PORE-WATER GEOCHEMISTRY NEAR THE SEDIMENT-WATER INTERFACE OF A ZONED,FRESH-WATER WETLAND IN THE SOUTHEASTERN UNITED-STATES

Sediment and its associated pore water were collected from a zoned, fr eshwater, riparian wetland, located in the Talladega National Forest, northeastern Hale County, Alabama, to study the porewater chemistry an d its spatial changes within and between the wetland ecological zones. Obvious changes in pH, Eh and element concentrations were observed be tween the different wetland ecological zones. Major cations (Ca, Mg, a nd Na) and trace elements (B, Ba, Sr, and Mn) have very good spatial c orrelation with Fe and Mn distributions, both in the pore water and th e sediment, suggesting that adsorption on, and desorption from, iron a nd manganese oxyhydroxides are important processes controlling the dis tributions of these elements in the wetland sediment. However, an equi librium adsorption model is not able to explain the distribution of tr ace elements between the pore water and sediment. A redox kinetic mode l gives similar vertical profiles for iron and the correlated elements as those measured in the field and thus suggests that the relative ra tes of ferrous iron oxidation and the reductive dissolution of ferric iron in the sediment are important variables determining the distribut ions of these elements in the wetland pore waters.