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Trace metal composition of and accumulation rates of sediments in the Upper Gulf of Thailand
Estuarine, Coastal and Shelf Science (1984) 19,133-142
Trace Metal Composition of and Accumulation Rates of Sediments Upper Gulf of Thailand
Herbert L. Windoma, Suchada Silpipatb, Aurapin Chanpongsangb, Ralph G. Smith, Manuwadi HungspreugsC
in the
Jr.a and
aSkidaway Institute of Oceanography, P.O. Box 13687, Savannah, GA 31416, U.S. A., bOceanographic Section, Department of Fisheries, Parknam, Samutprakarn, Bangkok 27, Thailand and CDepartment of Marine Science, Chulalongkorn University, Phya Thai Road, Bangkok 5, Thailand Received 25 July 1983 and in revised form 2 December 1983
Keywords:
sedimentationrates; trace elements;metals; sediments;Gulf of
Thailand Sedimentcoresand grab samples were collected in the Upper Gulf of Thailand to determine sedimentation rates and to determine if metal concentrations reflect anthropogenic inputs. Accumulationratesof sedimentsin the Upper Gulf measuredusingthe 210Pb method, appear to vary from ca. 4 to 11 mm yrr’. Sediment budgets suggest that little of the sediment delivered to the Upper Gulf by the major rivers is ultimately
transportedto the Lower Gulf. Metal concentrationsin Upper Gulf sediments appearto be dominantlycontrolledby naturalinputs.
Introduction
The Gulf of Thailand is a large shallow embayment (maximum depth of 86 m) adjacent to the South China Sea. The Upper Gulf (Figure 1) has a relatively flat bathymetry and a maximum depth of less than 50 m. Four major rivers debauching into the Upper Gulf are the major sourcesof sediment for the entire Gulf (Emery & Niino, 1963). Of the four rivers, the Chao Phraya is by far the largest. Sediments throughout the Upper and Lower Gulf are dominantly muds with somesandy regions (Emery & Niino, 1963). The dominant clay mineralsare montmorillomite and illite, presumably derived from the lateritic soils of the central basin of Thailand (Aoki, 1976). There have been few studies of heavy metals in Gulf sediments. A recent report (Menasveta & Cheevaparanapiwat, 1981), however, suggeststhat Upper Gulf sediments may receive significant anthropogenic inputs resulting from large population increasesand industrialization along the northern coast, particularly around Bangkok, during the last few decades. This report addressesthe following questions: 1. What fraction of the sedimentstransported by the four major rivers is trapped in the Upper
Gulf? 133
0272-7714/84/080133+10$03.00/0
G 1984
Academic
Press
Inc.
(London)
Limited
134
H. L. Windom et al.
THAILAND ,
Figure
1. Sediment
sampling
stations.
2. Are anthropogenic inputs of heavy metals into the Upper Gulf large enough to significantly affect concentrations in Upper Gulf sediments? Methods Sampling
Stations at which sampleswere collected are shown in Figure 1. All sampling was from the Fisheries Department of Thailand R/V Fisheries Research no. 1. Sediments for heavy metal analyseswere collected with a stainlesssteel sampler. Subsamplesof these were taken from the center of the grab samplesto minimize the possibility of the sediment having contacted the sidesof the sampler. Samplesfor sedimentation rate studies were collected with a 8 cm diameter gravity corer. Cores were frozen upright until returned to a shorebasedlaboratory. Samplesfor heavy metal analyseswere collected in February and September 1982.Cores to determine sedimentationrates were collected only in February. One additional vibracore was collected during the summerof 1982 for sedimentation rate measurements.This core
Sediments in Upper Gulf of Thailand
135
was collected using the Thailand Navy Oceanographic Research Vessel. This core was treated similarly to the gravity cores. Heavy metal analyses Aiiquots of oven dried sediments were totally digested and leached with concentrated nitric acid. Total digestion was accomplished using concentrated hydrofluoric and perchloric acids to break down the silcate lattice and to destroy organic matter. Approximately one gram of sediment was refluxed for several hours in a teflon screw top beaker on a hotplate, taken to dryness and the residue dissolved in 10%nitric acid. Separate one gram sampleswere boiled in concentrated nitric acid for about one hour, the supernatant filtered off and taken to dryness. The residue was redissolved in 10%nitric acid. Strong acid leachate (SAL) analyseswere accomplished in Thailand at the Fisheries Department laboratory near Bangkok. Total digests were analyzed at Skidaway. Analyses at both locations were carried out on Perkin Elmer 5000 atomic absorption spectrophotometers using either flame or furnace techniques. Analyses of NBS estuarine sediment standard reference material was used for evaluating accuracy. Precision of analyses,based on replicate samples,is estimated at + 15%or lessfor all metals. Sedimentation rate measurements Sedimentation rates were determined using the 2loPb method (Koide et al., 1972). Our approach was to measure 21OPoactivity and to assumeradioactive equilibrium with 2loPb (Nittrouer et al., 1979). Sediment sampleswere collected at 5 cm intervals through the length of the cores, dried and ground to passa 100pm sieve. 21OPowas isolated from the samplefollowing procedures described by Flynn (1968) and using a 2O*Pospike to correct for yield. Separated and plated sampleswere analyzed by alpha spectrometry.
