Assessing the aquatic environmental impact from a proposed discharge of production water from a land-based fish farm at Øra in Fredrikstad.

Summary

A land-based salmon farm is under construction by Fredrikstad Seafood AS at Øra in Fredrikstad, South-east Norway. The facility will be of a raceway type factory with internal recirculation of water collected in the near-by Glomma river and treatment of the discharge water that goes back to the river. The company that already has a permit to discharge water from a production of 800 tonnes/year, now applies for a production of 7500 tonnes/year of smolt and salmon. The discharge water containing BOF5, nitrogen and phosphorous will be treated using best available technology. The nitrogen and phosphorous load will not exceed the present permit limit, while BOF5 and ammonia will increase by 46.7 and 85%, respectively. The receiving water in Glomma is part of the water body “Glomma fra Greåker til sjøen”. This water body is negatively affected by load of organic matter and nutrients from the upstream river and tributary. The water is classified as moderate to heavily modified. Also, the adjacent, seaward water body “Østerelva” is classified as heavily modified, phosphorous being the key problem there. Questions have been raised about the proposed discharge relative to the water quality of the receiving water body. The Norwegian Institute for Water Research, NIVA, was asked by the company to address those questions, especially to assess whether the classification will be changed, or not. The Glomma river in the area under consideration, has a layered, estuarine-like structure with salty seawater near the river bed and fresh water on top. The fresh layer flows towards the sea, while the salty water flushes in- or out, according to the tide and changing freshwater flow, that on average is around 540 m3/s. The company’s discharge will be small relative to this; 121 l/s. The Glomma river transports 55000 tonnes of BOF5 annually to the sea, while the company’s contribution will be 32.3 tonnes/year (0.06% of the present load). The resulting theoretical river water concentration increase of maximum 0.025% is considered as being insignificant and hardly measurable. For Total-nitrogen the corresponding concentration increase will be maximum 0.3%, also regarded as insignificant and hardly measurable. The increased ammonia load is expected to be rapidly oxidized in the river water and be carried within 1 hour out of the receiving water body and into the adjacent one, where nitrogen is not the key problem parameter. To a noticeable impact with increasing algal growth in either water body is unlikely. The new salmon factory will not contribute with any traceable environmental contaminants other than those mentioned above. The present report contains description of a water monitoring programme for the recipient in the Glomma river. This will be combined with regular, daily control of the water treatment processes in the factory and the water quality of the discharge water.