Transverse Transects Research Articles

The role of sediments for phosphorus retention in the Kirinya wetland (Uganda)

Phosphorus dynamics were examined and modelled in a Cyperus papyrus and Phragmites mauritanus wetland on the Ugandan coast of Lake Victoria receiving secondary treated wastewater. Using a series of transversal transects, concentrations of nitrogen (N) and phosphorus (P) were found to decrease gradually as water moved downstream, giving nutrient retention capacities which ranged between 40% and 60%. Near-zero oxygen and nitrate concentrations were observed as well. To investigate the phosphorus retention characteristics in more detail, laboratory experiments were carried out on sediment samples and sediment cores retrieved from points along the wetland. Following a P shock load to cores of the wetland sediment, it was possible to determine a sediment P uptake rate of 0.016 day−1. Sediment P adsorption studies were also performed, showing significant Freundlich and Langmuir isotherm behaviour. With these data a maximum P adsorption capacity of 4 mg P/g for the wetland sediment could be estimated. A plug-flow model was used to evaluate the phosphorus retention dynamics of the Kirinya wetland. A good correspondence between the actual and simulated P retention was observed. Comparing the daily P uptake (g/m3day) in the Kirinya wetland with the maximum sediment P uptake capacity, it can be concluded that the total P retention capacity of the wetland will only be sufficient for 30 more years under the present P loading and wetland management.

Anisotropic radio-wave scattering from englacial water regimes, Mýrdalsjökull, Iceland

AbstractColinear-polarized 5 MHz radar profiling data were obtained on Mýrdalsjökull, a temperate glacier in Iceland. Radar transects, and therefore polarization planes, were aligned approximately parallel, transverse and oblique to the ice flow direction. Echoes from the shallower half to two-thirds of the ice were 10–20dB stronger on the oblique and longitudinal transects than those on the transverse transects. Anisotropy as a function of depth is clearly seen at the sites where the transects cross. Strong scattering on longitudinal transects apparently caused extinction of a radar-reflecting layer that was continuously profiled on the transverse transects. A radio-wave scattering model shows that scattering from a longitudinal water-filled conduit parallel to the glacier surface can explain the observed azimuthal variations of the echo. We conclude that low-frequency (~MHz) radio waves can help to characterize englacial water regimes.

Vegetation Succession Pattern and Diversity Changes in a Glacier Valley, Central Alps, Austria

The aim of this study was to assess the influence of comparable unequal environmental conditions on primary vegetation succession in an alpine glacier valley by the means of transects. Two longitudinal transects were established along the glacier foreland of the Rotmoosferner, Tyrol, Austria, and two transverse transects were established across the valley on the 1923 and 1858 moraines. The progressions of alpha- and beta-diversity were compared, and vegetation data within the glacier foreland were analyzed. Moraine age emerged as the primary factor within a canonical correspondence analysis (CCA), while the second axis separated the two valley sides. A clearly differentiated development of plant communities became obvious especially within the early development stages. Early development of vegetation cover and alpha diversity was further developed on the shaded valley side, and progression of beta diversity differed significantly among the valley sides. The results indicate two different successional pathways, on both the qualitative and the quantitative level. These can be attributed to differences in the extent of solar irradiation (sunny vs. shaded side), lithology, geomorphic processes, and a multitude of other factors, reinforcing the dissimilarity between the valley sides. Our approach highlights the necessity of a deliberate sampling design within different glacier forelands sensitive to environmental conditions created by the topography that may impact comparisons among the forelands.

Biogeography of Ground Beetles of Florida (Coleoptera: Carabidae): The Peninsula Effect and Beyond

