PROCEEDINGS OF THE 11 TH INTERNATIONAL SYMPOSIUM ON OSTRACODA WARRNAMBOOL / VICTORIA / AUSTRALIA / 8-12 JULy 1991

Ostracoda in the Earth and Life Sciences 'A. ~ 'I {e ("" I

Edited by

K.G. McKENZIE Department of Geology, University of Melbourne , Victoria, Australia

P.J.JONES Australian Geological Survey Organisation, Canberra , A.C.T , Australia

OFFPRINT

A.A. BALKEMA / ROTTERDAM / BROOKFIELD / 1993

Chemical composition of Leptocythere psammophUa carapaces (Ostracoda, Crustacea)

DIETMAR KEYSER & PATRICIA BEHRENS Zoologisches Institut und Museum. Universitiit Hamburg. 2000 Hamburg 13. Germany

MANFRED NIECKE IlIsrirurfiir Experimenralphysik. Universitiit Hamburg. 2000 Hamburg 36. Germany

ANNE MARIE BODERGAT Centre des Sciences de la Terre. Universite Claude-Bernard-Lyon 1.69622 ViIleurbanne. France

ABSTRACT: Shells of Leptocythere psammophila Guillaume 1976 have been collected in their brackish water environment from three different sampling sites (Baltic Sea, North Sea, and English Channel). The shells were analysed by means of the Proton Induced X-ray Energy Analysing system (PIXE) and the EDX-Microanalysing system connected to a Scanning Electron Microscope or a Microprobe. The detected elements. showed in some instances a connection to the environmental conditions at the sampling sites. The Sr/Ca ratio in the shells is related to the original amount of Sr in the seawater, and hence with the salinity. In the brackish water conditions in the North Sea lower Sr/Ca ratios exist than in the English Channel. An apparently different situation exists in the brackish Baltic Sea where the ratio is similar to that in the English Channel although there is lower salinity. The sediment uptake during feeding of the ostracods is thought to be the source of the Mn content of the shell. The connection of the different results are discussed and related to the environment and biology of the animal.

KEYWORDS: Recent Ostracoda, heavy metals, trace elements, crustacean calcified cuticle, PIXE, brackish water.

I INTRODUCTION

Ostracods are small crustaceans, commonly less than I mm in size, with a calcified shell enclosing the soft anatomy. They are found all over the world in different aquatic environments, and their calcified carapaces have many advantages in monitoring pollution and its status in a given environment. Because ostracods possess a calcified exoskeleton, they must shed their carapace in order to grow, and they do this several times before reaching adulthood, after which they do not moult again. The shed carapace is heavily calcified, so that after each period of moulting, the animal calcifies the new cuticle. During the moulting process, and the calcification of the new carapace, a number of trace-elements are incorporated into the shell. The amount of these trace-elements is certainly related to the environmental conditions which host the animal during the formation of the new calcified cuticle. In this case, it should be possible to infer from the composition of the ostracod shell, the environmental conditions that prevailed at the time the carapace was formed. Several attempts at determining shell composition and relating it to the environment have been made to date (Bodergat 1978, 1985; Cadot & Kaesler 1977; Chi vas et al. 1985; De Deckker

405

Figure I. Leptocythere psammophila Guillaume 1976, LV lateral view.

et al. 1988; Sohn 1958; Carbonel & TOIderer-Farmer 1988). However, it was only Bodergat (1978) who examined the cerium content in ostracod shells, and Chi vas, De Deckker & Shelley (1985) who related palaeosalinity in lacustrine lakes to the Sr ICa ratio of the ostracod shells. The latter technique appeared to be successful in determining some relationships with the environmental conditions. These authors demonstrated that it is possible to deduce the environmental conditions surrounding the animal at the time of moulting from the shell composition.

This study is aimed at determining the variation of the trace-elements in the shell of a single species, Leptocythere psammophila Guillaume 1976, from different salinities and geographical sites. The results are discussed and suggestions for further studies are proposed.

2 MORPHOLOGY OF LEPTOCYTHERE PSAMMOPHILA

The shell of Leptocythere psammophila Guillaume 1976 (Figure I) is built like the normal cuticle of podocopid ostracods. It has a thin epicuticle, a broad calcified exocuticle and a fairly small uncalcified endocuticle in adult specimens. The epidermal cell layer is situated beneath the cuticle. At the margin and the hinge, a matrix-enriched cuticle is found, thus enabling the animal to bend the cuticle at these places. The inner lamella of the carapace is only calcified at the margin , at other places, it is a thin cuticle about 0.1 IJ.m thick (Keyser 1990).

