The effect of the release of an artificial discharge of water on invertebrate drift in the R. Wye,Wales

An artificial discharge of water (3.0 m³/sec), over a 48 h period, from an impoundment into the R. Wye did not substantially affect water temperature or concentrations of dissolved oxygen and suspended solids at a site 16 km below the impoundment. However, the load of suspended material on the second day of the release was about 10 times greater than the pre-release load. The total number of drifting macroinvertebrates on the first and second days of the release were about 7 and 3 times greater than the number on the day preceding the release. The initial increase in flow at 15.00 h resulted in an immediate increase in the number of drifting larvae of Rheotanytarsus, a tubicolous chironomid. Subsequently there was an enhanced night-time increase in the total number of drifting invertebrates, particularly the mayfly, Ephemerella ignita (Poda), and this also occurred on the second night of the release. Increases in the number of drifting Rheotanytarsus and Ephemerella, the most abundant invertebrates, resulted in increase in drift density.Authors' address Llysdinam Field Centre, UWIST, Newbridge-on-Wye, Llandrindod Wells, Powys, Wales.     

Macroinvertebrate drift in a Rocky Mountain stream

An extensive series of drift collections from a Rocky Mountain stream was used to investigate quantitative patterns in the taxonomic composition of drift throughout spring, summer and fall for 1975–1978. Drift was estimated by drift rate, the number of organisms drifting past a point per 24 h; and by drift density, the numbers of organisms collected per 100 m³ of water sampled.Drift densities were up to ten times greater by night than by day, and 24 h drift densities for the total fauna approached 2000 per 100 m³ in June–July, declining to <500 by autumn. Ephemeroptera, and especially Baetis, dominated the drift. Drift rates were greatest in late spring, around 10⁶ per 24 h, which are among the highest values reported for small trout streams. Drift rates declined to <10⁵ during the summer, and shifts in the taxonomic composition are described.Multiple regression analysis of the relationship between drift rate and density, and the independent variables discharge, benthic density and temperature, showed that discharge typically was a significant predictor of 24 h drift rate, usually the best single predictor. In contrast, 24 h drift density most frequently was independent of discharge, indicating that this measure tends to correct for seasonal variation in discharge, as suggested in the literature. However, this was not invariably true. Drift density significantly correlated with benthic density in five of eight taxa inspected, thus seasonal declines in the benthos probably accounted for parallel declines in drift density.     

The relation between invertebrate drift and two primary controls,discharge and benthic densities,in a large regulated river

相似文献   

Diel,size-differential drift patterns of three macroinvertebrate species in the lower Mississippi River,Louisiana (USA)

We explored macroinvertebrate size-differential drift in the lower Mississippi River (a 9th order system). Because this river system is highly turbid, we hypothesized that visually-dependent vertebrate predators feeding on drifting organisms would be at a disadvantage. Thus, size-differential drift should not occur. For one 24-hour period in both January and April, six drift nets were used to sample surface drift. Nets were emptied once every four hours. Individual intra-ocular distances of three macroinvertebrate species (Hydropsyche orris: Trichoptera, Hexagenia limbata: Ephemeroptera, Macrobrachium ohione: Crustacea) were measured. Percentages of size classes in the drift were determined. In both months, large individuals of H. orris and H. limbata were prevalent in the nocturnal but scarce in the diurnal drift. In January, large M. ohione drifted regardless of time. In April, large M. ohione predominated the nocturnal drift. Our results could not be attributed solely to vertebrate predator avoidance. Other mechanisms such as diel microhabitat migration and current velocity may have accounted for the results.     

