- Email: [email protected]
Transport of particulate organic matter in the Ishikari River, Japan during spring and summer
NIM B Beam Interactions with Materials & Atoms
Nuclear Instruments and Methods in Physics Research B 259 (2007) 513–517 www.elsevier.com/locate/nimb
Transport of particulate organic matter in the Ishikari River, Japan during spring and summer Md. Jahangir Alam a, Seiya Nagao b,*, Takafumi Aramaki c, Yasuyuki Shibata c, Minoru Yoneda c a
Graduate School of Environmental Earth Science, Hokkaido University, Sapporo 060-0810, Japan b Faculty of Environmental Earth Science, Hokkaido University, Sapporo 060-0810, Japan c National Institute for Environmental Studies, Tsukuba 305-8506, Japan Available online 2 February 2007
Abstract Both D14C and d13C were used to study transport behavior of particulate organic matter (POM) in the Ishikari River in Japan. Water samples were collected once a month from April to September in 2004. Positive correlations were found between D14C and particulate organic carbon (POC) content and D14C and d13C values for the POM samples from June to September. However during snow-melt, distinctive minimum values were found for POC content, D14C and d13C. These results indicate the POC was supplied from different sources and by different mechanisms during spring snow-melt and summer because of variations in water level and discharge. Ó 2007 Elsevier B.V. All rights reserved. Keywords: Ishikari River; POC; D14C; d13C; Snow-melt
1. Introduction The annual load of riverine particulate organic carbon (POC) from land to ocean corresponds to half the total organic carbon [1]. Transportation of POC in river systems is one pathway of the carbon cycle in terrestrial ecosystems. For that reason, river systems are important for the carbon cycle. Carbon discharge and transport patterns vary among rivers and watershed conditions, which include geographical, hydrological and land use features [2–4]. The watershed environments vary from spring to summer because of snow-melt in sub-arctic and arctic areas. Snow-melt water considerably increases water discharge and transport of inorganic and organic materials from land to ocean [5–7]. Dynamics of particulate organic matter (POM) and its fate in river systems are unknown during snow-melting periods because POM exhibits tremendous temporal and spatial variations in physico-chemical char*
Corresponding author. Tel.: +81 11 706 2349; fax: +81 11 706 4867. E-mail address: [email protected] (S. Nagao).
0168-583X/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2007.01.194
acteristics [8]. To understand POC transport behavior in river systems, we must obtain information on residence time, patterns of transport and discharge of POC. Both D14C and d13C values have proven to be simple and useful parameters to study POM sources and residence times; they are very suitable for elucidating POM dynamics [9– 11]. This study applied carbon isotopic ratios (D14C and d13C) to POM of the Ishikari River waters to investigate transportation behavior in river systems during spring and summer seasons. 2. Materials and methods 2.1. Study area The Ishikari River runs through the lowland in eastern Hokkaido (Fig. 1); It has a catchment area of 14,330 km2 and is 268 km long. The main types of land use are forest, agriculture and urban. Rice is the main agricultural product along the river. The monthly average water discharge ranges from 150–1130 m3/s during 1999–2002 [12];
514
Md.J. Alam et al. / Nucl. Instr. and Meth. in Phys. Res. B 259 (2007) 513–517
Fig. 1. Sampling location.
50% of the precipitation falls as snow [13]. Monthly mean winter precipitation is 46–105 mm and the snow depth is from 38–108 cm from December to late April [14]. Snowmelting begins in March and increase in water levels and discharge. The highest water discharge at the Iwamizawa–Ohashi occurs in April and is up to 3–4 times greater than that in winter [14].
