Calcium carbonate precipitation–dissolution along a forest primary successional sequence on the Tanana River floodplain, interior Alaska

Abstract

Calcareous (alkaline) soils exist along the river floodplains of interior Alaska. In calcareous soils, the balance of CaCO3 reflects net system acidification–alkalinization. The objectives of this study were to determine the origin of the CaCO3, quantify CaCO3 precipitation–dissolution, and quantify net system acidification–alkalinization along a forest primary successional sequence (250 years) on the Tanana River floodplain of interior Alaska. The CaCO3 concentrations in the initial soil profiles were positively correlated (R2 = 0.883) with silt concentrations. Differences in CaCO3 concentrations in the early soil profiles between sites of similar age, between forest successional stages, and among soil horizons within a profile are primarily due to differences in silt concentrations, which are controlled by the alluvial deposition process. There was a curvilinear decrease in CaCO3 content along the forest successional sequence, suggesting that the CaCO3 originated with the alluvial material and was not formed insitu. The loss of CaCO3 was equivalent to a loss of acid-neutralizing capacity of 10.0 kequiv•ha−1•year−1, which is a high rate of soil acidification. These forested, relatively pristine ecosystems are dominated by internal sources of acidity.