Copper as an algicide in a tropical reservoir

Abstract

Copper sulphate, added at the surface, was retained in the epilimnion of a stratified tropical reservoir. For 12 days after the addition, most of the copper was associated with the soluble fraction (MW > 50,000). Later the low molecular weight fraction (MW < 50,000) dominated and persisted for more than 19 days. There was an immediate decline in algal density after copper addition, followed by an increase in numbers of the more copper-tolerant chlorophyte species. Zooplankton (and other aquatic fauna) were also affected by the copper treatment. Two forms of the rotifer Brachionus calyciflorous recovered first, followed by Hexarthra mira, Copepoda and Cladocera. Growth of cyanobacteria was suppressed in the short term, but any possible long term effects of copper were masked by flow induced rapid destratification which interrupted and re-set algal succession. It is concluded that copper treatment is not an effective control of cyanobacterial growth under the seasonal flow regime to which the Solomon Dam is subjected.