Results Sedimentationrates Gravity cores for sedimentation rate determinations were collected at stations 1, 2, 3, 5, 6, 7, 9 and 14 (Figure 1). The one vibracore was collected at station 8. Attempts to core at more southerly stations and at those in open waters (i.e. stations 12-19) failed due to the more coarse grain nature of the sediments there. With the gravity corer used, the maximum depth of penetration obtained was about 40 cm. Also, with the diameter of the corer used, it wasnecessaryto sample5 cm vertical segmentsof the core to obtain sufficient material for the analyses.With the vibracore a depth of 1 m was penetrated. The results of 2loPb (i.e. 2lOPo)analysesfor the vibracore are shown in Figure 2. The total 2loPbactivity of this core showsa zone of relatively uniform activity down to a depth of about 15 cm. From about 15cm to 40 cm the 2rOPbactivity exhibits exponential decay. At greater depths the activity is again uniform at about 0.46 f 0.05 dpm g-1. The mean 2loPb activity of the bottom of the core (i.e. depths > 40 cm) was assumedto represent the amount of 2lOPb supported by *26Ra decay in the sediments. This activity, 0.46 dpm g-1, was therefore subtracted from the total activities measuredin all cores to yield excess*lOPbactivity from which all sedimentation rates were measured. The best gravity core penetration was at nearshore stations. These cores also exhibit the most consistent trends in decreasingexcessZloPbactivity with depth (Figure 3). Cores at stations 9 and 14 show no clear trend. These two cores contained coarser sediment with
136
H. L. Windom et al.
*“Pb
octivcty
(dpm
g-‘1
Total
80
Excess 100
L
+ +
+
Figure 2. Total and excess zl”Pb activity with depth in vibracore line is the regression curve for excess activity versus depth.
taken at statlon 8. Dashed
considerable material greater than 200 p. All of the other cores contained relatively uniform fine sandto silt (mean grain size ca 62 ltm). The results of ZiOPbmeasurementson gravity cores (Figure 3) show no indication of a surface ‘mixed zone’ with uniform *lOPb activity typical of shelf sediments (Nittrouer et al., 1979). This may be due, in part, to the large depth interval of sampling. It is also likely that the gravity corer did not collect the surficial layer. As the corer penetrated the sediment, the upper, loosely consolidated, bioturbated or physically mixed zone was probably pushed aside, with the corer retaining only the more consolidated sediments below. The percent moisture in the vibracore was46 at 5-10 cm, decreasingto 32 at the bottom. The very top part of the core had a percent moisture of 58. No correction was made for porosity in the sedimentation determinations due to the relatively small change in the moisture content of the sedimentsover the core lengths and the rather large uncertainties in the low *loI?bactivities. Results of analyses on cores collected from stations 1, 2, 3, 5, 6, 7 and 10 indicate radioactive decay of ZloPbwith depth (i.e. exponential decreasein activity with depth) in the upper section of the cores. A best fit curve of the data from the upper part of the 210Pb2rsdepth profile can be used to determine sedimentation rates. Using a half life of 22.3 years for *iOPb, sedimentation rate estimatesvary from 4 ‘0 to 11‘2 mm yrrl. Heavy metal concentrations
Sediment samplescollected during February 1982were analyzed for total and strong acid
Sediments in Upper Gulf of Thailand
Excess 0 0
I
0.5
I.0
0.1
2’oPb
137
activity 0.5
(dpm I.0
2 0
g-l) 0-I
05
IO
20
stn I II 2 mm/Yr t
IO + 20 v
3ot
0
IO
20
0.1 0
0.5
I.0
2.0
3.0
Stn 7 4 Ommyr-’
IO 1 +
20 I77
0 I
05
I.020
30
0, I
0 5 1
Stn 14
Figure 3. Excess “OPb activity with depth data through which they are drawn.
