Rising CO2 Concentrations Research Articles

Atmospheric CO2and soil extracellular enzyme activity: a meta-analysis and CO2gradient experiment

Rising atmospheric CO2 concentrations can alter carbon and nutrient cycling and microbial processes in terrestrial ecosystems. One of the primary ways microbes interact with soil organic matter is through the production of extracellular enzymes, which break down complex organic molecules and release nutrients into the soil. We conducted a meta-analysis of 34 studies that examined responses in microbial enzyme activity to elevated CO2. We also conducted a field study of soil enzyme activity in a tallgrass-prairie ecosystem growing in sandy loam (lower organic matter content) and clayey soils (higher organic matter content) exposed to a continuous gradient of 250 to 500 ppm CO2. Of the 10 enzyme groups examined in the meta-analysis, including those degrading starch, β-glucan, cellulose, xylan/hemicellulose, lignin, organic P, and organic N, only the activity of one enzyme that degrades the C- and N-containing building blocks of chitin (N-acetyl-glucosaminidase) increased consistently at elevated CO2 by an average of 12.6% (p < 0.05), especially in field studies and in woody ecosystems. In our field study, increasing CO2 from subambient to elevated concentrations reduced the activity of leucine aminopeptidase by 32% in the black clay soil during the peak of the growing season, while β −1,4-N-acetyl-glucosaminidase increased by 44% near the end of the season, indicating increased N limitation with increasing CO2. In the sandy loam soil, alkaline phosphatase activity increased by 42% with CO2 enrichment at the end of the growing season, suggesting CO2-induced phosphorus limitation in these soils. Additionally, a 53–83% decrease in the carbon cycling enzymes cellobiohydrolase, α-glucosidase, and xylosidase activity with increased CO2 was found in July. Our field study shows that soil type can strongly influence how microbial functioning may change with rising CO2 concentrations and that microbial responses associated with C-, N-, and P-cycling are likely to change—and may already have changed—with increasing CO2 under some soil types and conditions. Our meta-analysis revealed that, despite variable enzyme activities with CO2, chitinase activity increased consistently with CO2 across ecosystems.

Growth and community responses of alpine dwarf shrubs to in situ CO2 enrichment and soil warming

• Rising CO₂ concentrations and the associated global warming are expected to have large impacts on high-elevation ecosystems, yet long-term multifactor experiments in these environments are rare. • We investigated how growth of dominant dwarf shrub species (Vaccinium myrtillus, Vaccinium gaultherioides and Empetrum hermaphroditum) and community composition in the understorey of larch and pine trees responded to 9 yr of CO₂ enrichment and 3 yr of soil warming at the treeline in the Swiss Alps. • Vaccinium myrtillus was the only species that showed a clear positive effect of CO₂ on growth, with no decline over time in the annual shoot growth response. Soil warming stimulated V. myrtillus growth even more than elevated CO₂ and was accompanied by increased plant-available soil nitrogen (N) and leaf N concentrations. Growth of Vaccinium gaultherioides and E. hermaphroditum was not influenced by warming. Vascular plant species richness declined in elevated CO₂ plots with larch, while the number of moss and lichen species decreased under warming. • Ongoing environmental change could lead to less diverse plant communities and increased dominance of the particularly responsive V. myrtillus in the studied alpine treeline. These changes are the consequence of independent CO₂ and soil warming effects, a result that should facilitate predictive modelling approaches.

Responses of European forest ecosystems to 21st century climate: assessing changes in interannual variability and fire intensity

Significant climatic changes are currently observed and, according to projections, will be strengthened over the 21st century throughout the world with the continuing increase of the atmospheric CO2 concentration. Climate will be generally warmer with notably changes in the seasonality and in the precipitation regime. These changes will have major impacts on the biodiversity and the functioning of natural ecosystems. The CARAIB dynamic vegetation model driven by the ARPEGE/Climate model under forcing from the A2 IPCC emission scenario is used to illustrate and analyse the potential impacts of climate change on forest productivity and distribution as well as fire intensity over Europe. The potential CO2 fertilizing effect is studied throughout transient runs of the vegetation model over the 1961-2100 period assuming constant and increasing atmospheric CO2 concentration. Without fertilisation effect, the net primary productivity (NPP) might increase in high latitudes and altitudes (by up to 40 % or even 60-100 %) while it might decrease in temperate (by up to 50 %) and in warmer regions, e.g., Mediterranean area (by up to 80 %). This strong decrease in NPP is associated with recurrent drought events occurring mostly in summer time. Under rising CO2 concentration, NPP increases all over Europe by as much as 25-75%, but it is not clear whether or not soils might sustain such an increase. The model indicates also that interannual NPP variability might strongly increase in the areas which will undergo recurrent water stress in the future. During the years exhibiting summer drought, the NPP might decrease to values much lower than present-day average NPP even when CO2 fertilization is included. Moreover, years with such events will happen much more frequently than today. Regions with more severe droughts might also be affected by an increase of wildfire frequency and intensity, which may have large impacts on vegetation density and distribution. For instance, in the Mediterranean basin, the area burned by wildfire can be expected to increase by a factor of 3-5 at the end of the 21st century compared to present.

