Abstracts on Global Climate Change

Jan 2007

Carbon sources and sinks in high-elevation spruce-fir forests of the Southeastern US

Van Miegroet, H Moore, PT Tewksbury, CE Nicholas, NS


This paper examines carbon (C) pools, fluxes, and net ecosystem balance for a high-elevation red spruce-Fraser fir forest [Picea rubens Sarg./ Abies fraseri (Pursh.) Poir] in the Great Smoky Mountains National Park (GSMNP), based on measurements in fifty-four 20 m x 20 m permanent plots located between 1525 and 1970 m elevation. Forest floor and mineral soil C was determined from destructive sampling of the 0 horizon and incremental soil cores (to a depth of 50 cm) in each plot. Overstory C pools and net C sequestration in live trees was estimated from periodic inventories between 1993 and 2003. The CO2 release from standing and downed wood was based on biomass and C concentration estimates and published decomposition constants by decay class and species. Soil respiration was measured in situ between 2002 and 2004 in a subset of eight plots along an elevation gradient. Litterfall was collected from a total of 16 plots over a 2-5-year period. The forest contained on average 403 Mg C ha(-1) almost half of which stored belowground. Live trees, predominantly spruce, represented a large but highly variable C pool (mean: 126 Mg C ha(-1), CV = 39%); while dead wood (61 Mg C ha(-1)), mostly fir, accounted for as much as 15% of total ecosystem C. The 10-year mean C sequestration in living trees was 2700 kg C ha(-1) year(-1), but increased from 2180 kg C ha(-1) year(-1) in 1993-1998 to 3110 kg C ha(-1) year(-1) in 1998-2003, especially at higher elevations. Dead wood also increased during that period, releasing on average 1600 kg C ha(-1) year(-1). Estimated net soil C efflux ranged between 1000 and 1450 kg C ha(-1) year(-1), depending on the calculation of total belowground C allocation. Based on current flux estimates, this old-growth system was close to C neutral. (c) 2006 Elsevier B.V. All rights reserved.

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Plant water sources in the cold semiarid ecosystem of the upper Kherlen River catchment in Mongolia: A stable isotope approach

Li, SG Romero-Saltos, H Tsujimura, M Sugimoto, A Sasaki, L Davaa, G Oyunbaatar, D


In the cold semiarid region of northeastern Mongolia, we used stable isotopes (180 and D) to determine potential plant water sources during the 2003 growing season (June to September) in two habitats: montane forest and an elevation gradient from the forest to Kherten river bank. The forest is dominated by larch (Larix sibirica) with patches of cinquefoil shrubs (Potentilla fruticosa). The latter also grow throughout the elevation gradient, while the Larch grows only on the top slope. Poplar (Populus spp.) and willow (Salix spp.) trees grow only on the river bank. All plant and soil samples showed isotopic signatures similar to summer precipitation, which is isotopically heavier in summer than winter. In July and August, [arch trees in the forest tended to shift their water uptake to shallow depths in response to recent rainfall, but during the remaining months (June and September), depths of water uptake were unclear. Further, both the larch trees and cinquefoil shrubs in the forest used water at similar depths, suggesting potential competition for water. Plants along the elevation gradient showed different patterns of water use: (1) in July, larch used recent rainfall only, but in other months, the pattern was unclear; (2) cinquefoil depended on rainfall from recent weeks (as in August), but sometimes used antecedent rainwater from one month prior; and (3) poplar and willow seemed to use water from the river (as in August) or from precipitation that felt a few weeks prior (as in September), but the factors controlling this unusual shift are unknown. This study contributes to our understanding of plant water use strategies in cold semiarid ecosystems, and provides baseline data for models designed to understand large-scale hydrological effects of global climate change. (c) 2006 Elsevier B.V. All rights reserved.

