The Effect of Acid Rain on Earthworm
Burrowing
Zoe Falk
Mr. Melis
Sustainability
26 February 2016
Abstract
We tested different worms’ reactions to different pH levels to see how this would affect
the amount of time it takes a worm to burrow itself fully under the soil. To set up our
experiment, we placed red worms in plastic cups filled with different pH levels of 6, 5, and 4.
After the worms were exposed to the different levels of the acidic rain for a certain amount of
time, we took the worms out of the cups and placed them into cups filled with potting soil and
recorded how long it took each worm to completely burrow into the soil. We did this over a four
day period of time and recorded our results. The worms exposed to water were significantly
slower than the worms exposed to a pH of 4 and 5.
Introduction
Earthworms have many positive effects on the environment. When earthworms burrow
they create pores in the soil allowing for oxygen and water to pass through the soil and carbon
dioxide to leave the soil (Earthworm Society of Britain, 2016). Earth worms also mix organic
material into the soil which increases its fertility (Earthworm Society of Britain, 2016). During
the worms burrowing and movement they mix the different soil layers (Earthworm Society of
Britain, 2016). However, these processes can become disrupted due to acid rain. This raises the
question of what would happen if we placed different pH levels of acid rain in an earthworm's
environment and how would the earthworm be affected?
The effect acid rain has on the environment depends on the soil’s chemistry and the
innate ecosystem’s sensitivity to acid (EPA, 2016). It consists of a compound substance of nitric
acid and sulfuric acid (EPA, 2016). Earthworms favor living in soil containing pH levels
between 6.5 to 7.5 (Wormsrus, 2009). Precipitation is considered acidic when it contains a pH
level less than 5. However, when acid rain does enter the soil it drains most of the soil’s
nutrients, creating a decrease in the number of micro-organisms such as earthworms (EPA,
2016). Because of the decrease in these micro-organisms there are less nutrients for plants to
grow (EPA, 2016). The lack of nutrients in the soil can seriously damage the roots of trees and
plants (EPA, 2016). This can also lead to the soil becoming more concentrated with acid. If the
plants are able to survive these conditions, they are more susceptible to disease (EPA, 2016). In a
previous study, worms were placed in soil soaked with a simulated acid rain with pH levels from
2.0-6.5 for up to 34 days (NCBI, 2016). After this time, the worms found their way out of the
soil, but died because the solution had been a pH of 2.0 (NCBI, 2016). We predict that
earthworms placed in a contained environment with hydrochloric acid with pH levels 6, 5, and 4
for twenty minutes will have a longer burrowing time than worms exposed to the solutions for
only 2.5 minutes.
Materials and Methods:
Materials:
- 12 Plastic cups
- filter paper
- scissors
- Plastic gloves for each group member
- Potting soil
- Distilled water
- 32 red Earthworms (8 per day)
- 8 ml of Hydrochloric acid with a pH of 6
- 8 ml of Hydrochloric acid with a pH of 5
- 8 ml of Hydrochloric acid with a pH of 4
- 4 stopwatches
Figure 1: Experiment Setup
Methods:
Day 1:
1. Prepare the experiment by creating four burrowing chambers by lightly packing potting
soil into four plastic cups.
2. Place a piece of the filter paper at the bottom of four plastic cups.
3. Starting with the experiment’s control, place 2 ml of water into each of the four cups.
4. After adding the water, place 2 worms at the bottom of each cup.
5. Place a second piece of filter paper in the cups covering the worms, then place a second
cup in each of the four cups covering the second piece of filter paper.
6. Allow one cup to remain this way for 2.5 minutes, another one for 5 minutes, the third
one for 10 minutes, and allow the fourth cup to remain this way for 20 minutes.
7. As each cup of worms reaches its own exposure time, take out the two worms and place
them into the prepared burrowing chamber.
8. As the worms are in the burrowing chamber, time how long it takes each worm to burrow
into the soil.
Day 2:
1. Repeat Day 1 steps 1-8 replacing the water with Hydrochloric acid with a pH of 6.
Day 3:
1. Repeat Day 1 steps 1-8 replacing the water with Hydrochloric acid with a pH of 5.
Day 4:
1. Repeat Day 1 steps 1-9 replacing the water with Hydrochloric acid with a pH of 4.
Data Tables and Graphs
Data Tables
Day 1: Burrowing Times of Earthworms’ Exposure to Water
Exposure Time (min.)
Worm 1 (min.)
Worm 2 (min.)
Average Burrowing
Time (min.)
Cup 1: 2.5
5.2
5.25
5.23
Cup 2: 5
4.11
10.58
7.35
Cup 3: 10
2.23
5.43
3.83
Cup 4: 20
3.11
4.07
3.59
Day 2: Burrowing Times of Earthworms’ Exposed to a pH of 6 of HCL
Exposure Time (min.)
Worm 1 (min.)
Worm 2(min.)
Average Burrowing
Time(min.)
Cup 1: 2.5
4.20
>20*
12.10
Cup 2: 5
3.39
6.09
4.74
Cup 3: 10
6.04
10.51#
16.55
Cup 4: 20
1.13
3.18
4.31
*At 10 minutes, the worm stopped moving
# Stopped moving at 8.07 and burrowed at 10.51
Day 3: Burrowing Times of Earthworms’ Exposed to a pH of 5 of HCL
Exposure Time (min.)
Worm 1 (min.)
Worm 2 (min.)
Average Burrowing
Time (min.)
