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Human Impact Lab

Page 1

Human Impact Lab (Pl, DCP, DEC)

Introduction

Human activities have a big impact on the environment in terms of affecting

various abiotic and biotic factors around them.In this investigation, I intend to investigate the impact of human walking in the

student village area of the college. I have selected a walking trail (not a proper

path, but path made due to continuous walking of humans) going from student

village towards the Hoegh building, which is used very often by everyone.

Aim

The purpose of this investigation is to find out how the presence of humans

(walking) on a walking trail impacts the soil composition and plant biodiversity of

the trail as compared to the area closer to the trail (with minimal human

intervention).

Research question

How is soil composition and plant biodiversity influenced by human

presence(walking) compared to the nearby areas (with minimal human

intervention).

Hypothesis

The biodiversity will be less on the trail as it is exposed to human disturbances.

Furthermore the soil composition will be affected on the walking trail due to

continued pressure of human weight, resulting in it being different from that of

nearby areas.

I expect to see some form of soil erosion due to humans walking on the trail.

Soil erosion is the decline in quantity and quality of soil caused by external

factors such as cultivation, formation of roads or tracks, grazing, rainfall, climate

and wind.


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Independent variable

Area with human activity : areas on the walking trail

Area with minimal human activity : areas next to the trail

Dependent variable

Soil composition: on the walking trail and areas next to it

Plant Biodiversity: on the walking trail and areas next to it

Controlled variables

Step 1)

Temperature

All samples and measures were taken within 30 minutes to prevent

fluctuations of temperatures to affect the result.

The air temperature of the region was measured randomly at several places

to ensure that the environmental temperature was not different for

different areas considered.

Step 2) The slope of the trail

The slope of the section of the trail considered and the area next to it was

the same. This was done to prevent the slope as the factor to affect the

results.

This was confirmed by random measurements on areas of the selected

section of trail and the areas next to it. They all were totally flat (zero

degree slope).

Step 3)

The weather conditions (sunlight, precipitation etc) and season were

held constant as the samples and measure were taken within 30 minutes.

Step 4)

The size of the quadrats

Each quadrat size considered was 1 m x 1 m.Step 5) The amount of soil sample

One scoop of soil (4 dl) was used for all soil samples collected.


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Equipment and material

1 weighing scale (0.01g)

8 trays

1 soil sieve

4 quadrats (1m x 1m)

1 fork

1 soil collecting scoop (4dl)

Figure 1:Illustration of the quadrats (1m x 1m) positions, from where count of

different plant species was taken and the soil samples were taken. There was 20cm distance between each quadrat position.

Off Trail On Trail

Areas 1, 2, 3 and 4 are on the walking track. Areas 5, 6, 7 and 8 are off the track,

close to the walking track.


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Method

Step 1)

A walking trail frequently used by humans (in this case, college

residents) was identified.

Care was taken to ensure that the section of trail considered is flat (zeroslope), 5-6 m long, and does not have any tree cover or another

construction close to it.

Step 2) Four quadrats (1m x 1m) were positioned (as per figure 1) with 20cm

distance on the trail and given identification numbers as Quadrat 1,

Quadrat 2, Quadrat 3 and Quadrat 4.

Step 3)

Another four quadrats (1m x 1m) positions were marked (as per

figure 1) with 20cm distance off the trail and given identification numbersas Quadrat 5, Quadrat 6, Quadrat 7 and Quadrat 8.

Once all data is collected from positions of Quadrat 1, Quadrat 2, Quadrat 3

and Quadrat 4, the 4 quadrats will be picked up and placed on the marked

positions for Quadrat 5, Quadrat 6, Quadrat 7 and Quadrat 8 for further

data collection off the trail.

Step 4)

The air temperature of the region was measured randomly at several

places to ensure that the environmental temperature was not different fordifferent areas considered.

The temperature was approximately 16.5oC for all 8 quadrat positions.

Step 5)

Weigh each of the sieves of the empty soil sieve set and note it. Mark

each tray as tray 1, 2,8.

For each quadrat position :

Step 6)

Measuring biodiversity

a.

Each type of plant variety in the quadrat is noted with a brief

description of its identifying features.

b.

Count of each plant type in the quadrat and note.


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Step 7) Measuring soil composition

a.

