Human activities have significantly increased riverine fluxes of carbon and nutrients. River-groundwater interactions facilitate retention and transformation of carbon and nutrients, and therefore profoundly impact carbon and nutrient cycles. From water column to the streambed, there is extensive variations in hydrodynamic transport and biogeochemical reaction over space and time. However, little is known about how these variations influence carbon and nutrient dynamics at the scale of river reaches, mainly because commonly-used reach-scale models lack physically-based representation of transport and reaction processes. To bridge this gap, my dissertation aims to advance capability to model reach-scale reactive transport, and to evaluate how variations in river-groundwater processes control carbon and nutrient dynamics at reach scale. Specifically, I developed a reach-scale particle tracking model that is able to physically represent transport and reaction processes (Chapter 2). By considering vertical covariation between transport and reaction, I found that rapid flushing near the sediment-water interface controls reach-scale nitrate removal (Chapter 3), and that residence time in the bioactive region of the streambed explains reach-scale nitrate dynamics (Chapter 4). By considering reaction variability of dissolved organic matter, I found that photochemical uptake of dissolved organic matter is limited by weak vertical mixing (Chapter 5), and that microbial uptake of dissolved organic matter decreases over downstream distance due to the decreasing reactivity over time (Chapter 6). My findings highlight that variations in transport and reaction should be considered when studying carbon and nitrogen dynamics.

Creator

• Li, Angang

DOI

• https://doi.org/10.21985/n2-gb66-0r52

Subject

• Environmental engineering

Language

• en

Alternate Identifier

• http://dissertations.umi.com/northwestern:14621
• etdadmin_upload_662009

Date created

• 2019-01-01

Resource type

• Dissertation

Rights statement

• In Copyright