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21.
Newport Bay is a large estuary in southern California that is subject to anthropogenic nutrient loading, eutrophication, and
hypoxia. Ground-based methods of assessing algal extent for monitoring and management are limited in that they cannot provide
a synoptic view of algal distribution over comparatively large areas. The goal of this study was to explore the application
of color infrared aerial photography as an alternative for analyzing the changes in the abundance of exposed macroalgae. Three
surveys combining remote sensing (color infrared aerial photography) and ground-based sampling to quantify macroalgal mat
coverage were carried out in Upper Newport Bay (UNB) between July and October 2005. Airborne photographs (scale 1:6000) collected
during daytime low tides, clear skies, and appropriate sun angle were digitized to 25-cm resolution, orthorectified, georegistered,
and combined into three mosaic composite digital images: one for each survey. During each aerial photography survey, macroalgal
percent cover was measured on the ground by the pointintercept method in a 6.25-m2 area at ca. 30 locations distributed along the water’s edge throughout the intertidal mudflat area. There were three main
types of cover:Ulva spp. (green algae),Ceranrium spp. (red algae), and bare surface (mud and mussel beds). To analyze similarities between spectral signatures in the images
and cover types, the pixels corresponding to the ground samples from each survey were grouped into clusters based on similarity
of their spectral signatures. To establish relationships between spectral signatures in the images and cover as determined
from ground data, pixels in each composite image corresponding to ground samples from the same day that were characterized
by > 90% of one cover type were attributed to that cover type. Ground samples comprised of a mixture of cover types were used
for accuracy assessment. Before classification, each digital image was transformed by the Minimum Noise Fraction Rotation
method to remove noise and enhance contrast between the classes. For classification of each composite image, the Spectral
Angle Mapper scheme was used: all pixels in each image were attributed to the identified classes and the areal extent of each
class was estimated. According to these assessments, the macroalgal coverage in UNB increased from 37% in July to 57% in September
to 80% in October, and during this timeUlva spp. replacedCeramium spp. as the dominant alga. This analysis showed that color infrared aerial photography is an effective tool for assessing
estuarine, intertidal macroalgal coverage. 相似文献
22.
Krista L. Jones Geoffrey C. Poole William W. Woessner Matt V. Vitale Brian R. Boer Scott J. O'Daniel Steven A. Thomas Brook A. Geffen 《水文研究》2008,22(13):2105-2113
Across 1·7 km2 of the Umatilla River floodplain (Oregon, USA), we investigated the influences of an ephemeral tributary and perennial ‘spring channel’ (fed only by upwelling groundwater) on hyporheic hydrology. We derived maps of winter and summer water‐table elevations from data collected at 46 monitoring wells and 19 stage gauges and used resulting maps to infer groundwater flow direction. Groundwater flow direction varied seasonally across the floodplain and was influenced by main channel stage, flooding, the tributary creek, and the location and direction of hyporheic exchange in the spring channel. Hyporheic exchange in the spring channel was evaluated with a geochemical mixing model, which confirmed patterns of floodplain groundwater movement inferred from water‐table maps and showed that the spring channel was fed predominantly by hyporheic water from the floodplain aquifer (87% during winter, 80% during summer), with its remaining flow supplied by upslope groundwater from the adjacent catchment aquifer. Summertime growth of aquatic macrophytes in the spring channel also influenced patterns of hyporheic exchange and groundwater flow direction in the alluvial aquifer by increasing flow resistance in the spring channel, locally raising surface water stage and adjacent water‐table elevation, and thereby altering the slope of the water‐table in the hyporheic zone. The Umatilla River floodplain is larger than most sites where hyporheic hydrology has been investigated in detail. Yet, our results corroborate other research that has identified off‐channel geomorphic features as important drivers of hyporheic hydrology, including previously published modeling efforts from a similar river and field observations from smaller streams. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
23.
