Date of Graduation

7-2021

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Engineering (PhD)

Degree Level

Graduate

Department

Biological and Agricultural Engineering

Advisor

Brian E. Haggard

Committee Member

Benjamin R. K. Runkle

Second Committee Member

Lauren Greenlee

Third Committee Member

Jung Ae Lee-Bartlett

Keywords

Alumninum Sulfate Treatments, Phosphorus, Remote Monitoring, Rivers, Sediment, Soil Water Assessment Tool (SWAT), Streamflow, Subwatersheds, Water Quality, Watershed Management

Abstract

Excess inputs of nutrients and sediments jeopardize drinking water sources, aquatic life habitats, and aesthetic quality of freshwater resources for recreation. The purpose of this dissertation was to analyze long-term water quality trends and loads in the Upper Poteau River Watershed (UPRW) and the Lake Wister Watershed (LWW), and analyze internal phosphorus (P) loads in Lake Wister, Oklahoma. Additionally, this dissertation sought to review the literature for methods of prioritizing subwatersheds for watershed management using watershed models, implement a cost efficient method to remotely monitor streamflow and estimate constituent loads in small-scale watersheds, and finally, to validate the Soil Water Assessment Tool (SWAT) at the small-scale watershed using the aforementioned monitoring data.

Water quality changed over time in the watersheds impacted by both point and nonpoint sources in the UPRW. At the James Fork, total P (TP) did not change and orthophosphate (OP) increased over time, while P decreased at the Poteau River; nitrogen (N) increased at both. Finally, sediment concentrations decreased over time at both the Poteau River and James Fork, with decreasing shifts also occurring in the early 2000’s. In the LWW, the largest magnitude of loads came from the Poteau River, and while the magnitude of constituent loads from the Fourche Maline is less, increasing P is a concern. The relatively undisturbed Black Fork watershed contributes the least amount of loads to Lake Wister, and concentrations are decreasing or not changing over time.

In Lake Wister, after 5 aluminum sulfate (alum) treatments across 6 years, sediment P fluxes under anaerobic conditions were not significantly different than prior to any alum treatments. The lack of overall improvement in anaerobic P fluxes over time is likely due to the magnitude of P and sediment loads entering Lake Wister from the LWW, where 92% of the total P load to Lake Wister from 2010 to 2020 was from external sources. Therefore, while alum treatments provide short term reductions in P fluxes at Quarry Island Cove, the effectiveness was short, suggesting external sources of P must be addressed.

When watershed models are used for subwatershed prioritization, model calibration is often conducted at minimal sites on the large watershed scale and model outputs on the subwatershed scale or smaller are used for prioritization, but little data exists to validate the small-scale model outputs. Therefore, a method was developed to monitor streamflow and estimate constituent loads in small-scale watersheds by using inexpensive pressure transducers to collect continuous records of stage, deploying SonTek-IQs during high flow events, and developing rating curves with stage and discharge data. The small-scale watershed data was then used to validate a SWAT model, which mostly resulted in unsatisfactory performances.

Ultimately, it is important to continue monitoring in the UPRW and LWW to ensure constituent concentrations do not exceed levels of concern. Watershed sources of P must be addressed in addition to internal sources of P in Lake Wister. Finally, it is important to continue exploring subwatershed prioritization techniques and improving watershed model outputs on the small watershed scale.

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