bluuebunny/crossref_metadata_2025 huggingface dataset:
Population dynamics and production of the pelagic amphipod Hyalella montezuma in a thermally constant system
Authors: DEHDASHTI B. , BLINN DEAN W.
Published: May 2006

SUMMARY.
1. The population dynamics and annual production of the multivoltine. pelagic amphipod Hyalella montezuma were studied over a 3‐year period in the thermally constant environment of Montezuma Well. Arizona.

2. H. montezuma showed two maxima which coincided with spring and autumn phytoplankton maxima. Juveniles comprised over 85% of the population in the pelagic zone compared to 37% in the littoral vegetation and there were significantly more females in the littoral vegetation. It appears that juvenile and adult H. montezuma show different habitat preferences.

3. Total annual mean production for H. montezuma calculated by the size frequency method and adjusted for multiple generations, was 357 kg ha−1 yr−1, which is higher than single‐species production estimates reported for most zoobenthic amphipods and multivoltine planktonic crustaceans. Average energy production for H. montezuma was 4640 kJ ha−1 yr−1 in the pelagic zone and 1072 kJ ha−1 yr−1 in the littoral vegetation.

4. Average cohort P/B̄ ratios for H. montezuma were higher in the pelagic zone (5.5) than in the litttoral vegetation (3.7). Juveniles had higher cohort PB̄ ratios than adults in the pelagic zone, while the reverse relationship was true in the littoral vegetation. We propose that different size‐selective predators may contribute to the differences in PB̄ ratios for juveniles and adults in these two habitats.
Consequences of tadpole shrimp predation on mayflies in some Californian ponds
Authors: WALTON WILLIAM E. , TIETZE NOOR S. , MULLA MIR S.
Published: May 2006

SUMMARY.
1. During two, 1‐month studies, the abundance of mayfly nymphs, Callibaetis californicus Banks, in small ponds that contained the tadpole shrimp, Triops longicaudatus (LeConte), often was significantly lower than in ponds without tadpole shrimps. Mayfly abundance was either positively correlated or not significantly associated with that of predacious insects.

2. Larger mayfly nymphs were a greater fraction of the population in ponds with Triops than in ponds without tadpole shrimps. Between 2 and 3 weeks after ponds were flooded, the smallest mayfly nymphs were absent from ponds in which T. longicaudatus densities were >5 individuals per square metre during the summer and >15 individuals per square metre during the autumn.

3. In prey‐choice trials, T. longicaudatus consumed predominantly small C. californicus nymphs (mean headwidth ± 1 SD: 0.44 ± 0.05 mm). After encounters with tadpole shrimps, small mayfly nymphs moved relatively shorl distances, were easily overtaken, and were, consequently, more susceptible to tadpole shrimps than larger‐sized nymphs.
Competition between Keratella cochlearis and Daphnia ambigua: effects of temporal patterns of food supply
Authors: MACISAAC HUGH J. , GILBERT JOHN J.
Published: May 2006

SUMMARY.
1. Population growth rates and relative competitive abilities of the rotifer Keratella cochlearis f. tecta and the small‐bodied cladoceran Daphnia ambigua were studied under different schedules of food addition but equal total food quantity (per 4‐day interval). The initial population growth rate of Keratella was significantly affected by the feeding schedule and by the presence of competitors, while that of Daphnia was affected by neither factor. Population densities of both species tended to increase as the frequency of food addition increased.

2. Daphnia suppressed and excluded Keratella from mixed‐species cultures when food was provided intermittently at a high concentration, but it failed to exclude the rotifer when food was provided in a near‐continuous supply at low concentration. Keratella had only a minor suppressive effect on Daphnia in all mixed‐species treatments.

3. Starvation experiments indicate that Daphnia is able to withstand food shortages for significantly longer periods of time than Keratella. These and other results indicate that the outcome of interspecific competition between these species may be influenced by me frequency and concentration at which food is supplied. Daphnia ambigua is competitively superior to K. cochlearis when food is concentrated or ‘pulsed’, but much less so when ambient food levels are chronically low. Patterns of food availability may have important effects in determining the relative abundance of rotifers and small cladocerans in natural zooplankton communities.
Micro‐environmental characteristics of filamentous algal communities in flowing freshwaters
Authors: DODDS WALTER K.
Published: May 2006

SUMMARY.
1. Filamentous algae in flowing freshwaters can represent a spatially and temporally distinct sub‐habitat for epiphytic diatom communities. This sub‐habitat is described in a low discharge, spring‐fed stream with extensive filamentous green algal mats, and in a tuft of Cladophora glomerata (L.) Kützing from a large river.

2. Oxygen micro‐electrodes, a thermistor current velocity probe, a standard pH probe and water chemistry were employed to assess spatial heterogeneity. Temporal patterns of epiphyte colonization were evaluated on filamentous artificial substrates.

3. There were steep spatial gradients in the low discharge stream. At mid‐day, O2 ranged from 0–1.5 times air‐saturated O2 concentrations, pH varied from 7.25–8.0, and current velocity spanned 0–0.5 m s−1. Areas near the surface of algal mats had high O2, pH and current velocity. These patterns were correlated with epiphyte community structure.

4. In the interior of C. glomerata tufts O2 concentration was raised and current velocity depressed compared to the surrounding water, even when external current velocity was as high as 0.4 m s−1.

