Iron and trace elements in Dutch coastals sands

Netherlands Journal of Sea Research 3, 1, 1966, p. 68-94

IRON

AND TRACE ELEMENTS COASTAL SANDS

IN DUTCH

by D. EISMA (Netherlands Institute for Sea Research, Den Helder)

and H.A. DAS, D. HOEDE, J.G. VAN R A A P H O R S T ANDJ. Z O N D E R H U I S (Reactor Centrurn Nederland, Petten)

CONTENTS I Introduction II Experimental III Results a. Fe b. Mn, Na, Au, Cr and As c. A1, Co, Sc IV Discussion . V Conclusions Acknowledgements References .

68 69 77 77 79 79 79 91 92 92

INTRODUCTION Sands along the main coast of Holland show considerable differences in iron content, which roughly coincide with differences in Ca- and Mgcontent and mineralogical composition. Thus beach and dune sands south of Egmond-Bergen contain more Fe, Ca and Mg than further north (VAN DER SLEEN, 1912) and in the so-called heavy fraction (s.g. > 2.88) garnet is predominant in the north, hornblende in the south (EDELMAN, 1933). Also there is a difference in quartz content and quartz types between the northern and southern sands (BAAK, 1936). Recently VAN STRAATEN ( 1961) noticed that seasands, occurring some four miles offshore near IJmuiden, have a more rusty colour than the adjacent beach sands and suggested that at present iron is slowly being precipitated on the seabottom off the Dutch coast. The aim of the present study was twofold: I) to study the distribution of Fe and some trace elements (Mn, Na, Au, Cr, As, A1, Co, Sc) in the coastal sands, and 2) to determine whether deposition of iron off the Dutch coast occurs at

I R O N A N D T R A C E E L E M E N T S I N SANDS

69

present: differences in iron content of sands of the same origin would indicate deposition or subsequent removal of iron, while differences in trace element composition might give an indication whether deposition occurred in seawater or in fresh water.

II. E X P E R I M E N T A L

Iron hydroxyde, whether deposited in seawater, fresh water or in soils, forms on sand grains yellowish brown, often irregular coatings. O t h e r elements are coprecipitated with the iron hydroxyde and are present as trace elements. By way of activation analysis the amounts ofFe, Mn, Na, Au, Cr and As were determined in the coatings, while the amounts of A1, Co and Sc were determined in the sand grains as a whole. Fe was chosen because it is the main element in the coatings, A1 because it is an indication for the feldspar content of the sands, the other elements because they occur in convenient quantities. The determinations were carried out in seasands sampled up to 8 miles off the Dutch coast between Hock van Holland and Wijk aan Zee, beach sands collected ,O o

jc::

=='

f 5o8,l 660-/

7051~ 7053~ n/-°ndv°° 7035yFN;oordwijk

.STB1038,103/, .STB99/, •STB 1029.1030 "STB1007 STB.595.STB 601.582 •STB 600 Wogeningen t, R6"R7 Rb'*'RR3. 2 RI~RI;obit h

Fig. 1. Location of samples.

70

D. E I S M A C.S.

between Hock van Holland and Den Helder, recent Rhine sands and some Pleistocene river sands. The samples w e r e taken at the localities indicated in fig. 1. At sea a Van Veen grab was used and positions were obtained by Decca Navigation. The beach sand samples were taken at the surface of the beach between high water mark and dune base. The Rhine samples were taken in the streambed between Lobith and Wageningcn. The samples of Pleistocene river sands were obtained from the Soil Survey Institute (Bennekom) by courtesy of D r . R . D . C r o m m e l i n . They were taken some distance below the zone of weathering, indicated by a fully developed soil profile. Before activation the sand was washed thoroughly, dried, and sieved in an E M L sieve shaker. Simple washing with distilled water proved effective to remove seasalts, as afterwards no chlorine could be detected. For analysis only the fraction 250-315 ~ was used in order to exclude difference in composition due to differences in surface area of the grains. Minerals containing iron were removed by separation with bromoform (s.g. 2.86), but shell fragments, which also contain iron and other metals, could not be removed in this way. As shells consist of calcite (s.g. 2.7 l) and/or aragonite (s.g. 2.94), a fluid with a s.g. of 2.69 was made by mixing bromoform with d e c a l i n e (s.g. 0.896, NOTA and BAKKER, 1960) but a good separation of the shell fragments from the quartz and feldspar grains by means of this fluid was not obtained. Probably many shell fragments arc lighter because of the admixture of some organic matter and the entrapment of air in small pores. After some trials with fluids of still lower s.g., the shell fragments were removed by hand with the help of tweezers and a magnifying-glass. This was done for a number of samples but was ommitted when it was established that the shell flagments contained too small amounts of the elements determined here to influence the analytical results significantly. The irradiations were carried out in both the Low Flux Reactor and the High Flux Reactor of the Reactorcentrum at Petten. In the Low Flux Reactor five minutes irradiations were performed for the determination of aluminum, at a thermal flux of 3.7 × 101° sec -1 cm -~, while for the determination of sodium and manganese the samples were irradiated during one hour in the same facility. For determination of the other elements two irradiation facilities in the High Flux Reactor were used : the pneumatic rabbit system (irradiation time 20 minutes, neutron flux 1.3 × 10 TM) and the "poolside facility" (irradiation time 24 hours, neutron flux 5 × 1013). In the Low Flux Reactor and the pneumatic rabbit system of the High Flux Reactor samples were irradiated in polythcne vials; in the case of the "poolside facility" irradiations the samples were scaled in quartz ampoulcs.

IRON AND TRACE ELEMENTSIN SANDS

71

HF 2 M

3)HCL9M+HFO.O0/,M

1) SAMPLE

x~ Mo-S n- Nb-Hg-To-Re-Au

211 13)

I

5)HBrlM

4)HCLSM -HBr 2,3M

~

~r

[~Hf-Zr-Ag-

zo_ ,~-Cd

I_~

P°-Sc-"" E

4)1 15)

i

I

,

7)HCL8M

6)HCLO.I M Na- K-Rb-Cs. Mn-Co-Sr-Bo

Cl H

M

[~

~

Co,ICu- Go-Fe

P-S

Fig. 2. Separation system used for qualitative analysis.

