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1.
Steven G. Morgan Jennifer L. Fisher Skyli T. McAfee John L. Largier Seth H. Miller Megan M. Sheridan Joseph E. Neigel 《Estuaries and Coasts》2014,37(5):1269-1283
The effectiveness of larval behavior in regulating transport between well-mixed, low-inflow estuaries and coastal waters in seasonally arid climates is poorly known. We determined the flux of an assemblage of benthic crustacean larvae relative to physical conditions between a shallow estuary and coastal waters on the upwelling coast of northern California (38°18′N, 123°03′W) from 29 to 31 March 2006. We detected larval behaviors that regulate transport in adjacent coastal waters and other estuaries for only two taxa in the low-inflow estuary, but they were apparent for taxa outside the estuary. Vertical mixing in the shallow estuary may have overwhelmed larvae of some species, or salinity fluctuations may have been too slight to cue tidal vertical migrations. Nevertheless, all larval stages of species that complete development in nearshore coastal waters were present in the estuary, because they remained low in the water column reducing seaward advection or they were readily exchanged between the estuary and open coast by tidal flows. Weak tidal flows and gravitational circulation at the head of the estuary reduced seaward transport during development for species that completed development nearshore, whereas larval release during nocturnal ebb tides enhanced seaward transport for species that develop offshore. Thus, nonselective tidal processes dominated larval transport for most species back and forth between the low-inflow estuary and open coastal waters, whereas in adjacent open coastal waters, larval behavior in the presence of wind-induced shear was more important in regulating migrations between adult and larval habitats along this upwelling coast. 相似文献
2.
Hydrological threshold behaviour has been observed across hillslopes and catchments with varying characteristics. Few studies, however, have evaluated rainfall–run‐off response in areas dominated by agricultural land use and artificial subsurface drainage. Hydrograph analysis was used to identify distinct hydrological events over a 9‐year period and examine rainfall characteristics, dynamic water storage, and surface and subsurface run‐off generation in a drained and farmed closed depression in north‐eastern Indiana, USA. Results showed that both surface flow and subsurface tile flow displayed a threshold relationship with the sum of rainfall amount and soil moisture deficit (SMD). Neither surface flow nor subsurface tile flow was observed unless rainfall amount exceeded the SMD. Timing of subsurface tile flow relative to soil moisture response on the shoulder slope of the depression indicated that the formation and drainage of perched water tables on depression hillslopes were likely the main mechanism that produced subsurface connectivity. Surface flow generation was delayed compared with subsurface tile flow during rainfall events due to differences in soil water storage along depression hillslopes and run‐off generation mechanisms. These findings highlight the substantial impact of subsurface tile drainage on the hydrology of closed depressions; the bottom of the depression, the wettest area prior to drainage installation, becomes the driest part of the depression after installation of subsurface drainage. Rapid connectivity of localized subsurface saturation zones during rainfall events is also greatly enhanced because of subsurface drainage. Thus, less fill is required to generate substantial spill. Understanding hydrologic processes in drained and farmed closed depressions is a critical first step in developing improved water and nutrient management strategies in this landscape. 相似文献
3.
Chakraborty Jayajit McAfee Ashley A. Collins Timothy W. Grineski Sara E. 《Natural Hazards》2021,106(3):2185-2205
Natural Hazards - This article contributes to research on social vulnerability to natural hazards by analyzing the relationship between spatial patterns of flooding caused by Hurricane Harvey and... 相似文献
4.
Adaptation planning in Alaska, as in other snowy parts of the world, will require snow projections, yet snow is a challenging variable to measure, simulate and downscale. Here we describe the construction and evaluation of 771‐m‐resolution gridded historical and statistically downscaled projections of snow/rain partitioning for the state of Alaska at decadal temporal resolution. The method developed here uses observational data to describe the relationship between average monthly temperature and the fraction of wet days in that month receiving snow, the snow‐day fraction. Regionally and seasonally specific equations were developed to accommodate variability in synoptic scale climatology of rain and snow events. These equations were then applied to gridded decadal temperature data and projections. The gridded products provide a reasonable characterization of snow‐day fraction throughout the state. However, there are local deviations from the regional relationships, particularly in the topographically complex areas ringing the Gulf of Alaska and Cook Inlet. When applied to questions about changing precipitation regimes in northern, western and south‐eastern Alaska, these data demonstrate the potential for marked changes from snow‐dominated to mixed precipitation regimes and also exhibit a wide range of potential future conditions. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
5.
Stephanie A. McAfee 《Climatic change》2013,120(4):915-930
There is growing concern that the higher temperatures expected with climate change will exacerbate drought extent, duration and severity by enhancing evaporative demand. Temperature-based estimates of potential evapotranspiration (PET) are popular for many eminently practical reasons and have served well in many research and management settings. However, a number of recent publications have questioned whether it is appropriate to use temperature-based PET estimates for long-term evaporative demand and drought projections, demonstrating that PET does not always track temperature. Where precipitation changes are modest, methodologically driven differences in the magnitude or direction of PET trends could lead to contrasting drought projections. Here I calculate PET by three methods (Hamon, Priestley-Taylor and Penman) and evaluate whether different techniques introduce disparities in the sign of PET change, the degree of model agreement, or the magnitude of those changes. Changes in temperature-based Hamon PET were more significantly and consistently positive than trends in PET estimated by other methods, and where methods agreed that summer PET would increase, trends in temperature-based PET were often larger in magnitude. The discrepancies in PET trends appear to derive from regional changes in incoming shortwave radiation, wind speed and humidity -- phenomena simpler equations cannot capture. Because multiple variables can influence trends in PET, it may be more justifiable to use data-intensive methods, where the source(s) of uncertainty can be identified, rather than using simpler methods that could mask important trends. 相似文献
6.
