Abstracts on Global Climate Change

May 2006

North American prairie wetlands are important nonforested land-based carbon storage sites

Euliss, NH Gleason, RA Olness, A McDougal, RL Murkin, HR Robarts, RD Bourbonniere, RA Warner, BG


We evaluated the potential of prairie wetlands in North America as carbon sinks. Agricultural conversion has resulted in the average loss of 10.1 Mg ha(-1) of soil organic carbon on over 16 million ha of wetlands in this region. Wetland restoration has potential to sequester 378 Tg of organic carbon over a 10-year period. Wetlands can sequester over twice the organic carbon as no-till cropland on only about 17% of the total land area in the region. We estimate that wetland restoration has potential to offset 2.4% of the annual fossil CO2 emission reported for North America in 1990. (c) 2005 Elsevier B.V. All rights reserved.

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Past hydrological events related to understanding global change: An ICSU research project

Gregory, KJ Benito, G Dikau, R Golosov, V Jones, AJJ Macklin, MG Parsons, AJ Passmore, DG Poesen, J Starkel, L Walling, DE

CATENA 66:1-2 2-13

Despite general agreement that global climate change is taking place there is less consensus about the consequences and impacts that may arise. The possibility of greater climatic variability, with changes in the incidence of particular types of events, requires multidisciplinary research so that associated impacts can be considered when devising environmental management strategies. Past hydrological events investigated using palaeoenvironmental techniques, over time periods longer than the period of continuous records, are a possible source of information to complement monitored records. Six international research groups (GLOCOPH Commission of INQUA, Water Sustainability Commission of IGU, LUCIFS in IGBP-PAGES, Geomorphic Challenges for the 21st Century Commission of IGU, International Commission on Continental Erosion of IAHS, and Fluvial Archives Group [FLAG] associated with INQUA and IGU) have each contributed results from their specific time and spatial scales in integrated research collaboration. Relevant research conclusions have been combined and a research project under-taken which is the subject of four later papers. A provisional protocol for use of past hydrological events in order to understand global change is proposed and adapted in the final paper, to take account of other papers included and contributions to the discussions. (c) 2005 Elsevier B.V. All rights reserved.

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Terminal Pleistocene braided to meandering transition in rivers of the Southeastern USA

Leigh, DS

CATENA 66:1-2 155-160

Thirteen paleomeanders on the oldest parts of meander belts on floodplains in the Coastal Plain of Georgia and the Carolinas (southeastern USA) were selected for radiocarbon dating to determine the onset of meandering following braiding during the Late Pleistocene during Oxygen Isotope Stage 2. The radiocarbon ages were compared to previously reported Late Pleistocene ages for braid bars and eolian dunes. Results indicate that meandering commenced at circa 15,000 to 16,000 cal years BP and continued throughout the terminal Pleistocene and Holocene. Correlation with other paleoenvironmental records indicates that this shift to meandering was associated with global warming and moister conditions in the Southeastern United States that led to a denser vegetation cover and a reduction in sediment yield. The shift to meandering was also associated with some incision and terracing of the Late Pleistocene braided fluvial surfaces. Paleodischarge of the bankfull condition of early Holocene meandering channels was apparently greater than under modem conditions, suggesting wetter conditions at that time than at present. This braided to meandering transition in the southeastern United States provides an example of river response to global climate change in a relatively low latitude region of the world that was not influenced by glacial or periglacial landscape conditions. (c) 2005 Elsevier B.V. All rights reserved.