After irradiation the coatings were removed from the grains by boiling twice during a few minutes with a mixture (3 : 1) of 12 N hydrochloric acid and hydrogenperoxyde. For qualitative analysis of the solutions an ion-exchange system was used (AuBoUIN and LAVERLOCHERE, 1963) : in this system the elements are separated into six groups (fig.2) and it is possible by means of specific elutions to isolate each element. In this case a group separation proved to be sufficient. Iron was determined in the acid solution by a polarographic method (SoucHAY and FAUCHERRE,1949) and by titration with EDTA. The analysis of gold was performed by extracting this element out of 10 % hydrochloric acid into aethylacetate, a gold solution (1 mg gold per ml) being used as a standard. Antimony, arsenic, chromium and cobalt were separated by means of a paperchromatographic method using cellulose-phosphate paper (capacity 2.1 meq/gr) with 1 N hydrochloric

I

0.47

0.31

0.44

0.22

0.25

E 58

7051

7053

7035

7021

0.27

0.33

0.24

Rt

R2

Rs

Rhine sands

0.22

0.34

0.24

648

0.02

508

660

E 57

0.02

0.02

175

412

0.02

% Fe

137

Beach sands

No.

.

.

31.5

48.5

48.0

54.0

53.5

61.5

.

31.5

30.0

2.1

3.0

1.6

2.5

Mn p.p.m,

.

.

0.012

0.019

0.022

0.012

0.017

0.013

.

0.015

0.011

0.011

0.015

0.008

0.013

M n : Fe

.

.

.

54

81

54

38

38

50

32

49

.

.

8.0

9.0

1.3

9.0

"hra p.p.m,

.

In the coatings

.

.

3.3

1.0

16.0

.

1.3

4.0

4.2

9.7

1.4

2.8

4.0

12.4

Au p.p.m,

.

.

.

.

10.2

4.8

2.9

5.4

5.2

.

2.8

7.6

0.1

-

5.6

4.9

Cr p.p.m,

.

.

5.9

9.3

7.0

6.7

9.7

.

6.8

45.3

-

-

1.0

3.3

As p.p.m,

.

1.46

1.41

.

1.24

1.20

1.08

0.87

0.22

0.35

0.22

0.35

% Al

.

.

-

1.91

2.38

2.73

1.65

2.01

0.88

0.98

0.41

0.29

Co p.p.m,

In the grains

-

0.82

0.88

0.73

0.69

0.84

0.22

0.29

0.16

0.28

S¢ p.p.m.

Fe-, Mn-, Na-, Au-, Cr-, As-, AI-, Co- a n d Sc-content o f the 250-315 ~ fraction of b e a c h sands, R h i n e sands, some Pleistocene sands a n d a sea.sand sample.

TABLE

w~ o~

0.22

R~

F 85

0.61

0 07

Sea sand

0 83

STB 1038 (Hell)

0.02

STB 1007 (NN)

STB 1034 (Hell)

0.10

STB 994 (NN)

0 07

0.06

STB 985 (NN)

0 07

0.36

STB 601 (S-AS)

STB 1030 (Hell)

0.16

STB 600 (S-AS)

STB 1029 (Hell)

0.48

STB 595 (S-AS)

Pleistocene sands

0.35

0.34

Re

0.30

R4

R~

119

2O

4.1

49.0

0.018

0 003

O.O25

0.036

m

37

16

22

41

2.4

17.2

104

22.4

4.9

6.9

161

9.8

5.3

5.4

22 4

1.1

1.9

0.9

CoO

r~

o

1 1 1 1 1

I l l l l

I1

II

I

I

I

I

I

I

I

I

J

I

I

I

I

I

I

I

I

IRON

AND

TRACE

ELEMENTS

IN

75

SANDS In the. grains

In the coatings

No.

% Fe

Mn p.p.m,

Na p.p.m,

Mn:~

76 87

18 19

-

15

-

57

16 14 17 19 15 19

0.015 0.011 0.016 0.018 0.016 0.011

~ p.p.m,

OffNoordwijk G727 G 730 G734 G737 G 741 G744 G748 G751 G755

0.42 0.44 0.36 0.38 0.36 0.25 0.25 0.31 0.32

41 40 45 49 36

0.018 0.020

i

Off Scheveningen G G G G G G G G G G G G G G G G G

989 993 1000 1007 1014 1021 1028 1035 1042 986 982 979 975 972 968 965 961

0.29 0.18 0.38 0.45 0.14 0.29 0.29 0.36 0.35 0.25 0.50 0.29 0.17 0.40 0.18 0.34 0.31

q

OffHoek van Hol~nd G1213 G1210 G1203 G 1196 G 1189 Gl182 Gl175 Gl168 G 1161 Gl157 G 1154 G I150 Gl147 Gl143 G 1140 Gl136 Gl133

0.22 0.33 0.32 0.62 0.49 0.22 0.22 0.23 0.25 0.17 0.94 0.97 0.62 0.36 0.48 0.42 0.36

100 120 72 -

76 69 35 -

0.011 0.012 0.012 -

E

p.p.m.

N

>0.~0%Fo >0.S0%F°

~ i

G 1133... .o ".,

°%

G

O.o

961... "%. ".°.

G 755.....

B

%

"O°o

9~°o°

F

F

[andvoort

~,Wijk aanZee IJmuiden

• 5ampting Location

258 . . . . . . . . . . . . .

Fig. 3. Fe-content of the 250-315 ~ fraction ofseasands (cf. Table II).

A

D.20-0./,0% Fe

~

~

.... ,

.< 0.20°/oFI

Noordwijk

Schevlningen

lock v, HoLiqnd

•

,Wljk oon Zee

P

IRON

AND

TRACE

ELEMENTS

IN SANDS

77

acid as the mobile phase. The Rf values found for these elements were: Sb 0.15, Co and Cr 0.65 and As 0.90, while Sb,Os, As,Os, KCr(SO4), and CoSO 4 were used as standard materials. The other elements were determined without any chemical separation. For the qualitative and quantitative measurements two multichannel analysers, connected to 3" × 3" NaI (TL) crystals, were used. The areas of the photopeaks of the elements involved were determined and compared to the areas observed for the standards.

