CO2 Accumulation Rate Research Articles

Prediction and Comparison of In-Vehicle CO2 Concentration Based on ARIMA and LSTM Models

An increase in the carbon dioxide (CO2) concentration within a vehicle can lead to a decrease in air quality, resulting in numerous adverse effects on the human body. Therefore, it is very important to know the in-vehicle CO2 concentration level and to accurately predict a concentration change. The purpose of this research is to investigate in-vehicle concentration levels of CO2, comparing the accuracy of an autoregressive integrated moving average (ARIMA) model and a long short-term memory (LSTM) model in predicting the change in CO2 concentration. We conducted a field test to obtain in-vehicle original concentration data of CO2 while driving, establishing a prediction model of CO2 concentration with ARIMA and LSTM. We selected mean absolute percentage error (MAPE) and root mean squared error (RMSE) as the evaluation indicators. The findings indicate the following: (1) With the vehicle windows closed and recirculation ventilation mode activated, in-vehicle CO2 concentration increases rapidly. During testing, CO2 accumulation rates were measured at 1.43 ppm/s for one occupant and 3.52 ppm/s for three occupants within a 20 min driving period. Average concentrations exceeded 1000 ppm, so it is recommended to improve ventilation promptly while driving. (2) The MAPE of ARIMA and LSTM prediction results are 0.46% and 0.56%, respectively. The RMSE results are 19.62 ppm and 22.76 ppm, respectively. The prediction results demonstrate that both models effectively forecast changes in a vehicle’s interior environment CO2, but the prediction accuracy of ARIMA is better than that of LSTM. The research findings provide theoretical guidance to traffic safety managers in selecting suitable models for predicting in-vehicle CO2 concentrations and establish an effective in-vehicle ventilation warning control system.

320 Oxygenated Peritoneal Perfluorodecalin Improves Response to Normobaric Hypoxic Exposure in Swine

OBJECTIVES/GOALS: Patients suffering from respiratory failure have few options to support oxygenation and carbon dioxide removal aside from mechanical ventilation. Our objective was to test a novel extrapulmonary mechanism of gas exchange via peritoneal oxygenated perfluorocarbon (PFC) in a large animal model. METHODS/STUDY POPULATION: Using two 50 kg swine, hypoxia was modeled with subatmospheric oxygen and hypercarbia induced with acute hypoventilation. Through a midline laparotomy, cannulas were placed into the peritoneal space to allow for PFC infusion and circulation. After abdominal closure, these cannulas were connected to a device capable of draining, oxygenating, and infusing PFC. One animal was subjected to acute hypoxia (12% FiO2) and another animal to acute hypoventilation (4 breaths per minute). Primary outcomes were times for SpO2 to reach 75 mmHg, respectively. Trials were performed without PFC and with PFC dwelling or circulating through the peritoneal space, during which abdominal and bladder pressures were monitored and maintained under 20 mmHg by regulation of the PFC volume contained in the animal. RESULTS/ANTICIPATED RESULTS: In the animal subjected to acute hypoxia (12% FiO2), survival time improved from 5:55 to 20:00 (min:sec) after 2.5 liters of oxygenated PFC was instilled in the peritoneal space. Oxygen percent saturation of PFC before and after dwelling in the peritoneal space was measured at 100% before and 70% after dwelling in the animal during this hypoxic period corresponding with a gas transfer of 300 mL of oxygen over the 20-minute trial (i.e., 15 mL/min). Continual PFC circulation did not further extend the survival time during hypoxic conditions over PFC dwelling in the abdomen. In the animal that was acutely hypoventilated, there were no detectable differences in the rate of CO2 accumulation as measured by EtCO2 or direct blood pCO2 measurements with PFC dwelling or circulating through the peritoneal space. DISCUSSION/SIGNIFICANCE: Oxygenated PFC dwelling in the peritoneal space increased the duration of systemic arterial blood saturation remaining greater than 50% during normobaric hypoxic (12% FiO2) conditions but did not appreciably clear blood carbon dioxide during hypoventilation. Future experiments will focus on maximizing the rate of systemic oxygen uptake.

