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Kelly M. Darnell Tim J. B. Carruthers Patrick Biber Ioannis Y. Georgiou Thomas C. Michot Ronald G. Boustany 《Estuaries and Coasts》2017,40(5):1288-1300
Seagrasses are submerged marine plants that are anchored to the substrate and are therefore limited to assimilating nutrients from the surrounding water column or sediment, or by translocating nutrients from adjacent shoots through the belowground rhizome. As a result, seagrasses have been used as reliable ecosystem indicators of surrounding nutrient conditions. The Chandeleur Islands are a chain of barrier islands in the northern Gulf of Mexico that support the only marine seagrass beds in Louisiana, USA, and are the sole location of the seagrass Thalassia testudinum across nearly 1000 km of the coastline from west Florida to central Texas. Over the past 150 years, the land area of the Chandeleur Islands has decreased by over half, resulting in a decline of seagrass cover. The goals of this study were to characterize the status of a climax seagrass species at the Chandeleur Islands, T. testudinum, in terms of leaf nutrient (nitrogen [N] and phosphorus [P]) changes over time, from 1998 to 2015, and to assess potential drivers of leaf nutrient content. Thalassia testudinum leaf nutrients displayed considerable interannual variability in N and P content and molar ratios, which broadly mimicked patterns in annual average dissolved nutrient concentrations in the lower Mississippi River. Hydrological modeling demonstrated the potential for multiple scenarios that would deliver Mississippi River water, and thus nutrients, to T. testudinum at the Chandeleur Islands. Although coastal eutrophication is generally accepted as the proximate cause for seagrass loss globally, there is little evidence that nutrient input from the Mississippi River has driven the dramatic declines observed in seagrasses at the Chandeleur Islands. Rather, seagrass cover along the Chandeleur Islands appears to be strongly influenced by island geomorphological processes. Although variable over time, the often elevated nutrient levels of the climax seagrass species, T. testudinum, which are potentially driven by river-derived nutrient inputs, raises an important consideration of the potential loss of the ecosystem functions and services associated with these declining seagrass meadows. 相似文献
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Kivanc Zorlu M. Celal Tunusluoglu Tolga Gorum Hakan A. Nefeslioglu Ali Yalcin Dilek Turer Candan Gokceoglu 《Environmental Earth Sciences》2011,62(8):1685-1693
The Cappadocia region has unique geomorphological features resulting from differential erosional processes which make it very attractive to tourists. Besides the fairy chimneys for which the area is best known, there are also impressive buttes and mesas. Buttes and mesas are formed in regions having flat-lying strata in which the uppermost levels are composed of well-cemented limestones and granular ignimbrites, whereas the lower parts and slopes consist of low-durability tuff and ignimbrites. This durability difference results in serious rockfall events. This study involves two-dimensional rockfall analyses in and near the Avanos, Zelve, and Çavusini areas, where volcano-sedimentary units of Neogene age outcrop, to provide a rockfall hazard map in which areas of tourism activity are also considered. 相似文献
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This article presents results of mercury in surface waters from Hunza River basin, Northern Areas, Pakistan. Small‐scale gold mining activities along the Hunza and Gilgit rivers are long known to be discharging mercury in the amalgamation and roasting processes. Previous studies reported high mercury concentrations in soils close to mining operations as well as serious health problems for miners. However, none of the studies have focused on the level of contamination in aqueous environments. This is the first study on the investigation of source and fate of sediment and river‐borne mercury in the Hunza River. The samples collected near gold panning sites showed higher mercury concentrations than critical levels established by the U.S. Environmental Protection Agency. The observed dissolved mercury concentrations ranged from 5.10 to 25.25 ng/l, whereas particulate‐bound mercury ranged from 4.85 to 154.62 ng/l. Particulate‐phase mercury corresponded to more than 75% of the total observed mercury concentrations for all of the sampled rivers. Thus, suspended sediments represented the major pathway of the riverine mercury transport. A mass balance calculation suggested an annual mercury flux of 48.6 g/km2 into the Hunza River basin. The samples collected from the most affected river, the Shimsal River, averaged to have 108 ng/l total mercury. This amount was close to the average soil mercury data of 151 ng/l as reported by the Pakistan Mineral Development Corporation in 2001. The dominant source of contamination was shown to be the leaching of large quantities of mercury from the mercury‐rich sediment and flood plain soil into the rivers, rather than the direct release from mining activities. Significant decrease in both dissolved and particulate‐bound mercury concentration downstream of Attabad Lake suggested that mercury is being accumulated or consumed in the lake. Although minimization or elimination of mercury loses from the mining process seems important for the well‐being of the miners, preventing the remobilization of accumulated mercury is equally important in mercury control in this region. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