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Evidence of methane release from Blake Ridge ODP Hole 997A during the Plio-Pleistocene: Benthic foraminifer fauna and total organic carbon

Bhaumik, AK Gupta, AK

CURRENT SCIENCE 92:2 192-199

Methane is a powerful greenhouse gas and may have played a significant role in global climate change in the geological past. Destabilization of gas hydrates, frozen methane stored within the ocean floor sediment and in permafrost, may have provided an important source of methane to the atmosphere. Ocean Drilling Program Hole 997A (water depth 2770 m), situated on the crest of the Blake Outer Ridge, is a potentially large reservoir of gas hydrate. Methane emissions from the Blake Outer Ridge have been reported previously, which has been suggested as a driver for global climate change. Methane at this site is of biogenic origin, produced by the bacterial decomposition of organic matter. We used benthic foraminifer faunal assemblages (> 125 mu m size fraction) and species diversity, combined with total organic carbon data from Hole 997A, to identify intervals of methane releases during the late Neogene (last 5.4 Ma). We identified a group of benthic foraminifera, which were taken to indicate methane fluxes based on previous work on seep-related benthic foraminifera. We then classified ‘seep-related’ benthic foraminifera, as well as high organic carbon taxa independent of deep-sea oxygenation. We recognized five intervals of increased abundance of the seep-related benthic foraminifera since last 3.6 Ma representing intervals of methane release, which coincide with intervals of lowered sea level. Changes in benthic foraminifera are more abrupt over the past 3.6 Ma when the northern hemisphere glaciation began to intensify and climate switched to a 41-kyr cycle world.

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Rapid evolution of flowering time by an annual plant in response to a climate fluctuation

Franks, SJ Sim, S Weis, AE


Ongoing climate change has affected the ecological dynamics of many species and is expected to impose natural selection on ecologically important traits. Droughts and other anticipated changes in precipitation may be particularly potent selective factors, especially in and regions. Here we demonstrate the evolutionary response of an annual plant, Brassica rapa, to a recent climate fluctuation resulting in a multiyear drought. Ancestral (predrought) genotypes were recovered from stored seed and raised under a set of common environments with descendant (postdrought) genotypes and with ancestor x descendant hybrids. As predicted, the abbreviated growing seasons caused by drought led to the evolution of earlier onset of flowering. Descendants bloomed earlier than ancestors, advancing first flowering by 1.9 days in one study population and 8.6 days in another. The intermediate flowering time of ancestor x descendant hybrids supports an additive genetic basis for divergence. Experiments confirmed that summer drought selected for early flowering, that flowering time was heritable, and that selection intensities in the field were more than sufficient to account for the observed evolutionary change. Natural selection for drought escape thus appears to have caused adaptive evolution in just a few generations. A systematic effort to collect and store propagules from suitable species would provide biologists with materials to detect and elucidate the genetic basis of further evolutionary shifts driven by climate change.

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High temperature acclimation of C-4 photosynthesis is linked to changes in photosynthetic biochemistry

Dwyer, SA Ghannoum, O Nicotra, A Von Caemmerer, S


With average global temperatures predicted to increase over the next century, it is important to understand the extent and mechanisms of C-4 photosynthetic acclimation to modest increases in growth temperature. To this end, we compared the photosynthetic responses of two C-4 grasses (Panicum coloratum and Cenchrus ciliaris) and one C-4 dicot (Flaveria bidentis) to growth at moderate (25/20 degrees C, day/night) or high (35/30 degrees C, day/night) temperatures. In all three C-4 species, CO2 assimilation rates (A) underwent significant thermal acclimation, such that when compared at growth temperatures, A increased less than what would be expected given the strong response of A to short-term changes in leaf temperature. Thermal photosynthetic acclimation was further manifested by an increase in the temperature optima of A, and a decrease in leaf nitrogen content and leaf mass per area in the high-relative to the moderate-temperature-grown plants. Reduced photosynthetic capacity at the higher growth temperature was underpinned by selective changes in photosynthetic components. Plants grown at the higher temperature had lower amounts of ribulose-1,5-bisphosphate carboxylase/oxygenase and cytochrome f and activity of carbonic anhydrase. The activities of photosystem II (PSII) and phosphenolpyruvate carboxylase were not affected by growth temperature. Chlorophyll fluorescence measurements of F. bidentis showed a corresponding decrease in the quantum yield of PSII (Phi(PSII)) and an increase in non-photochemical quenching (Phi(NPQ)). It is concluded that through these biochemical changes, C-4 plants maintain the balance between the various photosynthetic components at each growth temperature, despite the differing temperature dependence of each process. As such, at higher temperatures photosynthetic nitrogen use efficiency increases more than A. Our results suggest C-4 plants will show only modest changes in photosynthetic rates in response to changes in growth temperature, such as those expected within or between seasons, or the warming anticipated as a result of global climate change.

