Water Health

ABSTRACT Many factors affect river health. In this investigation the hows and whys of the effects that temperature and turbulence have on the concentrations of oxygen dissolved in water have been investigated. It has been hypothesised that when the temperature of a body of water is increased, the oxygen levels in it are reduced. And when the turbulence of water is increased, the oxygen levels must go up. The experiment was conducted by using a DO probe to measure the dissolved oxygen in the water after different samples of water were heated to various temperatures and another experiment was conducted by subjecting different samples of water to various levels of turbulence. In both cases the dissolved oxygen levels went down in a parabolic manner. By completing these experiments, the first hypothesis (about temperature) was proved correct, while the other hypothesis (about turbulence) was refuted.

RATIONALE FOR INVESTIGATION Rivers and waterways are very important to people for economical and agricultural growth, transport, and much more. Many ecosystems and animals also rely on rivers to provide for food and a secure place to live. So it is clear that taking care of our rivers is a significant issue. Many factors can have drastic effects on river health including temperature of the water, salinity, turbidity, phosphate and nitrate ions and dissolved oxygen. In this experiment we will investigate the effects that temperature and turbulence have on the levels of dissolved oxygen (DO) in the water. Temperature can have drastic effects on the dissolved oxygen levels in water. Water temperature regulates ecosystem functioning both directly through physiological effects on organisms, and indirectly, as a consequence of habitat loss (Water on the Web 2004). This may cause some changes to the photosynthetic and respiratory processes occurring in the water, causing changes in the levels of DO present in the water. But temperature also directly affects the concentrations of DO in the water. Turbulence also has an effect on the amount of DO present in the water. The churning and mixing of the water allows for oxygen from the air to get in and dissolve, providing more oxygen for aerobic organisms to perform respiration. Dissolved oxygen (DO) is vital to the health of the river as it allows for respiration in aquatic animals like fish and in plants. It is a very important indicator of a water body's ability to support aquatic life. Oxygen gets into water by diffusion from the surrounding air, by aeration (rapid movement), and as a waste product of photosynthesis in aquatic plants (KY Water Watch). Total DO concentrations in water should not exceed 110% as concentrations above this level can be harmful to aquatic life. Excessive dissolved oxygen in water may cause fish to suffer from "gas bubble disease", although this is a very rare event. The bubbles block blood flow through the blood vessels, causing death. Adequate dissolved oxygen is necessary for good water quality. Oxygen is a necessary element to all forms of life. Natural stream purification processes require adequate oxygen levels in order to provide for aerobic life forms. As DO levels in water drop below 5.0 mg/l, aquatic life is put under stress. The lower the concentration, the greater this stress. Oxygen levels that remain below 1-2 mg/l for a few hours can result in mass fish kills (KY Water Watch). Dissolved oxygen levels have to be kept at a balance. Many factors affect this balance including temperature, exposure to sunlight, turbidity, turbulence, pH, salinity and biological oxygen demand. What implications can these have on aquatic life and river health? One way to find out would be to experiment which is what we have done here.

RESEARCH PROPOSAL Research question: how and why do the temperature and turbulence of water affect the concentrations of dissolved oxygen (DO) in it? Aim: to investigate the relationships between DO and temperature and DO and turbulence. Hypotheses: the higher the temperature of a body of water, the lower the concentration of dissolved oxygen in it. AND The higher the amount of turbulence in water, the higher the concentration of dissolved oxygen in it.

JUSTIFICATION OF HYPOTHESIS Temperature and turbulence can greatly affect the levels of dissolved oxygen in water. Water temperature is the measure of the degree of hotness or coldness of a body of water and unnatural changes in water temperature can be an indicator of water quality. Temperature itself can cause almost the most change in DO levels than most other environmental factors. Temperature affects many processes in the water including photosynthesis and aerobic respiration, and the growth, reproduction, metabolism and the mobility of organisms. The rates of biochemical reactions double when temperature is increased by 10oC within the given tolerance range of an organism (OzCoasts, 2008). Aquatic organisms can only survive within a narrow temperature range and if the temperature goes beyond this range, it may compromise the organism’s ability to survive. And of course, aquatic organisms have a large influence on the levels of oxygen and carbon dioxide in water. Through respiration, organisms consume oxygen to give out carbon dioxide and through photosynthesis plants reintroduce oxygen into the water by consuming carbon dioxide. So if the survival of these organisms was threatened in any way, this may have an effect on the health of our waterways. However, temperature also has a more direct effect on DO concentrations in water. The higher the temperature of a body of water, the lower the amount of oxygen dissolved in it. The solubility of oxygen at 0oC is about twice its solubility at 30oC. Gases that dissolve in solvents like water release heat as they dissolve (Water on the Web 2004). An equation for the process of dissolving can be written as:

This process will continue until the water is completely saturated with oxygen. At this point gases will still dissolve into the water, but will be balanced by the gases that leave the solution. If heat is added to the solution, gas will be released in an endothermic reaction as it cannot dissolve anymore.

Le Chatelier's principle states that the solubility of a gas will increase as heat is lost in a system and will decrease as heat is gained (Water on the Web, 2004). Hydrogen bonding also has an effect on the way that gases dissolve in water. Hydrogen bonds are chemical bonds that form between molecules containing a hydrogen atom bonded to a strongly electromagnetic atom (that which attracts electrons), in the case of water, this being oxygen (refer to Figure 1).Because the oxygen atom attracts the electrons from the hydrogen atom, they form a very polar molecule where one end is slightly negatively charged and one end is slightly positively charged. Hydrogen bonds form between these molecules because the negative and positive ends of one molecule are attracted to those of another molecule (Microsoft Encarta, 2006). There are pockets of air between these molecules and oxygen atoms can easily fit into them. However, when the water molecules are heated, they gain energy, shaking and vibrating in the process. This causes the air pockets to lose their ability to hold the oxygen atoms. So an increase in temperature reduces the amount of oxygen in water.

Figure 1 – hydrogen bonding (Microsoft Encarta 2006).

Turbulence also has a substantial effect on the levels of oxygen dissolved in a body of water. Turbulence refers to the rapid and irregular movement of water due to physical forces such as wind, tides, wave action and currents. Because the concentrations of oxygen are very different between the atmosphere and water, diffusion occurs consistently between these two mediums. Water turbulence can increase DO concentrations in water by increasing the surface area available for mixing between the water and atmosphere. The movement and churning of the water makes the water jump and causes irregularity in the water surface. This momentarily provides a little more water surface area for which oxygen can dissolve into. This thereby increases the rate of diffusion (Water on the Web, 2004). As such, in theory, the higher the amount of turbulence in a body of water, the higher the concentrations of dissolved oxygen in it.

EXPERIMENTAL DESIGN Temperature on DO • • •

6 experiments are set up – 5 manipulated temperatures and 1 at room temperature All samples of water are at different temperatures Measure the amount of DO present in the water after heating or cooling to specific temperatures.

Dependant variable: concentration of dissolved oxygen in water Independent variable: temperature of water Controlled variables: type of water used, size of beaker used. Turbulence on DO • •

6 experiments with varying periods of subjection to turbidity being conducted Measure DO levels in water after each experiment

Dependant variable: concentration of dissolved oxygen in water Independent variable: time for which water is subjected to turbulence Controlled variables: type of water used, size of beaker used, speed of stirring on magnetic stirrer. These experiments are controlled and mostly unbiased. The type of water used was the same so that the chance of different types of water containing different minerals and hosting different amounts of oxygen is rules out. The size and shape of the beakers was the same as well. This ensures that the water has the same surface area to allow oxygen to get into it in all the experiments. In the experiment where the effect of turbulence on DO was investigated, the speed at which the magnetic stirrer spun the water was kept constant. This was to ensure that different speeds wouldn’t cause different steepness of the whirlpool caused by the spinning of the water. If this steepness was different, there would either be more or less surface area available for oxygen to get in.