III. RESULTS

a. Fe From Table I and Table II it is evident that with regard to iron content two groups of samples can be distinguished: 1) The Rhine sands, the Pleistocene sands of the S-AS type, the beach sands from sample 7021 up to sample 660, and the sea-sands. The 250315 ~ fraction of the sands normally contains 0.20-0.40 % Fe. The sands of this group also have a similar heavy mineral composition (EDELMAN, 1933, 1934; BAA•, 1936; VAN ANDEL, 1950; CROMMELIN, 1953) and have their source area in the Rhine basin. Most of the seasands have the same iron content as the recent Rhine sands and the adjacent beach sands, but some samples have a higher iron content ( > 0.40 % Fe) than normal, while a few samples have a comparatively low iron content ( < 0.20 % Fe; fig. 3). The area of relatively high iron content is drawn in fig. 3 as a narrow strip, but the actual distribution may be more patchy, since the distance between the rows of samples is rather wide. The Pleistocene sands show a somewhat wider variation in iron content than the recent Rhine sands and the beach sands, presumably because of leaching and secondary deposition of iron. According to its iron content also sample STB 1034 should be included in this group, although its heavy mineral composition is entirely different (CROMMELIN,1953). The very high iron content must be due to secondary deposition of iron (of. DEJONG, 1955). 2) The second group comprises the beach sands from sample 508 up to sample 137, and the Pleistocene river sands of the NN and Hell. types. The Pleistocene sands of this group have their source area presumably somewhere east of the Netherlands and were deposited sometime before the Riss glacial period (CROMMELIN, 1953). The similarity in iron content and, as will be seen below, in trace element content suggests that the beach sands and the Pleistocene sands of this group have at least partly the same origin.

78

D. E I S M A C.S.

Mn ppm 130 120 O

110

0

100

0

0

90 o

80

o

8

70 60 50 LO

oRetotivety

30

hlghMn-content

20 10

I. 0

I OJO

I 03.0

O~

I" OJ.O

0

I 0,50

I 0.60

I 0.70

I 0.80

I 0.90

I 1.00 °/oFe

I ~90

1.00 o/oFe

Fig. 4. T h e relation between Fe- a n d M n - c o n t e n t .

NO ppm 90 00 70 6O 50 "0 30 Q O

20

:

|•-

•

•

10 0.10

0

I 0.30

I 0~0

i ~50

i 060

i 0.70

I 0.80

Fig. 5. T h e relation between Fe- a n d Na-content.

i

IRON

AND TRACE

ELEMENTS

IN SANDS

79

b. Mn, Na, Au, Cr and As The same two groups as above can be distinguished with regard to Mnand Na-content (Table I, II). In the seasands, as well as in the southern beach- and recent Rhine-sands, the manganese content, with a few exceptions (samples F88, 89, 90, 93, G685, 692, 720, 1150, 1147), closely follows the iron content (fig.4). There is, however, no such relation between sodium content and iron content (fig. 5), although the sodium content of group 1 is much higher than the sodium content of group 2. The amounts of gold, chromium and arsenic do not follow the distribution of iron, manganese and sodium but vary irregularly. c. A1, Co and Sc The distribution of aluminium, cobalt and scandium is similar to the distribution of iron, manganese and sodium. Within group 1, however, these minerals occur like Na and do not follow iron closely like manganese. A1, Co and Sc were determined in the grains as a whole: they may be contained in the coatings as well as in the grains (quartz and feldspar) themselves. The 250-315 ~ fraction of the beach sands of group 1 contains about 7 % potassium feldspars and about 8 % plagioklase (determined by the method of GABRIEL and Cox (1927), improved by FAVEJEE, pers. comm.), while the same fraction of the beach sands of group 2 contains about 5 % potassium feldspars and less than 2 % plagioklase. Thus the beach sand samples of group 2 contain about 0.50 % A1 in the feldspars which is somewhat more than the Al-content as determined here (0.22-0.35 % A1). The aluminium content of the beach sand samples of group 1 (0.87-1.46% A1) indicates that the plagioklase is mainly albite.

IV. DISCUSSION

It is evident that Na, A1, Co and Sc can be used as tracers to distinguish the two types of sand that occur along the Dutch coast. Au, Cr and As are useless in this respect since they vary irregularly. Fe and Mn content is higher in the sands of group 1 than in those of group 2 but is much higher still in some of the seasands. Fig. 3 shows that the occurrence of these relatively high amounts of iron and manganese is not a general phenomenon offthe Dutch coast but is restricted to a rather small area, or perhaps to isolated patches. Three explanations may be suggested for the origin of this relatively high iron and manganese content: 1. Reworking of iron rich Pleistocene sands. PONS (1959) has described podzol soils with iron pans in the Pleistocene cover sands situated

80

D. EISMA C.S.

in the subsoil of Velsen (near IJmuiden) at 16-18 m below Dutch ordnance level (NAP). Between IJmuiden and Scheveningen the surface of these Pleistocene sands lies near the coast at about 18 m below NAP and slopes downward further south to about 25 m-NAP near Hock van Holland where a late Pleistocene valley was located (PANNEKOEK et al., 1956). On the seabottom off Zandvoort and Noordwijk the iron rich sands lie at 14-17 m depth, offScheveningen at 15 m and 18 m depth and off Hoek van Holland at 9, 12 and 21-23 m depth. Although reworked iron pans would have to be expected to occur at somewhat greater depths it should be considered a) that the seaward extension of the surface of the Pleistocene cover sands is not known, while elsewhere this surface has many local topographic irregularities (Du BURCK, 1959 ; PONS, 1959), and b) that the beach between IJmuiden and Scheveningen has steadily progressed in a seaward direction since about 1850, indicating a net transport of sand in a landward direction, which would bring the reworked iron pans in shallow water. Iron podzols also occur locally in the old holocene beachridges which are situated along the present coast (VAN DER SLEEN, 1912; VAN BAREN, 1927). South of about Scheveningen these ridges are intersected by the present coastline : erosion of the ridges may have caused local occurrences of high iron content at 9-12 m depth. 2. Deposition of iron due to the upwelling of iron-containing fresh water. BIEMOND (1940, 1948) has calculated that near ZandvoortNoordwijkerhout fresh groundwater extends from the coastal dunes seaward up to a maximum distance of about half a mile offshore. This distance depends, among other factors, on the storage capacity of the dunes for fresh water, which is related to the width of the dune belt. BIEMOND has based his calculations on the situation of 1850. Since then much fresh water has been withdrawn from the dunes for use as drinking water so that the seaward extension of the tongue of fresh groundwater is at present much reduced. The groundwater in the dunes contains about 0.5-4 mg Fe/1 and 0.05-1.0 mg Mn/1 (VAN DER SLEEN, 1912, Statistieken V.E.W.I.N. 1946-1956). Both elements are present in the bivalent state, due to the absence of oxygen. Contact of this groundwater with seawater, which is oxygen saturated, will lead to deposition of iron- and manganese hydroxydes. BISMOND (1940) has suggested that the lobe of freshwater may not reach the surface of the seabottom so that the contact between fresh water and sea water may be somewhere below the surface. If the seawater in the bottom sediment has not lost all its oxygen, a layer of iron-enriched sands may develop in the zone of contact. Subsequent erosion of the seabottom would expose these iron-enriched sands to the surface. If the relatively high iron content of the seasands discussed here, was

