Data
Data Tables
The tables below show a simplified view of the raw data used in this analysis. All codes in parentheses () are defined in the caption associated with Table 1. and Table 2.
Table 1. Raw data table showing unique identifier (ID), peatland name (CATCH; AVEN - Avenir, SEBA - Seba Beach), peat extraction treatment (TREAT; EXT - extraction, NAT - natural, REC - recovery), peat field name (FIELD), surface microform (MF; FLAT - flat, HUM - Hummock, HOL - Hollow), sample identification (SAMPID), site name (SITE), date sampled (DATESAMP), surface temperature (TEMPSURF), temperature 10 cm below ground (TEMPDEEP), depth of rust (DR), and soil moisture in percent volume (PERVOL).
Table 2. Raw data table showing unique identifier (ID), peatland name (CATCH; AVEN - Avenir, SEBA - Seba Beach), peat extraction treatment (TREAT; EXT - extraction, NAT - natural, REC - recovery), peat field name (FIELD), surface microform (MF; FLAT - flat, HUM - Hummock, HOL - Hollow), sample identification (SAMPID), site name (SITE), date buried (DATBUR), date retrieved (DATRET), number of anions (ANI) and cations (CAT), and chemical compounds (NO3 - nitrate, NH4 - ammonium, Ca - calcium, K - potassium, P - phosphate, Fe - iron, and Al - aluminum).
The data from the above tables can be interpreted as follows:
Sampling Units
An average of three sets of measurements (SITE) were used to create 5 individual sample locations (SAMPID) (Table 1. & Table 2.). However, due to limited independence, the 5 sample locations within each peatland location (TREAT + MF) were averaged to form one value for the peatland location. Therefore, there are 9 independent experimental units, each comprised of 5 sample locations and characterized as follows:
Natural Hummock: 2 units
Natural Hollow: 2 units
Extracted: 3 units
Restored: 2 units
Predictor Variables
Peat Extraction Treatment
These variables are categorical and are manipulated (names in the () below correspond to the FIELD column in Table 1. and Table 2.)
Natural: Hummock (HUM) and Hollow (HOL)
Extracted: Young (C), Mature (F16), Complete (F12)
Recovery: Unsaturated (F16) and Saturated (F5)
Physicochemical Properties
These variables are continuous and are not manipulated. They are considered predictor variables when determining if there is a relationship between the physicochemical environment and nutrient supply rates, but are the response variables when determining the effect of peat extraction activities on the physicochemical environment.
Depth of rust (DR)
Soil moisture (PERVOL)
Surface temperature (TEMPSURF)
Below-ground temperature (TEMPDEEP)
Response Variables
The response variables are the physicochemical properties (described above), and the nutrient supply rates (NH4, NO3, etc.) in Table 2.The nutrient supply rates are continuous, numeric variables.
Exploratory Graphics
Figure 28. Box plots showing surface peat physicochemical parameters for each peat extraction treatment. Whiskers indicate the minimum and maximum values not including outliers. Outliers are represented by black dots. (a) Soil moisture measured in percent volume. High values indicate saturated soil conditions. (b) Surface temperature measured in degrees Celsius. (c) Depth of rust observed on a steel rod inserted into the ground, measured in centimeters. Negative values indicate depth below ground surface where rust was observed. Increasing negativity indicates deeper aerobic soil conditions. (d) Temperature 10 cm below the ground surface measured in degrees Celsius.
Physicochemical Properties
Soil moisture, depth of rust, surface temperature and below ground temperature were visualized using box plots (Figure 28.). All sites were assessed together for an initial observation, then broken down into individual peat fields to observe variability within treatments.
Nutrient Supply Rates
Scatter plots were used to observe the effect of physicochemical properties on each chemical compound of interest (Figure 29.). The relationship between either soil moisture, depth of rust, surface temperature, or below ground temperature for each chemical compound at each peat extraction treatment was graphed to observe the relative effect of each physicochemical parameter. An example of a generated graph is shown in Figure 29. Log scale on the y-axis was used for parameters with highly variable values to better see the distribution of the data.
There appears to be a slight positive relationship between peat surface temperature and elevated ammonium (NH4) availability, and a slight negative relationship between peat below ground temperature and ammonium availability. However, the general trends are not strong.
Figure 29. Scatter plots displaying the relationship between measured physicochemical parameters and select available nutrients for each peat extraction treatment. Chemical compounds are listed in the grey box for each plot and are measured in µg per 10 cm2 over 4 weeks. Different colours represent different peat extraction treatments. Similar colours indicate same treatment at different catchment areas (Avenir or Seba Beach). Graph y-axis is displayed using logarithmic scale (a) Depth of rust observed on a steel rod inserted below ground, in cm; (b) Soil moisture in percent volume, measured at 6 cm below the ground surface; (c) Surface temperature in degrees Celcius; and (d) Below ground temperature in degrees Celcius measured at 10 cm below the ground surface.
Residual Plots
Figure 30. Residual plot of below ground temperature response variable showing relatively normal distribution with some outliers.
Figure 31 . Residual plot for ammonium response variable showing skewed distribution with some large outliers.
Physicochemical Properties
The physicochemical properties (depth of rust, soil moisture, surface temperature, and below ground temperature) were more-or-less normally distributed (Figure 30.). No data transformations were performed; however, increasing the sample number in future studies would be prudent. Due to the small sample size, outliers were not removed as they may be important values that represent the ecosystem. With additional samples, the validity of these outliers could be more accurately assessed and differences between treatment areas may be more pronounced.
Chemical Compounds
The nutrient supply rates for each chemical (NH4, NO3, P, Al, Ca, Fe) violated the assumption of normality and homogeneity of variances (Figure 31.). Although logarithmic data transformations were performed, there was minimal improvement to the residual plots. Therefore, non-parametric tests were used. As with the physicochemical properties above, increasing the number of samples would greatly improve the statistical power and reliability of the inferences gained from these data. Due to the small sample size, outliers were not removed.