Dr. Steve M. Raciti

Assistant Professor

Department of Biology

Hofstra University


Mapping carbon storage in urban trees with multi-source remote sensing data: Relationships between Biomass, Land Use, and Demographics in Boston Neighborhoods

High resolution maps of urban vegetation and biomass are powerful tools for policy-makers and community groups seeking to reduce rates of urban runoff, moderate urban heat island effects, and mitigate the effects of greenhouse gas emissions. We develop a very high resolution map of urban tree biomass, assess the scale sensitivities in biomass estimation, compare our results with lower resolution estimates, and explore the demographic relationships in biomass distribution across the City of Boston. We integrated remote sensing data (including LiDAR-based tree height estimates) and field-based observations to map canopy cover and aboveground tree carbon storage at ~1 m spatial scale. Mean tree canopy cover was estimated to be 25.5±1.5% and carbon storage was 355 Gg (28.8 Mg C ha-1) for the City of Boston. Tree biomass was highest in forest patches (110.7 Mg C ha-1), but residential (32.8 Mg C ha-1) and developed open (23.5 Mg C ha-1) land uses also contained relatively high carbon stocks.  In contrast with previous studies, we did not find significant correlations between tree biomass and the demographic characteristics of Boston neighborhoods, including income, education, race, or population density. The proportion of households that rent was negatively correlated with urban tree biomass (R2=0.26, p=0.04) and correlated with Priority Planting Index values (R2=0.55, p=0.001), potentially reflecting differences in land management among rented and owner-occupied residential properties. We compared our very high resolution biomass map to lower resolution biomass products from other sources and found that those products consistently underestimated biomass within urban areas.  This underestimation became more severe as spatial resolution decreased.  This research demonstrates that 1) urban areas contain considerable tree carbon stocks; 2) canopy cover and biomass may not be related to the demographic characteristics of Boston neighborhoods; and 3) that recent advances in high resolution remote sensing have the potential to improve the characterization and management of urban vegetation.

Raciti, S. M., L. R. Hutyra, and J. D. Newell. In review. Mapping carbon storage in urban trees with multi-source remote sensing data: Relationships between Biomass, Land Use, and Demographics in Boston Neighborhoods.

Putting urban biomass on the map: Contrasting case studies from three climactic zones

There is evidence that urban vegetation can provide important ecosystem services, however, existing maps of vegetation biomass tend to exclude developed land uses or report them as having little or no biomass. We used field and remote sensing data from the Boston, MA, Seattle, WA, and Phoenix Arizona metropolitan areas to 1) assess the potential for predicting urban biomass from remote sensing data, 2) explore the influence of land use and climate on urban biomass, 3) generate new biomass maps that explicitly include urban land uses, and 4) compare these biomass maps to existing products. For each metropolitan area, vegetation biomass was estimated for field plots using tree/shrub species, diameter at breast height (DBH) or ground level (DGL), and allometric equations. These field data were paired with geospatial data to assess the potential for creating vegetation biomass maps for each metropolitan area. The geospatial data included land use, land cover, impervious surface fraction, population density, and two remotely-sensed vegetation indices (Normalized Difference Vegetation Index [NDVI] and Enhanced Vegetation Index [EVI]). Preliminary findings suggest that the ability to predict biomass from remote sensing data varies with land use, climate, and dominant vegetation type. Existing vegetation biomass maps may considerably underestimate biomass, particularly in regions with extensive urban land cover. Urban areas are rapidly expanding and future development patterns will have significant impacts on terrestrial carbon stocks, anthropogenic emissions, and the ecosystem services provided by remnant and regrowing vegetation.

Raciti, S. M., L. R. Hutyra, P Rao, and M. R. McHale. Putting urban biomass on the map: contrasting case studies from three climactic zones.  American Geophysical Union Fall Meeting.  San Francisco, CA.  Dec 3-7, 2012.

