The inorganic chemistry of peat from the Maunachira channel-swamp system, Okavango Delta, Botswana

Coal-Bearing Depositional Systems

“…Several current examples of this type accumulate very effectively large masses of peat, although the latter is mostly based on herbaceous vegetation, which does not conform entirely with Model A. The dimensions of the peat seams formed in this manner are very large, as can be gauged by the Okavango Delta, or more commonly referred to as the Okavango Swamp, in Botswana, which shows some interesting aspects of peat formation (McCarthy et al 1989). While much of the so-called peat in the proximal portions of the delta contains around 60% ash (db), this proportion declines distally to an average of 14~/~ (db) with individual values as low as 6.3~/~ (db), due to the combined filtering effect by vegetation and rainwater leaching.…”

Stable-isotope (H, O, and Si) evidence for seasonal variations in hydrology and Si cycling from modern waters in the Nile Basin: implications for interpreting the Quaternary record

“…It should be noted that due to logistical and financial constraints, dry-season samples for the Upper and Lower Nile were collected two years apart and therefore do not reflect continuous sampling down the length of the river during a single dry season. Unfortunately political instability prevented travel through South Sudan, thereby ruling out sampling of the Sudd and Bahr el Ghazal swamps, which are believed to play important roles in both the hydrological (Sutcliffe, 1974), and Si cycles (McCarthy et al, 1989;Cardinal et al 2010).…”

“…Given the steep, exposed topography of the Ethiopian Highlands, flushing of DSi from soils and desorption of Si from suspendedsediment particles can be inferred to reach a maximum during the flood season (Hall et al, 1977;Sinada and Abdel Karim, 1984). In contrast, DSi concentrations in the White Nile headwaters were lower and declined much more rapidly downstream, which can be explained by a combination of: 1) quartz-rich, granitoid bedrocks that are more resistant to weathering; and 2) rapid silica uptake by Si-accumulating plants in the densely vegetated equatorial catchments, and by diatom blooms and stands of aquatic macrophytes in the chain of large lakes and swamps (Talling, 1963(Talling, , 1966McCarthy et al, 1989). Si composition of the local rock (basalt: -0.29‰ ± 0.08‰ (Savage et al, 2011)) and the river waters is greater than in the White Nile…”

Water quality in the Okavango Delta

“…Large quantities of salts enter the Okavango Delta ecosystem annually, however, the EC of water in the Delta remains low (less than 200 µS•cm−1) despite the high loss of water to evapotranspiration . The salt-water balance is kept in check by several processes, such as the accumulation of salt under islands (McCarthy et al, 2005), and by a combination of the removal of salts through seasonal flooding, uptake of solids in peat (McCarthy et al, 1989) as well as leakage of salts into underground aquifers (McCarthy and Metcalfe, 1990). In their evaluation of the salt mass balance of the entire Okavango Delta, Bauer et al (2006) showed that density-driven flow (precipitation of salts onto islands due to evaporation and transpiration) was a significant salt removal process in the Okavango Delta.…”