The 3rd BONUS Symposium “Sustainable Ecosystem Governance under Changing Climate and Land Use in the Baltic Sea Region” was organised jointly by four projects BONUS BALTICAPP, BONUS GO4BALTIC, BONUS MIRACLE and BONUS SOILS2SEA. In total, 126 participants joined the Symposium coming from 12 countries. Most participants were from countries across the Baltic Sea Region. Scientists and policymakers from the USA, Netherlands, and Australia also participated. The Symposium brought together scientists, policymakers, NGOs, representatives from the private sector and authorities from various levels, in the European Solidarity Centre in Gdańsk from 14‐16 March, 2018. The Programme and Book of Abstracts can be viewed.

The symposium introduced results from four BONUS projects ending in 2018, and comprised 47 oral and 24 poster presentations from these projects, as well as five oral and four poster presentations from other projects in two side events (Gypsum and TReNDS). Two moderated panel discussions and six well received keynote presentations by external, internationally leading scientists completed the programme.

The scope of the symposium was to present, disseminate and discuss results from novel Baltic Sea research on catchment nutrient flows and agro-environmental policies and governance towards sustainable ecosystem services in the Baltic Sea Region. The studies covered international, national and local scales in both short and long-term perspectives. Key messages from the presentations and discussions are highlighted below, organized according to the Symposium themes. These key messages were emphasized in the panel discussions, along with the need to consider mega-trends, like urbanization and increasing size of farms in the region, with accompanying challenges, e.g. storage and spreading of manure.

Scenarios for the future
• Climate change will lead to increased nutrient loads (nitrogen and phosphorus) to the Baltic Sea. Societal changes that drive land use, agricultural practices and investments in point source control technologies may lead to changes in the nutrient load to the Baltic Sea of the same, or higher, order of magnitude as the climate change impacts.
• Scenarios for nutrient loads in a future climate suggest large uncertainties and spatial differences in the region. When moving towards more adaptive policy frameworks, those uncertainties and differences should be acknowledged.
• Scenarios can help society shape and adapt to an uncertain future. Different kinds of scenario analyses and methods to visualize the results can be useful for an efficient communication between scientists, local and regional stakeholders and decision makers.
Policies and ecosystem services in water governance within the Baltic Sea Region
• The costs of nutrient abatement measures are often high, but the value of additional local benefits may outweigh these costs.
• Habitat values, recreation and enjoyment of landscapes are amongst the most important cultural ecosystem services of the Baltic Sea.
• The group of stakeholders involved in nutrient governance needs to be expanded to include new sectors, for example by identifying synergies with other issues (like flood protection, fishery, recreation) that are more relevant to local stakeholders in the Baltic Sea basin.
• The coordination and interconnections between different sectors and policy instruments (e.g. CAP, Rural Development Programs, Water Framework Directive, Floods Directive, climate policies) need to be strengthened. Using the ecosystem services framework can facilitate the design of measures with multiple objectives.
• A better coherence between local and regional stakeholders may be achieved by strengthening the mandate of local stakeholder groups currently involved in water and nutrient governance. Co-governance and participatory bottom-up approaches boost innovation, enable better usage of otherwise hidden information about the local conditions and increase involvement.

Novel approaches for managing nutrients in the Baltic Sea Region
• There is a need to improve the nitrogen use efficiency in the Baltic Sea Region in order to reduce the loads and at the same time maintain or even increase the agricultural crop yields.
• The gap between the current phosphorus load to the Baltic Sea and the target load is high, which calls for additional efforts to develop and adopt new approaches to reduce phosphorus losses from agriculture and other sources.
• Progress of agri-environmental policies is important in the Baltic Sea Region, as the public and private costs of nutrient abatement are high.
• Farmers are skilled problem solvers, but they need the right incentives and a governance framework that provide possibilities for flexible adjustments when including environmental management into farm business decision making.
• Implementation of spatially differentiated regulations and incentives can reduce nutrient loadings, but need new governance concepts to be implemented.
• One size does not fit all; the complex environmental conditions and diverse societies around the Baltic Sea Region require a variety of policy instruments. Water quality trading, spatially targeted regulations and performance based measures have a high potential to reduce the cost of nutrient load reductions. Policy barriers for their use should be removed.
• Demonstration examples of various cooperation schemes, such as hybrid payments with both public and private funding, should be implemented in the Baltic Sea Region.

Advanced modelling from field level to the entire Baltic Sea Region
• Adaptive and flexible policies require reliable models that have credibility among stakeholders. To gain the necessary credibility, model predictive uncertainties should be communicated. To assess the uncertainty when modelling impacts of climate change and future land use, it is recommended to use several models in an ensemble modelling approach rather than relying on just one model.
• Models can also be used to aid and inform policy implementation to choose the most appropriate and cost-effective decisions, and further develop the science-policy interface. Here, the most appropriate models are needed, not necessarily the most detailed.

In the panel discussions, it was emphasized that science and policy should go hand in hand. Further, it was pointed out, that the four BONUS projects are very good examples of natural and social scientists working together, and that this approach should be taken forward. It was advised, that scientists must also concentrate on how their results can affect change and create an impact. For example, outcomes of the projects are directly relevant for the further development of the Common Agricultural Policy of the EU. In a longer time perspective, successful policies lead to changes in the attitudes and behaviour of people living in the Baltic Sea Region. Finally, it was seen as very positive that the four projects joined forces to organize a final symposium together. Selected papers from the conference will be published as a special issue in the journal AMBIO in early 2019.