Biogeochemical studies of plants from stream banks in Northern Sweden

Journal of Geochemical Exploration, 27 (1987) 157-188

157

Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

Biogeochemical Studies of Plants from Stream B a n k s in Northern S w e d e n

N.H. BRUNDIN*, J.I. EK and O.C. SELINUS

Geological Survey of Sweden, P.O. Box 670, S-75128 Uppsala, Sweden (Received April 21, 1986; revised and accepted February 12, 1987)

ABSTRACT Brundin, N.H., Ek, J.I. and Selinus, O.C., 1987. Biogeochemical studies of plants from stream banks in northern Sweden. J. Geochem. Explor., 27: 157-188. This paper presents a study of the geochemistry of organic matter occurring along stream banks. It was designed to assess the relationship between element concentrations in different types of vegetation (living and dead) and the root systems and the aerial parts of plants. The variation of eight heavy metals, typical for the selected mineralization types (Cu, Pb, Zn, Co, Ni, Cr, Mo, U) expressed as limonite (Fe20~, MnO), is described. The results show that heavy metal concentrations in roots and mosses are, in general, correlated with those of the organic stream bank material, indicating that physiological barriers between the roots and growth media are lacking. However, the trace-element concentrations in aerial plant organs are in general less well correlated with the growth medium and roots at higher element concentrations. The degrees of correlation vary considerably between species and element, indicating the presence of physiological barriers for aerial plant organs. This barrier effect seems to be lacking for Pb, which has a high correlation for the aerial parts of all investigated species. It has also been shown that roots as well as aerial plant organs both respond closely to chemical variations at background levels related to different bedrock units. All investigated plant species showed seasonal and annual variation of heavy metal concentrations. For roots of the sedges Carex junceUa, Carex rostrata and organic stream bank material, this variation is correlated with the limonite content which in turn is a function of the variation in precipitation. The heavy metal concentrations should therefore be normalized against the limonite content. Plant roots have certain advantages over organic stream bank material in that the seasonal variation in the former sample medium is smaller. Of the investigated aerial plant organs, none appeared to be useful for multi-element geochemical surveys. Aerial parts of two Carex species display a gradual decrease in heavy metal contents during the season. The main conclusion of this study is that plant roots and aquatic mosses give geochemical patterns that reflect bedrock variations and are closely related to mineralizations. They are therefore suitable media for geochemical mapping and ore prospecting. "Deceased (1982).

0375-6742/87/$03.50

© 1987 Elsevier Science Publishers B.V.

158 INTRODUCTION

The first attempts to use biogeochemical methods in prospecting were carried out independently in the 1930's in Scandinavia by Brundin and Palmqvist (Brundin, 1939) and in the Soviet Union (Tkalich, 1938). Since then, much work has been done in different parts of the world developing biogeochemical prospecting techniques. Reviews have been given by several authors, notably Brooks (1972, 1983 ) and Kovalevskii (1979). At the Geological Survey of Sweden considerable efforts have been made to use biogeochemical methods in prospecting (e.g. Ek, 1974; Brundin, 1980). In regional work, minerogenic stream sediments have been replaced entirely by organic stream bank samples. This technique was developed by the Geological Survey of Sweden and is described by Brundin and Nairis (1972). Larsson (1976) used the technique in a large regional reconnaissance survey in northern Sweden and obtained very successful results for most heavy metals. Organic stream bank material, also called stream peat or organic stream sediments, is an inhomogeneous mixture of humus, living plant roots and minerogenic material from adjacent soil layers as well as precipitated limonite. All these components contribute to the heavy metal composition of the stream bank material. The approximate amount of minerogenic material and limonite is easy to determine and its effect on the heavy metal concentrations can be normalized by applying regression analysis (Selinus, 1983). The chemical contribution from living roots and humus is, however, more difficult to determine. It might be expected that important information on this subject could be found in the extensive biogeochemical literature, but this is not the case. Most biogeochemical investigations have been based on analysis of aerial parts of plants, and show that for a given area there are commonly one or two plantspecies suited for investigation of a particular element. However, these species may be unsuitable for prospecting for other elements. The main purpose of this study has been to investigate whether roots can be used for regional multi-element geochemical programs and whether roots offer any advantages over stream peat. The study was initiated by N.H. Brundin who also supervised the investigation, including field work, and undertook analysis of much of the data. Regrettably he died in December 1982 at the age of 73. The two other authors have continued his research and, together with Brundin's preliminary results, have arrived at the conclusions presented here. PLANNING OF T H E INVESTIGATION

Nine streams were chosen for sampling in 1975 (Fig. 1,800 samples). For three of them ( stream nos. 1-3 ), the heavy metal distribution in minerogenic stream sediments, stream peat and water had already been studied in detail by Brun-

159

Fig. I. Location of the eleven streams described. L and K are the locations of L~ngtr'dsk and Kikkejaure, respectively.

din and Nairis (1972). Stream no. 1 was found to be non-anomalous for all three sampling media, and it has been used as a "background" stream in this investigation. All the other streams are located close to known mineral prospects and, for most of them, geochemical exploration surveys based upon stream peat had revealed strong base metal anomalies. During 1976 two additional streams (K and L in Fig. 1) were sampled in order to study the local and seasonal variation (500 samples). In biogeochemical prospecting it is advisable to choose one or two related species that are commonly growing throughout the investigated area. The most common plant family in streams in northern Sweden is Carex (sedge), especially Carex juncella and Carex rostrata. Carex debris also constitutes a major part of the humus material in stream peat samples. In addition to Carex, the following species were also sampled when they were available: Salix phyllici-

pholia, Salix lapponium, Menyanthes trifoliata, Deschampsia caespitosa, Molinia coerulea, Eriophorum angustifolium, Scorpidium, different species of stream moss and Sphagnum. An important criterion for selecting species to be sampled was that they should be growing directly in the stream system, which means that the organic stream bank material could be considered as the growth medium for the species.

160 ____

Sept -77

[

Aug -77

[

July -77 June -77 May -77

Nov -76 - A p t - 7 7

I Accumutofed os snow

E

Okf -76

-

Sepf -75

l E

Aug -76

Jury -76 ~-

June -76 Hoy-76

[ Accumutofed as snow

Nov -75 - A p t - 7 6 Okt -75

[

Sept -75

[

Aug -75 July -75 June -75

Hoy -75 [ Accumu(ofed Precipitation in < , mm 200

os snow J IO0

Nov - 7 ~ - A p r -75 0

Fig. 2. Precipitation values for the period November 1974 to September 1977 frommeteorological station no. 16771 at Arjeplog. AREA DESCRIPTION All the areas investigated are situated in the continental subarctic region. The annual precipitation is about 700 mm in the northwestern parts of Sweden, of which approximately 200 mm falls as snow. The ground is snow-covered during approximately 7-8 months of the year. The monthly precipitation from November 1975 to September 1977 at Arjeplog near stream nos. 1-3 is shown in Fig. 2, and was similar around the other sampled streams. With the exception of the higher mountains in the western part where the vegetation is alpine, the region is a typical forest land with pine, birch and spruce on typical podsolic soil with the C-horizon starting at about 0.5 m. Peat areas are numerous, and have a dominant vegetation of the mosses (Sphagnum and Amblystegia) and various species of Carex. Other characteristic plants are Ledum, Myrica, Betula nana and Salix. Most streams are situated at an altitude of 400-600 m a.s.1. Only stream no. 6 and the upper reaches of stream no. 1 are at a higher altitude of 700-800 m.

