Which came first - the stagnant puddle or the microorganism?
An attempt to iron out the wrinkles of technical ignorance surrounding turbidity and bacteria with the Bunyanesque weight of scientific evidence and blistering logic.
By: Will Schrenkeisen
Dec. 11, 2008
Picture a tall glass full of fresh, crystal clear water. You hold it aloft, impaling the pellucid chalice on a brilliant shaft of purest sunlight, sending a dazzling pattern of refracted light cavorting throughout your surroundings. You quaff daintily from it to slake your overpowering thirst, your tender taste buds and olfactory nerves blessedly free of any fetid influence. For most, this is the very image of healthy cellular refreshment. Yet how many people would be as blasé about quenching their thirst if the glass in question was full of a murky, stagnant brew with a rancid odor? The word used to describe water in terms of these very attributes is turbidity. The more discolored, funky smelling, or otherwise offensive a water sample is, the higher its turbidity rating (more on this later). Obviously the turbid water mentioned above is not fit for consumption (drinking your own urine would probably be much safer), but a common misconception of this phenomena is that high bacteria levels somehow cause water to become turbid. In fact, the situation is reversed. Bacteria cannot spontaneously cause turbidity, but the more turbid a body of water is, the easier it is for bacteria to survive.
The visual indication of turbidity (cloudy, murky, discolored, or any other suitable adjective) is caused by suspended solids in the water; particles that can run the gamut from fine sediment to industrial by-products to planktonic life forms. These suspended solids cause the water to lose its clarity by scattering light, thus limiting visibility. Odor can be caused by the waste products of bacterial metabolism, but smelling water is not a very reliable test for bacterial concentrations (bacteria can smell very different from one another). Turbidity can be measured with any one of a plethora of tests, but perhaps the most simple, reliable, and effective measurement is obtained through a nephelometer. A nephelometer (more commonly referred to as a turbidimeter when used for water testing) functions by projecting a beam of light through a medium (liquid or gas) and measuring the amount of light reflected off the particles into a detector. In the United States the results are expressed in Nephelometric Turbidity Units (NTU), and internationally with Formazin Nephelometric Units (FNU), but can also be expressed in Formazin Turbidity Units (FTU).
First, clarification must be made on the term “bacteria”, as it will be used extensively in this article. Bacteria come in a bewildering array of forms with equally diverse effects and requirements, and not all of them malicious. Consider, for instance, that there are about 10 times as many bacteria cells in your body than your own cells. In seawater, the most common form of bacterial agents are Bacteriophages, with as many as 250,000,000 per milliliter of seawater. However, these miniscule viruses operate by infecting other viruses and bacteria, and so are of little consequence to the objective of this article. Pathogenic bacteria, on the other hand, are the organisms responsible for the majority of medical cases associated with swimming in (or drinking) polluted seawater, such as Amoebiasis, Otitis media and externa, Conjunctivitis, or Gastroenteritis. Viruses, though responsible for a great deal of much more potent maladies (including Adenovirus and some flesh eating diseases), generally cannot infect a host (swimmer) unless the individual’s skin, and thus their innate immune system, is compromised with a cut or lesion.
Unfortunately, these harmful bacteria are very difficult to test for, largely because of their tremendous variety of species and subgroups (making it inefficient, costly, and time consuming to test and catalogue their numbers). Due to this difficulty, biologists test for indicator bacteria, organisms that can be readily tested for and correspond significantly to the levels of other pathogenic bacteria (though the indicator species are not particularly virulent). Three common types of indicator bacteria biologists test for are total coliforms, E. coli, and Enterococci. The term total coliforms serves to define a very broad group of bacteria which can originate from soil, decaying vegetation, or the intestinal tracts of warm-blooded animals. E. coli (short for Escherichia coli) is a type of coliform found in the lower intestines of warm blooded animals, which when present even in small quantities is a strong indication of recent sewage or animal waste contamination. Enterococci is a subgroup of the fecal streptococcus group and closely mimics the behavior of many kinds of pathogenic bacteria, making it an ideal bacterium to test for. Finding the most probable number (MPN) of these indicator bacteria gives an indication (hence the name) of the population of their pathogenic cousins, and because of this relationship the EPA has set certain standards that when broken merit a beach advisory. These standards are; total coliforms - 10,000/100ml, E. coli - 235/100ml, and Enterococci - 104/100ml.