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Late Pliocene vegetation and climate in Namibia (southern Africa) derived from palynology of ODP Site 1082

Dupont, LM


[ 1] The present-day condition of bipolar glaciation characterized by rapid and large climate fluctuations began at the end of the Pliocene with the intensification of the Northern Hemisphere continental glaciations. The global cooling steps of the late Pliocene have been documented in numerous studies of Ocean Drilling Program (ODP) sites from the Northern Hemisphere. However, the interactions between oceans and between land and ocean during these cooling steps are poorly known. In particular, data from the Southern Hemisphere are lacking. Therefore I investigated the pollen of ODP Site 1082 in the southeast Atlantic Ocean in order to obtain a high-resolution record of vegetation change in Namibia between 3.4 and 1.8 Ma. Four phases of vegetation development are inferred that are connected to global climate change. ( 1) Before 3 Ma, extensive, rather open grass-rich savannahs with mopane trees existed in Namibia, but the extension of desert and semidesert vegetation was still restricted. ( 2) Increase of winter rainfall dependent Renosterveld-like vegetation occurred between 3.1 and 2.2 Ma connected to strong advection of polar waters along the Namibian coast and a northward shift of the Polar Front Zone in the Southern Ocean. ( 3) Climatically induced fluctuations became stronger between 2.7 and 2.2 Ma and semiarid areas extended during glacial periods probably as the result of an increased pole-equator thermal gradient and consequently globally enhanced atmospheric circulation. ( 4) Aridification and climatic variability further increased after 2.2 Ma, when the Polar Front Zone migrated southward and the influence of Atlantic moisture brought by the westerlies to southern Africa declined. It is concluded that the positions of the frontal systems in the Southern Ocean which determine the locations of the high-pressure cells over the South Atlantic and the southern Indian Ocean have a strong influence on the climate of southern Africa in contrast to the climate of northwest and central Africa, which is dominated by the Saharan low-pressure cell.

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Climate agreements based on responsibility for global warming: Periodic updating, policy choices, and regional costs

Rive, N Torvanger, A Fuglestvedt, JS


It has been suggested that calculations of historical responsibility for global warming should be used to distribute mitigation requirements in future climate agreements. For a medium-term mitigation scenario, we calculate regional mitigation costs resulting from global allocation schemes based on the Brazilian Proposal that solely incorporate historical responsibility as a burden sharing criterion. We find that they are likely to violate ability-to-pay principles. In spite of less stringent abatement requirements, developing country regions experience cost burdens (as a percentage of GDP) in the same range as those of developed countries. We also assess the policy options available for calculating historical responsibility. The periodic updating of responsibility calculations over time, concerns over the robustness and availability of emissions data, and the question of whether past emissions were knowingly harmful, may lead to policy choices that increase the relative historical responsibility attributed to developing countries. This, in turn, would increase their mitigation cost burden. (C) 2006 Elsevier Ltd. All rights reserved.

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Simulating the effects of temperature on individual and population growth of Rhinoptera bonasus: a coupled bioenergetics and matrix modeling approach

Neer, JA Rose, KA Cortes, E


Cownose rays Rhinoptera bonasus typify the K-selected life history strategy that makes their population dynamics susceptible to variation in natural and anthropogenic factors. We used an individual-based bioenergetics model, coupled to a matrix projection model, to predict how water temperatures warmer and cooler than current conditions would affect the individual growth and the population dynamics of cownose rays. The bioenergetics model simulated the daily growth, survival, and reproductive output of a cohort of female individuals from birth over their lifetime. Warmer and cooler temperature scenarios under alternative assumptions about ray movement were simulated. Under warmer conditions, daily consumption rate would have to increase by about 12 % or weights-at-age would decrease by 10 to 17 %, while under cooler conditions, daily consumption would have to decrease by about 14% or weights-at-age would increase by about 15%. Slowed individual growth under warmer water temperatures translated into slowed population growth rate, decreased net reproductive rate, longer generation time, and higher but delayed age-specific reproductive values. For example, under the scenario that resulted in the slowest individual growth rates, the population growth rate would decrease from 0.027 to 0.005 yr(-1). Population growth rates were more sensitive to variation in survival rates, especially those of mature age-classes, than to fertility rates. Our coupling of an individual-based bioenergetics model with a matrix projection model offers a potentially powerful approach for relating how, with limited to moderate information, changes in environmental variables and habitat that affect individual growth can be expressed as population-level responses.