5. After thirty‐five days of colonization of artificial substrate in the low discharge environment, epiphyte communities were similar to those on filamentous atgae. Epiphyte diversity on artificial substrates subsequently decreased compared to natural substrates as did the similarity between the types on substrates, suggesting that microscale renewal of epiphyte habitat (growth of filamentous algae) maintains high epiphytic diversity.
Seasonally and spatial distribution of the ostracods of Lake Zwai, Ethiopia (Crustacea: Ostracoda)
Authors: MARTENS KOEN , TUDORANCEA CLAUDIU
Published: May 2006

SUMMARY.
1. Quantitative benthic samples were collected monthly between June 1984 and May 1985 from seven stations at various depths in Lake Zwai, one of the Ethiopian Rift Valley lakes, situated in the northern part of the Rift Valley. The most common species of ostracods were Limnocythere thomasi thomasi Martens (a subspecies endemic to Lake Zwai), Gomphocythere angutata Lowndes (common in, but restricted to. East Africa) and Darwinula stevensoni (Brady & Robertson) (cosmopolitan).

2. Absolute densities of all species varied considerably over the year. In all stations, there were population peaks during the two dry seasons, followed by as yet unexplained population crashes during the short and the long rains.

3. The three common species had different habitat preferences. Darwinula stevensoni avoids parts of the lake where temperatures rise high and both G. angulata and L. thomasi had a preference for sheltered habitats close to vegetation and/or for a specific grain size of the sediment (300–350 μm).
Population dynamics and production of Daphnia hyalina and Bosmina longirostris in a shallow, eutrophic reservoir
Authors: MASON C. F. , ABDUL‐HUSSEIN M. M.
Published: May 2006

SUMMARY.
1. The population densities, dynamics and production of Daphnia hyalina and Bosmina longirostris were studied over a 2‐year period in a shallow eutrophic reservoir in eastern England. The diet of the two species was assessed and their ecology was compared in relation to environmental factors.

2. Daphnia hyalina was characterized by small overall body size, probably due to heavy size‐selective predation by fish. The first generation produced from the overwintering population appeared in April and Depopulation peaked in late spring and early summer. Adult survival was poor. Peak egg production varied between years, while mean brood size fell in summer probably due to food limitation during the cyanobacterial bloom. At this time selection for individual algal species was high and many guts were empty. Reproductive ratios were inversely related to population density. Bosmina longirostris exhibited a similar annual cycle.

3. Patterns of production were very different in the 2 years in D. hyalina. In 1981 production was high from August to early October, but in 1982 the peak was in spring. Annual production was 32.4 g C m−2 in 1981 and 13.3 g C m−2 in 1982. In 1981 B. longirostris production peaked in spring and late summer; in 1982 there was a high production in summer only. Annual production was 3.2 g C m−2 in 1981 and 2.2 g Cm−2 in 1982.

4. The number of adult D. hyalina was highly correlated with water temperature and total phytoplankton biomass, but these were negatively correlated with the number of eggs, mean brood size and instantaneous birth rate. In contrast, clutch size of B. longirostris was positively correlated with water temperature while birth rate was positively correlated with both temperature and phytoplankton biomass. The biomass of both species was positively related to total phytoplankton biomass, but neither relationship explained much of the variation in zooplankton biomass.

5. The significance of the observations on plankton in terms of managing the water quality in eutrophic reservoirs is discussed.
Environmental factors influencing chlorophyll v. nutrient relationships in lakes
Authors: STAUFFER ROBERT E.
Published: May 2006

SUMMARY.
1. A model relating log chlorophyll a concentration to log epilimnetic total phosphorus (TP) concentration was re‐examined based on: (a) comparative and temporal studies of four stratifying Wisconsin and other highly eutrophic temperate lakes; (b) comparative summer lake surveys from Iowa and Alberta.

2. Although P‐limited, deeper lakes with long hydraulic residence times and low external and internal nutrient loading in summer had summer chlorophyll a yields below model predictions based on spring and summer epilimnetic TP concentrations.

3. For lakes with summer epilimnetic TP between 30 and 80 mg m−3, chlorophyll a concentrations exceeded model predictions based on summer TP. This relationship held even for Lake Delavan, Wisconsin, where the ratio of available N to P was unfavourably low during spring turnover, and where the trans‐thermocline N:P flux ratio was sub‐optimal for algal needs in early summer.

4. With increasing summer TP concentrations and/or increasing epilimnetic circulation depth (>5m), chlorophyll a concentrations fell below model predictions—independent of the potential for N‐limitation. This plateauing in chlorophyll a response occurred at lower epilimnetic TP content (<c. 400 mg m−2) in lakes with elevated non‐algal light extinction coefficients. Using Tailing's algorithm for the‘column compensation point’ (algal photosynthesis = algal respiration over diel cycle), light limitation best explains this fall‐off in chlorophyll a yield.

5. The failure of the Dillon & Rigler (1974) spring TP v. summer chlorophyll a model for these Wisconsin lakes is unrelated to N‐limitation. Instead, it reflects internal adjustment in take TP in response to stratification and seasonal external P loading.
Movement patterns and ecology of Pteronarcys nymphs (Plecoptera)
Authors: FREILICH JEROME E.
Published: May 2006

SUMMARY.
1. Individually tagged Pteronarcys californica (Newport) nymphs were caught and recaptured over a 3‐month period to determine their movement patterns and home range size. Sex/age structure, population density, and food habits (from gut contents) were also recorded. More than 1000 nymphs were tagged of which 256 (25%) were recaptured at least once. Tagged insects were confined to contiguous fast water, cobble riffles. Low velocity, silt‐bottomed pools acted as barriers.

2. This stonefly has a 3‐year life cycle although only the two oldest nymphet size‐classes were tagged. Females were larger than males at all ages. The population sex ratio was skewed 60:40 towards females. Densities averaged 1.7 m−2±0.17 SE (range 0–19 m−2).

