bluuebunny/crossref_metadata_2025 huggingface dataset:
Distribution and life cycles of cladocerans in temporary pools from Central Italy
Authors: CROSETTI D. , MARGARITORA F. G.
Published: May 2006

SUMMARY 1. A study of twenty‐nine temporary pools located in a nature reserve in Central Italy was carried out for two successive years (1982–83 and 1983–84) to determine the distribution and life cycles of the cladocerans they contained.

2. The pools followed a typical autumnal cycle, filling up in early autumn and drying up in late spring. They differed in morphology (size, depth, type of soil) and in the length of the wet phase.

3. Nineteen cladoceran species were found. A few of these are early species, appearing at the beginning of the wet phase, whereas others appear much later in spring and these populations persist for a shorter time.

4. Species distributions did not show any clear correlation with the ponds’morphological features, and the life cycles of individual species were similar in all ponds. Thus populations did not adapt life history patterns to match conditions in particular ponds.
Effects of predation by Chaoborus flavicans on crustacean zooplankton of Lake Lenore, Washington
Authors: LUECKE CHRIS , LITT ARNI H.
Published: May 2006

1. After Chaoborus flavicans became established in 1974, the species composition of zooplankton in Lake Lenore changed. Diaptomus nevadensis disappeared and densities of Diaptomus siciliswere reduced.

2. A transplant experiment showed the D. nevadensis could survive in Lake Lenore water in the absence of Chaoborus. The disappearance of D. nevadensis was probably a consequence of Chaoborus predation.

3. Although densities of Daphnia pulicaria† were similar before and after the colonization of C. flavicans, juvenile D. pulicaria began producing neck‐teeth during the first summer Chaoborus was present.

4. The seasonal pattern of neck‐teeth production by juvenile D. pilicaria did not correlate with density of Chaoborus but rather with a combination of water temperature and Chaoborus density, suggesting that metabolic processes are a component of induction of neck‐teeth in this species.
Population growth in some Mesostoma species (Turbellaria) predatory on mosquitoes
Authors: KOLASA JERZY
Published: May 2006

SUMMARY 1. Turbellarian predators of the genus Mesostoma prey on the aquatic stages of mosquitoes. In order to evaluate their potential as control agents, a comparison of population parameters has been made on three species from Australia, Africa and Papua New Guinea: M. appinum, M. zariae and M. timbunke.

2. The life cycle of these species is relatively short at higher temperature ranges (22–30°C) and varies from 12 to 35 days, depending on the temperature. M. appinum does not increase in numbers at 30°C, white M. timbunke is unable to reach sexual maturity at 15°C. M. appinum, but not M. zariae, multiplies slowly at 15°C, although both species survive at this temperature. The fastest population growth was obtained for M. appinum at 22°C, and for M. zariae and M. timbunke at 30°C. The doubling time for the population is about 6–7 days in the multivoltine species, M. appinum and M. zariae, and about 18.5 days in univoltine M. timbunke.

3. A significant part of the growing population is composed of immature individuals, which corresponds to the high values of the reproductive parameters Ro and rm. In M. appinum and M. zariae, individuals rarely produce dormant resting eggs except under deteriorating conditions. M. timbunke produces only dormant eggs, and in this respect resembles arctic and subarctic species. A convergence of the reproductive modes between this equatorial species and the high latitude species might be interpreted as adaptation to harsh environments.

4. The overall population growth of all Mesostoma spp. is several times faster than in Dugesia dorotocephala and D. trigrina, other flatworms studied as potential biological control agents of mosquitoes
Production and litter processing by crayfish in an Appalachian mountain stream
Authors: HURYN ALEXANDER D. , WALLACE J. BRUCE
Published: May 2006

SUMMARY 1. Mean annual density and biomass (B̄) of Cambarus bartonii in an Appalachian mountain stream (U.S.A.) was 12 individuals m−2 and 1669 mg (ash‐free dry weight) m−2.

2. Annual production (P) of C bartonii was 961 mg AFDW m−2. Despite high biomass, low growth rates resulted in low production and a low P/B̄ ratio of 0.58.

3. While C bartonii constituted 61% of the total macroinvertebrate biomass, it contributed only 13% of annual community secondary production.

4. Litter processing was positively related to temperature and crayfish size. Cambariis bartotnii was estimated to comminute 36 g m−2 y−1 of leaf litter (>1 mm2) to 24 g m−>2 y−1 fine particulate material (<1 mm2). The annual pattern of litter comminution by crayfish was regulated by temperature. As a result, >5()% of shredding activity by crayfish occurred from June to September which was also the period of lowest litter standing crops and activity of other shredding macroinvertebrates.

5. We speculate that during summer crayfish play an important role in temperate woodland streams by converting slowly processed leaf litter species (e.g. Rhododendron) to fine particles which are then available to collector‐gatherers (e.g. Chironomidae, Oligochaeta).
Production of the three‐spined stickleback, Gasterosteus aculeatus L., in the River Weaver, England
Authors: O'HARA K. , PENCZAK T.
Published: May 2006

1. The production of three‐spined sticklebacks, Gasterosteus aculeatus, estimated in the margin of a large channelized lowland river, averaged 42.3 g m−2 yr−1 and the P/B ratio was 3.7. The production value greatly exceeds those previously recorded for G. aculeatus and results from the very high population densities.

