Skip to main content

Diatom-derived palaeoconductivity estimates for Lake Awassa, Ethiopia: evidence for pulsed inflows of saline groundwater

Abstract

A 6,500-year diatom stratigraphy has been used to infer hydrochemical changes in Lake Awassa, a topographically closed oligosaline lake in the Ethiopian Rift Valley. Conductivity was high from ~6400-6200 BP, and from 5200-4000 BP, with two brief episodes of lower conductivity during the latter period. Although the timing of the conductivity changes is similar to the timing of lake-level change in the nearby Zwai-Shalla basin, their directions are the reverse of that expected from a climatic cause. Dissolution of the tephras which precede both phases of high conductivity cannot explain the increases in salinity, because rhyolitic tephras are only sparingly soluble. Instead, the pulsed input of groundwater made saline by the reaction of silicate minerals and volcanic glass with carbonic acid, formed from the solution of carbon dioxide degassed from magma under the Awassa Caldera, is suggested as a plausible mechanism for the observed change in lake chemistry. Diatom-inferred hydrochemistry cannot therefore be used to reconstruct climate change in Lake Awassa.

This is a preview of subscription content, access via your institution.

References

  1. Abella, S. E. B, 1988. The effect of the Mt. Mazama ashfall on the planktonic diatom community of Lake Washington. Limnol. Oceanogr. 33: 1376-1385.

    Google Scholar 

  2. Barker, P. A., N. Roberts, H. F. Lamb, S. van der Kaars & A. Benkaddour, 1994. Interpretation of Holocene lake-level changes from diatom assembalages in Lake Sidi Ali, Middle Atlas, Morocco. J. Paleolim. 12: 223-234.

    Google Scholar 

  3. Baross, J. A., C. N. Dahm, A. K. Ward, M. D. Lilley & J. R. Sedell, 1982. Initial microbiological response in lakes to the Mt. St. Helens eruption. Nature 296: 49-52.

    Google Scholar 

  4. Battarbee, R. W., 1986. Diatom analysis. In Berglund, B.E., (ed) Handbook of Holocene Palaeoecology and Palaeohydrology. John Wiley & Sons, Chichester: 527-570.

    Google Scholar 

  5. Berhanu G., 1996. The origin of high bicarbonate and fluoride concentrations of the Main Ethiopian Rift Valley, East African Rift system. J. Afr. Earth Sci. 22: 391-402.

    Google Scholar 

  6. Bischoff, J. L. & R. J. Rosenbauer, 1996. The alteration of rhyolite in CO2 charged water at 200 and 350°C-the unreactivity of CO2 at higher temperature. Geochim. Cosmochim. 60: 3859-3867.

    Google Scholar 

  7. Broecker, W. S., R. Wanninkhof, G. Mathieu, T. H. Peng, S. Stine, S. Robinson, A. Herczeg & M. Stuiver, 1988. The radiocarbon budget for Mono Lake: An unsolved mystery. Earth planetary Sci Lett. 88: 16-26.

    Google Scholar 

  8. Darling, W. G., Berhanu G. & M. K. Arusei, 1996. Lake-groundwater relationships and fluid-rock interactions in the East African Rift Valley: isotopic evidence. J. Afr. Earth Sci. 22: 423-431.

    Google Scholar 

  9. Dawson, J.B., 1966. Oldoinyo Lengai-an active volcano with sodium carbonatite lava flows. In Tuttle, O. F. & J. Gittins (eds), Carbonatites. J. Wiley & Sons, NY. 155-168.

    Google Scholar 

  10. Dean, W. E., 1974. Determination of carbonate and organic matter in calcareous sediments and sedimentary rocks by loss on ignition: Comparison with other methods. J. sedimentary Petrol. 44: 242-248.

    Google Scholar 

  11. Di Paola, G. M., 1972. The Ethiopian Rift Valley (between 7°00′ and 8°40′lat North). Bull. Vulcanol. 36: 517-560.

    Google Scholar 

  12. Elizabeth K., Zinabu G.-M. & I. Ahlgren, 1994. The Ethiopian Rift Valley lakes: Chemical characteristics of a salinity-alkalinity series. Hydrobiologia 288: 1-12.

    Google Scholar 

  13. FAO, 1984. Agroclimatological data for Africa. Food and Agriculture Organization of the United Nations, Rome.

  14. Farrar, C. D., M. L. Sorey, W. C. Evans, J. F. Howle, B. D. Kerr, B. M. Kennedy, C.-Y. King & J. R. Southon, 1995. Forest-killing diffuse CO2 emission at Mammoth Mountain as a sign of magmatic unrest. Nature 376: 675-678.

