bluuebunny/crossref_metadata_2025_split huggingface dataset:
Regulation of algal biomass in a small lowland stream: field experiments on the role of invertebrate grazing, phosphorus and irradiance
Authors: KJELDSEN KARINA 
Published: November 2003

1. Field experiments were undertaken in a small Danish lowland stream to study the role of invertebrate grazing, phosphorus concentration and irradiance in the regulation of benthic algal biomass on stones.2. Algal biomass was regulated by invertebrate grazing. The gastropod Ancylus fluviatilis prevented algal biomass build up in early spring at a density of about 900 ind. m–2, and reduced algal biomass to very low levels during the algal growth period at a density of about 6000 ind. m–2. Grazing pressure therefore might regulate the magnitude of peak algal biomass in Gelbæk stream, a finding in agreement with earlier field observations.3. As phosphorus enrichment to around 152 μg l–1 during the period when irradiance was not limiting did not result in any further increase in algal biomass, it can be concluded that algal growth in spring was not controlled by phosphorus limitation.4. Algal biomass development differed significantly in a shaded and in a non‐shaded reach of the stream. Only very low algal biomass accumulation was evident in the shaded reach, while in the non‐shaded reach an algal biomass peak of about 800 mg chlorophyll m–2 was evident after 6 weeks of colonization. The shaded reach represented the light condition in Gelbæk stream after leaf proliferation of the overhead canopy and high bank vegetation. The findings therefore suggest that irradiance available to the algal community after shading from riparian vegetation prevents further algal biomass increase and hence determines the timing of peak algal biomass in the stream.5. The irradiance experiment also suggests that if not regulated by invertebrate grazing or shading by an overhead canopy in the summer, then the magnitude of peak biomass in Gelbæk stream will be regulated by self‐shading in the algal community.6. These field experiments support theories, derived from laboratory experiments and field studies, that regulation of algal biomass is a complex interaction of top‐down and bottom‐up mechanisms.
The effects of feeding regime on the growth and reproduction of the medicinal leech Hirudo medicinalis
Authors: DAVIES RONALD , McLOUGHLIN NATHAN 
Published: November 2003

1. The feeding frequency, the size of meals, the number of meals required to attain reproductive maturity and the number of meals taken between iteroparous reproductive bouts were determined in the laboratory under optimal conditions for the medicinal leech Hirudo medicinalis fed exclusively on mammalian (bovine) blood. In addition the number of bouts of reproduction and the numbers of cocoons and hatchlings per cocoon produced were determined.2. The average time for H. medicinalis to reach reproductive maturity at 20°C was 289 days, at an average wet biomass of 8143 mg with two–nine separate bouts of cocoon production. The number of meals to first reproduction was 8.9 (mean meal size of 3066.7 mg), with a significant correlation between total mass of blood ingested and the numbers of reproductive bouts and number of cocoons produced. Mean lifetime cocoon production per individual was 12.43, with 3.9 hatchlings per cocoon.3. The significant positive relationships between ingestion, fecundity and developmental rate observed support the hypothesis that declining abundances of field populations of H. medicinalis are the result of lower available energy for growth, reflecting leeches now feeding predominantly on amphibian blood of lower energetic value than mammalian blood.
Possible impact of mild winters on zooplankton succession in eutrophic lakes of the Atlantic European area
Authors: ADRIAN RITA , DENEKE RAINER 
Published: November 2003

1. We report on a long‐term study (1975–94) of water temperatures and plankton in a eutrophic lake (Heiligensee, Berlin, Germany). Using a phenomenological approach, we use historical data to infer how an increase in air temperature has influenced a natural zooplankton community.2. Air temperatures in Berlin showed a significantly rising trend between 1975 and 1994. Mean winter air temperatures in the last 8 years always exceeded the long‐term mean.3. A rising trend was also found for April water temperature, which increased significantly beginning in 1988–89. An increase of 2.58°C in the last 21 years was recorded using a linear model. A significantly decreasing trend was found in June but no trend was noted for the other summer months.4. Phytoplankton composition shifted from a dominance of diatoms and cryptophytes during winter and spring in the 1980s towards a dominance of cyanobacteria in 1990–94.5. The dominant zooplankton species in spring shifted in recent years from the large‐bodied Daphnia galeata to the smaller D. cucullata. Cyclops kolensis, previously the only invertebrate predator during winter, decreased in abundance while C. vicinus, usually present during spring and autumn, increased in abundance and was numerous during winter, a season passed in diapause in the earlier years.6. Because direct and indirect temperature effects are species specific, we put forward the hypothesis that zooplankton species, rather than functional groups, are the nexus between environmental stress, such as rising air temperatures, and ecosystem changes.
Effects of CO2 enrichment on mineral accumulation and nitrogen relations in a submersed macrophyte
Authors: TITUS JOHN , ANDORFER JOHN 
Published: November 2003