The shell is formed after moulting by the epidermal cells , which produce thin plaques of epicuticle underneath the shell, which later join together to form a thin continuous layer. Next to the epidermal cells, a network of thin cuticular filaments can be observed and is steadily growing at the top of the cells. On top of the completed epicuticle, substances are excreted, which dissolve the innermost layer of the endocuticle of the old shell and form the

406

moulting space between the old and newly developing shell. The cuticle fibres are extruded to the outside and build the new cuticular layer beneath

the old shell. After shedding the old cuticle, calcification begins and calcite crystals are deposited between the fibrils, thus enlarging the distance between the single fibres and thickening the entire new shell. This area is restricted to the region just beneath the epicuticle and a narrow sheet of remaining fibrous exocuticle. After the calcification is completed in the adult, the whole exocuticle is the largest part ot the outer lamella. A small portion of the shell remains uncalcified underneath the exocuticle, and it shows only cuticular fibres embedded in a homogenous matrix. It is referred to as the endocuticle.

3 SAMPLING SITES

The brackish water ostracod Leptocythere psammophila was sampled from three different sites: I) Bottsand near Kiel in the Baltic Sea, Germany; 2) Sahlenburg near Cuxhaven in the North Sea, Germany; 3) Roscoff along the coast of the English Channel, France (Figure 2).

Station I (S4°2S.4S'N, 10017.77'E) at Bottsand is situated at the mouth of the Kieler Forde in the western Baltic Sea. It is a nature reserve and a brackish water marsh area. The Baltic Sea in this region has a salinity of about 16 ppt. The actual sampling area is very shallow, and the tides in this region, which amount to a maximum of O.S m, mostly leave the sea floor exposed during low tide. During very hot summer days, the salinity can rise on the exposed seafloor to about 30 ppt (this study). Leptocythere are gathered here while feeding on diatoms in the small puddles which remain on the sandy and slightly muddy surface during lower tide. The area of Bottsand lies near the big sailing port of Wentorf Marina, where pollution takes place, caused by the painting of ships, and especially of their submerged hulls. Other environmental effects which influence the water in this area are the waste of the marina and the town of Wentorf, and the industrial and domestic waste in the Kieler Forde from the city of Kiel (population 600 000).

Station 2 (S4°S2.80'N, 08°3S.91 'E) lies in the North Sea near Sahlenburg, next to Cuxhaven at the mouth of the River Elbe. The sampling site is in the Waddenmeer area, where at each low tide the whole sea floor becomes dry for up to 20 km. The salinity varies here more than at Station I, as the North Sea has a salinity of about 33-3S ppt. During our sampling we measured a salinity of 27 ppt in April and 22 ppt in September. The temperature is very different on the exposed sea floor, with ice in winter, and with a drying phase in summer when a temperature of 40°C or more can be reached. But in the substrate (Smm depth) the seawater temperature is mostly maintained at 18-20°e. The environ­mental impact at this station is fairly high. The water masses discharged by the Elbe and Weser rivers are some of the most polluted in the North Sea. The sewage of nearby Cuxhaven is mostly discharged into the Elbe, but it also affects the coastline where the station is located.

Station 3 (48°41.3S'N, 03°36.40'W) is situated east of the small town of Roscoff at the southern end of the English Channel. Here the salinity was about the same as in the open ocean during our sampling, although during summer the salinity can rise to more than SO ppt. There the same conditions as at the other sites are found. The environmental conditions here appear pristine, with no proximity to a large city, and no discharge of rivers. In 1981 a large oilspill did occur at this beach which polluted the whole area. Since then, the ostracod

407

Leptocythere psammophila has returned to the area and appears to be almost exclusively the only habitant there.

Location Map

·0 ~ . ....

FRANCE

Figure 2. Location map.

408

4 METHODS

Sampling was done at Iow tide at nearly dried up sites where only small puddles remained. The substrate was sampled using a 180llm handnet, with the residue washed and taken to the laboratory. The samples were then put into a small aquarium and close to a window. The following day, most of the living animals gathered at the side directed towards the light, and were sucked out with a pipette. They were rinsed in distilled water, and either transferred into 70% ethanol or prepared for the analyses.