161 The streams in the lowlands commonly have steep, concave banks in the peat layers and below the surface there is a layer of decaying vegetation, the upper parts of which are penetrated by living roots. This layer is generally about 0.5 m thick, but can reach 1 m, sometimes more, and is referred to as organic stream bank material in this paper. It is also the growth medium of the plants sampled in this investigation. The bedrock in the areas sampled is almost entirely of Precambrian age (1600-1800 m.y.). It is dominated in all the areas by metamorphosed supracrustal rocks (mostly volcanics), but also some granites. All ore prospects, known from the drilling records, are sub-economic. Table 1 summarizes the geology, mineralization and vegetation along the nine streams studied. The investigated areas are mostly covered by glacial till, from 0 to 20 m thick, deposited directly on the bedrock surface. The glacial history is complex and many ice movements from different directions are noted, but the main direction is approximately from the northwest. Due to poor drainage, bogs have developed on the till over large parts of the surveyed areas. The higher mountains have generally a very thin till cover and the streams often flow directly on the bedrock surface. FIELD WORK During the summer of 1975, the nine streams were sampled with an average distance of 200 m between the sampling sites (approximately 800 samples). At each site, one sample of root material and one of the aerial part of the higher plants were taken, as well as one sample from the various mosses and stream peat. The sampling sites were located within the narrow bog-areas which are normally developed on both sides of Swedish streams. The plants were dug out in order to recover as much of the root system as possible. The root material, including the root stocks, was carefully washed in the stream water for removal of dead organic and minerogenic material. After that, roots and aerial parts were separated. At each sampling point all available plant species were collected. During 1976, stream nos. 1, 2 and 3 were resampled at 40-m intervals (212 samples). That year, a modified sampling procedure was used in order to obtain root material with as little contamination of minerogenic material as possible. The roots were separated using a knife and then placed on a screen for intense cleaning using a water jet from a motor-driven pump. In 1976 repeated sampling was carried out in two streams (K and L in Fig. 1, approximately 600 samples) located within areas of granitic bedrock. Both streams were sampled once a week during three months in order to obtain background data in one (L = L~ngtr~isk) and U, Mo, Cu, Zn and Co data in the other (K= Kikkejaure). In the latter stream, uranium mineralization occurs within the drainage area.

162 ,-M ,.M

Z

~

~9

a6 .M

0

e~

0

~q

u~

N o

.M 0 e~

,-M

,-M e~

d

~o

163 SAMPLE PREPARATIONAND ANALYTICALTECHNIQUES All samples were analyzed at the laboratory of the Geological Survey of Sweden. They were dried at 110 ° C, weighed and subsequently reduced to ash in an oxidizing atmosphere at 450 ° C. After reweighing, the difference between dry weight and the weight of ash was taken as an approximate figure for the amount of organic matter in the sample or the loss on ignition (L.O.I.). The ashed samples were analyzed by optical emission spectral techniques for Cu, Pb, Zn, Mo, Co, MnO, Fe203, Ni, MgO, V, Ti02, CaO, BaO, Sr, Ag, Bi, As, Sn, Be and Cr (Danielsson, 1967) and X-ray fluorescence for Ni, Y, U, Th, Zr, Zn, Rb and W. The major element data are adjusted to oxide concentrations throughout. VARIATIONIN ASH CONTENT Table 2 shows the concentration of nine elements within different ash intervals for root samples and aerial parts of CarexjunceUa. All samples were taken in the background stream, no. 1, and for each ash interval the mean value has been calculated for the nine elements. For roots it can be clearly seen that increasing ash contents are in most cases positively correlated with drastically decreasing heavy metal contents. This is certainly a result of increasing contamination from the parent soil and illustrates the importance of careful washing of the root samples. During 1976, the washing was extremely intense and, as a result, the root bark was more or less washed away so that only the inner white parts were recovered for analysis. As can be seen in Table 2, MnO and Co have enhanced values for interval 2 (1975) compared to interval 1 (1976). The explanation for this may be that the root bark contains more MnO and Co than the interior parts of the roots. Therefore the more or less bark-free roots from 1976 contained less MnO and Co compared to samples from 1975 in spite of the former having a lower ash content. This illustrates the importance of having the same washing procedure for all samples. For the aerial parts of Carexjuncella (Table 2 ) most elements had decreasing concentrations with increasing ash content. The results, however, indicate that it is more important to wash the roots than the aerial parts. Ideally, each type of plant sample should have a similar ash content in order to be comparable between different localities; this has been taken into account throughout this study. LOCAL VARIATION OF E L E M E N T CONCENTRATIONS For successfuluse of organic samples in mineral exploration it is important that the sample types have a localvariation which is minimized, and it should not exceed the variation between different localities.In order to study this variation, four different sample types (roots and aerialparts from Carex ros-

164 0

~

( ~

0

0 t~

e~

e~

e~

d

bl

d d x~ d

o

,-1

~ooooo . ~ ~ o i

i

i

i

i

165

trata and Carex junceUa roots and stream peat) were taken from a number of sites along the streams Kikkejaure and Lfingtr~isk (Table 3). Two or three samples from each locality having similar ash contents have been compared. The results indicate that the variation within each sample site is much smaller than the variation between sites. An important result is also that this is the case both for low- and high-element concentrations and for all four sample types, indicating that they could be suitable for both geochemical mapping and geochemical prospecting. SEASONALVARIATIONOF ELEMENT CONCENTRATIONS In order to study the seasonal variation, repeated sampling of CarexjunceUa, Carex rostrata and stream peat was carried out on a weekly basis from 4 July to 20 September 1976. Two localities were chosen in a stream at Kikkejaure (K in Fig. 1), known to be anomalous for U, Mo, Cu, Zn and Co, and two localities were chosen in a non-anomalous stream at L~ngtr~isk (L in Fig. 1 ). On each sampling occasion, two to three samples were taken of each sample type and the mean value of the element concentration was calculated on a dry weight basis. The results for Fe203, MnO, Cu, Pb, Zn, Mo, Co, Cr, Ni and U for Kikkejaure are shown as variation curves in Figs. 3-7. When studying the variation curves for stream peat it becomes evident that most of the ten elements tend to have drastically changing contents during or immediately after rainy periods. The peaks are most prominent for those localities having the highest mean element concentrations and they are particularly well developed for the elements Fe203, MnO, Zn, Mo and Co. It is interesting to note that the variation curves for MnO in stream peat are almost identical with those for Co at all four localities. It is also noteworthy that the curves for Fe203 have a certain resemblance with those for Zn and Mo. These covariations are easy to explain with regard to the well-documented affinity of Co to manganese hydroxides and of Zn and Mo to ferri-hydroxides. The marked change of element contents in stream peat during or immediately after rainy periods may be due to the following two counteracting processes: (1) During rainy periods the streams are fed mainly with water that has drained through surrounding top-soil layers, i.e. the humus layer, the Ahorizons and the B-horizon. Such water is enriched in humic material and limonite, which precipitates on the stream peat and increases its content of coprecipitated elements (e.g. Mo, Zn, Pb and Co). This process thus favours an increase of the heavy metal contents during rainy periods. (2) During periods of high flow, the precipitated limonite and humic material is gradually washed out of the stream peat and as a result the heavy metal concentrations decrease. It is probable that the two processes interact with each other in a complex way, and that their relative importance varies along the stream channels. As a whole, the variation curves for all the heavy metals in stream peat demonstrate the

166 TABLE 3 Local variation in the a s h of Carexjuncella roots (site nos. 1 - 5 ) , Carex rostrata roots (site nos. 6 - 1 0 ) , Carex rostrata aerial parts (site nos. 11-13) a n d s t r e a m peat (site nos. 14-20). T h e sites are located along t h e s t r e a m s at Kikkejaure a n d L ~ g t r ~ k Site

Ash

Fe203

MnO

Cu

Pb

Zn

Mo

no.

