Jinping (Bruce) Xue | ALES Graduate Seminar

Date(s) - 13/01/2021
2:00 pm - 2:45 pm

A graduate exam seminar is a presentation of the student’s final research project for their degree.

This is an ALES MSc Final Exam Seminar by Jinping (Bruce) Xue

Supervisor: Dr. Bill Shotyk

This seminar is open to the general public to attend via Zoom (link below).

Thesis Title: Variations in Size and Optical Properties of Dissolved Organic Matter During Mixing at Large River Confluences: Implications for Source Discrimination in the Boreal Zone

Seminar Abstract:  The functionality of dissolved organic matter (DOM) in natural waters depends on its size and composition. Identifying the sources and associated properties of DOM is vital to understand its effects on downstream ecosystems. River mixing has great potential to alter DOM quality, but its role in large boreal river confluences remains largely unknown, which limits our ability to realize the exact magnitude and composition of DOM exported to the ocean. Using asymmetrical flow field-flow fractionation (AF4) with offline excitation emission matrices (EEMs) measurements and parallel factor (PARAFAC) analysis, we found that inputs of DOM from the major tributaries shifted DOM quality in a typical large boreal river, namely, the lower Athabasca River (LAR). Flowing downstream, DOM tended to be higher in concentrations of dissolved organic carbon (DOC) and degrees of humification and aromaticity. Seasonal variations of DOM as a result of spring freshet were observed, during which times DOM tended to be higher in molecular mass (e.g., size) and highly richer in protein-like components (i.e., tryptophan-like) relative to humic-like components. Source discrimination of DOM was more apparent under base flow conditions compared with the snowmelt period. In addition, conservative mixing behaviors of DOM at river confluences were observed. Contrasting mixing patterns among mixing zones suggest that both hydrological conditions and river geomorphology affect mixing patterns of DOM between the LAR and its tributaries. Our results demonstrate that DOM could be used as a quasi-conservative tracer during mixing at large river confluences. Findings from this study will enhance our ability to determine sources of DOM and to distinguish trends of mixing between the mainstem and the tributaries for DOM-associated trace elements in the boreal zone.

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