Very high-resolution Net Ecosystem Exchange over India using Vegetation Photosynthesis and Respiration Model (VPRM) simulations

The terrestrial biosphere has a crucial role in controlling the rate of CO2 accumulation in the atmosphere. The quantification of Net Ecosystem Exchange (NEE) is critical to determine whether the regional terrestrial ecosystem is a net sink or source of CO2. This study uses a satellite-data derived light-use-efficiency model (the Vegetation Photosynthesis and Respiration Model, VPRM) to compute the biospheric CO2 fluxes over India from 2011–2020. A very high-resolution Land Use-Land Cover (LULC) data from the IRS-P6 satellite and MODIS derived surface reflectance are utilised to compute the NEE over distinct vegetation types at ∼9km× 9 km. The VPRM model for the Indian region captures the spatial pattern and seasonal features of NEE over the country. The magnitude of annual mean NEE over India from the VPRM model is relatively high compared to that from Carbon Tracker, FLUXCOM, and Soil Moisture Active Passive Level-4 carbon data products. However, the VPRM model simulated NEE agrees with the NEE observations from the eddy covariance estimates, which are accepted as the ground truth. The fusion of high-resolution LULC and surface reflectance data in VPRM suggests that the average NEE over the Indian region during 2011–2020 is −0.16 ± 0.02 PgC yr−1. Among this, the contribution from Gross Ecosystem Exchange is about −0.47 ± 0.02 PgC yr−1, and Respiration is 0.31 ± 0.01 PgC yr−1. The maximum biospheric CO2 absorption is during the post-monsoon season, and the minimum is during the pre-monsoon season. The very high spatial resolution and heterogeneity resolved in the NEE data derived in this work offer the first data product of this kind for a variety of NEE analyses over India.

Can mixed forests sequester more CO2 than pure forests in future climate scenarios? A case study of Pinus sylvestris combinations in Spain

Adapting forests to climate change is a critical issue for forest management. It requires an understanding of climate effects on forest systems and the ability to forecast how these effects may change over time. We used Spanish Second National Forest Inventory data and the SIMANFOR platform to simulate the evolution of CO2 stock (CO2 Mg · ha−1) and accumulation rates (CO2 Mg · ha−1 · year−1) for the 2000–2100 period in pure and mixed stands managed under different Shared Socioeconomic Pathways (SSPs) in Spain. We hypothesized that (1) the more optimistic climate scenarios (SSP1 > > SSP5) would have higher CO2 stock and accumulation rates; (2) mixed stands would have higher CO2 stock and accumulation rates than pure stands; and (3) the behavior of both variables would vary based on forest composition (conifer–conifer vs. conifer–broadleaf). We focused on Pinus sylvestris L., and its main mixtures with Pinus nigra, Pinus pinaster, Fagus sylvatica and Quercus pyrenaica. The SSP scenarios had correlating CO2 stock values in which SSP1 > SSP2 > SSP3 > SSP5, ranging from the most optimistic (SSP1) to the most pessimistic (SSP5). Though pure stands had higher CO2 stock at the beginning, differences with regard to mixed stands were drastically reduced at the end of the simulation period. We also found an increase in the aboveground CO2 proportion compared to belowground in conifer–broadleaf mixtures, while the opposite trend occurred in conifer–conifer mixtures. Overall CO2 accumulation rates decreased significantly from the beginning to the end of the simulation period, but our results indicated that this decline would be less drastic in mixed stands than in pure ones. At the end of the simulation period, CO2 accumulation rates were higher in mixed stands than in pure stands for all mixtures, fractions (aboveground and belowground) and SSPs. Knowing the evolution of mixed forests in different climate scenarios is relevant for developing useful silvicultural guidelines in the Mediterranean region and optimizing forestry adaptation strategies. Better understanding can also inform the design of management measures for transitioning from pure stands to more resource efficient, resistant and resilient mixed stands, in efforts to reduce forest vulnerability in the face of climate change. This work highlights the importance and benefits of mixed stands in terms of CO2 accumulation, stand productivity and species diversity.

The effect of dietary intake on apneic performance, cardiovascular and splenic responses during repeated breath holds.