(%)

(%)

(%)

(pg/g)

(/g/g)

(/g/g)

(/.~g/g) (pg/g)

Co

Cr

Ni

U

(/g/g)

(/g/g)

(/g/g)

1

2.3 2.4 2.4

17.1 15.3 20.2

1.06 1.12 1.37

97 121 111

31 47 41

1401 1640 1773

95 131 194

13 16 15

4 4 5

11 12 11

138 150 211

2

2.3 2.5 2.7

33.5 31.9 30.7

1.18 1.76 0.85

65 76 61

63 43 56

1150 1196 1134

112 83 96

23 37 19

6 6 7

14 18 13

193 188 114

3

2.5 2.7

26.0 29.2

4.49 4.00

194 147

58 51

3842 3141

234 242

85 74

27 23

36 31

559 457

4

4.3 4.4

33.5 41.9

6.36 5.23

121 128

83 89

2351 2109

339 455

107 105

29 36

33 34

613 689

5

4.3 4.7

34.6 37.6

1.81 1.64

63 44

47 54

1401 989

238 262

37 28

11 9

13 10

455 435

6

4.0 4.0

30.7 30.9

1.52 2.24

116 168

64 65

2267 1907

679 992

77 122

13 15

22 32

540 423

7

4.1 4.3

31.2 25.9

0.91 1.10

111 85

78 59

2059 1535

770 385

38 35

20 11

18 10

411 345

8

5.6 5.7

10.9 11.2

0.45 0.44

80 66

59 59

1117 1112

197 161

21 26

4 4

11 11

223 195

9

6.1 6.6

14.6 13.4

0.65 0.47

82 76

68 56

1261 992

329 271

24 22

5 6

11 12

82 111

10

7.3 7.4

15.6 16.8

0.60 0.67

80 81

85 76

1434 1457

293 257

33 32

6 7

14 13

122 94

11

6.4 7.1

3.8 3.1

1.01 1.16

76 51

21 13

1419 1326

318 326

7 3

1 1

6 4

60 48

12

8.5 11.2

1.7 2.2

1.18 1.11

37 27

14 12

787 608

88 70

3 1

2 1

4 1

14 18

13

11.3 12.2

5.1 3.1

0.99 0.88

49 53

16 40

978 1044

109 95

7 7

2 2

4 4

24 19

14

6.0 6.2

20.5 13.0

1.16 0.31

142 136

55 47

610 532

92 67

46 26

31 25

35 31

138 120

15

11.8 14.4

17.0 11.1

0.89 0.47

66 56

74 80

594 539

85 76

33 22

33 29

29 24

34 17

16

37.1 38.7

5.5 5.7

0.19 0.22

30 44

50 56

268 316

24 21

11 11

18 18

13 13

58 64

17

48.2 54.6

14.2 8.8

0.18 0.14

37 41

59 58

759 757

105 96

16 13

34 35

22 25

296 310

18

64.1 69.7

20.3 12.8

0.62 0.32

39 27

46 35

543 429

143 148

27 14

26 25

14 14

253 219

19

77.0 78.1

2.2 2.2

0.07 0.07

23 25

22 20

96 92

9 7

5 5

11 11

7 7

61 72

20

82.5 84.8

6.3 7.9

0.14 0.12

22 23

25 23

92 101

21 26

8 8

15 16

10 10

36 36

167

Fe203 %1.z.

HnO %o.15o.

08

o.loo

0./~

~

~ffi0.70.050' ~--''//~

0.0 5.0 3.0

0.000 0.50.

1.0 ZS ~ 15 5'

~=0,13

0.80 X=13.1 0.~

2=0.32

streampeat

• 0.00~ Corex j~nceLLo tocnLity

NnO %o.15 I O.lO ~ ' ~ x ~

0.# ~

~= 0.~

0.0 S,O 3.0 / ' ~ 1.0' / ~ ' ' ~

15 J

roofs

R=2.0 0.00 ~

Fe203 % o.8 ~

25' (

~=0.06 (:leriQ[ports

/~ ~,,.

0.05

aeriat parts ~ = 0.o9

0.100 _

0,050 ~=1.7

~

~

~=6.~

X=O.O5 roots

0.000

0.80 o.~o

stream peat ~

~=o.12

O.OO

Carex rosfroto LocaLity_ mm rainI

mm

rainI

oo I

t 3o.olm zo.otm • 100m = ~17 211713/8;15~ 130/8 ',1~ , 12/7 30/7 1/8 23/8 5/9 16/9

t.o.o

ooj

L

~o.01

3o.of zo.ot.,

lO.Op

~+/7 ]:'117 ~ 12/7 30/"/

,,,

318 h5/8 ]30/8113/9 ; 11/8 23/8 5/9 16/9

W e e kty_p__re c i pi.j._fo_..fion Fig. 3. Seasonal variation of Fe2Os and MnO in Carexjuncella, Carex rostrata and stream peat at Kikkejaure, summer 1976 (dry weight).

necessity of correcting the analyticalvalues for the presence of limonite and organic matter when using stream peat for geochemical mapping or mineral exploration purposes. The variation curves for the concentration of Fe203, M n O and Co in Carex

168

~b

Cu

ppm

°I

15

"~----_

5

X=3

aerial parrs

15 15

~=3

roofs

5

qO

~0-

30

30.

~=2z.

20

X=30 stream peat

20

10

lO

Corex iuncel[o locality Cu ppm 20

15

10.

aeriat parts

5

X=9

X=2

15

155

5

x=8

z,0-

X=5

roofs

&O

30-

30

20-

20

:22 10

~

X

=

2

8

stream

peat

10

C~r_ex r~s_.fr a fcz Io co [i ty mm

mm

"'1 o

50.0

40.0t

50.0

m~

J 20.0+ram, ,,, ~o.ol~ILII

40.0

20.0

I°.° U U I I ~ m L _ . ~ L

m

L,/7 ~J2117 ~ 318 115/8 3018 113,9 7 1217

~0/7

11/8 23/8

5/9

1619

j

~/7 12117 I 3/8 115/8 13018 11319 ', 12/7

30/7

1118 23/B

5/9

16/9

We ekLy_pr ecipi f a__fi_on Fig. 4. Seasonal variation of Cu and Pb in Carex juncella, Carex rostrata and stream peat at Kikkejaure, summer 1976 ( dry weight).

roots from the two localities at Kikkejaure tend to have certain similarities with those for stream peat. It is impossible to tell whether these relationships between roots and stream peat depend on uptake of these elements into the roots or upon precipitation of limonite on the surface of the roots. As a whole however, the seasonal variation of the investigated heavy elements is less extreme for roots than for stream peat.

169 Ha

Zn

ppm3OO

ppm

200 100 ~ .

....

~

.

~

X:103

50 X=11

aerial parts

X:15

roots

100

300

50

200 ~=85

100.

150 100~

500

X:326

~=Io2

300

50

stream peat

100

Corex iuncetto Locotify Zn ppm300

ppm

200 ~=IOZ

100

50

X=16

oerio{ports

lOO

300

SO

200

: 39

roots

X=115

100

150 100

500 300

X=37~

~

50

~=48

stream peat

100

Corex rostroto tocotif~L mm

~io

m.m

t,0.0

m

1

L,17 nn21/7, 318 ~15/8 n30/B ]13,9 I 12/7 30/7 11/~ 23/8 5F) 16/9

3o.ot

jj

~,/7 12117 I 3/8 115/8 13O/B 113/9 '~ 1217 30•7 11/8 2310 5/9 16/9

W eek !y_p_re_cipit _ofi o n Fig. 5. Seasonal variation of Zn and Mo in Carex juncella, Carex rostrata and stream peat at Kikkejaure, summer 1976 (dry weight).

The two localities at the non-anomalous stream at LAngtr~isk had variation curves for all elements that were much smoother, but with trends similar to those for the stream at Kikkejaure. This indicates that background levels of heavy metals are much less affected by seasonal variation than anomalous levels and that the variation in precipitation has a rather limited effect on the heavy metal concentration in Carex roots.

