The effect of quick freezing and fast thawing on stored seawater nutrient concentrations of dissolved inorganic phosphate, nitrate and ammonium
Master Thesis
2004
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University of Cape Town
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Abstract
In an attempt to improve the quality of preserving seawater nutrients for delayed analyses, a sample of unfiltered and aged nutrient-depleted seawater was obtained from Marine and Coastal Management (M&CM) and spiked with small different volumes of standard nutrient solutions. These were prepared into 100 mL glass bottles to constitute the lowest, intermediate and highest levels of dissolved inorganic phosphate (0.5, 1.5, 3.0 μM), nitrate (5, 15 and 30 μM) and ammonium (0.5, 1.5, 2.5 μM) that are found in the southern Benguela region. After spiking, the samples were analysed to determine their "true" initial concentrations and immediately quick frozen using liquid nitrogen. A time series analysis (up to seven weeks) was performed by first fast-thawing the samples using a microwave oven and fixing up the nutrients within 20 minutes. Variations in nutrient concentrations did not exceed 7% for phosphate, 4.0% for nitrate at all levels and 8% for ammonium at the intermediate and highest levels, but varied by 19.2% at the lowest level. Statistical tests for significance of the means were made at a = 0.05 level and no difference was found at any level for the nitrate, and the lowest level phosphate. The higher levels of phosphate, and all ammonium were found to be significantly different. Hence, the experimental conditions employed in this paper would not be recommended for the all ammonium and the higher levels of phosphate concentrations. These variations were however not large or regular in pattern but erratic, which suggested that they were not due to microorganisms and optimizing those conditions may well to yield improved results.
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Includes bibliographical references (leaves 43-44).
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Wedeinge, J. 2004. The effect of quick freezing and fast thawing on stored seawater nutrient concentrations of dissolved inorganic phosphate, nitrate and ammonium. University of Cape Town.