LECO Corp.). Prior to analysis, calcium carbonate was removed by adding 0.1 M HCl, rinsing with Milli Q water and subsequent drying. The obtained POC contents were expressed as wt.% unit (g C/100 g suspended solid dry basis). The POC concentrations were expressed using the following equation: POC concentration ðmg=lÞ
2.2. Sampling ¼ Ishikari River waters were collected at Iwamizawa– Ohashi once a month from April to September in 2004 (Fig. 1). About 70 l of water was collected in polyethylene containers, which were then transferred to the laboratory. Turbidity is the degree of opacity of water resulting from suspended solids measured during sampling using a nephelometer (U-21XD; Horiba Ltd.); it is expressed in NTU units. Suspended materials in river water samples were concentrated using a single-flow continuous flowing centrifuge with a flow rate of 15 l/h [15]. The inside temperature of the centrifuge was maintained at 15–20 °C to avoid transformation of solids [11]. These solids samples were dried at 40 °C. We calculated suspended solid concentrations in milligram-per-liter units, dividing the dried solids weight by the volume of centrifuged water. The continuous flow method is less efficient for separating low-density particulate matter than filtration at low turbidity [16]. Nagano et al. [15] showed that the recovery of suspended solids by continuous flow centrifugation was 91–114% at turbidity of 11–248, but was 48–100% (68 ± 20%; nine samples) at turbidity of less than 6 NTU. Therefore, in this study, the recovery of suspended particulate materials might be acceptable because of the high turbidity of 16–468 NTU.
POC ðwt:%Þ Mass of suspended solids ðmgÞ : Centrifuged water volume ðlÞ
Radiocarbon (14C) measurements were performed using accelerator mass spectrometry (AMS) at the National Institute for Environmental Studies, Japan. Dried POM samples were first converted to CO2 and then purified cryogenically. The purified CO2 was reduced to graphite with H2 over Fe. The 14C/12C and 13C/12C ratios were measured using an AMS system (Model 15 SDH-2; NEC Corp.). The D14C was defined as the deviation from the modern standard in parts per thousand (&). The d13C was defined as the deviation from the PDB standard in parts per thousand (&). The general mathematical formulae for the expression are as follows [17]: D14 C ð‰Þ ¼ ½ASN ekðy1950Þ =0:7459AON 1 1000;
ð1Þ
C=12 C of sample normalized to d13 CPDB ¼ 25‰;
ASN ¼
14
AON ¼
14
C=12 C of standard HOXII normalized to
d13 CPDB ¼ 25‰; k ¼ 1=8267 yr1 ;
2.3. Analysis
y ¼ Measurement year;
The POC contents for suspended particles isolated through continuous flowing centrifugation were determined using a total organic carbon analyzer (WR-112;
d13 C ð‰Þ ¼ ½ASample =AStandard 1 1000; A ¼
13
C=12 C:
ð2Þ
Md.J. Alam et al. / Nucl. Instr. and Meth. in Phys. Res. B 259 (2007) 513–517
3. Results and discussion 3.1. Variations in turbidity, POC amounts and carbon isotopic ratios Turbidity and POC concentrations ranged were 16– 468 NTU and 0.34–6.69 mg/l, respectively. The POC contents were 1.81–5.40% (Table 1). Turbidity decreased from 468 NTU in April to 16 NTU in July and increased to 36 NTU in September (Fig. 2(a)). Variations in POC concentrations were similar to those of turbidity. The highest value in POC concentration was found during snow-melting and was about 3–5 times larger than that of other samples, which indicates that substantial amounts of POM were transported during the snow-melt period. The POC
515
contents showed an opposite variation trend and were minimal during the snow-melt period (Fig. 2(a)). The D14C and d13C values, respectively, showed variation from 364& to 103& and from 30.6& to 25.9& (Table 1, Fig. 2(b)). The D14C values increased from 364& in April to 103& in June and decreased from 169& in July to 228& in September. The d13C values had two maxima in May and August. These values are within the published range of values [18–20]. 3.2. Relationships in POC contents, D14C and d13C values Fig. 3 shows relationships of POC contents versus D14C and D14C versus d13C. Positive correlations for the samples were found for June, July and September, with respective
Table 1 Turbidity, POC, suspended solid concentration for water samples and POC contents, D14C, d13C values for the POM samples in Ishikari River waters Sampling date
Turbidity (NTU)
Suspended solid (mg/l)
POC concentration (mg/l)
POC content (wt.%)
D14C (&)
d13C (&)
21-4-2004 19-5-2004 24-6-2004 22-7-2004 25-8-2004 29-9-2004
468 119 24 16 30 36
369.46 87.83 6.34 10.78 21.90 22.14
6.69 1.96 0.34 0.41 0.66 0.61
1.81 2.23 5.41 3.81 3.02 2.51
364 173 103 169 174 228
30.6 26.4 27.8 28.5 25.9 30.6
Fig. 2. Variations in turbidity and POM properties for the Ishikari River waters from April–September in 2004. (a) Turbidity and POC concentration of water samples and POC content of suspended solids samples. (b) D14C and d13C values of POM samples.
