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  • Wiley  (165)
  • Public Library of Science (PLoS)  (30)
  • American Association for the Advancement of Science (AAAS)  (17)
  • 1
    Publication Date: 2014-06-01
    Description: The Lancang/Mekong River Basin is presently undergoing a period of rapid hydropower development. In its natural undeveloped state, the river transports about 160 million metric tons of sediment per year, maintaining the geomorphologic features of the basin, sustaining habitats, and transporting the nutrients that support ecosystem productivity. Despite the importance of sediment in the river, currently little attention is being paid to reservoir sediment trapping. This study is devoted to assessing the potential for managing sediment and its impact on energy production in the Se San, Sre Pok and Se Kong tributaries of the Mekong River. These tributaries drain a set of adjacent watersheds that are important with respect to biodiversity and ecological productivity, and serve as a significant source of flow and sediment to the mainstream Mekong River. A daily sediment transport model is used to assess tradeoffs among energy production and sediment and flow regime alteration in multiple reservoir systems. This study finds that eventually about 40%-80% of the annual suspended sediment load may be trapped in reservoirs. Clearly, these reservoirs will affect the rivers' sediment regimes. However, even after 100 years of simulated sedimentation, reservoir storage capacities and hydropower production at most reservoir sites are not significantly reduced. This suggests that the strongest motivation for implementing measures to reduce trapped sediment is their impact not on hydropower production but on fish migration and survival and on sediment dependent ecosystems such as the Vietnam Delta and Cambodia's Tonle Sap Lake.
    Print ISSN: 0043-1397
    Electronic ISSN: 1944-7973
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
    Publication Date: 2014-03-23
    Description: Humic-like substances (HULIS) are a complex group of relatively high molecular weight organic compounds which contribute considerably to the mass of organic carbon (OC) and influence the light-absorbing properties of aerosols. In this work, HULIS were investigated for the first time in the high-Arctic atmosphere, focusing on the chemical characterization and mass contribution of HULIS to the total suspended particle (TSP) mass using weekly aerosol samples collected at Station Nord, north east Greenland every 4 th week during 2010. Average HULIS-C concentration was 11 ng C m -3 during the darker months (November - April) and 4 ng C m -3 during the other months (May - October) with an annual mass concentration of 0.02 ± 0.01 µg m -3 . HULIS-C contributed to 3 - 16 % of WSOC whereas HULIS accounted for 0.7 - 4.1 % of TSP mass, with TSP typically below 1.0 µg m -3 . Concentrations of OC, water soluble organic carbon (WSOC), HULIS, selected HULIS functional groups (carboxylic acids, aromatic carboxylic acids and organosulfates) and levoglucosan overlapped with the typical Arctic haze pattern with elevated concentrations during winter - early spring. The aromatic carboxylic acid portion accounted for a larger share of total carboxylic acid of HULIS during the darker months (7%) compared to the brighter months (3%). The more abundant aromatic carboxylic acid functional groups and the moderate correlation between HULIS and levoglucosan concentrations during the darker months both indicate that biomass burning aerosols and thereby emissions of aromatic compounds could contribute to HULIS in the Arctic, especially during late winter. During the brighter months, relatively higher average molecular weight (AMW) of HULIS was observed.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 3
    Publication Date: 2014-01-29
    Description: [1]  Airborne observations from the CalNex campaign in May and June 2010 are used to investigate the role of ammonia (NH 3 ) in fine particulate matter (PM 2.5 ) formation and surface air quality in California and test the key processes relevant to inorganic aerosol formation in the GEOS-Chem model. Concentrations of ammonia throughout California, sulfur dioxide (SO 2 ) in the Central Valley, and ammonium nitrate in the Los Angeles (LA) area are underestimated several-fold in the model. We find that model concentrations are relatively insensitive to uncertainties in gas-particle partitioning and deposition processes in the region. Conversely, increases to anthropogenic livestock ammonia emissions (by a factor of 5) and anthropogenic sulfur dioxide emissions in the Central Valley (by a factor of 3 - 10) and a reduction of anthropogenic NO x emissions (by 30 %), substantially reduces the bias in the simulation of gases (SO 2 , NH 3 , HNO 3 ) throughout California and PM 2.5 near LA, although the exact magnitudes of emissions in the region remain uncertain. Using these modified emissions, we investigate year-round PM 2.5 air quality in California. The model reproduces the wintertime maximum in surface ammonium nitrate concentrations in the Central Valley (regional mean concentrations are 3 times higher in December than in June), associated with lower planetary boundary layer heights and colder temperatures, and the wintertime minimum in the LA region (regional mean concentrations are 2 times higher in June than December) associated with ammonia-limitation. Year-round, we attribute at least 50 % of the inorganic PM 2.5 mass simulated throughout California to anthropogenic ammonia emissions.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 4
    Publication Date: 2015-09-25
    Description: The influence and fate of westward-propagating eddies that impinge on the Kuroshio were observed with pressure sensor-equipped inverted echo sounders (PIESs) deployed east of Taiwan and northeast of Luzon. Zero-lag correlations between PIES-measured acoustic travel times and satellite-measured sea surface height anomalies (SSHa), which are normally negative, have lower magnitude towards the west, suggesting the eddy-influence is weakened across the Kuroshio. The observational data reveal that impinging eddies lead to seesaw-like SSHa and pycnocline depth changes across the Kuroshio east of Taiwan, whereas analogous responses are not found in the Kuroshio northeast of Luzon. Anticyclones intensify sea surface and pycnocline slopes across the Kuroshio, while cyclones weaken these slopes, particularly east of Taiwan. During the 6-month period of overlap between the two PIES arrays, only one anticyclone affected the pycnocline depth first at the array northeast of Luzon and 21 days later in the downstream Kuroshio east of Taiwan.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 5
