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21.
Kelly Addy Arthur Gold Barbara Nowicki James McKenna Mark Stolt Peter Groffman 《Estuaries and Coasts》2005,28(6):896-908
Coastal waters are severely threatened by nitrogen (N) loading from direct groundwater discharge. The subterranean estuary,
the mixing zone of fresh groundwater and sea water in a coastal aquifer, has a high potential to remove substantial N. A network
of piezometers was used to characterize the denitrification capacity and groundwater flow paths in the subterranean estuary
below a Rhode Island fringing salt marsh.15N-enriched nitrate was injected into the subterranean estuary (in situ push-pull method) to evaluate the denitrification capacity
of the saturated zone at multiple depths (125–300 cm) below different zones (upland-marsh transition zone, high marsh, and
low marsh). From the upland to low marsh, the water table became shallower, groundwater dissolved oxygen decreased, and groundwater
pH, soil organic carbon, and total root biomass increased. As groundwater approached the high and low marsh, the hydraulic
gradient increased and deep groundwater upwelled. In the warm season (groundwater temperature >12 °C), elevated groundwater
denitrification capacity within each zone was observed. The warm season low marsh groundwater denitrification capacity was
significantly higher than all other zones and depths. In the cool season (groundwater temperature <10.5 °C), elevated groundwater
denitrification capacity was only found in the low marsh. Additions of dissolved organic carbon did not alter groundwater
denitrification capacity suggesting that an alternative electron donor, possibly transported by tidal inundation from the
root zone, may be limiting. Combining flow paths with denitrification capacity and saturated porewater residence time, we
estimated that as much as 29–60 mg N could be removed from 11 of water flowing through the subterranean estuary below the
low marsh, arguing for the significance of subterranean estuaries in annual watershed scale N budgets. 相似文献
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Arthur J. Horowitz 《水文研究》2014,28(12):3999-4000
25.
Land managers responsible for invasive species removal in the USA require tools to prevent the Asian longhorned beetle (Anoplophora glabripennis) (ALB) from decimating the maple-dominant hardwood forests of Massachusetts and New England. Species distribution models (SDMs) and spread models have been applied individually to predict the invasion distribution and rate of spread, but the combination of both models can increase the accuracy of predictions of species spread over time when habitat suitability is heterogeneous across landscapes. First, a SDM was fit to 2008 ALB presence-only locations. Then, a stratified spread model was generated to measure the probability of spread due to natural and human causes. Finally, the SDM and spread models were combined to evaluate the risk of ALB spread in Central Massachusetts in 2008–2009. The SDM predicted many urban locations in Central Massachusetts as having suitable environments for species establishment. The combined model shows the greatest risk of spread and establishment in suitable locations immediately surrounding the epicentre of the ALB outbreak in Northern Worcester with lower risk areas in suitable locations only accessible through long-range dispersal from access to human transportation networks. The risk map achieved an accuracy of 67% using 2009 ALB locations for model validation. This model framework can effectively provide risk managers with valuable information concerning the timing and spatial extent of spread/establishment risk of ALB and potential strategies needed for effective future risk management efforts. 相似文献
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José Antonio López-Sáez Francisca Alba-Sánchez Sandra Robles-López Sebastián Pérez-Díaz Daniel Abel-Schaad Silvia Sabariego-Ruiz Arthur Glais 《山地科学学报》2016,13(7):1139-1153
A high-altitude peat sequence from the heart of the Spanish Central System (Gredos range) was analysed through a multi-proxy approach to determine the sensitivity of high-mountain habitats to climate, fire and land use changes during the last seven hundred years, providing valuable insight into our understanding of the vegetation history and environmental changes in a mountain pass close to a traditional route of transhumance. The pollen data indicate that the vegetation was dominated by shrublands and grasslands with scattered pines in high-mountain areas, while in the valleys cereals, chestnut and olive trees were cultivated. Strong declines of high-mountain pines percentages are recorded at 1540, 1675, 1765, 1835 and 1925 cal AD, which may be related to increasing grazing activities and/or the occurrence of anthropogenic fires. The practice of mountain summer farming and transhumance deeply changed and redesigned the landscape of the high altitudes in central Spain (Gredos range) since the Middle Ages, although its dynamics was influenced in some way by climate variability of the past seven centuries. 相似文献
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Stuart J. Robbins Wesley A. Watters John E. Chappelow Veronica J. Bray Ingrid J. Daubar Robert A. Craddock Ross A. Beyer Margaret Landis Lillian R. Ostrach Livio Tornabene Jamie D. Riggs Brian P. Weaver 《Meteoritics & planetary science》2018,53(4):583-637
One important, almost ubiquitous, tool for understanding the surfaces of solid bodies throughout the solar system is the study of impact craters. While measuring a distribution of crater diameters and locations is an important tool for a wide variety of studies, so too is measuring a crater's “depth.” Depth can inform numerous studies including the strength of a surface and modification rates in the local environment. There is, however, no standard data set, definition, or technique to perform this data-gathering task, and the abundance of different definitions of “depth” and methods for estimating that quantity can lead to misunderstandings in and of the literature. In this review, we describe a wide variety of data sets and methods to analyze those data sets that have been, are currently, or could be used to derive different types of crater depth measurements. We also recommend certain nomenclature in doing so to help standardize practice in the field. We present a review section of all crater depths that have been published on different solar system bodies which shows how the field has evolved through time and how some common assumptions might not be wholly accurate. We conclude with several recommendations for researchers which could help different data sets to be more easily understood and compared. 相似文献
30.
We present a relatively simple time domain method for determining the bandpass response of a system by injecting a nanosecond pulse and capturing the system voltage output. A pulse of sub-nanosecond duration contains all frequency components with nearly constant amplitude up to 1 GHz. Hence, this method can accurately determine the system bandpass response to a broadband signal. In a novel variation on this impulse response method, a train of pulses is coherently accumulated providing precision calibration with a simple system. The basic concept is demonstrated using a pulse generator-accumulator setup realised in a Bedlam board which is a high speed digital signal processing unit. The same system was used at the Parkes radio telescope between 2–13 October 2013 and we demonstrate its powerful diagnostic capability. We also present some initial test data from this experiment. 相似文献