Individual study: The effect of adding Wollastonite in an attempt to ameliorate the effects of acidification in an anthropogenically acidified stream in the Hubbard Brook Experimental Forest, New Hampshire, USA
Likens G.E., Buso D.C., Dresser B.K., Bernhardt E.S., Hall R.O., Macneale K.H. & Bailey S.W. (2004) Buffering an acidic stream in New Hampshire with a silicate mineral. Restoration Ecology, 12, 419-428
In eastern North America many lakes and streams have been acidified in recent decades due to the effects of anthropogenic acidification which, amongst other effects, has led to impoverishment of species assemblages. In an attempt to rectify acidification, additions of neutralizing compounds, such as lime, to water bodies has been trialed, but this has produced limited amelioration so far and, as a result, aquatic ecosystems have recovered little. This study tested an alternative to lime, Wollastonite (CaSiO3) a natural calcium silicate mineral, which was added to an acidified stream in northeastern USA. Both changes in water chemistry and macroinvertebrate fauna were investigated.
Study site: A 50 m reach of an anthropogenically acidified stream was treated with milled and pelletized Wollastonite (Wo; CaSiO3) a natural calcium silicate mineral from the Adirondack Mountains, New York, within the Hubbard Brook Experimental Forest, New Hampshire, northeastern USA, to evaluate its buffering and restoration potential.
Wollastonite addition: On 18 June 1999, Wo granules were spread evenly using cups (each holding 350 g) and sprinkling into the water or onto the banks. Two 1 m long × 4 m wide PVC grids (moved successively downstream), centred on the stream channel, were used to guide application. The treated stream section varied from 1.7 to 3.5 m in width, with some Wo applied to the bank on both sides of the channel. In total, an area of 184 m² was treated.
Water chemistry: To establish pre-treatment water chemistry, samples were taken 15 and 8 days before Wo addition, and then twice each day for 4 days before the addition from sites above, within and below the experimental reach. Before Wo application, the chemistry of these sites was essentially identical. Samples were taken frequently (15 min intervals in the treated reach and 1 hour intervals in a nearby reference reach) during the first 3 hours of Wo application. This frequency was then reduced to twice a day, and then once a week after 3 weeks. Several additional samples were taken during high-flow events (spates). Particulate matter, and the dissolved and suspended particulate Ca² + flux into and out of the treated reach was assessed. The error for dissolved and particulate fluxes in stream water was estimated at approximately 5%.
Macroinvertebrates: To assess the effect of the Wo addition on stream macroinvertebrates, drift and emergence samples were collected before and after the application at multiple sites upstream and within the treated reach.
Water chemistry: The Wo was highly effective in raising the pH, acid-neutralizing capacity (ANC), dissolved inorganic carbon (DIC) and Ca²+ concentrations of the stream water. After initial sharp fluctuations in pH and concentrations of ANC, DIC and Ca²+, the relatively slow Wo dissolution rates dampened extreme concentrations and resulted in a relatively long-lasting (4 months) stream water acidity amelioration. Changes in concentrations of Ca²+, dissolved Si, ANC and DIC were related to water flow. After several high, stream-discharge events, concentrations quickly returned to pre-spate conditions.
Macroinvertebrates: Wo addition had no discernable effect on the stream biota but given the short duration of the experiment this was unsurprising. Wo application appeared not to affect the larval macroinvertebrate drift behaviour, density or emergence of an abundant stonefly Leuctra ferruginea. Over 25 aquatic taxa were collected (including some terrestrial adults) in drift samples, but there were no significant differences in the taxonomic composition after the Wo application.
Conclusions: The single application of Wollastonite produced an amelioration in water pH and acid-neutralizing capacity of the acidified stream over 4 months. Spate events due to rainfall diluted the stream water concentrations temporarily and increased acidity, but pH returned consistently to more alkaline conditions within a few hours. Wollastonite might therefore be considered on a wider scale in amelioration of anthropogenically acidified streams. Although Wo pellets may be washed out rather quickly, if stream flow is high, it may be longer lasting and produce less extremes in water chemistry than lime (calcite) applications.
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