3. Most movements were short, indicating that a majority of the stoneflies stayed within a few meters of their first capture point (mean 1.8 m downstream ±0.51 SE, range 44 m downstream to 40 m upstream). Significant patch size is a stream reach 24 m long that would contain 85% of the average individual's movements. Time between captures averaged 16 d ±0.734 SE (maximum 81 d). Eight individuals were notable for extremely rapid upstream movements ranging from 6 to 22 m d−1.

4. Frequency of movements up and downstream differed significantly between the sexes. Pteronarcys distribution was clumped with certain quadrate representing‘zones of attraction.’The stoneflies moved rapidly between zones, then stayed many days in those areas. Movements differed significantly from random walk models.

5. Guts contained 75% diatoms, 15% vascular plant material, and 8% animal remains. Females ate significantly more diatoms than males on a volumetric basis.
Immobilization of dissolved organic matter from groundwater discharging through the stream bed
Authors: FIEBIG DOUGLAS M. , LOCK MAURICE A.
Published: May 2006

SUMMARY.
1. In laboratory experiments, 9.7–25.7% of dissolved organic carbon (DOC) in groundwater (at concentrations of 18.7–24.8 mg 1‐−1) was immobilized after perfusion through 8‐cm‐deep (22‐cm‐diameter) cores of stony stream‐bed substratum.

2. This represented immobilization rates of 7.1–23.5 mg m−2 h−1 or, extrapolated across the year, potential immobilization rates within the stream bed of 62.2–205.9g m−2 yr−1. Actual rates in the entire stream bed were probably higher because perfusion through the experimental cores did not reduce groundwater DOC concentrations to levels measured in the adjacent stream.

3. Natural concentrations of dissolved free amino acids (DFAAs) in groundwater were generally unchanged following perfusion through the cores, suggesting the maintenance of a dynamic equilibrium in their concentrations.

4. Selective enrichments of amino acids in groundwater (up to 20‐fold) were entirely immobilized following perfusion, indicating their rapid retention and flux in this environment. Thus, immobilization of the bulk DOC in stream‐bed cores probably did not reflect net reductions in dissolved free, low‐molecular‐weight material, with higher molecular weight, more ‘refractory’ material being immobilized instead.

5. We conclude that groundwater can contribute substantial amounts of DOC, both high and low molecular weight, to a stream ecosystem. The stream bed is the site at which much of this material could be initially immobilized and made available to the stream trophic structure.
Relative vulnerabilities of natural rotifer and ciliate communities to cladocerans: laboratory and field experiments
Authors: WICKHAM STEPHEN A. , GILBERT JOHN J.
Published: May 2006

SUMMARY.
1. Two experiments with plankton communities from Storrs Pond (NH), one conducted in the laboratory and one in field enclosures, assessed the impact of different cladocerans on rotifers and ciliated protozoa.

2. The smallest cladoceran, Bosmina longirostris, did not depress rotifer or ciliate growth rates while the intermediate sized dadoceran, Daphnia galeata mendotae, reduced ciliate growth rates in the enclosure experiment but had only a marginal effect in the jar experiment. D. galeata mendotae had no effect on any of the rotifers in either experiment.

3. In both experiments the largest cladoceran, Daphniapulex, depressed the growth rates of ciliates and those rotifers known to be vulnerable to interference competition. Polyarthra vulgaris, previously shown to be resistant to cladoceran interference, was the only rotifer unaffected by D. pulex in the field experiment but was depressed by the much higher densities of this cladoceran in the laboratory experiment.

4. Cladocerans did not affect phytoplankton or bacterioplankton abundance in either experiment. Therefore the mechanism most likely to be responsible for the suppressive effect of cladocerans on rotifers and ciliates in these experiments is direct mechanical interference or predation, rather than exploitative competition.
Within‐lake patterns in depth penetration of emergent vegetation
Authors: WEISNER STEFAN E.B.
Published: May 2006

SUMMARY.
1. Within‐lake relations of wave exposure (WE), and substratum softness (cone penetration depth; CPD) and organic content (loss on ignition; LOI), to water depth penetration of the emergent vegetation (DPE) was investigated in seven eutrophic lakes in southern Sweden, ranging in area from 1 to 46km2.

2. There was a positive relationship between WE and DPE within lakes. This relationship, however, only occurred for sites with relatively soft substrata, for which CPD and LOI were negatively related to both WE and DPE.

3. Analysis of aerial photographs revealed that expansion of the emergent vegetation towards open water, or recession from open water, was not related to wave exposure or water depth, except in one lake where expansion mainly occurred at high exposures.

4. For relatively static vegetation on soft substrata, regressions with CPD°.5 explained 62–88% of the within‐lake variation of DPE. These regressions did not differ among lakes. Expanding and recessing vegetation were significantly dislocated towards shallower and deeper water, respectively, than predicted from the regression models for static vegetation.

5. Phragmites australis dominated at the lakeward edge of the emergent vegetation, followed in frequency by Typha angustifolia. More broad‐leaved species were generally restricted to shallow water and very soft substrata.