The Epipelic Algal Flora of the River Wye System,Wales, U. K. 2. Algal Phyla and Species Population Dynamics

The Bacillariophyta dominated over the other phyla and were mainly recorded in high densities during summer and autumn. The Chlorophyta and Myxophyta (Cyanobacteria) were represented by coccoid forms and by non-heterocystous, filamentous forms, respectively. Both were mainly recorded during summer and mostly absent during winter. Other phyla were occasionally recorded in low densities; the Chrysophyta being found in the River Elan and at one site on the River Wye during June 1980. Their members were considered as “contaminants” or “fall-out” from other communities. Pennate diatoms were the most “constant” species and either showed a general upstream or downstream increase or a general distribution throughout the study area. Populations of the same species colonising both sediments and stones were not correlated or insignificantly correlated with each other at most stations. It was concluded that sediments were unsuitable for algal colonisation. The River Elan and upper Wye were rated as oligosaprobic, the River Ithon and lower Wye as β-mesosaprobic and the River Lugg as α-mesosaprobic.     

Diel drift of Chironomidae larvae in a pristine Idaho mountain stream

Simultaneous hourly net collections in a meadow and canyon reach of a mountain stream determined diel and spatial abundances of drifting Chironomidae larvae. Sixty-one taxa were identified to the lowest practical level, 52 in the meadow and 41 in the canyon. Orthocladiinae was the most abundant subfamily with 32 taxa and a 24 h mean density of 294 individuals 100 m⁻³ (meadow) and 26 taxa and a mean of 648 individuals 100 m⁻³ (canyon). Chironominae was the second most abundant subfamily. Nonchironomid invertebrates at both sites and total Chironomidae larvae (meadow) were predominantly night-drifting. Parakiefferiella and Psectrocladius were day-drifting (meadow) whereas 8 other chironomid taxa (meadow) and 2 taxa (canyon) were night-drifting. All others were aperiodic or too rare to test periodicity, Stempellinella cf brevis Edwards exhibited catastrophic drift in the canyon only. The different drift patterns between sites is attributed to greater loss of streambed habitat in the canyon compared to the meadow as streamflow decreased. Consequent crowding of chironomid larvae in the canyon caused catastrophic drift or interfered with drift periodicty. This study adds to knowledge of Chironomidae drift and shows influences on drift of hydrologic and geomorphic conditions.     

The Epipelic Algal Flora of the River Wye System,Wales, U.K. 1. Productivity and Total Biomass Dynamics

The spatial and temporal fluctuations of the phytopigment content, “potential” primary productivity and total biomass of the epipelic algae of the River Wye System were studied during June 1979 to May 1981. Chlorophyll-a and productivity values showed a downstream increase, much less obvious for the total biomass. Phaeophytin-a values followed almost similar spatial and temporal fluctuations to those of chlorophyll-a. High chlorophyll-a productivity and total biomass values were recorded during warmer months due to favourable environmental conditions for algal growth, but lower values during unfavourable winter and flood periods.     

Invertebrate drift in the Dan River,Israel

The Dan river, a principal source of the Jordan River, Israel, is unusually constant in discharge (8 m³·s^–1) and water temperature (15–16 °C). The Jordan headwaters constitute the southernmost oasis of a palearctic north temperate fauna, and presumably the very constancy of the Dan contributes to its important role as a regional refuge. However, little is known of river ecology from this region. We report a twelve month study of drift, undertaken to assess diel, seasonal, and spatial patterns of the abundance of drifting invertebrates.Diel periodicity in drift was detectable but minimal. Baetidae nymphs showed a pronounced nocturnal increase, gammarid amphipods a modest, twofold increase, while dipteran larvae showed no diel variation. Seasonal variation likewise was minimal and due principally to the Baetidae, while gammarid amphipods showed no significant seasonality. The notably small diel and seasonal variation in aquatic drift in the Dan may be attributable to the extremely constant physical regime.Spatial variation was substantial. Two stations located 30 and 200 m below the karstic exsurgence of the Dan provided drift densities among the lowest reported anywhere, whereas two stations located 1 and 4.5 km downstream had more typical drift densities. A water diversion project completed halfway through the study resulted in a 50% reduction in flow at the most downstream stations, but had no discernible effect on drift.     

