Modelling aquaculture effects in the Firth of Thames

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Modelling aquaculture effects in the Firth of Thames

A new simulation model of nutrient and phytoplankton dynamics developed by NIWA is being used in the Firth of Thames.

Time & depth averaged simulated concentrations of dinoflagellates, dissolved inorganic nitrogen, diatoms, and phytoflagellates in the Firth of Thames, May 2003. The scale is the log of the concentration in milligrams per cubic metre. This work was funded by the Auckland Regional Council, Environment Waikato, and the Western Firth Marine Farming Consortium. The Wilson Bay Group A Consortium permitted use of their data for model verification.

The model’s performance was recently verified and applied to assess the effects of shellfish aquaculture in the Firth, on behalf of Environment Waikato, the Auckland Regional Council, and the Western Firth Marine Farming Consortium. The model provided valuable new information used in assessing potential Aquaculture Management Areas there.

We are now using it in a project for Environment Waikato to assess whether an increase in nitrogen from rivers will raise the probability of algal blooms in the southern Firth.

In future, we plan to apply the model to other coastal areas, notably the Marlborough Sounds and Tasman-Golden Bay, thanks to funding from the Foundation for Research, Science & Technology.

What’s special about NIWA’s model?

The model is fully 3-dimensional, so it reflects the complexity of water movements in an area.

The model takes account of the characteristics of different types of phytoplankton (microscopic plants). For example, diatoms are very fast growing but require silicates for growth and sink when starved of nutrients, whereas dinoflagellates are slow growing but can swim upwards to benefit from light and downwards to get more nutrients.

The model takes account of farm stocking practices and shellfish characteristics to determine how much phytoplankton is consumed, and particulate and dissolved organic material produced, by shellfish.

Research subject: Oceans