With the adoption of the Marine Strategy Framework Directive and the Water Framework Directive, EU Member States are obliged to achieve “Good” or “Good Environmental” Status within a certain time frame, or be obliged to take remedial action. There is therefore a need to quantify the quality of the monitoring programmes on which such status assessments are based, as a part of assessing the confidence in the status assessment. Within the framework of the OSPAR Convention on the Protection of the North East Atlantic, Germany and the Netherlands presented a suggestion for how such an assessment could be made. This report documents the application of this methodology to stations in the Swedish National Monitoring Programme within the OSPAR area, and also within the Sound, which may in future be included in the Greater North Sea region under the Marine Strategy Directive. The variability of eutrophication parameters with salinity was examined. In the Kattegat, inorganic nutrient variability was least at the highest salinities, suggesting that a reliable status assessment could be made more easily with data from this region, for example, rather than in the dynamic near coast region. Assessing the coverage of the existing monitoring programme, it was found that horizontal gradients in assessment parameters (generally seasonal averages) varied by less than about 30% between stations, which suggests that the programme has reasonable spatial coverage, though additional stations would improve matters. Looking at each station individually, the current vertical sampling resolution appears adequate for most parameters, apart from chlorophyll a and inorganic nutrients during the growing season. Temporal coverage is adequate for the total nutrient concentrations, but is insufficient for the inorganic nutrients and chlorophyll a, as well as for the deep water oxygen concentration in the Sound. The poor temporal coverage of chlorophyll a and inorganic nutrients could be relatively easily improved by the addition of a two channel (nitrate + nitrite, and orthophosphate) autoanalyser onto the existing ferrybox platforms in use in these waters. Addressing these problems using traditional measuring platforms and buoys would be more costly. The poor temporal coverage of chlorophyll a and inorganic nutrients could be relatively easily improved by the addition of a two channel (nitrate + nitrite, and orthophosphate) autoanalyser onto the existing ferrybox platforms in use in these waters. Addressing these problems using traditional measuring platforms and buoys would be more costly.

Despite a year of pandemic, the environmental monitoring in the pelagic could be done largely as planned in 2020. It was the warmest year on land since national statistics started in 1860. This was also shown in the sea where especially the surface temperature in winter was higher than usual. In the Baltic Sea, the lowest winter temperature was two degrees above normal and the maximum distribution of sea ice was the lowest ever measured. The autumn was also warm and in November the surface water in the Baltic Sea was about 1 degree warmer than normal.In the Kattegat, there were signs of the spring bloom in February with high chlorophyll levels and high species diversity. In March, the nutrients were largely depleted in the surface water and the spring bloom of diatoms was over for this time. At one occasion, in April, toxins were reported in mussels along the West Coast that exceeded the warning limit. In the Skagerrak, the spring bloom started a little later than in the Kattegat, and in the Baltic Sea even later. In April, the spring bloom was observed in the Western Gotland Basin with high chlorophyll concentrations and typical dinoflagellates species for the season. In the Gulf of Bothnia, there was an early spring bloom of diatoms in April. This early bloom may have been an effect of the mild winter. The bloom of cyanobacteria in the Baltic Sea started already in May when cyanobacteria were observed at several stations. In August, cyanobacteria were also observed along the West Coast. These had probably been transported out with water from the Baltic Sea. A late bloom of the microzooplankton Noctiluca scintillans was observed at several sites along the West Coast in December. N. scintillans turns the water red during blooms and when it is dark, its fluorescence causes beautiful bioluminescence.Throughout the year high levels of silicate were observed in the Baltic Sea and low levels of DIN in the surface waters of the Gulf of Bothnia. Otherwise, the levels of nutrients did not deviate much from normal.In the bottom water of the Baltic Sea, no direct improvement of the oxygen situation was seen. In December 2019, there was a small inflow to the Baltic Sea that temporarily raised oxygen levels in the southern and south-eastern parts at the beginning of 2020. But this increase in oxygen was consumed quickly. In the East Gotland Basin, there was an acute lack of oxygen from 80 m and hydrogen sulphide was measured from depths exceeding 125 m. In the Western Gotland Basin, acute oxygen deficiency was found from 70 m and completely oxygen-free conditions from 80 m. An effect of stagnation in the deep basin parts is, in addition to increased levels of hydrogen sulphide, also increased levels of ammonium. Ammonium levels in the deep water increase in both the Eastern and Western Gotland Basins. The highest concentration of ammonia was observed in the eastern parts, but in the western parts they were above normal levels and closer to the levels in the eastern parts than they have been before. In the Kattegat, oxygen concentrations just above the limit for acute oxygen deficiency were found at some stations during August-October.

