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241.
Marco Ghisalberti 《Environmental Fluid Mechanics》2010,10(3):329-343
Obstructed shear flows (i.e. those over permeable media) are common in the environment. An archetypal example, flow over a
submerged vegetation canopy, is investigated here. Like any flow through complex geometry, canopy flows are characterised
by strong spatial gradients. The focus of this experimental study is the three-dimensionality of aquatic canopy flow, in particular
that of the coherent interfacial vortices that govern mixing into and out of the canopy. It is shown here that the vortices
have a finite lateral scale that is comparable to their vertical scale; both are of the order of the drag length scale of
the canopy, (C
D
a)−1, where a is the frontal area density and C
D
is a bulk drag coefficient. The finite lateral extent of the vortices generates strong lateral hydrodynamic gradients, both
instantaneously and in the long-term. The instantaneous gradients, which can contribute greatly to the dispersion of dissolved
and particulate species, are far more pronounced. Finally, the potential for canopies to generate differential roughness secondary
circulation is examined. In the consideration of vertical scalar transport, this circulation can be of the same order as turbulent
diffusion. 相似文献
242.
Persistence models for mark-recapture 总被引:1,自引:0,他引:1
The stable of models available for analyzing mark-recapture data (Otis et al. Wild Momogr 66:135, 1978) includes those having
behavioral characteristics, time variation, heterogeneity, along with combinations of those characteristics. This paper proposes
use of a series of models based on the persistence model of Ramsey and Usner (Biometrics 59:331–339, 2003). We show that persistence
can be modeled in combination with behavior and with time variation. We apply the persistence model to situations in which
capture occasions are not equally-spaced in time. Two case studies illustrate the use of these extended persistence models. 相似文献
243.
Contrary to Bateman’s principle, polyandry appears to be a common female mating strategy. Several hypotheses have been proposed
to explain the evolution of polyandry. It is assumed that females gain either material or genetic benefits from multiple matings,
or that they are coerced into mating by males. In water striders, mating is generally assumed to be costly to females, and
they are thought to mate for reasons of convenience, adjusting their resistance to mating according to male harassment. Here,
we tested the effect of number of matings (with the same male) and number of partners on female fitness in a water strider
Aquarius paludum. In the first experiment, we regulated the time females spent with a male and found that females’ egg production increased
with multiple matings up to a point. The result supports the existence of an optimal female mating frequency. In the second
experiment, we tested how polyandry affects the number of eggs laid and egg hatching success. We conducted three different
trials: females mated four times with either a single male, two different males, or with four different males. Females that
mated with four different males laid the lowest number of eggs and had the lowest egg hatching success, suggesting that polyandry
reduces females’ egg production and egg hatching success in A. paludum. We conclude that A. paludum females probably gain material benefits from mating but no genetic benefits were found in this study. 相似文献
244.
Anthropogenic influence on surface water quality of the Nhue and Day sub-river systems in Vietnam 总被引:2,自引:0,他引:2
Pham Thi Minh Hanh Suthipong Sthiannopkao Kyoung-Woong Kim Dang The Ba Nguyen Quang Hung 《Environmental geochemistry and health》2010,32(3):227-236
In order to investigate the temporal and spatial variations of 14 physical and chemical surface water parameters in the Nhue
and Day sub-river systems of Vietnam, surface water samples were taken from 43 sampling sites during the dry and rainy seasons
in 2007. The results were statistically examined by Mann–Whitney U-test and hierarchical cluster analysis. The results show that water quality of the Day River was significantly improved during
the rainy season while this was not the case of the Nhue River. However, the river water did not meet the Vietnamese surface
water quality standards for dissolved oxygen (DO), biological oxygen demand (BOD5), chemical oxygen demand (COD), nutrients, total coliform, and fecal coliform. This implies that the health of local communities
using untreated river water for drinking purposes as well as irrigation of vegetables may be at risk. Forty-three sampling
sites were grouped into four main clusters on the basis of water quality characteristics with particular reference to geographic
location and land use and revealed the contamination levels from anthropogenic sources. 相似文献
245.
