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Chapter 2: All About Sand
A Brief Introduction to Sand
What is sand?
Sand is normally a reflection of nearby bedrock. It is a result of millions of years of mechanical and chemical breakdown of rocks. The composition of sand is largely dependent on the source material. For instance, the sand on some Hawaiian beaches is often composed of volcanic rock fragments, volcanic glass, and “cinder” from volcanic eruptions. In contrast, sediment found on many of the beaches of southern California comes from granites, a common rock which consists of quartz plus tiny amounts of mica, feldspar, and hornblende. The white sand beaches of Mexico are mainly composed of shell fragments and other organic material. Individual sand grains are the size of table salt grains (less than one millimeter in diameter) and resemble miniature gemstones when magnified.
Fig. 3. Sands from different beaches[i] (© Microbus)
What are most common beach sand issues?
Beaches play a very important role as habitat to a number of plants and animals. They serve as breeding grounds, shelters, sources of food for marine life, and are home to a number of endangered species.[ii] The overcrowding of beaches has led to large-scale destruction of some of these habitats and has reduced their ability to adapt to environmental changes. Development, climate change, and commerce have all played a part in increasing the pressure on beach ecosystems.
Beach erosion, defined simply as the loss of sand, is the direct consequence of a combination of different factors. These include building coastal developments too close to the beach and a gradual rise in sea level.[iii] In a move to compensate for the lost sand and prevent further losses, communities often undertake shoreline armoring and beach renourishment projects. A sand issue that has caused considerable debate is the slow but sure disappearance of sand dunes.
How are sand dunes formed? Why are they important?
Sand dunes are defined as natural or artificial ridges or mounds of sand landward of the beach.[iv] Dunes are geological landforms that are formed when there is a combination of abundant sand, strong winds, and sparse vegetation. Depending on proportions in which these three variables are present, different dune types may result, including U-shaped dunes (parabolic dunes), linear or longitudinal dunes and transverse dunes. Places with minimal sand supply, weak winds and/or abundant vegetation are not conducive to the formation of sand dunes.
Coastal dunes are of great ecological importance. They support the habitats of a number of rare and unique plant and animal species. They also play a vital role in providing a natural barrier against flooding and erosion. In the United States, the dunes on the shores of Lake Michigan are well known tourist attractions, bringing in more than half a million people each year. These dunes, created some 10,000 years ago, comprise the largest concentration of freshwater sand dunes in the world and support more unique species and communities than any other part of the Great Lakes system. Recently, the existence of these dunes has been severely threatened from continuous strip mining and the dunes continue to disappear at a rapid rate even though various anti-mining laws have been passed.[v]
Bacterial Contamination: Origins and Monitoring
What is the historical view of bacteria and beaches?
Pollution at beaches is typically regarded as a direct consequence of industrial, agricultural, or municipal activities that result in the bacterial contamination of water. Recreational waters are tested for the presence of fecal indicator bacteria. Fecal indicator bacteria, which include E. coli and enterococci, are abundant in feces and so their presence indicates that the water has been contaminated. With the number of beach advisories and closings seeming to increase with every passing summer, beachgoers have become fairly aware of the health hazards associated with swimming in contaminated waters. Human wastes are generally considered the main source of fecal contamination. Other sources, such as beach sand, have been overlooked as a source of fecal bacteria.[vi] However, recent studies are causing a change in perception. Results indicate:
- There are indirect sources of indicator bacteria, such as sand and plants, that may significantly affect recreational water quality.
- Indicator bacteria seems to be commonly found in beach sand, at levels sometimes greater than water.
How is beach water monitored?
The main objective of beach monitoring is to evaluate the presence and levels of fecal indicator bacteria in recreational water. Levels that exceed defined thresholds indicate that the beach water is contaminated and may be unfit for swimming. The levels of bacteria in the water are measured in colony forming units (CFUs) per 100 milliliters (mL) of water. A level of 100 CFU/100 mL would mean there are about 100 cells of these bacteria in every half-cup of water.
What are indicator bacteria? Are they harmful?
It is difficult, time-consuming, and expensive to test for all the potential pathogens in water. Therefore, the United States Environmental Protection Agency (EPA) recommends testing for fecal indicator bacteria. Fecal indicator bacteria are easy to analyze, relatively safe to handle, and are usually present when enteric (fecal) pathogens are present. Fecal indicator bacteria are microbes that also live and multiply in the digestive tract of humans and warm-blooded animals, but they normally do not cause disease.[vii] If these indicator bacteria are present, some amount of fecal material in the water is likely. A higher level of indicator bacteria signifies a greater level of contamination from fecal matter and a greater chance that pathogenic microbes being present, thus presenting a health risk to swimmers from waterborne illness.
