An increasing number of data delivery and processing ser- vices are available online from different environmental information sys- tems. However, these services are often described using different termi- nology and may therefore be difficult to find. Integrating services from multiple providers and combining services into a workflow is likewise complicated. Development of an interoperable environmental data portal requires a detailed definition of the semantics of the data being requested and the services being called. Existing descriptions of semantics, cap- tured in controlled vocabularies or ontologies, represent valuable knowl- edge that must be capitalised on. By ontology extension, we propose to “bridge” existing semantic resources, with the potential to represent more generic relationships and multilingual search and discovery. This ontology extension will be part of a toolkit for building environmental portals by means of standards for web-based data delivery and process- ing services.