The rate of downstream displacement of macroinvertebrates in the upper Wye, Wales

Quantitative data describing drift rates and benthic density of macroinvertebrates are utilised to estimate the rates of downstream displacement of invertebrate populations in the Wye, Wales. Calculations are based upon two models, one a classical exponential relationship between drift catch and distance travelled and the other derived from a solute balance equation. Results from the two models were significantly correlated. Estimates of the rate of benthic community displacement ranged from 2.8 to 70.7 m d^-1, with highest rates recorded in she summer period. There were considerable differences in rates between taxa and between sites. It was estimated that a displacement of 10 km downstream could be achieved by certain taxa during a generation period.     

The drift distances and time spent in the drift by freshwater shrimps, Gammarus pulex, in a small stony stream, and their implications for the interpretation of downstream dispersal

1. The objectives were (i) to determine experimentally and to model the relationship between mean water velocity and both the mean distance travelled, and the mean time spent, in the drift by freshwater shrimps, Gammarus pulex; (ii) to develop a drift distance–water velocity model from the experimental study, and validate it with field data; (iii) to examine the relationship between drift rate, water velocity and benthic density with the latter expressed as a mean value for the whole stream and a mean value corrected for the distance travelled in the drift. 2. In field experiments at 10 water velocities (0.032–0.962 m s^?1), the significant relationship between the mean drift distance and mean water velocity was described both by a power function (power, 0.96) and a linear relationship. The mean drift time was fairly constant at 8.3 s (95% CL ± 0.4). A simple model estimated the drift distance and time spent in the drift by different percentages of the drifting invertebrates. This model predicted correctly the positive relationship between drift rate and water velocity for field data over a year. 3. The relationship between drift rate per hour and the independent variables, water velocity and benthic density, was well described by a multiple‐regression model. Adding temperature and date did not improve model fit. Variations in water velocity and benthic density explained 96% of the variation in nocturnal drift rate (65% to velocity, 31% to benthic density), but only 40% of the variation in diurnal drift rate (29% to velocity, 11% to benthic density). Correcting benthic density for the drift distances did not improve model fit. 4. The significance of this study is that it developed models to predict drift distances and time, values being similar to those obtained in another, larger stream. It also illustrated the importance of spatial scale in the interpretation of drift by showing that when drift distances were taken into account, the impact of drift on the population was higher (4–10% lost day^?1) than when drift distances were ignored (usually < 3% lost day^?1), especially at a local level.     

Effects of experimental flow regulation on invertebrate drift and stranding in the Flathead and Kootenai Rivers,Montana, USA

Studies were conducted to determine the effects of experimental manipulations of discharge on invertebrate drift in two regulated rivers in northwestern Montana, USA. During these studies the discharge regime in the Flathead River was characterized by frequent flow fluctuations, while in the Kootenai River high discharge was maintained for much longer periods before flow was reduced to minimum discharge. The magnitude of the response of invertebrates to disturbance was different in the two rivers, in part because of the different frequencies of flow changes. Midstream invertebrate drift increased an order of magnitude during increasing discharges in the Flathead River but was not substantially increased during decreasing discharges. When the prior discharge regime had been sustained at high levels in the Kootenai River, invertebrate drift densities as high as 300 000/100 m³ were measured along the shoreline following reductions in discharge, both immediately after flow began to decrease and after dark on the same day. There was also more recolonization of shoreline areas and more stranding of insects following dewatering of nearshore regions when there had been sustained high discharge levels prior to the flow reduction. More insect stranding occurred during a faster rate of decrease in discharge (50 000 to 100 000 organisms m⁻²).     