Static apneas performed after an overnight fast as opposed to postprandially have been evinced to improve apneic performance. However, no study has explored the effect of dietary intake on apneic performance, cardiovascular or splenic responses over a series of repeated apneas. Ten healthy adults attended the laboratory on three separate occasions (≥48-h apart): after a 14-h fast (F14), 1 h postconsumption of a high-calorie, high-carbohydrate (HCHC) meal, or 1 h postconsumption of a low-calorie, low-carbohydrate (LCLC)-based meal. During each visit, the subjects performed a hyperoxic rebreathing trial and a series of three repeated maximal static apneas. Heart rate, peripheral oxyhemoglobin saturation ([Formula: see text]), and gas exchange were monitored continuously, whereas splenic volume (SV) and hematology were assessed after the rebreathing and apneas. At rest, after HCHC, the respiratory exchange ratio (0.87 ± 0.17, P ≤ 0.043), expired minute volume of carbon dioxide (CO2; HCHC, 0.35 ± 0.09 L/min, P ≤ 0.014), and SV (227 ± 45 mL, P ≤ 0.031) were higher compared with F14 (0.71 ± 0.08; 0.23 ± 0.04 L/min; 204 ± 49 mL) and LCLC (0.72 ± 0.07; 0.25 ± 0.03 L/min; 199 ± 49 mL). A faster CO2 accumulation was recorded during the HCHC (96 ± 35 s) rebreathing trial (F14, 162 ± 42 s, P = 0.001; LCLC, 151 ± 23 s, P = 0.002). Longer apneas were reported in F14 compared with HCHC (apneas 1-3, P ≤ 0.046) and LCLC (apneas 2-3, P ≤ 0.006). After the first apnea, SV was lower in F14 (141 ± 43 mL, P = 0.015) compared with HCHC (180 ± 34 mL). Moreover, after the third apnea, end-tidal partial pressure of oxygen and nadir [Formula: see text] were lower in F14 (8.6 ± 2.2 kPa, P = 0.028; 77 ± 13%, P = 0.009) compared with HCHC (10.1 ± 1.7 kPa; 84 ± 9%). No differences were measured in end-apneic end-tidal partial pressure of CO2, heart rate nor hematology across diets. Fasting improved apneic performance with apneas being terminated at lower oxygen levels through altering the rate of CO2 accumulation but without affecting the cardiovascular responses.

Iterative Algorithm for Time Series Decomposition into Trend and Seasonality: Testing Using the Example of CO2 Concentrations in the Atmosphere

An iterative algorithm for the decomposition of data series into trend and residual (including the seasonal effect) components is proposed. This algorithm is based on the approaches proposed by the authors in several previous studies and allows unbiased estimates for the trend and seasonal components for data with a strong trend containing different periodic (including seasonal) variations, as well as observational gaps and omissions. The main idea of the algorithm is that both the trend and the seasonal components should be estimated using a signal that is maximally cleaned of any other variations, which are considered a noise. In estimating the trend component, seasonal variation is a noise, and vice versa. The iterative approach allows a priori information to be more completely used in the optimization of models of both trend and seasonal components. The approximation procedure provides maximum flexibility and is fully controllable at all stages of the process. In addition, it allows one to naturally solve the problems in the case of missing observations and defective measurements without filling these dates with artificially simulated values. The algorithm was tested using data on changes in the concentration of CO2 in the atmosphere at four stations belonging to different latitudinal zones. The choice of these data is explained by the features that complicate the use of other methods, namely, high interannual variability, high-amplitude seasonal variations, and gaps in the series of observed data. This algorithm made it possible to obtain trend estimates (which are of particular importance for studying the characteristics and searching for the causes of global warming) for any time interval, including those that are not multiples of an integer number of years. The rate of increase in the CO2 content in the atmosphere has also been analyzed. It has been reliably established that in around 2016, the rate of CO2 accumulation in the atmosphere became stabilized and even tended to decrease. The extent of this stabilization will become clear in the next 2–3 years as new data are available.

An Unobstructive Sensing Method for Indoor Air Quality Optimization and Metabolic Assessment within Vehicles.

This work investigates the use of an intelligent and unobstructive sensing technique for maintaining vehicle cabin’s indoor air quality while simultaneously assessing the driver metabolic rate. CO2 accumulation patterns are of great interest because CO2 can have negative cognitive effects at higher concentrations and also since CO2 accumulation rate can potentially be used to determine a person’s metabolic rate. The management of the vehicle’s ventilation system was controlled by periodically alternating the air recirculation mode within the cabin, which was actuated based on the CO2 levels inside the vehicle’s cabin. The CO2 accumulation periods were used to assess the driver’s metabolic rate, using a model that considered the vehicle’s air exchange rate. In the process of the method optimization, it was found that the vehicle’s air exchange rate (λ [h−1]) depends on the vehicle speeds, following the relationship: λ = 0.060 × (speed) − 0.88 when driving faster than 17 MPH. An accuracy level of 95% was found between the new method to assess the driver’s metabolic rate (1620 ± 140 kcal/day) and the reference method of indirect calorimetry (1550 ± 150 kcal/day) for a total of N = 16 metabolic assessments at various vehicle speeds. The new sensing method represents a novel approach for unobstructive assessment of driver metabolic rate while maintaining indoor air quality within the vehicle cabin.

