Tactic TR-10: Tundra Sodding
Tundra sodding is the transplanting of intact tundra soil and live plant materials to restore native plants in an area where vegetation and soil have been removed to recover contaminants (Fig. 105). In addition, sodding may reduce heat transfer to permafrost, allowing a disturbed site to reach a stable thermal regime more quickly. Some thermokarst should be expected, however, and transplanted sod should contain species adapted to the hydrologic regime expected in the treated area once it has stabilized. This technique is based on traditional ecological knowledge used to build ice cellar roofs in northern Alaska.
Sod can be harvested from a mine site before gravel extraction begins, or from other sites prior to development. If sod must be stored before use, maintaining adequate soil moisture is critical. The best time to harvest sod is when the soil has thawed 6–12 inches. Sod can also be harvested in winter with heavy equipment, but survival will be lower and the cut pieces will be uneven in size and more difficult to transplant.
Sod for small sites can be harvested with hand tools (i.e., knives, shovels, reciprocating saws) (Fig. 106). Mechanical harvesting is recommended for larger sites. A 3.5-ft diameter, 0.75-inch steel disc sharpened and mounted on the bucket of an excavator, similar to an asphalt cutter, has been used successfully to harvest tundra sod in Prudhoe Bay (Fig. 107). The Inupiat term “Nuna ulu” (earth knife) was coined for this rolling cutter. Vertical cuts in the sod are made to a depth of 1–2 ft in PPRendicular directions, and sod is removed with the bucket of an excavator or loader. If a cutting disc is not available, sod can be removed with a loader bucket after making vertical cuts with hand knives (Figs. 108 and 109).
Sod pieces should be as large as practicable during harvesting (Fig. 110), but pieces larger than approximately 4-ft2 are too heavy for one person to carry. If sod must be moved by hand because the site is not accessible to heavy equipment, worker safety can be maximized by using a conveyor belt similar to those used to load airplanes. Non-motorized rails (6–8 ft long) provide a simpler and more mobile alternative (Fig. 111). If the site is road-accessible, an extendable fork lift (“Zoom Boom”) can be
used to place pieces that are too heavy to move by hand (Fig. 112). Prior to the placement of sod, fertilizer (20:20:10, granular pellets or tablets) should be placed on the soil surface. The pieces of sod should be placed touching each other to maximize soil contact, making the treated area as similar as possible to undisturbed tundra.
Considerations and Limitations
- A Material Sales Contract with Alaska Department of Natural Resources Division of Mining, Land & Water is needed to harvest sod from a mine site.
- Sodding success depends on transplanting appropriate plant species that are adapted to the growing conditions after the site has stabilized.
- Using thick pieces of sod will minimize heat transfer, but the addition of backfill material before the placement of sod may still be necessary if the transplanted sod is to be at the same grade as the surrounding tundra.
- A permit may be needed from the U.S. Army Corps of Engineers if backfill is used.
- Sodding has been used effectively for moist and wet tundra, and may also work for dry tundra, but is not recommended for aquatic tundra.
- Minimize the time between harvesting and transplanting.
- Surface stability may need to be monitored after transplanting.
- Possible locations for long-term storage of sod are unused areas at a mine site, an uncontaminated reserve pit, or a gravel pad.
- A permit may be needed from the landowner before harvesting tundra sod.
Equipment, Materials, and Personnel
- 12-inch serrated knives (1 worker per tool) – to make vertical cuts.
- Cutting disc (“Nuna ulu”) and excavator or backhoe (1 operator) – to harvest sod.
- Loader (1 operator) – to pick up and load sod at harvest site.
- Flatbed trailer or truck (1 operator) – to haul sod to transplant site.
- Portable aluminum rails or motorized conveyor belts (at least 2 operators) – to move sod beneath pipelines or away from road.