CO2 Isotopes and Elemental Carbon Measurements in air Samples at Canadian Baseline Stations: Can Human Impacts on Atmospheric CO2 be Detected and Quantified via an Integrated Approach?
Detecting and quantifying human induced CO2 and other air pollutants are important in air quality as well as in carbon cycle related climate research, particularly for addressing the issue of the continued increase of atmospheric CO2. It is known that isotope compositions are widely used as tracers in source identifications and attributions for atmospheric CO2. Due to a long life time (about 200 years) of CO2 and its exchanges with natural systems, the signal of human induced CO2 and its carbon isotopic compositions in the atmosphere is small. It is very challenging to quantify its impact within an accepted range of uncertainty at global/regional scales. Thus, the requirements for the precision and accuracy in CO2 and related tracers measurements, including its stable isotope, are very rigid. At the same time, measuring multi- species together with CO2, has been strongly recommended by the global carbon cycle research community. Elemental carbon or black carbon (EC or BC) in fine carbonaceous particulate matter (PM2.5μm) is an important air pollutant as well as a key player in climate change. Similar to CO2, EC is also called as greenhouse aerosol, absorbing light and warming the atmosphere. Since it is coemitted with CO2 from fossil fuel combustions and biomass burning, tracking the spatial and temporal distributions of EC may provide valuable insight to those emission sources/transport mechanisms. Having a short atmospheric life time (7-10 days), the atmospheric EC is sensitive to the emission strength of those related sources (i.e., fossil fuel combustions and biomass burning). Thus, with a combination of EC with CO2 and its isotope measurements, it is expected to provide independent constraints for detecting and quantifying the human induced CO2 at regional scales. In this talk, an integrated data set of CO2 concentration, CO2 isotopes (with a focus on δ13C) and EC measurements in fine PM at Canadian baseline sites will be presented. Those measurements have been focusing on a transit from a typical urban site (Toronto) to a rural area (Egbert, about 80 km northwest of Toronto), to boreal forest area (Fraserdale: a boreal east site and Berms/ETL: a boreal west site) and to the Arctic region (Alert: a background site). Those data will be used, including regular vertical aircraft measurements at Berm/ETL, to illustrate the concept and the method for quantifying human induced CO2 at regional scales. The results show that •EC in fine particles is a good tracer for fossil fuel combustions and biomass burnings; •Integrating EC with CO2 and its isotope measurements could be a very useful tool for detecting and attributing the human-induced CO2. At the same time, natural contributions to air CO2 can be also constrained at regional scales. The challenges of the method will be also discussed.
North American Land Change Monitoring System: Current Status and Future Development
At the Land Cover Summit meeting held in Washington, DC in September 2006 the North American Land Change Monitoring System (NLCMS) project was initiated between representatives from the US Geological Survey (USGS), the National Institute of Geographic Statistics and Information of Mexico (INEGI) and the Canada Centre for Remote Sensing (CCRS). The objective of the NALCMS is a joint effort to create a harmonized system for multi-scale and multi-temporal monitoring and reporting of North American land cover change. The proposed system couples 250m and 30m resolutions, offering products relevant at both spatial scales. The two spatial resolutions will provide users with investigation, confirmation, calibration, and assessment of 250m change products with 30m product support. This combination of spatial resolutions offers a valuable increase in temporal frequency, context, and strategic prioritization for 30m products. In due course these land change products can provide continental, national, and regional consistency to land cover and land cover change analysis.
