Forest top soils capture and stabilize nitrogen pollution very quickly but release it slowly, according to new research published in the journal Ecology. The findings indicate that mature forests may be providing an under-appreciated service by storing excess nitrogen, which can lead to algal blooms and oxygen-depleted dead zones if too much is released into lakes and waterways. Older forests store nitrogen more efficiently than young forests recovering from clear-cuts, the researchers found, because they have accumulated more top soil and organic matter within the forest floor. Previously, it had been unclear how mature forests continued to capture and store nutrients such as nitrogen after they stopped adding tree biomass. The new research indicates it’s likely due to the delay between nitrogen uptake, which happens within days, and nitrogen release, which unfolds over years and decades.