Good status (concentrations below threshold) for dissolved inorganic nitrogen (DIN) was not been achieved in any of the 17 open-sea sub-basins. Only in a few Polish and Swedish coastal areas (e.g. parts of the Gulf of Gdansk – the Puck bay area) was good status achieved (Results figure 1 and Results Table 2). The sub-basins causing greatest concern (ER values >2) regarding dissolved inorganic nitrogen status were the Gulf of Finland, Gulf of Riga, and Bornholm Basin. The status of Kattegat, Kiel Bay and Gdansk Basin are only slightly above the threshold values (ER < 1.2). Additionally, there has been a steady decrease in DIN in recent years in the Gulf of Riga and in the Northern Baltic Proper (Results figure 2). Some sub-basins showed elevated DIN values in 2015/2016 which might relate to the natural phenomenon of the major Baltic inflow that occurred. This might have contributed additional nitrogen from deeper waters and could have biased DIN concentrations in the Bornholm Basin, Gdansk Basin, Åland Sea and Bothnian Sea.
Results Figure 1. Status of the DIN, presented as eutrophication ratio (ER). ER shows the present concentration in relation to the threshold value, increasing along with increasing eutrophication. The threshold value is ER ≤ 1.00 (achieve good status).
Results figure 2. Winter DIN concentration on open sea assessment units (solid dark blue line; average for 2011-2016) and threshold values as agreed by HELCOM HOD 39/2012 (red dashed line). It should be noted that the results for Bornholm Basin strongly depend on stations in the open-sea area of Pomeranian Bay, which is influenced by the Odra river plume.
Results table 1. Threshold values, concentration during the assessment period (2011-2016 average), eutrophication ratio (ER) and status of DIN in the open-sea basins. ER is a quantitative value for the level of eutrophication, calculated as the ratio between the threshold value and the assessed concentration – when ER > 1 = threshold value is failed.
Winter DIN concentrations were only assessed in coastal waters of Latvia, Poland and Sweden (Results table2). In the Polish coastal and transitional waters 77% of the area (km2) was in good status and 23% failed to achieve good status. In Swedish coastal waters 7% of the area was in good status, 7% was not assessed and 86% failed to achieve good status. In the coastal waters of Latvia 100% of the areas failed to achieve good status. It should be noted that coastal or transitional waters assessed with annual DIN averages have been excluded from this analysis.
Results table 2. Results for national coastal DIP indicators by coastal WFD water type/water body. The table includes information on the assessment unit (CODE, defined in the HELCOM Monitoring and Assessment Strategy Annex 4), assessment period (start year and end year), average concentration during assessment period, threshold values, units, and Eutrophication Ratio (ER). The ER is coloured red or green to denote if the status evaluation has been failed or achieved, respectively. *indicates data used are annual, all other data are for the summer season, - indicates only status provided and not raw result value. In Swedish waters only the water bodies that were assessed are shown. ER is a quantitative value for the level of eutrophication, calculated as the ratio between the threshold value and the present concentration – when ER > 1, threshold value has not been reached. Note that the units used in table can be µmol l-1 or µg l-1 depending on Contracting Party.
The long-term trends are provided as additional information and do not influence the status assessment.
Though the wintertime DIN is at elevated levels in all 17 sub-basins, it decreased in the 1990s or the early 2000s in most sub-basins and has since then remained at that level (Results figure 3). Although the pattern is not as distinct as for dissolved inorganic phosphorus (DIP), the DIN concentration showed some disturbance (e.g. elevated concentrations and large error bars) in the concentration in recent years, most visible in the Bornholm Basin (2015 and 2016), Eastern Gotland Sea (2015), Åland Sea (2015) and the Bothnian Sea (2015) (see Results figure 2).
Result figure 3. Temporal development of winter dissolved inorganic nitrogen (DIN) concentrations in the open-sea assessment units from 1970-2016. Dashed lines show the five-year moving averages and error bars the standard deviation. Green lines denote the indicator threshold. Significance of trends was assessed with Mann-Kendall non-parametric tests for period from 1990-2016. Significant (p<0.05) improving trends are indicated with blue data points. No significant deteriorating trends were detected.
The confidence of the indicator status evaluation in open sea areas, based on the spatial and temporal coverage of data as well as the accuracy of the protocol for setting threshold values, was high only in the Kattegat, Arkona and Bornholm Basin and Gulf of Finland, while it was low in The Sound, Gdansk Basin, Gulf of Riga, Western Gotland Basin, Åland Sea and The Quark. The low confidence was caused by a lack of monitoring data.
Results figure 4. Indicator confidence, determined by combining information on data availability and the accuracy of the protocol for setting threshold values. Low indicator confidence calls for increase in monitoring.
The indicator confidence was estimated through confidence scoring of the threshold value (ET-Score) and the indicator data (ES-Score). The ET-Score was rated based on the uncertainty of the threshold value setting procedure. The ES-Score is based on the number as well as spatial and temporal coverage of the observations for the assessment period 2011-2015. To estimate the overall indicator confidence, the ET- and ES-Scores were combined. See Andersen et al. 2010 and Fleming-Lehtinen et al. 2015 for further details.