The Determination of Effective Phytoremediation Aquatic Plants through the
Study of the Impact of Nutrients on Population Growth Rate
By: Samar Almarzooqi
4/16/13
BIO 220W Section 018
Introduction:
Water-nutrient content is a concern due to the effects of contaminants in the water
caused by “runoff from fertilized agricultural fields and lawns” on the organisms living in
and surrounding the water area.1 All of the organism living within the streams and water
systems are a part of food webs that can be affected by the change in nutrient quality in
the water. The streams around the contamination causing sites move into larger bodies of
water, which then are conglomerated into the Chesapeake Bay and then eventually into
the Atlantic Ocean. Contamination of the water with common contaminants like nitrogen
and phosphorous at the stream-level then impacts the water quality possibly then on a
much larger level, oceanic.
The large concentration of excess phosphorous and nitrogen levels in water leads
to eutrophication, an occurrence caused by excessive richness of nutrients due to the
runoff from land. The density of the plant life in the water is then affected, often leading
to increasing growth. This causes “algal blooms in summer months resulting in anoxic
conditions”. 1These changes then affect the organisms living in the water, often leading to a
decrease in the diversity in the species and an increase in the plant and animal biomass in
the area.1 Eutrophication is a naturally occurring process, but the increase in
eutrophication due to the increased runoff from agricultural land and from areas with
high concentrations of nitrates and phosphates leads to an unnatural increase in the
amount of nutrients and organic substances present in the aquatic systems. This leads to a
rapid growth in algae, which further affects the conditions and health of organisms within
the area. There are two main consequences of the rapid algal blooms due to
eutrophication. The first effect of eutrophication is in the cloudiness of water, which
blocks the sunlight from reaching some underwater species, leading to their death.
Because all of the organisms are a part of a complex food web, the death of the grass,
which provided food and shelter, then affects the populations of organisms that rely on
the grass.
To control excessive eutrophication, a study proposes the use of the aquatic plants
Lemna and Salvinia to “take up excess nutrients and concentrate them in their tissue”.1
By using the aquatic plants, excess nitrogen and phosphorous concentration in water can
be controlled to prevent rapid algal blooms. By using the aquatic plants as “nutrient
sponges” in areas near where contaminant runoff occurs at the smallest level (streams and
ponds) the effects of extreme eutrophication can be controlled and minimized before
populations of organisms are threated. The use of plants to remove the pollutants from
the environment is called phytoremediation, and because it is an inexpensive and
sustainable process, it can be used effectively in areas with high water contaminants and
low resource availability (Sharma).2
Using the aquatic plants, Lemna and Salvinia in phytoremediation to prevent
eutrophication is an option, but the effects of the presence of the aquatic species on other
plant populations in terms of competition and also the effects of the nutrients
(phosphorous and nitrogen) on the aquatic plants needs to be further understood. In
previous studies on the usage of plants to remove contaminants, choice of the aquatic
plant is very important. Previous results show that in some circumstances, “management
and remediation of contaminated sediments are necessary to reduce the ecological risks
and risks associated with food chain contamination” (Bert V).3 Further research and study
was needed to determine the applicability and feasibility of phytoremediation.
In this lab, the feasibility of using either Lemna or Salvinia or possibly both in
environments with a high concentration of either nitrogen and phosphorous, or both, was
studied through the experimentation with different lab groups of BIO 220W with the
aquatic plants. The overall question of the lab was determining how competition and
changes in nutrient concentration affect the growth of Leman and Salvinia. “The effects
of nitrogen and phosphorous on the growth rates, and how competition between the two
species can affect the growth rate of each plant,” were studied.1 Our lab group studied the
effect of phosphorous on Lemna growth rates and the hypothesis was that due to the
“nutrient sponge” characteristic of the Lemna, the growth rate would increase at a greater
rate in the phosphorous environment as compared to a normal environment until it
reached the carrying capacity of the container.
Materials and Methods:
The lab procedure to test whether competition and changes in nutrient
concentration affected the growth of Lemna and Salvinia was taken from “A Preliminary
Study of the Effects of Excess Nutrients and Interspecies Competition on Population
Growth of Lemna and Salvinia” given to all students taking the class.1 The overall
experiment was divided into 6 weeks of experimentation and two parts, Part A and Part
B. Part A included Experiment 1, which served as a control for Part B, Experiments 2 and
3.
