On 19 November at 14:00 Evelin Pihlap will defend her doctoral thesis “Soil aggregate formation in soils derived from loess reclamation” for obtaining the degree of Doctor of Philosophy (in Environmental Technology).
Senior Research Fellow Ain Kull, University of Tartu
Associate Professor Arno Kanal, University of Tartu (2016–2019)
Professor Ingrid Kögel-Knabner, Technical University of Munich (Germany)
During the open-cast mining, huge amounts of geological deposits lying above the coal layer are removed. With the excavation, huge pits are created that can have the depth for several hundreds of meters. The depth of the mining pit can be compared to the height of Tallinn TV-tower or Eiffel Tower in Paris. After the termination of open-cast mining, the landscape is destroyed and there is a need to restore the landscape to its pre-mining conditions. Usually, geological deposits are used in reclamation procedures as a new substrate for initializing soil formation and establishing soil functionality and fertility. The initial state of the parent material is mostly characterized by destructed soil structure, and its basic chemical and biological properties. Development in soil structure is one indicator for assessing the state of soil formation. As a soil structure, we consider the formation of aggregates, i.e. arrangements of solid material in the soil. The importance of soil structure relies on the fact that soil organic matter, bacteria, fungal hyphae, mineral particles, plant roots take part in the aggregate formation, i.e. soil structural formation. Soils with good structure are healthy and resistant to changes happening in the environment. The thesis aims to characterize the soil structural development from the initial state of soil formation. We investigated young reclaimed loess soils by using a space-for-time chronosequence approach stages (0, 1, 3, 6, 12, and 24 years after the first seeding) in reclaimed sites in Garzweiler (Germany). In the reclamation procedure loess is used as a new substrate for soil formation and it can be characterized by a high proportion of silt content and high CaCO3 concentration. We found that carbonates inherited from loess dominated over the stability of soil structure despite the development in SOC content along the space-for-time chronosequence. Calcareous loess induced the formation of soft-rock like aggregate structures, which is related to the cementing effect inherited from loess. This cementation effect diminished after submersion in water, reflecting that reclaimed soils are prone to soil erosion. Soil management strategies influenced the dynamics of OC in soils, which was presumably connected to the formation of macroaggregates. It became evident that limited OM input (crop and root residues) could not sustain stable SOC content and macroaggregate formation. Results show that successful reclamation is not only achieved by reaching into a sufficient state of soil fertility, but we should take into account the whole complexity of soil. The parent material, decomposition of organic matter, and management strategies play a crucial role in soil formation in destructed soils.