Ozone risk for vegetation in the future climate of Europe based on stomatal ozone uptake calculations

The negative impacts of surface ozone (O3) on vegetation are determined by external exposure, leaf gas exchange and plant antioxidant defence capacity, all dependent on climate and CO2 concentrations. In this study the influence of climate change on simulated stomatal O3 uptake of a generic crop and a generic deciduous tree at ten European sites was investigated, using the LRTAP Mapping Manual stomatal flux model. O3 concentrations are calculated by a chemistry transport model (MATCH) for three 30-yr time-windows (1961–1990, 2021–2050, 2071–2100), with constant precursor emissions and meteorology from a regional climate model (RCA3). Despite substantially increased modelled future O3 concentrations in central and southern Europe, the flux-based risk for O3 damage to vegetation is predicted to remain unchanged or decrease at most sites, mainly as a result of projected reductions in stomatal conductance under rising CO2 concentrations. Drier conditions in southern Europe are also important for this result. At northern latitudes, the current parameterisation of the stomatal conductance model suggest O3 uptake to be mainly limited by temperature. This study demonstrates the importance of accounting for the influences by climate and CO2 on stomatal O3 uptake, and of developing their representation in models, for risk assessment involving climate change.

Changing Lanes from Concerted to Stepwise Hydrogenation: The Reduction Mechanism of Frustrated Lewis Acid–Base Pair Trapped CO2 to Methanol by Ammonia–Borane

Unabated anthropogenic release of carbon dioxide (CO2) is contributing to global climate change and represents a colossal environmental predicament. Furthermore, increasing demand for fossil fuel resources has raised concerns about the stability of the global energy supply. These problems have led the scientific community to look for renewable fuel alternatives. In nature, plants and algae trap and utilize CO2 in photosynthesis, but this process is not sufficient to combat the rapid rise of CO2 concentration in the atmosphere. The trapping of CO2 and its subsequent reduction has surfaced as a chemical challenge of great interest because this transformation could be a viable route for renewable carbonbased fuels. However, the limited reactivity of CO2 has slowed progress in developing efficient reduction methods. Primarily, CO2 reduction can be achieved by using electrocatalysts or heterogeneous photocatalysts that involve transition-metal containing complexes and materials. Recently, Stephan and Menard demonstrated the trapping of CO2 by a frustrated Lewis acid base pair (FLP) along with the subsequent reduction of the trapped CO2 to methanol by ammonia–borane. This is a rare instance where CO2 reduction to a liquid fuel has been achieved without the use of a transition metal. Additionally, this reaction has unfolded a new dimension to FLP-facilitated chemistry. Although ammonia–borane is a popular chemical hydrogen storage material, it has been recently shown to function as a hydrogenating agent for imines in a concerted fashion through simultaneous proton and hydride transfer from ammonia–borane to imines. Earlier theoretical investigations by Paul and co-workers suggested that ammonia– borane releases hydrogen in a similar fashion to transitionmetal complexes and N-heterocyclic carbenes. However, dehydrogenation of ammonia–borane is also known to initiate through stepwise routes, via N H activation, and in some cases B H activation. Thus, the FLP-CO2 reduction involves two interesting aspects: a) the mechanism of reduction of CO2 to methanol at room temperature and atmospheric pressure and b) the hydrogenation pathway by ammonia–borane for this particular substrate. A detailed understanding of the mechanistic features of this remarkable sequence of chemical reactions would provide valuable insights for developing strategies of CO2 reduction. In our current endeavor, we have used hybrid density functional theory to unravel the molecular pathways for the reduction of FLP trapped CO2 to methanol by ammonia–borane. Our computational investigation characterizes the crucial transition states and intermediates that are encountered along the reaction path of this intriguing reaction. Furthermore, we show the chameleon-like nature of ammonia–borane as a reducing agent by showing that the hydrogenation pathways change with similar substrates in different electronic environments. In the current study we have focused on unfolding the mechanistic details of the reduction of FLP-trapped CO2. The optimized molecular geometries of PMes3–AlCl3 and the FLP–CO2 adduct exhibit overall satisfactory agreement with the molecular structures obtained from X-ray crystallographic studies by Stephan and Menard. We find the trapping of CO2 by FLP is energetically favorable by 31.0 kcalmol , which is in good agreement with the experimental finding that the FLP–CO2 complex is stable at 80 8C. Scheme 1 displays the predicted route for the multistep reduction process of FLP–CO2 by ammonia–borane. Our computations show FLP–CO2 binds ammonia–borane through a weak stabilizing interaction (in the solution phase this is predicted to be less than 1 kcalmol , without zeropoint correction) between a hydridic hydrogen on the borane of ammonia–borane and the carbon of the trapped [a] L. Roy, Prof. Dr. A. Paul Raman Centre for Atomic, Molecular and Optical Sciences Indian Association for the Cultivation of Science 2A & 2B Raja S. C. Mullick Road, Kolkata-700032 (India) E-mail : rcap@iacs.res.in [b] Dr. P. M. Zimmerman College of Chemistry, University of California at Berkeley Berkeley, CA 94720. (USA) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem201002282.

