bluuebunny/crossref_metadata_2025 huggingface dataset:
Phosphorus inactivation in a eutrophic lake by the direct addition of ferric aluminium sulphate: impact on iron and phosphorus
Authors: FOY R. H.
Published: May 2006

SUMMARY.

Following addition of ferric aluminium sulphate (FAS) in February 1980 to a eutrophic lake, White Lough, Northern Ireland, the cycles of phosphorus (P) and iron (Fe) over 34 months were compared to those in the 18 months preceding the application.

During the summer of 1980, P release to the hypolimnion was reduced by 92% compared to 1979 but by 1982 had returned to pre‐treatment levels. Phosphorus budget calculations for the post‐ treatment period indicated that P was accumulating in the sediment at a rate sufficient to permit the recovery of P release.

In the three summers following FAS addition, Fe released into the hypolimnion increased by 56–71% compared to 1979 but this increase represented less than 10% of Fe added in the FAS.

Prior to FAS treatment, hypolimnetic Fe and P were mixed throughout the lake at overturn, resulting in high winter concentrations, but after treatment, overturn was accompanied by large reductions in the lake Fe and P content due to precipitation. As a result, overwintering P concentrations in 1980/81 and 1981/82 were in the range 31–53μg P1‐1 compared to 111–194μg P1‐1in 1978/79 and 1979/80.

The reduction of hypolimnetic P release in 1980 and 1981 and lower overwintering P had little impact on summer epilimnetic P concentrations which for 1979–82 were 51, 36, 47 and 48μg P1‐1respectively. Phosphorus concentrations in the epilimnion were raised between April and June in each year by a release of P into the epilimnion. August and September was the only period when reductions in hypolimnetic P were reflected in lower P concentrations in the epilimnion.
A dissolved oxygen budget model for Lake Erie in summer
Authors: PATTERSON J. C. , ALLANSON B. R. , IVEY G. N.
Published: May 2006

SUMMARY.

In this paper we extend a vertical mixing model of Lake Erie with an oxygen budget model. The model was tested against data gathered in the summers of 1979 and 1980 with good results, showing that it is capable of simulating vertical distributions of temperature and dissolved oxygen over relatively short time periods.

The results underline the importance of turbulent mixing in distributing oxygen throughout the water column in the Central Basin of the lake. In addition, the results indicate that production and respiration processes dominate the budget under the influence of low wind speeds, while surface fluxes dominate during periods of high wind.

Bottom mixing delays the onset of anoxic conditions at the sediment/water interface by distributing the sediment demand over the 5–6 m depth of the bottom mixed layer.
Determinants of ingestion rates in filter‐feeding larval blackflies (Diptera: Simuliidae)
Authors: HART DAVID D. , LATTA STEVEN C.
Published: May 2006

SUMMARY
1. The functional response of the filter‐feeding blackfly larva Frosimulium mixtum/fuscum was examined in laboratory experiments. We focused on the relationship between a component of the particle handling process (the cephalic fan flick rate) and ingestion rate, to determine whether ingestion rate is limited by handling‐time. The influence of food deprivation on ingestion rate and feeding efficiency also was assessed.

2. Ingestion rate rose asymptotically with increasing food availability, leveling off at a concentration of about 100 mg1−1. Satiation did not account for this plateau. Flick rate (the frequency with which larvae open and close their cephalic fans) increased in a similar fashion, though flick rate only accounted for about two‐thirds of the variation in ingestion rate.

3. A simple equation describing the components of the feeding process in blackfly larvae was developed to investigate alternate flick rate ‘decision rules’ capable of predicting relationships between food concentration, flick rate and ingestion rate. The flick rate did not follow a fixed time rule, in which larvae allow particles to accumulate in the fan for a fixed amount of time prior to retraction. For most food densities, flick rate patterns more closely approximated a fixed number rule, in which fans are retracted after a fixed number of particles accumulate.

4. Flick rate rose with increasing food concentration even after the ingestion rate had levelled off, whereas several optimal filter‐feeding models predict that filtering rate should decline as food concentration increases above this level. This predicted behavior was not observed because the number of particles ingested per flick failed to increase with increasing food concentration.

5. The efficiency of particle ingestion (number ingested × number available−1× 100) was very low (<0.1%), and declined with increasing food concentration.

6. An increase in food deprivation time prior to a feeding trial produced a significant increase in flick rate, ingestion rate and feeding efficiency. This adjustment of feeding behaviour allowed animals to replace their gut contents more quickly following longer periods of food deprivation, which agrees with the qualitative predictions of optimal digestion‐time models.
Peat and peat water chemistry of a flood‐plain fen in Broadland, Norfolk, U.K.
Authors: GILLER KENNETH E. , WHEELER BRYAN D.
Published: May 2006

SUMMARY. 1. Dominant chemical gradients in the peats of a flood‐plain fen in Broadland, Norfolk were poor‐fen (oligotrophic)  rich‐fen (minerotrophic) and freshwater  brackish water. These gradients were to some extent obscured by a complex of factors governing the concentrations of ions in the peats and peat waters.

2. The peats were almost totally organic and cation exchange capacities (CEC) varied with their macrofossil composition. Cladium mariscits L. peats had higher CEC than Phragmites communis Trin. peats of similar bulk density.

3. Amounts of dissolved and extractable N and P were very low. but total amounts of N and P were high and closely related to bulk density.

4. Large seasonal variation in concentrations of ions in the peat waters was due to dilution at times of flooding. There was strong evidence that little river water penetrated directly across the study area, contrary to classical descriptions of flood‐plain mires.

