HR: 14:45h
AN: H42I-05    [PDF]
TI: The Influence of Hydrologic Processes on the Transport and Biochemical Transformation of Aquatic Organic Matter in the Okavango Delta, Botswana
AU: * Mladenov, N
EM: mladenov@colorado.edu
AF: University of Colorado, 1560 30th Street 450 UCB, Boulder, CO 80309-0450 United States
AU: McKnight, D
EM: diane.mcknight@colorado.edu
AF: University of Colorado, 1560 30th Street 450 UCB, Boulder, CO 80309-0450 United States
AB: An annual flooding event in the Okavango Delta of Botswana was shown to exert controls on the quantity and quality of aquatic organic matter (OM) in permanently and seasonally inundated areas. The floods of 1999 and 2002 were significantly smaller in volume than the flood of 2001 and are indicative of potential future climate and hydrologic change scenarios. Less than one-third of the dissolved organic carbon (DOC) mass introduced into a study floodplain in 2001 was mobilized by the 1999 and 2002 floods. Results from spectrofluorometric and absorbance analyses revealed a direct relationship between DOC concentrations and flood where terrestrially-derived DOC was "flushed" into the water column during the rising limb of the hydrograph. After peak flood, microbial uptake, photodegradation and dilution were responsible for a decrease in DOC concentrations at seasonal channel and floodplain sites. During non-flood seasons, DOC of more microbial origin dominated. We also postulated that changes to flooding patterns in the Okavango Delta of Botswana may influence the quantity and quality of aquatic OM in seasonally inundated areas in the following ways: amount of DOC available may be compromised; timing of the DOC flush may be altered; and timing of the pulse of more labile DOC may also change. The annual flooding pattern in the Okavango Delta results in waters of different ages: older water stored in the Permanent Swamp and perennial channels and newer water entering the inlet to the Delta upstream of the Permanent Swamp. Longitudinal synoptic sampling of channels containing new flood water revealed higher specific UV light absorbance (SUVA) and the presence of more terrestrially-derived fulvic acids with increasing distance downstream, primarily in the Seasonal Swamp. This is indicative of greater flushing of fresh terrestrial vegetation products, especially in seasonally inundated areas. In older water, pushed ahead of the flood front, OM was found to be microbially-derived and had lower SUVA, indicative of photodegradation and microbial processing. This potentially labile aquatic OM may be important in stimulating productivity just before the onset of the flood.
DE: 1055 Organic geochemistry
DE: 1806 Chemistry of fresh water
DE: 1821 Floods
DE: 1871 Surface water quality
DE: 1890 Wetlands
SC: Hydrology [H]
MN: 2003 Fall Meeting