Microbial Activity and Fertiliser Management

Biodegradation of petroleum hydrocarbons occurs in cold areas (e.g. Margesin and Schinner 2001), even at temperatures below freezing (Rike et al. 2003), although the rate of microbially enhanced remediation of contaminants is constrained in polar regions compared with temperate regions. In Antarctica, the Antarctic Treaty (1961; and the Agreed Measures for the Conservation of Antarctic Fauna and Flora 1964; for a reference see SCAR 2008) prohibits the importation of non-indigenous species, which includes microorganisms. The discovery and encouragement of indigenous degrading microbial populations has assumed great importance for the biodegradation of fuel spills (Braddock et al. 1997; Aislabie et al. 2000; Ferguson et al. 2003). In the Arctic, it is possible to innoculate hydrocarbon-contaminated soils to encourage biodegradation (Mohn and Stewart 2000). Of broader significance is the correct fertilisation levels, particuarly of nitrogen compounds but in some cases also phosphorus (Mohn and Stewart 2000; Walworth et al. 2001), to stimulate biodegradation rates. It is now well-established that over-fertilisation suppresses microbial activity and inhibits biodegradation of petroleum hydrocarbons. The mechanism is microbial stress due to osmotic soil water potential depression (Braddock et al. 1997; Walworth et al. 1997, 2007), which occurs as the soil dries and the ionic concentration of nutrients in the soil water increases. This effect is enhanced by the desiccation that occurs during every freeze-thaw cycle in areas of freezing ground. Thus while the addition of nutrients is important to enhance biodegradation, it is crucial that the correct applications are used, otherwise efforts at remediation will be hindered. Controlled-release nutrient sources such as nutrient-loaded zeolites and encapsulated fertilizers are able to release nutrients slowly, helping to prevent over-fertilization and allowing nutrient release during periods when the contaminated site is unattended, which is important for reducing the operational costs of barriers in remote areas. However, encapsulated fertilizers may shatter due to the effects of freeze-thaw, particularly when moistened (Gore and Snape 2008), and this should be assessed prior to the use of controlled release nutrient sources in the field.

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