5. Amplitude of fluctuations in concentration varied between study sites although the pattern of change was similar. Fluctuations were small in poor‐fen. Sphagnum dominated sites.

6. An incursion of brackish water up river due to unusually high tides was observed, but it is likely that brackish conditions in the fens are caused by release of ions from underlying estuarine clays.
A pump sampler study of microdistribution in Walker Lake, Arizona, U.S.A.: a senescent crater lake
Authors: BLINN DEAN W. , GREEN J.
Published: May 2006

SUMMARY. 1. The seasonal microdistribution of physico‐chemical features and plankton were examined at close intervals in a high elevation (2493m) senescent crateri lake (1m deep) in the arid southwestern U.S.A.

2. The protective volcanic rim and dense growth of provided highly stable thermal conditions throughout much of the year with the thermocline frequently in the top 30cm of the water column during the summer and dissolved oxygen typically <3.0mgl−1 in surface waters and <1.0mgl−1 below 50cm.

3. The microdistribution of both phytoplankton and zooplankton was examined at close intervals (10cm) throughout the water column with the aid of a peristaltic pump.

4. Aglaodiaptomus leptopus, along with Dinobryon sertularia and certain diatom species, were largely restricted to the top 30cm, while the colonial phytoflagellate, Pyrobotrys elongata and certain euglenoids were mostly located in the anaerobic lower strata.

5. Cryptomonas obovata demonstrated subsurface maxima at various locations within the water column depending upon season.

6. The distribution of plankton was also compared during daylight and darkness on one date.
Contribution of fungal biomass to the diet of a freshwater isopod (Lirceus sp.)
Authors: FINDLAY STUART , MEYER JUDY L. , SMITH PHILLIP J.
Published: May 2006

SUMMARY. 1. The direct contribution of fungal biomass to the carbon needs of a freshwater isopod (Lirceus sp.) was measured using 14C‐labelled fungi on leaf material. 14C‐glucose was added to fungus‐inoculated leaf discs periodically throughout the growth of the fungus. Amount of label incorporated into fungal biomass, radioactivity appearing in Lirceus after feeding on labeled fungus and the standing stock of fungus were used to calculate incorporation of fungal C by the consumer.

2. Incorporation rates ranged from 0.06 to 70 ng fungal C mg wet wt isopod‐1h‐1. These rates of incorporation represent from 0.05 to 57% of C respired by the isopod.

3. Fungal C does not meet the carbon needs of this consumer and the role of fungi as modifiers of the leaf substrate may be more significant than their role as a food source.
Spatial variation of water temperature characteristics and behavior in a Devon river system
Authors: WEBB B. W. , WALLING D. E.
Published: May 2006

SUMMARY. 1. The results of 5 years of continuous monitoring of river water temperatures at seventeen stations within the Exe basin, Devon, U.K., are presented and discussed.

2. Systematic spatial variation in mean annual water temperature was evident and was strongly related to the topographic variable of elevation. Deviations from this relationship reflect local influences of vegetation shading, runoff source and channel character.

3. Considerable spatial variation in temperature extremes was also apparent, and the Exe basin differs from several other British river systems in exhibiting highest peak temperatures at downstream sites on the mainstream. Discharge from Wimbleball Reservoir exerted a significant influence on annual maxima and minima.

4. A clear seasonal cycle characterized all stations and was objectively defined by second‐order harmonic functions which varied in amplitude and phase across the study area. Marked spatial variability in the magnitude and timing of diurnal temperature fluctuations, in temperature duration curves and in accumulated temperatures was also recorded.

5. The implications of the spatial variation in thermal regime for the growth of brown trout was also investigated.
The occurrence of metacercariae of the trematode, Cyathocotyle opaca (Wisniewski), in three species of lake‐dwelling leeches
Authors: SPELLING S. M. , YOUNG J. O.
Published: May 2006

SUMMARY. 1. The leeches, Erpobdella octoculata, Glossiphonia complanata and Helobdella stagnalis, were collected at monthly intervals over a 2‐year period from a eutrophic English lake, and examined for the presence of metacercariae of the trematode. Cyathocotyle opaca.

2. Only one specimen of each of H. stagnalis and G. complanata was recorded with the parasite. Seasonal changes in prevalence levels in E. octoculata were similar for each of the three cohorts identified during the study period. Values, low in young leeches recruited in the autumn, rose slowly until the following spring, and then increased more rapidly till the autumn, when the cohort died out. Mean intensity and relative density showed similar patterns of seasonal change to that of prevalence.

There was no evidence of parasite induced mortality in E. octoculata. Attainment of sexual maturity did not differ between infected and uninfected leeches.
Gradients in the distribution of riverine benthos
Authors: SCHAEFFER DAVID J. , PERRY JAMES A.
Published: May 2006

SUMMARY. 1. Numerous hypotheses regarding the controls on species distributions in streams depend on longitudinal analyses of collections of stream organisms. Techniques for the detection of trends and for the detection of station groupings among biological collections have been widely reported, but rarely compared with each other. We have conducted an analysis of ten or eleven samples from each of thirteen stations along a stream abiotic gradient, and have compared several techniques.

