Two decades ago the first Earth Summit raised the question of how biological diversity loss alters ecosystem functioning and affects humanity; this Review looks at the progress made towards answering this question.

Excessive nutrient loading of water bodies is a leading cause of water pollution worldwide, and controlling nutrient levels in watersheds is a primary objective of most environmental policy. Over the past two decades, much research has shown that ecosystems with more species are more efficient at removing nutrients from soil and water than are ecosystems with fewer species.