Ecology investigsation

Ch. 1: What is infiltration rate and what affects it.

Infiltration is particularly important in soil conservation; if the infiltration rate is high, less water passes over the soil surface, hence reducing erosion, and more water is made available to plants.

Factors affecting infiltration rate:

-Water in the soil generally reduces or limits the infiltration rate. The reduction is due in large part to the fact the water causes some  (very small particles in the soil) to swell and thereby reduces both the pore space and the rate of water movement. In a completely saturated soil, infiltration will be zero.

-Physical characteristics of soil such as the size of particles, the degree of aggregation between them and the arrangement of particles. The larger the pore size and the greater the continuity of the pores that can be maintained, the greater is the resulting infiltration rate.

Crop cover is good for infiltration as it is important to maintain permanent channels, especially at the soil surface. The lack of vegetation means that no moisture is lost or delayed through interception and the rain is able to hit the ground with maximum force. The more intense the rate of rainfall, the larger the beating effect of raindrops. At the beginning of a rainfall, the rate of infiltration is good but it decreases rapidly, especially when the rainfall is of high intensity because soil gets saturated faster and sealing crust forms faster. This surface sealing effect can be eliminated by protecting soil by , , straw, etc. In general, vegetative cover and surface condition have more influence on infiltration rates than the soil type and texture.

Ch. 2: Methodology

1. Methods of Study

5 slopes were chosen systematically in order to obtain good results and a variation due to the different kind of soil texture. These slopes were situated in different locations which means that our results would show a general perspective on infiltration rate. The data that was collected was:

                                - Infiltration rate

                                - Vegetation percentage

                                - Angle of the slopes

                                

                Finding the angle of the slopes

1. Pegs are placed on the slope. From 0 to 25 meters. With an interval of 2 meters between each peg.
2. The slope angle is measured from the bottom towards the top.
3. The first measurement is made at 0 m. The person wih the clinometer stands at 0 meters and the second person stands at 2 m. The person holding the clinometer, sights it towards the other person focusing between his/her eyes. (Remember the 2 individuals carrying out this process must have the same height).
4. Step 3 is carried out up to the 24 m.
5. The results are plotted down on the recording sheet and afterwards a graph is constructed to reconstruct the slope profile.

                How to make a clinometer

1. Glue a protratctor unto the end of a ruler with the use of prestick.
2.  Thread some string through a hole at the point marked “0”. Secure with a knot and fix a weight to the loose end
3. Push two drawing pins through the points marked “X”. These serve as sights to help align the clinometer.

Measuring infiltration rate

1. Use as an infiltration ring a plastic pipe with at least 15 cm of diameter and more than 20 cm in height.
2. Make sure you have plentiful supply of water, a pencil, a stopwatch, a recording sheet. This process can be done individually but to correct uncertainties and make the measurements correct, two persons would be best.
3. Hammer the plastic pipe into the ground to a depth of about 10 cm on the chosen site. This measurement is done with an interval of 5 meters and is done till 25 meters. Which means it is done six times on each slope.
4. Place a ruler vertically inside the ring to record the fall in water level.
5. Pour water into the cylinder to a depth of 15 cm. Measure and record the drop in water level for each minute.
6. If the water falls by 5 mm or more then more water must be added so that the pressure exerced by the water doesn’t decrease. Eg; if the water drops by 7 mm then 7 mm are added back so the water level is 15 cm.

                Counting Vegetation Percentage

1. Like the infiltration rate, this process is done with an interval of 5 meters.
2. A quadrat is placed on the site and the number of plants within the quadrat are counted and recorded.

CH: 3

Data presentation and analysis

The following bar chart illustrate the soil depth:

Bar Chart 1:

- As seen on the diagram there is no relationship between the soil depth and infiltration rate. It’s only from 20 to 25 meters from start where they both decrease but due to the absence of a relationship before this, it is concluded that this happened by coincidence.

Bar Chart 2:

- This graph illustrates that there is no relationship between soil depth and av. Infiltration rate as the results vary randomly.

Bar Chart 3:

• Av. Infiltration rate increases from 0 to 10 meters from start, then it decreases from 10 to 20 and finally it increases from 20 to 25. This is not the pattern observed for soil depth or the inverse and therefore it is concluded that there is no relationship

Bar Chart 4:

• From 0 to 15 meters from start the result vary proportionally but from 15 to 25 they vary randomly. Therefore it is concluded that there is no relationship.

Bar Chart 5:

- The results vary randomly, there is no relationship.