Acute hyperglycemia does not alter central respiratory CO2 chemoreflex responsiveness

The control of breathing is modulated by two distinct but interacting respiratory chemoreceptor compartments: peripheral chemoreceptors (PCRs; carotid bodies) and central chemoreceptors (CCRs; brainstem). The PCRs respond to variety of chemostimuli, including arterial oxygen, arterial carbon dioxide, glucose, insulin and temperature, and are now thought to act as metabolic sensors. However, CCRs have only been characterized as carbon dioxide/acid sensors (PCO2/[H+]). PCRs respond to chemostimulation faster than CCRs, which may mask CCR responses to stimuli like acute hyperglycemia. The aim of this study was to characterize the relationship between alterations in blood glucose concentration and central respiratory chemoreflex responsiveness via hyperoxic rebreathing in healthy humans. We hypothesized that experimentally‐induced relative hyperglycemia following an oral glucose tolerance test (OGTT; 75g, 300 ml) would (a) increase the rate of CO2 accumulation during rebreathing and (b) augment central respiratory chemoreflex responsiveness due to a synergistic effect of hyperglycemia on the CO2 sensitivity of CCR neurons. In 10 healthy participants, we measured minute ventilation (VI; L/min; pneumotachometer) and end‐tidal carbon dioxide (PETCO2; Torr; gas analyzer). We used the modified hyperoxic rebreathing test to isolate CCRs and quantify the central chemoreflex responsiveness to increases in metabolically‐derived CO2. Blood glucose levels were higher 30‐min following the OGTT beverage (i.e., glucose‐loaded) compared to fasted (7.8±1.1 vs. 4.7±0.4 mmol/L; P<0.0001). During rebreathing, the rate of end‐tidal (PET)CO2 accumulation was greater in the glucose loaded trial compared to the fasted trial (0.086±0.007 vs. 0.07±0.008 vs. Torr/sec; P=0.0002). These findings confirm the hyperglycemic stimulation between trials. However, the central respiratory chemoreflex responsiveness during rebreathing was not different between glucose loaded and fasted trials (2.3±1.4 vs. 2.5±1.8 vs. L/min/Torr CO2; P=0.59). These preliminary findings suggest that relative hyperglycemia does not affect the central respiratory chemoreflex responsive to hyperoxic rebreathing. The CCRs may be a more specialized respiratory chemoreceptor, with a phenotype to detect only metabolically‐derived accumulations in CO2.Support or Funding InformationNSERC Discovery and MRU Faculty of Science and TechnologyThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Anthropogenic CO2 accumulation and uptake rates in the Pacific Ocean based on changes in the 13C/12C of dissolved inorganic carbon

AbstractThe anthropogenic CO2 accumulation rate for the Pacific Ocean was estimated from the decrease in δ13C of the dissolved inorganic carbon measured on six World Ocean Circulation Experiment cruises during the 1990s and repeated during Climate Variability and Predictability in the 2000s. A mean depth‐integrated anthropogenic δ13C change of −83 ± 20‰ m decade−1 was estimated for the basin by using the multiple linear regression approach. The largest anthropogenic δ13C decreases occurred between 40°S and 60°S, whereas the smallest decreases occurred in the Southern Ocean and subpolar North Pacific. A mean anthropogenic CO2 accumulation rate of 0.41 ± 0.13 mol C m−2 yr−1 (0.82 ± 0.26 Pg C yr−1) was determined based on observed δ13C changes and is in agreement with previous observation‐ and model‐based estimates. The mean dissolved inorganic carbon DIC13 inventory change of −178 ± 43‰ mol m−2 decade−1 was primarily the result of air‐sea CO2 exchange acting on the measured air‐sea δ13C disequilibrium of ~ −1.2 ± 0.1‰. Regional differences between the DIC13 inventory change and air‐sea 13CO2 flux yielded net anthropogenic CO2 uptake rates (independent of ΔpCO2) that ranged from ~0 to 1 mol m−2 yr−1 and basin‐wide mean of 1.2 ± 1.5 Pg C yr−1. High rates of surface ocean DIC increase and δ13C decrease observed in the Drake Passage (53°S–60°S) support above average anthropogenic CO2 accumulation since 2005. Observed δ13C changes in the Pacific Ocean indicate that ocean transport significantly impacted the anthropogenic CO2 distribution and illustrate the utility of δ13C as a tracer to unravel the processes controlling the present and future accumulation of anthropogenic CO2 in the ocean.

