Ukotije-Ikwut, Peter R. (2024) Trace elements in rivers draining tropical peat swamp forests. (PhD/ Doctoral thesis), Christian-Albrechts-Universität, Kiel, Germany, XIX, 175 pp.

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Abstract

Tropical peat swamp forests are wetland ecosystems characterized by peat accumulation from partially decomposing organic matter in lowland areas. In southeast Asia, tropical peat swamps account for about 11-14% of the carbon stored in all peatlands. However, converting these ecosystems for agricultural activities has potential implications for releasing materials, including trace elements. This study explores the interplay of anthropogenic activities and trace element export to the estuaries and coastal waters.

The result indicated the role of pH, salinity, dissolved organic carbon (DOC), and iron (Fe) and manganese (Mn) oxides in regulating the global biogeochemical cycling of trace elements. Seasonal variabilities contribute to trace element fluxes, especially during the wet season (December), with implications for material supplies to the coastal waters. The NICA- Donnan model was used to investigate the combined impact of DOC and pH on the formation of solid iron hydroxide (Fe(OH)3(s)). The Maludam River was predicted to be supersaturated for Fe hydroxides, and the field results affirmed our model prediction. The output showed Fe and Cu had a strong affinity for DOC and, to a lesser extent, Al and Ni in the conditions prevailing at the study sites.
Furthermore, the concentration of DOC (12000 μmol L−1) in the natural peat increased, while the concentration of trace elements increased in the disturbed peat. Porewater samples from the disturbed and natural peat also indicated enhanced trace element concentrations in the disturbed peat compared to the natural peat. The observed increase in trace element concentrations reflects the impact of peat conversion on agricultural activities and catchment chemistry.

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