1. Six‐ to eight‐week greenhouse experiments with independent control of pH and dissolved CO2 evaluated the potential for CO2 enrichment to stimulate the accumulation of Al, Fe, P and N in shoots of Vallisneria americana, particularly at pH 5. These minerals were provided only as they occurred in natural lake sediments.2. The effect of CO2 enrichment at pH 5 v pH 7.3 on growth and tissue N concentration was also determined.3. CO2 enrichment at pH 5 effected 5.5‐ and 7‐fold increases in total shoot accumulation of Al and Fe, respectively. In a two‐way factorial experiment, CO2 enrichment yielded 6‐ to 11‐fold greater total shoot P accumulation in plants grown on less and more fertile sediments, respectively.4. In a three‐way factorial experiment, CO2 enrichment stimulated Vallisneria growth, especially at pH 5, and resulted in a 31–58% reduction in tissue [N] for different pH × sediment combinations. These are greater reductions than previously reported. It also increased total shoot N accumulation up to 6‐fold, and there were significant interactions with pH and sediment source: the CO2 enrichment effect on shoot N accumulation was greater at pH 5 than at pH 7.3, and it was greater with the more fertile sediment at pH 5.5. Water chemistry (pH and/or [CO2]) and sediment fertility thus both indirectly influenced the accumulation of sediment‐derived minerals in macrophyte shoots within the water column.
Temperature effects on bioconcentration of DDE by Daphnia
Authors: NAWAZ SHAJITHA , KIRK Kevin 
Published: November 2003

1. Lake temperatures vary with season, latitude, elevation and as a result of thermal pollution. In addition, lake temperatures may increase with global warming. Radiotracer experiments were conducted to determine the effects of temperature on the bioaccumulation of lipophilic organic contaminants by zooplankton. Daphnia pulex were exposed to 14C‐labelled DDE, a stable metabolite of the organochlorine pesticide DDT, in particle‐free water for 24 h. An increase in temperature from 5 to 25 °C resulted in a 314% increase in bioconcentration factor (the ratio of contaminant concentration in the organism to contaminant concentration in the water).2. To mimic the fluctuating temperatures experienced by zooplankton during diel vertical migration, we conducted experiments in which animals were exposed to 25 °C for 12 h in the light, then 15 °C for 12 h in the dark. Exposure to this fluctuating temperature regime for 48 h resulted in a 27–33% increase in bioconcentration factor relative to a constant 20 °C control.3. Live animals accumulated more than twice the amount of DDE than freshly killed animals, indicating that the activity of the organism is important in bioconcentration. This finding sheds light on the possible mechanisms for the increase in bioconcentration at higher constant temperatures. Daphnia pump more water through their branchial chambers at higher temperatures. Thus, if the thoracic limbs are an important site of contaminant uptake, then animals are exposed to more contaminant molecules at higher temperatures. Other possible mechanisms include changes in the thickness of the diffusive boundary layer and changes in cell membrane permeability.
Influence of side‐arms on aquatic macroinvertebrate drift in the main channel of a large river
Authors: CELLOT BERNARD 
Published: November 2003