6. The results suggest that changes in the distribution of emergent vegetation in moderately wave exposed eutrophic lakes can be predicted largely from substratum character and water depth.
The photosynthetic and growth rate responses of two freshwater angiosperms in lakes of different trophic status: responses to light and dissolved inorganic carbon
Authors: RATTRAY M. R. , HOWARD‐WILLIAMS C. , BROWN J. M. A.
Published: May 2006

SUMMARY 1. Two rooted freshwater macrophytes (Lagarosiphon major (Ridley) Moss; Myriophyllum triphyllum Orchard) were grown in two lakes of differing trophic status on sediments collected from an eutrophic lake. In the two experiments (summer and winter) in the oligotrophic lake (Lake Taupo, New Zealand), the relative growth rates of both species were approximately double those recorded in the experiments in the eutrophic take (Lake Rotorua, New Zealand). These growth responses occurred even though the light and temperature regimes were similar at the experimental sites in both lakes and the concentrations of inorganic nutrients were higher in the eutrophic lake water.

2. Dissolved inorganic carbon (DIC) analysis of both lake waters indicated that the oligotrophic water had approximately 10‐fold more DIC than the eutrophic water. This corresponded, at natural pH, to a 2‐fold higher concentration of free‐CO2 in the oligotrophic lake water (49 μM) than in the eutrophic lake water (23 μM). Photosynthetic experiments demonstrated that the maximum rates of photosynthesis were 2.46 and 2.25‐fold higher in L. major and M. triphyllum, respectively, when the shoots were incubated in Lake Taupo water at Lake Taupo levels of free‐CO2 relative to Lake Rotorua water at Lake Rotorua levels of free‐CO2.

3. It is concluded that these differences in photosynthetic rates would lead approximately to a 2‐fold difference in growth rate, thus explaining the growth responses observed in the field experiments.
The effect of the water‐lily beetle, Galerucella nymphaeae, on leaf production and leaf longevity of the yellow water‐lily, Nuphar lutea
Authors: KOUKI JARI
Published: May 2006

SUMMARY.
1. The effect of the water‐lily beetle, Galerucella (=Pyrrhalta) nymphaeae (L.), (Coleoptera, Chrysomelidae), on the leaf production and leaf longevity of the yellow water‐lily, Nuphar lutea (=N. luteum) (L.) Sibth. & Sm., was studied experimentally in southern Finland during one growth season.

2. Twelve cages, each containing a single rosette of the water‐lily, were established in the lake during May. Two treatments were randomly applied to cages: (i) control (herbivory not allowed), and (ii) fifty beetles added at the beginning of the season. Leaves were marked individually and the production of new leaves was followed until October.

3. In both treatments the production of floating leaves continued until the end of August but declined towards the end of summer. Herbivory did not affect the number of leaves produced, i.e. the plants did not compensate for the loss of leaves.

4. Leaf longevity was reduced dramatically (up to —60%) when herbivores were present. Leaves that emerged during the most intense period of larval growth had a life‐span one‐third of that of the control group.
Microhabitats and diel downstream migration of young grayling (Thymallus thymallm L.)
Authors: BARDONNET AGNÈS , GAUDIN PHILIPPE , PERSAT* HENRI
Published: May 2006

SUMMARY.
1, Microhabitats chosen by young grayling (Thymallus thymallus L.) were investigated by electrofishing. The first feeding habitat was marginal areas where water velocity did not exceed 15 cms−1. Fry fed on drift in the first 10 cm of the water column below the surface. This location was very stable during the first weeks of growth (mid‐April to mid‐May). When they were 3–3.5 cm long, fry began using benthic areas and gradually moved away from the banks towards the channel.

2. A downstream migration was noted from the beginning of emergence (mid‐April) to the end of May. This mainly nocturnal movement involved all fish sizes and caused a complete removal of young‐of‐the‐year by June from the spawning tributary.
Pesticides as chemical agents inducing helmet formation in Daphnia ambigua
Authors: HANAZATO TAKAYUKI
Published: May 2006

SUMMARY.
1. Daphnia ambigua was exposed to harmful concentrations of pesticides (six insecticides, two herbicides, one fungicide) for 10 h from the final embryonic stage to the first instar, and effects on morphology were investigated.

2. The animals developed helmets at the second instar after exposure to the insecticides, but did not show the same response when exposed to the herbicides and the fungicide.

3. Some stimuli due to the insecticides on the nervous system of the animals may switch on the formation of the helmet, an antipredator morphology, which originally evolved as a response to chemicals released by predators.

4. It is suggested that a range of chemicals other than the predator/prey kairomone can induce the helmet formation in Daphnia.
The influence of chemistry and habitat features on the microcrustacea of some upland Welsh streams
Authors: RUNDLE S.D. , ORMEROD S.J.
Published: May 2006

SUMMARY.
1. Microcrustaceans were sampled during September 1990 from three microhabitats (margins, stony riffles and gravel) at thirteen stream sites in mid‐Wales.

2. Patterns in the distribution, abundance and community structure of microcrustacean taxa were related to stream chemistry, physiography, substratum composition and marginal habitat structure. Patterns of distribution between microhabitats were also assessed.

3. Chemical variables were the strongest correlates with microcrustacean parameters. Total numbers of microcrustaceans and harpacticoid copepods were reduced at sites with high aluminium concentrations, and ostracods were scarce or absent at the most acidic sites. In contrast, cyclopoid copepods were more abundant and species rich at low pH.

4. Microcrustacean communities were most species rich at sites with a high percentage cover of macrophytes on the substratum. Cladoceran species richness and abundance, and the abundance of several microcrustacean species, were also positively correlated with percentage macrophyte cover.

5. Three site groupings produced by TWINSPAN classification were primarily related to percentage macrophyte cover and marginal habitat structure, with chemistry and land use also of importance.

