Trace metal biogeochemical responses following wood ash addition in a northern hardwood forest

Wood ash may be useful as a forest soil amendment in Canada, but trace metals can have detrimental effects if they accumulate in, or are transported from, forest ecosystems. Metal concentrations in soil water and sugar maple (Acer saccharum Marsh.) seedling tissue chemistry were measured in a north temperate hardwood forest over 4 years following a biomass boiler ash addition field trial. Twenty plots (3 m x 3 m) were established in Haliburton Forest with both fly and bottom ash treatments of 0, 4, and 8 Mg.ha(-1) with four replicates, and tension lysimeters were positioned in each plot at 30, 50, and 100 cm depths. Over the 4 years, soil water metal concentrations in treated plots were not significantly different from those of the control plots. No differences in metal concentrations in foliage of sugar maple seedlings could be detected, but there were significantly higher concentrations of some metals (Al, Fe, Zn, Pb, Ni, and Sr) in roots of treated plots. Simulated drought mobilized several metals in upper mineral soil, but this mobilization occurred similarly in controls and ash-treated soils. These results suggest that doses below 8 Mg.ha(-1) industrial wood ash with trace metal concentrations below Canadian regulatory limits do not cause an increase in trace metal mobility or availability in northern hardwood forests with acidic soils during the first 5 years after application.

Automated summary

The study found that metal concentrations in soil water were not significantly different between treated plots and control plots over the 4 years following a biomass boiler ash addition field trial. The results suggest that industrial wood ash doses below 8 Mg.ha(-1) with trace metal concentrations below Canadian regulatory limits do not increase trace metal mobility or availability in acidic soils of northern hardwood forests during the first 5 years after application.