Seasonal and longitudinal changes in copper and iron in surface water of shallow eutrophic Lake Kasumigaura, Japan

Pergamon PII: S0043-1354(96)00251-5

Wat. Res. Vol. 31, No. 2, pp. 280-286, 1997 Copyright © 1996ElsevierScienceLtd Printed in Great Britain. All rights reserved 0043-1354/97$17.00+ 0.00

SEASONAL A N D LONGITUDINAL CHANGES IN COPPER A N D IRON IN SURFACE WATER OF

SHALLOW EUTROPHIC LAKE KASUMIGAURA, JAPAN KAZUHO INABA*, TATSUYA SEKINE t, NORIKO TOMIOKA and OSAMI Y A G I ~ National Institute for Environmental Studies, 16-20nogawa, Tsukuba, Ibaraki 305, Japan and ~Department of Chemistry, Science University of Tokyo, 1-3 Kagurazaka, Shinjuku, Tokyo 162, Japan (First received October 1995; accepted in final form July 1996) Abstract--The concentrations of copper and iron in surface water of the eutrophic Lake Kasumigaura, the second largest lake in Japan, have been monitored at three sites monthly from April 1989 until March 1994. The metals were analyzed by a graphite furnace AAS after filtration with a 0.45-#m membrane filter. The concentrations of copper in the water were in the range 10-9 to 5 × 10-8 M and showed clear seasonal changes, being higher in summer and lower in winter. The concentrations of copper did not decrease on passage through the lake. The values of dissolved chemical oxygen demand (CODM,) showed a similar behavior, an interaction of copper in the lake water with organic matter was estimated. The concentration of copper in the lake became sometimeshigher than the value of ECs0for Microcystis, however, the metal forms stable complex species with organic matter and the toxic effect may be reduced. The concentrations of iron, on the other hand, showed wide variation, but no obvious seasonal change. The concentrations of iron decreased very markedly during flow of water through the lake. Copyright © 1996 ElsevierScience Ltd Key words---eutrophic lake water, copper, iron, complexingcapacity, seasonal change, longitudinal change

I

INTRODUCTION Blue-green algal blooms have been reported from a number of lakes in Japan (Japan Environment Agency, 1994). They are responsible for several problems in the use of lake water, such as death of commercially cultivated fish due to decreased dissolved oxygen, production of a musty odor in the drinking water supply and contamination by toxic materials such as the microcystins from Microcystis viridis. In order to understand the mechanisms of formation of the algal bloom and how to control it, chemical and biological surveys have been carried at Lake Kasumigaura, a eutrophic lake in Japan, by members of the authors' Institute since 1976 (Aizaki, 1977, 1984, 1988, 1990; Goda, 1979; Yasuno and Otsuki, 1981; Ebise, 1994). The results of field investigations have shown that the bloom is dominated mainly by Microcystis spp. and that nitrogen and phosphorus are the most important factors influencing development of the bloom (Takamura and Watanabe, 1987). Pollution of lake waters with nitrogen and phosphorus in domestic and agricultural wastewaters is the main reason for the formation of the algal bloom. However, the formation of water bloom cannot always be explained by only the concentrations of these elements, *Author to whom correspondence should be addressed,

Some trace metals, such as copper and iron, are important both as nutrients and potential toxicants for the growth of these algae (Sunda and Lewis, 1978; Sunda and Hanson, 1987). Previously, we have determined the toxicities of copper, cadmium and cobalt to Microcystis aeruginosa K3A, M. viridis and Anabaena affinis in a synthetic nutrient medium, which contained excess nitrogen and phosphorus (Tomioka et al., 1988). The effective concentrations (ECs0) of copper were low and the metal seemed to be a potential inhibitor of algae in natural lake waters. There have also been many studies showing that iron is an essential nutrient for growth of algae (Murphy et al., 1976; Lange, 1974). Studies on the concentration and behavior of metals such as copper and iron in aquatic environments are therefore important. There have been many studies on levels of copper (Nojiri et al., 1985; Tan et al., 1988; Stripp et al., 1990; Waara, 1992; Balistrieri et al., 1992b; Salanki et al., 1992; Kawai et al., 1992; Welsh et al., 1993; Xue and Sigg, 1993) and iron (Kawai et al., 1992; Balistrieri et al., 1992a; Jones et al., 1993) in lakes throughout the world, but detailed data and critical discussion on their sources and behaviors based on a long-term monitoring study are limited. The aim of the present study was to measure the concentrations of copper and iron in the water of this lake in order to understand the behavior of these metals. Such

