Holistic Characterisation of Soils Developed on Contrasting Lithologies, in a Temperate Climate

  • Nicola Ashton

Student thesis: Phd


The influence of parent lithology on the development of soil biogeochemical environments and their microbial diversity is explored by characterising soil profiles with respect to their mineral, solution and organic chemistry. Soil profiles were collected from a total of 17 sites, above basalt, granodiorite, shale, sandstone and limestone, across Northern Ireland. The soil system developed above basalt was examined to assess the development of soil bio-physicochemical properties and microbial diversity through the profile. These basalt soils showed two distinct horizons have developed in the previous 15'000 years, where soils from the top 20 cm of the profile were highly influenced by the interactions of soil minerals with soil organic and biological processes. In line with the observed differences in soil properties the microbial community structure varied; in the surface soils the community composition was dominated by root-associated bacteria. However the relative abundance of phyla affiliated with nutrient-limited conditions increased in samples from the base of the profile. Detailed examination of the soil profiles above granodiorite, shale, sandstone and limestone revealed large variations in soil geochemistry between profiles, reflecting the mineral geochemistry of the parent rock. Molecular analysis of SOM revealed compositional changes with depth were comparable between profiles; however TOC concentrations were consistently higher in the soil profiles above basalt suggesting greater stabilisation of SOM in these soils. The chemistry of the soil waters was not reflective of the parent rocks; however variations in soil texture, specifically the abundance of less reactive residual minerals in the sandstone and limestone soils, led to higher concentrations of soluble elements in these soils. Soil pH and DOC were found to have a large control on buffering the release of free Al, Cr and Fe ions into solution. The microbial communities in near-surface soils were similar to each other, regardless of lithology, and were dominated by Proteobacteria, Actinobacteria, and Acidobacteria. However microbial diversity shifted with depth; the abundance of Actinobacteria decreased and Nitrospirae increased, and between rock types where soils next to the basalt, shale and granodiorite bedrock contained sequences affiliated with novel Candidate Phyla AD3 and GAL15. In these soils differences in SOM composition were the main driver of the observed variation with depth, however where labile SOM was depleted, mineral and solution geochemistry may have a larger control on the community composition. To assess the influence of parent lithology on selenium mobility, soils above basalt and granodiorite were amended with sodium selenate. Under anaerobic conditions, the proportion of soluble selenate removed varied (39-77 %) depending on the sample through a combination of abiotic and microbial reduction processes. However, under aerobic conditions, larger concentrations of selenate remained in solution (79-100%).
Date of Award1 Aug 2015
Original languageEnglish
Awarding Institution
  • The University of Manchester
SupervisorRichard Pattrick (Supervisor), Jonathan Lloyd (Supervisor) & Bart Van Dongen (Supervisor)


  • Selenium
  • Microbial Diversity
  • Soil Organic Matter
  • Soil Waters
  • Soil Geochemistry
  • Soil
  • Soil Parent Lithology

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