bluuebunny/crossref_metadata_2025 huggingface dataset:
The spectral absorption and scattering properties of dissolved and particulate components in relation to the underwater light field of some tropical Australian fresh waters
Authors: KIRK J. T. O. , TYLER P. A.
Published: May 2006

SUMMARY. 1. The inherent optical properties (scattering coefficients and absorption coefficients across the photosynthetic waveband) are presented from diverse tropical water bodies (billabongs) in the Alligator Rivers Region of northern Australia.

2. The data are used to interpret observed characteristics of the underwater light field as exemplified by the spectral distribution, and overall rate of attenuation, of photosynthetically available radiation (PAR).

3. Attenuation of PAR, especially in the blue waveband, is caused primarily by intense light absorption by the yellow‐brown humic pigments, both soluble and particulate, in the water.

4. It was estimated that in six moderately turbid billabongs, light scattering increased attenuation by an average of 58% above that attributable to absorption alone, whereas in a highly turbid billabong the increase was 111%.

5. A distinguishing feature of the optical character of these billabongs, compared with previously studied water bodies in southern Australia, is the great contribution to light absorption made by the particulate humic material.
The benthos of a natural West African lake, with emphasis on the diel migrations and lunar and seasonal periodicities of the Chaoborus populations (Diptera, Chaoboridae)
Authors: HARE LANDIS , CARTER JOHN C. H.
Published: May 2006

SUMMARY. 1. Three Chaoborus species dominated in abundance and biomass the mid‐lake benthic fauna of a small, natural Nigerian lake. Each population showed distinct seasonal varialitions. C. anomalus being most abundant during the early rainy season, while (ceratopogones and C edults were most abundant during the dry season. A fourth species. C. fuscinervis (not reported previously from West Africa), was collected only in the adult stage. Also abundant at mid‐lake were the Chironomidae. Chironomus seydeli, Prodadius brevipetiolatus and Tanypus brevipalpis. all of which showed a seasonal pattern most resembling that of C. anomalus.

2. Second. third and fourth instar larvae and pupae of the Clutoborus species underwent a diel vertical migration between the lake sediments (diurnal) and the water column (nocturnal) which was strongly related to prevailing light conditions.

3. Lunar periodicities of Chaoborus emergence determined from emergence trap collections are described for the first time. Corresponding lunar periodicities of larval abundance were observed in two of the species. The statistical techniques employed in describing the lunar periodicities permit the estimahon of generation times.

4. C. anomalus is believed to be parthenogenetie in the study lake (no males collected). while the other Chaoborus species are bisexual (1:1 sex ratios). The biology of this species is discussed in relation to the parthenogenetie condition.
The impact of planktivorous flsh on the structure of a plankton community
Authors: POST J. R. , McQUEEN D. J.
Published: May 2006

SUMMARY. 1. The abundance of pianktivorous juvenile yellow perch, Perca flavescens, was manipulated in three 750 m3 enclosures in a eutrophic lake.

2. There was a significant negative relationship between fish and zoopiankton biomasses. At high fish densities the zooplankton community was dominated by small filter‐feeding cladocera. primarily bosmi‐ nids. At low fish densities the zooplankton community was dominated by large filter‐feeding cladocera, primarily daphnids.

3. There was no significant relationship between zooplankton and phytoplankton biomasses when considered over the whole experiment but there was a trend towards lower phytoplankton biomass in the enclosure dominated by daphnids during mid‐summer.

4. We conclude that although planktivorous fish have a strong negative impact on zooplankton community biomass and size structure, the relationship at the next lower trophic level, zooplankton and phytoplankton, is much weaker. Therefore, the biomanipulation of planktivorous fish populations as a management technique to control phytoplankton abundance is largely ineffective.
A numerical model of nitrogen flxation and its application to Lake Valencia, Venezuela*
Authors: LEVINE SUZANNE N. , LEWIS WILLIAM M.
Published: May 2006

SUMMARY. 1. A numerical model for calculation of daily and annual nitrogen fixation in lakes is presented. The model is based on empirically‐derived equations for the rates of nitrogen fixation by heterocysts (nitrogen‐fixing cells) in relation to light and on functions for the vertical and tetnporal distributions of heterocysts and light in a lake.

2. Applications of the model to Lake Valencia, Venezuela, between December 1980 and December 1981 indicated that nitrogen fixation is largely a surface phenomenon in this lake: 80% of diurnal fixation occurred within 1m of the water surface.

3. Nitrogen fixation is largely restricted to periods of lake stratification, when the phytoplankton have sufficient light for growth, but dissolved inorganic nitrogen is scarce. Nitrogen fixation was maximal late in the stratification period of 1981: 85 % of fixation occurred within the last 3 months of the 9‐month period.

