Theses and Dissertations

Date of Award

7-2023

Document Type

Thesis

Degree Name

M.S.

Department

Environmental Toxicology

Committee Chair

John C. Lehrter

Abstract

Submerged macrophytes form the foundation of freshwater ecosystems. These organisms are sessile and are very susceptible to shifts in their environment. Heavy metals are of particular concern as they can be sequestered indefinitely in sediments and are readily taken up by rooted vegetation. In the presence of saltwater intrusions, these metals can interact with salt ions potentially changing their availability to submerged vegetation. In this study a freshwater macrophyte, Vallisneria neotropicalis, was used as a test species for interactive effects between Cd, a non-essential heavy metal, and salt stress. The metrics used to establish the individual as well as the combined stressor effects were clonal reproduction rate, leaf growth rate, and total Cd body burden after exposure to three levels of salinity (0, 5, and 10 PSU) and three levels of sediment Cd (0, 10, and 40 ppm). In the presence of low salinity (5 PSU), ramet production was impeded less by Cd than it was in the presence of freshwater. There was also a significant decrease in leaf length in these treatments, indicating that the ramet production was balanced by a change in biomass allocation. However, the plant’s Cd body burden did not vary as a function of salinity. The trend of Cd accumulation irrespective of salinity suggests that the plants’ rate of Cd export could be a function of heavy metal-induced leaf senescence and shedding. We emphasize the need for further research to understand heavy metal export strategies across a salinity gradient in freshwater macrophytes.

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