2. An analysis of longitudinal distribution must first assess the existence of a gradient in biotic composition. Random skewers on species proportions were the most sensitive in demonstrating such a gradient. Q and M statistics were most useful in further describing the trend due to their additive properties; i.e. the importance of one or more stations in dictating the trend may be determined. Cluster analysis, as well as percent faunal similarity, was most efficient at isolating station groupings. Techniques such as faunal replacement and species loss calculations are generally more useful in testing hypotheses about controls on species distributions, and should be employed where potential causal factors may be isolated.
Polymixis and algal production in a tropical lake: latitudinal effects on the seasonality of photosynthesis
Authors: VINCENT W.F. , WURTSBAUGH W. , NEALE P.J. , RICHERSON P. J.
Published: May 2006

SUMMARY. 1. Phytoplankton production was measured during 1981–82 in Bahia de Puno. a large polymictic system that is part of LakeTiticaca in the tropical Andes (Peru‐Bolivia), Photosynthesis followed aweak seasonal pattern through each 12‐month cycle but the largestvariations occurrud between years.

2. The large temporal variations in productivity appeared to becontrolled by biological events rather than by the direct effeets ofseasonal or aseasonal physical processes. Major shifts in production overthe 2‐year period were attributable to the proportional abundance andactivity of N2‐fixing blue‐green algae. Production was uncorrelated withthe seasonal radiation cycle.

3. In vivo fluorescence and photosynthetic assays revealed largechanges in phytoplankton community structure over time and depth.The shifts in vertical structure were associated with changes in transparency and water column stabilily.Physiological as well as floristiceffects dictated the variations in fluorescence per unit chlorophyll a.

4. An analysis of twenty‐seven primary productivity data sets fromdifferent latitudes shtiwed that Bahia dc Puno resembled other tropicallakes in its relatively weak coupling between algal photosynthesis andseasonal variations in light. Productivity in the temperate zone correlated with the annual cycle of incoming radiation while the tropicalproduction data did not. For many of the tropical lakes, but fewtemperate lakes, the between‐month variance in primary production wassignificantly higher than the between‐month variance for incomingradiation. There was a significant positive relationship between maximum production variance explained hy light (maximum r2 for each dataset) and latitude.

5. As in many tropical lakes. Bahia de Puno experiences moderatelylarge variations in algal photosynthesis.The muted seasonal cycle of light explains only a small portion of the total variation In productivity, and other factors such as weuther‐related events are disproportionately important.
Diatom flora of an Australian river system:spatial patterns and environmental relationships
Authors: CHESSMAN BRUCE C.
Published: May 2006

SUMMARY. 1. Qualitative diatom samples from various microhabitatswere collected at fifty‐three sites on the La Trobe River. Victoria, and itstributaries in late summer and early autumn. Measurements of severalphysico‐chemical variables of likely significance to diatom distributionwere also made.

2. Principal components analysis of the physico‐chemical data showedthat the dominant environmental pattern in the river system was agradient from cool, dilute upland streams to warmer, more turbid andenriched lowland waters.

3. A total of 267 diatom species was recorded; most were cosmopolitan and Navicula and Nitzschia were the dominant genera. Clusteranalysis allowed the sampling sites to be divided into six groups on the basis of their floras. These groupings corresponded closely to flow. landuse and wastewater discharge patterns and there were clearphysico‐chemical differences between the groups. Multiple discriminant analysisfound thataltitude. temperature. biochemical oxygen demand. turbidity, non‐filterable residue, pH. major ions, phosphorus and nitrogenwere important factors in distinguishing between site groups.

4. Diatom species richness was lowest in relatively undisturbed, forested upland streams, probably as a result of nutrient limitation. Forthe catchment as a whole significantcorrelations were establishedbetween species richness and altitude, temperature, biochemical oxygendemand, turbidity. non‐filterable residue, conductivity, calcium, alkalinity, organic nitrogen and phosphorus.
Predation on leeches in a weedy pond
Authors: YOUNG JOHNSTONE O.
Published: May 2006

SUMMARY. 1. A range of sizes of Erpobdelta octoculata fL.), Glossiphonia complanata(L.) and Helobdella stagnalis(L.) were introduced to a small weeded pond harbouring invertebrate and amphibian predators. Control leeches were kept in protective cages. Subsequently, gut contents of potential predators were tested against three anti‐leech sera, using the precipitin test. Five of fifteen species tested had fed on leeches; Agabus, Pyrrhosoma, Aeshna, Sympetrum and larval Trilurus.

2. The size distributions of introduced and surviving leeches were compared. Predation pressure had been greatest on smaller leeches and this may have accounted for the observed differential mortality between leech species.

3. It is concluded that predation may cause significant mortality in leech populations in weeded ponds, with severity determined by the types and abundance of predators present.
Metabolism of a sub‐tropical low gradient black water river
Authors: EDWARDS R. T. , MEYER J. L.
Published: May 2006

SUMMARY. 1. Single‐station diel oxygen curves were used to monitor the oxygen metabolism of the Ogeechee River, a sixth‐order blackwater river in the Coastal Plain of southeastern U.S.A., over a period of 4 years. Ecosystem production (P) and respiration (R) were estimated, and P/R ratios calculated to determine the extent of autotrophy characteristic of this type of river. The potential error in oxygen metabolism caused by photo‐oxidation of dissolved organic carbon (DOC) in the water was measured and found to be minor.

2. Rates of ecosystem primary production measured were intermediate compared to other rivers, ranging from 0.49 to 13.99g O2m−2 day −1.Primary production rates were highest during the summer when water levels were low. Regression analysis indicated that water depth and light absorption by DOM were significant predictors of primary production in this river. Incident light intensities were not significantly correlated with production rate.

3. Respiration rates were unusually high, varying between 3.70 and 11.5 g O2 m−2 day − 1. System respiration also varied seasonally, but less than primary production. Rates were slightly higher in spring and summer.