As briefly mentioned above, turbidity can be brought on by several things; algae, plankton, sediment, fecal matter, and storm runoff being among them. In fact, anything that can cause a great deal of small particles to mix with water is a potential culprit. High bacteria levels cannot create turbid conditions, as the organisms are too small to scatter any noticeable amount of light. However, turbid conditions can give rise to escalated bacterial concentrations, since the light scattering properties of sediment, algae, plankton, etc. serve to shield bacteria from the rays of the sun, including the ultraviolet spectrum, one of the major limits of aquatic bacterial growth (bacteria and viruses can also attach themselves to the solids, providing effective shelter and insulation from chlorine and other disinfectants). In addition to this, the suspended matter (possibly soil, runoff, or excrement) could itself be harboring various microorganisms or providing food for the bacteria as it decays (or perhaps both), as the case would be if the cloudy conditions are caused by human sewage, animal feces, or algae.
Unfortunately, this is only the tip of the iceberg, as high turbidity can reduce or eliminate the amount of light reaching aquatic plants, limiting their photosynthetic capacity and reducing the amount of oxygen they release into the water. In addition, particulate matter can adversely affect the function of gills and the development of eggs and larvae. All of this is especially true in lakes, reservoirs, and bays, as there is little if any current to dissipate the suspended solids (in many cases there is only enough to keep them suspended). If enough suspended solids have accumulated and enough plant life has been choked out, the fish, shellfish, and other animals which rely on them for both food and oxygen will begin to die. Obviously, increased levels of dead and dying animals in the water, along with organic detritus (possibly from algae, plankton, and decaying macrophytes), in combination with the sheltering properties of suspended solids will lead to high levels of bacteria. If this cycle continues for long enough, it can lead to the body of water in question undergoing hypoxia or anoxia, resulting in a dead zone.
Hopefully, having finished this article, the reader will possess a greater understanding of the nuances of turbidity than when they started. They (that is to say, you) are now equipped with the necessary tools to plumb the inky depths of scientific understanding, to avoid the deadly pits and mantraps that so often snare the unwary. After all, roughly 50% of all people surveyed with a brief series of water related questions expressed the opinion that bacteria is the primary determining factor in water quality. This shocking inaccuracy can be avoided through the simple expedient of reading the information presented above, cross-referencing it with the source material, and extrapolating to form a rock-solid, scientifically viable set of personal opinions. Just imagine what could be accomplished if more people knew that bacteria is a product of turbidity, and not the other way around.
“Turbidity.” Wikipedia. 7 Dec. 2008
“Turbidity.” Water on the Web. 17 Jan. 2008. 7 Dec. 2008
“Understanding Turbidity.” USGS. 7 Nov. 2002. 8 Dec. 2008 <http://ga2.er.usgs.gov/bacteria/helpturbidity.cfm>
“Office of Water.” U.S. Environmental Protection Agency. 21 Nov. 2008. 3 Dec. 2008
“Nephelometer.” Wikipedia. 6 Dec. 2008
“Bacteria.” Wikipedia. 5 Dec. 2008
“Total Suspended Solids.” Wikipedia. 5 Dec. 2008
This editorial is good work for me, and I am slightly proud of it. My opinion stems from what I see as proficient use of metaphor to "hook" the reader, a hook that rapidly devolves into a mire of inconsequential details and half-answers. It does have a relatively lengthy list of sources, even though four are from Wikipedia (incidentally, Wikipedia is the best internet source for everything imaginable, and I do not know why people insist on using Google, because all Google does is link you to related web pages, most of which are written by people with absolutely no knowledge of the subject).
I accomplished these glowing achievements by making extensive use of Thesaurus.com and Wikipedia. For once, I actually made drafts of my work, a practice that I generally eschew because it involves more work than is necessary to arrive at a passable final product. Ironically, the only person to provide consistent, helpful feedback and revisions was myself, somewhat limiting the effectiveness of the entire process and making me wish I had simply typed up the whole thing in the last two days, as is my wont. I feel that this approach would have saved me time, boredom, and frustration, while producing an editorial of comparable quality.
Sadly, this next example cannot be displayed directly on the page of this blog, but I urge the reader to view it by using this simple link. It is a satire I wrote with a good friend (named Nathan Eisenberg) in middle school, and every time I read it I get a laugh out of it. This satire is quite possible my favorite piece of writing, though some may find it slightly offensive. Reading it gives me pangs of nostalgia, from a time when I could actually write for fun and find the process inherently enjoyable (something that is happening less and less with all these damn analytical essays). I liked the piece so much that I substituted it for a slightly related project in 9th grade instead of writing one from scratch, which is how it ended up on the pages of my freshman DP.
Me and my pal accomplished this by brainstorming over a piece of scratch paper for an assignment in which we had to construct a satire on any issue after reading a historical satire as a class (I cant remember the details but it was from either Ireland or Scotland and had to do with food, possibly potatoes, and poor people). It was not very hard as we were both fairly competent writers and filled with humor and inspiration for this particular issue.
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