Date of Award

2004

Degree Type

Thesis

Degree Name

Bachelor of Science Honours

Faculty

Faculty of Computing, Health and Science

First Advisor

Dr Pierre Horwitz

Abstract

Wetlands of the Swan Coastal Plain (SCP) are acidifying because extended drying periods have exposed and oxidised sulphidic sediments creating sulphuric acid and lowering wetland pH. This appears to be the ecological equivalent of both Northern Hemisphere acid rain in lakes and streams, and acid mine drainage. This research aims to describe the characteristic acidic macroinvertebrate faunal assemblage of the SCP by identifying acidophobic and acidophilic taxa, and to examine their potential as indicators of acidification for routine biological monitoring. Four linked approaches were used in the study - analysis of a database, investigation of acidified wetland case studies, wetland sampling and a mesocosm study. The database was comprised of macroinvertebrate sampling results from 52 SCP wetlands. To analyse it wetlands were divided based on low or high pH and colour. Macroinvertebrate taxa were given one of four categories: those found only in low pH, not in low pH, only in low colour or not in low coloured wetlands. Species richness was significantly lower in low pH wetland categories. Four case study wetlands with an acid history were investigated in detail. Using sampling results from the last 10 years, acidophilic and acidophobic families were identified through their response to acidification. The database and case study findings were combined to create hypotheses for taxa showing acidophobic or acidophilic responses. These hypotheses were tested by sampling seven wetlands and targeting hypothesised taxa, confirming most trends derived from the database and case studies. Eight experimental mesocosms were set up with organics and rainwater. After being spiked with phytoplankton, zooplankton and macroinvertebrates, the communities were left to develop, after which four were acidified to pH - 3 using sulphuric acid. They were then left for a month. All tanks were sampled prior to and after acidification. Species richness was significantly lower in acidified mesocosms resulting from the loss of acid-sensitive taxa. The results of the database and mesocosms showed acidity significantly reduced macroinvertebrate species richness and altered macroinvertebrate communities. All phases of this research identified acidophobic and acidophilic taxa. Taxa were attributed positive or negative scores according to their acidity response which were combined to create "SCP Macroinvertcbrate Acid-sensitivity Grades" which were not correlated with other pollution sensitivity grades, indicating available pollution grades are not suitable for predicting SCP macroinvertebrate acidity response. The acid-sensitivity grades aided in the proposal of acidity indicator taxa for SCP wetlands, acidophobes identified were Austrochiltonia subtenuis, Alboa wooroa, Sarscypridopsis aculeaia; and acidophiles were Macrothrix breviseta, Paramerina Levidensis and Ablabesmyia notablis. This research indicated a relationship between low pH and reduced species richness, resulting from the loss of acid-sensitive taxa. The loss of sensitive taxa created proportionate domination of acid-tolerant taxa and changed community structure. The creation of acidity indicator taxa will aid in early identification of acidifying systems and decrease reliance on pollution indicators that may not be accurate for acidity.

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