The Difference between Bacterial Film and

Oil Sheen in Milkhouse Creek


John M. Brown, Department of Earth Sciences, University of South Alabama, Mobile, AL 36688. E-mail:


            Bacteria in the water in the Dog River Watershed are very common phenomena. The bacteria can often have a rainbow color, a color that is commonly associated with oil sheen that is seen in a parking lot after rainfall. The purpose of this research is to educate the general public on how to tell the difference between oil sheens and bacterial film. The methods of research included library and internet research, sampling of algae, bacteria and oil in Dog River Watershed streams and microscopic analysis of bacterial film. The end result of this research is to make people more aware of bacteria and inform them on how to know whether what they observe is harmful or not.

            Keyword: Bacteria, Oil Sheen, Film




When looking at oil on water, such as an oil slick in a parking lot, one cannot help but notice the shiny, rainbow like color that appears, as well as the film that it makes over the area it covers. There have been incidents of oil being in the water within the Dig River Watershed. Like the above stated, the oil gives a shiny appearance on the surface. This oil gets in the water from runoff on streets, leaks in vehicle engines and from parking lots where oil collects. Oil in water can have a negative effect on aquatic vegetation, fish and other characteristics of stream health (Burger 1997). It can cover leaves on vegetation, which inhibits photosynthesis and it is a potential danger for any wildlife that may consume these plants. Oil in water also has the potential to cause harm to humans (Adopt Your Watershed 2003). It can cause drinking water pollution and make water dangerous for swimming. There are cases where people have put oil in water to kill mosquitoes. This is illegal, even if it is on private property (West Nile Virus, 2004). Oil also has a tendency to give an odor reminiscent of a gas station (Adopt Your Watershed 2003). This odor is especially prevalent in marinas. Engines that have oil in the fuel, such as 2-cycle engines, leave oil sheen in the water from their exhaust (Powerboating 2004).



Research Question

The question I am attempting to answer is “what are the differences between bacterial film and oil sheen?” How do bacteria enter and benefit a stream? The Alabama Department of Environmental Management (ADEM) states that there have been several confusing reports on sheens made to their Mobile, Alabama office (Personal Interview). My goal is to shed light on and educate the general public on this matter and to help eliminate the confusion between oil and bacterial sheens.




To effectively answer the question on the difference between bacterial film and oil sheen in the Dog River Watershed, this research focused on a site on Milkhouse Creek beside North Mobile Baptist Church off of Airport Boulevard (Fig. 1). The site is a short walk down the stream to a wooded area. The stream is channelized with a concrete bottom and sides. The channelization is only along the church side. The rest of the stream flows natural and has a natural bottom. At the end of the concrete portion of the stream the water begins to pool up. At this point the water is somewhat stagnant and the amount of litter is very large. The litter accumulates when the water level rises after a rain and is washed to this area. There are also large amounts of sediment around the pooled area. This indicates that the stream has a flood plain, much like Halls Mill Creek at Demotropolis Rd. The stream bottom, on the concrete and on the natural bottom, is covered heavily with decaying vegetation, mainly leaves and twigs.

Time was also spent in the University of South Alabama library researching oil and bacteria and extensive research was performed online. Search engines, such as Google and Yahoo were employed using search phrases such as “bacteria oil sheen water,” and “film bacteria oil water pollution.” Online journals were employed as well.

 The research site chosen on Milkhouse Creek contained areas that exhibit surface sheens that have the characteristics of oil. To determine if the sheen is in fact bacteria and not oil, a simple test was employed. After locating a shiny sheen on the surface of the water (Fig. 2), the sheen was then disturbed by moving a twig through it. The results of this test will immediately tell if the sheen is a bacterial film or oil sheen.