170

Co

U

ppm

40 \ ~

ppm

2.0 1.o

oeriot ports

~=t0 40

8.0

20 x . . ~ / ~ . . _ _

X=23

o.o

12o.

x=1~,8

15

X=IZ

80 40

5

roots

stream peat

Ca l e x junce [[o locality Co

U

ppm

ppm

2.0

1.o ~

~

=

o

.

20 0

6

aerial ports

4o &O ~,.0

20 ~'"---~V

\

O.C 25

roofs

X=3.3 160 , ~ .,,q ,,'x r-120 " 'k"/" ~ k , ~ ~ J

15 X=8

5

X=2~,

80' 40.

sfreom peat

0

Corex rosfroto locality_ mm

mm

50.0

4°.°t

50.0

~ml

30"Of m 2o.ot~, m

j

"°-°t

U

30.Of

zo.o'o~,

,o.oLI m

,o.o,ml

4/7 I 21/71 3/8 115/8 t30/8 11]/9 q 1213 30}7 11/8 23)8 519 16}9

4/712/? 121/'/30/7I 318 8 ',30 5/9', 11/8 23/8

91

16/9

Week!y_precipifafion Fig. 6. Seasonal variation of Co and U in CarexjunceUa, Carex rostrata and stream peat at Kikkejaure summer 1976 (dry weight).

For aerial parts of the two Carex species, no elements showed any variation curves that were similar to those for roots or stream peat. It can thus be concluded that uptake of metals into the green parts is not correlated to the uptake by roots or with the metal content of the growth medium. This strongly indicates that exclusion mechanisms are operating between roots and aerial parts as described by Kovalevskii {1979 ).

171

Ni

Cr ppm3.o

ppm3.0

2.o

Z.O

1.o

R =0.6

..... ~

1.o

2.0 1.o

aeriat

parts

2.0

~

X=0.7

. ~ X = 0.8

1.0

roots

25 15

15. ~=17

s

S'

~

~

=

stream peat

g

.Carex ... junce [_[o_ local ity Ni

Cr ppm 32

pprn~O

2.0

ZO

1.0'

R=o.z

1.0

aerial ports

2.0 Z.O,

1.0. ~

~

-

~

~=1.0

~/~/~

1.0.

X=1.2

roofs

25'

15-

15.

X=IO

5

stream

peat

C__arex rostrn to LocaLity_ mm

mffl

50.0 l,O.O

rain

so.o]

!~

Jl m

.o.ot ~ t zo.ot~, l a ~

3o.ot zo.ot~ I ~ l

~o.o~]1~

10.0~

4/7 i 21/"/I 3/8 115/8 130~ ',1~"1 12/7 3017 11/8 23/8 5/9 16/9

.J

~/7 121/7 ~ 3/8 hS/6 130/8 113/9 1 12/7 30/'/ 1118 23/8 519 16/9

_We_ek_y[_lq.r__et i p i t a tio n Fig. 7. Seasonal variation of Cr and Ni in Carex juncella, Carex rostrata and stream peat at Kikkejaure, summer 1976 (dry weight).

Certain elements had successively decreasing contents in the aerial parts during the season. This was evident for Fe203, Cu, Pb, Cr, Ni and U. Other elements (M n O , Zn, Mo, Co ) showed variations that were neither correlated with the other two sampled types nor with the variation in rainfall.These variations are probably related to the dynamics of plant growth and metabolism. This has been observed also by others (Mitchell and Reith, 1966; Dunn,

172 1980; Erdman and Olson, 1985). It can thus be concluded that aerial parts of the two Carex species are unsuitable for biogeochemical exploration and geochemical mapping since they do not have metal contents that are related to those of the growth medium.

ANNUALVARIATIONOF ELEMENT CONCENTRATIONS

The annual variation was studied for the stream nos. 1, 2 and 3 located near Arjeplog (see Fig. 1 ). Stream peat and Carexjuncella were collected at the end of July in 1975 and 1976. On each occasion, samples were taken from the same localities along the streams, and mean values of the metal contents for the three streams were calculated. In this way a representative estimation of the average geochemical differences between the two years was obtained. The total precipitation during July 1975 was 43 mm and during July 1976 it was 106 mm. The results are shown in Table 4 and the dominating trend for all three investigated sample types is enhanced limonite and base metal contents in 1976 compared to 1975. These enhanced element concentrations in July 1976 are correlated with the much higher precipitation during that month compared with July 1975. However, correction of the analytical values for the presence of limonite and organic matter will reduce the annual variation to a minimum making it possible to compile heavy metal patterns from different years; this can be done with regression analysis as described by Selinus (1983).

GEOCHEMICALRESPONSE TO DIFFERENT BEDROCK ENVIRONMENTS

In order to study the response of the sampling media to different bedrock environments, dense sampling of stream peat and Carex juncella was carried out during 1975 along stream no. 1. This stream is 15 km in length and passes through three completely different rock units: Caledonian schists, granite and felsic lavas with ignimbrites. No mineralizations are known in this area and the stream can thus be considered as a "background" stream. The samples were divided into three groups according to the bedrock environments and mean values were calculated for each group respectively ( see Table 5 ). All three sample types showed similar trends with respect to the heavy metal contents. Samples from rock unit no. 1 (Caledonian schists) in the upper reaches of the stream had the highest values of Cu, Pb, Zn, Co, Ni and Cr, which are all characteristic elements for these schists. Samples from rock unit

173

¢4

0

174 TABLE 5 Mean metal contents in stream peat and CarexjunceUa within three rock units along stream no. 1 Element

Carexjuncella roots

Stream peat

CarexjunceUa aerial

parts

Rock unit no.l: Cu (/~g/g) Pb(/~g/g) Zn (/~g/g) Co(fig/g) Ni (/lg/g) Cr (/tg/g) Mo (#g/g) U (/~g/g) Fe203 ( To) MnO(To) Ash(To) No. of samples

1

2

3

1

2

3

1

2

3

18 37 155 30 35 40 7 15 7.5 0.4 84.2

19 33 114 22 31 34 7 22 6.5 0.2 81.1

11 22 76 14 21 29 7 20 5.4 0.2 91.8

56 76 538 63 61 37 19 15 13.8 1.5 32.8

42 78 453 67 68 30 20 34 15.4 1.1 33.1

37 37 233 36 34 28 22 27 13.2 0.6 38.4

144 20 924 13 61 8 46 42 3.7 1.6

129 18 776 12 54 8 42 54 3.2 1.1

120 16 630 12 44 8 39 48 2.9 0.8

24

24

18

28

29

18

28

32

25

~1: caledonian schists, Upper reaches of stream no. 1; 2: granite, middle reaches of stream no. 1; 3: felsic lavas and ignimbrites, lower reaches of stream no. 1. no. 2 { g r a n i t e ) in t h e m i d d l e r e a c h e s of t h e s t r e a m h a d c o n s i s t e n t l y lower values of b a s e m e t a l s c o m p a r e d to r o c k u n i t no. 1. H o w e v e r , t h e u r a n i u m cont e n t s were h i g h e s t in s a m p l e s f r o m t h i s granitic r o c k unit, w h i c h could be expected. S a m p l e s f r o m r o c k u n i t no. 3 h a d t h e lowest v a l u e s for all e l e m e n t s ( e x c e p t U ). T h i s is to be e x p e c t e d in view of t h e v e r y low h e a v y m e t a l c o n t e n t s of t h e felsic lavas. T h e clear g e o c h e m i c a l r e s p o n s e of t h e aerial p a r t s of Carex juncella to t h e geological e n v i r o n m e n t is c e r t a i n l y due to t h e f a c t t h a t t h e h e a v y m e t a l c o n t e n t s of t h i s b a c k g r o u n d s t r e a m are well below t h e p h y s i o l o g i c a l b a r r i e r s . T h e fact t h a t all t h r e e m e d i a r e f l e c t e d t h e b e d r o c k e n v i r o n m e n t in a quite s e n s i t i v e w a y i n d i c a t e s t h a t t h e y are reliable s a m p l e t y p e s in g e o c h e m i c a l m a p p i n g of b a c k g r o u n d v a r i a t i o n s of e l e m e n t s in t h e n a t u r a l e n v i r o n m e n t . L o u n a m a a (1956) a r r i v e d a t s i m i l a r r e s u l t s in a n i n v e s t i g a t i o n o f t r a c e e l e m e n t s in p l a n t s growing on d i f f e r e n t t y p e s of rock. An i n v e s t i g a t i o n of s t r e a m p e a t b y Selinus (1983) gave s i m i l a r results. GEOCHEMICAL RESPONSE TO MINERALIZATION Tables 6-8 show the mean element contents of twenty geochemical sample t y p e s f r o m t h e n i n e s t r e a m s . T h e y w e r e collected f r o m c a r e f u l l y selected local-

