Modeled based analysis of fish farm emissions impact on the fjord biogeochemistry

To investigate the impacts of fish farm emissions, we coupled the biogeochemical C-N-P-Si-O-S-Mn-Fe transformation model BROM with a 2-Dimensional Benthic-Pelagic transport model (2DBP), considering vertical and horizontal transport in the water and upper 5 cm  sediments along a 10000 m transect centered on a fish farm. The 2DBP model had 25 m horizontal resolution and was forced by hydrophysical model data for the Hardangerfjord in western Norway. The model predicted significant impacts on seafloor biogeochemistry up to 500 meters from the fish farm (e.g., increased organic matter in sediments, oxygen depletion in water and sediments, denitrification, metal and sulfur reduction) as well as detectable decreases in oxygen and increases in ammonia, phosphate and organic matter in the water near to the fish farm cages. The model results are compared with field data from the Hardangerfjord in August 2016 and indicated satisfactory model performance.