Abstract

The Arctic Canada beluga and Steller sea lion pools at the Vancouver Aquarium Marine Science Centre have had a history of unwanted algal growth. This growth contains a complex community of algae that, if left, over time directly affects pool water quality, application of treatment, and aesthetics.

These two pool systems are different in size and life support design. Arctic Canada beluga pool is a 13-year-old, 1,950,000-litre, semi-closed natural seawater system with diatomaceous earth filters, ozone and chlorine. The five-month-old Steller sea lion pools combine to form a 121,000-litre semi-closed natural seawater system with high-pressure sand filters and ozone.

Traditional algal control approaches (ozonation, chlorination, diver pool-scrubbings, and pool draining) have failed to resolve the problem. One of the most accepted approaches is to apply varying daily doses of chlorine and/or ozone to the pool systems. However, over time, the resultant nutrient loading in the water column encourages increased algal growth. This cyclic process not only increases nutrient loads within the water column, but also creates a eutrophic environment, destabilizing water quality control.

A new approach was adopted to regulate this algal growth by reducing levels of the primary nutrient, phosphate. This was accomplished by adding small doses of a lanthanum chloride suspension to each of the life support system filters. This has been effective with either diatomaceous earth or high-pressure sand filters. A mathematical model was derived for each pool's system to predict the daily flux in orthophosphate (reactive phosphate) bioloading and the dosage of lanthanum chloride required to remove excess dissolved phosphate. Results demonstrated a reduction in orthophosphate concentrations (70 to 88 percent), algal pool substrate growth, turbidity (~45 to 74 percent), and chlorine consumption for the beluga pool system (47 percent). Weekly physical pool cleaning and life support operational costs were also reduced by as much as 50 percent.