- Email: [email protected]
Concentrations of zinc and chromium in aquatic macrophytes from the sudbury and muskoka regions of Ontario, Canada
Environmental Pollution 79 (1993) 261 265
CONCENTRATIONS OF ZINC A N D CHROMIUM IN AQUATIC MACROPHYTES FROM THE S U D B U R Y A N D MUSKOKA REGIONS OF ONTARIO, C A N A D A P. Reimer & H. C. Duthie* Department of Biology. University of Waterloo, Waterloo. Ontario, Canada. N2L 3G1
(Received 26 March 1991: accepted 13 December 1991)
(Gleason et al., 1979; Larsen & Schierup, 1981), or to varying input !nto the waterbody (Harding & Whitton, 1978). Root concentrations of many metals exceed shoot concentrations in most aquatic plants, probably reflecting the greater availability of these metals in the sediments (Harding & Whitton, 1978). Conversely, Forstner & Wittman (1981) reported maximum concentrations of several metals in the leaves. The objectives of this study were: to obtain information regarding the levels of zinc and chromium in four species of aquatic macrophytes collected from lakes in the Sudbury and Muskoka-Haliburton regions of Ontario; to examine these data in the context of species, organ (root and shoot), and growth season differences; and to investigate possible relationships between zinc and chromium levels in aquatic macrophytes and water and sediment variables in lakes of varying contamination.
Abstract Root and shoot samples o f Eriocaulon septangulare, Nuphar variegatum, Nymphaea odorata and Pontederia cordata were collected f r o m 15 lakes in central Ontario during the summer o[ 1988 to investigate possible relationships between zinc + and chromium levels in aquatic + macrophytes and water and sediment variables. Although concentrations o f zinc" and chromium d(ffered greatly among the four ,species, both metals were consistently higher in Eriocaulon. Generally. root and rhizome tissue contained higher zinc' and chromium than shoot tissues o[" the same species and site. Zinc concentrations (dry weight) ranged./?ore 6.3 Ixg g~ in Nuphar shoots to 87.7 t~g g t in whole Eriocaulon. Chromium ranged Jhom 0.23 t~g g t in Pontederia shoots to 23.9 gg g t in whole Eriocaulon. No sign(ficant trends were detected throughout the growing season in macrophyte or sediment concentrations o[" either metal. Results o f multiple linear regression analyses o f several water quality and enviromnental variables on Eriocaulon indicated that sediment :inc' was the best predictor o f plant zinc, and sediment chromium and calcium were the best predictors o f plant chromium.
MATERIALS AND M E T H O D S Study area Fifteen lakes located in the Sudbury and MuskokaHaliburton regions of central Ontario were chosen for study (Table 1). The study lakes were selected at varying distances from Sudbury, Ontario and represent a wide range of variables, particularly pH (4-6-7.2) and sulfate (3.7 27.4 mg litre ~). Water chemistry data for these lakes supplied by the Ontario Ministry of the Environment represent epilimnetic averages for the 1986-87 hydrological year. The only alkaline lake, Hannah Lake, was the site of a neutralization project in the 1970s; it was previously acidic. Most lakes have low to moderate summer cottage development around them.
INTRODUCTION
Although it is established that aquatic macrophytes are capable of accumulating metals far beyond ambient water concentrations (Kovacs, 1978; Forstner & Wittman, 1981; Heisey & Damman, 1982; Reimer, 1989), considerable disparity exists in the literature in describing biological and environmental factors affecting the uptake of metals. Factors such as species, season, organ, site and analytical methodology have been examined (Mudroch, 1980: Bubicz et al., 1982; Campbell et al., 1985). Working in central Ontario lakes, Miller et al. (1983) reported that species-specific differences are metal dependent. Changes in the content of various metals in plant tissues throughout the growing season have been attributed to growth and attrition
Sample collection The collection of plant and sediment samples for analysis was conducted on three occasions throughout the summer of 1988. The sampling periods (29 May 9 June, 26 June-7 July, 31 July 11 August) were designed to allow the collection of multiple samples throughout the growing season. Four species of aquatic macrophytes: Eriocaulon
* To whom correspondence should be addressed. Environ. Pollut. 0269-7491/92/$05.00 ~) 1992 Elsevier Science Publishers Ltd, England. Printed in Great Britain
261
P. Reimer, H. C. Duthie
262
septangulare
With. (pipewort), Nuphar variegatum Engelm. (yellow water lily), Nymphaea odorata Ait. (white water lily), and Pontederia cordata L. (pickerelweed) were selected for analysis based on their wide distribution, differing growth forms, ease o f recognition, and high frequency in both contaminated and u n c o n t a m i n a t e d lakes. Individual macrophytes were collected by hand, raking, and dredging fiom waters no less than 10 cm and no more than 1.5 m deep. Only vigorous non-chlorotic plants free o f residue and excess algal growth were collected for the purposes o f this study. In all cases plants were rinsed with lake water to remove residue and sediment, and separated into root/rhizome and shoot/leaf portions prior to being sealed in new polyethylene bags and frozen. At least 5 and up to 20 individuals of each species were collected at several locations dictated primarily by vegetation growth and accessibility, It should be noted that Eriocaulon, due to its small size, was not separated into r o o t and shoot portions, Consequently, all estimates for this species are whole plant values. Frozen plant samples were oven dried in acid-washed polyethylene cups at 70°C for approximately 2 days. Approximately 1-2 g o f dried plant tissue was compressed at 700 kg cm 2 in a stainless steel pellet press. The resulting wafer was sealed in a 2 cm 2 polyethylene packet. Packets were arranged in a stacking pattern which was interspersed with standard materials prior to irradiation. Sediment samples were collected at each lake at the same time and place as the aquatic macrophytes. At each lake and sampling period, three acid-washed 200 ml disposable polyethylene cups were filled with sediment. Care was taken to avoid sampling near m a n - m a d e structures such as beaches and docks. Sediment samples were frozen until sample preparation. A 10 g aliquot o f sediment was removed from each o f the thawed sediment samples. These were oven dried in acid-washed polyethylene cups at 70°C ['or 24 h. A 0.5 1.0 g sample o f each sediment was
