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The aim of this study was to examine the effects of elevated carbon dioxide [CO2] and ozone [O3] and their interaction on wood chemistry and anatomy of five clones of 3-year-old trembling aspen (Populus tremuloides Michx.). Wood chemistry was studied also on paper birch (Betula papyrifera Marsh.) and sugar maple (Acer saccharum Marsh.) seedling-origin saplings of the same age. Material for the study was collected from the Aspen Free-Air CO2 Enrichment (FACE) experiment in Rhinelander, WI, USA, where the saplings had been exposed to four treatments: control (C; ambient CO2, ambient O3), elevated CO2 (560ppm during daylight hours), elevated O3 (1.5 × ambient during daylight hours) and their combination (CO2 + O3) for three growing seasons (1998–2000). Wood chemistry responses to the elevated CO2 and O3 treatments differed between species. Aspen was most responsive, while maple was the least responsive of the three tree species. Aspen genotype affected the responses of wood chemistry and, to some extent, wood structure to the treatments. The lignin concentration increased under elevated O3 in four clones of aspen and in birch. However, elevated CO2 ameliorated the effect. In two aspen clones, nitrogen in wood samples decreased under combined exposure to CO2 and O2. Soluble sugar concentration in one aspen clone and starch concentration in two clones were increased by elevated CO2. In aspen wood, α-cellulose concentration changed under elevated CO2, decreasing under ambient 03 and slightly increasing under elevated O3. Hemicellulose concentration in birch was decreased by elevated CO2 and increased by elevated O3. In aspen, elevated O3 induced statistically significant reductions in distance from the pith to the bark and vessel lumen diameter, as well as increased wall thickness and wall percentage, and in one clone, decreased fibre lumen diameter. Our results show that juvenile wood properties of broadleaves, depending on species and genotype, were altered by atmospheric gas concentrations predicted for the year 2050 and that CO2 ameliorates some adverse effects of elevated O3 on wood chemistry. [ABSTRACT FROM AUTHOR]

Sunlight can oxidize dissolved organic carbon (DOC) to dissolved inorganic carbon (DIC) in freshwaters. The importance of complete photooxidation, or photomineralization, as a sink for DOC remains unclear in temperate rivers, as most estimates are restricted to lakes, high latitude rivers, and coastal river plumes. In this study, we construct a model representing over 75,000 river reaches in the Connecticut River Watershed (CRW), USA, to calculate spectrally resolved photomineralization. We test the hypothesis that photomineralization is a negligible DOC sink across all reaches and flow conditions relative to DOC fluxes. Our model quantifies reaction rates and transport drivers within the river reaches for the ranges of flow conditions, incoming solar irradiance, and canopy cover shading observed throughout the year. Our model predicts average daily areal photomineralization rates ranging from 1.16 mg‐C m−2 day−1 in low flow river reaches in the winter, to 18.33 mg‐C m−2 day−1 in high flow river reaches during the summer. Even for high photomineralization fluxes, corresponding photomineralization uptake velocities are typically at least an order of magnitude smaller than those reported for other instream processes. We calculate DOC elimination by photomineralization relative to DOC fluxes through individual stream reaches as well as the entire riverine portion of the CRW. We find that relative photomineralization fluxes are highest in summer drought conditions in low order streams. In median flows and mean light intensities, for an average watershed travel distance, 3%–5% of the DOC fluxes are eliminated, indicating that photomineralization is a minor DOC sink in temperate rivers. Plain Language Summary: Rivers are an important part of the carbon cycle, moving carbon compounds from land to the ocean. Within rivers, dissolved organic carbon molecules can be broken down into inorganic carbon molecules, including the greenhouse gas carbon dioxide. Sunlight shining into rivers can cause these organic molecules to break down in a process called photomineralization, but it is not clear if this process is important compared to the total amount of organic carbon that travels through rivers every day. In this paper, we build a model for the river sections of temperate Connecticut River Watershed, which calculates photomineralization for possible river flow conditions, dissolved organic carbon concentrations, and seasons, and compares the size of the sunlight‐driven breakdown of dissolved organic carbon to the amount of dissolved organic carbon in the river. This is the first model that puts photomineralization rates in the context of a flowing temperate river network. We show that compared with the dissolved organic carbon amounts present in the river at any time of the year or any flow conditions, photomineralization is essentially an unimportant process, removing on average 3%–5% of the dissolved organic carbon through an average watershed river route. Key Points: We build a model calculating reaction and transport drivers for photomineralization in 75,000 temperate river reachesPhotomineralization is a negligible dissolved organic carbon (DOC) sink relative to DOC fluxesDOC elimination by photomineralization in temperate rivers is limited by short water residence times and canopy cover [ABSTRACT FROM AUTHOR]

