Indicators of soil degradation on a pipeline footprint, Alberta, Canada

Abstract

Monitoring data are needed to assess the effectiveness of soil conservation measures applied on agricultural lands during pipeline construction. Soil data were collected on the footprint of a pipeline constructed in 2016–2017 in west-central Alberta. Construction practices were expected to mitigate for topsoil loss and admixture, compaction, and erosion. Sites were established on the footprint and on adjacent reference areas on 24 parcels. Field measurements included point-sample results for horizon thickness, bulk density and soil erosion-rate including suspended sediment in runoff, and laboratory measurements from composite samples including pH, total organic carbon and texture. Admixture rate was estimated from change in percentage clay. Topsoil thickness was more variable on the reclaimed footprint than references. Topsoil pH was about 0.4 units higher and percent clay was 6.2% higher on the footprint than references but total organic carbon was not different. Admixture rates in the topsoil at six parcels ranged from 0.18 to 0.60. Penetration resistance on four measured aggregate size classes of subsoil was significantly higher on the footprint than reference. Subsoil loss from rill erosion ranged from 0.1 to 8.1 cm in the first year after construction when little vegetation was present and sediment concentrations in runoff sometimes exceeded 10 g L−1. Mitigations applied to limit soil degradation were less effective than expected. The use of quantitative techniques to monitor soil reclamation outcomes will improve the credibility of results but add costs to the process. Similar monitoring is needed to determine the effectiveness of current reclamation practices.