Abstract

The Myall Lakes are a series of interconnected, shallow and poorly flushed coastal lakes located within the Myall Lakes National Park in NSW, Australia. The following field study aims to uncover patterns in temporal variability in water quality and phytoplankton abundance, diversity and assemblage structure, in the upper and lower water bodies of the Myall Lakes system. The result showed that the two lakes differ greatly in their catchment to lake area ratios, freshwater inputs, degree of saline intrusion, light attenuation and submerged macrophyte biomass. The broadwater, which receives large inputs of freshwater from the catchment, and is influenced by saline inputs from the Port Stephen’s estuary, exhibited highly variable water quality and dissolved nutrient concentrations, and phytoplankton assemblages with much temporal variation in taxa present, biovolume, cell size and abundance, and taxonomic diversity. In contrast, the upper lake, Myall Lake, shows much greater stability in water chemistry and nutrient availability; the phytoplankton community is diverse, with relatively low and constant biovolume, and is dominated year-round by small-celled cyanobacteria. Differences in phytoplankton between the two lakes were greatest during the autumn and winter, and least during the summer, when the phytoplankton assemblages in both lakes were dominated by similar cyanophyte taxa. 

Key words: Seasonal variation, phytoplankton abundance and assemblages, Myall Lake and Bomba Broadwater.