For Week One of the experiment, an investigation into already known results and
behavior of experiments involving phytoremediation was done in order to understand
possible procedures and conditions for experimentation. By looking at already known
data and results even if the exact organism and conditions may vary, an understanding of
the possible outcomes was desired.
For Week Two of the experiment, the lab groups in the class discussed which
portion of the experiments to conduct. A group working protocol was completed that
addressed which aquatic plant would be used (Lemna or Salvinia) and which parameter
would be used (nitrogen, phosphorous, or both under competition). Our lab group chose
Lemna and phosphorous as the parameter to determine if the rate of the growth is
changed.
Starting with Week Three, students got to prepare their aquatic plants for
experimentation with the parameters for the experiment. Using artificial pond water and
10 oz. plastic containers, students set up 5 containers for the Lemna, 2 controls and 3 with
2 mL of phosphorous added. The students then counted out the Lemna by the number of
roots attached to the bottom of the leaves, and using forceps, 24 were counted out for four
containers and 12 were counted out for one of the containers. 2 mL of phosphorous were
then added to the three containers with 24 Lemna in each container and then other two
were untouched. Because in the future the number of leaves for the Lemna instead of the
number of roots would be counted, the number of leaves on was also counted. Using
masking tape, each container was labeled with our group name, plant type, and number of
leaves and roots for future reference. The containers were then carried over to a
greenhouse with all of the other plants for the BIO 220W class where they would remain
for the next 5 weeks when data would be collected. Because each group was held
responsible for the success of the experiment, the task of counting the leaves each week
and making sure the plant had ample water was divided amongst the group. Also,
whenever algae was seen to grow with the aquatic plants, the plants needed to be
transferred to another container to ensure the presence of the algae posed no impact on
the growth of the Lemna.
Tables were provided in the lab manual in order to record the number of leaves
(fronds) for each container before class each week. Two students went in to count
together, and two students from each group went in to add the phosphorous to the
containers being tested and the make sure enough water was present for the plants.
Because the number of Lemna growing exceeded 200, the plastic containers were divided
into four quadrants and the number of leaves were then counted in one quadrant and then
multiplied by four. Over the next 5 weeks, data was calculated and then tests were done
to determine the effects of the nutrients on the growth rate on the aquatic plants.
Results:
Figure 1: The Effect of Time on Growth of Lemna for Control Groups
Average Number of Leaves
(Thalli)
900
800
700
600
500
N=12
400
N=24
300
200
100
0
0
10
20
30
Time (Days)
The plot represents the average growth of the Lemna in the pond water for the control
groups N=12 and N=24 over a 4-week period. For the culture starting with 12 plants
(N=12), the increase in the number of thalli (leaves) occurs at a slower rate than the
increase in the number of thalli for the culture that started out with 24 plants. The N=24
culture did not level off near the end of the four weeks and does not depict a logistic
growth model as the N=12 line does, but an exponential growth model with unlimited
resources.
Natiral Log of Number of Leaves
(N)
Figure 2: Comparing the Values of rmax for Controls when N=12 for Lemna
9
8
7
6
5
4
3
N1
2
N2
1
N3
0
0
10
20
30
TIme (Days)
rmax: (y2-y1)/(x2-x1) = (5.53-2.84)/14 = 0.192
The graph above depicts the different trends for the ln(N) over time for the Lemna that
started out with 12 plants for each of the lab groups. The line that shows the average
(purple) shows that the group that counted the number of leaves (N2) was far greater than
the other lab group’s collected data. This causes the average to be pulled up to a greater
value. The other two lab groups counting the number of leaves for the control N=12
Lemna had data very similar, as shown by the N1 (blue) and N3 (green) lines above. The
value for rmax is most accurate near the beginning of the line because r=rmax at early time
points in the growth.
