A holistic approach to investigate the fate of naphthalene in simulated coniferous forest ecosystems
In this thesis the holistic fate of PAHs in coniferous forest ecosystems has been investigated, using microcosms which enabled the full fate of 14C-labelled PAHs to be followed. An initial experiment with naphthalene, fluorine and pyrene showed that between 60-70 % of naphthalene was either mineralised or volatilised, whereas over 90% of the fluorine and pyrene were retained within the soil. Naphthalene mineralization was reduced in the presence of enchytraeid worms, and the level of reduction was not correlated with the size of enchytraeid communities which the soil was inoculated with. The holistic fate of naphthalene in the presence of Scots pine was investigated and interestingly, planted soil had lower naphthalene mineralization (c.20 %) compared to unplanted soil (c. 40-60%). This may have been a result of the ‘Gadgil effect’, where saprotrophic fungal degradation activity was suppressed by plant and mycorrhizal uptake of moisture and nutrients. Alternatively, as fungal biomass increased (from 1x104 to 1.4x105) over time in planted soil, this may indicate that root exudates increased microbial activity enabling enhanced 14C labelled naphthalene degradation and assimilation. Thin sections were used to determine soil structure, and identified that oribatid mites were transferred into soil on the roots of field grown pine seedlings. Once in soil, mites consumed vast quantities (6.9%) of soil organic matter. Oribatid mites did not influence naphthalene mineralization or volatilisation from soil. The fate of naphthalene which had aged for 180 d in soil was investigated, and both mineralization and volatilisation totals were low, as desorption of naphthalene from soil organic matter was slow. Enchytraeids and Scots pine did not alter the fate of naphthalene. Sorption and desorption of naphthalene form coniferous forest soil followed a biphasic behaviour.