6. Total microcrustacean abundance was highest in margins, but of all the species, only the harpacticoid Bryocamptus cuspidatus showed a strong microhabitat preference.
Temporal and spatial patterns in the distribution and abundance of pico, nano and microphytoplankton in an upland lake
Authors: HAPPEY‐WOOD CHRISTINE M.
Published: May 2006

SUMMARY.
1. An investigation of the seasonal and depth distribution of populations of autotrophic picoplankton (0.2–2 μm), nanophytoplankton (>2<20 μm) and larger microalgal plankton (>20μm) was carried out over 21/2 years, 1988–90, in Llyn Padarn, a mesotrophic upland lake in North Wales.

2. Cell numbers of picophytoplankton ranged from <102 to >106 cells cm−3. Maximum numbers of nanoplankton were c. 104 cells cm−3 and the greatest abundance of microalgal plankton, diatoms, reached 12 × 103 cells cm−3.

3. Three types of picoalgae were distinguished: coccoid to oval Synechococcus—Synechocystis, the rod‐shaped Synchecococcus capitatus Bailey‐Watts & Komárek and Chlorella minutissima Fott & Nováková, with maximum numbers of 1.2 × 106, 37.8 × 103 and 44.1 × 103 cells cm−3, respectively.

4. Picophytoplankton exhibited periods of exponential growth: the first in spring, and the second in August—September with an intervening population minimum in early to midsummer. Specific rates of population increase for picophytoplankton were low, with minimum apparent generation times of 3.8 days in summer 1989.

5. Nanophytoplankton included seven species of phytoflagellates and two non‐motile species. These algae were present for about 10 months in each year exhibiting a fluctuation in population density of 102−‐103 cells cm−3.

6. There were spring and autumn maxima in chlorophyll a concentrations in the lake water corresponding to the growth of planktonic diatoms. Maximum total biomass concentration was 35 mg m−3 chlorophyll a, whereas pico, nano and microphytoplankton had individual maxima of 7.7, 8.4 and 31.0 mg m−3 chlorophyll a, respectively. Picophytoplankton often contributed > 60% of the total algal chlorophyll a in the epilimnion.

7. The growth patterns and seasonal periodicities of the three size‐categories of planktonic algae in Llyn Padarn were distinct. Picophytoplankton persist throughout much of the year with periods of very low abundance, < 100 cells cm−3, occurring in winter and midsummer. Thus for much of the year, there was a large inoculum of these cells in the lake to initiate growth leading to the population maxima in spring and late summer. Nanoplankton populations, a diverse assemblage, fluctuated in numbers over the period February–November; no population decline in midsummer comparable to picophytoplankton was observed. The larger microphyloplankton exhibited classical seasonal periodicity, namely diatom growth in spring and late summer–autumn with growth of large‐celled chlorophytes in the intervening summer period.
Vegetation and seed‐bank relationships on a lakeshore
Authors: GRELSSON GUNNEL , NILSSON CHRISTER
Published: May 2006

SUMMARY.

Possible convergence in species richness and species composition between the (standing) vegetation and soil seed bank was studied along gradients of wave exposure, estimated as soil organic matter content, on five levels of a shore of a river‐lake in northern Sweden.

Species with seeds having little natural ability to float were most common in the vegetation, whereas species with seeds capable of prolonged floating were most abundant in the seed bank. Species richness in the vegetation and seed bank varied with wave exposure in the same way. Species richness decreased with exposure in both communities at the upper three levels but did not vary with exposure at the lower levels.

Floristic similarity between the vegetation and seed bank was 0.25 (Sørensen's index of similarity) for the entire flora. The variation in floristic similarity between communities did not differ between levels. Floristic similarity per sample plot increased with wave exposure.
Temporal variations of trace metals in aquatic insects
Authors: HARE LANDIS , CAMPBELL PETER G.C.
Published: May 2006

1. Temporal fluctuations were measured in the concentrations of the trace metals cadmium (Cd), copper (Cu) and zinc (Zn) in six insect taxa collected from the same sites in a temperate zone lake over a 14‐month period. The consequences of temporal changes in insect contaminant concentrations for biomonitoring studies are assessed.

2. Significant temporal fluctuations in the concentrations of the three metals were measured in almost all of the insect taxa studied. In no case was there a greater than sixfold change in the concentration of a trace metal over the course of the year. The extent of the fluctuations was generally greater for CD, a non‐essential metal, than for the essential micronutrients Cu or Zn.

3. Temporal fluctuations in CD concentrations appeared to follow a seasonal periodicity for most taxa. Minima were measured during the winter period in the megalopteranSialisspp. and in the dipteran taxaChaoborus punctipennis, Glyptotendipessp., andProcladiusspp., whereas a maximum was measured in the mayflyHexagenia Hmbataduring the same season. In general, temporal fluctuations in Cu and Zn concentrations were less seasonal in character than were those of Cd.

4. For some of the taxon—metal combinations studied, temporal fluctuations in metal concentrations could be ignored in biomonitoring studies, whereas in other cases a temporal window of minimum variability should be chosen for the collection of organisms from different sites.
Variation in genetic structure among populations of the caddisfly Helicopsyche borealis from three streams in northern California, U.S.A.
Authors: JACKSON JOHN K. , RESH VINCENT H.
Published: May 2006

1. Allozyme electrophoresis was used to describe the genetic structure of Helicopsyche borealis caddisflies collected from three sites in each of three streams in northern California, U.S.A.: the Rice Fork of the Eel River; Big Sulphur Creek; and Alameda Creek. Between 7 and 11km separated adjacent sites within these three streams. Helicopsyche borealis from three additional streams in eastern North America (Christiana Creek, Indiana; Byrd's Mill Creek, Oklahoma; Susquehanna River, Pennsylvania) were also analysed electrophoretically to address taxonomic questions that arose during the study.