    Publication Date: 2014-10-25
    Description: In California, emission control strategies have been implemented to reduce air pollutants. Here we estimate the changes in nitrogen oxides (NO x  = NO + NO 2 ) emissions in 2005-2010 using a state-of-the-art four-dimensional variational (4D-Var) approach. We separately and jointly assimilate surface NO 2 concentrations and tropospheric NO 2 columns observed by Ozone Monitoring Instrument (OMI) into the regional-scale STEM chemical transport model on a 12 × 12 km 2 horizontal resolution grid in May 2010. The assimilation generates grid-scale top-down emission estimates, and the updated chemistry fields are evaluated with independent aircraft measurements during the NOAA CalNex field experiment. The emission estimates constrained only by NO 2 columns, only by surface NO 2 , and by both indicate statewide reductions of 26%, 29%, 30% from ~0.3 Tg N/year in the base year of 2005, respectively. The spatial distributions of the emission changes differ in these cases, which can be attributed to many factors including the differences in the observation sampling strategies and their uncertainties, as well as those in the sensitivities of column and surface NO 2 with respect to NO x emissions. The updates in California's NO x emissions reduced the mean error in modeled surface ozone in the western US, even though the uncertainties in some urban areas increased due to their NO x -saturated chemical regime. The statewide reductions in NO x emissions indicated from our observationally-constrained emission estimates are also reflected in several independently-developed inventories: ~30% in the California Air Resources Board (CARB) bottom-up inventory, ~4% in the 2008 National Emission Inventory, and ~20% in the annual-mean top-down estimates by Lamsal et al. using the global GEOS-Chem model and OMI NO 2 columns. Despite the grid-scale differences among all top-down and bottom-up inventories, they all indicate stronger emission reductions in the urban regions. This study shows the potential of using space/ground-based monitoring data and advanced data assimilation approach to timely and independently update NO x emission estimates on a monthly scale and at a fine grid resolution. The well-evaluated results here suggest that these approaches can be applied more broadly.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
    Publication Date: 2014-12-24
    Description: Hypoxia is commonly defined as dissolved oxygen (DO) concentrations below 2 mg L −1 . The occurrence of hypoxia within freshwater and marine ecosystems is stressful for respiring organisms across all trophic levels, leading to changes in community diversity, altered trophic interactions, and decreased physiological fitness of organisms. Whereas many field studies have identified changes in animal diets and species distribution due to hypoxia, the behavioral changes that drive these patterns are poorly understood. Additionally, many laboratory studies that subject organisms to a fixed DO concentration may not be entirely applicable to natural environments because many organisms are capable of sensing and avoiding hypoxic areas. Herein we describe two experimental tank systems developed to study the effects of oxygen gradients on fish behavior. These systems are novel in that 1) fish and potentially other aquatic organisms can freely move between hypoxic and well oxygenated areas, 2) the thermocline or oxycline is easily adjusted for multiple treatment levels, 3) they are large enough to study fish behavior on an ecological scale, and 4) are constructed with affordable, readily available materials and are easily maintained. In both systems, we were able to conduct fish behavior studies under stable thermal and oxic stratification comparable to conditions found in temperate freshwater lakes.
    Electronic ISSN: 1541-5856
    Topics: Biology , Geosciences
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  • 7
    Publication Date: 2014-04-01
    Description: Patterns of migratory connectivity are a vital yet poorly understood component of the ecology and evolution of migratory birds. Our ability to accurately characterize patterns of migratory connectivity is often limited by the spatial resolution of the data, but recent advances in probabilistic assignment approaches have begun pairing stable isotopes with other sources of data (e.g., genetic and mark?recapture) to improve the accuracy and precision of inferences based on a single marker. Here, we combine stable isotopes and geographic variation in morphology (wing length) to probabilistically assign Wood Thrush (Hylocichla mustilena) captured on the wintering grounds to breeding locations. In addition, we use known-origin samples to validate our model and assess potentially important impacts of isotopic and morphological covariates (age, sex, and breeding location). Our results show that despite relatively high levels of mixing across their breeding and nonbreeding ranges, moderate levels of migratory connectivity exist along an east?west gradient. In addition, combining stable isotopes with geographic variation in wing length improved the precision of breeding assignments by 10% and 37% compared to assignments based on isotopes alone or wing length alone, respectively. These results demonstrate that geographical variation in morphological traits can greatly improve estimates of migratory connectivity when combined with other intrinsic markers (e.g., stable isotopes or genetic data). The wealth of morphological data available from museum specimens across the world represents a tremendously valuable, but largely untapped, resource that is widely applicable for quantifying patterns of migratory connectivity. # doi:10.1890/13-1091.1
    Print ISSN: 1051-0761
    Electronic ISSN: 1939-5582
    Topics: Biology
    Published by Wiley on behalf of The Ecological Society of America (ESA).
