In response to recent droughts in central Africa, an accelerated well drilling programme was commissioned in Victoria Province, Zimbabwe. Geophysical techniques involved in the siting of 370 boreholes included electromagnetic profiling and resistivity sounding, the latter using the offset sounding system. An analysis of the field data showed that although observed errors were low, a significant proportion of the soundings were affected by strong lateral changes in resistivity, this probably indicating the presence of a very irregular bedrock surface. Nevertheless, mean regolith thickness and lithology were reliably estimated. Geomorphological features which were found to have the greatest potential for water supply boreholes include valleys and zones of weathering around bornhardts. In these situations geophysical surveys proved useful in locating areas of thickest regolith. Borehole yield could then be estimated from the measured formation resistivity although a precise relationship was somewhat masked by the clay mineralogy of the regolith and the type of bedrock which must be taken into account when siting boreholes.
Microbial communities in the marine environment drive biogeochemical and nutrient cycles. However, microbial composition and therefore their role in ecosystems is likely to be strongly influenced by the environment. Here, we examined Macquarie Harbour, a highly stratified system on the west coast of Tasmania, Australia, to determine environmental factors driving microbial diversity. Water was sampled along spatial and environmental gradients to examine the structure and composition of the microbial communities, using high-throughput sequencing. The spatial distribution of the communities was found to be homogenous throughout the harbour’s surface, although it differed from riverine and oceanic samples. In contrast, the distribution and composition of microbial communities varied with depth-related changes in salinity and oxygen. Prokaryotes associated with riverine and brackish waters dominated the oxic surface waters. Phytoplankton metabolite-related bacteria and nitrite oxidizers were abundant at the halocline, whereas microbes linked to the consumption of organic matter, nitrogen and sulphur metabolization inhabited the hypoxic bottom waters and may be acting as major players in oxygen consumption throughout the harbour’s water column. This study provides valuable insights into microbial community ecology in a semi-enclosed and highly stratified environment and will improve our knowledge on how bacterial and archaeal distribution may be influenced by a changing environment.
As a result of the recent drought in central Africa, an accelerated well drilling program was commissioned in Victoria Province, Zimbabwe, to help alleviate the shortage of water. An analysis of the data collected during the siting of these boreholes showed that geophysical techniques can be used reliably to determine regolith thickness and provide an indication of regolith lithology. Valleys and the zone of deep weathering around bornhardts were found to have the greatest potential for water‐supply boreholes. The relationship between regolith resistivity and specific capacity is masked by the clay mineralogy of the regolith which must be taken into account when siting boreholes. Despite this effect, optimum values of regolith resistivity for production boreholes in Victoria Province were established which may be of value in similar Basement terrain elsewhere.
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