Author ORCID Identifier

https://orcid.org/0000-0002-8855-7799

Year of Publication

2020

Degree Name

Master of Science in Biosystems and Agricultural Engineering (MSBiosyAgE)

Document Type

Master's Thesis

College

Agriculture; Engineering

Department

Biosystems and Agricultural Engineering

First Advisor

Dr. William Ford

Abstract

Harmful algal blooms (HABs) are of increasing concern in the Ohio River Basin. Fine sediment dynamics in riverine environments are increasingly recognized to play important roles in proliferation and toxicity of Microcystis blooms. Further, the fate of sediment at confluences of tributaries and the main river system are important zones for sediment retention and transient storage. The objective of this study was to improve understanding of watershed sediment loading dynamics and backwater inundation influencing sedimentation within confluence watersheds. The study site is the Fourpole Creek watershed in Huntington, WV which is a disturbed forested watershed impacted by a backwater confluence wetland at the junction of Fourpole Creek and the Ohio River. 16 months of high frequency turbidity data was collected at upstream and downstream nodes of the backwater influenced confluence feature near the watershed outlet. Governing hydraulic and sediment transport equations were used to develop a data driven model to estimate sediment fluxes within the confluence floodplain wetland. The continuous sediment yield model estimated an annual yield of 151 t/mi2. A modified sediment rating curve method estimated an annual suspended sediment yield of only 34.3 t/mi2. Hysteresis analysis was conducted using a source unmixing method and hysteresis index to quantify sediment source and flow pathways during events. The contribution of three major sources during events were highly variable, but seasonality and antecedent precipitation were both found to be influences. The confluence floodplain was found to have a quantitatively large role in intercepting and storing sediments, retaining 40% of the annual inputs. A numerical sediment transport model estimated 2,055 tons of sediment was permanently retained. Hysteresis was also found to influence the spatial variability of erosion and deposition mechanisms in the floodplain. The floodplain was found to have a particulate nitrogen removal rate from 0.5-0.9kgN/ha/year which is on the same order of magnitude as the nitrate removal rates in this same system. Our results suggest that particulate N fluxes from disturbed forested watersheds near rivers should be considered in watershed N budgets as well as a source for HABs in regulated rivers.

Digital Object Identifier (DOI)

https://doi.org/10.13023/etd.2020.360

Funding Information

This research was funded by the National Science Foundation Sensing and Educating the Nexus to Sustain Ecosystems (SENSE) 1632888 and Appalachian Freshwater Initiative (AFI) 1458952 from 2018-2020.

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