4. The annual nitrogen fixation in Lake Valencia is 26 kg ha−1, which is comparable to the nitrogen fixation in temperate eutrophic lakes with seasonal blue‐green algal blooms. However, nitrogen fixation accounted for only 23% of the total nitrogen supply to Lake Valencia in 1981.
Coldingham Loch, S.E. Scotland. II. Phytoplankton succession and ecology in the year prior to mixer installation
Authors: BAILEY‐WATTS A. E.
Published: May 2006

SUMMARY. 1. Total phytoplankton biomass in the small (8 ha), intermittently stratifying, eutrophic Coldingham Loch exhibited spring and autumn maxima of about 35 μg chlorophyll a l1. Late winter and early spring assemblages included Chlorococcales (dominated by Coetxochloris pyrenoidosa Korsch. and Dichotomococcus curvatus Korsch.), diatoms (unicellular Centrales and Asterionella formosa Hass.) and desmids (Closterium acutum Brèb. and Staurastrum chaetoceras(Schrod.) G. M. Smith). Small populations of Coetastrum and Oocystis characterized the summer period. The commonest “blue‐green alga”, Aphanizomenon flos‐aquae Morr. ex Born, et Flah. (Cyanobacteria) attained its maximum population density in September just after the loch had permanently de‐stratified. It was replaced by another growth of Closterium acutum which reached its annual peak density of 900 cells ml−1 in October.

2. It is likely that nitrogen in summer and silica at various times of the year limited the growth of certain species; it is also possible that phosphorus limited growth in spring.

3. When physical conditions and nutrient concentrations are resolved into their basic, simple, seasonal patterns, a number of species preferences for particular environmental requirements become apparent. Of special significance is the competitive advantage over other plankters of Aphanizomenon in being able to resist sinking losses under stratified conditions and thrive at low ambient nitrate levels. Equally, there are some species exhibiting adaptability to a wide range of conditions.

4. The observed periodicity is examined in relation to recently published schemes that summarize phytoplankton‐environment interactions.
Fossil diatoms and the paleolimnology of Lake Rukwa, Tanzania
Authors: HABERYAN KURT A.
Published: May 2006

SUMMARY. 1. A 23.1 m sediment core from Lake Rukwa, southwest Tanzania, records 13,000 years of climatic change in five diatom assemblage zones. Zone E (13,000–12,7000 bp) reflects the transition from the waning late glacial arid phase to pluvial conditions, as indicated by the co‐occurrence of diatoms associated with fresh and relatively saline conditions. Zone D (12,700–4400 bp) represents a moist period with frequent stratification, indicated by the halophobic genera Melosira and Stephanodiscus, whieh also represent alternating silica‐rich and silica‐dcpleled waters. Beginning with Zone C (4400–3900 bp) the lake became much more saline with Thalassiosira predominating. This drying trend was reversed slightly in Zone B (3900–3300 bp). During the last three millennia (Zone A), lake salinity was further reduced, while transitory moist phases were occurring in more northerly lakes such as Victoria and Kivu.

2. Lake Rukwa was relatively stable over a time scale of centuries, but on an annual basis is quite variable in salinity depending on the local rainy season.

3. These results agree well with the generalized paleoclimatie chronology of East Africa and suggest that the Holocene climatic regime of East Africa extended at least to 8°S.
Solar heating and its influence on mixing in ice‐covered lakes
Authors: MATTHEWS P. C. , HEANEY S. I.
Published: May 2006

SUMMARY 1. The influence of solar heating on the formation of temperature and density profiles of ice‐covered lakes is considered.

2. Mathematical models are derived to quantify the effect of solar heating on vertical stability and its dependence on critical parameters,

3. Solar heating is shown to be able to account for the thermal structure and mixing patterns of certain ice‐covered lakes.

4. The importance of convective mixing is discussed in relation to the distribution of phytoplankton and nutrients.
Handling of coarse and fine particulate organic matter by the aquatic insects Paraleptophlebia gregalis and P. temporalis(Ephemeroptera: Leptophlebiidae)
Authors: MATTINGLY ROSANNA L.
Published: May 2006

SUMMARY 1. Paraleptophlehia gregalis and P. temporalis were abundant throughout a flow‐controlled section of stream that contained large quantities of fine particulate organic matter (FPOM; 0.45 μm to 1 mm in diameter), and in upstream and downstream areas.

2. In laboratory studies, Paraleptophlebia spp. fed and grew on FPOM and CPOM (coarse particulate organic matter; greater than 1 mm in diameter); growth rate was not related to the particle size of food. In addition, these animals were able to survive and grow on various sizes of faecal material produced by shredders.

3. Paraleptopblehia spp. consumed relatively large amounts (0.16±0.09 mg per mg animal dry mass) of detrital material daily.

4. The mayflies had short gut content passage times (2–3 h) and low efficiencies of conversion of ingested food to body substance (0.08±0.07%). They egested relatively small, amorphous faeces,

5. The overall pattern exhibited by Paraleptophlebia spp. involved rapid processing and partial recycling, through relatively simple alimentary tracts, of large amounts of detrital material from a wide range of sources.
Resource utilization, overlap and temporal dynamics in a guild of mountain stream insects
Authors: RADER RUSSELL B. , WARD JAMES V.
Published: May 2006

SUMMARY 1. Resource utilization was quantified for six mayfly (Ephemeroptera) and one caddis (Trichoptera) species comprising a lotic scraper/collector‐gatherer guild across three niche dimensions (temporal, trophic and spatial). Based on trophic differences and inferred microspatial utilization, the members of this guild separated into two groups: (1) cryptic detritivores and (2) exposed algivores.

2. Each species demonstrated a slow seasonal univoltine life cycle except for Epeorus longimanus (Eaton) and Baetis iricaudatus (Dodds) which were fast seasonal univoltine and multivoltine, respectively.

