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  • 1
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    Isotopic signals (18O, 2H, 3H) of six major rivers draining the pan-Arctic watershed (2012)
    Wiley
    Details
    Publication Date: 2012-03-22
    Description: We present the results of a 4-year collaborative sampling effort that measured δ18O, δ2H values and 3H activities in the six largest Arctic rivers (the Ob, Yenisey, Lena, Kolyma, Yukon and Mackenzie). Using consistent sampling and data processing protocols, these isotopic measurements provide the best available δ2H and 3H estimates for freshwater fluxes from the pan-Arctic watershed to the Arctic Ocean and adjacent seas, which complements previous efforts with δ18O and other tracers. Flow-weighted annual δ2H values vary from −113.3‰ to −171.4‰ among rivers. Annual 3H fluxes vary from 0.68 g to 4.12 g among basins. The integration of conventional hydrological and landscape observations with stable water isotope signals, and estimation of areal yield of 3H provide useful insights for understanding water sources, mixing and evaporation losses in these river basins. For example, an inverse correlation between the slope of the δ18O-δ2H relation and wetland extent indicates that wetlands play comparatively important roles affecting evaporation losses in the Yukon and Mackenzie basins. Tritium areal yields (ranging from 0.760 to 1.695 10−6 g/km2 per year) are found to be positively correlated with permafrost coverage within the studied drainage basins. Isotope-discharge relationships demonstrate both linear and nonlinear response patterns, which highlights the complexity of hydrological processes in large Arctic river basins. These isotope observations and their relationship to discharge and landscape features indicate that basin-specific characteristics significantly influence hydrological processes in the pan-Arctic watershed.
    Print ISSN: 0886-6236
    Electronic ISSN: 1944-9224
    Topics: Biology , Chemistry and Pharmacology , Geography , Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Stream denitrification across biomes and its response to anthropogenic nitrate loading (2008)
    Nature Publishing Group (NPG)
    Details
    Publication Date: 2008-03-14
    Description: Anthropogenic addition of bioavailable nitrogen to the biosphere is increasing and terrestrial ecosystems are becoming increasingly nitrogen-saturated, causing more bioavailable nitrogen to enter groundwater and surface waters. Large-scale nitrogen budgets show that an average of about 20-25 per cent of the nitrogen added to the biosphere is exported from rivers to the ocean or inland basins, indicating that substantial sinks for nitrogen must exist in the landscape. Streams and rivers may themselves be important sinks for bioavailable nitrogen owing to their hydrological connections with terrestrial systems, high rates of biological activity, and streambed sediment environments that favour microbial denitrification. Here we present data from nitrogen stable isotope tracer experiments across 72 streams and 8 regions representing several biomes. We show that total biotic uptake and denitrification of nitrate increase with stream nitrate concentration, but that the efficiency of biotic uptake and denitrification declines as concentration increases, reducing the proportion of in-stream nitrate that is removed from transport. Our data suggest that the total uptake of nitrate is related to ecosystem photosynthesis and that denitrification is related to ecosystem respiration. In addition, we use a stream network model to demonstrate that excess nitrate in streams elicits a disproportionate increase in the fraction of nitrate that is exported to receiving waters and reduces the relative role of small versus large streams as nitrate sinks.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Mulholland, Patrick J -- Helton, Ashley M -- Poole, Geoffrey C -- Hall, Robert O -- Hamilton, Stephen K -- Peterson, Bruce J -- Tank, Jennifer L -- Ashkenas, Linda R -- Cooper, Lee W -- Dahm, Clifford N -- Dodds, Walter K -- Findlay, Stuart E G -- Gregory, Stanley V -- Grimm, Nancy B -- Johnson, Sherri L -- McDowell, William H -- Meyer, Judy L -- Valett, H Maurice -- Webster, Jackson R -- Arango, Clay P -- Beaulieu, Jake J -- Bernot, Melody J -- Burgin, Amy J -- Crenshaw, Chelsea L -- Johnson, Laura T -- Niederlehner, B R -- O'Brien, Jonathan M -- Potter, Jody D -- Sheibley, Richard W -- Sobota, Daniel J -- Thomas, Suzanne M -- England -- Nature. 2008 Mar 13;452(7184):202-5. doi: 10.1038/nature06686.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Environmental Sciences Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA. mulhollandpj@ornl.gov〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/18337819" target="_blank"〉PubMed〈/a〉
