The application of ecological theory to the remediation of macroinvertebrate communities impacted by acid mine drainage

摘要

Numerous streams on the West Coast drain catchments impacted by active or abandoned coal mining areas. Acid mine drainage (AMD) from coal mining can have significant negative effects on stream communities. Changing environmental ethics and regulations mean that mining companies are now encouraged to treat acid mine drainage to enable streams communities to recover. However, remediation efforts have not always been ecologically successful, and mining companies are seeking methods to enhance macroinvertebrate community recovery. Initially, I conducted an extensive survey of 45 streams draining the Stockton Plateau, which is the site of the largest opencast coal mine in New Zealand. I assessed physical and chemical conditions at each site as well as sampling benthic communities. This spatial survey showed streams impacted by acid mine drainage were comprised of chironomids and AMD-tolerant caddisflies such as Psilochorema and stoneflies such as Spaniocercoides. Un-impacted streams typically had a pH of ~5 and were dominated by mayflies (Deleatidium or Zephlebia). Analysis revealed that stream location within the landscape also had a significant influence on macroinvertebrate community composition. Another aspect of stream recovery is the ability of species to recolonise a stream. Therefore, I investigated the flight direction of adult aquatic insects in order to determine longitudinal and lateral flight preferences. No significant differences in flight direction were observed. I also investigated the influence of riparian habitat on lateral dispersal and found that a number of patterns were evident. Scrub vegetation supported higher densities of adult aquatic insects dispersing further from the stream, in contrast to the rapid decline in open bedrock and forest. Furthermore, a comparison between downstream drift and aerial flight showed significantly more individuals where drifting downstream, and this method is liable to provide rapid recolonisation of macroinvertebrates within connected stream networks. At the local scale, organic matter (comprising leaves bags and timber) and artificial moss cover were added to six streams to determine if organic matter and habitat availability would improve macroinvertebrate communities in manipulated streams. A series of floods during the experiment reduced taxonomic richness and density in manipulated streams. Overall, this study has shown that after AMD has been treated, the geographic position of streams within the landscape and lateral dispersal barriers may prevent streams being rapidly re-colonised. Therefore, to promote rapid re-colonisation of macroinvertebrates, stream remediation projects should be targeted at streams that either have un-impacted headwaters or tributaries. This will allow macroinvertebrates to drift in and re-colonise faster. In my experiment I did not find that organic matter significantly enhanced the macroinvertebrate community, but moss additions did provide additional habitat for macroinvertebrates. These results highlight the importance that disturbance events can have on remediation projects.