Drift Samples Research Articles

A self-organizing system for pattern classification: time varying statistics and sensor drift effects

This paper discusses the results related to a simulated experiment of pattern recognition in chemical sensing, employing a self-organizing map (SOM) and a sensor array. The sensor is formed by two sensors for the identification of two classes of input patterns in the presence of environmental statistical changes and sensor drift. Self-organizing map sampling clock rate, drift velocities and decay rate of the length scale in the self-organizing map learning algorithm are the parameters considered for studying the problem of class separation. Empirical relationships between SOM and input parameters will be presented and discussed.

The effect of sample duration on the quantification of stream drift

SUMMARY1. We performed computer simulations and a field experiment to determine the effect that sample duration and, thus, sample volume had on estimates of drift density and sample variance.2. In computer simulations, when the spatial arrangement of individuals in the water column approximated a random and a contagious‐random distribution, estimated mean drift density was not significantly affected by sample duration, but sample variance decreased curvilinearly as sample duration increased.3. Similar results were obtained in field experiments in habitats of high and low water velocity.4. Our findings from an Albertan stream indicate that the relationship between sample variance (i.e. coefficient of variation) and duration of drift samples is curvilinear. This relationship affected the number of samples required to achieve a specific level of precision (i.e. a standard error within 10% of the mean). For estimates in low and high current velocities, sample variation was halved by increasing the duration of sample collections from 10 to 20 min. The increased precision obtained with samples of 20 min duration reduced the amount of drift material that needed to be processed by approximately 50% compared with an equivalent 10% level of precision for samples of 10 min duration. This reduction in the number of samples required to obtain a given level of precision has important consequences to the cost of processing drift samples.5. Thus to optimize studies of stream invertebrate drift, both in terms of sample precision and processing effort, researchers must consider the effect that sample volume has on the variance of drift density estimates. Because researchers generally use drift nets with similar‐sized apertures (>300cm2), the problem for specific field applications becomes one of optimizing sample duration relative to variance estimates for drift density.

Derived constituents in the glacial sediments of the Vestfold Hills, East Antarctica

Sediment derived from pre-existing marine deposits and weathered surfaces is a common consituent of glacial drift in the Vestfold Hills, East Antarctica. Ninety-seven samples of glacial drift were examined for marine macrofossils and weathered clasts, and 41 were examined for foraminifera. Fragments or whole specimens of shells, worm tubes, sponge spicules and foraminifera were recovered from 25 samples. Clasts that exhibited evidence of subaerial weathering, such as tafoni and weathering rinds, were found in 53 samples. Derived sediment was found in 62% of all samples. These data indicate that the last advance of ice derived much of its sediment locally. The incorporation of marine fauna in the glacial deposits makes the identification of in situ interglacial sequences difficult.

Air Deflector Effects on Aerial Sprays

Air deflectors (Chimavir Air Services, Ltd., Israel) were installed on an agricultural aircraft and tests were run to investigate: (1) the alteration in downwind residue results (drift) due to release height, (2) the influence on droplet sizes conducted with a laser drop size analyzer in a wind tunnel, and (3) the changes in air flow near the spray boom as observed from wind tunnel tests. A turbine-powered monoplane with air defectors was evaluated for spray drift losses and deposit characteristics in a cotton field. Air-burden residue from application heights of 3.0, 4.6, and 6.1 m were investigated using high-volume air samplers along a 610-m sampler line oriented at 23.6 from a 700-m flightline. Spray deposit was measured (concurrent with the downwind airborne drift sampling) from collection of residue on Mylar plastic sheets spaced at 6.1-m intervals from the first air sampler to beyond the flightline. Gas chromatographic analysis was used to measure the concentration of cinnamyl alcohol tracer. Results from air samplers indicated that the 3.0-m release height had significantly (P = 0.05) less airborne drift (2.19 ppm) than the 4.6 m height (9.52 ppm) and 6.1 m height (11.37 ppm). No differences (P = 0.05) in fallout deposit levels were detected, although the 4.6 m height tended to have a higher level of deposit (6.06 ppm) than the 3.0 m height (4.29 ppm) and the 6.1 m height (4.62 ppm). Spray droplet sizes produced in a wind tunnel with and without a deflector were examined for a custom-sized RF 25 fan nozzle (3.06 L/min at 276 kPa, Delavan-Delta, Inc., Lexington, Tenn.) and a D6-46 disk and core nozzle (Spraying Systems Co., Wheaton, Ill.). Both nozzles were oriented 45 down and back with airstream velocities of 60 and 75 m/s. Water-soluble formulations were examined and included (1) cinnamyl alcohol, (2) bifenthrin, and (3) water. Overall mean droplet sizes (Malvern) with the deflector were 235 mm, whereas without the deflector they were 182 mm. The downwash of air around the deflector was quantified in terms of mean, steady-state air velocity and direction. Measurement points were selected on a two-dimensional grid that ran longitudinally with the axis of the wind tunnel. Air was deflected to an angle of 50 from horizontal. A 54 m/s air flow was decelerated to 40 m/s behind the deflector.