The temperatures in the surface layer were above normal in January, February (Figure 1), June and September. In August the surface temperature was below normal at many stations and for the rest of the year the surface temperature was generally normal. The minimum temperatures in the surface layer in 2023 were reached in March in Skagerrak, Kattegat and the Baltic Proper. In the Gulf of Bothnia, the maximum ice extent was reached in March and water temperatures remained low until May. By May 28, 2023, the ice had completely melted, and the 2022-2023 ice season was classified as mild. The next season, 2023-2024, started early on October 23, 2023.Temperatures above normal were measured in the deep and intermediate waters in the Baltic Proper. In the Baltic Proper the temperature in the deep waters show an increasing trend and the temperature in the bottom water is record high.The nutrient surveys in winter showed that the concentrations of dissolved inorganic nitrogen were below normal in the Baltic Proper and the Bothnian Bay, whereas silicate and phosphate were above normal in the Bothnian Bay. The latter is consistent with a trend of increasing phosphate and silicate concentration in the Bothnian Bay. The nutrients decreased during the spring bloom. In 2023, the spring bloom started in February in the Kattegat and March at the Skagerrak stations, with high biomasses and chlorophyll concentrations. At N14 Falkenberg the summer biomass was dominated by dinoflagellates. In the Baltic Proper the spring bloom occurred between the March and April cruises. In the Bothnian Sea the spring bloom occurred in April with a consequently drop of inorganic nitrogen to levels near the detection limit in May. In the Bothnian Bay the levels did not drop until July due to the later spring bloom. At station NB1/B3 in the Bothnian Sea, an unusual autumn bloom occurred in October.The largest areas of cyanobacteria surface accumulations occurred during the last week of June. In August, the storm Hans caused nutrients to come up towards the surface and become available making the cyanobacteria blooms start all over and continue until mid-September.No new inflows occurred that could renew the deep water, and therefore concentrations of nutrients in the deep basins of the Baltic Proper continued to increase during 2023. The deep waters show increasing concentrations of nutrients as well as hydrogen sulphide. The concentrations of both ammonium and hydrogen sulphide are at record high levels in both the eastern and western Gotland basins.

Summary

The temperature in surface layer was above normal in several months during 2022,temperatures below normal were measured only on a few occasions in the summer.These occasions were caused by upwelling events. The minimum temperatures in thesurface layer in 2022 were reached in March in Skagerrak, which is a month later thannormal. In Kattegat the temperature reached its minimum in January and in March inthe Baltic Proper.

Temperatures above normal were measured in the deep and intermediate waters in theBaltic Proper. In the Baltic Proper the temperature in the deep waters show anincreasing trend.

The ice season was classified as mild but the duration was longer than normal, with thefirst ice observations around 25th of October and the last ice seen on 2nd of June.

The nutrient surveys in winter showed that the concentrations of dissolved inorganicnitrogen were below normal, whereas silicate and phosphate were above normal in theBothnian Bay. The latter is consistent with a trend of increasing phosphate and silicateconcentration in the Bothnian Bay. The nutrients decreased in spring as the springbloom started, in 2022 this happened in March in Kattegat and in April in Skagerrak,which is later than normal. In the Baltic Proper it occurred between the February andMarch cruises in the southern parts while it started about a month later in the basinsaround Gotland. In the Bothnian Sea we lack nutrient data for the period when thespring bloom occurred, but phytoplankton data shows that the spring bloom occurred inApril. In the Bothnian Bay inorganic nitrogen dropped to levels near the detection limitin July.

The potentially toxic dinoflagellate Dinophysis acuta was found in cell numbers abovethe warning limit during autumn at the stations situated in Skagerrak and Kattegat.

