Urban areas are responsible for the majority of global anthropogenic CO2 emissions. Urbanization has altered the structure and function of terrestrial ecosystems and is increasing rapidly, further modifying global carbon cycling. The three research papers in this dissertation explore the role of urban vegetation in the carbon cycle using a combination of atmospheric observation, field measurements, remote sensing, and modeling. First, I characterized the spatiotemporal patterns of observed atmospheric CO2 mixing ratios and compared these data to estimated CO2 fluxes at three sites across Boston's urban-to-rural gradient. Total fossil fuel emissions estimates ranged from 1.5 to 37.3 Mg C ha-1 yr-1 between rural Harvard Forest and urban Boston. Despite large differences in emissions, atmospheric CO2 concentrations only differed by approximately 5%. The growing season length in Boston was approximately 31 days longer than in Harvard Forest, enhancing the period for biological carbon uptake. In Boston, gross primary production was 3.8 Mg C ha-1 yr-1, which was ~75% lower than gross primary production at Harvard Forest and ~10% of total anthropogenic carbon fluxes in Boston. Second, I assessed how forest-to-urban land cover change affected both aboveground biomass and productivity across eastern Massachusetts. I found that urban land covers contained less than half the biomass of adjacent forests, but the mean basal area increment of existing trees nearly doubled with development over time from 17.1 ± 3.0 to 35.8 ± 4.7 cm2 yr-1. Scaling this increase in growth suggests an aboveground biomass growth rate of 1.8 ± 0.4 Mg C ha-1 yr-1, a rate similar to that found in Harvard Forest, despite having only ~1/3 the standing aboveground biomass. Last, I assessed how above- and belowground ecosystem characteristics changed as a function of time since development and development intensity. I found that soil C and aboveground biomass showed significant differences with time since development. My data suggests that soil C, N, and bulk density are dependent on land use history, with previously agricultural sites consistently showing higher rates of soil N and C accumulation than previously forested and grassland sites. Taken as a whole, this dissertation highlights the potential consequences of altered ecological and environmental conditions on tree growth, the legacy effects of land use history, climate, and land management practices on below ground soil C and N, and the importance of vegetation in the C cycle in urban areas.

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This dissertation takes a retrospective look at the first decade of EPA's implementation of the Comprehensive Environmental Response, Compensation and Liability Act commonly known as Superfund. Two models are employed that reflect EPA's implementation of Superfund: a rational threats game-theoretic bargaining model and a discrete choice empirical model. The game theoretic hazardous waste bargaining model produces an elegant and simple decision rule. Using this decision rule, EPA compares the expected transaction costs incurred because of litigation against EPA's prospects for a court-ordered award. The agency enters into bargaining when the savings from avoiding litigation is equal to the court-ordered award. EPA and the coalition of responsible parties bargain about how to share site clean-up costs (mixed funding) and when successful, enter into a voluntary settlement. The discrete choice empirical analysis reveals that high transaction costs, lengthy delays in site clean-ups and limited enforcement/litigation characterize EPAs implementation of CERCLA during the decade ending in 1990. Differences in how EPA implements this legislation across EPA Regions is explored. Compared to the other Eastern EPA Regions, EPA Region 4 is less likely to litigate and more likely to use Superfund monies to clean up hazardous waste sites.

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