Dissolved nutrient fluxes through a sandy estuarine beachface (Cape Henlopen,Delaware, U.S.A.): Contributions from fresh groundwater discharge,seawater recycling,and diagenesis     

Rebecca L. Hays  William J. Ullman 《Estuaries and Coasts》2007,30(4):710-724

The sandy beachface at Cape Henlopen, Delaware, receives dissolved nutrient inputs from fresh upland groundwater and estuarine seawater and exports nutrients through intertidal and submarine groundwater discharge. The discharge of brackish beachface waters indicates that there must be additional diagenetic nutrient sources and sinks within the porous beachface aquifer. At some times of the year, diagenetic processes within the beachface remove nitrate from waters draining the beachface consistent with the stoichiometry of either denitrification or dissimilatory nitrate reduction to ammonium. Up to 50–100% of the nitrate load from the upland groundwaters is apparently reduced to N₂O/N₂ gas or ammonium during these periods. At other times, ammonium and nitrate are added to beachface waters consistent with the stoichiometry of organic matter remineralization and nitrification. Dissolved reactive phosphorus and silica are similarly consumed and produced by beachface processes at different times of the year, presumably by adsorption or desorption. Infiltration of reactive estuarine particles may be an additional source of nutrients and carbon that supports the diagenetic activity in the beachface aquifer. These observations suggest that sandy beachfaces are biogeochemically reactive systems that can serve as sources, sinks, and temporary reservoirs of nutrients to support the primary and secondary production of the adjacent intertidal zone.  相似文献   

A review of water column processes influencing hypoxia in the northern Gulf of Mexico   总被引：1，自引：0，他引：1  

Michael J. Dagg  James W. Ammerman  Rainer M. W. Amon  Wayne S. Gardner  Rebecca E. Green  Steven E. Lohrenz 《Estuaries and Coasts》2007,30(5):735-752

In this review, we use data from field measurements of biogeochemical processes and cycles in the Mississippi River plume and in other shelf regions of the northern Gulf of Mexico to determine plume contributions to coastal hypoxia. We briefly review pertinent findings from these process studies, review recent mechanistic models that synthesize these processes to address hypoxia-related issues, and reinterpret current understanding in the context of these mechanistic models. Some of our conclusions are that both nitrogen and phosphorus are sometimes limiting to phytoplankton growth; respiration is the main fate of fixed carbon in the plume, implying that recycling is the main fate of nitrogen; decreasing the river nitrate loading results in less than a 1:1 decrease in organic matter sinking from the plume; and sedimenting organic matter from the Mississippi River plume can only fuel about 23% of observed coastal hypoxia, suggesting significant contributions from the Atchafalaya River and, possibly, coastal wetlands. We also identify gaps in our knowledge about controls on hypoxia, and indicate that some reinterpretation of our basic assumptions about this system is required. There are clear needs for improved information on the sources, rates, and locations of organic matter sedimentation; for further investigation of internal biogeochemical processes and cycling; for improved understanding of the rates of oxygen diffusion across the pycnocline; for identification and quantification of other sources of organic matter fueling hypoxia or other mechanisms by which Mississippi River derived organic matter fuels hypoxia; and for the development of a fully coupled physical-biogeochemical model.  相似文献   

A Seasonal Statistical Evaluation of COAMPS® over the Arabian Gulf Region     

Rebecca E. Eager  Sethu Raman  Teddy R. Holt  Douglas Westphal  Jeffrey Reid  Jason Nachamkin  Ming Liu  Abdulla Al Mandoos 《Pure and Applied Geophysics》2007,164(8-9):1747-1764

A statistical evaluation of the Coupled Ocean/Atmosphere Mesoscale Prediction System (COAMPS^®) was performed over the Arabian Gulf region for the period, 1 August to 5 October, 2004. Verification skill scores of bias and root-mean-square error were estimated for surface variables and for vertical profiles to investigate any diurnal variations. The model predictions of boundary-layer heights are compared with the observations at Abu Dhabi, United Arab Emirates. The Middle East presents challenges to numerical weather prediction due to complex land-ocean-land mesoscale processes. An independent data set of surface measurements from 50 stations in the UAE was available from the Department of Water Resources Studies, Abu Dhabi for model verification. The results indicate a diurnal variation in the model errors. The errors are small considering the magnitudes of the observed variables. Errors in the coastal region can be attributed to the differences in the timing of the onset of sea and land breeze circulations in the simulations as compared to the observations. Errors are relatively smaller in the offshore locations.  相似文献   

An improved practical approach for estimating catchment-scale response functions through wavelet analysis     

Ravindra Dwivedi  Christopher Eastoe  John F. Knowles  Lejon Hamann  Thomas Meixner  Paul A. “Ty” Ferre  Christopher Castro  William E. Wright  Guo-Yue Niu  Rebecca Minor  Greg A. Barron-Gafford  Nathan Abramson  Bhaskar Mitra  Shirley A. Papuga  Michael Stanley  Jon Chorover 《水文研究》2021,35(3):e14082

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How much does dry‐season fog matter? Quantifying fog contributions to water balance in a coastal California watershed          下载免费PDF全文

Michaella Chung  Alexis Dufour  Rebecca Pluche  Sally Thompson 《水文研究》2017,31(22):3948-3961