Håkan Karlsson Johan Bäckman Cecilia Nilsson Thomas Alerstam 《Behavioral ecology and sociobiology》2010,64(12):2021-2031
Using tracking radars, we investigated the variability of flight directions of long-distance nocturnal passerine migrants
across seasons (spring versus autumn migration) and sites at the southern (56° N) and northern (68° N) ends of the Scandinavian
Peninsula (Lund versus Abisko). Whilst most migrants at Lund are on passage to and from breeding sites in Fennoscandia, the
majority of the migrants at Abisko are close to their breeding sites, and migration at Abisko thus to a large degree reflects
initial departure from breeding sites (autumn) or final approach to breeding destinations (spring). The radar data were used
to test predictions about differences in orientation and wind drift effects between adult and juvenile birds (a large proportion
of autumn migrants consists of juvenile birds on their first journey), between situations far away from or near the goals
and between different phases of migration (initial departure, en route passage, final approach to goal). The concentrations
(both total and within-night concentrations) of flight directions differed significantly between seasons as well as sites,
with the highest concentration at Lund in spring (mean vector length of track directions, r = 0.79) and lowest at Abisko during spring (r = 0.35). Partial wind drift and partial compensation were recorded at Lund, with a similar effect size in spring and autumn,
whilst possible wind drift effects at Abisko were obscured by the large directional scatter at this site. The results from
Lund support the prediction that the high proportion of juveniles in autumn contributes to increase the directional scatter
during this season, whilst there was no support for predictions of differential wind drift effects between seasons and situations
with different goal distances. The most striking and surprising result was the exceedingly large scatter of flight directions
at Abisko, particularly in spring. We suggest that such an exaggerated scatter may be associated with final approach orientation,
where migrants reach their specific goals from all various directions by final navigation within a more wide-ranging goal
region. The larger scatter of autumn flight directions at Abisko compared to Lund may be due to exploratory flights in variable
directions being more common at initial departure from breeding sites than later during migratory passage. These surprising
results highlight the importance of studying and analysing orientation during final approach to (and initial departure from)
migratory goals for understanding the orientation systems of migratory birds. 相似文献
246.
247.
Ali Akbar Safari Sinegani Hossein Mirahamdi Araki 《Environmental Chemistry Letters》2010,8(4):323-330
Sequential extraction has been used as a suitable method for fractionation of chemical forms of trace elements and study of
their plant availability. Surface soils were sampled from Guilan and Hamadan provinces in north and northwest of Iran with
temperate and semiarid climates. The chemical forms of Pb in the Pb(NO3)2-treated (400 μg Pb g−1) soils have been studied in solid state incubation (FC) at 27°C in sterile and unsterile conditions. After 20 min and 3600 h
a sequential extraction scheme was also used to fractionate Pb of incubated samples into soluble-exchangeable (Sol-Exch),
carbonates associated (ACar), organic matter associated (AOM), Mn oxide associated (AMnOx), Fe oxide associated (AFeOx), and
residual (Res) forms. Temperate soil samples had higher clay content, cation exchange capacity (CEC), dichromate oxidable
organic carbon (OC), total Kjeldahl-nitrogen (TN), biological activity, amorphous and crystalline Fe and Al, but semiarid
soil samples had higher sand content, pH, equivalent calcium carbonate (ECC), available P and K. Soil lead fractionation revealed
that in both groups of soils Pb largely changed to exchangeable, carbonates associated and organic associated forms after
20 min. The chemical forms of Pb differed widely among soils after 3600-h incubation. The conversion rate of Pb from more
available forms to less available forms was higher in temperate soils with higher Fe–Mn oxides and OM contents compared to
semiarid soils. In temperate soils after 3600-h incubation, greater content of Pb was observed in Res (68%), AOM (14%), ACar
(7%), and AMnOx (5%) fractions. However, in semiarid soils greater content of Pb was observed in Res (61%), ACar (16%), Sol-Exch
(8%), and AOM (8%) fractions. The sum of AMnOx and AFeOx chemical forms for Pb in semiarid soils compared to temperate soils
was lower. It was only 7% against 9% in temperate soils. Soil microorganisms in unsterile soils had significant effect on
AOM, AFeOx and Res fractions of Pb. They not only increased AOM and AFeOx fractions of Pb in soils but also decreased Res
fraction of Pb significantly. 相似文献
248.