4. With one exception, P/R ratios were considerably lower than l throughout the study period, indicating that the Ogeechee River was highly heterotrophic. PIR ratios ranged from 0.09 to 1.3, and averaged 0.25.

5. A carbon budget calculated for this river showed floodplain inputs were 7 times autochthonous production. Organic carbon turnover length was 690 km, considerably longer than has been reported for lower‐order rivers.
Grazing by oligochaetes and snails on epiphytes
Authors: KAIRESALO TIMO , KOSKIMIES IRMA
Published: May 2006

SUMMARY. 1. The isotope 33P was used to assess the effect of grazitig by oligochaetes (mainly Stylaria lacttstris L.) and the snail, Lymnaea peregra(Muller), on epiphytes within an Equisetum fluviatile L. stand.

2. Two 1 m2 polystyrene enclosures were set up within the emergent macrophyte zone of the lake. At the start of the experiment 33P‐solution was mixed with the water in both tanks. Algal and animal samples for 33P‐ analysis were collected during the peak occurrence of epiphytes in June.

3. Phosphorus release rates from the animals through defaecation and excretion were measured in the laboratory. The grazing rate of oligochaetes was 2.2–4.1 mg P m−2 (of bottom) d−1 of which about two ‐ thirds was released and recycled. The oligochaete density ranged from 13,400 to 20,900 m−2. The snails (25 ind. m−2) grazed 1.2‐1.5 mg P m−2d−1of whieh about a quarter was released through defaecation and excretion.

4. Daily consumption by the oligochaetes and snails corresponded to 22–45% of the average phosphorus uptake by the epiphytes.
Short‐term experimental acidification of a Welsh stream: comparing the biological effects of hydrogen ions and aluminium
Authors: ORMEROD S. J. , BOOLE P. , McCAHON C. P. , WEATHERLEY N. S. , PASCOE D. , EDWARDS R. W.
Published: May 2006

SUMMARY. 1. A soft‐water stream iti upland Wales was dosed with sulphuric acid and aluminiutn sulphate at two successive points to create sitnultaneous episodes of low pH, and low pH with increased aluminiutn. Chemical atid biological responses were measured before, during and after the episode and were compared with a reference zone.

2. The pH fell frotn ∼7.0 to 4.28 (±0.18 SD) and 5.02 (±0.10) respectively in the acid and aluminium zones. Corresponding aluminium concentrations during the episode were 0.052 g Al m−3 (±0.008) and 0.347 g Al nr3 (±0.047), the former not differing significantly from the reference zone. The concentration of cadmium rose to 0.002‐ 0.011 g Cd m−3in both treated areas, but the concentrations of other metals were unchanged.

3. In situ toxicity tests were performed with macroinvertebrates and fish. Chironomus riparius. Hydropsyche angustipennis and Dinocras cephalotes suffered no mortality. Ecdyonurus venosus, Baetis rhodani and Gammarus pulex showed up to 25% mortality in both treatment zones and further mortalities occurred after the episode. Brown trout Salmo trutta and salmon Valmo salar s howed 7–10% mortality in the acid zone, but 50–87% in the aluminium zone, where salmon had a significantly shorter LT50than trout.

4. The drift of Simuliidae increased during treatment in both acid and aluminium zones. Drift densities of Dixa puherula, Protonemura meyeri, Ephemeralla ignita and Dicranota sp. increased in the aluminium zone. The most pronounced response was by Baetis rhodani in the aluminium zone where drift density increased by ×8.4 during the episode.

5. Baetis rhodani was the only taxon to show a significant decline in benthic density during the treatment, and then only in the aluminium zone. Drift could account for most of the losses.

6. The depth distribution of invertebrates in the substratum differed between zones following treatment. More individuals were present at the surface of the reference zone (1287 m−2±747) than at the surface of the other zones (<400 m−2); however, densities at greater depths were similar. These patterns probably reflected differences prior to the treatments.
Faunal and chemical dynamics of some acid and alkaline New Zealand streams
Authors: COLLIER K. J. , WINTERBOURN M. J.
Published: May 2006

SUMMARY 1. Water from acid (pH 4.3–5.7), brown water streams was low in alkalinity (0–2.3 g m−3 CaCO3) and conductivity (2.5–4.1 mS m−1) but contained relatively high concentrations of dissolved organic carbon (6.6–16.3 gm−3). In contrast, alkaline (pH 6.6–8.0), clearwater streams had high CaCO3 (12.6–57.6 g m−3) and conductivity (3.7–22.3 mS m−1) but low dissolved organic carbon concentrations (0.3–4.7 g m−3).

2. Total reactive aluminium (Al) concentrations were high in acid streams (123–363 mg m−3) but never exceeded 84 mg m−3 in alkaline streams. Acid‐soluble and organic monomeric Al were the major Al species in the acid streams (31–168 and 84–178mg m−3, respectively). Concentrations of toxic inorganic monomeric Al were low in all streams (<50mg m−3).

3. Sixty‐four invertebrate taxa were collected from the alkaline streams compared to forty‐seven from the acid sites. Numbers of taxa in specific insect orders were similar at all sites, however. Benthic faunas at most sites were dominated by the mayfly Deleatidium sp. and chironomids.

4. Overall, mean densities of benthic invertebrates were 2.4–4.8 times higher in alkaline streams than acid streams. No seasonal patterns of abundance were evident at any site.

5. Temporal variability of invertebrate densities was correlated with stream channel stability such that fluctuations in densities declined as stability increased.

