Acid Mine Drainage
The impact of AMD on the structure of stream communities and food webs
Large-scale field surveys of algae, bacteria, fungi, benthic invertebrates and fish have been conducted at a range of sites near Reefton, Greymouth, Stockton and Denniston in order to assess the impacts of differing levels of mine drainage on stream ecosystems. To date our findings have indicated that all of these organisms vary in diversity and have markedly altered communities under differing levels of AMD impact. Decreasing pH leads to marked declines in macroinvertebrate and algal diversity (Fig. 1).
Figure 1. The influence of pH on the diversity of
macroinvertebrates in West Coast streams.
In general, communities in the most impacted sites (pH < 3.5 with high metal concentrations) were dominated by a small number of highly-tolerant taxa (Fig. 2). Preliminary results from molecular analysis indicate microbial communities are also strongly influenced by AMD.
Figure 2. Sandy tunnels produced by larval chironomids
(or non-biting midges) can be common in some AMD streams.
Fish species appeared especially vulnerable to AMD, and are absent from impacted streams with pH < 5.1. Furthermore, comparisons of observed fish distributions with those predicted by GIS models indicated AMD inputs can impede or reduce movement of migratory species through to non-impacted upstream locations (Harding et al. 2006, pdf, 4.5mb).
Despite the strong impact of AMD on stream communities, current biological monitoring indices do not necessarily provide accurate assessments of AMD. For example, the macroinvertebrate community index MCI, often miss-classified communities subject to considerable AMD stress (Fig. 3). This suggests mining-specific tolerance indices need to be developed to compliment biomonitoring activities.
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Figure 3. The Macroinvertebrate Community Index (MCI), which is commonly used as an
indicator of pollution in agricultural areas, does not always work in acid mine drainage (AMD) streams.
The MCI is based in tolerance scores of individual insect species, and as many species have |
PhD student, Kristy Hogsden, is taking a holistic approach by investigating the influence of acidity and heavy metals on the structure and function of stream food webs, encompassing interacting communities of bacteria, fungi, algae, invertebrates and fish (see Disrupted food webs in acid mine drainage streams).
People involved in this project
University of Canterbury
Jon Harding
Kristy Hogsden (PhD student)
Justin Kitto (Completed MSc Student)
Jonathan Bray (Completed MSc student)
Annabel Barnden (Completed MSc student)
Alice Bradley (Completed MSc student)
Missouri University of Science & Technology
Dev Niyogi
Publications
Barnden 2005. Ecology of streams affected by iron precipitates and iron flocculants. MSc thesis, University of Canterbury (pdf, 1.6mb).
Bray 2007. The ecology of algal assemblages across a gradient of acid mine drainage stress on the West Coast, South Island, New Zealand. MSc thesis, University of Canterbury (pdf, 1mb).
Bray, Broady, Niyogi & Harding 2008. Periphyton communities in New Zealand streams impacted by acid mine drainage. Marine and Freshwater Research 59: 1084-1091 (pdf, 350kb).
Harding, Bray & Niyogi 2008. Do algae grow in acid mine waters? Newsletter of the Freshwater Ecology Research Group, University of Canterbury (pdf, 320kb).
Harding & Champeau 2008. Can benthic invertebrates be used to predict impacts in streams with acid mine inputs? Newsletter of the Freshwater Ecology Research Group, University of Canterbury (pdf, 300kb).
Harding, McIntosh, Gray, Jellyman & Eikaas 2006. Distribution of native fish in the Ngakawau and Waimangaroa Rivers. University of Canterbury report for Solid Energy (pdf, 4.5mb).