Estimates of the marginal value of carbon dioxide-the social cost of carbon (SCC)-were recently adopted by both the U.S. and U.K. Governments in order to satisfy requirements to value estimated greenhouse gas (GHG) changes of new federal regulations. However, the development and use of SCC estimates comes with significant challenges and controversial decisions. This paper summarizes the key issues and then derives guidance for developing, selecting, and applying the estimates that follows from the fundamental scientific nature and economic principles associated with GHGs and climate change, as well as an understanding of the state of the art for estimating the SCC. The paper evaluates recent estimates in light of the guidance and finds the estimates inconsistent with the guidance in a number of significant areas. The paper also differentiates SCC policy applications in terms of policies with incremental versus nonincremental implications for global GHGs, and identifies serious issues for application of the SCC in setting and evaluating climate policy targets. WIREs Clim Change 2012, 3:163-195. doi: 10.1002/wcc.163 For further resources related to this article, please visit the . [ABSTRACT FROM AUTHOR]

This paper provides comparisons of a variety of time-series methods for short-run forecasts of the main greenhouse gas, carbon dioxide, for the United States, using a recently released state-level data set from 1960–2001. We test the out-of-sample performance of univariate and multivariate forecasting models by aggregating state-level forecasts versus forecasting the aggregate directly. We find evidence that forecasting the disaggregate series and accounting for spatial effects drastically improves forecasting performance under root mean squared forecast error loss. Based on the in-sample observations we attempt to explain the emergence of voluntary efforts by states to reduce greenhouse gas emissions. We find evidence that states with decreasing per capita emissions and a “greener” median voter are more likely to push toward voluntary cutbacks in emissions. [ABSTRACT FROM AUTHOR]

This paper discusses the current guidance given by the United States Environmental Protection Agency (EPA) on delineating the so-called Area of Review (AoR) for the permitting of geologic carbon sequestration (GCS) projects. According to the EPA's regulatory framework for GCS, the AoR refers to the region surrounding the CO2 injection well(s) wherein leakage of CO2 and/or the migration of formation fluids could possibly endanger overlying groundwater resources. Our evaluation of the current framework for delineating the size of this area finds unnecessary conservatism in the definition of the critical pressure, which could lead to a heavy burden on permit applicants that seek to get regulatory compliance, in particular for very large GCS projects. We propose a risk-based re-interpretation of this framework, separating the total Area of Review into different sub-areas with different regulatory requirements depending on whether the concern is about free-phase CO2 or pressure-driven brine migration. This leads to a tiered AoR definition in which the projected region of CO2 plume extent would have the highest regulatory standards regarding site characterization, monitoring, and corrective action. The requirements in the AoR outside this central region would be less burdensome because of a narrower focus on major pathways for brine leakage such as unplugged wellbores and large faults. We expect that this revised framework would allow for a reduction in the cost of regulatory compliance for projects with very large injection volumes, while ensuring that the objective of protecting valuable groundwater resources is preserved. [ABSTRACT FROM AUTHOR]

Streams and rivers are major sources of greenhouse gases (GHGs) to the atmosphere, as carbon and nitrogen are converted and outgassed during transport. Although our understanding of drivers of individual GHG fluxes has improved with numerous site‐specific studies and global‐scale compilations, our ability to parse out interrelated physical and biogeochemical drivers of gas concentrations is limited by a lack of consistently collected, temporally continuous samples of GHGs and their associated drivers. We present a first analysis of such a dataset collected by the National Ecological Observatory Network across 27 streams and rivers across ecoclimatic domains of the United States. Average concentrations of CO2 ranged from 36.9 ± 0.88 to 404 ± 33 μmol L−1, CH4 from 0.003 ± 0.0003 to 4.99 ± 0.72 μmol L−1, and N2O from 0.015 to 0.04 μmol L−1 and spanned ranges of previous global compilations. Both CO2 and CH4 were strongly affected by physical drivers including mean air temperature and stream slope, as well as by dissolved oxygen and total nitrogen concentrations. N2O was exclusively correlated with total nitrogen concentrations. Results suggested that potential for gas exchange dominated patterns in gas concentrations at the site level, but contributions of in‐stream aerobic and anaerobic metabolism, and groundwater also likely varied across sites. The highest gas concentrations as well as highest variability occurred in low‐gradient, warmer, and nonperennial systems. These results are a first step in providing unprecedented, continuous estimates of GHG flux constrained by temporally variable physical and biogeochemical drivers of GHG production. [ABSTRACT FROM AUTHOR]