175

TABLE6 Meanelementcon~n~int~ ashfmm motsamples~omthenine~reams Sample species

Stream No. of Cu no. samples (#g/g)

Pb Zn (/zg/g) (#g/g)

Co Ni Cr (pg/g) (pg/g) (pg/g)

Mo U Fe203 (p~g/g) (#g/g) (%)

Carex juncella

1 2 3 4 5 7 8 9

14 9 6 12 5 5 11 5

59 185 324 1311 218 756 373 126

63 2159 98 28 49 61 31 225

445 686 934 1068 437 495 537 1844

52 111 38 230 84 62 74 39

47 42 26 177 62 79 100 26

37 43 36 66 37 81 135 34

21 108 205 253 67 40 33 417

51 149 627 176 240 92 52 159

18.2 15.6 6.8 18.2 16.9 7.6 19.3 35.9

0.95 1.15 1.04 3.82 1.97 1.45 3.78 0.47

Carex rostrata

1 2 3 4 5 6 7 8 9

13 8 8 4 1 1 1 2 1

45 205 189 908 250 126 45 304 125

33 576 45 29 119 21 11 23 120

330 597 524 775 1148 204 113 487 5196

21 32 19 219 112 47 12 80 28

32 36 21 105 123 28 25 122 38

33 45 38 45 43 46 40 143 39

12 92 131 189 185 43 7 58 543

34 211 435 149 425 45 12 52 174

6.2 5.6 3.8 20.6 11.4 8.3 4.2 19.2 9.2

0.21 0.31 0.22 1.53 0.32 1.05 0.13 3.24 0.14

Salix phyllici/olia

1 2 3 4 6 7 8

6 4 9 1 1 1 2

108 238 244 830 141 290 413

40 1046 100 37 29 62 24

2986 6045 3300 601 2250 1512 3606

45 90 42 318 72 53 44

50 56 27 104 32 88 68

39 45 45 64 53 71 82

22 61 128 97 51 29 37

37 139 486 440 14 109 43

11.7 16.7 9.9 25.8 15.9 8.9 17.3

1.44 2.03 1.40 1.83 1.14 3.22 1.71

Salix lapponium

1 2 3 5 9

8 6 1 1 1

131 230 178 157 118

87 2057 185 76 243

4555 5722 4030 1611 8606

56 92 54 75 21

80 43 21 64 21

32 37 45 51 20

24 55 144 50 387

41 65 406 505 77

16.7 14.7 9.0 22.3 39.5

2.13 2.53 1.67 1.01 0.84

Menyanthes trifoliata

1 2 3 7

2 5 8 3

219 261 255 671

27 533 47 26

1196 1292 960 461

39 81 18 30

35 33 15 52

25 23 30 60

45 56 95 31

33 55 282 46

17.3 14.8 5.3 5.1

0.93 1.49 0.33 0.71

Molinia coerulea

1 2 3 8

6 6 1 6

59 145 183 319

37 882 126 23

455 594 568 389

36 71 34 55

40 34 24 98

34 40 68 171

10 93 95 21

37 180 660 25

6.9 14.0 7.5 15.9

0.63 0.85 0.45 2.03

Eriophorum 1 angustifoliurn 2

1 6 9 1

71 127 165 210

97 630 70 62

798 868 873 733

77 46 20 68

50 29 20 27

36 30 35 18

44 119 247 58

36 138 433 45

19.8 11.1 6.7 24.9

0.79 0.58 0.40 0.96

5 4 1 1

63 246 993 193

56 2227 21 74

569 838 1946 605

33 72 726 146

42 41 295 72

36 63 47 27

11 53 326 127

37 267 87 185

5.5 7.4 22.1 27.6

0.59 0.70 10.65 1.22

3 6

Deschampsia 1 caespitosa 2 4 5

MnO (%)

ities with as many plant species available as possible. All samples were collected during July and August 1975 in order to minimize seasonal and annual variation of element concentrations. As was shown in Table 1, the streams

176 TABLE 7 Mean element contents in the ash of aerial parts of samples from the nine streams Sampled species

Stream No. of Cu Pb Zn Co no. samples (#g/g) (pg/g) (pg/g) (#g/g)

Carex juncella

1 2 3 4 5 7 8 9

14 9 6 12 5 5 11 5

173 274 181 258 138 227 215 153

16 358 44 13 22 26 13 25

821 1254 1433 665 511 644 805 1603

15 17 17 36 15 11 11 10

65 31 20 38 25 17 18 15

8 10 16 13 12 13 15 7

33 68 133 47 25 66 56 170

34 45 91 44 23 47 36 36

3.0 3.2 3.9 2.4 2.0 3.1 3.3 3.8

1.20 1.25 1.37 1.51 0.45 1.01 1.27 0.88

Carex rostrata

1 2 3 4 5 6 7 8 9

13 8 8 4 1 1 1 2 1

65 152 133 188 57 90 93 131 55

14 129 17 18 19 21 13 14 31

643 1049 710 698 486 914 720 760 1320

11 11 3 45 25 21 8 7 2

39 22 8 31 24 17 13 19 6

7 8 3 6 2 11 12 18 4

22 95 71 70 39 40 56 64 168

24 41 62 12 18 5 2 40 7

2.3 2.0 1.4 3.2 4.0 4.2 2.9 2.7 7.1

0.64 0.81 0.52 1.93 0.79 0.60 0.47 1.72 0.55

Salix phyllicifolia

1 2 3 4 6 7 8

6 4 9 1 1 1 2

229 347 245 320 180 220 223

30 145 43 27 34 29 36

6526 9676 6132 5920 3862 4716 4614

50 55 32 72 29 37 35

108 55 22 91 20 27 51

20 32 24 24 15 27 36

29 69 77 48 43 37 43

44 18 72 4 34 1 31

6.2 8.7 4.9 6.9 5.0 4.8 6.7

2.80 4.77 1.91 5.48 1.18 1.24 1.36

Salix lapponium

l 2 3 5 9

8 6 1 1 1

309 339 230 140 172

30 365 64 68 71

7687 7875 12649 1347 14823

69 64 24 49 33

95 44 12 25 18

22 30 25 28 25

31 48 61 41 109

36 22 45 6 ll

6.6 6.6 5.9 6.9 8.6

5.28 4.86 2.86 3.14 3.73

Menyanthes trifoliata

1 2 3 7

2 5 8 3

92 114 144 159

18 63 13 32

1081 866 836 461

17 16 6 13

22 28 10 13

13 9 10 32

21 25 21 19

128 50 89 52

7.2 3.7 2.9 5.0

0.91 1.10 0.32 0.80

Molinia coerulea

1 2 3 8

6 6 1 6

187 300 230 174

15 114 35 15

1326 1784 1281 831

11 15 9 6

61 31 25 31

7 15 14 9

21 59 83 19

44 33 75 35

2.7 3.7 2.3 1.9

0.88 0.88 0.62 0.35

Eriophorum 1 angustifolium 2 3 6

1 6 9 1

63 148 113 160

22 154 30 68

972 1732 1052 1136

15 18 7 21

43 26 10 24

15 12 11 12

23 184 207 46

16 45 134 5

3.0 4.7 2.2 7.9

1.56 1.61 0.77 2.05

1 2 4 5

5 4 1 1

93 185 333 82

17 740 15 27

490 776 1046 616

9 23 330 103

47 27 127 35

8 11 18 13

17 56 97 87

37 47 71 50

1.4 2.9 10.7 12.2

0.40 0.54 3.43 2.50

Deschampsia caespitosa

Ni Cr Mo U Fe203 (#g/g) (#g/g) (#g/g) (~g/g) (%)

