Nutrient Cycling in St Georges Basin, South Coast NSW

Geoscience Australia conducted a survey of lakebed (benthic) nutrient fluxes in St Georges Basin, November 2003. The objectives were to:
1. determine the nature of nutrient cycling between the sediment and overlying water; and
2. determine the implications of benthic nutrient fluxes for water quality in the estuary.

The relevance to management of this work is that it gives an indication of the susceptibility of the estuary to eutrophication from increased nutrient loads from the catchment.

The key findings of the study were:
- St Georges Basin was mesotrophic to eutrophic at the time of the survey (spring) based on relatively high respiration rates and O2 demand in the sediments measured by in situ benthic chambers.
- Respiration rates were linked to phytoplankton biomass (mainly diatoms) where local fluvial discharge of dissolved nutrients created enhanced primary productivity in the water column, which in turn enhanced mineralisation rates.
- St Georges Basin had comparatively low denitrification efficiencies (less than 60%).
- St Georges Basin is likely to be prone to eutrophication and may have little tolerance for increases in nutrient and organic matter from the catchment due to the low denitrification efficiencies.