Conclusion

After conducting AP Lab #12, it became quite evident that temperature and light greatly affect the level of dissolved oxygen found in an aquatic ecosystem, and that to become a successful and productive water source dissolved oxygen levels must be high. Although our data does not support our final assertion  we were able to see that the amount of dissolved oxygen content varies inversely with temperature and directly with light. It is because our data is so incorrect which is why it does not support our final assertion that as water becomes cold dissolved oxygen increases and as water receives more light dissolved oxygen also increases. Cold water expose to great amounts of light is the way to properly grow and nurture life. All in all, our hypothesis was correct in that cold water and light were most beneficial to an aquatic ecosystem, although our data does not clearly show this. We use this lab to further understand the affect that abiotic factors have on biotic organisms.

Citations

Ruth Francis-Floyd. (2009). University of Florida IFAS Extension. In Dissolved Oxygen for Fish Production. Retrieved 10/01/2010, from http://edis.ifas.ufl.edu/fa002.

(2010). Home. In New Jersey Academy for Aquatic Sciences . Retrieved 10/01/2010, from http://www.njaas.org/index.html.

Analysis of charts

The data we collected is misleading.  By our data we thought that warm water held dissolved oxygen better than cold.  However, we read in the packet that this is not the case.  As the temperature of the water increases, the concentration of the dissolved oxygen decreases.  Our data was misleading due to sources of error mentioned prior (in the Winkler and Venier section). 

Our other set of data proves that the more light there is the more dissolved oxygen there is too.  However there are also some outliers here that don’t follow this trend.  These are also due to sources of error.  As you can see, it was very hard to limit sources of error in this lab.
Our third and final chart shows the results of several test on the three different types of water using the Vernier Probe. By using the probe are data became much more efficient and correct. The data with the vernier probe fell in or near the ideal levels. This really supports the fact that the Winkler method is very inaccurate compared to the Vernier probe.
                     In the data we acquired from the Vernier Probe the Canal water had the most dissolved oxygen, followed by the pond and beach waters. However this is an odd case since the Canal water was the warmest. In the first chart the Canal water had more dissolved oxygen than the beach water at all 3 different temperatures. However this trend of more dissolved oxygen in Canal water did not continue in chart two. It may because our data may be off but Beach constantly had more oxygen than Canal.

Action Plan

In order to maintain the quality of local ecosystems we must do whatever it takes to fuel good conditions for dissolved oxygen. Local ecosystems must receive an adequate amount of sunlight in order to help fuel agriculture life that is dependent on light for photosynthesis. This will get energy and nutrients into the water supply. Photosynthesis also adds extra oxygen into the water supply. Additionally water must be at a cool temperature to be most effective in holding oxygen. Cool water holds oxygen best. Thus we as humans must not introduce any external objects which would warm the water. In addition we as humans must not obscure light from reaching aquatic ecosystems. If we do either we will negatively affect the health of local ecosystems

How can this be used?

The New Jersey State Aquarium in Camden utilizes information similar to the data we collected.  Just like humans, fish also need oxygen.  They take oxygen in through their gills.  They need higher levels of oxygen in order to perform respiration.  Low dissolved oxygen can kill fish.  This may be the case if all the fish die at the same time.  This affects large fish more than small fish.  Some fish may even be at the surface of the water trying to get oxygen (piping).  This is often severe if in a water with large populations of algae or aquatic plants. 

What to do???

If this happens the most important thing to do is turn on an aerator.  If this isn’t available, not much can be done.  Although we were unable to contact the aquarium or find this information on the website, we bet that the aquarium has an aerator.    

Winkler and Vernier methods

In the Winkler method, we used titration to learn how much dissolved oxygen was in the sample.  We filled the container to the top with water, making sure that there weren’t any air bubbles.  (There always seemed to be a bubble that didn’t want to leave the container, so this part was harder than it sounds.)  We then added alkaline iodide and manganous sulfate to the water sample.  This produces manganous hydroxide.  Upon acidification, the oxygen in the sample converts this to a manganese compound.  This reacts with the iodide and colors the water yellow.  Then, using titration we can tell the amount of iodine.  We did this by adding sodium thiosulfate until the sample is once again clear.  This method is .1 to .6 percent precise.

Then we performed the Vernier method.  Using a handheld measuring device we measured the carbon dioxide, dissolved oxygen, pH level, temperature, turbidity, and nitrates of water.  This method is easier and more accurate.  Using a computer to measure the data cuts down on human error.  The two methods are similar in the fact that we were able to accomplish the same experiment of measuring the dissolved oxygen plus much more.  They are different because of the ease of use and the ability to do more things with the Vernier.  Also, the Vernier method makes it much easier to do the experiment right at the ecosystem, while the Winkler method is much more inconvenient to do on scene.  Doing the experiment right away cuts down on sources of error.  We encountered one of these sources of error.  The water sat for three days in the classroom.  That will definitely change the data.  If we were on scene with the Vernier we would have taken data quickly and never have ran into this source of error. 

While on the topic of sources of error, there was also a source of error if we stirred up the water while trying to get the air bubbles out of the container.  Also when titrating if it didn’t turn yellow that means that the data was 0.  Since we didn’t know this in the beginning of our experiment, when it didn’t turn yellow we just added more of the solutions, which can definitely distort the data.    

Data Tables

Be sure to click on the graphs to enlarge them!

In this second graph it wouldn't let us input the data right into the boxes.  So don't get confused by data in the box above or below.  There is the same amount of data and spaces.  Sorry!