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Erosion in northwest Tibet from in-situ-produced cosmogenic Be-10 and Al-26 in bedrock

Kong, P Na, CG Fink, D Ding, L Huang, FX


Concentrations of in-situ-produced cosmogenic nuclides Be-10 and Al-26 in quartz were measured by accelerator mass spectrometry for bedrock basalts and sandstones located in northwest Tibet. The effective exposure ages range between 23 and 134 ka (Be-10) and erosion rates between 4.0 and 24 mm ka(-1). The erosion rates are significantly higher than those in similarly and Antarctica and Australia, ranging between 0.1 and 1 mm ka(-1), suggesting that precipitation is not the major control of erosion of landforms. Comparison of erosion rates in and regions with contrasting tectonic activities suggests that tectonic activity plays a more important role in controlling long-term erosion rates. The obtained erosion rates are, however, significantly lower than the denudation rate of 3000-6000 mm ka(-1) beginning at c. 53 Ma in the nearby Godwin Austen (K2) determined by apatite fission-track thermochronology. It appears that the difference in erosion rates within different time intervals is indicative of increased tectonic activity at c. 5-3 Ma in northwest Tibet. We explain the low erosion rates determined in this study as reflecting reduced tectonic activity in the last million years. A model of localized thinning of the mantle beneath northwest Tibet may account for the sudden increased tectonic activity at c. 5-3 Ma and the later decrease. Copyright (c) 2006 John Wiley & Sons, Ltd.

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Geographic variation in the immunoglobulin levels in pygoscelid penguins

Barbosa, A Merino, S Benzal, J Martinez, J Garcia-Fraile, S

POLAR BIOLOGY 30:2 219-225

Antarctic organisms, including penguins, are susceptible to parasites and pathogens. Effects of infestation could differ in different locations along a geographical gradient from north to south consistent with conditions that affect the prevalence and virulence of parasites and pathogens. The immune system, including immunoglobulins as the main component of the humoral immune response, is the major way by which organisms confront infestation. We investigated the variation in immunoglobulin levels in three species of antarctic penguins (Pygoscelis antarctica, Pygoscelis papua, and Pygoscelis adeliae) along a geographical gradient from King George Island (62 degrees 15’S) to Avian Island (67 degrees 46’S). We found that immunoglobulin levels increased northwards in all the three species. This could indicate a higher impact of parasites and/or pathogens relative to the existing gradient in temperatures along this coast. Changing temperatures, consistent with global climate change, could be altering the ecology of parasite or pathogen infestation within the biota of northern Antarctica. We have also found marginal differences in immunoglobulin levels between sexes in both chinstrap and gentoo penguins.

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Clean development mechanism and off-grid small-scale hydropower projects: Evaluation of additionality

Tanwar, N

ENERGY POLICY 35:1 714-721

The global climate change mitigation policies and their stress on sustainable development have made electrification of rural mountainous villages, using small hydro, an attractive destination for potential clean development mechanism (CDM) projects. This invariably involves judging the additionality of such projects. The paper suggests a new approach to judge the additionality of such stand-alone small hydropower projects. This has been done by breaking up additionality into two components: external and local. The external additionality is project developer dependent. For determining the local additionality, the paper takes into account the probability of a village getting electrified over a period of time, which is kept equal to the possible crediting period. This is done by defining an electrification factor (EF) whose value depends on the degree of isolation, financial constraints and institutional constraints encountered while electrifying a mountainous village. Using this EF, the additionality of a CDM project can be judged in a much easier and accurate way. The paper is based on the data and inputs gathered during site visits to many isolated villages located in the eastern Indian Himalayas. (c) 2006 Elsevier Ltd. All rights reserved.

