Effects of hydro-electrically induced water level fluctuations on benthic communities in Lake Hawea, New Zealand

Artificially inducedlake level fluctuations influence benthic communities in numerous lakes, but their effects are relatively poorly understood. Littoral communities were described from three habitat types in two oligotrophic lakes in New Zealand, one subject to a natural hydrological regime with limited lake level fluctuations, the other subject to >5 m fluctuations as a result of hydro-electric management. The fluctuated lake showed evidence of littoral compression and the replacement of macrophyte beds at shallow and intermediate depths by green filamentous algae. Macroinvertebrate biomass was higher in the fluctuated lake, despite this lake having a lower standing crop of primary producers compared with the unfluctuated lake. Disturbance of the littoral zone may reduce macrophyte biomass but may maintain high levels of primary producer productivity through an increase in benthic algae such as diatoms.