2. Four genetically distinct groups of individuals were identified (i.e. Helicopsyche types A, B, C, and D). Lack of interbreeding between sympatric groups (as evidenced by fixed allelic differences) and large genetic differences (mean Nei's genetic distances = 0.396–0.693) indicate that these four groups of Helicopsyche were actually reproductively isolated species rather than genetic variants of a single species.

3. Occurrence of Helicopsyche type A at multiple sites permitted an analysis of spatial variation in genetic structure. Within a drainage basin, small differences in allele frequencies were observed among sites in the Rice Fork and Big Sulphur Creek, but not in Alameda Creek. Larger genetic differences were found among sites in separate drainage basins. Genetic distances (Nei's) between Helicopsyche type A from California and from eastern North America sites (mean = 0.236) were greater than interpopulation differences commonly observed for insects, which suggests that Helicopsyche type A from California may represent a different species than Helicopsyche type A from eastern North America.

4. Geographical and taxonomic differences observed in this study underscore the importance of understanding both population structure and genetic relationships among populations in the design and interpretation of stream faunal studies.
Contribution of benthic blue‐green algal recruitment to lake populations and phosphorus translocation
Authors: BARBIERO R.P. , WELCH E.B.
Published: May 2006

1. A two‐season investigation was undertaken to determine the contribution of benthic recruitment to the population development of several species of blue‐green algae.

2. Gloevtrichia echinulata populations were shown to be heavily subsidized by benthic recruitment, deriving on average 40% of their planktonic colonies from the benthos.

3. Benthic recruitment of Aphanizomenon flos‐aquae, Anabaena flos‐aquae and a second Anabaena species contributed less than 2% to planktonic increases, while Microcystis aeruginosa recruitment was negligible.

4. Phosphorus translocation via migrating G. echinulata accounted for most of the phosphorus (P) in the planktonic colonies, and constituted a significant portion of the internal loading of the lake.

5. Estimated P translocation via Aph. flos‐aquae was relatively minor, although there was evidence of luxury uptake in the benthos.
Efficient estimation of temperature distribution, heat storage, thermocline migration and vertical eddy conductivities in stratified lakes
Authors: STAUFFER ROBERT E.
Published: May 2006

1. Factorial designs were used to investigate the spatial and temporal components of temperature sampling error in two medium‐sized (maximum fetch = 9 and 11 km; maximum depth = 24 and 70m) Wisconsin lakes (Mendota and Green). Sampling designs were then optimized for estimating temperature distributions, thermocline migration, lake heat content, and vertical eddy conductivities in these and similar stratified lakes.

2. Errors were at a minimum for: (i) isotherms positioned1/3‐1/2of the way down through the seasonal thermocline; (ii) at lake stations located near the node of the principal internal seiche; (iii) after an extended interval of low windpower. If seven spatially distributed lake stations were sampledn1,n2times during the two low‐power intervals bracketing a weather front, and the rime delay between revisits was randomized with respect to the period of the uninodal temperature seiches, the resulting standard error (cm) in ΔZ̄17(depth of 17° isotherm; an unbiased, minimum‐variance estimator for main thermocline migration) was (144/n1+ 144/n2)1/2. Ifn1=n2= 2 ‘revisits’, the resulting CV (coefficient of variation) was 5–10% for ΔZ̄17accompanying major individual cold fronts in early summer.

3. When estimatingKz, the vertical eddy conductivity, the most important component of error relates to ΔHz, the change in heat content below depthz. The error in ΔHzis minimized in the same manner as for lake‐mean isotherm depth. Using the Mendota sampling design described above, the RMS error in ΔHzdecreases from ∼90 cal cm−2in the upper metalimnion to ∼35calcm−2near the base of the metalimnion. For seven take stations, andn1= n2= 2,Kzcan be estimated with a CV ∼10% bracketing a single major cold front. The CV decreases approximately as ΔHz−1, hence is roughly proportional to Δt−1or to (cumuiative windpower)−1.
Quantification of submerged wood in a lowland Australian stream system
Authors: O'CONNOR NICHOLAS A.
Published: May 2006

1. The importance of submerged wood (snags) as macroinvertebrate habitat was evaluated in the Pranjip‐Creightons Creek system, a lowland stream system in northern Victoria. Snag surface area and biomass were measured at ten sites along the system. The first four upstream sites, located in the foothills of the Strathbogie Ranges, and the next three sites, on the northern Victorian riverine plain, were affected by streambank erosion and high sediment loads and contained little instream wood. A further three sites (Sites 8, 9 and 10) downstream on the riverine plain were not as affected by erosion and possessed extensive stands of riparian river redgum, Eucalyptus camaldulensis, which contributed large amounts of wood to the stream channel.

2. Wood quantities at Site 8 were less than at Sites 9 and 10 downstream where the density of riparian redgum was greater. At Sites 9 and 10, snag surface area per m2 of stream bed was 0.57–0.92m2 and 0.38–0.71m2 depending on discharge. Total snag biomass in the stream channel at the same sites was 26 and 41kg m−2, respectively. Redgum was important to macroinvertebrates as habitat, at one site contributing 25% of total macroinvertebrate densities and over 30% of total macroinvertebrate biomass m−2 of stream bed.