Three strains of the chain-forming diatom Skeletonema marinoi, differing in their production of polyunsaturated aldehydes (PUA) and nutritional food components, were used in experiments
on feeding, egg production, hatching success, pellet production, and behavior of three common planktonic copepods: Acartia tonsa, Pseudocalanus elongatus, and Temora longicornis. The three different diatom strains (9B, 1G, and 7J) induced widely different effects on Acartia tonsa physiology, and the 9B strain induced different effects for the three copepods. In contrast, different strains induced no
or small alterations in the distribution, swimming behavior, and turning frequency of the copepods. 22:6(n-3) fatty acid (DHA)
and sterol content of the diet typically showed a positive effect on either egg production (A. tonsa) or hatching success (P. elongatus), while other measured compounds (PUA, other long-chain polyunsaturated fatty acids) of the algae had no obvious effects.
Our results demonstrate that differences between strains of a given diatom species can generate effects on copepod physiology,
which are as large as those induced by different algae species or groups. This emphasizes the need to identify the specific
characteristics of local diatoms together with the interacting effects of different mineral, biochemical, and toxic compounds
and their potential implications on different copepod species. 相似文献
249.
Spatial distribution and temporal variation of epibenthic assemblages of coralligenous biogenic rocky outcrops occurring in
the northern Adriatic Sea (45°04′–45°24′N; 12°23′–12°43′E) were investigated by photographic sampling from 2003 to 2006 at
12 randomly selected sites. The dominant reef-forming organisms were the encrusting calcareous algae (Lithophyllum stictaeforme, Lithothamnion minervae and Peyssonnelia polymorpha), while the main bioeroders were boring sponges (Cliona viridis, C. celata, C. thoosina, C. rhodensis, Piona vastifica) and the bivalve Gastrochaena dubia. Composition of the assemblages varied thorough years and among sites. Spatial heterogeneity, at local and regional scale,
prevailed over temporal variation. This variability was related both to the geo-morphological features of the outcrops and
to environmental variables. Sites clearly differed in the percent cover of reef builder and bioeroder species while only limited
temporal variation within site was found. Some taxa revealed complex intra-site temporal trends. These results provide valuable
information on the diversity and variability of epibenthic assemblages of the northern Adriatic coralligenous reefs, essential
for the management and conservation of these unique biogenic habitats. 相似文献
250.
Shrimp trawling is common throughout the southeastern and Gulf of Mexico coasts of the USA and is the primary contributor
to fisheries discards in these regions. Tens of thousands of nearshore seabirds nest near shrimp trawling grounds in the USA,
but to date, there has been no assessment of the relationship between seabirds and shrimp trawlers. We examined the taxonomic
composition of bycatch, rate at which seabirds scavenged bycatch, and energy density of discarded bycatch in a nearshore commercial
shrimp fishery. Bycatch was primarily comprised of demersal fish that are not typically accessible to the plunge-diving and
surface-feeding seabirds that occur in the area. Hence, seabird diets in the region appear to be broadened taxonomically by
the availability of discards. Results from discard experiments indicated that 70% of the nearly 5,500 items discarded by hand
were scavenged by seabirds and that the fate of a discarded item was most strongly predicted by its taxonomic order. Laughing
gulls scavenged the greatest proportion of discards, although brown pelicans were the only species to scavenge more discards
than predicted based upon their abundance. Because this is the first such study in the region, it is difficult to ascertain
the extent or intensity of the impact that discards have on nearshore seabirds. Nonetheless, our results suggest that it will
be difficult for managers to clearly understand fluctuations in local seabird population dynamics without first understanding
the extent to which these species rely upon discards. This may be especially problematic in situations where seabird populations
are recovering following natural or anthropogenic stressors. 相似文献