Fig. 3. Relationships in POC contents, D14C and d13C values for POM in the Ishikari River waters in 2004. Regression lines are used for samples collected in June, July and September.
516
Md.J. Alam et al. / Nucl. Instr. and Meth. in Phys. Res. B 259 (2007) 513–517
correlation coefficients of 0.95 and 0.96. The relationship between POC contents and D14C indicates that the older POM was mixed with newly produced and younger organic matter from the watershed. The POC contents and carbon isotopic ratios in May and August appear to deviate little from the equation lines. The snow-melt POM deviated considerably. The decreased POC content during snow-melt indicates dilution through the addition of higher amounts of minerals from watershed and river bottom sediments [21,22]. The dilution indicates that POC is low (1.81%) with respect to the bulk weight of suspended solids (22.09 g) during the snow-melt period. In suspended solids, CaCO3, alumino silicates etc. are present in large quantities. POC is higher (2.51–5.41%) (less diluted) with respect to the bulk weight of suspended solids (0.86–1.51 g) during summer. The dilution can depend on water discharge and watershed erosion.
4. Summary We collected river water samples at a fixed station in the Ishikari River and used D14C and d13C values to study transportation behavior of particulate organic matter (POM) during spring and summer. Significant D14C and d13C maxima (364& and 30.6&) were found in waters with turbidity of 468 NTU and a POC concentration of 6.69 mg/l. This occurred during the snow-melt period. These values deviated greatly from the correlation lines of D14C versus d13C and D14C versus POC content for other samples during the year. These results indicate that a significant amount of POM was transported during snow-melt from distinct sources through different mechanisms such as re-suspension of river bottom sediments and river bank erosion. Acknowledgements
3.3. Transportation behavior of POM Particulate organic matter (POM) is probably supplied from sources such as direct inputs through soil erosion of litter and soil organic matter [4]. Extensive soil erosion of the river bank is a common phenomenon for rivers during high-flow events [7,23]. The Ishikari River showed the maximum water discharge and water level during the snowmelt period. The water level at the Iwamizawa–Ohashi water flow monitoring station was 5.4 m on 21 April, 3.1 m on 19 May and 1.7–1.5 m during June–September in 2004 [14]. The D14C values of soil organic matter decreases with increasing depth in soil, but d13C values remain constant or vary with soil depth [24–27]. In a disturbed soil watershed, microbial decomposition is nearly nonexistent and bulk organic materials are submerged in soil during soil development having lower d13C values as surface soil. In contrast, in an undisturbed soil watershed (like that for forest soil) microbial decomposition (12C uptake) is very common and considerably more d13C residual organic matter is preserved deeper in soil. Consequently, d13C values tend to be increased or decreased with soil depth depending on watershed conditions. Therefore, the minimum values in D14C and d13C of the Ishikari POM samples might occur through spatial soil erosion, especially from older POM in the river bank. Another candidate for the supply of POM is re-suspension of bottom sediments by high-water discharge [28]. The D14C and d13C values of river bottom sediment that was collected in September in 2004 near Iwamizawa–Ohashi, were, respectively, about 217& and 29.6&. Therefore, river bottom sediments are one source of riverine POM during high-flow events caused by snow-melt. To better understand the minimum values in D14C and d13C of POM during snow-melt, we are planning to collect POM samples from the Ishikari River water at shorter time intervals and also investigate carbon isotopic values of soil and bottom sediments.
