Nature-Based Benefits in Focus: Forest Water Quality
Nature-based carbon offset projects produce myriad co-benefits that advance climate change adaptation and resilience goals in addition providing cost-effective GHG mitigation. Over the next few weeks, The Climate Trust will take a deeper dive into these specific co-benefits to help carbon credit buyers and other market participants better understand how nature-based projects build ecosystem and community resilience.
One of the primary benefits of forest land cover and climate-smart forestry (i.e. extending rotations, single and group tree reserves, wider riparian buffers etc.) is increased water quality. While there are many factors that contribute to water quality such as slope, precipitation patterns, soil texture, and the type of harvest, there is a general trend: increased forest cover results in increased water quality. This carbon mitigation strategy builds climate change resilience by blunting the impacts of increasingly severe precipitation events.
The most comprehensive forest watershed study in the United States is the Hubbard Brook Ecosystem Study, located in the White Mountains of New Hampshire. This study, which began in 1963, used entire forest watersheds to conduct experiments comparing the ecosystem effects of complete de-vegetation and various clearcuts (strip and block) to no-harvest controls. These study units are analogous to avoided forest conversion and improved forest management carbon projects, whose business-as-usual scenarios are similar to the de-vegetation and clearcut watersheds. The results are clear: increases in sediment and nitrate levels were extremely significant in the de-vegetated watershed and modest in the clearcut watersheds. It is important to note that timber harvest best management practices (seasonal logging, equipment type, proper road construction, riparian buffers etc.) can significantly reduce water quality impacts but are voluntary in many states.
Water quality directly impacts many wildlife species and communities. For example, sedimentation of streams can cause streambeds to become inhospitable to fish eggs (gravel beds clogged with silt) and thus effect fisheries, recreation and the entire food chain. Improving water quality at the source can also supply communities with reliably clean water at reduced costs. New York City was able to avoid spending $8-10 billion (in 2006 dollars) on a water filtration plant by spending $1.5 billion to protect its watershed. This approach ensures that even the most vulnerable communities have access to clean, healthy drinking water without expensive filtration systems.
While quantifying water quality improvements resulting from individual forest carbon projects would be expensive, forest carbon projects have clear and significant water quality benefits that build climate change resilience for wildlife and communities.
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