Significant Effect Of Depth Research Articles

Torsional Shear Strength and Size Effect in Laminated Veneer Lumber

Abstract This study investigates the effect that specimen depth has on the torsional shear strength of full-size Eastern Species Laminated Veneer Lumber (LVL). Characterization of this effect is valuable for structural design purposes as well as for use in constitutive modeling when predicting member strength of one depth based on member strength of a different depth derived from testing. To this end, torsion tests were carried out on three depths (140, 184, and 235 mm) of 1.98 m long by 44 mm thick 1.9E Eastern Species LVL. The shear strength of each depth was determined based on homogeneous, orthotropic theory for beams of rectangular cross-section. Despite a perceptible trend of slightly decreasing shear strength with increasing depth, an analysis of variance test indicated that no statistically significant depth effect exists as it relates to torsional shear strength. Further, a three dimensional finite element model of the 44 mm by 140 mm specimen indicated that stresses are uniform within the shear span of 2 times the depth plus the grip distance away from each end of the specimen. The predicted average maximum shear stress in this region compared well to the maximum shear stresses obtained experimentally.

Changes in soil properties and soil solution nutrients due to conservation versus conventional tillage in Vertisols

Understanding of tillage effects on soil chemical properties and cations in soil solution dynamics is essential for making appropriate land-management decisions. Measurements were made after more than 25 years of different tillage treatments: conventional tillage (CT) and conservation tillage, which includes no-till (NT) and minimum tillage (MT). pH and bulk density did not show important changes but exchangeable cations and cations in soil solution were affected by depth and different tillage. The highest concentration of exchangeable Ca2+ and Mg2+ was found in NT, decreased in MT and the lowest concentration was found in CT (mean values were 26.0, 24.4 and 23.3 cmolc kg−1 for exchangeable Ca2+ and 4.2, 3.7 and 3.3 cmolc kg−1 for exchangeable Mg2+ in NT, MT and CT, respectively). In addition, the highest concentration of exchangeable Na+ was found in NT, decreased in CT and the lowest concentration was found in MT. However, the highest concentration of exchangeable K+ was found in MT. A significant depth effect was observed for cations in soil solution: Na+ increased with depth whereas K+ and Ca2+ decreased with depth. This study aims to demonstrate the effect of tillage on the distribution and concentration of certain chemical soil properties.

A kinematic study and membership analysis of the Lupus star-forming region

This paper is dedicated to investigating the kinematic properties of the Lupus moving group of young stars with the primary objective of deriving individual parallaxes for each group member. We identify those stars in the Lupus star-forming region that define the comoving association of young stars by utilizing our new and improved convergent point search method that allows us to derive the precise position of the convergent point of the comoving association from the stars' proper motions. We used published proper motion catalogs and searched the literature for radial velocities, which are needed to compute individual parallaxes. We supplemented the radial velocity data with new measurements from spectroscopic observations performed with the FEROS spectrograph mounted on the MPG/ESO 2.2m telescope at La Silla. We identify a comoving group with 109 pre-main sequence stars and candidates that define the kinematic properties of the Lupus low-mass star-forming region. We derive individual parallaxes for stars with known radial velocity and tentative parallaxes for the remaining group members by assuming that all stars share the same space motion. The convergent point method, combined with the k-NN algorithm, makes it possible to distinguish the Lupus and Upper Centaurus Lupus stars from the adjacent Scorpius-Centaurus association. We find significant depth effects in this region and show that the classical T Tauri stars, located in the close vicinity of the Lupus molecular clouds, form a background population, while the weak-emission line T Tauri stars are dispersed not only in angular extent but also in depth. The newly derived individual parallaxes will be used in a forthcoming paper to refine the masses and ages of Lupus T Tauri stars, with the aim of better constraining the lifetimes of their circumstellar, protoplanetary disks.

