Mr Olaf Brock1, Mr Rick Helmus1, Prof. Dr. Karsten Kalbitz2, Dr. Boris Jansen1
1University Of Amsterdam (IBED-ELD), Amsterdam, Netherlands, 2Technische Universität Dresden (Soil resources and land use), Dresden, Germany
The interaction of metal cations – iron and aluminium – with dissolved organic matter (DOM) derived from leaf litter leads to the formation of the dark coloured and resistant Bh horizons in podzols. The characteristics of these Bh horizons – especially the effect on water permeability – partly inspired the innovative SoSEAL project (Soil Sealing by Enhanced Aluminium and DOM Leaching). SoSEAL aims at making dykes more stable by reducing water permeability through the dyke body by enhancing metal-DOM precipitation. In order to use metal-DOM interaction for engineering purposes, it is important to identify the molecular characteristics of DOM involved in metal-DOM interaction. This allows us to select suitable DOM sources and be able to better control the formation of metal-DOM flocs. Molecular characterisation of DOM was done with a new non-target screening method using liquid chromatography (LC) coupled to high resolution quadrupole time-of-flight mass spectrometry (QTOF-MS). DOM solutions were prepared from coniferous, deciduous and mixed leaf litter and from HUMIN-P 775, a commercially available leonardite material which dissolves completely in water and has a high number of carboxylic groups. We measured the molecular characteristics of the DOM solutions before and after the addition of aluminium. The amount of precipitation was quantified by measuring aluminium and dissolved organic carbon content. Results show that humin-DOM precipitation is up to twice as high as that of leaf litter DOM. Preliminary results suggest that there is preferential precipitation of larger/heavier compounds and of aromatic compounds. However, we did not observe preferential precipitation of specific compound groups (such as lignin and tannin) and also not of nitrogen poor compounds. These findings mean that we can increase the formation of aluminium-DOM precipitates by selecting a source of DOM with a DOM composition that is more suitable for aluminium-DOM precipitation.
I am a PhD student at the University of Amsterdam (UvA) in the Netherlands. My PhD is part of a larger project in which we are developing a method to reduce water permeability through sandy layers, e.g. in dykes. This method consists of injecting a mixture of dissolved organic matter (DOM) and aluminum that together form flocs or Al-DOM precipitates. These flocs/precipitates block the soil pores, thereby reduce water permeability and inhibit unwanted water flow. In my research I study the role of organic matter in the precipitation process, also known from podzolization. I conduct this by investigating the molecular composition of different natural and commercially available DOM sources using liquid chromatography coupled to high resolution mass spectrometry (LC-QTOF-MS). I also work on the effect of forest conversion on SOM composition (former master thesis topic). For this pyrolysis-GC–MS was used to study SOM beneath deciduous and (converted) spruce forests, with a focus on lignin and cutin/suberin.