The impact of sinkholes on species richness and diversity: implications for mine rehabilitation
Date
2011-02-25
Authors
Keiller, Bronwen May
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Abstract
Mining often results in numerous detrimental impacts on the surrounding environment.
One such potential impact is the formation of sinkholes on mining property, commonly
resulting from dewatering operations initiated by mines to keep working conditions dry
and safe. The rehabilitation of these sinkholes poses problems for mines that near
closure; not only because of the potential costs involved, but also in determining the best
methods to rehabilitate a sinkhole.
In order to determine the best rehabilitation requirements the differences in biodiversity
found between sinkholes and the surrounding area were examined. Two sinkholes and
the areas surrounding each sinkhole were sampled for small mammals, reptiles,
amphibians, invertebrates. Basic vegetation and environmental variables studies were
also conducted.
Grass cover was significantly higher than all other environmental variables (woody, forbs,
rock, bare ground and plant litter cover) outside the sinkhole. Inside the sinkholes plant
litter, grass and rock cover were significantly higher than the other environmental
variables. Woody cover was significantly higher inside the sinkholes, compared to woody
cover outside the sinkholes. The average percentage cover of broad-leaved plants was
significantly lower than narrow‐leaved plants outside the sinkholes. The cover of broad
leaved plants outside the sinkholes was significantly lower in comparison to cover inside
the sinkholes. No significant differences were recorded between different seed dispersal
types outside the sinkholes. However, inside the sinkholes, the average percentage cover
of plants with other types of seed dispersal was significantly higher than animal dispersed
seed types. The floral composition analyses found that Tagetes minuta featured
prominently inside the sinkholes, while Digitaria longiflora was the most important
species outside the sinkhole. The multivariate analysis showed a certain degree of
separation between inside and outside quadrats, based on the environmental variables
studied. A total of six animal classes were recorded in the study sites. Insecta were most
abundant both outside and inside the sinkholes. Outside the sinkholes, Insecta were significantly higher than Arachnida and Myriapoda. Amphibians were significantly lower
than all other animal classes. Inside the sinkholes, Insecta and Arachnida were
significantly higher than Mammalia and Reptilia.
The sinkholes examined in this study do not appear to have decreased levels of
biodiversity, but rather present altered environmental conditions to those found outside
the sinkholes, allowing the establishment of different species. The exclusion of fire,
grazing and frost from sinkholes are likely to be contributing factors in the different
growth type abundances and may also impact on invertebrate abundances. The
environmental conditions inside the sinkhole that differ from surrounding conditions may
be preferred by certain species, while they are avoided by others. Faunal species appear
to exhibit individual preferences on sinkhole selection based on their life strategies.
Given sufficient time it would appear that sinkholes regenerate to sufficient levels that
allow ecosystem functioning. As a result of this, it may not be necessary to refill sinkholes
unless out of safety concerns.
Only a limited number of variables were examined in this study and future work is
required to justify the findings and explanations given herein. Additional environmental variables, such as slope, and detailed studies on the exact differences in moisture,
humidity, sunlight, temperature etc. between the sinkholes and surrounding areas should
be included in further studies. Both the grazing and burning regimes of the sinkholes and
surrounding areas should be established to provide further insight and understanding in
the differences between sinkholes and the surrounding areas.