Influence of a metal-contaminated tributary on the invertebrate drift fauna of the King River (Tasmania,Australia)

Drifting invertebrates were collected upstream of, at, and downstream of the input of metal contaminated water into the previously unpolluted King River in western Tasmania. In the upstream section the drift fauna showed characteristics similar to those observed by other workers with a marked nocturnal peak. Changes in drift rates at the site of input were observed and it is hypothesized that mayfly nymphs, and possibly other animals, respond to the change in water quality by leaving the water column and randomly searching the substrate for clean water. Most nymphs re-enter the drift in a current of clean water which was displaced towards the opposing bank by the entry of contaminated water. This re-entry of animals into the drift occurs some four hours after the main nocturnal peak in drift rates.     

The effect of long pools on the drift of macro-invertebrates in a mountain stream

Macro-invertebrate drift was measured entering and leaving two pools on the Middle Fork of the Cosumnes River, a third order California stream. Drift rates for Baetis spp., Chironomidae, Simulium spp., Capniidae and total drift were calculated. Significant differences in the numbers of organisms entering the two pools were found for Baetis, Chironomidae, and Capniidae. Comparisons of drift rates at the upstream and downstream ends of each pool showed that the abundance of Chironomidae, Simulium, Capniidae and total drift changed in different directions across the pools. The numbers of organisms leaving the two pools, however, were not significantly different for Baetis, Simulium, Capniidae and total drift. These findings lead us to hypothesize that long pools act as barriers, not filters, to stream macro-invertebrate drift. The composition of drift leaving the pools in this experiment appeared to be controlled by the composition of the benthic habitat at the tail of the pool and not by the composition of upstream drift entering the pools.     

The production of juvenile Atlantic salmon, Salmo salar in the upper Wye, Wales

The production of juvenile Atlantic salmon ( Sulmo salur L.) was investigated in 16 study sites in the upper Wye catchment during the period February 1975 to November 1976. The population structure was characterised by large numbers of 0+ fish whose abundance decreased with respect to time so that the numbers of each of the older year-classes was a function of the year-class strength of the original fry. The range of parr densities was similar to that recorded for other rivers: the estimates of 2+ smolts did not exceed about 0.04 m⁻². Production ranged from 0.3 to 11.0 gm⁻² a^−l; Of and 1+ fish contributed over 72% and 3+ fish less than 1 % of the total annug production. The relationship between production P (gm⁻² a⁻¹) and mean biomass B (gm⁻²) for all yeatclasses considered separately and in combination can be expressed by the relationship P=a^b . The values for a vary with age-composition and season but the values for b are not significantly different. Differences in growth rate of salmon between sites are small and differences in production result principally from differences in standing crop (biomass density). In most cases low values for salmon production can be attributed to poor spawning.     

Time spent in the drift by downstream-dispersing invertebrates in a Lake District stream

1. The objective was to determine the time spent in the drift by different taxa of stream invertebrates. Most data were obtained from an earlier experimental study to determine the distances travelled by drifting invertebrates of 16 taxa in Wilfin Beck. Experiments were performed at two sites: ‘site 4’ in a stony, fast‐flowing, section of stream, ‘site 3’ in a deeper stream section where macrophytes were abundant. 2. The significant relationship between the mean distance x (m) travelled in the drift and modal water velocity V (m s^?1) was described by a power function in the earlier study but, as the power was close to one, a linear relationship has now been found to provide a satisfactory model. The rate of increase in x (m) with increasing V varied considerably between taxa. The mean time [mean t (s)] spent in the drift was estimated by dividing each x (m) by the appropriate V. Mean t (s) for each taxon was usually very constant over a wide range of V at each site (0.10–0.60 m s^?1 at site 4, 0.15–0.53 m s^?1 at site 3). A simple model estimated the time spent in the drift by different percentages (e.g. 75, 50, 10 and 1%) of the drifting invertebrates. 3. The experimental taxa at site 4 were divided into three groups according to the mean time spent in the drift. Mean t (s) for the five taxa in group 1 (32.8 s) was not significantly different from that obtained in control experiments with a mixed group of dead invertebrates. A similar time (33.0 s) was obtained for the five taxa in group 2, except at water velocities less than 0.2 m s^?1 when the mean t (s) decreased to 15–21 s. Mean t (s) was constant for each of the six taxa in group 3, and significantly less than that for groups 1 and 2. Mean values ranged from 28.8 s for Ephemerella ignita to only 9.4 s for Baetis rhodani and Gammarus pulex. All mean values were lower at site 3, presumably because of the dense stands of macrophytes, with mean values of 12.9 s for the five taxa in group 1 (equalling the value for dead invertebrates). Mean values for the six remaining taxa varied from 6.4 s for Simulium spp. to only 4.9 s for Baetis rhodani and 4.8 s for Gammarus pulex. It was concluded from a discussion of this study that the time spent in the drift may provide a useful measure for comparing the downstream dispersal of invertebrates in different streams, and may be a useful addition to models for the drift feeding of salmonids.     