3. Temporal sequencing of periods of peak resource utilization were not demonstrated by the members of this guild. A null analysis indicated that periods of peak resource utilization were aggregated.
Short‐term movements of chalk‐stream invertebrates
Authors: PEARSON R. G. , JONES N. V.
Published: May 2006

SUMMARY 1. Trays of gravel were implanted for 24 h periods in several chalk streams. The trays were variously modified to monitor colonization from different sources, particularly drift (D), other downstream movements (DSM), upstream movements (USM), and all sources combined (ALL).

2. The abundance of invertebrates in the streams was high (maximum of 717 per 0.04 m2) and colonization of the trays was extensive, especially by Gammarus pulex, the predominant species in all but one of the streams (maximum number of individuals of G. pulex per tray: for D, 473; for DSM, 462; tor USM, 286; and tor ALL, 639). In some cases benthic densities were achieved in the trays in the 24 h exposure period, and in most cases any one source of colonization could provide benthic densities in a few days.

3. Patterns of movement differed between species, between size classes of G. pulex, and between sites for particular species. No one source of colonization could be regarded as generally predominant although downstream movements in total (D + DSM) usually far exceeded USM. DSM was usually an important source of colonization.

4. The extent and direction of movement appeared to be determined by local factors and were explained in terms of the high densities of invertebrates and the current and substratum characteristics of each site.

5. Estimates of the relative importance of different sources of colonization varied greatly according to the criteria used in determining proportions.
Competition for perches between larval damselflies: the influence of perch use on feeding efficiency, growth rate and predator avoidance
Authors: CONVEY PETER
Published: May 2006

SUMMARY. 1. In an investigation of perch use by two species of larval damselfies, Coenagrion puella (Linn.) and Ischnura elegans (van der Linden), larvae spaced out on a grid of vertical cocktail sticks, in the absence of food, to a greater extent than expected from a random model. Spacing was the result of direct interaction between larvae, and was not related to the level of hunger of the larvae over a 10 day starvation period.

2. Prior ownership of a perch was not a predictor of success in conflicts between larvae of the same instar. In contests between different instars larger larvae were more likely to win conflicts. Some small larvae appear to remain undetected in the presence of larger conspecifies.

3. At one level of food availability, perch ownership did not influence growth rate or mortality of C. puella or I. etegans. However, it did allow greater prey capture success rate.

4. Coenagrion puella larvae showed more movement in the absence of perches both in terms of actual distance moved and amount of swimming activity. The amount of swimming activity was reduced by addition of a predator (sticklebacks. Gasterosteus aculeatus or Pungitius pungitius) to the tank both in the absence and presence of an alternative food supply for the fish. Duration of individual swimming bouts was unaffected.

5. Sticklebacks attacked C. puella larvae significantly more often in the absence of perches, with a strong bias towards swimming larvae.

6. It is proposed that the major advantage of perch possession to C. puella larvae is in the reduction of predation as a consequence of the reduction in larval movement.
Modern diatom assemblages in Central Mexico: the role of water chemistry and other environmental factors as indicated by TWINSPAN and DECORANA
Authors: METCALFE S. E.
Published: May 2006

SUMMARY. 1. Modern diatom samples, for which physical and chemical environmental conditions were recorded, were collected from forty‐seven sites across Central Mexico

2. The results of the diatom counts were analysed using the clustering program TWINSPAN and the ordination program DECORANA.

3. Results from ‘Laguna Zacapu and associated sites’ showed that where water chemistry varies little between sample sites the effects of habitat are emphasized. This data set highlighted the problems of looking for modern analogues where anthropogenic disturbance is great.

4. TWINSPAN results from the ‘Other Sites’ data set suggested possible changes in diatom assemblages with chemical composition. The DECORANA analyses, however, again seemed to emphasize habitat.

5. In the context of this study, bottom sediment samples appeared to provide the most useful picture of ‘average’ conditions and to be the best source of analogues for the interpretation of fossil assemblages.
Epilithic bacteria in an acid and a calcareous headstream
Authors: GOULDER R.
Published: May 2006

SUMMARY. 1. Environmental variables and epilithic bacteria on small stones were monitored during summer and winter in Burbage Brook and the River Lathkill, two headstreams in the Derbyshire Peak District.

2. Burbage Brook was usually near‐neutral in summer, but acid in winter; the River Lathkill was circumneutral throughout the year.

3. In summer, epilithic bacteria showed few between‐stream differences. In winter, however, total bacteria, colony‐forming units, per cent chromogenic colony‐forming units, per cent viable bacteria, Vmax for glucose mineralization and Vmax/bacterium were all significantly less in the acid Burbage Brook.

4. Inhibition of epilithic bacteria in Burbage Brook was also observed when pH fell to a low level during a summer spate.

5. Multiple‐regression analysis confirmed that epilithic bacteria were less successful at low pH but also suggested that pH was not the only environmental variable to influence epilithic bacteria. Especially notable were positive relationships with density of epilithic chlorophyll a and temperature in Burbage Brook and with chlorophyll a in the River Lathkill.
Natural community bioassays to determine the abiotic factors that control phytoplankton growth and succession
Authors: van DONK E. , VEEN A. , RINGELBERG J.
Published: May 2006

SUMMARY. 1. The successional patterns of the dominant phytoplankton species in Lake Maarsseveen (The Netherlands) were very similar in 1980 and 1981. In December/January the diatoms Stephanodiscus hantzschii Grun., Stephanodiscus astraea (Ehr.) Grun. and Asterionella formosa Hass. dominated the algal community (A. formosa had several further population increases during the year). Fragilaria crotonensis Kitt. came to dominance in March/April, followed by the chrysophyte Dinobryon divergens Imhof and the diatom Cyclotella comta (Ehr.) Kütz in May/June. A second appearance of D. divergens was observed in July/August, followed in 1980 by F. crotonensis and a third small increase of D. divergens. In both years S. astraea and S. hantzschii started to grow again in November/December. Cryptophyceae and Chlorophyta were present throughout the year, but did not show a distinct succession.