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Effects of aphid herbivory on biomass and leaf-level physiology of Solanum dulcamara under elevated temperature and CO2

Flynn, DFB Sudderth, EA Bazzaz, FA


Forecasted increases in atmospheric CO2 and global mean temperature are likely to influence insect-plant interactions. Plant traits important to insect herbivores, such as nitrogen content, may be directly affected by elevated CO2 and temperature, while insect herbivores are likely to be directly affected only by temperature. This study investigates changes in the effects of herbivory by the aphid Macrosiphum euphorbiae (Homoptera: Aphididae) on the C-3 perennial Solanum dulcamara under two conditions of atmospheric CO2 concentration (350/750ppm) and three temperature treatments (20/15, 23/18, 26/21 degrees C; day/night temperatures). Plants were grown in glass-topped chambers and initially infested with three apterous, adult aphids. Aphid population size, leaf photosynthetic capacity, carbon to nitrogen (C:N) ratio, specific leaf area, plant height, and total plant biomass were measured after 3 weeks of infestation. Aphid herbivory reduced photosynthetic capacity under all conditions, and resulted in smaller leaf C:N ratios. Aphid populations did not change significantly under elevated CO2, but tended to increase slightly. Average aphid weight decreased at high temperatures. Plant height and biomass were not significantly affected by the CO2 treatment, but growth rates before infestation were enhanced by elevated CO2. These results indicate that the combined effects of both elevated CO2 and temperature may exacerbate aphid damage to certain plants, particularly to plants which respond weakly to increases in atmospheric CO2. Modifications of plant physiology under altered CO2 and temperature do not impair, and may slightly enhance aphid population growth. (c) 2004 Elsevier B.V. All rights reserved.

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Modelling responses of pine savannas to climate change and large-scale disturbance

Beckage, B Gross, LJ Platt, WJ


Global warming can potentially influence ecological communities through altered disturbance regimes in addition to increased temperatures. We investigate the response of pine savannas in the southeastern United States to global warming using a simple Lotka-Volterra competition model together with predicted changes to fire and hurricane disturbance regimes with global climate change. In the southeastern United States, decreased frequency of both fires and hurricanes with global warming will shift pine savannas toward a forested state. A CO2 fertilization effect that increases the growth rate of tree populations will also push southeastern landscapes from open savannas towards closed forests. Transient dynamics associated with climate driven changes in vegetation will last on the order of decades to a century. In our model, the sensitivity of savannas to relative changes in the frequency of fire versus hurricanes is linearly dependent on the growth rate and mortality of trees in fire and hurricane disturbances.

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Climatic variability in the southwest Pacific during the Last Termination (20-10 kyr BP)

Turney, CSM Kershaw, AP Lowe, JJ van der Kaars, S Johnston, R Rule, S Moss, P Radke, L Tibby, J McGlone, MS Wilmshurst, JM Vandergoes, MJ Fitzsimons, SJ Bryant, C James, S Branch, NP Cowley, J Kalin, RM Ogle, N Jacobsen, G Fifield, LK


The degree to which palaeoclimatic changes in the Southern Hemisphere co-varied with events in the high latitude Northern Hemisphere during the Last Termination is a contentious issue, with conflicting evidence for the degree of ‘teleconnection’ between different regions of the Southern Hemisphere. The available hypotheses are difficult to test robustly, however, because there are few detailed palaeoclimatic records in the Southern Hemisphere. Here we present climatic reconstructions from the southwestern Pacific, a key region in the Southern Hemisphere because of the potentially important role it plays in global climate change. The reconstructions for the period 20-10 kyr BP were obtained from five sites along a transect from southern New Zealand, through Australia to Indonesia, supported by 125 calibrated C-14 ages. Two periods of significant climatic change can be identified across the region at around 17 and 14.2 cal kyr BP, most probably associated with the onset of warming in the West Pacific Warm Pool and the collapse of Antarctic ice during Meltwater Pulse-1A, respectively. The severe geochronological constraints that inherently afflict age models based on radiocarbon dating and the lack of quantified climatic parameters make more detailed interpretations problematic, however. There is an urgent need to address the geochronological limitations, and to develop more precise and quantified estimates of the pronounced climate variations that clearly affected this region during the Last Termination. (c) 2005 Elsevier Ltd. All rights reserved.

