Watershed studies at the Hubbard Brook Experimental Forest: Building on a long legacy of research with new approaches and sources of data     

John L. Campbell  Lindsey E. Rustad  Scott W. Bailey  Emily S. Bernhardt  Charles T. Driscoll  Mark B. Green  Peter M. Groffman  Gary M. Lovett  William H. McDowell  Kevin J. McGuire  Emma J. Rosi 《水文研究》2021,35(1):e14016

The Hubbard Brook Experimental Forest (HBEF) was established in 1955 by the U.S. Department of Agriculture, Forest Service out of concerns about the effects of logging increasing flooding and erosion. To address this issue, within the HBEF hydrological and micrometeorological monitoring was initiated in small watersheds designated for harvesting experiments. The Hubbard Brook Ecosystem Study (HBES) originated in 1963, with the idea of using the small watershed approach to study element fluxes and cycling and the response of forest ecosystems to disturbances, such as forest management practices and air pollution. Early evidence of acid rain was documented at the HBEF and research by scientists at the site helped shape acid rain mitigation policies. New lines of investigation at the HBEF have built on the long legacy of watershed research resulting in a shift from comparing inputs and outputs and quantifying pools and fluxes to a more mechanistic understanding of ecosystem processes within watersheds. For example, hydropedological studies have shed light on linkages between hydrologic flow paths and soil development that provide valuable perspective for managing forests and understanding stream water quality. New high frequency in situ stream chemistry sensors are providing insights about extreme events and diurnal patterns that were indiscernible with traditional weekly sampling. Additionally, tools are being developed for visual and auditory data exploration and discovery by a broad audience. Given the unprecedented environmental change that is occurring, data from the small watersheds at the HBEF are more relevant now than ever and will continue to serve as a basis for sound environmental decision-making.  相似文献   

Spatiotemporal Variability in Dissolved Organic Matter Composition is More Strongly Related to Bacterioplankton Community Composition than to Metabolic Capability in a Blackwater Estuarine System     

Emma K. Wear  Eric T. Koepfler  Erik M. Smith 《Estuaries and Coasts》2014,37(1):119-133

The composition and metabolic capability of bacterioplankton communities were examined over seasonal and spatial gradients and related to the source, composition, and quantity of dissolved organic matter (DOM) in the blackwater estuary Winyah Bay, Georgetown County, SC, USA and its tributary rivers. Bacterial community composition (BCC) was measured by terminal restriction fragment length polymorphism, and bacterial metabolic capability (BMC) was measured by defined substrate utilization patterns (Biolog GN2 plates). Spatial patterns were not important, despite the anticipated watershed effects and the well-documented influence of salinity gradients on estuarine bacterioplankton, but DOM, BCC, and BMC all showed varying degrees of temporal patterns; DOM-based groupings differentiated BCC samples better than spatiotemporal categories, but not BMC. BCC was closely related to properties describing DOM composition, particularly those related to DOM source (i.e., cypress swamps vs. in situ phytoplankton production, indicated by chlorophyll a, colored DOM spectral slope, α355/dissolved organic carbon (DOC), and DOC concentration), and to associated physicochemical variables, such as temperature, pH, and salinity. BMC was more strongly related to abiotic factors, such as temperature and dissolved nutrients, as well as to chlorophyll a and percent bioavailable DOC. In contrast with previous studies, BCC and BMC were significantly correlated in this highly heterotrophic estuary, suggesting that DOM source variability may select for specialist phylotypes above a background of generalists. This study, therefore, supports a causative pathway from DOM to BMC to BCC while suggesting that BCC and BMC may be simultaneously influenced by different suites of DOM characteristics and physicochemical parameters.  相似文献   

Distinction between the Youngest Toba Tuff and Oldest Toba Tuff from northern Sumatra based on the area density of spontaneous fission tracks in their glass shards     

John A. Westgate  Nicholas J.G. Pearce  Emma Gatti  Hema Achyuthan 《Quaternary Research》2014

Determination of the area density of spontaneous fission tracks (ρ_s) in glass shards of Toba tephra is a reliable way to distinguish between the Youngest Toba Tuff (YTT) and the Oldest Toba Tuff (OTT). The ρ_s values for YTT, uncorrected for partial track fading, range from 70 to 181 tracks/cm² with a weighted mean of 108 ± 5 tracks/cm², based on 15 samples. Corrected ρ_s values for YTT are in the range of 77–140 tracks/cm² with a weighted mean of 113 ± 8 tracks/cm², within the range of uncorrected ρ_s values. No significant difference in ρ_s exists between YTT samples collected from marine and continental depositional settings. The uncorrected ρ_s for OTT is 1567 ± 114 tracks/cm² so that confusion with YTT is unlikely.  相似文献   

