Distribution of benthic invertebrates in acid,brown water streams in the South Island of New Zealand |
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Authors: | M J Winterbourn K J Collier |
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Institution: | (1) Department of Zoology, University of Canterbury, Christchurch 1, New Zealand |
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Abstract: | Acid, brown water streams are common on the west coast of the South Island, New Zealand. Acid precipitation is not a significant
problem in this region where stream water acidity is brought about by high concentrations of humic substances. The interrelationships
between pH, alkalinity, conductivity, DOC and total reactive aluminium were investigated at 45 running water sites. pH (range
3.5–8.1) was strongly correlated with alkalinity (range 0–49 g·m−3 CaCO3) and less strongly with conductivity (range 2.0–9.7 mS·m−1). A strong positive correlation was found between DOC and total reactive aluminium concentration both of which were correlated
negatively with pH. In all brown water streams, most aluminium was probably in the non-toxic, organically complexed form.
Benthic invertebrate assemblages were examined at 34 sites. Taxonomic richness was not correlated with pH and similar numbers
of ephemeropteran, plecopteran and trichopteran taxa were taken from acidobiontic (pH ⩽ 5.5), acidophilic (pH 5.6–6.9) and
moderately alkaline (pH ⩾ 7.0) groups of streams. Many species occurred over a wide pH range and had a lower limit of about
pH 4.5. The mayfly, Deleatidium occurred at 33 sites and was amongst the five most abundant taxa at 32 of them. The stoneflies, Zelandobius confusus, Austroperla cyrene and Stenoperla maclellani, an elmid, Hydora sp. and a caddisfly, Psilochorema sp. also occurred in over half the streams and frequently were abundant. Few habitat specialists were found. Benthic assemblages
were not associated strongly with measured physicochemical factors but streams in close proximity tended to have similar faunas.
This suggests that the availability of suitable colonizers sets the limits to species richness and is important in determining
the composition of benthic assemblages at a particular locality. |
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Keywords: | acid streams aluminium aquatic insects benthic invertebrates dissolved organic carbon New Zealand |
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