A sample of soil of 4 deciliters was collected from the top layer of the

soil from the marked quadrat position. Do not go deeper than 15 cm

in the soil.b.

Empty the measured soil in a marked tray (Tray 1 for quadrat 1).

Step 8) Repeat Step 6 and Step 7 for all 8 quadrat positions.

Step 9)

After collecting biodiversity data and soil samples for each quadrat

position, leave all 8 trays with soil samples indoors for 48 hours, to allow it

to dry.

Step 10) Lumps were crushed into smaller pieces with a fork after the drying

period.

Step 11) For each soil sample:

a.

Weigh the sample using weighing scale.

b.

Pour the soil sample into the soil sieve and shake gently from side

to side in order to sieve the soil. (Do this for a couple of minutes).

c. The weight of soil left on each of the four sieves was measured

with the weighing scale.

Biodiversity : Qualitative Data

There were several species of plants present in the area.

Pointy Grass: Grass with pointy ends, dark green or brown in color. Can be

counted.

Trifoliate leaf plant: small plants with trifoliate leaf, dark green in color. Canbe counted.

Star Moss: Star shaped green colored moss . Difficult to count.

Grass moss: Pointy shaped green colored moss. Difficult to count.


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The qualitative data makes it clear that the data should be recorded as

percentage to be able to do any calculations on raw data (units should be same

for calculations).

Biodiversity: Quantitative data

Table 1: Table recording raw data as % cover of different species on the trail and

off the trail.

Type of

plant

% cover of different types of plants

Quadrat1 Qudrat2 Quadrat3 Quadrat4 Quadrat5 Quadrat6 Quadrat7 Quadrat8

Grass

moss

0 0 0 0 80 76 82 87

Star moss 0 0 0 0 44 64 50 55

trifoliate

leaf plant

0 0 1 1 10 7 3 5

Pointy

grass

7 5 8 9 22 24 19 18

Quadrats are positioned as per figure 1.

The collected data shows that more species are present off trail than on trail.

Furthermore the number of individuals present off trail is greater than on it.

Figure 3: Trifoliate leaf plantFigure 2: Pointy Grass


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Biodiversity : Data processing

Simpsons biodiversity index is used to calculate the biodiversity. The formula is

where N is the total number and n is number of individuals of one

species.

At quadrat 5 the biodiversity is

Table 2: Table calculating biodiversity index for different quadrat positions on the

trail and off the trail.

On walking trail Off walking trail

Quadrat1 Qudrat2 Quadrat3 Quadrat4 Quadrat5 Quadrat6 Quadrat7 Quadrat8

Biodiversity 1.00 1.00 1.29 1.25 2.76 2.82 2.50 2.51

Average

Biodiversity1.13 2.65


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Soil composition: Qualitative data

After 48 hours of drying, all samples of soil were quite dry and any lumps, if there

were crushed. More gravel in soil collected from trail seen.

Soil composition: Quantitative data

Table 3: Table recording data as weight of empty sieves.

Sieve number from

the bottom

Soil type sieve will hold

after sieving

Weight of empty sieve

(0.01 g)

1 Gravel 57.22

2 sand 56.51

3 silt 47.52

4 clay 32.50

The sieve set has 4 sieves one on top of the other.

Table 4: Table recording data as weight of total soil sample and sample in

different sieves for the eight quadrat positions.

Soil

sample

total/in

sieve

Sieve + soil weight (0.01g)

Quadrate

1

Quadrate

2

Quadrate

3

Quadrate

4

Quadrate

5

Quadrate

6

Quadrate

7

Quadrate

8

Totalsoil

weight

(0.01g)

189.62 200.64 201.75 177.98 172.32 165.05 185.29 176.38

Gravel

(0.01g)96.27 105.76 108.38 100.64 89.09 85.54 89.61 83.65

Sand

(0.01g)84.01 88.13 80.89 82.50 73.66 67.93 75.84 72.71

Silt(0.01g)

75.61 71.39 76.20 71.89 75.72 72.89 73.73 80.95

Clay

(0.01g)118.58 124.60 126.88 113.52 117.86 123.70 129.48 127.49

Each sieve section is measured with the soil sample that settles in the sieve. This

is done for all 4 sections of the soil sieve.


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Soil composition: Data processing

The amount of soil sample in each sieve is calculated by subtracting the weight of

empty sieve(table 3 ) from total sieve + soil sample weight (table 4).

