Effects of Agricultural Pollutants on Daphnia magna: An Experimental Study on Reproductive Rates When Exposed to Pollutants from Nitrogenous Fertilizer (Research Update)
NAMES: Aziz Bajouri, Alanna Barnett, Robert Barker, and Melanie Nguyen
Figure 1. Ecosystem Jars of Different Levels of Nitrogen Set Up. Photo taken by Aziz Bajouri.
HYPOTHESIS: Domestic and industrial fertilizers will have an effect on daphnia rate of reproduction. We had to eliminate the original idea of also calculating mortality rates because it was impossible to count the number of deceased individuals since the bodies disintegrated too quickly between observation days.
PREDICTIONS: One group (control) will have an average reproduction rate rate under the research conditions, and two groups (domestic/industrial fertilizers) will likely have a predicted below average reproduction rate, with the Industrial fertilizer group having the lowest reproduction rate.We had to eliminate the original idea of also calculating mortality rates because it was impossible to count the number of deceased individuals since the bodies disintegrated too quickly between observation days.
RESULTS:
Number of living D. magna observed
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Contents
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Day 1
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Day 5
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Day 7
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Day 11
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Day 12
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Control (Remade)
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8
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5
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Control 2 (small)
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10
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0
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10*
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7
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8
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Control 1 (large)
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10
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5
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2
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0
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0
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Domestic (remade)
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3
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4
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Domestic 2 (small)
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10
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0
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6*
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Domestic 1 (large)
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10
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16
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12
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5
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8
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Industrial (remade)
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3
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2
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Industrial 2 (small)
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10
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0
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8*
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7
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8
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Industrial 1 (large)
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10
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4
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1
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0
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2
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* On Day 6, 10 D. magna were added to each of the “small” containers, as all existing D. magna in those groups had died by Day 5.
Table 1. Results after Experimentation on Control, Domestic, and Industrial Fertilizer Containers. The overall reproduction rates were negative for all three groups for Days 1 through 7, meaning that more D. magna died than were produced. This trend was also relatively consistent, even after new jars were made after Day 5.
DESCRIPTION:
Our experiment started with 10 Daphnia in each container (Day 1), but ended with the number on Day 7 and Day 12 in Table 1. A trend that is easy to see is that our control had the best living conditions/reproductive rate for our daphnia; Domestic and Industrial had very similar results meaning that the reproductive rate could be similar. We had to add 10 more Daphnia into all containers as well as making 3 new containers labeled as remade. The reason for this was because our Daphnia had nearly went extinct in most of out containers half way through the experiment. We were unsure of the reason so we added new Daphnia as well as making 3 more samples in order to see if the results would continue in this direction. From our results we can see that while some containers went extinct, our other containers had better outcomes. This experiment supported our hypothesis based on our results. We ran chi-square analysis on our results, using an error limit of 5% (0.05). The chi-square value came to 2.9 for the control group, which falls below the p-value of 5.99 when using 2 degree of freedom. The industrial group, which also used 2 degrees of freedom, had a chi-square value of 13.2; well above the p-value. Our domestic group only had two jars at the end of our experiment, so we used 1 degree of freedom when running its analysis. The p-value for a single degree of freedom comes to 3.84, and our chi-square value for this group fell just above the p-value at 4.0. As such, the change in our industrial and domestic data groups fall outside the range of standard error, while our control data group falls within that range. We must reject the null hypothesis of no change and accept that the industrial and domestic populations were significantly influenced in a way that had a negative effect on those populations.
After working on this experiment for nearly two weeks our group learned how to improve the experiment, if we ever decided to re experiment, through trial and error. Some suggestions for groups planning on using Daphnia is to make sure to use a container that is not too big. Our group was offered quart sized containers which were oversized, making the counting process more difficult, especially if the size of the Daphnia is very small. Another suggestion would be to try and use a container that does not have engravings on it, this contributed to the difficulty our group had when counting the Daphnia. Our last suggestion would be to not overuse plants in each container. For our experiment we used Ludwigia repens as a food source for the Daphnia; some containers had more of the plant while others had less. Containers with too much plant made it harder to see what was in the container, resulting in a harder counting process. Do not starve the Daphnia by limiting its food source, but do not go overboard with it as well. It may take a few trials before getting the right amount.