In an environment with economic policy uncertainty, the policies of energy efficiency are probably compromised due to weak regulation measures. Inconsistent economic policies may lead to higher energy consumption, which damages the environment. However, works of literature are silent on the role of economic policy uncertainty in carbon emission and energy nexus. Hence, the study is an attempt to investigate the role of economic policy uncertainty in the relationship between energy intensity and carbon dioxide (CO2) emissions in the United States by using annual data spanning from 1985 to 2017. A recent time series method proposed by Jordan and Philips (2018) is employed to get robust and consistent estimation results in the study. Empirical results reveal that (a) higher energy intensity contributes to pollution, (b) economic policy uncertainty adversely affects environmental quality, (c) economic policy uncertainty strengthens the detrimental effect of energy intensity on CO2 emissions. [ABSTRACT FROM AUTHOR]

Production and consumption of nitrous oxide (N2O), methane (CH4), and carbon dioxide (CO2) are affected by complex interactions of temperature, moisture, and substrate supply, which are further complicated by spatial heterogeneity of the soil matrix. This microsite heterogeneity is often invoked to explain non‐normal distributions of greenhouse gas (GHG) fluxes, also known as hot spots and hot moments. To advance numerical simulation of these belowground processes, we expanded the Dual Arrhenius and Michaelis–Menten model, to apply it consistently for all three GHGs with respect to the biophysical processes of production, consumption, and diffusion within the soil, including the contrasting effects of oxygen (O2) as substrate or inhibitor for each process. High‐frequency chamber‐based measurements of all three GHGs at the Howland Forest (ME, USA) were used to parameterize the model using a multiple constraint approach. The area under a soil chamber is partitioned according to a bivariate log‐normal probability distribution function (PDF) of carbon and water content across a range of microsites, which leads to a PDF of heterotrophic respiration and O2 consumption among microsites. Linking microsite consumption of O2 with a diffusion model generates a broad range of microsite concentrations of O2, which then determines the PDF of microsites that produce or consume CH4 and N2O, such that a range of microsites occurs with both positive and negative signs for net CH4 and N2O flux. Results demonstrate that it is numerically feasible for microsites of N2O reduction and CH4 oxidation to co‐occur under a single chamber, thus explaining occasional measurement of simultaneous uptake of both gases. Simultaneous simulation of all three GHGs in a parsimonious modeling framework is challenging, but it increases confidence that agreement between simulations and measurements is based on skillful numerical representation of processes across a heterogeneous environment. [ABSTRACT FROM AUTHOR]

In this article, we propose a stochastic formulation of mass balances that impose physical constraints on production technologies. The estimation of the model involves a composed error term structure that is commonly applied in the literature on stochastic frontier analysis of productive efficiency. Moreover, we discuss how ordinary least squares and maximum likelihood methods can be used to estimate emission coefficients based on the proposed model and compare the results to estimates based on linear programming techniques from input–output analysis. In contrast to previous approaches, our model allows one to estimate the physical limitations to production possibilities in the presence of statistical noise and depends on substantially weaker data requirements. We apply our approach to estimate emission coefficients for sulfur dioxide and carbon dioxide using a sample of fossil‐fueled power plants in the United States. [ABSTRACT FROM AUTHOR]

The ice‐covered period on lakes in the northern hemisphere has often been neglected or assumed to have less importance relative to the open water season. However, recent studies challenge this convention, suggesting that the winter period is more dynamic than previously thought. In this review, we synthesize the current understanding of under‐ice carbon dioxide (CO2) and methane (CH4) dynamics, highlighting the annual importance of CO2 and CH4 emissions from lakes at ice‐melt. We compiled data from 25 studies that showed that the ice‐melt period represents 17% and 27% of the annual CO2 and CH4 emissions, respectively. We also found evidence that the magnitude and type of emission (i.e., CO2 and CH4) varies with characteristics of lakes including geographic location, lake morphometry, and physicochemical conditions. The scarcity of winter and spring carbon data from northern lakes represents a major gap in our understanding of annual budgets in these lakes and calls for future research during this key period. [ABSTRACT FROM AUTHOR]

The article reports on the results of a workshop sponsored by three United States federal agencies regarding the impact of carbon dioxide emissions on coral reefs. The paper entitled "Impacts of Ocean Acidification on Coral Reefs and Other Marine Calcifiers," indicate that calcification rates in coral could decrease by as much as 60 percent within the 21st century as a direct result of the increasingly acidic ocean condition.

