Spatial dynamics of chromophoric dissolved organic matter in nearshore waters of Lake Victoria

Authors

  • Steven A. Loiselle University of Siena, Dipartimento Farmaco Chimico Tecnologico, CSGI, 53100 Siena, Italy
  • Nicholas Azza Directorate of Water Resources Management, Entebbe, Uganda
  • John Gichuki Kenyan Marine Fisheries Research Institute, Kisumu, Kenya
  • Luca Bracchini University of Siena, Dipartimento Farmaco Chimico Tecnologico, CSGI, 53100 Siena, Italy
  • Antonio Tognazzi University of Siena, Dipartimento Farmaco Chimico Tecnologico, CSGI, 53100 Siena, Italy
  • Arduino M. Dattilo University of Siena, Dipartimento Farmaco Chimico Tecnologico, CSGI, 53100 Siena, Italy
  • Claudio Rossi University of Siena, Dipartimento Farmaco Chimico Tecnologico, CSGI, 53100 Siena, Italy
  • Andres Cozar University of Siena, Dipartimento Farmaco Chimico Tecnologico, CSGI, 53100 Siena, Italy

Keywords:

organic carbon dynamics, photodegradation, conservative mixing, Africa

Abstract

The underwater light conditions in the African Great Lakes depend on the complex dynamics of ecological and hydrological forces, and are strongly influenced by local environmental conditions and global biogeochemical cycles. Changes in the optical conditions in these lakes have direct impacts on ecosystem productivity, carbon dynamics and nutrient availability. A central role in the underwater light climate is played by dissolved organic matter which is present in all aquatic ecosystems. The chromophoric fraction of these compounds can mediate ecosystem change through its influence on the attenuation of ultraviolet and PAR radiation, microbial carbon cycling and radiative transfer. In the African Great Lakes, little information is available regarding the dynamics of dissolved organic matter and those sources and sinks which control its presence in the water column. We present an extensive spatial analysis of three major bays on the Kenyan and Ugandan shores of Lake Victoria. We use these data to examine the dynamics of chromophoric dissolved organic matter in different bays and we develop a model to estimate its flow from these bays to the Lake, considering both conservative mixing and photodegradation processes. While some bays release chromophoric dissolved organic matter practically unmodified into the Lake, increased residence time and exposure to solar ultraviolet radiation create conditions where chromophores are lost before entering the open lake.

References

Bracchini, L., Loiselle, S. A., Tognazzi, A., Dattilo, A. M., Focardi, S., Cózar, A. and Rossi, C. 2007. The optical qualities of shallow wetland lined bays in Lake Victoria. Wetlands Ecology and Management, 15: 509–519.

Bertilsson, S. and Tranvik, L. J. 1998. Photochemically produced carboxylic acids as substrates for freshwater bacterioplankton. Limnology and Oceanography, 43: 885–895.

Bertilsson, S. and Tranvik, L. J. 2000. Photochemical transformation of dissolved organic matter in lakes. Limnology and Oceanography, 43: 753–762.

Carrillo, P., Medina-Sánchez, J. M. and Villar-Argaiz, M. 2002. The Interaction of Phytoplankton and Bacteria in a High Mountain Lake: Importance of the Spectral Composition of Solar Radiation. Limnology and Oceanography, 47: 1294–1306.

Cózar, A., Bracchini, L., Azza, N., Dattilo, A. M. and Loiselle, S. A. 2004. Characterization of Ugandan inshore waters (Lake Victoria) based on temperature-conductivity diagrams. Water Resources. Research, 40: W12303

DeGrandpre, M. D., Vodacek, A., Nelson, R. K., Bruce, E. J. and Blough, N. V. 1996. Seasonal seawater optical properties of the US Middle Atlantic Bight. Journal of Geophysical Research, 101C: 22727–22736.

Grzybowski, W. 2000. Effect of short-term irradiation on the absorbance spectra of the chromophoric organic matter dissolved in the coastal and riverine waters. Chemosphere, 40: 1313–1318.