The largest area of cyanobacteria surface accumulations was observed by satellite onthe 28th of June when about 83 300 km2 of the Baltic Proper and Gulf of Finland wereaffected.

No new inflows occurred that could renew the deep water, and thereforeconcentrations of nutrients in the deep basins of the Baltic Proper continued to increaseduring 2022. The deep waters show increasing concentrations of nutrients as well ashydrogen sulphide. The concentrations of both ammonium and hydrogen sulphide areat record high levels in both the Eastern and Western Gotland Basins. 

2021 was a year with more normal temperatures compared to 2020, which was record warm. Not a single classified storm occurred in our Swedish coastal waters during the year. There were no larger inflows to the Baltic Sea, but three smaller inflows were observed during the autumn.The temperature in the surface water was above normal throughout the Baltic Sea during the winter, and the coldest month was March which is normal for this sea area. In the Skagerrak and the Kattegat, it was colder than in the Baltic Sea and the coldest month was February and, unlike the previous year, the surface water temperature was not above normal. In mid-February, the entire Gulf of Bothnia was covered in ice, which did not happen last season. The ice winter of 2021 was classified as normal. In the Bothnian Sea, the minimum temperature was unusually high this winter. The highest concentrations of nutrients, although within the normal range, were measured in January in the Skagerrak and the Kattegat and in March in the Baltic Sea. Silicate levels were still high and above normal in the Baltic Sea.Surface water temperatures were normal during spring and in May it started to get warmer. The spring bloom started earlier in the Skagerrak than in the Kattegat this year, normally it is the other way around. In the Baltic Sea the spring bloom started later, in March-April which is normal for this sea area. In the Bothnian Sea the spring bloom started in April and in the Gulf of Bothnia in May-June.Surface water temperatures were at their highest and above normal in July at many stations in the Baltic Sea, the Skagerrak and the Kattegat. In August, surface water temperatures were below normal in coastal parts of the Bornholm Basin, which was caused by upwelling of colder deep water. The nutrient levels were mostly normal, but an interesting detail was the unusually high silicate content measured in the Kattegat in June, which was the result of outflowing water from the Baltic Sea. This summer’s cyanobacterial blooms were less intense than last year. The accumulations were most intense in the Bothnian Sea and the southern Baltic Sea, especially southeast of Öland. At the mouth of the Gulf of Finland, the blooms were also intense.The autumn was relatively undramatic, but in November surface water temperatures above normal could be measured at several stations in the Skagerrak and the Kattegat and below normal at some stations in the Bothnian Sea during September and October.The oxygen situation in the Baltic Sea continues to be severe and increasing oxygen deficiency in the form of increasing hydrogen sulphide levels was noted during 2021. The concentrations are now approaching the highest levels of hydrogen sulphide in the Western Gotland Basin since the measurements started. In the Eastern Gotland Basin, the levels of hydrogen sulphide are at their highest and continue to increase since the last major Baltic inflow in 2014. In the Bothnian Sea, a decreasing oxygen concentration was observed in the bottom water during 2021. However, the levels are close, but not below the limit for oxygen deficiency (<4ml/l). In the Skagerrak and Kattegat, the oxygen concentration in the bottom water was lowest during the autumn and below normal at a couple of stations but returned to normal levels towards the end of the year.

