please help me with these problems?

Question

How do scientists measure the quality of our waters?

Give two reasons why scientists measure water's temperature.

What is Dissolved Oxygen?

Why is D.O. important in measuring water quality?

What affects the D.O. of a stream?

http://www.epa.gov/owow/monitoring/nationswaters/whatdo.pdf

Answer 1

Lea has a great answer.

Answer 2

You should do your own homework. My class did a project on water quality a few months ago. It is easy. Just do your own homework, and use common sense.

Answer 3

Measuring Water Quality
Scientists use many different instruments to determine the quality of water, including Secchi disks (measure water clarity), probes, nets, gauges and meters. Water quality is not just measured by direct sampling. Information can also be derived from aerial and satellite photographs by observing the surrounding environment and by collecting organisms that live in the body of water.
Although you might not have access to the resources of a scientist, there are some simple tests you can perform to get an idea of the quality of a particular water body:

Temperature
The temperature of water can affect it in many different ways. Some organisms prefer cool water, while some like it warm. Most aquatic organisms are cold-blooded. This means that the temperature of their bodies match the temperature of their surroundings. Reactions that take place in their bodies, like photosynthesis and digestion, can be affected by temperature. It is also important to know that when the temperature goes up, water will hold more dissolved solids (like salt or sugar) but fewer dissolved gases (like oxygen). The opposite is true for colder water. Plants and algae that use photosynthesis prefer to live in warm water, where there is less dissolved oxygen. Generally, bacteria tend to grow more rapidly in warm waters. Colder water contains more oxygen, which is better for animals like fish and insect larvae.

Dissolved Oxygen (DO)
Oxygen is necessary for many aquatic species to survive. This test tells you how much oxygen is dissolved in water for fish and other organisms to breathe. Most healthy water bodies have high levels of DO. Certain water bodies, like swamps, naturally have low levels of DO in the water. Lots of organic debris (fallen leaves, sewage leak) can cause a decrease in DO concentration. Microorganisms, in the process of decomposing the organic material, use all the oxygen in water. How does oxygen get in water in the first place? Much of the oxygen in water comes from plants during photosynthesis and also from air as wind blows across the water's surface.

pH (acidity)
The potential of Hydrogen, also known as pH, is a measure of acidity and ranges from 0 (extremely acidic) to 14 (extremely basic) with 7 being neutral. Most water is in the range of 6.5-8.5. Let's see some examples to compare pH values. Lemon juice has a pH of 3 ‐ this makes it an acid. We all know how it feels to accidentally get lemon juice on a cut finger. Stronger acids have the ability to eat through solid objects if spilled. Liquid bleach has a pH of 11 — this makes it a base. Strong bases, just like acids, can burn your skin. Let's think about why. Our bodies are made mostly of water. Water has a pH of 7. Things that are close to pH 7 work well with our bodies. The same holds true for aquatic organisms. If the water becomes too acidic or basic, it can kill them. Not all acids and bases are bad. Aspirin and tomatoes are acidic, while milk of magnesia and baking soda are both bases.

Turbidity
Turbidity refers to the clarity of water, or how clear it is. This determines how much light gets into the water and how deep it goes. Excess soil erosion, dissolved solids or excess growth of microorganisms can cause turbidity. All of these can block light. Without light, plants die. Fewer plants mean less dissolved oxygen. Dead plants also increase the organic debris, which microorganisms feed on. This will further reduce the dissolved oxygen. No dissolved oxygen means other aquatic life forms cannot live in the water.

After testing these parameters, make a note of the time of year, current weather conditions, cloud cover, air temperature and any other environmental observations that may affect the tests.



Temperature
The temperature of the water in your river or lake is very important for water quality. The temperature of the water affects many physical, biological and chemical characteristics of a river or lake. Do you know why cool water can hold more oxygen than warm water? Because gases dissolve easier in cooler water!

Why is the temperature of water so important? For a number of reasons! Temperature affects:

the amount of oxygen that can be dissolved in the water;
the rate of photosynthesis by algae and larger aquatic plants;
the metabolic rates of aquatic organisms; and,
the sensitivity of organisms to toxic wastes, parasites and diseases.
One way that the temperature of water can increase in a river or lake is from thermal pollution. Thermal pollution is an increase in water temperature caused by adding relatively warm water to a body of water. Industries, such as nuclear power plants, may cause thermal pollution by discharging warmer water from their plant that was used to cool machinery. Thermal pollution may also come from stormwater running off warmed urban surfaces, such as streets, sidewalks and parking lots.
Why do we measure changes in the temperature of water? As water temperature rises, the rate of photosynthesis and plant growth (and decay) increases. As plants die, they are decomposed by bacteria that consume oxygen, increasing the biochemical oxygen demand in the water. The metabolic rate of organisms also rises with increasing water temperatures, resulting in an even greater oxygen demand.

Most aquatic organisms have adapted to survive within a range of water temperatures. Some organisms prefer cooler water, such as trout and stonefly nymphs, while others thrive under warmer conditions, such as carp and dragonfly nymphs. As the temperature of a river or lake increases, cool water species will be replaced by warm water organisms. Few organisms can survive in temperatures of extreme heat or cold.




Oxygen saturation is a relative measure of the amount of oxygen that is dissolved or carried in a given medium. It can be measured with a dissolved oxygen probe in liquid media, usually water.
In aquatic environments, oxygen saturation is a relative measure of the amount of oxygen (O2) dissolved in the water. Dissolved oxygen (DO) is measured in standard solution units such as millimoles O2 per liter (mmol/L), milligrams O2
20 °C, normal pressure, freshwater: 9.1 mg/L = 100% saturation



Dissolved Oxygen
Just as sufficient oxygen is necessary for human survival, it is also critical for the survival of aquatic animals. In most swiftly flowing streams with riffles, there is plenty of dissolved oxygen (DO) to support aquatic animals because the water is aerated as it flows and bubbles over rocks. However, in some sluggish, low gradient streams on the Coastal Plain, DO may drop below the state surface water criterion of 5 mg/L (or parts per million). When DO is low, only those organisms adapted to low DO levels can live. Although DO may be naturally low in many of these slow-flowing streams, nutrients in fertilizers, runoff from urban lands, and untreated sewage can act as pollutants when they trigger a series of changes that lower stream DO levels.

Statewide, 6% of all stream miles have DO levels less than 5 mg/L. But more than 25% of the stream miles in the Chester, Lower Potomac, and Pocomoke river basins have DO levels below this criterion (Figure 10). Seven river basins contained no stream miles with low DO. Because DO varies by time of day and season, the single DO sample per site taken by the Survey during the day underestimates the extent of the low DO problem in Maryland streams.


Water Temperature
Water temperature affects the health of streams in many ways. Feeding, reproduction, metabolism, and the abundance of aquatic biota may all be altered by water that is too warm or even too cold. Streams that become too warm usually contain only organisms able to tolerate the stresses of heat. Stream temperatures also affect the solubility of compounds and rate of downstream nutrient flow to Chesapeake Bay.

Runoff of heated water from impervious surfaces (such as streets, parking lots, and rooftops) is a serious and widespread problem in Maryland streams. During summer, rain that runs off of hot impervious surfaces and flows directly into streams causes temperatures to rise abruptly during storms. Even during dry periods, water temperature is usually more variable in streams draining urban lands than those draining farms and forests. Reasons for this increased variability include a reduced supply of cool groundwater and less shade than in forested streams. Constructed ponds and lakes, especially those located directly on streams, also affect stream temperature because they are sources of heated water in summer and near-freezing water in winter.