The Effects on the Erosion of Topsoil Caused by Obstacles

Embedded in the Soil

 

 

 

 

Table of Contents:

 

Return to Research 2001

 

 

 

I.  Introduction

Erosion can be defined as to wear away (Foth 374).  The erosion of soil is the general wearing away of soil and rock from the earth’s surface, and the transportation of this material, by means of moving water, wind, ice, and temperature variations, to name a few methods.  It naturally shapes the land by wearing down mountains and other land forms,  and also carrying soil to other locations to be used to form new land forms and increase the size of others.  This process tends to bring the surface of the earth to one, uniform level, over time.  An example of this is the Appalachian Mountains, which now stand at about one-half their original height (Foth 375).  This process is generally a slow one, occurring over thousands or millions of years.  The gradual manner of erosion helps preserve an environmental equilibrium, by bringing more nutrient-rich soil to the surface and covering the more weathered, less nutritious soil.  However, as with many other aspects of the environment, human activities have altered the erosion process in many areas of the globe, causing problems.

 

The top layer of dirt, called the topsoil, is vulnerable to erosion via human alterations to the environment, such as agriculture, forestry, and construction.  Different land uses cause soil disturbances, and this causes erosion to occur far above natural rates.  Erosion of the topsoil is harmful because the layer of dirt under the topsoil does not contain the nutrients that the topsoil does, and so plants have a hard, sometimes impossible, time growing in places where there is low or no topsoil. Also, removing the topsoil greatly reduces the soil’s ability to regulate water flow and prevent pest and disease infestations.

 

Naturally, erosion control is assisted by the presence of plants and trees, which shield the topsoil from wind and rain.   The roots of these plants and the waste material, such as dead leaves and fruits, stabilize the soil by acting as an anchor and helping to  keep the topsoil in place. 

 

This experiment, using nails in substitute for plant roots, will investigate the change in the amount of soil eroded, measured by the volume of soil that is moved out of the box, due to the number of nails in the setup in each trial, measured by number of nails per square centimeter.  It is predicted that the more nails in the trial, the less soil will erode out of the box. 

II.   Setup

 

 

            The setup for experimentation was of unique design.  The box was designed to allow for experimentation with running water in a uniform manner, so that conditions would be a better replica of what occurs in nature.  The box held potting

soil, and water was poured into the PVC pipe using a funnel so as not to spill the measured amount of water.  The water flowed through the tube to the horizontal portion, where little holes were bored into the pipe in the bottom.  The water came through the little holes onto the soil in a uniform manner.  The box was tipped at a 20° angle, so that the water ran down over the soil into a container at the end of the box.  

 

            The box was divided into sections, with each section containing 287 square centimeters, and marked off with pieces of yarn stapled into place.  As the trials were being run, and as more nails were needed, they were hammered into the bottom of the box, with most of the nail still remaining above the wood at the bottom of the box.  Trials were run with a certain number of nails per section of 10 centimeters by 28.7 centimeters.  

 

III.  Method

                The method used to conduct this investigation consists, in short, of two pre-trials, and the experimental trials.  After the setup was put together, two pre-trial runs were performed to make adjustments in the setup and establish which constants were needed for the experiment to work correctly.  Then, after all the adjustments, the trials were run one after another, and the data for each trial was recorded.    After each set of three trials with the same nail count, more nails were added. There were 24 trials run, three for each of the different amounts of nails in the experiment.  In each pre-trial and trial, fresh potting soil was used that was dry and had not been used before.  After potting soil was used once, it was disposed of and not used in another trail.

 

IV. The Pre-Trials 

            Two pre-trials were conducted before the trials in which data was collected.  The purpose of these trials was to guess and check the amount of soil and water needed to produce measurable results, and to make sure that the setup functioned as anticipated.

            During the first pre-trial, the box was filled with soil to the halfway mark, which had been measured and marked with ink pen during the construction of the box.  .5 L of water was poured into the tube.  The result was that the majority of the water was absorbed by the soil, and no runoff was noted.  Also, the water tended to flow to one side of the box.  To correct these errors, a level was used to make sure that the box was level to prevent the water collecting at any one side, and the amount of 500mL was noted to be not enough water.  However, the soil level proved to be just right and the half way mark was deemed a constant for the experiment.

 

            The second pre-trial was conducted with the same amount of soil as the first, but with 1 L of water.  This amount of water produced results, as soil and water ran out of the box, and 1 L became the water constant for the experiment.  The water flowed evenly across the soil, and so the level problem was corrected.