    Google Scholar 

  15. Foucault, A., & D. J. Stanley, 1989. Late Quaternary paleoclimatic oscillations in East-Africa recorded by heavy minerals in the Nile Delta. Nature 339: 44-46.

    Google Scholar 

  16. Freeze, R. A. & J. A. Cherry, 1979. Groundwater. Prentice-Hall, Englewood Cliffs, 604pp.

  17. Gasse, F., 1977. Evolution of Lake Abhé (Ethiopia and TFAI) from 70,000 b.p. Nature 265: 42-45.

    Google Scholar 

  18. Gasse, F., 1986. East African diatoms: Taxonomy, ecological distribution. Bibliotheca Diatomologica, Band 11. Cramer, Berlin, 201pp.

  19. Gasse, F. & C. Descourtieux, 1979. —Diatomées et évolution de trois milieux Ethiopiens d'altitude différente, au cours du Quaternaire supérieur. Palaeoecol. Africa 11: 117-134.

    Google Scholar 

  20. Gasse, F. & F.A. Street, 1978. Late Quaternary lake-level fluctuations and environments of the northern Rift Valley and Afar region (Ethiopia and Djibouti). Palaeogeogr. Palaeoclim. Palaeoecol. 24: 279-325.

    Google Scholar 

  21. Gasse, F., S. Juggins & K. Ben Khelifa, 1995. Diatom-based transfer functions for inferring past hydrochemical characteristics of African lakes. Palaeogeogr. Palaeoclim. Palaeoecol. 117: 31-54.

    Google Scholar 

  22. Gasse, F., P. Barker, P.A. Gell, S.C. Fritz & F. Chalié, 1997. Diatominferred salinity in palaeolakes: An indirect tracer of climatic change. Quat. Sci. Rev. 16: 547-563.

    Google Scholar 

  23. Gasse, F., R. Téhet, A. Durand, E. Gilbert & J.Ch. Fontes, 1990. The arid-humid transition in the Sahara and the Sahel during the last deglaciation. Nature 346: 141-156.

    Google Scholar 

  24. Gillespie, R., F. A. Street-Perrott & R. Switsur, 1983. Post-glacial arid episodes in Ethiopia have implications for climate prediction. Nature 306: 680-683.

    Google Scholar 

  25. Gittins, J., 1966. Summaries and bibliography of carbonatite complexes. In Tuttle, O. F. & J. Gittins (eds), Carbonatites. J. Wiley & Sons, NY. 417-540.

    Google Scholar 

  26. Grimm, E.C, 1987. CONISS: a FORTRAN 77 program for stratigraphically constrained cluster analysis by the method of incremental sum of squares. Computers Geosci. 13: 13-35.

    Google Scholar 

  27. Grove, A. T., F. A. Street & A. S. Goudie, 1975. Former lake levels and climatic change in the rift valley of southern Ethiopia. Geograph. J. 141: 177-202.

    Google Scholar 

  28. Haberyan, K. A. & R. E. Hecky, 1987. The late Pleistocene and Holocene stratigraphy and paleolimnology of Lakes Kivu and Tanganyika. Palaeogeogr. Palaeoclim. Palaeoecol. 61: 169-197.

    Google Scholar 

  29. Hecky, R. E. & P. Kilham, 1973. Diatoms in alkaline, saline lakes: ecology and geochemical implications. Limnol. Oceanogr. 18: 53-71.

    Google Scholar 

  30. Hickman, M. & M. A. Reasoner, 1994. Diatom responses to late Quaternary vegetation and climate change, and to deposition of two tephras in an alpine and a sub-alpine lake in Yoho National Park, British Columbia. J. Paleolim. 11: 173-188.

    Google Scholar 

  31. Inbar, M., H. A. Ostera, C. A. Parica, M. B. Remesal & F. M. Salani, 1995. Environmental assessment of 1991 Hudson volcano eruption ashfall effects on southern Patagonia region, Argentina. Economic Geol. 25: 119-125.

    Google Scholar 

  32. Johnson, M. C., A. T. Anderson & M. J. Rutherford, 1994. Preeruptive volatile contents of magmas. Re-views in Mineralogy 30: 281-330.