Characterization of the pelagic fish community of the north‐western and northern Spanish shelf watersa

This study demonstrates the utility of trawl data, collected during acoustic surveys of pelagic fish stocks as a way of confirming fish identification, to characterize the pelagic community, as well as allowing description and prediction of fish distribution patterns, based on data from Spanish Atlantic Ocean shelf surveys during spring 2005-2011. The composition of the pelagic community is described, as well as spatial and temporal patterns of variation in both the community composition and the presence and importance of two of the main exploited pelagic species, sardine Sardina pilchardus and anchovy Engraulis encrasicolus. The most important species in terms of both frequency of occurrence and standardized mass in hauls were mackerel Scomber scombrus, hake Merluccius merluccius, horse mackerel Trachurus trachurus, S. pilchardus and bogue Boops boops. Multivariate analysis indicated significant effects of depth, geographical area and year on haul composition. Descriptive generalized additive models (GAM), with latitude, longitude and depth as predictors, identified clear spatial patterns in the occurrence and abundance of both S. pilchardus and E. encrasicolus, with abundance being highest closer to the coast and, in the case of E. encrasicolus, higher near the French and Portuguese borders. Further GAM analysis, using environmental variables to explain spatial patterns, revealed significant effects of depth and sea surface temperature (SST) gradient and depth on S. pilchardus importance, while E. encrasicolus importance was related to SST. The importance of both species in hauls was higher in the years of higher spawning stock biomass (SSB) and E. encrasicolus also appeared to expand its range when SSB was higher.

An experimental evaluation of the influence of water depth and bottom color on the Common kingfisher's foraging performance

To investigate how depth and bottom color affect prey selectivity in Common kingfisher (Alcedo atthis), we developed several experimental procedures using captive birds. We used 20 young kingfishers to test depth (25 or 50cm) and color (natural gravel or white) effects on foraging behavior. Live freshwater fish were used as target prey. To assess differences resulting from the natural behavior of different fish, we chose bottom-dwelling [Ebro barbel (Barbus graellsii)] and open-water benthopelagic species [Ebro nase (Parachondrostoma miegii) and Pyrenean minnow (Phoxinus bigerri)]. The number of attempts and captures, as well as the effects of hunger and experience, were assessed relative to feeding behavior. The effect of fish behavior, as observed in grouped vs. isolated fish, on the kingfisher's performance was also tested. The results showed a significant effect of depth, with more attacks and greater success in shallow waters. No significant differences in catch success between natural- and white-colored bottoms were observed. Hunger had no effect on fishing success, but experience had a positive effect in shallow waters and on white bottoms. Both bottom- and open-water species were consumed equally. Kingfishers preyed more often upon grouped prey than upon isolated prey, although capture success did not vary between the two cases. Our results suggest that kingfishers prey upon the most accessible types of prey.

Insights into the reproductive biology and fisheries of two commercially exploited species, shortfin mako (Isurus oxyrinchus) and blue shark (Prionace glauca), in the south-east Pacific Ocean

In 2005 and 2010, 1241 Isurus oxyrinchus and 1153 Prionace glauca were collected from 178 longline sets in a ship-board observer programme in coastal waters off Caldera, Chile (27°S). Catch composition was significantly biased towards I. oxyrinchus in 2005, but both species were caught in the same proportion in 2010. The sex ratio for I. oxyrinchus and for P. glauca did not differ significantly from unity within or between years. Sharks matured (L50) at a total length of 190.3cm for male and 199.2cm for female for P. glauca, and 180.2cm for male I. oxyrinchus. Size-at-maturity for female I. oxyrinchus was not determined due to the near absence of mature specimens examined. Generalised additive models (GAMs) were used to examine catch per unit effort (CPUE) in relation to sea surface temperature, wind speed, time of day, hook depth and soak time. The GAMs revealed a significant effect of depth on P. glauca CPUE, and depth and wind speed for I. oxyrinchus CPUE. The predominance of small, immature sharks caught in the coastal, artisanal fishery indicates that both species may use the area as a pupping, and possibly a nursery zone during spring and summer. National data on catch composition and annual landings provide evidence of an increasing trend to land P. glauca, possibly to satisfy the international shark fin trade. Conservation measures, such as the introduction of a minimum capture size for sharks to protect the recruitment into the population, conservative fishing quotas and delimitation of fishing areas are necessary to ensure the sustainability of both species in the region.