prepared for irradiation in acid-washed 10 ml polyethylene vials. Chemical analysis N e u t r o n activation analysis ( N A A ) was used since it had multi-element capabilities, no matrix effect, and could be used for both tissue and sediment. Irradiated samples were analysed using two lithium drift germanium detectors and a Canberra multi-channel analyser located at M c M a s t e r University Nuclear R e a c t o r in Hamilton, Ontario. National Bureau o f Standards (NBS) tissue standards 1573 ( t o m a t o leaves) and 1572 (citrus leaves) were analysed in conjunction with aquatic m a c r o p h y t e tissue. NBS standard coal fly ash (1633a, 1633b) were analysed with sediment samples. Additional standard materials were prepared from Fisher chemical atomic absorption standards. Plant tissues, packaged in groups o f 40 samples, were irradiated for approximately 3 h. Following a decay period o f 10-14 days, the radioactive wafers were removed from the polyethylene packets and placed in new sealed glass vials prior to g a m m a counting. Sediment samples were irradiated for 1 h and allowed to decay for approximately 1 week before counting commenced. All values expressed for plant tissue and sediment are expressed i n / z g g t (dry weight). Statistical analysis All statistical analysis was performed using the statistical analysis package S Y S T A T with the level o f significance maintained at 95% for all tests. In order to meet h o m o geneity o f variance and normality assumptions o f the tests, all plant and sediment data were logarithmically transt\~rmed. Analysis o f variance ( A N O V A ) on the transformed data indicated that differences between the growth seasons were insignificant for both macrophytes and sediment. To increase the manageability o f the data sets, they were reduced by averaging the values obtained for each sampling period to yield a single mean and standard deviation. The reduced data sets were used for all subsequent tests of analysis o f variance and
Table 1. Selected water quality variables and sediment (dry weight) zinc and chromium for 15 Central Ontario lakes
Lake Clearwater Crosson Dickie Fawn Gullfeather Hannah Harp Heney Leech Leonard kohi McKay Moot Plastic Ril
Location 46°23'N 45° 02'N 45° 09' N 45 ° 10'N 45°01'N 46° 27' N 45° 23'N 45° 08' N 45°0Y N 45° 04' N 46° 23' N 45°03'N 45°09'N 45 ° I I'N 45° 09'N
81°02'W 79° 05'W 79° 05' W 79 ° 15'W 79°05'W 81° 02'W 79° 08' W 79° 06'W 79° 06'W 79° 22'W 81°02'W 79 ° 10'W 79 ° 10'W 78°49'W 79 ° 10'W
pH 4.7 5.8 6-0 5.9 6.0 7.2 6.7 5.9 6.3 5.9 4.7 6.3 5.7 5.7 5.4
DOC Alkalinity Ca SO4 PPUT NNO Sediment mgliter ~ mgliter r mgliter L mgliter~ i ~gliter ~ /~gNliter i Zn/~gg i 0-36 4,13 4,87 9.10 5.30 3.36 4,31 2.75 4.20 3.13 0.54 5.30 7.15 2.04 4.20
1.14 0.55 1.09 1.53 1.20 12.70 3.41 0.64 1.50 0.57 1.17 2.02 0.95 0.21 0.06
5.6 2.0 2.3 2.5 2-4 13.1 2-7 1.9 2.6 2-3 6.0 2-8 1.7 1.9 2.8
15-6 6-6 6.0 5.1 7.4 27-4 6.8 6.0 7.4 6.5 17.6 6.7 3.7 6.2 6.9
2.52 9.58 10-2 19.5 ll.0 6.93 6.61 6.77 7.20 5.04 2.94 9.59 20.3 3.32 6.0
32.0 32.4 12.5 12.5 39.0 8.20 21-0 29.0 19.5 82.7 53-0 18.5 15.0 6,42 N/A
DOC, dissolved organic carbon: PPUT, total unfiltered phosphorus: NNO. nitrate and nitrite as N.
37.5 72.5 85.2 76.5 64.5 86.8 90-8 105.8 85.8 87.9 53.9 102.3 90.7 86-0 79-0
Sediment Cr/~gg 1 69.5 35.8 36.6 45.1 35.1 90-6 57-4 69.2 46.7 45.5 89.9 58.5 38.6 44.5 42.2
Concentrations of zinc and chromium in aquatic macrophytes
263
Table 2. Concentrations of zinc (/zg g-I dry weight) and root to shoot ratios (R/S) for the study species
Eriocaulon septangulare
Lake
Nuphar variegatum
Whole plant
Shoot
Root
15.9 42.7 85-7 52-6 49.1 59.0 53.6 77-8 63.2 62.3 22.7 66.1 47.4 59.4 50-9
. 7.3 11-2 10.7 10.2 8-I 9-1 16.5 6.3 14.6 9.3 10.0 14-1 9.2 12.1
15.7 19-2 14.7 17.3 15.8 17.8 21.2 16.4 15.8 8.8 18.1 21.3 14-0 15-9
Clearwater Crosson Dickie Fawn Gullfeather Hannah Harp Heney Leech Leonard Lohi McKay Moot Plastic Ril
Nymphaea odorata
R/S ratio . 2.15 1.72 1.37 1.69 1-95 1-95 1.29 2.60 1.13 0.95 1.81 1.51 1-55 1.32
Pontederia cordata
Shoot
Root
R/S ratio
. 15.2 12.2 18.7 19-0 15.3 13.1 14.5 13.2 14-4
14-7 16.4 28.5 23-4 20.7 20.6 13.2 24.7 14.6
0.97 1.34 1-53 1.23 1.35 1.57 0.91 1.87 1.01
16-0 18.7 13.3 11-4
23.3 22.4 10.5 7-3
1-46 1.19 0.79 0.63
Shoot
Root
R/S ratio
16.7 18.8 19.2 16.3 11.2 18.4 25.8 20.4 19-5 -29-4 19-1 26.3 18-8
38.3 56-4 30.9 40-3 27.0 78.9 64.5 68-2 39.2
2.29 3.00 1-61 2.47 2-41 4.28 2.50 3.34 2.01 -2-37 1.95 2.67 2.26
.
69.7 37.1 70.5 42-6
Values represent the mean concentration observed over three sampling periods. Missing values shown by - - . Eriocaulon was not separated into root and shoot portions. regression. It should be n o t e d t h a t H a n n a h L a k e was o m i t t e d f r o m statistical analysis involving l a k e w a t e r p a r a m e t e r s , since its w a t e r qua!ity was artificially altered t h r o u g h the n e u t r a l i z a t i o n process. RESULTS
Zinc S e d i m e n t zinc (Table l) a n d tissue zinc levels (Table 2) varied c o n s i d e r a b l y a m o n g species a n d lakes. Eriocaulon c o n t a i n e d the greatest q u a n t i t i e s o f zinc a m o n g the four s t u d y species, r a n g i n g f r o m 15-9 to 8 5 . 7 / z g g 1 (dry weight). It was followed closely by Pontederia which r a n g e d from 11-2 to 29.4 /zg g ~ in s h o o t tissue a n d 30-9 to 78.9 /zg g~ in r o o t tissue. Nuphar a n d Nymphaea yielded c o n s i d e r a b l y less tissue zinc, r a n g i n g f r o m 6.3 /~g g~ in Nuphar s h o o t s to 28.5 /xg g~ in Nymphaea roots. O n e - w a y analyses o f v a r i a n c e conducted on logarithmically transformed d a t a for sediments i n d i c a t e d t h a t there were no significant differences a m o n g s a m p l e s collected d u r i n g the three s a m p l i n g
p e r i o d s ( F -- 1.43, p -- 0-5, n -- 90). Similarly, a twow a y analysis o f v a r i a n c e on d a t a for m a c r o p h y t e tissue revealed no significant differences a m o n g s a m p l i n g p e r i o d for a n y o f the species ( F = 1.37, p -- 0.37, n = 99). H o w e v e r , highly significant differences were f o u n d for species c o m p a r i s o n s ( F = 40.6, p < 0.001, n = 99). R o o t to s h o o t (R/S) ratios were used to e x a m i n e the d i s t r i b u t i o n o f zinc within Pontederia, Nuphar, a n d Nymphaea. L i n e a r regression o f the R/S ratio a n d the p H o f the c o r r e s p o n d i n g lake s h o w e d g o o d c o r r e l a t i o n (Fig. 1). M u l t i p l e linear regression c o n d u c t e d on whole p l a n t zinc levels for Eriocaulon suggested t h a t sediment zinc m a y be the d e t e r m i n i n g f a c t o r in Eriocaulon zinc c o n c e n t r a t i o n s (Fig. 2). T h e c o n t r i b u t i o n to the regression m o d e l o f l a k e w a t e r p H , alkalinity, dissolved o r g a n i c c a r b o n , nitrogen, t o t a l unfiltered p h o s p h o r u s , a n d sulfate was n o t significant.