Cup 1: 2.5
0.34
2.18
1.26
Cup 2: 5
2.21
3.15
2.68
Cup 3: 10
1.32
2.21
1.77
Cup 4: 20
2.11
3.51
2.81
Day 4: Burrowing Times of Earthworms Exposed to a pH of 4 of HCL
Exposure Time (min.)
Worm 1 (min.)
Worm 2 (min.)
Average Burrowing
Time (min.)
Cup 1: 2.5
1.15
4.55
2.85
Cup 2: 5
0.35
1.49
1.32
Cup 3: 10
2.16
2.57
2.37
Cup 4: 20
2.08
2.57
2.33
Day 4: Burrowing Times of Earthworms Not Placed in Exposure Chamber
Control Worm (min.)
Cup 1
Worm 1 (min.)
1.48
Worm 2 (min.)
3.36
Average Burrowing
Time of Earthworm
not placed in the
exposure chamber
(min.)
2.42
Observations
Liquid Used
Observations
Day 1: Water
The more water exposure time the worms endure, the faster the
worms burrowed.
Day 2: Hydrochloric
Solution with a pH of 6
After being exposed to the solution, the worms moved slower and
did not move as much.
Day 3: Hydrochloric
Solution with a pH of 5
Worms moved very fast and reacted strongly to the Hydrochloric
Solution
Day 4: Hydrochloric
Solution with a pH of 4
We observed that the worms did not slow down from being affected
by the Hydrochloric solution when burrowing.
Day 4: Ultimate Control
The earthworms taken straight out of their container into the
burrowing chamber moved quickly without stopping.
Graph 1: Average Burrowing Times of Earthworms when exposed to HCL solutions
Graph 2: Effect of Exposure Time to HCL Solutions on Worm Burrowing Times
Results
The pH of the solution and the time the worms were in contact to the solution in the
exposure chamber in this experiment were the independent variables, because they had changed
in quantity over the course of the experiment. Their change was measured through the
dependent variable which was how long it took each worm to burrow after the exposure. The
amount of solution the worms were in contact with in the exposure chamber was a controlled
variable. The worms when exposed to water and when exposed to nothing before placing them
into the burrowing chamber were also controlled groups. The controls were used to get a basic
time for the worms of how long it normally and naturally takes them to burrow to compare with
the times of the hydrochloric acid exposed worms. Through the data we gathered from the
experiment, we found the worms exposed to water were burrowing at a slower speed compared
to the worms that were exposed to the hydrochloric solution with a pH of 4 and 5. Within each
control and experimental group, no trend was found in the earthworms’ burrowing times. The
worms’ burrowing times increased when exposed to water from 2.5 to 5 minutes; however, the
times decreased when exposed to water for 20 minutes. The burrowing times of the worms
exposed to a pH of 6 had not developed a trend, starting at 12.10 minutes the worms’ times had
gone back and forth from increasing then decreasing. Solutions with a pH of 5 also had no
burrowing trends. There were no specific trends as some groups increased and decreased
inconsistently, but comparing the control to the highest concentration of pH, the burrowing times
were faster compared to the times of the control group of water.
Figure 2: Worms burrowing
Discussion:
Our hypothesis was supported in one out of the four pH concentration grouping, the soil
with pH 5. The other three groups; the water, pH 6 and pH 4, where the 20 minute exposure was
shorter compared to the other exposure times. Our hypothesis had been disproved through this
experiment, due to worms exposed to hydrochloric acid with pH levels of 6, 5, and 4 for twenty
minutes had a faster burrowing time than the worms exposed to the solution for five minutes.
One source of error in this experiment was the small sample size. Burrowing times of only two
worms were recorded for each group. As a result, if one worm had an abnormal time, it greatly
affected the average time of the group. One abnormal piece of data can throw off the data
significantly. Also, the worms used in this experiment were involved in other experiments; they
might have been affected by these prior experiments’ chemicals. The earthworms we used could
have also had different energy levels, meaning that some earthworms’ mobility skills worked
faster than others. These differences in earthworms could have largely affected the time at which
the earthworms burrowed. Our results showed how acid rain can affect a worm’s environment.
Worms that are burrowing slower can effect what is going on in their environment based on what
worms do and where acid rain is found the most.
Further questions:
After doing the experiment questions were raised, such as “how acidic can the soil
become until the worm can no longer survive?” and “is there a certain amount of acid that the
worms can survive in without being affected by it?” To test these questions we could do the
same experiment but use higher and lower pH levels of the acid rain. Another question created
was “why did the earthworms exposed to the hydrochloric acid for a longer period of time have a
faster burrowing time than the worms exposed to the solutions for less time?” The experiment to
answer this question would be solved through this same experiment using lower pH levels and
exposing the worms to the solutions for longer periods of time to see how they would then be
affected. Then, with data from the worms exposed to the hydrochloric acid pH(s) for twenty
minutes taken from this lab, we can compare to see if the results are similar or drastically
different.
Works cited
● "Result Filters." National Center for Biotechnology Information. U.S. National Library of
Medicine, n.d. Web. 19 Feb. 2016. <http://www.ncbi.nlm.nih.gov/pubmed/25351717>
● "Why Are Earthworms Important?" Why Are Earthworms Important? N.p., n.d. Web. 19
Feb. 2016. <http://www.earthwormsoc.org.uk/earthworm-information/earthworminformation-page-3>
● "Environmental Effects of Acid Rain." Environmental Effects of Acid Rain. N.p., n.d.
Web. 19 Feb. 2016. <http://www3.epa.gov/region1/eco/acidrain/enveffects.html>
● About Earthworms. (2009). Retrieved January 18, 2014, from WormsRus website:
http://www.wormsrus.co.nz/aboutearthworms.htm