The following graphs show the angle slopes and the infiltration rate for each 5 meters:

Graph 1:

• As seen on the graph the infiltration rate increases from 0 to 14 meters from start, by 5.
• The slope angle does the opposite because it decreases from 0 to 14 meters from start by 7.
• But, this pattern is distorted and the figures don’t coincide with the hypothesis because where slope angle is the highest (12) the av. infiltration rate is 2.8 and where slope angle is 11 av. Infiltration rate is 7. This disproves the hypothesis that states that the higher the slope angle the lower the infiltration rate.

Graph 2:

• This slope is steep because it has an average slope angle of 12 degrees. Therefore the average infiltration rate should be low because the hypothesis states that these values are inversely proprtional.
• The infiltration rate is not as expected because the slope’s average infiltration rate 4 which is high.
• From 0 to 8 meters from start the slope angle decreases but, the av.infiltration rate fluctuates between 5 and 3.
• From 14 to 22 meters from start the angle goes from 9 to 12 and then decreases to 5. If related to the hypothesis then the pattern of the infiltration rate should be the opposite which means that it would decrease and the increase.

Graph 3:

- From 0 to 5 meters from start the slope angle is very gentle and therefore the  av. infiltration rate should be highest at these points. But, this is not the case since the highest infiltration rate is where the slopest is steepest. This is at 8 meters from start and disproves the hypothesis

Graph 4:

• This slope starts with a very steep angle of 16 degrees. This is the steepest point of the slope and therefore it should be here where the av. Infiltration rate is lowest but this is not the case as where the slope angle is lowest the infiltratoin rate is the same as where it’s highest.
• The slope declines with an angle of –2 and then flattens out from 14 to 22 meters from start.

Graph 5:

• From 0 to 8 meters from start the slope angle increases from 3 to 10 and according to the hypothesis the infiltration rate should decrease but, this doesn’t happen as infiltration rate increases from 2 to 4.
• The slope angle is lowest at 0 and 22 meters from start where it’s 3 and it should also be here where the infiltratoin rate is highest but this is not the case.

CONCLUSION:

Both the hypothesis where proven wrong and therefore it was decided to make a scattergraph and afterwards test for significance to see if there is a relation between these results.

To analyze the data obtained and test them scattergraphs were constructed and afterwards “the Spearman’s rank correlation coefficient” was used to test if there was any relationship between the variables.

Ranked data: Vegetation and Av. Infiltration rate

To test for correlation coefficient, the formula used is: r = 1- 6∑d²

                                                                  n³-n

Therefore r = 6 x 2619 =

                26³-26

               = 1- 15714  = 0.1 - This means that there is NO CORRELATION.

                   17550         

Ch: 4

Ways in which the study can be improved

1. One of the problems encountered during data collection was the lack of time. We didn’t have enough time to gather all the data in one day. This means that we would gather data about one slope and the next day we would gather data about another slope. During one of the nights it rained and this could also lead to a change in the infiltration rate. Because the soil would be moistured and therefore would absorb less water.
2. Namibian soil is very dry and hard and therefore it was difficult to hammer the plastic pipe into the ground. This resulted in a failure to meet the criteria which states that the plastic pipe must be hammered 10 cm into the ground. This sometimes resulted in water pouring out from the bottom of the pipe and therefore we had to hammer it in again.
3. As time wasn’t on our side we had to measure the infiltration rates individually and therefore could had created uncertainties in the results.

Conclusion:

By looking at the data I can conclude that there is no relationship between slope angle and infiltration rate, vegetation and infiltration rate or soil depth and infiltration rate. With the use of a scattergraph I plotted the results and afterwards tested them for correlation the results obtained were:

• 0.1 for vegetation and infiltration rate
• 0.4 for slope angle and infiltration rate

These results show that there is no correlation between these results.

This doesn’t coincide with my background theory and proved my hypotheses wrong. This is because my hypotheses states that:

• The higher the angle is the less infiltration rate. This wasn’t seen as the results varied randomly.
• The less infiltration rate there is the less vegetation there will be. The same was observed here as the results varied randomly.
• My other hypotheses stated that the as soil depth increases so does infiltration rate but, this wasn’t observed neither because the results varied randomly.

I think that my hypotheses weren’t proven because the experiment wasn’t carried out correctly and due to certain factors that weren’t in our favor like the hard soil which made it almost impossible to hammer the pipe in. This experiment was very interesting and also provided a better perspective on how infiltration rate is affected by various factors even though the results weren’t as expected. But, if carried out again correcting the few errors it could possibly create results that coincide with the background theory and hypotheses.

Ch:5

Appendix

Slope 1

Slope 2

Slope 3

Slope 4

Slope 5

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