6. Sources of dissolved organic carbon and aluminium in acid, brown water streams are discussed. We suggest that changes in the food supply available in acid streams account for the depauperate faunas found there.
Gut passage and insect grazer selectivity of lotic diatoms
Authors: PETERSON CHRISTOPHER G.
Published: May 2006

SUMMARY 1. Grazing experiments were conducted in a small Kentucky stream to determine if epilithic diatom taxa differed in susceptibility to grazing by the larval caddisfly, Neophylax autumnus, and whether ingested taxa varied in digestibility. Live/dead ratios of diatom cells from N. autumnus faecal material were compared with live/dead ratios of cells taken from adjacent epilithic habitats to determine diatom digestibility. Selectivity was studied by comparing relative abundances of diatom taxa on substrata with the relative abundances of these taxa in grazer faecal material.

2. 73% of the diatoms collected from epilithic habitats contained intact chloroplasts and were characterized as live cells. Only 42% of diatoms eliminated in caddisfly faeces were living. The five dominant diatom taxa did not differ in digestibility. Elimination of viable diatoms in grazer faecal material may contribute to diatom drift in streams, and thus supply individuals for downstream recolonization. Failure to document live/dead ratios of diatoms from grazed substrata can lead to overestimation of the digestibility of taxa and misinterpretation of results.

3. Grazers in this investigation were more successful at ingesting large, high‐profile diatom taxa (i.e. Cymbella, Meridion and Gomphonema) and less able to remove small, adnate forms (Achnanthes minutissima). Such 'selectivity’may be one mechanism by which A. minutissima maintains dominance in this system.
Alterations in periphyton characteristics due to grazing in a Cascade foothill stream
Authors: JACOBY JEAN M.
Published: May 2006

SUMMARY 1. In situ experiments were conducted in a Washington stream to quantify the effects of grazing by a caddisfly larva, Dicosmoecus gilvipes (Trichoptera: Limnephilidae), and a mayfly nymph, Nixe rosea (Ephemeroptera: Heptageniidae) on periphyton biomass, structure, and function.

2. Dicosmoecus gilvipes reduced periphyton biomass from 92 mg m−2(as mean chlorophyll a) to 33 mg m−2. The grazed assemblage was less diverse and composed of smaller, closely attached diatoms, whereas there was a higher proportion of overstorey and filamenttius algae in the diverse, ungrazed periphyton.

3. By maintaining the periphyton community as a thin layer of diatoms, grazing by D. gilvipes appeared to promote a healthier, more vigorous community relative to the ungrazed mat, which became senescent in the latter part of the experiment.

4. Nixe rosea had little measurable effect on any characteristics of the periphyton measured. These nymphs apparently preferred small diatoms, which resulted in only micro‐scale alterations in periphyton characteristics that were difficult to detect.

5. Biomass accrual of ungrazed and grazed periphyton was described by the logistic growth equation. Loss of biomass due to grazing by D. gilvipesor to senescence and sloughing were incorporated in the model to account for changes in grazed and ungrazed periphyton. respectively. Proposed mechanisms which described biomass accumulation were largely sup ported by model predictions.
Growth and food choice by two species of limnephilid caddis larvae given natural and artiflcial foods
Authors: PRITCHARD G. , BERTÉ S.B.
Published: May 2006

SUMMARY 1. Larvae of the caddisfly Limnephilus externus grew faster than those of Nemotaulius hostilis in a permanent pond in southern Alberta.

2. We investigated whether this was due to more efficient food processing by L. externus, whether their growth coincided with high environmental temperatures, or whether they had the ability to choose and exploit higher quality food.

3. Of five foods used, protein content was highest in wheat flakes, similar in alder, bur‐reed and willow leaves, and lowest in the moss Leptodictyum.

4. Both species grew faster and survived better on the wheat flakes, but there was no statistically significant difference between species on the same food when reared at 4 or 8°C in the laboratory.

5. At 16°C L. externusgrew better than N. hostilis when fed wheat, but N. hostilis survived better on alder. Both species had higher survival and growth rates per day‐degree at 8 and 4 than at 16°C.

6. Thus, faster growth rates of L. externtus in the field appear to be due simply to higher temperatures during the larval growth period. Indeed, N. hostilis had a significantly higher growth rate per day‐degree in a field experiment.

7. In food preference experiments, L. externus chose wheat first, moss second, alder third, and willow last; N. hostilis chose alder first, bur‐reed second, moss third, and wheat last.

8. Protein content, leaf texture, microbial conditioning, and an interaction between larval behaviours selecting for food quality and case materials, are potential factors that influence‘food preference’results.
Macro‐floral assemblages in upland Welsh streams in relation to acidity, and their importance to invertebrates
Authors: ORMEROD S. J. , WADE K. R. , GEE A. S.
Published: May 2006

SUMMARY 1. Macro‐flora (angiosperms. bryophytes and macroscopic algae) and macroinvertebrates were sampled in 1984 at eighty‐eight sites on soft‐water streams in upland Wales. Assemblage patterns were related to stream chemistry using TWINSPAN, DECORANA and multiple discriminant analysis.

2. Floral assemblages could be related most strongly to pH and aluminium concentration, with Scapania undulata, Nardia compressa and filamentous chlorophytes characterizing streams of mean pH5.2–5.8, whilst Fontinalis squamosa occurred mostly at pH 5.6–6.2 and Lemanea at pH 5.8–7.0. We propose an indicator system based on thesetaxa.