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  • 8
    Publication Date: 2015-03-01
    Description: Organosulfates are important secondary organic aerosol (SOA) components and good tracers for aerosol heterogeneous reactions. However, the knowledge of their spatial distribution, formation conditions, and environmental impact is limited. In this study, we report two organosulfates, an isoprene-derived IEPOX (2,3-epoxy-2-methyl-1,4-butanediol) sulfate and a glycolic acid (GA) sulfate, measured using the NOAA Particle Analysis Laser Mass Spectrometer (PALMS) onboard the NASA DC8 aircraft over the continental US during the DC3 and SEAC4RS campaigns. During these campaigns, IEPOX sulfate was estimated to account for 1.4% of submicron aerosol mass (or 2.2% of organic aerosol mass) on average near the ground in the southeast US, with lower concentrations in the western US (0.2-0.4%) and at high altitudes (〈0.2%). Compared to IEPOX sulfate, GA sulfate was more uniformly distributed, accounting for about 0.5% aerosol mass on average, and may be more abundant globally. A number of other organosulfates were detected; none were as abundant as these two. Ambient measurements confirmed that IEPOX sulfate is formed from isoprene oxidation and is a tracer for isoprene SOA formation. The organic precursors of GA sulfate may include glycolic acid and likely have both biogenic and anthropogenic sources. Higher aerosol acidity as measured by PALMS and relative humidity tend to promote IEPOX sulfate formation, and aerosol acidity largely drives in situ GA sulfate formation at high altitudes. This study suggests the formation of aerosol organosulfates depends not only on the appropriate organic precursors but also on emissions of anthropogenic sulfur dioxide (SO 2 ), which contributes to aerosol acidity.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 9
    Publication Date: 2015-02-12
    Description: Bacterial assemblages, especially diazotroph assemblages residing in the rhizomes and the rhizosphere soil of Miscanthus ×giganteus contribute to plant growth and nitrogen use efficiency. However, the composition of these microbial communities has not been adequately explored, nor have the potential ecological drivers for these communities been sufficiently studied. This knowledge is needed for understanding and potentially improving M. ×giganteus - microbe interactions, and further enhancing sustainability of M. ×giganteus production. In this study, cultivated M. ×giganteus from four sites in Illinois, Kentucky, Nebraska, and New Jersey were collected to examine the relative influences of soil conditions and plant compartments on assembly of the M. ×giganteus -associated microbiome. Automated ribosomal intergenic spacer (ARISA) and terminal restriction fragment length polymorphism (T-RFLP) targeting the nifH gene were applied to examine the total bacterial communities and diazotroph assemblages that reside in the rhizomes and the rhizosphere. Distinct microbial assemblages were detected in the endophytic and rhizosphere compartments. Site soil conditions had strong correlation with both total bacterial and diazotroph assemblages, but in different ways. Nitrogen treatments showed no significant effect on the composition of diazotroph assemblages in most sites. Endophytic compartments of different M . × giganteus plants tended to harbor similar microbial communities across all sites, whereas, the rhizosphere soil of different plant tended to harbor diverse microbial assemblages that were distinct among sites. These observations offer insight into better understanding of the associative interactions between M. ×giganteus and diazotrophs, and how this relationship is influenced by agronomic and edaphic factors. This article is protected by copyright. All rights reserved.
    Print ISSN: 1757-1693
    Electronic ISSN: 1757-1707
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Published by Wiley
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  • 10
    Publication Date: 2015-02-13
    Description: Population growth in cities has resulted in the rapid expansion of urbanized land. Most research and management of stream ecosystems affected by urban expansion has focused on the maintenance and restoration of biotic communities rather than their basal resources. We examined the potential for urbanization to induce bottom-up ecosystem effects by looking at its influence on dissolved organic matter (DOM) composition and bioavailability and microbial enzyme activity. We selected 113 headwater streams across a gradient of urbanization in central and southern Maine and used elemental and optical analyses, including parallel factor analysis of excitation-emission matrices, to characterize DOM composition. Results show that fluorescent and stoichiometric DOM composition changed significantly across the rural to urban gradient. Specifically, the proportion of humic-like allochthonous DOM decreased while that of more bioavailable autochthonous DOM increased in the more urbanized streams. In laboratory incubations, increased autochthonous DOM was associated with a doubling in the decay rate of dissolved organic carbon as well as increased activity of C-acquiring enzymes. These results suggest that urbanization replaces upstream humic material with more local sources of DOM that turnover more rapidly and may drive bottom-up changes in microbial communities and affect the quality and quantity of downstream DOM delivery.
    Print ISSN: 0024-3590
    Electronic ISSN: 1939-5590
    Topics: Biology , Geosciences , Physics
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