Thirteen transverse latitudinal transects are used to examine the biogeographic pattern of the peninsula effect on 341 species of Florida carabid beetles. In this fauna, 278 species are grouped to be of temperate affinity or origin, 28 of tropical affinity or origin, and 35 are endemic to Florida; 39 of the species are flightless. The species are ecologically grouped as riparian, hygrophile, halophile, mesophile, subxerophile, arboricole, and endogean. Both the total fauna and the temperate group show a peninsula effect, that is, a decrease in species richness from peninsula base to tip. The tropical group shows an inverse peninsula effect: their species richness decreases toward the base. The endemic group displays a much different pattern, with maximum richness at the middle of the peninsula, a possible reflection of former Tertiary or Quaternary islands as centers of isolation and speciation. Over-water dispersal has been important: 61 species crossed the water gap between Florida and West Indies; 36 temperate species moved from Florida into the West Indies; 25 West Indian (tropical) species have crossed the water gap into Florida (69% of these are preadapted hygrophilic, riparian, and halophile species). Species movements between Florida and the West Indies were probably more prevalent at times of Pleistocene low sea levels, when these lands were larger in area and closer to each other. The Gulf Coastal Plain has provided an avenue for carabid movement to and from Florida and the continental Neotropics with 44 species occurring in both areas, and 70% of these are preadapted hygrophilic, riparian, and halophilic species.

Morphogenesis in Planarians Dugesia tigrina

We carried out computer morphometry in regenerates of planarians Dugesia tigrina. The blastema growth was analyzed in fragments of planarians after their fission and after transverse transection at different body levels. The blastema was growing at a higher rate on tail fragments than on the head fragments and the growth rate was the higher, the closer the transection was to the head end. After fission, the blastema was growing at a slower rate than after transection in the fission zone. The growth of adjacent blastemas formed on both sides after fission or transection proceeded at different rates as a function of new body polarity.

SURFACE FEATURES OF THE CIRCULATION IN FJORDS OF SOUTHERN CHILE OBSERVED IN ERS AND LANDSAT IMAGES

Surface features of the hydrodynamics at the mouth of Aysen Fjord, in the Chilean Inland Sea, were described using Landsat and ERS-SAR images in combination with field data. A set of seventeen radar images from ERS, along with one Landsat (ETM) were analyzed to study the surface features observed in this region, where fresh water input is an important contributor to the dynamics of the estuarine system. Field data were provided by current measurements obtained with an Acoustic Doppler Current Profiler (ADCP) mounted in a catamaran looking downward, which was towed from a boat during two semidiurnal cycles to obtain repetitions over two transverse transects. There were also density measurements obtained from CTD (Conductivity, Temperature and Depth) vertical profiles in the water column and from a surface termosalinograph (Conductivity, Temperature) mounted onboard of a research vessel. The results of this campaign in Aysen Fjord were associated to the surface features observed in satellite images. The results show the main features of the circulation at the mouth of this fjord and other phenomena of interest for physical oceanography. Noteworthy is a frontal structure suggested on both types of images. This feature is partially supported by ADCP measurements and strongly suggested by density measurements. Packages of internal waves in Costa Channel are also suggested in radar images, while the distribution of the fresh water plume is supported by the Landsat image. Satellite images provided valuable guidance to focus the research in a selected area and phenomena.

Influence of substrate on the distribution of the Hawaiian Silversword ( Argyroxiphium sandwicense DC.) in Haleakala (Maui, HI)