3. Estimations of nitrogen content and C:N ratios of decayed redgum were carried out to provide information on its putative nutritional quality to xylophagous macroinvertebrates. Decayed redgum wood has a comparatively high N content and therefore a low C:N ratio, but appeared to be unpalatable to most macroinvertebrates. Only two macroinvertebrate species, the chironomid larvae Stenochironomus sp. and Dicrotendipes sp., were found to consume decayed redgum.
Fluxes of bacteria and organic matter into a blackwater river from river sediments and floodplain soils
Authors: WAINRIGHT SAM C. , COUCH CAROL A. , MEYER JUDY L.
Published: May 2006

1. The Ogeechee River, in south‐eastern Georgia, U.S.A, is a blackwater river with an extensive floodplain that is inundated regularly during winter months. Previous studies have shown that low to moderate bacterial production rates cannot support the relatively high suspended bacteria concentrations observed (107−‐108 cells ml−1), suggesting an allochthonous source of bacteria. We report the results of a combination of field and flume experiments which demonstrate that river sediments and floodplain soils are significant sources of suspended bacteria during seasonal flooding. Benthic bacteria are also entrained by normal discharges. There are sizeable fluxes of POC and DOC from river sediments and floodplain soils.

2. Bacterial, POC and DOC fluxes (14, 250, and 790 mg Cm−2 h−1, respectively) were substantial when water was percolated upward through floodplain soils.

3. Simulation of overland flow using a flume demonstrated further fluxes of bacteria and POC from floodplain soils (up to 61 and 10700 mg Cm−2h−1, respectively) and river sediments, but did not yield additional DOC from floodplain soils.

4. These laboratory results are supported by experiments in which we measured significant increases in concentrations of bacteria and DOC in a downstream direction in (i) the main river channel during a winter flood in 1986, and (ii) a floodplain slough (channel side‐arm) which re‐entered the main channel 800m from its initial divergence. Inputs of bacteria and DOC from the surrounding floodplain were estimated to be up to 3500 kg DOC h−1, and 4000 kg bacteria Ch−1 over a 50‐km reach.

5. These previously unmeasured fluxes of organic carbon help to explain the high concentrations of suspended bacteria in the Ogeechee River.
Diatom communities along stream longitudinal gradients
Authors: MOLLOY JENNIFER M.
Published: May 2006

1. Summer diatom communities on artificial substrates were sampled weekly for a month in three first‐ to sixth‐order tributaries of the Kentucky River to determine how community structure varied with stream size.

2. Diatom cell abundances were generally higher in the headwaters. Species diversity increased in a downstream direction in two of the streams, and in an upstream direction in the third. However, diversity in general seemed more closely related to current regimes than to stream size per se, with highest species diversity at intermediate current velocities.

3. Variation in diatom accumulation rates was greater in downstream communities than in the headwater assemblages of two streams, suggesting that downstream communities may experience greater fluctuations in abundance, at least under low‐flow conditions.

4. Patterns of species distributions suggested a relationship between morphological growth forms (guilds) and stream size, as well as the influence of current. Achnanthes spp., Eunotia spp., erect, and stalked taxa were more commonly associated with headwater assemblages. Filamentous and centric diatoms occurred with greater frequency downstream.
The coexistence of Bosmina and Ceriodaphnia in a south Andes lake
Authors: BALSEIRO E.G. , MODENUTTI B.E. , QUEIMALIÑOS C.P.
Published: May 2006

1. The coexistence of Bosmina and Ceriodaphnia was studied in relation to phytoplankton succession in a small lake (Laguna Ezquerra) in the araucanian region of Argentina.

2. The study involved field sampling and single species cultures of each of the two cladocerans in lake water under laboratory conditions.

3. Ceriodaphnia showed a unimodal cycle while Bosmina had a bimodal pattern during 4 months of coexistence. Ceriodaphnia exhibited a direct relationship between clutch size and biovolume of edible algae, whereas Bosmina's fecundity was related to the density of flagellates.

4. We found that the fecundity of these species responded differently to laboratory and field conditions. The fecundity of Ceriodaphnia followed the same pattern in both the field and laboratory, whereas Bosmina showed higher fecundity values in laboratory experiments.

5. Our results are in good agreement with predictions derived from Northern Hemisphere studies, indicating that food‐limited populations of daphnids and Bosmina can coexist for extended periods in spatially homogeneous environments.

6. The variation in food availability, measured as biovolume of edible algae, determines the loss of Ceriodaphnia and the persistence of Bosmina.
Immobilization and mineralization of dissolved free amino acids by stream‐bed biofilms
Authors: FIEBIG DOUGLAS M. , MARXSEN JORGEN
Published: May 2006

1. Radiolabelled (14C) amino acids were used to investigate the influence of sediment size as well as dissolved free amino acid (DFAA) concentration and composition on immobilization and mineralization of DFAAs by biofilms from a first‐order stream.

2. Over time (240 min), biofilms on stony substrata immobilized a DFAA mixture more effectively than those on sandy substrata, however proportional mineralization of immobilized DFAAs was higher for sandy substrata (36 v 20%).

3. Using stony substrata, the DFAA mixture was immobilized more rapidly than glycine alone at ‘near‐natural’ amino acid concentrations (c. 37 μgl−1), as well as enriched concentrations (1 and 100 mg 1‐−1). Instantaneous rates of glycine immobilization and mineralization were not saturated at glycine enrichments of up to 980 mgl−1.

4. With both the amino acid mixture and glycine alone, proportional mineralization of the immobilized amino acids increased on enrichment to Img 1‐−1 (DFAA mixture: from 25 to 37%; glycine alone: from 50 to 54%), but then fell on further enrichment to 100mgl−1 (DFAA mixture: 11%; glycine alone: 7%).