1. Drift from lotic and lentic side‐arms to the main channel was studied over 2 years in different sections of the Upper Rhône River (France). The hypothesis of an influence of drift on the main channel was tested by measuring drift in the main river at sites downstream and upstream from the confluences with two side‐arms, as well as in the two side‐arms themselves.2. Side‐arms were differentiated from the main channel by having a typical composition of macrofauna with a high propensity to drift, particularly in spring–summer and during spates. Drift densities in side‐arms averaged more than twice those measured in main channel sites, but these inputs did not significantly affect taxon richness and total drift density in the main channel.3. Nevertheless, some taxa found in the more lotic of the two side‐arms were more abundant downstream of the confluence than upstream, indicating that they had drifted into the main channel; no such direct effect was found throughout the sampling period for the more lentic side‐arm. The densities of two competitive filter feeders (Hydropsyche and Simuliidae) were significantly higher below the confluences than above, suggesting that side‐arms were also contributing substantial amounts of seston to the main channel.4. Therefore, side‐arms influence the community structure of drifting macroinvertebrates in the Upper Rhône River, both directly through immigration—depending on the degree of connectivity to the river—and indirectly via food supply.
Total metal burdens in the freshwater amphipod Gammarus fasciatus: contribution of various body parts and influence of gut contents
Authors: AMYOT MARC , PINEL‐ALLOUL BERNADETTE , CAMPBELLS PETER , DESY JOEL 
Published: November 2003

1. The distribution of trace metals among body parts of the freshwater amphipod Gammarus fasciatus was investigated and the effect of depuration on the total body burden was assessed.2. Concentrations of Cr, Fe, Mn and Ni were one order of magnitude higher in the gut contents than in the various body parts, accounting for 40–72% of the total body burdens of amphipods. Depuration caused a decrease of total metal concentrations of 35–88%.3. Levels of Cd and Cu were higher in the hepatopancreas than in other body parts, whereas levels of Zn were relatively constant throughout the body. For Cd, Cu and Zn, depuration had no effect on mean body concentrations.4. For Pb, an important fraction of the total body burden was associated with the exoskeleton; depuration caused a decrease in Pb body concentrations.5. Regression between amphipod metal concentrations before and after depuration is a potential tool for correcting for the effect of gut contents. This correcting method was found to be promising for Cd, Cu, Mn and Zn, with R2 varying between 0.66 and 0.98. It was less efficient for Cr, Fe and Pb, and was useless for Ni.
Effects of experimentally enhanced flows on fishes of a small Texas (U.S.A.) stream: assessing the impact of interbasin transfer
Authors: MATTHEWS WILLIAM , SCHORRS MARK , MEADOR MICHAEL 
Published: November 2003

1. Completion of a large interbasin water transfer system in northern Texas (U.S.A.) provided the opportunity to test the effects of pre‐planned, experimental increases (≈×30) in flow on the fish fauna of a small, low‐gradient, natural stream that was included as part of the conveyance system. Water from Lake Texoma (Red River basin) was pumped via a 16‐km pipeline to the headwaters of Sister Grove Creek (Trinity River basin), which then carried the donor water 50 km downstream to Lake Lavon.2. Baseline (pre‐transfer) data on the composition of fish assemblages at seven stations on the creek or at its confluence with the receiving reservoir were collected monthly for 3 years, and similar data were collected for 2 years during and after trial flows of Lake Texoma water to Sister Grove Creek. We also documented fish abundance at five creek stations immediately before and after three trial flow periods of 10–14 days each in summer and autumn.3. Multivariate analysis of all routine monthly samples over the 5‐year pre‐ and post‐transfer period showed moderate changes in the fish fauna of the creek after initiation of the trial flows. Samples taken within a week before and after the artificial high flows showed little overall change in abundance of individual fish species, but at some stations the quantitative or qualitative change in composition of the local assemblage was substantial.4. The trial flows lasted 2 weeks or less. Long‐term effects of water transfer on the fish fauna of Sister Grove Creek can only be determined after the conveyance system goes into normal operation, with periods of artificial flow of longer duration.
Instream habitat use by blue duck (Hymenolaimus malacorhynchos) in a New Zealand river
Authors: COLLIER KEVIN , WAKELIN MICHAEL 
Published: November 2003

