British Columbia Mine Reclamation Symposium

Faro Mine Complex revegetation activities Carter, L.; Tobler, P. 2014

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FARO MINE COMPLEX REVEGETATION ACTIVITIES   L. Carter, B.Sc., M.R.E.M. P. Tobler, R.P.Bio., CPESC   EDI Environmental Dynamics Inc. (EDI) 2195 – 2ND Avenue,  Whitehorse, YT  Y1A 3T8  ABSTRACT  In preparation for remediation and closure of the Faro Mine Complex (FMC) in central Yukon, significant work has been completed to develop and test revegetation methods at the mine site. Design and implementation of various revegetation field trials and strategies has been proceeding since 2007. This paper focuses on revegetation efforts and subsequent monitoring at two FMC sites: the Grum Overburden slope and Grum Sulphide Cell (GSC).  Grum Overburden slope revegetation trials cover an area of approximately two hectares with surficial soil characterization similar to material to be used as a reclamation cover for the entire FMC. Different grass seed mixes were applied with and without fertilizer, and woody species (alder, willow, and poplar) were planted in the seeded plots. Five years of monitoring has demonstrated that revegetation success primarily depended on fertilization, while site preparation method heavily influenced erosion protection.  Revegetation and site preparation at the 26 ha GSC was intended to provide ground cover for erosion protection and facilitate development of a long-term, self-sustaining ecological system integrated with the mine surroundings. Building on results from the Grum Overburden site, the 2012 revegetation prescriptions included hydroseeding, fertilization, planting of woody species, and testing of fertilization and hydration teabag-like packs. Results from the 2013 and 2014 monitoring programs provided preliminary insight on the success of the revegetation works at the GSC site.   Collectively, these sites signify many of the reclamation challenges faced by development projects across northern Canada, including a short growing season, harsh climate, and nutrient poor soils. The need to address multiple objectives across various time scales provides many research opportunities.  Key Words:  Fertilizer; nurse and native seed; site preparation; hydroseeding; northern mining   INTRODUCTION  Yukon Government - Assessment and Abandoned Mines (YG-AAM) branch is responsible for planning for remediation and closure of the Faro Mine Complex (FMC), a large abandoned lead, zinc, silver and gold mine site in central Yukon.  In preparation for closure, research has been conducted to test revegetation methods at the mine site. The short growing season, nutrient poor soils and the physical properties of the soils all combine to make establishment of vegetation at the FMC challenging. Therefore, establishing vegetation in FMC soils requires planning, care, and maintenance to ensure revegetation success. Revegetation must advance quickly to achieve the short-term goals of mitigating run-off (e.g. reducing run-off velocity) and reducing soil erosion but also must set the stage for natural succession trajectories.    Revegetation activities and trials have been conducted by EDI Environmental Dynamics Inc. (EDI) at two sites at the FMC: the Grum Overburden site and the Grum Sulphide Cell (GSC). Grum Overburden trials (~2 ha; 2009) were designed to identify the most effective combination of surface treatments and revegetation options to mitigate run-off and slope erosion. The GSC revegetation activities (~26 ha; 2012) were conducted using knowledge gained from outcomes at the Grum Overburden trials. Additional variation/experimentation was included to refine, evaluate, and provide further direction for future revegetation practices at the FMC.   This paper provides an overview of revegetation activities conducted and results and observations from the Grum Overburden trials and GSC revegetation treatments implemented in 2009 and 2012, respectively.    METHODOLOGY  Grum Overburden Trials The Grum Overburden site was selected as a test site because surficial soil characterization and slope were considered to be representative of materials/topography intended for final cover during reclamation of the FMC. At an average altitude of 1,285 m, the site is approximately 260 m wide with a 70 m long slope and a gradient of about 3:1. The following objectives were addressed in the Grum Overburden trials:  Determine vegetative cover for various grass seed mixes (with and without fertilizer);  Evaluate erosion protection potential provided by prescribed application rates of grass mixes;  Evaluate progress of inter-planting grass mixes with woody species using different methods/species;  Evaluate planting and propagation methods and site suitability for large-scale implementation; and   Evaluate efficacy of physical surface treatment options for erosion protection and vegetation establishment.  In a randomized block design, different grass seed mixes were applied with and without fertilizer, and woody species (alder, willow, and poplar) were inter-planted in the seeded plots. All test plots were established in the fall of 2009 and the following variables were included in the revegetation trials:  Three grass seed mixes (agronomic, native, and nurse and native);  Three woody plant treatments (horizontal and vertical willow and poplar stakes and alder seedlings), including some seeding of spruce and dwarf birch collected at site;   Two fertilizer treatments: unfertilized and fertilized (8-38-15), 400 kg/ha and 200 kg/ha for initial year (2009) and first growing season (2010), respectively; and  Three soil surface treatments (micro-rill, planar, and rough-and-loose).                                               