Atmospheric nitrogen inputs and losses along an urbanization gradient in the Boston metropolitan region

Urbanization alters nitrogen (N) cycling, but the spatiotemporal distribution and impact of these alterations on ecosystems are not well-quantified. We measured atmospheric inorganic N inputs and soil leaching losses along an urbanization gradient from Boston, MA to the Harvard Forest in Petersham, MA. Atmospheric N inputs at urban sites (12.3 ± 1.5 kg N ha-1 yr-1) were significantly greater than non-urban (5.7 ± 0.5 kg N ha-1 yr-1) sites with NH4+ (median value of 77 ± 4 %) contributing thrice as much as NO3-. Proximity to urban core correlated positively with NH4+ (R2 = 0.57, p = 0.02) and total inorganic N inputs (R2 = 0.61, p = 0.01); on-road CO2 emissions correlated positively with NO3- inputs (R2 = 0.74, p = 0.003). Inorganic N leaching rates correlated positively with atmospheric N input rates (R2 = 0.61, p = 0.01), but did not differ significantly between urban and non-urban sites (p > 0.05). Our empirical measurements of atmospheric N inputs are greater for urban areas and less for rural areas compared to modeled regional estimates of N deposition. Five of the nine sites had NO3- leached that came almost entirely from nitrification, indicating that the NO3- in leachate came from biological processes rather than directly passing through the soil. A significant proportion (17 - 100 %) of NO3- leached from the other four sites came directly from the atmosphere. Surprisingly, the four sites where atmospheric sources made up the largest proportion of leachate NO3‑ also had relatively low N leaching rates, suggesting that atmospheric N inputs added to terrestrial ecosystems can move to multiple sinks and losses simultaneously, rather than being lost via leaching only after abiotic and biotic sinks have become saturated. This study improves our understanding of atmospheric N deposition and leaching in urban ecosystems, and highlights the need to incorporate urbanization effects in N deposition models.

Rao, P., L. R. Hutyra, S. M. Raciti, and P. H. Templer. 2013. Atmospheric nitrogen inputs and losses along an urbanization gradient from Boston to Harvard Forest, MA. Biogeochemistry. 

Economic valuation of local carbon sequestration along an urban-to-rural gradient

Most climate-related carbon research has focused on large geographic scales or forest ecosystems, but substantial amounts of carbon are stored in vegetation and soils within urban, suburban, and exurban lands.  Economic valuation studies conducted along urban-to-rural gradients have focused on broad categories of open space or wetlands, but have not explored the economic value of carbon sequestration.  This leaves important questions unanswered:  Do residents value local carbon sequestration distinct from general measures of open space?  How do these values vary along an urban-to-rural gradient?  Are these values comparable to other carbon prices?  We explore these questions using a spatial hedonic property price model that includes the sales price of single-family homes, distance from environmental amenities/disamenities, and measures of vegetation greenness and biomass from a unique empirically based dataset. 

Bauer, D. M., S. M. Raciti, and L. R. Hutyra. Valuing local carbon sequestration along an urban-to-rural gradient. Annual Meeting of the Northeastern Agricultural and Resource Economics Association, Lowell, MA, June 10-12, 2012.

Characterization of urban methane emissions in Boston, Massachusetts using tower-based observations and an inverse modeling framework

There is much uncertainty about the magnitude of methane emissions from natural gas production and delivery infrastructure, yet this quantity is necessary for understanding the climate impact of natural gas as a major fuel source and for partitioning the global methane budget. Preliminary evidence suggests that leaks from urban natural gas distribution systems may release substantial quantities of methane to the atmosphere, but this source has seldom been directly investigated in the scientific literature. As a case study, we seek to describe and quantify the natural gas fraction of the total methane source in the Boston, Massachusetts metropolitan region. We describe the design of an atmospheric methane monitoring network in and around the city. Periodic measurements of atmospheric ethane are used to estimate the fractional contribution of natural gas to the total observed urban methane enhancement. A methane emission inventory is compiled from high-resolution information on biogenic methane sources, street-level methane concentrations, and the natural gas distribution infrastructure. We present preliminary results from the observational network and an inverse modeling framework.

McKain, K., S. C. Wofsy, J. Budney, L. R. Hutyra, S. M. Raciti, B. Briber, N. P. Phillips, R. B. Jackson, A. Down, J. W. Munger, and C. L. Schaaf. Characterization of urban methane emissions in Boston, Massachusetts using tower-based observations and an inverse modeling framework. American Geophysical Union Fall Meeting. San Francisco, CA.  Dec 3-7, 2012.

