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Kaelin M. Cawley Youhei Yamashita Nagamitsu Maie Rudolf Jaffé 《Estuaries and Coasts》2014,37(2):399-410
Dissolved organic carbon (DOC) concentration and dissolved organic matter (DOM) optical properties were analyzed along two estuarine river transects during the wet and dry seasons to better understand DOM dynamics and quantify mangrove inputs. A tidal study was performed to assess the impacts of tidal pumping on DOM transport. DOM in the estuaries showed non-conservative mixing indicative of mangrove-derived inputs. Similarly, fluorescence data suggest that some terrestrial humic-like components showed non-conservative behavior. An Everglades freshwater-derived fluorescent component, which is associated with soil inputs from the Northern Everglades, behaved conservatively. During the dry season, a protein-like component behaved conservatively until the mid-salinity range when non-conservative behavior due to degradation and/or loss was observed. The tidal study data suggests mangrove porewater inputs to the rivers following low tide. The differences in quantity of DOM exported by the Shark and Harney Rivers imply that geomorphology and tidal hydrology may be a dominant factor controlling the amount of DOM exported from the mangrove ecotone, where up to 21 % of the DOC is mangrove-derived. Additionally, nutrient concentrations and other temporal factors may control DOM export from the mangroves, particularly for the microbially derived fluorescent components, contributing to the seasonal differences. The wet and dry season fluxes of mangrove DOM from the Shark River is estimated as 0.27?×?109 mg C d?1 and 0.075?×?109 mg C d?1, respectively, and the Harney River is estimated as 1.9?×?109 mg C d?1 and 0.20?×?109 mg C d?1. 相似文献
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F. Krennrich C.W. Akerlof J.H. Buckley J. Bussóns-Gordo D.A. Carter-Lewis M.F. Cawley M.A. Catanese V. Connaughton D.J. Fegan J.P. Finley J.A. Gaidos K.H. Harris A.M. Hillas R.C. Lamb M.J. Lang G. Mohanty J. Quinn A.J. Rodgers H.J. Rose A.C. Rovero M.S. Schubnell G.H. Sembroski T.C. Weekes C. Wilson 《Astroparticle Physics》1998,8(4):213-221
Observations of photons at E ≥ 550 GeV from the Crab Nebula are presented and used to assess the potential of multi-telescope systems for γ-ray astronomy.
The Whipple observatory 10 m and 8 m imaging atmospheric erenkov telescopes have been used to provide a stereoscopic view of air showers to make a more complete measurement of air shower parameters. Here we present a measurement of the spread in the arrival direction of primary γ-rays originating from a point source. The data show that the shower arrival direction can be reconstructed with an accuracy of σ = 0.°14. 相似文献
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KM Cawley KD Butler GR Aiken LG Larsen TG Huntington DM McKnight 《Marine pollution bulletin》2012,64(8):1678-1687
Using fluorescence spectroscopy and parallel factor analysis (PARAFAC) we characterized and modeled the fluorescence properties of dissolved organic matter (DOM) in samples from the Penobscot River, Androscoggin River, Penobscot Bay, and the Gulf of Maine (GoM). We analyzed excitation-emission matrices (EEMs) using an existing PARAFAC model (Cory and McKnight, 2005) and created a system-specific model with seven components (GoM PARAFAC). The GoM PARAFAC model contained six components similar to those in other PARAFAC models and one unique component with a spectrum similar to a residual found using the Cory and McKnight (2005) model. The unique component was abundant in samples from the Androscoggin River immediately downstream of a pulp mill effluent release site. The detection of a PARAFAC component associated with an anthropogenic source of DOM, such as pulp mill effluent, demonstrates the importance for rigorously analyzing PARAFAC residuals and developing system-specific models. 相似文献
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Kaelin M. Cawley John Campbell Melissa Zwilling Rudolf Jaffé 《Aquatic Sciences - Research Across Boundaries》2014,76(4):611-622
Dissolved organic matter (DOM) source and composition are critical drivers of its reactivity, impact microbial food webs and influence ecosystem functions. It is believed that DOM composition and abundance represent an integrated signal derived from the surrounding watershed. Recent studies have shown that land-use may have a long-term effect on DOM composition. Methods for characterizing DOM, such as those that measure the optical properties and size of the molecules, are increasingly recognized as valuable tools for assessing DOM sources, cycling, and reactivity. In this study we measured DOM optical properties and molecular weight determinations to evaluate whether the legacy of forest disturbance alters the amount and composition of stream DOM. Differences in DOM quantity and composition due to vegetation type and to a greater extent, wetland influence, were more pronounced than effects due to disturbance. Our results suggest that excitation-emission matrix fluorescence with parallel factor analysis is a more sensitive metric of disturbance than the other methods evaluated. Analyses showed that streams draining watersheds that have been clearcut had lower dissolved organic carbon (DOC) concentrations and higher microbially-derived and protein-like fluorescence features compared to reference streams. DOM optical properties in a watershed amended with calcium, were not significantly different than reference watersheds, but had higher concentrations of DOC. Collectively these results improve our understanding of how the legacy of forest disturbances and natural landscape characteristics affect the quantity and chemical composition of DOM in headwater streams, having implications for stream water quality and carbon cycling. 相似文献