28o

Behaviors of Cu and Fe in lake water data will in turn aid discussion about the role of these metals as a secondary factor in formation of the blue-green algal bloom, MATERIALS AND METHODS Field investigation Field investigation was carried out at Lake Kasumigaura. An outline of the lake is shown in Fig. I. The lake is the second largest in Japan, with a surface area of 171 km 2 and a mean depth of 4 m, and is located 50 km northeast of Tokyo. The lake i:; too shallow for a distinct thermal stratification to form normally. The lake has two large bays, Takahama-Iri and Tsuchiura-Iri, and the former was used for the present investigation. Water samples were collected at three stations shown in Fig. 1. Station 1 is in the deepest part of the bay and is affected directly by River Koise, the largest river flowing i~to the bay. Station 3 is at the center of the bay and St. 9 is located at the center of the lake. Sampling and sample treatment Monitoring was performed monthly from April 1989 until March 1994 (Sts 1 and 9 for copper), from June 1989 until March 1994 (Sts 1 and 9 for iron) and from April 1991 until March 1994 (St 3 for copper and iron). Data for March 1992 were eliminated because of contamination during the pretreatment procedures. Surface water at each station was coll~=ted directly into a 1 litre stoppered polypropylene bottle, which was kept cool in an ice box. The samples were brought back to the Institute and filtered with a 0.45-#m membrane filter, ultipor N~ (Pall Trinity Micro Co.), as soon as possible. The filtered solutions were acidified to 0.5 M by addition of analytical grade nitric acid. All bottles and glassware were washed with 6 M nitric acid for at least 3 days and then rinsed by an excess of ion-exchanged distilleeL water just before use. The amounts of copper and iron in the sample solutions were determined by a Perkin-Elmer Z-5100A graphite furnace atomic absorption spectrometer using absorption lines at 324.8 nm for copper and 248.3 nm for iron with deuterium backgrouncl correction. A pyrocoated graphite tube with a L'vov platform was used. Usually, 10/tl of the sample was injected irLto the graphite tube, but 20 gl was used when the metal concentration was low. The standard temperature-control program recommended by the manufacturer was utilized for the determination. The amounts of copper and iron in the samples were calculated using calibration curves obtained by sets of standard solutions containing up to 10.00 ,ug 1-~ (1.57 x 10-7 M) copper and up to 100.0/tg 1-~ (1.79 x 10-rM) iron.

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~._ /fl ~ / ~ J 140°18 ' 140"30' Fig. 1. Map of the monitoring sites on L. Kasumigaura. 5 ~

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Estimation o f error in A A S determination In order to estimate any error in the measurement of copper and iron by the present AAS method, the sensitivity and accuracy of the present analysis were tested. Calibration curves for copper and iron showed good linearity in the above concentration range. Blank absorbances, measured using ion-exchanged distilled water, were almost zero and the values for standard deviation (N = 10) were 0.4 pg for copper and 0.8 pg for iron. The detection limits (3 x SD) were therefore l pg for copper and 2 pg for iron, and the quantitative limits (10 x SD) were 4 pg for copper and 8 pg for iron. Samples (usually l0 #l) were injected into the AAS, the limit concentrations for detection and quantification being 0.1 and 0.4 #g l -~ (1.57 x 10-9 M and 6.28 x l0 -9 M) for copper and 0.2 and 0.8/zg I-~ (3.58 x 10-9 M and 1.43 × 10-8 M) for iron, respectively. The total contamination from the sample bottles and glassware during the whole sample treatment prior to AAS determination was estimated by a blank experiment. One litre of ion-exchanged distilled water was stored overnight in the acid-washed polypropylene bottle and then filtered with the 0.45-/tm membrane filter. The concentrations of copper and iron in the stored and the filtered solutions were determined (N = 6); the ion-exchanged distilled water before the treatment contained 0.03 -I- 0.03/zg 1-~ (4.72 x 10-~° _ 4.72 x 10-~° M) copper and 0.2 _ 0.2/zg 1-' (3.58 x 10-9 + 3.58 × 10-9 M) iron before filtration, whilst the filtered solution contained 0.03 + 0.04 pg 1-1 (4.72 x 10-1° + 6.29 x 10-~° M) copper and 0.1 -I- 0.2/zg 1-~ (1.79 x 10-9 + 3.58 × 10-9 M) iron. As the values before and after the filtration agreed well, contamination from the apparatus and treatment was negligible.