Methane source identification in Boston, Massachusetts using isotopic carbon and ethane

Methane (CH4) has substantial greenhouse warming potential and is the principle component of natural gas. Fugitive natural gas emissions could be a significant source of methane to the atmosphere. However, the cumulative magnitude of natural gas leaks is not yet well constrained. We used a combination of point source measurements and ambient monitoring to characterize the methane sources in the Boston urban area. We developed distinct fingerprints for natural gas and multiple biogenic methane sources based on hydrocarbon concentration and isotopic composition. We combine these data with periodic measurements of atmospheric methane and ethane concentration to estimate the fractional contribution of natural gas and biogenic methane sources to the cumulative urban methane flux in Boston. These results are used to inform an inverse model of urban methane concentration and emissions.

Phillips, N. P., E. Crosson, A. Down, L. R. Hutyra, R. B. Jackson, K. McKain, S. M. Raciti, C. Rella, and S. C. Wofsy. Methane source identification in Boston, Massachusetts using isotopic carbon and ethane. American Geophysical Union Fall Meeting. San Francisco, CA.  Dec 3-7, 2012.

Shifting Land Use and Forest Conservation: Understanding the Coupling of Social and Ecological Processes along Urban-to-Rural Gradients

Landowners are particularly important agents of forest change in New England, where 80% of forest land is privately held.  Their decisions strongly influence the region’s land use and associated ecosystem services.  The Conservation Awareness Index (CAI; Van Fleet et al 2012) is a survey instrument designed to assess private landowner knowledge of four specific actions that can directly influence the future of New England forests: timber harvest; participation in a current-use property taxation program; application of a conservation easement; and estate planning. We used CAI in a mail survey to 1,200 private woodland owners of 10 acres or greater along two urban-rural gradients that radiate from Boston.  Key questions:  To what extent are landowners across the gradient aware of their conservation options?  Are landowners making fully informed management decisions?  And does conservation awareness vary across the urban-rural gradient? Our initial results suggest that overall owner awareness of conservation alternatives is poor, and may not vary appreciably across urban-rural gradients, at least among those who own more than 10 acres of land. Awareness of conservation restrictions and estate planning appears higher in the urbanized ends of the gradients, where real estate values are appreciably higher, and development pressure is greater. Ownership goals, however, appear to be oriented towards development under these circumstances. These results suggest the need for increased outreach to improve conservation awareness across the urban-rural gradient. Our future research seeks to more directly test the hypothesis that conservation awareness influences the conservation decisions of landowners. 

A. Short, D. B. Kittredge, L.  Bartock, E. Schnur, S. M. Raciti, and L. R. Hutyra. The future of forests: it's who and what you know.  LTER All Scientists Meeting, Estes Park, CO, September 10-13, 2012.

Field and remotely sensed measures of soil and vegetation carbon and nitrogen across an urbanization gradient in the Boston Metropolitan Area

Understanding the impact of urbanization on terrestrial biogeochemistry is critical for addressing society’s grand challenge of global environmental change. We used field observations and remotely sensed data to quantify the effects of urbanization on vegetation and soils across a 100-km urbanization gradient extending from Boston to Harvard Forest and Worcester, MA. At the field-plot scale, the normalized difference vegetation index (NDVI) was positively correlated with aboveground biomass (AGB) and foliar nitrogen (N) content and negatively correlated with impervious surface fraction. Unlike previous studies, we found no significant relationship between NDVI or impervious surface area (ISA) fraction and foliar N concentration. Patterns in foliar N appeared to be driven more strongly by changes in species composition rather than phenotypic plasticity across the urbanization gradient. For forest and non-residential development, soil nitrogen content increased with urban intensity. In contrast, residential land had consistently high soil N content across the gradient of urbanization. When field observations were scaled-up to the Boston Metropolitan Statistical Area (MSA), we found that soil and vegetation N content were negatively correlated with ISA fraction, an indicator of urban intensity. Our results demonstrated the importance of accounting for the influence of impervious surfaces when scaling field data across urban ecosystems. The combination of field data with remote sensing holds promise for disentangling the complex interactions that drive biogeochemical cycling in urbanizing landscapes. Empirical data that accurately characterize variations in urban biogeochemistry are critical to gain a mechanistic understanding of urban ecosystem function and to guide policy makers and planners in developing ecologically sensitive development strategies.

Rao, P., L. R. Hutyra, S. M. Raciti, and A. C. Finzi. 2013. Field and remotely sensed measures of soil and vegetation carbon and nitrogen across an urbanization gradient in the Boston Metropolitan Area. Urban Ecosystems.

