Abstract: This study applies spatial analyses to examine the consequences of accelerated urban expansion on a hydrologic system over a period of 24 years. Three sets of historical aerial photos are used in a GIS analysis to document the geomorphic history of Las Vegas Wash, which drains the rapidly growing Las Vegas urban area in southern Nevada. New spatial techniques are introduced to make quantitative measurements of the erosion at three specific time intervals in the hydrologic evolution of the channel and floodplain. Unlike other erosion studies that use two different elevation surfaces to assess erosion, this study used a single elevation surface to remove systematic and nonsystemic elevation errors. The spatial analysis quantifies channel changes for discrete time periods, calculates erosion volumes, and provides a foundation to examine how the specific mechanisms related to urban expansion have affected Las Vegas Wash. The erosion calculated over 24 years is the largest documented sediment loss attributed to the effect of rapid urban growth. 相似文献
The tiger shark (Galeocerdo cuvier) is the largest shark in the family Carcharhinidae and the only carcharhinid with aplacental viviparous (ovoviviparous) reproduction.
Despite its size and prevalence, many details of tiger shark reproductive biology are unknown. Size at maturity and litter
size have been reported by several authors, but a lack of large numbers of pregnant females has made it difficult to determine
gestation period, seasonality, and timing of the female reproductive cycle. Here we analyze data from shark control program
fishing and incidental catches in Hawaii (n = 318) to construct the most complete picture of tiger shark reproduction to date. Males reached maturity at approximately
292 cm total length (TL) based on clasper calcification, whereas females matured between 330 and 345 cm TL based on oviducal
gland and uterus widths. Litter sizes ranged from 3 to 57 with a mean of 32.6 embryos per litter. Data from 23 litters from
various months of the year indicate that tiger sharks are usually 80–90 cm TL at birth, and that the gestation period is 15–16
months. Mating scars were observed in January–February and sperm is presumably stored for 4–5 months until ovulation takes
place in May–July. Gestation begins in June–July and pups are born in September–October of the following year. Our data suggest
that female tiger sharks in Hawaii give birth only once every three years. This could have major implications for conservation
and management of this species, as it suggests that tiger shark fecundity is 33% lower than previously thought. This could
greatly reduce the ability of this species to rebound from fishing pressure.
This work demonstrated a simple, low-cost, rapid, and effective biochemical oxygen demand (BOD) estimation system based on a packed-bed bioreactor that can be easily self-built on-site at a particular wastewater treatment plant for continuous monitoring of the influent and effluent. The use of natural microbial consortium that were collected from the target wastewater and immobilized on a cheap porous carrier simply by adhesion resulted in an acceptable accuracy of over 95%. The newly developed semi-continuous operating mode with peak-type signals was shown to be able to continuously estimate BOD at a high flow rate to overcome the flow dependence of the oxygen electrode, limit clogging issues, enhance the response time, and lower the limit of detection. The resulting packed-bed bioreactors could work continuously for 22 h with a coefficient of variance (CoV) of only 1.8% or for 13 h a day for several days with a maximum CoV of 1.4% and their response was observed to be stable over 80 consecutive measurements. They exhibited stable responses at a wide pH range of 6.5–8.5, which is also the recommended range for aerobic wastewater treatment, emphasizing the greater ease of use of natural microorganisms for BOD estimation.
