Author ORCID Identifier

https://orcid.org/0000-0002-1828-1408

Year of Publication

2020

Degree Name

Master of Science in Biosystems and Agricultural Engineering (MSBiosyAgE)

Document Type

Master's Thesis

College

Agriculture; Engineering

Department/School/Program

Biosystems and Agricultural Engineering

First Advisor

Dr. William I. Ford

Abstract

In-stream fate of nutrients in karst agroecosystems remains poorly understood, despite the known impact of karst on water resources at local to global scales. In the Inner-Bluegrass region of central Kentucky, heterogeneity of karst maturity, flow pathways, and nutrient sources adds to the complexity of quantifying nutrient dynamics, thus requiring novel monitoring and modeling approaches. The significance of these streams is recognized given spring/surface water confluences have been identified as hotspots for biogeochemical transformations. In slow-moving streams high in dissolved inorganic nutrients (particularly dissolved inorganic nitrogen (DIN) and dissolved reactive phosphorus (DRP)), benthic and floating aquatic macrophytes are recognized to proliferate and drastically impact nutrient fate; however, models that quantify coupled interactions between these pools are lacking. Current in-stream nutrient models place emphasis on benthic and hyporheic nutrient processing, but often neglect the potential for floating aquatic macrophytes to uptake nutrients and facilitate denitrification. This thesis presents a new reach-scale modeling framework of nitrogen dynamics in bedrock-controlled streams that accounts for coupled interactions between hydrology, hydraulics, and biotic (benthic and floating aquatic macrophytes) dynamics downstream of springs and is validated using a biweekly monitoring dataset from 2000-2003. Comprehensive budget results are presented to quantify transformation dynamics for the DIN pool using a GLUE-like modeling framework. Further, we collected high-frequency data from September 2018 - December 2019 including nitrate (validated with biweekly grab samples), dissolved oxygen, temperature, pH, conductivity, turbidity, fluorescent dissolved organic matter (fDOM), and depth all at 15-minute intervals. Model results from a 10,000 run uncertainty analysis yielded 195 acceptable parameter sets for the calibration period (2000-2002) and 47 acceptable parameter sets for the validation period (2003) (NSE > 0.65; PBIAS < ±15), with significantly different posterior parameter spaces for multiple parameters, including denitrification coefficients and vegetation growth factors. The high-frequency data shows significant diurnal and storm flow effects on nitrate and dissolved oxygen fluctuations. This modeling and data collection has broader implications for watershed scale-water quality modeling and implementation strategies of nutrient best management practices for karst agroecosystems.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2020.339

Funding Information

National Science Foundation #1632888 RII Track-2 FEC: Sensing and Educating the Nexus to Sustain Ecosystems (SENSE). A Kentucky-West Virginia Partnership.

I received funding from 2018-2020.

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