Observing the Effects of Acid Rain on the Growth and Development of Daphnia
Eric Alpert, Dr. Christine Marshall-Walker, Biology 610, Phillips Academy Andover
DAPHNIA:
AIMS AND OBJECTIVES:
A population of Daphnia, under good living conditions consists entirely of
females, with males only being produced when the population is under
considerable environmental stress. Some known stressors include: lack of food,
low oxygen supply, a high population density, or low temperatures.
The purpose of this experiment was to observe the effect of simulated
acid rain on the growth, development, and reproduction on the water
crustacean Daphnia. Daphnia are well researched and well known
models used to test the affects of various aquatic pollution and external
stimuli. The experiment as carried out by lowering the pH of a salt
water mixture in a series of culture dishes using diluted sulfuric acid.
Two Daphnia from a pH 5 trial. In the photo
below (taken on day 14), the Daphnia is
visibly redder in coloration than the above
photo (taken on day 11). One of the most important regulatory mechanisms for changing oxygen and
temperature conditions is the respiratory protein hemoglobin (Hb)
Daphnia are normally a pale white or clear color. However, an individual has four
different globin genes, some of which are individually induced by hypoxia. These
genes give the affected Daphnia a visible red pigmentation when under the stress
of oxygen deprivation.
This experiment was designed to best represent various low pH levels
in aquatic environments in order to study the rate of growth and
survival of Daphnia throughout several generations. It has been that shown the hb2 and hb3 genes are given preference at low pO2 and
production of these proteins is increased significantly more than hb1 and hb4.
Most of the chemicals responsible come from human activities such as the
burning of fossil fuels.
Rain naturally has an acidity of about 5.0 and alkaline metals in the soil are
usually responsible for countering that acidity. However, too much acid in rain
can wash away these neutralizing agents and lead to further damage in crops,
trees, lakes, and rivers.
Decreased pH and increased aluminum can cause chronic stress that may not kill
individual fish, but leads to lower body weight and smaller size, making fish less
able to compete for food in their habitat. Typically, the young of any species is
the most sensitive to environmental changes. At pH of 5.0, many fish eggs cannot
hatch. At an even lower pH many adult fish will die Without acid rain, most lakes and streams would have a pH level near 6.5. 3
2.5
Size of Daphnia (in mm)
2
1.5
CURRENT RESULTS:
Growth Rates of Daphnia in Trials
1
0.5
Water (in ml)
pH
SO4 added
1
200
7.0
0
2
200
5.5
60
3
200
5.0
80
4
200
4.5
95
Daphnia Survival Rates
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
Day
The average life span of a
healthy Daphnia is
approximately 40 days. 120
100
Control Ave
pH 5.5. Ave
pH 5 Ave
pH 4.5 Ave
80
Control 60
pH 5.5
pH 5.0
pH 4.5
40
20
0
Eric Alpert
[email protected]
Dish #
Survival Rate (in %)
ACID RAIN:
Acid rain is a phenomenon created by a chemical reaction between elements like
sulfur and nitrogen with oxygen, creating oxides that can easily rise into the
atmosphere and dissolve into water.
MATERIALS AND METHODS
Culture dishes were set up using glass dishes filled with 200ml of a stock solution of salt
water.
The pH was lowered using 0.3 molar sulfuric acid according to the chart to the right. 5 adult Daphnia that were in late stages of pregnancy were added to each dish and
allowed to reproduce. The adults were subsequently removed after they had all given birth
or died to prevent mixing of generations. Numbers of living Daphnia were recorded each day.
Photographs of Daphnia were used to collect samples of the sizes of the Daphnia from
each dish. Photos were taken using a Boreal 2 Photographing Microscope and photos
compiled using Motic Imaging Plus 2.0 software. Hypoxia:
Noted on day 14 for pH trial 5.0
Noted on day 13 for pH trial 5.5
Noted on days 20 and 25 for pH
trial 4.5
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
Day
Current results show a relatively smooth growth pattern in the control and highly erratic growth in other trials, but it is clear that Daphnia in water of a lower pH
tend to grow at a slower rate than those in a natural pH. It was also observed that Daphnia in the control group tended to be similar sizes throughout the
experiment, but significant differences in size were noted in trials of lower pH.