Differences in composition of territories in relation to behaviour, stage, and depth of the three-spot damselfish, Stegastes planifrons, in Caribbean coral reefs

Coral reef diversity is correlated with the depth at which the reefs are found, the energy available for biological processes, and the species’ roles and presence throughout the food chain. Can a specific species activity alter the whole ecosystem? Can a small-scale, short-term activity such as fish behaviour have a long-term effect on a larger scale, that of the reef? Can the life stage of a species mediate substrate competition? The three-spot damselfish (Stegastes planifrons) is hypothesized to regulate competition between substrate coverage by actively farming – protecting from herbivores and weeding – in order to regulate the algal species composition and percent coverage of the reef. This behaviour is observed in both juvenile and adult fish. Deeper patches are predicted to have less coral diversity and higher algal diversity; juvenile fish are predicted to have less diversity in their patches than adults. Coral and algal diversity are hypothesized to be negatively correlated. In this study, behaviour of the S. planifrons was classified into one of four categories (active patrolling, passing patrolling, farming, and hiding) and palatable algae surface area coverage was digitized from photographs; life stage was either juvenile or adult. Coral and algal genus diversity were measured along a depth gradient of 0-16 m where the diversity of the reef was thought to be the highest. A three-way ANCOVA was performed to test whether fish behaviour (a small-scale, short-term process), depth, or fish development stage (juvenile or adult) had a significant effect on coral or algal diversity (a large-scale, long-term process). Results showed a significant effect of fish behaviour category on algal genera diversity, and a significant effect of depth on both algal and coral genera diversity. Farming yielded significantly more algal coverage than hiding. This study shows that small-scale, short-term behaviours by S. planifrons can have an effect on algal genera diversity on coral reefs in Utila, Honduras.
 
 Keywords: Stegastes planifrons (three-spotted damselfish); behaviours (short-term, small-scale); stage of development (juvenile, adult); depth; coral reef and algal diversity (long-term, large-scale); damselfish territories

Seasonal variations of cellular stress response of the gilthead sea bream (Sparus aurata)

The present study aimed to investigate the seasonal cellular stress response in vital organs, like the heart, the liver, the whole blood and the skeletal (red and white) muscles of the Mediterranean fish Sparus aurata during a 1-year acclimatization period in the field, in two examined depths (0-2m and 10-12m). Processes studied included heat shock protein expression and protein kinase activation. Molecular responses were addressed through the expression of Hsp70 and Hsp90, the phosphorylation of stress-activated protein kinases and particularly p38 mitogen-activated protein kinase (p38 MAPK), the extracellular signal-regulated kinases (ERK-1/2) and c-Jun N-terminal kinases (JNK1/2/3). The induction of Hsp70 and Hsp90 and the phosphorylation of p38 MAPK, JNKs and ERKs in the examined five tissues of the gilthead sea bream indicated a cellular stress response under the prism of a seasonal pattern which was characterized by distinct tissue specificity. Specifically, Hsp induction and MAPK activation occurred before peak summer water temperatures, with no further increases in their levels despite increases in water temperatures. Moreover, although water temperature did not vary significantly with depth of immersion, significant effects of depth on cellular stress response were observed, probably caused by different light regime. The expression and the activation of these certain proteins can be used as tools to define the extreme thermal limits of the gilthead sea bream.

Variação espaço-temporal da assembleia de peixes demersais em uma área de pesca do camarão sete-barbas no sul do Brasil

The temporal and spatial variability of demersal fish assemblage in a sea-bob-shrimp fishing area at the coast of northern Santa Catarina was examined over a sampling period of one year. Monthly samplings were conducted by bottom trawl tows during day and night hours in nine stations between October 2003 and September 2004. 8,967 specimens of 72 species representing 31 families were captured. Larimus breviceps, Stellifer rastrifer, Stellifer brasiliensis, Paralonchurus brasiliensis, Menticirrhusamericanus and Isopisthus parvipinnis were predominant among the fish caught. The average number of species and individuals varied significantly over time and space. A smaller number of fish and species seem to occupy the area in the spring. There was a negative gradient in terms of abundance and species diversity between inner and outer areas. The time of the year and of the day significantly affected the use of the area by the fish, but no significant effects of depth on the fish assemblage were found. This monitoring has contributed to the expansion of knowledge and conservation of fish fauna in the area studied.Key words: spatial variability, temporal variability, demersal fish.