MnO (%)

have different geochemical characteristics with respect to heavy metals. The tables therefore give information about the geochemical response to mineralization of the different sampling media. From the tables it is evident that some

177

TABLE 8 Mean element contents in the ash from mosses and stream peat from the nine streams Sampled species

Stream No. of Cu Pb Zn Co Ni Cr Mo U Fe203 M n O no. samples (#g/g) (pg/g) (p.g/g) (p.g/g) (#g/g) (,ug/g) (#g/g) (/Jg/g) (%) (%)

Sphagnum

1 2

14 10

53 125

35 1494

435 927

3

10

125

203

4

4

255

65

5 6

1 2

174 140

7

3

8

2

Scorpidium scorpioides

29 55

33 31

39 42

8 40

30 94

5.7 7.8

0.61 0.87

882

23

30

30

93

263

5.4

1.24

939

127

81

49

77

42

10.0

2.09

82 80

965 561

136 41

107 21

60 32

71 50

303 41

26.2 28.7

2.07 0.54

312

100

646

28

57

47

26

63

5.3

0.71

303

37

420

35

72

141

15

26

9.2

0.71 0.49

1

7

35

28

262

31

36

30

6

40

6.1

2

4

53

214

330

32

23

23

28

88

8.1

0.35

3

10

72

81

284

33

24

40

52

584

7.5

0.50

7 9

2 1

868 70

37 126

194 5292

33 32

54 66

41 25

16 63

29 105

5.0 13.1

0.46 0.30

Stream moss 1 (unspecified) 2

9 9

42 114

36 1911

454 893

45 172

46 46

37 41

9 38

43 151

6.1 8.8

0.83 2.32

4

8

1084

25

2246

741

367

335

41

191

19.8

10.40

5 6 7

1 6 3

94 253 238

19 34 43

877 322 345

390 59 48

106 31 67

18 39 53

130 58 16

239 96 29

41.2 15.4 4.8

9.80 1.36 2.48

8

1

388

23

291

34

82

136

19

44

7.7

0.55

Stream peat

1

15

23

47

116

30

39

47

11

19

5.9

0.32

2

10

135

1411

226

52

48

53

76

208

5.1

0.30

3 4 5

10 12 5

88 551 261

74 44 44

259 493 489

39 264 175

46 170 129

63 92 55

102 240 87

505 140 434

8.5 18.4 18.5

0.14 2.82 1.92

6 7 8 9

7 5 11 6

348 801 220 107

39 73 27 166

107 502 136 1620

40 69 56 19

53 141 110 25

51 149 204 27

67 62 31 300

101 45 36 85

16.1 12.8 14.9 23.1

0.25 0.55 0.69 0.23

species are much more enriched in metals than others. For example, the Salix species are very strong Zn-enrichers. The Carex species generally have higher metal contents (Cu, Pb, Zn, Co, Ni, Cr, Mo, U, Fe203, MnO) in roots as well as in aerial parts compared to other species. Stream moss is characterized by high mean values of Co, Ni and Cr indicating that geochemical barriers against these elements are lacking. The anomaly contrasts between the most anomalous stream and the background stream no. 1 are shown in Table 9. Mean element concentrations for each stream were used and calculations were made for stream peat as well as

178 TABLE 9 Anomaly contrasts for the plant species and stream peat calculated as metal(most . . . . . ,ous stream)/metal (backgroundstream n o . 1 ) Species

Cu

Pb

Zn

Co

root aerial stream root aerial stream root aerial stream root aerial stream part no. part no. part no. part no.

Carexjuncella Carexrostrata Salix phyllicifolia Salix

lapponium Menyanthes trifoliata Molinia coerulea Eriophorum angustifolium

Deschampsia caespitosa Sphagnum Scorpidium scorpioides Stream moss Stream peat

22.2 20.2 7.7

1.5 2.9 1.4

(4) (4) (4)

34.3 17.5 26.2

22.4 (2) 9.2 (2) 4.8 (2)

4.1 2.0 15.8 2.1 0.2 0.9

(9) (9) (4)

4.4 10.4 7.1

2.4 (4) 4.1 (4) 1.4 (4)

1.8

1.1

(2)

23.6

12.2 (2)

1.9

1.9

(9)

1.6

0.9 (2)

3.0

1.7

(7)

19.7

3.5 (2)

1.1

0.8

(2)

2.1

0.9 (2)

2.5

1.6

(2)

23.8

7.6 (2)

1.3

1.4

(2)

2.0

1.4 (2)

1.8

2.4

(2)

6.5

7.0 (2)

1.1

1.8

(2)

0.6

1.7 (2)

15.8 3.6

(4)

40.0

43.5 (2)

3.4

2.1

(4)

22.0

36.7 (4)

4.8 1.5

(4) (2)

42.8 7.6

(2) (2)

2.2 1.3

(4) (2)

4.4 1.0

(4) (2)

25.8 24.0

(4) (4)

53.1 30.0

(2) (2)

2.0 14.0

(2) (9)

16.5 8.8

(4) (4)

Values in brackets indicate the most anomalous stream chosen

for all plant species sampled. A general trend is that the anomaly contrasts are highest for stream peat, somewhat lower for roots, and in general very low for aerial parts. The reason for stream peat having the highest anomaly contrasts is probably due to the fact that this material takes up heavy metals by three different processes: uptake by living roots, coprecipitation with limonite, and adsorption by humus material. Among the different root species, Carex junceUa, Carex rostrata and Deschampsia caespitosa had the highest anomaly contrasts for Cu, Pb, Zn, Co, Ni, Mo. The lowest contrast values were obtained for Ni and Cr which may be because they are less easily taken up by plants. Aerial parts mostly had contrasts around or below 1.0, indicating that geochemical barriers are operating between roots and above ground parts. One exception is Pb which is obviously more freely admitted into the aerial parts of the plants compared to most other metals. Both Warren {1978) and Kovalevskii (1979) found that Pb is a very useful element for biogeochemical prospecting. The Pb contents of plants growing on both mineralized and non-

179 TABLE 9 (continued)

Species

Carexjuncella Carexrostrata Salix phyllicifolia Salix lapponium Menyanthes trifoliata Molinia coerulea Eriophorum angustifolium Descharnpsia caespitosa Sphagnum Scorpidium scorpioides Stream moss Stream peat

Ni

Cr

Mo

U

root aerial part

stream root aerial no. part

stream root aerial stream root aerial stream no. part no. part no.

3.8 3.3 1.4

(4) (4) (8)

3.7 4.3 2.1

1.9 2.6 1.8

(8) (8) (8)

-

-

-

0.6 0.8 0.5

19.9 5.2 45.3 7.6 4.4 1.7

(9) (9) (4)

12.3 2.7 12.8 2.6 13.1 1.6

(3) (3) {3)

16.1 3.5

(9)

11.3

1.3

(3)

1.5

0.6

(7)

2.4

2.5

(7)

1.2

1.2

(2)

8.6

0:.7

(3)

2.5

0.5

(8)

5.0

1.3

(8)

9.3

2.8

(2)

17.8

1.7

(3)

2.7

8.0

(2)

12.0 0.5

(3)

28.9

5.7

(4)

. 7.0

2.7

.

