WATER-QUALITY AND PHYTOPLANKTON DYNAMICS IN MORETON BAY, SOUTH-EASTERN QUEENSLAND - II - MATHEMATICAL-MODELING

A coupled hydrodynamic water-quality model of Moreton Bay was develope d to enable better management of nutrient loads and to predict eutroph ication-related problems. The hydrodynamic submodel was calibrated to available tidal data, and the transport submodel was calibrated to a s alinity dataset, A 15-month time-series of field data was used togethe r with historical data to calibrate and validate the water-quality sub model, Model simulations suggest that denitrification removes over hal f the external N inputs with about one-third exported to the open ocea n. Approximately 8% of N and 20% of the P loading accumulates in the s ediments. Short-term variations due to hydrodynamic effects tend to ma sk the seasonal cycle in phytoplankton biomass except at inshore local ities. The model predictions confirm the field data that indicate that water quality in the western bay is severely affected while the bette r flushed eastern region remains relatively unaffected. Future increas es in nutrient loading due to population pressure are predicted to ext end the severely affected region eastwards. Over most of the bay, alga l productivity is N-limited except for the western margins where nutri ents are saturating and light availability regulates growth. Model hin dcasts suggest that system-wide mean algal production has increased by a factor of ten since European settlement.