Temporal and spatial changes of demersal fish assemblage in a sea-bob-shrimp fishing area in south Brazil

The temporal and spatial variability of demersal fish assemblage in a sea-bob-shrimp fishing area at the coast of northern Santa Catarina was examined over a sampling period of one year. Monthly samplings were conducted by bottom trawl tows during day and night hours in nine stations between October 2003 and September 2004. 8,967 specimens of 72 species representing 31 families were captured. Larimus breviceps, Stellifer rastrifer, Stellifer brasiliensis, Paralonchurus brasiliensis, Menticirrhus americanus and Isopisthus parvipinnis were predominant among the fish caught. The average number of species and individuals varied significantly over time and space. A smaller number of fish and species seem to occupy the area in the spring. There was a negative gradient in terms of abundance and species diversity between inner and outer areas. The time of the year and of the day significantly affected the use of the area by the fish, but no significant effects of depth on the fish assemblage were found. This monitoring has contributed to the expansion of knowledge and conservation of fish fauna in the area studied. Key words: spatial variability, temporal variability, demersal fish.

Spatial Distribution of Soil Nematode Communities in Stable and Active Sand Dunes of Horqin Sandy Land

To explore the ecological significance of artificial plantation and the restoration process in sand dune ecosystems, the spatial distribution of soil nematode communities in stable and active sand dunes were investigated in northeastern Inner Mongolia, China. Soil nematode community structure and composition at five soil depths (0–5 cm, 5–10 cm, 10–20 cm, 20–40 cm, and 40–60 cm) and three slope positions (windward slope, top slope, and leeward slope) in the stable and active sand dunes were compared. The results showed that the total abundance of soil nematodes decreased with increasing soil depth in the stable sand dune, while increasing in the active sand dune. Bacterivores were found to be the most abundant group in both the stable and active dunes. Significant depth effects were found in the four nematode trophic groups. Thirty-eight and 29 genera were observed in the stable and active sand dunes, respectively. Acrobeles was dominant genus in the stable sand dune, while Acrobeloides was most prevalent in the active sand dune. The increasing values of generic diversity, evenness, and species richness, and the decreasing trend of the Simpson index from 0–5 cm to 20–40 cm were found in the stable sand dune. Nematode faunal analysis indicated that the soil food web in the stable sand dune was barely disturbed in comparison to the active sand dune. The positive interfeedback between soil and vegetation was the key to restoring the sandy ecosystems. Soil nematode communities can be used as bioindicators for assessing the rehabilitation of the sand dune ecosystems.

Understanding Depth of Vocabulary Online With Bilingual and Monolingual Children

The sheer quantity of words known (breadth) is strongly predictive of reading comprehension, yet little is understood about how quality of word knowledge (depth) affects comprehension. A group of 35 bilingual and monolingual 5th-grade students worked on developing depth of knowledge of 8 words, culminating in an activity in which the students produced captions for images related to each word. The captions were scored using a 4-point depth scale, and similarities and differences between bilingual and monolingual students were assessed. Results indicated a significant effect of depth of word knowledge in predicting reading comprehension, particularly for students with average to strong oral language skills.

An Evaluation of Perceptual Depth to Enhance Change Detection

Two experiments investigated the effect of perceptual depth as a cue to highlight unexpected or changing stimuli. We used a new display technology known as a Multi-Layered Display (MLD). The results of the first experiment showed a significant effect of depth on the detection of an unexpected event when it is located in the front layer regardless of the depth plane in which the distracters were located. Detection was three times higher when the unexpected event was located less than 20 degrees of visual angle from the focus of attention. The second experiment indicated that the depth cue, although slower than the colour transient, presented the highest accuracy. The results suggested that depth may not always be the best transient to highlight changes, however, in cases where colour and flashing are no longer appropriate, the use of depth is a viable alternative.

Missing in action: the effect of obstacle position and size on avoidance while reaching

When reaching to objects, our hand and arm rarely collide with non-target objects, even if our workspace is cluttered. The simplicity of these actions hides what must be a relatively sophisticated obstacle avoidance system. Recent studies on patients with optic ataxia and visual form agnosia have demonstrated that obstacle avoidance is an automatic process, likely governed by the dorsal stream (Schindler et al. 2004; Rice et al. 2006). The current study sought to quantify how normal participants react to changes in the size and position of non-target objects in and around their workspace. In the first experiment, 13 right-handed subjects performed reaches to a target strip in the presence of two non-target objects, which varied in depth and horizontal configuration. We found that objects with horizontal alignments that were asymmetric about midline created systematic deviations in reach trajectory away from midline, with participants seeming to maximize the distance away from the two objects. These deviations were significantly greater for objects nearer in depth and nearly disappeared when the objects were placed beyond the target strip. Accompanying this pattern of deviation were other significant obstructing effects whereby reaches were executed more slowly when objects were close in depth and close to the participants reaching (right) hand. In the second experiment, we varied the height of the two objects, as well as the depth. Object pairs were now both tall, both short, or one-short/one-tall. We replicated the significant depth effects of the first experiment, extending the finding to include sensitivity to the size of the objects. Here the obstructing effect caused by short objects was similar to tall objects when those objects were placed at the depth of the reach target, but less than the tall objects when placed at mid-reach. Taken together, these experiments suggest that humans possess a sophisticated obstacle avoidance system that is extremely sensitive and conservative in evaluating potential obstacles and adjusting the reach accordingly.

