Formerly Aquatic Sciences and Fisheries Abstract (ASFA). International database for marine, freshwater and brackish water resources, early 1900's-present.
Articles on ecosystem ecology, energy, natural resources, marine & freshwater science, geography, pollution & waste management, environmental technology, environmental law, public policy, and urban planning.
The process of choosing keywords is important no matter what database you will use.
Begin by breaking your research question into its component parts, and then brainstorm synonyms for each of those concepts. You may need to do some background research to find out basic information about the topic to figure out appropriate terms. This is a time when a Google search can come in handy. An alternative is looking at keywords in an article on your topic - look at what keywords are listed for the article and you might find some new ways of searching.
How is climate change affecting the health of deciduous trees in the Pacific Northwest?
May expand to the following in a search:
Climate change OR global warming
deciduous trees
health OR phenology
"Pacific Northwest" OR Washington OR Oregon