Experimental manipulations of winter snow and summer rain influence ecosystem carbon cycling in a mixed‐grass prairie, Wyoming, USA

AbstractWater‐limited grasslands may be exceedingly vulnerable to changes in the timing or amount of precipitation which may result in shifts in the magnitudes and patterns of carbon cycling. Shifts in CO2 exchange may lead to alterations in carbon sequestration or net losses and could accentuate the rising CO2 concentrations in the atmosphere or ameliorate the increases. The objective of our project was to quantify how changes in winter, summer, and combined winter and summer precipitation may alter rates of ecosystem C cycling in the mixed‐grass prairie of the United States. Three replicated 50 m snow fences were installed to increase winter snow while summer precipitation was manipulated by either increasing (+50%) or decreasing (−50%) precipitation amounts. Measurements of net ecosystem exchange (NEE), gross ecosystem photosynthesis (GEP), and ecosystem respiration (ER) and plant biomass were conducted throughout the snow‐free period. Deeper snow in winter increased summer ER by an average of 27%, GEP by 45%, NEE by 90% and plant biomass by 50% compared to ambient snow conditions. Average plant biomass increased 44% with the addition of summer rain and decreased by 18% where rainfall was excluded under ambient snow conditions. Average NEE was also lower where rain was excluded. Our findings indicate that seasonality changes of precipitation may be important in regulating the future extent of C sequestration and C cycling in one of the most extensive, intact grasslands of North America. Copyright © 2010 John Wiley &amp; Sons, Ltd.

Enhanced biomimetic sequestration of CO2 into CaCO3 using purified carbonic anhydrase from indigenous bacterial strains

Abstract Phenomenal rise in CO2 concentration have led to disastrous consequences. The present study endeavors the biomimetic sequestration of CO2 into CaCO3 using biological catalyst; carbonic anhydrase (CA) purified from Pseudomonas fragi, Micrococcus lylae and Micrococcus luteus 2 along with a comparative evaluation of their efficiency against commercial bovine carbonic anhydrase (BCA). At pH range 8.0–9.0 and temperature range 35–45 °C, maximum stability was observed for CA from M. luteus 2 followed by P. fragi CA, M. lylae CA and BCA. P. fragi CA demonstrated maximum stability as function of time with respect to pH and temperature. The anionic inhibitors, Cl−, SO42−, NO3−, HCO3 and toxic metal ions viz., lead, arsenic and mercury showed varied inhibitory profile against the four different CAs. The level of inhibition was significantly higher for BCA and M. luteus 2 CA compared to P. fragi CA and M. lylae CA. Calcium estimation was found to be a reliable method for the determination of sequestration efficiency. Indigenous CAs and their consortia exhibited enhanced CO2 sequestration competence compared to commercial BCA. Sequestration efficiency at 45 °C, under process parameters was found to be maximum for CA consortia (61%) and minimum for commercial BCA (17.8%) indicating its potential application in an onsite scrubber.

