Numerical modelling of organic waste dispersion from fjord located fish farms |
| |
Authors: | Alfatih Ali Øyvind Thiem Jarle Berntsen |
| |
Institution: | 1.Bergen Center for Computational Science,Uni Research,Bergen,Norway;2.Department of Mathematics,University of Bergen,Bergen,Norway |
| |
Abstract: | In this study, a three-dimensional particle tracking model coupled to a terrain following ocean model is used to investigate
the dispersion and the deposition of fish farm particulate matter (uneaten food and fish faeces) on the seabed due to tidal
currents. The particle tracking model uses the computed local flow field for advection of the particles and random movement
to simulate the turbulent diffusion. Each particle is given a settling velocity which may be drawn from a probability distribution
according to settling velocity measurements of faecal and feed pellets. The results show that the maximum concentration of
organic waste for fast sinking particles is found under the fish cage and continue monotonically decreasing away from the
cage area. The maximum can split into two maximum peaks located at both sides of the centre of the fish cage area in the current
direction. This process depends on the sinking time (time needed for a particle to settle at the bottom), the tidal velocity
and the fish cage size. If the sinking time is close to a multiple of the tidal period, the maximum concentration point will
be under the fish cage irrespective of the tide strength. This is due to the nature of the tidal current first propagating
the particles away and then bringing them back when the tide reverses. Increasing the cage size increases the likelihood for
a maximum waste accumulation beneath the fish farm, and larger farms usually means larger biomasses which can make the local
pollution even more severe. The model is validated by using an analytical model which uses an exact harmonic representation
of the tidal current, and the results show an excellent agreement. This study shows that the coupled ocean and particle model
can be used in more realistic applications to help estimating the local environmental impact due to fish farms. |
| |
Keywords: | |
本文献已被 SpringerLink 等数据库收录! |
|