I-O
2.0
1
1
in gravity
cores. Lines are regression
curves
of
H. L. Windom et al.
138
leachable (SAL) aluminum, iron, manganese,copper and nickel. Total concentrations only were determined for cobalt, lead and cadmium (Table 1). All values are derived from the average of duplicate analyses. Generally, little variation in metal concentrations between most stations is apparent although sedimentsfrom the northernmost stations near the river mouths have the highest levels. TABLE 1. Trace during February Leached
Station I 2 3 4 8 9 11 12 16 17 19 Mean
Aluminum (g kg-‘) 31 38 39 61 32 16 20 16 19 15 16
(62) (59) (64) (68) (64) (44) (59) (46) (39)
27+14
metal concentrations 1982
Iron k kg-‘)
Manganese bg kg-‘)
Copper (mg h-7
17 21 22 33 20 12 13 12 17 21 28
900 (107) 800 (91) 720 (87) 830 (85) 820 (95) 500 (92) 770 600 (120) 510 (72) 710 590 (84)
10 13 11 24 10 4.0 5.0 3.3 2.8 2.5 3.5
700 AZ 140
8.1f6.5
(77) (72) (73) (80) (87) (70) (92) (68) (68)
2Ot-6
Aluminum k kg-‘)
I 2 3 4 5 7 8 9 10 11 12 13 14 15 16 17 18 19
34 40 37 53 55 45 27 16 33 20 15 6 17 4 19 17 15 17
Mean
26+15
collected
in the Upper
(per cent of total given in parentheses)
TABLE 2. Strong acid leachable Upper Gulf of Thailand during
Station
in sediments
Iron k kg-]) 21 22 21 32 32 22 21 12 20 24 12 33 14 11 24 22 34 31 23i7
(83) (85) (69) (77) (83) (49) (65) (36) (56)
Total
Nickel (mg kg-‘) 20 26 28 38 30 18 20 8.8 14 14 15
740 750 780 840 1210 700 800 440 590 510 410 300 590 370 430 430 650 950 640 f 230
concentrations
only
Cobalt 0% kg-9
Lead 6% kg-l)
(110) (96) (103) (102) (150) (120)
9.3 12 12 15 10 6.4
7.5 8,2 7.6 8.6 5.2 4.7
15 23 25 19 10
(110) (100)
5.5 8.5
5.0 5.4
10 18
6-3
10
6.5h1.5
15~6
(105)
21 i8.6
10 9.8-12.9
trace metal concentrations September 1982
Manganese (w kg-l)
Gulf of Thailand
in sediments
Cadmium (pg kg-l)
collected
from the
Copper (mg kg-‘)
Nickel img kg-‘)
Cobalt (mg kg- I)
10 12 10 20 20 15 9.5 4.5 12 3-8 2.0 1.0 2-5 0.5 2.5 2-o 1.5 2.5
25 26 24 31 25 22 20 8.8 17 7.5
10 9.3 13 14 14 10 8.3 4.3 2.7 4.5 2.5 cl.0 2-5 5.0 4.3 6 5 6.5 9,5
7.3k6.5
14t9-8
7.11
4-o
139
Sediments in Upper Gulf of Thailand
The SAL fraction of the total metal content in the sedimentsis fairly constant for each metal. The SAL fractions of aluminum, iron, manganese,copper and nickel were 56& 10, 76 & 8, 92 f 14, 67 k 17 and ca loo%, respectively, of the total concentrations. Sediments collected during September 1982 were analyzed only for the SAL fraction (Table 2). Although there is some difference in SAL concentrations at given stations between the two sampling periods the mean concentrations at all stations are generally similar in both samplesets. Metal concentrations are generally higher in fine grain marine sediments when clay minerals are abundant. Typically aluminum is also enriched in fine grain, clay rich sediments. In natural deposits of varying grain size (i.e. varying clay mineral concentrations) metal concentrations should therefore covary with aluminum. Both total and SAL metal concentrations (except Cd) are plotted against aluminum in Figure 3. Also shown, for comparison, are solid lines which represent hypothetical
15
T ,o P u”
IO
5 0 0
50
100 AL(Q
Figure Closed line is curves
0
50
100
kg-‘)
4. Metal concentration versus aluminum concentrations in the Upper Gulf sediments. dots represent acid leached fractions. Open dots represent total concentrations. Solid the hypothetical natural abundance curve of metal OS Al. Dashed lines are regression based on 99% confidence level.
140
H. L. Windomet al.
(a) AL(g kg-‘)
(b) (Fe/AL)
(cl (Mn/AL)
x IO2
Thailand
n
*
Thailand -
13*
Figure 5. (a) Distribution of aluminum in acid leached fraction m Upper Gulf sediments (b) and (c) Variation in Fe : Al and Mn : Al ratios, respectively, in Upper Gulf sediments.
