Civil Engineering ETDs

Publication Date

Summer 7-8-2020

Abstract

Nutrient enrichment has led to impaired waterways across the globe with an estimated 90% of waterways in the U.S. being negatively impacted from anthropogenic sources. In the past 30 years, there has been significant focus on studying nutrient uptake within fluvial systems. However, there are still critical knowledge gaps about the controls of nutrient dynamics and how these processes scale. This study combined the results from traditional instantaneous nutrient addition experiments and sensor data averaged over ±5 days from the time of addition to determine mechanisms that affect nutrient dynamics in two contrasting streams within the same watershed, over almost two years. We found that the meandering third order East Fork Jemez River (EFJR) experienced significantly higher nitrate uptake (pthorder Jemez River (JR). The primary mechanisms associated with nitrate uptake within the experimental reach at the EFJR was denitrification. Results from the JR reach indicated that increased discharge led to decreased uptake, likely due to reduced residence times and nutrient to benthos availability. The EFJR site had its highest uptake rates in the spring and fall, and its lowest in the summer, while the JR site experienced gradual increase in uptake, peaking in November. Principal component analyses determined that biological processes were the most dominant drivers in water quality in the EFJR, while the JR was controlled by flow regimes. Nondimensional parameters were explored to determine if nutrient uptake metrics could be estimated from flow and geomorphology conditions; we found that the Reynolds number was allowed estimates of uptake lengths and uptake velocities at both sites, with R squared values of 0.841 and 0.546, respectively. This study illustrates the complexity and non-linearities involved in nutrient uptake dynamics and offers a quantitative framework to generate nutrient scaling patterns in fluvial systems.

Keywords

Nutrient Dynamics, Nitrate Uptake, Denitrification, Autotrophic Assimilation, Fluvial, Nutrient Spiraling, Ecohydrology, Stream Metabolism, Continuous Sensors, High Frequency Aquatic Data

Document Type

Thesis

Language

English

Degree Name

Civil Engineering

Level of Degree

Masters

Department Name

Civil Engineering

First Committee Member (Chair)

Dr. Ricardo González-Pinzón

Second Committee Member

Dr. David Van Horn

Third Committee Member

Dr. Mark Stone

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