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Kivanc Ertugay Sebnem Duzgun 《International journal of geographical information science》2013,27(9):1491-1506
The term physical accessibility has long been used by geographers, economists, and urban planners and reflects the relative ease of access to/from several urban/rural services by considering the traveling costs. Numerous accessibility measures, ranging from simple to sophisticated, can be observed in the geographical information systems (GIS)-based accessibility modeling literature. However, these measures are generally calculated from a constant catchment boundary (a most likely or average catchment boundary) based on constant deterministic transportation costs. This is one of the fundamental shortcomings of the current GIS-based accessibility modeling and creates uncertainty about the accuracy and reliability of the accessibility measures, especially when highly variable speeds in road segments are considered. The development of a new stochastic approach by using global positioning system (GPS)-based floating car data and Monte Carlo simulation (MCS) technique could enable handling the variations in transportation costs in a probabilistic manner and help to consider all possible catchment boundaries, instead of one average catchment boundary, in accessibility modeling process. Therefore, this article proposes a stochastic methodology for GIS-based accessibility modeling by using GPS-based floating car data and MCS technique. The proposed methodology is illustrated with a case study on medical emergency service accessibility in Eskisehir, Turkey. Moreover, deterministic and stochastic accessibility models are compared to demonstrate the differences between the models. The proposed model could provide better decision support for the decision-makers who are supposed to deal with accessibility, location/allocation, and service/catchment area related issues. 相似文献
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Martin Sahlén Pedro T. P. Viana rew R. Liddle A. Kathy Romer Michael Davidson Mark Hosmer Ed Lloyd-Davies Kivanc Sabirli Chris A. Collins Peter E. Freeman Matt Hilton Ben Hoyle Scott T. Kay Robert G. Mann Nicola Mehrtens Christopher J. Miller Robert C. Nichol S. Adam Stanford Michael J. West † 《Monthly notices of the Royal Astronomical Society》2009,397(2):577-607
We forecast the constraints on the values of σ8 , Ωm and cluster scaling-relation parameters which we expect to obtain from the XMM Cluster Survey (XCS). We assume a flat Λ cold dark matter Universe and perform a Monte Carlo Markov Chain analysis of the evolution of the number density of galaxy clusters that takes into account a detailed simulated selection function. Comparing our current observed number of clusters shows good agreement with predictions. We determine the expected degradation of the constraints as a result of self-calibrating the luminosity–temperature relation (with scatter), including temperature measurement errors, and relying on photometric methods for the estimation of galaxy cluster redshifts. We examine the effects of systematic errors in scaling relation and measurement error assumptions. Using only ( T , z ) self-calibration, we expect to measure Ωm to ±0.03 (and ΩΛ to the same accuracy assuming flatness), and σ8 to ±0.05, also constraining the normalization and slope of the luminosity–temperature relation to ±6 and ±13 per cent (at 1σ), respectively, in the process. Self-calibration fails to jointly constrain the scatter and redshift evolution of the luminosity–temperature relation significantly. Additional archival and/or follow-up data will improve on this. We do not expect measurement errors or imperfect knowledge of their distribution to degrade constraints significantly. Scaling-relation systematics can easily lead to cosmological constraints 2σ or more away from the fiducial model. Our treatment is the first exact treatment to this level of detail, and introduces a new 'smoothed ML' (Maximum Likelihood) estimate of expected constraints. 相似文献
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Seagrasses are typically light limited in many turbid estuarine systems. Light attenuation is due to water and three optically active constituents (OACs): nonalgal particulates, phytoplankton, and colored dissolved organic matter (CDOM). Using radiative transfer modeling, the inherent optical properties (IOPs) of these three OACs were linked to the light attenuation coefficient, K PAR, which was measured in North River, North Carolina, by profiles of photosynthetically active radiation (PAR). Seagrasses in the southern portion of Albemarle-Pamlico Estuarine System (APES), the second largest estuary in the USA, were found to be light limited at depths ranging from 0.87 to 2 m. This corresponds to a range of K PAR from 0.54 to 2.76 m?1 measured during a 24-month monitoring program. Turbidity ranged from 2.20 to 35.55 NTU, chlorophyll a from 1.56 to 15.35 mg m?3, and CDOM absorption at 440 nm from 0.319 to 3.554 m?1. The IOP and water quality data were used to calibrate an existing bio-optical model, which predicted a maximum depth for seagrasses of 1.7 m using annual mean water quality values and a minimum light requirement of 22% surface PAR. The utility of this modeling approach for the management of seagrasses in the APES lies in the identification of which water quality component is most important in driving light attenuation and limiting seagrass depth distribution. The calibrated bio-optical model now enables researchers and managers alike to set water quality targets to achieve desired water column light requirement goals that can be used to set criteria for seagrass habitat protection in North Carolina. 相似文献
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