British Columbia Mine Reclamation Symposium

Assessing soil carbon storage and climate change mitigation in biosolids mine reclamation projects Trlica, A.; Teshima, M.


Carbon release due to land-use change and clearance of natural cover contributes significantly to anthropogenic climate change. Biosolids, the treated and stabilized solids from municipal wastewater treatment, have been applied to mines for decades to facilitate reclamation success. Using biosolids as a soil amendment in mine reclamation may help mitigate climate change by reversing carbon losses in land degraded by surface mining. However, the magnitude of long-term soil carbon storage increases with biosolids use in reclamation is largely unknown. This study compared carbon storage in biosolids-amended and conventionally reclaimed mine soils several years after closure. Soil samples from 0-15 cm and 15-30 cm depths were taken from five surface mined areas, each containing sites reclaimed either with biosolids or with conventional reclamation approaches (e.g. topsoil + synthetic fertilizer). A focus of the sampling was to acquire information on sites with greater age since final reclamation (up to 27 years). Mines reclaimed with biosolids stored an average of 32.47 ± 3.16 tonnes of carbon per hectare more in the top 15 cm of soil than conventionally reclaimed sites; in the 15-30 cm soil layer differences in carbon storage were generally not significant. Using estimates of carbon storage from one of the mine areas and other published studies, a life cycle assessment was conducted to estimate the net greenhouse gas (GHG) emissions from the use of biosolids in reclamation in the Pacific Northwest region of the United States. The assessment compared using biosolids to reclaim and reforest degraded land versus using biosolids in agriculture combined with conventional reclamation to forest. Accounting for GHG flows such as biomass and soil carbon increases and project-related fuel use, the assessment showed that using biosolids for reclamation had a greater GHG sink potential than conventional reclamation combined with agricultural biosolids applications. The results of the life cycle assessment show that coupling land reclamation with biosolids reuse carried a large potential for increases in on-site carbon storage. Incorporating biosolids into a mine reclamation program can reduce reclamation costs as well as promote climate change mitigation through increased organic carbon storage on-site.

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