Modeling transport and dilution of produced water and the resulting uptake and biomagnification in marine biota
Authors: Rye H. , Reed M. , Slagstad D. , Melbye A. , Johnsen S. 
Published: December 2007

Modeling transport and dilution of produced water and the resulting uptake and biomagnification in marine biota.

The paper explains the numerical modelling efforts undertaken in order to study possible marine biological impacts caused by releases of produced water from the Haltenbanken area outside the western coast of Norway.

Acute effects on marine life from releases of produced water appear to be relatively small and confined to areas rather close to the release site. Biomagnification may however be experienced for relatively low concentrations at larger distances from the release point. Such effects can be modelled by performing a step-wise approach which includes:–The use of 3-D hydrodynamic models to determine the ocean current fields–The use of 3-D multi-source numerical models to determine the concentration fields from the produced water releases, given the current field–The use of biologic models to simulate the behaviour of eggs and larvae (passive marine biota) and fish (active marine biota) and their interaction with the concentration field

The paper explains the experiences gained by using this approach for the calculation of possible influences on marine life below the EC50 or LC50 concentration levels. The models are used for simulating concentration fields from 5 simultaneous sources at the Haltenbank area and simulation of biomagnification in some marine species from 2 simultaneous sources in the same area. Naphthalenes and phenols, which are both present in the produced water, were used as the chemical substances in the simulations.

The hydrodynamic model

General.

The hydrodynamic model is an integrated part of the modelling effort. The reason why is that the currents are important in determining the transport of effluent, as well as describing the horizontal advection of passive eggs and larvae from spawning areas.

In principle, any hydrodynamic model, producing 3-D current fields with some resolution in time and space may be applied. In this particular case, a hydrodynamic model applied to produce 3-D current fields outside the western coast of Norway has been applied. A short description of the model is given in the following.

The model used here is denoted "SINMOD-3D". This model was originally developed in order to produce hydrodynamical input to biological models applied in the Barents Sea (Stole-Hansen and Slagstad 1991; Slagstad and Stole-Hansen 1991). However, the model has also been applied to simulate currents along the Norwegian coast.

Input to the model is wind and atmospherical pressure, four tidal components, and density field (temperature and salinity) for the ocean. One of characteristic features of stratified waters is inertial oscillations which may take place after the passage of a storm. The frequency of the oscillation depends on the latitude and has a characteristic period for the Norwegian coastal areas close to the semidiurnal tidal period. In order to resolve such oscillations it is necessary to store the current field with a time interval of two hours.

Basic equations. The model is a 3-dimensional, baroclinic, finite-difference "level model" that is defined by a sequence of fixed but permeable levels. Each level has a fixed thickness, except the level near the surface and the level that happens to be near the bottom. Thus, the number of levels will be a function of horizontal coordinates.

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