Ecological studies of phytoplankton in the Waikato River and its catchment

Most of the main streams and lakes of the Waikato catchment were surveyed for phytoplankton in April 1974 and February 1975; 69 genera (118 species) of phytoplankton were identified. Phytoplankton density increased going downstream along the Waikato River and the diversity of phytoplankton communities increased with distance from the river mouth. An explosive increase in algal density in the centre of Lake Ohakuri was found in both surveys. The increase was believed to be associated with an increase of nutrients and a shift from river to lake environment in this part of the river system. Diatoms dominated the Waikato River and most of its tributaries. Blue‐green algae formed blooms in the lowland lakes. Green algae were common, but were never dominant in any locality. The seasonal succession of some major species in the lower Waikato River (i.e., at Ngaruawahia, Rangiriri, and Tuakau) was determined from September 1973 to August 1974. Most species were most abundant in summer. Phytoplankton density was positively correlated with temperature and negatively with nitrate concentration. Flow rate may exert an overall control on phytoplankton growth in the Waikato River.

Keywords:

• Waikato River
• phytoplankton
• seasonal succession
• aquatic organisms
• freshwater ecology
• nutrients
• water currents

Notes

Present address: Environmental Protection Unit, Environment Branch, MC Block, Victoria Barracks, Hong Kong