Date of Award

12-2017

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Division of Agriculture (SAFES)

Committee Member

Dr. John H. Rodgers Jr., Committee Chair

Committee Member

Dr. William C. Bridges Jr.

Committee Member

Dr. James W. Castle

Committee Member

Dr. George M. Huddleston III

Committee Member

Dr. Burton C. Suedel

Abstract

Pulse exposures are fundamentally different from static exposures in that they temporarily exceed pretreatment concentrations. Given this fundamental difference, responses of organisms to pulse exposures should also differ from responses to static exposures. In this dissertation, copper-based algaecides were studied because they have notable characteristics that can be used to ask questions regarding pulse exposure durations and consequent effects. Specifically, the time, location and applied concentration are predetermined allowing for measurement of copper exposures in situ. Additionally, algaecides are intended to result in effects to noxious species so that responses can be measured. For the first experiment in this dissertation, copper dissipation rates following an algaecide application were calculated and modeled both physically and mathematically by characterizing individual fate processes for copper (i.e. algal sorption, sediment sorption, copper precipitation and dilution). After characterizing copper pulse exposures, the influence of exposure duration on organism responses was discerned. The target cyanobacterium Lyngbya wollei and the non-target fish Pimephales promelas were used to demonstrate relationships between pulse-exposure durations and organism responses. For Lyngbya wollei, initial cyanobacterial biomass may be another characteristic that alters responses of the cyanobacterium in addition to exposure duration. From the characterization of copper pulse exposures, aqueous phase copper concentrations dissipated rapidly (half-life = 0.03 days) in situ. This rapid half-life was comparable to the half-life for dilution (half-life = 0.03 days), whereas the half-lives for sediment sorption (half-life = 3 days), copper precipitation (no significant differences in aqueous copper concentrations in 13 days) and algal sorption (no significant differences in aqueous copper concentrations in 8 days) were greater, indicating that dissipation was mainly due to dilution. Mathematic and physical (mesocosm) models of copper pulse exposures resulted in similar dissipation half-lives (mathematic half-life = 0.03 days and mesocosm half-life = 0.02 days) relative to half-lives calculated from copper concentrations measured in situ (half-life = 0.03 days) demonstrating that these approaches could be used to predict exposure durations. In terms of L. wollei responses to copper pulse exposures, the biomass of the cyanobacterium at exposure initiation is a variable in addition to exposure duration and copper concentration that drives responses. For a series of initial cyanobacterial biomasses from 13 g wet weight (WW)/m2 to 1,558 g WW/m2 exposed to the same copper concentration and exposure duration (1 mg Cu/L for 24 hours), responses of L. wollei range from the maximum response (> 90% response in terms of percent damaged trichomes) to non-detect demonstrating the impact of biomass at exposure initiation. A model was subsequently designed using initial biomass, copper concentration and exposure duration to predict responses of L. wollei to a copper algaecide. For the non-target fish, P. promelas, copper exposures with 1.5 hour half-lives resulted in LC50s (calculated from percent survival measured 96 hours following exposure initiation) that exceeded those of static exposures by an order of magnitude (i.e. 164 µg Cu/L to 1,134 µg Cu/L). LC50s (calculated from measurements 96 hours following exposure initiation) for copper pulses with half-lives of 4 and 8 hours exceeded static exposures by a factor of approximately 3 while half-lives of 15 hours resulted in comparable P. promelas responses relative to 96 hour static LC50s. The experiments presented in this dissertation provided approaches to understand the limits and bounds of pulse exposures in terms of exposure durations and effects on both target and non-target organisms.

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