pH Analysis
Methods
Soil samples were collected from both sites. Then, each soil sample was resuspended in sterile water and the samples were vortexed. The pH of each sample was measured using a pH probe. There were 6 total samples for each condition.
pH of Rain Garden and Non-Rain Garden Soil Samples
Figure 1
pH Probe Data
Legend
The pH of Non-Rain Garden and Rain Garden Soil Samples. samples of both a rain garden and a lawn (non-rain garden) were collected and the pH of each sample was then determined using a pH probe. The average (mean) of each data set is represented by the X mark on the plots. The line dividing the boxes represents the median. The upper portion of each large rectangle represents the 3rd quartile range for each data set. The lower portion of the large rectangle represents the 1st quartile range for each data set. The upper whisker line represents the maximum value of each data set. The lower whisker line represents the minimum value of each data set. The inner points are used to identify any potential outliers between the box section of the plot, or they may be used to simply determine any differences between data sets. An unpaired t-test assuming unequal variance was used to determine the p-value of 0.140 with a critical value of 0.05.
Evidence
The mean pH for the non-rain garden sample was 7.667 and 7.927 for the rain garden sample. The mean pH for the non-rain garden was 0.26 lower than the pH of the rain garden samples. This means that, on average, the pH of the rain garden samples was 3.39% higher than the average pH of the non-rain garden samples. The standard deviation for the non-rain garden was 0.257 and 0.348 for the rain garden samples. This means that the rain garden had a higher degree of variance of pH between the different samples. The rain garden had a 35% higher standard deviation in comparison to the non-rain garden sample. The p-value for the t-test was 0.140, which is higher than the critical value of 0.05. Thus, we fail to reject the null hypothesis that there is no significant difference in the pH of the two soil types.
Conclusion
Based on our evidence we can conclude that there is not a significant difference between the pH values from the rain garden and the lawn. Though the values for the rain garden can be seen to be slightly more basic than those values from the lawn, by using the p-value, 0.140 we can determine there is not a significant difference. We know this because of the p-value being greater than 0.05, where there is only a significant difference if the value is below 0.05. By using the values of our data, we can conclude we are quite confident in our assessment. The p-value shows us there is not a big enough difference between the two areas’ pH’s to draw any further conclusions about the effectiveness of rain gardens lowering pH values.
Explanation
The two different condition sites having similar pH values can be explained for several reasons. To explain the alkalinity of the soil we can assume based on the area from where we took the soil there was relatively the same number of hydrogen ions, as shown in our evidence for figure one (Factors Affecting Variations of Soil pH in Different Horizons in Hilly Regions, 2019). We did not measure the minerals present, although we did note that both of the sites contained clay-like soil, neither being very sandy or dry. We did collect the soil during and the day after a rainfall which may have caused the soil to act like more of a clay. We can also assume there was not a significant change in the pH as we took our sample from the rain garden in the middle of winter. We can assume that since the plants in the garden are dormant at this time they are not as active with filtering out pollutants. Thus this explains why the pH values for the two sites are relatively similar (Factors Affecting Variations of Soil pH in Different Horizons in Hilly Regions, 2019).
