From their “About” page:
“Intute is a free online service providing access to the very best web resources for education and research. All material is evaluated and selected by a network of subject specialists to create the Intute database.
The Intute database makes it possible to discover the best and most relevant resources in one easily accessible place. You can explore and discover trusted information, assured that it has been evaluated by specialists for its quality and relevance.”
They have organized the pages by very broad subject areas: Health & Life Sciences, Arts & Humanities, Social Sciences and Science Engineering & Technology Environment has recently gained separate category status: Intute Environment Gateway
Look at the number of vetted websites!
You may run a simple or advanced search, or browse the categories.
Agriculture and the Environment 
Biodiversity and Conservation 
Climate and Environment 
Energy and Resources 
Environmental Economics 
Environmental Law and Legislation  Environmental Management 
Environmental Policy 
General Environment 
Landscapes and Landscape Architecture 
Pollution Science 
Waste Management