Responses of a Watershed Manipulated By Calcium Silicate at a Northern Hardwood Forest Ecosystem: Mass Balance and Landscape Position

Youngil Cho, Charles T. Driscoll and Chris E. Johnson
Department of Civil and Environmental Engineering
151 Link Hall, Syracuse University
Syracuse, NY 13244

In spite of decreases in atmospheric sulfate (SO42-) deposition, stream pH in watershed 1 (W1: 11.8 ha) at the Hubbard Brook Experimental Forest (HBEF) in New Hampshire (NH) had remained acidic. W1 was experimentally treated by a calcium silicate (CaSiO3; wollastonite) addition in October of 1999 to assess the role of calcium (Ca) and silica (Si) supply in the structure and function of base poor forest ecosystems. In this study, we discuss landscape position and mass balances of Ca and Si in soil water and stream water to determine how much wollastonite is retained and lost from the ecosystem in response to the watershed application.

A long-term sampling program was initiated to evaluate longitudinal patterns of watershed response to the wollastonite treatment. Soil water and stream water samples within sub-watersheds were collected monthly prior to and after treatment to investigate changes in soil, soil water and stream chemistry. CaSiO3 addition significantly increased Ca and Si fluxes in both organic soil solution and stream water at all elevations following the treatment. The magnitude of changes in fluxes decreased with increasing soil depth, since much of Ca and Si derived from the dissolution of the wollastonite addition remained in upper soil horizons during the study period. Approximately 5.3% of the added Ca and 20.3% of the added Si was exported from the high elevation spruce-fir-white birch (SFB) zone, 4.7% and 14.8% from the high-elevation hardwood (HH) zone, 4.9% and 15.3% from the low-elevation hardwood (LH) zone, and 5.2% and 18.4% from the whole watershed (W1) over the six year study period. These removals suggest that 94.7% of the added Ca and 79.2% of the added Si at SFB, 95.3% and 85.2% at HH, 95.1% and 84.7% at LH, and 94.8% and 81.6% for all W1 was retained. The SFB zone showed somewhat greater export of Ca and Si than the HH and LH zones due to its shallow soil depth and greater soil water content.