Assessing the seasonal distribution, dynamics, and flocculation of organic matter from the land to sea across two boreal systems

Khoo, Celyn L.L. (2022) Assessing the seasonal distribution, dynamics, and flocculation of organic matter from the land to sea across two boreal systems. Masters thesis, Memorial University of Newfoundland.

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Abstract

Boreal zones contain globally significant organic matter (OM) reservoirs and are currently in a state of rapid change due to shifting temperatures and regional hydrology. Such ongoing change has the ability to alter the export of substantial amounts of OM from these C-rich systems to the coastal environment, which may have major consequences on coastal food web dynamics. In this thesis, I investigate the distribution, dynamics, and salt-induced flocculation of OM across two small adjacent boreal rivers and their immediate coastal zones over three consecutive seasons. Overall, biogeochemical diversity and variation in flocculation potential at local and weekly time scales emphasize the relevance and important inclusion of these underrepresented small coastal systems within regional and global elemental budgets, which will increase the efficacy of future biogeochemical flux predictions from the land to sea. In the second chapter of my thesis, observations of the distribution and dynamics of particulate and dissolved (D)OM highlight important linkages between OM dynamics and local and seasonal physico-chemical, biological, and hydrological processes that were potentially enhanced at a weekly scale during the summer-to-fall transition period. The findings of this observational study also revealed that over 95% of the freshwater organic carbon is in the dissolved fraction with characteristics of being terrestrially derived, aromatic, and C-rich. These characteristics, along with dissolved iron, were also selectively removed by salt-induced flocculation processes, as highlighted in the third chapter of my thesis. Overall, results from the experimental study emphasize the relevant contribution of flocculation as a process affecting the removal of OM from pelagic zones to the benthos, which can occur across a broad range of salinities (1-25 psu). The findings in my thesis also encourage the use of dissolved iron measurements and calculations for dissolved iron to dissolved organic carbon ratios in future biogeochemical studies as they were found to be especially informative for assessing the temporal stability of DOM as well as degree of flocculation across adjacent systems with differing catchment types. Changing environmental conditions will result in greater day-to-day variability in river hydrology and subsequently affect the fluxes, cycling, and fate of OM, and to better predict and understand the consequences of these changes, an increased representation of small near-shore coastal systems with recognition of its biogeochemical diversity in regional and global elemental budgets is required.

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