Date of Graduation

5-2022

Document Type

Thesis

Degree Name

Master of Science in Crop, Soil & Environmental Sciences (MS)

Degree Level

Graduate

Department

Crop, Soil & Environmental Sciences

Advisor/Mentor

Haggard, Brian E.

Committee Member

Savin, Mary C.

Second Committee Member

Wood, Lisa S.

Keywords

Aquatic Sciences; Cyanobacteria; Harmful Algal Bloom; Lake Fayetteville; Microcystin

Abstract

The occurrence of cyanobacterial harmful algal blooms (HABs) and toxins are a nationwide concern. Although Lake Fayetteville likely experienced HABs for many years, microcystin, an algal toxin, was not monitored until 2019. The objectives of this study were to: 1) observe temporal variation in water quality and total microcystin concentrations, 2) quantify thresholds with microcystin and nutrients, algal parameters, and environmental factors, and 3) evaluate complex relationships between total microcystin and nutrient supplies, algal parameters, and environmental factors using a classification and regression tree model (CART). Three sites (dam, inlet, and mid) at Lake Fayetteville were sampled weekly to monthly from 2019 to the end of 2021. Water samples were analyzed for temperature, pH, dissolved and total nutrients, chlorophyll-a, chlorophyll raw fluorescence units (RFU), phycocyanin (RFU), and total microcystin. Peak mean total microcystin concentrations (1.9 to 6.2 μg/L) and the longevity of toxin production varied between years. Many parameters had significant thresholds with total microcystin across the time periods in this study including temperature, algal biomass, inorganic N concentrations, and molar TN:TP ratio. Significant thresholds with total microcystin concentration varied across years, and the parameters with the greatest R2 values were increased water temperatures, elevated algal biomass, low inorganic N concentrations, and an intermediate molar TN:TP ratio. The CART models for the all data and each study year varied in the number of splits, the parameters included, and amount of variation in total microcystin explained, and the 2020 model explained the most variation (76%) in the total microcystin concentrations. Overall, the factors triggering a HAB and toxin production are not well known, but monitoring a lake over multiple years and developing waterbody specific guidelines can help guide future management decisions and help protect human health.

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