METHOD Materials:

- 12 beakers - Aluminium foil - Dissolved oxygen probe - Hot plate/ Bunsen burner - Magnetic stirrer - Normal tap water or distilled water if desired (water must kept in a bucket or container for a day or overnight so that excess oxygen doesn’t get in through churning of the water from coming out the tap or water bottle.) - Stop watch - Thermometer - Tongs - Tripod Stand and wire gauze if using Bunsen burner. Method: temperature on DO • In a beaker pour approx. 200mL of water. • Measure the temperature and dissolved oxygen in this water. This will be the control or [DO]* at room temperature. • In 5 more beakers pour approx. 200mL of water. • Cool down one beaker of water to 5o. • Measure the dissolved oxygen in this sample of water. • Heat the other beakers of water to 40o, 60o, 80o and 100o. • Measure the dissolved oxygen in each of these samples at once using the DO probe. • If you cannot measure the DO in these samples immediately, then cover the beakers with aluminium foil so that no more oxygen can get in or out. • Record the data. • • • • • • • • • • •

Turbulence on DO In a beaker pour 200mL of water Measure the temperature and dissolved oxygen in this water. This will be the control sample or [DO] after no turbulence. In 5 more beakers pour 200mL of water. Use the magnetic stirrer to stir (cause turbulence in) the water in one beaker for 1 minute. When turning off the magnetic stirrer, do not turn the knob on it. Switch it off at the wall so that when repeating the experiment, a different level of turbulence will not be supplied. Measure the dissolved oxygen in this sample of water. Do the same for the other beakers of water but subject these to 2, 3, 4 and 5 minutes of turbulence. Also record the temperatures of the water samples, just in case the change in concentration of DO is caused by change in temperature. Cover the beakers with foil so that no more oxygen can get in if you cannot measure the DO immediately. Measure the dissolved oxygen in each of these samples using the DO probe. Record the data.

* [DO] means “concentration of DO”

RESULTS

Experiment 1: the effects of temperature on dissolved oxygen. Table 1: Table showing the effect of temperature on DO

16 .0 *) at

at 15 .7 *) (m

10 0*

80 *

(m ea su r

17 .5 *C

ed

ea su re d

60 *

40 *

te m p.

6

ro om

6.4

te m p.

4.7 3.9 2.8

5*

6.3

10 9 8 7 6 5 4 3 2 1 0

16 .1 *C

5C 16.1oC (room temperature) 17.5oC (room temperature) 40oC 60oC 80oC (measured at 15.7oC) 100oC (measured at 16.0oC)

Dissolved Oxygen - Temperature

ro om

o

Dissolved Oxygen (parts per million) 8.9

Dissolved Oxygen (ppm)

Temperature (oC)

Figure 2 – Graph showing the effect of temperature on dissolved oxygen

Tem perature (oC)

Experiment 2: the effects of turbulence on dissolved oxygen. Table 2: Table showing the effect of turbulence on DO Dissolved Oxygen (parts per million) 9 8.8 8 7.3 6.6 6.5

Temperature (oC) 15.3o 15.4o 15.3o 15.4o 15.6o 15.9o

Figure 3 – Graph showing the effect of Turbulence on DO Dissolved Oxygen Trial 2 Turbulence

Dissolved Oxygen (ppm)

Turbulence (time in minutes and seconds) 0 min 1min 2min 3min 4min 5min 10sec

10 9 8 7 6 5 4 3 2 1 0 0 min

1min

2min Tim e (min)

