| This study is designed to investigate the effect of temperature on chemical weathering in the field. Two small pristine watersheds, where moisture and topographic conditions are conducive to weathering (Jamieson Creek in British Columbia and the Rio Icacos in Puerto Rico), are studied in detail and compared. The watersheds have very similar area, bedrock lithology, and annual rainfall, and both have mountainous topography. However, the two sites differ substantially in temperature.; The Rio Icacos watershed was the site of lithium bromide tracer experiments. Approximately 75% of the tracer was observed to move laterally away from the application area through a thin surface horizon. Tracer that entered the regolith was observed to move vertically at a rate of 1.8 to 2.6 m/yr. Results were used to determine quartz and biotite weathering rates, and explain enigmatic phenomena related to the dissolution of quartz.; Analysis of weathered rock samples from below the Rio Icacos saprolite reveals that weathering is dominated by kaolinization of plagioclase. A mass balance indicates that virtually all primary minerals in bedrock weather completely to secondary phases. Weathering of porous rock in the subsurface is modeled as a system of fronts weathering in parallel where the rate of advance of individual fronts is a fraction of the total denudation rate. Based on steady-state assumptions, weathering rates for plagioclase are calculated.; It is observed that weathering within the permeable and unsaturated ablation till at the Jamieson Creek site is dominated by plagioclase dissolution. On a watershed scale, fluxes of Ca and K are higher than would be expected from plagioclase and hornblende dissolution alone. This indicates that preferential leaching of these solutes occurs in some part of the system, possibly in the relatively unweathered lodgement till underlying the ablation till.; When compared to Jamieson Creek, weathering rates of plagioclase from the Rio Icacos are 3.8 to 5.2 times greater at the warmer site. This suggests that the Arrhenius effect, which predicts a 3.5- to 9-fold increase in the dissolution rates of plagioclase as temperature is increased from 3.4° to 22°C, may explain the greater weathering fluxes of the Rio Icacos. |
