In the framework of the investigation of enrichment processes of nitrate in groundwater of the Kalahari of Botswana near Serowe, recharge processes were investigated. The thick unsaturated zone extending to up to 100 m of mostly unconsolidated sediments and very low recharge rates pose a serious challenge to study solute transport related to infiltration and recharge processes, as this extends past the conventional depths of soil scientific investigations and is difficult to describe using evidence from the groundwater due to the limitations imposed by available tracers. To determine the link between nitrate in the vadose zone and in the uppermost groundwater, sediment from the vadose zone was sampled up to a depth of 15-20 m (in one case also to 65 m) on several sites with natural vegetation in the research area. Among other parameters, sediment and water were analysed to determine chloride and nitrate concentration depth profiles. Using the chloride mass balance method, an estimation of groundwater infiltration rates produced values of 0.2-4 mm a(-1). The uncertainty of these values is, however, high. Because of the extreme thickness of the vadose zone, the travel time in the unsaturated zone might reach extreme values of up to 500 years and more. For investigations using groundwater, we applied the chlorofluorocarbons CFC-113, CFC-12, sulphur hexafluoride (SF(6)) and tritium to identify potential recharge, and found indications for some advective transport of the CFCs and SF(6), which we accounted for as constituting potential active localised recharge. In our contribution, we show the potential and limitations of the applied methods to determine groundwater recharge and coupled solute transport in semi-arid settings, and compare travel time ranges derived from soil science and groundwater investigations.
This is a study of abundances of the elements He, C, N, O, Ne, Mg, Si, S, Ar,
Ca, and Fe in solar energetic particles (SEPs) in the 2 - 15 MeV amu-1 region
measured on the Wind spacecraft during 54 large SEP events occurring between
November 1994 and June 2012. The origin of most of the temporal an...
We investigate the link between luminous blue variable
(LBV) as SN progenitors and the appearance of episodic light curve modulations
In the radio light curves of the SN event. We use the 20 Msun and 25
Msun models with rotation at solar metallicity, part of an extended grid of
We observed all
Of the three maser species with the Australia Telescope Compact Array with
Angular resolutions of 6'' , 0.6'' , 0.3'' , and 1.7'' at 18 cm, 13 mm, 7 mm,
And 3 mm, respectively. While double peaks are routinely seen in OH and water
Masers and interpreted as due to expanding envelopes,...
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