Edeboviken and outlying water
Holmen Paper's Hallsta Paper Mill annually monitors Edeboviken and the outlying waters as receiving bodies of water. In addition to emissions of treated wastewater from the mill, the inlet is also fed by various watercourses and subject to emissions from a municipal wastewater treatment plant, surface water from the Hallstavik community, ship traffic to and from the mill, and a marina.
The ecological status of Edeboviken and the outlying waters is determined primarily by biological variables such as phytoplankton, bottom fauna and rooted vegetation. The nutrient levels, visible depth and oxygen conditions of the water are used to help assess the status of the water according applicable regulations (HVMFS 2013:19). An overall assessment shows a poor status for Edeboviken and a moderate status for both Galtfjärden and Singöfjärden. The change compared with the previous year is that the situation in Galtfjärden has been judged to have improved due to a better result for the bottom fauna in this area. Edeboviken and Singöfjärden are deemed to have remained unchanged.
Oxygen conditions and chemical oxygen demand
Measurements taken during the period 2012–2014 show good oxygen conditions and a high status in both Edeboviken and the outlying waters. In stratified conditions in 2015, low but not critically low oxygen levels were recorded in the deep water of Edeboviken (July, August). Low levels of oxygen were also recorded in Galtfjärden (October). The oxygen situation in Singöfjärden was consistently good. Hallsta is the source of around 33 per cent of the chemical oxygen demand (COD) in Edeboviken.
Over the past decades, a clear trend of rising phosphorus levels has been noted in Edeboviken, and until 2013 for the outlying waters too. Over the same period, rising nitrogen levels have been observed in these areas of water. The highest levels of phosphorus and nitrogen are normally recorded in Skeboån, the largest of the watercourses draining into Edeboviken, with levels declining away from the inner area of the water. In 2015 phosphorous levels in Skeboån were significantly lower than normal, the same level as in inner Edeboviken.
In terms of nutrients this bay appears to be the most impacted sea area included in the current monitoring of receiving waters. The bay is characterised by high levels of nitrogen during the winter (unsatisfactory status) and high levels of phosphorous in summer (poor status). Singöfjärden is the least affected sea area. Taken together Edeboviken and Galtfjärden are assessed to have unsatisfactory status regarding nutrients. Singöfjärden is assessed to have moderate status. In terms of total emissions of phosphorus and nitrogen to Edeboviken, Hallsta accounts for around 29 per cent and 17 per cent respectively.
Bottom fauna and rooted vegetation
An assessment of the environmental status of the bottom fauna (HVMS 2013:19) indicates a poor status in Edeboviken and a moderate status in Galtfjärden and in Singöfjärden. Compared with the previous year, this represents an improvement in the status of Singöfjärden, but a deterioration for Galtfjärden. The assessment index for the waters is very close to the limit for the higher status class, which makes the classification somewhat uncertain.
A survey of rooted vegetation, which takes place every three years, was conducted in 2014. The survey indicates poor to moderate status at the three stations visited in Edeboviken, good status in Galtfjärden and high status in Singöfjärden. Compared with the most recent survey (2011) this means an improvement in status for both waters.
In 2014 a survey was carried out of metals and extractive substances in sediment. As in previous years (2006, 2011) analysis of the metal content shows large to very large deviations from natural levels for some substances and stations. Compared with the previous year, this represents an improvement in the status of Galtfjärden and no change for Edeboviken and Singöfjärden. The assessment index for Galtfjärden is close to the limit for the lower status class, which makes the classification somewhat uncertain. In a corresponding way the classification of Singöfjärden is somewhat uncertain as the index is on the boundary of the higher status class.
Where copper is concerned, the content at all stations, including Galtfjärden and Singöfjärden, seems to be at a level where there is a risk of effects, at least in cases of long-term exposure. The same risk assessment can be made for mercury in Singöfjärden. No limit values for metals in sediment have been established and the assessment should be viewed as indicative. The levels of what are known as extractive substances were more than halved in inner Edeboviken compared to the previous survey (2011). Other stations, on the other hand, showed a substantial increase. The highest levels were measured in central and outer Edeboviken.
A survey of fish health is carried out every five years. The next survey is due in 2018.