    Keywords: Agriculture ; Bacteria/metabolism ; Computer Simulation ; *Ecosystem ; Geography ; *Human Activities ; Nitrates/*analysis/*metabolism ; Nitrites/*analysis/*metabolism ; Nitrogen/analysis/metabolism ; Nitrogen Isotopes ; Plants/metabolism ; Rivers/*chemistry ; Urbanization
    Print ISSN: 0028-0836
    Electronic ISSN: 1476-4687
    Topics: Biology , Chemistry and Pharmacology , Medicine , Natural Sciences in General , Physics
    Published by Nature Publishing Group (NPG)
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  • 3
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    A major ecosystem shift in the northern Bering Sea (2006)
    American Association for the Advancement of Science (AAAS)
    Details
    Publication Date: 2006-03-11
    Description: Until recently, northern Bering Sea ecosystems were characterized by extensive seasonal sea ice cover, high water column and sediment carbon production, and tight pelagic-benthic coupling of organic production. Here, we show that these ecosystems are shifting away from these characteristics. Changes in biological communities are contemporaneous with shifts in regional atmospheric and hydrographic forcing. In the past decade, geographic displacement of marine mammal population distributions has coincided with a reduction of benthic prey populations, an increase in pelagic fish, a reduction in sea ice, and an increase in air and ocean temperatures. These changes now observed on the shallow shelf of the northern Bering Sea should be expected to affect a much broader portion of the Pacific-influenced sector of the Arctic Ocean.〈br /〉〈span class="detail_caption"〉Notes: 〈/span〉Grebmeier, Jacqueline M -- Overland, James E -- Moore, Sue E -- Farley, Ed V -- Carmack, Eddy C -- Cooper, Lee W -- Frey, Karen E -- Helle, John H -- McLaughlin, Fiona A -- McNutt, S Lyn -- New York, N.Y. -- Science. 2006 Mar 10;311(5766):1461-4.〈br /〉〈span class="detail_caption"〉Author address: 〈/span〉Marine Biogeochemistry and Ecology Group, Department of Ecology and Evolutionary Biology, 10515 Research Drive, Building A, Suite 100, University of Tennessee, Knoxville, TN 37932, USA. jgrebmei@utk.edu〈br /〉〈span class="detail_caption"〉Record origin:〈/span〉 〈a href="http://www.ncbi.nlm.nih.gov/pubmed/16527980" target="_blank"〉PubMed〈/a〉
    Keywords: Animals ; Arctic Regions ; Ducks ; *Ecosystem ; Fishes ; Geologic Sediments/chemistry ; *Ice Cover ; Oxygen/analysis ; Pacific Ocean ; Population Dynamics ; Temperature ; Walruses ; Whales
    Print ISSN: 0036-8075
    Electronic ISSN: 1095-9203
    Topics: Biology , Chemistry and Pharmacology , Computer Science , Medicine , Natural Sciences in General , Physics
    Published by American Association for the Advancement of Science (AAAS)
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  • 4
    Electronic Resource
    Electronic Resource
    Stable carbon isotope ratio variations in marine macrophytes along intertidal gradients (1988)
    Springer
    Oecologia 77 (1988), S. 238-241 
    Details
    ISSN: 1432-1939
    Keywords: Seagrasses ; Phyllospadix ; δ13C ; Halosaccion ; Egregia
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Summary The hypothesis that relative water motion and boundary layer diffusion processes affect carbon isotope ratios of aquatic plants was tested in tidal pool and surge zone comparisons of the surfgrass Phyllospadix spp. No evidence was found that submerged plants growing in still upper tidal pools were isotopically different from those growing submerged in lower tidal surge zones. Significant decreases in 13C/12C ratios for plants growing emersed in the intertidal may have been caused by uptake of atmospheric carbon dioxide. Marine algae (Egregia menziesii and Halosaccion americanum) growing at the same location and tidal elevations as the seagrasses showed somewhat different isotopic fractionation patterns, suggesting that causes of isotopic variability in the seagrasses were not necessarily the same as those in the two marine algae.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00379192
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  • 5
    Electronic Resource
    Electronic Resource
    Iodine-129 and plutonium isotopes in Arctic kelp as historical indicators of transport of nuclear fuel-reprocessing wastes from mid-to-high latitudes in the Atlantic Ocean (1998)