The E. coli used to measure water quality does not cause illness in humans. There are only a few types of E. coli pathogens that cause outbreaks of disease. The pathogenic E. coli occur quite rarely in feces. The regular (non-pathogenic) E. coli on the other hand is present in the gastrointestinal tract of humans and does not cause diseases in humans.[viii]
An Emerging Emphasis on Sand
In 1994, Ghinsberg et. al. examined the occurrence of indicator bacteria in shallow surface sands of a Mediterranean beach. During the same time, studies in Lake Michigan revealed that indicator bacteria (E. coli) in foreshore sands were 5 to 10-fold higher than the adjacent lake water. It became known that while the concentrations of indicator bacteria remained roughly constant within the first 5 meters landward of the lake (i.e. in the sand), the counts rapidly decreased while moving into deeper water of the lake. Furthermore, indicator bacteria concentrations were found in places where there was absolutely no indication of any human contamination. So where was the bacteria coming from? All clues pointed in the direction of sand and scientists began to examine the relationship between sand and fecal bacteria more closely.
Analysis shows that bacteria are often unable to survive longer in water, finding sand more favorable and possibly increasing their numbers in sand environments. Bacteria harbored in the sand may persist longer than in the water because they adhere to sediment particles and are protected from harmful effects of radiation from sunlight, unlike free bacteria in the water. [ix]
Also, the movement of sand by wave action due to storms and commercial or recreational boating may increase the bacterial counts in the shallow waters near the shores, which could prove to be a health hazard for children playing there. [x]
When faced with a swimming health advisory or closing, many beachgoers will opt to remain at the beach and enjoy sand play activities. Hence, there is a legitimate interest among the scientific community to better understand how contamination in sand affects public health. Children are a particular concern because they spend a great deal of time playing and digging in the wet sand and are more susceptible to intestinal illness; the elderly and infirm would also be more susceptible to illnesses associated with contamination. [xi]
In 2003, an intensive study by the United States Geological Survey at a freshwater beach in Chicago revealed some interesting details on the relationship between sand and indicator bacteria (E. coli). The study found that indicator bacteria levels in sand averaged 5-10 times higher than levels in adjacent swimming waters. During the course of this study, the city replaced the contaminated sand with truckloads of fresh sand; however, within two weeks, indictor bacteria levels were similar to those collected before sand removal. What surprised the scientists most was that these indicator bacteria remained consistently high regardless of beach water quality. Scientists determined that these bacteria were self-sustaining in sand and did not need any additional sources to help boost their counts.
The finding that indicator bacteria concentrations were higher in shallow water than in deeper water served to indicate that one source of contamination in beach waters may also be the surrounding sand and sediments. After completing their research, scientists were able to conclude that sand was a major contributor of fecal indicator bacteria in lake water. The following two studies profiled in this report demonstrate the research being done in this area. These studies clearly show the presence of indicator bacteria in freshwater sands and marine sands.
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[i]Microbus, “Take a Microscope Trip” <http://www.microscope-microscope.org/microscope-home.htm>
[ii] U.S. Commission on Ocean Policy.
[iii] United States Geological Survey, “Coastal Change” <http://pubs.usgs.gov/circ/c1075/change.html> (Accessed March, 2005).
[iv] “NOAA Coastal Services Center” <http://www.csc.noaa.gov/> (Accessed February, 2005).
[v] Lake Michigan Federation, “An Advocate’s Field Guide to Protecting Lake Michigan” <http://www.greatlakes.org/field_guide/habitat_sand.asp>, 2004.
[vi] Alm et. al. 2003. Fecal Indicator Bacteria Are Abundant in Wet Sand at Freshwater Beaches; Water Res 37:3978-3982.
[vii] Dr. Dufour, “E.coli and Public Health (2003)”; U.S. EPA; Lakeline 23:2: 13-15.
[viii] Whitman RL, Nevers MB, “Foreshore sand as a source of Escherichia coli in nearshore water of a Lake Michigan beach.” Appl Environ Microbiol. 2003 Sep;69(9):5555-62.
[ix] Ghosh et. al. “Serovars of multi-antibiotic resistant Escherichia coli from the freshwater environs of Calcutta India.” Microbiol Immunol 1991;35(4):273–88.
[x] Ibid.
[xi] Ibid.
