Individual study: Establishment of a cover of tundra grasses on Kimberlite mine tailings through nutrient additon, structure enhancement and seed-sowing at Ekati Diamond Mine, Northwest Territories, Canada
Reid N.B. & Naeth M.A. (2005) Establishment of a vegetation cover on tundra Kimberlite mine tailings: 2. A field study. Restoration Ecology, 13, 602-608
Kimberlite tailings are the primary waste product of diamond mine operations in northern North America. Their coarse texture (80% sand), lack of organic matter and nutrients, and a serpentine state are the principal reasons for being inhospitable to plant colonisation. At a diamond mine in the Canadian subarctic, studies were undertaken aimed at establishing a permanent tundra vegetation cover on dewatered tailings. The study focussed on stabilization of the kimberlite tailings with vegetation, focusing on kimberlite substrate improvement by addition of structure-improving and nutrient-providing materials.
Study site: The study was undertaken at Ekati Diamond Mine located in a heath tundra ecosystem, approximately 300 km north of Yellowknife, Northwest Territories, Canada. Beginning October 1999, kimberlite tailings were pumped from the mine and deposited into the Long Lake Containment Facility (LLCF). By spring 2000, tailings at the most northerly end had consolidated but without a surface cover, had a high erosive potential and stabilization was considered necessary.
The area has an annual precipitation of around 160 mm (mostly falling between July and October). Temperatures range between −40 and 25°C, with only 4 months having average temperatures above freezing.
Experimental design: Nine structure-improving (peat moss, lake sediment, and sewage sludge) and nutrient-providing (fertilizer, rock phosphate, calcium carbonate, and gypsum) amendments were tested to ameliorate the conditions and facilitate plant establishment. Seven native grass species, polar grass Arctagrostis latifolia, bluejoint Calamagrostis canadensis, tundra bluegrass Poa glauca, glacier alpine bluegrass Poa alpina, Bering's tufted hairgrass Deschampsia beringensis, tufted hairgrass Deschampsia caespitosa and red fescue Festuca rubra were evaluated to measure amendment success and suitability for large-scale reclamation.
In August 2000 experimental plots were established on the tailings. Small plots (2 × 2 m) were used to investigate amendment performance, species trial plots (2 × 5 m) to investigate species tolerances to amendments. Plots were randomly assigned treatments. An unamended seeded treatment was also included.
Structure-improving amendments: Peat was applied to 4 cm depth, lake sediment 10 cm and sewage sludge 10 cm. Application rates were based on substrate limitations and feasible quantities for large-scale field application. Materials were hand-raked level, and incorporated into the tailings with a rototiller, creating a 28-cm-deep tilled surface. Treatment areas not receiving structure-improving amendments were also tilled to 28 cm.
Nutrient-providing amendments These were applied by weight, spread over each plot with a drop spreader and rototilled to 17-cm depth. Inorganic fertilizer (by weight 10% N, 34% P, 10% K, and 5% S) was applied at 280 kg/ha, gypsum at 2,173 kg/ha, rock phosphate at 2,080 kg/ha, and calcium carbonate at 1,667 kg/ha. Plots were then seeded with a mix of equal numbers of seeds of each of the grass species.
Small plots were broadcast seeded at 40 kg/ha, combined with fertilizer, lightly hand-raked in and covered with a Curlex (American Excelsior Company, Arlington, TX, U.S.A.) erosion blanket to prevent surface erosion and amendment contamination. In the species trial plots, individual species were hand-seeded at a 1- to 2-cm depth in randomly assigned rows (three replicate rows of each species). After seeding, fertilizer was broadcast over each plot at 280 kg/ha.
Soil analysis: Soil was sampled randomly in the small plots in 2000 and 2001. Each sample was analyzed for available nutrients, pH, cations, total carbon and total inorganic carbon.
Vegetation measurements: A 1 × 1–m area in the centre of the small plots was randomly sampled three times using a 20 × 50–cm quadrat. In the species trial plots, random positions along each seeded row were selected with a 20 × 50–cm quadrat. The first assessment was completed at the end of August 2000 and the second in August 2001. Treatment effectiveness was based on: plant height (average plant height of all individuals rooted in the quadrat); plant development (tillers and flowers of individuals within each quadrat); vegetation cover (estimated as the percentage of each quadrat covered by vegetation); and shoot dry biomass (measured in second year only).
With the addition of structure-improving and nutrient-providing amendments, plant growth on these kimberlite tailings under field conditions was significantly improved over unamended tailings material. Tailings properties, including cation exchange capacity, organic carbon, and macronutrient availability, were also improved with amendment addition. Peat moss performed well, increasing water- and nutrient-holding capacities and overall tailings structure. Sewage sludge was the most effective nutrient amendment and combined with peat moss produced the most favorable plant responses.
Lake sediment showed promising initial plant growth but in only two seasons started to show a negative tailings property response, and subsequent reduced plant growth. This suggest that lake sediment will not sustain acceptable plant growth over time.
Conclusions: Plant growth under field conditions was most favorable when both structure and nutrient limitations of the Ekati kimberlite tailings were improved. The sewage-peat moss combination outperformed all other amendment combinations in almost all quantified parameters. Calcium addition had no significant effect on plant growth but there could be longer-term benefits not identified in this 2-year study. Festuca rubra and Deschampsia beringensis produced the best plant growth responses, although all species, except Arctagrostis latifolia, performed acceptably well and are recommended for seeding of kimberlite tailings.
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