Inconsistent definitions of 'urban' result in different conclusions about the size of urban carbon and nitrogen stocks

There is conflicting evidence about the importance of urban soils and vegetation in regional C budgets that is caused, in part, by inconsistent definitions of 'urban' land use. We quantified urban ecosystem contributions to C stocks in the Boston Metropolitan Statistical Area (MSA) using several alternative urban definitions. Development altered aboveground and belowground C and N stocks and the sign and magnitude of these changes varied by land use and development intensity. Aboveground biomass (DBH > 5 cm) for the MSA was 7.2 ± 0.4 kg C/m2, reflecting a high proportion of forest cover. Vegetation C was highest in forest (11.6 ± 0.5 kg C/m2) followed by residential (4.6 ± 0.5 kg C/m2) and then other developed (2.0 ± 0.4 kg C/m2) land uses. Soil C (0 to 10 cm) followed the same pattern of decreasing C concentration from forest, to residential, to other developed land uses (4.1 ± 0.1, 4.0 ± 0.2, and 3.3 ± 0.2 kg C/m2, respectively). Within a land use type, urban areas (which we defined as >25% impervious surface area [ISA] within a 1 km2 moving window) generally contained less vegetation C, but slightly more soil C, than non-urban areas. Soil N concentrations were higher in urban areas than non-urban areas of the same land use type, except for residential areas, which had similarly high soil N concentrations. When we compared our definition of urban to other commonly used urban extents (US Census, GRUMP, and the MSA itself), we found that urban soil (1 m depth) and vegetation C stocks spanned a wide range, from 14.4 ± 0.8 to 54.5 ± 3.4 Tg C and from 4.2 ± 0.4 to 27.3 ± 3.2 Tg C, respectively. Conclusions about the importance of urban soils and vegetation to regional C and N stocks are very sensitive to the definition of urban used by the investigators. Urban areas, regardless of definition, are rapidly expanding in their extent; a systematic understanding of how our development patterns influence ecosystems is necessary to inform future development choices.

Raciti, S. M., L. R. Hutyra, P. Rao, and A. C. Finzi. 2012. Inconsistent definitions of 'urban' result in different conclusions about the size of urban carbon and nitrogen stocks. Ecological Applications. doi: 10.1890/11-1250.1.

Economic and political realities present challenges for implementing an aggressive climate change abatement program in the United States.  A high efficiency approach will be essential.  In this synthesis, we compare carbon budgets and evaluate carbon mitigation potential for nine counties across the northeastern United States that represent a range of biophysical, demographic and socioeconomic conditions.  Most counties are net sources of CO2 to the atmosphere, with the exception of rural forested counties where sequestration in vegetation and soils exceed emissions.  Protecting forests will ensure that the region’s largest CO2 sink does not become a source of emissions.  For rural counties, afforestation, sustainable fuelwood harvest for bioenergy, and utility-scale wind power could provide the largest and most cost-effective mitigation opportunities among those evaluated.  For urban and suburban counties, energy efficiency measures and energy saving technologies would be most cost-effective.   By implementing locally tailored management and technology options large reductions in CO2 emissions could be achieved at relatively low costs.

Raciti, S. M., T. J. Fahey, C. Driscoll, F.J. Carranti, D. Foster, P. Gwyther, B. Hall, S. Hamburg, J. C. Jenkins, J, Jenkins, C. Neill, S. Ollinger, B. Peery, E. Quigley, R. Sherman, R.Q. Thomas, M. Vadeboncoeur,  D. Weinstein, G. Wilson, P. Woodbury. 2012. Local Scale Carbon Budgets and Mitigation Opportunities for the Northeastern United States.  Bioscience 62(1): 23-38.

Local Scale Carbon Budgets and Mitigation Opportunities for the Northeastern United States