Carbon dynamics of terrestrial ecosystems on the Tibetan Plateau during the 20th century: an analysis with a process‐based biogeochemical model

ABSTRACTAim The Tibetan Plateau accounts for about a quarter of the total land area of China and has a variety of ecosystems ranging from alpine tundra to evergreen tropics. Its soils are dominated by permafrost and are rich in organic carbon. Its climate is unique due to the influence of the Asian monsoon and its complex topography. To date, the carbon dynamics of the Tibetan Plateau have not been well quantified under changes of climate and permafrost conditions. Here we use a process‐based biogeochemistry model, the Terrestrial Ecosystem Model (TEM), which was incorporated with a soil thermal model, to examine the permafrost dynamics and their effects on carbon dynamics on the plateau during the past century.Location The Tibetan Plateau.Methods We parameterize and verify the TEM using the existing data for soil temperature, permafrost distribution and carbon and nitrogen from the region. We then extrapolate the model and parameters to the whole plateau.Results During the 20th century, the Tibetan Plateau changed from a small carbon source or neutral in the early part of the century to a sink later, with a large inter‐annual and spatial variability due to changes of climate and permafrost conditions. Net primary production and soil respiration increased by 0.52 and 0.22 Tg C year−1, respectively, resulting in a regional carbon sink increase of 0.3 Tg C year−1. By the end of the century, the regional carbon sink reached 36 Tg C year−1 and carbon storage in vegetation and soils is 32 and 16 Pg C, respectively. On the plateau, from west to east, the net primary production, soil respiration and net ecosystem production increased, due primarily to the increase of air temperature and precipitation and lowering elevation. In contrast, the decrease of carbon fluxes from south to north was primarily controlled by precipitation gradient. Dynamics of air temperature and associated soil temperature and active layer depth resulted in a higher plant carbon uptake than soil carbon release, strengthening the regional carbon sink during the century.Main conclusions We found that increasing soil temperature and deepening active layer depth enhanced soil respiration, increasing the net nitrogen mineralization rate. Together with the effects of warming air temperature and rising CO2 concentrations on photosynthesis, the stronger plant nitrogen uptake due to the enhanced available nitrogen stimulates plant carbon uptake, thereby strengthening the regional carbon sink as the rate of increase net primary production was faster than that of soil respiration. Further, the warming and associated soil thermal dynamics shifted the regional carbon sink from the middle of July in the early 20th century to early July by the end of the century. Our study suggests that soil thermal dynamics should be considered for future quantification of carbon dynamics in this climate‐sensitive region.

Modelled effects of rising CO2 concentration and climate change on native perennial grass and sown grass-legume pastures

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 42:65-78 (2010) - DOI: https://doi.org/10.3354/cr00863 Modelled effects of rising CO2 concentration and climate change on native perennial grass and sown grass-legume pastures M. P. Perring1,4,*, B. R. Cullen2, I. R. Johnson3, M. J. Hovenden1 1School of Plant Science, University of Tasmania, Private Bag 55, Hobart, Tasmania 7001, Australia 2Melbourne School of Land and Environment, University of Melbourne, Parkville, Victoria 3010, Australia 3IMJ Consultants, Armidale, New South Wales 2350, Australia 4Present address: Ecosystem Restoration Lab, School of Plant Biology (M090), The University of Western Australia, 35 Stirling Highway, Crawley, Western Australia 6009, Australia *Email: michael.perring@uwa.edu.au ABSTRACT: Native perennial grass and sown grass-legume pastures are an important agricultural and environmental resource. We investigated the impact of rising carbon dioxide concentration ([CO2]) and projected climate changes on these pasture ecosystems in southeastern Tasmania, Australia, using a biophysical simulation model, EcoMod. The model consists of interdependent modules that describe soil physicochemical and hydrological characteristics, and pasture growth and senescence, with fluxes described by empirical and mechanistic equations. Our simulations showed that in native pastures, projected climate change increased the biomass of C4 grasses, with limited impact upon C3 grasses, a trend reversed by rising [CO2]. In sown pastures, projected climate change decreased the biomass of perennial rye grass Lolium perenne and total biomass markedly by 2070, whilst subterranean clover Trifolium subterraneum biomass increased. Subterranean clover biomass changed little with increased [CO2] alone, whereas perennial rye grass biomass increased. Responses across pastures reflected species’ tolerances to environmental factors, with projected climate change generally having more of an impact on biomass than rising [CO2]. Changes in both [CO2] and climate led to a reduction in protein content and digestibility. Soil inorganic nutrient concentrations decreased with increasing [CO2] and increased with projected climate change. Further simulations should investigate whether these patterns are robust for different sites and alternative environmental futures. Our results reinforce the need to pursue adaptation strategies in response to environmental change in order to maintain productive pasture ecosystems. KEY WORDS: Lolium perenne · Ecosystem model · Simulation · Nutrient availability · Productivity · Tasmania Full text in pdf format PreviousNextCite this article as: Perring MP, Cullen BR, Johnson IR, Hovenden MJ (2010) Modelled effects of rising CO2 concentration and climate change on native perennial grass and sown grass-legume pastures. Clim Res 42:65-78. https://doi.org/10.3354/cr00863Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 42, No. 1. Online publication date: June 03, 2010 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2010 Inter-Research.