Predicting and measuring drift of Bacillus thuringiensis sprays

AbstractDrift of the pesticide Bacillus thuringiensis Berliner var. kurstaki (Bt) was measured downwind from a gypsy moth (Lymantria dispar L.) treatment block in mountain terrain. The study was conducted in conjunction with a project to eradicate the moth along the Wasatch mountain range of Utah. Objectives of the study were to quantitate drift, to evaluate drift sampling methods, and to compare FSCBG (Forest Service Cramer‐Barry‐Grim) computer model predictions to field measurements of Bt based on colony‐forming units. The treatment block was sprayed by helicopter three times, within a 12‐d period during June 1991, which provided a study of three replicates. During each spray, downslope drainage winds carried the spray over an array of samplers that extended 3,150 m downwind. The FSCBG dispersion model, exercised after the treatments, used meteorological inputs measured during the treatments to predict spray deposition and airborne dosage of Bt. Results of the study demonstrated a correlation among dosage, deposition and total flux samplers; a potential of Bt drift of at least 3,150 m; and FSCBG model predictions that generally followed the field recovery data.

Changes in Habitat Use and Feeding Chronology of Juvenile Rainbow Trout (Oncorhynchus mykiss) in Fall and the Onset of Winter in Silver Creek, Idaho

We assessed changes in density, distribution, and microhabitat of age-0 rainbow trout (Oncorhynchus mykiss) in Silver Creek, a partially spring-fed stream, by periodic snorkeling in August 1987 through January 1988. We examined trout stomach contents and invertebrate drift samples in diel collections in August, September, October, and January to test if the period of feeding shifted from daytime to nighttime, concurrent with a transition to day concealment. In late September, fish aggregated briefly during the day and then began to conceal themselves in macrophyte beds, undercut banks, and submerged sedges and grasses along streambanks as temperature dropped below 8 °C in early October. Fish emerged from concealment at night, and numbers of trout visible were greatest 30–60 min after sunset and about 30 min before sunrise. Periods of peak feeding changed from afternoon and evening in August and September, when fish were day active, to mainly at night in October after the initiation of day concealment. Trout did not feed upon abundant chironomids in the daytime drift in October. In January, fish fed at 1–4 °C on mayflies, and stomachs were fullest in the early morning. Observations suggest that Silver Creek trout experienced a metabolic deficit that began in September.