2. Life‐bistory tactics of the sticklebacks included both r‐ and K‐selected traits.

3. The fish were carnivorous in the summer months but predominantly detritivorous in the winter.
Effects of chronic chlorine exposure on litter processing in outdoor experimental streams
Authors: NEWMAN RAYMOND M. , PERRY JAMES A. , TAM ERIC , CRAWFORD RONALD L.
Published: May 2006

SUMMARY 1. The effects of chlorine on litter (Potamogeton crispusL.) processing were examined using six outdoor experimental streams. Downstream portions of two streams were dosed at c. 10 μg l−1 Total Residual Chlorine (TRC), one stream at 64 μgl1, and one stream at 230μg l−1. Two control streams were not dosed; upstream riffles of each stream served as instream controls.

2. Two 35 day litter breakdown (per cent AFDW remaining) experiments indicated significantly lower decay rates in the high dose riffle. No other concentration of chlorine significantly affected decay rate.

3. A third experiment, conducted in medium and high dose streams, indicated that high dose chlorine exposure reduced litter decomposition rates significantly, and reduced microbial colonization, microbial electron transport system activity, and microbial litter decomposition after 4 days but not after 11 days of exposure. The number of amphipod shredders colonizing litter bags was also reduced significantly with high chlorine dose.

4. A fourth experiment, after dosing was terminated, provided direct evidence that amphipod shredders were important in facilitating litter decomposition: litter bags stocked with amphipods had significantly higher decomposition rates than bags which excluded shredders.

5. Overall results indicate that the high dose (c. 230 μgl−1 TRC) of chlorine reduced litter processing rates partly by reducing initial microbial conditioning, but primarily by reducing the colonization of amphipod shredders.
Laboratory breeding studies of freshwater crayfish, Austropotamobius pallipes (Lereboullet)
Authors: WOODLOCK BRIAN , REYNOLDS JULIAN D.
Published: May 2006

SUMMARY. 1. Mature crayfish, collected from an Irish lake before breeding had started, were held in breeding combinations and their mating and brooding activities observed.

2. All mating attempts were initiated by the male. A single mating led to spawning within 6 days but a subsequent mating cancelled the effects of the first. Males mated more often when there were more females present. Males lacking a major cheliped mated less often than did normal males.

3. Larger males mated more often than did smaller males, and although males showed no female size preference, matings were less frequent and generally unsuccessful when males were much larger than females; the female was usually killed. Large females mated successfully with smaller males.

4. Females held at high densities with a larger male mated earlier than at low densities. However, aggression also increased with density; at high densities males fought and killed females.

5. Males held in pairs without females fought; in occasional mating attempts spermatophores were not positioned correctly. Paired females rarely fought; all spawned normally although unmated. Although their eggs soon died and were removed during grooming, brooding behaviour continued for at least 2 months.

6. Brooding females held in pairs shed pleopodal eggs during aggressive encounters. Females held singly showed a lower initial rate of egg loss.
Effects of previous diet and frequency of feeding on development of larval damselflies
Authors: BAKER ROBERT L.
Published: May 2006

SUMMARY. 1. Food availability during instar F‐3 affected duration of instar F‐3 of larval Ischnura vertiealis (Say) maintained in the laboratory but did not affect the increase in head width at the moult to instar F‐2.

2. Food availability during instar F‐2 altered both duration in instar F‐2 and weight per unit head width of newly moulted F‐l larvae, but not the increase in head width at the moult to instar F‐1.

3. Food availability during instar F‐3 had no effect on instar duration, weight per unit head width, or increase in head width of F‐2 larvae at the moult to instar F‐l.

4. Survival of larval Coenagrion resolution (Hagen) reared in the laboratory was dependent on mean number of Daphnia offered per day. In addition, larvae fed less frequently, but on the same mean number of Daphnia per day. had lower survival rates than larvae fed more frequently.
Cadmium toxicity to the freshwater amphipod Gammarus pulex (L.) during the moult cycle
Authors: McCAHON C. P. , PASCOE D.
Published: May 2006

SUMMARY. 1. The toxicity of cadmium to mature Gammarus pulex at different stages in the moult cycle is described.

2. Immediate post‐moult animals are significantly more sensitive than intermoult specimens at cadmium concentrations between 1.0 and 0.1 mg 1−1 but not at 0.03 or 0.01 mg Cd 1−1.

3. At a calcium concentration of 40mgl−1, post‐moult animals undergo recalcification within 7 days and thereafter there is little variation in their response to cadmium.

4. External calcium concentrations of 40 and 115mg 1−1 do not affect cadmium toxicity but at 180 mg Ca1−1 the sensitivity of immediate post‐moult specimens is significantly reduced.

5. The results are discussed with regard to the protection of G. pulex by present water quality standards.
Differential use of food resources by the instars of Chaoborus punctipennis
Authors: MOORE MARIANNE V.
Published: May 2006

SUMMARY. 1. Differential use of food resources by instars I‐1V of Chaoborus punctipennis was examined in a mesotrophic New Hampshire lake during midsummer when all instars coexisted. Diet composition and prey preference were quantified first, at night when all instars were feeding at the same depth, and second, during the day when the early instars (I‐II) and instar III were segregated by depth. Relative abundance, per cent biomass, and per cent frequency of occurrence of soft and hard‐bodied rotifers, flagellated phytoplankton, protozoans, and crustaceans in C. punctipennis diets were quantified using crop content analyses.