Mechanisms for the Onset of the African Humid Period and Sahara Greening 14.5–11 ka BP*

Abstract The mechanisms leading to the onset of the African Humid Period (AHP) 14 500–11 000 yr ago are elucidated using two different climate–vegetation models in a suite of transient glacial–interglacial simulations covering the last 21 000 yr. A series of sensitivity experiments investigated three key mechanisms (local summer insolation and ice sheet evolution, vegetation–albedo–precipitation feedback, and CO2 increase via radiative forcing and fertilization) that control the climate–vegetation history over North Africa during the last glacial termination. The simulations showed that neither orbital forcing nor the remote forcing from the retreating ice sheets alone was able to trigger the rapid formation of the AHP. Only both forcing factors together can effectively lead to the formation of the AHP. The vegetation–albedo–precipitation feedback enhances the intensity of the monsoon and further accelerates the onset of the AHP. The experiments indicate that orbital forcing and vegetation–albedo–precipitation feedback alone are insufficient to trigger the rapid onset of the AHP. The sensitivity experiments further show that the increasing radiative forcing from rising CO2 concentrations had no significant impact on the temporal evolution of the African monsoon during the last deglaciation. However, the fertilization effect of CO2 is important for the terrestrial carbon storage. The modeling results are discussed and compared with paleoproxy records of the African monsoon system. It is concluded that the model results presented here do not lend support to the notion that simple insolation thresholds govern the abrupt transitions of North African vegetation during the early to middle Holocene.

Simulation of Mediterranean forest carbon pools under expected environmental scenarios

Simulating the effects of possible environmental changes on the forest carbon budget requires the use of calibrated and tested models of ecosystem processes. A recently proposed simulation approach based on the use of the BIOME-BGC model was applied to yield estimates of present carbon fluxes and pools in Tuscany forests (central Italy). After the validation of these estimates against existing ground data, the simulation approach was used to assess the impact of plausible climate changes (+2 °C and increased CO2 concentration) on forest carbon dynamics (gross primary production (GPP), net primary production (NPP), and relevant allocations). The results indicate that the temperature change tends to inhibit all production and allocation processes, which are instead enhanced by the CO2 concentration rise. The combination of the two factors leads to a general increase in both GPP and NPP that is higher for deciduous oaks and chestnut (+30% and 24% for GPP and +42% and 31% for NPP, respectively). Additionally, vegetation carbon is slightly increased, while total soil carbon remains almost unchanged with respect to the present conditions. These findings are analyzed with reference to the Tuscany forest situation and previous studies on the subject.

Short-term response of the coccolithophore &amp;lt;i&amp;gt;Emiliania huxleyi&amp;lt;/i&amp;gt; to an abrupt change in seawater carbon dioxide concentrations