Chromium Results for c h r o m i u m (Table 3) indicated that Eriocaulon a c c u m u l a t e d greater quantities o f c h r o m i u m t h a n the TOO
--
-
Nuphof -
-
4 --
---
voriegatum
IVymphaea Pontederza
odorata cofdota
.i"
i
//"
z n¢
J
3
+
/~"
8o
zo ~
2 /
g 0r-
i
20
/ ///
+
/
I
pH
Fig. 1. Relationships between root to shoot ratios of zinc in three aquatic macrophytes and the pH of the study lakes. (a) Nuphar variegatum, r 2 = 0-559, y = 0-757x-3.337. (b) Nymphaea odorata, r 2 = 0-417, y = 1.366x 5.733. (c) Pontederia cordata, r 2 = 0.468, y = 0.615x-1.998.
0
20
40
6'0
I
'
80
I00
120
Sediment Zinc ( F g / g )
Fig. 2. Relationship between zinc concentrations in sediments and whole Eriocaulon septangulare collected from the study lakes. Dotted lines represent 95% confidence interval, r 2 = 0-707, y -- 0.857x-14.931.
P. Reimer, H. C. Duthie
264
Table 3. Concentrations of chromium (/~g g-I dry weight) and root to shoot ratios (R/S) for the study species Eriocaulon septangulare
Lake
Nuphar variegatum
Nymphaea odorata
Pontederia cordata
Whole plant
Shoot
Root
R/S ratio
Shoot
Root
R/S ratio
Shoot
Root
R/S ratio
13.0 3-9 8.5 10-6 3.6 23-9 6.8 6.6 5.5 8.5 12.5 9.3 9.0 4.2 5.7
-1.15 0.60 1.14 0.39 0.79 0.57 0.66 0.48 0.47 1.21 0.98 0.43 0.40 0.68
3.53 0.96 1.90 0.76 4.29 3-21 2-03 0.57 0.54 1-09 1-56 1.30 0-81 1.10
3.07 1.60 1.68 1.96 5.43 5.63 3.09 1.19 1.13 0.90 1.59 3.02 2.02 1.62
0.26 1.12 0.57 1.28 2.24 0.62 0.52 0.66 0.38
0.91 4.62 5-20 3.89 4.94 4.28 1.43 1.35 0.72
3.50 4.12 9.18 3.02 2.20 6.87 2.74 2.05 1.89
0.31 0.40 1.18 0-31 1-69 1.01 0.65 0.50 0.94
-1-34 2.88 3.64 1-63 13-46 4.19 3.18 1-77 2-62
-4.37 7.20 3.07 5.25 15.15 4.13 4.87 3.55 2.78
1-15 1-04 0.33 0-53
2.18 1.81 1.43 2.35
1.89 1.74 4.38 4-42
0.70 0.42 0.23 0.32
6.54 2.79 0.84 0.98
9.32 6.64 3.61 3.12
Clearwater Crosson Dickie Fawn Gullfeather Hannah Harp Heney Leech Leonard Lohi McKay Moot Plastic Ril
Values represent the mean concentration observed over three sampling periods. Missing values shown by separated into root and shoot portions. other three species. C h r o m i u m content in Eriocaulon ranged from 3.6 to 23-9 p~g g t while Nuphar, Nymphaea, and Pontederia ranged from 0.23 to 2-24 p~g g~ in shoot tissue and 0.54 to 13.46 /~g g~ in roots. Sediment concentrations o f c h r o m i u m varied from 35.1 to 90.6 p~g g ~ (Table 1). One-way analysis o f variance on logarithmically transformed sediment data indicated that there were no significant differences between samples collected during the three sampling periods (F = 1-37, p -- 0-27, n = 85). Results o f analysis o f variance on m a c r o p h y t e tissue data also indicated that there were no significant differences resulting from sampling period for any o f the species ( F = 1.33, p -0.27, n -- 96). A t w o - w a y analysis o f variance performed on c h r o m i u m data for Nuphar, Nymphaea, and Pontederia showed that root and shoot portions accumulated c h r o m i u m to significantly different levels (F -- 43-7, p < 0.001, n -- 65). Species differences were not significant a m o n g the three species tested. R/S ratios calculated for c h r o m i u m concentrations in n m c r o p h y t e tissue were highly variable, ranging from 0-9 to 9.35. 25 A
/
2o
E ~: o
15
10
:~
+
+
::
5
/
J 20
:~: 40
60
Sediment C h r o m i u m
80
I00
(p.g/g)
Fig. 3. Relationship between chromium concentrations in sediments and whole Eriocaulon septangulare collected in the study lakes. Dotted lines represent 95% confidence interval. r2 -- 0.564, y -- 0-207x 2.349.