            More times than not, the sheen that appears to be oil on the surface of the water is the result of the natural bacterial breakdown of organic matter (The Resource, p.1, 2004). When the twig was passed through the sheen it broke into several fragments. These fragments failed to return to their original form as a complete sheen (Fig. 3). This is evidence that the sheen was bacterial film and not oil. When passing a foreign object through an oil sheen, the sheen will immediately return to its original state. There was also the absence of any kind of petroleum odor, which is an indicator of oil pollution. Decaying vegetation also gives off a “rotten egg” odor, which is hydrogen sulfide gas (H2S). This gas is the natural byproduct of organic decomposition in wet environments and is harmless (The Resource, 2004). The bacterial film was surrounded by natural vegetation and there were also several places in the creek where dead leaves and other sorts of vegetation were present, which is why the bacterial film forms. The bacterial film is harmless to the environment and there is no reason to call ADEM (Table 1).

Bacteria enter the water through the surrounding soil. The soil is a vast plethora of micro-organisms going through a myriad of activities. Some decompose the wastes of man and animals and the tissues of plants. Some provide nutrients essential to plant life and others destroy these nutrients. Certain types of bacteria invade the tissue of living plants and animals with some beneficial results (Gordon, 1968). More specifically, the bacteria can be referred to as part of the soil biota. Soil biota is the biologically active “powerhouse” of soil. Along with bacteria, the biota is made up of fungi, algae, earthworms, protozoa, nematodes, mites and several other organisms. All of these play a part in the breaking down of organic matter. The larger organisms break down the larger organic matter and make it available to the smaller organisms. This process is called the “food web of soil biota.” For example, earthworms and millipedes shred dead leaves and residue and make it available to immobile bacteria. The biota is found in the upper few inches of the soil. The smallest organisms in the biota are microscopic bacteria and fungi and they make up the bulk of the biota. The microscopic organisms finish the process of decomposition by breaking down the remaining material of organic matter and store its energy and nutrients in their cells. When the bacteria die, these nutrients are released into the surrounding area. This promotes the growth of other aquatic plants. Some biota can even break down pesticides and pollutants. Without bacteria, the decomposition of organic material would be significantly slower and there would be a vast amount of leaves, twigs and other organic material covering the earth and important nutrients would not be accessible to other plants (Rangeland Soil Quality, Sheet 8, 2001). Bacteria help keep organic debris amounts in streams low, otherwise streams would be congested due to the huge amount of organic debris in the water.

The microscopic analysis of the bacterial film contained visible bacterial cells within the sheen. This indicated that the sheen was in fact bacteria and not oil.




Bacterial film from organic decay in Milkhouse creek shows no threat to water quality. In fact, it is good that it is there. The test is very easy to execute and does not require any expensive, sophisticated scientific equipment. Any oil one might find in the Dog River Watershed is most likely to be around a marina. The importance of this research is to educate the public and to make an effort to prevent people from reporting oil to ADEM. By using this data, the general public should have a firm understanding on how to determine the difference between bacteria and oil sheens and the effects oil can have on the watershed and the surrounding environment.



References Cited

Adopt Your Watershed. EPA. 2003. < adopt/patch/html/streamins.html> Accessed: February 26, 2004.


Burger, Joanna. Oil Spills. 1997. Rutgers University Press.


Davies, Jim. Personal Interview. April 23, 2004.


Dog River Watershed Map. <> Accessed: April 16, 2004.


Gasoline Engines: Two Cycle. <> Accessed: April 9, 2004.


Rangeland Soil Quality - Soil Bacteria. USDA, Natural Resources Conservation Service, Sheet 8. 2001. <> Accessed: April 20, 2004.


The Resource. A Publication of the City of North Augusta Stormwater Management Department. 2004. <>

Accessed: February 26, 2004.


Gordon, Ruth E. The Ecology of Soil Bacteria: An International Symposium –The Taxonomy of Soil Bacteria. 1968.  p. 293. University of Toronto Press, Toronto.


West Nile Virus. Mosquito Control on Private Property. <> Accessed: April 9, 2004.