Iron is an essential micronutrient that is required by some microorganisms in relatively large quantities. This is problematic for those inhabiting marine environments, where iron is highly insoluble and the dissolved fraction is predominantly strongly bound to organic compounds. Due to low supply and high demand, iron limits primary productivity in many oceanic waters, and may also limit growth of organisms in coastal waters under some circumstances. Recent incidents of explosive growth (???blooms???) of the noxious filamentous cyanobacterium Lyngbya majuscula in the coastal marine waters of Moreton Bay, Queensland, have prompted speculation that terrestrial human activities have increased iron availability to the organism, thus overcoming previous limitations on growth imposed by scarcity of the nutrient. This thesis describes work investigating the chemical form of iron in coastal waters under various environmental conditions and the way in which this influences its availability to L. majuscula. Chemical speciation of iron was investigated as a function of terrestrial-derived inputs of natural organic matter (NOM) of variable origin and sunlight in coastal marine waters, employing chemiluminescence-based and spectrophotometric techniques with high sensitivity and temporal resolution. These techniques allowed determination of iron and other chemical parameters at naturally occurring (typically nanomolar) concentrations. The mechanism of iron acquisition by L. majuscula was also investigated using a radioisotope-labelling labelling technique in addition to the other techniques described. Results indicated that iron speciation can be described by five classes: inorganic dissolved and organically complexed dissolved iron in both ferrous (reduced) and ferric (oxidised) forms, and precipitated inorganic iron. Simulation of laboratory results by numerical kinetic modelling of the processes investigated indicated that while the thermodynamic impetus is strongly towards precipitated iron, iron complexation by NOM and its reduction by sunlight-mediated processes and/or L. majuscula results in meta-stable dissolved species that are more readily available to L. majuscula. Superoxide is a critical intermediate in iron reduction by both sunlight and L. majuscula. Thus L. majuscula is capable of altering iron speciation to increase its availability, however uptake is also strongly dependent on environmental conditions and may be enhanced by increased inputs of iron, NOM and sunlight into coastal waters.
| Identifer | oai:union.ndltd.org:ADTP/258531 |
| Date | January 2005 |
| Creators | Rose, Andrew, Civil & Environmental Engineering, Faculty of Engineering, UNSW |
| Publisher | Awarded by:University of New South Wales. Civil and Environmental Engineering |
| Source Sets | Australiasian Digital Theses Program |
| Language | English |
| Detected Language | English |
| Rights | Copyright Andrew Rose, http://unsworks.unsw.edu.au/copyright |
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