2. Natural community bioassays, performed under natural light and temperature conditions in a newly developed outdoor bioassay apparatus, showed that phosphate was the major nutrient limiting the growth rate of the phytoplankton. From January till June, during the decline in phosphorus concentration, the diatoms became successively phosphate limited in the sequence: S. hantzschii, S. astraea, F. crotonensis, A. formosa and C. comta. Light limitation was probably the major cause of the relatively late start of F. crotonensis in early spring.

3. D. divergens, increasing after the diatoms from June till September, was stimulated by the addition of a chelator (EDTA). The chelator might stimulate the formation of trace metal species favouring their uptake (e.g. iron).

4. The patterns of succession of the diatoms observed from January till June and from July till December were to a large extent symmetrical. The controlling factors followed opposite trends: declining phosphorus concentrations with increasing irradiance from winter till spring and increasing phosphorus concentrations with decreasing irradiance from summer till late winter.
Planktonic bloom‐forming Cyanobacteria and the eutrophication of lakes and rivers
Authors: STEINBERG CHRISTIAN E. W. , HARTMANN HELGA M.
Published: May 2006

SUMMARY. 1. Eutrophication of water bodies involves the enrichment of plant nutrients, often followed by significant shifts in the phytoplankton towards Cyanobacteria. When comparing different aquatic systems, even with similar nutrient contents and in the same climatic region, inverse deductions are not valid; i.e. (a) the presence of Cyanobacteria does not necessarily indicate eutrophic conditions, or (b) eutrophic or even poly‐trophic conditions do not necessarily support cyanobacterial development.

2. Above a threshold of 10 μg 1−1 total phosphorus, the development of Cyanobacteria can be described by physical factors, such as water column stability. By characterizing different forms of turbulence, the presence or absence of Cyanobacteria in lakes and rivers can be predicted.

3.When the turbulence of the water column is rather low, as it is in sheltered or meromictic lakes, Cyanobacteria can build up dense populations. In nutrient poor systems, species of Oscillatoria and (seldom) Aphanizomenon are dominating.

4.If the turbulence of the water column is high (mixing depth much greater than euphotic depth) or the mixing pattern is irregular, as in slowly flowing or regulated rivers, Cyanobacteria are outcompeted.

5. In the presence of frequent or permanent turbulence, but with mixing depths lower or not much greater than the euphotic zone (as it is the case in shallow, unstratified lakes, mostly eutrophic or even hypertrophic), Cyanobacteria can outgrow normally dominant r‐strategists under conditions of low N:P ratios, high water temperatures, pH >9.0 or low light availabilities.

6. If turbulence is comparatively great (10 to $15 m) and stable for a longer period of time, some cyanobacteria are able to adapt.

7. Our statements are discussed on the basis of physiological characteristics.
Effects of temperature and food quality on life‐history parameters in Parameletus chelifer and P. minor (Ephemeroptera): a laboratory study
Authors: SÖDERSTRÖM OLLE
Published: May 2006

SUMMARY. 1. Growth rate of Parameletus minor was greatest between 10.8 and 19.8°C, survival rate peaked at 5.9°C, developmental time was shortest at 14.6°C, and adult size and fecundity reached maximum values between 5.9 and 10.8°C. Growth rate of P. chelifer was greatest between 14.6 and 19.8°C, survival rate peaked at 5.9°C, and developmental time was shortest at 14.6°C. A large adult size was found at 10.8°C, and highest fecundity between 10.8 and 14.6°C.

2. Food quality significantly affected growth rate, developmental time, adult size and fecundity of both species. Both P. chelifer and P minor attained highest growth rate, largest adult size and highest fecundity when the C/N ratio of food was 5.95. Developmental time was shortest at a C/N ratio between 5.95 and 12.8.

3. Nymphs of P. chelifer had a higher temperature ‘optimum’ for growth than nymphs of P. minor. Growth rate of nymphs of P. chelifer reared on detritus from a seasonal stream (C/N ratio 12.8) was about 3 times that of nymphs reared on detritus from a river margin (C/N ratio 20.9). The corresponding growth rate difference for nymphs of P. minor was only about 1.5.

4. When all life‐history parameters are taken into consideration, P. chelifer had a higher temperature ‘optimum’ than P. minor.
A comparison of zooplankton production estimates obtained from three commonly used methods and a computer simulation program
Authors: KING C. R.
Published: May 2006

SUMMARY 1. Zooplankton production in a eutrophic reservoir was estimated by three common methods.

2. Estimates of daily production from the growth increment method and the birth and death rate versions of the biomass turnover method were poorly correlated (r=0.58–0.60). Estimates of daily production rates from the above two versions of the biomass turnover method were strongly correlated (r=0.90).

3. The mortality rate version of the biomass turnover method is illogical and yields anomalous results.

4. The growth increment method assumes steady state conditions and zero deaths within each stage and hence calculates potential production for each stage.

