Figure 2
Average Soil Moisture
Figure 2: Average Soil Moisture
Figure 2 depicts the percent soil moisture content measured for the two rain garden conditions, new and old, included in our experiment. To measure the percent soil moisture, the mass of the soil was taken of the thawed-out sample. The sample was dried out in the oven, removing all moisture from the sample, and the new mass of the sample was taken. The percent moisture content was then calculated by (Mass of soil sample−mass of dried soil)/ mass of dried soil. The average and standard deviation was then calculated from the class data (sample size of 3), which is the data displayed in figure 1 for our two conditions of new and old rain gardens. The statistical test that was used to analyze this data was an unpaired t-test assuming unequal variance. The test resulted in a p-value of 0.64 which is greater than the critical value of 0.05.
Method
In order to find the moisture content, we took 1 gram of soil from each of our samples and placed them into a glass vial. We took the mass of the empty glass vial and then the mass of the glass vial with the soil sample, and then subtract to find 1 gram of soil. We then placed the vial into the laboratory oven set at 105 –110 °C for one week. We then took the weight of the soil sample after it sat in the oven for a week and then subtracted that from our original weight of the sample.
Evidence
As we can see from our bar graph over moisture content the old rain garden had a higher moisture content. The mean average for old was 49.6% and for new was 42.1% so we can see that the old rain garden has 17.8% greater moisture content than in the new rain garden. This is not a very large difference between the two sets of data, and looking at the graph we can see that they are not too far off from each other. We then used error bars to represent the standard deviation for our data. The standard deviation of our data for old is 20.0% and for new is 16.2% the mean of our standard deviations is 18.1% which shows that there is variation between our data. To see how similar or different our data was between old and new rain gardens we used a t-test. A t-test is a calculation used to compare the means of both samples. The t-test gave us a p-value of 0.64. Since our p-value was greater than 0.05 it means that the soil moisture between the old and new rain gardens is not significantly different.
Conclusion
From the statistical test that we performed, the t-test, we were given our p-value, which was 0.64. Since our p-value is above 0.05, this means that the moisture content values of the old and new rain gardens are not significantly different. This means that they do not have unique values. Therefore, we can confidently conclude that the moisture content values of the samples are not different. In conclusion, we are certain that the age of rain gardens does not make a difference in the moisture content.
Explanation
Moisture content is defined as the ratio between the mass of water and the solid mass of soil expressed as a percentage. The graph indicates that new and old rain gardens have the same amount of water present in the soil. The overall goal of this experiment is to test for biodiversity in the rain gardens and in this specific scenario, soil moisture is being used as a determining factor. Since both conditions resulted in no statistical difference as shown by the t-test, we can conclude that both soils have the same biodiversity. Data collected from tests in Figure 3 and 4 will help determine how biodiversity between new and old rain gardens differs. What may cause the soil moisture data to show up remarkably similar between the gardens? An explanation can be formulated by looking at the three main ways water leaves a rain garden; “overflow to an outlet, percolation to the underlying soil, and evapotranspiration (ET) to the atmosphere” (Hess, Amanda). When looking at the structure of both rain gardens, the results indicated that the “underdrain design” of each rain garden is the same (Zhou, Zikai, and Qizhong Guo). The “aggregate bed within the underdrain design (...) is typically designed as a pathway/passage of water to the underdrain pipe network and the subsoil further below” (Zhou, Zikai, and Qizhong Guo). This is applicable because if both rain gardens have the same design, they will have the same process in which the water is directed, thus the soil moisture will be similar.