The authors thank Mr. H. Yamamoto of our laboratory for assisting with sampling. This work was funded partly by a Grant-in-Aid for Science Research, No. 15310002 and the 21st Century Centre of Excellence (COE) program of the Ministry of Education, Culture, Sports, Science and Technology, Japan. References [1] M. Meybeck, Am. J. Sci. 282 (1982) 401. [2] S.A. Telang, R. Pocklington, A.S. Naidu, E.A. Romankevich, I.I. Gitelson, M.I. Gladyshev, Biogeochemistry of major world rivers, in: E.T. Degens, S. Kempe, J.E. Richey (Eds.), SCOPE 42, John Wiley and Sons, Chichester, 1991, p. 85, 104. [3] D. Hope, M.F. Billett, M.S. Cresser, Environ. Pollut. 84 (1994) 301. [4] D. Hope, M.F. Billett, M.S. Cresser, J. Hydrol. 193 (1997) 61. [5] S.A. Telang, in: E.T. Degens, S. Kempe, R. Herrara (Eds.), Transport of carbon and minerals in major worlds rivers, part 3, Mitt Geol.Paleont. Inst. Univ. Hamburg, SCOPE/UNEP Soderbd, 1985, pp. 337–344. [6] J.L. Meyer, C.M. Tate, Ecology 64 (1983) 33. [7] J.B. Thornes, Vegetation and Erosion: Processes and Environments, John Wiley and Sons Ltd., Baffins Lane, Chichester, West Sussex PO19, England, 1990. [8] J.E. Hobbie, Estuarine Science: The Key to Progress in Coastal Ecological Research, Inland Press, Washington, DC, 2000. [9] S.J. Kao, K.-K. Liu, Limnol. Oceanogr. 41 (1996) 1749. [10] P.A. Raymond, J.E. Bauer, Org. Geochem. 32 (2001) 469. [11] S. Nagao, T. Usui, M. Yamamoto, M. Minagawa, M. Iwatsuki, A. Noda, Chem. Geol. 218 (2005) 63. [12] Ministry of Land, Infrastructure, and Transport.
Md.J. Alam et al. / Nucl. Instr. and Meth. in Phys. Res. B 259 (2007) 513–517 [19] [20] [21] [22] [23]
P.A. Raymond, J.E. Bauer, Nature 409 (2001) 497. S.J. Kao, F.J. Lin, K.K. Liu, Deep Sea Res. II 50 (2003) 1203. H.B.N. Hynes, Proc. XVI Int. Congr. Zool. 4 (1963) 324. S.G. Fisher, G.E. Likens, Bioscience 27 (1972) 33. E. Veyssey, C. Colas, H. Etcheber, E. Maneux, J.L. Probst, Sci. Geol. Bull., Strasbourg, 49 (1996) 127. [24] M.S. Torn, S.E. Trumbore, O.A. Chadwick, P.M. Vitousek, D.M. Hendricks, Nature 389 (1994) 170.
517
[25] D. van Dam, E. Veldkamp, N. van Breemen, Biogeochemistry 39 (1994) 343. [26] Y. Wang, T.G. Huntington, L.J. Osher, L.I. Wassenaar, in: C. Kendall, J.J. McDonnell (Eds.), Isotope Tracers in Catchment Hydrology, Elsevier, Amsterdam, 1998, p. 577. [27] J. Guo, M. Atarashi-Ando, H. Amano, J. Radioanal. Nucl. Chem. 255 (2003) 223. [28] A.W. Morris, M.J. Howarth, Cont. Shelf Res. 18 (1998) 1203.