The valves used for analyses were freed from the body with the aid of fine needles and stored dry in slides. During preparation for the Proton Induced X-ray Emission-analysis (PIXE) they were thoroughly washed in distilled water and inspected for remaining debris adhering to the shell. They were then placed on a fine organic foil which covered the object holder for the PIXE. This membrane and the glue used were analysed to ensure that they did not contain any elements of the kind under investigation. After this, the shells were analysed using the characteristic X-rays induced by a 2 MeV proton beam. A detailed description of the experimental setup is given in Grossmann et al. (1990).

For comparison, several shells were also analysed by Energy-Dispersive-Analysis of X-rays (EDX) (ORTEC 6230) attached to a CAMS CAN DV4 scanning electron micro­scope. In this case, the shells were cleaned following the same procedures, but then coated with carbon, analysed, and photographed.

For sediment analysis, cores were taken, dried over five days at 30°C and weighed. The organic material was then eliminated by heating for two hours at 600°C and weighed again. The difference between the dried and heated sediment is given as the amount of organic substance. The heated sediment was set to 100% and the different grain sizes related to this value (Figure 3). Water analyses of filtered (0.2Ilm) water were done by using ICP-AES­Spectroscopy. These data are given in Table 2. Morphological investigations were per­formed with a SEM (CAMS CAN DV4) and a TEM (ZEISS EM 9).

5 RESULTS

The analysis performed with the different methods showed that the PIXE-analysis was more sensitive than the EDX-analysis. The EDX could analyse about I ng of Fe, while the PIXE could detect 0.1 ng or even less. It clearly showed that the detection limits of heavier metals, starting with K and higher elements were at least 10 times lower in the PIXE than in the EDX. So with detection limits in the vicinity of 0.05-0.1 Ong PIXE is one of the most powerful pieces of analytical equipment available. It is especially useful because the analysing area is well defined and easily adjusted, so one can analyse a certain area, which is often not possible for other types of chemical analysis. Our results from the PIXE analyses are presented in Table 1.

5.1 Substrate

The substrate in all three stations differed only slightly. Leptocythere seems to prefer fine sand with little organic matter. Grain size is mainly smaller than 250llm (Figure 3).

The substrate at Bottsand has the lowest organic content (4.18%) of all three stations.

409

Table I. Leptocythere psammophila: PIXE analysis of shells in ng.

Station Date Ca Mn Fe Cu Sr

Bottsandl 01.04.87 916 0.23 0.72 0.13 11.62 856 0.25 1.22 0.09 10.43 870 0.24 3.02 0.13 10.61 991 0.22 2.15 0.13 10.94 921 0.32 1.35 0.14 10.71 891 0.25 1.48 0.17 10.99 891 0.39 2.42 0.13 10.45 758 0.23 1.39 0.15 9.79 795 0.31 0.95 0.13 9.57 786 0.40 0.76 0.13 9.71

Bottsand2 14.11.86 753 0.00 0.83 1.37 7.67 897 0.00 1.17 1.16 9.19 743 0.00 1.20 0.40 8.79 872 0.00 1.22 0.57 9.30 861 0.00 0.00 0.00 0.00 855 0.00 0.00 0.00 0.00 806 0.19 1.26 0.88 9.04 739 0.10 1.18 0.77 8.25

Roscoff 18.03.87 873 0.00 3.25 0.14 10.13 1009 0.00 3.70 0.15 10.31 859 0.00 1.22 0.12 8.52 819 0.00 0.98 0.13 8.29 797 0.00 1.41 0.00 7.50 907 0.00 0.00 0.00 0.00 756 0.00 1.92 0.15 7.79 779 0.07 1.18 0.10 7.61 853 0.14 1.10 0.08 6.29 910 0.00 1.69 0.27 9.76 862 0.00 2.64 0.16 8.18

1016 0.00 3.01 0.13 11.12 1180 0.00 3.69 0.10 11.45 872 0.00 0.98 0.16 9.36

Sahlenburg 1 31.03.87 750 0.77 4.83 0.13 7.81 632 0.00 1.80 0.13 6.14 802 0.62 1.76 0.21 8.81 698 0.59 2.53 0.19 6.97 694 0.00 0.00 0.00 0.00 766 0.66 1.68 0.13 7.64 780 0.00 0.00 0.00 0.00 760 0.65 1.20 0.19 8.75 807 0.64 4.46 0.11 7.61 680 0.66 1.95 0.15 6.17