Remote Sensing of Vegetation Nitrogen Content for Spatially Explicit Carbon and Water Cycle Estimation
Foliage nitrogen concentration is a determinant of photosynthetic capacity of leaves, thereby an important input to ecological models for estimating terrestrial carbon and water budgets. Recently, spectrally continuous airborne hyperspectral remote sensing imagery has proven to be useful for retrieving an important related parameter, total chlorophyll content at both leaf and canopy scales. Thus remote sensing of vegetation biochemical parameters has promising potential for improving the prediction of global carbon and water balance patterns. In this research, we explored the feasibility of estimating leaf nitrogen content using hyperspectral remote sensing data for spatially explicit estimation of carbon and water budgets. Multi-year measurements of leaf biochemical contents of seven major boreal forest species were carried out in northeastern Ontario, Canada. The variation of leaf chlorophyll and nitrogen content in response to various growth conditions, and the relationship between them,were investigated. Despite differences in plant type (deciduous and evergreen), leaf age, stand growth conditions and developmental stages, leaf nitrogen content was strongly correlated with leaf chlorophyll content on a mass basis during the active growing season (r2=0.78). With this general correlation, leaf nitrogen content was estimated from leaf chlorophyll content at an accuracy of RMSE=2.2 mg/g, equivalent to 20.5% of the average measured leaf nitrogen content. Based on this correlation and a hyperspectral remote sensing algorithm for leaf chlorophyll content retrieval, the spatial variation of leaf nitrogen content was inferred from the airborne hyperspectral remote sensing imagery acquired by Compact Airborne Spectrographic Imager (CASI). A process-based ecological model Boreal Ecosystem Productivity Simulator (BEPS) was used for estimating terrestrial carbon and water budgets. In contrast to the scenario with leaf nitrogen content assigned as a constant value without differentiation between and within vegetation types for calculating the photosynthesis rate, we incorporated the spatial distribution of leaf nitrogen content in the model to estimate net primary productivity and evaportranspiration of boreal ecosystem. These regional estimates of carbon and water budgets with and without N mapping are compared, and the importance of this leaf biochemistry information derived from hyperspectral remote sensing in regional mapping of carbon and water fluxes is quantitatively assessed. Keywords: Remote Sensing, Leaf Nitrogen Content, Spatial Distribution, Carbon and Water Budgets, Estimation
Small-Scale Temporal and Spatial Variability in Regional-Scale CO2 Mixing Ratio Measurements
The study of regional-scale CO2 concentrations and fluxes lies between the detailed understanding of ecological processes that can be gathered via intensive local field study, and the overarching but mechanistically poor understanding of the global carbon cycle that is gained by analyzing the atmospheric CO2 budget. In addition to the importance of regional studies toward the fundamental goal of understanding the carbon balance of the continent, regional-scale studies are becoming increasingly important as the necessity of tracking progress in CO2 emissions reduction arises. This work is part of the NACP's Midcontinental Intensive (MCI) study. Specifically it adds a regional network of five communications-tower based atmospheric CO2 observations ("Ring 2") from April 2007 through October 2008 to the long-term atmospheric CO2 observing network (tall towers, aircraft profiles, and well- calibrated CO2 measurements on Ameriflux towers) in the mid-continent intensive region. The Ring 2 measurements are based on relatively new technology for CO2 measurement, wavelength-scanned cavity ring down spectroscopy (Picarro, Inc.), and the locations are regional in scale (roughly a 500-km diameter ring). We present results concerning data quality of the new instruments, including water vapor correction and uncertainties, as well as small-scale temporal and spatial variations that can be seen with this unique network. For example, the daily daytime average throughout the 2007 and 2008 growing seasons indicated a 50-ppm seasonal drawdown, with significant synoptic variability. The drawdown in this largely agricultural region (heavily influenced by corn) is significantly larger than the 20-30 ppm typically seen in forested regions. Also during the 2007 and 2008 growing seasons, the CO2 mixing ratio at the sites nearly always differs by more than 5 ppm, while at times the inter-site difference is as large as 30-50 ppm. While variability in the regional spatial gradients is expected because of synoptic changes and differing source regions, the magnitude observed is surprisingly large given the sites' relative proximity. The data suggest that similarly constructed networks could form the essential framework for the continuous monitoring of continental, regional and municipal CO2 fluxes as required to support, for example, international treaty verification, regional ambient air regulations and cap-and-trade programs.
