Narrator: This is Science Today. A mathematical technique similar to one used in astrophysics has helped researchers measure how long watersheds hold water and over what time scales they released that water into streams. James Kirchner, a professor of geology and geophysics at the University of California, Berkeley, was one of the study's lead authors.
Kirchner: In general, watersheds flush themselves out over much longer time scales and having much longer chemical memory of the rain that has fallen on them or the fertilizers that have been spread on them or what have you, than anyone previously expected.
Narrator: Basically, contaminants will initially be flushed out quickly, but then low-level contamination will be fed to streams for a surprisingly long time. Kirchner recently used a similar mathematical technique to measure the time lag of the Earth's recovery after an extinction event.
Kirchner: The actual sort of mathematics is all done fairly simply on a personal computer. So, intellectually it's rocket science, but these days it's very simple to do the calculations.
Narrator: For Science Today, I'm Larissa Branin.