A conference paper about blueprint for global warming's molecular basis is presented. It discusses that a new study shows that major chemicals most frequently referred as primary causes of climate change, such as methane and carbon dioxide, are outclassed in their warming capability by compounds receiving less attention. National Aeronautics and Space Administration (NASA) and Purdue University studied more than a dozen chemicals, most of which are produced by humans.

Smart irrigation controllers (SICs) can save water by adapting watering schedules to climate and soil conditions. The potential benefit of SICs is particularly high in southwestern U.S. states, where the arid climate makes water scarcer and increases watering needs of landscapes. A number of studies have tested the ability of SICs to save water in residential and small commercial settings. Results generally show overall savings, but there is substantial variability, including cases of increased water use. Though there are many controllers on the market, we argue there is a further need for optimization of design and field performance. To inform the technology development process, we develop a design for environment method, which overlays economic and environmental performance parameters under different operating conditions. This method is applied to characterize design goals for controller price and water savings that SICs must meet to yield life cycle carbon dioxide reductions and economic savings in southwestern U.S. states, accounting for regional variability in electricity and water prices and carbon overhead. Results from applying the model to SICs in the Southwest suggest that some areas are significantly easier to design for. One concept to realize improved design in practice is to build out the controller market in a staged set of niches, starting from a more favorable area then moving toward more challenging conditions. [ABSTRACT FROM AUTHOR]

Interest in liquid biofuels production and use has increased worldwide as part of government policies to address the growing scarcity and riskiness of petroleum use, and, at least in theory, to help mitigate adverse global climate change. The existing biofuels markets are dominated by U.S. ethanol production based on cornstarch, Brazilian ethanol production based on sugarcane, and European biodiesel production based on rapeseed oil. Other promising efforts have included programs to shift toward the production and use of biofuels based on residues and waste materials from the agricultural and forestry sectors, and perennial grasses, such as switchgrass and miscanthus—so-called cellulosic ethanol. This article reviews these efforts and the recent literature in the context of ecological economics and sustainability science. Several common dimensions for sustainable biofuels are discussed: scale (resource assessment, land availability, and land use practices); efficiency (economic and energy); equity (geographic distribution of resources and the “food versus fuel” debate); socio-economic issues; and environmental effects and emissions. Recent proposals have been made for the development of sustainable biofuels criteria, culminating in standards released in Sweden in 2008 and a draft report from the international Roundtable on Sustainable Biofuels. These criteria hold promise for accelerating a shift away from unsustainable biofuels based on grain, such as corn, and toward possible sustainable feedstock and production practices that may be able to meet a variety of social, economic, and environmental sustainability criteria. [ABSTRACT FROM AUTHOR]

The use of cap-and-trade to regulate air pollution promises to achieve environmental goals at lower cost than traditional prescriptive approaches. Cap-and-trade has been applied to various air pollutants including sulphur dioxide, nitrogen oxides and volatile organic compounds in the United States and carbon dioxide (CO2) in the European Union. This corresponds to what is likely to become the most expensive environmental undertaking in history – the effort to reduce the heating of the planet. However, the efficacy of a cap-and-trade policy for CO2 depends in large part on the design of the program. In addition to the level of the cap, the most important decision facing policymakers will be the initial allocation of emissions allowances. The method used to allocate tradable emissions allowances will have significant influence on the distributional impact and efficiency of the program. [ABSTRACT FROM AUTHOR]

The biomass of tropical forests plays an important role in the global carbon cycle, both as a dynamic reservoir of carbon, and as a source of carbon dioxide to the atmosphere in areas undergoing deforestation. However, the absolute magnitude and environmental determinants of tropical forest biomass are still poorly understood. Here, we present a new synthesis and interpolation of the basal area and aboveground live biomass of old-growth lowland tropical forests across South America, based on data from 227 forest plots, many previously unpublished. Forest biomass was analyzed in terms of two uncorrelated factors: basal area and mean wood density. Basal area is strongly affected by local landscape factors, but is relatively invariant at regional scale in moist tropical forests, and declines significantly at the dry periphery of the forest zone. Mean wood density is inversely correlated with forest dynamics, being lower in the dynamic forests of western Amazonia and high in the slow-growing forests of eastern Amazonia. The combination of these two factors results in biomass being highest in the moderately seasonal, slow growing forests of central Amazonia and the Guyanas (up to 350 Mg dry weight ha−1) and declining to 200–250 Mg dry weight ha−1 at the western, southern and eastern margins. Overall, we estimate the total aboveground live biomass of intact Amazonian rainforests (area 5.76 × 106 km2 in 2000) to be 93±23 Pg C, taking into account lianas and small trees. Including dead biomass and belowground biomass would increase this value by approximately 10% and 21%, respectively, but the spatial variation of these additional terms still needs to be quantified. [ABSTRACT FROM AUTHOR]

