Fate of Organic Matter: Association with Iron Oxyhydroxides and Nutrient Dynamics

Nana Osei Asibey OSAFO, MSc.

Disertační práce

Fate of Oreganic matter in freshwater dediments; A clue to P immobilization?"

Anotace:

This PhD thesis investigates the fate of organic matter (OM) in freshwater lake ecosystems, its interactions with iron (Fe) oxyhydroxides, and the influence of these interactions on OM and nutrient dynamics. The thesis addresses several knowledge gaps regarding the role of OM-Fe associations in lake biogeochemistry. The findings are presented through three manuscriptstwo published in international peer-reviewed journals, and one currently under review. Paper I explores the influence of catchment soil geochemistry on the distribution of OM quantity and quality in freshwater systems, and how this distribution impacts nutrient dynamics. The study demonstrates that lakes in catchments with Fe-rich and acidic soils promote the immobilization of dissolved organic carbon (DOC) and humic-like OM, in contrast to lakes in catchments with Fe-poor and neutral pH soils. Furthermore, the stability of OM in Fe-rich lake systems results in lower concentrations of mobile nutrients in both the sediment porewater and water column. Paper II employs a combination of sequential extraction and OM optical property analyses to elucidate the interactions between OM and Fe in both reactive and stable phases. These methods were chosen for their wide accessibility and cost-effectiveness. The study shows that OM-Fe associations differ between reactive and stable phases. Specifically, humic-like OM dominates in the reactive phase, with lower DOC:Fe molar ratios, while protein-like OM, present in the stable phase, exhibits higher DOC:Fe molar ratios. Paper III investigates two association types (coprecipitation and adsorption) of dissolved OM (DOM) from both allochthonous sources (leaf litter and peat) and autochthonous sources (algae and Typha senescent tissue) with Fe oxyhydroxides, as well as the stability of these associations under reducing conditions. The study concludes that OM-Fe associations involving Typha-derived DOM are less susceptible to dissolution compared to those involving peat and algae. Moreover, OM-Fe associations formed through coprecipitation are more stable under reducing conditions. Finally, protein-like OM remains more stable within OM-Fe associations under reducing conditions, irrespective of OM source or association mechanism.

Abstract:

This PhD thesis investigates the fate of organic matter (OM) in freshwater lake ecosystems, its interactions with iron (Fe) oxyhydroxides, and the influence of these interactions on OM and nutrient dynamics. The thesis addresses several knowledge gaps regarding the role of OM-Fe associations in lake biogeochemistry. The findings are presented through three manuscriptstwo published in international peer-reviewed journals, and one currently under review. Paper I explores the influence of catchment soil geochemistry on the distribution of OM quantity and quality in freshwater systems, and how this distribution impacts nutrient dynamics. The study demonstrates that lakes in catchments with Fe-rich and acidic soils promote the immobilization of dissolved organic carbon (DOC) and humic-like OM, in contrast to lakes in catchments with Fe-poor and neutral pH soils. Furthermore, the stability of OM in Fe-rich lake systems results in lower concentrations of mobile nutrients in both the sediment porewater and water column. Paper II employs a combination of sequential extraction and OM optical property analyses to elucidate the interactions between OM and Fe in both reactive and stable phases. These methods were chosen for their wide accessibility and cost-effectiveness. The study shows that OM-Fe associations differ between reactive and stable phases. Specifically, humic-like OM dominates in the reactive phase, with lower DOC:Fe molar ratios, while protein-like OM, present in the stable phase, exhibits higher DOC:Fe molar ratios. Paper III investigates two association types (coprecipitation and adsorption) of dissolved OM (DOM) from both allochthonous sources (leaf litter and peat) and autochthonous sources (algae and Typha senescent tissue) with Fe oxyhydroxides, as well as the stability of these associations under reducing conditions. The study concludes that OM-Fe associations involving Typha-derived DOM are less susceptible to dissolution compared to those involving peat and algae. Moreover, OM-Fe associations formed through coprecipitation are more stable under reducing conditions. Finally, protein-like OM remains more stable within OM-Fe associations under reducing conditions, irrespective of OM source or association mechanism.

Klíčová slova

dissolved organic matter, iron association, stabilisation, PARAFAC, FTIR, Sediment, Fractionation, Freshwater reservoir, redox reactivity, UV-Vis, coprecipitation, sorption

Jazyk práce: čeština

Datum vytvoření / odevzdání či podání práce: 23. 10. 2024

Obhajoba závěrečné práce

• Vedoucí: RNDr. Jakub Borovec, Ph.D.

JIHOČESKÁ UNIVERZITA V ČESKÝCH BUDĚJOVICÍCH

Přírodovědecká fakulta

Doktorský studijní program / obor:
Biology / Ecosystem Biology