Sediments in Upper Gulf of Thailand
141
deposits having constant metal : aluminum ratios based on average crustal abundancesof the elements (Taylor, 1964). Except for lead the total concentrations of all metals covary with aluminum at a 99 percent confidence level. Total lead covaries with aluminum at a 95 percent confidence level. The concentrations of copper and nickel alsocovary (P < 0.01) with aluminum in the SAL fraction. The regressionof these two metals against aluminum, in both the SAL and total digests, are generally parallel and lower than the ‘ natural abundance curve’ suggesting that Cu and Ni are not enriched in either fraction and variations in concentrations are controlled by natural processes. The SAL concentrations of iron, manganeseand cobalt show no relationship to aluminum concentrations. Also ratios of these metals to aluminum, in many instances, exceed the hypothetical ‘ natural ratio ‘.
Discussion Sediment dischargeby the Chao Phraya River, the largest of the four rivers emptying into the Upper Gulf, is about 3.4~ 106 metric tons per year (Port Authority of Thailand). Although discharge values are not available for the other rivers, sediment discharge by them may equal that of the Chao Phraya, suggesting that a total ca 7 x 106metric tons are delivered to the Upper Gulf annually. The Upper Gulf of Thailand hasan area of about 6 8 x 109m2.If we assumethat Upper Gulf sediments have a density of 2 g cm-3 the 7 x 106metric tons per year spread evenly over the area would account for a deposition rate of only 0.5 mm yr-1, or one tenth of that measured. Our measurementswere, however, restricted to the northern part of the Upper Gulf relatively near river mouths and thus can be expected to be higher than the average for the entire Gulf. *loPb results on other cores (e.g. stations 9 and 14; Figure 4) and surface samples collected at other stations suggestthat the sedimentsthere accumulate very slowly or that they are relict. Emery and Niino (1963) identified a band of relict sedimentsthat extends acrossthe boundary between the Upper and Lower Gulf. Our results suggest that the sediments transported by the Chao Phraya, Mae Klong, Ta Chin and Bang Pakong Rivers are, for the most part, deposited in the northern part of the Upper Gulf of Thailand. The distribution of aluminum [Figure 5(a)] also suggests that the greatest influence of river transported sedimentsis in the northern Upper Gulf. With the exceptions of iron and manganesethe distributions of metals in Upper Gulf sedimentsfollows that of aluminum and are apparently dominated by natural inputs. Iron and manganesedistributions deviate from that of aluminum, particularly in SAL fractions. The distributions of these metalsrelative to aluminum is reflected in the Fe : Al and Mn : Al ratios of Upper Gulf sediments[Figure 5, (b), (c)l. Highest ratios are near the boundary between the Upper and Lower Gulf indicating that iron and manganeseenrichments, relative to aluminum, are associatedwith the relict sedimentsdescribed by Emery and Niino (1963).
Acknowledgements This research was jointly funded by the National ResearchCouncil of Thailand and U.S. National Science Foundation Office of International Programs (grant INT81-16705). The authors wish to thank Captain Jarroug Sreevanich, the officers and crew of the Department
142
H. L. Windom et al.
of Fisheries Research Vessel Number 1. Thanks are also due to MS Dannah McCauley who provided secretarial assistance. References Aoki,
S. 1976 Clay mineral distribution in sediments of the Gulf of Thailand and South China Sea. Journal of the Oceanography Society ofJapan 32,169-174. Emery, K. 0. & Niino, H. 1963 Sediments of the Gulf of Thailand and adjacent Continental Shelf. Geologrcal Society of America Bulletin 74, 541-554. Flynn, W. W. 1968 The determination of low levels of polonium-210 in environmental materials. Anuly~zca Chimica Acta 43, 221-227. Koide, M., Soutar, A. & Goldberg, E. D. 1972 Marine geochronology with Pb-210. Earth and Planetary Science Letters 14, 442-446. Menasveta, P. & Cheevaparanapiwat, V. 1981 Heavy metals, organochloride pesticides and PCBs in green mussels, mullets and sediments of river mouths in Thailand. Marine Pollution Bulletin 12, 19-25. Nittrouer, C. A., Sternberg, R. W., Carpenter, R. L? Bennett, J. T. 1979 The use of Pb-210 geochronology as a sedimentological tool: Application to the Washington Continental Shelf. Marine Geology 31, 297-316. Taylor, S. R. 1964 Abundance of chemical elements in the continental crust: a new table. Geochimica et Cosmochimica Acta 28, 1273-1285.
