Water Table Effects On Fate of Carbon and Metals in Soil Columns.

Soil organic carbon (SOC) fluxes are relevant to global C dynamics. Soil moisture is an important determinant of SOC fate. Effects of seasonal water tables on SOC dynamics of humid region sandy coastal plain soils are not well understood.  A laboratory column study was conducted to test hypotheses that shallow water table (SWT) conditions reduce CO₂ loss to the atmosphere (H1), increase leaching of dissolved organic C (DOC) and metals (H2), and increase net SOC storage (H3). The A and E-horizon material of moderately-well drained sandy soils from 5 sites were collected for the study. Ten 90-cm columns (2 per site) were packed with A-horizon (20 cm) over E-horizon material (60-cm). Five columns, one from each site, were subjected to SWT treatments and 5 to deep water table (DWT) treatments. Upward CO₂ flux was measured using 1 M NaOH trap. The DOC and metal (Al and Fe) concentrations in leachates and in solution sampled at the surface of columns were measured via C analyzer and ICP-OES, respectively, and degree of aromaticity (E₄/E₆ ratio) was measured by UV-vis spectrophotometer. A significant decrease in upward CO₂ release occurred for SWT (supporting H1). Higher DOC (for all events) and Fe concentrations (for first 18 days) were measured in SWT leachates (supporting H2). Carbon and metal concentrations of surface solutions and E4/E6 ratios were higher under SWT than DWT. Net loss of C was less under SWT (supporting H3).  Results indicate significant water-table effects on magnitude and direction of C flux (solution or gaseous) for sandy coastal plain soils.