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Post-Eocene climate change, niche conservatism, and the latitudinal diversity gradient of New World birds

Hawkins, BA Diniz, JAF Jaramillo, CA Soeller, SA


Aim The aim of this study was to test a variant of the evolutionary time hypothesis for the bird latitudinal diversity gradient derived from the effects of niche conservatism in the face of global climate change over evolutionary time. Location The Western Hemisphere. Methods We used digitized range maps of breeding birds to estimate the species richness at two grain sizes, 756 and 12,100 km(2). We then used molecular phylogenies resolved to family to quantify the root distance (RD) of each species as a measure of its level of evolutionary development. Birds were classified as ‘basal’ or ‘derived’ based on the RD of their family, and richness patterns were contrasted for the most basal and most derived 30% of species. We also generated temperature estimates for the Palaeogene across the Western Hemisphere to examine how spatial covariation between past and present climates might make it difficult to distinguish between ecological and evolutionary hypotheses for the current richness gradient. Results The warm, wet tropics support many species from basal bird clades, whereas the northern temperate zone and cool or dry tropics are dominated by species from more recent, evolutionarily derived clades. Furthermore, crucial to evaluating how niche conservatism among birds may drive the hemispherical richness gradient, the spatial structure of the richness gradient for basal groups is statistically indistinguishable from the overall gradient, whereas the richness gradient for derived groups is much shallower than the overall gradient. Finally, modern temperatures and the pattern of climate cooling since the Eocene are indistinguishable as predictors of bird species richness. Main conclusions Differences in the richness gradients of basal vs. derived clades suggest that the hemispherical gradient has been strongly influenced by the differential extirpation of species in older, warm-adapted clades from parts of the world that have become cooler in the present. We propose that niche conservatism and global-scale climate change over evolutionary time provide a parsimonious explanation for the contemporary bird latitudinal diversity gradient in the New World, although dispersal limitation of some highly derived clades probably plays a secondary role.

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Conservation and restoration of the Pinus palustris ecosystem

Gilliam, FS Platt, WJ


The well-documented decline of the Pinus palustris ecosystem has resulted from several anthropogenic influences, such as forest clearing (e.g. pine plantation forestry, agriculture) and urban development, both of which are closely related to increases in human populations. Other impacts have arisen from alterations in disturbance regimes responsible for maintaining the structure and function of these ecosystems. Restoration and management of degraded pine savanna ecosystems is critical. Identification of ecological processes that determine the structure and function of the intact system are important because successful restoration efforts should be based on sound scientific understanding. In this paper, we introduce this special issue on the ecology, conservation, and restoration of the Pinus palustris ecosystem. Some global climate change scenarios have suggested that future changes may occur that alter frequency and severity of disturbances such as fires and hurricanes. Such changes may have large effects on pine stands, and ultimately entire Pinus palustris savanna ecosystems, thus presenting further challenges to their sustainable management.

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Reduction processes in forest wetlands: Tracking down heterogeneity of source/sink functions with a combination of methods

