Climate benefits of Green Stormwater Infrastructure Revision as of 20:15, 23 May 2018 by Mtrojan (talk | contribs) (Created page with "{{alert|This page is in development|alert-under-construction}} Vegetated stormwater practices (bioretention, tree trenches/boxes, green roofs, vegetates swales, constructed p...")(diff) ← Older revision | Latest revision (diff) | Newer revision → (diff) Climate benefits of Green Stormwater Infrastructure

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Vegetated stormwater practices (bioretention, tree trenches/boxes, green roofs, vegetates swales, constructed ponds and wetlands) can be designed, constructed, and maintained to capture and store atmospheric carbon dioxide. The sequestration of atmospheric carbon can be used to mitigate or defer climate change by slowing the atmospheric accumulation of greenhouse gases. Carbon sequestration is impacted mainly by the age, type, and density of vegetation¹.

Bioretention

Bioretention basins (infiltration and filtration) are often constructed with a variety of native and non-native species plantings (shrubs, grasses, sedges, etc.). Due to their extensive and deep rooting characteristics, native prairie plantings are able to store more carbon in soil than non-native plantings². More specifically, studies shows that grasses and shrubs are likely to accumulate higher concentrations of Carbon then other planting types³. Grasslands that are predominantly populated with native species accumulate more carbon in soil than those grasslands that are predominantly accumulated by non-native species. The amount of carbon accumulated in the plants is affected by the plant species. Different species of grasses and shrubs have varying potential to accumulate and sequester carbon and species selection should be taken into consideration during the plant design and selection process. It is important to ensure consistent plant cover and to avoid soil exposure/disturbance as soil organic carbon can be released by oxidation into the atmosphere in the form of carbon dioxide².

Tree Trench

Nowak (2002) states that “urban forests both sequester CO2, and affect the emission of CO2 from urban areas,” and that “urban forests can play a critical role in helping combat increasing levels of atmospheric carbon dioxide. Nowak (2013) states that “Trees act as sink for carbon dioxide (CO2) by fixing carbon during photosynthesis and storing carbon as biomass. He outlines that in urban areas trees can both sequester carbon and emit carbon depending on that life cycle stage of the tree. As a tree grows it will sequester carbon, and when a tree dies carbon can be emitted back into the atmosphere. Additionally, urban trees can have an influence on local climate as they can help reduce air temperatures. With the increase in urban land growth, trees within these areas can help sequester considerable amounts of carbon⁴.

Green Roofs

Green roofs can contribute to reducing atmospheric CO2 by two means. One, the plant structures on green roofs are largely comprised of carbon, which is naturally sequestered in the plant tissues and into the green roof soil layer through plant litter and root exudate. Two, a building with a green roof will reduce the building’s heat island effect and energy needs and corresponding regional electricity demand as the roof will function as an insulator⁵. Major components to green roof effectiveness that should be taken into consideration are plant species selections, substrate (soil) depth, substrate composition and management practices. Rowe found that “above-ground sequestration ranged from 64 g C m-2 to 239 g C m-2 for S. acre and S. album, respectively.” Some ways to increase carbon sequestration effectiveness would be to implement the following design strategies.

• Increase depth of soil slayer – helps provide more volume for carbon storage and allow for deeper rooted vegetation
• Soil mix – can maximize carbon sequestration
• Plant species selection – vegetation with deeper roots have higher potential to store more carbon
• Operation and maintenance practices that address irrigation/watering and landscape care

A properly designed green roof cam help reduce the need for power from regional power plants. The reduction in energy demand is a result of the green roof’s ability to insulate the building it serves and also reducing the heat island effect. In the U.S., buildings are responsible for 38% of carbon dioxide emissions⁵. By reducing the need to use energy provided by regional power plants, green roofs act as a natural insulator and decrease the amount of carbon released into the atmosphere.

Vegetated Swales

Vegetated swales can sequester carbon within the vegetation and soil that grows in the swales. A study performed alongside North Carolina highway right-of-ways (ROWs) examined carbon sequestration potential in swales. Results showed that carbon sequestration was more significant in wetland swales than dry swales and that in order to promote carbon sequestration in the vegetated ROW, wetland swales appear to be preferable over dry swales⁶.

Constructed Ponds and Wetlands

Constructed stormwater ponds and wetlands provide carbon sequestration benefits, albeit more research must be done to have a greater understanding of carbon sequestration in these stormwater BMPs. It appears that emergent vegetation is one of the most important contributors to the accumulation of carbon in stormwater pond and wetland soils⁷. Again, more research must be done to determine the effectiveness of stormwater ponds and wetlands and their ability to sequester carbon, though it is believed that stormwater ponds/wetlands could play an important role in global carbon cycles⁸.