1. The feeding habitat of a river specialist, blue duck (Hymenolaimus malacorhynchos (Gmelin 1789): Anatidae), was characterized in terms of water depth and velocity on eight occasions over a 13‐month period in a river in the central North Island of New Zealand using video to record activity and relocate feeding sites.2. Of the five feeding activities identified (‘pecking’, ‘grazing’, ‘head‐dipping’,up‐ending’ and ‘diving’), adult blue duck used mostly head‐dipping (> 60% of feeding events on all dates), although diving or grazing from submerged surfaces of exposed boulders comprised major proportions of feeding behaviour (up to 33%) on occasions. Variations in feeding behaviour between dates partly reflected changes in antecedent flow conditions and the annual cycle of the birds.3. Grazing and diving occurred in significantly faster water (mostly 0.3–0.45 m s–1) and at significantly different depths (mean = 0.10 and 0.55 m, respectively) than head‐dipping (0.20 m depth and 0.28 m s–1 velocity). Adult feeding depths and velocities at four sites on different dates averaged 0.20 m and 0.31 m s–1, respectively. Most feeding by 3–4‐week‐old ducklings occurred over a similar distribution of water velocities to adults but over a wider range of depths.4. Adult birds fed in significantly shallower and lower velocity water than was available on the two dates that comparisons could be made. Ducklings also fed over a slower range of water velocities but were not selective in terms of water depth.5. Energetically more expensive search methods were employed at times of high apparent energy demand to access flow microhabitats where larger bodied prey were more likely to be encountered.6. These data indicate that, like other aquatic organisms, river birds can be influenced by basic hydraulic elements of river flow, but show at the same time that adult blue duck can accommodate variable lotic environments efficiently.
Effects of bioturbation by tube‐dwelling chironomid larvae on oxygen uptake and denitrification in eutrophic lake sediments
Authors: SVENSSON JONAS , LEONARDSON LARS 
Published: November 2003

1. Oxygen uptake and denitrification were determined in two bioturbated sediments from a eutrophic lake in southern Sweden. In laboratory mesocosms, an organic profundal sediment was incubated with Chironomus plumosus L. and a sandy littoral sediment with an organic‐rich top layer was incubated with Polypedilum sp. Both species of chironomid are sediment tube‐dwelling.2. Oxygen consumption, expressed per gram of larval dry weight, was enhanced to the same extent by the larvae in both sediments. Measurements of the respiration rate of individual larvae revealed that the respiration per gram dry weight of the smaller Polypedilum sp. was more than three times higher than that of C. plumosus.3. Denitrification was measured using the ‘nitrogen isotope pairing’ technique. In the organic sediment, denitrification of nitrate from the water phase (dw) and denitrification of nitrate from coupled nitrification (dn) were each correlated with the biomass of C. plumosus. In the sandy sediment, dw was correlated with the biomass of Polypedilum sp., while dn did not show any correlation with Polypedilum sp.4. Oxygen uptake in the organic sediment was increased by a factor of 2.5, dw 5‐fold and dn 2.5‐fold at a biomass of 10 g m–2 dry weight of C. plumosus. The same biomass of Polypedilum sp. in the sandy sediment resulted in a 2‐fold stimulation of oxygen uptake and a 3‐fold stimulation of dw, while dn was not affected. These differences in stimulation between oxygen uptake and denitrification by the larvae in the sediments suggest that the stimulation pattern cannot be explained by simple extension of the sediment surface. The burrows evidently reduce the distance between the nitrate source in the water column and the denitrifiers in the anoxic zones.5. This study indicates that bioturbation by macrofauna elements can have a great impact on denitrification in lake sediments, and that different organisms can influence nitrogen turnover in specific ways.
A method for estimating larval life spans of aseasonal aquatic insects from streams on Bougainville Island, Papua New Guinea
Authors: MARCHANT R. , YULE C.M. 
Published: November 2003