The spatial patterns of the Hawaiian silversword ( Argyroxiphium sandwicense DC.) were studied in Haleakala (Maui, HI). The silversword is a “giant” rosette plant nearly brought to extinction by human impact and goat browsing during the 1920s, but stern protection has resulted in the resurgence of plant populations. Silversword regeneration is occurring vigorously in soils with surficial layers of volcaniclastic fragments. Ten sites with sizable silversword populations and the associated substrates were examined in Haleakala's crater between 2175 and 2755 m. At each site, the population structure of 100 plants was determined along wandering-quarter transects, which limit sampling bias. Substrates where rosettes were rooted and the size of the biggest stone fragments upslope and downslope from the plant's base were determined. Volcaniclastic substrates were examined with photographs along 12-m-long transverse transects. Fine-debris samples (gravel and pebbles) were analyzed by mechanical sifting of surficial fragments gathered from 15×15 cm miniplots. Volcaniclastic fragments in silversword areas have different sources. (i) Most were ejected during eruptions yielding pyroclastic materials (ash to blocks) that built cinder cones on Haleakala's crater. (ii) On steep slopes, weathering of (olivine alkali) basalt outcrops and subsequent mass wasting of rock fragments contributed a mantle of clasts to slopes below. (iii) On some cinder cones, welded spatter was produced during late eruptive stages; this coalesced into ruff-like agglutinate layers around crater rims, called Pohaku-o-Hanalei (“wreath of stones”). Agglutinate deposits weather gradually, supplying clasts that roll downhill and accumulate on cone flanks. (iv) On weathered aa lava flows, stone fragments and rocky crags abound along eroding lava-flow ridges, associated with vegetation; but the intervening troughs, covered with fine ash and cinder, remain bare. Silversword population structures indicate healthy regeneration. All populations display a typical pattern of decreasing silversword numbers with increasing size (=age). Nearly 65% of the rosettes are rooted near cobbles (5–10 cm long) or pebbles (2.5–5 cm), and ∼23% grow at the base of blocks (>10 cm) or outcrops; 9% of the plants are on gravel (<2.5 cm), but only 1% have germinated on sandy soil without granules or stones; 2% of the silverswords grow on organic litter of dead rosettes. Plants on six sites showed noticeable differences in clast size between their upslope and downslope sides; particles are significantly larger upslope from rosettes. This suggests that successful seedlings germinate below clasts, which deflect finer downslope-moving sediment, thus protecting young plants from burial by descending debris. Statistical tests indicate a few blocks above plants may have been stopped by adult rosettes. Such a relationship underscores the dynamic nature of steep cinder and rubble (talus) slopes, regularly affected by dry debris slides, frost creep, and other mass-wasting processes. Slope instability is also evinced by (i) common bending and deformation of silversword roots—particularly in seedlings—which trail upslope; (ii) pronounced downhill tilting and asymmetry of tall rosettes on steep gradients; (iii) presence of accumulated fine-debris steps (9.9–13.8 cm thick) upslope from plants and blocks; (iv) ubiquitous fine-earth flags exposed below embedded blocks, which intercept descending debris and deflect it laterally; (v) widespread miniature sorted stripes.

Spatial variability of biotic and abiotic factors of the aquatic habitat in French Guiana

AbstractResearch on tropical fish ecology in South America is focused mainly on the effect of environmental variables on aquatic organisms. Physical, chemical and biological characteristics of water measured at a local scale (local variables) are used, although geomorphological and hydrological factors measured at a regional scale (regional variables), as well as temporal and spatial heterogeneity, can also be considered. However, the use of this multi‐scale approach increases the perceived complexity, heterogeneity and variability of rivers. Thus, it is important to determine the magnitude of habitat variability and those parameters having the greatest influence on it. In this study, 28 stations distributed on 16 different rivers in French Guiana were sampled during high water at a meso spatial scale. Physical features of the rivers were sampled along an 800‐m stretch, where nine transversal transects were established on the main channel. At each river, 17 local and six regional variables were measured. Local variables relating to the physical characteristics of the channel bank and main channel and regional variables characterizing the whole basin and the position of the station in the basin were qualitatively and quantitatively described. All variables were submitted to multivariate analysis in order to determine their relative contribution to total variance. Two quantitative regional variables (drainage area upstream from station and river drainage basin), five quantitative local variables (channel width, water temperature, channel depth, Secchi transparency and conductivity) and one qualitative local variable (channel substrate) were shown to differentiate the 16 rivers sampled. This result shows the poor contribution of qualitative variables compared with quantitative ones. Gradual change in qualitative variables is probably responsible for this poor contribution to the total variance; thus, the use of such variables is not possible for spatial habitat differentiation in this study. Copyright © 2001 John Wiley &amp; Sons, Ltd.

Surface sediment characteristics and present dynamics in alluvial fans of the central Spanish Pyrenees

Three alluvial fans in the Ribera de Biescas, upper Gállego Valley, and central Spanish Pyrenees, have been studied in order to explain the most recent changes and to identify the spatial organization of the sediment. In the alluvial fans surveyed, the proximal area is dominated by debris flows, which pass downslope into transitional and fluvial deposits. The relative importance of each type of sediment is closely related to the size and gradient of the alluvial fan, as well as to the gradient in the final stretch of the stream. In general, the size of the sediment decreases from the proximal to the distal area, while the roundness increases. Nevertheless, there are noticeable irregularities in the trend both in longitudinal and transverse transects, due mainly to the sedimentary dynamics of the debris flows, as they advance towards the inner part of each alluvial fan during the most intense peak flows. A sudden shrinkage of the most active area and incision along the fan channels has been assessed and related to land-use changes in the catchments.