5. Estimates from a new computer simulation (PROD) were strongly correlated with (r=0.92) but lower than those from the growth increment method. Estimates from PROD were more poorly correlated (r=0.78) with those from the biomass turnover method.

6. There is a strong need for improved methods for estimating secondary production; computer based methods would seem to be the most promising.
Effects of temperature on the rate of development of eggs of a planktonic water mite, Piona exigua
Authors: BUTLER MARGARET I. , BURNS CAROLYN W.
Published: May 2006

SUMMARY. 1. The eggs of a planktonic, predatory water mile Piona exigua Viets were reared in the laboratory at constant temperatures ranging from 10°C to 280C. Egg development rates increased with increase in temperature.

2. Five models describing the effect of temperature on egg development times were fitted to the data.

3. The variances of the egg hatching times at each temperature differed widely, but these variances were not made more equal by In‐transformation.

4. A simple power curve, fitted to the raw data, accounted for ≥.97% of the variation in the data. Two further models, both of which included a third parameter, provided a better fit at the temperature extremes.

5. Close examination of the patterns of variance at difference temperatures may provide information relating to the pattern of emergence of aquatic poikilotherms.

6. At temperatures below 230C. eggs of Piona exigua developed more rapidly than eggs of Piona constricta, from Heney Lake. Quebec (Riessen, 1982)
Classification of water beetle assemblages in arable fenland and ranking of sites in relation to conservation value
Authors: FOSTER G. N. , FOSTER A. P. , EYRE M. D. , BILTON D. T.
Published: May 2006

SUMMARY. 1. Water beetles were recorded from 157 sites around the Wash, England, in 1986. Most sites were ditches in arable land. Eight main types of water beetle assemblage were identified by multivariate analysis. The habitats of these assemblages were characterized by measurement of a range of physical and chemical factors.

2. Of the 130 species recorded, four are listed in the British Red Data Book and a further thirty‐five are rated as Nationally Notable. Records from 1904 to 1938 for the same area indicate that only three species have been lost in the subsequent period of intensification of water management and arable farming. A rich water beetle fauna can thus survive in drainage systems in arable fen.

3. Vegetation management was important in maintaining the ‘species quality score’, proposed as a measure of conservation value, of larger ditches but management reduced the species quality of one type of assemblage associated with smaller ditches. One type of assemblage was found only in ditches subject to management.
Heterotrophic bacterioplankton production and grazing mortality rates in an Ethiopian rift‐valley lake (Awassa)
Authors: GEBRE‐MARIAM ZINABU , TAYLOR WILLIAM D.
Published: May 2006

SUMMARY. 1. Heterotrophic bacterioplankton growth and production rates were estimated in a tropical lake by various methods. Mean growth rates, determined by tritiated thymidine incoporation into DNA, frequency of dividing cells and increase in cell density varied between 0.013 and 0.014 (with a range of 0.006–0.026) h−1 corresponding to bacterial production of 1.16–1.22 (0.34–3.63) mg C m−3 h−1.

2. Heterotrophic bacterial production estimated from oxygen and inorganic carbon consumption in the dark were compared with these values. The oxygen method gave similar results, while values from dark carbon uptake were as much as 2.5 times higher.

3. Although the different estimates of rates of bacterial production showed different patterns, the existence of spatial (vertical) and temporal (diel and seasonal) variation was demonstrated. Bacterial production was 13–41% of the net primary production and 10–30% of gross primary production.

4. Bacterial grazing mortality rate was estimated from size‐fractionation and metablic inhibitor experiments. Average grazing rates were between 0.34 and 3.77 mg C m−3 h−1 corresponding to 76–120% of the mean bacterial production rate. Organisms 1–12 μm in size, possibly mainly ciliates. were implicated as important bacterial grazers.
Floating meadow epiphyton: biological and chemical features of epiphytic material in an Amazon floodplain lake
Authors: ENGLE DIANA L. , MELACK JOHN M.
Published: May 2006

SUMMARY. 1. Quantities and the chemical composition of epiphyton on the roots of floating aquatic macrophytes were measured in Lake Calado, an Amazon floodplain lake. Growth of epiphytic algae following physical disturbance and losses of epiphyton due to grazing and storms were investigated.

2. Deposition of silt from invading river water decreased chlorophyll and nutrient content (%C, %N, %P) of epiphyton during rising water. N:P ratios of epiphyton indicated that proximity to the river increased supplies of phosphorus. Attached algal biomass per unit root tissue was higher overall during the falling water period, when light was greater, storms less frequent, and new host plant tissue produced more slowly.

3. Epiphytic algal biomass at the margins of floating meadows exceeded that of the phytoplankton in the open water on a per unit area basis. Increases in attached algal chlorophyll ranged from two‐ to ten‐fold over 1 week. Artificial denudation of roots was followed by rapid regrowth of attached algae, leading, after I week, to four‐fold increases in chlorophyll over the pre‐denuded state.

4. Wind‐blown macrophytes experienced an episodic loss of 70% of epiphytic material in less than 1 h. Particulate material lost from roots grazed by snails included root tissue and contained significantly more carbon than material lost from ungrazed roots.
Life history and habitat use of Norwegian brown trout (Salmo trutta)
Authors: JONSSON BROR
Published: May 2006

SUMMARY. 1. Brown trout (Salmo trutta) life history and habitat use were studied in two Norwegian rivers: the Vosso river system, western Norway, and the Søre Osa, eastern Norway.

