Biosphere Atmosphere Exchange Of Reactive Nitrogen Oxides Between The Atmosphere And A Ponderosa Pine Forest

Oxidative forms of reactive nitrogen (NOy) impact air quality, nutrient dynamics, and climate. Our understanding of the sources and sinks of atmospheric NOy that result from exchange between the atmosphere and biosphere is poorly constrained due to the lack of adequate instrumentation. In this dissertation, I apply novel technologies to the question of NOy exchange and describe observations of fluxes at the atmosphere-forest interface. I use thermal-dissociation laser-induced fluorescence, chemiluminescence, and the micrometeorological eddy-covariance method. Simultaneous observations of the rate and magnitude of exchanges and vertically resolved concentration measurements of the NOy species (NO, NO2, RO2NO2, RONO2 and HNO3) were measured in addition to a wide suite of relevant parameters including canopy structures, meteorological parameters, and associated chemical species as part of the Biosphere Effects on AeRosols and Photochemistry EXperiment (BEARPEX), which took place June 15 - July 31, 2009 at a Ponderosa pine plantation on the western slope of Sierra Nevada Mountains in California. I present observational evidence for active within canopy chemistry resulting in simultaneous production and removal of NOX within a forest canopy. My observations provide direct evidence for a NOX canopy reduction factor and for an NO2 compensation point. I also establish that an unusual peroxynitrate is formed within the canopy and then emitted to the atmosphere above underscoring the importance of coupling between biogenic volatile organic compounds and NOX to the fluxes of NOX, NOy and BVOC.

The book contains information on geology, climate and vegetation of the Sierra Nevada with a special emphasis on air pollution effects on the mixed conifer forests. A history of the extent of air pollution effects on mixed conifer forests, especially ponderosa and Jeffrey pines is provided. The physiological basis for ozone-type injury development in ponderosa pine, a discussion of ozone uptake by plants at different levels of biological organization and the effects of air pollution and other stresses on mountain forests are discussed. A considerable portion of the book is dedicated to development of statistical models and maps of ambient ozone distribution in the Sierra Nevada based on the 1999 monitoring data with passive samplers. The implications of the methodological results, formulation and application of regional air quality models for integrated assessment of urban and wildland pollution and the need for functionally integrated models of ozone deposition to the Sierra Nevada forests are also discussed. Management and monitoring needs for improved long-term understanding air pollution effects on forest ecosystems, discussion of options for proper management of the air pollution affected forests, and comparison of monitoring and modelling of ozone and forest health status in the Sierra Nevada with similar efforts in mountains of North American and European mountain ranges are the focus of the later chapters of the book.

Atmospheric Nitrogen Deposition in Global Forests: Spatial Variation, Impacts, and Management Implications provides the most comprehensive knowledge on spatial variation and ecological impacts of reactive nitrogen deposition in global forests, as well as forest management options to mitigate the negative impacts. Written and edited by international experts in the field, this book synthesizes recent research developments and insights in monitoring and modeling nitrogen deposition in global forests. The book also assesses ecological impacts of enhanced nitrogen deposition on forest structure and function and responses of forest ecosystems to decreasing nitrogen deposition in regions such as the European Union and North America. Finally, the book reviews indicators and thresholds for nitrogen saturation in global forests and analyzes remediation options to reduce impacts of excess nitrogen deposition. This is an important resource for researchers in forestry and biodiversity conservation, as well as graduate students, policymakers and others who want to understand environmental issues of reactive nitrogen deposition in global forests. Offers a systematic view of the ecological impacts of enhanced nitrogen deposition Provides the most comprehensive knowledge on spatial variation and the ecological impacts of reactive nitrogen deposition in global forests Presents expert research and findings on forest management options to remediate negative impacts

This is the final technical report containing a summary of all findings with regard to the following objectives of the project: (1) To quantify and understand the effects of wildfire on carbon storage and the exchanges of energy, CO2, and water vapor in a chronosequence of ponderosa pine (disturbance gradient); (2) To investigate the effects of seasonal and interannual variation in climate on carbon storage and the exchanges of energy, CO2, and water vapor in mature conifer forests in two climate zones: mesic 40-yr old Douglas-fir and semi-arid 60-yr old ponderosa pine (climate gradient); (3) To reduce uncertainty in estimates of CO2 feedbacks to the atmosphere by providing an improved model formulation for existing biosphere-atmosphere models; and (4) To provide high quality data for AmeriFlux and the NACP on micrometeorology, meteorology, and biology of these systems. Objective (1): A study integrating satellite remote sensing, AmeriFlux data, and field surveys in a simulation modeling framework estimated that the pyrogenic carbon emissions, tree mortality, and net carbon exchange associated with four large wildfires that burned ~50,000 hectares in 2002-2003 were equivalent to 2.4% of Oregon statewide anthropogenic carbon emissions over the same two-year period. Most emissions were from the combustion of the forest floor and understory vegetation, and only about 1% of live tree mass was combusted on average. Objective (2): A study of multi-year flux records across a chronosequence of ponderosa pine forests yielded that the net carbon uptake is over three times greater at a mature pine forest compared with young pine. The larger leaf area and wetter and cooler soils of the mature forest mainly caused this effect. A study analyzing seven years of carbon and water dynamics showed that interannual and seasonal variability of net carbon exchange was primarily related to variability in growing season length, which was a linear function of plant-available soil moisture in spring and early summer. A multi-year drought (2001-2003) led to a significant reduction of net ecosystem exchange due to carry-over effects in soil moisture and carbohydrate reserves in plant-tissue. In the same forest, the interannual variability in the rate carbon is lost from the soil and forest floor is considerable and related to the variability in tree growth as much as it is to variability in soil climatic conditions. Objective (3): Flux data from the mature ponderosa pine site support a physical basis for filtering nighttime data with friction velocity above the canopy. An analysis of wind fields and heat transport in the subcanopy at the mesic 40-year old Douglas site yielded that the non-linear structure and behavior of spatial temperature gradients and the flow field require enhanced sensor networks to estimate advective fluxes in the subcanopy of forest to close the surface energy balance in forests. Reliable estimates for flux uncertainties are needed to improve model validation and data assimilation in process-based carbon models, inverse modeling studies and model-data synthesis, where the uncertainties may be as important as the fluxes themselves. An analysis of the time scale dependence of the random and flux sampling error yielded that the additional flux obtained by increasing the perturbation timescale beyond about 10 minutes is dominated by random sampling error, and therefore little confidence can be placed in its value. Artificial correlation between gross ecosystem productivity (GEP) and ecosystem respiration (Re) is a consequence of flux partitioning of eddy covariance flux data when GEP is computed as the difference between NEE and computed daytime Re (e.g. using nighttime Re extrapolated into daytime using soil or air temperatures). Tower-data must be adequately spatially averaged before comparison to gridded model output as the time variability of both is inherently different. The eddy-covariance data collected at the mature pondero ...