Sahlenburg2 17.09.88 540 0.78 0.88 0.15 5.72 609 0.75 1.14 0.15 6.09 720 1.28 1.95 0.08 8.80 686 1.28 1.78 0.06 8.67 540 0.73 1.00 0.13 5.92 589 0.73 1.18 0.10 6.40

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Table 2. ICP-AES water analyses at the different stations. Salinity in parts per thousand = ppt; all elemental values in mg/I.

Station Date ppt Ca Mn Fe Cu Sr

Bottsandl 01.04.87 12.3 183 0.12 0.62 0.020 3.30 Bottsand2 17.09.87 15.2 142 0.020 2.60 Sahlenburg 1 31.03.87 26.8 235 0.10 0.050 0.020 4.40 Sahlenburg2 17.09.87 24.1 142 0.017 2.60 Roscoff 18.03.87 33.4 340 0.01 0.50 0.020 6.40 Roscoff 04.10.87 35.0 310 0.020 6.30

The grain size, with nearly 60% between 1251lm and 250llm, and another 34% between 63Jlm and I 251lm, is the coarsest of the three sites.

Sahlenburg has a substrate with the highest organic content (8.24%) of the total dry weight. The grain size is smaller than that in Bottsand, with a maximum of 64% between 65Jlm and I 25Jlm. The overall appearance is mostly muddy. The colour is light grey, which indicates a high clay content in the sand, which is probably in the 21 % of the fraction less than 63Jlm.

At Roscoff the substrate consists mainly of sand, with an organic portion amounting to 4.81 % of the dry weight. Fifty percent of the sand has a grain size between 631lm and I 25Jlm, and 33% of the fraction is less than 631lm. This is the finest grain size of all three sites, but the Roscoff samples, unlike those from Sahlenburg, do not contain mud.

5.2 Elements incorporated in the shell

The largest concentration of the trace-elements occurs in the exocuticle, where the main mineral constituent is calcium carbonate as calcite. Ca is always present in about the same absolute amount in a fully calcified adult specimen. This is true not only in the marine environment, but also in brackish water, although in brackish water one finds more shells which are not quite fully calcified than in the marine areas.

The water chemistry at the three different stations shows a calcium content which seems to be related to the salinity. In Bottsand we find a salinity of about 15 ppt and a Ca content about 183mg/1 while in Sahlenburg the salinity is 27.3 ppt and 235mg/1 Ca and in Roscoff we find 35 ppt with 340mg/1 (Table 2).

In spite of the different concentrations in the water, the amount of calcium in fully calcified shells did not vary much in our investigation. Only, the number of specimens found with lesser calcified shells was higher in Bottsand than at the other sites. In one shell we could detect about I mg of Ca (Table 1). No animals with unbranched radial pore canals were included in our study, because they show a lesser degree of calcification. The branching of the radial pore canals occurs only when the calcification has proceeded as far as to include the first ganglia of the radial nerves in the calcified area.

As with Ca, the amount of Sr in the water samples also showed a direct relationship with salinity: Bottsand 3.3mg/l, Sahlenburg 4.4mg/l, and Roscoff 6.4mg/1 (Table 2).

Measured against the other elements (Mn, Fe, Cu), Sr is found in fairly high concentra­tions in the shells of all animals in this study (Table 1). At Roscoff, it occurs in a smaller

411

ngx100 8o.---------------------------------~80

80+-------------~~1---------------~~80

40+---------~---- ----------------~~~40

20+---------~---

1000 600 260 126 83 c83

um

20

o organic·) Mn(ngx100)

_ Bottaand _ 8ahlenburg trH\) Roacoff

·)Organlc alllOunt of whole dry weight

Figure 3. Grain size analysis, with Mn analyses of shells included for comparison.

amount than in Bottsand, although the amount of Ca in the shells is about equal in animals from both stations. A particular location on the carapace could not be associated with Sr.

Significant for the coast of the North Sea is the high amount of Fe and Mn observed in the shell. The amount of Mn in the shells from Bottsand was less than in Sahlenburg, but it was definitely higher than in Roscoff.

