Experimental Design

The experimental procedures for the dissolved oxygen and primary productivity lab were fairly simple.

Experiment #1: Dissolved Oxygen

Process/Design: Each group was assigned to test a sample of water from either Sandy Hook Beach or the Delaware Raritan River Canal, and to compare the level of dissolved oxygen in each to see how temperature affected dissolved oxygen levels. We were specifically assigned to test the Delaware Raritan River Canal water. Using a small sampling bottle, we collected the canal water from a bucket, making sure to fill our bottle all the way and screw the top on while it was still submerged in the bucket to limit the amount of extra oxygen that would get in our sample and possibly alter our results. We were assigned to keep our sample at room temperature. Next, we added eight drops of manganous sulfate followed by eight drops of alkaline iodide making sure we capped the sample right away to prevent any extra oxygen from entering. Then, once we saw precipitate forming, we had to invert the bottle several times. After the precipitate settled, a scoop of acid was added and we continued to invert the sample until our bottle was a yellow color. Then, we put 20 ml. of our sample into a titration vial. We then put eight drops of starch indicator into the vial making the water turn a deep purple. Finally, we used a titration syringe and one drop at a time used the syringe to drop sodium thiosulfate working solution into the titration vial until the water turned clear again. 


Measurements: First, we measured the temperature of our canal water at the start of the experiment and it read 22.5 degrees Celsius. We did this so we knew our sample was starting at room temperature and it would help us later when reading a nomograph. Another important measurement we made was the amount of ml. of the sodium thiosulfate working solution that was necessary to turn our water clear. We measured that was used about 0.4 ml. This measurement was important because the amount of ml. we used to titrate the water is equivalent to mg/L of dissolved oxygen in our sample. Therefore, we knew that there were 0.4 mg/L of dissolved oxygen in our sample. Finally, using a nomograph, we lined up our mg/L of dissolved oxygen with the starting temperature of our water to find out the percent saturation of oxygen. We found out that our water was 7% saturated with dissolved oxygen.


Techniques: Throughout our experiment, we used a couple techniques to provide the most accurate results possible. Between adding certain chemicals to our sample, we made sure to place the cap on in order to prevent oxygen from entering. Also, as mentioned before we also prevented extra oxygen from entering by filling our sample to the top and capping it while under water. Finally, when studying the color of the sample, we placed it on a white sheet of paper to better observe any changes.


 Experiment #2: Primary Productivity

 Process/Design: Again, we took a small sample of the Delaware Raritan River Canal water in a small sample bottle by filling it from a bucket. We capped it while submerged in the bucket, and filled it to the top. The focus of this experiment was how light affected the level of dissolved oxygen. Different groups were assigned a different percentage of light and placed screens over the sample in order to block out light based on their assigned percentage. We were assigned 100% light, so we did not need to put any screens over our bottle. We left it over night under a lamp and used the same process from the first experiment to again measure the amount of dissolved oxygen.


Measurements: Just like the first experiment, we measured the amount of ml. of the sodium thiosulfate working solution that was necessary to turn our water clear. Again, we measured that we used about 0.4 ml. This measurement was important because the amount of ml. we used to titrate the water is equivalent to mg/L of dissolved oxygen in our sample. Therefore, we knew that there were 0.4 mg/L of dissolved oxygen in our sample. Finally, using a nomograph, we lined up our mg/L of dissolved oxygen with the starting temperature of our water to find out the percent saturation of oxygen. We found out that our water was 7% saturated with dissolved oxygen. Also, we made sure to measure the temperature of our water in the beginning of the experiment to make sure it was room temperature so the temperature of the water wouldn't act as a variable and alter our results.

Techniques: We really did not use many techniques in the experiment. However, again between adding certain chemicals to our sample, we made sure to place the cap on in order to prevent oxygen from entering. We also prevented extra oxygen from entering by filling our sample to the top and capping it while under water.


Additional Observations- vernier readings and microscopes

Procedure/Design: Using several vernier probes, we tested samples of the canal water, beach water, and pond water and recorded their dissolved oxygen, carbon dioxide, pH, and temperature along with their colors. Also, but observing samples of each type of water under a microscope, we identified various organisms in the water. 