. (4)

. -

-

7.2

1.3

(2)

2.5 1.5

(4) (7)

3.6 1.4

(8) (7)

9.6 4.7

(4) (2)

8.8 14.6

(3) (3)

8.0 4.4

(4) {4)

3.7 4.3

(8) (8)

4.6 27.3

(4) (9)

3.5 26.6

(2) (3)

mineralized areas are, in general, highly correlated with the lead concentration in the growth medium.

Copper The strongest Cu mineralization is located in stream no. 4. There are also weak Cu mineralizations at stream nos. 2, 5, 6, 7 and 8. Practically all investigated root species showed a good response to these mineralizations though the best response was obtained for the two Carex species. For aerial parts there was only a weak or no response. The strong capability of root tissues to hold Cu against the transport to shoots under conditions of both copper deficiency and copper excess has been observed, but these processes are not yet fully understood {Jarvis, 1978; Thornton and Howarth, 1986). It has also been noticed that Cu has a low mobility relative to other elements in plants, with only small amounts moving to young organs. Within roots, Cu is associated mainly with cell walls and is largely immobile (Kabata-Pendias and Pendias,

180 1984). Scorpidium showed no response for Cu, whilst Sphagnum, stream moss and stream peat showed a strong response.

Lead Stream no. 2 is located within a Pb-mineralized area. There is a very good response for all investigated species in roots, aerial parts, mosses and stream peat. However, root species have much higher Pb concentrations than aerial parts. Kovalevskii (1979) has shown that Pb concentration in plants growing over Pb-bearing deposits is usually considerably higher than the background Pb concentration, which is in accordance with the results in Tables 6-8. However, physiological barriers do exist for Pb, but they seem to be much less pronounced than for other elements for all sample types studied. Lead should therefore be one of the most useful elements for prospecting by means of aerial parts of the plants.

Zinc The strongest Zn mineralization occurs in stream no. 9, though stream no. 4 is also known to have Zn disseminations. The Zn concentration in all plant species is considerably higher than most other heavy metals due to the many important functions of Zn in plant metabolism. The concentrations in aerial parts were, in general, higher compared to roots, which could in part be due to the fact that Zn is one of the most mobile elements in plants, especially under conditions where the plants have abundant supply ofZn ( Kabata-Pendias and Pendias, 1984). With high levels of soil Zn for example, this element may be translocated from the roots and accumulated in the top of the plant. The best geochemical response was obtained for Carex juncella roots, stream moss and stream peat. Aerial parts showed no response to mineralization which indicates that the transport of Zn to the aerial parts is more a function of plant metabolism than of the concentration in the growth medium. A similar result has been obtained by Matthews and Thornton (1982), showing low rates of metal translocation between roots and aerial parts of the grass Holcus lanatus at Shipham, Somerset, in an area heavily contaminated by Zn ( see also Thornton, 1983 ).

Cobalt, nickel, chromium Streams anomalous for Co, Ni and Cr are shown in Table 1. These elements showed a good response for the root material, but no response for the aerial parts. Plants are known to restrict transfer of Cr from soil and water to animal and human diets, most Cr remaining in the roots (Huffmann and Allaway, 1973). The mosses and stream peat showed a good response to all three ele-

181

I-I a~

e',--

, ~ ¢.D Cxl

Cxl ~ O~ ~ t-- Cxl

II

c,l v,-I ¢~

I

I I I I

m m m

I

I

O

¢~

bl

I

I

....

C'

~

q

. ~ q ~ . . II

I

•

..~ ~ . ~ . ~ ~ ' ~

°

.

co o,l

~.~

v r , V, II ,ll ~

r.D ( D

182

800-

a

400200-

~00

~

c

t

0"

800

i

260

160

400

8O

200.

80

y

O.

160

520

~o

3~o

Cr

4 . 8 ~ . .

e.

SZOt

U

.

f

32. 16 2'0

~,'0

0÷("

0

6'0 >

,

260

,

520

Stream peat

Fig. 8. Non-barrier relationships between heavy metal concentrations (ppm) in ashed stream peat and plant roots, a and b: Cu and U in Carex rostrata; c and d: Ni and Mo in Carexjuncella; e and f: Cr and U in Salix lapponiurn.

ments. There is no evidence yet of an essential role of Cr and Ni in plant metabolism, and their availability to plants seems to be very limited.

Molybdenum, uranium Stream no. 3 is located within a zone of Mo and U mineralization, and stream no. 9 transects Mo mineralization. The response for both elements was good for most root species, mosses and stream peat. For aerial parts a good response was obtained only for a few species; for example Mo in Carexjuncella, Carex rostrata, Eriophorum angustifolium and Deschampsia caespitosa; and U in Carex junceUa and Eriophorum angustifolium.

183 Ni 280

100

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800

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6°°I°/

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Fig. 9. Non-barrier relationships between heavy metal concentrations (ppm) in ashed stream peat and mosses, a,b and c" U, Ni and Co in Sphagnum; d and e:U and Cu in Scorpidium;f:U in unspecified stream moss. CORRELATION BETWEEN HEAVY METAL A N D D I F F E R E N T P L A N T SPECIES

CONCENTRATIONS

IN S T R E A M

PEAT

The mean element concentrations in biogeochemical samples from the nine streams were used in calculatingcorrelationcoefficientsbetween plant species and stream peat. For the higher plants, coefficientswere calculated for roots and stream peat as well as for aerialparts and stream peat (Table 10 ). Eleven species were investigated,but only Carex rostratawas availableat allthe nine streams. For the other species,samples were obtained from four to eightstreams. Table 10 shows that root species and mosses have significant correlation coefficients (P < 0.05 ) for more species and elements compared to aerialparts. A n exception to this is Pb, which for all species had correlation coefficients close to 1.00.Roots from the two Carex species had significantcorrelationcoef-

184

56O0[ Zn 281]

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800 CU

./

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¢00

-. i

800

125

145

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c0 /

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Fig.10. Relationships between heavy metal concentrations

(ppm) in &shed roots and aerial parts of plants, a and b: Zn and Cu in Carex rostrata; c: Zn in Carex juncella; d: Cu in Menyanthes trifoliata; e: Co in Deschampsia caespitosa; f: Co in Salix phyllicifolia.

ficients for all the investigated elements. This is very fortunate from a methodological point of view since Carex is among the most common plant species in Swedish streams. Carex roots are also a major constituent in stream peat. Other root species had significant coefficients for some elements and very low or negative coefficients for other elements. There are two possible explanations for this: (1) the roots do not absorb certain elements in relation to the concentration in the growth medium; or (2) the correlation coefficients are not relevant for certain species and elements because samples were not available from both background and anomalous streams. The results for the two Salix species indicate that the latter explanation is the more probable. For example Salix phyUicifolia, was available at the most Cu-anomalous stream ( no. 4) but not at the most Zn-anomalous stream (no. 9), whilst the situation for Salix lapponium was reversed. When comparing the correlation coefficient values for roots from these two species one finds a significant Cu-coefficient for Salix phyllicifolia and the highest Zn-coefficient for

185

Pb

Q.

2000

2~ooT

Pb

1000

180

0

360

180

360

d.

~,8.0

32,0

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27,0

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°0°oi

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.

