Graduation Year

2013

Document Type

Thesis

Degree

M.S.

Degree Granting Department

Geology

Major Professor

Matthew Pasek

Keywords

contamination, freshwater, hypophosphite, phosphate, phosphite, redox

Abstract

Phosphorus (P) has long been acknowledged as a vital nutrient for living organisms and is a key factor responsible for the fresh water eutrophication. Our understanding of the phosphorus cycle has been limited by: (1) the common assumption that all P in the environment occurs primarily as phosphates and (2) by the limited analytical methods available to identify P speciation. In an attempt to understand the distribution and chemistry of phosphorus within a freshwater system we must be able to identify individual P species. To this end, we used a coupled High Performance Liquid Chromatograph (HPLC) - Inductively Coupled Plasma Mass Spectrometer (ICPMS) to determine concentrations of orthophosphate (+5), phosphite (+3) and hypophosphite (+1) in aqueous samples using methods modified from IC techniques developed by Ivey & Foster (2005) and Pech, et al. (2009) and Atlas et al. (in prep). The identification of different P species provides insight pertaining to contamination, bioavailability and sustainability within a freshwater system.

Thirty-two individual water samples were collected from six different bodies of freshwater in the Tampa Bay area between the months of November 2012 to March 2013. The freshwater samples collected were from river and pond/swamp water locations. Two sampling sites were chosen at each location. At each site, one sample was collected from the water's surface and a second sample was collected from the sediment pore water. When depth was sufficient a third sample was obtained from the midpoint between the surface and sediment.

Analytical results show that redox reactions of P occur in all freshwater samples collected as identified by HPLC-ICP-MS analysis. Our data show that the distribution and concentration of reduced P is controlled primarily by pH, and secondarily by water circulation, ORP and sediment type. Our results also imply biologic influence as a potential primary control of reduced P flux. Additional samples must be collected in order to quantify and differentiate the processes controlling P speciation. The ability to identify P speciation raises many questions concerning the validity of current methods used to measure P; other forms of reduced P may be present. Additional sample analysis will be necessary to determine how and if reduced forms of P affect the P cycle.

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