Abstract. The response of the coccolithophore Emiliania huxleyi to rising CO2 concentrations is well documented for acclimated cultures where cells are exposed to the CO2 treatments for several generations prior to the experiment. The exact number of generations required for acclimation to CO2-induced changes in seawater carbonate chemistry, however, is unknown. Here we show that Emiliania huxleyi's short-term response (26 h) after cultures (grown at 500 μatm) were abruptly exposed to changed CO2 concentrations (~190, 410, 800 and 1500 μatm) is similar to that obtained with acclimated cultures under comparable conditions in earlier studies. Most importantly, from the lower CO2 levels (190 and 410 μatm) to 750 and 1500 μatm calcification decreased and organic carbon fixation increased within the first 8 to 14 h after exposing the cultures to changes in carbonate chemistry. This suggests that Emiliania huxleyi rapidly alters the rates of essential metabolical processes in response to changes in seawater carbonate chemistry, establishing a new physiological "state" (acclimation) within a matter of hours. If this relatively rapid response applies to other phytoplankton species, it may simplify interpretation of studies with natural communities (e.g. mesocosm studies and ship-board incubations), where often it is not feasible to allow for a pre-conditioning phase before starting experimental incubations.

Changes in the abundance of C3/C4 species of Inner Mongolia grassland: evidence from isotopic composition of soil and vegetation

AbstractGlobal warming, increasing CO2 concentration, and environmental disturbances affect grassland communities throughout the world. Here, we report on variations in the C3/C4 pattern of Inner Mongolian grassland derived from soil and vegetation. Soil samples from 149 sites covering an area of approximately 250 000 km2 within Inner Mongolia, People's Republic of China were analyzed for the isotopic composition (δ13C) of soil organic carbon (SOC). The contrast in δ13C between C3 and C4 plants allowed for calculation of the C3/C4 ratio from δ13C of SOC with a two‐member mixing model, which accounted for influences of aridity and altitude on δ13C of the C3 end‐member and for changes in δ13C of atmospheric CO2. Maps were created geostatistically, and showed a substantially lower C4 abundance in soil than in recent vegetation (−10%). The difference between soil and vegetation varied regionally and was most pronounced within an E–W belt along 44°N and in a mountainous area, suggesting a spread of C4 plants toward northern latitudes (about 1°) and higher altitudes. The areas of high C4 abundance for present vegetation and SOC were well delineated by the isotherms of crossover temperature based on the climatic conditions of the respective time periods. Our study indicates that change in the patterns of C3/C4 composition in the Inner Mongolia grassland was mainly triggered by increasing temperature, which overrode the antagonistic effect of rising CO2 concentrations.

Antarctic winter tropospheric warming—the potential role of polar stratospheric clouds, a sensitivity study

AbstractOver the last 30 years, Antarctic mid‐tropospheric temperatures in winter have increased by 0.5 K per decade, the largest regional tropospheric warming observed. Over this period, amounts of polar stratospheric cloud(PSC) have also increased, as rising CO2 concentrations cooled the stratosphere. By imposing an idealisation of these increases in PSC within the radiation scheme of an atmosphere‐only general circulation model, we find that they could have contributed to the observed warming. The present generation of global climate models do not properly represent PSCs, and so these results demonstrate the need to improve the representation of PSCs. Copyright © 2009 Royal Meteorological Society and Crown Copyright

Global climate changes and the soil cover

The relationships between climate changes and the soil cover are analyzed. The greenhouse effect induced by the rising concentrations of CO2, CH4, N2O, and many other trace gases in the air has been one of the main factors of the global climate warming in the past 30–40 years. The response of soils to climate changes is considered by the example of factual data on soil evolution in the dry steppe zone of Russia. Probable changes in the carbon cycle under the impact of rising CO2 concentrations are discussed. It is argued that this rise may have an effect of an atmospheric fertilizer and lead to a higher productivity of vegetation, additional input of organic residues into the soils, and activation of soil microflora. Soil temperature and water regimes, composition of soil gases, soil biotic parameters, and other dynamic soil characteristics are most sensitive to climate changes. For the territory of Russia, in which permafrost occupies more than 50% of the territory, the response of this highly sensitive natural phenomenon to climate changes is particularly important. Long-term data on soil temperatures at a depth of 40 cm are analyzed for four large regions of Russia. In all of them, except for the eastern sector of Russian Arctic, a stable trend toward the rise in the mean annual soil temperature. In the eastern sector (the Verkhoyansk weather station), the soil temperature remains stable.

Can biological invasions induce desertification?

Can biological invasions induce desertification?

