The conversion of agricultural soils into wetlands has become a popular topic, particularly in terms of reducing greenhouse gas emissions while enhancing carbon sequestration. However, with this comes a high risk of phosphorous discharge with consequent eutrophication, because a switch to wetlands means that oxygen levels in the soil will decrease (i.e., reducing conditions become more frequent), and iron redox transformations can occur that release phosphorous. While we predict such processes, we have little experimental observations of the changes in soil biogeochemical cycles and balances (carbon, nitrogen, iron, sulfur, phosphorus) that occur when soil water content increases and redox state changes.
This project aims to perform soil column experiments using cores from drained, agricultural lands. We will expose these soil cores to different saturation states, and study the effect of changing redox states (i.e., varied oxygen pressure) on the elemental composition of the drainage fluid (i.e., iron, nitrate, phosphorous, dissolved organic carbon). The soil properties will also be analysed in terms of changes in their mineralogical and microbial composition. In a second set of experiments, we aim to amend the soils with a suite of biochars to evaluate their impact on the observed soil processes. Specifically, we hypothesise that biochar, which is produced by pyrolysis of biomass in an oxygen-limited atmosphere, could be an effective way to limit nutrient mobility in these redox fluctuating wetlands, while also contributing to soil quality, fertility and carbon sequestration.
The work will be carried out in the Section for Environmental Chemistry and Physics, Department for Plant and Environmental Sciences, Faculty of Science at Copenhagen University, under the supervision of Assoc. Prof. Dominique J. Tobler (firstname.lastname@example.org) and Prof. Hans Chr. Bruun Hansen (email@example.com) within the Environmental Chemistry group.