Figure 1. Long-term annual mean concentrations of Total Nitrogen (totN) in the Gulf of Riga and the Baltic Sea. A – Baltic coastal waters, B – western coast of the Gulf of Riga, C – open waters of the Gulf of Riga, D – eastern coast of the Gulf of Riga, E – transitional waters, F – open waters of the Baltic Sea (data source – SMHI).
Observations of annual mean Total Nitrogen concentrations in the open waters of the Gulf of Riga are intermittently available from 1990 onwards. In the coastal and transitional waters of the Gulf of Riga, however, observations are available since 1991, in the open waters of the Baltic Sea since 1971 and in the coastal waters since 1992. In the open Baltic Sea, the increase in concentrations observed up to the 1990s (Figure 1) corresponds well with the increase in winter DIN concentrations. However, unlike winter DIN (dissolved inorganic nitrogen), total nitrogen concentrations have not shown a decreasing trend since the 1990s. In the open waters of the Gulf of Riga, however, the concentrations observed in the 1990s were higher than in subsequent years. However, it should be noted that the decline in concentrations stopped in the late 1990s. In addition, it should be noted that long-term increases and decreases in concentrations in coastal water bodies cannot be assessed because observations are patchy.
The annual average total nitrogen concentrations for the assessment period, as well as for the previous period, are summarised in Table 1. Overall, the environmental status does not meet the criteria for good environmental status, with the exception of one water catchment. Unfortunately, the frequency of surveys during the reporting period varied from twice per period to none (Figure 1). For the open waters of the Gulf of Riga it was possible to model the missing values, but not for the other basins. In addition, only two stations represent the open part of the Baltic Sea in this assessment. The level of confidentiality of the assessment is therefore low. In general, there are no noticeable changes in concentrations in all the basins examined, unlike in winter DIN.
Table 1. Annual total nitrogen (TAN) (µmol L-1) limit values, assessment and previous period averages, trends, and assessment confidentiality assessment.
|Water object||Threshold||Period||Trends||Confidentiality of the assessment|
|2007 – 2011||2012 – 2016|
|Open waters of the Baltic Sea||15,51||21,57||20,81||«||Low|
|Coastal waters of the Baltic Sea||27,52||30,2||–||–||–|
|West coast of the Gulf of Riga||35,62||33,2||31,73||«||Low|
|Open waters of the Gulf of Riga||281||32,4||31,8||«||Low|
|Eastern coast of the Gulf of Riga||35,62||43,3||–||–||–|
3Based onone year of data