    Google Scholar 

  33. Krammer, K. & H. Lange-Bertalot, 1986. Band 2/1: Bacillariophyceae. 1. Teil: Naviculaceae. Süßwasserflora von Mitteleuropa. Gustav Fischer Verlag, Stuttgart, 876pp.

  34. Krammer, K. & H. Lange-Bertalot, 1988. Band 2/2: Bacillariophyceae. 2. Teil: Bacillariaceae, Epithemiaceae, Surirellaceae. Süßwasserflora von Mitteleuropa. Gustav Fischer Verlag, Stuttgart, 576pp.

  35. Krammer, K. & H. Lange-Bertalot, 1991. Band 2/3: Bacillariophyceae. 1. Teil: Centrales, Fragilariaceae, Eunotiaceae. Süßwasserflora von Mitteleuropa. Gustav Fuscher Verlag, Stuttgart, 596pp.

  36. Laird, K. R., S. C. Fritz, E. C. Grimm & P.G. Mueller, 1996. Centuryscale paleoclimatic reconstruction from Moon Lake, a closedbasin lake in the Northern Great-Plains. Limnol. Oceanogr. 41: 890-902.

    Google Scholar 

  37. Leng, M. J., A. L. Lamb, H. F. Lamb & R. J. Telford, In press. Palaeoclimatic implications of isotopic data from modern and early Holocene shells of the freshwater snail Melanoides tuberculata, from lakes in the Ethiopian Rift Valley. J. Paleolim.

  38. Lotter, A. F., H. J. B. Birks & B. Zolitschka, 1995. Late-glacial pollen and diatom changes in response to two different environmental perturbations: volcanic eruption and Younger Dryas cooling. J. Paleolim. 14: 23-47.

    Google Scholar 

  39. Makin, M. J., T. J. Kingham, A. E. Waddams, C. J. Birchall & T. Teferra, 1975. Development prospects in the Southern Rift Valley, Ethiopia. Land Resources Study 21, Land Resources Division, U.K. Ministry of Overseas Development, Tolworth, 266 pp.

  40. Samuel F., 1983. Review of fishery development potential in Ethiopia. Trade focus (Addis Ababa) 2: 29-36.

    Google Scholar 

  41. Sanford, W. E. & W. W. Wood, 1991. Brine evolution and mineral deposition in hydrologically open evaporite basins. Am. J. Sci. 291: 687-710.

    Google Scholar 

  42. Seyoum M. & C. H. Fernando, 1991. Seasonality and abundance of some dominant crustacean zooplankton in Lake Awasa, a tropical rift valley lake in Ethiopia. Hydrobiologia 226: 137-152.

    Google Scholar 

  43. Sturchio, N. C., P. N. Dunkley & M. Smith, 1993. Climate-driven variations in the geothermal activity in the northern Kenya rift valley. Nature 362: 233-234.

    Google Scholar 

  44. von Damm, K. L. & J. M. Edmond, 1984. Reverse weathering in the closed-basin lakes of the Ethiopian rift. Am. J. Sci. 284: 835-862.

    Google Scholar 

  45. Wissmar, R. C., A. H. Devol, J. T. Staley & J. R. Sedell, 1982. Biological responses of lakes in the Mount St. Helens blast zone. Science 216: 178-181.

    Google Scholar 

  46. Woldegabriel, G., J. L. Aronson & R. C. Walter, 1990. Geology, geochronology, and rift basin development in the central sector of the Main Ethiopian Rift. Geol. Soc. Am. Bull. 102: 439-458.

    Google Scholar 

  47. Wood, R. B. & J. F. Talling, 1988. Chemical and algal relationships in a salinity series of Ethiopian inland waters. Hydrobiologia 158: 29-67.

    Google Scholar 

  48. Wright, H. E., D. H. Mann & P. H. Glaser, 1983. Piston corers for lake and wetland sediments. Ecology 65: 657-659.

    Google Scholar 

Download references

Author information

Affiliations

Authors

Rights and permissions

Reprints and Permissions

About this article

Cite this article

Telford, R.J., Lamb, H.F. & Umer Mohammed, M. Diatom-derived palaeoconductivity estimates for Lake Awassa, Ethiopia: evidence for pulsed inflows of saline groundwater. Journal of Paleolimnology 21, 409–422 (1999). https://doi.org/10.1023/A:1008092823410

Download citation

  • Africa
  • climate change
  • conductivity
  • diatoms
  • Ethiopia
  • Holocene
  • lake levels
  • palaeolimnology
  • Rift Valley