Evaluation of Tissue Oxygen Measurements for Flap Monitoring in an Animal Model

Tissue oxygen tension (p(ti)O(2)) measurements are common in neurosurgery but uncommon in plastic surgery. We examined this technique as a monitoring method with probe placement in the subcutaneous tissue and addressed the importance of probe placement. Myocutaneous flaps were raised in an animal model and p(ti)O(2) measurements performed at different levels in the subcutaneous fat. Flap artery and vein were occluded until a 50% p(ti)O(2) reduction had occurred (T(1/2)). We found no significant effect of depth (P>0.10) on the level of p(ti)O(2). T(1/2)(arterial) was 7.2 minutes and T(1/2)(venous) was 18 minutes. We found no significant relation between initial levels of p(ti)O(2) and T(1/2). Location of the probe and absolute p(ti)O(2) value is of little relevance for flap monitoring. It is the relative change in p(ti)O(2) that is important. The p(ti)O(2) technique is well suited for monitoring in the subcutaneous tissue and is highly sensitive to changes in both arterial and venous blood flow.

Effect of subgingival depth of implant placement on the dimensional accuracy of the implant impression: An in vitro study

In some instances, an implant needs to be placed deep subgingivally, which may result in a less accurate impression of the implant. PURPOSE.: The purpose of this study was to evaluate the effect of subgingival depth of implant placement on the accuracy of implant impressions. A stone master model was fabricated with 5 implant analogs (RN synOcta analog), embedded parallel to each other, at the center (E) and the 4 corners (A, B, C, and D). The vertical position of the shoulders of the implants was intentionally different among the implants: A and E were flush with the top surface of the model; B was 2 mm below, and C and D were 4 mm below the surface. The horizontal distances of implants A, B, C, and D from E were measured with a measuring microscope. A cross-shaped metal measuring bar was then fabricated and connected to E, with the arms of the casting designed to be 2 mm above the top surface of the model and incorporating a reference mark. With the measuring bar connected to E, the vertical distances from the apical surface of A, B, C, and D to the measuring reference marks were measured with a digital micrometer. The body of the impression coping for implant D was modified by adding 4 mm of additional impression coping, while standard impression copings were used for all other implants. Open tray impressions were made using medium-body polyether material (Impregum Penta) or a combination of putty and light-body vinyl polysiloxane (VPS) material (Elite HD+) (n=15). Then casts were poured with type IV dental stone. The vertical and horizontal distances of the casts were measured with the methods outlined above for the master model. The distortion values that were determined as differences between the measurements of the master model and those of the casts were collected for statistical analysis. Two-way and 1-way repeated measures ANOVA followed by Tukey's HSD test were performed to compare the distortion values (alpha=.05). For vertical measurements, 2-way repeated measures ANOVA showed no significant depth (P=.36), material (P=.24), or interaction effects (P=.06). However, it showed significant depth effect for horizontal measurements (P=.01). Within the polyether group, 1-way repeated measures ANOVA showed significant differences in horizontal measurements among the implants with different depths (P=.03). The post hoc Tukey's test showed that the impression of 4-mm-deep implants with normal impression copings (C) was significantly less accurate than impressions of 0-mm-deep implants (A) (P=.02). Within the VPS group, there was no significant difference among the implants with different depths (P=.09). There was no effect of implant depth on the accuracy of the VPS group. However, for the polyether group, the impression of an implant placed 4 mm subgingivally showed a greater horizontal distortion compared to an implant placed more coronally. Adding a 4-mm extension to the retentive part of the impression coping eliminated this difference.

