The cumulative impact of anthropogenic pressures on coastal seas is important to consider for a strategic and sustainable management of marine ecosystems. We aim to demonstrate how, and to what extent, incorporating interactions among ecosystem components (species and habitats) and indirect effects of pressures through other ecosystem components can develop existing cumulative impact assessment (CIA) models. A Swedish case study area was selected to test a simplified version of the extended regional Symphony CIA model. Five pollution- and climate-driven pressures acting on three trophically connected ecosystem components, i.e. cod, herring and plankton species/organism groups, were used. In addition, we conducted a systematic review of the scientific literature to determine the impact weight scores for an advancement of the method. The results from the development of CIA models clearly indicate the importance of introducing ecosystem component interactions and indirect effects into CIA models. The total cumulative impact increased by 117 % in the test area, but even more importantly, the development of the model resulted in a spatially more detailed outcome with a greater spatial variability in the magnitude of the total cumulative impact. New areas were highlighted that are under pressure compared to the original model. Thus, the development of the model captures cumulative impacts that would otherwise be overlooked if ecosystem component interactions and indirect effects were ignored. These types of changes to CIA models are required to increase the predictive power and ecological relevance to accommodate solid holistic and ecosystem-based marine management.

Several decades of remedial work have reduced the supply of nutrients from land to sea. Despite this, large-scale eutrophication remains a significant environmental problem along the Swedish coast and release of phosphorus from the sediments exacerbate the problem and reduces the effect of land load reductions. Thus, there is a need to identify where targeted remedial actions would have the most significance, and the highest likelihood to succeed. Additionally, there is a need to map the long-term relation between oxygen concentration and phosphate release from marine sediments in the Swedish coastal zone, which will support the aim to provide a scientific basis for prioritizing remedial targeted actions.

The results presented in this report indicate that there are more than 100 waterbodies along the Swedish coast with significant correlation between low oxygen concentrations and increased release of phosphorus from bottom sediments. However, oxygen concentrations below 1 ml L-1 is not the main driver for phosphorus release from Swedish coastal sediments and only three water bodies were found to actually have a net long-term internal source of phosphorus. The results also indicate that the number of years and autumns with an internal net release of phosphorus in the Swedish coastal zone seems to be decreasing, generally, and especially in late summer and autumn. An exception is the coastal zone bordering the northern Baltic Sea where, on an annual basis, the number of years and autumns with a net phosphorus outflux from the sediments seem to increase instead. Finally, it should be noted that locations with a significant correlation between low oxygen concentrations and increased release of phosphorus from bottom sediments do not necessarily overlap with areas with a generally high sediment phosphorus outflux. Thus, both types of areas need to be considered for targeted actions.

Colored Dissolved Organic Matter (CDOM), is the light absorbing fraction of the Dissolved Organic Matter (DOM) and is mainly of terrestrial origin. These substances are highly variable in the coastal zone and absorb and scatter light at different wavelengths and increase the light attenuation in the water column. As a consultation response from the latest Action Program for the Marine Environment an initial literature search of CDOM in Sweden's coastal waters and summary of the available literature and data was completed. It showed that the Swedish coastal observations of CDOM in the SHARKweb database are sparse and only locally occuring. However,  the availiable litterature indicates that CDOM likely has a significant effect on the light attenuation in Swedish coastal waters. Future changes in light attenuation in the coastal zone are assumed to be driven largely by the changes in the terrestrial inputs. River discharge is expected to increase in a future climate, and thus also the supply of CDOM and nutrients to the coastal zone.

Flera decennier av åtgärdsarbete har minskat tillförseln av näringsämnen från land till våra hav. Trots detta kvarstår storskalig övergödning som ett betydande miljöproblem längs den svenska kusten och utsläpp av fosfor från bottensedimenten förvärrar problemet och minskar effekten av åtgärdsarbetet. Det finns därmed ett behov av att identifiera var riktade åtgärder kan ha störst betydelse och störst sannolikhet att vara framgångsrika. Dessutom finns det ett behov av att kartlägga sambandet mellan syrekoncentration och fosfatsläpp från sedimenten i kustzonen, vilket kommer att stödja arbetet med att tillhandahålla en vetenskaplig grund för att prioritera riktade åtgärder.