2. All four instars ingested large, flagellated phytoplankton (mainly Dinobryon and Ceratium). This unexpected result suggests that the effects of phytoplankton on Chaoborus growth and survival should be investigated. All instars also consumed rotifers (mainly Kellicottia, Gastropus, Polyarthra), but only instars III and IV fed upon crustaceans (mainly Daphnia, Bosmina and Diaphanosoma). Small rotifers (Gastropus spp., Keratella cochlearis, Trichocerca similis) occurred more frequently and were more abundant in early instar diets than late instar (III and IV) diets, whereas large rotifers (Asplanchna priodonta and Keratella crassa) were eaten only by instars III and IV. Zooplankton with gelatinous sheaths (e.g. Ascomorpha, Collotheca and Holopedium) were rarely ingested.

3. Developmental increase in gape diameter of C. punctipennis seemed to be the major proximate mechanism causing dietary differences among instars. Body widths of hard‐bodied prey in C. punctipennis crops were always less than gape diameter. The relationship between prey body width and Chaoborus gape diameter, coupled with knowledge of prey escape behaviour, should be useful for predicting the presence of hard‐bodied prey taxa in diets of other Chaoborus species.

4. All four instars of C. punctipennis selected soft‐bodied, or weakly loricate, rotifer prey over crustaceans and phytoplankton. Early instars preferred the small rotifer T. similis and the protozoan Difflugia sp. to other rotifers and phytoplankton when feeding in the epilimnion or thermocline during the day or night. Late instars positively selected the rotifer, Asplanchna. Prey value (prey weight ingested per unit handling
Input, movement and exchange of organic matter within a subtropical coastal black water river‐flood plain system
Authors: CUFFNEY THOMAS F.
Published: May 2006

SUMMARY. 1. Inputs, movements and exchanges of particulate organic matter were measured on two contrasting floodplains of the Ogeechee River, Georgia, U.S.A. A model, which incorporated measurements of standing crop, respiration, litterfall, inundation, and litter processing rates, was used to estimate annual exchanges of organic matter between the river and floodplains.

2. Annual litterfall was higher on the East floodplain than on the lower elevation West floodplain (902 v. 784 g ash‐free‐dry‐mass [AFDM] m−2).

3. Experiments with tagged leaves and sticks demonstrated that litter was readily displaced during floods. The distance and direction of displacement varied within and between floodplains but tended to be higher closer to the river and was generally parallel to the river.

4. The model indicated that both floodplains lost organic matter to the river. The lower elevation floodplain (East) lost more organic matter to the river (208 g AFDM m−2 year−1) than did the higher elevation (West) floodplain (79g AFDM m−2 year−1).

5. Inputs of organic matter from the floodplain to the river exceeded the amount of litterfall typically entering heavily forested high gradient headwater streams (5.5 v. 0.4‐0.6 kg AFDM m−2 year−1).

6. Floodplain organic matter inputs may exert a greater influence upon structure and function within these streams than do upstream inputs or primary production. Consequently, current conceptualizations of stream structure and function need to be modified to account for the effects of floodplain inputs on stream channel processes within large, low‐gradient rivers.
The phytoplankton of an enriched, soft‐water lake subject to intermittent hydraulic flushing (Grasmere, English Lake District)
Authors: REYNOLDS C. S. , LUND J. W. G.
Published: May 2006

SUMMARY. 1. The abundance and species composition of the phytoplankton of Grasmere were monitored over a 12‐year period following the commissioning of a small sewage treatment works, upstream of the lake.

2. Although Grasmere has been subject to increased phosphorus‐loading and has quickly developed many features associated with eutrophication, the composition of its plankton has retained the characteristics of a mesotrophic, soft‐water lake: a vernal diatom maximum, generally dominated by Asterionella, is followed by summer growths of nanoplanktonic species, of various colonial Chlorophyceae, before a substantial return to Asterionella‐dominance in the autumn. In cooler summers there have been episodes of renewed diatom growth. followed by truncated recapitulations of the essential summer sequence. Anabaena solitaria was relatively common in drier summers when dissolved inorganic nitrogen fell to low concentrations, although many of the ‘larger’ algal species associated with stratified eutrophic lakes (Aphanizomenon, Microcystis, Ceratium spp.) have failed to become abundant in Grasmere.

3. Mean biomass levels (as indicated by chlorophyll concentration) have increased in response to the enrichment, though they do not conform well with most chlorophyll/phosphorus regression‐models.

4. The key factor resisting a more complete transition to a typical eutrophic plankton appears to be the efficiency of episodic flushing of the lake during periods of high fluvial discharge sustained by heavy rainfall over the extensive, mountainous catchment. The probabilities that these limnological conditions might fail to deter the development of ‘nuisance’ blooms are briefly assessed.
In vitro studies on sulphate reduction and acidification in sediments of shallow soft water lakes
Authors: SCHUURKES J. A. A. R. , KOK C. J.
Published: May 2006

SUMMARY. 1. The sulphate reduction capacity of six shallow soft water sediments, differing in pH and organic matter content, was studied under controlled pH adjustments ranging from pH 3 to pH 8.

