PhD defence: Sárka Václavková
Šárka Václavková defends her thesis,
Microbial Oxidation of Iron Sulfides in Anaerobic Environments
Supervisors:
Professor Bo Elberling, IGN
Professor Jens Aaamand, GEUS
Senior Researcher Ole Stig Jacobsen, GEUS
Assessment Committee:
Professor Henrik Breuning-Madsen (chairman), IGN
Professor Karsten Pedersen, Chalmers University of Technology, Göteborg
Senior Scientist Vibeke Ernstsen, GEUS
Abstract (shortened):
Iron sulfides (FeSx), representing 0.04-10 % of Danish dry soil weight, oxidize in a presence of oxygen, releasing sulfuric acid and free iron. Environmental impact of FeSx oxidation is commonly seen on agricultural sites cultivated by drainage as acid sulfate soil formation. Under anaerobic conditions FeSx serves as an electron donor in nitrate (NO3-) reduction processes. In this PhD thesis, unknown controls of microbial FeSx oxidation by NO3- (MISON), as a potentially important NO3- reducing process, were investigated. The importance of understanding the NO3- removal processes in natural anoxic soils is supported by the fact that about 17 % of drinking water wells in Denmark were lately found to be contaminated by NO3- in concentrations exceeding the allowed limit of 50 mgL-1. This study experimentally documented potential for MISON in a range of anoxic aquatic environments including sandy aquifer, freshwater peatland and moderately brackish muddy marine sediment. An apparent salinity limitation of MISON was shown in heavily brackish sediment, where FeSx oxidation was inhibited while other NO3-reduction processes did not appear to be affected by the salinity levels. MISON was found to count for about 1/3 of the net NO3- reduction in MISON active environments, despite the presence of alternative electron donor, organic carbon. The rate of MISON was found to be dependent on the available reactive surface area of FeSx and on the microorganism involved. The findings presented in this PhD study may be important for the future planning of agricultural NO3--buffer zones and may be used as an input into the reactive transport models, predicting the behavior of NO3- in the aquatic environments.
The thesis is available at the PhD administration office, 04.1.409