Figure 3: Comparing the Values of rmax for Controls when N=24
Natural Log of Number of Leaves
(N)
8
7
6
5
4
N1
3
N2
2
N3
1
Average ln(N)
0
0
10
20
30
Time (Days)
rmax: (y2-y1)/(x2-x1) = (5.25-3.66)/14 = 0.113
The graph above depicts the different trends for the ln(N) over time for the Lemna that
started out with 24 plants for each of the lab groups. The three lines for the data collected
by individual lab groups (N1, N2, and N3) show a similar initial increase trend, but N2
(red) decreases around 12 days. The average of the ln(N) line (purple) follows the N1 and
N3 lines. The rmax value of 0.113 is calculated near the beginning because near the
beginning time points because r=rmax at early times for growth. The slope of the N=24
control line, 0.113, is less than that of the N=12 line rmax value, 0.192.
Figure 4: Determining the Growth Rate of the Lemna Using the Average of ln(N)
Average Natural Log of the
Number of Thalli
8
7
6
5
4
N=12
3
N=24
2
1
0
0
5
10
15
Time (Days)
20
25
30
rmax N=24 = (y2-y1)/(x2-x1)= (5.32-3.58)/14= 0.124
rmax N=12 = (y2-y1)/(x2-x1)= (5.52-3.84)/14 = 0.120
The graph above represents the natural log (ln(Navg)) of the number of thalli (leaves) for
Lemna over the time, in days, for both the controls groups took data for the N=12 and
N=24. The two lines are slightly linear and there is a positive correlation between
Average ln(N), number of leaves, and time (days). The two averages do not take into
account the data for N2 group because both of the results for N=12 and N=24 deviated
from the other lines greatly. The slope of the N=24 line is steeper than the N=12. The
slope of the N=24 line is steeper because there is a greater initial number of plant
individuals in the N=24 container, so the rate of the increase in the number of leaves is
therefore greater. Both lines steady off and decrease in their rate of increase after Day 20.
Table 1: The Geometric Growth Rates for Lemna growth rate for N=12 plants
Number of Leaves Counted for
Groups
Day
Star
Planteers Crayola Λ Star ΛPlanteers Λ Crayola Λ Avg
0
12
30
14
9.17
40.87
8.43
8.80
14
110
1226
118
5.13
1.06
3.53
4.33
21
564
1304
417
1.27
2.17
1.51
1.39
28
716
2826
628
The table above represents the geometric growth rates Λ = Nt+1/Nt
For each lab group for N=12 plants. The highest geometric growth rate recorded is for
Group Planteers, 40.85. The value is due to the high increase in the number of plants
leaves between Days 0-14.
*Exclude geometric growth rate for group Planteers because data not consistent with
other data and could lead to gross overestimation of growth rate.
Table 2: The Geometric Growth Rates for Lemna growth for N=24 plants
Number of Leaves Counted for
Groups
Day
Star
Planteers Crayola Λ Star Λ Planteers Λ Crayola Λ Avg
0
37
45
35
4.57
3.62
6.86
5.72
14
169
163
240
3.67
1.12
2.55
3.11
21
620
183
611
1.35
1.90
1.98
1.67
28
840
347
1213
The table above represents the geometric growth rates Λ = Nt+1/Nt
For each lab group for N=24 plants. The highest geometric growth rate recorded is for
Group Star, 4.57. The value is due to the high increase in the number of plants leaves
between Days 0-14.
* Exclude geometric growth rate for group Planteers because data not consistent with
other data and could lead to gross overestimation of growth rate.
Figure 5: Determining Carrying Capacity by Using Growth Rate and Population
Size
10
9
8
Lambda
7
6
5
4
N=24
3
N=12
2
1
0
0
100
200
300
400
Population Size (N)
500
600
700
The graph above represents the geometric growth rate of the population of Lemna plants
as the population’s size increases. For both the containers that started out with N=24 and
N=12 plants, there is an inverse relationship between geometric growth rate and
population size. As the geometric growth rate approaches 1, the population size reaches
the carrying capacity (K). This occurs around 620, but it is approximated because the data
was not collected long enough for the population to reach the carrying capacity of the
area (container). The N=12 (red) line reaches carrying capacity at around 600. The result
will be discussed in the section of the lab report.