2. In the acid sediments, relatively rich in organic matter, the sulphate reduction capacity reached values of 0.09‐0.12 μmol g−1 d−1. In the circumneutral mineral sediments the values ranged between 0.04 and 0.08 μmol g−1 d−1.

3. The latter group of sediments was very sensitive to the effects of experimental acidification as sulphate reduction was almost fully inhibited when pH decreased from 7 to 5. In the acid sediments inhibition occurred at lower pH values, in the range pH 5 to pH 3.

4. Sulphate reduction governed the production of free sulphides, whereas putrefaction processes were only of minor importance. It is suggested that in acid sediments, relatively rich in organic matter, the sulphate reducing bacterial population is less sensitive to acidification than in circumneutral mineral sediments.

5. The presence of organic matter appeared to be important in counteracting the inhibiting effects of acidification on sulphate reduction. This is important for the in situ sulphate reduction in sediments of soft waters which become enriched with organic matter during the long‐term process of acidification.
Community structure of Trichoptera in a mountain stream: spatial patterns of production and functional organization
Authors: HURYN ALEXANDER D. , WALLACE J. BRUCE
Published: May 2006

SUMMARY. 1. Annual production was estimated for Trichoptera occurring in each of three distinct habitats of a mountain stream: bedrock‐outcrops, riffles and pools. Production was greatest on bedrock‐outcrops (2608 mg ash‐free dry weight m−2), followed by riffles (1038) and pools (950).

2. Annual production in bedrock‐outcrops and pools was dominated by single functional groups, with collector‐filterers and shredders contributing 73% and 75% of the annual production, respectively. Production in riffles was due primarily to shredders (46%), followed by collector‐filterers (27%).

3. Taking account of the amount of stream area occupied by each habitat type, total annual production was estimated at 1336 mg AFDW m−2. 53% of this production was attributable to four taxa: Parapsyche cardis Ross (25%), Pycnopsyche gentilis (MacLachlan) (10%), Neophylax mitchelli Carpenter (9%) and Rhyacophila nigrita Banks (9%).

4. Habitat‐weighted production was distributed among functional groups as follows: collector‐filterers (41%), shredders (29%), engulfing‐predators (15%), scrapers (13%) and collector‐gatherers (2%).

5. The distinct taxonomic and functional structures of trichopteran sub‐communities were shaped by the distinct physical characteristics of their principal habitats. Bedrock‐outcrops were characterized by low roughness and high current and were sites of low deposition or organic matter; thus the predominance of collector‐filterers. In contrast, the other habitats of greater roughness (riffles) and/or lower current (pools) were sites of deposition of food (e.g. leaf litter) and greatest shredder production.

6. By distinguishing discrete mesoscale habitats, each with a functionally distinct caddisfly sub‐community, we speculate that small mountain streams provided the diverse physical templates essential for the evolution of the major feeding tactics (e.g. scraping, shredding, filter‐feeding) of the. Trichoptera.
Effects of turbidity on life history parameters of two species of Daphnia
Authors: SCHOLTZ S. , SEAMAN M. T. , PIETERSE A. J. H.
Published: May 2006

SUMMARY.1. Life table experiments were carried out in a range of turbidities onD. pulex, representing a ‘clear‐water’, and onD. barbata, representing a ‘turbid‐water’ species.

2. In contrast to predictions based on seasonal occurrence patterns,D. pulexhad a higher intrinsic rate of increase (rc)s over most of the turbidity range thanD. barbata.Consistent differences in life history between the two species were found, but life history characteristics were rather insensitive to turbidity levels. Although turbidityper seappears to have little direct effect on life history parameters, it could influence the seasonal succession of these two species by interacting with other factors.

3. It is suggested that visual predation by fish rather than turbidityper seprobably influenced the seasonality ofDaphniaspecies. During the warmer months, selective removal ofD. pulexby visually foraging fishes may allowD. barbatato gain dominance. Effects of temperature and nutrition also merit further study.
Impact of biological activity on detritus transported in the lower river Rhine: an exercise in ecosystem analysis
Authors: ADMIRAAL WIM , VAN ZANTEN BOB
Published: May 2006

SUMMARY. 1. Published data are used to construct a tentative carbon budget for the ecosystem of the lower river Rhine and its sedimentation areas in The Netherlands.

2. It is estimated that 287 × 106kg Cy−1 of particulate organic material is transported by the river Rhine, and 100 × 106 kgCy−1 of this material is deposited in the delta.

3. Phytoplankton and nitrifying bacteria seem to contribute significantly to the carbon budget, by producing c. 78 × 106kgCy−l.

4. The mineralization in the water (estimated from routine determinations of biological oxygen demand and from in situ diurnal fluctuations of oxygen) and in the bottom (estimated from the denitrification rates in the delta, from the production rate of methane and from overall oxygen consumption) is shown to degrade c. 50% of the carbon input plus autochthonous production.

5. The carbon budget and oxygen regime in the lower Rhine suggest that after decades of severe organic pollution the river has more or less resumed the normal, slightly heterotrophic state of a large lowland river.
Rapid flow through the sediments of a headwater stream in the southern Appalachians
Authors: MUNN NANCY L. , MEYER JUDY L.
Published: May 2006

SUMMARY. 1. The flow of water through the sediment layer (underflow) of streams can influence nutrient uptake dynamics and the supply of materials to microbes, meiofauna and macroinvertebrates living within stream sediments. We examined the extent of underflow in Hugh White Creek, a headwater stream in the southern Appalachian Mountains and compared underflow at different depths and at different sites within the stream.