Resultaten från denna rapport indikerar att det finns mer än 100 vattenförekomster längs den svenska kusten som har signifikant korrelation mellan låga syrehalter och ökat utsläpp av fosfor från bottensediment. Syrekoncentrationer under 1 ml L-1 är dock inte den huvudsakliga orsaken till fosforutsläpp från sedimenten och endast tre vattenförekomster visade sig ha en långsiktig intern fosforkälla. Resultaten tyder också på att nettoutsläpp av fosfor från sedimenten i den svenska kustzonen generellt sker alltmer sällan, särskilt under sensommaren och hösten. Ett undantag är kustzonen som gränsar till Bottniska viken, där nettofosforutflöde från sedimenten på årsbasis istället tycks ske allt oftare. En slutsats är också att platser med en signifikant korrelation mellan låga syrekoncentrationer och utsläpp av fosfor från bottensediment inte nödvändigtvis överlappar med områden med generellt högt sedimentfosforutflöde. Båda typerna av områden måste därför övervägas som lämpliga för riktade åtgärder.

Colored Dissolved Organic Matter (CDOM) är en den ljusabsorberande delen av det lösta organiska material som finns i havs- och kustvatten och är huvudsakligen av terrestriskt ursprung. Dessa ämnen absorberar och sprider ljus vid olika våglängder och ökar ljusutsläckningen i vattenpelaren. Som ett remissvar från det senaste åtgärdsprogrammet för havsmiljön gjordes en första litteratursökning av CDOM i Sveriges kustvatten samt en sammanfattning av tillgänglig litteratur och data. Den visade att de svenska kustobservationerna av CDOM i SHARKweb-databasen är få och endast lokalt förekommande. Dock tyder litteraturen på att CDOM sannolikt har en betydande effekt på ljusutsläckningen i svenska kustvatten och framtida förändringar i ljusutsläckningen i kustvattnet antas till stor del bero av förändringarna i de lösta ämnen som når kusten med flodvattnet. Flodtillrinningen förväntas öka i ett framtida klimat och därmed väntas också tillförseln av CDOM och näringsämnen till kustzonen att öka.

The Baltic Sea is a heavily impacted ecosystem with multiple pressures acting simultaneously. In order to quantify ecosystem impacts of integrated climate change and eutrophication pressures under constant high fishing pressure, and to support decision-making and policies in generating environmental and economic sustainable systems, the Baltic Atlantis holistic and mechanistic ecosystem model was applied. The overall aim was to run scenarios of separate and integrated impacts of climate and riverine nutrient load changes, taking into account the interactions of the full food web in the entire Baltic Sea. This was done to identify which of those two pressures will likely dominate the future of the Baltic Sea ecosystem, and to test effects of different riverine nutrient forcing sources as well as the Baltic Atlantis functions in relation to hydrographic spawning thresholds. By integrating the hydrography, the biology covering all trophic levels of the food web, and multiple pressures, i. e. eutrophication, climate change and fishery, we were able to evaluate relative impacts of 3 climate scenarios and 3 nutrient load scenarios, using two sources of nutrient forcing and predict likely trends in ecosystem effects. With focus on major fish stocks, our model, with its assumptions, indicated that nutrient loads are the main driver of the changes in the ecosystem as long as the hydrographic thresholds for spawning are not reached. If the thresholds are reached for the Baltic cod, climate change impact will become most important. Furthermore, higher nutrient loads resulted in cod decrease, and increase in sprat and herring. This effect is amplified by stronger climate change. Overall, it is of crucial importance for the future of the Baltic Sea fisheries and stocks that potential impacts are considered both separate and integrated in a dynamic ecosystem-based management approach.