IRON AND TRACE ELEMENTS IN SANDS

81

formed in this way, considerable transport of sand in an offshore direction should be assumed to explain the present distribution. However, the Dutch coast has been subject to many changes since about the middle of the Atlanticum (about 7000 years B.P.) so that upwelling fresh groundwater may have caused deposition of iron and manganese when the dune belt was locally broader and/or when the coastline was situated further west, and possibly at a lower level, than at present. Very near to the beach and under the beach itself fresh groundwater is known to flow off in a seaward direction, which not results, however, in deposition of iron and manganese on the beach and in the surfzone. As this water has migrated only a relatively short distance through the dunes before flowing off, it may not have had sufficient time to dissolve iron and manganese from the dune sands. 3. Recent deposition of iron. From a chemical point of view deposition of iron along the Dutch coast is well possible. The solubility of bi- and trivalent iron as calculated by COOPER (1937) and CORRENS (1941, 1947), indicates that the amount of iron that can be present in sea water in solution is in the order of 10-8-10 -7 ~gr Fe/1. The amount of iron usually found in solution in seawater, however, is about 107 times higher (CoRRENS, 1941). In July 1963 19-50 ~gr Fe/1 was found to be present in solution in seawater sampled 2-4 miles off Wijk aan Zee (determined with ~-e-dipyridyl after filtration through a 0.8 ~ millipore filter, c.f. COOPER, 1935). These concentrations are much like those found in Pacific inshore waters (14-40 ~xgr Fe/1, THOMSONand BREMNER, 1935; 5.5--32 ExgrFe/1, LAEVASTUand THOMSON, 1958) and near the coast of Norway (3-21 ~gr Fe/1, BRAARUDand KLEM, 1931 in: H~gdahl 1963), but are high in comparison with the concentrations fbund in open ocean waters (less than 8.5 ~xgr Fe/1, H~GDAHL, 1963). These low concentrations occur over large stretches of the oceans, are remarkably uniform with depth and latitude and thus may indicate more or less equilibrium conditions, supply being balanced by deposition. On the other hand the relatively high concentrations in coastal waters may lead to a comparatively rapid deposition of iron. The exact solubility of iron and ironcompounds in seawater, however, is not known. Since the values calculated by COOPER (1937) and CORRENS (1941) are evidently far too low, CORRENSsuggested that a high solubility of iron might be caused by the presence of complex and dissolved fluorides, but COOPER (1948) showed empirically that FeF6-- is not stable in seawater. On the other hand LEwis and GOLDBERG (1954) suggested that the high iron content is caused by dissolved and colloidal organic compounds and colloidal anorganic compounds < 0.5 ~x, such as ferric hydroxyde and ferric phosphate. In view of these uncertainties it is not possible to decide whether the seawater is undersaturated or oversaturated with regard to 6

82

D. F.ISMA C.S.

iron. Deposition of iron therefore may occur, either by direct precipitation or by way of an intermediate particulate state. The presence in seawater of apparently colloidal iron containing particles > 0.5 ~ has been demonstrated among others by COOPER (1948) and GOLDBERG (1952). The particles, probably electrically charged, will tend to accumulate near the bottom and may be attached to the surface of the sandgrains which are probably also electrically charged. Moreover, there is the possibility, even if the seawater would be undersaturated with regard to iron, of deposition of iron by micro-organisms. O n the base of present knowledge iron thus may be deposited anywhere on the seabottom. Actual deposition of iron, however, apart from the iron associated with mud, is mainly known from the deep seas (c.f. MERO, 1965). Fresh water of the Rhine and the Meuse, flowing seawards through the Nieuwe Waterweg and the Haringvliet, just south of the area investigated, contains on the average 1.3 mg Fe/1 and 0.03 mg Mn/1, with a maximum of about 2.8 mg Fe/1 and 0.18 mg Mn/1 and a minimum of about 0.5 mg Fe/1 and less than 0.01 mg Mn/1 (BIEMOND, 1940, Reports Rhine-Commission 1960-1962). Most of this iron and manganese probably occurs as organic compounds and is in a bivalent state, due to the low oxygen-content of the riverwater (20-80 o/o saturation, average about 50%) and the rather low pH (7.0-7.8). They are oxydised in contact with seawater, which is saturated with oxygen and has a pH of about 8. Since the iron content of the seawater is much lower than that of the river water, the iron compounds have to be either deposited together with the clay-particles or brought into the sea in solution or suspension, and diluted. DE GROOT (pers. comm.) found that freshly deposited clays from the Haringvliet contain less iron than similar clays from the Biesbos, further inland, which indicates that adsorption of iron to the clays or deposition of colloidal iron together with the estuarine clays is improbable. It is thus more likely that the iron compounds are brought into the sea. There they may settle locally on the nearshore seabottom where they are adsorbed to the sand grains. This would mean that also some iron would be deposited among the siltyclays which are deposited on the nearshore seabottom (fig. 6). Since, however, the unconsolidated iron-enriched clays are much more easily moved than sand grains of 250-315 ?t, and thus are easily mixed with clays of normal iron content, it is not surprising that Waddensea clays have about the same iron content as the Haringvliet clays. If the sandgrains of 250-315 had been tully mixed on the sea bottom, the iron content of the seasands would have been 0.34% Fe, which does not differ m u c h from the average Fe-content of the normal sands of group l, which is 0,30 o/o Fe. This explanation points to the fact that iron deposition off the Dutch coast should be a local phenomenon, bound to the influence of fresh

IRON

AND

TRACE

ELEMENTS

IN SANDS

83

r.Wijk o.Zee

IJmuiden

*Zandvoort

Noordwijk

cheveningen

=ek t Hottand

o-1% <502~ ~ 140% <50,u. ~>10% < 50./.s.

