CALCIUM-CARBONATE PRECIPITATION DISSOLUTION ALONG A FOREST PRIMARY SUCCESSIONAL SEQUENCE ON THE TANANA RIVER FLOODPLAIN, INTERIOR ALASKA

Calcareous (alkaline) soils exist along the river floodplains of inter ior Alaska. In calcareous soils, the balance of CaCO3 reflects net sys tem acidification-alkalinization. The objectives of this study were to determine the origin of the CaCO3, quantify CaCO3 precipitation-disso lution, and quantify net system acidification alkalinization along a f orest primary successional sequence (250 years) on the Tanana River fl oodplain of interior Alaska. The CaCO3 concentrations in the initial s oil profiles were positively correlated (R2 = 0.883) with silt concent rations. Differences in CaCO3 concentrations in the early soil profile s between sites of similar age, between forest successional stages, an d among soil horizons within a profile are primarily due to difference s in silt concentrations, which are controlled by the alluvial deposit ion process. There was a curvilinear decrease in CaCO3 content along t he forest successional sequence, suggesting that the CaCO3 originated with the alluvial material and was not formed in situ. The loss of CaC O3 was equivalent to a loss of acid-neutralizing capacity of 10.0 kequ iv . ha-1 . year-1, which is a high rate of soil acidification. These forested, relatively pristine ecosystems are dominated by internal sou rces of acidity.