Surface freshwaters — lakes, reservoirs, and rivers — are among the most extensively altered ecosystems on Earth. Transformations include changes in the morphology of rivers and lakes, hydrology, biogeochemistry of nutrients and toxic substances, ecosystem metabolism and the storage of...

The value of the services provided to human societies by natural ecosystems and biogeochemical cycles has recently been the topic of discussion and research. Here I review some of the basic economic principles necessary for understanding some of the questions that arise in this area. I argue...