Long-term declines in two apex predators,bull sharks (<Emphasis Type="Italic">Carcharhinus leucas</Emphasis>) and alligator gar (<Emphasis Type="Italic">Atractosteus spatula</Emphasis>), in Lake Pontchartrain,an oligohaline estuary in southeastern Louisiana     

Martin T. O’Connell  Travis D. Shepherd  Ann M. U. O’Connell  Ransom A. Myers 《Estuaries and Coasts》2007,30(4):567-574

We analyzed historic and current fishery independent data to determine if the abundance of two apex predators, bull sharks (Carcharhinus leucas) and alligator gar (Atractosteus spatula), in Lake Pontchartrain had changed significantly over the last half century. Lake Pontchartrain is an environmentally degraded oligohaline estuary in southeastern Louisiana that has experienced considerable changes in fish assemblage composition over this interval. Using gillnet, beach seine, and trawl data collected during three time periods (1953–1955, 1977–1978, and 1996–2005), we analyzed trends in abundance forC. leucas andA. spatula using generalized linear models with a negative binomial error structure and a log link. Lake Pontchartrain data were divided into four spatial locations (northwest, northeast, southwest, southeast) since each region represents a unique combination of anthropogenic and natural influences that could affect catches. For each species and gear type, we produced log-likelihood profiles for the instantaneous rate of change in relative abundance through time. Raw catches were generally lower for both species in the later surveys.C. leucas were not captured in beach seines since the 1950s andA. spatula were rarely captured in trawls or seines since the 1970s. Likelihood profiles of changes in abundance forC. leucas andA. spatula showed very large declines in both species since 1953.C. leucas declined by 98.6% (95% CI: 73.4–99.9%) in gillnets and became functionally extirpated in beach seines with a decline of 99.9% (95% CI: 23–99.9%). Among all gears,C. leucas declined by the same rate as in gillnets. The decline inA. spatula was also large with a decrease of 98.6% (95% CI: 73.4–99.9%) in beach seines and a decline of 99.2% (95% CI: 54.8–99.9%) in trawls since 1953. Catches ofA. spatula in gillnets did not show a significant change over the study period. The continued decline of these two apex predators could seriously affect efforts to restore this degraded estuarine ecosystem.  相似文献   

America's Changing Farmscape: A Study of Agricultural Tourism in Michigan*     

Gregory Veeck  Deborah Che  Ann Veeck 《The Professional geographer》2006,58(3):235-248

Agricultural tourism incorporates visits to farms for the purposes of on‐site retail purchases, enjoyment, and education. Long popular in the European Union (EU), agritourism is gaining popularity throughout the United States. Interest has grown as a result of stagnant grain prices, rising farm costs, and growing international competition. For rural areas seeking new economic options, the potential of these operations to generate new sources of income through sales and horizontal linkages to other tourism‐based activities has sparked interest beyond the farm gate. This article, based on a survey and a statistical analysis of 300 agritourism operations in Michigan, summarizes factors associated with successful operations.  相似文献   

THE IMPACT OF METAL AND ORGANIC CONTAMINANTS ON THE STRUCTURE OF PERIPHYTON IN LOTIC SEDIMENTS: OBSERVATIONS AT VARIOUS SCALES     

Jill A. KOSTEL  Kimberly A. GRAY  Ann L. St. AMAND 《国际泥沙研究》2003,(2)

1 INTRODUCTION While wastewater discharge regulations have significantly reduced water column pollution, historical and accidental releases of organic pollutants and heavy metals continue to pose an ecological threat as these contaminants have become 搃n-place?sediment pollutants. It had been previously assumed that natural attenuation processes, such as burial or biodegradation, would decrease the contamination levels in surface sediments and, thus, diminish the environmental impact of t…  相似文献   

The Impacts of Socioeconomic Development and Climate Change on Severe Weather Catastrophe Losses: Mid-Atlantic Region (MAR) and the U.S.     

Onelack Choi  Ann Fisher 《Climatic change》2003,58(1-2):149-170

One strand of research relates the magnitude of severe weather disasters to climatic and human development factors; another highlights dramatic growth in catastrophe losses. However, there have been few attempts to put the two strands together. Here we use an explicit modeling framework to determine the contribution of climate variability relative to human factors in reported catastrophe losses. We then examine how future climate change can be expected to affect losses from natural disasters. Simultaneous regression models are constructed from three equations in which the dependent variables are U.S. flood loss, U.S. hurricane loss and U.S. catastrophe loss. Then two kinds of simulation under two climate change scenarios explore how climate change would affect losses. The climate change scenarios respectively project 13.5% and 21.5% increases in annual precipitation. The first simulation increases only the mean value of annual precipitation; the second simulation assumes that the mean and standard deviation of annual precipitation change in the same proportion. Results show that the growth in reported losses from weather-related natural disasters is due mainly to three socioeconomic factors: inflation, population growth and growth in per capita real wealth. However, weather variables such as precipitation and the number of hurricanes per period also clearly affect losses. The three stage least squares (3SLS) simultaneous equation model shows that a 1% increase in annual precipitation would enlarge catastrophe loss by as much as 2.8%. These findings are suggestive as planning signals to decision makers.  相似文献   

Equus species as stratigraphic markers reality or wishful thinking?     