Shallow-water refuge paradigm: conflicting evidence from tethering experiments in a tropical estuary

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 349:13-22 (2007) - DOI: https://doi.org/10.3354/meps07102 Shallow-water refuge paradigm: conflicting evidence from tethering experiments in a tropical estuary Ron Baker1,2,3,*, Marcus Sheaves1,2 1Estuarine and Coastal Ecology Group, School of Marine and Tropical Ecology, James Cook University, Townsville, Queensland 4811, Australia 2Cooperative Research Centre for Coastal Zone, Estuary and Waterway Management, Indooroopilly Sciences Centre, 80 Meiers Road, Indooroopilly, Queensland 4068, Australia 3Present address: NOAA Fisheries Service, SEFSC Galveston Lab, 4700 Ave U, Galveston, Texas 77551, USA *Email: ronnie.baker@noaa.gov ABSTRACT: The shallow-water refuge paradigm has been globally applied to help explain the high abundances of juvenile fishes that utilise shallow-water estuarine nursery habitats. Despite the wide application and acceptance of the paradigm, there is little direct evidence to indicate that small juvenile fishes benefit from reduced predation pressure in shallow water habitats relative to adjacent deeper waters. The present study employed chronographic tethering experiments to examine patterns in predation potential across a depth gradient (0.2 to 3 m) in the lower reaches of a tropical estuary in northeastern Queensland, Australia. Over 6 mo, 17 replicate experimental trials were conducted, deploying a total of 183 tethered fish prey. Despite the clear and consistent patterns found in the few previous studies elsewhere in the world, there was no significant effect of depth on predation pressure, and thus no evidence of lower predation pressure in the shallow relative to the adjacent deeper estuarine waters examined in the present study. The findings suggest that the shallow-water refuge paradigm may be too simplistic for diverse and complex tropical estuarine nursery grounds. KEY WORDS: Nursery · Tropical estuary · Predation · Refuge paradigm Full text in pdf format PreviousNextCite this article as: Baker R, Sheaves M (2007) Shallow-water refuge paradigm: conflicting evidence from tethering experiments in a tropical estuary. Mar Ecol Prog Ser 349:13-22. https://doi.org/10.3354/meps07102 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 349. Online publication date: November 08, 2007 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2007 Inter-Research.

Depth-related patterns in benthic community condition along an estuarine gradient in Chesapeake Bay, USA

Abstract We tested whether macrobenthic community condition varies significantly with water depth in a variety of regions of Chesapeake Bay, USA. Benthic community condition was characterized using the Benthic Index of Biotic Integrity (B-IBI) previously developed for the Bay. We applied two water depth thresholds intended to emphasize the ecological importance and/or anthropogenic impacts upon shallow-water regions. The first threshold of 2 m emphasizes restoring and supporting submerged aquatic vegetation while the second threshold of 4 m emphasizes the zone of maximum anthropogenic impact upon natural ecosystem functions. An a priori expectation is that benthic community condition may worsen with increasing depth, specifically in regions (1) where water column stratification at depth results in prolonged low dissolved oxygen levels or (2) where net deposition at depth results in higher levels of hydrophobic, sediment-bound contaminants. Samples collected from a major tributary of Chesapeake Bay, the York River estuary, spanned the entire salinity range from tidal freshwater to polyhaline. We also tested the shallow-water depth thresholds using data from the Virginia Mainstem of Chesapeake Bay and the Southern Branch of the Elizabeth River. These two polyhaline regions are characterized as having the best and worst benthic community condition in Chesapeake Bay. At the scale of the entire tidal York River system, there were no significant differences in benthic community condition with water depth. However, two salinity regions, low mesohaline and polyhaline, had significant depth effects with the shallowest water depth zone significantly different from the other two depth regions. For the low mesohaline region benthic community condition was worse at the shallowest depth and for the polyhaline region the shallowest depth was better comparing the three depth regions. No depth-related differences in the B-IBI were found for the two additional Chesapeake Bay strata, the Virginia Mainstem characterized with the lowest levels of benthic community degradation and for the Southern branch of the Elizabeth River, characterized by the highest levels of benthic community degradation. We conclude that the ecological state of Chesapeake Bay subtidal benthic communities is adequately characterized by randomly sampling all depths without further stratification into shallow and deeper regions.