Cephalopod paralarvae and upwelling conditions off Galician waters (NW Spain)

A total of 103 cephalopod paralarvae were sampled during June 1995 in Galician waters (NW Spain). Samples were taken with Bongo nets of 300 and 500 µm mesh size at 48 sampling stations along 10 transverse transects ranging from 80 to 600 m water depth. Paralarvae of loliginid squid were most abundant (40%). The Rhynchoteuthion paralarvae of ommastrephid squid accounted for 25%, whereas sepiolids comprised 23% of the total sample. Octopods were scarce, at only 6.6%. Other cephalopod families accounted for 5%. Sizes of paralarvae ranged from 1.0 to 7.1 mm mantle length. Temperature and salinity distribution showed the presence of an intense upwelling during the survey period. The sampling data obtained before and during the presence of upwelled water off Rias of Pontevedra and Vigo (southern zone) showed that paralarval cephalopod abundance and distribution were closely related to the upwelled Eastern North-Atlantic Central Water (ENACW).

Functional Relationship between the Hypothalamic Vigilance Area and PAG Vigilance Area

Duan, Y.-F., R. W. Winters, P. M. M cCabe, E. J. Green, Y. Huang and N. Schneiderman. Functional relationship between the hypothalamic vigilance area and PAG vigilance area. Physiol Behav 62(3) 675–679, 1997.—The vigilance reaction is characterized by a large bradycardia, a pressor response, and inspiratory apnea in anesthetized rabbits and the inhibition of movement in conscious rabbits. This affective response pattern can be elicited by electrical stimulation of the dorsolateral hypothalamus (the hypothalamic vigilance area) or the ventrolateral periaqueductal gray (the periaqueductal gray vigilance area). The present study sought to advance our understanding of the functional relationship between the hypothalamic vigilance area (HVA) and the periaqueductal gray vigilance area (PVA) by measuring the effects of transverse transections of the caudal portion of the ventrolateral PAG (vlPAG) upon the cardiovascular responses elicited from the dorsolateral hypothalamus and the rostral vlPAG. Selective transverse transections of the caudal vlPAG significantly reduced the magnitudes of the bradycardia and pressor response elicited by stimulation of the PVA rostral to the transection site, but had minimal impact on the cardiovascular responses evoked by stimulation of the HVA. These findings suggest that the cardiovascular responses elicited by stimulation of the vlPAG are mediated by a neural pathway that is parallel, at least in part, to the one that subserves the response elicited from the HVA. The results also provide support for the view that the PAG is not an essential structure in the mediation of the autonomic components of affective behaviors involving behavioral inhibition.

Chlorinated Hydrocarbons in Surface Sediments From the Open Adriatic

Abstract This paper presents the results of the examination of concentrations of chlorinated hydrocarbons in surface sediments from the middle of the Adriatic. the sampling area was chosen as part of the protection programme of the Adriatic Sea and is located at two transverse transects, each consisting of four stations. the sediments were collected during the summer cruise of 1990. Quantification of individual components was performed by Capillary Gas Chromatography (CGC) using reference standards. Areal distribution of the concentrations of HCB, lindane, DDT and its metabolites, dieldrin, endrin and PCBs are presented. the values obtained varied within a wide range of concentration from 20 pg/g dry weight for lindane to 700 pg/g dry weight for Σ DDT and the sum of PCBs as Aroclor 1254 from 0.3 to 6.6 ng/g. The main source of these compounds is thought to be from suspended matter entering the Adriatic sea via the River Po and transported by currents to its middle part.

