Chemical Oxygen Demand (COD)
Iggesund Mill is the source of about 41 per cent of the total Chemical Oxygen Demand in Iggesundsfjärden and Gårdsfjärden.
The bottom water in Gårdsfjärden had an oxygen saturation level of 85.8 per cent in 2015 as an annual average. The surface water in the vicinity of the mill has an oxygen saturation level of 85 per cent as an annual mean, while the annual mean value for the bottom water in the immediate vicinity is 75 per cent.
Nitrogen: The annual average in the surface water of Gårdsfjärden in 2015 was 390 micrograms per litre (µg/l). The mean value in surface water for summer (417 µg/l) is also classified by the Swedish Environmental Protection Agency as 'high', and the mean value for winter (375 µg/l) is classified as 'moderate'. Iggesund is the source of 29 per cent of the total nitrogen entering Gårdsfjärden.
Phosphorus: The annual average level in the surface water of Gårdsfjärden in 2015 was 24 µg/l. The mean value in surface water for summer (34 µg/l) is classified by the Swedish Environmental Protection Agency as a 'very high level', and the mean value for winter (21 µg/l) is classified as 'very low level'. Iggesund is the source of approximately 58 per cent of the total phosphorus entering Gårdsfjärden.
The mill's emissions of eutrophicating substances have fallen sharply since the 1980s. In trial fishing in 1987, the fish life in Gårdsfjärden was characterised as typical of areas of water high in nutrients. Some changes in the direction of more normal status were noted in 1996, but fish production remained high and with a preponderance of the carp family.
Recovery proceeds slowly in such enclosed areas as Gårdsfjärden, where large amounts of organic material and mineral nutrients from earlier emissions have accumulated on the bottoms.
In 1996 impairment of liver function and reproduction was observed in perch in Gårdsfjärden. However, growth and survival were normal. Further studies of perch in the waters off Iggesund were performed, with similar results to those found in the study in 1996.
Reproductive studies were performed on both perch and zebra fish in 2001 and 2002. The results show that perch that have spawned in the receiving body of water produce eggs with just as good hatchability and larval survival as the perch in an unaffected reference area, and the studies in the laboratory on zebra fish did not indicate any effects.
In late 2009 a treatment plant was brought on line with chemical flotation after the existing aerated lagoon. This has resulted in a reduced load on the receiving bodies of water, particularly regarding mineral salts.
In connection with an application for a new environmental permit, the company conducted a follow-up fish study in autumn 2009, which showed that a small number of significant differences, which cannot be regarded as biologically significant, existed between the sites studied. No evidence was discovered of the inhibition of reproduction found in previous studies, and the results therefore indicate clear recovery. The fish study was conducted before the chemical flotation plant was commissioned, which means that the recovery that has occurred must have had another cause, such as internal measures already taken.
As part of the permit application procedure, a hard-bottom inventory was also conducted in August 2010, and the study showed that there has been a large-scale improvement in the inner reaches of Gårdsfjärden and the outer reaches of Enångersfjärden since 1987. It is impossible today to differentiate the effect of outflow from the Iggesundsån river in the studied reaches of Gårdsfjärden on the plant communities on the bottoms from the effect of the point source Iggesund Mill in the same receiving body of water. There is no visible toxic effect.
The sediments in Gårdsfjärden are finely divided, oxidised and teeming with life. Filtering organisms such as freshwater fungi, barnacles and hydras occur on rocks. Nor do TOC concentrations in water and sediment suggest any unusual conditions.