Paul, S Kusel, K Alewell, C


Wetlands are considered to be the biggest unknowns regarding the influence of global climate change on element dynamics, so knowledge of processes and conditions controlling sink and source functions of redox processes is crucial. The aim of this study was to investigate the sink/source function of nitrate, Fe, sulfate reduction and methanogenesis of an upland and a lowland fen within a boreal spruce catchment, southern Germany. We used suction cups and anaerobic dialysis chambers for soil solution sampling, FeS probes for the determination of S oxidation potential and stability of anoxic conditions and analysis of the soil solid phase (contents of C, S and Fe species). Both fens had high rates of nitrate reduction and potentially high rates of CH4 production. The upper few cm of all profiles were oxic with low CH4 concentrations, suggesting low CH4 emission rates from the soil, though emission by vascular plants cannot be excluded. Sulfate and Fe reduction processes differed significantly in the fens. The upland fen was characterized by relatively stable anoxic conditions, low Fe contents but high contents of organic S and low C/S ratios. We concluded that the upland fen is an effective sink for sulfate with long-term S storage. In contrast, the lowland fen was characterized by alternating oxidation-reduction cycles with high Fe contents, lower contents of organic S and higher C/S ratios. Thus, even though low sulfate and high Fe concentrations in soil solutions indicated high reduction rates in the lowland fen, long-term storage of S is not likely in this fen. Differences in biogeochemical processes between sites are most likely not associated with hydrology but rather with the role of vascular plants. (c) 2005 Elsevier Ltd. All rights reserved.

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Natural disturbances and the physiognomy of pine savannas: A phenomenological model

Gilliam, FS Platt, WJ Peet, RK


Question: The decline of the Pinus palustris ecosystems has resulted from anthropogenic influences, such as conversion to pine plantation forestry, agriculture and land development, all of which are closely related to increases in human populations. Other effects, however, have arisen from alterations in disturbance regimes that maintain the structure and function of these ecosystems. How have alterations of the disturbance regime altered the physiognomy of ‘old-growth’ stands, and what are the implications for ecosystem conservation and restoration? Methods: In contrast to models that emphasize close interactions among the vertically complex strata, we develop a conceptual phenomenological model for the physiognomic structure of Pinus palustris stands. We relate two natural disturbances (tropical storms and fire) that affect different stages of the life cycle to different aspects of the physiognomic structure. We then compare overstorey stand structure and ground cover composition of two old-growth longleaf stands near the extremes of different composite disturbance regimes: the Wade Tract (frequent hurricanes and fire) and the Boyd Tract (infrequent hurricanes and long-term fire exclusion). Results: We predict that tropical storms and fires have different effects on stand physiognomy. Tropical storms are periodic, and sometimes intense, whereas fires are more frequent and less intense. Hurricanes directly influence the overstorey via wind-caused damage and mortality, and indirectly influence the herb layer by altering the spatial distribution of shading and litter accumulation. Fire exerts direct effects on juvenile stages and indirect effects on the herb layer via fine fuel consumption and selective mortality of potential competitors of P. palustris juveniles. These differences in effects of disturbances can result in widely different physiognomies for P. palustris stands. Finally, some global climate change scenarios have suggested that changes may occur in tropical storm and fire regimes, altering frequency and severity. Such changes may greatly affect pine stands, and ultimately entire pine savanna ecosystems. Conclusions: Our phenomenological model of disturbance regimes in Pinus palustris old-growth produces very different physiognomies for different disturbances regimes that reflect natural process and human management actions. This model can be used to derive restoration strategies for pine savannas that are linked to reinstitution of important ecological processes rather than specific physiognomic states.

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Calibrating remotely sensed chlorophyll-a data by using penalized regression splines