A major error while performing this experiment was the loss of one of our containers. A lab mate accidently dropped one container during our lab period. While it was tragic, we only lost one interval for the container; it probably won't have any major effects on the outcome of our data. Our group made the mistake of not having any detritus materials for our Daphnia at the beginning of this experiment which may have lead to some Daphnias dying out from food deprivation. Some parts of the plant may have become detritus as time went on, but none were present at the start of the experiment. Another error would be the loss of Daphnia in the containers labeled (small). The Daphnia in these containers were extracted from a different population—a tiny container—than the ones in containers labeled (large) and (remade). The Daphnia in (small) containers went extinct. We were not sure why this happened, so we decided to add 10 new Daphnia into all the containers, this time not using any Daphnia from the tiny container population. Our results came out different, so we believe that the small container’s population may have been contaminated. Our last error would occur when counting. As stated in our suggestions our group found a lot of trouble when counting the Daphnia. Some members came up with different results when counting the containers. The results between members were never too different, but we had members who for example only saw five Daphnia instead of six. This was rare, but had occurred sometime during our experiment. The most notable instance of this was when group members noted a Daphnia count of zero for a day’s data point, but the during the next count Daphnia were observed in that same jar when no human interference had occurred between counts.
QUESTIONS:
- Did any other groups that used Daphnia experience problems with keeping them alive? Particularly those who got theirs from the small white container originally provided?
- For the groups who tried to find mortality rates, did you experience difficulty counting the “deceased” individuals?
Hi, everyone!
ReplyDeleteI enjoyed reading your group's post, especially since our experiment was measuring the mortality rates of Daphnia magna in different pH levels, so it was interesting to read about a different experiment on Daphnia. To answer a couple of your questions, we did experience difficulty counting the Daphnia that had died. We had a layer of rocks at the bottom of our jars, so we believe several Daphnia corpses were buried in the rocks. This would explain why we had several Daphnia that were unaccounted for. Most of our Daphnia were dead by the end of the experiment, but like your results, our control group had the highest survival rate. If you could redo the experiment, would you begin with more than 10 Daphnia in each jar?
I think after doing this experiment, we would probably start with way more than 10 Daphnia, for the reason that if there was something wrong, such as disease or parasites, the less individuals we had, the more our data would be skewed.
DeleteWonderful post. Interesting that your experiment is focused on reproduction rate of daphnia and not it's heart rate. Our group did an experiment on Daphnia magna and measured it's heart rate with respect to different pH. We had most of our daphnia dying in the same day except the control group and we had to modify the experiment my limiting the pH range, but we used expired pH buffer pills which could be the cause of their death and we used a previously used daphnia. In your guy's experiment, with the high rate of mortality rate, how you guys kept track of the newly born daphnia? I saw videos on Youtube and i saw that you could see the pregnant daphnia, but how you guys counted the new daphnia and collected data? It must have been challenging to see through the jars, and I saw that you guys mentioned that in the post.
DeleteI am sorry you guys accidentally broke one jar. However, it's an exciting experiment as I keep track of it since your intro. Compare to checking Daphnia's heart rate, counting the reproductive rate seems much more challenging. No mention that Daphnia are pretty fragile that they die super easy. I also have the same question as Amina mentioned: do you take the mortality rate into account when you collect the reproductive rate? It seems tricky. However, I think you guys might want to do a chi-square table to see if there is a trend of your result. Anyway, I am looking forward to the outcome of your experiment still! Great idea guys!!
ReplyDeleteHello , great post. Its great to see you guys using a more difficult animal like Daphnia because they are so small to count and keep track of as seem here in the explanation. I like the independent variables you chose because the results can be applied to real life. I was thinking that the small Daphnia may have die because they were too younger to be able to acclimate to large changes in their environment unlike the larger ones who are older and can probably acclimate better especially since they are larger so would need more chemicals to effects them.
ReplyDelete