Limnological changes in a small lake stocked with grass carp

Abstract

A heavy infestation of aquatic weeds (Egeria densa and Eleocharis sphacelata) in a 1.92 ha lake (Parkinsons Lake, North Island, New Zealand) disappeared within 2 years of the introduction of Chinese grass carp (Ctenopharyngodon idella Val). The elimination of aquatic plants did not result in any significant change in dissolved oxygen, water temperature, or annual fluctuations in lake levels over the successive 2 years. Dissolved inorganic phosphorus concentrations did not increase appreciably although there was a short term rise in particulate phosphorus levels. Oxidised nitrogen fluctuations were small in the lake over the experimental period. Some reduction in water transparency occurred although chlorophyll a levels showed no overall increase. There were increases in zooplankton numbers and biomass. A large increase of ammonium nitrogen in the lake accrued 12 months after all macrophytes had been eliminated, this possibly was a result of heavy use of inshore water by cattle. © 1984 Taylor & Francis Group, LLC.