Environmental Engineering Reference
In-Depth Information
Primary sites
Primary sites are those with metallophytes where elevated concentrations
of metals are due to natural mineralisation or ore outcropping, and not that
which is anthropogenically influenced. Primary sites in Europe are therefore
extremely rare today and mostly found as very patchy small sites in Central
Europe, in the Pyrenees and in the Alps (Ernst 1974 ). Virgin sites like those in
tropical woodlands and rainforests (Duvigneaud 1958 ; Brooks et al. 1985 ) are
virtually non-existent, although many of the African sites are also threatened
by mining activities (Leteinturier et al. 1999 ). Besides a high concentration of
metals like zinc, lead, cadmium or copper in soil, heavy-metal vegetation types
are characterised by a low nutrient availability. Hence, these plant commu-
nities are of very low productivity.
Secondary sites
Almost all primary metal-enriched sites in Europe have been anthropologically
influenced by mining activities. These secondary sites result from mining
activities, e.g., disturbed primary sites, spoil and slag heaps, ore processing
and concentration (beneficiation) areas. The distinction between primary and
secondary is often difficult to elaborate especially with ancient sites. Early
mining has diminished most primary occurrences of metallophytes. From the
Bronze Age to the late Middle Ages mining had a relatively low impact on the
local environment. Metallophytes occurred locally on primary sites, and super-
ficial mining created secondary habitats. Both habitat types were ecologically
very similar. At that time mining was restricted to areas with metals outcrop-
ping. After the Middle Ages, much larger secondary habitats were created,
often far away from areas with primary habitats, by deep underground mining
or by metal refining on site. Exceptionally high concentrations of metals in
soils at primary habitats result from weathering of natural mineralisation on
well-developed soils. Modern secondary habitats, however, have a totally differ-
ent substratum; mining has created soils with altered metal composition,
depleted phosphorus and organic matter concentrations and low water reten-
tion capacity. Besides evolving metal tolerance, plants growing on these wastes
were co-selected for tolerance to P-deficiency, resistance to drought and an
ability to grow on loose substrates (Ernst 2000 ). This has affected the edaphic
conditions and is a major cause of differences between primary and early
secondary habitats.
Tertiary sites
Tertiary metal vegetation types can be subdivided into those communities
whose genesis is a result of atmospheric deposition in the vicinity of metal
smelters or alluvial deposition of metal-enriched substrates by sedimentation
Search WWH ::




Custom Search