Mitigating or slowing an increase in atmospheric carbon dioxide concentration ([CO2]) has been the focus of international efforts, most apparent with the development of the Kyoto Protocol. Sequestration of carbon (C) in agricultural soils is being advocated as a method to assist in meeting the demands of an international C credit system. The conversion of conventionally tilled agricultural lands to no till is widely accepted as having a large-scale sequestration potential. In this study, C flux measurements over a no-till corn/soybean agricultural ecosystem over 6 years were coupled with estimates of C release associated with agricultural practices to assess the net biome productivity (NBP) of this no-till ecosystem. Estimates of NBP were also calculated for the conventionally tilled corn/soybean ecosystem assuming net ecosystem exchange is C neutral. These measurements were scaled to the US as a whole to determine the sequestration potential of corn/soybean ecosystems, under current practices where 10% of agricultural land devoted to this ecosystem is no-tilled and under a hypothetical scenario where 100% of the land is not tilled. The estimates of this analysis show that current corn/soybean agriculture in the US releases ∼7.2 Tg C annually, with no-till sequestering ∼2.2 Tg and conventional-till releasing ∼9.4 Tg. The complete conversion of land area to no till might result in 21.7 Tg C sequestered annually, representing a net C flux difference of ∼29 Tg C. These results demonstrate that large-scale conversion to no-till practices, at least for the corn/soybean ecosystem, could potentially offset ca. 2% of annual US carbon emissions. [ABSTRACT FROM AUTHOR]

Cheatgrass ( Bromus tectorum) is a recognized, invasive annual weed of the western United States that reduces fire return times from decades to less than 5 years. To determine the interaction between rising carbon dioxide concentration ([CO2]) and fuel load, we characterized potential changes in biomass accumulation, C : N ratio and digestibility of three cheatgrass populations from different elevations to recent and near-term projections in atmospheric [CO2]. The experimental CO2 values (270, 320, 370, 420 μmol mol−1) corresponded roughly to the CO2 concentrations that existed at the beginning of the 19th century, that during the 1960s, the current [CO2], and the near-term [CO2] projection for 2020, respectively. From 25 until 87 days after sowing (DAS), aboveground biomass for these different populations increased 1.5–2.7 g per plant for every 10 μmol mol−1 increase above the 270 μmol mol−1 preindustrial baseline. CO2 sensitivity among populations varied with elevational origin with populations from the lowest elevation showing the greatest productivity. Among all populations, the undigestible portion of aboveground plant material (acid detergent fiber ADF, mostly cellulose and lignin) increased with increasing [CO2]. In addition, the ratio of C : N increased with leaf age, with [CO2] and was highest for the lower elevational population. These CO2-induced qualitative changes could, in turn, result in potential decreases in herbivory and decomposition with subsequent effects on the aboveground retention of cheatgrass biomass. Overall, these data suggest that increasing atmospheric [CO2] above preambient levels may have contributed significantly to cheatgrass productivity and fuel load with subsequent effects on fire frequency and intensity. [ABSTRACT FROM AUTHOR]

This article focuses on the emission trading. The Kyoto Protocol, which took effect on February 16, 2005, includes emissions trading as one of three market-oriented strategies for reducing the buildup of greenhouse gases in the atmosphere. Competing bills to revise the Clean Air Act, including U.S. President George W. Bush's "Clear Skies" legislation, are vying for congressional favor. Both Clear Skies and its rival, the Clean Power Act, rely on marketable allowances as a strategy to reduce emissions from coal-fired power plants. The chief difference between the two involves carbon dioxide, a major greenhouse gas. Clear Skies does not regulate carbon dioxide emissions, while the Clean Power Act does. Senators John McCain and Joseph Lieberman also have reintroduced the Climate Stewardship Act, which would establish a cap-and-trade program of marketable allowances to reduce emissions of carbon dioxide and other greenhouse gases from power plants, refineries, and other large commercial and industrial facilities. President Bush sees cap-and-trade as a business-friendly approach to environmental management.