Detta är ett underlag för revidering av bilaga 5 i HVMFS 2013:19, Bedömningsgrunder för fysikaliskkemiskakvalitetsfaktorer i kustvatten och vatten i övergångszonen. Underlaget innefattar främst enuppdatering av referensvärden för näringsämnen samt förslag på uppdatering av viss text i föreskriftengällande syrebalans och siktdjup. Den generella metoden för var och en av stödparametrarna ibedömningsgrunderna bibehålls. I rapportens sista kapitel presenteras de uppdateringar av föreskriftenHVMFS 2013:19 som rekommenderas utifrån detta uppdrag.Efter en jämförelse av tidigare framtagna referensvärden för näringsämnen och de som tagits fram iden här rapporten rekommenderas att nya referensvärden i tillrinnande sötvatten används men atttidigare referensvärden för TN och TP vid utsjösalthalt samt att klassgränser behålls. En mindrejustering av referensvärden för DIN och DIP utifrån havsmiljöförordningens G/M värden föreslåsdock. De nya referensvärdena är framtagna med modellen S-HYPE (Lindström m.fl. 2010) förtillrinnande sötvatten och utifrån utsjövärden för oorganiskt fosfor och kväve (HVMFS 2012:18) samteffektsamband i mätdata. Det förtydligas också att ett konstant referensvärde för näringsämnenanvänds vid salthalter ≤2 psu.Den S-HYPE körning som använts för referensvärden i tillrinnande sötvatten är en bakgrundskörningsom är anpassad till definitionen av bakgrundsbelastning i PLC6 (Pollution Load Compilation 6,HELCOM).Utöver uppdatering av referensvärden för näringsämnen så föreslås en förändrad sammanvägning avkväve och fosfor i bedömningsgrunden. Det innebär att de ingående parametrarna för kväve och fosforsammanvägs var för sig. Bedömningsgrunderna ger då en separat status för varje näringsämne (kväveoch fosfor) baserat på de ingående parametrarna. Detta ger både en större möjlighet till att se vilketnäringsämne som bidrar till att eventuellt sänka status och stämmer överens med hur rapporteringentill EU-kommissionen ska ske.För syre rekommenderas en uppdatering om vilka mätmetoder som får användas, så att ävenmätningar med sensorer kan användas för statusbedömning. För siktdjup var ambitionen att ta fram etthumusgränsvärde för när kvalitetsfaktorn inte ska tillämpas. En fullständig statistisk analys har intehunnits med och en tydlig rekommendation kan inte ges.Det har under arbetet med att ta fram nya referensvärden för näringsämnen enligt nuvarande metodblivit tydligt att metoden för att bedöma näringsämnen behöver en mer övergripande uppdatering. Tillexempel kan metoden för salthaltskorrektion troligen förbättras med hjälp av en analys av mätdata ikombination med kustzonsmodellen.

This report contains two parts which are self standing reports and a contribution to the HELCOM project EUTRO-OPER. The work has been funded and commissioned by SwAM (Swedish agency for marine and water management) 2014-2015.

• Coastal eutrophication status assessment using HEAT 1.0 (WFD methodology) versus HEAT 3.0 (MSFD methodology)

Eutrophication status is assessed nationally in coastal waters within the Water Framework Directive (WFD) and in open sea areas within the Marine Strategy Framework Directive (MSFD). Both WFD and MSFD consider eutrophication but with different approaches and it is therefore a need for harmonisation in the assessment process.   The Excel based tool HEAT (HELCOM Eutrophication Assessment Tool) has been used in previous assessments in the HELCOM region. There are two versions of the tool; HEAT 1.0 and HEAT 3.0, the first is based on the WFD methodology and the second is based on the MSFD methodology. The main difference between HEAT 1.0 and HEAT 3.0 is how the indicators are grouped. Here we assess the eutrophication status in coastal waters by applying HEAT and compare the results with the national WFD assessments. The present test includes data on 33 selected coastal water bodies in five countries: Estonia, Finland, Latvia, Poland and Sweden. Data on reference condition, acceptable deviation, status and class boundaries of all indicators used in WFD for reporting ecological status (biological and physical-chemical) have been provided for each tested water body. The data has been inserted in the HEAT 1.0 and HEAT 3.0 tools and been compared with the national WFD assessments.   Both HEAT versions gave lower status in more than 50 % of the cases. For some tests the status changed to sub-GES from GES when HEAT is applied. The good/moderate boundary is the same in both HEAT and the WFD while the lower class boundaries in general are stricter in HEAT, which explains the lower status. In national WFD assessments expert judgment is used when there is little, no or very uncertain in situ data. The status in HEAT is given by the one-out-all-out principle but it is still possible to include expert judgment through the weighting factors.

• Development of an oxygen consumption indicator

It was investigated if the oxygen consumption can be used as an oxygen indicator for the Baltic Sea. The method is based on the idea of calculating the oxygen consumption in a stabile layer below the productive zone during summer and relating this to nutrient concentrations. With more nutrients available there is an increased biological production. By estimating how much oxygen is needed to mineralise the biological material it may be possible to link the oxygen consumption to eutrophication.