Trace Metal Composition of and Accumulation Rates of Sediments Upper Gulf of Thailand
Herbert L. Windoma, Suchada Silpipatb, Aurapin Chanpongsangb, Ralph G. Smith, Manuwadi HungspreugsC
in the
Jr.a and
aSkidaway Institute of Oceanography, P.O. Box 13687, Savannah, GA 31416, U.S. A., bOceanographic Section, Department of Fisheries, Parknam, Samutprakarn, Bangkok 27, Thailand and CDepartment of Marine Science, Chulalongkorn University, Phya Thai Road, Bangkok 5, Thailand Received 25 July 1983 and in revised form 2 December 1983
Keywords:
sedimentationrates; trace elements;metals; sediments;Gulf of
Thailand Sedimentcoresand grab samples were collected in the Upper Gulf of Thailand to determine sedimentation rates and to determine if metal concentrations reflect anthropogenic inputs. Accumulationratesof sedimentsin the Upper Gulf measuredusingthe 210Pb method, appear to vary from ca. 4 to 11 mm yrr’. Sediment budgets suggest that little of the sediment delivered to the Upper Gulf by the major rivers is ultimately
transportedto the Lower Gulf. Metal concentrationsin Upper Gulf sediments appearto be dominantlycontrolledby naturalinputs.
Introduction
The Gulf of Thailand is a large shallow embayment (maximum depth of 86 m) adjacent to the South China Sea. The Upper Gulf (Figure 1) has a relatively flat bathymetry and a maximum depth of less than 50 m. Four major rivers debauching into the Upper Gulf are the major sourcesof sediment for the entire Gulf (Emery & Niino, 1963). Of the four rivers, the Chao Phraya is by far the largest. Sediments throughout the Upper and Lower Gulf are dominantly muds with somesandy regions (Emery & Niino, 1963). The dominant clay mineralsare montmorillomite and illite, presumably derived from the lateritic soils of the central basin of Thailand (Aoki, 1976). There have been few studies of heavy metals in Gulf sediments. A recent report (Menasveta & Cheevaparanapiwat, 1981), however, suggeststhat Upper Gulf sediments may receive significant anthropogenic inputs resulting from large population increasesand industrialization along the northern coast, particularly around Bangkok, during the last few decades. This report addressesthe following questions: 1. What fraction of the sedimentstransported by the four major rivers is trapped in the Upper
Gulf? 133
0272-7714/84/080133+10$03.00/0
G 1984
Academic
Press
Inc.
(London)
Limited
134
H. L. Windom et al.
THAILAND ,
Figure
1. Sediment
sampling
stations.
2. Are anthropogenic inputs of heavy metals into the Upper Gulf large enough to significantly affect concentrations in Upper Gulf sediments? Methods Sampling
Stations at which sampleswere collected are shown in Figure 1. All sampling was from the Fisheries Department of Thailand R/V Fisheries Research no. 1. Sediments for heavy metal analyseswere collected with a stainlesssteel sampler. Subsamplesof these were taken from the center of the grab samplesto minimize the possibility of the sediment having contacted the sidesof the sampler. Samplesfor sedimentation rate studies were collected with a 8 cm diameter gravity corer. Cores were frozen upright until returned to a shorebasedlaboratory. Samplesfor heavy metal analyseswere collected in February and September 1982.Cores to determine sedimentationrates were collected only in February. One additional vibracore was collected during the summerof 1982 for sedimentation rate measurements.This core
Sediments in Upper Gulf of Thailand
135
was collected using the Thailand Navy Oceanographic Research Vessel. This core was treated similarly to the gravity cores. Heavy metal analyses Aiiquots of oven dried sediments were totally digested and leached with concentrated nitric acid. Total digestion was accomplished using concentrated hydrofluoric and perchloric acids to break down the silcate lattice and to destroy organic matter. Approximately one gram of sediment was refluxed for several hours in a teflon screw top beaker on a hotplate, taken to dryness and the residue dissolved in 10%nitric acid. Separate one gram sampleswere boiled in concentrated nitric acid for about one hour, the supernatant filtered off and taken to dryness. The residue was redissolved in 10%nitric acid. Strong acid leachate (SAL) analyseswere accomplished in Thailand at the Fisheries Department laboratory near Bangkok. Total digests were analyzed at Skidaway. Analyses at both locations were carried out on Perkin Elmer 5000 atomic absorption spectrophotometers using either flame or furnace techniques. Analyses of NBS estuarine sediment standard reference material was used for evaluating accuracy. Precision of analyses,based on replicate samples,is estimated at + 15%or lessfor all metals. Sedimentation rate measurements Sedimentation rates were determined using the 2loPb method (Koide et al., 1972). Our approach was to measure 21OPoactivity and to assumeradioactive equilibrium with 2loPb (Nittrouer et al., 1979). Sediment sampleswere collected at 5 cm intervals through the length of the cores, dried and ground to passa 100pm sieve. 21OPowas isolated from the samplefollowing procedures described by Flynn (1968) and using a 2O*Pospike to correct for yield. Separated and plated sampleswere analyzed by alpha spectrometry.