2. Age‐groups were partly segregated in feeding habitats, the youngest fish living mainly in running water and in the littoral zone of lakes, the older fish also exploiting pelagic waters and deeper epibenthic habitats. In a population with free access to and from the sea, some individuals smoltified and became sea‐run migrants, performing yearly migrations to the coastal sea, whereas others stayed as freshwater residents throughout their entire life span.

3. Within local populations, females were larger and less variable in size than males. This was partly because females matured at an older age than males, partly because the sexes tended to exploit feeding habitats with different food and growth Conditions. Within age‐groups, females were more pelagic and migrated more than males, whereas males were more confined to running water and epibenthic areas than females. In the pelagic zone, males were more abundant in near‐surface water, and females more abundant in deeper areas. When exploiting the same feeding areas, the two sexes grew at the same rate. There therefore appears to be a connection between feeding habitat and the reproductive ecology of brown trout.
Assessing the status of British wild brown trout, Salmo trutta, stocks: a pilot study utilizing data from game fisheries
Authors: GILES N.
Published: May 2006

SUMMARY. 1. This paper describes an analysis of results from a questionnaire (Giles, 1987) which requested information on the status of game fish stocks (especially wild brown trout Salmo trutta L.) from those Game Conservancy members who own or manage fisheries. Also included are data arising from fishery log book records which are used to indicate trends in brown trout catch per unit effort (CPUE) over past decades.

2. The key finding from questionnaire returns was the widespread reporting of apparent declines of wild brown trout stocks in a total of twenty‐seven sites throughout Britain. The affected waters are geographically widespread from the south‐west of England through southern and south‐east England, south Wales, northern England and Scotland including the Western Isles. Suspected stock declines of migratory (sea) trout, salmon Salmo salar L. and grayling Thymallus thymallus L. were also reported. Where brown trout occur alone, a significantly higher proportion of questionnaire returns recorded a stock decline compared with fisheries containing both brown and rainbow trout Salmo gairdneri Richardson.

3. Trout catch records from a small selection of differing fishery types are presented and the value of such data in fish stock assessment is discussed.
Habitat patchiness and macrobenthic community structure in an upland stream in temperate Victoria, Australia
Authors: BARMUTA L. A.
Published: May 2006

SUMMARY. 1. Patterns of co‐occurrence of benthic macroinvertebrates across different habitat patches were monitored for 1 year at one site on the Acheron River, Victoria.

2. There was a gradual transition in community structure between erosional and depositional habitat extremes. The correspondence between faunally defined sample groups and habitats was not exact.

3. Seasonal changes in community pattern were demonstrated only for erosional habitats. Again the transition was gradual rather than abrupt and contrasted sharply with data from more severe hydrological regimes.

4. Most of the community pattern was conferred by a minority of the species present. These species generally had special requirements that apparently could be satisfied only by being confined to the surface layer of sediments.
Microbial growth and detritus transformations during decomposition of leaf litter in a stream
Authors: FINDLAY STUART E. G. , ARSUFFI THOMAS L.
Published: May 2006

SUMMARY. 1. Despite the widely accepted importance of bacteria and fungi in degrading detritus in aquatic ecosystems there is still very little quantitative information on the abundance and dynamics of these microorganisms. Using epifluorescent microscopy, we measured the biomass of bacteria and fungi during decomposition of three types of leaf detritus. Bacterial production was determined from the rate of incorporation of 3H‐thymidine into DNA.

2. The transformation of leaf carbon into dissolved organic carbon and fine particulate organic carbon was followed in order to compare the amounts of leaf material that were converted into these ‘end‐products’ of decomposition versus the amount converted into microbial biomass.

3. The amount of microbial carbon in the leaf‐detritus complex never exceeded 5.2% of the total carbon, and fungal biomass was always much greater than bacterial biomass. Despite the greater standing stock of fungi, the rapid turnover of bacteria (doubling about once per day) implies that their role in degrading leaf litter or as a food source for detritivores might be as great as for fungi.

4. Removal of microbial biomass from leaf litter may occur as release of fungal spores and consumption or shedding of bacterial biomass. Fungal spores can be a significant part of the fine particulate organic carbon released from leaf detritus and potentially represent an important food resource for filter‐feeding organisms.
The need for long‐term investigations in ecology and the contribution of the Freshwater Biological Association
Authors: ELLIOTT J. M.
Published: May 2006

1. Long‐term investigations have provided critical data on a number of practical issues that are of concern to society, and have made important contributions to the development and testing of ecological theory.

2. Some of the questions answered by long‐term investigations are briefly reviewed. The major objectives of such investigations are usually to provide reliable estimates of base‐line variation, to detect long‐term trends in the mean level of the base‐line, to detect rare events and to provide information for meaningful, testable hypotheses.

3. The contributions of the Freshwater Biological Association are listed in a summary table that covers all projects lasting for 20 years or longer with at least one sample per year. Most projects are in the Windermere catchment and it is proposed that the latter should become the first U.K. Long Term Reference Site for the freshwater environment.
Contrasting responses of two cladocerans to changes in the nutritional value of nannoplankton
Authors: MATVEEV VLADIMIR F. , BALSEIRO ESTEBAN G.
Published: May 2006

SUMMARY. 1. The potential tor competition in the zooplankton of small Araucana Lake (Andes, Argentina) was tested experimentally.

