Date of Award

2000

Document Type

Thesis

Publisher

Edith Cowan University

Degree Name

Bachelor of Science Honours

Faculty

Faculty of Communications, Health and Science

First Supervisor

Dr Pierre Horwitz

Second Supervisor

Dr Mark Lund

Abstract

Acidification (pH< 4.5) was detected at Lake Jandabup, a shallow, seasonal wetland on the Swan Coastal Plain. Western Australia. Concern has been raised because populations of invertebrate species have declined or disappeared since acidification, potentially compromising the status of the lake as a nature reserve. The Jake bed is underlain with pyrite (feS2), which oxidises when dry producing sulfates, hydrogen ions and ferrous iron. Being seasonal, Lake Jandabup would be expected to be naturally acidic, but the more recent trend has been a prolonged (> 1 year) and extreme acidification (pH < 4.0). This study endeavoured to explain why the Jake may have undergone an acidic change, why it may have recovered and whether it will happen again. It was hypothesised that the acidification may have been caused by prolonged drying of the lake causing excessive oxidation of pyrite which produced more acid than the wetland could neutralise through buffering. The hypothesis was tested through laboratory and field experiments. The laboratory experiment involved taking intact sediment cores from around the lake, drying them for various lengths of time, and measuring pH, sulfate, total iron, total alkalinity and total aridity upon rehydration. Dried sediment from diatomaceous earth under Fe(OH)3 precipitate gave the lowest pH of less than 4.0. High sulfates, low alkalinity and low pH were interrelated. While drying in its own right produced low pH, generally there was no significant difference between drying times for release of selected variables. The field experiment involved the establishment of small in situ mesocosms to test for the effects of isolation of water on acid production and buffering capacity. Over an 18 week period between April and August 2000 weekly physico-chemical properties were taken inside and outside each in situ core and monthly, sulfate, total iron, total acidity and total alkalinity were tested. The field experiment showed an acidity producing area in the south western comer of the wetland in the diatomaceous sediment where iron hydroxide precipitate (an indication of acidification) occurs. Generally high sulfates and low total alkalinity were associated with low pH. providing evidence for pyrite oxidation. Over the study period the pH appeared to recover from

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