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81.
Ylitalo GM Stein JE Hom T Johnson LL Tilbury KL Hall AJ Rowles T Greig D Lowenstine LJ Gulland FM 《Marine pollution bulletin》2005,50(1):30-39
Wild California sea lions (Zalophus californianus) have an unusually high prevalence of neoplasms (18% of stranded dead adults) and high levels of contaminants. The contribution of organochlorine (OC) tissue burdens to the probability of sea lions dying from carcinoma was explored using a logistic regression model. Levels of PCBs and DDTs were determined in blubber of sea lions diagnosed with metastatic carcinoma and animals that had died from non-carcinoma-related incidents (e.g., gunshot, domoic acid poisoning). Animals with carcinoma had higher mean concentrations (based on wet weight) of PCBs and DDTs (more than 85% and 30% higher, respectively) in blubber than did sea lions without carcinoma; the highest concentrations of OCs in the sea lions affected with carcinoma were measured in the males. Blubber thickness was significantly different between the two groups of sea lions, but after controlling for this difference, there was still a significant effect of PCBs, but not DDTs, on the probability of sea lions dying with carcinoma. Age, sex, mass and length did not affect the probability of dying from carcinoma. 相似文献
82.
Research on the effects of declining abundances of the Eastern oyster (Crassostrea virginica) in Chesapeake Bay and other estuaries has primarily focused on the role of oysters in filtration and nutrient dynamics,
and as habitat for fish or fish prey. Oysters also play a key role in providing substrate for the overwintering polyp stage
of the scyphomedusa sea nettle,Chrysaora quinquecirrha, which is an important consumer of zooplankton, ctenophores, and icthyoplankton. Temporal trends in sea nettle abundances
in visual counts from the dock at Chesapeake Biological Laboratory, trawls conducted in the mesohaline portion of the Patuxent
River, and published data from the mainstem Chesapeake Bay indicate that sea nettles declined in the mid 1980s when overfishing
and increased disease mortality led to sharp decreases in oyster landings and abundance. Climate trends, previously associated
with interannual variation in sea nettle abundances, do not explain the sharp decline. A potentially important consequence
of declining sea nettle abundances may be an increase in their ctenophore prey (Mnemiopsis leidyi), and a resultant increase in predation on icthyoplankton and oyster larvae. Increased predation on oyster larvae by ctenophores
may inhibit recovery of oyster populations and reinforce the current low abundance of oysters in Chesapeake Bay. 相似文献
83.
Denise Goerisch 《The Professional geographer》2017,69(2):307-313
In this article, I argue that there is a need to examine the feminist ethics of volunteering in the field, specifically as it relates to issues of positionality, power and reciprocity, and participatory methods. Reflecting on dilemmas I experienced as a volunteer with the Girl Scouts of San Diego while conducting research on their annual Girl Scout cookie sale, I debate the relationship between volunteerism and fieldwork more broadly and question the effectiveness of volunteerism within a feminist geographic methodological framework. In light of the dilemmas that arose in the field as a volunteer and researcher, I question whether we can consider volunteering as “good work.” 相似文献
84.
