Science

The Effect of the Amount of Plants on Soil Erosion 

Riparian buffers are areas of trees, shrubs and other vegetation growing near bodies of water. The root systems of the trees stabilize the soil and absorb excess water, playing a huge role in preventing erosion. As well as helping with erosion, riparian buffers contribute to many other areas of river health, they provide habitats for animals, and  shade for the river (consequently  keeping the water cooler) and they contribute greatly to water quality as well. I wanted to perform an experiment that would demonstrate, on a smaller level, how plants affect soil erosion. I will plant a mix of grass and mizuna in small baking tins, then let them grow for a couple of weeks. My independent variable is the amount of seedlings per pan, which would then affect the amount of soil erosion (my dependent variable). My constants are the type of plant, type of soil, amount of water being poured on the plants, age of seedlings, amount of watering before the experiment, exposure to light & other growing conditions, how they were planted etc… After my plants have started to grow, I will pour water over all the tins, both the planted ones and those with only soil. Essentially I will try to emulate heavy rains and floods that could happen in real rivers. To collect qualitative data, I will take pictures of the eroded soil and observe how much soil was lost as well as the conditions of the plants afterward. Afterwards I will collect my quantitative data by measuring the amount of soil eroded in milliliters. I am excited to see how this goes. While my plants will be much less established than the trees and shrubs forming riparian buffers in the wild, it may help to give me a sense of what plants do for river banks. 



Testable Question: 

What is the effect of the amount of plants on soil erosion?


Hypothesis:

If the amount of plants increases then the amount of soil erosion will decrease, because the roots of the plants  help to stabilize the soil.


Materials Needed:





Procedure


Part 1 : Setting up the experiment 

Step 1: Label the 12 pans (3 pans labeled “control” 3 pans labeled “#1” 3 pans labeled “#2” and 3 pans labeled “#3”). Then cut a 1 inch slit running parallel to the bottom of the tin and about 1 cm up from the bottom

Step 2: Mix a combination of Organic Seed Starter and Moo Grow soil as well as some water. Measure 250 ml of the mix soils and pour it into the first pan. Level out the soil, and repeat this step with all 12 pans. 

Step 3: Leave the control pans with only soil (They won’t have seeds planted in them). For each of the #1 pans, count out approximately 40 grass seeds, and 20 mizuna seeds. Then remove about 50 ml of soil from the containers (This will be added back in over then seeds to bury them.)  even out the soil again and sprinkle both varieties of seeds across the surface. Replace the removed soil. 

Step 4:  For the #2 pans 100 mizuna seeds and 200 grass seeds for each pan. For the #3 pans plant 200 mizuna seeds and 400 grass seeds. Then plant the seeds following the rest of the directions in step 3. 

Step 5: water the pans (including the control pan) with 50ml of water each and place the three pans of each group in the larger trays and then place them under grow lights. 

Step 6: Water every few days, giving them 50-100 ml of water, keeping the soil moist. Water all trays equally


Part 2 : Conducting the experiment 

Step 1: Cut the ends off every pan (as shown in the photos) with a pair of scissors.  

 

Then place the small pan in the larger tray

Step 2: Fill a watering can with a sprinkler head with 1200 ml of water. Then hold the watering can about three inches above the smaller pan and pour the water evenly over the pan until you’ve used all of the water. When you are finished, some of the soil should have eroded and be in the larger pan. 

Step 3: Remove the tin, then pour off as much water as you can from the large pan. Most of the water is gone, pour the dirt and remaining into some sort of container, and label with the test run and seed amount. 

Step 4: Rinse  out the large pan and repeat this step for every small tin. 


Part 1 : Collecting Data 

Step 1: After conducting the experiment you will have 12 containers of water/dirt. Put a strainer over a sink or another container to collect the excess water, and pour the first container of dirt/water through the strainer.

Step 2: Put dirt from the strainer and any dirt still in the container into a 50 ml measuring cup. 

Step 3: Press down the soil and record the amount of soil as well as the amount of seeds and test run. 


Results: 

Milliliters of soil eroded from each pan

 

 

Control: 0 mizuna seeds 0 grass seeds 

Pan #1: 20 mizuna seeds 40 grass seeds

 

Pan #2: 100 mizuna seeds 200 grass seeds

 

Pan #3: 200 mizuna seeds 400 grass seeds

Data Analysis:: 

Seedlings helped to prevent soil erosion.

When I poured water over my control pans (the one with no seed) the average amount of soil eroded was 56.6 ml of soil. This is significantly more erosion than the other three pans, the ones containing seedlings. The pans planted with 200 mizuna seeds and 400 grass seeds lost an average of 19 ml of soil when “eroded” and those with 100 mizuna seeds and 400 grass seeds only lost 9 ml of soil on average. Even the pans with only 20 mizuna seeds and 40 grass seeds only had an average of 35 ml of soil eroded which is still significantly less than the pans with no seedlings to help prevent erosion. 

As you can see in the photos (in results) there is less soil eroded from the pans with seeds, but additionally, the soil in the pans with seeds is much more intact, whereas in the control pan, whole chunks of soil were washed out. 

While the data did show that seedlings decrease the amount of erosion, it did not entirely make sense. More soil eroded from the pan with 200 mizuna seeds and 400 grass seeds (pan #3), than from the pan with 100 mizuna seeds and 200 grass seeds (pan #2). Compared with the rest of the data, this shouldn’t have happened. The tray with more seeds should have eroded less. However the #2 pans appeared to have seedlings that actually germinated. So the inconsistent data is likely due to seed germination variability rather than problems with the experiment. 

Conclusion: 

My hypothesis stated that “If the amount of plants increases then the amount of soil erosion will decrease, because the roots of the plants  help to stabilize the soil.”, and it was supported by the evidence I gathered in my experiment, less soil eroded from the pans with seedlings. However there seemed to be some errors in my data. While most of the pans showed that more seeds produced less erosion, the pans with 200 mizuna seeds and 400 grass seeds lost more soil than those with half as many seeds planted. While the number of seeds to erosion didn’t make sense, the number of seedlings that germinated in each pan did reflect the pattern. The pan with more seeds had less seedlings. This was most likely due to variabilities in germination (as you can see in the photos below the amount of seeds varied for each group), and if I were to perform the experiment again, I would try to keep their growing conditions more alike. I would try to move around their placement under the lights so that some plants didn’t get more light than others and make sure that the plants didn’t get dehydrated and die like some of mine did this time. The seeds may have also been old, and therefore less reliable. While my plants weren’t fully established trees or shrubs, I was able to see how the roots stabilize the soil. The pans with no seeds remained loose dirt, while the roots and soil in the planted pans held their form better. On river banks, loose soil would be more likely to erode when exposed to water, heavy rain or flooding, the trees and their roots help to hold together the soil as well as absorb excess water and create a healthier environment overall. Riparian buffers are an important part of ecosystems  and play a huge role in the health of our rivers.