The oxygen consumption was calculated for the BY15-Gotland Deep in the Eastern Gotland Basin. We identified a stabile layer between 30 and 50 m and a large change in both oxygen and nutrients from June to August. However, the oxygen consumption had a very high inter-annual variation and there were no significant correlation with the winter mean of nutrient concentrations. It was not possible to calculate the diffusion between the layers because of too sparse measurements at the stratification which limits the method. The calculation of the diffusion is however possible to improve with a model. Further on, the depth of the stabile layer is varying between areas and also between years.   We realised that the method has too many restrictions to be a functional indicator. A functional indicator shall not be dependent on heavy modelling or demand too much on expert judgement. We also investigated if a possible candidate to use as a more simple oxygen consumption indicator could be the use of oxygen saturation at a specific depth. If we assume that the temperature has not changed much since the establishment of stratification we may expect that changes in oxygen saturation observed in August at this depth would be caused by the biological oxygen consumption occurring during late spring and summer. The correlation with winter mean nutrients slightly improved in this case.

The Swedish OSPAR waters were assessed by applying the OSPAR Common Procedure for the time period 2006 – 2014. The Swedish parts of Skagerrak, Kattegat and the Sound constitute the outer part of the transition zone between the estuarine Baltic Sea and the oceanic North Sea and were investigated for nutrients, chlorophyll-a,oxygen, macrophytes, phytoplankton and zoobenthos. The conclusion from the overall assessment of the Swedish OSPAR waters was that only Skagerrak open sea could be classified as a Non-Problem Area and all other assessment units were classified as Problem Areas.  Atmospheric input of nitrogen significantly decreased in both Skagerrak and Kattegat and the land based input of total nutrients also decreased in Skagerrak, Kattegat as well as the Sound. However, the short-term trend of nitrogen input to the Sound was positive. Skagerrak is governed by trans-boundary transports from the North Sea of mainly nitrogen but also phosphorus. Kattegat receives trans-boundary nutrients from both the Baltic Sea through the Sound and from Skagerrak and transports nutrients towards the coast and the western part of the basin.  Overall, concentrations of DIN, DIP, TN and chlorophyll-a decreased in most areas, however, no significant trends were found for DIP. Increasing concentrations were found in silicate, POC and TP. The Secchi depth increased in most areas. Oxygen deficiency was mainly a problem in the fjords and the Kattegat open sea.  In Skagerrak coastal waters winter nutrients were only elevated in the fjords. Concentrations of DIN generally decreased significantly and there were tendencies of decreasing DIP. This pattern was also supported by the total nitrogen while total phosphorus increased. Secchi depth was improving and there was a significant positive trend of increasing depths. However, zoobenthos were still in bad condition and phytoplankton indicator species were often elevated. Chlorophyll-a concentrations were generally decreasing but still elevated in the inner coastal waters. There were also problems with algal toxins such as DST (Diarrhetic Shellfish Toxin) and PST (Paralystic Shellfish Toxin) infections in the area. According to the OSPAR classification scheme, a unit with no evident increased nutrient enrichment can be classified as a Problem Area but the cause might be due to trans-boundary transport from adjacent areas. In the open area of Kattegat there were still problems with oxygen deficiency, especially in the southern parts, even though the trend was significantly positive for the assessment period 2006 – 2014. Concentrations of chlorophyll-a and DIN decreased significantly, however, DIN levels were still generally elevated, especially in the southern parts of Kattegat while DIP was closer to the assessment level. In Kattegat coastal waters winter nutrients were elevated in all assessment units, except from the inner coastal waters, even though there was a general pattern of decreasing going trends. Chlorophyll-a was mainly elevated in the Sound and the estuaries. Secchi depth is generally improving and a significant increase was seen in the Sound. Also in Kattegat, zoobenthos were in bad condition and phytoplankton indicator species were often elevated. 

