Results 1 - 10 of 46337
Results 1 - 10 of 46337. Search took: 0.047 seconds
|Sort by: date | relevance|
[en] Knowledge of spatial variability is important for management of land affected by various anthropogenic activities. This study was conducted at West Mesa land application site to determine the spatial variability of electrical conductivity (EC1:1) and suggest suitable management strategy. Study area was divided into five classes with EC increasing from class I to V. According to the coefficient of variation (CV), during 2009 and 2010, EC1:1 values for different classes were low to moderately variable at each depth. Semivariogram analysis showed that EC1:1 displayed both short and long range variability. Area coverage of classes I and II were much higher than classes III, IV, and V during 2009. However, during 2010 area coverage decreased from 26% to 14.91% for class II, increased from 12.11% to 22.97%, and 10.95% to 20.55 for classes IV and V, respectively. Overall area under EC1:1= 4 dS/m increased during 2009. Soil EC map showed EC classes IV (4.1-5dS/m) and V (>5.1 dS/m) were concentrated at northwest and southeast and classes I and II were at the middle of the study plot. Thus, higher wastewater should be applied in the center and lower in the northwest and southwest part of the field.
[en] The concentrations of naturally occurring radionuclides (226Ra, 228Ra, 228Th, and 40K) in ashes of papers such as magazines and newspapers were determined from the nuclide concentrations in the papers and the ash contents of the papers. The average 226Ra, 228Ra, 228Th, and 40K concentrations in the 34 ashes were respectively 27, 68, 75, and 75Bq kg-1. The radium equivalent activities of the ashes were calculated to evaluate the hazard of γ-ray radiation from the ashes in the environment. A copying paper sample showed a high radium equivalent activity of 602Bq kg-1. However, the average radium equivalent activity was 140Bq kg-1 and was lower than the level that causes an environmental health problem. (author)
[en] Near-record warmth over much of the United States during March 2007 promoted early growth of crops and vegetation. A widespread arctic air outbreak followed in early April, resulting in extensive agricultural losses over much of the south-central and southeastern US. This 'false spring' event also resulted in widespread damage to newly grown tissues of native deciduous forest species, shown by previous researchers to have had measurable effects on the terrestrial carbon cycle. The current study reconstructed the historical occurrence of false springs over most of the southeastern quarter of the conterminous US (32-39 deg. N; 75-98 deg. W) from 1901 to 2007 using daily maximum and minimum temperature records from 176 stations in the Global Historical Climatology Network database, and enhanced vegetation index (EVI) data derived from Moderate Resolution Imaging Spectroradiometer (MODIS) satellite observations. A false spring index was derived that examined the timing of the start of the growing season (SGS), or leaf emergence, relative to the timing of a potentially damaging last hard freeze (minimum temperature ≤ - 2.2 deg. C). SGS was modeled for the domain by combining EVI data with ground-based temperature 'degree day' calculations reflecting the rate of springtime warming. No significant area-wide, long-term SGS trend was found; however, over much of a contiguous region stretching from Mississippi eastward to the Carolinas, the timing of the last hard freeze was found to occur significantly later, this change occurring along with increased frequency of false springs. Earlier last hard freeze dates and decreased frequency of false springs were found over much of the northwestern part of the study region, including Arkansas and southern Missouri.
[en] Ozone is associated with health impacts including respiratory outcomes; however, results differ across studies. Meta-analysis is an increasingly important approach to synthesizing evidence across studies. We conducted meta-analysis of short-term ozone exposure and respiratory hospitalizations to evaluate variation across studies and explore some of the challenges in meta-analysis. We identified 136 estimates from 96 studies and investigated how estimates differed by age, ozone metric, season, lag, region, disease category, and hospitalization type. Overall results indicate associations between ozone and various kinds of respiratory hospitalizations; however, study characteristics affected risk estimates. Estimates were similar, but higher, for the elderly compared to all ages and for previous day exposure compared to same day exposure. Comparison across studies was hindered by variation in definitions of disease categories, as some (e.g., asthma) were identified through ≥ 3 different sets of ICD codes. Although not all analyses exhibited evidence of publication bias, adjustment for publication bias generally lowered overall estimates. Emergency hospitalizations for total respiratory disease increased by 4.47% (95% interval: 2.48, 6.50%) per 10 ppb 24 h ozone among the elderly without adjustment for publication bias and 2.97% (1.05, 4.94%) with adjustment. Comparison of multi-city study results and meta-analysis based on single-city studies further suggested publication bias.
[en] In this study we investigate the possible reasons for the widespread differences between the seasonal cycles of carbon production and export compared to those of hypoxia in eastern boundary upwelling systems. An idealized model is proposed that qualitatively characterizes the relative roles of physics and biogeochemical fluxes. The model is tested on three contrasting upwelling systems: the Benguela (from relatively aerated to interannual anoxic), the Humboldt (sub-oxic and interannually anoxic) and the Cariaco (permanently anoxic). Overall we propose that shelf hypoxia variability can be explained on the basis of the interaction between ventilation by ocean boundary forcing through ocean-shelf exchange and the role of shelf geometry in the retention of shelf-based particulate organic carbon (POC) fluxes. We aim to identify the hypoxia regimes associated with low ventilation-wide-shelf systems and high ventilation-narrow-shelf systems, considering them as extremes of conditions controlled by the two factors. We propose that this may help to explain differences in the seasonal cycles of the biogeochemical drivers and responses as well as difference between upwelling systems and within individual upwelling systems. It is suggested that when seasonal hypoxia emerges it does so preferentially at a wide-shelf part of a system.