. Eriocaulon was not
The R/S ratios showed no significant correlation (p > 0-05) with water pH, dissolved organic carbon, calcium, alkalinity, or sediment chromium. Multiple linear regression for whole plant chromium in Eriocaulon indicated that calcium and sulfate were significant variables (p < 0.01) in the model. Dissolved organic carbon and pH did not contribute significantly (p > 0-05) to the model. In addition, sediment c h r o m i u m appears to be a m a j o r predictor o f whole plant c h r o m i u m in Eriocaulon (Fig. 3), and is thus comparable to zinc. DISCUSSION Our results show that the quantities o f zinc and c h r o m i u m accumulated in aquatic m a c r o p h y t e tissue may be influenced by lake location, plant species, organ, and water and sediment chemistry. Concentrations o f zinc observed in this study fall within the range o f data presented by other authors for various species and regions (Kovacs, 1978; M u d r o c h , 1980; Wells et at., 1980). Similarly, M u d r o c h (1980) reports levels o f 4-0 and 3.5 /_~g g t for c h r o m i u m in Nuphar and Nymphaea, respectively. Both m a c r o p h y t e and sediment levels o f c h r o m i u m are comparable with those observed in this study. The ability o f aquatic m a c r o p h y t e s to accumulate metals in their tissues appears to be a highly speciesspecific process ( M u d r o c h & C a p o b i a n c o , 1978; Friant, 1979; M u d r o c h , 1980; Miller et al., 1983; Kelly & Whitton, 1989). These differences also appear to be element-specific, as Mudroch (1980) reported with Elodea, Chara, and Myriophyllum. Our data show that significant species differences occur for both zinc and c h r o m i u m and that these differences are also metal-specific. In general, the orders o f accumulation are as follows: Zn: Eriocaulon > Pontederia > Nymphaea = Nuphar Cr: Eriocaulon >> Pontederia -- Nymphaea -- Nuphar The comparatively high levels o f zinc and c h r o m i u m
Concentrations o f zinc and chromium in aquatic macrophytes observed for Eriocaulon in relation to the other species suggests that surface area may be a factor in metal uptake. Our results concerning the absence of growth seasonal changes in metal concentration in plant tissues is in agreement with the conclusions of Peverly (1979). However, both Mudroch & Capobianco (1978) with Typha, and Gleason et al. (1979) with Spartina reported seasonal variability. Wehr & Whitton (1983 a, b), working with aquatic mosses, observed that seasonal changes were negligible in newer shoots but became more apparent in older tissue. This may explain the lack of seasonal variability in this study since we made an attempt to collect only vigorous shoots. Our results show that R/S ratios of metal concentrations are a useful way of quantifying the relative distribution of metals within the plant, particularly for non-translocated metals where the plant concentration generally reflects that of the surrounding media. In the case of zinc, these ratios were correlated with the pH of the lakewater, supporting the observation of Schindler et al. (1980) that zinc is more available in acidic water. Unlike zinc, significant correlations were not observed between R/S ratios for chromium and the measured environmental variables. However, chromium ratios did follow the trend to higher ratios in Pontederia that were also seen with zinc. The finely divided roots of Pontederia likely provide a greater surface area in which to absorb metals than do the tuberous roots of Nymphaea and Nuphar. The relationship between sediment and plant zinc in Eriocaulon seen in our multiple regression models was not observed by Miller et al. (1983) in their study of Eriocauhm in central Ontario lakes. The results of Kelly & Whitton (1989) working with algae and bryophytes support our conclusions that the plant's source (sediment vs water) of zinc is the most significant of the predictor variables in such models. The negative relationship between sediment zinc and sulfate in our regressions is consistent with observations that in areas of high sulfur input, unbuffered lakes become more acidic, increasing the solubility of zinc. In circumneutral lakes zinc accumulates in the sediment. The relationship between plant chromium and calcium found here was also reported by Mudroch (1980) who suggested that chromium may be adsorbed on the calcium carbonate which frequently covers the surface of aquatic plants. If this were the case, the size of the plant and its available surface area would certainly play a key role in controlling the levels of chromium observed in aquatic plants. This hypothesis is not consistent with our observations for Hannah Lake, where exceptionally high calcium was associated with high root chromium. However, liming experiments in Hannah Lake may have produced the anomalous results. We suggest that aqueous chromium has been precipitated, elevating the sedimentary chromium. This theory is supported by the high levels of chromium observed in roots collected from Hannah Lake, particularly those for Pontederia which yielded 13.46 p,g g ~ dry weight.
265
ACKNOWLEDGEMENTS We thank A. Pidruczny, McMaster University Nuclear Reactor, for assistance with the NAA. Water quality data were provided by P. J. Dillon, Ontario Ministry of the Environment, Dorset Research Centre, Dorset, Ontario P0A IE0, and we also thank N. Yan for his advice. The research was funded by a Natural Sciences and Engineering Research Council of Canada grant to H.C.D.
REFERENCES Bubicz, M., Kozak, L., Mikos, M. & Warda, Z. (1982). Heavy metals in the aquatic environment of some water bodies of the Lublin coal basin. Acta Hydrobiologia, 24, 125 38. Campbell, P. G. C., Tessier, A., Bisson, M. & Bougie, R. (1985). Accumulation of copper and zinc in the yellow water lily, Nuphar variegatum: relationships to metal partitioning in the adjacent lake sediments. Can. J. Fish. Aquat. Sei., 42, 23 32. Forstner, U. & Wittman, G. T. W. (1981). Metalpollution in the aquatic environment. Springer-Verlag, New York. Friant, S. L. (1979). Trace metal concentrations in selected biological, sediment, and water column samples in a northern New England River. Water, Air, Soil Pollut., It, 455 65. Gleason, M. L., Driftmeyer, J. E. & Zieman, J. C. (1979). Seasonal and environmental variation in Mn, Fe, Cu, and Zn content of Spartina. Aquat. Bot., 7, 385- 92. Harding, J. P. C. & Whitton, B. A. (1978). Zinc, cadmium and lead in water, sediments and submerged plants of the Derwent reservoir, northern England. Water Res., 12, 307 16. Heisey, R. M. & Damman, A. W. H. (1982). Copper and lead uptake by aquatic macrophytes in eastern Connecticut, U.S.A. Aquat, Bot., 14, 213 29. Kelly, M. G. & Whitton, B. A. (1989). Interspecific differences in Zn, Cd, and Pb accumulation by freshwater algae and bryophytes. Hydrobiol., 175, 1 11. Kovacs, M. (1978). The element accumulation in submerged aquatic plant species in Lake Balaton. Acta Bot. Acad. Sei. Hungar., 24, 273 83. Larsen, V. J. & Schierup, H. H. (1981). Macrophytes cycling of zinc, copper, lead, and cadmium in the littoral zone of a polluted and a non-polluted lake. II. Seasonal changes in heavy metal content of above-ground biomass and decomposing leaves of Phragmites autralis (Car.) Trin. Aquat. Bot., 11,211 230. Miller, G. E., Wile, I. & Hitchen, G. G. (1983). Patterns of accumulation of selected metals in members of the softwater macrophyte flora of Central Ontario lakes. Aquat. Bot., 15, 53-64. Mudroch, A. (1980). Biogeochemical investigation of Big Creek Marsh, Lake Erie, Ontario. J. Gt. Lakes Res., 6, 338~,7. Mudroch, A. & Capobianco, J. (1978). Study of selected metals in marshes on Lake St. Clair, Ontario. Archiv. Jur Hwtrobiol., 84, 87 108. Peverly, J. H. (1979). Elemental distribution and macrophyte growth downstream from an organic soil. Aquat. Bot., 7, 319 38. Reimer, P. (1989). Concentrations of lead in aquatic macrophytes from Shoal Lake, Manitoba, Canada. Environ. Pollut., 56, 77 84. Schindler, D. W., Hesslein, R. H., Wageman, R. & Broecker, W. S. (1980). Effects of acidification mobilization of heavy metals and radionuclides from the sediments of a freshwater lake. Can. J. Fish. Aquat. Sci., 37, 373 7. Wehr, J. D. & Whitton, B. A. (1983a). Accumulation of heavy metals by aquatic mosses. 2. Rhynchostegium riparioides. tIydrobiol., 100, 261 84. Wehr, J. D. & Whitton, B. A. (1983b). Accumulation of heavy metals by aquatic mosses. 3. Seasonal changes. Hydrobiol., 100, 285-91. Wells, J. R., Kaufman, P. B. & Jones, J. D. (1980). Heavy metal contents in some macrophytes from Saginaw Bay (Lake Huron, U.S.A.). Aquat. Bot., 9, 185 93.