2. Initially rhodamine dye was used to trace the flow of water through the sediments; however, the dye was strongly absorbed by the sediments in Hugh White Creek. Thus rhodamine was not suitable as a tracer of water flow. Chloride reacted conservatively in laboratory experiments and was used as a tracer.

3. The tracer infiltrated the sediments within 5 min to depths of 10 cm at all six sites. Chloride infiltration tended to decrease with depth of sediments at all sites although there was no consistent statistical pattern in chloride concentration with depth for the different sites. Equilibrium between the water column and sediments was reached rapidly, within minutes for the sites with coarse sediments and within a few hours for sites with finer sediments. Minimum rates of chloride infiltration into the sediments ranged between 1.0 cm min−1 for the sites with cobble substrate to 0.2 cm min−1 for sites with fine sand sediments associated with debris dams. These data suggest that underflow may be a major component in the functioning of Appalachian mountain streams.
Exoenzyme activity associated with lotic epilithon
Authors: SINSABAUGH R. L. , LINKINS A. E.
Published: May 2006

SUMMARY. 1. Epilithic communities were developed on glass slides under four regimes of relative current velocity and light exposure, designated as slow‐light, slow‐dark, fast‐light and fast‐dark, in a fourth‐order boreal stream. Ten samples were collected over an 8‐month period and analysed for biomass, chlorophyll and exoenzyme activity. Fourteen assays were used to monitor the activity of eleven types of exoenzymes involved in the degradation of cellulose, lignin, chitin, xylan, protein, glycogen, organic phosphates and organic sulphates.

2. The communities that developed under each current and light regime were distinct in structure and species composition, but had similar patterns of exoenzyme activity. Overall, exoenzyme activity was closely correlated with biomass. The most readily detected enzymes were phenol oxidase, phosphatase, alpha‐1, 4‐glucosidase, beta‐1, 4‐N‐acetylglucosamidase, and beta‐1, 4‐glucosidase.

3. Calculating exoenzyme activities per unit biomass eliminated the covariance between biomass and enzyme activity, revealing quantitative differences in exoenzyme activity among communities. The highest exoenzyme activity was associated with the slow‐dark epilithon and the least with the slow‐light. Fast‐light and fast‐dark were intermediate.

4. Biomass, chlorophyll and exoenzyme activity showed marked seasonal variations. In general, carbohydrases and the phenol oxidases had different seasonal activity patterns with carbohydrase activity peaking in the summer and phenol oxidase activity increasing markedly in the autumn.

5. Differences among epithilic communities could not be readily accounted for by single factors. Community development was determined by the interactions among current, light, macroinvertebrates and season.
An inexpensive, deep‐water limnocorral that compensates for wave action
Authors: SPENCER CRAIG N.
Published: May 2006

SUMMARY. 1. A large reusable limnocorral is described, suitable for use in water bodies with substantial wave action. The clear plastic enclosure is 1 m in diameter, 25m deep, lightweight (∼50 kg), and inexpensive ($350 U.S.A.).

2. The lower portion of the limnocorral is designed to hang motionless below the water surface, while an expandable floating collar section moves freely up and down with any wave action.

3. Two limnocorrals, equipped with removable sedimentation traps at the bottom, were field tested successfully for 6 weeks in Flathead Lake, Montana, withstanding wave heights up to 1m. Chlorophyll levels and profiles of various physical‐chemical parameters measured inside the limnocorrals were comparable to Flathead Lake values.

4. Despite their large size, the limnocorrals are relatively easy to transport, install and retrieve.
Phytoplankton nutrient limitation in Colorado mountain lakes
Authors: MORRIS DONALD P. , LEWIS WILLIAM M.
Published: May 2006

SUMMARY. 1. Limiting nutrients for phytoplankton were studied experimentally in eight mountain lakes of central Colorado between May and November of 1984.

2. Five categories of phytoplankton limitation were identified: no limitation, N limitation, P limitation, concurrent limitation (stimulation only by simultaneous additions of N and P), and reciprocal limitation (stimulation by addition of either N or P). The phytoplankton communities of three lakes were primarily N‐limited, one was primarily phosphorus‐limited, and four showed primarily combined limitation (concurrent or reciprocal). Switching between categories of limitation was also observed within lakes. Nitrogen was the most frequently limiting nutrient; N, either alone or in combination with P, accounted for 79% of all observed instances of limitation.

3. Nine indices were tested for effectiveness in predicting phytoplankton limitation by N and P. The best indices for discriminating all limitations were ratios of dissolved inorganic N: total P (84% accuracy) and dissolved inorganic N:total dissolved P (80% accuracy). The effectiveness of these indices may be explained by the degree to which they represent N and P fractions actually available to the phytoplankton.
In vivo algal fluorescence, spectral change due to light intensity changes and the automatic characterization of algae
Authors: HILTON J. , RIGG E. , JAWORSKI G.
Published: May 2006

SUMMARY. 1 Total fluorescence spectra of thirty‐two freshwater algae show that the majority of the information is contained in the excitation spectrum of emission at 680 nm.