Figure 6: The Growth of Lemna Thalli Over Time With Added Nutrients
Mean Number of thalli (N)
1200
1000
800
600
400
N=24 Control
200
N= 24 + P
0
0
5
10
15
20
Time (Days)
25
30
The graph above shows the increase in the mean number of plants leaves (thalli) of the
Lemna for the three replicates with added phosphorous. The N= 24 Control (blue) line
shows the mean number of thalli (leaves) for the three groups in Experiment 1 as a
logistic growth model. The blue line, the control, levels off at the carrying capacity, but
the Lemna with the added phosphorous nutrient represented an exponential rate of
increase without any steadying of the increase of plant leaves over time.
Table 3: Geometric Rate of Increase for Time Intervals for Lemna with phosphorous
Day
Navg
Λ
0
31.33
6.18
14
193.67
2.51
21
486.67
1.63
28
792
The table above calculates the geometric rate of increase for time intervals where
geometric rate of increase = Nt+l /Nt. The control values for the geometric rate of increase
for Time interval 1 =5.72, Time Interval 2 = 3.11, Time Interval 3 = 1.67 are less than the
time interval values for the geometric rate of increase for the Lemna plants with the
added phosphorous.
Figure 7: Determining Carrying Capacity for Lemna with Added Phosphorous
Nutrient
Geometric Rate of Increae
7
6
5
4
3
N=24 +P
2
1
0
0
200
400
Population Size (N)
600
The graph above represents the relationship between the geometric rate of increase of the
number of Lemna and the population size of the Lemna. The relationship shows a
negative relationship where as the population size increases, the geometric rate of
increase of the Lemna population decreases until it reaches a steady state where the rate is
near a constant. When the geometric rate of increase is equal to one, then the population
size is at its carrying capacity. The carrying capacity needs to be approximated because
the data was not calculated for a long enough period for it to reach carrying capacity,
which is around 600 Lemna thalli. The carrying capacity as given by the control, 620
Lemna plants, is a little bit greater than the carrying capacity calculated by the geometric
rate of increase and population size of the Lemna plant.
Table 4: Class Results for Aquatic Plant Growth
Added Nitrogen
Added Phosphorous
Lemna
Salvinia
Competition (Lemna
Salvinia)
Decrease
Increase
Increased
Increased
Same rate of
Increased
Growth
The class results from each of the individual experiments were obtained. Depending on
the responses of the growth rates of Lemna and Salvinia in an environment of nitrogen,
phosphorous, or in competition with each other, the effectiveness of using the aquatic
plant for phytoremediation can be determined. Lemna experienced an increase in growth
rate in the presence of both nutrients, nitrogen and phosphorous. Salvinia experienced the
same rate of growth in the presence of nitrogen when compared to an environment
without nitrogen, and an increased rate of growth with the added nutrient phosphorous.
When Lemna and Salvinia were put into the same environment, the rate of growth of the
Salvinia population increased and the rate of growth of the Lemna population decreased.
Discussion:
In order to determine whether the use of aquatic plants, Lemna and Salvinia, is effective
in the removal of nutrients, phosphorous and nitrogen, from ponds, the effects of the
nutrients on the growth rate of the plant population needed to be determined. From the
lab, Lemna growth was thought to be positively affected by the presence of phosphorous
in increasing the rate of growth relative to the normal growth in aquatic water. From an
analysis of Experiment 1, observing the growth rates depending on initial population size,
the difference between the container that started out with N=12 plants and N=24 plants
was observed. From the average growth rate of the N=24 container for the three class
Groups (Planteers, Crayola, and Start), a normal growth rate was determined for the
Lemna that would be used to determine whether the presence of nutrients negatively
affect the growth rate of the Lemna. From individual group data, a consensus on
phytoremediation was made for both the Lemna and Salvinia in the presence of the
nutrients nitrogen and phosphorous.