Nuclear Instruments and Methods in Physics Research B 259 (2007) 513–517 www.elsevier.com/locate/nimb
Transport of particulate organic matter in the Ishikari River, Japan during spring and summer Md. Jahangir Alam a, Seiya Nagao b,*, Takafumi Aramaki c, Yasuyuki Shibata c, Minoru Yoneda c a
Graduate School of Environmental Earth Science, Hokkaido University, Sapporo 060-0810, Japan b Faculty of Environmental Earth Science, Hokkaido University, Sapporo 060-0810, Japan c National Institute for Environmental Studies, Tsukuba 305-8506, Japan Available online 2 February 2007
Abstract Both D14C and d13C were used to study transport behavior of particulate organic matter (POM) in the Ishikari River in Japan. Water samples were collected once a month from April to September in 2004. Positive correlations were found between D14C and particulate organic carbon (POC) content and D14C and d13C values for the POM samples from June to September. However during snow-melt, distinctive minimum values were found for POC content, D14C and d13C. These results indicate the POC was supplied from different sources and by different mechanisms during spring snow-melt and summer because of variations in water level and discharge. Ó 2007 Elsevier B.V. All rights reserved. Keywords: Ishikari River; POC; D14C; d13C; Snow-melt
1. Introduction The annual load of riverine particulate organic carbon (POC) from land to ocean corresponds to half the total organic carbon [1]. Transportation of POC in river systems is one pathway of the carbon cycle in terrestrial ecosystems. For that reason, river systems are important for the carbon cycle. Carbon discharge and transport patterns vary among rivers and watershed conditions, which include geographical, hydrological and land use features [2–4]. The watershed environments vary from spring to summer because of snow-melt in sub-arctic and arctic areas. Snow-melt water considerably increases water discharge and transport of inorganic and organic materials from land to ocean [5–7]. Dynamics of particulate organic matter (POM) and its fate in river systems are unknown during snow-melting periods because POM exhibits tremendous temporal and spatial variations in physico-chemical char*
Corresponding author. Tel.: +81 11 706 2349; fax: +81 11 706 4867. E-mail address: [email protected] (S. Nagao).
0168-583X/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.nimb.2007.01.194
acteristics [8]. To understand POC transport behavior in river systems, we must obtain information on residence time, patterns of transport and discharge of POC. Both D14C and d13C values have proven to be simple and useful parameters to study POM sources and residence times; they are very suitable for elucidating POM dynamics [9– 11]. This study applied carbon isotopic ratios (D14C and d13C) to POM of the Ishikari River waters to investigate transportation behavior in river systems during spring and summer seasons. 2. Materials and methods 2.1. Study area The Ishikari River runs through the lowland in eastern Hokkaido (Fig. 1); It has a catchment area of 14,330 km2 and is 268 km long. The main types of land use are forest, agriculture and urban. Rice is the main agricultural product along the river. The monthly average water discharge ranges from 150–1130 m3/s during 1999–2002 [12];
514
Md.J. Alam et al. / Nucl. Instr. and Meth. in Phys. Res. B 259 (2007) 513–517
Fig. 1. Sampling location.
50% of the precipitation falls as snow [13]. Monthly mean winter precipitation is 46–105 mm and the snow depth is from 38–108 cm from December to late April [14]. Snowmelting begins in March and increase in water levels and discharge. The highest water discharge at the Iwamizawa–Ohashi occurs in April and is up to 3–4 times greater than that in winter [14].
