In the clay rich, calcareous soils of Western Canada, managing phosphorus is critical to ensuring the long-term successful bioremediation of residual hydrocarbons. As part of the Sustainable In Situ Remediation Cooperative Alliance (SIRCA), a large scale field experiment explored how soil mineralogy interacted with biostimulatory solutions to control phosphorus bioavailability in a PHC-contaminated site. Two large (1 m diameter) infiltrators were installed to 5 m and backfilled with quartz sand and injected with a biostimulatory solution containing phosphate, sulfate (as an electron acceptor), and Mg (as an electrolyte). Soils from eight western Canadian sites of varying mineralogy and texture were dried, homogenized and then manipulated by either increasing (saturating with calcium) or decreasing (acid wash followed by magnesium) total soil Ca to alter the solubility of phosphate in the systems. Soils were then spiked with diesel, and duplicates placed in each injector using in situ bioreactors. After 3 months of contact in situ with the biostimulatory solution, three principal phosphate phases formed in the soil: newberyite, brushite and adsorbed phosphorus. All indicators of degradation (in situ degradation estimates, mineralization assays, culturable bacteria and catabolic genes) were significantly dependent on the soil’s phosphorus speciation. Specifically, there was a strong link between the phosphorus phases and anaerobic phenanthrene mineralization along with the associated catabolic genes (bzdN and bcrC). Adsorbed phosphorus was the dominant controlling species with bzdN increasing in response to increasing adsorbed phosphorus and bcrC decreasing. This change in catabolic prevalence as a result of mineralogy was clearly demonstrated in the community composition analysis in which the amount of adsorbed phosphorus, newberyite and brushite were the dominant mineralogical controllers of community composition in these soils. This study highlights that the combination of advanced molecular-scale chemical speciation using synchrotron techniques and next generation molecular biological tools shows particular promise in elucidating the complex relationships between soil mineralogy, nutrient availability, and microbial remediation in natural systems.

Mineralogical controllers on phosphate bioaccessibility during subsurface PHC remediation

251st National Meeting (2016)

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