Water column distribution of stable isotopes and carbonate properties in the South-eastern Levantine basin (Eastern Mediterranean): Vertical and temporal change

Water column distributions of the oxygen isotopic composition of sea-water (δ18OSW) and the stable carbon isotope ratio of dissolved inorganic carbon (δ13CDIC), total alkalinity (AT) and the pH (total scale) at 25°C (25°CpHTotal) were investigated along the Southeast Mediterranean (SE-Med) shelf and open water, during 2009–2010. While, the vertical profiles of δ18OSW lacked a clear depth signature, those of δ13CDIC were characterized by a structure that reflects the major water masses in the Levantine basin, with noticeable vertical gradients.The δ13CDIC Suess effect of the Levantine water column was estimated from the difference between the average profiles of 1988 and 2009–2010 (Δδ13CDIC). We observed δ13CDIC temporal change, which indicates propagation of anthropogenic CO2 (Cant) to depth of about 700m. The Modified Atlantic Water (MAW; 0–200m) and the Levantine Intermediate Water (LIW; 200–400m) exhibited a depletion rate of −0.13±0.03 and −0.11±0.03‰ decade−1, respectively, representing ~50% of the atmospheric change, while the deep water of the Adriatic source (700–1300m) did not change during this period. A Δδ13CDIC depletion trend was also recognized below 1350m, corresponding to the Aegean source deep water (EMDWAeg) and therefore associated to the Eastern Mediterranean Transient (EMT) event.Anthropogenic CO2 accumulation rate of 0.38±0.12molCm−2yr−1 for the upper 700m of the SE-Med, over the last 22yr, was estimated on the basis of mean depth-integrated δ13CDIC Suess effect profile. Our results confirm lower accumulation rate than that of the subtropical North Atlantic, resulting due to the super-saturation with respect to CO2 of the well-stratified Levantine surface water. High pCO2 saturation during summer (+150μatm), in oppose to a small degree of under-saturation in winter (−30μatm) was calculated from surface water AT and 25°CpHTotal data. However, the δ13CDIC depletion trend of the LIW and the EMDWAeg supports isotopically light Cant penetrating into the Levantine interior during convection events, such as the EMT.

Multidecadal accumulation of anthropogenic and remineralized dissolved inorganic carbon along the Extended Ellett Line in the northeast Atlantic Ocean

AbstractMarine carbonate chemistry measurements have been carried out annually since 2009 during UK research cruises along the Extended Ellett Line (EEL), a hydrographic transect in the northeast Atlantic Ocean. The EEL intersects several water masses that are key to the global thermohaline circulation, and therefore the cruises sample a region in which it is critical to monitor secular physical and biogeochemical changes. We have combined results from these EEL cruises with existing quality‐controlled observational data syntheses to produce a hydrographic time series for the EEL from 1981 to 2013. This reveals multidecadal increases in dissolved inorganic carbon (DIC) throughout the water column, with a near‐surface maximum rate of 1.80 ± 0.45 µmol kg−1 yr−1. Anthropogenic CO2 accumulation was assessed, using simultaneous changes in apparent oxygen utilization (AOU) and total alkalinity (TA) as proxies for the biogeochemical processes that influence DIC. The stable carbon isotope composition of DIC (δ13CDIC) was also determined and used as an independent test of our method. We calculated a volume‐integrated anthropogenic CO2 accumulation rate of 2.8 ± 0.4 mg C m−3 yr−1 along the EEL, which is about double the global mean. The anthropogenic CO2 component accounts for only 31 ± 6% of the total DIC increase. The remainder is derived from increased organic matter remineralization, which we attribute to the lateral redistribution of water masses that accompanies subpolar gyre contraction. Output from a general circulation ecosystem model demonstrates that spatiotemporal heterogeneity in the observations has not significantly biased our multidecadal rate of change calculations and indicates that the EEL observations have been tracking distal changes in the surrounding North Atlantic and Nordic Seas.