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Subsurface erosion,scarp retreat,and sedimentation at Mountain Lake,Virginia, USA: groundwater geomorphology in a flow‐through lake with subsurface drainage 
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下载免费PDF全文 The complete natural drainage in 2008, 2011, and 2012 of Mountain Lake in Giles County, Virginia, allowed detailed observations of the only natural lake basin in the southern Appalachian Mountains. Here we use these observations to support geomorphic analysis and develop a model of basin evolution, which may advance the understanding of rare flow‐through lakes with subsurface drainage elsewhere. Key features included (a) an angle‐of‐repose slope with a smoothly concave planform across the entire 260 m width of the north end of the basin, (b) an arc of steep‐sided depressions along the deep northern margin of the basin floor, and (c) an abrupt transition between colluvial and finer‐grained sedimentary deposits on the floor. Our geomorphic analysis suggests that subsurface erosion has enabled long‐term northward scarp retreat in the basin by removing water and sediment. Mountain Lake formed on the northern limb of a breached anticline along the Eastern Continental Divide, where strong‐over‐weak stratigraphy and a small watershed have enabled the basin to evolve generally as follows. (1) Pond Drain, a first‐order tributary of the New River, incised north‐dipping sandstones and underlying shales on the northern limb of the anticline. The valley floor subsequently accumulated meters to tens of meters of mostly late Pleistocene colluvial fill. (2) Subsurface drainage developed likely along the contact between the sandstones and shales, facilitated by pre‐existing fractures. (3) Ongoing subsurface erosion has progressively undermined the sandstone, causing scarp retreat along the northern margin of the basin while a surface stream intermittently incised the shallow southern end. Sedimentary deposits indicate that only the deeper northern portion of the basin is usually flooded under Holocene conditions. Our basin evolution model suggests slow development of the basin over hundreds of thousands of years rather than sudden damming by a catastrophic landslide. Copyright © 2018 John Wiley & Sons, Ltd. 相似文献
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M. F. Cawley D. J. Fegan K. Harris A. M. Hillas P. W. Kwok R. C. Lamb M. J. Lang D. A. Lewis D. Macomb P. T. Reynolds D. J. Schmid G. Vacanti T. C. Weekes 《Experimental Astronomy》1990,1(3):173-193
Details are presented of an atmospheric Cherenkov telescope for use in very high energy gamma-ray astronomy which consists of a cluster of 109 close-packed photomultiplier tubes at the focus of a 10 meter optical reflector. The images of the Cherenkov flashes generated both by gamma-ray and charged cosmic-ray events are digitized and recorded. Subsequent off-line analysis of the images improves the significance of the signal to noise ratio by a factor of 10 compared with non-imaging techniques. 相似文献
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Mountain Lake is the only natural lake of significance in the unglaciated southern Appalachian Highlands. It is located near the summit of Salt Pond Mountain, Giles County Virginia, at an elevation of 1177 m. It is underlain by Ordovician and Silurian non‐calcareous shale and sandstone of the Martinsburg, Juniata and Clinch formations. Historical (250 years) and sediment (6000 years) records suggest that the size of the lake has varied periodically. In the 1930s lake origin was proposed as due to valley damming by a lateral landslide (Hutchinson and Pickford, 1932) or damming by scree (Sharp, 1933). A later theory modified the landslide hypothesis to the primarily vertical collapse of a canyon feature in the Clinch (Parker et al., 1975). Fracture trace analysis now reveals a regional lineation feature associated with the lake. This feature is present surficially both downgradient from the lake to the northwest, and upgradient to the southeast. Sonar bathymetry and diver reconnaissance show it expressed as a (relatively sediment‐free) narrow open crevice in the deepest (33 m) portion of the lake, probably a fault. Hydrologic observation and resistivity suggest preferential water movement along this fracture, as well as leakage directly from the lake. The present study suggests conduit erosion within this feature and periodic vertical downsettling of overlying Clinch material as the primary mechanism of lake origin and water‐level fluctuations through time. Copyright © 2001 John Wiley & Sons, Ltd. 相似文献
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Considerable progress has been made in the last half-decade in the field of very high energy (VHE) gamma-ray astronomy (photons with energies between 1011 and 1013 eV). The high background level due to the isotropic cosmic ray flux which has bedevilled the field since its inception in the early 1960's can now be reduced to such a degree that significant gamma-ray signals from several sources become visible within a few hours of observation. The instrumentation and methodologies which have made this possible are reviewed. A brief historical introduction is followed by a summary of the salient properties of the atmospheric Cherenkov flash associated with VHE gamma-ray events. The major components of a VHE gamma-ray astronomy telescope are then reviewed. This is followed by a discussion of the different methodologies currently being used to discriminate against the cosmic ray background. Properties of several specific installations are then summarized, and possible future developments in VHE instrumentation are briefly discussed. 相似文献