Results Sedimentationrates Gravity cores for sedimentation rate determinations were collected at stations 1, 2, 3, 5, 6, 7, 9 and 14 (Figure 1). The one vibracore was collected at station 8. Attempts to core at more southerly stations and at those in open waters (i.e. stations 12-19) failed due to the more coarse grain nature of the sediments there. With the gravity corer used, the maximum depth of penetration obtained was about 40 cm. Also, with the diameter of the corer used, it wasnecessaryto sample5 cm vertical segmentsof the core to obtain sufficient material for the analyses.With the vibracore a depth of 1 m was penetrated. The results of 2loPb (i.e. 2lOPo)analysesfor the vibracore are shown in Figure 2. The total 2loPbactivity of this core showsa zone of relatively uniform activity down to a depth of about 15 cm. From about 15cm to 40 cm the 2rOPbactivity exhibits exponential decay. At greater depths the activity is again uniform at about 0.46 f 0.05 dpm g-1. The mean 2loPb activity of the bottom of the core (i.e. depths > 40 cm) was assumedto represent the amount of 2lOPb supported by *26Ra decay in the sediments. This activity, 0.46 dpm g-1, was therefore subtracted from the total activities measuredin all cores to yield excess*lOPbactivity from which all sedimentation rates were measured. The best gravity core penetration was at nearshore stations. These cores also exhibit the most consistent trends in decreasingexcessZloPbactivity with depth (Figure 3). Cores at stations 9 and 14 show no clear trend. These two cores contained coarser sediment with
136
H. L. Windom et al.
*“Pb
octivcty
(dpm
g-‘1
Total
80
Excess 100
L
+ +
+
Figure 2. Total and excess zl”Pb activity with depth in vibracore line is the regression curve for excess activity versus depth.
taken at statlon 8. Dashed
considerable material greater than 200 p. All of the other cores contained relatively uniform fine sandto silt (mean grain size ca 62 ltm). The results of ZiOPbmeasurementson gravity cores (Figure 3) show no indication of a surface ‘mixed zone’ with uniform *lOPb activity typical of shelf sediments (Nittrouer et al., 1979). This may be due, in part, to the large depth interval of sampling. It is also likely that the gravity corer did not collect the surficial layer. As the corer penetrated the sediment, the upper, loosely consolidated, bioturbated or physically mixed zone was probably pushed aside, with the corer retaining only the more consolidated sediments below. The percent moisture in the vibracore was46 at 5-10 cm, decreasingto 32 at the bottom. The very top part of the core had a percent moisture of 58. No correction was made for porosity in the sedimentation determinations due to the relatively small change in the moisture content of the sedimentsover the core lengths and the rather large uncertainties in the low *loI?bactivities. Results of analyses on cores collected from stations 1, 2, 3, 5, 6, 7 and 10 indicate radioactive decay of ZloPbwith depth (i.e. exponential decreasein activity with depth) in the upper section of the cores. A best fit curve of the data from the upper part of the 210Pb2rsdepth profile can be used to determine sedimentation rates. Using a half life of 22.3 years for *iOPb, sedimentation rate estimatesvary from 4 ‘0 to 11‘2 mm yrrl. Heavy metal concentrations
Sediment samplescollected during February 1982were analyzed for total and strong acid
Sediments in Upper Gulf of Thailand
Excess 0 0
I
0.5
I.0
0.1
2’oPb
137
activity 0.5
(dpm I.0
2 0
g-l) 0-I
05
IO
20
stn I II 2 mm/Yr t
IO + 20 v
3ot
0
IO
20
0.1 0
0.5
I.0
2.0
3.0
Stn 7 4 Ommyr-’
IO 1 +
20 I77
0 I
05
I.020
30
0, I
0 5 1
Stn 14
Figure 3. Excess “OPb activity with depth data through which they are drawn.
