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Factors Affecting Sediment Oxygen Demand of the Athabasca River Sediment under Ice Cover
- Author / Creator
- Sharma, Kusumakar
This research was conducted in a response to the dissolved oxygen (DO) decline in winter in the Athabasca River. Sediment oxygen demand (SOD) is considered as one of the major factors contributing to the DO decline in the Athabasca River. The SOD is influenced by physical phenomena, chemical reaction and microbial activities in river water as well as in the sediment. The overall objective of this thesis research was to determine factors affecting the SOD in river sediment in winter. The factors that influence the SOD in this research were: water chemistry, sediment characteristics, nutrient flux across the sediment water interface (SWI) and microbially mediated nitrogen dynamics inside sediment.
In the first phase of the research, sediment samples collected at different sites along the Athabasca River were incubated in sediment cores to determine the SOD. In order to obtain reliable SOD, a newly designed SOD measurement technique was used. The new SOD measurement technique has addressed the issue of hydrodynamics inside the benthic chamber, continuous DO monitoring, and its flexibility in operation at low temperature. Furthermore, advanced features added to the technique enabled us to conduct a study on nutrient fluxes across the SWI. The fall and winter SOD measurement revealed that the SOD was correlated with water chemistry in the fall season, but not in the winter season. In general, total organic carbon (TOC) was the main driving force for the SOD variations in fall and winter seasons. The SOD was also correlated with porosity in both fall and winter seasons. The nutrient flux analysis of three sites along the Athabasca River in winter revealed that an efflux (from sediment to water column) of ammonium was observed. The ammonium efflux was correlated with the SOD. This indicates that nutrient rich sediment exerts higher SOD.
Having determined the relationship between ammonium flux and the SOD, the research in the second phase aimed to study microbially mediated nitrogen transformation in the sediment and the impact of the nitrogen transformation on the SOD. The impact of increased nutrient load on the SOD was also studied by spiking the overlying water of the sediment core with nutrients. To undertake this study, a suite of microsensors were used to measure concentrations profiles of oxygen, ammonium, nitrate and pH in the sediment at near zero temperature. The concentration profiles revealed that oxygen penetration depth in the sediment reduced when the water was spiked with nutrient load. Higher amount of oxygen consumption was observed due to an increase in the microbially mediated ammonium oxidation when nutrient was added. Therefore addition of nutrient increased SOD in the experimental condition. Although addition of particulate TOC did not increase microbial activity immediately in winter, the solubilisation process in the long run would affect ammonium oxidation. In order to maintain the DO level in the river in winter, the result suggested that either nutrient load should be reduced or supply of oxygen should be increased.
- Graduation date
- Fall 2012
- Type of Item
- Doctor of Philosophy
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