2. Laboratory enrichment of lake water with nutrients resulted in an increased abundance of nannoplankton with the cyanobacteria Gloeocapsa minor predominating.

3. The dominant species of zooplankton showed contrasting responses to enrichment: the abundance of Bosmina longirostris increased, whereas that of Ceriodaphnia dubia decreased relative to the corresponding controls.

4. The clearance rates for various nannoplankton by these cladocerans were similar, resulting in high niche overlap as estimated by the Pianka index.

5. Life table experiments showed that when fed on a pure suspension of lake flagellates (103 cells ml−1) Ceriodaphnia had a significantly higher average intrinsic rate of natural increase (r) than on a suspension of Gloeocapsa (0.28v. 0.146); in the case of Bosmina no significant differences for the two foods were found (0.182 and 0.141, respectively).

6. The contrasting responses of the animals to enrichment are explained by the differing suitability of particular nannoplankton species as food for different cladoceran species. The seasonal succession in the species composition and food quality of nannoplankton may be important for the coexistence of competing zooplankters in lakes.
Experimental evidence quantifying the role of benthic invertebrates in organic matter dynamics of headwater streams
Authors: CUFFNEY THOMAS F. , WALLACE J. BRUCE , LUGTHART G. JOHN
Published: May 2006

SUMMARY. 1. The insecticide methoxychlor was applied seasonally to one of three small headwater streams in the southern Appalachian Mountains in North Carolina, U.S.A. The initial application caused massive invertebrate drift (>1,000,000 organisms/week) and resulted in a community with few shredders and reduced abundances of most insect taxa.

2. Bacterial densities and microbial respiration rates were not affected by treatment.

3. Disruption of the invertebrate community resulted in significant reductions in leaf litter processing rates (50–74% reduction depending on leaf species) and in the amount of leaf litter processed annually (reduction of 25–28%).

4. Reductions in leaf litter processing rates resulted in significant reductions in fine particulate organic matter (FPOM) export. Declines in both concentration and total export were detectable within 1 week of treatment. Annual FPOM export was reduced to 33% of pretreatment levels. Alteration to the invertebrate community had a much greater effect on FPOM export than a severe (50–200 year) drought.

6. Course particulate organic matter (CPOM) export was not significantly influenced by treatment but was influenced by hydrologic differences among years.
Intra‐ and inter‐specific variations in egg survival and brood development time for Austrian populations of Gammarus fossarum and G. roeseli (Crustacea: Amphipoda)
Authors: PÖCKL M. , HUMPESCH U. H.
Published: May 2006

SUMMARY. 1. Egg survival (ES, percentage of eggs hatched in vitro), reproductive success (RS, percentage of live young released from the brood pouch) and brood development lime (d, days) in four populations of Gammarus fossarum and two populations of Gammarus roeseli were studied, in the laboratory at water temperatures of 2.0–26.1°C. Intraspecific differences between populations were not significant, but interspecific differences were found between the two species.

2. In natural stream populations, the reproductive period of G. fossarum lasted from December to September, that of G. roeseli from March to September.

3. In the experimental temperature range 2–26°C, 73% of the total number (771) of G. fossarum females and 69% of 469 G. roeseli females were ovigerous. Of these, 45% of G. fossarum and 43% of G. roeseli females successfully released live young from their brood pouches.

4. For G. fossarum, the optimum temperatures were 11.4°C for ES, where 76% of the eggs hatched, and 11.8°C for RS, where 77% of the females released live young from their brood pouches. For G. roseli, the optimum temperatures were 13.5°C for ES (51% hatched) and 14.0°C for RS (76% released). Over 50% of eggs hatched at temperatures of 3.6–19.2°C in G. fossarum and at 1 1.9–15.1°C in G. roeseli. Development time increased from 12 days at 21.9°C to 251 days at 2.0°C in G. fossarum, and from 10 days at 24.1°C to 212 days at 4.1°C in G. roeseli.

5. interspecific differences between the effects of water temperature on ES, RS and d are used to explain the different distributional patterns of G. fossarum and G. roeseli in central European running water systems. assuming that other physico‐chemical variables are suitable for both species.
Competition and coexistence in submerged aquatic plant communities: the effects of species interactions versus abiotic factors
Authors: CHAMBERS P. A. , PREPAS E. E.
Published: May 2006

SUMMARY. 1. Aquatic plant biomass and species composition were studied at three sites in Long Lake, Alberta, Canada, to examine the role of biotic and abiotic factors in determining species diversity.

2. Results of controlled in situ experiments to test for interspecific competition showed that biomass of plants in four different mixed communities did not increase in response to selected species removals (P>0.1,n=16).

3. In contrast, biomass of the dominant taxa (Myriophyllum exalbescens, Ceratophyllum demersum and Chara sp.) were correlated (P<0.05) with abiotic factors (i.e. distance from shore, water depth, sediment exchangeable phosphorus concentration and/or sediment organic content).

4. These results suggest that interspecific competition between naturally coexisting species of submerged aquatic plants is slight and that spatial heterogeneity or differential utilization of abiotic resources promotes species diversity in submerged plant communities.
Responses of periphyton to changes in current velocity, suspended sediment and phosphorus concentration
Authors: HORNER RICHARD R. , WELCH EUGENE B. , SEELEY MARGUERITE R. , JACOBY JEAN M.
Published: May 2006

SUMMARY.