    Springer
    Marine biology 131 (1998), S. 391-399 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Iodine-129:iodine-127 ratios were determined using accelerator mass spectrometry in 34 Arctic marine algae collected between 1930 and 1993. A smaller set (5) of marine algae were also analyzed mass spectrometrically to determine plutonium-isotope ratios. The 129I:127I ratio increased as much as three orders of magnitude from a mean of 〈1×10−11 (atom/atom) in the pre-nuclear era (before 1945) to nearly 1000×10−11 in 1993 for marine algae collected from the Novaya Zemlya archipelago separating the Barents and Kara Seas. The predominant basis for the higher ratios in the Novaya Zemlya kelps appears to be upcurrent sources of 129I from nuclear fuel-reprocessing facilities at Sellafield (UK) and La Hague (France). Relatively high 241Pu:239Pu ratios (compared to observed bomb fallout at boreal latitudes, decay corrected to the date of collection) also corroborate the influence of non-fallout sources. The small size of the data set precludes determining if there are significant contributions of 129I and other radionuclides from Russian sources. In contrast, marine algae collected between 1969 and 1993 in the Bering, Beaufort and East Siberian Seas had much lower 129I:127I ratios (mean=14.04×10−11±3.15 SD) than those observed in the European Arctic. The narrow range of ratios in Ameriasian Arctic kelps, and the modest change over that time period, indicate that there were no major contributions of non-fallout 129I to North American Arctic surface waters at the time that the algae were collected. The potential for timing the transport of fuel-reprocessed 129I through analysis of additional archived samples is outlined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s002270050332
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  • 6
    Electronic Resource
    Electronic Resource
    Depletion of heavy isotopes of oxygen and hydrogen in tissue water of intertidal plants: implications for water economy (1989)
    Springer
    Marine biology 101 (1989), S. 397-400 
    Details
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Stable oxygen and hydrogen isotope ratios of leaf and thallus water of the intertidal seagrasses Phyllospadix scouleri and P. torreyi and the marine algae Egregia menziesii, Gelidium coulteri, and Corallina vancouverensis from three locations in California, USA, were determined in 1987. Compared with subtidal seawater, most plant-water samples were depleted in the heavy isotopes 18O and deuterium. Depletion of heavy isotopes was greatest in plants growing at the highest intertidal elevations. This was an unexpected result, because enrichment of heavy isotopes occurs during evapotranspiration in terrestrial plants. Two possible mechanisms for this isotopic depletion are proposed: direct uptake of heavy isotope-depleted water vapor and preferential diffusion of 16O and 1H into littoral plants from water remaining in the intertidal zone at low tide.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00428136
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  • 7
    Electronic Resource
    Electronic Resource
    Forest soil carbon inventories and dynamics along an elevation gradient in the southern Appalachian Mountains (1999)
    Springer
    Biogeochemistry 45 (1999), S. 115-145 
    Details
    ISSN: 1573-515X
    Keywords: climate ; C/N ratios ; light-fraction organic matter ; particulate organic matter ; soil C turnover
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Soil organic carbon (SOC) was partitioned between unprotected and protected pools in six forests along an elevation gradient in the southern Appalachian Mountains using two physical methods: flotation in aqueous CaCl2 (1.4 g/mL) and wet sieving through a 0.053 mm sieve. Both methods produced results that were qualitatively and quantitatively similar. Along the elevation gradient, 28 to 53% of the SOC was associated with an unprotected pool that included forest floor O-layers and other labile soil organic matter (SOM) in various stages of decomposition. Most (71 to 83%) of the C in the mineral soil at the six forest sites was identified as protected because of its association with a heavy soil fraction (〉1.4 g/mL) or a silt-clay soil fraction. Total inventories of SOC in the forests (to a depth of 30 cm) ranged from 384 to 1244 mg C/cm2. The turnover time of the unprotected SOC was negatively correlated (r=−0.95, p〈0.05) with mean annual air temperature (MAT) across