We used a spatially nested hierarchy of field and remote-sensing observations and a process model, Biome-BGC, to produce a carbon budget for the forested region of Oregon, and to determine the relative influence of differences in climate and disturbance among the ecoregions on carbon stocks and fluxes. The simulations suggest that annual net uptake (net ecosystem production (NEP)) for the whole forested region (8.2 million hectares) was 13.8TgC (168gCm-2yr-1), with the highest mean uptake in the Coast Range ecoregion (226gCm-2yr-1), and the lowest mean NEP in the East Cascades (EC) ecoregion (88 g C m-2 yr-1). Carbon stocks totaled 2765TgC (33 700gCm-2), with wide variability among ecoregions in the mean stock and in the partitioning above- and belowground. The flux of carbon from the land to the atmosphere that is driven by wildfire was relatively low during the late 1990s ( ∼ 0.1TgC yr-1), however, wildfires in 2002 generated a much larger C source (∼ 4.1TgC). Annual harvest removals from the study area over the period 1995–2000 were ∼ 5.5TgCyr-1. The removals were disproportionately from the Coast Range, which is heavily managed for timber production (approximately 50% of all of Oregon's forest land has been managed for timber in the past 5 years). The estimate for the annual increase in C stored in long-lived forest products and land fills was 1.4TgCyr-1. Net biome production (NBP) on the land, the net effect of NEP, harvest removals, and wildfire emissions indicates that the study area was a sink (8.2Tg C yr-1). NBP of the study area, which is the more heavily forested half of the state, compensated for ∼ 52% of Oregon's fossil carbon dioxide emissions of 15.6TgC yr-1 in 2000. The Biscuit Fire in 2002 reduced NBP dramatically, exacerbating net emissions that year. The regional total reflects the strong east-west gradient in potential productivity associated with the climatic gradient, and a disturbance regime that has been dominated in recent decades by commercial forestry. [ABSTRACT FROM AUTHOR]

Investigates the mechanical properties of alternating poly(propylene carbonate) (PPC) copolymer in the U.S. Method used to determine the thermal stability of PPC; Molecular weight of PPC; Percentage rate used to purify propylene oxide and carbon dioxide.

Abstract We present the annual patterns of net ecosystem-atmosphere exchange (NEE) of CO[sub 2] and H2O observed from a 447 m tall tower sited within a mixed forest in northern Wisconsin, USA. The methodology for determining NEE from eddy-covariance flux measurements at 30, 122 and 396 m above the ground, and from CO[sub 2] mixing ratio measurements at 11, 30, 76, 122, 244 and 396 m is described. The annual cycle of CO[sub 2] mixing ratio in the atmospheric boundary layer (ABL) is also discussed, and the influences of local NEE and large-scale advection are estimated. During 1997 gross ecosystem productivity (947-18 g C m[sup -2] yr[sup -1] ), approximately balanced total ecosystem respiration (963±19 g C m[sup -2] yr[sup -1] ), and NEE of CO[sub 2] was close to zero (16±19 g C m[sup -2] yr[sup -1] emitted into the atmosphere). The error bars represent the standard error of the cumulative daily NEE values. Systematic errors are also assessed. The identified systematic uncertainties in NEE of CO[sub 2] are less than 60 g C m[sup -2] yr[sup -1] . The seasonal pattern of NEE of CO[sub 2] was highly correlated with leaf-out and leaf-fall, and soil thaw and freeze, and was similar to purely deciduous forest sites. The mean daily NEE of CO[sub 2] during the growing season (June through August) was -1.3 g C m[sup -2] day[sup -1] , smaller than has been reported for other deciduous forest sites. NEE of water vapor largely followed the seasonal pattern of NEE of CO[sub 2] , with a lag in the spring when water vapor fluxes increased before CO[sub 2] uptake. In general, the Bowen ratios were high during the dormant seasons and low during the growing season. Evapotranspiration normalized by potential evapotranspiration showed the opposite pattern. The seasonal course of the CO[sub 2] mixing ratio in the ABL at the tower led the seasonal pattern of NEE of CO[sub 2] in time: in spring, CO[sub 2] mixing ratios began to decrease prior to the onset of daily net uptake of CO[sub 2] by the forest, and in fall mixing ratios began to increase before the forest became a net source for CO[sub 2] to the atmosphere. Transport as well as local NEE of CO[sub 2] are shown to be important components of the ABL CO[sub 2] budget at all times of the year. [ABSTRACT FROM AUTHOR]