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Nonlinear effects of climate change on phosphorus stability in wetlands: Concept and estimation

Pant, HK


Effects of climate change on ecosystems like freshwater wetlands cannot be understood without focusing research on getting sense of vulnerability and resiliency at the systemic level, involving tipping points, rapid changes in events and states, because of the interdependency of various components that are subject to nonlinear changes even though they may exert significant inertia to short-term hydro-climatic fluctuations. Depending on resilience, threshold and lag times, hydro-climatic changes brought upon by global climate change may cause nonlinear and/or irreversible changes in phosphorus (P) dynamic, and instigate P enrichment in freshwater wetlands. Thus, the studies of the influence of expected global climate change and its direct and indirect effects on bioavailability/stability of organic P in wetlands are in critical need to help manage or increase the resilience of wetland ecosystem against any abrupt or irreversible changes that may adversely affect the ecosystem and its services. Phosphorus dynamic in freshwater wetland system is likely to behave nonlinearly due to expected changes in temperature, and sediment/soil and water acidity and redox status because of global climate change in the decades to come, thereby freshwater wetland, a sensitive ecosystem that plays critical role ranging from water quality management to atmospheric CO2 removal, could face irreversible or hysteretic adverse changes. The overall objectives of this paper are to provide consolidated information on identification and estimation of any nonlinear behaviors in the stability/bioavailability of various P forms, which are present in water columns, detritus and soils/sediments, at different levels of stressors in light of changing global climate. Addressing how stable organic P is, and at what threshold level and lag time would organic P behave nonlinearly and release back into the water column, in turn, exacerbate eutrophic conditions, are crucial. Learning the resilience, threshold level and lag times allows us to gauge the strengths and weaknesses of our technological advances and policies that may help us to cope with nonlinear impacts of global climate change on ecosystems such as wetlands. The relationships developed between P mobilization processes, stressors’ levels and lag time can provide invaluable insights for the formulation of management strategies that could increase resilience in freshwater wetlands, which may be subjected to nonlinear ecological responses.

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Carbon emission control strategies for China: A comparative study with partial and general equilibrium versions of the China MARKAL model

Chen, WY Wu, ZX He, JK Gao, PF Xu, SF

ENERGY 32:1 59-72

China’s carbon dioxide emissions from fossil fuel combustion had increased with an annual growth rate of 4.36% since 1980, hitting 1 GtC in 2003. The global climate change issue is becoming more and more important and hence to be the fourth challenge for China’s future energy development, following energy supply shortages, energy security, and local environmental protection. This paper used three MARKAL (MARKet ALlocation) family models, that is, MARKAL, MARKAL-ED (MARKAL with elastic demand), and MARKAL-MACRO, to study China energy system’s carbon mitigation strategies and corresponding impacts on the economy. The models’ structures and the economic feedback formulations used in MARKAL-MACRO and MARKAL-ED are briefly described. The endogenous demands in MARKAL-MACRO and MARKAL-ED enable them to partly satisfy carbon abatement constraints via energy service demand reductions, and the reduction levels for the 30 demand sectors from these two kinds of models for given carbon emission constraints are presented and compared. The impact of carbon mitigation on social welfare from MARKAL and MARKAL-ED, and on GDP, investment and consumption from MARKAL-MACRO are evaluated. The changes in both final and primary energy mix, changes in technology development, as well as marginal abatement costs for given carbon constraints from the three models, are analyzed. (c) 2006 Elsevier Ltd. All rights reserved.