 

V.    The Trials

            Each of the 24 trials was conducted using the method mentioned in the Setup and Method sections.  Water was poured into the pipe, and flowed over the soil and created water and soil runoff.  The runoff was collected in a pan at the bottom of the box.  This runoff was poured into a measuring container.  However, because part of the runoff was soil particles, much of the soil did not flow off the pan into the measuring container.  To remove the rest of the soil, a measured amount of water was used to wash the soil from the pan to the container.  This value of water needed to wash depended on the amount of soil stuck to the pan, and so was not always consistent because sometimes more water was needed.  This particular volume of water, whatever it happened to be, was subtracted from the volume measured during the calculations.  The measured volume of water was recorded, and then disposed of.

 

            After each trial, the wet soil was removed from the box.  All the measuring containers (the pan, the container to measure volume) were washed with water to remove any remaining soil.  Then, if more nails were needed, they were added at this time.  To add them, the nails were hammered into the bottom of the box.  This prevented them from coming loose during the trials.

 

VI. Results

            The constants and variable used in this experiment are as follows:

Table A: Constants and Variables in the Experimentation

 

The results of each individual trial are listed in Appendix i.  The resulting volume of runoff shown in Appendix i was calculated in this manner:

Total amount of soil               minus              the volume of              =          the volume of

and water measured                                       water used to wash                 runoff for the

the pan off                              trial

            From the three trials tested for each amount of nail per 287 square centimeters, the average volume of soil and water displaced was:

Table B: Average Volume of Runoff in Trials

 

VII. Analysis

            At first glance, the data of the trials does not appear to have any meaning or show any correlation or decisive results from the experiment.  However, by examining the averages of the three trials in each nail count, a small pattern can be seen in the data.      

 

            The data of the individual trials does not prove much by itself.  Throughout the trials, there is a great variation among trials of the same nail count.  There were some trials that produced surprisingly low runoff volumes.  This was due to when the all the water ran to one side of the box unexpectedly, and created a dam for itself, and keeping most of the soil in the box.  Because of these trials, the patterns in the data are dampened and hard to determine.

 

            By taking the averages of the trials, as shown in Table B, a pattern can seen.  From one nail to four nails, the volume of soil runoff shows a decrease.  This decrease is not linear or consistent, but is there all the same.  The trials with higher nail counts had less runoff than the trials with lower nail counts, enough difference in the nail count to conclude that the nail count affected the runoff value.   

 

One would expect the trials with no nails to displace more water than the trial with one nail, but proved not to be correct.  This was because once the first nails were put in the setup, they changed the flow of the water over the soil.  The water with no nails traveled over more area and spread itself out, allowing for more opportunity for the water to be absorbed by the soil and stay put.  Once the nails were included, the water had obstacles to move around, and so more of the water stayed together and provided a force to move the soil.  This is why the amount of soil moved in the no-nail trials moved less water.

 

The uncertainty of the experiment, due to the variation in values among trials of the same nail count, is somewhat high.  The highest variation between values is .5 L, as seen in the 1.5 and 2 nail trials.

 

VIII. Conclusion

            Because of the trend seen in the mean values data, in Table B, the hypothesis is proved to be correct.  Even though the pattern is not exactly consistent, nonetheless the pattern is there that the more nails, the less soil eroded out of the box.  Therefore, the nail count affected the runoff value in a noticeable way, as expected.

 

For the most part, the experiment was conducted exactly as planned.  No problems other than the low values came up, and the data fit with the hypothesis.  However, because of the uncertainty of the experiment, the experiment was analyzed and some factors were discovered that may have contributed to the uncertainty.  These factors that may have contributed are: the patterns in water distribution, as discussed before, that produced low runoff values, the method used in the experiment, and the materials used in the experiment.  Each of these factors would need further experimentation to prove or disprove that they were a contributor to the uncertainty.

 

As mentioned before, the trials in which the water gathered at one side caused a variation in measured volumes of runoff.  This is thought to be the only major cause of uncertainty.  Although the cause of this problem is not exactly known, there are suggestions as to factors that may have contributed to this problem.  These factors are included above in the hypothesized causes for uncertainty; they are the method used to conduct the experiment, and the materials used in the setup.  By the method of the experiment, it is meant that the measuring of runoff was measured with both water and soil mixed, and may not be accurate.  By materials used in the experiment, it is meant that the materials that the box consisted of or the potting soil may have caused inconsistencies in the experimentation.

