Coastal dune waterbodies of north-eastern New South Wales

Abstract

Twenty-two lakes, swamps and ponds on, or adjacent to, siliceous coastal dunes from Newcastle to Tweed Heads were investigated. Most of the waterbodies originated by deflation, with organic accumulation and development of perched water-tables involved in establishing those in higher dunes inland. Some were located in depressions in hard rock, blocked by dunes. Most had low total dissolved solids content with Na⁺ and Cl^- dominant, but in and near frontal dunes Ca²⁺ and HCO₃^- were important and salinity was higher. Dissolved organic matter coloured the water of those with swampy environs. Humic waters were markedly acidic, frontal dune ponds alkaline, and lakes in contact with dunes near neutral. The physicochemical features of the only waterbody connected to the sea, Blue Lagoon, varied spatially and temporally with rainfall. Lake muds were dys.

The dominant plants were all emergents, with Lepironia auriculata (Retz) prominent in most waterbodies on or near leached dunes. Calamoecia tasmanica (Smith) dominated the plankton; species diversity was higher in lakes in contact with dunes than in those surrounded by leached dunes. No euzooplankters were recovered from frontal dune ponds or Blue Lagoon. Overall, littoral invertebrates were reasonably diverse but limited in frontal dune ponds. Most notable was the restriction of molluscs and ostracods to sites on or adjacent to frontal dunes, the presence of some characteristic microcrustaceans in sites on or near leached dunes, and the ubiquity of many insect groups, particularly hemipterans and coleopterans. Benthos was depauperate in species and numbers in lakes surrounded by leached dunes; diversity and standing crops were higher in lakes in contact with dunes.

<P.A typology scheme, based on, and showing the interrelationships between, mode of origin, water chemistry and salient biological features, showed much greater heterogeneity among dune lakes in eastern Australia than previously thought.