".%

Fig. 6. Silt-clay content of the bottom sediment.

water from the Rine. This is corroborated by the salinity data available for the Dutch coast: measurements by the State Fisheries Research Institute (R.I.V.O., IJmuiden) indicate that offScheveningen salinities of 11-14 %0 CI' are not exceptional, even in the summer when riverflow is lowest, while near IJmuiden salinities are usually 15-17 %0 CI'. Fig. 7 (published here by courtesy of J.VERWEY) gives, roughly, the general distribution of salinity off the Dutch coast. Also the tongue of iron-rich seasands is drawn in fig. 7. It is evident that this tongue lies within the area of direct influence of riverwater. North of about Zandvoort the 32 ~o isohaline bends away from the coast, presumably due to increased mixing of fresh and salt water and the influx of water of lower salinity

84

D. E I S M A

C.S.

34"/~S,"

(Sur face~ / / / / / /

/ //

///

// { I

/ / I

/ /

/

/

/

/

/

)[ ,/

I /

/

/

/

-- ~-32

/"

/

,/?

£

/

/

~

~

O/ooS

/~-')

_

~

?

'/ /

I I I I

\

(Bottom)

/

/

/

\

./

j

/3"4%oS

/

/

/

/

/

/

/ I I I

/

/

/ /

ff"

t

1"

/

/

/

/

/ / /

/

Imuiden

3 / /

mdvoort

/ /

/

~

>0./,0% Fe in the 250-315~. fraction.of the Seasands

4oek ¥. HoLI.on d

Fig. 7. Average distribution of salinity along the Dutch coast (drawn by V E R W E Y after data published in the Hydrographical Bulletin 1902-1914, 1920-1937).

I R O N A N D T R A C E E L E M E N T S IN S A N D S

85

from the Waddensea through the Marsdiep. It can be assumed that north of about Zandvoort-IJmuiden the concentration of iron compounds becomes too low to lead to a detectable deposition of iron. Deposition of complex organic iron compounds seems to be more probable than direct deposition of ironhydroxyde from ions present in solution. The flocculation ofironhydroxydes takes a long time at the low concentrations of iron found in sea water (HARVEY, 1937). If deposition in this way occurred, a more regular distribution of iron in the nearshore seasands should be expected, the more so, since the content of iron present in solution in the nearshore seas of the world seems to be rather uniform. Of the three possibilities given here to explain the high iron and manganese content of some of the seasands, deposition of ironhydroxyde by upwelling fresh water is obviously the most hypothetical and leaves the present distribution of the iron-rich seasands unexplained. Reworking of Pleistocene and old-Holocene soils is a more plausible cause but it also leads to some difficulties in explaining the present distribution of the iron-rich seasands. Recent deposition of iron under influence of fresh water from the Rhine and the Meuse seems therefore the most likely cause. Further support to the latter possibility will be given below. a. the Mn/Fe ratio DEGENS (1958), comparing Ruhr- and Saar-shales, found that freshwater shales have low Mn/Fe ratio's, while the Mn/Fe ratio of marine shales is comparatively high. In Table I I I some Mn/Fe ratios of fresh water deposits and marine deposits, as found in the litterature, are listed. Not included in Table III are local accumulations such as bog iron ores. The data for the sands considered here are added. It is evident that, except for seven seasand samples which have a rather high Mn-content without a correspondingly high Fe-content (indicated in Table II with an asterisk), the beach sands and sea sands, including the seasands with high iron content, have low Mn/Fe ratio's. This would confirm the view that the iron and manganese in the iron-rich seasands are deposited under influence of fresh water. The Mn-rich sands may indicate marine influence, but may equally well point to reworking of old podzol soils, since analysis of the B-layer of similar soils from the central Netherlands (samples obtained by courtesy of the Soil Survey Institute, Bennekom) showed that in a total of 14 samples four samples had high Mn/Fe ratio's (average 0.100), while the remaining samples had rather low Mn/Fe ratio's (average 0.006), the average of all samples being 0.046. The incomplete data of PoNs (1959) indicate an average Mn/Fe ratio of about 0.001 for the podzol soils in the subsoil of Velsen.

86

D. EISMA C,S. TABLE

llI

Mn/Fe ratio of some marine and freshwater sediments. Mn : Fe

Number of samples

Norwegian Quaternary loams Mississippi silts Ferrigenous marine silts Freshwater shales (Saar) Freshwater shales (Pennsylvanian)

0.016 0.019 0.014 0.014 0.016

78 235

Marine shales (Ruhr; paralic) Marine shales (Pennsylvanian)

0.025 0.093

16 15

0.035-0.484 0.112 0.092 0.067 0.767-21.652 0.185-1.144

-5--1 10 83

Pacific deep sea clays Red deep sea clays Pacific red deep sea clays Atlantic deep sea sediments Pacific manganese nodules Atlantic manganese nodules Rhine sand J/ Beach sands fraction Normal sea sands | 250-315 bt Mn-rich sea sands

0.012 0.016 0.014 0.029

52 16 15

-

-1] 11 43 7

Author

GOLDSCHMIDT,1954 GOLDSCHMIDT,1954 GOLDSCHMIDT,1954 DEGENS,1958 KEITH and DEGENS, 1959 DECENS,1958 KEITHand DEGENS, 1959 M E R O ,1965 GOLDSCHMIDT,1954 GOLDSCHMIDT,1954 GOLDSCHMIDT,1954 M E R O ,1965 M E R O ,1965

present investigation

b. the C/N ratio The podsol soils in the subsoil of Velsen have rather high C/N ratio's, varying from 12 up to 81 (PoNs, 1951). Since these ratio's had been determined in the whole sample, the C/N ratio of the 250-315 ~ fraction of some B-layers ofpodsols from the central Netherlands was determined and found to vary between 15.8 and 45.3 (organic matter was determined by oxidation with chromic acid, N by the Kjehldahl method). The C/N ratio of the 250-315 ~t firactions of the seasands was found to vary between 0.5 and 12 with a few exceptional values of 13.8, 15.7, 27.3 and 43.5. These high values were found at localities where the composition of the bottom fauna points to the influence of fouling (EIsMA, 1965, in press), so that an admixture of organic waste is only to be expected. The lowest C/N ratio's (0.03-0.06) were found where the total amount of organic matter was less than 0.02 %, so that these ratio's can not be considered reliable. This leaves the bulk of the C/N ratio's found in the