Measurements/Calculations: Using several equations, we were able to come up with the gross productivity, net productivity,  and gross productivity in mg/Cm^3. We calculated the the gross productivity by subtracting the amount of dissolved oxygen from the dark bottle from the light bottle. We calculated the net productivity by subtracting the dissolved oxygen level from the initial bottle from the light bottle. Finally, we calculated the gross productivity in mg/Cm^3 by taking the dissolved oxygen levels, multiplying them by 0.698, and the multiplying that answer by 0.536.

Where were the samples taken from?

The water samples came from Sandy hook beach, the Delaware Raritan River Canal and Tommy Pond and each had a different population density and development in the area. 

Tommy Pond

Tommy Pond in Metuchen is surrounded by a suburban community of homes, and there are two acres of trees surrounding the small lake. The population density is about 4800 people per square mile and there are no large businesses in the area.

Sandy Hook Beach

Sandy Hook Beach in Sandy Hook, New Jersey is a peninsula that contains mostly beach. There is a large population density during the summer time,  and the only buildings there are the shore houses and small businesses. There is a large grassy area in the middle of Sandy Hook Beach as well.

The Delaware and Raritan Canal in Princeton New Jersey is in a secluded area with a large forest surrounding it. There is a low population density and very few buildings surrounding it. However, there is a main road along side the canal.

Objectives

The objective of the lab was to test the amount of dissolved oxygen in different samples of water in New Jersey. After calculating the dissolved oxygen through the Vernier and Winkler method, we had to calculate the net productivity, gross productivity, and respiration rate for the different water samples with different amounts of sunlight. Through identifying different biological factors affecting the solubility of dissolved cases in the water samples, we were able to identify the importance of carbon and oxygen cycles in an ecosystem. Through putting screens on different water samples, we were able to identify the effect of light and nutrients on photosynthesis. Also, we also identified many different microorganisms living in the various water samples.

Hypothesis

After looking at the population density and the development in the area for each water sample, we thought that each water sample would have a different amount of dissolved oxygen. 

Dissolved Oxygen Hypothesis

Since Tommy Pond is surrounded by two acres of trees and forested area, we thought that there would be a moderately high amount of dissolved oxygen. Since the water is fresh water, the water is more soluble and it can hold more dissolved oxygen. Trees that let off oxygen would benefit the pond because it could absorb into the pond. However, since there is no stream or current occurring, wind or turbulence would not be a main source for dissolved oxygen. Plants growing at the bottom of the pond would release oxygen into the water, however since the pond is only .4 acres, there is not a significant source of oxygen coming from plants. The temperature of the water at Tommy Pond was also slightly higher then the beach, and  higher temperatures hold less amounts of dissolved oxygen.

Since Sandy Hook Beach has a high population density, we believed the water there would be polluted from boats and humans swimming in the water. Gas exhaust from the boats could cause a large amount of CO2 to accumulate in the water, lowering the amount of dissolved oxygen available. There are also not a lot of plants growing at the bottom of the ocean near the shore, so there would be little oxygen entering the water through plants. Also, high amounts of salinity lowers the amount of solubility in water. Since Sandy Hook Beach contains salt water, the amount of dissolved oxygen is lowered because it cannot dissolve in the water. However, wind near the shore is always very strong, so a lot of wind could enter the ocean through the waves crashing on the shore. This would result in extremely low amounts of dissolved oxygen at Sandy Hook Beach.

The Delaware and Raritan Canal is close to Rutgers University in Princeton, New Jersey where there are a lot large buildings. With the population of Rutgers university reaching about 50,000 students alone, there is a high population density. These factors could cause a lot of pollution to enter the canal from both littering and pollution from the buildings and people living there. High amounts of pollution prevents a large amount of plant life to grow in the water, resulting in a low amount of photosynthesis as well. Since there is a small amount of plants able to take in the carbon dioxide put in the water from pollution and release oxygen to put back into the water, we expected low amounts of dissolved oxygen to be in the canal water.


Amount of Sunlight/ Screen Hypothesis
Adding on to our hypothesis for the different amounts of dissolved oxygen in the water samples, our class also tested the amount of dissolved oxygen after being subjected to different amounts of sunlight. We hypothesized that as more screens were added on, and less sunlight was allowed into the water samples, the amount of dissolved oxygen would lessen. This is because without sunlight, organisms cannot preform photosynthesis, which releases oxygen into the water. Also, organisms take in the available oxygen through cellular respiration, lowering the amount of dissolved oxygen even further.