There is great uncertainty about the fate of nitrogen (N) added to urban and suburban lawns.   We used direct flux and in situ chamber methods to measure N2 and N2O fluxes from lawns instrumented with soil O2 sensors.   We hypothesized that soil O2, moisture, and available NO3- were the most important controls on denitrification and that N2 and N2O fluxes would be high following fertilizer addition and precipitation events.  While our results support these hypotheses, the thresholds of soil O2, moisture, and NO3- availability required to see significant N2 fluxes were greater than expected.  Denitrification rates were high in saturated, fertilized soils, but low under all other conditions.  Annual denitrification was calculated to be 14.0 ± 3.6 kg N/ha/yr with 5% of the growing season accounting for over 80% of the annual activity.    Denitrification is thus an important means of removing reactive N in residential landscapes, but varies markedly in space, time, and with factors that affect soil saturation (texture, structure, compaction) and NO3- availability (fertilization).  Rates of in situ N2O flux were low, however when recently fertilized soils saturated with water were incubated in the laboratory we saw extraordinarily high rates of N2O production for the first few hours of incubation, followed by rapid N2O consumption later in the experiment.  These findings indicate a lag time between accelerated N2O production and counter-balancing increases in N2O consumption, thus we cannot yet conclude that lawns are an insignificant source of N2O in our study area. 

Raciti, S. M., A. J. Burgin, P. M. Groffman, D. Lewis, and T.J. Fahey. 2011. Denitrification in Suburban Lawn Soils.  Journal of Environmental Quality 40:1932-1940.

Denitrification in Suburban Lawn Soils

Lawns are a dominant cover type in urban ecosystems and there is concern about their impacts on water quality.  However, recent watershed-level studies suggest that these pervious areas might be net sinks, rather than sources, for nitrogen (N) in the urban environment.  A 15N pulse-labeling experiment was performed on lawn and forest plots in the Baltimore metropolitan area to test the hypothesis that lawns are a net sink for atmospheric N deposition and to compare and contrast mechanisms of N retention in these vegetation types.  A pulse of 15N-NO3-, simulating a precipitation event, was followed through mineral soils, roots, Oi-layer/thatch, aboveground biomass, microbial biomass, inorganic N and evolved N2 gas over a one-year period.  The 15N label was undetectable in gaseous samples, but enrichment of other pools was high.  Gross rates of production and consumption of NO3- and NH4+ were measured to assess differences in internal N cycling under lawns and forests.  Rates of N retention were similar during the first 5 days of the experiment, with lawns showing higher N retention than forests after 10, 70, and 365 days.  Lawns had larger pools of available NO3- and NH4+; however, gross rates of mineralization and nitrification were also higher, leading to no net differences in NO3- and NH4+ turnover times between the two systems.  Levels of 15N remained steady in forest mineral soils from days 70 to 365 (at 23% of applied 15N), but continued to accumulate in lawn mineral soils over this same time period, increasing from 20% to 33% of applied 15N.  The dominant sink for N in lawn plots changed over time.  Immobilization in mineral soils dominated immediately (1 day) after tracer application (42% of recovered 15N); plant biomass dominated the short term (10 days - 51%), thatch and mineral soil pools together dominated the medium term (70 days - 28% and 36% respectively), while the mineral soil pool alone dominated long term retention (one year - 70% of recovered 15N).  These findings illustrate the mechanisms whereby urban and suburban lawns under low to moderate management intensities are an important sink for atmospheric N deposition.

Raciti, S. M.,  P. M. Groffman, and T. J. Fahey.  2008.  Nitrogen Retention in Urban Lawns and Forests.  Ecological Applications 18(7): 1615-1626.

Nitrogen Retention in Urban Lawns and Forests

15N tracer recovery by ploty type (lawn vs forest) and nitrogen pool

Exploring Space-Time Variation in Urban Carbon Metabolism

Carbon dioxide is a well-mixed greenhouse gas, but how, where, and when it is exchanged with Earth’s surface is a complex spatio-temporal, coupled natural-human problem. Nowhere is this challenge more pronounced than in the urban environment. Fixed objects like buildings and trees, and mobile elements like cars and people, exchange carbon (C) across a wide range of spatial and temporal scales with a dynamic set of driving variables. As cities, states, and nations undertake efforts to reduce and regulate greenhouse gas emissions, we must understand these space-time variations and the underlying drivers of biogenic and anthropogenic exchange in order to develop robust monitoring, reporting, and verification systems. Within urban areas, the concept of urban metabolism provides a framework for monitoring, reporting, and verification that allows us to account for imports, exports, and transformations of carbon within urban areas.

Hutyra, L.R., N.P. Phillips, S. M. Raciti, and J.W. Munger. 2011. Exploring Space-time Variation in Urban Carbon Metabolism. Urbanization and Global Environmental Change Viewpoints 6: 11-14.