CONCENTRATIONS OF ZINC A N D CHROMIUM IN AQUATIC MACROPHYTES FROM THE S U D B U R Y A N D MUSKOKA REGIONS OF ONTARIO, C A N A D A P. Reimer & H. C. Duthie* Department of Biology. University of Waterloo, Waterloo. Ontario, Canada. N2L 3G1
(Received 26 March 1991: accepted 13 December 1991)
(Gleason et al., 1979; Larsen & Schierup, 1981), or to varying input !nto the waterbody (Harding & Whitton, 1978). Root concentrations of many metals exceed shoot concentrations in most aquatic plants, probably reflecting the greater availability of these metals in the sediments (Harding & Whitton, 1978). Conversely, Forstner & Wittman (1981) reported maximum concentrations of several metals in the leaves. The objectives of this study were: to obtain information regarding the levels of zinc and chromium in four species of aquatic macrophytes collected from lakes in the Sudbury and Muskoka-Haliburton regions of Ontario; to examine these data in the context of species, organ (root and shoot), and growth season differences; and to investigate possible relationships between zinc and chromium levels in aquatic macrophytes and water and sediment variables in lakes of varying contamination.
Abstract Root and shoot samples o f Eriocaulon septangulare, Nuphar variegatum, Nymphaea odorata and Pontederia cordata were collected f r o m 15 lakes in central Ontario during the summer o[ 1988 to investigate possible relationships between zinc + and chromium levels in aquatic + macrophytes and water and sediment variables. Although concentrations o f zinc" and chromium d(ffered greatly among the four ,species, both metals were consistently higher in Eriocaulon. Generally. root and rhizome tissue contained higher zinc' and chromium than shoot tissues o[" the same species and site. Zinc concentrations (dry weight) ranged./?ore 6.3 Ixg g~ in Nuphar shoots to 87.7 t~g g t in whole Eriocaulon. Chromium ranged Jhom 0.23 t~g g t in Pontederia shoots to 23.9 gg g t in whole Eriocaulon. No sign(ficant trends were detected throughout the growing season in macrophyte or sediment concentrations o[" either metal. Results o f multiple linear regression analyses o f several water quality and enviromnental variables on Eriocaulon indicated that sediment :inc' was the best predictor o f plant zinc, and sediment chromium and calcium were the best predictors o f plant chromium.
MATERIALS AND M E T H O D S Study area Fifteen lakes located in the Sudbury and MuskokaHaliburton regions of central Ontario were chosen for study (Table 1). The study lakes were selected at varying distances from Sudbury, Ontario and represent a wide range of variables, particularly pH (4-6-7.2) and sulfate (3.7 27.4 mg litre ~). Water chemistry data for these lakes supplied by the Ontario Ministry of the Environment represent epilimnetic averages for the 1986-87 hydrological year. The only alkaline lake, Hannah Lake, was the site of a neutralization project in the 1970s; it was previously acidic. Most lakes have low to moderate summer cottage development around them.
INTRODUCTION
Although it is established that aquatic macrophytes are capable of accumulating metals far beyond ambient water concentrations (Kovacs, 1978; Forstner & Wittman, 1981; Heisey & Damman, 1982; Reimer, 1989), considerable disparity exists in the literature in describing biological and environmental factors affecting the uptake of metals. Factors such as species, season, organ, site and analytical methodology have been examined (Mudroch, 1980: Bubicz et al., 1982; Campbell et al., 1985). Working in central Ontario lakes, Miller et al. (1983) reported that species-specific differences are metal dependent. Changes in the content of various metals in plant tissues throughout the growing season have been attributed to growth and attrition
Sample collection The collection of plant and sediment samples for analysis was conducted on three occasions throughout the summer of 1988. The sampling periods (29 May 9 June, 26 June-7 July, 31 July 11 August) were designed to allow the collection of multiple samples throughout the growing season. Four species of aquatic macrophytes: Eriocaulon
* To whom correspondence should be addressed. Environ. Pollut. 0269-7491/92/$05.00 ~) 1992 Elsevier Science Publishers Ltd, England. Printed in Great Britain
261
P. Reimer, H. C. Duthie
262
septangulare
With. (pipewort), Nuphar variegatum Engelm. (yellow water lily), Nymphaea odorata Ait. (white water lily), and Pontederia cordata L. (pickerelweed) were selected for analysis based on their wide distribution, differing growth forms, ease o f recognition, and high frequency in both contaminated and u n c o n t a m i n a t e d lakes. Individual macrophytes were collected by hand, raking, and dredging fiom waters no less than 10 cm and no more than 1.5 m deep. Only vigorous non-chlorotic plants free o f residue and excess algal growth were collected for the purposes o f this study. In all cases plants were rinsed with lake water to remove residue and sediment, and separated into root/rhizome and shoot/leaf portions prior to being sealed in new polyethylene bags and frozen. At least 5 and up to 20 individuals of each species were collected at several locations dictated primarily by vegetation growth and accessibility, It should be noted that Eriocaulon, due to its small size, was not separated into r o o t and shoot portions, Consequently, all estimates for this species are whole plant values. Frozen plant samples were oven dried in acid-washed polyethylene cups at 70°C for approximately 2 days. Approximately 1-2 g o f dried plant tissue was compressed at 700 kg cm 2 in a stainless steel pellet press. The resulting wafer was sealed in a 2 cm 2 polyethylene packet. Packets were arranged in a stacking pattern which was interspersed with standard materials prior to irradiation. Sediment samples were collected at each lake at the same time and place as the aquatic macrophytes. At each lake and sampling period, three acid-washed 200 ml disposable polyethylene cups were filled with sediment. Care was taken to avoid sampling near m a n - m a d e structures such as beaches and docks. Sediment samples were frozen until sample preparation. A 10 g aliquot o f sediment was removed from each o f the thawed sediment samples. These were oven dried in acid-washed polyethylene cups at 70°C ['or 24 h. A 0.5 1.0 g sample o f each sediment was
