The Bells Creek catchment covers an area of 100 km2 in the northern part of the Pumicestone Passage region of southeast Queensland. This catchment is an example of a low-lying sub-tropical coastal plain including both freshwater and estuarine settings. The main creeks drain into Pumicestone Passage, a large shallow estuary, which is a declared marine habitat and a Ramsar listed wading bird location. The Bells Creek catchment has undergone land-use change from bushland to grazing to pine plantations and is now coming under pressure for urban development. Quaternary age unconsolidated sediments are the dominant surface material in this area and formed during the last marine transgression. Of significance for such a setting is that estuarine sediments can retain metals mobilised as a result of natural processes (e.g. weathering) and anthropogenic activities (e.g. land-use disturbance). As trace metals can also occur naturally in rocks and their weathered products, it is of value to clearly distinguish natural and anthropogenic controls over metal source, distribution and mobility. To achieve this aim two approaches were taken: 1) to determine the factors controlling the geochemistry of weathered profiles, unconsolidated sediments, soils and natural waters, and 2) to identify the most effective analytical and numerical methods for evaluating metal concentration in different solid materials. This investigation is structured around four linked papers. The influence of mineralogy, geological setting, location of water table and depth of burial on the geochemistry of weathered profile are assessed in Paper 1. The second paper is an investigation of different analytical approaches for studying weathered sedimentary rocks, as well as the testing of several numerical methods for evaluating geochemical data from weathered profiles. In paper 3, a large heterogeneous geochemical data set including trace metals, total organic carbon and sulfur content, in addition to mineralogy and land use practices are integrated to enable evaluation of geochemical and anthropogenic processes controlling metal distribution. The fourth paper considers the distribution of iron and its transport as well as variations in size and morphology of different forms of framboidal pyrite within a smaller sub-catchment in the southern part of the study area. The labile and heterogeneous nature of the bedrock of the region, the Landsborough Sandstone, along with the sub-tropical climate of the area have resulted in weathering profiles up to 26 m deep. Due to the absence of industrial activity in the Bells Creek catchment, such weathering of the bedrock constitutes the major process governing metal distribution throughout the area. Analysis by X-ray diffraction (XRD) shows that the primary minerals occurring in the weathered profiles are quartz, plagioclase and K-feldspars while kaolinite is the most dominant secondary mineral present. Overall, parent rock silicates have been extensively replaced by clay minerals and Fe oxides. The relative influence of mineralogy, geological setting and groundwater over chemical weathering and geochemical cycling of metals can be summarised as follows: Mineralogy>geological setting>watertable position>depth of profile burial As the relationship between the total metal composition and the extractable and mobile component has environmental significance, a comparison was made between these forms of metals in weathered material. This comparison shows that metals such as V, Cr and Fe are part of the aluminosilicate matrix and remain largely in primary mineral structures. The retention of these metals may lead to their future release to the environment during on-going weathering. Other elements such as Cu, Zn, Pb, however, are found to be primarily adsorbed to sediment particles and therefore, easily releasable to the environment. As limited information on weathering of sedimentary rocks is reported in the literature, a variety of chemical analysis and numerical assessment methods were used to understand the geochemical processes involved in trace metal mobility in the weathered profiles. Two analytical methods of digestion, hydrofluoric acid and x-ray fluorescence were tested and found to be highly comparable except for refractory elements such as V and Cr. Among the numerical methods applied to the dataset were "chemical and mineralogical indices", "weight loss factor" and "immobile element approach". The "immobile element approach" was found to be the most appropriate method to characterise the weathering profiles typical of the catchment. This method considers a weathering system to be open and transforms the absolute values of trace metals enabling a quantitative evaluation of metal mobility. The following sequence of mobility was determined after applying this method to the data generated in this study: Zn>Pb>Cu>Cr>V The above sequence of mobility is supported by the comparison between extractable and total metal concentrations where Cr and V were identified as being part of aluminosilicate matrix and less mobile. On the other hand, Zn, Pb and Cu were found to exist in adsorbed form and to be readily released to the environment. Trace elements released through weathering and erosion of the bedrock can accumulate in estuarine and coastal sediments. Therefore, both the lateral and vertical distribution of trace metals within sediments and soils of Bells Creek catchment were investigated. Natural and anthropogenic factors