Date Available

1-21-2021

Year of Publication

2020

Degree Name

Master of Science in Civil Engineering (MSCE)

Document Type

Master's Thesis

College

Engineering

Department/School/Program

Civil Engineering

First Advisor

Dr. James Fox

Abstract

Fluvial sediment is well recognized as a critical factor in both carbon and nutrient budgets within stream systems. However, we find very few studies of reactivity and isotope enrichment for stream water from agricultural and urban streams and the class of substrate known as fluvial sediment organic matter. This study investigated the hypothesis that fluvial sediment is subject to degradation even though many previous studies have considered this class of substrate generally inert. Therefore we qualify that elemental and isotopic signatures of fluvial sediment organic matter should be considered potentially non-conservative when used in tracer studies. Methods applied to this research project included field measurements, laboratory incubation experiments, and numerical modelling. Sediment and water samples were analyzed to determine the elemental concentration of carbon and nitrogen, as well as isotopic ratios of oxygen, nitrogen, and carbon in order to (1) elucidate the fate of carbon and nutrients during elemental decomposition and spiraling as well as isotope fractionation, (2) investigate the role of biotic processes in transforming nitrogen and carbon, (3) and combine the data results with a kinetics model that incorporates knowledge of biogeochemical processes in streams. Results of this study suggest a moderately active system dominated by dissolved- and sediment-organic carbon oxidation, CO2 evasion, nitrogen mineralization, and nitrification. Best estimates of isotope enrichment factors ranged from -3 to +1‰ for dissolved- and sediment-organic matter oxidation, -1 to +1‰ for nitrogen mineralization, and 0.05 to 0.2‰ for nitrification. While biochemical processes are occurring, results suggest lack of isotopic enrichment during carbon oxidation, nitrogen mineralization and nitrification.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2020.302

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