Long-term responses in soil solution and stream-water chemistry at Hubbard Brook after experimental addition of wollastonite

Abstract

In October 1999, 3450 kg ha–1 of wollastonite (CaSiO3) was applied to Watershed 1 at the Hubbard Brook Experimental Forest in New Hampshire, USA, with the objective of restoring calcium that had been depleted from soil-exchange sites by chronic inputs of acid deposition. After the treatment, the concentrations and fluxes of calcium and dissolved silica significantly increased in both soil solution and stream water throughout Watershed 1, as did the acid-neutralising capacity. The concentrations and fluxes of inorganic monomeric aluminium significantly decreased. The treatment improved the acid–base status and decreased the potential for aluminium toxicity in stream water, especially in the lower reaches of the watershed. Approximately 4.7 % of the added calcium and 17 % of the added silica from the wollastonite treatment was exported from Watershed 1 in stream water by the end of 2010. Meanwhile, ~1825 mmol m–2 of the added calcium and 2125 mmol m–2 of the added silica were either transported to lower mineral soil horizons – as particulate wollastonite, or as dissolved solutes (calcium 77.6 mmol m–2; silica 592.2 mmol m–2), thus contributing to increases in soil pools – or were taken up by vegetation and incorporated into internal calcium and silica cycles of the watershed ecosystem. This experimental wollastonite addition was an effective tool for mitigating the acidification of the ecosystem and restoring the calcium status and forest health of this base-poor watershed.