 

 The method of the experiment might have indirectly caused the uncertainty by causing the problem with the low volume data values.  This is possible, due to the fact that runoff was calculated using both the water and soil that ran out of the box.   It was discovered early in the experimentation process that the easiest way to calculate the runoff would be to measure the volume of both the water and soil that ran off out of the box.  However, the amount of water that ran out of the box each time changed, due to absorption into the soil, and it was impossible to measure how much water was absorbed in the soil still left in the box.  The pattern of flow in the box varied in each trial, and so the amount of soil that the water encountered was different each trail.  In order to rectify this problem, a few assumptions were made.  First,  it was decided if a variation in the data occurred if in one trial, the absorption of water into the soil that remained in the box was significantly different than in another trial, this variation was negligible.  It was also decided that the water that ran off with the soil would be measured and considered an important part of the erosion problem, since water that is absorbed into the soil rather than run off makes that soil healthier.  It is suggested that at another time it could be investigated whether or not these assumptions significantly altered the data to this investigation, and that another experiment could be conducted taking into account and somehow measuring accurately both the absorbed water in the soil that remained in the box and measuring only the soil particles that ran out of the box.

 

The volume of both water and soil that was calculated represents the amount of topsoil that would be eroded, and the amount of water that was not absorbed into the soil.  For soil to be healthy, topsoil must be in abundance and water must be there to help nurture plants and other life.  When both are removed in great amounts, the soil is less healthy and life cannot flourish in those areas.

 

The materials used in the experiment may have contributed to the uncertainty by influencing the absorbency of the potting soil used at different points during the experiment.  The box was made of wood, and wood absorbs water, so it is possible that during one trial the wood became wet and caused in the next trial for some of that moisture to pass into the dry potting soil before the water was even poured onto the soil.  This may have, in some way, caused the soil to react differently with future trials, in a disruptive manner.  Looking at the data from the trials, the occurrence of low volume data points does not appear to be different in the earlier or later trials, but who is to say whether those low volume trials were caused by low nail counts and would have died off and not appeared in later trials had the wood not added moisture to the soil.  It is purposed that this experiment be repeated, but with a non-absorbent material used in the construction of the box, so that moisture does not escape the soil.

 

            Careful planning was put into this experiment to create an event (the experiment) that replicates what occurs in nature when great amounts of water flow over topsoil that does not have any protection from roots or plants.  The earlier trials represent soil that has almost no cover or anchor, and the later trials represent soil that has some anchorage.  As the results of the experiment show, it is better to have more cover for topsoil, and that every bit of anchorage helps both preserve what topsoil is there, and also to hydrate the soil and make conditions favorable for

more plant life to grow.  By having some anchorage, soil can repair itself by getting more and more hydrated, and nurturing more and more protective plant life.

 

            From this experiment, suggestions can be made to preserve the health of the environment.  This experiment has shown that even a little bit of anchorage for soil is better than nothing, and that if given even a little bit, soil can regenerate and heal.  Erosion occurs most frequently in agriculture and building sites, and if more precautions were taken at these locations to control erosion, especially with heavy rainfall and water flow, these areas would stay healthy.  It is important to preserve that health of our soil, because the quality of the environment depends on it.  

 

Links:

• Erosion and Soil Degradation:  http://royal.okanagan.bc.ca/mpidwirn/agriculture/erosion.html  This page contains detailed information about erosion and causes, especially the human component, and what can be done to decrease harmful erosion.  This is the best summary page that I have found. 

• U.S. Global Change Research Office Page:    http://www.gcrio.org/geo/soil.html  This page contains a good description of  what erosion is and what causes it.  It's a good start for understanding erosion.

• Corn, Soil Tillage, and Erosion:  http://www.ontariocorn.org/envsoil.html  The corn page has information about crops on soil and how plant life prevents erosion, and how the soil health affects plant health.

• Soil Erosion and Residue Management:  http://ozone.crle.uoguelph.ca/manure/soil.management/soileros.html  This page contains information about the effects that farming has on soil and erosion rates.

• Soil Erosion in Agricultural Systems:  http://www.msu.edu/user/dunnjef1/rd491/soile.htm  Another page on soil erosion, this page adds a few new things to what the above pages cover.

• Types of Erosion:  http://danpatch.ecn.purdue.edu/~epados/erosbmp/src/types.htm  This page has information on all types of erosion, not just soil, and provides links to more erosion information.
  

 

 

Appendix i : Data of Trials 1 to 24 text version