The water analysis shows only a slightly higher amount of Fe and Mn in Bottsand than in the other stations, where the concentration of these elements were under the detection limits of the ICP.

412

Cu was very high in shells from Bottsand in spring 1987; however, the water analysis for this station does not give any hint of the origin of this Cu value.

3.6r---------------------------------------~

Ca

_ ·aott8.1

_ aahlenb.2

Sr Mn

_ &Ott8.2

Il!i!!iliI Roacoff 1

Figure 4. Mean values of elements in the shell.

6 DISCUSSION

Fe Cu

m0~J aahlenb. 1

Generally it can be said that there is some variation between the individual concentrations of the elements. However, taking the mean value, it is possible to come up with useful trends (Figure 4, Table 3).

Analyses on Sr in ostracods have already been carried out, especially by Chivas & De Deckker (1983, 1985, 1988), who found that the shells of ostracods contain Sr and Ca in a certain ratio, and this ratio varies with the amount of salinity of the water. These observations were based on analyses of animals from saline lakes in Australia. In our samples from brackish water to marine conditions we find a comparable situation. The

413

10 ;..&~/~C~a~(x~~~3~) ______________________ --,

8

8

1-----____ ---4

2

oL-~-----L----__ ~L-______ ~ ______ -J

-12.3 16.2 -24.1

0/00 Salinity

28.8

- SMIle -+-- Water

33.4

Figure 5. Sr/Ca ratio of shells and ambient water at the study sites against salinity.

animals of Bottsand (15 ppt) had a higher Sr /Ca ratio than the animals of the North Sea and the Channel (35 ppt).

If we compare the data from the water samples and the shell data we get to an interesting problem. Although the salinity and the amount of Ca and Sr in the water rises from Station 1 to 3, we find that the amount of Ca and Sr in the shells of ostracods from the respective samples declines (Table 4). The relationship is graphed in Figure 5 using the mean values of Sr/Ca in the water and the shells at each locality. The results show an unexpected lowering of the Sr/Ca amount in the shells compared to a rising of Sr/Ca in the water.

This finding is different from the results of Chi vas et al. from the salt lakes in Australia. One explanation might be that the total amount of Ca in the salt lakes they investigated was about one-tenth of the measured values of our brackish water station. The explanation for the lowering of Sr in our samples from higher concentrations is not easy, but could be related to the ease of calcification for the animals in Ca-rich water, e.g. at the Roscoff marine station. Here the water contains so much Ca that calcification proceeds rather rapidly thus accounting for the relatively low amount of Sr which is fortuitously absorbed into the cuticle. At Bottsand however, the ambient water is low in Ca, the time taken for calcification is longer, and hence there is more opportunity for the chance uptake of Sr.

So as we understand it, the important factors governing the incorporation of Sr into the shell are the amount of Ca in the ambient water and also the time taken for the calcification process. If this idea is correct, there should be an upper limit for Ca in the ambient water

414

Table 3. Leptocythere psammophila: mean values (in ng/meq) of the chemical elements found in the ostracod shells at the different stations.

Station Ca Mn Fe Cu Sr

Bottsandl 867/43.26 0.28/0.010 1.55/0.056 0.13/0.004 10.48/0.24 Bottsand2 815/40.67 0.15/0.006 1.14/0.041 0.86/0.027 8.71/0.20 Sahlenburg I 737/36.78 0.68/0.025 2.53/0.091 0.16/0.005 7.49/0.17 Sahlenburg2 614/30.64 0.92/0.033 1.32/0.047 0.11/0.003 6.93/0.16 Roscoff 892/44.51 0.105/0.004 2.06/0.074 0.14/0.004 8.95/0.20

Table 4. Leptocythere psammophila: Sr/Ca analysis of shells and water from the different stations. Values for water in meq/l; values for shells in meq; Sr/Ca ratios at 10-3.

Station Salinity Water Water Shell Shell Water Shell ppt Sr Ca Sr Ca Sr/Ca Sr/Ca

Bottsandl 12.3 0.0753 9.1317 0.239 43.26 8.25 5.52 Bottsand2 15.2 0.0593 7.0858 0.199 40.67 8.37 4.89 Sahlenburg I 26.8 0.1004 11.7265 0.171 36.78 8.56 4.65 Sahlenburg2 24.1 0.0593 7.0858 0.158 30.64 8.37 5.16 Roscoff 33.4 0.1438 15.4690 0.204 44.51 9.29 4.58

such that there is no measurable change in the Sr/Ca ratio for Ca values above this limit. More work is required to find out whether or not the Sr ICa and ambient water Ca

relationship is different in other marine environments in which water temperature might affect the calcification time.