Stephanie E. Chang Timothy L. McDaniels Joey Mikawoz Krista Peterson 《Natural Hazards》2007,41(2):337-358
This paper addresses the problem of interdependent failures of critical infrastructures in disasters. Disruptions to critical
infrastructure systems such as electric power or transportation frequently cause major social and economic loss in disasters,
both directly and through failures in one system leading to or compounding disruptions in another. Strategic approaches regarding
infrastructure failures are needed to guide community mitigation and preparedness efforts. This paper defines and provides
a conceptual framework for investigating infrastructure failure interdependencies (IFIs) from the standpoint of societal impacts.
In order to identify empirical patterns, a unique database has been developed of IFIs observed in major electric power outage
events. This paper presents analysis of this data for a major Canadian disaster, the 1998 Ice Storm that affected the northeastern
region of the country. The analysis identifies IFIs due to power outage caused by the storm that are of greatest societal
concern. These represent potential foci for effective, targeted pre-disaster mitigation and preparedness efforts. The framework
and approach are broadly applicable across a range of natural and human-induced hazards. 相似文献
24.
Molecular characterization of dissolved organic matter associated with the Greenland ice sheet 总被引：1，自引：0，他引：1
Maya P. Bhatia Krista Longnecker Elizabeth B. Kujawinski 《Geochimica et cosmochimica acta》2010,74(13):3768-9950
Subsurface microbial oxidation of overridden soils and vegetation beneath glaciers and ice sheets may affect global carbon budgets on glacial-interglacial timescales. The likelihood and magnitude of this process depends on the chemical nature and reactivity of the subglacial organic carbon stores. We examined the composition of carbon pools associated with different regions of the Greenland ice sheet (subglacial, supraglacial, proglacial) in order to elucidate the type of dissolved organic matter (DOM) present in the subglacial discharge over a melt season. Electrospray ionization (ESI) Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry coupled to multivariate statistics permitted unprecedented molecular level characterization of this material and revealed that carbon pools associated with discrete glacial regions are comprised of different compound classes. Specifically, a larger proportion of protein-like compounds were observed in the supraglacial samples and in the early melt season (spring) subglacial discharge. In contrast, the late melt season (summer) subglacial discharge contained a greater fraction of lignin-like and other material presumably derived from underlying vegetation and soil. These results suggest (1) that the majority of supraglacial DOM originates from autochthonous microbial processes on the ice sheet surface, (2) that the subglacial DOM contains allochthonous carbon derived from overridden soils and vegetation as well as autochthonous carbon derived from in situ microbial metabolism, and (3) that the relative contribution of allochthonous and autochthonous material in subglacial discharge varies during the melt season. These conclusions are consistent with the hypothesis that, given sufficient time (e.g., overwinter storage), resident subglacial microbial communities may oxidize terrestrial material beneath the Greenland ice sheet. 相似文献
25.
Abstract. Hermit crab shells are often encrusted with diverse communities of epibionts. To explore the effects of hermit crabs on the interactions of these encrusting species, two species of hydractiniid hydroids, Hydractinia symbiolongicarpus and Podocoryna carnea , were examined in the presence and absence of Pagurus longicarpus hermit crabs. Colonies growing on Littorina littorea snail shells with hermit crab hosts were compared to those growing on shells without crabs. These experiments suggest that hermit crabs variably affect colony polyp number, colony morphology and the outcome of interspecific competition, according to the size and number of crabs; other factors include water temperature, food availability and hydroid clonal genotype. In order to allow image analysis of perturbations of colony morphology, hydroids were grown on glass surfaces both exposed and unexposed to hermit crabs. Relative to colonies growing on unexposed surfaces, colonies growing on exposed surfaces exhibited larger within-colony patches, thus decreasing the total encrusted surface area and polyp number of colonies. Further, on glass surfaces, hermit crabs accelerated the time to the resolution of interspecific competition ( i.e. , the overgrowth of one colony by the other). While a number of factors may contribute to the relative abundance of these encrusting species, under most circumstances P. longicarpus have large effects on hydractiniid hydroids. Mechanisms underlying these effects likely include hydrodynamics and mechanical disturbance. 相似文献