Browsing by Author "Kallio, Antti-Jussi"

Eutrophication is a global challenge, where chemical processes in bottom sediments play a key role. Yet, eutrophication science lacks understanding of the role of terrestrial matter on the processes that mobilize or immobilize phosphorus, a central algal nutrient, in sediments. Eroded field soil is carried into sea by runoff and soil is settled on the bottom and then buried. During burial the sediment microbial processes change the redox-conditions which affect the chemistry of settled soil. Here, methods were developed to follow the evolution of the chemical state of soil during burial with iron K-edge X-ray absorption near edge spectroscopy, with a novel home-laboratory based spectrometer. The chemical state of soil, and especially the chemistry of iron is linked to the release and binding of phosphorus in bottom sediments. The chemical path of field soil was simulated with anaerobic incubation, where organic carbon and sulfates were added to represent various sea bottom conditions. In order to measure the spectra of soil-water mixtures, a sample preparation method was developed, where the sample is gellified in both aerobic and anaerobic conditions. The gel makes the suspension uniform and homogeneous. We also developed a sample environment for anaerobic measurements. The measured spectra were compared with spectra obtained from reference iron compounds and the iron species were quantified. The sulfate and addition of organic carbon enhanced the formation of iron sulfides, causing iron bound phosphorus to be released to water. As expected, the release of phosphorus was higher in anaerobic conditions than in aerobic conditions. The addition of organic carbon and sulfate enhanced the formation of iron sulfides, causing iron bound phosphorus to be released to the aquatic system. The results shed light on iron chemistry in anoxic sediments, which can be used in management of eutrophication.