Lake Paranoá, management approaches for a tropical urban reservoir

Summary

Lake Paranoá was created in 1960 both for recreation and as the design focus for the master plan for the new Brazilian capital, Brasília. This 40km² lake was doomed to be culturally eutrophied from its inception. Riverine forests and residential dwellings were left relatively undisturbed during reservoir creation. Major nutrient loading to the lake currently comes from raw to poorly treated sewage from a portion of the city of Brasília (> 600,000 people in its inner part) attended by two WWTP, and residential and agricultural runoff from the large watershed (> 1,000km²). Past lake management has been limited, in addition to the WWTP operation, to application of copper sulfate either immediately prior or during the height of algal blooms, but this practice has been only marginally successful. Expansion of the existing two sewage treatment plants to employ tertiary treatment has been partially completed since January 1992 to reduce watershed nutrient loading, but an inlake management plan is still lacking. While past lake management techniques have been developed primarily for the temperate zone, many show little merit for management of subtropical and tropical lakes. Applicability of temperate techniques and the experience of managing eutrophication problems in subtropical Florida lakes were discussed as alternatives for Lake Paranoá.