Urban areas are growing in size and importance; however we are only beginning to understand how the process of urbanization influences ecosystem dynamics.  In particular, there have been few assessments of how the land use history and age of residential soils influence carbon and nitrogen pools and fluxes, especially at depth.  In this study, we used one-meter soil cores to evaluate soil profile characteristics and carbon and nitrogen pools in 32 residential home lawns that differed by previous land use and age, but had similar soil types.  These were compared to soils from 8 forested reference sites.  Residential soils had significantly higher C and N densities than nearby forested soils of similar types (6.95 vs. 5.44 kg C/m2 and 552 versus 403 g N/m2, p < 0.05).  Results from our chronosequence suggest that soils at residential sites that were previously in agriculture have the potential to accumulate C (0.082 kg C/m2/y) and N (8.3 g N/m2/y) rapidly after residential development.  Rates of N accumulation at these sites were similar in magnitude to estimated fertilizer N inputs, confirming a high capacity for N retention.  Residential sites that were forested prior to development had higher C and N densities than present-day forests, but our chronosequence did not reveal a significant pattern of increasing C and N density over time in previously forested sites.  These data suggest that soils in residential areas on former agricultural land have a significant capacity to sequester C and N.  Given the large area of these soils, they are undoubtedly significant in regional C and N balances. 

Raciti, S. M., P. M. Groffman, J. C. Jenkins, R. V. Pouyat, T. J. Fahey, S. T. A. Pickett, and M. L. Cadenasso.  2011.  Accumulation of Carbon and Nitrogen in Residential Soils with Different Land Use Histories.  Ecosystems 14(2): 287-297.

Accumulation of Carbon and Nitrogen in Residential Soils

The rapid increase in residential land area in the United States has raised concern about water pollution associated with nitrogen fertilizers.  Nitrate (NO3-) is the form of reactive N that is most susceptible to leaching and runoff; thus, a more thorough understanding of nitrification and NO3- availability is needed if we are to accurately predict the consequences of residential expansion for water quality. In particular, there have been few assessments of how the land use history, housing density, and age of residential soils influence NO3- pools and fluxes, especially at depth.  In this study, we used one-meter deep soil cores to evaluate potential net nitrification and mineralization, microbial respiration and biomass, and soil  NO3- and NH4+ pools in 32 residential home lawns that differed by previous land use and age, but had similar soil types.  These were compared to eight forested reference sites with similar soils.  Our results suggest that a change to residential land use has increased pools and production of reactive N, which has clear implications for water quality in the region.  However, the results contradict the common assumption that NO3- production and availability is dramatically higher in residential soils than in forests in general.  While net nitrification (128.6 ± 15.5 versus 4.7 ± 2.3 mg/m2/day) and exchangeable NO3- (3.8 ± 0.5 versus 0.7 ± 0.3 g/m2) were significantly higher in residential soils than forest soils in this study, these measures of NO3- production and availability were still notably low - comparable to deciduous forest stands in other studies.  A second unexpected result was that current homeowner management practices were not predictive of NO3- availability or production.  This may reflect the transient availability of inorganic N after fertilizer application.  Higher housing density and a history of agricultural land use were predictors of greater NO3- availability in residential soils.  If these factors are good predictors across a wider range of sites, they may be useful indicators of NO3- availability and leaching and runoff potential at the landscape scale.

Raciti, S. M., P. M. Groffman, J. C. Jenkins, R. V. Pouyat, T. J. Fahey, S. T. A. Pickett, and M. L. Cadenasso.  2011.  Nitrate Production and Availability in Residential Soils. Ecological Applications 21(7): 2357–2366.

Nitrate Production and Availability in Residential Soils

A carbon budget was calculated for Tompkins County, NY, a semi-rural upstate county with a population density of 78 pp/km2. The costs and potential for several carbon mitigation options were analyzed in four categories: terrestrial C sequestration, local power generation, transportation, and energy end-use efficiency. This study outlines a methodology for conducting this type of local-scale analysis, including sources and calculations adaptable to different localities. Effective carbon mitigation strategies for this county based on costs/ Mg C and maximum potential include reforestation of abandoned agricultural lands, biomass production for residential heating and co-firing in coal power plants, changes in personal behavior related to transportation (e.g., public transportation), installation of residential energy efficient products such as programmable thermostats or compact fluorescent light bulbs, and development of local wind power. The total county emissions are about 340 Gg C/year, with biomass sequestration rates of 121 Gg C/year. The potential for mitigation, assuming full market penetration, amounts to about 234 Gg C/year (69%), with 100 Gg C/year (29%) at no net cost to the consumer. The development of local-scale C mitigation plans based on this sort of model of analysis is feasible and would be useful for guiding investments in climate change prevention.

