Response of a Tundra Ecosystem to Elevated Atmospheric Carbon Dioxide and CO2-induced Climate Change, Annual Technical Report PDF Download
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![Response of a Tundra Ecosystem to Elevated Atmospheric Carbon Dioxide and CO2-induced Climate Change. [Annual Report]. PDF](https://books.google.com/books/content/images/frontcover/epQNkAEACAAJ?fife=w80-h100)
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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.
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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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Author: Walter C. Oechel
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Pages : 9
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Pages : 34
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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. Measurements were made on small (e.g. 0.5 m2) plots using a portable gas-exchange system and cuvette. The sample design allowed frequent measurements of net CO2 exchange and respiration over diurnal and seasonal cycles, and a large spatial extent that incorporated both locally and regionally diverse tundra surface types. Measurements both within and between ecosystem types typically extended over soil water table depth and temperature gradients, allowing for the indirect analysis of the effects of anticipated climate change scenarios on net CO2 exchange. In situ experiments provided a direct means for testing hypotheses.
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Pages : 92
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Our past research shows that arctic tussock tundra responds to elevated atmospheric CO2 with marked increases in net ecosystem carbon flux and photosynthetic rates. However, at ambient temperatures and nutrient availabilities, homeostatic adjustments result in net ecosystem flux rates dropping to those found a contemporary CO2 levels within three years. Evidence for ecosystem-level acclimation in the first season of elevated CO2 exposure was found in 1987. Photosynthetic rates of Eriophorum vaginatum, the dominant species, adjusts to elevated CO2 within three weeks. Past research also indicates other changes potentially important to ecosystem structure and function. Elevated CO2 treatment apparently delays senescence and increases the period of positive photosynthetic activity. Recent results from the 1987 field season verify the results obtained in the 1983--1986 field seasons: Elevated CO2 resulted in increased ecosystem-level flux rates. Regressions fitted to the seasonal flux rates indicate an apparent 10 d extension of positive CO2 uptake reflecting a delay of the onset of plant dormancy. This delay in senescence could increase the frost sensitivity of the system. Major end points proposed for this research include the effects of elevated CO2 and the interaction of elevated atmospheric CO2 with elevated soil temperature and increased nutrient availability on: (1) Net ecosystem CO2 flux; (2) Net photosynthetic rates; (3) Patterns and resource controls on homeostatic adjustment in the above processes to elevated CO2; (4) Plant-nutrient status, litter quality, and forage quality; (5) Soil-nutrient status; (6) Plant-growth pattern and shoot demography.
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