prepared for irradiation in acid-washed 10 ml polyethylene vials. Chemical analysis N e u t r o n activation analysis ( N A A ) was used since it had multi-element capabilities, no matrix effect, and could be used for both tissue and sediment. Irradiated samples were analysed using two lithium drift germanium detectors and a Canberra multi-channel analyser located at M c M a s t e r University Nuclear R e a c t o r in Hamilton, Ontario. National Bureau o f Standards (NBS) tissue standards 1573 ( t o m a t o leaves) and 1572 (citrus leaves) were analysed in conjunction with aquatic m a c r o p h y t e tissue. NBS standard coal fly ash (1633a, 1633b) were analysed with sediment samples. Additional standard materials were prepared from Fisher chemical atomic absorption standards. Plant tissues, packaged in groups o f 40 samples, were irradiated for approximately 3 h. Following a decay period o f 10-14 days, the radioactive wafers were removed from the polyethylene packets and placed in new sealed glass vials prior to g a m m a counting. Sediment samples were irradiated for 1 h and allowed to decay for approximately 1 week before counting commenced. All values expressed for plant tissue and sediment are expressed i n / z g g t (dry weight). Statistical analysis All statistical analysis was performed using the statistical analysis package S Y S T A T with the level o f significance maintained at 95% for all tests. In order to meet h o m o geneity o f variance and normality assumptions o f the tests, all plant and sediment data were logarithmically transt\~rmed. Analysis o f variance ( A N O V A ) on the transformed data indicated that differences between the growth seasons were insignificant for both macrophytes and sediment. To increase the manageability o f the data sets, they were reduced by averaging the values obtained for each sampling period to yield a single mean and standard deviation. The reduced data sets were used for all subsequent tests of analysis o f variance and
Table 1. Selected water quality variables and sediment (dry weight) zinc and chromium for 15 Central Ontario lakes
Lake Clearwater Crosson Dickie Fawn Gullfeather Hannah Harp Heney Leech Leonard kohi McKay Moot Plastic Ril
Location 46°23'N 45° 02'N 45° 09' N 45 ° 10'N 45°01'N 46° 27' N 45° 23'N 45° 08' N 45°0Y N 45° 04' N 46° 23' N 45°03'N 45°09'N 45 ° I I'N 45° 09'N
81°02'W 79° 05'W 79° 05' W 79 ° 15'W 79°05'W 81° 02'W 79° 08' W 79° 06'W 79° 06'W 79° 22'W 81°02'W 79 ° 10'W 79 ° 10'W 78°49'W 79 ° 10'W
pH 4.7 5.8 6-0 5.9 6.0 7.2 6.7 5.9 6.3 5.9 4.7 6.3 5.7 5.7 5.4
DOC Alkalinity Ca SO4 PPUT NNO Sediment mgliter ~ mgliter r mgliter L mgliter~ i ~gliter ~ /~gNliter i Zn/~gg i 0-36 4,13 4,87 9.10 5.30 3.36 4,31 2.75 4.20 3.13 0.54 5.30 7.15 2.04 4.20
1.14 0.55 1.09 1.53 1.20 12.70 3.41 0.64 1.50 0.57 1.17 2.02 0.95 0.21 0.06
5.6 2.0 2.3 2.5 2-4 13.1 2-7 1.9 2.6 2-3 6.0 2-8 1.7 1.9 2.8
15-6 6-6 6.0 5.1 7.4 27-4 6.8 6.0 7.4 6.5 17.6 6.7 3.7 6.2 6.9
2.52 9.58 10-2 19.5 ll.0 6.93 6.61 6.77 7.20 5.04 2.94 9.59 20.3 3.32 6.0
32.0 32.4 12.5 12.5 39.0 8.20 21-0 29.0 19.5 82.7 53-0 18.5 15.0 6,42 N/A
DOC, dissolved organic carbon: PPUT, total unfiltered phosphorus: NNO. nitrate and nitrite as N.
37.5 72.5 85.2 76.5 64.5 86.8 90-8 105.8 85.8 87.9 53.9 102.3 90.7 86-0 79-0
Sediment Cr/~gg 1 69.5 35.8 36.6 45.1 35.1 90-6 57-4 69.2 46.7 45.5 89.9 58.5 38.6 44.5 42.2
Concentrations of zinc and chromium in aquatic macrophytes
263
Table 2. Concentrations of zinc (/zg g-I dry weight) and root to shoot ratios (R/S) for the study species
Eriocaulon septangulare
Lake
Nuphar variegatum
Whole plant
Shoot
Root
15.9 42.7 85-7 52-6 49.1 59.0 53.6 77-8 63.2 62.3 22.7 66.1 47.4 59.4 50-9
. 7.3 11-2 10.7 10.2 8-I 9-1 16.5 6.3 14.6 9.3 10.0 14-1 9.2 12.1
15.7 19-2 14.7 17.3 15.8 17.8 21.2 16.4 15.8 8.8 18.1 21.3 14-0 15-9
Clearwater Crosson Dickie Fawn Gullfeather Hannah Harp Heney Leech Leonard Lohi McKay Moot Plastic Ril
Nymphaea odorata
R/S ratio . 2.15 1.72 1.37 1.69 1-95 1-95 1.29 2.60 1.13 0.95 1.81 1.51 1-55 1.32
Pontederia cordata
Shoot
Root
R/S ratio
. 15.2 12.2 18.7 19-0 15.3 13.1 14.5 13.2 14-4
14-7 16.4 28.5 23-4 20.7 20.6 13.2 24.7 14.6
0.97 1.34 1-53 1.23 1.35 1.57 0.91 1.87 1.01
16-0 18.7 13.3 11-4
23.3 22.4 10.5 7-3
1-46 1.19 0.79 0.63
Shoot
Root
R/S ratio
16.7 18.8 19.2 16.3 11.2 18.4 25.8 20.4 19-5 -29-4 19-1 26.3 18-8
38.3 56-4 30.9 40-3 27.0 78.9 64.5 68-2 39.2
2.29 3.00 1-61 2.47 2-41 4.28 2.50 3.34 2.01 -2-37 1.95 2.67 2.26
.
69.7 37.1 70.5 42-6
Values represent the mean concentration observed over three sampling periods. Missing values shown by - - . Eriocaulon was not separated into root and shoot portions. regression. It should be n o t e d t h a t H a n n a h L a k e was o m i t t e d f r o m statistical analysis involving l a k e w a t e r p a r a m e t e r s , since its w a t e r qua!ity was artificially altered t h r o u g h the n e u t r a l i z a t i o n process. RESULTS
Zinc S e d i m e n t zinc (Table l) a n d tissue zinc levels (Table 2) varied c o n s i d e r a b l y a m o n g species a n d lakes. Eriocaulon c o n t a i n e d the greatest q u a n t i t i e s o f zinc a m o n g the four s t u d y species, r a n g i n g f r o m 15-9 to 8 5 . 7 / z g g 1 (dry weight). It was followed closely by Pontederia which r a n g e d from 11-2 to 29.4 /zg g ~ in s h o o t tissue a n d 30-9 to 78.9 /zg g~ in r o o t tissue. Nuphar a n d Nymphaea yielded c o n s i d e r a b l y less tissue zinc, r a n g i n g f r o m 6.3 /~g g~ in Nuphar s h o o t s to 28.5 /xg g~ in Nymphaea roots. O n e - w a y analyses o f v a r i a n c e conducted on logarithmically transformed d a t a for sediments i n d i c a t e d t h a t there were no significant differences a m o n g s a m p l e s collected d u r i n g the three s a m p l i n g
p e r i o d s ( F -- 1.43, p -- 0-5, n -- 90). Similarly, a twow a y analysis o f v a r i a n c e on d a t a for m a c r o p h y t e tissue revealed no significant differences a m o n g s a m p l i n g p e r i o d for a n y o f the species ( F = 1.37, p -- 0.37, n = 99). H o w e v e r , highly significant differences were f o u n d for species c o m p a r i s o n s ( F = 40.6, p < 0.001, n = 99). R o o t to s h o o t (R/S) ratios were used to e x a m i n e the d i s t r i b u t i o n o f zinc within Pontederia, Nuphar, a n d Nymphaea. L i n e a r regression o f the R/S ratio a n d the p H o f the c o r r e s p o n d i n g lake s h o w e d g o o d c o r r e l a t i o n (Fig. 1). M u l t i p l e linear regression c o n d u c t e d on whole p l a n t zinc levels for Eriocaulon suggested t h a t sediment zinc m a y be the d e t e r m i n i n g f a c t o r in Eriocaulon zinc c o n c e n t r a t i o n s (Fig. 2). T h e c o n t r i b u t i o n to the regression m o d e l o f l a k e w a t e r p H , alkalinity, dissolved o r g a n i c c a r b o n , nitrogen, t o t a l unfiltered p h o s p h o r u s , a n d sulfate was n o t significant.
