Scientists have long recognized that the way humans use land—say, for agriculture or development—affects the quality of the water that drains and flows from it. New research on a Michigan watershed maps how these effects persist over time. Since rain may travel through the ground for 100 years or more to reach a river or lake, land use decisions from long ago influence the chemical constituents that the water may carry.

This research, which was conducted by scientists at Purdue and Michigan State University, demonstrates how land use today affects the water quality of rivers and streams far into the future.