| dc.description.abstract | This study was carried out in the Carnon valley, which is located in Cornwall, south-west England. A river runs through the Carnon valley while former settlement ponds for processing tin and copper ore from the Wheal Jane mine are found on the floodplain. Tailings and waste rocks have accumulated on the floodplain to a height of about 6 meters. The valley is physically divided by a country road into the Middle valley and the Lower valley. Plant growth on tailings in the Middle valley, where tailings heaps were bulldozed, is visibly different from plant growth in the tailings and coarse waste rock observed in the Lower valley. The Lower valley, which features hummocks and hollows, appears to be less rehabilitated than the Middle valley. However, flora diversity in the Lower valley is considerably higher compared to the Middle valley, where a relatively homogeneous vegetation coverage is dominated by a few species. Other noticeable differences between the Lower and Middle valleys are a relative consistent soil compaction and the absence of visible ponds in the Middle valley. This research aims to identify the main drivers and limiting factors in the natural rehabilitation process and local biodiversity development in the middle and lower sections of the Carnon Valley. Through close year-round recording of natural plant species and colonies and habitat survey in the evolving terrain, it was attempted to correlate biota to progressive structural amelioration of the site. Species success was observed in relation to habitat evolution, restrictions imposed by residual toxicity of the former metal-mining terrain, advantages gained by artificial topographic diversity present on abandonment, and the stages reached in the dynamic progression of the combination of all of these features. By observing and recording the outcome of natural revegetation and identifying the impacts of abiotic factors, recommendations are made about the significance of such abandoned mine-sites in relation to ecological conservation value of such former disturbed land, and derive proposals for its onward management. We conclude that, on the site, complex interwoven processes occur of which we observe the state at one moment in time. The volume of data collected in the Carnon Valley is probably greater than available for any other known mine site of comparable history and size. While the data enabled inference of important biotic progressions, this study suggests that the 9 approaches may be applied to other abandoned mine sites, especially for assessment of natural attenuation of residual toxic legacies and ways to engineer future biotic rehabilitation patterns. The potential development of abandoned mine sites to re-establish natural biodiversity is thus recommended, together with a strategy for monitoring of future rehabilitation progression. The study consists of a field survey to record the present vegetation assemblage pattern, laboratory experiments to investigate soil features, data interpretation with statistical software, and evaluation of the interrelationship between emerging vegetation patterns and soil features. Extensive field work was undertaken within a one-year period, observing the highly heterogeneous vegetation community in a state of succession towards natural rehabilitation. The study generated up-to-date, detailed insight into year-round biodiversity development, notably of species diversity and seasonal stages of its development. Both transect surveys and quadrat surveys were carried out to capture general and spatial vegetation distribution variances. Fifty-seven quadrats, deemed to be representative, are surveyed in terms of plant species present and physical and chemical properties of the soil. While the natural vegetation of areas surrounding the valley has already been mapped, it is possible to build a factually-based picture of the progression of on-site species-assembly in relation to taxa that are, or are not, present in the surrounding landscape’s natural vegetation. This revealed that, out of a total of 87 species found in the valley, 9 are classified as very rare species in Cornwall. The presence of local rare species suggests the Carnon valley and other post-mining sites potentially have a significant ecological conservation value. This diversity and biotic taxonomic content of the former mine site highlights the importance of allowing natural biotic colonisation to continue in the wider interest of biodiversity conservation and utilisation of such sites as future biotic reserves. Vegetation survey revealed a host of unusual species assemblage settling on the contaminated soil, which is especially true in the community around ditches. The significantly high species richness and presence of rare species in the ditch community indicates the potential of an edge effect, which has a benefit for biodiversity and may be applied in mine site rehabilitation. The prominent high species richness in the core area (excluding the ditch community) of the Lower valley (75 species compared to 18 10 species in the Middle valley) emphasizes the value of heterogeneity. Bulldozing and human disturbance proved to be effective to improve vegetation coverage, but failed to promote biodiversity recovery. To investigate the effect of chemical contaminants on vegetation development, data is interpreted with ordination techniques such as redundancy analysis (RA) and principal component analysis (PCA). Both techniques indicate that arsenic and copper have a negative impact on vegetation development. Absorbed arsenic or phosphate exchangeable arsenic were found to be the most influential fractions of total arsenic in the soil which affect local species richness and biodiversity. Controlling arsenic fractionation is therefore an important strategy towards supporting vegetation recovery. The thesis postulates that sites with mine waste have special conservation value and that an edge effect may exist -from observing relatively high species diversity in zones along ditches. Water availability has great influence in ditch community development, but is remains unclear how it interacts with other factors to contribute to biodiversity development. The study shows the potential of natural rehabilitation, which should be considered as an option when planning for rehabilitation of former mine sites. | en_GB |