RESULTS AND DISCUSSION The metals reported here are not only dissolved species such as ionic metal and soluble complex species, but include suspended materials such as hydroxide colloids that can pass through the 0.45-/~m pores of the filter paper. Physical, chemical and biological investigations have been carried out by the other members associated with the present research programme (Aizaki, 1990; Ebise, 1994). Discussion about the other data will be reported elsewhere by the members individually. Concentration a n d behavior o f copper

The values for copper at Sts 1, 3 and 9 are shown in Fig. 2. The concentrations of copper at all these three sampling sites varied with the season, being higher in summer and lower in winter. The values ranged f r ° m 0'1/~g 1-1 t ° 3/~g 1-' (1"6 x 10-9 t ° 4.7 x 10 -s M); those are similar to values determined for other freshwater aquatic systems throughout the world ( N o j i r i e t a l . , 1 9 8 5 ; T a n e t a l . , 1 9 8 8 ; S t r i p p et al., 1990; Waara, 1992; Balistrieri et al., 1992b; Salanki et al., 1992; Kawai et al., 1992; Welsh et al., 1993; Xue and Sigg, 1993). The complexing capacity ( C u C C ) a n d its stability constant of some samples were measured by a copper titration method at p H 6.0 using an ion-selective electrode (Scatchard el al., 1957; Turner et al., 1985). Although the results were analyzed by a two-site calculation technique using Scatchard plots reported previously, often only one site value could be ealcu-

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Fig. 2. Copper concentrations in the surface water of L. Kasumigaura from April 1989 until March 1994. The samples were collected at St. 1, St. 3 and St. 9.

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lated due to the limitations in accuracy of the data. The values of CuCC and the conditional stability constant at pH 6 that was calculated together with CuCC are shown in Figs 3 and 4. The estimated values for CuCC showed wide variations, however, the values seems to be somewhat high in summer and there were no large differences between the three sampling stations. The chemical oxygen demands of the filtered solution that was determined using

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•.. "~? ............. , ........... , . . . . . 1~o laeo 1~1 1~2 1~ Fig. 3. Concentrations of CuCC in the surface water of L. Kasumigaura from May 1989 till March 1994. The samples were collected at St. 1, St. 3 and St. 9. Closed circle gives CuCC for the strong ligand and bar gives for the weak one, which are calculated by the two-site analysis,

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Fig. 4. Values of conditional stability constant of CuCC materials in the surface water of L. Kasumigaura from May 1989 until March 1994. The samples were collected at St. 1, St. 3 and St. 9. Closed circle gives the value for the strong ligand and closed triangle for the weak ligand, which are calculated by the two-site analysis.

potassium permanganate (D-CODMn) (Japan Industrial Standard, 1986), determined by other members involved in the present investigations, also showed seasonal changes, being higher in summer and lower in winter (Aizaki, 1990; Ebise, 1994). The D-CODM, does not indicate all the organic materials in the sample, however, a relationship of the parameters has been studied by Fukushima (in preparation). It has been concluded that the value of D-CODM~ is proportional to that of dissolved total organic carbon, D-TOC, in a certain aquatic system. Thus, the similarity among the patterns of change in copper, CuCC and D-CODM. suggests that copper in the lake water is interacting with organic compounds. The values of conditional stability constant, Fig. 4, are in the range of 1 x 105 to 3 x 107 M -~, showing wide variatiOns but nO °bviOus seasOnal change' On the other hand, the stability constant seems to be somewhat increasing with flow. The fact that the amount of CuCC did not change with flow through the lake, whilst the stability constant increased with flow, may suggest that the structure of the materials converted by degradation during lake flow, was a stronger ligand in St. 9 than in the upper sites. An effect of the different water body from Tsuchiura-Iri seems to be another reason for the higher stability constant in St. 9. The values of CuCC concentration and of the stability constant are within the ranges reported previously (Sunda and Lewis, 1978; Akaiwa e t a l . , 1986; Sunda and Hanson, 1987; Tan e t a l . , i 988). Since the values of CuCC were always higher than the copper concentration in the lake water, and the