 Research was performed in laboratory streams to evaluate periphytic biomass accrual, export, and community composition over a range of limiting nutrient (phosphorus) concentrations with variable velocity, and suspended sediment addition, in comparison to constant velocity and no suspended sediment. In fixed‐velocity treatments, velocity increase to 60 cm s−1 significantly enhanced biomass accrual, but further increase resulted in substantial biomass reduction. Average biomass loss rates did not change significantly over a velocity range of 10–80 cm s−1. Diatoms were favoured at relatively high velocities and low phosphorus concentrations, whereas the blue‐green Phormidium tended to dominate at higher SRP concentrations and the green Mougeotia seemed to prefer lower velocities.

 Sudden increases in velocity raised instantaneous loss rates by an order of magnitude or more, but these high rates persisted only briefly. As a result, marked biomass reductions were not apparent a day after the velocity change. Dominance change from filamentous green or blue‐green to diatoms immediately after the increase was reversed within 2 days. Loss rate increases due to solids addition were much smaller than those accompanying velocity increase, but simultaneous velocity elevation and solids addition produced instantaneous loss rates approximately double those with velocity increase alone.

 The experiments demonstrated that an elevation in velocity, above that to which algae were accustomed, led to increased loss rates and temporarily reduced biomass. However, recolonization and growth after biomass reduction were apparently rapid. Substantial export of periphyton following solids addition required erosion of the protective boundary layer accompanied by a velocity increase. These results arc applicable to understanding the response of lotic periphytic algae to elevated, turbid storm discharges and similar runoff or high‐flow events.

 Areal uptake rates of P by algae growing in the laboratory streams increased with soluble reactive phosphorus (SRP) concentration, up to approximately 15 μg I−1 in overlying water. They also increased above 35 cm s −1. Overall, uptake rate seemed to vary inversely with biomass. The ralio of areal uptake rate/biomass was significantly less where mean biomass was 411±6 mg chl a m−2 compared to 223±17 mg chl a m−2.

 The results suggested that although nutrient uptake is primarily a surface phenomenon, diffusion to interior cells can also determine the responses of attached communities. Both diffusion and uptake rate were stimulated by increasing nutrient concentration and velocity up to certain levels, but became limited by biofilm thickness and scouring.
Microhabitat use by Blennius fluviatilis in the Río Matarraña, Spain
Authors: FREEMAN MARY C. , VIÑOLAS DOLORS , GROSSMAN GARY D. , DE SOSTOA ADOLFO
Published: May 2006

SUMMARY.

 Microhabitat use by Blennius fluviatilis in the Río Matarraña, Spain, varied significantly among dates during a 19‐month study. Most temporal variation, however, was attributable to changes in microhabitat availability.

 B. fluviatilis demonstrated non‐random use of available microhabitats during each sampling period, and generally occupied deeper microhabitats with higher average current velocities dominated by rubblegravel substrates.

 B. fluviatilis also demonstrated non‐random use of available nest sites; males generally nested under the largest available pieces of rubble, in areas with less gravel or sand. Water column depth influenced nest site use in two of four study areas.

 We found few microhabitat differences between spawning and nonspawning periods, or between males and females. In addition, microhabitat use was similar among B. fluviatilis size‐groups.

 Although B. fluviatilis often were over‐represented in deeper, erosional areas, blennies necessarily inhabited a wide range of microhabitats because average current velocities and water depths fluctuated greatly during the study. Tolerance of a broad range of environmental conditions may contribute to the species' persistence in habitats that exhibit extreme seasonal changes in discharge such as the Matarraña.
Fire and the dynamics of allochthonous detritus in a South African mountain stream
Authors: BRITTON D. L.
Published: May 2006

SUMMARY.

 Input of allochthonous material, standing stocks of benthic organic matter (BOM) and suspended paniculate organic matter (POM) were measured in a south‐western Cape mountain stream from March 1986 to February 1988. The surrounding fynbos‐dominated catch‐ment was subjected to a prescribed burn in March 1987.

 Litter‐fall in the pre‐burn year exhibited a distinct seasonal pattern, with peak falls during the early summer. Although the riparian canopy was not directly affected by the fire, in that it did not burn, a heavy, aseasonal leaf‐fall occurred shortly afterwards. The following summer, litter‐fall was less than half that of the pre‐burn summer.

 Standing stocks of BOM were significantly higher in autumn than in winter in the pre‐burn year and were inversely related to discharge. Despite the heavy post‐burn leaf‐fall and low litter‐fall during the post‐burn summer, there was no significant difference between pre‐ and post‐burn BOM standing stocks.

 Proportions and quantities of fine benthic organic matter (FBOM) in the soft BOM fraction were significantly higher in the post‐burn spring, and monthly accumulation of ultra‐fine benthic organic matter (UBOM) was also significantly higher in the post‐burn spring and summer. These results may reflect accelerated decay rates of BOM in response to enhanced post‐burn nitrate concentrations in stream water.

 Export of CPOM was low in comparison to FPOM and particularly to UPOM, and the stream appears to be highly retentive of CPOM.

 The natural resilience of the riparian vegetation minimizes the potentially disturbing effects of fire on the stream environment. As a result, the prescribed burn had a less than expected effect on both standing stocks of BOM and the stream environment in general.