Traumatic Fracture of the Pancreas

Pancreatic fracture is a rare injury caused by blunt abdominal trauma. Few proven cases have been diagnosed by abdominal CT. The typical clinical triad of upper abdominal pain, leukocytosis, and hyperamylasemia is nonspecific. Abdominal CT gives the best opportunity for an immediate diagnosis. Nevertheless, few cases of traumatic pancreatic fracture have been diagnosed by abdominal CT within 24 h following injury and proven at laparotomy. In this report we describe five cases of traumatic pancreatic fracture identified on CT; four cases were verified at laparotomy. Traumatic pancreatic fracture generally occurs as a transverse transection across the neck of the pancreas. Commonly, an accompanying injury to other visceral organs is present. The diagnosis of pancreatic fracture requires a high index of suspicion with close scrutiny of the CT images.

Distribution of polycyclic aromatic hydrocarbons (PAH) in recent sediments of two transversal transects in the middle part of the adriatic sea

The contents of polycyclic aromatic hydrocarbons (PAH) were examined in surface sediments from the open Adriatic Sea. UV-fluorescence spectroscopy was used for the analysis, and continued emission spectra were scanned for the lower and higher aromatic fractions. The samples were collected in three seasons, December 1986, May 1987 and September 1987 on two transects between Yugoslavia and Italy. Higher values were found near the Italian coast. From spectral line shapes it is evident that there was no local source of pollution and that PAH are of petrogenic and pyrolytic origin. The spatial distribution of PAH contents is in good agreement with the dispersion pattern of recent sediments of the Adriatic Sea.

Pathways of Propagation of the Canine Gastric Pacesetter Potential

Our objective was to determine what structures propagate the canine gastric pacesetter potential (PP). Of 15 dogs, 4 underwent transverse transection of the entire gastric wall, followed by immediate anastomosis, and 11 had excision of a 1-cm circumferential band of (1) the circular oblique muscle alone, (2) the entire tunica muscularis, or (3) the longitudinal muscle alone. Gastric electrodes were implanted orad and aborad to the operative sites, all of which were 5 cm orad to the pylorus. After recovery, recordings were made intermittently, during 4 to 6 months, from the conscious animals during fasting, during intravenous infusion of pentagastrin (0.1 μg per kg per min), and during hypoglycemia induced by intravenous injection of insulin (1 U per kg). Gastric transection and circular myomectomy temporarily interrupted propagation of the PP across operative sites, but recovery occurred by 14 days. In contrast, excision of the entire tunica muscularis or longitudinal myomectomy interrupted propagation permanently; the mean frequencies of the PP were 4.8 cycles per min orad and 2.0 cycles per min aborad to the operative sites 3 months after operation. Neither pentagastrin nor insulin restored disrupted propagation. Our experiments demonstrate that the longitudinal muscle layer, or structures associated with it, propagates the canine gastric PP.

Effect of brain transections on the respiratory response to nerve stimulation

Respiratory responses to nerve stimulation in the cat were examined after transverse transections at various brain levels. Stepwise elimination of rostral parts of the brain reduces the rate of spontaneous breathing progressively. The respiratory responses to vagal and sciatic stimulation are very similar in decorticate and intact animals. In decorticate cats, vagal stimulation can produce either tachypnoea or apnoea, depending on the frequency used. After precollicular cuts, vagal excitation causes exclusively inhibition of breathing. The tachypnoea, following sciatic stimulation, is converted into oligopnoea or apnoea only by intercollicular transection. The effects of pentobarbitone injections and of transections, progressing in caudal direction, are additive. Both procedures eliminate first the acceleratory neurons. The latter possess therefore a more rostral localisation than their deceleratory antagonists. The tachypnoeic responses involve polysynaptic pathways; they exhibit a longer latency and higher sensitivity to anaesthetics.

Effect of brain stem transections on blood pressure responses to medullary stimulation

1. Electrical stimulation in the posterior medulla of the unanesthetised rabbit shows diffuse distribution and intermingling of pressor and depressor points.2. Transverse transections, caudally of the hypothalamus, convert the majority of bulbar pressor responses into depressor reactions. This effect is similar to the barbiturate-induced reversal of hypertensise responses.3. It is assumed that medullary pressor neurons act mainly through higher brain centers, while the bulbar depressor elements have chiefly descending connections to the spinal cord, in addition to some ascending links.