Behaviors of Cu and Fe in lake water

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Fig. 5. Changes in average concentrations of copper corresponding to summer (May to October) and winter (November to April) s,:asons associated with flow of water through St. 1 to St. 9. The periods averaged are: 1989.51989.10 (<)), 1989.11-1990.4 (O), 1990.5-1990.10 (~), 1990.11-1991.4 (V), 1991.5-1991.10 (O), 1991.11-1992.4 (O), 1992.5-1992.10 (A), 19!)2.11-1993.4 (A), 1993.5-1993.10 (I-q) and 1993.11-1994.3 (E).

values for the stability constant were high enough, the copper should dissolve stably as complex species, The averaged concentration of copper for each 6month period corresponding to summer and winter, calculated using the data from May to October and November to April, was plotted as a function of distance from St. 1 to St. 9 (Fig. 5). The average values did not change much during passage from St. 1 to St. 9, although the pH of the lake water was high enough to form precipitates by hydrolysis, namely the pH value at these sites was 7 to 10 during the investigations (Aizaki, 1990; Ebise, 1994). The sources of

SL 1

283

SL3

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Fig. 7. Changes in average concentrations of D-CODMn corresponding to summer (May to October) and winter (November to April) seasons associated with flow of water through St. 1 to St. 9. The periods averaged are: 1989.51989.10 (O), 1989.11-1990.4 (O), 1990.5-1990.10 (V), 1990.11-1991.¢(I'), 1991.5-1991.10 (O), 1991.11-1992.4 (O), 1992.5-1992.10(A), 1992.11-1993.4 (&), 1993.5-1993.10 ([]) and 1993.11-1994.3 (1).

copper in the lake were not clearly identified, however, copper is one of the typical pollutants from human activity, being high in urban rivers (Ministry of Construction, 1992), since, it may mainly be supplied through rivers that contain domestic and industrial wastewaters. The concentration of copper dissolved in the R. Koise, the biggest river in the basin, was first measured four times in 1993, the values are between 0.2 and 1.2 #g 1-~ (3.14 x 10 -91.88 x 10 -8 M), being similar to the values in the lake. Although the distribution and total amount of the metal entering the lake cannot be estimated, the similar tendency of change in CuCC and D-CODM, during flow from St. 1 to St. 9 (Figs 6 and 7) to those of the copper, strongly suggests that the copper forms stable complex species with organic compounds. a The fact that the copper in the lake water forms ,., stable soluble-type species can also be explained __--o lOO 'ra # by results obtained from a separate experiment ~ _ - - ~~- - ~ ~ (Table 1). The lake water was still able to dissolve 80% of the copper after 2 weeks at pH 8 following the 1 addition of 6.4/~g 1-~ (1.0 x 10 -7 M) copper, which is 5o ten times higher than the concentration normally 04~-:------!~---- ........ -~:~ contained. On the other hand, copper in a synthetic ...... • nutrient medium at pH 8, was decreased by more vthan 90% within 1 day after the addition of 6.4 #g 1-~ i I i (1.0 x 10 -7 M). This indicates that the lake water ,1.1 St,,3 St.9 contains masking materials that can solubilize koe,nUon stably a concentration of copper at least ten times Fig. 6. Changes in average concentrations of CuCC higher than that contained on average in the lake corresponding to sumraer (May to October) and winter water. (November to April) seasons associated with flow of water It was observed that the concentrations of copper through St. 1 to St. 9. The periods averaged are: 1989.5- in the lake were higher in 1992 than in the other years 1989.10 (O), 1989.11-1990.4 (0), 1990.5-1990.10 (~7), (Fig. 2). The reasons for the change in concentrations 1990.11-1991.4 (V), 199].5-1991.10 (O), 1991.11-1992.4 (O), 1992.5-1992.10 (A), 1993.5-1993.10 (1"7) and 1993.11- are unclear, however, as seen from Figs 3 and 4, no 1994.3 (ll). obvious change is found in CuCC and the conditional

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al.