3. Assemblages of invertebrates and flora concorded highly significantly, sites with Scapania and Nardia holding impoverished faunas. Because some acid sensitive invertebrates (e.g. Ecdyonurus and Ancylus) can feed from acid tolerant plants (e.g. Scapania), we hypothesize that they are restricted physiologically from acid streams.
A quantitative diving survey of benthic vegetation and fauna in Lake Kariba, a tropical man‐made lake
Authors: MACHENA CECIL , KAUTSKY NILS
Published: May 2006

SUMMARY. 1. The biomass distribution of submerged vascular vegetation and benthic fauna were investigated by diving in Lake Kariba. The vegetation was well correlated with transparency of the water. Maximum biomass (1400 g dryweight m−2) and a depth penetration of 6 m were found in areas little influenced by river inflow, while these were only 110 g m−2 and 2 m, respectively, in the basin receiving water from the Zambezi river.

2. The lake is mesotrophic‐oligotrophic. The total biomass for the lake was 101,000 tons dryweight of rooted vegetation composed of Lagarosiphon ilicifolius Oberm. (52%), Najas pectinata (Parl) Magnus (33%), Vatlisneria aethiopica Frenzl (11%), Ceratophyllum demersum L. (3%) and Potamogeton octandrus L. (0.5%). Average plant biomass for the potentially colonizable depth zone of 0‐12 m and for the total lake amounted to 79.9 g m−2 and 18.8 g m−2, respectively.

3. The distribution of the benthic fauna generally followed that of the vegetation. The total animal biomass of 118,840 tons dryweight. including shells, consisted of mussels (95.8%), snails (4.1%) and insect larvae (0.1%). Four species of mussels were found: Caelatura mossambicensis (von Martens) (81% of mussel biomass), Corbicula africana (Krauss) (9%). Mutela dubia (Gmelin) (5%) and Aspatharia wahlbergii (Krauss) (5%). Among the snails Melnoides tuberculuta (Müller), Cleopatra spp. and Bellamya capillata (Frauenfeld) dominated.

4. The average animal biomass was high compared to most other lakes perhaps due to lack of predators. For the colonizable 0‐12 m depth interval and the total lake it was 96.2 g m−2 including shells (15.0 g m−2 shell‐free dryweight) and 22.6 g m−2 including shells (3.4 g m−2 shell‐free dryweight). respectively. Biomass of plants and animals was even higher prior to the recent lowering of the water level by 7 m, which was estimated to have stranded 84,000 tons of mussels on the shore.
Tropical zooplankton: phenotypic and spatial analyses of polymorphic Ceriodaphnia cornuta (Crustacea: Cladocera)
Authors: MORT MONA A. , KERFOOT W. CHARLES
Published: May 2006

SUMMARY. 1. The predation‐balanced polymorphism of Ceriodaphnia cornuta (a small‐eyed horned form and a large‐eyed unhorned form) in Lake Gatun, Panama, is re‐examined approximately 12 years after the original study (Zaret, 1972a). We consider morphological variability, distribution and fecundity of the population inhabiting Laboratory Bay.

2. The two morphological characters emphasized by Zaret, eye size and horn length, are studied in detail. The C. cornuta population exhibits wide, yet continuous variation; coefficients of variation are 28% or eye diameter and range from 114% to 136% for horn and spine lengths. Phenotypic variation in the population is characterized by: (1) negative correlations between spine lengths and eye size; (2) positive correlations among spines from different body regions (anterior horn, lateral spines, and tail spine); and (3) weak correlations between body length and spine lengths.

3. While the horned and unhorned forms continue to coexist in Laboratory Bay. the frequencies of horned forms have increased in the open water areas since the time of the original study. The increase in horned form frequencies may be due to changes in fish predation intensity. Did vertical distribution patterns of the forms remain very similar to each other.

4. In contrast to previous laboratory findings, egg ratio calculations from field samples revealed similar clutch sizes for the horned and unhorned forms. The egg development time of the horned form, however, was found to be approximately 30% longer than that of the unhorned form, perhaps because of increased moulting difficulties produced by the presence of spines.
Individual vulnerability to predation: the effect of alternative prey types
Authors: JEFFRIES MICHAEL
Published: May 2006

SUMMARY. 1. Many examples of predator‐prey interactions from freshwaters suggest that apparent predator preferences result more from the relative vulnerabilities of prey than any positive choice by the predator.

2. The rank order of vulnerability of seven invertebrate prey to nine invertebrate predators was measured in the laboratory. The ranks were used as a measure of relative vulnerability.

3. The vulnerability of individuals of Simocephalus vetulus (Muller) (Crustacea: Cladocera) to predation by Enallagma cyathigerum (Char‐pentier) (Insecta: Odonata) and Notonecta glauca L, (Insecta: Hemiptera) was investigated in the presence of alternative prey of differing relative vulnerabilities, based on the rank order measures.

4. With E. cyathigerum, vulnerability of individual S. vetulus depended greatly on the relative vulnerability of other prey types available. With N. glauca the intrinsic defences of S. vetulus were very effective.

5. The importance of relative prey vulnerability is discussed with particular reference to small habitats with marked annual species turnover.
Submerged aquatic macrophyte biomass in relation to sediment characteristics in ten temperate lakes*
Authors: ANDERSON M. ROBIN , KALFF JACOB
Published: May 2006

SUMMARY. 1. This study links maximum biomass from eighteen aquatic macrophyte communities in the Eastern Townships of Quebec, Canada, to sediment characteristics: chemically exchangeable nitrogen, phosphorus and potassium, per cent organic matter, water content and texture, and to biotic variables: number of species and depth of maximum biomass.