LECO Corp.). Prior to analysis, calcium carbonate was removed by adding 0.1 M HCl, rinsing with Milli Q water and subsequent drying. The obtained POC contents were expressed as wt.% unit (g C/100 g suspended solid dry basis). The POC concentrations were expressed using the following equation: POC concentration ðmg=lÞ
2.2. Sampling ¼ Ishikari River waters were collected at Iwamizawa– Ohashi once a month from April to September in 2004 (Fig. 1). About 70 l of water was collected in polyethylene containers, which were then transferred to the laboratory. Turbidity is the degree of opacity of water resulting from suspended solids measured during sampling using a nephelometer (U-21XD; Horiba Ltd.); it is expressed in NTU units. Suspended materials in river water samples were concentrated using a single-flow continuous flowing centrifuge with a flow rate of 15 l/h [15]. The inside temperature of the centrifuge was maintained at 15–20 °C to avoid transformation of solids [11]. These solids samples were dried at 40 °C. We calculated suspended solid concentrations in milligram-per-liter units, dividing the dried solids weight by the volume of centrifuged water. The continuous flow method is less efficient for separating low-density particulate matter than filtration at low turbidity [16]. Nagano et al. [15] showed that the recovery of suspended solids by continuous flow centrifugation was 91–114% at turbidity of 11–248, but was 48–100% (68 ± 20%; nine samples) at turbidity of less than 6 NTU. Therefore, in this study, the recovery of suspended particulate materials might be acceptable because of the high turbidity of 16–468 NTU.
POC ðwt:%Þ Mass of suspended solids ðmgÞ : Centrifuged water volume ðlÞ
Radiocarbon (14C) measurements were performed using accelerator mass spectrometry (AMS) at the National Institute for Environmental Studies, Japan. Dried POM samples were first converted to CO2 and then purified cryogenically. The purified CO2 was reduced to graphite with H2 over Fe. The 14C/12C and 13C/12C ratios were measured using an AMS system (Model 15 SDH-2; NEC Corp.). The D14C was defined as the deviation from the modern standard in parts per thousand (&). The d13C was defined as the deviation from the PDB standard in parts per thousand (&). The general mathematical formulae for the expression are as follows [17]: D14 C ð‰Þ ¼ ½ASN ekðy1950Þ =0:7459AON 1 1000;
ð1Þ
C=12 C of sample normalized to d13 CPDB ¼ 25‰;
ASN ¼
14
AON ¼
14
C=12 C of standard HOXII normalized to
d13 CPDB ¼ 25‰; k ¼ 1=8267 yr1 ;
2.3. Analysis
y ¼ Measurement year;
The POC contents for suspended particles isolated through continuous flowing centrifugation were determined using a total organic carbon analyzer (WR-112;
d13 C ð‰Þ ¼ ½ASample =AStandard 1 1000; A ¼
13
C=12 C:
ð2Þ
Md.J. Alam et al. / Nucl. Instr. and Meth. in Phys. Res. B 259 (2007) 513–517
3. Results and discussion 3.1. Variations in turbidity, POC amounts and carbon isotopic ratios Turbidity and POC concentrations ranged were 16– 468 NTU and 0.34–6.69 mg/l, respectively. The POC contents were 1.81–5.40% (Table 1). Turbidity decreased from 468 NTU in April to 16 NTU in July and increased to 36 NTU in September (Fig. 2(a)). Variations in POC concentrations were similar to those of turbidity. The highest value in POC concentration was found during snow-melting and was about 3–5 times larger than that of other samples, which indicates that substantial amounts of POM were transported during the snow-melt period. The POC
515
contents showed an opposite variation trend and were minimal during the snow-melt period (Fig. 2(a)). The D14C and d13C values, respectively, showed variation from 364& to 103& and from 30.6& to 25.9& (Table 1, Fig. 2(b)). The D14C values increased from 364& in April to 103& in June and decreased from 169& in July to 228& in September. The d13C values had two maxima in May and August. These values are within the published range of values [18–20]. 3.2. Relationships in POC contents, D14C and d13C values Fig. 3 shows relationships of POC contents versus D14C and D14C versus d13C. Positive correlations for the samples were found for June, July and September, with respective
Table 1 Turbidity, POC, suspended solid concentration for water samples and POC contents, D14C, d13C values for the POM samples in Ishikari River waters Sampling date
Turbidity (NTU)
Suspended solid (mg/l)
POC concentration (mg/l)
POC content (wt.%)
D14C (&)
d13C (&)
21-4-2004 19-5-2004 24-6-2004 22-7-2004 25-8-2004 29-9-2004
468 119 24 16 30 36
369.46 87.83 6.34 10.78 21.90 22.14
6.69 1.96 0.34 0.41 0.66 0.61
1.81 2.23 5.41 3.81 3.02 2.51
364 173 103 169 174 228
30.6 26.4 27.8 28.5 25.9 30.6
Fig. 2. Variations in turbidity and POM properties for the Ishikari River waters from April–September in 2004. (a) Turbidity and POC concentration of water samples and POC content of suspended solids samples. (b) D14C and d13C values of POM samples.
