Accumulation and mineralization of fish farming residuals in the benthic footprint area at two different farming locations in a Faroese fjord

In order to quantify the accumulation of farming derived organic carbon in the footprint area of two hydrographically different fish farming sites in a Faroese fjord, a simple distribution estimate based on current profile records was combined with measurements of organic carbon content in the sediment. One farming site (F1) had low near seabed current speeds while they at the other
site (F2) frequently exceeded 10 cm s-1. The calculated estimate successfully described the organic carbon distribution at F1, while frequent resuspension events at F2 implied not valid estimates.
The total inorganic carbon (DIC) release from the sediment due to mineralization increased linearly with increasing sediment organic carbon content. There furthermore was a substantial release of dissolved organic carbon from the fish farming impacted sediments. As for the DIC efflux the sediment oxygen uptake increased with increasing organic carbon content of the sediment. The
average DIC efflux was, however, 1.8 times higher than the sediment oxygen uptake, reflecting a continuous accumulation of reduced metabolites in the farming affected sediments. The ammonium efflux from the sediments was site specific, with considerably higher effluxes at low current site (F1) than at the site with stronger resuspension (F2).