Helbling, E. W. and Zagarese, H. E., eds. 2003. UV effects in aquatic organisms and ecosystems, Comprehensive Series in Photochemical and Photobiological Sciences Cambridge: The Royal Society of Chemistry.

Kowalczuk, P., Cooper, W. J., Whitehead, R. F., Durako, M. J. and Sheldon, W. 2003. Characterization of CDOM in an organic-rich river and surrounding coastal ocean in the South Atlantic Bight. Aquatic Sciences, 65: 284–401.

Loiselle, S. A., Azza, N., Cózar, A., Bracchini, L., Tognazzi, A., Dattilo, A. M. and Rossi, C. 2008. Variability in factors causing light attenuation in Lake Victoria. Freshwater Biology, 53: 535–545.

Lung'Ayia, B. O., M'Harzi, A., Tackx, M., Gichuki, J. and Symoens, J. J. 2000. Phytoplankton community structure and environment in the Kenyan waters of Lake Victoria. Freshwater Biology, 43: 529–543.

LVEMP (Lake Victoria Environment Management Project)/COWI Consulting Engineers. 2002. Integrated water quality/Limnological Study for Lake Victoria, Part II, Kenya: LVEMP. Technical Report

Mazzuoli, S., Bracchini, L., Loiselle, S. A. and Rossi, C. 2003. An analysis of the spatial and temporal variation evolution of humic substances in a shallow lake ecosystem. Acta Hydrochimica et Hydrobiologica, 31: 461–468.

Muggide, R. 1993. The increase in phytoplankton primary productivity and biomass in Lake Victoria (Uganda). Verhandlungen International Vereinigung für Theoretische und Angewandte Limnologie, 25: 846–849.

Neale, P. J., Helbling, E. W. and Day, T. A. 2007. Symposium-in-Print: UV Effects in Aquatic and Terrestrial Environments Introduction. Photochemistry and Photobiology, 83: 775–776.

Nelson, N. B., Carlson, C. A. and Steinberg, D. K. 2004. Production of chromophoric dissolved organic matter by Sargasso Sea microbes. Marine Chemistry, 89: 273–287.

Njiru, M., Kazungu, J., Ngugi, C. C., Gichuki, J. and Muhoozi, L. 2008. An overview of the current status of Lake Victoria fishery: Opportunities, challenges and management strategies. Lakes and Reservoirs: Research and Management, 13: 1–12.

Osburn, C. L. and Morris, D. P. 2003. “Photochemistry of chromophoric dissolved organic matter in natural waters”. In UV Effects in Aquatic Organisms and Ecosystems, Edited by: Helbling, E. W. and Zagarese, H. 185–217. Cambridge: The Royal Society of Chemistry.

Saunders, M. J., Jones, M. B. and Kansiime, F. 2007. Carbon and water cycles in tropical papyrus wetlands. Wetlands Ecology and Management, 15: 489–498.

Stedmon, C. A. and Markager, S. 2003. Behaviour of the optical properties of coloured dissolved organic matter under conservative mixing. Estuar. Coast. Shelf S., 57: 973–979.

Strickland, J. D. H. and Parsons, T. R. 1972. A Practical Handbook of Seawater Analysis, , 2nd ed Fish. Board Can., Bulletin 167

Talling, J. F. and Lemoalle, J. 1998. Ecological Dynamics of Tropical Inland Waters, Cambridge University Press.

Wetzel, R. G. 2001. Limnology Lake and River Ecosystems, Philadelphia: Academic Press.

Zepp, R. G. 2003. “Solar ultraviolet radiation and aquatic biogeochemical cycles”. In UV Effects in Aquatic Organisms and Ecosystems, Edited by: Helbling, E. W. and Zagarese, H. 137–184. Cambridge: The Royal Society of Chemistry.

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Published

2010-05-28

Issue

Vol. 13 No. 2 (2010): Assessing Great and Large Lakes of the World (GLOW V, Part II)

Section

Research article

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