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Does the El Nino-Southern Oscillation control the interhemispheric radiocarbon offset?

Turney, CSM Palmer, JG


Since the 1970s it has been recognised that Southern Hemisphere samples have a lower radiocarbon content than contemporaneous material in the Northern Hemisphere. This interhemispheric radiocarbon offset has traditionally been considered to be the result of a greater surface area in the southern ocean and high-latitude deepwater formation. This is despite the fact that the El Nino-Southern Oscillation (ENSO) is known to play a significant role in controlling the interannual variability of atmospheric carbon dioxide by changing the flux of ‘old’ CO2 from the tropical Pacific. Here we demonstrate that over the past millennium, the Southern Hemisphere radiocarbon offset is characterised by a pervasive 80-yr cycle with a step shift in mean values coinciding with the transition from the Medieval Warm Period to the Little Ice Age. The observed changes suggest an ENSO-like role in influencing the mterhemispheric radiocarbon difference, most probably modulated by the Interdecadal Pacific Oscillation, and supports a tropical role in forcing centennial-scale global climate change. (c) 2006 University of Washington. All rights reserved.

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Pathways of anaerobic carbon cycling across an ombrotrophic-minerotrophic peatland gradient

Keller, JK Bridgham, SD


Peatland soils represent globally significant stores of carbon, and understanding carbon cycling pathways in these ecosystems has important implications for global climate change. We measured aceticlastic and autotrophic methanogenesis, sulfate reduction, denitrification, and iron reduction in a bog, an intermediate fen, and a rich fen in the Upper Peninsula of Michigan for one growing season. In 3-d anaerobic incubations of slurried peat, denitrification and iron reduction were minor components of anaerobic carbon mineralization. Experiments using C-14-labeled methanogenic substrates showed that methanogenesis in these peatlands was primarily through the aceticlastic pathway, except early in the growing season in more ombrotrophic peatlands, where the autotrophic pathway was dominant or codominant. Overall, methane production was responsible for 3-70% of anaerobic carbon mineralization. Sulfate reduction accounted for 0-26% of anaerobic carbon mineralization, suggesting a rapid turnover of a very small sulfate pool. A large percentage of anaerobic carbon mineralization (from 29% to 85%) was unexplained by any measured process, which could have resulted from fermentation or possibly from the use of organic molecules (e.g., humic acids) as alternative electron acceptors.

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Species richness of migratory birds is influenced by global climate change

Lemoine, N Schaefer, HC Bohning-Gaese, K


Aim Global climate change is increasingly influencing ecosystems. Long-term effects on the species richness and composition of ecological communities have been predicted using modelling approaches but, so far, hardly demonstrated in the field. Here, we test whether changes in the composition of bird communities have been influenced by recent climate change. Location Europe. Methods We focus on the proportion of migratory and resident bird species because these groups are expected to respond differently to climatic change. We used the spatial relationship between climatic factors and bird communities in Europe to predict changes in 21 European bird communities under recent climate change. Results Observed changes corresponded significantly to predicted changes and could not be explained by the effects of spatial autocorrelation. Alternative factors such as changes in land use were tested in a first approximation as well but no effects were found. Main Conclusions This study demonstrates that global climate change has already influenced the species richness and composition of European bird communities.

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The influence of major dams on hydrology through the drainage network of the Sacramento River basin, California