Tobias Schneider Denise Rimer Christoph Butz Martin Grosjean 《Journal of Paleolimnology》2018,60(3):381-398
Eutrophication, prompted by anthropogenic activities and climate change has led to multiple adverse effects in freshwater systems across the world. As instrumental measurements are typically short, lake sediment proxies of aquatic primary productivity (PP) are often used to extend the observational record of eutrophication back in time. Sedimentary pigments provide specific information on PP and major algal communities, but the records are often limited in the temporal resolution. Hyperspectral imaging (HSI) data, in contrast, provide very high seasonal (sub-varve-scale) resolution, but the pigment speciation is limited. Here, we explore a combined approach on varved sediments from the Ponte Tresa basin, southern Switzerland, taking the advantages of both methods (HSI and high performance liquid chromatography, HPLC) with the goal to reconstruct the recent eutrophication history at seasonal to interannual resolution. We propose a modified scheme for the calibration of HSI data (here: Relative Absorption Band Depth between 590 and 730 nm RABD590–730) and HPLC-inferred pigment concentrations (here: ‘green pigments’ {chlorophyll a and pheophytin a}) and present a calibration model (R2?=?0.82; RMSEP?~?12%). The calibration range covers >?98% of the spectral index values of all individual pixels (68 µm?×?68 µm) in the sediment core. This allows us to identify and quantify extreme pigment concentrations related to individual major algal blooms, to identify multiple algal blooms within one season, and to assess interannual variability of PP. Prior to the 1930s, ‘green pigment’ concentrations and fluxes (~?50 µg g?1;?~?2 µg cm?2a?1, chlorophyll a and pheophytin a) and interannual variability was very low. From the 1930s to 1964, chlorophyll a and pheophytin a increased by a factor of ~?4, and ββ-carotene appeared in substantial amounts (~?0.4 µg cm?2a?1). Interannual variability increased markedly and a first strong algal bloom with ‘green pigment’ concentrations as high as 700 µg g?1 is observed in 1958. Peak eutrophication (~?12 µg cm?2a?1 chlorophyll a and pheophytin a) and very high interannual variability with extreme algal blooms (‘green pigment’ concentrations up to 1400 µg g?1) is observed until ca. 1990, when eutrophication decreases slightly. Maximum PP values after 2009 are likely the result of internal nutrient cycling related to repeated deep mixing of the lake. 相似文献
85.
86.
Many controversial questions about the shape and evolution of city size distributions can be solved if reliable, large and comparable set of data are used for several countries. We provide new empirical evidence by using the large data base Geopolis, which has strictly comparable figures for all towns and cities of the world over 10,000 inhabitants between 1950 and 1990. A Pareto model is used for identifying as metropolises one or a few large cities for each national urban system. From those data, two empirical power laws are established, linking the size of the metropolises to the size of their national urban system. The first is a transversal law: for a set of countries at a given date, the share of population concentrated in metropolises tends to decrease when larger countries are considered. The second law, which is longitudinal, shows that metropolises in the past have grown in a systematic way more rapidly than the rest of their urban system, invalidating Gibrat's urban growth model. Such empirical regularities could help for predicting the future of nowadays observed metropolisation trends. 相似文献
87.
Matthew S. Kornis Denise Breitburg Richard Balouskus Donna M. Bilkovic Lori A. Davias Steve Giordano Keira Heggie Anson H. Hines John M. Jacobs Thomas E. Jordan Ryan S. King Christopher J. Patrick Rochelle D. Seitz Heather Soulen Timothy E. Targett Donald E. Weller Dennis F. Whigham Jim UphoffJr 《Estuaries and Coasts》2017,40(5):1464-1486
Human alteration of land cover (e.g., urban and agricultural land use) and shoreline hardening (e.g., bulkheading and rip rap revetment) are intensifying due to increasing human populations and sea level rise. Fishes and crustaceans that are ecologically and economically valuable to coastal systems may be affected by these changes, but direct links between these stressors and faunal populations have been elusive at large spatial scales. We examined nearshore abundance patterns of 15 common taxa across gradients of urban and agricultural land cover as well as wetland and hardened shoreline in tributary subestuaries of the Chesapeake Bay and Delaware Coastal Bays. We used a comprehensive landscape-scale study design that included 587 sites in 39 subestuaries. Our analyses indicate shoreline hardening has predominantly negative effects on estuarine fauna in water directly adjacent to the hardened shoreline and at the larger system-scale as cumulative hardened shoreline increased in the subestuary. In contrast, abundances of 12 of 15 species increased with the proportion of shoreline comprised of wetlands. Abundances of several species were also significantly related to watershed cropland cover, submerged aquatic vegetation, and total nitrogen, suggesting land-use-mediated effects on prey and refuge habitat. Specifically, abundances of four bottom-oriented species were negatively related to cropland cover, which is correlated with elevated nitrogen and reduced submerged and wetland vegetation in the receiving subestuary. These empirical relationships raise important considerations for conservation and management strategies in coastal environments. 相似文献
88.
