calendar Add meeting dates to your calendar.


Paper No. 49
Presentation Time: 8:00 AM-6:00 PM


GEYER, Christopher1, PAIZIS, Nicole1, KGAODI, Oratile2, KOONTSE, Thobo2, AKOKO, Eric1, ATEKWANA, Eliot A.1, CRUSE, Anna M.1, MOLWALEFHE, Loago N.2, MASAMBA, Wellington3 and RINGROSE, Susan4, (1)Boone Pickens School of Geology, Oklahoma State University, 105 Noble Research Center, Stillwater, OK 74078-3031, (2)Department of Geology, University of Botswana, Private Bag UB00704, Gaborone, Botswana, (3)Henry Oppenheimer Okavango Research Center, University of Botswana, Private Bag 285, Maun, Botswana, (4)Harry Oppenheimer Okavango Research Center, University of Botswana, Maun, PB 285, Botswana,

The Okavango River Delta, located in the semi arid region of northwestern Botswana, is the world’s largest continental alluvial fan, covering more than 22,000 km2. The Okavango delta annually floods from March to August, expanding the permanently flooded areas from <4,000 km2 to ~12,000 km2. A long river transit time and evapotranspiration control water balance in the delta, yet the effects of vegetation on short- to long-term changes in water quality is largely unknown. We investigated the short term (diel) variations in water chemistry in order to assess vegetative effects on riverine properties.

The experiments were conducted at Mohembo, where the Okavango River first enters Botswana, and at Maun, located at the distal end of the Delta. We measured photosynthetically available radiation (PAR), water level, temperature, electrical conductivity, dissolved oxygen (DO), oxidation-reduction potential (ORP), pH, alkalinity and silica. Overall, the values of water quality parameters were lower at Mohembo compared to Maun, consistent with evaporative concentration in the downstream direction. Diel variations in river level were observed at Maun but not at Mohembo, suggesting stronger vegetative effects on the water balance and consequently water chemistry. At both sites, DO remained at or above saturation with no clear diel trend. At Mohembo, ORP and pH were steady with higher ORP values during the day and lower pH values during the day. However, at Maun, the ORP and pH increased and decreased at night and decreased and increased, respectively, during the day. Alkalinity at Mohembo was higher at night than during the day, while at Maun, alkalinity fluctuated with no clear diel trend. Silica at both sites showed decreasing trends at night and increasing trends during the day.

Diel variations in PAR appear to be correlated to changes in redox and alkalinity at Maun, but not at Mohembo. Thus, processes other than photosynthesis must also be considered in any models of water balance in this system. Given the growing concern over the availability of water in the Okavango River, and the need to allocate its resources among several nations, these results will be critical in informing future models for water utilization in this river, and can be applied to other river systems.

Meeting Home page GSA Home Page