Singer, MB


This paper reports basinwide patterns of hydrograph alteration via statistical and graphical analysis from a network of long-term streamflow gauges located various distances downstream of major dams and confluences in the Sacramento River basin in California, USA. Streamflow data from 10 gauging stations downstream of major dams were divided into hydrologic series corresponding to the periods before and after dam construction. Pre- and post-dam flows were compared with respect to hydrograph characteristics representing frequency, magnitude and shape: annual flood peak, annual flow trough, annual flood volume, time to flood peak, flood drawdown time and interarrival time. The use of such a suite of characteristics within a statistical and graphical framework allows for generalising distinct strategies of flood control operation that can be identified without any a priori knowledge of operations rules. Dam operation is highly dependent oil the ratio of reservoir capacity to annual flood Volume (impounded runoff index). Dams with high values of this index generally completely cut off flood peaks thus reducing time to peak, drawdown time and annual flood volume. Those with low values conduct early and late flow releases to extend the hydrograph, increasing time to peak, drawdown time and annual flood Volume. The analyses reveal minimal flood control benefits from foothill dams in the lower Sacramento River (i.e. dissipation of the down-valley flood control signal). The lower part of the basin is instead reliant on a weir and bypass system to control lowland flooding. Data from a control gauge (i.e. with no upstream dams) suggest a background signature of global climate change expressed as shortened flood hydrograph failing limbs and lengthened flood interarrival times at low exceedence probabilities. This research has implications for flood control, water resource management, aquatic and riparian ecosystems and for rehabilitation strategies involving flow alteration and/or manipulation of sediment Supplies. Copyright (c) 2006 John Wiley & Sons, Ltd.

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Insect development under predation risk, variable temperature, and variable food quality

Logan, JD Wolesensky, W Joern, A


We model the development of an individual insect, a grasshopper, through its nymphal period as a function of a trade-off between prey vigilance and nutrient intake in a changing environment. Both temperature and food quality may be variable. We scale up to the population level using natural mortality and a predation risk that is mass, vigilance, and temperature dependent. Simulations reveal the sensitivity of both survivorship and development time to risk and nutrient intake, including food quality and temperature variations The model quantifies the crucial role of temperature in trophic interactions and development, which is an important issue in assessing the effects of global climate change on complex environmental interactions.

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Temperature-dependent effects of cadmium and purine nucleotides on mitochondrial aconitase from a marine ectotherm, Crassostrea virginica: a role of temperature in oxidative stress and allosteric enzyme regulation

Cherkasov, AA Overton, RA Sokolov, EP Sokolova, IM


Temperature and heavy metals such as cadmium (Cd) are important environmental stressors that can strongly affect mitochondrial function of marine poikilotherms. In this study, we investigated the combined effects of temperature (20 degrees C and 30 degrees C) and Cd stress on production of reactive oxygen species (ROS) and oxidative stress in a marine poikilotherm Crassostrea virginica (the eastern oyster) using mitochondrial aconitase as a sensitive biomarker of oxidative damage. We also assessed potential involvement of mitochondrial uncoupling proteins (UCPs) in antioxidant protection in oyster mitochondria using purine nucleotides (GDP, ATP and ADP) as specific inhibitors, and free fatty acids as stimulators, of UCPs. Our results show that exposure to Cd results in elevated ROS production and oxidative damage as indicated by aconitase inactivation which is particularly pronounced at elevated temperature. Unexpectedly, oyster mitochondrial aconitase was inhibited by physiologically relevant levels of ATP (IC50 = 1.93 and 3.04 mmol l(-1) at 20 degrees C and 30 degrees C, respectively), suggesting that allosteric regulation of aconitase by this nucleotide may be involved in regulation of the tricarboxylic acid flux in oysters. Aconitase was less sensitive to ATP inhibition at 30 degrees C than at 20 degrees C, consistent with the elevated metabolic flux at higher temperatures. ADP and GDP also inhibited mitochondrial aconitase but at the levels well above the physiological concentrations of these nucleotides (6-11 mmol l(-1)). Our study shows expression of at least three UCP isoforms in C. virginica gill tissues but provides no indication that UCPs protect mitochondrial aconitase from oxidative inactivation in oysters. Overall, the results of this study indicate that temperature stress exaggerates toxicity of Cd leading to elevated oxidative stress in mitochondria, which may have important implications for survival of poikilotherms in polluted environments during seasonal warming and/or global climate change, and suggest a novel temperature-dependent mechanism of allosteric regulation of TCA flux in oyster mitochondria.

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