Controls (Experiment 1):
The average of the number of thalli over the four-week time period for Lemna growth in
aquatic water was taken from the class group data. The difference in the number of thalli
over time for the N=12 and N=24 containers is shown in Figure 1. The results show that
the container with 24 plans increased in the number of thalli more than the container with
12 plants. Between the different groups in the lab, the data taken for the control container
of N=12 and N=24 Lemna plants, a large difference was seen in the data taken by Group
Planteers. Figure 2 shows the different data from each group for the N=12 Lemna growth
over time. The red line is the data taken by the Group Planteers, and it is much higher
than the other lines. The rapid increase in the number of thalli for the population of
Lemna over time is not consistent with the other results. Therefore, the data taken by the
Group Planteers was not used in further calculations because the very high number for
the amount of thalli could lead to a gross over calculation of the growth rate of the Lemna
in the controlled, aquatic water environment. Similarly, Figure 3 shows the different
results for the three groups for the number of thalli in the Lemna population over time.
The red line does not follow the general increasing trend of the other lines. Group
Planteers’ data indicates that after some time, the number of thalli of the Lemna
population actually decreased, which indicates either a miscount of the thalli or the
presence of another population competing and having a negative effect on the growth
rate. Since algae was present in many of the containers at points during growth, groups
had to move the Lemna into new containers. If the Group Planteers failed to do so, then
the competing algae could have caused a decline in the growth of the Lemna population.
This decline affects the average of the number of thalli present in the population over
time, which could lead to an underrepresentation of the growth rate of Lemna when the
initial population size is 24. Therefore, the Group Planteers’ results were also taken out
for the calculation of the growth rate for Lemna population when N=24 in the controlled,
aquatic pond water environment.
The growth rate of the Lemna population over time (Figure 4) shows that the
container with 24 initial plants had a larger growth rate, indicated by the steeper slope of
the red line (N=24) compared to the blue line (N=12). The rmac value, the intrinsic rate of
increase, is equal to the rate of increase near the beginning of the graph. The calculated
values of the rmac value for the N=24 and N=12 Lemna populations were .124 and .120
respectively. Therefore, the container with an initial number of 24 Lemna plants had a
greater growth rate than the container with N= 12 plants. Because the Figure 4 shows that
both populations of Lemna plants initially had a higher rate of growth that then leveled
off to a stable rate of growth, it indicates that there is a carrying capacity (K) that the
container can hold. The growth of the aquatic plant is a logistic growth curve because the
limitation of a resource, space and nutrients, causes the population number of reach a
maximum value. To determine the carrying capacity (K), the geometric growth rates of
the Lemna populations needed to be calculated. The geometric growth rates (Tables 1 and
2) for the population in the N=12 and N=24 containers for the class show that for the
N=12 containers, the initial geometric growth rates are higher from Day 0 to Day 14
compared to the other time intervals. Group Planteers’ geometric growth rate was far
higher than any other geometric growth rate, 40.87 compared to 9.17 and 8.43, so their
data was excluded since it could lead to error in the basic growth rate of the Lemna
population in a normal environment without added nutrients. For Table 2, the geometric
growth rates also exhibited the same pattern where the initial geometric growth rate was
highest in the first time interval, and it decreased with each successive time interval. This
is because as the number of thalli present in the limited resource environment increase,
the population of Lemna reaches its carrying capacity, so the geometric growth rate also
decreases. For the Group Planteers, the geometric growth rate the Day 14 to Day 21 time
interval was lower than the geometric growth rate in Day 21 to Day 28 growth rates. To
determine the carrying capacity of the container, the geometric growth rate vs. the
number of thalli present in the population of Lemna was graphed (Figure 5). The carrying
capacities estimated at Λ (geometric growth rate) =1 for the N=12 and N=24 differed
slightly. The carrying capacities estimated were 600 for N=12 and 620 for N=24. Since
the containers were the same size, the carrying capacities should be the same under
controlled conditions. The values for the rmax, geometric growth rate, and carrying
capacity for the N=24 containers are used to compare to the value of the Lemna with the
added nutrient phosphorous to determine whether the nutrient phosphorous affects the
growth rate of the Lemna populations.
