WEATHERING DYNAMICS IN THE ACID IMPACTED SLEEPERS RIVER: COMBINING OBSERVATIONS OF STREAM AND SOIL DATA

Weathering, an important ecosystem service, is strongly impacted by acid deposition with potential long-term consequences for both the ecosystem and climate. For example, silicate weathering with carbonic acid consumes atmospheric CO₂, however strong acids (nitric and sulfuric acid) do not have this capacity and can release CO₂ through carbonate weathering. This study investigates weathering in the acid impacted Sleepers River Watershed in VT using both historical data sets (1991-present), and recent water and soil samples. We hypothesize that reduced acid deposition led to reduced weathering rates, which is supported for carbonates by a steady decrease in groundwater Ca concentration and stream water Ca flux. However, fluxes of Si and base cations (other than Ca) remained unchanged over the past 20 years, suggesting no change in silicate weathering due to reduced acid deposition. Soil elemental analysis for several transects (hilltop to riparian zones) revealed an important control on landscape position on the distribution of base cation weathering products: soils in low lying landscape positions are typically enriched (positive tau values) in base cations whereas hillslopes and hill tops are generally depleted of base cations. Soil water and ground water data suggest a combination of Ca enriched ground water upwelling at the base of hillslopes and lateral transfer of weathering products, both leading to accumulation of weathering products and secondary minerals near streams.