Editor's note: The concept of accounting for natural capital gained traction this week at the Rio+20 conference, with a new report estimating that companies use $72 trillion in natural resources without paying for them and 86 CEOs agreeing to develop natural capital accounting methodologies to inform business decisions. World Resources Institute has already developed a methodology to evaluate the costs of what it dubs "green infrastructure" -- a tool it says can help make the financial case for investing in the preservation of natural ecosystems.

Infrastructure is essential for economic growth. But as governments debate the future of sustainable development at the Rio+20 conference, there is one infrastructure solution that can provide a good return on investment: nature.

People often don’t think of forests, wetlands, coral reefs, and other natural ecosystems as forms of infrastructure. But they are. Forests, for instance, can prevent silt and pollutants from entering streams that supply freshwater to downstream cities and businesses. They can act as natural water filtration plants. As such, they are a form of “green infrastructure” that can serve the same function as “gray infrastructure,” the human-engineered solutions that often involve concrete and steel.

Examples of public and private investments in green infrastructure already exist. For instance, Bogotá, Columbia is pursuing upstream landscape conservation and restoration as an alternative to more conventional water treatment technologies. Ho Chi Minh City restored mangroves instead of building dikes in order to protect shorelines from storm damage. And a chemical facility in Texas built a wetland instead of using deep well injection to treat wastewater.

Photo: Ho Chi Minh City elected to invest in mangrove restoration instead of building dikes as a way to protect shorelines. Photo of Can Gio mangrove forest near Ho Chi Minh City, Vietnam provided by Tho nau via Wikimedia Commons

Next page: Costs of green vs. gray infrastructure