Murray State Theses and Dissertations

Abstract

Calcium is the fifth most abundant element on earth’s crust. Plants and animals require calcium for structure and intracellular metabolism. Recent studies have shown that dissolved calcium (Ca2+) freshwater ecosystems is of growing concern as the increasing concentrations of this element are implicated in altering the natural environment and biota. Elevated levels of dissolved calcium and sporadic re-emergence of an invasive species, namely zebra mussels (Dreissena polymorpha) in Kentucky Lake in the recent years served as a motivation for this study. The objective of this study was to determine spatial and temporal variations in dissolved calcium in selected streams, Kentucky Lake, and the Ohio River. Possible sources of this element to these water resources, as well as its relevance (threshold levels) for the prevalence of zebra mussels in Kentucky Lake were explored. Sites chosen for this study included tributary streams and embayment’s that empty into the Kentucky Lake, ten sites in Kentucky Lake, and two sites in the Ohio River. Sites were selected by the Kentucky Lake Long Term Monitoring Program and used potentially identify sources of calcium to these waters. Monthly sampling events for this study coincided with the Kentucky Lake Long-Term Monitoring Program (KLMP) cruises conducted during the years 2012 and 2017-2022. Water samples were collected using pre-cleaned I-Chem glass bottles. 40 mL of the samples were filtered using a 0.45µm filter into a 50ml centrifuge tube. The filtrate was acidified to 0.32 M with 800 µL trace metal grade nitric acid and stored at .4°C until analysis. Dissolved calcium in the water samples were determined using a Flame atomic absorption spectrometer. Perkin Elmer Analyst 900F-PinAAcle Flame Atomic Absorption Spectrometer (FAAS) was used for analysis. The FAAS was calibrated using calcium standards with concentrations of 1, 10, 20, 40, 50, 60, and 100 ppm. For quality assurance/control purposes, blank analysis, duplicates, matrix spike recovery, calibration, and calibration verification (seven-point calibration with r2=0.99) were checked routinely. In general, dissolved calcium concentration in Panther Creek sites varied with different seasons (BDL-41.0ppm) in each of the years studied. Among the Panther Creek sites 2N exhibited unusually larger fluctuation in concentrations during different months (12.0 – 41.0ppm +/- 9.43ppm). Therefore, an upstream spring on Panther Creek was added and monitored to determine the calcium source (This site was originally KLMP-4N site). Our results revealed that the primary source of calcium for 2N appeared to be from the upstream KLMP-4N spring site, hereafter referred as PS: Panther Creek Spring. In Kentucky Lake, dissolved calcium concentrations (average of all sites during the years studied) ranged from 15-25 ppm throughout this research. Statistical analysis revealed no significant monthly variations were found throughout the sites on Kentucky Lake during the period of this study. However, slightly higher dissolved calcium was found during the winter and early spring months. Among the two sampling sites in the Ohio River, the Ohio River at Paducah, KY (OH-P) consistently exhibited lower concentration (19.5 - 30.2ppm +/- 3.16ppm) of dissolved calcium than the Ohio River at Brookport (OH-B) (36.6 - 45.8ppm +/- 3.20ppm). Although calcium levels varied from month to month at all sites, there were no significant seasonal variations. Our results revealed that the Ohio River contained higher calcium concentration than the streams and Kentucky Lake during the period of this study. The variations in calcium concentrations may be due to different natural and anthropogenic sources, as well as patterns of input of calcium in these sites during different seasons. The elevated calcium levels may be attributable to natural minerals and road salt applications during the winter and spring with subsequent runoff due to precipitation. Occasional emergence and disappearance of zebra mussels in Kentucky Lake were related to the calcium levels during these months. Local emergence of zebra mussels in 2017-2018 and in August 2022 also may be due to presence of sleeper populations that were triggered by some environmental factor including dissolved calcium levels in Kentucky Lake water. Further, about 75 percent (216 samples out of 866 samples analyzed) exhibited average dissolved calcium concentration above 20 ppm on Kentucky Lake, which is near the threshold level for zebra mussel survival and reproduction. Zebra mussels may persist in Kentucky Lake at low or inconspicuous abundance and have negligible impact until reproduction is triggered by an abiotic/biotic factor(s). The results of this study highlight the value of and need for future monitoring of calcium in the Kentucky Lake watershed to examine any abnormal spike in calcium as well as zebra mussel populations. Furthermore, Kentucky Lake is an integral part of the landscape and economy of the Western Kentucky and Tennessee. Understanding the calcium levels and their influence on zebra mussel’s biological cycles could provide useful information about their relationship within the man-made freshwater ecosystem such as Kentucky Lake Reservoir.

Year manuscript completed

2022

Year degree awarded

2023

Author's Keywords

Zebra mussel, Kentucky Lake, Watershed, Dissolved Calcium, Ohio Rver

Thesis Advisor

Bommanna Loganathan

Committee Member

Kevin Revell

Committee Member

David White

Committee Member

Jonathan Lyon

Document Type

Thesis

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