'

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go

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porf~ Fig.1 I. Non-barrierrelationshipsbetweenheavymetalconcentrations(ppm) inashedrootsand aerial partsof plants,a:Pb in Salix lapponium; b: P b in Carex junceUa; c:Ni in Eriophorum angustifolium; d:Cr inMenyanthes trifoliata;e:Co inCarex rostrata;f:Mo inSalix lapponium. ~, AeriQ[

Salix lapponium. For this reason it can be concluded that the coefficients in Table 10 are not relevant for those species and elements where anomalous streams are not represented. Nevertheless the results indicate that roots from most of the investigated species are at least as suitable as stream peat in geochemical exploration or geochemical mapping. In order to more closely compare the relationships of element concentrations in plants with those in stream peat, a number of plots were made. Figure 8 shows plots of Cu, Ni, Cr, Mo and U concentrations in roots versus stream peat for various species. They all show a linear relationship indicating that roots of these plants are barrier-free with respect to heavy metal uptake. The same can be said about mosses (Fig. 9 ). When studying plots of element concentrations of roots versus aerial parts it becomes evidel~t that physiological barriers are operating between roots and the aerial parts of the plants. This

186

can be seen for Cu, Zn and Co in Fig. 10. However, there are some examples of species having barrier-free aerial parts, for example Pb for all species, Ni in Eriophorum angustifolium, Cr in Menyanthes trifoliata, Co in Carex rostrata and Mo in Salix lapponium (Fig. 11). Kovalevskii (1979) presents numerous examples of barrier-free, above-ground plant organs, but these mostly apply to one or two heavy metals only. On the other hand, our results have shown that aquatic mosses and roots from plants growing along stream channels seem to be the most suitable multi-element biogeochemical sample types. Similar results were reported by Magnusson (1984) from a pilot study in the tropical environment of Sumatra. SUMMARY AND CONCLUSIONS

This study has shown that aquatic mosses and roots of plants growing on stream banks in Sweden are mostly of non-barrier type with respect to uptake of heavy metals. Both sampling media reflect in a very sensitive way, chemical variations in the stream peat material on which they were growing. Aerial parts of the investigated species did not, in general, respond to high heavy metal concentrations in the growth medium. This is due to the fact that plants have physiological barriers between roots and above-ground parts protecting them from uptake of toxic levels of heavy metals into the vital reproductive organs. This means that aerial parts of plants are less suitable for geochemical prospecting. However, aerial parts of Carex junceUa gave a good geochemical response for eight heavy metals with respect to three different geological formations within a background area. This indicates that aerial parts of plants may respond to the availability of heavy metals in the growth medium provided the metal concentrations are below the physiological barriers. However, seasonal variation studies of two Carex species showed that the heavy metal concentration of the aerial plant organs displayed pronounced variations during the summer season; some elements having a gradual decrease and some other elements having an erratic variation. Therefore, if green, reproductive plant organs are used, sampling should be completed within as short a time interval as possible in order to minimize the seasonal variation. On the other hand, root samples showed variations for most heavy metals that were less drastic and to a certain degree similar to that of the growth medium. These heavy metal variations were also positively related to the concentration of limonite in the growth medium (stream peat) as well as in the root samples. It has also been shown that the variation in limonite concentration is correlated with the variation in precipitation during the summer season. This demonstrates the necessity of normalizing seasonal and annual variations in heavy metal concentrations using the limonite concentration as a dependent variable. One major result of the investigation is that roots from plants growing on stream banks as well as aquatic mosses give geochemical patterns that are

187 closely r e l a t e d to v a r i a t i o n s in t h e b e d r o c k c o m p o s i t i o n s . T h u s t h e s e s a m p l i n g m e d i a can be u s e d in g e o c h e m i c a l m a p p i n g as well as for geochemical exploration. In Sweden, roots a n d mosses are t o d a y successfully used in a n a t i o n wide geochemical p r o g r a m m e . T h e samples are t h o r o u g h l y w a s h e d in o r d e r to m i n i m i z e c o n t a m i n a t i o n f r o m t h e p a r e n t soil. ACKNOWLEDGEMENTS F o r critically r e a d i n g t h e m a n u s c r i p t a n d for m a n y c o n s t r u c t i v e discussions we are greatly i n d e b t e d to Dr. C.A. N i l s s o n of t h e Geological S u r v e y o f S w e d e n a n d our o t h e r colleagues at t h e geochemical b r a n c h .

REFERENCES Brooks, R.R., 1972. Geobotany and Biogeochemistry in Mineral Exploration. Harper and Row, New York, NY, 290 pp. Brooks, R.R., 1983. Biological Methods of Prospecting for Minerals. Wiley, New York, NY, 322 pp. Brundin, N.H., 1939. U.S. Patent 21589-0. Brundin, N.H., 1980. Aspects of geomedical problems from a biogeochemical point of view. In: J. L~g (Editor), Geomedical Aspects in Present and Future Research. Universitetsforlaget,Oslo, pp. 35-37. Brundin, N.H. and Nairis,B., 1972. Alternative sample types in regionalgeochemical prospecting. J. Geochem. Explor., I: 7-46. Danielsson, A., 1967. Spectrochemical analysis for geochemical purposes. In: A.H. Gillieson (Editor), XIII Colloquium Spectroscopium International.A d a m Hilger, London, pp. 311-323. Dunn, C.E., 1980. Gold biogeochemistry investigations -Flin Flon area (Manitoba). Sask. Dep. Miner. Resour., Misc. Rep., 80-4: 81-85. Ek, J., 1974. Trace elements in till,vegetation and water over a sulfideore in Vtisterbottencounty, northern Sweden, Sver. Geol. Unders., ~krsb.,68: 1-50. Erdman, J.A. and Olson, J.C., 1985. The use of plants in prospecting for gold: a briefoverview with a selectedbibliography and topic index. J. Geochem. Explor., 24: 281-304. Huffman, E.W.D. and Allaway, W.H., 1973. Chromium in plants: distributionin tissues,organelles,and extractsand availabilityof bean leafCr to animals. J. Agric.Food Chem., 21:982 -986. Jarvis, S.C., 1978. Copper uptake and accumulation by perennial ryegrass grown in soiland solution culture.J. Sci. Food Agric.,29: 12-18. Kabata-Pendias, A. and Pendias, H., 1984. Trace Elements in Soils and Plants. C R C Press, Boca

Raton, 315 pp. Kovalevskii, A.L., 1979. Biogeochemical Exploration for Mineral Deposits. Amerind, New Delhi, 136 pp. Larsson, J.O., 1976. Organic stream sediments in regional geochemical prospecting, Precambrian Pajala district, Sweden. J. Geochem. Explor., 6: 233-249. Lounamaa, J., 1956. Trace elements in plants growing wild on different rocks in Finland. Ann. Bot. Soc. 'Vanamo', 29: 1-196. Magnusson, J., 1984. Experimental geochemical exploration programme in Indonesia, Vol. 1 and 2. INS/80/011 U.N. Tech. Rep. Matthews, H. and Thornton, I., 1982. Seasonal and species variation in the content of cadmium and associated metals in pasture plants at Shipham. Plant Soil, 66: 181-193.

188 Mitchell, R.L. and Reilh, J.W.S., 1966. The lead content of pasture herbage. J. Sci. Food Agric., 17: 437-440. Selinus, 0., 1983. Regression analysis applied to interpretation of geochemical data at the Geological Survey of Sweden. In: R.J. Howarth (Editor), Handbook of Geochemistry, Part 2: Statistics and Data Analysis in Geochemical prospecting. Elsevier, Amsterdam, pp. 293-301. Thornton, I., 1983. Applied Environmental Geochemistry. Academic Press, London, 501 pp. Thornton, I. and Howarth, R.J. (Editors), 1986. Applied Geochemistry in the 1980's. Graham and Trotman, London, 347 pp. Tkalich, S.M., 1938. Investigation of vegetation as a guide in prospecting. Abstr., U.S.G.S. Bull., 1000A, 34 pp. (in Russian). Warren, H.V., 1978. Biogeochemical prospecting for lead. In" J.O. Nriagu (Editor), The Biogeo° chemistry of Lead in the Environment. Wiley, New York, N.Y., pp. 395-408.