Author(s): Trinity Lavenhouse
Mentor(s): Changwoo Ahn, Environmental Science and Policy Department
AbstractThis study was conducted in Dr. Ahn’s wetland mesocosm on West Campus at George Mason University. Inside there are 40 wetland mesocosms that were created in 2012. The mesocosms were initially planted with 0 to 4 different native wetland species. Since COVID-19, maintenance halted which allowed the colonization of invasive species for the past three to five years. The goal of this study was to determine the amount of soil organic matter in each mesocosm after the colonization of invasive species. The hypothesis was that because there were more plants than there were previously, there will be a higher amount of soil organic matter in these mesocosms. The soil organic matter percentage was processed using the loss on ignition method. It was found that mesocosms that had sparsely spread, or no plants had the lowest soil organic matter while overgrown and dense mesocosms had the highest soil organic matter. After about 10 years, soil organic matter seemed to increase from a range of 2.36% to 2.59% to now a range of 4.15% to 6.21%. In the future a soil bulk density will be processed to analyze how soil porosity or compaction correlates with the soil organic matter found within the mesocosms. Also, plant identification will be conducted for all 40 mesocosms.
Audio TranscriptHello, my name is Trinity Lavenhouse, and I am presenting my research on assessing soil organic matter in a legacy wetland mesocosm after the colonization of invasive species. My mentor is Dr. Changwoo Ahn.
So, to start off I am going to explain the importance of measuring soil organic matter! Soil organic matter is made up of decomposed plant and animal material. They contain quite a lot of organic compounds and are full of nutrients that help plants grow. So in general, it is important to measure the amount of soil organic matter that is present because it can indicate how healthy and fertile the soil is for plants to grow.
This study was conducted in Dr. Ahn’s wetland mesocosm on West campus in George Mason University. Inside there are 40 wetland mesocosms that were created in 2012. The mesocosms were initially planted with 0 to 4 different native wetland species. This picture is from 2014 after 2 growing seasons. Since COVID-19, maintenance halted. Unwanted plants weren’t removed and the water levels weren’t monitored like they use to be. This allowed the colonization of invasive species for the past three to five years. So, the goal of this study was to determine the amount of soil organic matter in each mesocosm after the colonization of invasive species. The hypothesis was that since there were more plants than there were previously, there will be a higher amount of soil organic matter in these mesocosms.
To take samples the mesocosms were split into 5 sections and one sample was taken from each section within the top 20 centimeters where organic matter is the most present, because soil organic matter decreases as you go further down. This was repeated for all 40 mesocosms. The soil organic matter percentage was processed using the loss on ignition method. To carry this out each sample was dried at 105°C for two days. After they were completely dry, they stayed in a desiccator to cool and were then crushed in with a mortar and pestle and sieved through a 2mm filter to get everything that is too big to go into the crucibles. The fine dirt was then placed in crucibles and fired at 360 Celsius for two hours and they were placed back into the desiccator to cool. Soil organic matter percentage is the percentage change of mass.
The results were all collected and all five of the samples were compiled and averaged represent the one mesocosm. It was found that mesocosms that had sparsely spread, or no plants had the lowest soil organic matter while overgrown and dense mesocosms had the highest soil organic matter. The standard error bars are large in mesocosms that had more plants or organic matter in a section than other sections. The mesocosms were then grouped by the initial number of species planted. There seems to be no significant difference across the board and the reason for that will be analyzed further.
In a previous study conducted by another person in this lab named Mary Means, they measured the total carbon content of all of the 34 planted mesocosms in 2014. Total carbon content is a is about 58% of soil organic matter so that conversion was used to estimate what the soil organic matter content was back in 2014. About ten years until now, later soil organic matter seemed to increase from a range of 2.36% to 2.59% to now a range of 4.15% to 6.21%. In the future a soil bulk density will be processed to analyze how soil porosity or compaction correlates with the soil organic matter found within the mesocosms. Also, plant identification will be conducted for all 40 mesocosms as when these samples were initially taken most of the plants were dead because it was the end of the winter.
Thank you for listening!
So, to start off I am going to explain the importance of measuring soil organic matter! Soil organic matter is made up of decomposed plant and animal material. They contain quite a lot of organic compounds and are full of nutrients that help plants grow. So in general, it is important to measure the amount of soil organic matter that is present because it can indicate how healthy and fertile the soil is for plants to grow.
This study was conducted in Dr. Ahn’s wetland mesocosm on West campus in George Mason University. Inside there are 40 wetland mesocosms that were created in 2012. The mesocosms were initially planted with 0 to 4 different native wetland species. This picture is from 2014 after 2 growing seasons. Since COVID-19, maintenance halted. Unwanted plants weren’t removed and the water levels weren’t monitored like they use to be. This allowed the colonization of invasive species for the past three to five years. So, the goal of this study was to determine the amount of soil organic matter in each mesocosm after the colonization of invasive species. The hypothesis was that since there were more plants than there were previously, there will be a higher amount of soil organic matter in these mesocosms.
To take samples the mesocosms were split into 5 sections and one sample was taken from each section within the top 20 centimeters where organic matter is the most present, because soil organic matter decreases as you go further down. This was repeated for all 40 mesocosms. The soil organic matter percentage was processed using the loss on ignition method. To carry this out each sample was dried at 105°C for two days. After they were completely dry, they stayed in a desiccator to cool and were then crushed in with a mortar and pestle and sieved through a 2mm filter to get everything that is too big to go into the crucibles. The fine dirt was then placed in crucibles and fired at 360 Celsius for two hours and they were placed back into the desiccator to cool. Soil organic matter percentage is the percentage change of mass.
The results were all collected and all five of the samples were compiled and averaged represent the one mesocosm. It was found that mesocosms that had sparsely spread, or no plants had the lowest soil organic matter while overgrown and dense mesocosms had the highest soil organic matter. The standard error bars are large in mesocosms that had more plants or organic matter in a section than other sections. The mesocosms were then grouped by the initial number of species planted. There seems to be no significant difference across the board and the reason for that will be analyzed further.
In a previous study conducted by another person in this lab named Mary Means, they measured the total carbon content of all of the 34 planted mesocosms in 2014. Total carbon content is a is about 58% of soil organic matter so that conversion was used to estimate what the soil organic matter content was back in 2014. About ten years until now, later soil organic matter seemed to increase from a range of 2.36% to 2.59% to now a range of 4.15% to 6.21%. In the future a soil bulk density will be processed to analyze how soil porosity or compaction correlates with the soil organic matter found within the mesocosms. Also, plant identification will be conducted for all 40 mesocosms as when these samples were initially taken most of the plants were dead because it was the end of the winter.
Thank you for listening!
2 replies on “Assessing Soil Organic Matter In a Legacy Wetland Mesocosm after the Colonization of Invasive Species”
Interesting project and well done video. Will you be performing the next steps?
Very interesting study! You explained the concepts very well and it was easy to understand even as someone with no background in this field.