The assessment of total phosphorus in the open sea areas is made as the average of total phosphorus concentration in the upper (0-10 m) water layer throughout the year.
One assessment unit, namely the Great Belt, was found to achieve the threshold value during the assessment period 2011-2016. The remaining sub-basins were assessed as failing the threshold value or could not be assessed as threshold values still need to be agreed upon at HELCOM-wide level (Results figures 1 and Results table 1). In the Kattegat, Gdansk Basin and Bothnian Bay the concentrations were only slightly above the threshold value (Results table 1).
Although some fluctuation was apparent during the current assessment period the levels of total phosphorus remained relatively unchanged (Results figure 2).
Results figure 1. Detailed eutrophication status assessment with the Eutrophication ratio (ER) of total phosphorus split into 5 classes. A more differentiated picture than the 2-class division used in the key message figures. ER is calculated as the ratio of the average concentration during assessment period and the threshold value (Fleming-Lehtinen et al. 2015). Please note that for some open sea areas threshold values still are under discussion, and that only those coastal areas are assessed differently by the Contracting Parties reporting coastal data and evaluations (see Results table 2 for details).
Some coastal areas in the south-western Baltic are highly eutrophied. In the remaining coastal areas, seasonal instead of annual averages were used for assessment. Based on mean summer concentrations (June-August / June-September), some areas along the coasts of Sweden, Finland, Estonia and Poland are classified as achieving good status (Results figure 1), but highly eutrophied areas are found as well. If compared with the total nitrogen assessment, these coastal areas are somewhat more strongly affected by phosphorus than nitrogen.
Results figure 2. Average annual surface total phosphorus concentrations (black line; average for 2011-2016) in open sea assessment units. The dashed red line displays the threshold value. For Kiel Bay, Bay of Mecklenburg, Arkona Basin, Bornholm Basin and Eastern Gotland Basin, threshold values are still under discussion. Therefore, no dashed red line is shown in these cases, and these basins occur as "not assessed" in the maps above.
Results table 1. Threshold values, present concentration (as average 2011-2016), eutrophication ratio (ER) and status of total phosphorus in the open sea basins. ER is a quantitative value for the level of eutrophication, calculated as the ratio between the present concentration and the threshold value – when ER >1, threshold value has not been reached.
*NOTE: Danish measurements presented in this report are underestimated. This might affect content and conclusions in this report in regard to the status assessment and assessment of nutrient inputs to Danish waters.
**NOTE: Finnish monitoring open-sea estimates of phosphate and total phosphorus in 2011-2014 are in general 10 % lower than in 2015-2017 due to the changes in instrumentation and accompanying methodology. This might affect the indicator values in these assessment units.
Coastal area assessment results are based mostly on summer and annual average TP values, and in some cases (in Sweden) also winter averages are used (Results table 2). In Estonian coastal waters, the threshold value was achieved in 1 waterbody out of 16 and in Finland in 3 out of 14, based on summer estimates. In the coastal areas of Germany, the threshold value was achieved in one waterbody out of 45, based on annual values. In Lithuania, the threshold value was achieved in 2 of the 6 coastal areas. In Poland, 4 coastal areas were assessed using annual values, and in 3 waterbodies the threshold value was achieved. For the remaining 15 areas summer averages were used, with 3 of them achieving the threshold value. In Sweden, both summer and winter averages were used when assessing coastal areas. Concerning summer values, the threshold value was achieved in 7 areas out of 24, and using winter values in 10 areas out 22. The percentage of total assessed area achieving the threshold value, i.e. in good status, per country (if good status was achieved in some basins) represents over half of the assessed area in Poland and Sweden (winter values), 60% and 52%, respectively. Lithuania has 41% of the coastal area in good status. According to summer values in Sweden, 35% of the assessed area is in good status. Finland, Estonia and Germany have 23%, 4% and <1% of the area in good status, respectively.
Results table 2. Threshold values, present concentration (as average 2011-2016), eutrophication ratio (ER) and status of total phosphorus in the coastal-sea basins. ER is a quantitative value for the level of eutrophication, calculated as the ratio between the present concentration and the threshold value – when ER >1, threshold value has not been reached. Note that the used units can be either µmol l-1 or µg l-1 depending on Contracting Party. The majority of data is from the summer season, though differences in sampling season also occur between countries, indicated in the table as follows: no symbol = summer, * = annual sampling, and ** = winter sampling.
Temporal trends provide additional information on the total nutrients in the Baltic Sea that supports the interpretation of the indicator results (Results figure 4). It should be noted that the temporal trends do not affect the indicator result, which is a status assessment where a concentration is compared to a threshold value.
Results figure 4. Temporal development of total phosphorus (TP) concentrations in the open-sea assessment units from 1970s to 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 and deteriorating trends with orange data points.
The confidence of the total phosphorus indicator status evaluation for the open sea areas (Results figure 5) is high in most of the assessed sub-basins. The confidence was moderate in the Quark and low in the Åland Sea. It should be noted that the confidence is only based on data availability, not the threshold confidence since the latter was not available for the indicator calculation.
Results figure 5. Indicator data confidence, determined combining information on data availability for the indicator when using observations from all months of the year. Low indicator confidence calls for increase in monitoring.
The indicator confidence was estimated only for the indicator data (ES-Score) due to absence of ET-Score, which describes 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 2011-2016. To estimate the overall indicator confidence, the ET-score should be defined and ET- and ES-Scores combined. See Andersen et al. 2010 and Fleming-Lehtinen et al. 2015 for further details.
As the indicator period and method of calculation varies between open sea and coastal areas, and thus the threshold or assessment concentrations are not directly comparable between the open sea and coast, nor between all coastal assessment units where nationally binding threshold values may have been set, only the confidence for the open sea areas are shown in Results figure 5.