## LSU Historical Dissertations and Theses

#### Title

Hydrocarbon Degradation in Louisiana's Salt and Freshwater Marshes: Inherent Potential, Enhancement, and in Situ Monitoring Techniques.

1996

Dissertation

#### Degree Name

Doctor of Philosophy (PhD)

#### Department

Civil and Environmental Engineering

John H. Pardue

#### Abstract

The ability to effectively remediate crude oil from marsh systems is important due to the coexistance of the economically important hydrocarbon industry and ecologically and economically valuable marshes. Laboratory and field studies were initiated to examine the intrinsic ability of coastal marshes to biodegrade crude oil, to determine the ability to enhance degradation using nutrient additions, and develop a superior monitoring technique. The alkane and poly aromatic hydrocarbon (PAH) fractions seem to be independently degraded and these systems appear to have much greater capacity to degrade PAHs than alkanes. Nitrogen was found to be a limiting factor for both alkane and PAH fractions, although the PAH fraction in this crude oil was completely degradable with or without nitrogen enhancements. Phosphate had only a minimal beneficial effect on alkane transformation rates and none for PAH transformation. Seasonal variations were found in both marsh systems although they were greater in the fresh marsh. Seasonal trends in mineralization rates were different for phenanthrene and hexadecane as well as for each marsh. Removing nutrient limitations greatly increased the rate of hexadecane mineralization for most months in both marshes and significantly reduced the lag time to mineralization. Phenanthrene mineralization increased for specific months in the salt marsh and decreased or remained the same in the fresh marsh. Limited correlation was found between environmental conditions and crude oil respiration potential. In laboratory microcosms using salt marsh soils and in field trials it was possible to monitor and quantify crude oil mineralization by measuring changes in CO$\sb2\ \delta\sp{13}$C signatures and the rate of CO$\sb2$ production. These values are easy to obtain and can be combined with simple isotope mass balance equations to determine the rate of mineralization from both the crude oil and indigenous carbon pool. Hydrocarbon degradation was confirmed by simultaneous decreases in alkane-, isoprenoid-, and PAH-hopane ratios. This procedure appears to offer a means of definitively quantifying crude oil mineralization in a sensitive, inexpensive and simple manner in environments with appropriate background $\delta\sp{13}$C signatures.

9780591133554

95

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