2. Previously suggested characteristics for the automatic identification of blue‐green algae from their fluorescence properties, i.e. the presence of high phycoerythrin fluorescence and low chlorophyll fluorescence, are shown to be inapplicable to the freshwater blue‐green algae studied here.
Predation and the prey community of a headwater stream
Authors: SCHOFIELD K. , TOWNSEND C. R. , HILDREW A. G.
Published: May 2006

SUMMARY 1. Predatory, net‐spinning larvae of the caddis Plectrocne‐mia conspersa (Curtis) were abundant in the acid headwaters of some southern English streams where fish were absent, but were scarce or absent downstream where brown trout (Salmo trutta L.) occurred.

2. Field enclosure experiments showed that both underyearling and older brown trout reduced the density of P. conspersa. However, whereas small trout affected the overall density of caddis, older fish reduced that of large larvae only.

3. Although P. conspersa is itself an important invertebrate predator there was little evidence of an indirect effect of brown trout on the prey of P. conspersa. Perhaps the diets of brown trout and P. conspersa are so similar that fish simply replaced the caddis as top predator.
The temperature dependence of embryonic and larval development in Protonemura intricata (Plecoptera: Nemouridae)
Authors: MARTEN MICHAEL , ZWICK PETER
Published: May 2006

SUMMARY. 1. Egg development and larval growth of Protonemura intricata (Ris, 1902) (Plecoptera: Nemouridae) were studied in the laboratory and in the Breitenbach, a small stream‐in Germany (F.R.G.).

2. The mean number of eggs in batches collected from the field was 627 (S=314).

3. Mean batching success in the laboratory was 60–100% at 2–18°C. Cumulative hatch in individual batches could be described by asymmetrically sigmoid curves. The length of the hatching period was positively correlated with the length of the incubation period.

4. The incubation period of I', intricata normally consists of an initial dormancy followed by subsequent development. The length of embryonic development (Y. days) is strongly inversely temperature (T, °C) dependent and can be described by the equation:

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5. The length of dormancy is dependent on oviposition dale, and is shorter the later that the eggs are laid. It also depends on temperature during incubation and is increased by rising temperatures. As a consequence, larvae hatch more or less synchronously in the field during autumn. Total incubation period, i.e. dormancy and actual development, exhibits a complex dependence on both incubation temperature and oviposition date. Under constant laboratory temperatures, a late sharp fall in temperature can terminate dormancy earlier.

6. Photoperiod probably induces dormancy and may already act on the last larval instars of the parent generation. The dormancy of P. intricata is classified as an oligopause (Müller. 1970, 1976).

7. In the laboratory. P. intricata larvae from early batches with long dormancy grew faster than larvae from late batches with direct development. Final size was the same in both cases. This acted against the population synchrony induced through egg dormancy. Benthos samples suggest the same in the field.

8. Avoidance of the suboptimal summer conditions in streams by the cold stenothermous P. intricata is suggested to partly explain the success of the species, which contributes more to total emergence biomass than do other Plecoptera in the Breitenbach.
Decomposition of leaf litter exposed to simulated acid rain in a buffered lotic system
Authors: GARDEN ANNE , DAVIES RONALD W.
Published: May 2006

SUMMARY. 1. Exposure to simulated acid rain resulted in changes in the chemical content of riparian vegetation and terrestrial leaf litter and had significant effects on leaf litter decay rates in a well‐buffered lotic ecosystem.

2. Foliar nitrogen and phosphorus decreased with decreasing pH of the simulated acid rain and microbial activity was greater on leaf litter exposed to rain of pi I 5.4 than on leaf litter exposed to pH 3.0 or pH 4.0.

3. Detritivore numbers and biomass were significantly higher on leaf litter exposed to pH 5.4, probably due to the greater palatability of the leaf substrate.

4. Decay rates of leaf litter processed in the summer months were significantly lower than decay rates of leaf litter processed during the autumn/winter due to reduction in nitrogen content and microbial respiration.
Macroinvertebrate movements in a large European river*
Authors: CELLOT BERNARD
Published: May 2006

SUMMARY. 1. Quantitative variations in downstream movements of benthic macroinvertebrates were studied in a large European river, the Rhône, upstream from Lyon. Artificial substrates were suspended at three depths in the water column, both near a bunk and in mid‐channel, monthly from December 1978 to March 1980. Drift nets were used to determine the diurnal rhythm in drift and to investigate the efficiency of our suspended artificial substrates in capturing the drifting macrofauna.

2. Drift densities (number and biomass) reached a maximum during summer, especially near the river bank, and at night. Mean individual weight of organisms was higher close to the bottom and at night.

3. Artificial substrates were reliable, but underestimated drift by about a quarter in number and a sixth in biomass. compared with drift nets. Two detailed analyses of the drift distribution across the width of the river revealed similar densities along both banks, and uniformity in the channel as a whole.

4. Mean annual drift densities estimated for the section of river were 100 individuals, per 100 m3 and 60 mg dry weight per 100 m3. These densities are similar to those obtained from other temperate rivers.
The loss of submerged plants with eutrophication I. Experimental design, water chemistry, aquatic plant and phytoplankton biomass in experiments carried out in ponds in the Norfolk Broadland
Authors: BALLS HILARY , MOSS BRIAN , IRVINE KENNETH
Published: May 2006

SUMMARY. 1 During eutrophication of shallow lakes, communities of submerged plants are often replaced by dense phytoplankton populations, but the mechanism by which this occurs is obscure though often assumed to involve shading.

