Study Area and Methods

Figure 1. The map is from Hailey Cole personal communication which shows the sampling sites of the reclaimed wells.

Study Area

The study area was located in the Central Mixedwood and Lower Foothills Natural Subregions in northwest Alberta, around the town of Fox Creek (NRC 2006). This region is rich in oil and natural gas reserves and these valuable resources have made it a focal point for oil and gas extraction and production (Fox Creek, Alberta 2023).

The mean annual temperature of Central Mixedwood is 0.2 °C, with the average temperature in the warmest month being 15.9 °C, and in the coldest month, it is -18.7 °C (NRC 2006). The mean annual precipitation in Central Mixedwood is 477.5 mm, with an average of 336.2 mm during the growing season (NRC 2006). The Central Mixedwood Natural Subregion is defined by a blend of deciduous stands dominated by aspen, aspen-white spruce forests, and stands of white spruce and jack pine on elevated terrain (NRC 2006).

The mean annual temperature of Lower Foothills is 1.8°C, with the average temperature in the warmest month being 14.7°C, and in the coldest month, it is -12.8°C(NRC 2006). The mean annual precipitation in Lower Foothills is 588.4 mm, with an average of 429.7 mm during the growing season(NRC 2006). The Lower Foothills Natural Subregion in Alberta boasts the highest diversity of forests, featuring various forest types and a wide range of tree species including aspen, balsam poplar, white birch, lodgepole pine, black spruce, white spruce, balsam fir, tamarack thrive (NRC 2006).

Site selection

There are 60 sites in total, but actually 25 of them are used for data collection. All the sites include 2 parts: the abandoned well pad and the nearby forest. All the sites must meet the following criteria (Hailey Cole personal communication):

Upland boreal - Central Mixedwood subregion
Surrounding reference condition uninterrupted by road, pipeline, etc.
Accessible via road or ~30-minute walk from access road
Well pad is clearly reclaimed and appears undisturbed post-reclamation
No readily visible disturbances within 100 meter of the well pad
Site is not flat or nearly so (max 5% incline)
No logistical issues are discovered - e.g., decommissioned or washed out road

The pictures below show several sampling sites.

Site 1

Site 5

Site 6

Site 14

Site 52

Site 59

Data Collection

First, we collected the data for plant species by using the contact-point method at these 25 locations. We collected species data information from 60 points for each well pad and reference forest. We selected species for leaf collection based on their occurrence in each plot, choosing those that were present in at least 25% of the plot's contact points (15 out of 60). From this subset, we picked species that were also present in at least 25% of all sites (6 out of 25, including well pads and reference areas). During late July and early August, we visited sites with the selected species, gathering leaves from multiple individuals. The quantity of leaves collected depended on their size, such as 30 for small-leaf species like Linnaea borealis and 10 for medium-leaf species like Aralia nudicaulis. We collected from three different sites for each species, stored them in a moist container, and refrigerated them for 24 hours.

For the recovery pattern by age, we collected the information for the well pads including the spud date, the reclamation certificate date, the final drill date and the abandoned date. Then we calculated the year difference between the spud date and the reclamation certificate date, as well as the age of the abandoned well pads at sampling time.

Processing of samples

We scanned all the leaves and their petioles before placing them into separate envelopes. Next, we dried the leaves in an oven at 70°C for 48 hours and measured the weight of the leaves and petioles individually. Besides, we used image J (Schindelin et al. 2012) to calculate the area of leaves and petioles of the scanned picture. We used the formula: Specific leaf area = leaf area/leaf mass to calculate the SLA value (Kimball et al. 2002).

Data analysis

This research will use JASP to plot the CWM SLA value for the well pad and reference forest (JASP Team 2023). Also, we will use the regression approach to analyze the abandoned well pad’s recovery pattern by age. The x-axis will be the age of the abandoned well pads at sampling time and the y-axis will be the CWM SLA values.

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