IRON AND TRACE

ELEMENTS

IN SANDS

87

seasands between 2.8 and 11.4, with an average of 5.3. Since the C/N ratio of marine plankton is on the average about 5.7 (EMERY and RITTENBERG, 1952) this would point to a marine origin of the organic matter in this size fraction of the seasands. This organic matter can be contained in shell fragments and (or) can adhere to the sandgrains, since plantfibers or particles of peat, wood etc. were not found in this size fraction. Fresh shells contain about 0.5-4 % organic matter (VINOGRADOV, 1953). As the 250-315 ~ fraction of the seasands contains about 2-5 (weight) % of shell fragments the amount of organic matter in this size fraction, contained in shell fragments, can be calculated to vary between about 0.001 and 0.2 %. Since the actual organic content of this size fraction was found to vary between 0.006 and 0.16 °/o, this organic matter could be contained wholly in the shell fragments. The shell fragments, however, are not fresh and have been subject to a considerable fragmentation, which may have favoured (or many have been favoured by) the loss of organic matter. Somewhat coarser fragments (500-1000 ~) were found to contain 0.29-0.45% organic matter, which indicates that most of the organic matter in the 250-315 ~. fraction is adhering to the sandgrains. This is corroborated by a determination of organic content of the 250-315 ~ fractions of Rhine sands, which were found to contain 0.05-0.12 % organic matter. Since the organic matter is mainly adhering to the sandgrains, it is significant that the C/N ratio's are low. The podzols in the subsoil of Velsen and also the 250-315 ~ fraction of similar soils have high C/N ratio's. If the iron-rich sea sands had been reworked podsols, higher C/N ratio's should have been found. The assumption, however, that low C/N ratio's indicate a marine origin of the organic matter (e.g. VAN ANDEL and POSTMA,1954), is not quite valid. VAN DIJK (1959) found that in some Dutch soils the C/N ratio decreases with the amount of organic matter present in the soil (fig. 8a). A similar relation exists for the well-aerated sandy podzol soils studied by PONS (1959) and the podzol soils from the central Netherlands (fig. 8a), while the low-lying peaty, humic, loamy podzolic soils studied by PONS (1959) form an irregular group with C/N ratio's varying between 12 and 20. The decomposition of organic matter in many soils apparently leads to lower C/N ratio's. A similar effect of the aging of the soils on the C/N ratio was noticed in marine clays and peaty soils by ZI:UR (1954) and in fresh water clays in the Biesbos, a fl'esh water tidal area in the southern Netherlands, by ZONNEVELD (1960). It is evident from fig. 8 that the relation between C/N ratio and organic matter content is different for different soils, which is probably related to the original amount and composition of the organic matter in the soil and to the structure of the soil. It can therefore be expected that this relation

88

D. E I S M A

C.S.

%organic matter

100 5O

/-

/

/ 10.0

/

/

,,

J

50

j f J .+~ . + ~ + " o

++/ /

\\

i Van D+jk (19S9)

1&3

•

0.5

.~./o

0.1

o po~lzot soils ]*Pens(1959) li 9tly-humi¢ podzoLic soits / • pmzat soits<2+0-3+Sl~ Central Netherlands • Rhin* sands (250-315,tLJ . Sea sands 1250-315,~}

+

0 . 0 5 --

. ,+4. /

/ /

0.01 ~/+ 0

I

I

I

I

I

10

20

30

40

50

/

60C/N

Fig. 8 a.

Figs. 8 a-d. T h e relation b e t w e e n C / N ratio a n d c o n t e n t of o r g a n i c m a t t e r for various soils a n d sediments. %organic matter

100 50

/ /+ lOO

/

50

/

/

/ / / 10

/. " •

o;5

/

/0,

:

/

• • .

•/ / "

.

o

o.

i ."

.:./

• ~2~.J / / (Postma. unpubtished d a t a )

0.1

/0o •

o .~ >/

Q05

•

Woddensea

o

IJsetLoke

/ /o

0.01

0

Fig. 8 b.

o

I 10

I 20

I

30

I

40

I

50

I

60C/N

IRON

AND

TRACE

ELEMENTS

%organic matter 100

%organic matter 100~

50

50

IO0

100

IN SANDS

..

.

• ~. I

• e

89

..~.

•

*.'*

e

.

**

Q

50

5.0--

": "..°

•

1.0--

.'% . • •. =

° • •°

~°

o

•

tO

°

G5--

05

* Zonnivl|d {1960),Biesbes e freshwater treys detuT;jdschrlft }Ne¢LH~dl My , m a r i n e clqys t9|4-1965

0.1

0.1-(Andersohli3g)

0 0 5 --

(I01

I

10

005

0.01

I

20

I 10

I 20

310C/N

Fig.8c.

%organic matter 10C

%organic matter 1OQ -

50

50-

1QC

--

10,0

50--

50 ..:.:

t0--

I£

0.5--

0.5, •

°° eB

Gulf of

O I

Perle (Van And*It ond *hostme 19S& )

British Guio.o (DGtft Hydrouti¢ Loborotory 1982)

0.I

0.~15

0.01

Fig. 8 d.

