Morphology and benthos of three volcanic lakes in the Mt. Gambier district, South Australia

Abstract

Lakes Valley, Leake and Edward are medium sized (< 65 ha) maars, 16, 4.5 and 7 m deep respectively. Each has a low shoreline development and a high volume development.

Valley Lake supports at least 24 benthic species, Leake 12 and Edward 17. Austrochiltonia spp., Hemicordulia tau, Antipodrilus davidis, Procladius villosimanus, Chironomus duplex and Chaoborus sp. occur, some abundantly, in each, and in addition Cryptochironomus ?curtivalva is abundant and Sphaerium sp. common in Valley Lake and in Edward Ablabesmyia ?notabilis and Tanytarsus paskevillensis are present. Many species live at all depths, but some, e.g. Chaoborus sp., are restricted to greater depths and others, e.g. Austrochiltonia spp., to the littoral and sublittoral zones.

Mean weighted biomass during winter was 16.8 g/m² in Valley Lake, 23.3 g/m² in Lake Leake and 8.7 g/m² in Lake Edward. In Lakes Valley and Edward there was a marked sublittoral maximum in the distribution of biomass with depth. These high values are in accord with the large amounts of organic matter (32-51 %) in the substrates and suggest that each lake is eutrophic, Leake particularly so.