Forested lands are the US and Canada’s single largest source of drinking water: At least 180 million people in over 68,000 communities in the US, and two-thirds of the Canadian populace, rely on forested watersheds to clean their drinking water.

In healthy watersheds, forest vegetation naturally catches and purifies fresh water. Much of the water is immediately soaked up by healthy soils, where organic matter traps and microbes degrade pollutants like pesticides and fertilizer. Water that isn’t absorbed runs along the surface of the ground, slowed by diverse stems and detritus on the ground, which allows sediment and chemicals to drop out before the water arrives at streambanks. Wetland plant roots, like blueberry and winterberry, take up excess nutrients like nitrogen and phosphorus.

These natural processes are so effective that major cities rely on them for millions of residents. New York City is the classic example: In the late 1990s, the city spent $1.4 billion to restore and protect the upstate Catskills forest watershed. As a result, they avoided having to spend $6 billion to build a new water filtration plant, plus an estimated $300 million in annual maintenance costs. Many other cities have followed New York’s suit, including New Jersey, which spent $55 million on its Sterling Forest watershed to save $160 million, and Portland, ME, which invested $729K and saved over $25 million. Unlike man-made built infrastructures, natural watersheds grow more resilient and capable of providing services over time, not less.

Jumping Worms Degrade Watersheds

• Jumping worms convert organic soil into dry, nutrient-rich castings that sit, unattached, on the surface of the ground. When it rains, these nutrients move with the eroding castings and flow into water bodies. Just like agricultural runoff, these nutrients can promote toxic algae blooms and bacterial overgrowth. Castings themselves also contribute harmful sedimentation as well. 

• When jumping worms reduce forest biodiversity, they reduce the number of stems and roots that would normally slow water down above and below ground.

• Soil microbes perform most of the pollutant breakdown in soils and the organic matter in the soil immobilizes certain nutrients, to keep it from running off. But when jumping worms consume the organic horizon, they take away the habitat those microbes require. Scientists have observed large changes in microbial community composition, and are now working to understand what changes in soil function will follow from these effects.

• Finally, jumping worms bioaccumulate heavy metals that may be immobilized in soil organic matter, like mercury, cadmium, and lead. By remobilizing these toxins, the worms can re-introduce them to the food web and water cycle.