2. Total biomass was positively and significantly related to sediment potassium content and to sediment texture.

3. Sediment nitrogen and potassium levels are correlated in the spring but not at the end of the growing season.

4. It appears that sediment potassium is a surrogate variable for the availability of sediment nitrogen which has been shown to limit aquatic macrophyte growth in this area.
Decay rates of autumn and spring leaf litter in a stream and effects on growth of a detritivore
Authors: GARDEN ANNE , DAVIES RONALD W.
Published: May 2006

SUMMARY. 1. Differences in decay rates of autumn and spring balsam poplar (Populus balsamifera L.) leaf litter input to a stream and their effects on a lotic detritivore Tipula commiscibilis Diane were investigated.

2. Autumnal leaf litter decay rates were significantly greater than spring decay rates despite higher initial quality of spring leaves. Reduced spring/summer decomposition rates were the result of decreased microbial activity and biomass, and significantly lower numbers, kinds and biomass of macroinvertebrate detritivores.

3. Growth of the detritivore Tipula commiscibilis was significantly lower when fed spring leaves indicating that they were a poorer quality food source than autumn leaves.

4. Lower numbers of detritivores coupled with reduced leaf quality resulted in lower leaf litter decay rates characteristic of spring/summer.
Acidification of three moorland pools in The Netherlands by acid precipitation and extreme drought periods over seven decades
Authors: VAN DAM HERMAN
Published: May 2006

SUMMARY. 1. Relations between acidification by atmospheric deposition, water depth and the occurrence of dry summers in this century, as well as their effects on chemistry, macrophytes and diatoms in three moorland pools, are described.

2. Direct observations and biological data indicate a decrease of pH by c. 0.5 unit over a period of seven decades in a pool where 20% of the bottom desiccates in extremely dry years, and 2 pH units over the same period in a pool where 70% of the bottom is exposed to the atmosphere in such years.

3. Acidification promotes the growth of Juncus bulbosus L., Sphagnum and the acidobiontic diatom Eunotia exigua (Bréb.) Rabenh. and suppresses the growth of isoetids (e.g. Lobelia dortmanna L.) and of acidophilus and circumneutral diatoms. Also the acidobiontic Frustulia rhomboides var. saxonica (Rabenh.) Toni and Navicula subtilissima Cleve, characteristic of humic waters, decline by acidification.

4. In two pools where more than half of the bottom desiccated in 1976, observed concentrations of sulphate were highest in 1977–78 and decreased later on. Juncus bulbosus had a maximum in 1977–80. Eunotia exigua became the dominant diatom after 1976 and decreased after 1981 in the pool with the shortest residence time (3 years).

5. In desiccating pools the long‐term decrease of pH is apparently much larger than in softwater lakes in Scandinavia and North America. During the last 50 years, pH dropped rapidly after dry summers, probably due to oxidation of sulphur and nitrogen compounds which were originally derived from the atmosphere, reduced and stored in the sediments. Rapid falls in pH were followed by an increase, presumably due to alkalinity production during sulphate reduction and denitrification.
Preliminary empirical models of the historical and future impact of acidification on the ecology of Welsh streams
Authors: ORMEROD S. J. , WEATHERLEY N. S. , VARALLO P. V. , WHITEHEAD P. G.
Published: May 2006

SUMMARY 1. We describe a preliminary approacb to modelling the impact of acidification on the ecology of two Welsb streams. Output from the hydrochemical Model of Acidification of Groundwaters in Catchments (MAGIC) was used to drive empirical models which predicted brown trout Salmo trulta (L.) survival, trout density and invertebrate assemblage type. The models were used for hindcasts between 1844 and 1984 under conifer forest and moorland conditions. Forecasts involved each of these land uses with sulphate deposition either continued at 1984 levels or reduced by 50%.

2. Trout survival times and trout densities in the models declined markedly between 1844 and 1984. The most severe decline occurred under simulated forest, where high aluminium concentration led to the virtual elimination of trout in both streams.

3. In forecasts, only in simulated moorland with sulphate deposition reduced by 50% of 1984 levels, was further decline in trout population retarded. There was no marked recovery in trout density under any of the conditions examined.

4. Invertebrate assemblages in streams during the nineteenth century may have differed from those now existing in nearby moorland streams which are presently circumneutral. Past chemical conditions were unusual (<3mg 1−1 total hardness, but pH >5.7 and low aluminium) by present‐day standards, and were outside the range of the invertebrate model until ‐1940.

5. Between the 1940s and 1984 there was no change in invertebrate fauna under the moorland scenario despite some acidification. However, simulated forest advanced the appearance of the most impoverished assemblage type, which did not recover in spite of reduced deposition.

6. We discuss several uncertainties with the models in their present form, but suggest some methods for their testing and validation.
Growth of macrophytes and ecosystem consequences in a lowland Danish stream
Authors: SAND‐JLNSEN KAJ , JEPPESEN ERIK , NIELSEN KURT , VAN DER BIJL LILLIAN , HJERMIND LUISE , NIELSEN LISBETH WIGGERS , IVLRSLN TORBEN MOTH
Published: May 2006

SUMMARY. 1. The River Suså is a small, nutrient‐rich stream situated in an open landscape with clayish subsoil under intensive cultivation. Discharge was variable daily and seasonally due to low groundwater input. Above‐ground development of submerged macrophytes was restricted to late May to November, when water velocity and depth were low. Dominant macrophytes were rooted Potamogeton pectinatus and Sparganium emersum and unrooted Cladophora. Biomass development was closet) related to light availability.

