Abstract
One possible solution to the recent decline of calcium (Ca) concentrations in Canadian Shield forests and lakes in eastern North America is the addition of Ca-rich wood ash to watersheds. We investigated the feasibility of using small, mainly residential sources of non-industrial wood ash (NIWA) for this purpose by quantifying concentrations of its major nutrients and metals, its toxicity to Daphnia in aqueous extracts, and estimating the amount of NIWA available in the District of Muskoka in central Ontario. Locally collected NIWA averaged 30% Ca, and also contained smaller but significant amounts of K, Mg, Na, and P. Of these, K was so soluble that it was toxic to Daphnia over 48 h in the concentrate and 10-fold dilution; however, sedimented ash was not toxic over 15 d. Most metal levels in NIWA were below targets permitting unrestricted land application. However, Cu and Zn were just above these targets, but well below those for conditional use. Muskoka residents generate about 235 000 kg of NIWA annually, not enough to treat all central Ontario areas affected; however, a NIWA recycling programme implemented across southern Ontario could generate enough ash to solve the Ca decline problem in Muskoka’s forests and lakes.
Highlights
Calcium (Ca) concentrations have fallen in forest soils in eastern North America following decades of atmospheric acid deposition (Likens et al 1998; McLaughlin 2014)
The methods for safe and efficient collection, transport, and distribution of non-industrial wood ash (NIWA) have not been developed, but they would clearly differ from industrial ash sources. To address these hurdles in the development of a NIWA recycling programme designed to combat environmental Ca decline in Muskoka watersheds, our objectives were to: (i) quantify the total cations and metal concentrations in typical NIWA generated from the combustion of hardwood firewood in central Ontario; (ii) quantify the soluble levels of Ca and other major cations, anions, and nutrients in NIWA; (iii) compare metal concentrations in NIWA with provincial guidelines and with industrial wood ash; (iv) quantify the actual toxicity of aqueous extracts of NIWA in both water column and sediment deposition scenarios; and (v) estimate the amount of NIWA that might be available in Muskoka, Ontario to launch a residential wood ash recycling programme that could help solve the provincial Ca decline problem
We examined the influence of NIWA ash source on the concentrations of the trace metals and total nutrients in the dry hardwood ash using one-way analysis of variance (ANOVA)
Summary
Calcium (Ca) concentrations have fallen in forest soils in eastern North America following decades of atmospheric acid deposition (Likens et al 1998; McLaughlin 2014). Despite reductions in acid deposition, the natural recovery rate of Ca will be extremely slow (Likens et al 1996; Aherne et al 2003; Watmough and Aherne 2008); adding Ca as a crushed mineral or wood ash to forested watersheds is an attractive option. Calcite additions have certainly improved chemistry and biota in acidified lakes (Yan et al 1996), soil chemistry (Driscoll et al 1996; Geary and Driscoll 1996; Löfgren et al 2006), and forest health, regeneration, and productivity (Wilmot et al 1996; Moore and Ouimet 2010, 2014; Mainwaring et al 2014).
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