Tuesday, November 14, 2006

Effects of Varying Soil Properties on Reduction Rates of Saturated Soils.

Amanda Zelasko, Dean Hesterberg, and Michael Vepraskas. NC State Univ, 100 Derieux St, Williams Hall, Raleigh, NC 76950-6190

Determining the relationships between Fe(III) reduction rates and variables such as amount and type of organic matter will improve the accuracy of wetland delineation and the effectiveness of wetland restoration.  Because of the complexity of soil organic matter and its connection to electron acceptors such as Fe-oxides, predicting rates of soil reduction under water-saturated conditions requires further study.  Laboratory incubation experiments were completed on soils from two toposequences to determined how soil properties including total organic carbon (TOC), dissolved organic carbon, and proportions of different humic substances affect the rate of soil reduction under water-saturated conditions.  Amounts and forms of Mn(IV)- and Fe(III)- oxides as electron acceptors, and microbial populations were also characterized in relation to reduction rates.  After water saturating soil samples in incubators, Eh decreased from an average of 360 mV to  -105 mV within 5 days for most soils, but was slower for upland soils with <10 g TOC/kg.  Dissolved Fe(II) concentrations increased as soils where reduced, but no correlation was found between initial amounts and extractable forms of Fe and the concentration of dissolved Fe(II) following reduction.  Results to date suggest that reduction rates are slower in soils containing TOC less than a threshold level of 10 g/kg.