General circulation models (GCMs) have demonstrated success in simulating global climate, and they are critical tools for producing regional climate projections consistent with global changes in radiative forcing. GCM output is currently being used in a variety of ways for regional impacts projection. However, more work is required to assess model bias and evaluate whether assumptions about the independence of model projections and error are valid. This is particularly important where models do not display offsetting errors. Comparing simulated 300-hPa zonal winds and precipitation for the late 20th century with reanalysis and gridded precipitation data shows statistically significant and physically plausible associations between positive precipitation biases across all models and a marked increase in zonal wind speed around 30°N, as well as distortions in rain shadow patterns. Over the western United States, GCMs project drier conditions to the south and increasing precipitation to the north. There is a high degree of agreement between models, and many studies have made strong statements about implications for water resources and about ecosystem change on that basis. However, since one of the mechanisms driving changes in winter precipitation patterns appears to be associated with a source of error in simulating mean precipitation in the present, it suggests that greater caution should be used in interpreting impacts related to precipitation projections in this region and that standard assumptions underlying bias correction methods should be scrutinized. 相似文献
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8.
Kathleen McAfee 《Geoforum》2008,39(1):148-160
Disputes about genetically engineered crops are linked to wider debates about the globalization of agro-food systems and its consequences for food security, social equity, and rural life. Biotechnology expert discourse rarely addresses these wider issues. An exception is the assessment of transgenic maize by the NAFTA Commission on Environmental Cooperation (CEC), which recommended a moratorium on Mexican imports of US-grown maize. Controversy about “contamination” of indigenous maize varieties by US-grown transgenic corn has been intensified by rising Mexican discontent with the terms of regional economic integration. In this context, scientists and officials were pressured to consider not only risks to maize biodiversity but also the ecological, and cultural characteristics of maize in its Mexican settings and the implications of asymmetric power in North American agricultural trade. In contrast to most narrowly-framed biotechnology risk assessments, the review took account of interventions by rural social movements. While the new moratorium was not adopted by the state, continuing conflicts over GMOs in Mexico have blocked introduction of transgenic maize and have enlarged the political space for debate over Mexico’s development direction. These conflicts reflect the differing interests of various state actors and economic sectors with regard to trade liberalization. They also reveal contrasting food-system paradigms: further agricultural modernization, export competition, and food-import dependence versus an alternative vision of revitalized rural life, farmers’ rights, and national food sovereignty. 相似文献
9.
The Mariner 6 and 7 infrared spectrometers provided data which, in principle, determine upper limits on the possible atmospheric abundance of every gaseous substance that was undetected but which has recognized absorptions in the accessible spectral region, 1.9 to 14.4 μ. Through supporting laboratory determinations of curves of growth under pressure broadening conditions appropriate to Mars, upper limits can be specified (expressed first in cm-atm, STP, for a vertical column and then in parts per million) for the following gases: NO2 (<0.0016, 0.23); NH3 (<0.0031, 0.44); C3O2 (<0.0032, 0.45); SO2 (?0.0037, 0.52); OCS (<0.0040, 0.56); NO (<0.0050, 0.70); O3 (<0.0061, 0.86); CH4 (<0.026, 3.7); N2O (<0.13, 18); HCl (<3.7, 520); HBr (?8.2, 1150); H2S (<27, 3800). In addition, considerations of band contours, moments of inertia, and experimental absorption coefficients permit us to place useful upper limits on twenty-seven additional substances that were not detected and for which curves of growth have not been measured: less than 1.0ppm (or, <0.0071cm-atm); SF6, NF3, Cl2CO, CF4, CHF3, Br2CO, SiF4; less than 6.0ppm (or, <0.035 cm-atm); C2F6, CO3, F2CO, C2H4, BF3, CS2, CHCl3, C2H6, H2CO, CH3F, C6H6, CH2I2; less than 50ppm (or, <0.35 cm-atm): C2H2, HCN, CH2Br2, CH2Cl2, CH3Br, PH3, CH3I, and CH3Cl. These upper limits are compared to earlier limits based upon terrestrial measurements. The present limits placed upon the possible atmospheric content of the molecules C3O2 and CO3 are of particular interest because of their relevance to the photochemistry of the Martian atmosphere. 相似文献
10.
Kathleen McAfee 《Geoforum》2003,34(2):203-219
New agro-biotechnologies promise bounty from fine-tuned molecular manipulation of food crops. They already provide profits and export opportunities to a few transnational seed/ agrochemical/ biotechnology firms. Against growing resistance in international arenas, industry and US government spokespeople have aggressively promoted genetic engineering, arguing that it permits precise control of life processes. However, this claim is based on a deceptive form of molecular-genetic reductionism which uses outdated notions of “genes” and “genetic codes” and disregards the interactions among molecules, organisms, their environments, and their social settings. This discourse, in turn, supports economic-reductionist arguments that genetic information should be patentable and that market-based management of biotechnology will benefit everyone. This double reductionism furthers the extension of the commodity realm to the molecular level. It treats biotechnology inputs (genetic resources) and outputs (transgenic products) as ordinary, tradable factors of production under globally standardized intellectual property regimes and bolsters proposals to regulate biotechnology under the World Trade Organization. Critics of this approach find some support in the Biodiversity Convention and its Biosafety Protocol, which would allow consideration of scientific uncertainty, socioeconomic factors, and pluralism in intellectual property regimes. They stress that natural-resource values and knowledge about nature are inseparable from place-specific ecologies, cultural practices of farming and science, and power relations. 相似文献