Characterization of arsenic occurrence in the water and sediments of the Okavango Delta, NW Botswana

Major Factors Controlling Arsenic Occurrence in the Groundwater and Sediments of the Chianan Coastal Plain, SW Taiwan

“…No significant correlation was found between As content and pH values (Fig. 4d), although a positive correlation between As and pH was previously reported (e.g., Huntsman-Mapila et al 2006). Most of the Eh-pH data points are located within the H 3 AsO 3° stability field in the simplified Eh-pH diagram (Inskeep et al 2002) for As-S-H 2 O system at 25°C based on the assumptions: SO 4 2-= 10 -3 M, H 3 AsO 3°= 10 -5 M (Fig.…”

“…The occurrence and factors controlling the arsenic contents in groundwater have drawn much attention in recent years (e.g., Hering and Kneebone 2001;Inskeep et al 2002;Mandal and Suzuki 2002;Smedley and Kinniburg 2002;Anawar et al 2003;Ahmed et al 2004;Huntsman-Mapila et al 2006;Pedersen et al 2006;Varsanyi and Kovács 2006). The Chianan coastal plain in southwestern Taiwan (Fig.…”

Chemical characterization of DOM in channels of a seasonal wetland

“…In the Okavango Delta, there is a strong input of DOM into groundwater (Mladenov et al, 2007) and its reactivity may play an important role in DOM-metal interactions in the subsurface. The presence of arsenic has been documented in Okavango Delta groundwater near Maun, Botswana and originates from weathering of bedrock in the region (Huntsman-Mapila et al, 2006). The mechanisms for arsenic mobilization are still unknown in this system, but high DOC concentrations in groundwater (Mladenov, 2004) and the presence of iron-oxides have been implicated in the arsenic liberation process (Huntsman-Mapila et al, 2006).…”

“…For example, iron solubility and reactivity in anoxic groundwaters has been linked to the electron-shuttling role of humic substances (Lovley et al, 1996). Concentrations of dissolved organic carbon (DOC) and arsenic in groundwater have been shown to be highly correlated, especially in deltaic systems, such as the Ganges-Bramaphutra Delta (McArthur et al, 2001;Zheng et al, 2004;Harvey et al, 2004), the Mekong Delta (Stanger et al, 2005), and most recently the Okavango Delta (Huntsman-Mapila et al, 2006).…”

“…Thus, these DOM-rich (10 -20 mg C L -1 ) surface waters continually replenish the local groundwater aquifer with annual export of DOM to groundwater being on the order of 2 x 10 7 g C yr -1 (Mladenov et al, 2007). Significant groundwater storage of this DOM is especially important given recent findings of high concentrations of arsenic in Delta groundwater near Maun, Botswana (Huntsman-Mapila et al, 2006). Therefore, greater knowledge of the chemical quality of DOM in surface waters will aid in understanding its relationship to metal cycling, specifically of iron and arsenic, in groundwaters of the Delta and in other similar systems.…”