Project properties

Title Unravelling the composition of the hydrophilic acids SOM fraction
Group Soil Chemistry and Chemical Soil Quality
Project type thesis
Credits 24-39
Supervisor(s) Walter Schenkeveld and Rob Comans
Examiner(s) Prof..dr. R. Comans
Contact info
Begin date 2022/03/01
End date
Description Natural organic matter is a key constituent of soils that plays a prominent role in generating the soil structure, the water holding capacity, the capacity to bind ions, etc. Soil organic matter (SOM) is very heterogeneous in nature and consists of a huge variety of different substances. Van Zomeren and Comans (2008) have developed a method for fractionating the SOM into several operationally defined pools of organic substances with similar properties. This protocol can empirically separate 5 SOM fractions: humine (HUM), humic acid (HA), fulvic acid (FA), hydrophylic acids (Hy), and hydrophobic neutral organic matter (HON).

For the availability and transport of cationic nutrients and contaminants like Fe, Cu, Zn, Pb and Cd, particularly the water soluble ionic carbon fractions are of interest. These include HA, FA and Hy. The properties and reactivity of HA and FA have been extensively studied and are captured in mechanistic soil chemical models like the NICA-Donnan model. The composition and reactivity of the Hy-fraction have been much less studied, although it might be an important contributor to the dissolved organic matter (DOM) in soils solution. Characterization and inclusion of the Hy fraction in our chemical speciation models may strongly improve the predictive value of these models.

The aim of this MSc thesis project is to better characterize the composition and reactivity of the Hy fraction. To this end, Hy fractions from several soils with different properties (e.g. pH, OM content) will be collected and quantified in terms of dissolved organic carbon (DOC) concentration. Subsequently the composition will be further characterized by UV-vis spectroscopy, high pressure liquid chromatography (HPLC) and mass spectroscopy (MS), in order to identify specific (classes of) substances. Reactivity will be characterized in terms of reducing and metal binding capacity through batch interaction experiments with ferrihydrite. Also, the effect of drying/storage of soil on the composition of the Hy-fraction will be explored.

Results from this study will provide groundwork necessary for a quantitative description of the reactivity of the Hy fraction. Including such a quantitative description into our chemical speciation models will improve our predictions of the speciation and fate of ions in the environment.
Used skills Literature review, proposal writing, laboratory work (soil organic carbon extraction, fractionation and characterization), data processing, thesis writing
Requirements Some laboratory experience, as well as required courses for the MSc thesis Soil Chemistry and Chemical Soil Quality (SOC-81336), preferably including Environmental Analytical Techniques (SOC33806) and the Carbon Dilemma (SBL-35306)