Construction materials account for a significant proportion of nonfuel materials flows throughout the industrialized world. Hydraulic (chiefly portland) cement, the binding agent in concrete and most mortars, is an important construction material. Portland cement is made primarily from finely ground clinker, a manufactured intermediate product that is composed predominantly of hydraulically active calcium silicate minerals formed through high-temperature burning of limestone and other materials in a kiln. This process typically requires approximately 3 to 6 million Btu (3.2 to 6.3 GJ) of energy and 1.7 tons of raw materials (chiefly limestone) per ton (t) of clinker produced and is accompanied by significant emissions of, in particular, carbon dioxide (CO[sub 2]), but also nitrogen oxides, sulfur oxides, and particulates. The overall level of CO[sub 2] output, about 1 ton/ton clinker, is almost equally contributed by the calcination of limestone and the combustion of fuels and makes the cement industry one of the top two manufacturing industry sources of this greenhouse gas. The enormous demand for cement and the large energy and raw material requirements of its manufacture allow the cement industry to consume a wide variety of waste raw materials and fuels and provide the industry with significant opportunities to symbiotically utilize large quantities of by-products of other industries. This article, the second in a two-part series, summarizes some of the environmental challenges and opportunities facing the cement manufacturing industry. In the companion article, the chemistry, technology, raw materials, and energy requirements of cement manufacture were summarized. Because of the size and scope of the U.S. cement industry, the article relies primarily on data and practices from the United States. [ABSTRACT FROM AUTHOR]

Abstract Soil-surface CO2 efflux and its spatial and temporal variations were examined in an 8-y-old ponderosa pine plantation in the Sierra Nevada Mountains in California from June 1998 to August 1999. Continuous measurements of soil CO2 efflux, soil temperatures and moisture were conducted on two 20 × 20 m sampling plots. Microbial biomass, fine root biomass, and the physical and chemical properties of the soil were also measured at each of the 18 sampling locations on the plots. It was found that the mean soil CO2 efflux in the plantation was 4.43 µmol m-2 s-1 in the growing season and 3.12 µmol m-2 s-1 in the nongrowing season. These values are in the upper part of the range of published soil-surface CO2 efflux data. The annual maximum and minimum CO2 efflux were 5.87 and 1.67 µmol m-2 s-1, respectively, with the maximum occurring between the end of May and early June and the minimum in December. The diurnal fluctuation of CO2 efflux was relatively small (< 20%) with the minimum appearing around 09.00 hours and the maximum around 14.00 hours. Using daytime measurements of soil CO2 efflux tends to overestimate the daily mean soil CO2 efflux by 4–6%. The measurements taken between 09.00 and 11.00 hours (local time) seem to better represent the daily mean with a reduced sampling error of 0.9–1.5%. The spatial variation of soil CO2 efflux among the 18 sampling points was high, with a coefficient of variation of approximately 30%. Most (84%) of the spatial variation was explained by fine root biomass, microbial biomass, and soil physical and chemical properties. Although soil temperature and moisture explained most of the temporal variations (76–95%) of soil CO2 efflux, the two variables together explained less than 34% of the spatial variation.... [ABSTRACT FROM AUTHOR]

Abstract The effects of elevated atmospheric CO2 on fine root decomposition over a 828-day period were investigated using open top chambers with both ambient and elevated (700 ppm) CO2 treatments in an oak–palmetto scrub ecosystem at Kennedy Space Center, Florida. Carbon dioxide enrichment of the chambers began 15 May 1996. The experiment included roots grown in ambient and elevated carbon dioxide. Vertical litterbags installed in September 1996 in each elevated and ambient chamber incubated from December 1996 to December 1998 showed no significant treatment effect on fine root or rhizome mass loss. Initial fine root percentage mass loss varied from 10.3% to 13.5% after three months; 55.5% to 38.3% of original mass had been lost after 828 days. A period of nitrogen immobilization occurred in both fine roots and rhizomes in the elevated CO2 incubation, which is a potential mechanism for nitrogen conservation for this system in an elevated CO2 world. [ABSTRACT FROM AUTHOR]

Summary • Understanding and predicting the impacts of elevated atmospheric CO2 , elevated nitrogen deposition, and decreases in plant diversity require better understanding of the way in which plant species influence soil CO2 flux. • In experimental grassland plots where atmospheric CO2 , nitrogen supply, and species composition and diversity were manipulated, species effects on soil CO2 flux during 19 sampling periods over 2 yr were determined for 16 grassland species. • The average effect of a species on soil CO2 flux was correlated with biomass of the species grown in monoculture, suggesting that effects of species on soil CO2 flux are related to the potential productivity of a species and total belowground C allocation. During dry, warm conditions there is a greater effect of elevated atmospheric CO2 on soil CO2 flux and during these times deeper-rooted species contribute to soil CO2 flux more than average. • Although differences in responses to elevated CO2 and nitrogen among species were not great, decreases in diversity can affect belowground carbon allocation depending on the plant traits of the species that are lost from ecosystems. [ABSTRACT FROM AUTHOR]

