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Pages : 27

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This renewal represents a continuation request for the third year of our current research program. While this renewal follows the original research proposed, it is modified to reflect information gained in the first two years of the project. Important findings of the last 12 months include the fact that carbon is being lost as CO2 from most sites measured along a latitudinal transect from Toolik Lake to Prudhoe Bay, Alaska. All locations measured but one showed a net loss of carbon as CO2 to the atmosphere. The drier sites tended to show greater rates of carbon loss. The only site showing net carbon accumulation was the wettest tussock tundra site measured. The average rate of loss for all sites was about 180 g C m−2 y−2, or about 0.2 GtC y−1 for the circumpolar wet sedge tundra and tussock tundra combined. This observation fits well with the conclusion of Tans et al. (1990) that there is currently a high latitude terrestrial source of CO2 to the atmosphere. These high rates of carbon loss, combined with the very large store of carbon in northern ecosystems (about 500 GtC) suggested that the current rates of carbon loss from arctic tundra to the atmosphere should be further examined. This includes analysis of the temporal and spatial pattern of carbon flux, the pattern of carbon flux for different vegetation types and micro-habitats, and the moisture and temperature controls on ecosystem carbon loss to the atmosphere.

Author: Walter C. Oechel
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Languages : en
Pages : 9

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Pages : 35

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The overall objective of this research was to document current patterns of CO2 flux in selected locations of the circumpolar arctic, and to develop the information necessary to predict how these fluxes may be affected by climate change. In fulfillment of these objectives, net CO2 flux was measured at several sites on the North Slope of Alaska during the 1990--94 growing season (June--August) to determine the local and regional patterns of seasonal CO2 exchange. In addition, net CO2 flux was measured in the Russian and Icelandic Arctic to determine if the patterns of CO2 exchange observed in Arctic Alaska were representative of the circumpolar Arctic, while cold-season CO2 flux measurements were carried out during the 1993--94 winter season to determine the magnitude of CO2 efflux not accounted for by the growing season measurements. Manipulations of soil water table depth and surface temperature, which were identified from the extensive measurements as being the most important variables in determining the magnitude and direction of net CO2 exchange, were carried out during the 1993--94 growing seasons in tussock and wet sedge tundra ecosystems. Finally, measurements of CH4 flux were also measured at several of the North Slope study sites during the 1990--91 growing seasons.

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Predicting the response of northern ecosystems to increases in atmospheric CO[sub 2] and associated climatic change is important for several reasons, including the fact that northern ecosystems contain large stores of carbon, most of which is below ground and because northern ecosystems could conceivably be either sources or sinks for CO[sub 2] under future climatic and atmospheric CO[sub 2] concentrations. The carbon in northern ecosystems is equal to about 20% of the world's terrestrial carbon and about 70% of the carbon currently in the atmosphere. Eighty-three percent of this carbon is below ground in the seasonally-thawed upper soil layers and in the permanently frozen zone, the permafrost. Because of bogs and permafrost, northern ecosystems are unusual in that they can potentially store significant amounts of carbon over long time periods. Most other mature ecosystems have little capacity for long- term carbon storage. Given the right conditions, northern ecosystems can also release a significant amount of carbon. A substantial amount of the carbon stored in northern ecosystems, and much of the future storage potential, is in the tundra regions. These systems could conceivably act as sources or sinks depending on developing climatic and atmospheric conditions. Our recent work indicates that elevated CO[sub 2] alone will have little effect on carbon storage in the tundra. However, the combination of elevated atmospheric CO[sub 2] (+ 340 ppm) and air temperature (+4[degrees]C) in the absence of any change in soil water table or soil moisture content, should result in significant increases in carbon sequestering in the tundra. However, if changing climate results in a decrease in the water table and soil moisture levels, this may lead to sizeable losses of carbon from the tundra soils.

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Languages : en
Pages : 85

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OAK B188 Response of Tundra Ecosystems to Elevated Atmospheric CO2. Atmospheric CO2 is expected to double by the end of the next century. Global mean increases in surface air temperature of 1.5-4.5 C are anticipated with larger increases towards the poles predicted. Changes in CO2 levels and temperature could have major impacts on ecosystem functioning, including primary productivity, species composition, plant-animal interactions, and carbon storage. Until recently, there has been little direct information on the impact of changes in CO2 and temperature on native ecosystems. The study described here was undertaken to evaluate the effects of a 50 and 100% increase in atmospheric CO2, and a 100% increase in atmospheric CO2 coupled with a 4 C summer air temperature rise on the structure and function of an arctic tussock tundra ecosystem. The arctic contains large stores of carbon as soil organic matter, much frozen in permafrost and currently not reactive or available for oxidation and release into the atmosphere. About 10-27% of the world's terrestrial carbon occurs in arctic and boreal regions, and carbon is accumulating in these regions at the rate of 0.19 GT y−1. Mean temperature increases of 11 C and summer temperature increases of 4 C have been suggested. Mean July temperatures on the arctic coastal plain and arctic foothills regions are 4-12 C, and mean annual temperatures are -7 to -13 C (Haugen, 1982). The projected temperature increases represent a substantial elevation above current temperatures which will have major impacts on physical processes such as permafrost development and development of the active layer, and on biological and ecosystem processes such as primary productivity, carbon storage, and species composition. Extreme nutrient and temperature limitation of this ecosystem raised questions of the responsiveness of arctic systems to elevated CO2. Complex ecosystem interactions with the effects of increasing temperature and CO2 and changes in the physical environment made a priori predictions impossible. The short stature of the vegetation, the large number of individuals and species encountered in a relatively small area, and the short growing season were advantages which were thought to increase the probability that manipulation of physical conditions would result in short- and moderate-term response. These factors were coupled with an appreciation of the important role of the arctic as a major carbon store, a carbon sink, and the unpredictability of the carbon balance under future global conditions. These factors all contributed to the selection of the arctic as the first ecosystem for in situ manipulation of CO2 and temperature to determine effects on ecosystem structure and function.