Background From an environmental point of view, acid sulphate soils (AS-soils) are regarded as the most problematic soil types in the world. Finland has Europe's largest areas of AS-soils (c. 1 000-2 000 km2). Land uplift has caused these sulphide-bearing sediments to emerge above the current sea-level. Through reclamation, burning of the peat cover and heavy liming, they constitute today some of the most productive farm lands in Finland. To a lesser extent, sulphide bearing sediments have been reclaimed for forestry, construction works and infrastructure. Unfortunately, as a result of the measures outlined above, the groundwater level is considerably lowered during dry spells, enabling oxygen to penetrate the soil. When exposed to oxygen, sulphides oxidize and produce sulphuric acid and make the soil extremely acid (pH 2,5-4), which in turn mobilizes enormous quantities of metals (including Al, Cd, Co, Ni and Zn) stored in the soil. Together with acidity, these metals are flushed from the soils into drains and recipient estuaries during wet spells. Metal discharges from AS-soils are estimated to significantly exceed the corresponding industrial discharges from all Finnish industry. This is also the case for cadmium, one of the priority substance metals regulated by the EU Environmental Quality Standard (EG-EQS) Directive (2008/105/EC). Moreover, cadmium concentrations also exceed the environmental quality standards in many waterbodies affected by AS-soils. The extensive pool of toxic metals in these soils with high risk of mobilisation has not been adequately understood until very recently. The chemical composition and drainage water quality of AS-soils resembles those of sulphur rich metal ores, which cause similar acidity problems in Europe and worldwide. Objectives The project aimed to develop climate change adaptation tools for the Finnish River Basin Districts to mitigate impacts of increased leaching of acidity and metals from acid sulphate soils drained for agriculture and forestry. Climate change is expected to increase environmental damage if no targeted mitigation measures are developed. The overall objective was to promote the application of techniques and actions that reduce acidity and metal concentrations in drainage waters. In this way it would help achieve the environmental objectives according to the EU Water Framework (2000/60/EC), Flood (2007/60/EC), Habitat (92/43/EEC) and EQS (priority substances) directives. Another key objective was to consolidate the knowledge base for adapting pollution control methods to the changing precipitation, runoff and temperature conditions. The project aimed to develop effective mapping, identification and risk classification methods of AS-soils. Furthermore, by constructing prototype testing fields with infrastructure and the necessary equipment (such as subsurface controlled drainage systems, pumping systems, tailored cropping and cultivation schemes), the project would be able to demonstrate climate change adaptation tools under practical field conditions. Other specific goals included the establishment of learning environments and forums for participatory planning to involve farmers, forest owners, authorities and specialists in decision making concerning adaptation of land use to climate change. Results The CATERMASS project developed methods for the classification and risk mapping of the specific AS-soils in Finland. It carried out field measurements, sampling and analyses, in line with the project proposal. Information was collected from more than 7 000 sites and more than 2 000 samples have been analysed. A guidance document was prepared on how to identify, characterise and map acid sulphate soils with a more detailed working instructions for specialists. The project also conducted an eco-toxicological risk assessment in 14 Ostrobothnian river estuaries affected by AS-soils in the target area – an eco-toxicological risk classification was generated for them. The collected information on the ecological end eco-toxicological effects of AS-soils was made available in a free online database and presented in two published scientific reports. Pollution abatement prototypes were developed and demonstrated by the project. Good results were obtained by combining a vertical plastic sheet to main surface drains and pumping excess water to the field. It was found that in the level fields, the sulphide layers can be kept under groundwater level through controlled subsurface drainage, and the effect can be enhanced by pumping additional water from ditches to the drainage pipes. This process is called ‘subirrigation’. Plastic film mounted to the field and extending to the sulphide layer was shown to effectively block water escaping from the field. Combining these methods allows the sulphide layers to be maintained in a reduced state. The socio-economic effects of the mitigation measures were analysed in the multi-criteria cost-benefit analysis in cooperation with the stakeholders – local watershed councils, farming associations, NGOs, regional authorities, municipalities and fishermen. A shared understanding of the problem, the necessary mitigation measures and the socio-economic benefits of them was achieved. The controlled subsurface drainage in fields with subsurface drainage is the most cost-efficient way to reduce acidity in the water bodies. Further information on the project can be found in the project's layman report and After-LIFE Communication Plan (see "Read more" section).