Experiment 2 (Added Nutrient):
A graph of the average number of thalli over time for the Lemna population with
phosphorous compared to the control for the containers with N=24, shows that they both
follow the same trend of a logistic growth curve. The data for the Lemna plus added
phosphorous population does not level off as the data for the Lemna population in an
environment with no added nutrients. This can occur due to the added nutrient
phosphorous allowing for the Lemna population to grow at a higher rate than the Lemna
population in an environment with limited resources.
The geometric rates of increase for the different time intervals for the containers
with Lemna and phosphorous were calculated from the average number of Lemna thalli at
each time interval since 3 replicates were used in the experiment. The geometric growth
rate values (Table 3) follow the same trend as the control values with the initial time
interval growth rate value higher than the other time interval values. The geometric
growth rate values for each interval for the containers with the Lemna and the nutrient
phosphorous are higher than the control geometric growth rate values. For the first
interval Day 0 to Day 14, the geometric growth rate value for the containers with the
Lemna and phosphorus was 6.18 compared to 5.72 for the average control geometric
growth rate for that interval. Similarly, the last time interval (Day 21 to Day 28) shows
that the value for the Lemna populations with added phosphorous is higher than the
control geometric growth rates, 1.68 and 1.67 respectively. For the time interval from
Day 14 to Day 21, the control geometric growth rate (3.11) was higher than the geometric
growth rate of the container of Lemna and phosphorous (2.51). The decrease in the
geometric growth rate can be due to the presence of algae in the replicates with the
Lemna and phosphorous. Algae can have a negative affect on the growth of other aquatic
plants by competing for resources, in this case space within the container4. During that
time interval, a larger amount of algae was seen in all three of the replicates compared to
the algae present in the control containers of Lemna. Due to the presence of the higher
presence of algae affecting the growth rate of the Lemna, the lower geometric growth rate
of the Lemna population with phosphorous can be explained. Even if the added nutrient
phosphorous increases the growth rate of the Lemna population, the presence of a
competing species vying for space within a limited container can affect the rate of
growth.
The carrying capacity (K) calculated from the geometric growth rate vs. number
of thalli present in Lemna population (Figure 7) shows that where the geometric growth
rate = 1, the carrying capacity estimated is 600 Lemna. Because the Lemna populations
in the experiment never reached the carrying capacity, the line on the graph does not
reach 1, which means that a prediction of the carrying capacity needed to be made based
on the trend of the graph. The carrying capacity estimated, 600 Lemna, is very close to
the carrying capacities estimated for the controls of N=12 and N=24, 600 and 620 Lemna
respectively. Because the containers used for the experiments and replicates were all the
same size, the carrying capacity of the populations are expected to be equal since the
carrying capacity depends on the resources, one of which is the space of the environment.
An alternate way of calculating the carrying capacity (K) is to determine the area
of the water surface of the containers and by using the area of one thallus of the Lemna;
the maximum number of Lemna can be determined. Due to the growth of the Lemna in in
inconsistent layers below the water, the determination of the carrying capacity using this
method was deemed inaccurate. If the carrying capacity was calculated this way, then the
value would be lower than the actual carrying capacity since the Lemna did not only
grow at the surface of the water and did grow on top of each other.
The different results for the growth rates of the Lemna and Salvinia in different
environments, in competition with each other or with added nutrients nitrogen or
Phosphorous, were obtained and show that in environments with no competing aquatic
plants, Lemna populations will have an increased growth rate compared to the growth
rate in an environment without nutrients. Using aquatic plants for phytoremediation,
Lemna would be more effective at acting as a sponge and absorbing the excess nutrients.
In an environment with competition from other aquatic plants, Salvinia will overtake the
Lemna populations, leading to an increase rate of growth in Salvinia and decrease rate of
growth in Lemna populations.
From the results, it can be determined that the presence of the added nutrient
phosphorous increases the growth rate of the Lemna population. Because aquatic plants
like Lemna do act as sponges that can filter out harmful nutrients like phosphorous that
can lead to eutrophication of environments, the positive effect of the phosphorous on the
Lemna population means that the Lemna populations can be effectively used to filter out
the phosphorous in aquatic environment naturally without the risk of Lemna populations
being negatively impacted. The growth rate of the Lemna populations, as determined by
the number of thalli present, in the presence of phosphorous initially was higher than the
growth rate of Lemna without the nutrient available. Therefore, with the presence of
phosphorous, Lemna populations will increase at a higher rate until the carrying capacity
of the environment is reached, at which the rate of increase of the population will reach a
steady state.
