The objective of this report is to show results from the field study comparing vegetation and soil properties (i.e., indicators of recovery) at certified reclaimed wellsites with adjacent reference locations (i.e., sites without industrial disturbance) across a range of age classes post certification (~10, 20, and 30 yrs) in native grasslands in the Dry Mixedgrass Natural Subregion.
We measured vegetation (percent cover by species and strata, species richness, Shannon diversity, and Sørensen’s similarity index) and soil (bulk density, electrical conductivity, pH, total nitrogen (TN), total organic carbon (TOC), TOC:TN) indicators for up to four soil depths (0-15 cm, 15-30 cm, 30-60 cm, and 60-100 cm), comparing them among 18 wellsites and adjacent reference locations. For each indicator we conducted two-way ANOVAs to test for differences among location (wellsite vs reference) and age class (10, 20, 30 yrs post certification). We also used non-metric multidimensional scaling (NMS) ordination and a multi-response permutation procedure to explore plant community composition patterns among sites.
Vegetation analyses highlighted differences among the wellsite and reference locations, including lower species richness, Shannon diversity, and total vegetation cover on the wellsites compared with the reference sites, regardless of age class. In contrast, wellsites had significantly higher cover of non-native vegetation compared with the reference sites across age classes. Several vegetation indicators only showed significant differences for the wellsite and reference locations in some age classes (i.e., forb (including non-native), graminoid (including non-native), clubmoss, and lichen cover, and Sørensen’s similarity index). There were no significant differences among wellsite and reference sites for shrub cover. The plant community composition ordination illustrated separation of the wellsite and reference
locations among age classes, with the 10-yr wellsite community composition more similar to the composition of the reference sites compared with the 20- and 30-yr age classes. These differences among site locations and age classes were primarily correlated with the cover of plant species (e.g., higher cover of crested wheatgrass in 20- and 30-yr wellsites).
For all soil indicators there were significant differences among the wellsite and reference locations for at least one soil depth. Bulk density (only measured for the two shallowest depths) and electrical conductivity (all four depths measured) values were higher in the wellsites for all sampled depths. Compared with reference sites, wellsite pH was significantly higher at 15-30 cm depth and significantly lower at 60-100 cm depth. Total nitrogen levels were significantly higher in the reference sites for the two
shallowest depths and total organic carbon levels were significantly higher for the reference sites in the most shallow depth (0-15 cm). The ratio of total organic carbon: total nitrogen was significantly higher on wellsites in the deepest depth (60-100 cm).
Overall, data show that for many vegetation and soil indicators, wellsite development impacts are long lasting and may remain for 30 years or more after reclamation. This lack of recovery was evident across the different age classes, although there was some evidence for plant communities in the youngest age class being more similar to reference locations compared with the older age classes post-certification. This suggests that newer conservation and reclamation practices may have less impact on native prairie plant communities than older practices did. We do not yet know how long it will take for these reclaimed wellsites to recover, and thus longer-term monitoring is needed to evaluate recovery trajectories. These study findings provide baseline information on differences between wellsite and reference locations that
will aid in the development of an integrated, scientifically robust and financially sustainable monitoring program to enable the assessment of ecological recovery of physical, chemical, and biological indicators at certified reclaimed wellsites across Alberta.