226Ra is weathered from waste rock and fluxing from sediments, which have been deposited downstream from the former Rabbit Lake ore deposit in the Link Lake drainage basin in northern Saskatchewan. Lower Link Lake, below the effluent discharge point is populated with Nitella flexilis, an algal species of the Characeae with a high affinity for 226Ra. The use algae to contain 226Ra within the drainage basin is evaluated, through the establishment of an algal population in Upper Link Lake. This lake is void of algae and located upstream from the effluent discharge point. As concentrations of 226Ra in the algal biomass were determined as high as 60 Bq/g dry weight, it could be expected that a healthy algal population growing in this location would reduce226Ra load from the sediments of former Rabbit Lake to the water in
Upper Link Lake.
In 1989, 12 tonnes (fresh weight) of Nitella were transplanted to Upper Link Lake. The development of the algal population was monitored over five growing seasons. After five years the algal biomass has increased 13 times since transplanting. The growth dynamics of the algal populations suggest, that during one growing season, due to continued growth and decay the population is replaced once. The standing biomass of Nitella contained a total of 1.0 x 10° Bq of 226Ra. This is based on estimates of total biomass present in the lake and its concentrations. Load calculations indicate that the algal population retains about 3.9 x 10° Bq of 226Ra in the biomass and in the sediment. This quantity represents about 65% of the annual loading arriving at the discharge point. The algal populations growing over the former
Rabbit Lake sediments reduce the 226Ra flux from this area into Upper Link Lake water. Monitoring data at the discharge point, show a reduction in the seasonal fluctuations of 226Ra concentrations after 5 years of growth. These reductions are evidence of the effectiveness of the algae in retaining 226Ra in the drainage basin.