Structure and diversity of small-sized fish community in Lake Niushan, Hubei Province

研究了牛山湖小型鱼类的群落结构、种群密度和多样性.共捕获14种小型鱼类,以1龄鱼为主,其中红鳍原鲌、似鱎、麦穗鱼和鳑鲏是优势种群.小型鱼类的密度为5.9ind/m²或14.0g/m².小型鱼类的群落多样性较低,以个体数为单位计算的Shannon-Wiener多样性指数为1.802,Simpson优势度指数为0.484, Pielou种类均匀度指数为0.503.水生植被是牛山湖小型鱼类群落分布的主要影响因子,水草生境中小型鱼类数量显著比无水草生境中多,水深和透明度对小型鱼类群落分布无显著性影响.通过合理调控湖泊鱼类群落结构和放养食鱼性鱼类来合理持续利用小型鱼类,有利于提高湖泊经济效益和生态效益.;This paper investigated community structure，density and diversity of small-sized fish with seine in Lake Niushan,Hubei Prowince. 14 species were collected. Cultrichthys erythropteras, Taxabramis swinhonis, Pseudoras-bora parva, and Acheilognathinae, including Rkodeus ocellatus, R. lighti and Paracheilognathus imberbis, were the dominant species. Majority of small-sized fishes were one year old. The density of small-sized fishes in the seine was about 5. 8 ind/m² or 14. 0 g/m². Diversity of fish community in the seine was low. The diversity index(H^,)， dominance index(A) and evenness index(J^,) of small-sized fish community were 1. 802，0. 484 and 0. 503 respectively. The macrophyte played an important role in determining the distribution of fish community. The biomass of small-sized fishes in the macrophyte regions was significantly higher than it in the regions without macrophyte. There was no significant effect of depth and transparence on the distribution of small-sized fish community in the Lake Niushan. Small-sized fish can be use reasonably, in order to increase economic and ecological benefit, through optimizing fish community structure and enhancing piscivorous fish.

Treatment at different depths and vertical mixing within a 1-m deep horizontal subsurface-flow wetland

The aim of this study was to examine the variation in treatment performance at three depths, and the degree of vertical mixing, within a 1.0 m deep horizontal subsurface-flow constructed wetland (HSSF-CW) planted with Schoenoplectus tabernaemontani (Gmel.) Palla, and treating primary settled municipal wastewater in sub-tropical New South Wales, Australia. Water samples were collected from the upper (0.17 m), middle (0.5 m), and lower (0.83 m) depths at five equi-spaced sample points along the longitudinal axis of the 8.8 m 2 bed during two trials. Analysis of covariance (ANCOVA) indicated that the rate of pollutant concentration reduction between the three depths was not significantly different ( p > 0.05) for all of the measured parameters (dissolved oxygen (DO), hydrogen electrode potentials ( E h), 5-day biochemical oxygen demand (BOD 5)) total nitrogen (TN), TKN, and NH 4-N. Thus, it can be concluded that the break-down of contaminants as wastewater moved through the HSSF-CW was approximately uniform across the 1.0 m depth profile. The lack of a significant depth effect can be largely explained by the substantial amount of vertical mixing that was observed when a pulse of lithium tracer was injected into the middle depth of the first intermediate sampling point. The tracer rapidly migrated vertically into the upper and lower depths as water moved through the bed and was almost completely mixed between the three depths by the time it reached the last intermediate sampling point. The majority of BOD 5 removal occurred within the first-third of the bed where vegetation cover was poor. Performance of the bed declined over time from Trial 1 to Trial 2, possibly due to a cumulative build-up of organic matter within the substrate as a result of limited oxygen transfer throughout the 1.0 m depth of substrate via root leakage or diffusion across the air–water interface. Root penetration was limited to the upper 0.4 m of the substrate, with the majority of below-ground biomass forming a dense mat in the upper 0.2 m. A comparison of two-parameter ( K– C *) first-order volumetric rate constant ( K v20) with those obtained from 0.4 to 0.6 m deep HSSF-CW in the same region indicate that a doubling of the wetted depth resulted in no improvement in BOD 5 removal and a decline in TN removal on an areal basis. Further investigations are warranted, comparing the performance of replicated beds spanning a range of depths (e.g. 0.25, 0.5 and 1.0 m) in order to quantitatively determine the optimal depth of HSSF-CWs treating domestic wastewater.