The seasonally‐dry climate of Northern California imposes significant water stress on ecosystems and water resources during the dry summer months. Frequently during summer, the only water inputs occur as non‐rainfall water, in the form of fog and dew. However, due to spatially heterogeneous fog interaction within a watershed, estimating fog water fluxes to understand watershed‐scale hydrologic effects remains challenging. In this study, we characterized the role of coastal fog, a dominant feature of Northern Californian coastal ecosystems, in a San Francisco Peninsula watershed. To monitor fog occurrence, intensity, and spatial extent, we focused on the mechanisms through which fog can affect the water balance: throughfall following canopy interception of fog, soil moisture, streamflow, and meteorological variables. A stratified sampling design was used to capture the watershed's spatial heterogeneities in relation to fog events. We developed a novel spatial averaging scheme to upscale local observations of throughfall inputs and evapotranspiration suppression and make watershed‐scale estimates of fog water fluxes. Inputs from fog water throughfall (10–30 mm/year) and fog suppression of evapotranspiration (125 mm/year) reduced dry‐season water deficits by 25% at watershed scales. Evapotranspiration suppression was much more important for this reduction in water deficit than were direct inputs of fog water. The new upscaling scheme was analyzed to explore the sensitivity of its results to the methodology (data type and interpolation method) employed. This evaluation suggests that our combination of sensors and remote sensing allows an improved incorporation of spatially‐averaged fog fluxes into the water balance than traditional interpolation approaches.  相似文献   

Metamorphic petrology of a high‐T/low‐P granulite terrane (Damara belt,Namibia) – Constraints from pseudosection modelling and high‐precision Lu–Hf garnet‐whole rock dating     

Stefan Jung  Soenke Brandt  Rebecca Bast  Erik E. Scherer  Jasper Berndt 《Journal of Metamorphic Geology》2019,37(1):41-69

Migmatites comprise a minor volume of the high‐grade part of the Damara orogen of Namibia that is dominated by granite complexes and intercalated metasedimentary units. Migmatites of the Southern Central Zone of the Damara orogen consist of melanosomes with garnet+cordierite+biotite+K‐feldspar, and leucosomes, which are sometimes garnet‐ and cordierite‐bearing. Field evidence, petrographic observations, and pseudosection modelling suggest that, in contrast to other areas where intrusion of granitic magmas is more important, in situ partial melting of metasedimentary units was the main migmatite generation processes. Pseudosection modelling and thermobarometric calculations consistently indicate that the peak‐metamorphic grade throughout the area is in the granulite facies (~5 kbar at ~800°C). Cordierite coronas around garnet suggest some decompression from peak‐metamorphic conditions and rare andalusite records late, near‐isobaric cooling to <650°C at low pressures of ~3 kbar. The inferred clockwise P–T path is consistent with minor crustal thickening through continent–continent collision followed by limited post‐collisional exhumation and suggests that the granulite facies terrane of the Southern Central Zone of the Damara orogen formed initially in a metamorphic field gradient of ~35–40°C/km at medium pressures. New high‐precision Lu–Hf garnet‐whole rock dates are 530 ± 13 Ma, 522.0 ± 0.8 Ma, 520.8 ± 3.6 Ma, and 500.3 ± 4.3 Ma for the migmatites that record temperatures of ~800°C. This indicates that high‐grade metamorphism lasted for c. 20–30 Ma, which is compatible with previous estimates using Sm–Nd garnet‐whole rock systematics. In previous studies on Damara orogen migmatites where both Sm–Nd and Lu–Hf chronometers have been applied, the dates (c. 520–510 Ma) agree within their small uncertainties (0.6–0.8% for Sm–Nd and 0.1–0.2% for Lu–Hf). This implies rapid cooling after high‐grade conditions and, by implication, rapid exhumation at that time. The cause of the high geothermal gradient inferred from the metamorphic conditions is unknown but likely requires some extra heat that was probably added by intrusion of magmas from the lithospheric mantle, i.e., syenites that have been recently re‐dated at c. 545 Ma. Some granites derived from the lower crust at c. 545 Ma are the outcome rather than the cause of high‐T metamorphism. In addition, high contents of heat‐producing elements K, Th, and U may have raised peak temperatures by 150–200°C at the base of the crust, resulting in the widespread melting of fertile crustal rocks. The continuous gradation from centimetre‐scale leucosomes to decametre‐scale leucogranite sheets within the high‐grade metamorphic zone suggests that leucosome lenses coalesced to form larger bodies of anatectic leucogranites, thereby documenting a link between high‐grade regional metamorphism and Pan‐African magmatism. In view of the close association of the studied high‐T migmatites with hundreds of synmetamorphic high‐T granites that invaded the terrane as metre‐ to decametre‐wide sills and dykes, we postulate that crystallization of felsic lower crustal magma is, at least partly, responsible for heat supply. Late‐stage isobaric cooling of these granites may explain the occurrence of andalusite in some samples.  相似文献   

Imagined Landscapes: Geovisualizing Australian Spatial Narratives     

G. Rebecca Dobbs 《The Cartographic journal》2017,54(2):186-187

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Fire,climate and the origins of agriculture: micro‐charcoal records of biomass burning during the last glacial–interglacial transition in Southwest Asia     

Rebecca Turner  Neil Roberts  Warren J. Eastwood  Emma Jenkins  Arlene Rosen 《第四纪科学杂志》2010,25(3):371-386

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Erratum to: Zn (II) and Cu (II) adsorption and retention onto iron oxyhydroxide nanoparticles: effects of particle aggregation and salinity     

Chesne  Rebecca B.  Kim  Christopher S. 《Geochemical transactions》2015,16(1):1-1

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Origin and kinematics of a basin-scale,non-polygonal,layer-bound normal fault system in the Levant Basin,eastern Mediterranean     

Amir Joffe  Christopher A.-L. Jackson  Josh Steinberg  Rebecca E. Bell  Yizhaq Makovsky 《Basin Research》2023,35(2):662-691

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