5. Results are discussed in terms of the potential trophic utility of immobilized DFAAs as well as the apparent roles of biotic and abiotic immobilization mechanisms. Immobilization and mineralization responses to variables investigated in this study give an insight into potential variability of carbon immobilization and retention in stream‐bed sediments. This is fundamental to an understanding of how DOC may become available to higher trophic levels.
Reversal of eutrophication in Lake Geneva: evidence from the oligochaete communities
Authors: LANG CLAUDE , REYMOND OLIVIER
Published: May 2006

1. In Lake Geneva (Switzerland), total phosphorus concentrations have decreased from 90 mg m−3 in 1979 to 55 mg m−3 in 1990.

2. To assess the effects of this improvement, tubificid and lumbriculid communities were sampled in 1982 and in 1991 in the same areas, at a depth of 40 m.

3. Abundance of mesotrophic species (mostly Potamothrix vejdovskyi) and of eutrophic species (mostly Potamothrix hammoniensis) was lower in 1991 than in 1982; in contrast, oligotrophic species (mostly Peloscolex velutinus) were more abundant in 1991 than in 1982.

4. The changes recorded in 1991 were the same as those associated with a decrease of organic sedimentation.

5. Mean relative abundance of oligotrophic species increased from 17% in 1982 to 41% in 1991. According to these values, Lake Geneva was mesoeutrophic in 1982, but mesotrophic in 1991.
Nutrients, algae and grazers in some British streams of contrasting pH
Authors: WINTERBOURN MICHAEL J. , HILDREW ALAN G. , ORTON STUART
Published: May 2006

1. The relationship between algal biomass accumulation, invertebrate colonization, and stream‐water pH was investigated in seven streams in three regions of England and Wales. Possible nutrient limitation of algal production at all sites was examined with diffusion substrata.

2. Periphyton assemblages on experimental substrata after 30 days were dominated by diatoms, notably Eunotia spp., at all sites. Algal pigment concentration (chlorophyll a and phaeopigments) was not correlated with stream‐water pH, and mean concentrations on control (unenriched) substrata ranged from 0.08 to 1.94 μg cm−2.

3. The growth response of periphyton to nutrient additions was site specific. Algal production was stimulated by nutrient additions at sites in the English Lake District and Llyn Brianne (south‐west Wales), but not in the Ashdown Forest (southern England).

4. Larval Chironomidae were the main invertebrates retrieved from substrata at all sites. Within all three regions, larval abundance was positively related to algal pigment concentration (biomass). Abundance of the stonefly Nemurella pictetii was also positively correlated with algal biomass at the one site where it occurred.

5. Our results indicate that epilithic algal production in small, oligotrophic streams is unlikely to be determined primarily by pH. Neither do they support the view that an absence of grazers from acid streams is necessarily due to an inadequate food supply.
Mortality of the terrestrial adult and aquatic nymphal life stages of Baetis vernus and Baetis rhodani in the Breitenbach, Germany (Insecta: Ephemeroptera)
Authors: WERNEKE ULRICH , ZWICK PETER
Published: May 2006

1. The mortality of Baetis vernus Curtis and Baetis rhodani Pictet during the terrestrial‐aerial and aquatic life stages was studied at the Breitenbach near Schlitz, Hesse, Germany. The number of females emerging from the stream was recorded with emergence traps. To estimate mortality of females of both species during terrestrial life, numbers of emerging females were compared with numbers of females returning to the stream for oviposition, as shown by numbers of egg masses found in the stream.

2. Mortality of female B. vernus during their terrestrial life stage was 98.8%. It was 91.2 and 96.6%, respectively, during the first and second generations of B. rhodani.

3. To estimate the mortality of both sexes of B. rhodani during the aquatic life stage, the number of eggs laid by the first generation was compared with the number of adults emerging during the second generation.

4. Mortality during the aquatic phase (both sexes combined) of B. rhodani was 91.1%.

5. Mortality during the terrestrial life stages was at least as high, if not higher than during the aquatic stages. Evidently, there is a considerable export of organic material into the terrestrial environment around the stream. Mortality during terrestrial life may be an important regulator of population size.
Mixotrophic algae in three ice‐covered lakes of the Pocono Mountains, U.S.A.
Authors: BERNINGER ULRIKE‐G. , CARON DAVID A. , SANDERS ROBERT W.
Published: May 2006

1. The occurrence and grazing activity of mixotrophic (phagotrophic) algae in three icecovered freshwater lakes of different trophic status were examined (oligotrophic Lake Giles, mesotrophic Lake Lacawac, eutrophic Lake Waynewood), Microbial population densities were low (4.1–7.2 × 105 bacteria ml−1 and 1.2–2.4 × 103 nanoplanktonic protists ml−1). All three nanoplankton communities were dominated by chloroplast‐bearing forms (60–96%).

2. Mixotrophs formed up to 48% of the phototrophic nanoplankton in Lake Lacawac and were responsible for up to ∼90% of the observed uptake of bacteria‐sized particles. The abundance of mixotrophic algae in Lakes Giles and Waynewood were extremely low (3 and 2% of the phototrophic algae, respectively), and heterotrophs dominated nanoplankton bacterivory.

3. The overall impact of nanoplankton feeding activity on the bacterial assemblage was low under the ice in Lakes Giles and Waynewood. Removal rates of bacteria based on our particle uptake experiments were 1.0 and 4.0% of the bacterial standing stock day−1 in these lakes, respectively. Removal rates were higher in Lake Lacawac and ranged from 4.9 to 11% of the bacterial standing stock day−1 on 2 successive sampling days.