Rheological study of biodegradable blends of starch and polyvinyl alcohol

The rheological behavior of biodegradable blends of starch and poly(vinyl alcohol) (PVOH) was measured as a function of temperature, shear rate, and moisture content using a capillary rheometer. An excellent correlation was found with a rheological model which was used as a means to characterize the influence of starch/PVOH content as well as a qualification of the viscosity for simulation studies. This model consisted of a power law dependence on shear rate, an Arrhenius dependence on temperature, and an exponential dependence on moisture.Paper presented at the Biodegradable Materials and Packaging Conference, September 22–23, 1993, Natick, Massachusetts.Guest Editor: Dr. Randall Shogren, USDA.     

Hydrodynamic and chemical conditions during onset of a red-tide assemblage in an estuarine upwelling ecosystem

The hydrodynamics and nitrogen/silicon biogeochemistry accompanying the development of a red-tide assemblage were examined in the Ría de Vigo (northwest Spain), a coastal embayment affected by upwelling, during an in situ diel experiment in September 1991. Despite a low N:Si molar ratio (0.5) of nutrients entering the surface layer, which was favourable for diatom growth, the diatom population began to decline. Limited N-nutrient input, arising from moderate coastal upwelling in a stratified water column, restricted net community production (NCP = 630 mg C m⁻² d⁻¹). In addition, light-limitation of gross primary production (GPP = 1525 mg C m⁻² d⁻¹) was observed. The relatively high f-ratio (= NCP:GPP) recorded (0.41, characteristic of intense upwelling conditions) would have been as low as 0.15 had not GPP been limited by light intensity. Temporal separation of carbohydrate synthesis during the photoperiod from protein synthesis in the dark could be inferred from the time-course of the C:N ratio of particulate organic matter. Severe light-limitation would lead to diatom collapse were the diatoms not able to meet all their energy requirements during the hours of darkness. Under the hydrodynamic, nutrient and light conditions of the experiment, an assemblage of red-tide-forming species began to develop, aided by their ability to migrate vertically and to synthesize carbohydrates during the light in surface waters and protein during the dark at the 4 m-deep pycnocline. Thermal stratification, reduced turbulence, intense nutrient mineralization, and the limited nitrogen input through moderate upwelling were all favourable to the onset of a red-tide assemblage. Received: 15 February 1997 / Accepted: 26 September 1997     

Maternal exposure to specific perfluoroalkyl substances is associated with increasing blood glucose in pregnant women

正Imagine if a group of toxic substances that increase oxidative stress and disrupt glucose and lipid metabolism have been broadly used worldwide for applications such as repellent,food packaging,and non-stick frying pan coatings.Now imagine if some of these substances have half-lives as long as 3-8 years.This is an environmental reality that has come to light with perfluoroalkyl and polyfluoroalkyl substances(PFASs)–high     

Anguilliform fishes and sea kraits: neglected predators in coral-reef ecosystems

Despite intensive sampling efforts in coral reefs, densities and species richness of anguilliform fishes (eels) are difficult to quantify because these fishes evade classical sampling methods such as underwater visual census and rotenone poisoning. An alternative method revealed that in New Caledonia, eels are far more abundant and diverse than previously suspected. We analysed the stomach contents of two species of sea snakes that feed on eels (Laticauda laticaudata and L. saintgironsi). This technique is feasible because the snakes return to land to digest their prey, and (since they swallow their prey whole) undigested food items are identifiable. The snakes’ diet consisted almost entirely (99.6%) of eels and included 14 species previously unrecorded from the area. Very large populations of snakes occur in the study area (e.g. at least 1,500 individuals on a small coral islet). The snakes capture approximately 36,000 eels (972 kg) per year, suggesting that eels and snakes play key roles in the functioning of this reef ecosystem.     

Production and Consumption of NO in Forest and Pasture Soils from the Amazon Basin

NO production and the rate constant of NO consumptionin soil samples from Amazonian forest and pasturesites were determined in the laboratory. The purposewas to study NO production and consumption in soilsfrom both types of land use as functions of soiltemperature and soil moisture. NO productionincreased exponentially with soil temperature. Thedegree of increase depended on soil moisture,indicating that the response of NO production to achange in soil temperature is most pronounced at acertain intermediate soil moisture. NO productionpeaked at a soil moisture of 0.10 g g^-1, correspondingto 0.27 and 0.38 water-filled pore space for forestand pasture soils, respectively. The optimum soilmoisture for which maximum NO release was observedwas independent of soil temperature. NO consumptionwas most efficient at high soil temperatures andunder dry soil conditions. NO release wasapproximately 10 times larger for forest than pasturesoil. The difference may be related to the higherNO₃ ^- content in forest soil.     