Chromium Results for c h r o m i u m (Table 3) indicated that Eriocaulon a c c u m u l a t e d greater quantities o f c h r o m i u m t h a n the TOO
--
-
Nuphof -
-
4 --
---
voriegatum
IVymphaea Pontederza
odorata cofdota
.i"
i
//"
z n¢
J
3
+
/~"
8o
zo ~
2 /
g 0r-
i
20
/ ///
+
/
I
pH
Fig. 1. Relationships between root to shoot ratios of zinc in three aquatic macrophytes and the pH of the study lakes. (a) Nuphar variegatum, r 2 = 0-559, y = 0-757x-3.337. (b) Nymphaea odorata, r 2 = 0-417, y = 1.366x 5.733. (c) Pontederia cordata, r 2 = 0.468, y = 0.615x-1.998.
0
20
40
6'0
I
'
80
I00
120
Sediment Zinc ( F g / g )
Fig. 2. Relationship between zinc concentrations in sediments and whole Eriocaulon septangulare collected from the study lakes. Dotted lines represent 95% confidence interval, r 2 = 0-707, y -- 0.857x-14.931.
P. Reimer, H. C. Duthie
264
Table 3. Concentrations of chromium (/~g g-I dry weight) and root to shoot ratios (R/S) for the study species Eriocaulon septangulare
Lake
Nuphar variegatum
Nymphaea odorata
Pontederia cordata
Whole plant
Shoot
Root
R/S ratio
Shoot
Root
R/S ratio
Shoot
Root
R/S ratio
13.0 3-9 8.5 10-6 3.6 23-9 6.8 6.6 5.5 8.5 12.5 9.3 9.0 4.2 5.7
-1.15 0.60 1.14 0.39 0.79 0.57 0.66 0.48 0.47 1.21 0.98 0.43 0.40 0.68
3.53 0.96 1.90 0.76 4.29 3-21 2-03 0.57 0.54 1-09 1-56 1.30 0-81 1.10
3.07 1.60 1.68 1.96 5.43 5.63 3.09 1.19 1.13 0.90 1.59 3.02 2.02 1.62
0.26 1.12 0.57 1.28 2.24 0.62 0.52 0.66 0.38
0.91 4.62 5-20 3.89 4.94 4.28 1.43 1.35 0.72
3.50 4.12 9.18 3.02 2.20 6.87 2.74 2.05 1.89
0.31 0.40 1.18 0-31 1-69 1.01 0.65 0.50 0.94
-1-34 2.88 3.64 1-63 13-46 4.19 3.18 1-77 2-62
-4.37 7.20 3.07 5.25 15.15 4.13 4.87 3.55 2.78
1-15 1-04 0.33 0-53
2.18 1.81 1.43 2.35
1.89 1.74 4.38 4-42
0.70 0.42 0.23 0.32
6.54 2.79 0.84 0.98
9.32 6.64 3.61 3.12
Clearwater Crosson Dickie Fawn Gullfeather Hannah Harp Heney Leech Leonard Lohi McKay Moot Plastic Ril
Values represent the mean concentration observed over three sampling periods. Missing values shown by separated into root and shoot portions. other three species. C h r o m i u m content in Eriocaulon ranged from 3.6 to 23-9 p~g g t while Nuphar, Nymphaea, and Pontederia ranged from 0.23 to 2-24 p~g g~ in shoot tissue and 0.54 to 13.46 /~g g~ in roots. Sediment concentrations o f c h r o m i u m varied from 35.1 to 90.6 p~g g ~ (Table 1). One-way analysis o f variance on logarithmically transformed sediment data indicated that there were no significant differences between samples collected during the three sampling periods (F = 1-37, p -- 0-27, n = 85). Results o f analysis o f variance on m a c r o p h y t e tissue data also indicated that there were no significant differences resulting from sampling period for any o f the species ( F = 1.33, p -0.27, n -- 96). A t w o - w a y analysis o f variance performed on c h r o m i u m data for Nuphar, Nymphaea, and Pontederia showed that root and shoot portions accumulated c h r o m i u m to significantly different levels (F -- 43-7, p < 0.001, n -- 65). Species differences were not significant a m o n g the three species tested. R/S ratios calculated for c h r o m i u m concentrations in n m c r o p h y t e tissue were highly variable, ranging from 0-9 to 9.35. 25 A
/
2o
E ~: o
15
10
:~
+
+
::
5
/
J 20
:~: 40
60
Sediment C h r o m i u m
80
I00
(p.g/g)
Fig. 3. Relationship between chromium concentrations in sediments and whole Eriocaulon septangulare collected in the study lakes. Dotted lines represent 95% confidence interval. r2 -- 0.564, y -- 0-207x 2.349.
