Abstract

Soil Iron reduction influences ecosystem form and function by altering the cycling of carbon, nutrients, and trace elements in both the aqueous and solid (or particulate) phases. Nearly all of our understanding of soil iron reduction comes from work on saturated soils (wetlands). However, recent work shows iron reduction can be a pivotal process in upland soils that experience dynamic redox conditions. We hypothesized that in upland soils, iron reduction intensity and prevalence would be affected by seasonal variations in soil moisture. We tested this by delineating the spatial and temporal distribution of the potential for iron reduction to 70 cm depth in upland sub-tropical forested watersheds using rusted steel “Indicators of Iron Reduction in Soil” (steel IRIS) probes, and non-invasive moisture sensing at three time-points over the course of a year: (a) after an extreme rainfall event in October 2015; (b) during the end-of-winter warming in March 2016; (c) and during a period of high evapotranspirational demand in June 2016. Our results indicate that the potential for iron reduction varied with depth and intensity over the year. Iron reduction was greatest at depth (40 – 60+ cm) following a rainfall event that generated prolonged subsurface soil saturation; whereas iron reduction was greatest near the surface (0 – 30 cm) in late winter/early spring when biological oxygen demand was likely high due to labile carbon and soil warming. In June 2016, the potential for Fe reduction was low across all depths. Our results indicate that soils of the Southeastern Piedmont likely experience strong seasonal trends in Fe reduction, as well as periodic spikes in response to large rain events. This work illustrates that otherwise oxic upland soils are likely to be shaped by Fe reduction processes at various points throughout the year.

Citation

Hodges, Caitlin (2017): Drivers and Variability of Iron Reduction in Upland Soils. M.S. Thesis, Department of Crop & Soil Sciences, University of Georgia.