Fig. 3. Relationships in POC contents, D14C and d13C values for POM in the Ishikari River waters in 2004. Regression lines are used for samples collected in June, July and September.
516
Md.J. Alam et al. / Nucl. Instr. and Meth. in Phys. Res. B 259 (2007) 513–517
correlation coefficients of 0.95 and 0.96. The relationship between POC contents and D14C indicates that the older POM was mixed with newly produced and younger organic matter from the watershed. The POC contents and carbon isotopic ratios in May and August appear to deviate little from the equation lines. The snow-melt POM deviated considerably. The decreased POC content during snow-melt indicates dilution through the addition of higher amounts of minerals from watershed and river bottom sediments [21,22]. The dilution indicates that POC is low (1.81%) with respect to the bulk weight of suspended solids (22.09 g) during the snow-melt period. In suspended solids, CaCO3, alumino silicates etc. are present in large quantities. POC is higher (2.51–5.41%) (less diluted) with respect to the bulk weight of suspended solids (0.86–1.51 g) during summer. The dilution can depend on water discharge and watershed erosion.
4. Summary We collected river water samples at a fixed station in the Ishikari River and used D14C and d13C values to study transportation behavior of particulate organic matter (POM) during spring and summer. Significant D14C and d13C maxima (364& and 30.6&) were found in waters with turbidity of 468 NTU and a POC concentration of 6.69 mg/l. This occurred during the snow-melt period. These values deviated greatly from the correlation lines of D14C versus d13C and D14C versus POC content for other samples during the year. These results indicate that a significant amount of POM was transported during snow-melt from distinct sources through different mechanisms such as re-suspension of river bottom sediments and river bank erosion. Acknowledgements
3.3. Transportation behavior of POM Particulate organic matter (POM) is probably supplied from sources such as direct inputs through soil erosion of litter and soil organic matter [4]. Extensive soil erosion of the river bank is a common phenomenon for rivers during high-flow events [7,23]. The Ishikari River showed the maximum water discharge and water level during the snowmelt period. The water level at the Iwamizawa–Ohashi water flow monitoring station was 5.4 m on 21 April, 3.1 m on 19 May and 1.7–1.5 m during June–September in 2004 [14]. The D14C values of soil organic matter decreases with increasing depth in soil, but d13C values remain constant or vary with soil depth [24–27]. In a disturbed soil watershed, microbial decomposition is nearly nonexistent and bulk organic materials are submerged in soil during soil development having lower d13C values as surface soil. In contrast, in an undisturbed soil watershed (like that for forest soil) microbial decomposition (12C uptake) is very common and considerably more d13C residual organic matter is preserved deeper in soil. Consequently, d13C values tend to be increased or decreased with soil depth depending on watershed conditions. Therefore, the minimum values in D14C and d13C of the Ishikari POM samples might occur through spatial soil erosion, especially from older POM in the river bank. Another candidate for the supply of POM is re-suspension of bottom sediments by high-water discharge [28]. The D14C and d13C values of river bottom sediment that was collected in September in 2004 near Iwamizawa–Ohashi, were, respectively, about 217& and 29.6&. Therefore, river bottom sediments are one source of riverine POM during high-flow events caused by snow-melt. To better understand the minimum values in D14C and d13C of POM during snow-melt, we are planning to collect POM samples from the Ishikari River water at shorter time intervals and also investigate carbon isotopic values of soil and bottom sediments.