Table 1. Copper solubilizationability of water collectedfrom Lake Kasumigaura [Cu],.~ ( p g I t)

Medium L. K a s u m i g a u r a L Nutrient medium 2

[Cu]..~

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(,ug 1 ')

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6.1 1.5

5.8 1.2

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~Collected at St. 9 on July 7, 1993. The p H was kept at 8.0 by 1 g 1-' HEPES. 2Modified M - I I medium: N a N O 3 100 mg, MgSO4.7H20 75 mg, C a C h - 2 H 2 0 40 mg, Na2CO3 20 mg, K2HPO, 10 mg and FeSO4'7H20 1.4 mg were dissolved in I 1 Mini-Q water. The p H was kept 8.0 by I g I ~ H E P E S .

stability constant throughout the recent 5 years. The high concentration levels of copper in 1992 may be due to changes of its source and/or amount supplied, It is noteworthy that dredging operations were carried out in the lake through the year, and these could be effective in releasing copper from the sediments, The concentration levels in 1992 were higher than the ECs0 values for M i c r o c y s t i s , ECs0 = 2 × 10 -8 M (Tomioka e t a l . , 1988), the toxic effect for the growth of the algae was found by a bioassay test obtained separately. During this period, formation of water blooms were observed in the lake, however, the dominant species in the bloom was found to be O s c i l l a t o r i a (Ibaraki Prefecture, 1994). The concentrations of the complexing capacity were found to show no obvious change due to the increase of copper; the ratio between the complexing capacity and the copper seemed to become small. (However, the measurements on 1992 did not cover all samples because of the absence of one of the authors in the Institute during this period.) The value of the ratio was usually about 100 although sometimes it moved to about 50, while in 1992 the value dropped to about 20. As reported previously, the toxicity of copper for algae is probably due to free copper ionic species (Sunda and Lewis, 1978; Sunda and Hanson, 1987; Allen e t a l . , 1980). Thus, the effect of masking on

the value for iron was the highest in this station. The concentration of iron in the R. Koise in 1993 was monitored initially, and the values were in the range of 30--100/~g 1-t (5.37 x 10-7-1.79 x 10-6M). The concentrations of iron contained in waters in some large rivers that flowed into the lake were monitored by Nishikawa (personal communication), and were 100/~g 1-' or less. However, the effect of the rivers on the supplement of iron into the lake seemed to be large. Iron in lake sediments can dissolve as a bivalent cation, Fe 2+ when lake sediments become reductive. Although the oxidation-reduction potential of Lake Kasumigaura is generally high because of its shallowness, very low dissolved oxygen (DO) values were often observed in the bottom water, usually in the summer season, at each sampling site during previous investigations (Aizaki, 1977, 1984, 1990; Goda, 1979; Yasuno and Otsuki, 1981). The iron concentration increased when the DO of the bottom water showed very low values (Aizaki, 1984), and this could be one of the sources in the lake. However, the DO values of the bottom water did not fall below 1 mg 1-] during the present investigation (Aizaki,

15o st- 1

reducing the toxicity of copper to the algae should be decreased. As mentioned above, the levels of copper in the lake water sometimes reached the concentration range that inhibit blue-green algae and seemed to be a controlling factor in its growth. Detailed discussion about this effect will be presented in another paper together with data from bioassay experiments.

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The concentrations of iron at Sts 1, 3 and 9 are shown in Fig. 8. Although the values show large variation at all the sampling stations, there were no obvious seasonal changes. The concentrations of iron in the lake, however, show a clear decrease from St. ! to St. 9 (Fig. 9). The sources of iron in lake waters are largely from rivers and sediments. If iron in lake water is supplied mainly from rivers, the concentration should be highest at a site located near the biggest river inflow. Station 1 is the largest river estuarine area in the three stations in the present investigation area and

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~ ~ 1~o lm 1~ ~m lm Fig. 8. Iron concentrations in the surface water of L. Kasumigaura from June 1989 until March 1994. The samples were collected at St. 1, St. 3 and St. 9. . . . . . . . . . . .

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showed a clear seasonal change, being higher in summer and lower in winter, but they did not show a decrease associated with flow of the water through St. 1 to St. 9. The facts indicate that copper in the lake water interacts with organic matter dissolved in the water. The levels of copper in the lake water are sometimes potentially high enough to inhibit the growth of blue--green algae such as Microcystis, but in practice this probably does not occur due to the reduction in toxicity associated with the formation of complex species. Since, to decrease water pollution with organic materials as well as that with main nutrients, phosphorus and nitrogen may effectively control the formation of blue-green algal blooms in the lake. The iron concentration in the lake water showed wide variations, but no seasonal changes. The concentrations were high at St. 1, the estuarine area of R. Koise, decreasing with water flowing to St. 9,

