The misrepresentation of the planktonic diatom assemblage in traps and sediments: southern Lake Malaŵi, Africa
Tóm tắt
Sediment trap collections near Cape Maclear, Lake Malaŵi, were compared to phytoplankton and surface sediment diatoms to assess taphonomic variations. The sedimenting diatom community became progressively different from the diatom plankton with increasing depth: long Nitzschia species were strongly under-represented in the traps (annually, 53% among planktonic diatoms vs. 14% in the offshore 29 m trap; p≪0.005 by Kruskal-Wallis test), while Melosira was greatly over-represented in traps (32% vs. 57%; p<0.005). The abundances of the minor taxa (Rhopalodia, Fragilaria, Cymbella, and Surirella) were greatly enhanced in traps relative to the plankton, but they were still relatively uncommon (<3% of all diatoms each). Differences in grazing, dissolution, and sinking rates alone are insufficient to account for these distortions; a combination of these, plus perhaps unknown factors, strongly influence the deposited assemblage. These misrepresentations were also present at the sediment surface. The greatest discrepancy was noted for Melosira (32% of plankton vs. 53% of sediment surface diatoms; p<0.005) and for elongate Nitzschia species (53% of plankton vs. 0.8% in sediments; p<0.005). In Lake Malaŵi, at least, paleolimnologists must not assume a straightforward correlation of modern and fossil assemblages.
Tài liệu tham khảo
BattarbeeR. W., 1981. Changes in the diatom microflora of a eutrophic lake since 1900 from a comparison of old algal samples and the sedimentary record. Holarc. Ecol. 4: 73–81.
BeadleL. C., 1981. The inland waters of tropical Africa. 2ed. Longman, New York. 475 pp.
BeauchampR. S. A., 1953. Hydrological data from Lake Nyasa. J. Ecol. 41: 226–239.
BeauchampR. S. A., 1964. The rift valley lakes of Africa. Verh. int. Ver. Limnol. 15: 91–99.
BloeschJ. & N. M.Burns, 1980. A critical review of sediment trap technique. Schweiz. Z. Hydrobiol. 42: 15–55.
BlomqvistS. & L.Hakanson, 1981. A review on sediment traps in aquatic environments. Arch. Hydrobiol. 91: 101–132.
BonnyA. P., 1976. Recruitment of pollen to the seston and sediment of some English Lake District lakes. J. Ecol. 64: 859–887.
DavisM. B., 1963. On the theory of pollen analysis. Amer. J. Sci. 261: 897–912.
DavisM. B. & L. B.Brubaker, 1973. Differential sedimentation of pollen grains in lakes. Limnol. Oceanogr. 18: 635–646.
EcclesD. H., 1974. An outline of the physical limnology of Lake Malaŵi (Lake Nyasa). Limnol. Oceanogr. 19: 730–742.
EppleyR. W., 1977. The growth and culture of diatoms. In WernerD. (ed), The Biology of Diatoms. University of California Press, Berkeley. 498 pp.
FaegriK. & J.Iverson 1975. Textbook of pollen analysis. 3ed. Monksgaard, Copenhagen, 295 pp.
FerranteJ. G. & J. I.Parker, 1978. The influence of planktonic and benthic crustaceans on silicon cycling in Lake Michigan, USA. Verh. int. Ver. Limnol. 20: 324–328.
GardnerW. D., 1980. Field assessment of sediment traps. J. Mar. Res. 38: 41–52.
HaberyanK. A., 1985 The role of copepod fecal pellets in the deposition of diatoms in Lake Tanganyika. Limnol. Oceanogr. 30: 1010–1023.
Haberyan, K. A., 1988. Phycology, sedimentology, and paleolimnology near Cape Maclear, Lake Malaŵi, Africa. Ph. D dissertation, Duke University, Durham, N. C. 246 pp.
Haberyan, K. A. & O. K. Mhone, submitted. Observations on the algae near Cape Maclear, southern Lake Malaŵi, Africa. 21 ms pp., 6 tab., 6 fig. Submitted to Limnol. Oceanogr., December 1988.
HaworthE. Y., 1976. The changes in the composition of the diatom assemblages found in the surface sediments of Blelham Tarn in the English Lake District during 1973. Ann. Bot. 40: 1195–1205.
HaworthE. Y., 1980. Comparison of continuous phytoplankton records with the diatom stratigraphy in the recent sediments of Blelham Tarn. Limnol. oceanogr. 25: 1093–1103.
HeckyR. E. & H. J.Kling, 1987. Phytoplankton ecology of the great lakes in the rift valleys of central Africa. Arch. Hydrobiol. Beih. Ergebn. Limnol. 25: 197–228.
HonjoS., 1976. Coccoliths: production, transportation, and sedimentation. Mar. Micropaleontol. 1: 65–79.
HustedtF., 1949. Susswässer diatomeen. In Exploration du Parc National Albert, Mission 2, fasc. 8. Institute des Parcs Nationaux du Congo Belge, Brussels, 199 pp.
HutschinsonG. E., 1957. A treatise on limnology, v. 1(1). The geography and physics of lakes. Wiley, New York. 540 pp.
JohnsonT. C. & R. E.Hecky, 1988. A silica budget for Lake Malaŵi: net fluvial input, biogenic opal preservation and burial. Eos 69: 1144 (abstract).
Owen, R. B., R. Crossley, T. C. Johnson, S. Davidson-Hirschmann, D. Tweddle, D. Eccles & D. E. Engstrom, in prep. Major low levels of Lake Malawi and implications for evolution rates in cichlid fishes. 24 ms pp.
PorterK. G., 1973. Selective grazing and differential digestion of algae by zooplankton. Nature 244: 179–180.
SchraderH. J., 1971. Fecal pellets: role in sedimentation of pelagic diatoms. Science 174: 55–57.
SimolaH., 1977. Diatom succession in the formation of annually laminated sediment in Lovojärvi, a small eutrophicated lake. Ann. Bot. Fennici 14: 143–148.
VanMeelL., 1954. Le phytoplancton. In Exploration Hydrobiologique du Lac Tanganyika, vol. 4(1). Institute Royal des Sciences Naturelles de Belgique, Brussels. 680 pp.