Regional curves relate drainage area to the bankfull channel characteristics discharge, cross‐sectional area, width, and mean depth. These curves are used for a variety of purposes, including aiding in the field identification of bankfull elevation and in the natural channel design process. When developing regional curves, the degree to which landform, geology, climate, and vegetation influence stream systems within a single physiographic province may not be fully considered. This study examined the use of the U.S. Geological Survey's Hydrologic Landscape Regions (HLR), as well as data from 2,856 independent sites throughout the contiguous United States (U.S.), to develop a set of regional curves (bankfull discharge, cross‐sectional area, width, and mean depth) for (1) the contiguous U.S., (2) each of the 20 HLRs, (3) each of the eight physiographic divisions, (4) 22 of the 25 physiographic provinces, and (5) individual HLRs within the physiographic provinces. These regional curves were then compared to each other, as well as those from the literature. Regional curves developed for individual HLRs, physiographic divisions, and physiographic provinces tended to outperform the contiguous U.S. indicating increased stratification was beneficial. Further stratifying physiographic provinces by HLR markedly improved regional curve reliability. Use of HLR as a basis of regional curve development, rather than physiographic region alone, may allow for the development of more robust regional curves. 相似文献
The U.S. Department of Energy (DOE) Chronic Beryllium Disease Prevention Program Rule, 10 CFR Part 850 became effective in 2000 in response to the prevalence of Chronic Beryllium Disease (CBD) in workers. The rule requires surface and air monitoring for beryllium to determine exposure levels and the evaluation of the effectiveness of controls used to minimize or eliminate that risk. The most common methods for surface sampling use wet or dry wipes. Wipe sampling techniques may be impractical for many surfaces common to most buildings such as cinder block, textured wall surfaces, fabric and carpet. Vacuum sampling methods have been developed for the evaluation of lead or pesticides on residential surfaces such as carpets, bare floors and window sills. However, the current vacuum methods may be impractical for many workplace situations such as sampling of protective clothing, complex facility structures, or equipment surfaces. Recent work using vacuum sampling for potential bio-terrorism agents such as anthrax spores may have significant application to industrial hygiene evaluations of the workplace and may be extendable for use in sampling of metals such as beryllium. Validated vacuum sampling methods that provide meaningful data would be of great value to industrial hygienists in identifying areas having surface contamination, evaluating existing controls and work practices and determining the potential of toxic material on surfaces to become airborne and present a potential risk to workers and the public. This article discusses various vacuum sampling methodologies and recommends harmonization of sampling methods. 相似文献
Heavy metal concentrations and pH of pore-water in contaminated substrates are important factors in controlling metal uptake by plants. We investigated the effects of phytoextraction on these properties in the solution phase of biosolids and diluted biosolids in a 12-month phytoextraction column experiment. Phytoextraction using Salix and Populus spp. temporarily decreased pore-water pH of the substrates over the experimental period followed by a return to initial pH conditions. Salix × reichardtii and Populus balsamifera effectively extracted Ni, Zn and Cd and actively mobilized these metals from the solid to the solution phase. S. × reichardtii had the stronger effect on mobilization of metals due to its larger root system. Phytoextraction did not affect Cu in the solution phase of the biosolids. Heavy metals were leached down to lower depths of the columns during the phytoextraction process. 相似文献
Field experiments were conducted from dusk to dawn off St. John (18° 18′ 59.32″ N, 64° 43′ 24.5″ W) and Guana Island (18°
28″ 28.31″ N, 64° 34′ 30.83″ W), Virgin Islands from June through August 2008-2010 to assess the sensory cues used by the
nocturnal/crepuscular fish-parasitic gnathiid isopod, Gnathia marleyi, to locate fish hosts. Experimental traps providing both visual and olfactory cues from live French grunts (Haemulon flavioliniatum) attracted significantly more gnathiids than traps providing only visual cues or control traps (empty or with a rock), which
were not significantly different from each other. In another experiment, traps providing both cues and only olfactory cues
attracted significantly more gnathiids than empty control traps, but were not significantly different from each other. Our
findings suggest that during nocturnal and crepuscular periods, visual cues provided by resting or slow-moving fish are not
alone sufficient to attract gnathiids, while olfactory cues alone are. The traps designed for this study offer a new method
of sampling free-living gnathiid isopods. 相似文献
Environmental Science and Pollution Research - This study aims to capture groundwater potential zones integrating deep neural network and groundwater influencing factors. The present work was... 相似文献