I-O
2.0
1
1
in gravity
cores. Lines are regression
curves
of
H. L. Windom et al.
138
leachable (SAL) aluminum, iron, manganese,copper and nickel. Total concentrations only were determined for cobalt, lead and cadmium (Table 1). All values are derived from the average of duplicate analyses. Generally, little variation in metal concentrations between most stations is apparent although sedimentsfrom the northernmost stations near the river mouths have the highest levels. TABLE 1. Trace during February Leached
Station I 2 3 4 8 9 11 12 16 17 19 Mean
Aluminum (g kg-‘) 31 38 39 61 32 16 20 16 19 15 16
(62) (59) (64) (68) (64) (44) (59) (46) (39)
27+14
metal concentrations 1982
Iron k kg-‘)
Manganese bg kg-‘)
Copper (mg h-7
17 21 22 33 20 12 13 12 17 21 28
900 (107) 800 (91) 720 (87) 830 (85) 820 (95) 500 (92) 770 600 (120) 510 (72) 710 590 (84)
10 13 11 24 10 4.0 5.0 3.3 2.8 2.5 3.5
700 AZ 140
8.1f6.5
(77) (72) (73) (80) (87) (70) (92) (68) (68)
2Ot-6
Aluminum k kg-‘)
I 2 3 4 5 7 8 9 10 11 12 13 14 15 16 17 18 19
34 40 37 53 55 45 27 16 33 20 15 6 17 4 19 17 15 17
Mean
26+15
collected
in the Upper
(per cent of total given in parentheses)
TABLE 2. Strong acid leachable Upper Gulf of Thailand during
Station
in sediments
Iron k kg-]) 21 22 21 32 32 22 21 12 20 24 12 33 14 11 24 22 34 31 23i7
(83) (85) (69) (77) (83) (49) (65) (36) (56)
Total
Nickel (mg kg-‘) 20 26 28 38 30 18 20 8.8 14 14 15
740 750 780 840 1210 700 800 440 590 510 410 300 590 370 430 430 650 950 640 f 230
concentrations
only
Cobalt 0% kg-9
Lead 6% kg-l)
(110) (96) (103) (102) (150) (120)
9.3 12 12 15 10 6.4
7.5 8,2 7.6 8.6 5.2 4.7
15 23 25 19 10
(110) (100)
5.5 8.5
5.0 5.4
10 18
6-3
10
6.5h1.5
15~6
(105)
21 i8.6
10 9.8-12.9
trace metal concentrations September 1982
Manganese (w kg-l)
Gulf of Thailand
in sediments
Cadmium (pg kg-l)
collected
from the
Copper (mg kg-‘)
Nickel img kg-‘)
Cobalt (mg kg- I)
10 12 10 20 20 15 9.5 4.5 12 3-8 2.0 1.0 2-5 0.5 2.5 2-o 1.5 2.5
25 26 24 31 25 22 20 8.8 17 7.5
10 9.3 13 14 14 10 8.3 4.3 2.7 4.5 2.5 cl.0 2-5 5.0 4.3 6 5 6.5 9,5
7.3k6.5
14t9-8
7.11
4-o
139
Sediments in Upper Gulf of Thailand
The SAL fraction of the total metal content in the sedimentsis fairly constant for each metal. The SAL fractions of aluminum, iron, manganese,copper and nickel were 56& 10, 76 & 8, 92 f 14, 67 k 17 and ca loo%, respectively, of the total concentrations. Sediments collected during September 1982 were analyzed only for the SAL fraction (Table 2). Although there is some difference in SAL concentrations at given stations between the two sampling periods the mean concentrations at all stations are generally similar in both samplesets. Metal concentrations are generally higher in fine grain marine sediments when clay minerals are abundant. Typically aluminum is also enriched in fine grain, clay rich sediments. In natural deposits of varying grain size (i.e. varying clay mineral concentrations) metal concentrations should therefore covary with aluminum. Both total and SAL metal concentrations (except Cd) are plotted against aluminum in Figure 3. Also shown, for comparison, are solid lines which represent hypothetical
15
T ,o P u”
IO
5 0 0
50
100 AL(Q
Figure Closed line is curves
0
50
100
kg-‘)
4. Metal concentration versus aluminum concentrations in the Upper Gulf sediments. dots represent acid leached fractions. Open dots represent total concentrations. Solid the hypothetical natural abundance curve of metal OS Al. Dashed lines are regression based on 99% confidence level.
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(a) AL(g kg-‘)
(b) (Fe/AL)
(cl (Mn/AL)
x IO2
Thailand
n
*
Thailand -
13*
Figure 5. (a) Distribution of aluminum in acid leached fraction m Upper Gulf sediments (b) and (c) Variation in Fe : Al and Mn : Al ratios, respectively, in Upper Gulf sediments.
