The Fate and Effect of Low Levels of Crude Oil on the Ecosystem of the Gulf Coast Area
Authors: Brown L.R. , Minchew C.D. 
Published: October 2008

ABSTRACT
This paper describes the establishment of a stable pilot-plant ecosystem and the utilization of that system in determining some of the chronic effects of oil pollution on the aquatic environment of the Gulf Coast area. Impacts on microorganisms, phytoplankton, zooplankton, marsh grass, shrimp, mullet, and oysters are described.

INTRODUCTION
The acute effects of oil on the ecosystem have been fairly well documented through case histories of oil spills or through laboratory studies. Much less defined are the long lasting or chronic effects of pollution. Pertinent data on the acute and some chronic effects of oil on the marine environment have been obtained from postspill studies of major oil spills. These studies, however useful, suffer from problems related to the establishment of adequate controls and to separating population responses to oil from population responses to natural phenomena. Lewis states that "chronic conditions present much greater interpretative problems than the aftermath of a severe spill because the detection of subtle effects has to be made against the usually unknown scale of natural changes taking place".1 He further states that unless sublethal effects impair competitive efficiency sufficiently to have an ecological repercussion at the population and community level, he finds them of little concern, especially when set against the scales of naturally induced ecological events. It also is probable that predation on diseased and/or dying organisms following a spill in the environment increases the difficulty in obtaining organisms exhibiting sublethal chronic effects.2 It is evident that studies using large amounts of oil can yield valuable data on the effects of various toxicants on the species level, and it is equally evident that such studies will never be able to adequately study oil spills with sufficient controls to yield needed data on the effects of oil at the community or population levels found in nature. There have been only a few studies designed to gather "community type data" via chronic studies in controlled "ecosystems" established in natural marine ecosystems3 and on land in specially designed systems using a constant flow of water from selected marine environment4. This paper will summarize the results from two studies using a pilot-plant ecososytem to investigate the chronic effects of a low level of oil pollution on the aquatic environment of the Gulf Coast Region.

DESCRIPTION OF THE STUDY
In 1973, a pilot-plant ecosystem was constructed at the National Science and Technology Laboratory (NSTL) in Hancock County, MS. Four ponds measuring 46 × 46 × 2.5 m from the center of the levees and 30 × 30 × 2 m at the normal water line were constructed on a relatively pristine area within sight of NASA's rocket motor test stands and within pumping distance of a canal network used to transport rocket motors. The ponds were filled with seawater (28 parts per thousand (ppt)) obtained in from the Gulf of Mexico. The final salinities were adjusted to approximately 14 ppt with fresh well-water. Clumps of Juncusroemerianus, mixed with other species (e.g. Spartina, Scirpus, and Distichlus), were dug from selected areas in the St. Louis Bay marsh (Hancock County, MS), trans-ported to NSTL, and immediately planted along the banks on three sides of each pond.