IDENTIFYING OPPORTUNITIES TO ENHANCE SOIL ORGANIC CARBON IN MANAGED SUBURBAN LANDSCAPES

Soil is the largest terrestrial carbon reservoir. Growing concerns about arctic and boreal carbon stocks has directed attention to the carbon storage potential of managed ecosystems. Management practices in urban/suburban green spaces (lawns, parks, wetlands, forests) may provide opportunities for enhanced carbon storage. In this study, we compared soil organic matter and carbon storage under different types of vegetation and management practices. The study site, which includes a golf course, is a small (~ 1 km²) humid temperate watershed. It receives 115 cm of precipitation per year, which is distributed throughout the year, but plant growth is limited to the warm seasons. The golf course was constructed 60 years ago on eroded agricultural lands. Vegetation categories include grasses (fairways, roughs, and a Typha-dominated wetland) and forests (unmanaged forest, groomed forest with leaf litter removed, and managed forest with imported leaf litter and wood). Streamflow and wetland water levels were gauged to assess the water balance. To assess carbon stocks, a minimum of 3 core samples were taken from each vegetation/management category. The 50 cm cores were sectioned and analyzed for bulk density, soil organic matter (SOM), and % carbon (C). Relationships of bulk density to SOM and of SOM to % C were determined for vegetation/management categories. Cores taken from the wetland, located at the basin outlet, were also analyzed for carbon and nitrogen isotopes. In each core, bulk density was lowest and SOM was highest near the surface. The wetland accumulated an average of 150 gCm^-2year^-1 for the past 20 years. SOM stocks were compared by normalizing SOM under each vegetation/management category to the average unmanaged forest SOM. Carbon-export sites (turf grass and groomed forests) had SOM ratios of 0.74-0.76. Ratios for the roughs (tall grasses and herbaceous plants) were 0.99-1.04 and the carbon-imported forests had SOM ratios of 1.2-1.8, but these imported carbon sites were very spatially limited. This suggests that a potential 25% increase in carbon stocks on existing lawns and parks could be achieved by decreasing carbon export through grass clippings and raked leaves and shifting lawns to herbaceous vegetation. This change, however, would require a change in landscape esthetics and park management.