Idea Transcript
Swater quality
table of contents 1 > introduction 2 > data 3 > research & results 4 > related sites
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introduction
A fresh glass of water can quench the biggest person's thirst. However, fresh water is becoming hard to find. What about Lake Temescal? How about the water? "I would never drink that water," says an anonymous student, "let alone swim in it. The water is green." Well so is broccoli, and everybody loves to eat that.
Map of Lake Temescal
Many students are not a big fan of the water at Lake Temescal, and are not willing to find an explanation. The eye can be very deceiving. The fisherman seem to be optimistic that the water will be okay. "I don't care, I just wanna fish."
Rebecca at site 5
TEAM WATER QUALITY has been assigned to investigate the water at Lake Temescal. So far the consenus of the group is we would not want to be immersed in the Lake. Special Field Researchers have been working around the clock taking samples of the water at six different sites and testing pH and dissolved oxygen levels. We strive to find out where the water flows from and if there are any precautions that come with drinking, swiming or fishing by the Lake.
Miriam at site 3
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data
Site
Dissolved oxygen (ppm)
1
2
15.2
16.2
3
4
5
17 8.2
8.6
6
7
11 11
Oxygen level
Site
1
2
3
4
5 67
pH 8.3 8.3 8.3 8.3 7.5 8 9 Level
pH levels
Site
Temperature (°C)
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2
3
4
5
6
7
8
8
8
8
11
8
8
Temperature levels
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S 3
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research & results
Pollution As defined by Encyclopedia Britannica, "water pollution involves the release into lakes, streams and oceans of substances that become dissolved or suspended in the water or deposited upon the bottom and accumulate to the extent that they interfere with the functioning of aquatic ecosystems . . .If the capacity of a body of water to dissolve, disperse, or recycle is exceeded, all additional substances or forms of energy become pollutants." Under this definition, it is clear that anything has the potential to pollute. Even "natural" parts of the environment can be harmful to a lake’s ecosystem. For example soil erosion can add excesses of silt to lake water. Or decaying algae can reduce oxygen levels (see dissolved oxygen section). Lake Temescal also has its share of "unnatural" pollutants. Hwy 13 adds harmful chemicals to the air, which are then added to the lake water through gas exchange at the lake-air interface. It is also reported that sewage is drained into parts of the lake at certain times during the year. Additionally, Temescal Creek, which flows into Lake Temescal, could become polluted by any number of things along its course. These pollutants would then travel to the lake and be added to its water. Finally, Lake Temescal is heavily used for recreation, and many visitors throw trash in and around the lake.
Naturally, we had to
violate a city ordinance or two...
PH level pH level is determined in large part by the amount of carbon dioxide in the water. Carbon dioxide creates carbonic acid. When that acid disassociates, it increases the number of hydrogen ions in the water, resulting in increased acidity. Therefore, a low pH level indicates a high carbon dioxide level. This fact seems to be compatible with the data we gathered about pH and oxygen levels. Oxygen is consumed by biological decay (see dissolved oxygen section); depending on the type of bacteria causing the decay, carbon dioxide may be produced. At site #5, oxygen level was only 8.6 ppm, and pH level was 7.5 (slightly basic, but closer to acidic than the majority of sites); perhaps biological decay at that site was consuming oxygen while producing carbon dioxide which increased the water’s acidity. Another source of carbon dioxide might be the atmospheric pollution produced by cars on Hwy 13, which is nearer to site #5 than to any other site. Impacts of pH level on the water quality of Lake Temescal seem relatively minor. According to Encyclopedia Americana, a pH level between 6 and 9 "appears to provide protection for the life of freshwater fish and bottom-dwelling invertebrates." Trout, with which Lake Temescal is stocked, can survive an even wider range of 4.1 ? 9.5. It should be noted, however, that 8.7 is considered the upper limit fo good fishing water (so site #7’s water quality is questionable).
Miriam performs a test at site 3
Oxygen Levels Oxygen levels in lake water vary according to numerous factors. They are affected by temperature and season; when the lake stratifies during warm weather (see Temp. section), most of the lake’s oxygen is concentrated in the surface layer (epilimnion), since the air-water interface is the lake’s main source of oxygen. During cold weather, however, the epilimnion cools and mixes with the lake’s underlayer (the hypolimnion). This replenishes oxygen throughout the lake. Pollution is another factor which affects oxygen levels, generally by reducing them. When more organic material than that system is able to break down enters the system, the excess nutrients in the material cause an increase in algae growth. When that algae decays, oxygen is consumed. Pollution also harms organisms that use oxygen; when anaerobic organisms attack the decayed algae or other organic wastes, they release methane and hydrogen sulfide, which are harmful to aerobic organisms.
Temperature
More testing at site 3
Pollution may have decreased the oxygen level at sites # 4 &5. There is some inflow at 4 & 5, which could bring polluting materials into the lake. There is also heavy vegetation near these sites, including algae, resulting in the scenario described.
Temperature is affected by several factors. One, the transfer of heat at the air-water interface (i.e. the surface), is not yet well understood. Another important factor is the amount of solar heat absorbed by the water. During the winter, as much as 14% of the sunlight which hits a lake surface can be reflected off. The amount reflected is determined partly be the sun’s angle; we hypothesize that site #5, which had a much higher temperature than other sites, is in a position (on the northeast side of the lake) which receives more direct, constant sunshine than the other sites do. Water temperature also varies with season, not only because of changes in number of hours of sunlight, air temperature, etc., but because of the way lake waters stratify. During warm weather, the lake surface (epilimnion) heats up and stops mixing with the colder under-layer (hypolimnion). When cold weather returns (as it has at the time of our tests), the epilimnion cools and is mixed by wind with the hypolimnion. This mixing cools the entire lake. In very shallow parts of the lake, however, the hypolimnion is minimal or nonexistent (since all the water is near enough to the surface to be heated). As a result, shallow areas experience less mixing/cooling. This might explain why sites 4 and 5, which are along the lake’s shore, were warmer that sites 6 and 7, which are in the middle of the lake.
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Some other sites to check out... EBMUD Home Page
> The East Bay Municipal Utility District homepage, with information on East Bay drinking water.
EBRPD Home Page
> The East Bay Regional Parks District manages and controls Lake Temescal.
Water Quality Association Home Page > Great facts & background on our nation's water. Water Resources of U.S.
> A U.S. Geological Survey fact & link site.
Or Check out the Quotes Page.
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