Table 5:Table showing actual amount of soil in each sieve showing the

composition of soil taken from different quadrat positions.

Soil

sample

weight

Quadrate

1

Quadrate

2

Quadrate

3

Quadrate

4

Quadrate

5

Quadrate

6

Quadrate

7

Quadrate

8

Gravel

(0.02g)39.05 48.54 51.16 43.42 31.87 28.32 32.39 26.43

Sand

(0.02g)27.50 31.62 24.38 25.99 17.15 11.42 19.33 16.20

Silt

(0.02g)28.09 23.87 28.68 24.37 28.20 25.37 26.21 33.43

Clay

(0.02g)86.08 92.10 94.38 81.02 85.36 91.20 96.98 94.99

Calculat-

ed soil

sample

weight

(0.02g)

180.72 196.13 198.60 174.80 162.58 156.31 174.91 171.05

The percentage of each type of soil is calculated with the formula

.

At quadrate 1 the percentage of gravel in the soil sample is

Similarly, loss of soil as percentage, for each sample, can be calculated as


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Table 6:Table showing different types of soil present in each quadrate measured

as percentage, and loss of soilas percentage during the experiment

Soil

sample

weight

Quadrate

1

Quadrate

2

Quadrate

3

Quadrate

4

Quadrate

5

Quadrate

6

Quadrate

7

Quadrate

8

Gravel%

21.61 24.75 25.76 24.84 19.60 18.12 18.52 15.45

Sand % 15.22 16.12 12.28 14.87 10.55 7.31 11.05 9.47

Silt % 15.54 12.17 14.44 13.94 17.35 16.23 14.98 19.54

Clay % 47.63 46.96 47.52 46.35 52.50 58.35 55.45 55.53

Loss ofsoil %

4.69 2.25 1.56 1.79 5.65 5.30 5.60 3.02

As an average:

On trail: Gravel 24%, Sand 15%, Silt 14 % and Clay 47 %

Off trail: Gravel 18%, Sand 10%, Silt 17 % and Clay 55%

Data presentation

Figure 4: Graph showing diversity index of the quadrats as per figure 1.

Quadrat 1, 2, 3 and 4 are on walking trail. Quadrat 5, 6, 7 and 8 are on walking

trail (as per figure 1).

2.76 2.82

2.50 2.51

1.00 1.00

1.29 1.25

0.00

0.50

1.00

1.50

2.00

2.50

3.00

0 1 2 3 4 5 6 7 8Simpson

'sDiversityIndex(D)

Quadrat positions

Simpson's Diversity Index


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Figure 5:A graph showing average biodiversity on trail and off trail.

Figure 6:A graph showing composition of soil, on trail and off trail.

1.13

2.65

0

0.5

1

1.5

2

2.5

3

On trail Off trail

Simpson'sBiodiversityIndex(D)

Areas with different level of human impact

Average Biodiversity : On walking trail and

Off trail

24

15

14

47

On trail

Gravel Sand Silt Clay

18

10

17

55

Off trail

Gravel Sand Silt Clay


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Discussion

Biodiversity is greatest off trail where more species are present and the

population of each species is greater. As per figure 4, the biodiversity off trail is

between 2.50 to 2.76 (average 2.65) which are rather high values compared to onthe trail where the greatest biodiversity measured was 1.29.

The average biodiversity off trail is less than half of the average biodiversity on

trail showing that some species such as star moss and grass moss cannot exist at

places where they are stepped on, whereas a species such as grass is more tough1

and exist both off and on the trail thus resulting in some biodiversity on the trail.

However, there are not many of such specimen on the trail.

Figure 5 shows that the biodiversity index is much higher off trail. This means that

more species with a greater population exists off trail where they are not directly

influenced by human walking and interference.

As per figure 6, the composition of soil on trail differs from the composition off

trail as the average percentage of clay on trail is less than the one off trail. It

seems like clay is lost from the presence of humans on the trail as it is not present

in the same amount as off trail, thus the heavier and bigger types of soil sand and

gravel are left on the trail therefore taking up a greater percentage. The average

percentage of gravel on the trail is 24 % compared to 18 % off trail, but this is only

significant when measured in percentage as there is no clear difference in the

weight of gravel off and on trail.

