ARS | Publication request: Soil structure, colloids, and chemical transport as affected by short-term reducing conditions: a laboratory study

Submitted to: American Geophysical Union
Publication Type: Abstract
Publication Acceptance Date: October 23, 2008
Publication Date: December 15, 2008
Citation: De-Campos, A.B., Mamedov, A., Huang, C., Wagner, L.E. 2008. Soil structure, colloids, and chemical transport as affected by short-term reducing conditions: a laboratory study. Eos Trans. AGU, 89(53), Fall Meeting Supplement. Abstract V23D-2159, American Geophysical Union.

Technical Abstract: Upland soils in the Midwestern US often undergo reducing conditions when soils are temporally flooded during the spring and remain water saturated for days or weeks. Short-term reducing conditions change the chemistry of the soil and may affect soil structure and solution chemical transport. The effects of short-term reducing conditions on chemical and physical properties of the soils, colloids, and associated chemical/nutrients transport are still not well understood and was the objective of our study. A biogeochemical reactor was built to achieve reducing conditions. Three cultivated and three uncultivated soils with different organic carbon contents were incubated in the reactor for 1 hour and 3 days under anaerobic conditions. Effects of the redox state on soil structure (pore size distribution) and drainable porosity, colloids mobility, and chemical transport were determined using high energy moisture characteristic and analytical methods. After each treatment, the soil solution was collected for redox potential (Eh), pH, and electrical conductivity (EC) measurements, and chemical analysis of metals (Ca, Mg, K), nutrients (N, P), and dissolved organic carbon. Strongly reducing conditions were achieved after 3 days of incubation and were followed by a decrease in soil porosity and an increase in pH, EC, clay dispersion, swelling, colloids mobility, and associated chemical transport. The trend for each soil depended on their initial structural stability and chemical properties. The structure of cultivated soils and the leaching of nutrients and carbon from uncultivated soils were more sensitive to the redox state. A strong correlation was found between changes in Eh and drainable porosity. The role of short-term reducing conditions on changes in redox sensitive elements, organic matter decomposition, pH, and EC and their influence on soil structure and soil particles or colloids/chemical transport for both soil groups are discussed in the paper. This study showed that short-term reducing conditions influence colloids/chemical transport and it should be taken into account for modeling because dissolved compounds and colloids facilitated nutrient and associated pollutant transport during coupled overland and soil-matrix flow conditions.