The probability of fixation of a favoured allele in a subdivided population

SummaryIn a stably subdivided population with symmetric migration, the chance that a favoured allele will be fixed is independent of population structure. However, random extinction introduces an extra component of sampling drift, and reduces the probability of fixation. In this paper, the fixation probability is calculated using the diffusion approximation; comparison with exact solution of the discrete model shows this to be accurate. The key parameters are the rates of selection, migration and extinction, scaled relative to population size (S = 4Ns, M = 4Nm, Λ = 4Nλ); results apply to a haploid model, or to diploids with additive selection. If new colonies derive from many demes, the fixation probability cannot be reduced by more than half. However, if colonies are initially homogeneous, fixation probability can be much reduced. In the limit of low migration and extinction rates (M, Λ ≪ 1), it is 2s/{1 + (Λ/MS)(1 −exp(−S))}, whilst in the opposite limit (S≪ 1), it is 4sM/{Λ(Λ +M)}. In the limit of weak selection (M, Λ ≫ 1), it is 4sM/{Λ(Λ +M)}. These factors are not the same as the reduction in effective population size (Ne/N), showing that the effects of population structure on selected alleles cannot be understood from the behaviour of neutral markers.

Thermoluminescence dating tests for lacustrine, glaciomarine, and floodplain sediments from western Washington and British Columbia

To help further develop reliable procedures for accurate thermoluminescence (TL) dating of Quaternary waterlaid sediments, we tested TL dating procedures on sediment types rarely examined: six glaciolacustrine samples, three samples of glaciomarine drift, and eight samples of floodplain deposits. We used the partial-bleach (R-beta/gamma) technique applied to fine-silt polymineral grains. Results from our younger known-age glaciolacustrine sediments confirm earlier observations that only the clayey laminae are generally suitable for TL dating. A clayey lamina older than ca. 140 – 150 ka produced no age underestimation, and this result (ca. 300 ka) suggests that such older lake sediments are probably suitable for TL dating. Two proximal samples of glaciomarine drift produced large TL age overestimates, whereas the single distal glaciomarine-drift sample yielded an expected age (177 ± 38 ka), suggesting that follow-up studies are warranted. Our results for eight flood-plain samples confirm that zeroing of light-sensitive TL is more likely to be effective for sediments deposited in quiet, ponded water on the floodplain than for proximal sediments deposited from turbid floodwater. TL age estimates for floodplain sediments of the regional Whidbey Formation are consistent with its expected last-interglacial age, and those for two samples from stratigraphically older beds are consistent with deposition near or beyond 200 ka. Two of our younger samples (one lacustrine and one floodplain) gave TL age underestimates, perhaps because of use of ultraviolet TL emissions for these samples.

Effects of permethrin as Simulium larvicide on non-target aquatic fauna in an African river

: The side-effects of permethrin (20% EC) as a Simulium larvicide on aquatic invertebrates and fish was studied under operational vector control conditions to contribute to the evaluation of the product for its possible adoption by the Onchocerciasis Control Programme in West Africa. After 15 weekly applications of the formulation at 0.045 litre per m(3) of water discharge, drift samples virtually contained no Ephemeroptera. Saxicolous fauna density and proportional diversity were also affected. However, both drift and saxicolous fauna recovered to almost pretreatment levels a month after treatment was terminated. Fish showed some evidence of stress but remained in the active treated zone to make trends of catches in the area comparable with those of the control station. The treatment did not result in fish mortalities, and the condition of fish before and after the experimental period was significantly unchanged. Thus, operational use of permethrin by the Programme would not be expected to have permanent adverse effects on the non-target fauna.

Anthropogenic changes in the fish fauna of the Amu Darya River (based on data from sampling drift of eggs and larvae): L. P. Pavlovskaya & I. M. Zholdasova, Journal of Ichthyology, 31(8), 1991(1992), pp 106–117; translated from: Voprosy Ikhtiologii, 31(4), 1991, pp 585–595

Anthropogenic changes in the fish fauna of the Amu Darya River (based on data from sampling drift of eggs and larvae): L. P. Pavlovskaya & I. M. Zholdasova, Journal of Ichthyology, 31(8), 1991(1992), pp 106–117; translated from: Voprosy Ikhtiologii, 31(4), 1991, pp 585–595

Diel variations in the effect of spates on mayflies (Ephemeroptera: Baetis)

