Nitrogen Retention in Urban Lawns and Forests

Committee members: Timothy J. Fahey, Peter M. Groffman, David R. LeeHome lawns are a dominant cover type in urban and suburban 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 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 nitrogen 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 soils, roots, Oi-layer/thatch, aboveground biomass, microbial biomass, inorganic nitrogen and evolved N2 gas over a one-year period. Gross rates of production and consumption of NO3- and NH4+ were measured to assess differences in internal nitrogen cycling under the two vegetation types. Rates of nitrogen retention in forests and lawns were similar during the first 5 days of the experiment, with lawns showing higher nitrogen 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 soils from days 70 to 365 (at 23% of applied 15N), but continued to accumulate in lawn soil organic matter (SOM) over this same time period, increasing from 20% to 33% of applied 15N. The dominant sink for nitrogen in lawn plots changed over time; abiotic immobilization in soils dominated immediately (1 day) after tracer application (42% of recovered 15N), plant biomass dominated the short (10 days) term (51%), thatch and SOM pools together dominated the medium (70 days) term (28% and 36% respectively), while the SOM pool alone dominated long (1 year) term retention (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 nitrogen.National Science Foundation funded IGERT in Biogeochemistry and Environmental Biocomplexity at Cornell University, National Science Foundation funded Baltimore Ecosystem Study Long Term Ecological Research project (DEB-0423476

Variations in Atmospheric CO2CO_2 Mixing Ratios across a Boston, MA Urban to Rural Gradient

Urban areas are directly or indirectly responsible for the majority of anthropogenic $CO_2$ emissions. In this study, we characterize observed atmospheric $CO_2$ mixing ratios and estimated $CO_2$ fluxes at three sites across an urban-to-rural gradient in Boston, MA, USA. $CO_2$ is a well-mixed greenhouse gas, but we found significant differences across this gradient in how, where, and when it was exchanged. Total anthropogenic emissions were estimated from an emissions inventory and ranged from $1.5 to 37.3 mg·C·ha^{-1}·yr^{-1}$ between rural Harvard Forest and urban Boston. Despite this large increase in anthropogenic emissions, the mean annual difference in atmospheric $CO_2$ between sites was approximately 5% $(20.6 \pm 0.4 ppm)$. The influence of vegetation was also visible across the gradient. Green-up occurred near day of year 126, 136, and 141 in Boston, Worcester and Harvard Forest, respectively, highlighting differences in growing season length. In Boston, gross primary production—estimated by scaling productivity by canopy cover—was ~75% lower than at Harvard Forest, yet still constituted a significant local flux of $3.8 mg·C·ha^{-1}·yr^{-1}$. In order to reduce greenhouse gas emissions, we must improve our understanding of the space-time variations and underlying drivers of urban carbon fluxes.Engineering and Applied Science

The Engaged University: Providing a Platform for Research That Transforms Society

Despite a growing recognition that the solutions to current environmental problems will be developed through collaborations between scientists and stakeholders, substantial challenges stifle such cooperation and slow the transfer of knowledge. Challenges occur at several levels, including individual, disciplinary, and institutional. All of these have implications for scholars working at academic and research institutions. Fortunately, creative ideas and tested models exist that provide opportunities for conversation and serious consideration about how such institutions can facilitate the dialogue between scientists and societ

Global urban environmental change drives adaptation in white clover

Urbanization transforms environments in ways that alter biological evolution. We examined whether urban environmental change drives parallel evolution by sampling 110,019 white clover plants from 6169 populations in 160 cities globally. Plants were assayed for a Mendelian antiherbivore defense that also affects tolerance to abiotic stressors. Urban-rural gradients were associated with the evolution of clines in defense in 47% of cities throughout the world. Variation in the strength of clines was explained by environmental changes in drought stress and vegetation cover that varied among cities. Sequencing 2074 genomes from 26 cities revealed that the evolution of urban-rural clines was best explained by adaptive evolution, but the degree of parallel adaptation varied among cities. Our results demonstrate that urbanization leads to adaptation at a global scale

