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Coarse woody debris extract decreases nitrogen availability in two reclaimed oil sands soils in Canada

Kwak, Jin-Hyeob, Chang, Scott X., Naeth, M. Anne, Schaaf, Wolfgang
Ecological engineering 2015 v.84 pp. 13-21
ammonium compounds, carbon nitrogen ratio, coarse woody debris, forest litter, habitats, leachates, mineral soils, mineralization, mining, nitrification, nitrogen, nitrogen cycle, oil sands, organic matter, peat, plant growth, rain, Canada
Forest floor mineral soil mix (FMM) and peat mineral soil mix (PMM) are common cover soils and sources of organic matter for reclamation of open-pit mining disturbed land in the Athabasca oil sands region. Coarse woody debris (CWD) can be an additional source of organic matter and can provide nutrient and habitat for plant growth. However, the effect of CWD on nitrogen (N) cycling in reclaimed oil sands soils has not been studied. A laboratory incubation experiment was conducted to assess chemical effects of a CWD extract on gross and net N transformation rates in FMM and PMM using the 15N pool dilution method. The CWD extract was used to simulate CWD leachates (with rainwater as a control) that are produced in the field. The effect of the simulated CWD leachate on the cover soils was studied in a 2 (FMM vs PMM)×2 (CWD extract vs rainwater addition) factorial design. There was no difference in gross N mineralization rates between FMM and PMM, although net N mineralization rates were greater in FMM than in PMM (p<0.001) due to greater NH4+ immobilization rates in PMM. Gross and net nitrification rates were greater in FMM than in PMM (p<0.001). The ratio of gross nitrification to gross NH4+ immobilization rates (N/IA) was greater in FMM than in PMM (p<0.001), as the greater NH4+ immobilization rates in PMM decreased gross nitrification rates by decreasing NH4+ availability. Addition of the CWD extract decreased gross (p<0.01) and net (p<0.001) N mineralization rates, increased (p<0.001) NH4+ immobilization and decreased (p<0.001) gross nitrification rates in both cover soils. The N/IA ratios were decreased by the CWD extract addition, indicating that heterotrophic NH4+ immobilization was superior to autotrophic nitrification due to the high C/N ratio of the CWD extract. We conclude that FMM will have greater N availability for oil sands reclamation than PMM. Leachates from CWD would decrease N availability by decreasing gross N mineralization and nitrification rates and by increasing N immobilization rates.