Origin,evolution and anatomy of silt‐prone submarine external levées     

Emma A. Morris  David M. Hodgson  Rufus L. Brunt  Stephen S. Flint 《Sedimentology》2014,61(6):1734-1763

Submarine external levées are constructional features that develop outside slope channel systems, and are a volumetrically significant component of continental margins. However, detailed observations of their process sedimentology and depositional architecture are rare. Extensive exposures of external levées at multiple stratigraphic intervals and well‐constrained palaeogeographic positions in the Fort Brown Formation, Karoo Basin, South Africa, have been calibrated with research boreholes. This integrated data set permits their origin, evolution and anatomy to be considered, including high‐resolution analysis of sedimentary facies distribution and characterization of depositional sub‐environments. An idealized model of the stratigraphic evolution and depositional architecture of external levées is presented, and variations can be attributed to allogenic (for example, sediment supply) and autogenic (for example, channel migration) factors. Initiation of external levée construction is commonly marked by deposition of a basal sand‐rich facies with sedimentary structures indicating rapid deposition from unconfined flows. These deposits are interpreted as frontal lobes. Propagation of the parent channel, and resultant flow confinement, lead to partial erosion of the frontal lobe and development of constructional relief (levées) by flow overspill and flow stripping. Overall fining‐upwards and thinning‐upwards profiles reflect increased flow confinement and/or waning flow magnitude through time. Identification of a hierarchy of levée elements is not possible due to the absence of internal bounding surfaces or sharp facies changes. The down‐slope taper in levée height and increasing channel sinuosity results in increasing numbers of crevasse lobe deposits, and is reflected by the increased occurrences of channel avulsion events down‐dip. External levées from the Fort Brown Formation are silt‐rich; however their stratigraphic evolution and the distribution of many components (such as sediment waves and crevasse lobe) share commonalities with mud‐rich external levées. This unique integrated data set has permitted the first high‐resolution characterization of external submarine levée systems.  相似文献   

Infrasound produced by debris flow: propagation and frequency content evolution   总被引：4，自引：1，他引：3  

Arnold Kogelnig  Johannes Hübl  Emma Suriñach  Ignasi Vilajosana  Brian W. McArdell 《Natural Hazards》2014,70(3):1713-1733

Rapid mass movements such as avalanches, debris flows, and rock fall are periodic or episodic phenomena that occur in alpine regions. Recent studies have shown that debris flows generate characteristic signals in the low-frequency infrasonic spectrum (4–15 Hz). Infrasound can travel thousands of kilometers and can still be detectable. This characteristic provides a basis for the development of wide area automated monitoring systems that can operate in locations unaffected by the activity of the process. This study focuses on the infrasound vibrations produced by a debris flow at the Lattenbach torrent, Tyrol (Austria), and by two events at the Illgraben torrent, Canton of Valais (Switzerland). The Lattenbach torrent is a very active torrent, which is located in the west of Tyrol in a geologic fault zone between the Silvrettakristallin and the Northern Limestone Alps. It has a large supply of loose sediment. The Illgraben torrent, which is well known for its frequent sediment transport and debris flow activity, has been equipped with instruments for debris flow monitoring since the year 2000. This study shows that debris flow emits low-frequency infrasonic signals that can be monitored and correlated with seismic signals. During the passage of the debris flow, several surges were identified by ultrasonic gauges and detected in the time series and the running spectra of infrasonic data.  相似文献   

The column density distribution function at z= 0 from H i selected galaxies     

Emma V. Ryan-Weber  Rachel L. Webster  Lister Staveley-Smith 《Monthly notices of the Royal Astronomical Society》2003,343(4):1195-1206

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Unusual behaviour of epikarst in the Acqua dei Faggi carbonate aquifer (Southern Italy)     