Results from the Swedish national marine monitoring in the pelagic during 2016 are presented. The institutes who conduct the national monitoring are SMHI (Swedish meteorological and hydrological institute), SU (Stockholm University) and UMF (Umeå marine sciences centre). The presented parameters in this report are; salinity, temperature, oxygen, dissolved inorganic phosphorous, total phosphorous, dissolved inorganic nitrogen, total nitrogen, dissolved silica, chlorophyll and phytoplankton. Secchi depth, zooplankton, humus, primary production, pH and alkalinity are also measured but not presented. Seasonal plots for surface waters are presented in Appendix I.  Time series for surface waters (0-10 m) and bottom waters are presented in Appendix II. The amount of nutrients in the sub-basins of the Baltic Sea is presented per season and year in Appendix III.Exceptional events 2016 

• A warm September due to several high pressure systems, with temperatures more than one standard deviation above mean in almost all stations from Skagerrak, Kattegat and the Baltic Proper.
• Low oxygen in Kattegat bottom water during autumn as can be seen in the seasonal plots for both Anholt E and Fladen.
• Improved oxygen condition in the East Gotland Basin, due to an increased frequency of deep water inflows in comparison to the period 1983 until the large inflow in December 2014. The inflow of 30 km3 in the beginning of the year could be tracked in the deep water in the Eastern Gotland Basin in June.
•  Elevated levels of silicate have been observed in the Baltic Sea since 2014 and the silicate levels were also elevated this year but mainly in the central and the northern parts of the Baltic Proper.
• In July there were high cell numbers of the dinoflagellate Dinophysis acuminata, which caused high levels of toxins in blue mussels. During this period it was forbidden to harvest blue mussels along the Bohus coast.
• Unusual long period of cyanobacteria bloom in the Baltic Sea.

This report presents the main results of the Swedish national marine monitoring programme of thepelagic during 2018. The monitoring data of hydrography, nutrients and phytoplankton are analysedfor the seas surrounding Sweden: the Skagerrak, the Kattegat, the Sound, the Baltic Proper, theBothnian Sea and the Bothnian Bay.The national environmental monitoring of the pelagic is carried out by SMHI (SwedishMeteorological and Hydrological Institute), Stockholm University and UMF (Umeå Marine SciencesCentre). Data is collected, analysed and reported with support from Swedish environmentalmonitoring and on behalf of by SwAM (Swedish Agency for Marine and Water Management). TheSMHI monitoring is made in cooperation between the national environmental monitoring of thepelagic and the SMHI oceanographic sampling programme for the seas surrounding Sweden and is cofinancedby SwAM and SMHI. This annual summary of the national monitoring is made by SMHI andis financed by the contract between SwAM and SMHI.The weather in 2018 was characterized by high air temperatures and a few storms that impliedconsequences for the state in the sea. The spring arrived quickly and the sea surface temperatureincreased rapidly from April to May. In August and September two storms, named Johanne and Knud,passed the region and the surface layer was well-mixed at several stations. At the East coast upwellingevents were noted in both the Baltic Proper and the Bothnian Sea.During the year there were two small deep water inflows to the Baltic Proper that temporarilyimproved the oxygen condition in the southern parts. No improvements of the oxygen condition wereseen in the Eastern and Western Gotland Basins, instead the amount of hydrogen sulphide increased inthese basins during the year.The spring bloom had arrived in the Skagerrak and the Kattegat in March and concentrations ofdissolved inorganic phosphorus (DIP) and dissolved inorganic nitrogen (DIN) were close to or at thedetection limit from April to September. In the Skagerrak and the Kattegat the spring bloom wasdominated by the diatom Skeletonema marinoi. In the Baltic Proper the spring bloom was observed amonth later, in April. The extensive cyanobacteria bloom in the Baltic Proper started already in Mayand during the late September cruise cyanobacteria were still abundant. The dinoflagellateProrocentrum compressum was found in high cell numbers during the autumn at all stations on theWest coast. This flagellate has rarely been observed previously and although it is not harmful it isinteresting when species suddenly occur and stay for a longer period. The potentially harmful diatomgenus Pseudo-nitzschia bloomed in the beginning of December.Surface concentrations of DIP and DIN were mainly normal except from in the Skagerrak and theKattegat where concentrations were lower than usual in December. Concentrations of silicate wereabove normal levels before the spring bloom at most of the stations and in the Baltic Proper silicatewas also high in the autumn.In 2018 there were some difficulties with available research vessels for the planned cruises and somecruises needed to be cancelled with short notice. Many planned observations were therefore missed, inparticular during the summer period.

