of the sulfuric acid
production process and the mechanism of sulfuric acid
transport from peat soil to river systems via canal systems,
as well as the impact of sulfuric acid on both freshwater and
human communities in the basin of the Sebangau and
Kahayan Rivers, are now in progress.
Acknowledgments The author thanks Mr. Suwido H. Limin of The
University of Palangkaraya for support in the research in Central
Kalimantan, Indonesia. The author also thanks Mr. Untung Darung,
Ms. Yulintine Liwat, Ms. Linda Wulandari, Mr. Imar Ardianor, Mr.
Yurenfrie, Ms. Tris Liana, Ms. Tri Septiani, and Ms. Sepmiarna
Welsiana of The University of Palangkaraya and Mr. Dai Sugiura, Mr.
Keisuke Michiki, Ms. Kyoko Shikasho, Mr. Yasuhiro Suzuka, and Mr.
Yoshihide Tanaka of The University of Kitakyushu for their support
of my field research, and Ms. Miki Nagai, Ms. Chihiro Yoshihara, Ms.
Hitomi Ikeda, and Ms. Ayumi Kuboyama for their support with the
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