From 1 - 10 / 1169
  • These documents have been scanned by the GA Library. Please refer to the document for contents.

  • Legacy product - no abstract available

  • Executive Summary Between the 6th and 10th December 1999, the Australian Geological Survey Organisation, in collaboration with the NSW Environment Protection Authority and the Department of Land and Water Conservation, conducted a field survey of Durras Lake, South East, NSW. The objectives of the survey were to: (i) measure the net fluxes of sediment metabolites from the major sediment facies; (ii) estimate the rate and significance of denitrification; and (iii) field test modifications to AGSO automated benthic chambers. Eight chambers were deployed on two sediment facies (sand and mud). Time series of water samples collected from these chambers were used to determine nutrient flux rates and sediment respiration. The following observations were made: At the time of the survey, the deep mud basin was stratified with an anoxic, saline bottom layer and fresher well oxygenated surface waters.. Respiration dominated (ie oxygen demand of the sediments was greater than production via photosynthesis) in each chamber incubation in the mud and sand facies. TCO2 fluxes ranged between 13.3 ?57.4 mmol m-2 day-1 in the mud facies and 39.0 ?106.3 mmol m-2 day-1 in the sand facies. Organic carbon being degraded in the deeper mud basin was primarily of a diatomaceous composition. Dark respiration in the sand facies was not consistent with a mainly diatomaceous origin of organic carbon. Denitrification efficiencies were relatively low in both the sand and mud facies. Low denitrification rates in the mud facies may be related to the low concentrations of dissolved oxygen in the water overlying the sediments. Tests of AGSO system for direct measurement of denitrification using benthic chambers and N2 measurement by quadropole mass spectrometer were successful.

  • EXECUTIVE SUMMARY AGSO, MAFRI and MARBOT collected surface samples (0-2 cm) from 56 Sites in Moreton Bay and the Brisbane River between the 16and 26 of September, 1997. Samples were analysed for; (i) sediment grain size, (ii) total organic carbon, N & P (iii) porewater nutrient concentrations of ammonium, nitrite, nitrate, phosphate and silicate, (iv) exchangeable nutrients N & P. Analyses for sediment grain size, porewater nutrients and exchangeable nutrients were performed at the Stradbroke Island Research Station, during the field period and samples for total N & P were analysed in the MAFRI labs. Samples were also collected and analysed on-site for benthic chlorophyll (part of BFND). Each day two sediment cores were collected from a typical sediment facies sampled on that day. The cores were sectioned into 2 cm intervals and the porewater nutrients were analysed. The distribution of muddy sediment (< 64 micron) in Moreton Bay occurs in a broad band which extends in an arc from Deception Bay, through the midbay and south to Waterloo Bay. Sandy sediments occur at the river mouths (Brisbane, Caboolture and Pine), in Pumicestone Passage, on Amity and Moreton Banks and on the tidal delta of North Passage. The distribution of total organic carbon (TOC), TN and TP in sediments was similar to that of muddy sediments, implying that the total nutrient content of sediment is determined by the sediment facies. The distribution of porewater silicate and the proportions of N reduced (ammonia)/ DIN (ammonia + nitrate + nitrite) appear similar to the bay-wide distribution of muddy sediments. All other nutrient species, nitrate, nitrite, ammonia and phosphate do not show any apparent relationship to the TOC, TN and TP in sediments. These observations indicate that it is the interplay between (i) TOC, TN and TP (ii) the availability of oxidants and (iii) the mediation of supply and demand by sedimentary microbial communities, which determine the distributions of different species of N and P. It is also likely that sediment/pore water interactions also exert some control on the distributions of N and P speciation. In general, the high values of Nred/DIN in the surface sediments, are indicative of anoxic interfacial sediments, while trends toward decreasing Nred/DIN are more indicative of sub-oxic-to-oxic sediments, and increasing influences of denitrification (in sub-oxic sediments), and subsequently nitrification in the oxic surficial sediments. Exchangeable PO4-3 was highest at sites with muddy sediment and in a dense seagrass bed near Stradbroke Island. In contrast the distribution of exchangeable NH4+ was not related to the sediment grain size, with the highest concentrations occurring in Waterloo Bay , southern Moreton Bay and near Cabbage Tree Creek in Bramble Bay. The nutrients released from the sediment using seawater extractions was highly variable and did not correlate with the porewater or exchangeable nutrient distributions, suggesting that local microphytobenthos communities may be rapidly taking up nutrients as they are released from the sediment. The down core distributions of porewater nutrients at most sites had the highest nutrient concentrations at the surface and lowest in the porewater from the base of the core. This indicates that nutrients would most likely flux from the sediments to the overlying waters at these sites. Two notable exceptions to this observation occurred in Deception Bay and the Brisbane River: First, at Site F4 (N. of Cabbage Tree Point), phosphate dissolved in the surface sediment porewater was less than the bottom porewater concentration, suggesting that the sediments are a sink for phosphate at this site. Second, the concentrations of nitrate and nitrite were undetectable in the sediment porewater from two sites in the Brisbane River, including Breakfast Creek (Site H7) and the entrance to Aquarium Passage (Site H8).

  • Legacy product - no abstract available

  • Undiscovered hydrocarbon resource assessment at AGSO is currently calculated using the AUSTPLAY program. This program has not been continually developed to take advantage of advances in computingtechnology and software. While the program can still produce an assessment, there are many shortcomings that make the program unmanageable. AUSTPLAY outputs are suitable for input to hydrocarbon production forecasts but the results of the assessment do not represent an estimate of the ultimate recoverable resource. The USGS (2000) has recently published the results of a worldwide assessment of undiscovered resources and their methodology gives a better estimate of the ultimate recoverable. Powell (2001) advocates the use of the USGS assessment to become Australia's undiscovered hydrocarbon resource assessment with the caveat that we now need to evaluate the results produced by the USGS.