This report presents the main results of the Swedish national marine monitoring programme of the pelagic during 2017. The monitoring data of hydrography, nutrients and phytoplankton are analysed for the seas surrounding Sweden: Skagerrak, Kattegat, The Sound, Baltic Proper, Bothnian Sea and Bothnian Bay. The monitoring is carried out by SMHI (Swedish Meteorological and Hydrological Institute), SU (Stockholm University) and UMF (Umeå Marine Sciences Centre) and the monitoring programme is co-funded by SwAM (Swedish Agency for Marine and Water Management), SMHI, SU and UMF. Data is collected, analysed and reported with support from Swedish environmental monitoring and commissioned by SwaM.

The Baltic current along the Swedish west coast implies large variations in surface salinity and the unusually large outflow of brackish water from the Baltic Sea in 2017 was reflected as low surface salinity in Skagerrak and Kattegat in the beginning of the year. There were no major deep water inflows to the Baltic Sea during 2017 but a few inflows of minor magnitude. These minor inflows only temporarily improved the oxygen condition in the Bornholm Basin and in the southern part of the Eastern Gotland Basin.

The salinity below the halocline was above normal in the Gotland Basins and in the Northern Baltic Proper, and also in the surface layer in the Eastern Gotland Basin for almost the whole year.

In Skagerrak and Kattegat, surface concentrations of phosphate and dissolved inorganic nitrogen were normal while dissolved silica concentrations were elevated especially in spring. In the Baltic Sea, the concentration of silicate in the surface water was elevated in all basins. According to the estimated total content of silicate there has been an increase in silica content in the Baltic Sea since the early 1990’s. Surface concentrations of phosphate were above normal in the Gotland basins and the Northern Baltic Proper while inorganic nitrogen content was above normal in parts of the Arkona and Bornholm basins. During spring and summer, the inorganic nitrogen was consumed at greater depths than usual in the Baltic Proper. In particular concentrations of phosphate and dissolved silica were generally lower than normal in the bottom layer.

Instead of diatoms, the flagellate genus Pseudochattonella, which is potentially toxic to fish, bloomed in the Kattegat and Skagerrak areas in February – April. During autumn there was a prolonged diatom bloom though. In the Baltic Sea spring bloom occurred in April. The cyanobacteria bloom began in May already with Aphanizomenon flos-aquae. During June and July all three of the filamentous cyanobacteria, A. flos-aquae, Dolichospermum lemmermannii and the potentially harmful Nodularia spumigena were found in the phytoplankton samples in various amounts.

In the Bothnian Sea, the sea surface temperature during summer was lower than normal and the oxygen conditions in the bottom layer was not critical but still below normal levels.

The Swedish national marine monitoring programme of the pelagic, the water column, includes monthly measurements of hydrography, nutrient concentration and phytoplankton for the seas around Sweden; the Skagerrak, the Kattegat, the Sound, the Baltic Proper and the Gulf of Bothnia. Data is collected, analysed and reported on behalf of SwAM (Swedish Agency for Marine and Water Management).

This annual report describes interesting observations from the monitoring and summarizes the main results of 2019. At the end of the report and in the Appendix time series from 1960 to 2019 are also presented.

2019 was the 10th warmest year since reporting started in 1860 and the precipitation was also higher than normal, despite this; groundwater levels were low, especially in southern Sweden. Two stronger storms passed Sweden during the beginning of the year, Alfrida (January 1-2) and Jan (January 10- 11). This year's winter was very mild and the maximum ice spread was only 88,000 km2 which is less than normal, the ice season ended in mid-May. There were no autumn storms in 2019 and the autumn was slightly colder than normal in the north but warmer in the south.

During the year, only a few minor inflows of water from the Kattegat to the Baltic Sea occurred through the Sound. Three inflows were large enough to improve the oxygen situation in the southern Baltic Proper. The largest occurred in late November to mid-December. The effects of this inflow will be observable in spring 2020. A small change was observed in the oxygen concentration in the Eastern Gotland Basin at the beginning of the year, as a result of an inflow during the fall of 2018.