Clarke, ED Speirs, DC Heath, MR Wood, SN Gurney, WSC Holmes, SJ


The distribution and biomass of phytoplankton in the upper layers of the ocean are important indicators of productivity and carbon cycling. Large scale perturbations in phytoplankton are linked to global climate change, so accurate monitoring is increasingly important. The chlorophyll-a pigment concentration in the water is routinely measured as an index of algal biomass. Direct water sampling from ships and moorings provides accurate data, but woefully poor spatial and temporal coverage of the oceans. In contrast, multispectral sea surface reflectance data from orbiting satellite-borne sensors, which in principle can be used to derive pigment concentration, give the prospect of globally detailed spatial and temporal coverage. Unfortunately, there are some locally variable confounding factors, which the algorithms for converting reflectance data to ocean chlorophyll-a concentration do not take into account. Hence, statistical methods are needed to obtain accurate predictions of chlorophyll-a. concentration by using data from both these sources. We use penalized regression splines to model water sample data as a three-dimensional function of satellite measurements, seabed depth and time of year. The models are effectively complex calibrations of the satellite data against the bottle data. We compare the results by using thin plate regression splines and tensor product splines using generalized cross-validation to choose the relative amounts of smoothing for each of the covariates. Since the thin plate spline penalty functional is isotropic, this requires the introduction of two scaling parameters, which are also chosen by generalized cross-validation, to scale the covariates relatively to one another. The tensor product spline smooths each covariate appropriately by use of separate smoothing parameters for each covariate. The models are tested by application to data from the north-east Atlantic, first randomly subsampling the data to achieve even coverage over the entire region. Both approaches perform equally well, achieving R-2 approximate to 65%, both for the data that are used to fit the model and for a validation data set. Of particular concern in this application is that monthly predictions from the models should be biologically plausible over the whole region, describing the broad regional features that are apparent in the satellite data and extrapolating sensibly where satellite data are not available. To achieve this, the satellite data must be one of the covariates in the model; spatiotemporal covariates alone are not sufficient to extrapolate sensibly into areas where no data are available.

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Coastal processes and morphological change in the Dunwich-Sizewell area, Suffolk, UK

Pye, K Blott, SJ


The Suffolk coast around Dunwich and Sizewell has experienced major changes during the past 2000 years, with significant loss of land caused by marine erosion. Against a background of projected acceleration in sea level rise and storminess resulting from global climate change, concern has been expressed that present coastal defences may become unsustainable in the medium to longer term, and that the survival of internationally important wildlife habitats is under threat. This paper examines the past coastal evolution in the light of natural processes, and provides a discussion of future management options. Based on analysis of historical maps, charts, air photographs, and ground survey data, it is shown that rates of coastal erosion have actually been much lower in the last 50 years than historically, and at present there is little scientific evidence to support a case for large-scale managed realignment or abandonment of flood and coastal defences. However, in some areas, notably the very northern end of the Minsmere barrier and the middle part of the Dunwich-Walberswick barrier, local realignment and/or construction of stronger secondary flood defences are required to establish a coastal condition that is more in equilibrium with current processes, and to provide adequate protection against marine flooding even under present climatic and sea level conditions.

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Impact of climate change on the regional hydrology - Scenario-based modelling studies in the German Rhine catchment

Menzel, L Thieken, AH Schwandt, D Burger, G

NATURAL HAZARDS 38:1-2 45-61

The aim of the study is an impact analysis of global climate change on regional hydrology with special emphasis on discharge conditions and floods. The investigations are focussed on the major part of the German Rhine catchment with a drainage area of approx. 110,000 km(2). This area is subdivided into 23 subcatchments. In a first step, the hydrological model HBV-D serves to simulate runoff conditions under present climate for the individual subbasins. Simulated, large scale atmospheric fields, provided by two different Global Circulation Models (GCMs) and driven by the emission scenario IS95a (“business as usual”) are then used as input to the method of expanded downscaling (EDS). EDS delivers local time series of scenario climate as input to HBV-D. In a final step, the investigations are focussed on the assessment of possible future runoff conditions under the impact of climate change. The study indicates a potential increase in precipitation, mean runoff and flood discharge for small return intervals. However, the uncertainty range that originates from the application of the whole model chain and two different GCMs is high. This leads to high cumulative uncertainties, which do not allow conclusions to be drawn on the development of future extreme floods.