Sediments in Upper Gulf of Thailand
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deposits having constant metal : aluminum ratios based on average crustal abundancesof the elements (Taylor, 1964). Except for lead the total concentrations of all metals covary with aluminum at a 99 percent confidence level. Total lead covaries with aluminum at a 95 percent confidence level. The concentrations of copper and nickel alsocovary (P < 0.01) with aluminum in the SAL fraction. The regressionof these two metals against aluminum, in both the SAL and total digests, are generally parallel and lower than the ‘ natural abundance curve’ suggesting that Cu and Ni are not enriched in either fraction and variations in concentrations are controlled by natural processes. The SAL concentrations of iron, manganeseand cobalt show no relationship to aluminum concentrations. Also ratios of these metals to aluminum, in many instances, exceed the hypothetical ‘ natural ratio ‘.
Discussion Sediment dischargeby the Chao Phraya River, the largest of the four rivers emptying into the Upper Gulf, is about 3.4~ 106 metric tons per year (Port Authority of Thailand). Although discharge values are not available for the other rivers, sediment discharge by them may equal that of the Chao Phraya, suggesting that a total ca 7 x 106metric tons are delivered to the Upper Gulf annually. The Upper Gulf of Thailand hasan area of about 6 8 x 109m2.If we assumethat Upper Gulf sediments have a density of 2 g cm-3 the 7 x 106metric tons per year spread evenly over the area would account for a deposition rate of only 0.5 mm yr-1, or one tenth of that measured. Our measurementswere, however, restricted to the northern part of the Upper Gulf relatively near river mouths and thus can be expected to be higher than the average for the entire Gulf. *loPb results on other cores (e.g. stations 9 and 14; Figure 4) and surface samples collected at other stations suggestthat the sedimentsthere accumulate very slowly or that they are relict. Emery and Niino (1963) identified a band of relict sedimentsthat extends acrossthe boundary between the Upper and Lower Gulf. Our results suggest that the sediments transported by the Chao Phraya, Mae Klong, Ta Chin and Bang Pakong Rivers are, for the most part, deposited in the northern part of the Upper Gulf of Thailand. The distribution of aluminum [Figure 5(a)] also suggests that the greatest influence of river transported sedimentsis in the northern Upper Gulf. With the exceptions of iron and manganesethe distributions of metals in Upper Gulf sedimentsfollows that of aluminum and are apparently dominated by natural inputs. Iron and manganesedistributions deviate from that of aluminum, particularly in SAL fractions. The distributions of these metalsrelative to aluminum is reflected in the Fe : Al and Mn : Al ratios of Upper Gulf sediments[Figure 5, (b), (c)l. Highest ratios are near the boundary between the Upper and Lower Gulf indicating that iron and manganeseenrichments, relative to aluminum, are associatedwith the relict sedimentsdescribed by Emery and Niino (1963).
Acknowledgements This research was jointly funded by the National ResearchCouncil of Thailand and U.S. National Science Foundation Office of International Programs (grant INT81-16705). The authors wish to thank Captain Jarroug Sreevanich, the officers and crew of the Department
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of Fisheries Research Vessel Number 1. Thanks are also due to MS Dannah McCauley who provided secretarial assistance. References Aoki,
S. 1976 Clay mineral distribution in sediments of the Gulf of Thailand and South China Sea. Journal of the Oceanography Society ofJapan 32,169-174. Emery, K. 0. & Niino, H. 1963 Sediments of the Gulf of Thailand and adjacent Continental Shelf. Geologrcal Society of America Bulletin 74, 541-554. Flynn, W. W. 1968 The determination of low levels of polonium-210 in environmental materials. Anuly~zca Chimica Acta 43, 221-227. Koide, M., Soutar, A. & Goldberg, E. D. 1972 Marine geochronology with Pb-210. Earth and Planetary Science Letters 14, 442-446. Menasveta, P. & Cheevaparanapiwat, V. 1981 Heavy metals, organochloride pesticides and PCBs in green mussels, mullets and sediments of river mouths in Thailand. Marine Pollution Bulletin 12, 19-25. Nittrouer, C. A., Sternberg, R. W., Carpenter, R. L? Bennett, J. T. 1979 The use of Pb-210 geochronology as a sedimentological tool: Application to the Washington Continental Shelf. Marine Geology 31, 297-316. Taylor, S. R. 1964 Abundance of chemical elements in the continental crust: a new table. Geochimica et Cosmochimica Acta 28, 1273-1285.