[en] Manufacturing of PCBs is highly complicated and involves many processes. Recycling of PCB wastewater receives wide concerns as the recent international growth in the electronics industry has generated a drastic increase in the amount of waste PCBs with profound environmental impacts such as soil and groundwater contamination. This paper reports on the chemical characterization of PCB wastewater as the initial investigation for selective metal recovery.
[en] Selenium (Se) is an essential micronutrient for human health, but its deficiency may affect at least one billion people worldwide. Plants and plant-derived products transfer the soil-uptaken Se to humans through the food chain, which is hardly enough when soils have been always poor or already exhausted in bioavailable Se species. Other than agronomic approaches for enhancing Se levels in cereals, such as soil and foliar supplements, seed enrichment may be viewed as an alternative Se-biofortification technique. This study addresses the protocol for preparing Se-enriched wheat seeds, with the specific purpose of optimizing the administration of Se to the seeds prior to sowing. The first step was to soak an amount of bread-wheat seeds in an active Se solution, made with irradiated [Na2O4Se], and then monitoring 75Se in periodically-retrieved samples from that original amount. To avoid losing Se to soil (after sowing), and, especially, to ensure that Se gets really absorbed into the seeds - and not just adsorbed onto them - the washing time of the seeds should be optimized as well. This was carried out by washing Se-treated seeds several times, until no significant amount of the radiotracer could be detected in the washing water. In what concerns the full optimization procedure, the overall results of the present study point to an optimum time of 48 h for soaking and 24 h for washing. (author)
[en] Since 2000, collaborative studies for applying NAA have been performed through the Forum for Nuclear Cooperation in Asia (FNCA) sponsored by the Japanese Government. White rice is a main food for Asians and thus was selected as a common target sample for a collaborative study in 2008. Seven Asian countries including China, Indonesia, Japan, Korea, Malaysia, Philippines and Thailand, are greatly concerned about the composition of arsenic, heavy metals, and essential trace elements and took part in this study. Rice samples were purchased and prepared by following a protocol that had been proposed for this study. Samples were analyzed by their own NAA systems. In each country, more than 10 elements were examined and the results were compared. These data will be very useful in the monitoring of the levels of food contamination and to evaluate the nutritional status for people living in Asia. (author)
[en] Heavy metal pollution in surface and groundwater has considerably increased in the last few years. It is essential to have an effective removal mechanism of these toxic metals. Current research includes the need to develop environment friendly and cost effective technologies for removing heavy metals from water. In several studies cadmium and nickel have been considerably removed using phytoremediation. The removal efficiency of cadmium and nickel by Spirodela polyrhiza, common duckweed has been examined in the present study for 3 different concentrations of cadmium (1, 2 and 3 mg/L) and nickel (4, 5 and 6 mg/L). Two sets of experiments for cadmium and nickel were conducted separately. Effect of metal toxicity on Spirodela polyrhiza was evaluated in terms of relative growth factor and cadmium was found to be more toxic than nickel. Under experimental condition BCF value for cadmium removal was more than >1000 in all the 3 concentrations of cadmium. But the BCF value was found to be more than > 1000 only when input nickel concentration was 4 mg/L during phytoremediation process. Experimental results suggest that Spirodela polyrhiza has the potential of accumulating cadmium and nickel from aqueous solution at lower metal concentration. (author)
[en] Photosynthetic assimilation of carbon dioxide and inorganic nutrients by phytoplankton constitutes a necessary prerequisite for sustaining marine life. This process is tightly linked to the concentration of chlorophyll in the ocean's euphotic zone. According to a recent field study marine chlorophyll(a) concentrations have declined over the last century with an estimated global rate of 1.0% of the global median per year. Here we attempt to identify possible mechanisms which could explain such trends. We explore these questions using an ocean general circulation model forced with documented historic and projected future anthropogenic emissions of carbon dioxide according to the IPCC SRES A1FI emission scenario until the year 2100. We further extend the time period covered by the A1FI scenario by assuming a linear decline in emissions from 2100 to 2200 and keeping them at zero levels until 2400. Our numerical simulations reveal only weak reductions in chlorophyll(a) concentrations during the twentieth century, but project a 50% decline between 2000 and 2200. We identify a local and a remotely acting mechanism for this reduction in the North Atlantic: (I) increased sea surface temperatures reduce local deep mixing and, hence, reduce the nutrient supply from waters at intermediate depths; (II) a steady shoaling of the Atlantic overturning cell tends to transport increasingly nutrient depleted waters from the Southern Hemisphere toward the north, leading to further diminishment of nutrient supply. These results provide support for a temperature-driven decline in ocean chlorophyll(a) and productivity, but suggest that additional mechanisms need to be invoked to explain observed declines in recent decades.