2. Growth rates of macrophytes were linearly related to light availability when self‐shading was accounted for. Potamogeton pectinatus grew rapidly m May‐June, concentrated the biomass at the water‐surface during July‐August, and then declined exponentially when the shoots became basally senescent. Sparganium emersum had linear, flexible leaves that were continuously replaced from a basal meristem. Sparganium emersum was less susceptible to high water velocities than Potamogeton pectinatus and the biomass declined later and at lower rates during autumn. Sparganium emersum also regrew after culling that left its meristem intact in the sediment. Unrooted Cladophora developed a high biomass during sunny periods and subsequently disappeared at high discharges. The summer biomass of rooted macrophytes was greater in years with high summer discharge, whereas the biomass of Cladophora and of the epiphytic microbial community was lower due to scouring.

3. Submerged macrophytes played a key role in structure and functioning of the ecosystem. They reduced water velocities two to four fold during summer and promoted extensive organic sedimentation. The biomass of benthic diatoms declined parallel to increased macrophyte shading and sedimentation. In addition, submerged macrophytes formed a large substratum for macroinvertebrates and for a microbial community.
Experimental colonization of sand, gravel and stones by macroinvertebrates in the Acheron River, southeastern Australia
Authors: DOEG T. J. , MARCHANT R. , DOUGLAS M. , LAKE P. S.
Published: May 2006

SUMMARY. 1. The contribution of drift to macroinvertebrate colonization was studied over 10 days using pairs of substratum‐filled trays, one suspended above the streambed (and thus able to be colonized by drift only) and one buried flush with the streambed (and thus open to colonization from all directions). Trays were filled with sand, gravel or stones.

2. Colonization of sand‐filled trays was rapid, being completed within 24h (i.e. no subsequent change in numbers of individuals per tray); colonization of gravel or stone‐filled trays was not completed by the end of the experiment.

3. Drift contributed an average of 86% of the colonizing fauna of the sand‐filled trays, 36% of the fauna of the gravel‐filled trays and 25% of the fauna of the stone‐filled trays. The low contribution of the drift to the gravel and stones is at odds with some studies which, using similar techniques, suggest that drift is the primary source of colonizing individuals.

4. Most individual species showed low contributions by drift to colonization, with the majority having contributions under 66%.

5. Distinct differences were noted between the fauna colonizing the sand‐filled trays and those colonizing the gravel or stone‐filled trays (which were similar).

6. Several species common in the drift were rare in the colonizing fauna and several species which were common colonizers were absent or rare in the drift.
The distribution and habitat preference of ostracods (Crustacea: Ostracoda) in a coastal sand‐dune lake, Loch of Strathbeg, north‐east Scotland
Authors: BENZIE JOHN A. H.
Published: May 2006

SUMMARY. 1. Ostracods were a numerically abundant component of the benthos >0.1 mm in size (up to 20% of the total) in the Loch of Strathbeg.

2. Distinct assemblages of species were associated with some habitats: Cypridopsis vidua (Müller) and Herpetocypris reptans (Baird) with Eleocharis palustris (L.) beds; Cypria uphtalmica (Jurine), Candona Candida Müller and Cypria exsculpta (Fischer) with Phragmites communis Trin. beds; and Limnocythere inopinata (Baird) with open sand. In contrast, no distinct ostracod assemblage was associated with submerged beds of Chara aspera Detharding, or Myriophyllum spicatum (L.).

3. The number of ostracod species and ostracod diversity increased from open sand through macroalgal and submerged macrophytes to emergent macrophyte habitats and was associated with increasing number of types of detritus.

4. Laboratory experiments suggested that substratum particle size played a dominant role in determining the distribution of L. inopinata. This species preferred sandy sediments. The distributions of both H. reptans and C. vidua were affected by food supply and H. reptans also preferred fine‐grained sediments. The absence of these taxa from some habitats where food supply and sediment particle size conditions were suitable suggested that unmeasured factors played a role. A possible predatory exclusion of H. reptans from such habitats was indicated by a negative association of this species with a predatory mite.
Biomass and oxygen dynamics of the epiphyte community in a Danish lowland stream
Authors: SAND‐JENSEN KAJ , BORG DANNA , JEPPESEN ERIK
Published: May 2006

SUMMARY. 1. We examined the abundance and oxygen metabolism of epiphytic organisms on the dominant macrophyte, Potamogeton pectinatus, in headwaters of the eutrophic River Suså. Microbenthic algae were abundant in the stream during spring and macrophytes during summer.

2. The low macrophyte biomass in spring supported a dense epiphyte cover whereas the high macrophyte biomass during summer had a thin epiphyte cover of 10–100‐fold lower abundance per unit area of macrophyte surface. The epiphyte community was dominated by microalgae in spring and by heterotrophs, probably bacteria, during summer. This seasonal shift was shown by pronounced reductions of the chlorophyll a content (from 2–3% to 0.1–0.7% of organic DW), the gross photosynthetic rate (from 20–85 to 3–15 mg O2, g‐1 organic DW h−1) and the ratio of gross photosynthesis to dark respiration in the epiphyte community (from 5–18 to 1). The reduced contributions of epiphytic microalgae correlated with reduced light availability during summer.

3. Both the density and the photosynthetic activity of epiphytic algae were low on a stream area basis relative to those of microbenthic algae and macrophytes. Rapid variations in water velocity and extensive light attenuation in water and macrophyte stands probably constrained the development of epiphytic algae. The epiphyte community was more important in overall stream respiration, contributing c. 10% to total summer respiration and c. 20% to summer respiration within the predominantly heterotrophic microbial communities on sediments and macrophyte surfaces.