Abstract. Cracks in dry saline montmorillonitic clay allow the soil to wet rapidly when flooded with negligible redistribution of salts. Once closed the only effective pathways remaining for the movement of leaching water are old root channels and faunal burrows. However, their effectiveness in conducting water and for leaching is severely restricted because of the lack of horizontal connections between them. Restructuring of clay can introduce sufficient permeability to a depth of about 0.7 to 0.8 m to allow salt to be leached provided that the soil's initial moisture content is sufficiently large to prevent disintegration upon wetting (about 24%) and that the clay is not allowed to become unsaturated during the leaching.
Abstract. Nickel tailings were deposited between 1978 and 1988 in Falcon bridge's New Tailings Area located northeast of Sudbury, Ontario, Canada. In 1996, construction of a new dam and dredging split the site into an Upper Terrace (56 ha) and a Lower Terrace (30 ha) to facilitate flooding. Water covers minimize the oxidation of acid generating tailings but some oxidation and release of metals may still occur. The effectiveness of a water cover could be improved by establishing aquatic plants to control tailings resuspension, remove metals from the water column and develop an organic layer to consume oxygen and support sulphate-reducing bacteria. Research was conducted from 1997 to 1999 to evaluate establishing submerged aquatic plants in the New Tailings Area.In 1998, six submerged aquatic species were introduced into the site using 540 transplant 'sandwiches' constructed by placing shoot biomass between layers of wire mesh. In 1999, aquatic plant distribution was assessed along transects every I 00 m across the Lower Terrace. In addition, aboveground biomass was determined for each species using a 0.25 m 2 quadrat placed every IO m along each transect.In the Lower Terrace, due to natural invasion, 189 of the 226 sites sampled in 1999 contained aquatic plants. Of the seven species identified, Potamogeton pusil/us was found at 113 sites (mean cover 49.9% and mean biomass 60.8 g DW/m2 ) and Chara spp., at 79 sites (mean cover 18.3% and mean biomass 20.6 g DW/m'). Aquatic plant growth was limited in water less than 0.5 m deep due to wave action and in water greater than 2.0 m deep from suspended solids in the water column that restricted light penetration. In the transplant trials, Potamogeton richardsonii was successfully established, but growth of the other species was limited due to the transplant method or site conditions.
Abstract. Nickel tailings were deposited between 1978 and 1988 in Falconbridge's New Tailings Area located northeast of Sudbury, Ontario, Canada. In 1996, construction of a new dam and dredging split the site into an Upper Terrace (56 ha) and a Lower Terrace (30 ha) to facilitate flooding. Water covers minimize the oxidation of acid generating tailings but some oxidation and release of metals may still occur. The effectiveness of a water cover could be improved with aquatic plant establishment to control tailings resuspension, remove metals from the water column and develop an organic layer to consume oxygen and support sulphate-reducing bacteria.In the New Tailings area the natural development and changes in the aquatic plant community over the five years since flooding was monitored. In 1999 and 2001 aquatic plant distribution was assessed at 121 plots along 5 transects across the Lower Terrace. Every 10 m along each transect a 0.25 m 2 quadrat was established from which aboveground biomass was harvested and samples were analyzed for nutrients.In the Lower Terrace, Potamogeton pusillus and Chara were the dominant aquatic species. In 1999, 88 plots contained aquatic plants, which increased to 113 by 2001. Over the same period, mean biomass increased from 40.2 to 103.0 g DW/m 2 . Biomass decreased, however, at 22 sites from 166.3 g DW/m 2 in 1999 to 74.6 2 g DW/m 2 in 2001. Potamogeton pusillus tissue nitrogen and phosphorus concentrations decreased from 2.18 % and 0.20 % to 1.43 % and 0.12 % with 1.3 % and 0.13% being the critical concentrations that indicate potential deficiencies. The nitrogen phosphorus ratio is typically 7 but in the Lower Terrace is 12.9 indicating that phosphorus is more limiting than nitrogen.
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