Gravel have a poor water-holding ability due to its considerable size and since it

takes up a relative great part of the soil on trail, the water is not stored but drains

through instead2. On the other hand the soil off trail consists of more than 50 %

clay on average which has relative small particles thus it has a greater water-

holding ability and store more water.

1Berthelsen, Hans Erik. Ny Biologi 1liv Og Natur Grundbog. 1st ed. Copenhagen: Gyldendal, 2009. Print.

2Davis, Andrew, and Nagle, Garrett. "The Soil System." Environmental Systems and Societies. Edinburgh:

Pearson Education Limited, 2010. 124. Print.


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The biodiversity is less on trail compared to off trail and at the same time the soil

contains less clay but more gravel here thus the soil do not hold as much water as

off trail. The soil might have been eroded because of the human influence on

biodiversity meaning that less plants are present to hold the soil, thus clay is

flushed away as. This process is shown in the diagram below where human

presence cause less biodiversity causing erosion of soil.

Figure 7:Illustration of the influence of human presence on biodiversity and soil

On the other hand clay might be eroded directly by humans resulting in

diminishing biodiversity on the trail as less clay is available to store water for the

plants. This process is shown in the diagram below here.

Figure 8:Illustration of the influence of human presence soil and biodiversity.

Since both diminishing biodiversity cause erosion of soil as less plants hold on to

the soil and soil erosion cause less biodiversity as less water is stores it seems like

a system of positive feedback is happening on the trail as positive feedback

occurs when a change in the state of a system leads to additional and increasedchange

3as shown in diagram below.

3Davis, Andrew, and Nagle, Garrett. "The Soil System." Environmental Systems and Societies. Edinburgh:

Pearson Education Limited, 2010. 7. Print.


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Figure 9:Illustration of diminishing biodiversity and erosion of soil as positive

feedback.

EvaluationSimpsons biodiversity index gives an index number, but it only compares the

number of different species present and the size of each population and not the

total number. An example where it goes wrong could be an area with a total

number of five plants, but each plant is a different species, then the biodiversity

would be

, but if there are five plants and four different

species the biodiversity would be

, so a better way of doing it

would have been to use the Simpsons biodiversity index, but at the same timelook at the total number of species, thus conclude whether the area provides a

habitat for several species to reside.

Doing a bit research on each plant habitat requirements could give indications of

abiotic environment of the area and helped in discussion. Direct measurements,

like pH of soil using a pH meter, could have also helped in analyzing the

distribution of plants in the area and thus the impact on biodiversity and soil.

Although I was extra careful, still there has been a loss of soil (upto 5.6 %) whilesieving, which is evident from table 6 . To minimize this, I could have waited after

sieving for some time, to let the soil settle down, so that when the sieve is

opened, there is no loss of fine soil particles. Since clay is the finest particle, my

assumption is that the loss is mostly of clay.

Diminishingbiodiversity

erosion ofsoil


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More readings could help minimize the random errors.

Conclusion

As both soil erosion affect biodiversity and diminishing biodiversity affect the

composition of soil in a system of positive feedback it seems to have been startedby human presence as both biodiversity and the composition of soil on the

chosen trail differs from off trail, thus humans can be assumed to have been the

initial factor starting erosion of soil and diminishing biodiversity. Biodiversity is

considerable greater off trail and more clay with water-holding ability is present

off trail showing that the presence of humans on a trail affects nature in certain

ways.

The biodiversity off trail is between 2.50 to 2.76 (average 2.65) which are rather

high values compared to on the trail which is between1.00 to 1.29 (average 1.13).

Also on trail, the percentage composition of soil is found to be : Gravel 24%, Sand

15%, Silt 14 % and Clay 47%, whereas Off trail, the percentage composition of soil

is found to be: Gravel 18%, Sand 10%, Silt 17% and Clay 55%.

Further investigation

The experiment has shown the biodiversity and soil composition and certain

points on a trail and next to it but for those observations to be valid more

measures over a longer period of time might be necessary where the number ofhumans presence varies to see whether it has a direct impact upon biodiversity

and soil composition.

References

Davis, Andrew, and Nagle, Garrett. "The Soil System." Environmental Systems and

Societies. Edinburgh: Pearson Education Limited, 2010. 7, 124. Print.

Berthelsen, Hans Erik. Ny Biologi 1liv Og Natur Grundbog. 1st ed. Copenhagen:

Gyldendal, 2009. Print.

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