The authors thank Mr. H. Yamamoto of our laboratory for assisting with sampling. This work was funded partly by a Grant-in-Aid for Science Research, No. 15310002 and the 21st Century Centre of Excellence (COE) program of the Ministry of Education, Culture, Sports, Science and Technology, Japan. References [1] M. Meybeck, Am. J. Sci. 282 (1982) 401. [2] S.A. Telang, R. Pocklington, A.S. Naidu, E.A. Romankevich, I.I. Gitelson, M.I. Gladyshev, Biogeochemistry of major world rivers, in: E.T. Degens, S. Kempe, J.E. Richey (Eds.), SCOPE 42, John Wiley and Sons, Chichester, 1991, p. 85, 104. [3] D. Hope, M.F. Billett, M.S. Cresser, Environ. Pollut. 84 (1994) 301. [4] D. Hope, M.F. Billett, M.S. Cresser, J. Hydrol. 193 (1997) 61. [5] S.A. Telang, in: E.T. Degens, S. Kempe, R. Herrara (Eds.), Transport of carbon and minerals in major worlds rivers, part 3, Mitt Geol.Paleont. Inst. Univ. Hamburg, SCOPE/UNEP Soderbd, 1985, pp. 337–344. [6] J.L. Meyer, C.M. Tate, Ecology 64 (1983) 33. [7] J.B. Thornes, Vegetation and Erosion: Processes and Environments, John Wiley and Sons Ltd., Baffins Lane, Chichester, West Sussex PO19, England, 1990. [8] J.E. Hobbie, Estuarine Science: The Key to Progress in Coastal Ecological Research, Inland Press, Washington, DC, 2000. [9] S.J. Kao, K.-K. Liu, Limnol. Oceanogr. 41 (1996) 1749. [10] P.A. Raymond, J.E. Bauer, Org. Geochem. 32 (2001) 469. [11] S. Nagao, T. Usui, M. Yamamoto, M. Minagawa, M. Iwatsuki, A. Noda, Chem. Geol. 218 (2005) 63. [12] Ministry of Land, Infrastructure, and Transport.
Md.J. Alam et al. / Nucl. Instr. and Meth. in Phys. Res. B 259 (2007) 513–517 [19] [20] [21] [22] [23]
P.A. Raymond, J.E. Bauer, Nature 409 (2001) 497. S.J. Kao, F.J. Lin, K.K. Liu, Deep Sea Res. II 50 (2003) 1203. H.B.N. Hynes, Proc. XVI Int. Congr. Zool. 4 (1963) 324. S.G. Fisher, G.E. Likens, Bioscience 27 (1972) 33. E. Veyssey, C. Colas, H. Etcheber, E. Maneux, J.L. Probst, Sci. Geol. Bull., Strasbourg, 49 (1996) 127. [24] M.S. Torn, S.E. Trumbore, O.A. Chadwick, P.M. Vitousek, D.M. Hendricks, Nature 389 (1994) 170.
517
[25] D. van Dam, E. Veldkamp, N. van Breemen, Biogeochemistry 39 (1994) 343. [26] Y. Wang, T.G. Huntington, L.J. Osher, L.I. Wassenaar, in: C. Kendall, J.J. McDonnell (Eds.), Isotope Tracers in Catchment Hydrology, Elsevier, Amsterdam, 1998, p. 577. [27] J. Guo, M. Atarashi-Ando, H. Amano, J. Radioanal. Nucl. Chem. 255 (2003) 223. [28] A.W. Morris, M.J. Howarth, Cont. Shelf Res. 18 (1998) 1203.