Patterns of δ13C in a woody shrub distributed along a topoedaphic gradient in burned and grazed grassland
Woody shrub encroachment into grasslands ecosystems is rapidly altering site biogeochemistry as well as ecosystem structure and function. The mechanisms responsible for woody shrub encroachment in North American grasslands are often site-specific and confounded with varying local environmental conditions. To assess differences in leaf-level carbon and water exchange as a function of land history and site demography, we measured the δ13C in leaves of roughleaf dogwood (Cornus drummondii) growing in mesic grassland. This research occurred at the 3487 ha Konza Prairie Biological Station (KPBS) located in eastern Kansas, USA. KPBS is a mesic grassland with complex topoedaphic gradients on site and is divided into replicated watersheds with varying management history of burning (1, 2, 4, 10, and 20 year intervals) and grazing (with bison and no grazing). Roughleaf dogwood leaves were collected from 70 discrete islands distributed along topoedaphic gradients and across and all burning and grazing regimes at KPBS. Mature, new leaves were sampled from each dogwood island in late June and revisited in late July and early September, 2008. Burn frequency, grazing, elevation, aspect, slope and soil type were used as predict changes in leaf δ13C over the summer. Leaf δ13C varied significantly by land history (grazing and burn frequency) and by site demographic characteristics. These results suggest that leaf-level physiological functioning varied despite similar site-level environmental conditions (air temperature, precipitation, relative humidity) and may help explain non-uniform patterns and interpret the mechanisms of woody encroachment into grasslands.
Prospects for the Regional Assessment of Aboveground Carbon Stocks of Northern Forests Using the ICESAT-GLAS Spaceborne Sensor
Northern forests in North America contain a vast amount of sequestered carbon that is potentially vulnerable to climate change. Scientists from Canada and the US are working in close collaboration to assess the capacity of the GLAS lidar sensor on the ICESAT satellite to estimate the amount, spatial distribution and statistical uncertainty of aboveground tree biomass of these forests. A pilot study in the 1.2 million km2 forest region of Quebec has demonstrated the capability and precision of this spaceborne sensor and we are now applying the technique we developed to the ∼6.2 million km2 area of the boreal biome of North America, i.e. both Canada and Alaska. The biomass of ground plots located in different regions is related to tree height data collected from an airborne profiling small-footprint lidar system. The airborne data is then related to GLAS data for a sample of ICESat orbits. Finally, the full set of available GLAS data is combined with land cover and topographic data to predict aboveground tree biomass as well as the sources and magnitude of the uncertainty. Aboveground biomass for the Quebec study area averaged 39.0 ± 2.2 Mg ha-1 and totalled 4.9 ± 0.3 Pg. Biomass distributions in Quebec were 12.6% northern hardwoods, 12.6% northern mixedwood, 38.4% commercial boreal, 13% non-commercial boreal, 14.2% taiga, and 9.2% treed tundra. Non-commercial forests represented 36% of the estimated aboveground biomass, thus highlighting the importance of remote northern forests to C sequestration.
Carbon flux simulation and data assimilation in North America forest ecosystems
A process-based model, TRIPLEX-Flux, was utilized to estimate net ecosystem production (NEP), as well as analyzing the model's response on parameterization by simulating CO2 flux for forest ecosystems in US and Canada. The research objectives were: (1) to test the TRIPLEX-Flux model simulations against flux tower measurements; (2) to examine the effects of parameter and input variable on model response via parameters optimization in different ecoregions. Field data were assimilated at a 30 min time step and presented as 15- day average. The validation of NEP data at 30 min intervals derived from tower and chamber measurements showed that the modeled NEP data corresponded well with the measured NEP from the forest ecosystem. The optimized parameters varied significantly in different seasons and ecoregions. The key parameters for inter- annual simulation also showed detectable variations. Our preliminary results suggested that parameters optimization improved carbon flux simulation.
Nested Inversion of the North America Carbon Flux with Forest Stand Age Constraint
On the basis of our previous inversion using GlobalView CO2 data for 30 regions of the North America and 20 regions for the rest of the globe, we have improved the inversion results through an additional constraint using a forest stand age map of the USA and Canada. The first version of this age map has been produced through a collaborative effort. It is demonstrated through our ecosystem modeling that the forest carbon source and sink distribution is closely related to forest stand age, and this source of information would be useful for constraining the CO2 flux inversion for the 30 sub-continental regions. For this purpose, we have converted the forest age map into an age factor map, indicating the overall forest age structure is in favor of carbon uptake, and the USA southeast region is the most favorable region. This spatial distribution pattern of the age factor significantly altered the nested inversion results. We have also explored the effect of the diurnal variation of terrestrial ecosystem and atmospheric boundary layer on the inversion results. For this purpose, we used a terrestrial ecosystem model and an atmosphere transport model with short time steps to reflect the diurnal pattern of them. In this presentation, the improvements in the North America carbon cycle estimation using this additional forest age constraint and through the diurnal timing normalization will be assessed by comparing with bottom-up results in Canada and USA.