Quantifying air–sea re-equilibration-implied ocean surface CO2 accumulation against recent atmospheric CO2 rise

To understand better the role of ocean surface chemical buffering capacity in mitigating the recent atmospheric CO2 rise, we investigated potentials of wintertime mixed-layer dissolved inorganic carbon (DIC) to increase after re-equilibration with decadal atmospheric CO2 rise and the corresponding anthropogenic CO2 accumulation rates, based upon carbonate system chemistry over the global ocean surface above the wintertime thermocline. This is an idealized study to quantify the isolated effect of atmospheric CO2 rise on the DIC content of the global mixed layer, assuming all else constant. Our results show that the potentials of wintertime DIC over the global open ocean surface to rise after re-equilibration with the elevated atmospheric CO2 mol fraction in a reference year 2000 ranged from 0.28 to 0.70 μmol kg−1 ppm−1 (ppm = parts of CO2 per million dry air), while the global mean wintertime sea surface DIC increase rate was close to 1.0 μmol kg−1 year−1. From 1995 to 2005, the decadal mean atmospheric CO2 rise implies an anthropogenic CO2 accumulation rate of 0.40 × 1015 g C year−1 within the global ocean surface. From the 1960s to 2000s, the air–sea re-equilibration-implied ocean surface anthropogenic CO2 accumulation rate may have increased by 46 % due to the accelerated atmospheric CO2 rise. However, the chemical buffering capacity within the ocean surface may have declined by 16 % during the same period.

Responsiveness of Atmospheric CO2 to Anthropogenic Emissions: A Note

A statistically significant correlation between annual anthropogenic CO2 emissions and the annual rate of accumulation of CO2 in the atmosphere over a 53-year sample period from 1959-2011 is likely to be spurious because it vanishes when the two series are detrended. The results do not indicate a measurable year to year effect of annual anthropogenic emissions on the annual rate of CO2 accumulation in the atmosphere.

Benthic and pelagic sources of carbon dioxide in boreal lakes and a young reservoir (Eastmain‐1) in eastern Canada

Lakes and reservoirs typically emit CO2to the atmosphere as a result of respiration in excess of primary production. For reservoirs, this respiration is often assumed to be primarily of benthic origin, associated with drowned vegetation and soils. This study took measurements from a young hydroelectric reservoir (Eastmain‐1) in boreal Canada and nearby natural lakes to compare the rates of water column respiration and hypolimnetic CO2 accumulation during a stratified period. Reservoir water column respiration rates were significantly higher than those in natural lakes, with surface means of 61.4 ± 4.6 mg C m−3 d−1in Eastmain‐1 and 40.2 ± 3 mg C m−3 d−1 in lakes and profundal means of 58.1 ± 11 mg C m−3 d−1in Eastmain‐1 and 17.6 ± 7.5 mg C m−3 d−1 in lakes. Reservoir hypolimnetic CO2 accumulation rates were also higher than those in natural lakes, with means of 78.8 ± 16 mg C m−3 d−1in Eastmain‐1 and 19.8 ± 2.7 mg C m−3 d−1 in lakes. Our findings further indicate that the relative contribution of benthic respiration (estimated as the difference between hypolimnetic CO2 accumulation and water column respiration) toward total net CO2production during stratified periods was similar in both aquatic systems (23% in lakes, 27% in Eastmain‐1). By identifying the major role of the water column in the reservoir's CO2 production, this study calls for a significant paradigm shift away from the common assumption that reservoir CO2 emissions are predominantly the result of decaying vegetation in the benthic environment.

The carbon implications of large‐scale afforestation of agriculturally marginal land with short‐rotation willow in Saskatchewan