A continuous study of the total drift of freshwater shrimps, Gammarus pulex, in a small stony stream in the English Lake District

1. The objective was to determine the major factors affecting the downstream dispersal (drift) of freshwater shrimps, Gammarus pulex. Sample replication and frequency are major problems in the quantification of drift. For the first time, these problems were avoided by sampling the whole stream continuously so that all the shrimps drifting downstream at the sampling point were caught in a net emptied at dusk and dawn in 1966, and every 3 days in 1967. 2. There was no consistent seasonal pattern in drift rates, but a high proportion of annual drift was taken in only a few samples. There was a nocturnal diel pattern of drift with peaks soon after dusk and just before dawn. A power function described the significant (P < 0.001) relationship between drift and flow, and was used to neutralise the dominant effects of flow by standardising total drift over 24 h, nocturnal drift and diurnal drift (drift per 50 m³). These were all significantly (P < 0.001) related to benthos density, but not to date, temperature, or length of the night or day. 3. The relationship between drift values and the independent variables, flow and benthos density, was well described (P < 0.001) by a multiple‐regression model. Adding temperature, date, and/or the length of the night or day did not improve model fit. Variations in flow and benthos density explained 94% of the variation in total drift over 24 h, 97% of the variation in nocturnal drift, but only 44% of the variation in diurnal drift. A power function described (P < 0.001) the relationship between total drift and the volume of water sampled over 3‐day periods in 1967. Flow explained 95% of this drift variation; it was unnecessary to add another variable such as benthos density. 4. The significance of this study is that it avoided the problems associated with the quantification of drift samples. Therefore, the conclusions are more robust than those of many previous studies. A high proportion of the annual drift losses would have been undetected by intermittent sampling. Temperature, season, night or day length had no significant effect on drift densities, and the relationship between drift and benthos densities was proportional, not density dependent. The nocturnal increase in drift could not be interpreted as an antipredator behaviour. The dominance of flow and benthos density was apparent but the quantitative relationships posed further questions, especially those related to drift distances at different velocities.     

A comparison of the relative contributions of temporal and spatial variation in the density of drifting invertebrates in a Dorset (U.K.) chalk stream

1. Invertebrate drift is commonly investigated in streams, with the majority of studies focussed on temporal (typically diel) variation. In comparison, few studies have investigated spatial variation in drift and there is little consensus among them. We tested the hypothesis that spatial variation in invertebrate drift is as important as temporal variation. 2. The density of drifting invertebrates in a chalk stream was sampled using an array of nets arranged to determine vertical, lateral and longitudinal variation. Samples were collected at dawn, during the day, at dusk and by night, on four separate monthly occasions. Insecta and Crustacea were analysed separately to identify the effect of differing life history strategies. The density of drifting debris was also recorded, to act as a null model. 3. Time of day and vertical position together explained the majority of the variance in invertebrate drift (79% for Insecta and 97% for Crustacea), with drift densities higher at dusk and night, and nearer the stream bed. Independently, time of day (38%, Insecta; 52%, Crustacea) and vertical position (41%, Insecta; 45%, Crustacea) explained a similar amount of the observed variance. Month explained some of the variance in insect drift (9%) but none for Crustacea. 4. Variation in the density of drifting debris showed little in common with invertebrate drift. There was little variation associated with time of day and only 27% of the observed variation in debris could be explained by the factors investigated here, with month explaining the largest proportion (20%). We suggest the difference in drifting debris and invertebrates provides further evidence for a strong behavioural component in invertebrate drift. 5. Spatial variation in invertebrate drift can be of the same order of magnitude as the much‐described diel temporal variation. The extent of this spatial variation poses problems when attempting to quantify invertebrate drift and we recommend that spatial replication should be incorporated into drift studies.     