The effect of natural flow of aquifers and associated dispersion on the onset of buoyancy‐driven convection in a saturated porous medium

AbstractCarbon dioxide injection into deep saline aquifers is an important option for managing CO2 emissions. Injected CO2 dissolves into formation brines from above, increasing brine density and creating an unstable hydrodynamic state favorable for natural convection. Long‐term buoyancy‐driven flow of high‐density CO2‐saturated brine leads to faster trapping through improved dissolution and can reduce the risk of CO2 leakage from storage sites. We investigate the role of natural flow of aquifers and associated dispersion on the onset of convection. A linear stability analysis of a transient concentration field in a laterally infinite, horizontal, and saturated porous layer with steady horizontal flow is presented. The layer is subjected to a sudden rise in CO2 concentration from the top and is closed from the bottom. Solution of the stability equations is obtained using a Galerkin technique and the resulting equations are integrated numerically. We found simple scaling relationships that follow tDc∼60(1 + PeT)Ra‐2 for the onset time of convection and a∼0.05Ra/(1 + PeT) for the wavenumber of the initial instabilities. Results reveal that transverse dispersion increases the time to onset of convection for the entire range of Ra. Furthermore, transverse dispersion decreases the critical wavenumber of the instabilities. These results facilitate screening candidate sites for geological CO2 storage. © 2008 American Institute of Chemical Engineers AIChE J, 2009

EFFECTS OF ELEVATED SEAWATER CO2 CONCENTRATION ON THE MEIOFAUNA

An increase in atmospheric CO2 concentration leads to a rise in CO2 concentrations and a decrease in pH of the ocean surface water due to continuous gas exchange between air and seawater, which may have serious impacts on neritic marine organisms. In this study, we assessed the impacts of elevated CO2 concentrations on meiobenthic organisms by exposing them to seawater equilibrated with air (control: CO2 concentration 380 ppm) or CO2-enriched air (2,000 ppm higher than control, CO2 concentration predicted by the year 2300) for 56 days in microcosms. We observed no significant differences in the abundance of total meiofauna, nematodes, harpacticoid copepods (including adults and copepodites) and nauplii by the end of the experiment. These results suggest that the projected atmospheric CO2 concentration in the year 2300 does not have acute effects on the meiofauna. However, further studies are needed to evaluate longerterm effects of elevated CO2 on meiobenthic organisms.

Effects of Elevated Seawater CO2 Concentration on the Meiofauna

An increase in atmospheric CO2 concentration leads to a rise in CO2 concentrations and a decrease in pH of the ocean surface water due to continuous gas exchange between air and seawater, which may have serious impacts on neritic marine organisms. In this study, we assessed the impacts of elevated CO2 concentrations on meiobenthic organisms by exposing them to seawater equilibrated with air (control: CO2 concentration 380 ppm) or CO2-enriched air (2,000 ppm higher than control, CO2 concentration predicted by the year 2300) for 56 days in microcosms. We observed no significant differences in the abundance of total meiofauna, nematodes, harpacticoid copepods (including adults and copepodites) and nauplii by the end of the experiment. These results suggest that the projected atmospheric CO2 concentration in the year 2300 does not have acute effects on the meiofauna. However, further studies are needed to evaluate longerterm effects of elevated CO2 on meiobenthic organisms.

Contributions of nitrogen deposition and forest regrowth to terrestrial carbon uptake

BackgroundThe amount of reactive nitrogen deposited on land has doubled globally and become at least five-times higher in Europe, Eastern United States, and South East Asia since 1860 mostly because of increases in fertilizer production and fossil fuel burning. Because vegetation growth in the Northern Hemisphere is typically nitrogen-limited, increased nitrogen deposition could have an attenuating effect on rising atmospheric CO2 by stimulating the vegetation productivity and accumulation of carbon in biomass.ResultsThis study shows that elevated nitrogen deposition would not significantly enhance land carbon uptake unless we consider its effects on re-growing forests. Our results suggest that nitrogen enriched land ecosystems sequestered 0.62–2.33 PgC in the 1980s and 0.75–2.21 PgC in the 1990s depending on the proportion and age of re-growing forests. During these two decades land ecosystems are estimated to have absorbed 13–41% of carbon emitted by fossil fuel burning.ConclusionAlthough land ecosystems and especially forests with lifted nitrogen limitations have the potential to decelerate the rise of CO2 concentrations in the atmosphere, the effect is only significant over a limited period of time. The carbon uptake associated with forest re-growth and amplified by high nitrogen deposition will decrease as soon as the forests reach maturity. Therefore, assessments relying on carbon stored on land from enhanced atmospheric nitrogen deposition to balance fossil fuel emissions may be inaccurate.