AbstractAfforestation with short‐rotation coppice (SRC) willow plantations for the purpose of producing bioenergy feedstock was contemplated as one potential climate change mitigation option. The objectives of this study were to assess the magnitude of this mitigation potential by addressing: (i) the land area potentially available for SRC systems in the province of Saskatchewan, Canada; (ii) the potential biomass yields of SRC plantations; and (iii) the carbon implications from such a large‐scale afforestation program. Digital soils and land‐use data were used to identify, map, and group into clusters of similar polygons 2.12 million hectares (Mha) of agriculturally marginal land that was potentially suitable for willow in the Boreal Plains and Prairies ecozones in Saskatchewan. The Physiological Principles in Predicting Growth (3PG) model was calibrated with data from SRC experiments in Saskatchewan, to quantify potential willow biomass yields, and the Carbon Budget Model of the Canadian Forest Sector (CBM‐CFS3), was used to simulate stand and landscape‐level C fluxes and stocks. Short‐rotation willow plantations managed in 3 year rotations for seven consecutive harvests (21 years) after coppicing at Year 1 produced about 12 Mg ha−1 yr−1 biomass. The more significant contribution to the C cycle was the cumulative harvest. After 44 years, the potential average cumulative harvested biomass C in the Prairies was 244 Mg C ha−1 (5.5 Mg C ha−1 yr−1) about 20% higher than the average for the Boreal Plains, 203 Mg C ha−1 (4.6 Mg C ha−1 yr−1). This analysis did not consider afforestation costs, rate of establishment of willow plantations, and other constraints, such as drought and disease effects on biomass yield. The results must therefore be interpreted as a biophysical mitigation potential with the technical and economic potential being both lower than our estimates. Nevertheless, short‐rotation bioenergy plantations offer one potential mitigation option to reduce the rate of CO2 accumulation in the earth's atmosphere and further research is needed to operationalise such a mitigation effort.

Evolution of CO2 in Lakes Monoun and Nyos, Cameroon, before and during controlled degassing

Evolution of CO2 in Lakes Monoun and Nyos (Cameroon) before and during controlled degassing is described using results of regular monitoring obtained during the last 21 years. The CO2(aq) profiles soon after the limnic eruptions were estimated for Lakes Monoun and Nyos using the CTD data obtained in October and November 1986, respectively. Based on the CO2(aq) profiles through time, the CO2 content and its change over time were calculated for both lakes. The CO2 accumulation rate calculated from the pre-degassing data, was constant after the limnic eruption at Lake Nyos (1986‐ 2001), whereas the rate appeared initially high (1986‐1996) but later slowed down (1996‐2003) at Lake Monoun. The CO2 concentration at 58 m depth in Lake Monoun in January 2003 was very close to saturation due to the CO2 accumulation. This situation is suggestive of a mechanism for the limnic eruption , because it may take place spontaneously without receiving an external trigger. The CO2 content of the lakes decreased significantly after controlled degassing started in March 2001 at Lake Nyos and in February 2003 at Lake Monoun. The current content is lower than the content estimated soon after the limnic eruption at both lakes. At Monoun the degassing rate increased greatly after February 2006 due to an increase of the number of degassing pipes and deepening of the pipe intake depth. The current CO2 content is ~40% of the maximum content attained just before the degassing started. At current degassing rates the lower chemocline will subside to the degassing pipe intake depth of 93 m in about one year. After this depth is reached, the gas removal rate will progressively decline because water of lower CO2(aq) concentration will be tapped by the pipes. To keep the CO2 content of Lake Monoun as small as possible, it is recommended to set up a new, simple device that sends deep water to the surface since natural recharge of CO 2 will continue. Controlled degassing at Lake Nyos since 2001 has also reduced the CO2 content. It is currently slightly below the level estimated after the limnic eruption in 1986. However, the current CO 2 content still amounts to 80% of the maximum level of 14.8 giga moles observed in January 2001. The depth of the lower chemocline may reach the pipe intake depth of 203 m within a few years. After this situation is reached the degassing rate with the current system will progressively decline, and it would take decades to remove the majority of dissolved gases even if the degassing system keeps working continuously. Additional degassing pipes must be installed to speed up gas removal from Lake Nyos in order to make the area safer for local populations.

Anthropogenic CO2 accumulation rates in the North Atlantic Ocean from changes in the 13C/12C of dissolved inorganic carbon

The anthropogenic CO2 accumulation rate for the North Atlantic Ocean was estimated on the basis of the decrease in the δ13C of the dissolved inorganic carbon measured between cruises in 1981 (Transient Tracers in the North Atlantic), 1993 (OACES) and 2003 (Repeat Hydrography). A mean depth‐integrated δ13C change of −15.0 ± 3.8‰ m yr−1 was estimated by applying a multiple linear regression approach to determine the anthropogenic δ13C decrease at 22 stations where δ13C depth profiles were compared. The largest and deepest anthropogenic δ13C decreases occurred in the subpolar ocean and, in contrast, the smallest and shallowest decreases occurred in the tropical ocean. A mean anthropogenic CO2 accumulation rate of 0.63 ± 0.16 mol C m−2 yr−1 (0.32 ± 0.08 Pg C yr−1) in the North Atlantic Ocean over the last 20 years was determined from the mean depth‐integrated δ13C change and a ratio of anthropogenic δ13C to DIC change of −0.024‰ (μmol kg−1)−1. Only half of the accumulated anthropogenic CO2 in the North Atlantic during the last 20 years was the result of air‐sea CO2 uptake, based on a comparison of the air‐sea 13CO2 flux to the DIC13 inventory change, with the other half likely a result of northward advective transport.