Emma Petrella  Paolo Capuano  Fulvio Celico 《地学学报》2007,19(1):82-88

Hydrogeological and geophysical investigations demonstrated the existence of an epikarstic zone in a carbonate aquifer of Southern Italy, about 10 m thick. Nevertheless, the hydrogeological behaviour of the epikarst is different from that schematized by several authors. In the test site, the contrast in permeability at the bottom of the epikarst does not cause retention of percolation and storage of water in a perched temporary aquifer within the uppermost portion of the carbonate medium. Because of the high fracture density and good interconnection of openings within the underlying limestone, the percolation is diffuse also below the epikarstic zone, as well as the groundwater flow. The ‘funnelling’ effect into larger shafts does not play an important role on the hydrogeological behaviour of the aquifer.  相似文献   

Change in carbon flux (1960–2015) of the Red River (Vietnam)     

Thi Phuong Quynh Le  Nhu Da Le  Viet Nga Dao  Emma Rochelle-Newall  Thi Mai Huong Nguyen  Cyril Marchand  Thi Thuy Duong  Thi Xuan Binh Phung 《Environmental Earth Sciences》2018,77(18):658

Global riverine carbon concentrations and fluxes have been impacted by climate and human-induced changes for many decades. This paper aims to reconstruct the longterm carbon concentrations and carbon fluxes of the Red River, a system under the coupled pressures of environmental change and human activity. Based on (1) the relationships between particulate and dissolved organic carbon (POC, DOC) or dissolved inorganic carbon (DIC), and suspended sediments (TSS) or river water discharge and on (2) the available detailed historical records of river discharge and TSS concentration, the variations of the Red River carbon concentration and flux were estimated for the period 1960–2015. The results show that total carbon flux of the Red River averaged 2555?±?639 kton C year^?1. DIC fluxes dominated total carbon fluxes, representing 64% of total, reflecting a strong weathering process from carbonate rocks in the upstream basin. Total carbon fluxes significantly decreased from 2816 kton C year^?1 during the 1960s to 1372 kton C year^?1 during the 2010s and showed clear seasonal and spatial variations. Organic carbon flux decreased in both quantity and proportion of the total carbon flux from 40.9% in 1960s to 14.9% in 2010s, reflecting the important impact of dam impoundment. DIC flux was also reduced over this period potentially as a consequence of carbonate precipitation in the irrigated, agricultural land and the reduction of the Red River water discharge toward the sea. These decreases in TSS and carbon fluxes are probably partially responsible for different negatives impacts observed in the coastal zone.  相似文献   

Spatial variability of recent macroscopic charcoal deposition in a small montane lake and implications for reconstruction of watershed-scale fire regimes     

Colin J. Courtney Mustaphi  Emma L. Davis  Joelle T. Perreault  Michael F. J. Pisaric 《Journal of Paleolimnology》2015,54(1):71-86

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Flow of Canadian basin deep water in the Western Eurasian Basin of the Arctic Ocean     

Göran Björk  Leif G. Anderson  Martin Jakobsson  Dennis Antony  Björn Eriksson  Patrick B. Eriksson  Benjamin Hell  Sofia Hjalmarsson  Timothy Janzen  Sara Jutterström  Johanna Linders  Ludvig Löwemark  Christian Marcussen  K. Anders Olsson  Bert Rudels  Emma Sellén  Morten Sølvsten 《Deep Sea Research Part I: Oceanographic Research Papers》2010,57(4):577-586

The LOMROG 2007 expedition targeted the previously unexplored southern part of the Lomonosov Ridge north of Greenland together with a section from the Morris Jesup Rise to Gakkel Ridge. The oceanographic data show that Canadian Basin Deep Water (CBDW) passes the Lomonosov Ridge in the area of the Intra Basin close to the North Pole and then continues along the ridge towards Greenland and further along its northernmost continental slope. The CBDW is clearly evident as a salinity maximum and oxygen minimum at a depth of about 2000 m. The cross-slope sections at the Amundsen Basin side of the Lomonosov Ridge and further south at the Morris Jesup Rise show a sharp frontal structure higher up in the water column between Makarov Basin water and Amundsen Basin water. The frontal structure continues upward into the Atlantic Water up to a depth of about 300 m. The observed water mass division at levels well above the ridge crest indicates a strong topographic steering of the flow and that different water masses tend to pass the ridge guided by ridge-crossing isobaths at local topographic heights and depressions. A rough scaling analysis shows that the extremely steep and sharply turning bathymetry of the Morris Jesup Rise may force the boundary current to separate and generate deep eddies.  相似文献