During monitoring from 2010 to 2013, percent vegetation cover was estimated visually in each plot. In 2011 to 2013, percent cover was visually estimated using a rectangular quadrat (0.5 m²), six subsamples per plot, and calculating average percent cover.  Table 1 - Summary of seed mix and application rates Seed Mix and Application Rate Seeds by Weight Agronomic                (40 kg/ha)  Red Fescue (Arctared)    15% Meadow Foxtail (Common)   11% Kentucky Bluegrass (Nugget)   5% Slender Wheatgrass (Adanac)  49% Alsike clover (Common)                 20% Native                       (29 kg/ha)  Slender Wheatgrass    10% Northern (Rocky Mountain) Fescue  20% Glaucous Bluegrass    37% Tufted Hairgrass                  33% Nurse and Native      (33.5 kg/ha)  Slender Wheatgrass    14% Northern (Rocky Mountain) fescue               27% Glaucous Bluegrass    58% Barley     0.5%  All live stems of poplar, willow, alder, and other woody plants were also counted in each plot. Live stems are defined as any shoot, or cluster of shoots, emerging independently of other shoots. Monitoring results continue to indicate that horizontal staking of willow/poplar produces more stems than vertical staking, over time. Horizontal staking is also less labour intensive than vertical staking for the number of stems produced.  Alder planting of plugs (from seed collected onsite) appeared to be the most successful method of establishing woody stems.     Grum Sulphide Cell Revegetation Key treatments in the 2012 GSC revegetation program were guided by outcomes from the Grum Overburden trials and included the following treatments:  Nurse and native seed mix;   Fertilizer included in hydroseeding;  Surface treatment similar to rough and loose, ripping across the slope (more cost effective and achieved similar results);   Nursery grown plugs from local plant materials; and,  Horizontally staked willow and balsam poplar cuttings.  YG-AAM was responsible for overseeing and implementing the soil surface preparation. Prior to planting, a D7 Caterpillar dozer using three rippers on the back excavated furrows of 10 – 30 cm depth perpendicular to the slope. Soil surface preparation was completed between July 9 and August 8, 2012.   TerraStar Solutions Inc., a B.C. based company, applied the hydroseed from August 11 – 13, 2012. A native seed mix was used with annual rye grass as a nurse crop. The seed mix consisted of the following grasses (% by weight):    54.1% Slender Wheatgrass       17.1% Northern (Rocky Mountain) Fescue   0.5% Glaucous Bluegrass      7.1% Tufted Hairgrass      21.2% Annual Rye Grass      The seed was applied at a rate of 35 kg/ha over the 26 ha GSC. Additives to the hydroseed mix included fertilizer (18-18-18; 400 kg/ha) and mulch/tackifier mix (Hydrostraw® Guar Plus).   Treatments Native woody vegetation plugs and cuttings were planted at the GSC not only for long-term erosion control and site stabilization, but also to initiate restoration of the site to a more natural state, along local successional trajectories. More than 14 ha of the 26 ha GSC were planted with woody species in either experimental plots or general planting plots. Specific treatments are as follows:  Plugs Only (P plots) Woody vegetation plugs (willow, balsam poplar, birch, and alder) were planted without any amendments. The ‘plugs only’ treatment acts as a control for the treatments involving teabags. The treatment can also be compared to treatments that include horizontal staking.  Staking (S Plots) Balsam poplar and willow species stakes were collected at the FMC, near the GSC, within days of planting. Stakes were cut in September as plants were going into dormancy, bundled, and soaked in a ponded area east of the GSC one to two days prior to planting. Cut to ~45 cm in length, stakes were laid in shallow trenches dug perpendicular to the slope, and backfilled to approximately 10 – 20 cm below the ground surface.    Plugs and Staking (PS plots) Planting stakes with plugs supplemented the plug numbers and potentially increases the number of resultant stems in the plot; thus, increasing density of woody vegetation. Stakes were planted alternately with plugs, both across and with the slope.  Fertilizer-packs (Pf plots) Chilcotin blend teabag packs (17-5-7) are used for disturbed planting sites with low levels of organic matter. One 10-gram teabag was placed in a separate hole, immediately upslope of the plug, about 5 cm below the soil surface. Placing the Chilcotin teabag in the separate hole prevents the fertilizer from burning the plug roots. The Chilcotin blend teabag releases the following ingredients over twelve months: total nitrogen 17%; available phosphate 5.0%; soluble potash 7.0%; magnesium 1.2%; sulfur 10.4%; humic acid (leonardite-derived) 4.5%; kelp extract (Ascophyllum nodosum) 4.0%; co-polymer of acrylamide 4.0% (intended to help retain moisture during periods of reduced soil moisture).    Hydration-packs (Ph plots) Hydration-pack teabags (16-8-5) are similar to the Chilcotin-pack fertilizer, but they also contain more moisture-retaining polymer to assist seedlings with establishment during times of moisture stress. One 10-gram hydration-pack teabag was placed in the planting hole with the plug. The hydration-pack includes the following ingredients: total nitrogen 16.0%; available phosphate 8.0%; soluble potash 5.0%; sulphur 6.6%; co-polymers of acrylamide 19.0%.  