The Effect of Vegetation on Erosion Rates

This topic submitted by Nathaniel Minto, Charlie Hansen, Mike Frager, Will Brisbane, Jill White at 12:21 pm on 12/13/00. Additions were last made on Wednesday, May 7, 2014. Section: Smith

Will Brisbane
Nathaniel Minto
Charlie Hansen
Jill White
Mike Frager

The Effects of Vegetation on Erosion
Introduction
The purpose of our lab is to determine the effect of varying degrees of vegetation (no vegetation, grass, brush or bushes, and trees) and their root structures on the erosion of soil along the bank of the creek in Peffer Park, while taking into account common environmental factors to each sample site. These factors are rainfall, temperature, and wind speed. Our hypothesis concerning this problem is that the instance in which a sample site has no vegetation will have the greatest degree of soil erosion. We believe that the degree of erosion in the other sites will decrease from the greatest amount to the least amount in the following order: the site with grass, then the site with brush or bushes, and finally the site in which trees are the dominant environmental surrounding.
We tentatively believe this theory to be correct because of the structure of the roots in respect to each type of vegetation, or in some cases no vegetation at all. It would then be fair to hypothesize that larger root-structure leads to less erosion. We are also taking into account the progressively larger canopy that is part of vegetation with bigger root-structures. This is relevant in that it theoretically will serve as a shield against the aforementioned environmental factors, thus reducing erosion even further.
This particular problem struck as fascinating during our naturalist hike along the creek. While walking, we noticed that the bank of the creek displayed visual signs of soil erosion and it struck as a pressing question as to how the factors surrounding the creek bed would affect the rate of erosion. By answering this question, we plan to gain a better understanding of the topic of erosion and more specifically what factors in the environment most hinder or aid in the rate of soil loss. Furthermore, through this experiment, we will be enlightened to the aspects of the scientific process, statistics, as well as our surrounding environment in general.
This particular topic holds more than simply personal importance or interest. The problem of soil erosion can be seen as a worldwide issue. Relevant to our study, deforestation can be seen as a major contributing factor to the loss of soil along any body of water. This idea can be taken even further to the topic of agriculture and its problematic effects on the rate of erosion. Bringing us back to our specific question, these two issues are quite relevant and are notable examples of how the topic of soil erosion has affected the environment and subsequently us.
Relevance of our research question
Many of the soil erosion related projects we researched were focused on creating ways to accurately forecast the amount of soil erosion that will occur to a particular piece of land. This was the goal of an experiment titled “Field-Evaluation of Methods to Estimate Soil-Erosion” (1). The researchers compared three different methods to estimate soil loss from erosion. They compared predictions based on the amount of plants, the chemical composition of the soil and the Universal Soil-Loss Equation (2) to the actual erosion they observed. The results of this research have immediate applications for farmers and anyone else that can benefit from accurately predicting soil erosion. To make this possible, researchers at the National Soil Erosion Research Laboratory (3) have developed a software package that can accurately predict soil erosion on a personal computer.
Materials and Methods
In order to take measurements of the loss of soil along the banks of the creek, we plan to strategically place dowel rods horizontally into the bank. To accurately portray the effects of many types of vegetation and their corresponding root structures on soil erosion, a variety of sites will be chosen in the following manner:
1. An emphasis will be placed on keeping as many environmental factors as close as possible between the sites to control for outside effects, for instance the distance from the creek and the nature of the soil. Also we will try to keep the sites as close to each other to minimize discrepancies such as different amounts of rainfall and other possible varying environmental factors.
2. Our sample sites will consist of the following four different types of vegetation: no vegetation, grass, brush or low-lying bushes, and trees. Each type of site will contain three marked stakes driven a prescribed distance (to the mark on the stake) into the bank. The stakes will be placed one to two feet from the surface of the creek and one to two feet from each other. This should be done as best as is possible considering the terrain. Measurements of the loss of soil will be taken weekly by measuring the amount of stake visible on the top from the mark to the bank. These varying types of vegetation were chosen because they are essential in determining our overall objective for the lab, and because they were found abundantly along the creek in which we plan to perform our sampling.
3. We will also keep a record of common environmental factors (basic weather measurements: rainfall, wind-speed, and air temperature). We are keeping track of these factors because, through our research, we have found that each of these factors could have an affect on the overall rate of erosion. These factors will be common to each site and therefore not necessarily pertinent to our lab objective, but the cognizance of these factors gives us a better understanding of erosion as a scientific topic as well as providing us with more practice in taking data.
Statistically we will be comparing two main things, the three stakes within each site to each other in order to test whether they are representative of the actual amount of erosion for that site, and whether each site as a whole is statistically the same as the site with no vegetation to see if the data does indeed confirm our experimental hypothesis.
Unbiased results will come about by sticking to our timeline and the schedule of site checks that we have set for ourselves. It is also important that we make accurate and precise measurements concerning the degree of soil loss at each site. Basically, as long as we are consistent with our schedule that we have set, unbiased results will surely be obtained.
Specific materials will include:
· 500 centimeter dowel rods marked with permanent marker
· Measuring device
· Hammer
· Weather data will be collected at:
http://jrscience.wcp.miamioh.edu/coriolis/miamiweather.html

