Restoring even narrow swaths of forest on riverbanks can have transformative effects on improving water quality, say scientists who have examined the benefits of increasing riparian vegetation in Costa Rica.
Vegetation planted along rivers and streams between 10 and 50 meters wide would serve as natural filters and buffers, absorbing harmful pollutants in runoff and keeping them out of waterways, according to Stanford University scientists.
“Forests around rivers are key sites for restoration because they offer enormous benefits with very few impediments to productive land,” says Kelley Langhans, a Stanford biology doctoral student and author of the study. studying . “A small investment can have a huge impact on the health of people and ecosystems.”
Digital models of river bank reforestation.
Using computers, the scientists modeled the effects of reforesting 10-meter-wide strips along Costa Rica’s rivers. Their results showed that reforestation would increase phosphorus retention by almost 86%, nitrogen by over 81% and sediment by about 4%.
“Such reforestation would be most impactful in areas below steep slopes with erosion-prone land uses (such as grassland), high levels of fertilizer application (such as widely cultivated oil palms) and low levels of nutrient retention (such as urban areas). . . )”, they explain.
Furthermore, reforestation in this way would also expand forest cover by approximately 2% across the country, resulting in a 1.4% increase in carbon sequestration.
All of these changes could be very beneficial for a large number of people who depend on rivers for drinking water in Costa Rica, scientists say.
“When quantifying the benefits of ecosystem restoration, it is crucial to consider how it affects people, especially the most vulnerable populations,” says Langhans. “That’s why in this research we explicitly mapped how increases in water quality would reach those who are most dependent on rivers.”
Additional benefits
Even regions with water treatment infrastructure can benefit because this infrastructure is vulnerable to hurricanes and earthquakes. “Recently, in 2020, a tropical storm combined with a hurricane left 120,000 Costa Ricans without water service for several days, forcing people to temporarily rely on other sources of water, including streams,” the researchers note.
“Typical water treatment methods also do not remove nitrates, which are especially prone to leach into groundwater due to their high solubility. This is of particular concern in Costa Rica, which uses nitrogen-based fertilizers at one of the highest rates in the world.
Most of the land that scientists set aside for reforestation to create vegetation buffers now comprises farmland and grasslands.
“Previous research has shown that Costa Rican farmers value trees on their land and generally support reforestation, but feel that the initial costs of transitioning to forests and, on more productive lands, the opportunity costs of giving up agricultural production are too high.” , say the scientists. “Improving financial incentives and community efforts can help.”
Costa Rica is currently implementing a National Decarbonization Plan, which includes increasing forest cover to 60%. The new research may help inform this policy.
“Our study provides a model for using realistic policy-based scenarios to identify areas where forest restoration could have the greatest impact in terms of improving people’s health and meeting national adaptation and emissions targets,” the study emphasizes. study author Rafael Monge Vargas, director of the Costa Rican National Geoenvironmental Information Center at the Ministry of the Environment and Energy.
For Times of Sustainability. Article in English