Genesis-pack (Phf plots) One 40-gram Genesis-pack was placed in the planting hole and broken open prior to planting the plug. Genesis-packs release the following ingredients over twelve months: total nitrogen 8.00%; available phosphoric acid 5.00%; soluble potash 5.00%; sulfur 2.00%; boron 0.037%; humic acid (leonardite-derived) 7.5%; kelp meal (Ascophyllum nodosum) 5.0%; composted vegetative matter 30%.  General Shrub/Tree Planting Plots In addition to the experimental plots, larger plots were set up in areas to add woody plant material treatments on a larger scale. The following treatments were implemented:   S2 Plots: poplar and willow stakes were buried at a spacing of 2.5 m between centre points of stakes.   Pr Plots: This area was planted with plugs that remained after all experimental plots were planted. Approximately 3,354 plugs were planted on the uppermost slope in a random arrangement. Some areas were planted at very high densities to simulate a more natural setting; other areas were planted with equidistance.                                                                  RESULTS AND DISCUSSION  Grum Overburden Trials Results of the 2013 Grum Overburden revegetation trial monitoring found that fertilizer application is necessary to establish herbaceous vegetation at the FMC. Unfertilized plots had minimal ground cover (less than 5%); vegetative cover on fertilized plots ranged from 5 to 24% in 2013. Results from 2013 indicated that the agronomic seed mix resulted in higher vegetative cover in two of three fertilized surface treatments and higher cover from the native seed mix in the third fertilized surface treatment. The 2013 results indicated that the native grasses could establish as successfully as other seed mixes, but needed more time to develop.  Regarding woody plant survival, it is unclear whether fertilizer application influenced success of willow/poplar stakes; however, alder establishment appeared to be negatively correlated with fertilizer application. For example, stem counts of alder in fertilized plots were an average of 50% lower than in unfertilized plots. This divergence may be attributed to competitive effects between alder and the grass cover. Results also showed consistently higher stem counts for horizontal staking in contrast to vertical staking.  Of all the surface treatments at the Grum overburden, the most effective at controlling erosion due to run-off was the rough-and-loose surface treatment, even in the areas with minimal vegetative cover. This treatment created micro-sites (depressions) providing areas for pooling water, ideal for germinating seeds; consequently, run-off was prevented (i.e. enhancing infiltration). The depression micro-sites appeared to be areas of competition between herbaceous vegetation and woody plants but most of the grass has now died off. Very little growth was observed in the rough-and-loose treatment on the upper parts of the hummocks.   The amount of vegetation cover established during these trials was not at a level that will meet the objectives of controlling erosion and stabilizing slopes alone. Nonetheless, the Grum Overburden trial results indicate that the rough-and-loose treatment with seeding, horizontal staking and fertilization can be key parts of a successful revegetation and erosion control prescriptions.  Grum Sulphide Cell Monitoring at the GSC was conducted in mid-August 2013 and 2014. Data were gathered to determine revegetation success of herbaceous and woody species; site stability. The following activities took place as components of the GSC monitoring program.  Soil sampling;  Estimation of herbaceous vegetation cover;   Assessment of woody species establishment (stems per hectare, health and vigour, height);  Photo point monitoring;  Overall grass cover was not as high as expected, in 2013, likely due to a relatively dry spring. In 2014, overall cover from herbaceous species increased from 7.7% in 2013 to 20.7%. Cover was highest in the deeper cross-slope furrows of the slope where moisture appeared to be highest.  Vegetative cover is still below a level to control erosion and stabilize slopes alone; however, combined with the site preparation, site erosion was minimal.    In 2013, all treatments of woody species planting resulted in higher densities than unplanted areas. Treatments with staking seemed to provide the best overall results with the highest average survival rate, better health and vigour ratings, and greater than average heights. Teabag amendments appeared to increase height and vigour of grass growing around woody species plug, potentially reducing survival of woody species due to competition.   In 2014, moss was commonly observed across the GSC and provided substantial cover in some areas to assist in soil/slope stabilization. Considerable natural regeneration of woody species was also observed and recorded throughout the site and appeared to be more prevalent in the areas of mossy growth. Woody stem planting appears to have been moderately successful; on-going data analysis will determine the success of individual planting treatments. Overall, the site preparation combined with the seeding/fertilizing prescription appeared to be effective in controlling erosion, while still allowing for the natural establishment of native mosses, forbs and woody stems.     


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