bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.