ABSORPTION OF ATMOSPHERIC CO2 IN PEACH TREES AND PARTITIONING IN THE DIFFERENT PLANT ORGANS

The concentration of CO2 has increased during the 20 th century and it is estimated that if some actions are not taken against this increase, current CO2 concentrations are expected to double before the end of this century. Agricultural techniques play a key role in CO2 emission and fixation. In the present investigation, we examined carbon fluxes in a peach orchard. We hypothesized that correct utilisation of agricultural techniques, and soil management in particular, could increase the absorption of atmospheric CO2 and its storage in the soil, thereby mitigating the environmental damages caused by the greenhouse effect. Trials were carried out in southern Italy (N 40°20', E 16°48') from the first to the fifth year after planting on peach trees (Prunus persica (L.) Batsch, cultivar 'Springcrest') budded on GF677. Trees were trained to transverse Y or delayed vase, at planting densities of 1111 trees/ha -1 and 416 trees/ha -1 , respectively. At the end of the vegetative season, values of fixed atmospheric CO2 and CO2 accumulation rates were calculated by measuring the dry matter partitioning in the different plant organs. In the first years after planting, CO2 was mainly allocated to the permanent structures (trunk and roots), while in the mature orchards, fixed CO2 was also distributed in leaves, pruning material and fruits. Green manure increased CO2 fixation to about 11 t ha -1 . The results underline the importance of training system, plant density and cultivation techniques in the absorption of atmospheric CO2 and its storage as organic matter in the soil.

Inferring nocturnal surface fluxes from vertical profiles of scalars in an Amazon pasture

AbstractEcosystem carbon budgets depend on there being good representative surface flux observations for all land use types during the entire diurnal cycle. In calm conditions that often occur at night, especially in areas of small roughness (such as pastures), ecosystem respiration rate is poorly measured using the eddy covariance (EC) technique. Nocturnal vertical profiles of temperature, humidity and winds were observed using tethered balloon soundings in a pasture in the eastern Amazon during two campaigns in 2001. The site is characterized by very weak winds at night, so that there is insufficient turbulence for the EC technique to determine fluxes accurately. To compensate, the time evolution of the profiles is used to determine surface fluxes at early morning and these are compared with those observed by EC at a nearby micrometeorological tower. The nocturnal boundary layer thickness h is determined as the height to which the surface fluxes must converge so that energy budget closure is achieved. The estimated values range from 30 m, around 22:00 hours LST, to more than 100 m just before dawn. These are in good agreement with the observed thickness of a frequently observed fog layer during the middle of the night. During the early portion of the night, when the accumulation layer is shallow, there is appreciable decrease of dCO2/dt with height. On calm nights, CO2 accumulation rate is larger near the surface than at higher levels. On windier nights, this accumulation rate is vertically uniform. Hence, extrapolation of tower profiles for estimating fluxes must be done carefully. Although uncertainties remain large, an alternate approach to the EC method is described for measuring nighttime surface CO2 fluxes under stable atmospheric conditions.

Effect of sodium chloride on the growth and gas exchange of young Ziziphus seedling rootstocks

SummaryAn experiment was conducted to study the effect of saline water (EC 0, 5, 10, 15 and 20 as NaCl) on growth, gas exchange and ion uptake in Ziziphus rotundifolia and Z. nummularia seedlings. No plants of Z. nummularia survived EC > 15 dS m–1. Shoot dry weight, leaf area and relative water content decreased significantly with variable magnitude in both species with increasing salinity. Reduction in gas exchange and stomatal conductance on account of salinity was higher in Z. nummularia. Salinity decreased the soluble sugars content whereas proline content increased. Absorption of sodium did not vary in roots of either species but Z. rotundifolia restricted the translocation of sodium to the shoot at the cost of potassium which is reflected in the Na/K ratio of roots and shoots. Present investigation suggest that rootstocks of Z. rotundifolia are comparatively salt tolerant due to a high rate of CO2 accumulation, osmotic adjustment, chlorophyll retention and restricted translocation of sodium from root to shoot. However, the results need to be tested under field conditions.