The high value ofMn in the shells in our study from Sahlenburg (Figure 6) can normally be referred to the high amount of organic debris, which seems always to be correlated with the occurrence of Mn in the water. The theoretical explanation for this relates the appearance of Mn to the amount of 0 available via the organic particles.

In our samples, the amount of organic material at Sahlenburg is about double that of the other stations, although the total figure (8%) is not very high in comparison to other substrates. Studies in the River Elbe have shown that the amount of Mn is extremely high in the filtered organic material from the water column (Forstner et al. 1988). MnO 'coats' the organic parts. Its origin could be resuspended sedimental sources or autochthonous, forming in the water column. An interesting result is that some heavy metals can be resuspended into the water column only when the 0 saturation is zero. This might also account for the availability of MnO at organic surfaces in the Waddenmeer (Forstner et al. 1990).

For most of the animals this organic debris is the source of Mn, while Fe and AI are derived rather from the muddy substrate. Both of these substances are taken up by Leptocythere during feeding, which enables the animals to incorporate a measurable amount of these elements into their shells.

Fe itself does not show any particular pattern. It is about equally distributed throughout the shells, although there is a difference in Fe concentration in the water at the three sample sites. This implies that the incorporation of Fe into the shells may be specially regulated.

The case with Cu is different. Normally, its distribution in the shells at all stations is comparatively low. The only exception was at Bottsand in Autumn 1986. Here the amount

415

12

10

8

8

4

2

° R08coff 8,92 8,96 0,106 0,14 2,08 Sahlenb.2 8,14 8,93 0,92 0,11 1,32 Sahlenb.1 7,37 7,49 0,88 0,18 2,63 Bott8.2 8,16 8,71 0,16 0,88 1,14 8ott8.1 8,87 10,48 0,28 0,13 1,66

_ Botta.1 _ Botta. 2 tW~iil8ah"nb.1

_ Sahlenb.2 II!i!lmD Roacoff

Figure 6. Mean values of elements in the shell.

in the shell was high while the water chemistry did not show any abnormal conditions. The available data from the Baltic at that time give fairly high eu amounts in autumn and spring and a decline during the summer, reaching another high the following spring. Whether this had some connection to painting the hulls of ships, or with the lack of 0 saturation as already mentioned in connection with Mn is not yet clear and will be studied. Nevertheless, it is interesting that so much eu is incorporated into the ostracod shells. This might enable us to judge the grade of pollution, relative to eu, just by analysing ostracod shells.

Although only limited in its scope and data base, this study shows strikingly that, with the right analytical equipment, the ostracod shell has a remarkable potential for assessing environmental impacts.

416

7 SUMMARY

Leptocythere psammophila GuiIIaume 1976 was analysed for trace elements from three stations with different salinities: Bottsand, Kieler F6rde, Baltic Sea (Germany), Sahlen­burg, German Bight, North Sea (Germany), and Roscoff, English Channel (France). The substrate at all 3 sites differed only slightly. Grain size is mainly smaller than 250~m indicating that the species seems to prefer a fine sand sediment with little organic matter. The Sr/Ca ratio in the shells is inversely proportional to the amount of Ca (and also the salinity) of the ambient water at our sites. We explain this by reference to the process, and duration, of calcification at differing concentrations of ambient Ca. Mn is highest in the shells of animals from Sahlenburg, because of the feeding pattern of the species on organic debris with a 'coating' of MnO. Cu values are extremely high in the spring swarms at Bottsand; this is thought to be related to the local occupational practice of painting the hulls of ships, or to a severe lack of 0 just prior to the last moulting of the animals.

ACKNOWLEDGEMENTS

We thank Miss R. Waiter, Hamburg, for help in the preparation of the animals and with the manuscript; Miss M. HaneJ, Hamburg, for her drawings; and the DAAD, Bonn, for help with traveIling expenses. Dr Meyberg, from the Staatshiitten Laboratorium in Hamburg, also deserves our thanks for carrying out the water chemistry analyses.

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