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CSIRO Marine and Atmospheric Research
Past Seminars

Seminar Abstract

Scaling nutrient loading and eutrophication in NSW coastal lakes and estuaries

There are more than 200 coastal lakes and estuaries in NSW and demographic trends increasingly impact coastal catchments. Relationships based on scale analysis of physical and biogeochemical mechanisms are used to quantify eutrophication and changes in ecological state that might result from increased nutrient export from a catchment to a coastal lake or tidal estuary. Analysis shows runoff, nutrient load, flushing and exchange are not independent quantities in the calculation of effective nutrient forcing. Consideration of observations and a complex biogeochemical model indicates the coefficient of light attenuation broadly scales according to the square root of nutrient forcing.

Coastal lakes have a typical time scale for mixing within the lake that is short compared to the time scale for exchange or flushing to the ocean. Scaling relationships are used, along with bathymetry, to compute potential coverage of coastal lakes with benthic macrophytes and how sensitive this is coverage is to nutrient forcing. In coastal lakes the relative role of exchange and biogeochemical sinks has been found to depend upon a flushing-exchange speed scale defined as mean depth divided by the flushing-exchange time scale. Increased exchange can effectively offset increments in nutrient forcing when nutrient forcing is low but is less effective when nutrient forcing is high.

Tidal estuaries have time scales for internal mixing that are not separable from those for exchange with the ocean and so have intrinsic along-channel gradients in properties of the water column. A scaling of the relative roles of biogeochemical sinks to advection and along-channel mixing is formulated in order to quantify the response of tidal estuaries to changes in nutrient forcing.

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CSIRO = Marine Laboratories Auditorium, Castray Esplanade, Hobart

For further information, or to schedule a seminar, contact:
Karen Wild-Allen, (Oceanographic seminars) CSIRO Marine and Atmospheric Research (03) 6232 5010
Piers Dunstan, (Biological seminars) CSIRO Marine Research (03) 6232 5382
Kerrie Bidwell, Antarctic Climate and Ecosystems CRC (03) 6226 2265 & IASOS, University of Tasmania (03) 6226 2509