AQAUTIC PLANT ESTABLISHMENT ON NICKEL TAILINGS FIVE YEARS AFTER FLOODING 1

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.