MEPS 431:223-241 (2011)  -  doi:10.3354/meps09113

Environmental impacts of coastal fish farming: carbon and nitrogen budgets for trout farming in Kaldbaksfjørður (Faroe Islands)

Gunnvør á Norði1,*, Ronnie N. Glud2,3,4, Eilif Gaard1, Knud Simonsen5

1Faroe Marine Research Institute, FO-110 Tórshavn, Faroe Islands
2The Scottish Association for Marine Science, Scottish Marine Institute, Oban, Argyll, PA37 1QA, UK
3Southern Danish University, Institute of Biology and Nordic Center for Earth Evolution (NordCEE), Odense M, Denmark
4Greenland Climate Research Centre, 3900 Nuuk, Greenland
5University of the Faroe Islands, Faculty of Science and Technology, FO-100 Tórshavn, Faroe Islands

ABSTRACT: Flow of organic carbon (OC) and nitrogen through a sea cage trout farm was calculated on the basis of detailed studies of the farming operation, water circulation, OC and nutrient transport and recycling processes in sediment. A third of the OC and nitrogen provided by fish food was incorporated into fish biomass, which is more than has been found in previous studies. Most OC input was respired by the fish (52 to 70%), and ~63% of the associated nitrogen was lost as dissolved inorganic nitrogen (DIN), potentially stimulating pelagic primary production. Approx. 6% of carbon and 5% of nitrogen derived from fish food settled on the seabed, where it was either mineralized or accumulated in the sediment. Based on transect measurements of diagenetic activity, the farm footprint was found to cover an area ~10 times the farm area. OC mineralization in the sediment increased linearly with increasing food input; the divergence between carbon efflux and oxygen uptake in sediment likewise increased with increasing food input, reflecting an increasing level of sediment reduction. Directly below the farm, the dissolved organic carbon (DOC) efflux was high (on average 53% of dissolved inorganic carbon efflux), indicating that DOC efflux is an important pathway for benthic carbon release below aquaculture farms. Overall, microbial processes removed 56 and 38% of OC and nitrogen, respectively, that settled to the seabed. ­During a 39 d break in farming activity, due to the combined effect of mineralization and resuspension of surface sediment, sediment conditions improved considerably.

KEY WORDS: Fish farming · Sediment · Organic enrichment · Nutrient enrichment · Organic matter mineralization · Carbon budget · Sedimentation · Benthic recovery

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Cite this article as: á Norði G, Glud RN, Gaard E, Simonsen K (2011) Environmental impacts of coastal fish farming: carbon and nitrogen budgets for trout farming in Kaldbaksfjørður (Faroe Islands). Mar Ecol Prog Ser 431:223-241

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