Date of Award:

2016

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Civil and Environmental Engineering

Advisor/Chair:

R. Ryan Dupont

Abstract

The transport and transformation of nitrogen within streams receiving high nitrate loads has become increasingly important as restrictions on water quality continue to tighten due to an increased awareness that pollutant loading impacts the environment at concentrations lower than previously recognized. Silver Creek in Park City, Utah, is one of many streams in the state of Utah being evaluated for its ability to process high nitrate loads coming from a water reclamation facility. Previous modelling techniques at Silver Creek revealed that the lack of information on site-specific nitrogen transformation rates left modelers unable to represent the true processes occurring within the system. To address these concerns, six in situ benthic chambers were installed in Silver Creek downstream of the confluence with the Silver Creek Water Reclamation Facility discharge. Isotope dilution and pairing techniques using labeled nitrate (N 15O3−) were used to track the transport and transformation of nitrogen within the chambers. Samples were collected from the sediment, water, and plant material within the chambers over 21 hours. A suite of laboratory methods was compiled and modified as needed to quantify the mass of labelled nitrogen incorporated as nitrate, ammonium, organic nitrogen, and dissolved nitrogen gas from the collected samples. The rate of denitrification was only able to be determined from one chamber. A complete data set was unable to be obtained from the other chambers due to: 1) leaking chambers, 2) procedural error within the laboratory and 3) error in data reported from samples sent to external laboratories. The rate of assimilation was determined using data from three chambers containing macrophytes. The rate of denitrification and assimilation were 0.032 mg L-1 d-1 and 0.205 mg kg-1 d-1, respectively, and were comparable to those found in literature. Rates of nitrification, anaerobic oxidation of ammonium, and dissimilatory nitrate reduction to ammonium were also considered, but were found to be non-detect. Overall, the study resulted in a proposed methodology for collecting and processing data to determine site-specific nitrogen transformation rates required for improving water quality modeling techniques.

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