. Eriocaulon was not
The R/S ratios showed no significant correlation (p > 0-05) with water pH, dissolved organic carbon, calcium, alkalinity, or sediment chromium. Multiple linear regression for whole plant chromium in Eriocaulon indicated that calcium and sulfate were significant variables (p < 0.01) in the model. Dissolved organic carbon and pH did not contribute significantly (p > 0-05) to the model. In addition, sediment c h r o m i u m appears to be a m a j o r predictor o f whole plant c h r o m i u m in Eriocaulon (Fig. 3), and is thus comparable to zinc. DISCUSSION Our results show that the quantities o f zinc and c h r o m i u m accumulated in aquatic m a c r o p h y t e tissue may be influenced by lake location, plant species, organ, and water and sediment chemistry. Concentrations o f zinc observed in this study fall within the range o f data presented by other authors for various species and regions (Kovacs, 1978; M u d r o c h , 1980; Wells et at., 1980). Similarly, M u d r o c h (1980) reports levels o f 4-0 and 3.5 /_~g g t for c h r o m i u m in Nuphar and Nymphaea, respectively. Both m a c r o p h y t e and sediment levels o f c h r o m i u m are comparable with those observed in this study. The ability o f aquatic m a c r o p h y t e s to accumulate metals in their tissues appears to be a highly speciesspecific process ( M u d r o c h & C a p o b i a n c o , 1978; Friant, 1979; M u d r o c h , 1980; Miller et al., 1983; Kelly & Whitton, 1989). These differences also appear to be element-specific, as Mudroch (1980) reported with Elodea, Chara, and Myriophyllum. Our data show that significant species differences occur for both zinc and c h r o m i u m and that these differences are also metal-specific. In general, the orders o f accumulation are as follows: Zn: Eriocaulon > Pontederia > Nymphaea = Nuphar Cr: Eriocaulon >> Pontederia -- Nymphaea -- Nuphar The comparatively high levels o f zinc and c h r o m i u m
Concentrations o f zinc and chromium in aquatic macrophytes observed for Eriocaulon in relation to the other species suggests that surface area may be a factor in metal uptake. Our results concerning the absence of growth seasonal changes in metal concentration in plant tissues is in agreement with the conclusions of Peverly (1979). However, both Mudroch & Capobianco (1978) with Typha, and Gleason et al. (1979) with Spartina reported seasonal variability. Wehr & Whitton (1983 a, b), working with aquatic mosses, observed that seasonal changes were negligible in newer shoots but became more apparent in older tissue. This may explain the lack of seasonal variability in this study since we made an attempt to collect only vigorous shoots. Our results show that R/S ratios of metal concentrations are a useful way of quantifying the relative distribution of metals within the plant, particularly for non-translocated metals where the plant concentration generally reflects that of the surrounding media. In the case of zinc, these ratios were correlated with the pH of the lakewater, supporting the observation of Schindler et al. (1980) that zinc is more available in acidic water. Unlike zinc, significant correlations were not observed between R/S ratios for chromium and the measured environmental variables. However, chromium ratios did follow the trend to higher ratios in Pontederia that were also seen with zinc. The finely divided roots of Pontederia likely provide a greater surface area in which to absorb metals than do the tuberous roots of Nymphaea and Nuphar. The relationship between sediment and plant zinc in Eriocaulon seen in our multiple regression models was not observed by Miller et al. (1983) in their study of Eriocauhm in central Ontario lakes. The results of Kelly & Whitton (1989) working with algae and bryophytes support our conclusions that the plant's source (sediment vs water) of zinc is the most significant of the predictor variables in such models. The negative relationship between sediment zinc and sulfate in our regressions is consistent with observations that in areas of high sulfur input, unbuffered lakes become more acidic, increasing the solubility of zinc. In circumneutral lakes zinc accumulates in the sediment. The relationship between plant chromium and calcium found here was also reported by Mudroch (1980) who suggested that chromium may be adsorbed on the calcium carbonate which frequently covers the surface of aquatic plants. If this were the case, the size of the plant and its available surface area would certainly play a key role in controlling the levels of chromium observed in aquatic plants. This hypothesis is not consistent with our observations for Hannah Lake, where exceptionally high calcium was associated with high root chromium. However, liming experiments in Hannah Lake may have produced the anomalous results. We suggest that aqueous chromium has been precipitated, elevating the sedimentary chromium. This theory is supported by the high levels of chromium observed in roots collected from Hannah Lake, particularly those for Pontederia which yielded 13.46 p,g g ~ dry weight.
265
ACKNOWLEDGEMENTS We thank A. Pidruczny, McMaster University Nuclear Reactor, for assistance with the NAA. Water quality data were provided by P. J. Dillon, Ontario Ministry of the Environment, Dorset Research Centre, Dorset, Ontario P0A IE0, and we also thank N. Yan for his advice. The research was funded by a Natural Sciences and Engineering Research Council of Canada grant to H.C.D.
REFERENCES Bubicz, M., Kozak, L., Mikos, M. & Warda, Z. (1982). Heavy metals in the aquatic environment of some water bodies of the Lublin coal basin. Acta Hydrobiologia, 24, 125 38. Campbell, P. G. C., Tessier, A., Bisson, M. & Bougie, R. (1985). Accumulation of copper and zinc in the yellow water lily, Nuphar variegatum: relationships to metal partitioning in the adjacent lake sediments. Can. J. Fish. Aquat. Sei., 42, 23 32. Forstner, U. & Wittman, G. T. W. (1981). Metalpollution in the aquatic environment. Springer-Verlag, New York. Friant, S. L. (1979). Trace metal concentrations in selected biological, sediment, and water column samples in a northern New England River. Water, Air, Soil Pollut., It, 455 65. Gleason, M. L., Driftmeyer, J. E. & Zieman, J. C. (1979). Seasonal and environmental variation in Mn, Fe, Cu, and Zn content of Spartina. Aquat. Bot., 7, 385- 92. Harding, J. P. C. & Whitton, B. A. (1978). Zinc, cadmium and lead in water, sediments and submerged plants of the Derwent reservoir, northern England. Water Res., 12, 307 16. Heisey, R. M. & Damman, A. W. H. (1982). Copper and lead uptake by aquatic macrophytes in eastern Connecticut, U.S.A. Aquat, Bot., 14, 213 29. Kelly, M. G. & Whitton, B. A. (1989). Interspecific differences in Zn, Cd, and Pb accumulation by freshwater algae and bryophytes. Hydrobiol., 175, 1 11. Kovacs, M. (1978). The element accumulation in submerged aquatic plant species in Lake Balaton. Acta Bot. Acad. Sei. Hungar., 24, 273 83. Larsen, V. J. & Schierup, H. H. (1981). Macrophytes cycling of zinc, copper, lead, and cadmium in the littoral zone of a polluted and a non-polluted lake. II. Seasonal changes in heavy metal content of above-ground biomass and decomposing leaves of Phragmites autralis (Car.) Trin. Aquat. Bot., 11,211 230. Miller, G. E., Wile, I. & Hitchen, G. G. (1983). Patterns of accumulation of selected metals in members of the softwater macrophyte flora of Central Ontario lakes. Aquat. Bot., 15, 53-64. Mudroch, A. (1980). Biogeochemical investigation of Big Creek Marsh, Lake Erie, Ontario. J. Gt. Lakes Res., 6, 338~,7. Mudroch, A. & Capobianco, J. (1978). Study of selected metals in marshes on Lake St. Clair, Ontario. Archiv. Jur Hwtrobiol., 84, 87 108. Peverly, J. H. (1979). Elemental distribution and macrophyte growth downstream from an organic soil. Aquat. Bot., 7, 319 38. Reimer, P. (1989). Concentrations of lead in aquatic macrophytes from Shoal Lake, Manitoba, Canada. Environ. Pollut., 56, 77 84. Schindler, D. W., Hesslein, R. H., Wageman, R. & Broecker, W. S. (1980). Effects of acidification mobilization of heavy metals and radionuclides from the sediments of a freshwater lake. Can. J. Fish. Aquat. Sci., 37, 373 7. Wehr, J. D. & Whitton, B. A. (1983a). Accumulation of heavy metals by aquatic mosses. 2. Rhynchostegium riparioides. tIydrobiol., 100, 261 84. Wehr, J. D. & Whitton, B. A. (1983b). Accumulation of heavy metals by aquatic mosses. 3. Seasonal changes. Hydrobiol., 100, 285-91. Wells, J. R., Kaufman, P. B. & Jones, J. D. (1980). Heavy metal contents in some macrophytes from Saginaw Bay (Lake Huron, U.S.A.). Aquat. Bot., 9, 185 93.