SummaryThe long-term effects of elevated (ambient plus 350 μmol mol-1) atmospheric CO2 concentration (Ca) on the leaf senescence of Quercus myrtifolia Willd was studied in a scrub-oak community during the transition from autumn (December 1997) to spring (April 1998). Plants were grown in large open-top chambers at the Smithsonian CO2 Research Site, Merritt Island Wildlife Refuge, Cape Canaveral, Florida. Chlorophyll (a + b) concentration, Rubisco activity and N concentration decreased by 75%, 82%, and 52%, respectively, from December (1997) to April (1998) in the leaves grown at ambient Ca. In contrast, the leaves of plants grown at elevated Ca showed no significant decrease in chlorophyll (a + b) concentration or Rubisco activity, and only a 25% reduction in nitrogen. These results indicate that leaf senescence was delayed during this period at elevated Ca. Delayed leaf senescence in elevated Ca had important consequences for leaf photosynthesis. In elevated Ca the net photosynthetic rate of leaves that flushed in Spring 1997 (last year's leaves) and were 13 months old was not different from fully-expanded leaves that flushed in 1998, and were approximately 1 month old (current year's leaves). In ambient Ca the net photosynthetic rate of last year's leaves was 54% lower than for current year's leaves. When leaves were fully senesced, nitrogen concentration decreased to about 40% of the concentration in non-senesced leaves, in both CO2 treatments. In April, net photosynthesis was 97% greater in leaves grown in elevated Ca than in those grown at ambient. During the period when elevated Ca delayed leaf senescence, more leaves operating at higher photosynthetic rate would allow the ecosystem dominated by Q. myrtifolia to gain more carbon at elevated Ca than at ambient Ca. [ABSTRACT FROM AUTHOR]

Forests in the south-eastern United States experienced a prolonged dry spell and above-normal temperatures during the 1995 growing season. During this episode, nearly continuous, eddy covariance measurements of carbon dioxide and water vapour fluxes were acquired over a temperate, hardwood forest. These data are used to examine how environmental factors and accumulating soil moisture deficits affected the diurnal pattern and magnitude of canopy-scale carbon dioxide and water vapour fluxes. The field data are also used to test an integrative leaf-to-canopy scaling model (CANOAK), which uses micrometeorological and physiological theory, to calculate mass and energy fluxes. When soil moisture was ample in the spring, peak rates of net ecosystem CO[sub2] exchange (N[subE] occurred around midday and exceeded 20 μmol m[sup-2] s[sup-1]. Rates of N[subE] were near optimal when air temperature ranged between 22 and 25°C. The accumulation of soil moisture deficits and a co-occurrence of high temperatures caused peak rates of daytime carbon dioxide uptake to occur earlier in the morning. High air temperatures and soil moisture deficits were also correlated with a dramatic reduction in the magnitude of N[subE]. On average, the magnitude of N[subE] decreased from 20 to 7 μmol m[sup-2] s[sup-1] as air temperature increased from 24 to 30°C and the soil dried. The CANAOK model yielded accurate estimates of canopy-scale carbon dioxide and water vapour fluxes when the forest had an ample supply of soil moisture. During the drought and heat spell, a cumulative drought index was needed to adjust the proportionality constant of the stomatal conductance model to yield accurate estimates of canopy CO[sub2] exchange. The adoption of the drought index also enabled the CANOAK model to give improved estimates of evaporation until midday. On the other hand, the scheme failed to yield accurate estimates of evaporation during the afternoon. [ABSTRACT FROM AUTHOR]

The article reports on the geologic sequestration (GS) rule developed by the U.S. Environmental Protection Agency (EPA) in regulating carbon dioxide in the country. It mentions that the GS rule contains specific requirements designed to protect groundwater resources across the country. It also notes that the agency is developing a series of guidance documents for implementing the rule to ensure that wells for GS are well constructed and monitored.

The article offers a report about the United States warmth record for 2006. According to four climate scientists from United States National Oceanic and Atmosphere Administration, the greenhouse effect in America was behind more than half of last year's, 2005, record-breaking warmth across the contiguous United States. It states that global warming in 2006 was aggravating all manners of U.S. extremes: severe droughts, the rising cost of air conditioning, pine bark beetles ravaging once-cool western forests.