0,05 --

I

10

I

20

(10

0

i 10

J 20

3~qN

90

D° EISMA C.S,

is less evident when different soils are compared, or when soils or sediments are compared which contain mixtures of organic matter in different stages of decomposition. This is shown in fig. 8b-8f where the relation between C/N ratio and organic matter content is given for various Dutch soils (data in Tijdschrift Ned. Heide Mij 1964-1965), Biesbos soils (ZONNEVELD, 1960), sediments from the Waddensca (PoSTMA,unpublished data), from the Gulf of Paria (VANANDEL and POSTMA,1954), from the British Guiana coast (Delft Hydraulic Laboratory 1962) and from the Atlantic between 35°-43 ° NL and 670-70 ° WL (ANDERSON,1939). The data for the various Dutch soils, the Biesbos and the Atlantic do not indicate a relation between C/N ratio and organic matter content, but it is evident from the data for the Gulf of Paria, the Guiana coast and the Waddensea that such a relation exists, although the organic matter in these sediments has a composite origin. It follows that decomposition of organic matter of terrestrial origin may lead to C/N ratio's that are similar to those found in marine sediments, which is also apparent from the data of VAN DIjK ( 1959 ; fig. 8a), the low C/N ratio's of the Rhine sands (fraction 250-315 ~t) and the data for the IJsel Lake (fig. 8b). The low C/N ratio's in marine sediments may thus be caused by continued decomposition of organic matter of terrestrial origin, by the remains of freshwater plankton and by the remains of marine plankton. This indicates that the low C/N ratio's in the ironrich seasands might have been caused by decomposition of the organic matter ofreworked podzols. This would imply, however, the removal of about 96 °/o of the organic matter in the reworkcd podzol soils, which is unlikely. Summarizing, the above considerations point to recent deposition of iron and manganese offthe Dutch coast between Hock van Holland and IJmuiden, resulting in comparatively high iron and manganese contents of some of the seasands. The other possibilities, deposition of iron by upwelling groundwater and reworking of Pleistocene podzol soils, lead to difficulties in explaining the present distribution of the iron-rich sands and their low C/N ratio's. Some of the seasands have a relatively low iron content (Table III, fig.3): the 250-315 ~ fraction of these sands contains on the average 0.17 % Fe (~ ~ 0.03), as against 0.30 % Fe in the seasands with normal iron content. These low iron contents are always associated with bluish colours in the sediment, indicating anaerobic conditions. As reduced, bivalent Fe is more soluble than trivalent iron, some Fe from the coatings goes as Fe ++ in solution in the interstitial water, probably as organic Fe++-compounds. After disturbance, the interstitial water is mixed with normal seawater and the iron is oxydized. Since hydroxyde floccules are not immediately formed and organic iron compounds not precipitated

IRON

AND

TRACE

ELEMENTS

IN SANDS

91

immediately, thisprocess resultsin a lossof iron from the sands. Solution of iron from the bottom sediment under anaerobic conditions is well known in lakes (HUTCHINSON, 1956) while a similar process of leaching occurs in the Dutch Wadden Sea and the Biesbos where brown iron-rich water can sometimes be seen flowing out of the small gullies during ebbtide. V. C O N C L U S I O N S

Determination of the Fe-, Mn-, Na-, Au-, Cr-, As-, AI-, Co- and Sccontent of the 250-315 ~ fraction of Rhine sands, Dutch beach sands and seasands collected off the southern Dutch coast, indicates that the sands which have their origin in the Rhine basin have a high Fe-, Mn-, Na-, A1-, Co- and Sc-content while sands which have their origin, presumably, somewhere east of the Netherlands, have a low, Fe-, Mn-, A1-, Co- and Sc-content. Fe, M n and Na are contained in the yellowish-brown coatings on the grains, while A1, Co and Sc may be contained in the coatings as well as in the sandgrains themselves. The A1 is probably entirely contained in the feldspars. Pleistocene river sands of different origin similarly differ in chemical composition but have a greater variation in Fe-content, presumably due to leaching and redeposition. Au-, Cr- and As-content is apparently not correlated with the origin of the sand, but varies irregularly. In the seasands relatively high Fe- and Mn-contents occur locally, although the Mn/Fe ratio is in most samples the same as in the other sands of the same origin. Na-, Co- and Sc-content, however, do not increase together with Fe- and Mn-content. The distribution of the ironrich sands on the seabottom and their C/N ratios make it probable that they are being formed by recent deposition of iron and manganese under influence of fresh water from the Rhine and the Meuse, which agrees with their Mn/Fe ratio. The other possibilities, reworking of pleistocene podzol soils and iron deposition by upwelling fresh water are less probable 1. Some of the seasand samples have a relatively low iron content, which is due to loss of iron under anaerobic conditions. 1 VAN STRAATEN,in a recent p u b l i c a t i o n (Coastal b a r r i e r deposits ~n South- a n d N o r t h - H o l l a n d . Meded. Geol. Stichting, N.S. 17, 1965, 41-75), concluded t h a t the h i g h iron content found in old b r o w n coloured shells has been due to upwelling of fresh water, w h i c h p r o b a b l y also caused the h i g h iron c o n t e n t of the sands. T h e deposition of iron in the shells however is most p r o b a b l y not due to the same process as the deposition of iron on the sandgrains. A more detailed discussion will be given in a n o t h e r paper.

92

D. ~ISMA C.S. ACKNOWLEDGEMENTS

T h e a u t h o r s a r e m u c h i n d e b t e d to D r . R . D . C r o m m e l i n , B e n n e k o m , for p r o v i d i n g t h e m w i t h s a m p l e s o f p l e i s t o c e n e r i v e r s a n d s , to Prof. D r . P . K o r r i n g a , I J m u i d e n , for t h e use o f s a l i n i t y d a t a , to P r o f . D r . H . P o s t m a a n d D r . A . J . d e G r o o t , G r o n i n g e n , for t h e i r c r i t i c a l r e m a r k s w h i l e d i s c u s s i n g t h e s u b j e c t , a n d to M i s s Y. Bosch, for c a r r y i n g o u t m o s t of the Fe- and all C- and N-analyses.