Carbon And Nitrogen Dynamics In Urban Ecosystems

Chapter 1: 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. Chapter 2: The rapid increase in residential land area in the United States has raised concern about water pollution associated with nitrogen fertilizers. Nitrate (NO[-] ) is the form of reactive N that is most susceptible to leaching and 3 runoff; thus, a more thorough understanding of nitrification and NO[-] avail3 ability is needed if we are to accurately predict the consequences of residential expansion for water quality. In this study, we evaluated potential net nitrification and mineralization, microbial respiration and biomass, and soil NO[-] and 3 NH+ pools in residential home lawns and forests. 4 Chapter 3: We previously created a mass balance for residential lawns, however, a major N flux was missing - gaseous losses from denitrification. Using recent advances in instrumentation, we were able to measure field-relevant rates of denitrification from lawns. We calculated annual denitrification rates of 14.0 ± 3.6 kg N/ha/yr for the lawns in this study, which suggests that denitrification is an important means of removing reactive N from the residential landscape. Further work is required before these findings can be generalized to a wider range of residential lawns and soils. Chapter 4: 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 compared carbon budgets and evaluated carbon mitigation costs for nine counties across the northeastern United States that represent a range of biophysical, demographic and socioeconomic conditions

Mapping carbon storage in urban trees withmulti-source remote sensing data: Relationships between biomass, land use, and demographics in Boston neighborhoods

This dataverse repository contains two datasets: 1. A one square meter resolution map of biomass for the City of Boston. Units are Mg biomass per hectare (Mg/ha). 2. A one square meter resolution map of canopy cover for the City of Boston. Units are binary: 0 = no canopy, 1 = canopy Both datasets are derived from LiDAR and high resolution remote sensing imagery. Details of the methodology are provided in the following publications: Raciti, SM, Hutyra, LR, Newell, JD, 2014. Mapping carbon storage in urban trees withmulti-source remote sensing data: Relationships between biomass, land use, and demographics in Boston neighborhoods,Science of the Total Environment, 500-501, 72-83. http://dx.doi.org/10.1016/j.scitotenv.2014.08.070 Raciti, SM, Hutyra, LR, Newell, JD, 2015. Corrigendum to “Mapping carbon storage in urban trees with multi-source remote sensing data: Relationships between biomass, land use, and demographics in Boston neighborhoods”, Science of the Total Environment, 538, 1039-1041. http://dx.doi.org/10.1016/j.scitotenv.2015.07.154<br

Data from: Characterizing forest structure variations across an intact tropical peat dome using field samplings and airborne LiDAR

Tropical peat swamp forests (PSF) are one of the most carbon dense ecosystems on the globe and are experiencing substantial natural and anthropogenic disturbances. In this study we combined direct field sampling and airborne LiDAR to empirically quantify forest structure and aboveground live biomass (AGB) across a large, intact tropical peat dome in Northwestern Borneo. Moving up a 4m elevational gradient, we observed increasing stem density but decreasing canopy height, crown area and crown roughness. These findings were consistent with hypotheses that nutrient and hydrological dynamics co-influence forest structure and stature of the canopy individuals, leading to reduced productivity towards the dome interior. Gap frequency as a function of gap size followed a power law distribution with a shape factor (?) of 1.76 ± 0.06. Ground-based and dome-wide estimates of AGB were 217.7 ± 28.3 Mg C ha-1, and 222.4 ± 24.4 Mg C ha-1, respectively, which were higher than previously reported AGB for PSF and tropical forests in general. However, dome-wide AGB estimates were based on height statistics and we found the coefficient of variation on canopy height was only 0.08, three times less than stem diameter measurements, suggesting LiDAR height metrics may not be a robust predictor of AGB in tall tropical forests with dense canopies. Our structural characterization of this ecosystem advances the understanding of the ecology of intact tropical peat domes and factors that influence biomass density and landscape-scale spatial variation. This ecological understanding is essential to improve estimates of forest carbon density and its spatial distribution in PSF and to effectively model the effects of disturbance and deforestation in these carbon dense ecosystems

Mendaram live tree survey 2014

Csv contaning biometric data for live trees in Mendaram, Belait, Brunei

STEM LOCATIONS AND HEIGHTS IN ULU MENDARAM

THE STEM LOCATIONS AND HEIGHTS WERE EXTRACTED USING LOCAL MAXIMA FILTERING FROM A CANOPY HEIGHT MODEL AT 0.5M. THE CANOPY HEIGHT MODEL WAS PRODUCED USING SMALL FOOTPRINT AIRBORNE LIDAR DATA ACQUIRED IN 2010 OVER BRUNEI