During our student-generated lab in which the class will collect data for us, we will take the class to one of our sites and demonstrate our data taking process. The class will then be separated into three groups, one for each of the remaining sites. These groups, under the supervision of one of our group members, will take the data for that particular day. The class will record all of the measurements except for the weather data, which we will provide for that day.
Observations and Results
As seen in the tables of data and statistics that follow our results did not agree with our hypothesis in any way. The reasons for this will be discussed in our conclusions section but it would suffice to say that our experimental design had several fatal flaws.
Even with our data being obviously useless we put it through all of the tests anyway just to complete our experiment and show what should have been done if we had obtained good data. Statistically, we compared the each of the stakes within the site to each other using a one sample t-test. As you can see the stakes in the grass site were not statistically from the same population having a p-value of 0.0351.
We then compared each of the sites to the no vegetation site which was to serve as our control. But because our data was invalid and the no vegetation site had no erosion our statistical tests were equally invalid.

Discussion and Conclusion
After four weeks of observation, several shortcomings of our experiment have become apparent. First of all, our duration of data collection is much too short to provide any meaningful results in determining the actual rate of erosion per the objectives of this lab. In five weeks there has been almost no observable erosion, the largest amount being a quarter of an inch at the grass site. For any real change to be observed we would need to collect data for a much longer stretch of time than five weeks, probably somewhere along the lines of five months or even five years.
Another problem regarding our experimental design that we have noticed is the soil makeup. In trying to keep our sites as close together as possible, we chose sites that did not have the same type or density of soil. The worst case of this is our no vegetation site, which we predicted to erode the most. This site is composed almost entirely of clay and therefore has not eroded at all, whereas our grass site is a much looser and a more loamy type of soil and therefore has shown some erosion. The other sites fall somewhere in between these two in terms of soil composition and thus have shown very little to no erosion.
In attempting to further study the effects of root structure on soil erosion, we would have to design a more relevant experiment method. Rather than identifying how root structures affect soil erosion, it might be more revealing to see how soil composition plays a role in erosion. From the results of that experiment, we could retest our original experiment while keeping the composition of the soil as a controlled factor. We would also have to collect data for a much longer period of time.


Citations
(1)
FIELD-EVALUATION OF METHODS TO ESTIMATE SOIL-EROSION
KREZNOR WR, OLSON KR, JOHNSON DL
SOIL SCIENCE
153: (1) 69-81 JAN 1992

(2)
Universal Soil Loss Equation
http://topsoil.nserl.purdue.edu/nserlweb/usle/USLEqn~1.htm

(3)
National Soil Erosion Research Laboratory
http://topsoil.nserl.purdue.edu/nserlweb/


Time Line
Thursday, October 12- Prepare sites for research by placing stakes in the pre-selected areas on the bank of the creek.
Thursday, October 19- Collect data from stakes.
Thursday, October 26- Collect data from stakes.
Thursday, November 2- Collect data from stakes.
Tuesday, November 7- Student generated lab: class obtains data from stakes.
Site Data (in INCHES) Vegetation Type: No Vegetation

Site in place on 10-12-00

Date: 10-19-00

Stake 1: 0
Stake 2: 0
Stake 3: 0

Date: 10-26-00

Stake 1: 0
Stake 2: 0
Stake 3: 0

Date: 11-2-00

Stake 1: 0
Stake 2: 0
Stake 3: 0

Date: 11-7-00

Stake 1: 0
Stake 2: 0
Stake 3: 0


Site Data (in INCHES) Vegetation Type: Grass

Site in place on 10-12-00

Date: 10-19-00

Stake 1: 0
Stake 2: 0
Stake 3: 0

Date: 10-26-00

Stake 1: 0.0625
Stake 2: 0.0625
Stake 3: 0.125

Date: 11-2-00

Stake 1: 0.25
Stake 2: 0.125
Stake 3: 0.1875

Date: 11-7-00

Stake 1: 0.25
Stake 2: 0.125
Stake 3: 0.1875


Site Data (in INCHES) Vegetation Type: Brush

Site in place on 10-12-00

Date: 10-19-00

Stake 1: 0
Stake 2: 0
Stake 3: 0

Date: 10-26-00

Stake 1: 0
Stake 2: 0
Stake 3: 0

Date: 11-2-00

Stake 1: 0
Stake 2: 0
Stake 3: 0

Date: 11-7-00

Stake 1: 0
Stake 2: 0.125
Stake 3: 0


Site Data (in INCHES) Vegetation Type: Trees

Site in place on 10-12-00

Date: 10-19-00

Stake 1: 0
Stake 2: 0
Stake 3: 0

Date: 10-26-00

Stake 1: 0
Stake 2: 0
Stake 3: 0

Date: 11-2-00

Stake 1: 0
Stake 2: 0
Stake 3: 0.125

Date: 11-7-00

Stake 1: 0
Stake 2: 0
Stake 3: 0.125

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