Vadas, T. M., T. J. Fahey, R. E. Sherman, J. D. Demers, J. M. Grossman, J. E. Maul, A. M. Melvin, B. O’Neill, S. M. Raciti, E. T. Rochon, D. J. Sugar, C. Tonitto, C. B. Turner, M. J. Walsh, and K. Xue. 2007. Approaches for analyzing local carbon mitigation strategies:Tompkins County, New York, USA.  International Journal of Greenhouse Gas Control 1:360-373.

Approaches for analyzing local carbon mitigation strategies: Tompkins County, New York, USA

Depleted soil carbon and nitrogen pools beneath impervious surfaces

Urban soils and vegetation contain large pools of carbon (C) and nitrogen (N) and may sequester these elements at considerable rates; however, there have been no systematic studies of the composition of soils beneath the impervious surfaces that dominate urban areas.  This has made it impossible to reliably estimate the net impact of urbanization on terrestrial C and N pools.  In this study, we compared open-area and impervious-covered soils in New York City and found that the C and N content of the soil (0-15cm) under impervious surfaces was 66% and 95% lower, respectively.  Analysis of extracellular enzyme activities in the soils suggests that recalcitrant compounds dominate the organic matter pool under impervious surfaces.  If the differences between impervious-covered and open-area soils represent a loss of C and N from urban ecosystems, the magnitude of these losses could offset sequestration in other parts of the urban landscape.

Raciti, S. M., L. R. Hutyra, and A. C. Finzi. 2012. Depleted soil carbon and nitrogen pools beneath impervious surfaces. Environmental Pollution 164: 248-251. DOI:10.1016/j.envpol.2012.01.046.

Modeling and validation of on-road CO2 emissions inventories at the urban regional scale

On-road emissions are a major contributor to rising concentrations of atmospheric greenhouse gases. In this study, we applied a downscaling methodology based on commonly available spatial parameters to model on-road CO2 emissions at the 1 x 1 km scale for the Boston, MA region and tested our approach with surface-level CO2 observations. Using two previously constructed emissions inventories with differing spatial patterns and underlying data sources, we developed regression models based on impervious surface area and volume-weighted road density that could be scaled to any resolution. We found that the models accurately reflected the inventories at their original scales (R2 = 0.63 for both models) and exhibited a strong relationship with observed CO2 mixing ratios when downscaled across the region. Moreover, the improved spatial agreement of the models over the original inventories confirmed that either product represents a viable basis for downscaling in other metropolitan regions, even with limited data.

Brondfield, M. N., L. R. Hutyra, C. M. Gately, S. M. Raciti, and S. A. Peterson. 2012. Modeling and validation of on-road CO2 emissions inventories at the urban regional scale. Environmental Pollution. 170: 113-123.

Ecological Impacts of Leaf Litter Removal from the City of Boston

Urban areas around the world are growing in population and extent and their effect on ecological processes is being increasingly recognized. In many urban areas, leaves and other organic material that fall from trees are collected as yard waste and taken to central collection facilities where they are converted to compost. We found that up to 52 + 17% of residential litterfall carbon (C) and nitrogen (N) is exported through yard waste removed from the City of Boston , which is equivalent to 6.5 kg N ha-1 yr-1 and more than half of annual N outputs from urban areas as gas loss (i.e. denitrification) or leaching. While some of the N exported from residential areas as yard waste is offset by inputs from atmospheric deposition (12 kg N ha-1 yr-1), fertilizer (0-200 kg N ha-1 yr-1) and pet waste (15 kg N ha-1 yr-1), the removal of leaf litter from residential areas disrupts nutrient cycling and residential yard management practices are an important modification to urban biogeochemical cycling, which could contribute to spatial heterogeneity of hotspots that are either N limited or saturated within urban ecosystems. A better understanding of nutrient sources, sinks, and patterns of limitation and saturation within urban environments is critical for mitigating the consequences of urban development on ecosystems, air, and water quality.

Templer, P. H.,  J. W. Toll, L. R. Hutyra, and S. M. Raciti. In review. Nitrogen and Carbon Export from Urban Areas Through Removal and Export of Litterfall.

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