Field experiments were carried out to determine whether there are diel variations in the effect of spates on baetid mayflies. Short-term spates were created in experimental streamside channels by pumping filtered creek water into selected channels at various times of day, resulting in three- or four-fold increases in discharge. Drift samples were collected before, during, and after spates; benthic samples were collected before and after. Drift rates of Baetis from channels in spate were higher than controls at all times of day. Natural increases in drift were observed in all channels after sunset, and drift rates from channels in spate were highest at this time. The susceptibility of nymphs to drift from channels was calculated as the ratio of drift densities in spate and control channels. Baetis appeared to be more vulnerable to spates after sunset than at dawn or midday. In unmanipulataed flow, large nymphs occurred most frequently in the drift after sunset. Spates had no apparent effect on the size distribution of nymphs in the drift compared with unmanipulated flows at the same time. These spates were not large enough and (or) long enough to greatly decrease mayfly densities in the benthos. It is notable, however, that benthic densities of Baetis were reduced significantly only by one spate at dusk.

Effects of Permethrin on Aquatic Organisms in a Freshwater Stream in South-Central Alaska

Permethrin (0.5%) was applied to individual Lutz spruce, Picea x lutzii Little, to protect them from attack by spruce beetles, Dendroctonus rufipennis (Kirby). Residue levels were monitored in a freshwater stream above, adjacent to, and below the treatment site at intervals before, during, and after treatment. Maximum residue levels in the stream within the treatment site ranged from 0.05 +/- 0.01 ppb 5 h after treatment to 0.14 +/- 0.03 ppb 8-11 h after treatment, with a decrease to 0.02 +/- 0.01 ppb 14 h after treatment. Levels of permethrin in standing pools near the stream within the treatment site were 0.01 +/- 0.01 ppb. Numbers of drifting aquatic invertebrates increased 2-fold during treatment and 4-fold 3 h after treatment and declined to before spray numbers within 9 h. Terrestrial insects did not appear to respond to treatments because none was found in stream drift samples. Trout fry (Dolly Varden), aquatic insect larvae, and periphyton (attached algae) within and below the treatment site during and after treatment did not show signs of mortality compared with an upstream untreated control site.

Macroinvertebrate activity in the water column of backwaters in an upland stream in Victoria

The activity of benthic invertebrates was monitored in the water column of slowly flowing backwaters of the Acheron River during summer. Samples were taken throughout 24 h on two occasions, and densities of fauna were compared with densities in drift samples taken concurrently in the main channel. Drift densities were generally higher than those in backwaters, but not by orders of magnitude. Also, drift densities displayed significant die1 variation, whereas densities in backwaters did not consistently show such a pattern. Species composition generally differed between the two habitats. This brief study demonstrates that benthic invertebrates do swim in the water column of stream backwaters and that they may use this opportunity for colonization.

Size-dependent drift responses of mayflies to experimental hydrologic variation: active predator avoidance or passive hydrodynamic displacement?

Larger nymphs within aquatic insect taxa have been frequently observed to be transported down-stream in the stream drift only at night. Others have hypothesized this pattern results primarily from large nymphs' behavioural avoidance of entering drift during daylight, when size-selective, visually-feeding fish predators are most active. This hypothesis assumes that animals can actively control their entry into the drift, which may not be the case under all flow conditions. We experimentally induced streamflow increases and decreases in adjacent riffles in a hydrologically-stable stream during the daytime to examine whether changes in diel patterns of drift abundance and size-distribution of mayflies were consistent with the hypothesis of active avoidance of diurnal drift. We assessed the likelihood of active vs. passive mechanisms of diurnal drift entry and transport for four taxa that differ with respect to body size, morpho-behavioural attributes, microhabitat use, and general propensity to drift. In each of three seasons, diurnal and nocturnal drift samples were collected in three riffles over two diel cycles. Background drift patterns were established on the first day (no flow manipulation). Six h before sunset on the second day, flow was experimentally increased in one riffle, decreased in the second, and not altered in the third (control). Between-day differences in diurnal and nocturnal drift rate and size composition were then compared among the treatment and reference riffles. Responses of two taxa were consistent with active control over drift entry, transport, or both. For Baetis spp., drift-prone mayflies typically preyed upon by fish, diurnal drift rates immediately increased following both flow reduction and flow elevation in all seasons, but only small individuals comprised the drift. Drift by large individuals was delayed until nighttime. Epeorus longimanus also exhibited significant increases in drift rates following flow reduction and elevation, but responses of this large-bodied species were restricted to nighttime. Drift responses for these two taxa were largely independent of direction of hydrologic change, thus indicating a strong behavioural control over drift. By contrast, numbers and sizes of drifting Paraleptophlebia heteronea and Ephemerella infrequens depended strongly on direction of flow change. Drift rates for both species generally declined after flow reduction and increased after flow elevation. Moreover, after flow elevation, larger individuals often drifted diurnally, a finding consistent with expectations under a passive hydrodynamic model. These experiments indicate that size-dependent mayfly drift reflects not only presumed risk from visual fish predators, but also functional attributes of species such as morphology, behaviour, and microhabitat affiliation, which influence aspects of drift entry and transport under variable hydrologic conditions.