A screening model-based study of transport fluxes and fate of airborne mercury deposited onto catchment areas.

Dynamics of airborne mercury deposited onto catchment areas is investigated within the framework of a simulation model. Model results show that, for a particular atmospheric deposition rate, significant interannual variability in mercury transport flux in catchments is caused by climatology and corresponding differences in catchment soil loss rates; in comparison to the normal year, runoff flux increased by a factor of 2-3 for the wet year (rainfall 35% above normal) while for the dry year (rainfall 18% below normal) runoff flux decreased by factors of 5-7. The interaction of parameters describing soil type, topography and vegetation cover causes variability in both transport and emission fluxes among catchments; as soil loss rate increases by a factor of 5 due to variations in these parameters among the examined catchments, annual average transport flux increases by a factor of 3; and annual average emission flux of mercury (as Hg0) from soil to the atmosphere decreases by a factor of 2 due to the decreased levels of soil mercury associated with catchment soil loss increases. Seasonal variability of transport flux is associated with seasonal changes in precipitation and soil loss rates while seasonal changes of emission flux are primarily due to changes in soil moisture regime and temperature. Although modeled results are consistent with observational data from previous studies, they must be interpreted in a relative sense due to the screening-level character of this study.     

QSAR study on the toxicity of substituted benzenes to the algae (Scenedesmus obliquus).

50% effective inhibition concentration 48h-EC50 of 40 substituted benzenes to the algae (Scenedesmus obliquus) was determined. The energy of the lowest unoccupied molecular orbital (E(LUMO)) was calculated by the quantum chemical method MOPAC6.0-AM1. By using E(LUMO) and the hydrophobicity parameter log K(OW) the quantitative structure-activity relationship model (QSAR) was developed: log1/EC50=0.272 logK(OW) - 0.659E(LUMO) + 2.54, R2 = 0.793, S.E. = 0.316, F = 71.07, n = 40. A series of equations were obtained about the measured EC50 values of different subclasses of compounds. For those compounds containing double -NO2, their toxicity may be related chiefly to the intracellular reduction of -NO2 obtaining electron, while for anilines and phenols, K(OW) contributes most to the QSAR and E(LUMO) very little.     

Empirical assessment of state-and-transition models with a long-term vegetation record from the Sonoran Desert

Resilience-based frameworks, including state-and-transition models (STM), are being increasingly called upon to inform policy and guide ecosystem management, particularly in rangelands. Yet, multiple challenges impede their effective implementation: (1) paucity of empirical tests of resilience concepts, such as alternative states and thresholds, and (2) heavy reliance on expert models, which are seldom tested against empirical data. We developed an analytical protocol to identify unique plant communities and their transitions, and applied it to a long-term vegetation record from the Sonoran Desert (1953-2009). We assessed whether empirical trends were consistent with resilience concepts, and evaluated how they may inform the construction and interpretation of expert STMs. Seven statistically distinct plant communities were identified based on the cover of 22 plant species in 68 permanent transects. We recorded 253 instances of community transitions, associated with changes in species composition between successive samplings. Expectedly, transitions were more frequent among proximate communities with similar species pools than among distant communities. But unexpectedly, communities and transitions were not strongly constrained by soil type and topography. Only 18 transitions featured disproportionately large compositional turnover (species dissimilarity ranged between 0.54 and 0.68), and these were closely associated with communities that were dominated by the common shrub (burroweed, Haplopappus tenuisecta); indicating that only some, and not all, communities may be prone to large compositional change. Temporal dynamics in individual transects illustrated four general trajectories: stability, nondirectional drift, reversibility, and directional shifts that were not reversed even after 2-3 decades. The frequency of transitions and the accompanying species dissimilarity were both positively correlated with fluctuation in precipitation, indicating that climatic drivers require more attention in STMs. Many features of the expert models, including the number of communities and participant species, were consistent with empirical trends, but expert models underrepresented recent increases in cacti while overemphasizing the introduced Lehmann's lovegrass (Eragrostis lehmanniana). Quantification of communities and transitions within long-term vegetation records presents several quantitative metrics such as transition frequency, magnitude of accompanying compositional change, presence of unidirectional trajectories, and lack of reversibility within various timescales, which can clarify resilience concepts and inform the construction and interpretation of STMs.