To increase the safety and efficiency of tunnel constructions, online seismic exploration ahead of a tunnel has become a valuable tool. One recent successful forward looking approach is based on the excitation and registration of tunnel surface‐waves. For further development and for finding optimal acquisition geometries it is important to study the propagation characteristics of tunnel surface‐waves. 3D seismic finite difference modelling and analytic solutions of the wave equation in cylindrical coordinates reveal that at higher frequencies, i.e., if the tunnel‐diameter is significantly larger than the wavelength of surface‐waves, these surface‐waves can be regarded as Rayleigh‐waves confined to the tunnel wall and following helical paths along the tunnel axis. For lower frequencies, i.e., when the tunnel surface‐wavelength approaches the tunnel‐diameter, the propagation characteristics of these surface‐waves are similar to S‐waves. We define the surface‐wave wavelength‐to‐tunnel diameter ratio w to be a gauge for separating Rayleigh‐ from S‐wave excitation. For w > 1.2 tunnel surface‐waves behave like S‐waves, i.e. their velocity approaches the S‐wave velocity and the particle motion is linear and perpendicular to the ray direction. For w < 0.6 they behave like Rayleigh‐waves, i.e., their velocity approaches the Rayleigh‐wave velocity and they exhibit elliptical particle motion. For 0.6 < w < 1.2 a mixture of both types is observed. Field data from the Gotthard Base Tunnel (Switzerland) show both types of tunnel surface‐waves and S‐waves propagating along the tunnel. 相似文献
89.
Sarah A. Lewis Peter R. Robichaud Bruce E. Frazier Joan Q. Wu Denise Y.M. Laes 《Geomorphology》2008,95(3-4):192-205
A principal task of evaluating large wildfires is to assess fire's effect on the soil in order to predict the potential watershed response. Two types of soil water repellency tests, the water drop penetration time (WDPT) test and the mini-disk infiltrometer (MDI) test, were performed after the Hayman Fire in Colorado, in the summer of 2002 to assess the infiltration potential of the soil. Remotely sensed hyperspectral imagery was also collected to map post-wildfire ground cover and soil condition. Detailed ground cover measurements were collected to validate the remotely sensed imagery and to examine the relationship between ground cover and soil water repellency. Percent ash cover measured on the ground was significantly correlated to WDPT (r = 0.42; p-value < 0.0001), and the MDI test (r = − 0.37; p-value < 0.0001). A Mixture Tuned Matched Filter (MTMF) spectral unmixing algorithm was applied to the hyperspectral imagery, which produced fractional cover maps of ash, soil, and scorched and green vegetation. The remotely sensed ash image had significant correlations to the water repellency tests, WDPT (r = 0.24; p-value = 0.001), and the MDI test (r = − 0.21; p-value = 0.005). An iterative threshold analysis was also applied to the ash and water repellency data to evaluate the relationship at increasingly higher levels of ash cover. Regression analysis between the means of grouped data: MDI time vs. ash cover data (R2 =0.75) and vs. Ash MTMF scores (R2 = 0.63) yielded significantly stronger relationships. From these results we found on-the-ground ash cover greater than 49% and remotely sensed ash cover greater than 33% to be indicative of strongly water repellent soils. Combining these results with geostatistical analyses indicated a spatial autocorrelation range of 15 to 40 m. Image pixels with high ash cover (> 33%), including pixels within 15 m of these pixel patches, were used to create a likelihood map of soil water repellency. This map is a good indicator of areas where soil experienced severe fire effects—areas that likely have strong water repellent soil conditions and higher potential for post-fire erosion. 相似文献
90.
We propose a general method for evaluating, and possibly improving, the interface between scientific research and policy-making institutions. The method considers the adequacy of both institutional structures for incorporating research, and research for addressing institutional needs. It involves both interviews (with policy makers and scientists) and formal analyses of the links between the research and the decisions described in the interviews. A case study applies the method in analyzing the usefulness of climate change research for managing salmon runs in the Pacific Northwest. It shows these policy makers to be receptive to the research, which is, in principle, relevant to them. However, they are unable to use it because the research is not currently formulated in ways compatible with current decision-making models. For their part, these models are not comprehensive enough to capture the full range of potentially relevant environmental forcers, including climate change. 相似文献