Fig. 9. Changes in average concentrations of iron corresponding to summer (May to October) and winter (November to April) seasons associated with flow of water through St. 1 to St. 9. The periods averaged are: 1989.51989.10 (0), 1989.11-1990.4 (0), 1990.5-1990.10 (~), the centre of the lake. 1990.11-1991.4 (V), 1991.5-1991.10 (O), 1991.11-1992.4 (O), 1992.5-1992.10 (A), 1~92.11-1993.4 (&), 1993.5-1993.10 (I-q) Acknowledgements--The authors are grateful to Drs S. and 11993.11-1994.3 (ll). Ebise, T. Kawai, T. Fukushima and M. Nishikawa of the National Institute for Environmental Studies for their comments. The field investigations were carried out as part 1990; Ebise, 1994). Since, the release of iron from the of the research project, Limnological Survey on Lake Kasumigaura. We thank all members of the project for their lake sediment seems to be small, this is probably a cooperation. negligible source of the metal. On the other hand, the iron supplied to the water would quickly be oxidized, hydrolyzed and then polymerized. The polymerized REFERENCES iron should form coi[loids, whose size should increase. Aizaki M. (1977) Limnological Data in Lake Kasumigaura. Due to these reactions, the concentration of iron in Res. Data Natl lnst. Environ. Stud. 1, 1-28 (in Japanese). the lake should dec~rease with flow of water through Aizaki M. (Ed.) (1984) Limnological Data in Lake the lake. Kasurnigaura. Res. Data Natl Inst. Environ. Stud. 25, 1-188 (in Japanese). The behavior of iron in the lake water, Figs 8 Aizaki M. (Ed.) (1988) Limnological Data in Lake and 9, was dominated by the balances of the above Kasumigaura. Res. Data Natl Inst. Environ. Stud. 33, sources and reactions. The amounts of iron supplied 1-105 (in Japanese). from rivers will be affected by stream conditions, Aizaki M. (Ed.) (1990) Limnological Data in Lake such as flow, flux and contamination by suspended Kasumigaura. Res. Data Natl Inst. Environ. Stud. F-25, 1-83 (in Japanese). matter, and those from sediments will depend on Akaiwa H., Kawamoto H. and Ogura H. (1986) A new the oxidation-reduction potential. The iron, once method for the measurement of copper(II)-complexing supplied to the lake, would quickly form hydrolyzed capacity of natural waters by back-extraction technique. polymer species, these reactions being controlled by Chem. Lett. 1986, 605-608. Allen H. E., Hall R. H. and Brisbin T. D. (1980) Metal chemical conditions such as oxidation-reduction speciation: Effects on aquatic toxicity. Environ. Sci. potential and pH. Thus, this is a potential reason why Technol. 14, 441-446. iron concentration between stations and sampling Balistrieri L. S., Murray J. W. and Paul B. (1992a) The dates become large. Mechanical forces such as cycling of iron and manganese in the water column of stirring and lifting letke sediments by wind or rainfall Lake Sammamish, Washington. Limnol. Oceanogr. 37, 510-528. would also affect the supply and the oxidation of Balistrieri L. S., Murray J. W. and Paul B. (1992b) The iron species, and are probably another reason for the biogeochemical cycling of trace metals in the water variations, column of Lake Sammamish, Washington: response to The results given in Figs 8 and 9 also indicate that seasonally anoxic conditions. Limnol. Oceanogr. 37, 529-548. the iron in the lake water did not form stable Ebise S. (Ed.) (1994) Limnological Data in Lake soluble-type species such as the complex species with Kasumigaura. Res. Data Natl lnst. Environ. Stud. F-61, organic compounds observed in the case of copper. 1-113 (in Japanese). Fukushima T. (Hiroshima Univ., Faculty Engineering, 1-4 Kagamiyama, Higashi-Hiroshima, Hiroshima 724 Japan), MS in preparation. CONCLUSION Goda T. (Ed.) (1979) Limnological Data in Lake Kasumigaura. Res. Data Natl Inst. Environ. Stud. 6, From the present field investigations, the following 335-375(in Japanese). results are obtained. The concentrations of copper in Ibaraki Prefecture (1994) Data on Lake Kasumigaura the lake were in the :range 10 -9 to 5 x 10 -8 M . These (in Japanese).

286

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