the elevation gradient. Measured SOC inventories, annual C returns to the forest floor, and estimates of C turnover associated with the protected soil pool were used to parameterize a simple model of SOC dynamics. Steady-state predictions with the model indicated that, with no change in C inputs, the low-(235–335 m), mid-(940–1000 m), and high-(1650–1670 m) elevation forests under study might surrender ≈ 40 to 45% of their current SOC inventory following a 4°C increase in MAT. Substantial losses of unprotected SOM as a result of a warmer climate could have longterm impacts on hydrology, soil quality, and plant nutrition in forest ecosystems throughout the southern Appalachian Mountains.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF01106778
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  • 8
    Electronic Resource
    Electronic Resource
    Organic carbon isotope ratios (δ13C) of Arctic Amerasian Continental shelf sediments (2000)
    Springer
    International journal of earth sciences 89 (2000), S. 522-532 
    Details
    ISSN: 1437-3262
    Keywords: Arctic Amerasian shelf Sediment carbon and nitrogen isotopes
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences
    Notes: Abstract. Organic matter origins are inferred from carbon isotope ratios (δ13C) in recent continental shelf sediments and major rivers from 465 locations from the north Bering-Chukchi-East Siberian-Beaufort Sea, Arctic Amerasia. Generally, there is a cross-shelf increase in δ13C, which is due to progressive increased contribution seaward of marine-derived organic carbon to surface sediments. This conclusion is supported by the correlations between sediment δ13C, OC/N, and δ15N. The sources of total organic carbon (TOC) to the Amerasian margin sediments are primarily from marine water-column phytoplankton and terrigenous C3 plants constituted of tundra taiga and angiosperms. In contrast to more temperate regions, the source of TOC from terrigenous C4 and CAM plants to the study area is probably insignificant because these plants do not exist in the northern high latitudes. The input of carbon to the northern Alaskan shelf sediments from nearshore kelp community (Laminaria solidungula) is generally insignificant as indicated by the absence of high sediment δ13C values (–16.5 to –13.6‰) which are typical of the macrophytes. Our study suggests that the isotopic composition of sediment TOC has potential application in reconstructing temporal changes in delivery and accumulation of organic matter resulting from glacial–interglacial changes in sea level and environments. Furthermore, recycling and advection of the extensive deposits of terrestrially derived organic matter from land, or the wide Amerasian margin, could be a mechanism for elevating total CO2 and pCO2 in the Arctic Basin halocline.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s005310000121
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  • 9
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    Nitrous oxide emission from denitrification in stream and river networks [Environmental Sciences] (2011)
    National Academy of Sciences
    Details
    Publication Date: 2011-01-05
    Description: Nitrous oxide (N2O) is a potent greenhouse gas that contributes to climate change and stratospheric ozone destruction. Anthropogenic nitrogen (N) loading to river networks is a potentially important source of N2O via microbial denitrification that converts N to N2O and dinitrogen (N2). The fraction of denitrified N that escapes as N2O rather than N2 (i.e., the N2O yield) is an important determinant of how much N2O is produced by river networks, but little is known about the N2O yield in flowing waters. Here, we present the results of whole-stream 15N-tracer additions conducted in 72 headwater streams draining multiple land-use types across the United States. We found that stream denitrification produces N2O at rates that increase with stream water nitrate (NO3−) concentrations, but that
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
    Published by National Academy of Sciences
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  • 10
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    Forest soil carbon inventories and dynamics along an elevation gradient in the southern Appalachian Mountains (1999)
    Springer
    Details
    Publication Date: 1999-05-01
    Print ISSN: 0168-2563
    Electronic ISSN: 1573-515X
    Topics: Chemistry and Pharmacology , Geosciences
    Published by Springer
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