REFERENCES

ANDEL,TJ. H. VAN, 1950: Provenance, transport and deposition of Rhine sediments. Thesis Wageningen, Veenman & Zonen, 129 p. ANDEL,TJ. VAN, and H. POSTMA, 1954 : Recent sediments of the Gulf of Paria. Verh. Kon. Ned. Akad. van Wet., Afd. Natuurk., le reeks, 20 (5), 1-245. ANDERSON,D.G., 1939: Distribution of organic matter in marine sediments and its availability to further decomposition. Jour. Mar. Res. 2, 225-235. AUBOIN,G. andJ. LAVERLOCHERE, 1963 : Sfparation par des resins et changeuses d'ion appliqude h l'analyse par radioactivation. Rapport Commission de l'Energie Atomique, 2359. BAAK,J.A., 1936: Regional petrology of the southern North Sea. Thesis Wageningen, 127p. BAREN,J. VAN, 1927 : Diine und Moor bei Vogelenzang. Mitt. Geol. Inst. Landbouwhogeschool, Wageningen, 11, 1-40. BIEMOND,J., 1940: De watervoorziening van Amsterdam. Rapport Gemeentewaterleiding, I - I I I , 325+ 199 p. BIEMOND,C., 1948: De watervoorziening van Amsterdam. Toelichting. Rapport Gemeente-waterleiding, 260 p. BRAARUD,T. and A. KLEM, 1931 : Hydrographical and chemical investigations in the coastal waters off M6re. Hvalr~d. Skr. 1, 88 p. BURCK,P. DU, 1959 : Over de opbouw en de vorming van het Laagterras en de oudere holocene afzettingen in de Kop van Noord-Holland. Boor en Spade, X, 58-73. CooPER, L.H.N., 1935: Iron in the sea and in marine plankton. Proc. Royal Soc. (London), B, 118, 419-438. COOPER, L. H. N., 1937 : Some conditions governing the solubility of iron. Proc. Royal Soc. (London), B, 124, 299-307. COOPER, L. H.N., 1948: The distribution of iron in the waters of the western English Channel. Jour. Mar. Biol. Ass. U.K. 27, 279-313. CooPER, L.H.N., 1948: Some considerations on the distribution of iron in the sea. Jour. Mar. Biol. Ass. U.K. 27, 314-321. CORRENS,C.W., 1941 : Beitr~ige zur Geochemie des Eisens und Mangans. Naehr. d. Akad. d. Wiss. in GSttingen, Math. Phys. K1. H. 5, 217-230. CORRENS,C.W., 1947 : Ueber die Bildung der sediment~ren Eisenerze. Forsehungen und Fortschritte, 21/23, 59-60. CRO~ELIN, R. D., 1953" Over de stratigrafie en herkomst van de preglaciale afzettingen in Midden-Nederland. Geologie en Mijnbouw, 15, 305-321. DELFT HYDRAULICLABORATORY',1962: Demerara coastal investigation. 240 p.

IRON AND T R A C E E L E M E N T S I N S A N D S

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DECENS,E.T., 1958: Geochemische Untersuchungen zur Faziesbestimmung im Ruhrkarbon und Saarkarbon. Glfickauf, 12, 513-520. DUK, H. VAN, 1959: Samenstelling en eigenschappen van organische stof in de grond. in : Bodemkunde, 59-66. EDELMJ~N,C.H., 1933: Petrologische provincies in het Nederlandse Kwartair. Thesis Amsterdam, 104 p. EDELMAN,C.H., 1934: Die Petrologic der Sande der niederl~indischen Flfisse Rijn, Lek, Waal, Merwede und Geldersche IJssel. Meded. Landbouwhogeschool, Wageningen, 38 (3), 3-12. EMMA,D., 1965 : The distribution of benthic marine molluscs offthe main Dutch coast. Netherl. Journ. Sea Res., in press. EMERY,K.O. and S.C.RITTENBERO, 1952 : Early diagenesis of California basin sediments in relation to origin of oil. Bull. A.A.P.G. 36, 735-806. GABRIEL,A. and E. P. Cox, 1929: A staining method for the quantitative determination of certain rock minerals. American Mineralogist, 14, 290-292. GOLDBERO,E. D., 1952 : Iron assimilation by marine diatoms. Biol. Bull. 102, 243-248. GOLDSCHMIDT,V.M., 1954: Geochemistry. Oxford, Clarendon Press, 730 p. HARVEY,H.W., 1937 : The supply of iron to diatoms. Jour. Mar. Biol. Ass. U.K. 22, 1937, 205-209. HOGDAHL,O. T., 1963 : The trace elements in the ocean. A bibliographic compilation. Central Institute for Industrial Research, Oslo, 170 p. HUTCHINSON,G.E., 1956 : A treatise on limnology. I. Geography, Physics and Chemistry. New York, Willey and Sons, 1017 p. JoNo,j. D. DE, 1955: Geologische onderzoekingen in de stuwwallen van oostelijk Nederland. Meded. Geologische Stichting, N.S. 8, 33-58. KEITH,M.L. and E.T.DEOENS, 1959 : Geochemical indicators of marine and freshwater sediments. In: Researches in Geochemistry, ed. Ph.H.Abelson, N.Y. Wiley and Sons, 38-61. LAEVASTU,T. and T.G.THOMPSON, 1958: Soluble iron in coastal waters. Jour. Mar. Res. 16, 192-198. LEWIS,G.J. and E. D. GOLDBERO,1954: Soluble and particulate Fe in marine waters of the North Pacific. Jour. Mar. Res. 13, 183-197. MERO,J. L., 1965: The mineral resources of the sea. Amsterdam, Elsevier 312 p. NOTA,D.J.G. and A. M. G. BAKKER,1960 : Identification of soil minerals using optical characteristics and specific gravity separation. Meded. Landbouwhogeschool, Wageningen, 60, 1-11. PANNEKOEK,A.J. el al., 1956: Geologische geschiedenis van Nederland. Den Haag, 154 p. PONS,L.J., 1959 : Fossiele bodemprofielen in het dekzand in de tunnelput van Velsen. Boor en Spade X, 170-209. REPORTS International Commission for protection of the Rhine against pollution. Luxembourg 1953-1962. SLEEN,W. G. N. VAN DER, 1912: Bijdrage tot de kennis der chemische samenstelling van het duinwater in verband met de geo-mineralogische gesteldheid van den bodem. Thesis Amsterdam, 157 p. SOUCHAY,P. et J. FAUCHERRE,1949: Dosages polarographiques du cobalt et du fer l'aide de nouvelles solutions de base au trilon. Anal. Chim. Acta 3, 252-261. STATISTIEKENV.E.W.I.N., 1946-1956. Statistisch overzicht der Waterleidingen in Nederland. STRAATEN,L.M.J.U. VAN, 1961: Directional effects of winds, waves and currents along the Dutch North Sea coast. Geologic en Mijnbouw, 40, 333-346, 363-391. THOMPSON,T. G. and R. W. BREMNER, 1935 : The occurrence of iron in the water of the northeast Pacific Ocean. Jour. Conseil Intern. Explor. de la Mer, 10, 39-47.

94

D. EISMA C.S.

VmOGRXDOV,A. P., 1953 : The elementary chemical composition of marine organisms. Mem. Sears Found. for Marine Res. II, 647 p. ZONNEV~L9,I.S., 1960: De Brabantse Biesbos. Med. Stichting voor Bodemkartering, Bodemk. Studies 4, 396+210 p. ZUuR, A.J., 1954: Bodemkunde der Nederlandse bedijkingen en droogmakerijen. B. De hoofdsamenstelling en enkele andere z.g. chemische bestanddelen van de op bet water gewonnen gronden. Kampen, 100 p.