Drift sampling in the transition areas of the River Rhine and some of its tributaries

Drift sampling in the transition areas of the River Rhine and some of its tributaries

Continuous drift samples of macroinvertebrates in a large river, the Danube in Austria

SUMMARY 1. A new method is described for sampling the drift in large rivers continuously and automatically, using equipment based on the marine, continuous plankton sampler of Hardy (1936). 2. Between April and November 1989, about 790 h were sampled continuously, equivalent to a water volume of 2937m3 and the total catch was 527 drifting macroinvertebrates, in forty-nine taxa. Twenty-five of these taxa are recorded in the drift for the first time and twenty-eight of the drifting taxa were present in benthos samples from the Danube. 3. Total drift density varied between 12 and 31 animals per 100m3 of water sampled throughout the year, with a maximum of 31 animals in May, The composition of major faunal groups showed a significant seasonal pattern, with Oligochaeta and Diptera predominant in spring, Crustacea and Insecta in summer and only Crustacea in autumn. The overall density of the macrozoobenthos from October 1986 to December 1987 was about 19360 animals m−2 and the proportion of total benthos animals, drifting at any instant in time, ranged from 0.0026 to 0.0064%. 4. The relationship between drift density day−1 and mean daily discharge was described by a power-function. Total mean drift rate of macroinvertebrates in the Danube was estimated to be 13 600 000 animals per 24 h and the mean drift distance was estimated to vary between about 4 and 31 m, dependent on the animal group and the water velocity. 5. No obvious consistent diel pattern could be established from the continuous samples, and no marked diel rhythm could be detected for Oligochaeta, Diptera larvae and Crustacea.

Mesh-size effects on drift sample composition as determined with a triple net sampler

Nested nets of three different mesh apertures were used to study mesh-size effects on drift collected in a small mountain stream. The innermost, middle, and outermost nets had, respectively, 425 µm, 209 µm and 106 µm openings, a design that reduced clogging while partitioning collections into three size groups. The open area of mesh in each net, from largest to smallest mesh opening, was 3.7, 5.7 and 8.0 times the area of the net mouth. Volumes of filtered water were determined with a flowmeter. The results are expressed as (1) drift retained by each net, (2) drift that would have been collected by a single net of given mesh size, and (3) the percentage of total drift (the sum of the catches from all three nets) that passed through the 425 µm and 209 µm nets. During a two day period in August 1986, Chironomidae larvae were dominant numerically in all 209 µm and 106 µm samples and midday 425 µm samples. Large drifters (Ephemerellidae) occurred only in 425 µm or 209 µm nets, but the general pattern was an increase in abundance and number of taxa with decreasing mesh size. Relatively more individuals occurred in the larger mesh nets at night than during the day. The two larger mesh sizes retained 70% of the total sediment/detritus in the drift collections, and this decreased the rate of clogging of the 106 µm net. If an objective of a sampling program is to compare drift density or drift rate between areas or sampling dates, the same mesh size should be used for all sample collection and processing. The mesh aperture used for drift collection should retain all species and life stages of significance in a study. The nested net design enables an investigator to test the adequacy of drift samples.

