Chapter 4 – Soil Integrity and Revegetation Protocol

Principal Investigators: Mike Rutherford, Keith Egger, Hugues Massicotte, Joselito Arocena


Soils are naturally occurring materials resulting from interactions between parent geological material, biota, climate, topography and time. Geological materials are minerals from rocks and sediments that form the bulk (i.e., 90–99% by mass) of inorganic soil while biota or organic matter comprises both the living and decomposed organic materials (i.e., carbon, hydrogen, oxygen, nitrogen-containing materials). Soil properties continually change with time because matter (e.g., minerals, organic matter and water) and energy are constantly subject to four basic soil-forming processes of addition, loss, transformation and translocation within and outside of the soil. The intensity of each soil process is regulated by rainfall and temperature (i.e., climate) and the location of soil on the landscape (i.e., slope or topography). Soils are dynamic and any significant additions or losses (e.g., deposition of new minerals by flooding, turn over and exposition of underlying rocks) of geological materials reset soil formation and alter its ecosystem functions. Thus, soils are sensitive to effects in the environment including anthropogenic activities such as pipeline construction.

Healthy soil delivers many ecosystem functions, including medium for plant growth, habitat for organisms, natural filtering of water, recycling of nutrients, sources of pharmaceutical ingredients and, in many places, cultural values as well (Brady and Weil 2008). Any measure of soil integrity should center on the ability of soil to carry out its ecosystem functions, and it is the microbial community that is integral to soil’s ability to carry out these functions. Fungi in soil decompose organic matter and form mycorrhizal associations that act as the liaison between plant roots and soil nutrients. Soil bacterial communities cycle nutrients between forms that differ in their availability to the living biomass of the soil. One of the most important functions is nitrogen fixation, which fixes atmospheric nitrogen into a form that can be taken up by plants. Any measure of soil health must include assessment of the taxonomic and functional diversity of the soil microbial community.

Developing microbial diversity and establishment of pioneer native plant species are initial indicators of a properly functioning soil system. Pioneer plant species deposit roots, leaves, twigs and other plant debris and their subsequent decomposition enriches the organic matter content of soils (e.g., Ottenhof et al. 2007). Recruitment of native species will then follow the natural vegetation succession in steady state with the climatic and edaphic factors in the environment. The continued active biological processes — both plant roots and organisms — will effectively mix mineral and organic materials in soils to generate optimal soil granular structure for efficient flow of air and water within the soil (Young and Crawford 2004). The formation of granular structure was observed under pioneer plant species established in new soil parent materials resulting from intensive mining activities in southeast Spain (e.g., Zanuzzi et al. 2009; Arocena et al. 2012).

A healthy soil should have optimal soil structure (e.g., granular) to continuously provide the plants and microorganism with sufficient supply of water and oxygen. Soil structure is assessed through several physical properties including bulk density, water-holding capacity, soil strength, hydraulic conductivity, aggregate stability (e.g., Burt 2004) and fabric analysis (Stoops 2003).

The current practice for pipeline placement is to strip off the upper 20 cm of duff or mineral horizons and place this in a pile, or continuous row, along the Right-of-way (RoW); this is considered “topsoil”. Then, the underlying mineral horizons are removed and placed in another pile; this can be considered “subsoil”. Once the pipe has been placed in the ground, the subsoil is first placed in the trench, followed by the topsoil. Although root debris might serve as an inoculum or seed of soil organisms for reclamation, it is our understanding that it is not acceptable to include debris in the trench directly over the pipe during backfilling operations. That said, fine root fragments will be present in the duff (i.e., LFH) and topsoil horizons; these surface layers are saved and replaced during reclamation activities (i.e., normal practice). These horizons should contain sufficient microbial inoculum for reclamation and restoration activities. The post-construction replacement of coarse-woody debris (e.g., fallen logs; decomposing vegetation) on the soil surface has also shown to serve as an effective biological inoculum in other reclamation studies.

By using environmental DNA (eDNA), a technique that is sensitive enough to detect changes due to disturbance, we had the potential to monitor the reestablishment of soil ecosystem function throughout the restoration process. We first needed to assess the ability of eDNA methods, however, to detect different types of perturbations of the soil (i.e., to see how specific disturbances affect the soil community and its function). Because there is a lot of environmental noise around the eDNA ‘signal’ associated with various aspects of soil function, we conducted a series of experiments — the microcosm experiments — to determine bacterial and fungal community function with soils that have been manipulated to simulate disturbance by pipeline installation. Given the taxonomic richness of soil microbial communities, we used next-generation sequencing methods to broadly profile microbial diversity over 12 months. In addition, we measured enzymes involved in carbon degradation, available soil nutrient (e.g., total N, P) and the abundance of genes involved in biochemical cycling (e.g., N mineralization) and soil physical properties (bulk density, aggregate stability, hydraulic conductivity and fabric analysis such as soil structure) as measures of soil ecosystem function.

The Soil Integrity and Revegetation Protocol was designed to monitor the ecosystem functions of soils through the phases of construction to operation of the pipeline. Specifically, the research team investigated microbial community composition, key soil properties and processes (i.e., chemical, physical), both of which are indicative of soil health. The studies described, and data presented, in this report correspond to biological, chemical and physical characterization of soils from interior region near Summit Lake, BC and coastal region near Kitimat. Information from this study can contribute to the scientific literature on reclamation and restoration ecology of linear projects in general, on management policy of those sites, and on the development of the pipeline project long-term restoration plan in the future. Because of the early termination of the BMAP program, we were not able to address any of the restoration aspects of the Protocol, either during or after construction.