United States Department of Transportation
i
Assessing the Potential to Sequester Carbon within State Highway Rights-of-Way in New Mexico Phase 2: Development of a Right-of-Way Carbon Sequestration Program
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2017-04-01
[PDF-10.94 MB]
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TRIS Online Accession Number:01611976
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Edition:Final Report
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Abstract:Selected rights‐of‐way (ROW) vegetation management treatments were evaluated over three growing seasons to determine if they could increase soil organic carbon (SOC) along state highways in New Mexico. Eight test plots were established in north central and north eastern portions of the state along a SOC/precipitation gradient in Prairie and Lower Montane biomes. Treatments were to maintain biomass, increase soil moisture and increase available soil nitrogen. In actively managed zones of the ROW, treatments included a modified mowing regime to retain more biomass (High Mow) compared to current mowing operations (Low Mow) combined with interseeding legumes (Legume). The natural zone (ROW outside of managed areas) were treated with soil imprinting (Imprinting) and legume interseeding (Legume) compared to unmodified control (Natural). Unfortunately, the legumes broadcast seeding into established ROW plant communities was ineffective and monitoring the treatment was discontinued in the second growing season. Field measurements included SOC and nitrogen, vegetation biomass and cover, soil temperature and moisture, and carbon dioxide (CO₂) efflux. The project also considered the feasibility of a carbon offset protocol for highway ROW roadside vegetation management that could a be sold within a cap‐and‐trade carbon commodity market. High Mow subplots showed a trend of increased aboveground biomass and canopy cover at the end of the growing season compared to Low Mow. Aboveground biomass and canopy cover responses to Imprinting compared to the Natural subplots were varied and insignificant. Differences in soil carbon stock among managed and natural zone treatments were generally insignificant and equivocal in response. Continuous measurements of soil temperature and moisture did not identify any significant differences between treatments in either managed or natural ROW zones. Unmowed summertime net ecosystem exchange (NEE) was negative, indicating net sequestration of atmospheric CO₂ by photosynthetic plants. After mowing, daytime NEE were either positive for Low Mow or less negative for High Mow treatments. Low Mow nighttime fluxes were also positive after mowing and exceeded NEE observed in High Mow and Control subplots. This response to mowing is consistent with the reduction in the leaf area and increased respiration as plants replace their leaves following defoliation. The discrete chamber‐based measurements of CO₂ flux used characterized the ecosystem CO₂ dynamics at the ROW test plots where benchmarked against Ameriflux long‐term NEE data from semi‐arid grassland eddy covariance stations. Qualitatively, the magnitude of NEE observations at the test plots were typically within 2 standard deviations of the 10‐year mean for the Kendall long‐term ecological research.
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