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Land cover change and its impacts on soil C and N in two watersheds in the center of the Qinghai-Tibetan Plateau

Wang, GX Wang, YB Qian, J Wu, QB


The responses of the ecosystems along the 0 degrees C mean annual isotherm to global climate change are intense and involve significant changes in land cover at the water shed scale. This paper evaluates changes in land cover in the center of Qinghai-Tibet, the headwater region of the Yangtze and Yellow Rivers, on the basis of two sets of remote sensing data (1986 and 2000) and field investigations. Over a period of 15 years, 23% and 34% of alpine cold swamp were recently turned into alpine cold meadow or alpine cold steppe, and decreased in area by 25.9% and 42.7% in the headwater areas of the Yellow and Yangtze Rivers, respectively. Moreover, more than 20% of high-coverage alpine cold meadow and alpine cold steppe were converted to lower-coverage alpine cold meadow (vegetation coverage > 80%) and alpine cold steppe (vegetation coverage > 50%). Desertified land increased by 18.4% (bare rocks and sparse land) and 31.1% (sandy land) in the headwater area of the Yellow River and by 17.8%-18.5% in the headwater area of the Yangtze River. Land cover change in this region involves a complex transition between land cover types, which have a great influence on soil nutrients and the soil organic carbon (SOC) pool. Land cover changes in the study area over the 15-year study period led to the loss of 336.6 Gg of SOC, of which 61.6% were lost by alpine cold swamp transformation, and a total nitrogen (N) loss of 26.9 Gg, of which 81.9% occurred in the headwater area of the Yangtze River. The changes in the carbon and nitrogen cycles have serious implications for greenhouse gas emissions due to land cover change caused by climate warming in the Qinghai-Tibetan Plateau.

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Modeling generator power plant portfolios and pollution taxes in electric power supply chain networks: A transportation network equilibrium transformation

Wu, K Nagurney, A Liu, ZG Stranlund, JK


Global climate change and fuel security risks have encouraged international and regional adoption of pollution/carbon taxes. A major portion of such policy interventions is directed at the electric power industry with taxes applied according to the type of fuel used by the power generators in their power plants. This paper proposes an electric power supply chain network model that captures the behavior of power generators faced with a portfolio of power plant options and subject to pollution taxes. We demonstrate that this general model can be reformulated as a transportation network equilibrium model with elastic demands and qualitatively analyzed and solved as such. The connections between these two different modeling schemas is done through finite-dimensional variational inequality theory. The numerical examples illustrate how changes in the pollution/carbon taxes affect the equilibrium electric power supply chain network production outputs, the transactions between the various decision-makers the demand market prices, as well as the total amount of carbon emissions generated. (c) 2006 Elsevier Ltd. All rights reserved.

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Effects of river discharge, temperature, and future climates on energetics and mortality of adult migrating Fraser River sockeye salmon

Rand, PS Hinch, SG Morrison, J Foreman, MGG MacNutt, MJ Macdonald, JS Healey, MC Farrell, AP Higgs, DA


We evaluated the effects of past and future trends in temperature and discharge in the Fraser River on the migratory performance of the early Stuart population of sockeye salmon Oncorhynchus nerka. Fish of lower condition exhibited disproportionately higher mortality during the spawning run, elucidating a critical link between energetic condition and a fish’s ability to reach the spawning grounds. We simulated spawning migrations by accounting for energetic demands for an average individual in the population from the time of entry into the Fraser River estuary to arrival on the spawning grounds (about 1,200 km upstream) and estimated energy expenditures for the average migrant during 1950-2001. The model output indicates relatively high interannual variability in migration energy use and a marked increase in energy demands in recent years related to unusually high discharges (e.g., 1997) and warmer than average water temperature (e.g., 1998). We examined how global climate change might effect discharge, water temperature, and the energy used by sockeye salmon during their spawning migration. Expected future reductions in peak flows during freshets markedly reduced transit time to the spawning ground, representing a substantial energy savings that compensated for the effect of the increased metabolic rate resulting from exposure to warmer river temperatures. We suggest that such watershed-scale compensatory mechanisms may be critical to the long-term sustainability of Pacific salmon, given expected changes in climate. However, such compensation will probably only be applicable to some stocks and may be limited under extremely high temperatures where nonenergetic factors such as disease and stress may play a more dominant role in defining mortality. Our results further indicate that a long-term decline in the mean mass of adult sockeye salmon completing their marine residency could erode their migratory fitness during the river migration and hence jeopardize the sustainability of sockeye salmon and the fishery that targets them.

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