Náttúra og náttúrutilfeingi
Resuspension of sediments impacted by fish farm wastes
Gunnvør á Norði
Øystein Patursson, Pia Kupka Hansen, Raymond Bannister, Ronnie N. Glud og Knud Simonsen
Stuðul úr Granskingargrunninum:
The large fish farming operations applied today set great knowledge requirements on how the local environment copes with organic load from the farming units. This issue has received a lot of attention, and attempts have been made to predict the environmental impact, using models based on site specific characteristics such as the mean current speed. In the Faroe Islands the mean current speeds at farming locations are generally low, and thus the local environmental impact is expected to be relatively high. However, the weather conditions are highly unstable, with frequent episodes of wind generated waves and at some sites episodes with ocean swell. This might induce sediment resuspension and diminish the benthic impact.
In this study the influence of short time variations in hydrodynamics on the seabed below a fish plants will be investigated. The organic carbon removal by mineralization and infaunal activity will be quantified by sediment water fluxes, and the resuspension will be quantified by turbidity measurements and short time deployments of sedimentation traps.
The purpose of this project is to specify what happenings in the hydrodynamics are likely to induce resuspension and facilitate a faster recovery of farming affected sediments. This project contributes significantly to the ongoing research on the carrying capacity of fish farming sites in the Faroe Islands.
In this project we have investigated, how bottom currents and waves can resuspend seabeds impacted by fish farm waste, and what effect such resuspension may have on the nature of the impact. Two fish farming sites were investigated, one sheltered site, and one site which was periodically exposed to ocean swells. High current speed above the seabed (up to 25 cm s-1) did not induce resuspension of the seabed. But ocean swells reaching the exposed farming site, did induce massive resuspension events. Although only a small amount of material was physically removed during the resuspension events, the resuspension significantly decreased the benthic impact of fish farming activity and speeded up the recovery of the seabed.
Norði, G. á, Patursson, Ø., and Simonsen, K. (2013) Hvat reinsar botnin undir alibrúkum. Fiskaaling rit 2013-10. Technical report in Faroese. 27pp.
Norði, G. á, and Patursson, Ø. (2012) Influence of waves and current speed on resuspension of fish farm waste: Case study in Funningsfjørður, Faroe Islands. ICES CM 2012/Q:13
Aquaculture Europe 2013, Trondheim, ”Wave induced resuspension of fish farm waste”
Aliráðstevnan 2013, Tórshavn, “Alduávirkan á botnin undir alibrúkum”
ICES Annual Science Conference 2012, Bergen, ”Influence of waves and current speed on resuspension of fish farm waste: Case study in Funningsfjørður, Faroe Islands”