1. The larval life spans of twelve species of aseasonal aquatic insects (eight Trichoptera, three Ephemeroptera, one Odonata) were investigated in two tropical streams with near constant water temperatures.2. Life spans were estimated from equations relating larval life span to the ratio between cohort production (estimated from the size–frequency technique) and annual production (estimated from regressions in the literature).3. Life spans varied from 40 to 250 days and were positively correlated with maximum larval dry weight (r = 0.73, P < 0.001). Ephemeroptera had the shortest larval life spans (40–110 days), Trichoptera intermediate (95–185 days) and Odonata the longest (250 days).
Hydraulic influences on periphyton and benthic macroinvertebrates: simulating the effects of upstream bed roughness
Authors: QUINN JOHN , HICKEY CHRISTOPHER , LINKLATER WAYNE 
Published: November 2003

1. Hydraulic conditions, periphyton biomass and invertebrate communities were compared on artificial substrates exposed to a range of upstream roughness conditions across an area of uniform current velocity and depth in a gravel‐bedded river. The effect of river bed roughness was simulated by installing roughness elements upstream of artificial substrates.2. Increasing upstream roughness reduced the average near‐bed velocity above the substrates and increased short‐term variability in velocity (i.e. turbulence).3. Periphyton chlorophyll a density showed a general decline with near‐bed velocity and was significantly lower on the substrates exposed to the river bed reference and 0 mm roughness treatments than the 110 mm roughness elements. Chlorophyll a was also negatively correlated with the abundance of larger collector‐browsing invertebrates. This indicates that effects of the changes in hydraulic conditions on invertebrates may have contributed to the observed treatment effects on periphyton.4. Invertebrate abundance and diversity declined with increasing upstream roughness. Filter‐feeders, collector‐browsers and predatory invertebrates all declined in abundance with increasing upstream roughness, but the effect was strongest for filter‐feeders. Eight of the nine most common taxa showed significant treatment effects. The orthoclad chironomid, Eukiefferiella sp., was not influenced strongly by upstream roughness, but its abundance was correlated significantly with periphyton biomass.
Accumulation of free amino acids and humic substances in a freshwater modular system and their ecological significance
Authors: THOMAS J.D. , EATON P. 
Published: November 2003

1. Methods for measuring concentrations of total and individual free amino acids (TFAA, FAA), other amino compounds and humic substances (HS) in media containing the following three treatments and the control are described: (i) the non‐axenic aquatic macrophyte Ceratophyllum demersum alone; (ii) the pulmonate snail, Biomphalaria glabrata alone; (iii) the snail, plant and the epiphytic bacteria and algae together as a four‐component modular system; (iv) control without organisms.2. TFAA accumulated to give asymptotic values of 2.5 μm, 10 μm and 15 μm in treatments (i), (ii) and (iii), respectively, by the end of the 30‐day incubation period. The mass‐specific accumulation rate in the treatment with the snail alone [89.4 nmol g–1 (wet weight minus shell) day–1] was approximately ten times that with the plant alone [8.4 nmol g–1 (wet mass) day–1]. No FAA or HS could be detected at any time in (iv).3. On the second day of incubation the concentrations of TFAA and of some individual amino acids were significantly higher in the treatment containing the snail and plant together than the sum of the concentrations in the treatments with the plant and snail alone, presumably due to an increase in the snails’ metabolic rate and ‘sloppy feeding’.4. The differences in the relative abundance of amino compounds accumulating in media conditioned by snails alone (e.g. much larger proportions of ammonia, ethanolamine and phosphoserine than in plant‐conditioned media) and plants alone (e.g. larger proportions of asparagine and glutamine than in snail‐conditioned media) suggest that snails and plants may derive mutual benefits by exchanging amino compounds.5. The accumulation patterns of the more recalcitrant HS differ from those of the amino acids in two respects. First, the HS concentrations continued to increase throughout the 30‐day incubation period in all three treatments. Second, most of the HS in the module originates from the plant as both the concentrations and mass‐specific accumulation rates were significantly higher in the treatment with the plant alone [2.6 mg l–1, 9.09 μg g–1 (wet mass) day–1, respectively] than in the treatment with the snail alone [0.75 mg l–1 and 7.7 μg g–1 (wet mass) day–1, respectively].6. The possible reasons for the differences in the accumulation patterns of FAA and HS in the three treatments are discussed. Evidence is also given in support of the testable hypothesis that the four components of the module derive several mutual benefits, including those arising from the release of dissolved organic matter, such as FAA and HS, by living organisms.