Reproductive Biology and Fish Hosts of the Tennessee Clubshell Pleurobema oviforme (Mollusca: Unionidae) in Virginia

-The reproductive cycle and fish hosts of the freshwater mussel Pleurobema oviforme were determined during a 14-mo study (1979-1980) in Big Moccasin Creek, southwestern Virginia. Histological sectioning of mussel gonads collected throughout the year showed that gametogenesis for both sexes began in late spring and continued into early autumn; fertilization began in late March. Glochidial development in the outer gills of females required 3-5 wk. Judged by biweekly samples of stream drift, glochidia were released from mid-April through July. Six species of cyprinids, collected between May and September 1979, were naturally infested with amblemine glochidia. Induced infestations of putative fish hosts in the laboratory confirmed five host species: whitetail shiner (Notropis galacturus), common shiner (N. cornutus), river chub (Nocomis micropogon), stoneroller (Campostoma anomalum) and fantail darter (Etheostoma fiabellare).

The neutral theory of molecular evolution: A review of recent evidence.

In sharp contrast to the Darwinian theory of evolution by natural selection, the neutral theory claims that the overwhelming majority of evolutionary changes at the molecular level are caused by random fixation (due to random sampling drift in finite populations) of selectively neutral (i.e., selectively equivalent) mutants under continued inputs of mutations. The theory also asserts that most of the genetic variability within species at the molecular level (such as protein and DNA polymorphism) are selectively neutral or very nearly neutral and that they are maintained in the species by the balance between mutational input and random extinction. The neutral theory is based on simple assumptions, enabling us to develop mathematical theories based on population genetics to treat molecular evolution and variation in quantitative terms. The theory can be tested against actual observations. Neo-Darwinians continue to criticize the neutral theory, but evidence for it has accumulated over the last two decades. The recent outpouring of DNA sequence data has greatly strengthened the theory. In this paper, I review some recent observations that strongly support the neutral theory. They include such topics as pseudoglobin genes of the mouse, alpha A-crystallin genes of the blind mole rat, genes of influenza A virus and nuclear vs. mitochondrial genes of fruit flies. I also discuss such topics as the evolution of deviant coding systems in Mycoplasma, the origin of life and the unified understanding of molecular and phenotypic evolution. I conclude that since the origin of life on Earth, neutral evolutionary changes have predominated over Darwinian evolutionary changes, at least in number.

Seasonal dynamics of invertebrate drift in a Hong Kong stream

Drift samples were taken with paired nets on 19 occasions over a 12‐month period in Tai Po Kau Forest Stream (TPKFS), Hong Kong. Mean drift density (±1 S.E.) was 277·9 ± 25·0 individuals 100 m‐3; peaks in density were apparent during autumn and spring. One hundred and two taxa were recovered from the drift, and the total number of taxa drifting was positively related to water temperatures. Over 99% of the aquatic animals collected in drift samples were insects, 10 taxa of which constituted 67·3% of the entire catch. Baetid mayflies dominated the composition of the drift, comprising 40·4% of individuals caught.Seasonal changes in the drift of individual taxa were evident, reflecting significant relationships between drift densities and water temperature: Simulium T1 (Diptera). Anisocentropus maculatus (Trichoptera) and Amphinemura chui (Plecoptera) drifted most in winter, whereas Chimarra T1, Polymorphanisus astictus (Trichoptera), Helodes#1 and cf. Rhantus sp. (Coleoptera) were most numerous in summer. Drifting mayflies showed spring (Indobaetis sp., Cinygmina T1, Serratella T2), autumn (Baetiella sp., Pseudocloeon T2), or spring and autumn (Baetis nr pseudofrequentus) peaks which were not clearly related to water temperature. In only two cases (A. maculatus and P. astictus) was TPKFS drift seasonality associated with life‐cycle events. Overall, there was no evidence of community‐level trends in the periodicity of stream drift in this seasonal tropical habitat.