2. This paper introduces a series investigating this change and describes a system of experimental ponds which were variously fertilized with nitrogen and phosphorus, had fish added or removed, and had their submerged aquatic plants cleared or left intact.

3. Fertilization with phosphate and ammonium nitrate in quantities effectively greater than those in a series of lakes in the adjacent Norfolk Broads, which have lost their submerged plants, did not displace the plant populations.

4. Total phosphorus and soluble reactive phosphorus concentrations in the water did not increase much with increasing loading in the presence of submerged plants but did so if the plants were manually cleared. Ammonium and nitrate concentrations were kept low, despite large additions in both plant dominated and manually cleared ponds.

5. In the absence of fish there were modest increases in chlorophyll a concentrations with phosphorus loading in the presence or absence of submerged plants. The concentrations achieved, however, were much lower than anticipated probably because of grazing by large‐bodied Cladocera.

6. Ponds dominated by plants continued to have low phytoplankton populations even when fish were stocked. Low fish survival in these ponds permitted grazing zooplankters to flourish. In ponds cleared of plants, however, there were significant relationships between cholorophyll a concentration with Daphnia biomass (inverse) and log stock of potentially zooplanktivorous fish (positive). There was a significant relationship between chlorophyll a and total phosphorus concentrations in the plant and cleared ponds in 1982 but only in the plant ponds in 1983. In all cases the phytoplankton communities were dominated by small, often flagellated, organisms.
The fitration rate of Dreissena polymorpha (Bivalvia) in three Dutch lakes with reference to biological water quality management
Authors: REEDERS H. H. , DE VAATE A. BU , SLIM F. J.
Published: May 2006

SUMMARY. 1. The filtration rate of Dreissena polymorpha Pallas measured in the field in three shallow Dutch lakes shows an inverse exponential relationship with the dry matter content of the water.

2. Temperature seems to set only a gross level to the filtration rate in summer and winter season respectively; within a season no clear relation between the filtration rate and temperature exists.

3. Under laboratory conditions the risk of measuring abnormal behaviour of Dreissena polymorpha is shown to be substantial; hence field‐measurements of the filtration rate are preferable.

4. The clearing capacity of the Dreissena polymorpha populations in Lakes IJsselmeer and Markermeer is sufficient to filter both lakes at least once or twice a month. This indicates the potential importance of this species for restoration of turbid, eutrophic lakes by means of biomanipulation.
Life cycle, horizontal microdistribution and current resistance of Allogamus auricollis Trichoptera: Limnephilidae in an Austrian mountain brook
Authors: WARINGER J. A.
Published: May 2006

SUMMARY. 1. The life history, horizontal distribution at the sediment surface and the effect of water flow on the microdistribution of Allogamus auricollis (Pictet, 1834), a case‐bearing caddisfly, was investigated in a mountain brook near Lunz, Lower Austria.

2. The average head‐width increment per moult was proportionately constant at c. 48%; therefore Dyar's rule was applicable.

3. Allogamus auricollis has a 1‐year life cycle with first and second instars most abundant in October. It overwinters primarily as third and fourth instars; pupae were observed in August.

4. Horizontal distribution patterns were investigated by means of bimonthly samples taken along the stream profile. All instars were most abundant near the banks: 86.5% of the total catch 1987–88 were collected 0–1.5 m from the banks.

5. Current speeds were measured at the sites of 2191 larvae (including all instars) and eighty‐six pupae. Larvae were most abundant at current speeds of 0–5 cm s−1 (i.e. 86.6% of the total catch 1987–88).

6. Laboratory data on different stages of resistance to drift in A. auricollis (Waringer, 1989) were tested for their application to field conditions. 90% of the total catch 1987–88 preferred areas at the substrate surface where they could remain fully retracted within their cases, unattached, even when the large lateral case surface area was directed towards the water flow. This was also true at times of high discharge where the size of these areas was considerably reduced.
Towards a biological and chemical definition of the hyporheic zone in two Canadian rivers
Authors: WILLIAMS D. DUDLEY
Published: May 2006

SUMMARY. 1. A series of samples of interstitial water and fauna was taken along transects from the channel into the bank in two small rivers in southern Ontario, Canada. These were examined for any discontinuities which might indicate the position of the hyporheic/groundwater interface.

2. There were several chemical discontinuities in Duffin Greek, with “break lines” occurring from about the river margin obliquely downwards under the bank for dissolved oxygen and carbon dioxide, B.O.D., alkalinity, suspended solids and amount of organic matter. Break lines in nitrate and sulphide concentration ran from near the margin obliquely down under the river bed. In the Rouge River, a discontinuity extending from a point approximately 1.5 m landwards from the margin obliquely down under the river was indicated by dissolved carbon dioxide, B.O.D., conductivity, suspended solids, organic matter, nitrate and alkalinity.

3. Ordination (DECORANA) and community classification (TWIN‐SPAN) revealed that, in both rivers, linear distance from mid‐river was the major factor associated with community structure. In both rivers the community under the bank was distinct from the river community and these two communities were separated by another community characteristic of the river margin. In Duffin Creek the classification procedure additionally discriminated surface and interstitial sub‐sets within the river community.