controlling metal distribution were compared and it was concluded that the natural sediment character such as its mineral content is more significant than anthropogenic influences in controlling lateral and vertical metal distribution. Further, due to varying degrees of weathering and the heterogeneous nature of soils and sediments, the data were normalised. After testing several methods, it was concluded that calculation of an enrichment factor was the most appropriate. The enrichment factor revealed that elevated trace metal concentrations at some sites are due to bedrock weathering. Due to the environmental persistence of iron, excess of this common metal has always been of environmental concern in many coastal settings. In the small Halls Creek sub-catchment, for example, iron anomalies were detected in bottom sediments (Fe up to 14%). This finding has significance in the area, as iron has been identified as one of the major contributors in the growth of the toxic cyanobacteria "Lyngbya majuscula" which can negatively impact on aquatic fauna. Iron concentrations were also shown to be high in natural stream waters of this coastal zone (up to 16 mg/L); in the bottom sediments of the creek, iron occurs as hematite (freshwater section) or pyrite (estuarine section). A variety of pyrite morphologies were identified in both bottom sediments and particulate matter samples including spherical closely packed framboids, and the rare form of euhedra which indicates slow crystallisation. The different components of this investigation have: 1) established the order and extent to which natural factors control weathering, 2) tested a number of analytical and numerical methods in evaluating weathering profiles, 3) assessed natural and anthropogenic factors and established the mobility sequence for trace metals in weathered profiles and, 4) determined the iron mineral speciation and established morphological variations of pyrite. As the area of Bells Creek catchment will be under development pressure in the future, findings of this study represent a baseline of comparison for environmental assessment and are of importance for environmental management.

Estuaries can be considered as vital natural resources and are unique ecosystems at the interface between terrestrial and marine environments. The increase of population density centred on these coastal features and associated anthropogenic activities such as trade, industry, agriculture and recreation can adversely affect these sensitive environments. The Pumicestone Passage, located in northern Moreton Bay, Australia, is one such estuarine environment where there are concerns about degradation of water quality resulting from rapid land use change. These changes are both immediate to the Passage and within its wider catchment. Of notable concern are the outbreaks of Lyngbya (a toxic blue-green algae) in the Passage itself and near its interface with Deception Bay to the south. Other factors of concern are increased suspended and dissolved loads, and maintenance of ecosystem integrity. In this study, numerical modelling, graphical methods and water surface elevation and current velocity parameter calculations are used to describe hydrological processes in the Pumicestone Passage. A hydrodynamic model is developed using the modelling software SMS and RMA2 as a foundation for future hydrodynamic and water quality modelling. In addition, observed data are used to interpret general hydrodynamic behaviour in the passage, and determine various parameters for use in model development and calibration. Tidal prediction is also discussed and used for model calibration. To support the modelling and for preliminary interpretation of hydrodynamic processes within the Passage, measurements were made in the field of (a) water surface elevation variation at 17 sites; (b) tidal current velocities in four of the tributary creeks and at the northern boundary; (c) volumetric flow rates at two cross-sections within the Passage; and (d) cross-sectional bathymetry at sites where tidal current velocities were measured in the creeks. In general, examination of the observational data reveals a number of important processes in the Pumicestone Passage. Almost all sites within Pumicestone Passage and its tributaries are flood dominant indicating that tidal storage and bottom friction effects are significant. Mesotidal ranges occur at sites close to the southern boundary of the passage, however, bottom friction greatly reduces the tidal response at the remaining sites which results in microtidal ranges. The influence of both the southern and northern tides can be seen in the deformation of tidal waveforms in the central passage. Extensive intertidal areas at and inside the northern inlet to the Passage markedly reduce tidal ranges in the northern estuary and its tributary creeks. Issues involved in hydrodynamic model development and performance are discussed. Overall, model results for the southern estuary have satisfactory correlation with observed data whereas model results for the northern estuary are less satisfactory. In addition, water surface elevation variation model results are generally more accurate than tidal current velocity model results. Reasons for the differences between model and observed values are considered and possible solutions given. Factors discussed relate to boundary condition locations, resolution of bathymetric and geographical data, mesh development methods and parameter assignment.