Possible sources of error that could have affected the calculated rate of growth of
each aquatic plant population include the nutrient insertion technique variation, the
accountability of dead plants into the population size, and the presence of competing
algae. When inserting the Phosphorous into the three replicates, there was no way to
ensure that it was being added the same way every time. Even if the same volume (2 mL)
of the nutrient was added, it does not ensure the nutrient is spread out over the container
evenly. If it was concentrated in one area, then that creates an error in calculating the
growth rate of the entire Lemna population because the nutrient was only added to
differing portions every time. The accountability of dead plants into the population size
could pose an error because if there were plants that were dead, then counting those
plants into the population size then overestimates the rate of increase of the growth of the
Lemna population. The most error for calculating the growth rates of the Lemna
populations could be due to the presence of algae at differing points in the experiment.
Algae can compete with aquatic plants, therefore decreasing their population size when
competing for resources and space. Since algae was observed numerous times and often
the Lemna populations needed to be transferred into a new container, it was clear that
algae was acting as a competitor throughout the experiment. This would lead to an
underrepresentation of the growth rate of the Lemna because the presence of algae
limited their growth.
To further understand the use of aquatic plants in removing excess nutrients to
prevent eutrophication, further study into the change in the rate of growth of the Lemna
and Salvinia should be done in the presence of both the phosphorous and nitrogen. Since
Lemna served as a poor competitor, using the aquatic plant for phytoremediation could be
a problem even though their rate of growth increased and were therefore more effective at
removing nutrients from their environment. Therefore, further understanding into how the
Lemna populations are affected by other competitors, like algae, should be done to decide
whether their poor competition impedes their use in phytoremediation. If Salvinia is less
affected by the growth of algae, then it can be used more effectively in removing
nutrients because other competitors will not impact it. By conducting further study into
the effect of algae on Lemna and Salvinia, then it can be determined which one is more
effective in removing nutrients.
Conclusions:
Using aquatic plants to remove excess nutrients from pond water, phytoremediation, by
using Lemna and Salvinia is effective. Both aquatic plants were successful in acting as
sponges to suck up the excessive nutrients. When in an environment with the excess
nutrient phosphorous, the Lemna populations increased slightly in the rate of population
growth when compared to populations without added nutrients. Therefore, Lemna is more
effective at removing nutrients when in an environment with no competing aquatic plants
while Salvinia plants are better competitors, but do not remove the excess nutrients as
effectively. Therefore, using the aquatic plant Lemna to clean water of excess nutrients is
a more effective alternative to spending money and energy to remove it unnaturally
through filtration processes.
Resources:
1
Hass, C.A., D. Burpee, R. Meisel, and A. Ward. 2013. A Preliminary Study of the Effects of
Excess Nutrients and Interspecies Competition on Population Growth of Lemna minor
and Salvinia minima In A Laboratory Manual for Biology 220W: Populations and
Communities. (Burpee, D. and C. Hass, eds.) Department of Biology, The Pennsylvania
State University, University Park, PA.
Adapated from Beiswenger, J. M. 1993. Experiments To Teach Ecology. A Project of the
Education Committee of the Ecological Society of America. Ecological Society of
America, Tempe, AZ. pp. 83-105.
2
H.K. Sharma, S.K. Bhasin, Pernita Dogra, Shilpi Khatri, Sunita Ahuja. “Removal of
contaminants using plants.” Current Trends in Biotechnology and Chemical
Research. 1(1) (2011).
3
V, Bert, Seuntjens P, Dejonghe W, Lacherez S, Thuy HT, and Vandecasteele B.
"Phytoremediation as a Management Option for Contaminated Sediments in Tidal
Marshes, Flood Control Areas and Dredged Sediment Landfill Sites." NCBI 74564 7.16 (2009): n. pag. Print.
4
"Control Solutions for Your Pond or Lake." AlgaeControl.US. AlgaeControl, 2009.
Web. 08 Apr. 2013.