4. Most taxa showed no significant correlations with the chemistry of the interstitial water but. in Duffin Creek, the densities of the copepod Diacyclops crasscaudis brachycercus (Kiefer) and Oligochaeta were positively correlated with nitrate: worms were also negatively correlated with sulphide. In the Rouge River, density of hyporheic animals was negatively correlated with both conductivity and alkalinity of interstitial water; oligochactes were positively correlated with both nitrate and organic matter; and density of nematodes was positively correlated with sulphide concentration.

5. The hyporheic faunas of these two rivers were dominated by insects, particularly chironomids. Compared with the hyporheos of rivers in Europe and Colorado, the two Ontario rivers lack significant numbers of harpacticoid copepods as well as bathynellacid, amphipod and isopod crustaceans.
Periphyton biomass dynamics in gravel bed rivers: the relative effects of flows and nutrients
Authors: BIGGS BARRY J. F. , CLOSE MURRAY E.
Published: May 2006

SUMMARY. 1. Periphyton chlorophyll a and ash free dry weight (AFDW) were monitored in nine rivers to examine the relative importance of flows and nutrients for regulating periphyton biomass in gravel bed rivers.

2. Mean annual flows in the rivers ranged from 0.94 to 169 m3 s−1, mean dissolved reactive phophorus (DRP) from 1.3 to 68 μ g 1−1, periphytic chlorophyll a from 4.6 to 73 mg m −2. and AFDW from 2.8 to 16 g m−2.

3. For eight of the nine rivers NH4‐N. DRP, total Kjeldahl nitrogen, total phosphorus and total suspended solids were correlated (P<0.01) with flow, and for seven rivers conductivity was inversely correlated (P<0.05) with flow.

4. There was a hyperbolic relationship between flows and biomass, with chlorophyll a >100 mg m −2 and AFDW >20 g m−2 occurring most frequently in flows of <20 m3 s−1.

5. Floods prevented the development of medium term (i.e. up to 2 months) maxima in biomass in five of the rivers, but maxima occurred over summer‐autumn and winter‐spring in the three rivers where floods were absent.

6. Chlorophyll a biomass was more resistant to flooding than AFDW. Only 5993 of the forty‐six recorded floods caused chlorophyll a scouring, whereas 74% of the floods caused AFDW scouring. The efficiency of scour was more influenced by the pre‐flood biomass than the magnitude of the event.

7. Biomass maxima were significantly correlated (P<0.01) with mean DRP concentration during the accrual period. Overall, up to 53% of the mean annual biomass difference between rivers was explained by the mean annual DRP concentrations. However, the high correlations between nutrient concentrations and flow indicated that the nutrient data were also carrying hydrological information and that simple causal relationships between nutrients and biomass are difficult to establish in rivers.

8. It is concluded that hydrological factors contribute at least equally with nutrients to the differences in periphyton biomass between the gravel‐bed study rivers. They combined to explain up to 63.3% of the variance in biomass, compared with 57.6% for nutrients. It is recommended that periphyton data from gravel‐bed rivers should always be viewed within the context of the flow history of the site, and not just as a function of nutrient concentrations.
The dissolution of calcite in acid waters: mass transport versus surface control
Authors: COMPTON RICHARD G. , PRITCHARD KEITH L. , UNWIN PATRICK R.
Published: May 2006

SUMMARY. 1. A new experimental method for the study of kinetics and mechanism of reactions at the solid‐liquid interface has shown that the dissolution of calcite in acidic waters is, under conditions of high mass transport, controlled by the first order heterogeneous reaction of H+ at the interface and not by diffusion as previously thought.

2. The implications of this for lake liming strategies (aimed at countering the effects of ‘acid rain’) are significant in that under typical liming conditions, the rate of calcite dissolution will be surface controlled and consequently appreciably slower than previously considered.
The distribution of macroinvertebrate communities in two Portuguese rivers
Authors: GRAÇA M. A. S. , FONSECA D. M. , CASTRO S. T.
Published: May 2006

SUMMARY. 1. The distribution of macroinvertebrates in two chemically different rivers of Central Portugal (Soure and Alva) was analysed.

2. In the Soure, a lowland, alkaline river (mean values for alkalinity, conductivity and pH, 101 mg I−1 CaCO3, 255 μS cm−1 and 7.8, respectively), a relatively high number of individuals and low diversity (mean H’= 2.27) was found. There was considerable temporal variation in the number of individuals present.

3. In the Alva, a highland, acidic river (mean values for alkalinity, conductivity and pH. 4.8 mg 1−1 CaCO3, 22 μS cm−1 and 5.7, respectively), diversity was higher (mean H'=3.41). There were large temporal changes in the number of species present, but not in the number of individuals.

4. Similarity indices and cluster analysis identified six site‐types and seventeen groups of co‐occurring taxa. Some of the taxonomic groups were characteristic of one or more sites, hut others had no strong association with a particular site. Although the rivers differed considerably in terms of physico‐chemistry, communities in the upper sections of the two rivers were more similar to each other, than to other communities in the same river. The way the samples of both rivers were clustered seems to indicate that community structure was influenced by factors associated with (1) within river longitudinal variation (e.g. substrate grain size), (2) water chemistry, and (3) seasonal variations (e.g. temperature, flow).