Gold Prospecting and Mining
Descriptions of the parks emphasize these vegetation types, linking the forest to the wider biogeographic unit of the Albertine rift forests, one of the most biodiverse and least extensive ecosystems in Africa. It is thought that the parks served as a refuge for forest species in the period of deep aridity about 15,000 years ago. The richness of their flora and fauna reflect the depth of time over which biodiversity has evolved. The parks are seen as important both for their rare and endemic species (primates of course, but also birds and butterflies and other taxa) but also because they provide what commentators describe as 'rare local examples of relatively natural ecosystems'.30 The Management Plan for Bwindi states bluntly that the forest is 'a climax ecosystem', implying a stable final stage of succession. The forest is described as 'natural', although it goes on to note past and present human activity on 90 per cent of it.31 Those activities include pitsawing of timber,...
The Yellowknife environment is rich in arsenic because of high background levels (NRCC, 1978). Anthropogenic input has also been considerable because of extensive gold mining activity. The effluent from one mine, Royal Oak Giant Mine, flows down Baker Creek in the summer season into Back Bay, which is where the fish were caught.
In the fifth century b.c.e., the Greek philosopher Dem-ocritus reasoned that we can cut matter such as a gold nugget into smaller and smaller pieces, but there must ultimately be particles so small that nothing could cut them. He called these imaginary particles atoms1 ( indivisible ). Atoms were only a philosophical concept until 1803, when English chemist John Dalton began to develop an atomic theory based on experimental evidence. In 1913, Danish physicist Niels Bohr proposed a model of atomic structure similar to planets orbiting the sun (figs. 2.1 and 2.2). Although this planetary model is too simple to account for many of the properties of atoms, it remains useful for elementary purposes.
In a retrospective cohort study (also sometimes called a historical cohort study), a cohort is assembled by reviewing records to identify exposures in the past (often decades ago). Based on the recorded exposure histories, cohort members are divided into exposed and nonexposed groups, or according to level of exposure. The investigator then reconstructs health experience subsequent to exposure, up to some defined point in the more recent past or up to the present time. A common application of the retrospective cohort design is to assess the effects on disease of occupational exposures, such as prostate cancer in farmers exposed to herbicides and other agents (Morrison et al. 1993) and silicosis in gold miners exposed to silica (Steenland and Brown 1995). Other cohorts assembled retrospectively have included college students with certain attributes and armed forces veterans (Bullman and Kang 1996).
Microbial activity has also been found in even deeper environments such as the gold mines of South Africa, with Takai et al. (2001) reporting that South African gold mines harbor novel archael communities distinct from those observed in other environments. These subsurface environments and their microbial communities are of interest, not only because of their unique nature, their lack of direct reliance on solar radiation, and the fact that they may represent a large percentage of the Earth's biosphere, but also because subsurface environments represent the most likely location for life on other planets (Boston et al., 1992). Other evidence suggests that a deep crustal biosphere exists beneath both land and sea, reaching 3 km below the Earth's surface, with oil degradation suggesting that this may be extended to at least 4 km (Head et al., 2003).
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