3min

4min

5min 10sec

DISCUSSION Experiment 1: the effect of temperature on dissolved oxygen. In this experiment, as was predicted, the levels of dissolved oxygen in the water fell as the temperature was increased (refer to Table 1). As the temperature of the water was increased, the concentration of dissolved oxygen fell in a slightly quadratic curve, as shown in Figure 2. However, this trend is not followed as we reach the trials with water at 80oC and 100oC. These values go back up to 6.4 ppm (parts per million) and 6 ppm respectively. This may have been because the dissolved oxygen in these two trials was measured at room temperature. This had to be done because the DO probe does not work in temperatures above 60 oC. To reduce any chances of oxygen getting into the beakers, they were covered immediately with aluminium foil. The next day when the water had cooled down to room temperature, the DO was measured. A hole was pierced in the aluminium foil to allow the probe to be placed into the water. At this point it is possible that oxygen got into the beaker and dissolved into the water. This may have been the reason why these two trial values are in such contrast with the rest of the experiment. However, disregarding these two values the hypothesis was proved right. The concentrations of oxygen dissolved in water do decrease as temperature of water is increased. To improve this experiment instead of doing just 6 trials, more trials could have been conducted. As you can see in Table 1, the two room temperatures used (16.1 oC and 17.5oC) are very different from each other. This does not seem normal, as there should not be so much difference between samples that are only 1.4o apart. So there is obviously some irregularity with this. So in an improved experiment, we could not use the room temperatures and instead use 5o, 10o, 15o, 20o … 100o etc. This would provide a wider database to look at and it would be easier to plot a graph. Also, some of the trials were done on different days. The weather and climatic factors like humidity could have changed in these days. It is also possible that there were slightly different atmospheric pressures on the different days. This could have accounted for some error in the experiment. Perhaps, the experiment could have been more valid if distilled water had been used instead. This may have prevented any chance of any impurities like Iron or other gases in the water from corrupting the experiment. From the experiment conducted, we can clearly see that temperature has a substantial effect on the dissolved oxygen in water. Other related experiments could be conducted like the effect that pressure has on DO levels, the effects that different minerals present in the water have on the DO levels in the water and other such experiments. With future research we can investigate ways that we can reduce the effects that temperature have on river health or even reduce the amount of hot effluent dumped into the rivers. Experiment 2: effect of turbulence on dissolved oxygen. In this experiment the levels of dissolved oxygen in the water decreased as the levels or amount of turbulence was increased (refer to Table 2). As the periods for which the water was subjected to turbulence were increased, the concentrations of dissolved oxygen fell in a slightly quadratic curve (refer to Figure 3). In the first minute, not much change in the DO levels occurred. However, from the second minute to the fourth minute, the water experienced great change in DO levels. However, after the fourth minute, there was not as much drastic change. So there is a limit to which the oxygen can escape the water. But seeing as the oxygen concentration is going down instead of up this is a clear contradiction of the original hypothesis that stated that as the turbulence goes up, the oxygen dissolved in water goes down. This may have been due many things.

The magnetic stirrer is a device that employs the use of a magnet that spins around very fast to twist the water in the beaker into a whirlpool. It is possible that as the water spun around at high speeds, the pressure within the water was so high that gases could not dissolve into the water anymore and had to instead escape it. This could explain why the levels of oxygen dissolved in the water kept going down as time was increased. Another reason could have been that the beakers of water were not covered immediately after each experiment. This could allow for more oxygen to go in or out of the water, jeopardising the validity of the experiment. Also, as stated in the previous experiment, some of these trials were conducted on different days. This might have had an effect on the experiment since climatic factors such as humidity could have differed on the separate days. This experiment could have been improved by conducting more trials so that we could verify the results. Also, steps could be taken to reduce the effect of temperature on the experiment. As you can see from Table 2, temperature seems to have increased slightly over the last two trials. If the temperature of all the water could be kept constant, then this might increase the validity of the experiment. The magnetic stirrer does not seem to be an ideal instrument for ‘stirring’ the water since it makes the water into a whirlpool rather than churning it. Perhaps, if an air pump or other such devices were used, the experiment could have been better. From the experiment conducted, we can say that turbulence has a considerable effect on the dissolved oxygen in water. Further investigations could be conducted later using different machines to provide turbulence and see if these might have an effect on the dissolved oxygen. Other investigations could also be conducted considering the difference between highly turbulent and stagnant waters and the effect this may have on plant growth in the water.

In these experiments we have investigated the relationships between temperature and turbulence and the levels of dissolved oxygen in river water. The experiments were conducted in controlled environments to improve their validity such as a constant atmospheric pressure, a constant temperature in the turbulence experiment and the same DO probe used for all experiments. The results support the theory that an increase in temperature will reduce the oxygen dissolved in water, but contradict the theory that an increase in turbulence will lead to an increase in dissolved oxygen concentrations. More research has to be done to prove these results but it is still clear to see that many factors can easily affect the health of our rivers.

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