The spring bloom started in February in the Kattegat and sometime between March and April in the Skagerrak. In April, a small bloom of the fish toxic genus Pseudochattonella was observed at stations Anholt E and N14 Falkenberg. The nontoxic coccolitophoride Emiliania huxleyi was found in the Kattegat and Skagerrak from May to November in varying quantities. The potentially toxic diatom genus Pseudo-nitzschia was present in high cell numbers in October and November. In the Baltic Proper, the spring bloom was observed from March to April with high cell numbers of diatoms and a dinoflagellate typical for the spring, Peridiniella catenata. Cyanobacteria were observed in elevated quantities as early as May and increased in late June to culminate at the end of July when they had also spread into the Bothnian Sea. The amount of filamentous cyanobacteria decreased in August, and colony forming pico cyanobacteria increased.

Nutrient concentrations in the surface water were mainly within normal levels except in the Skagerrak and the Kattegat at the start of the year when slightly lower levels of phosphate, silicate and dissolved inorganic nitrogen were measured. Even in Skagerrak's and Kattegat's deep waters, the levels of dissolved inorganic nitrogen were lower than normal during parts of the first half of the year, and in the Kattegat and the Sound phosphate levels were also low. The levels of dissolved inorganic nitrogen were also low during the beginning of the year in the Baltic Proper, while phosphate levels were more normal. In the Baltic Proper, elevated silicates and phosphate levels were observed in deep water with little or no oxygen.

För att uppskatta dynamiken i den marina miljön genom miljöövervakning och för att ta fram bra beslutsunderlag till åtgärder i havet så behövs mätningar med hög upplösning i tid och rum. Dagens mätprogram utförs traditionellt med lägre upplösning i tid, i princip månadsvisa provtagningar men med relativt hög rumslig upplösning på olika stationer i svenska vatten.Målet med projektet är att utvärdera kostnadseffektiva mätsystem med kapacitet att mäta viktiga oceanografiska variabler med hög upplösning i tid som komplement till nuvarande mätprogram. I projektet ingår tre positioner med bottenmonterade system i områden där det kan råda stor variation på korta tidsskalor för variabler som temperatur, salt, syre och ström. De bottenmonterade mätsystemen har mätt temperatur, salinitet och syre vid stationerna L9, Hanöbukten och Understen. Vid Hanöbukten och Understen har även ström mätts. Parametrarna har samlats in med hög upplösning i tid, i snitt var 20:e minut.De bottenmonterade mätsystemen planerades att sättas ut med R/V Svea och byte av mätsystemen planerades till varje halvår. I en utvärdering av projektet, 1,5 år efter första utsättningen, kan man konstatera att det var svårt att kombinera R/V Sveas schemalagda veckor med bra väder för utsättning och upptag av bottenmätsystemen. Möjligheten för byte av bottenmätsystem är mycket liten då R/V Svea oftast bara passerar förbi varje position för bottenmätsystemen en gång under SMHIs utsjöexpedition. Vid ett tillfälle uppstod ett tekniskt problem som bidrog till att L9-riggen slet sig inför upptag i juni 2021 samt att bottenmätystemet vid Hanöbukten var borta och inte kunde hittas i oktober 2021, trots upprepade försök. Hanöbukten är en intressant station, men problematisk för bottensystem då området har mycket fiske och framförallt trålande fartyg.Resultaten från projektet visar att samtliga bottenmätsystem fångar en stor variation och viktig dynamik i temperatur, salinitet, syre och strömförhållanden som den traditionella månadsvisa provtagningen inte lyckas fånga. Månadsvisa mätningar behöver kompletteras med högupplöst data för att oceanografiska händelser, med potentiella viktiga effekter i den marina miljön, skall åskådliggöras tydligt. SMHIs analys av data i denna rapport visar att bottenmonterade mätsystem har stor potential för att förstå processer som sker på kortare tidsskala i den marina miljön. Till exempel kan de användas för att identifiera områden med korta perioder med syrebrist som har stark negativ inverkan på bottenfauna. Dessa mätsystem ger även värdefulla och kostnadseffektiva data som kompletterar de data som insamlas inom befintliga mätprogram. I rapporten fastslår SMHI att bottenmätsystemen vid L9 Laholmsbukten och Understen bör långsiktigt inkluderas i den nationella miljöövervakningen. SMHI rekommenderar att nästa steg är att testa och utvärdera profilerande flöten, s.k. Argo floats, i lämpliga områden av Östersjön