Ann Forsten   《Quaternary Science Reviews》1998,17(12)

This paper addresses the use of fossil species of the horse Equus as stratigraphic markers in the Pliocene and Pleistocene. Current research shows that the species recently so used do not succeed one another in orderly fashion, but occur and co-occur at ages other than presupposed by the stratigraphic schemes (usually earlier). Horse species should be identified on their morphology, not on their stratigraphic age. ‘Subspecies’ of fossil horses do not conform to subspecies in zoology, as they lack a geographic range. They thus lack taxonomic status and stratigraphic significance and should be avoided.  相似文献   

Solar Total Irradiance: A Reference Value for Solar Minimum     

Ann T. Mecherikunnel 《Solar physics》1998,177(1-2):11-23

Simultaneous solar total irradiance observations performed by absolute radiometers on board satellites during the quiet-Sun period between solar cycles 21 and 22 (1985–1987), are analyzed to determine the solar total irradiance at 1 AU for the solar minimum. During the quiet-Sun period the total solar irradiance, UV irradiance, and the various solar activity indices show very little fluctuation. However, the absolute value of the solar total irradiance derived from the observations differ within the accuracy of the radiometers used in the measurements. Therefore, the question often arises about a reference value of the solar total irradiance for use in climate models and for computation of geophysical, and atmospheric parameters. This research is conducted as a part of the Solar Electromagnetic Radiation Study for Solar Cycle 22 (SOLERS22). On the basis of the study we recommended a reference value of 1367.0 ± 0.04 W m^-2 for the solar total irradiance at 1 AU for a truly quiet Sun. We also find that the total solar irradiance data for the quiet-Sun period reveals strong short-term irradiance variations.  相似文献   

Gas Production from an Ombrotrophic Bog-Effect of Climate Change on Microbial Ecology   总被引：1，自引：0，他引：1  

D. Ann Brown 《Climatic change》1998,40(2):277-284

Gases are produced from wetlands when plant biomass is degraded by microbial consortia, producing carbon dioxide aerobically and methane when oxygen is lacking. In anaerobic waterlogged situations, such as the catotelm of ombrotrophic bogs, this methane forms minute gas bubbles that severely reduce the hydraulic conductivity and hence the degradation of biomass due to the lack of nutrients. The bogs thus become carbon sinks, formed from the partially degraded biomass that accumulates as peat. The results of an investigation of an ombrotrophic bog, Mer Bleue, Ontario, Canada are summarized here, and the effects that climate change may have on such bogs are discussed. Any change of the water table in wetlands will have a substantial effect upon their ecology. If the water table should fall allowing bogs to become aerobic, most of the accumulated biomass carbon could be returned to the atmosphere by degradation to carbon dioxide, and as well, methane entrapped within the matrix would be released directly to the atmosphere. If on the other hand, the bogs are flooded, then the entrapped bubbles will coalesce allowing the gas to escape to the atmosphere, while at the same time the degradation of the peat will be enhanced.  相似文献   

A method for the separation of paramagnetic, ferrimagnetic and haematite magnetic subfabrics using high-field torque magnetometry   总被引：2，自引：0，他引：2  

Fátima Martín-Hernández  Ann M. Hirt 《Geophysical Journal International》2004,157(1):117-127

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Role of Volcanic Tuffs in Ground-Water Regime of Valle Central, Costa Rica   总被引：1，自引：0，他引：1  

Stephen S. D. Foster  Ann T. Ellis  Marcelino Losilla-Penon  Hugo V. Rodriguez-Estrada 《Ground water》1985,23(6):795-801

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Turbulence mechanisms at an agricultural site   总被引：8，自引：0，他引：8  

Högström  Ulf  Smedman-Högström  Ann -Sofi 《Boundary-Layer Meteorology》1974,7(3):373-389

An extensive set of turbulence data from the 3- and 12-m heights taken over an agricultural site (Marsta, Sweden) are analyzed and compared with data from ideal sites.In unstable air, Monin-Obukhov similarity is found to be valid for the non-dimensional gradients of wind, _m , temperature, _h , and humidity, _e , for (only a few data), for _T /|T _*|,/ _E /|E _*| and for the non-dimensionalized inertial subrange spectra of temperature and humidity. Where comparison is possible, the unstable data also agree with those found in the Kansas study, with one remarkable exception, the inertial subrange constant of the temperature spectrum, ₁, being only 0.39, compared to the value 0.80 found at the Kansas site.On the stable side, most similarity predictions break down, with most of the data differing systematically from the corresponding Kansas results, the only exception being . The inertial subrange constants for temperature, ₁, and for humidity, ₁ are found to have the same values, 0.39 and 0.30, respectively, as they do on the unstable side. Remarkable similarity is found for the shape of the stable u- and - and e-spectra. In addition, this shape is found to be identical with that found in Kansas. The peak wavelength of the stable u-, and -spectra is found to be about four times larger than it is for the corresponding Kansas spectra. This is interpreted to be a result of the increased macro-roughness at the Marsta site as compared with that at the Kansas site. A possible explanation for the low ₁-value is discussed, suggesting that ₁ is not a universal constant, but instead dependent on the turbulent structure.  相似文献