Date of Award

8-16-2024

Document Type

Open Access Dissertation

Department

Chemistry and Biochemistry

First Advisor

Timothy Shaw

Abstract

Eutrophication is one of the most serious water quality issues affecting aquatic systems in the United States. Densely populated urban areas as well as mining and agriculture are major sources of anthropogenic nutrient loading into lakes and rivers. Excess loading of nutrients like phosphorus (P) into these ecosystems can cause native algal species to be outcompeted by harmful algal bloom (HAB) species. Increases in these HAB events are a growing public health concern as contact with excreted toxins can be harmful for human, aquatic, and land species. Remediation techniques like total maximum daily loads (TMDLs) have been implemented to reduce nutrient loading, however TMDLs only account for nutrient loading in the water column neglecting the potential availability of legacy sediment nutrient reservoirs. Benthic cyanobacteria species like Microseira wollei, which sit on the sediment surface, have the advantage as they can utilize both the water column and sediments to maintain nutrient requirements. In this study, a continual M. wollei bloom at Lake Wateree, SC was investigated over a two-year sampling period to assess the availability and utilization of sediment P forms in this system. M. wollei blooms persisted despite TMDL implementation to reduce nutrient loading in this system. Sediment P concentrations for > 40 sediment cores were evaluated over a two-year period to verify a model study that predicted sediment total P (TP) as a significant factor for supporting benthic HAB proliferation.

Phosphorus can exist in a dissolved or particulate form where dissolved P can adsorb onto, or complex with iron oxides to form authigenic iron-phosphate phases. These phases are redox-active and can become mobilized when environmental conditions like dissolved oxygen change. Sediment surface concentrations of total carbon, TP, organic P (OP), and inorganic P (IP) at two locations in Lake Wateree were plotted to model spatial and temporal trends in the P inventory. Phosphorus concentrations as high as 1.16 mg P/g dried sediment were detected in this system as well as seasonal variations which identified an increase in sediment OP over winter months and mobilization from the reservoir in warmer months, coincident with increased biomass presence suggesting the importance of OP in this system. Microbial turbation processes between particulate P in the overlying water column and sediments as deep as 10 cm were also identified in this system. Sediment matrices were analyzed via inductively coupled plasma-optical emission spectroscopy (ICP-OES) using analytical methods optimized and modified for interferences in environmental systems. A two-step sequential extraction method for labile iron oxides in sediments was used to investigate the cycling between reducible iron oxide minerals and associated P phases. It was determined that more than 60% of the TP reservoir in the sediments at Lake Wateree cycled with a reducible iron phase. This study also suggested that sediments with higher concentrations of hydroxylamine extractable iron phases were more susceptible to benthic HAB proliferation. Ultimately this study elucidated dominant mechanisms for P bioavailability in benthic HAB systems where recycled bioavailable P from algal detritus sustained bloom proliferation. This study also demonstrated that labile iron oxide phases catalyzed the recycling of OP where algal mats controlled environmental conditions for these processes.

The findings of this study are also applicable to other lacustrine systems as identifying factors to mitigate nutrient bioavailability in vulnerable water supplies. In all, both OP and IP loading in sediments should be considered when identifying factors that mitigate P bioavailability in vulnerable water supplies.

Rights

© 2024, Cassidy Ann Crandell

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