Spring and summer macroinvertebrate drift in the Lower Mississippi River,Louisiana

Macroinvertebrate drift was sampled dielly each month at three stations across the lower Mississippi River, Louisiana. At least 134 taxa were identified from seven phyla. Total drift catches varied with respect to month, time of day, and station. Relative abundance was greatest in June and August, moderate in July, and lowest in April and May. Dipterans, ephemeropterans and trichopterans numerically dominated the catches and each tended to have its zenith in July, August and June respectively. Important non-insect groups were hydroids, oligochaetes, pelecypods and amphipods and with the exception of pelecypods, were most abundant in April. The presence of certain apparent exotic oligochaetes suggested that at least some elements of the drift may be derived from rather remote areas — perhaps even the drainage headwaters. Diel periodicity was most pronounced during the summer months of high total drift densities. Ephemeropterans exhibited strong, nocturnally — oriented diel periodicity, both at the ordinal and lower taxonomic levels, trichopterans and dipterans showed varying tendencies with respect to individual lower taxa. Catches for the dielly-periodic taxa indicated a preponderance of the bigeminus forms. But each major insect order may have had one lower taxon exhibiting the alternans pattern. The stations were decreasingly productive from right-shore to left-shore, while taxonomic richness was greater at midstream and approximately equal along the shores. But spatial patterns of occurrence varied according to months.     

Aspects of the breeding biology of Dippers Cinclus cinclus in the southern catchment of the River Wye,Wales

Laying dates, clutch and brood size, and the incidence of double brooding, in Dippers breeding in the southern catchment of the Welsh River Wye between 1978 and 1983 are described and compared with data from other regions of Britain and mainland Europe. The mean size of 222 clutches (4.78±0.08) was found to be significantly larger than values given by all other studies in Britain where data were sufficient for statistical comparison. This is discussed in relation to territory quality and other influences.     

Macroinvertebrate drift density in relation to abiotic factors in the Missouri River

Changes in flow management to restore ecosystem health have been proposed as part of many restoration projects for regulated rivers. However, uncertainty exists about how the biota will respond to flow management changes. The objectives of this study were to estimate the relative importance of key abiotic predictor variables to aquatic macroinvertebrate drift densities in the Missouri River and to compare these results among reaches of the river. A multi-year, multi-location database of spring macroinvertebrate drift net sampling was used to develop relations between drift density and variables representing discharge, temperature, and turbidity in the Missouri River from Fort Randall Dam, South Dakota to the mouth of the Little Nemaha River, Nebraska. Multimodel inference using generalized linear mixed models and an information theoretic approach were used to estimate the relative importance of the predictor variables and the parameters. The results varied by reach. Discharge-related factors were more important at the upstream end of the study area, and turbidity was more important at the downstream end of the study area. Water temperature or degree days were also important predictors in the upstream reaches. The results below Gavins Point Dam suggest that increased macroinvertebrate drift densities are a response to reduced habitat and food availability. The results identify important variables for drift density that could be used in future experimental studies of flow manipulation for the Missouri or other large, regulated rivers. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Handling editor: L. Mauricio Bini