bluuebunny/crossref_metadata_2025 huggingface dataset:
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.
Response of benthic invertebrates to natural versus experimental disturbance in a Swiss prealpine river
Authors: MATTHAEI CHRISTOPH , UEHLINGER URS , FRUTIGER ANDREAS
Published: November 2003

1. The crucial point of disturbance experiments in streams is the extent to which they can simulate a natural spate. Ideally, disturbance experiments should proceed side by side with a phenomenological study to allow a direct comparison. In the present study conducted in a prealpine Swiss river, the River Necker, fortuitous events made such a comparison possible.

2. In summer 1994, we took Surber samples one day before and on several sampling dates after a major flood (recurrence interval ≈ 5 years), which was followed by a long period of uniform discharge in a river characterized by frequent spates. Beginning 19 days after this flood, patches of the stream bed (≈ 9 m2) were physically disturbed by kicking and raking.

3. The degrees of reduction in the total number of individuals and the dominant taxa were similar after both types of disturbance, as were the recolonization patterns of Rhithrogena spp., Leuctra spp. and Hydracarina. Chironomidae, Baetis spp., Simuliidae, Pentaneurini and Corynoneura/Thienemanniella spp. showed a distinct lag phase after the flood before recolonization began, whereas there was no such lag phase after the experiment. Therefore, the time needed to recover to pre‐flood densities was longer for these taxa. Nevertheless, recolonization rates and patterns after the lag phase were similar to those after the experimental disturbance.

4. Size‐class measurements indicated that recruitment from egg hatching may have been more important after the flood than after the experimental disturbance for Rhithrogena spp., but not for Chironomidae, Baetis spp., Simuliidae, Pentaneurini and Leuctra spp. Invertebrate drift was probably the most important pathway of recolonization after both types of disturbance.

5. Our experiment allowed a realistic simulation of several important effects of the large flood on the invertebrate community. Smaller spates that induce substratum movement at a spatial scale similar to our experimental plots are much more common than large floods in the River Necker. For these spates, our experiment should provide an even more realistic simulation of natural disturbance.
The influence of landscape position on lakes in northern Wisconsin
Authors: KRATZ TIMOTHY , WEBSTER KATHERINE , BOWSER CARL , MAGUSON JOHN , BENSON BARBARA
Published: November 2003

1. Using data from the North Temperate Lakes Long‐Term Ecological Research site in northern Wisconsin, we present a series of examples illustrating how landscape setting can influence the static and dynamic aspects of many physical, chemical and biological properties of lakes.

2. One important landscape attribute is the hydrologic position of a lake within the regional flow regime. Lake position determines the relative importance of groundwater and precipitation input to a lake, with lakes high in the landscape receiving a greater proportion of their input waters from precipitation than lakes lower in the landscape. Landscape position is strongly correlated with the concentration of base cations such as calcium and magnesium.

3. Landscape position also influences how lakes respond to drought conditions. Lakes high in the landscape responded to a 4‐year drought with decreases in calcium mass, whereas lakes low in the landscape increased in mass of calcium. During extended dry conditions, these differential responses of lakes suggest that lakes already low in calcium (i.e. in a high position in the flow system) will have further reductions in calcium concentrations. These reductions could decrease the number of lakes offering suitable habitat for organisms such as crayfish and snails whose distributions are limited by calcium.

4. Landscape position also affects silica concentrations in lakes, with lakes low in the landscape having silica concentrations up to three orders of magnitude greater than lakes high in the landscape. Differences in silica concentration affect robustness of freshwater sponge spicules which can potentially alter some aspects of the dynamics of littoral zone food webs.

5. Landscape position can influence the vertical distribution of primary production. Concentrations of dissolved organic carbon are affected by landscape setting and can influence vertical light penetration, thus affecting the depth at which primary production can occur.

6. Lake area and fish species richness are correlated with landscape position: larger, species‐rich lakes are low in the landscape, whereas smaller lakes with fewer species tend to be high in the landscape.

7. By taking a landscape‐scale view, in addition to the more usual lake‐specific view, it is possible to reach a more robust understanding of lake dynamics and avoid some of the problems associated with extrapolating from single lake results.
Species traits in relation to temporal and spatial heterogeneity in streams: a test of habitat templet theory
Authors: TOWNSEND COLIN , DOLÉDEC SYLVAIN , SCARSBROOK MIKE
Published: November 2003

1. The habitat templet approach depends on defining templet axes appropriate to the organism(s) of interest, predicting the traits of species associated with different parts of the templet, and testing these predictions in a range of habitats whose positions in the templet have been determined.

2. In this study of thirty‐five benthic insect taxa at fifty‐four tributary sites of the Taieri River on the South Island of New Zealand, we chose as the temporal axis the intensity/frequency of disturbance, defined in terms of bed movement during high discharge events. As the spatial axis, we postulated that three features would provide refugia and therefore ameliorate disturbance—percentage of the bed with low shear stress, percentage of the bed made up of large substratum particles and availability of interstitial space in the bed—from which we derived a combined multivariate refugium axis.

3. More disturbed communities contained a significantly higher percentage of individuals possessing the following traits: small size, high adult mobility, habitat generalist (each predicted to confer resilience in response to disturbance), clinger, streamlined/flattened and with two or more life stages outside the stream (each predicted to confer resistance in the face of disturbance). When analyses were performed on the percentage of taxa having particular traits, the predicted positive relationships with average bed movement were found for high adult mobility and habitat generalist traits.

4. The percentage of variance in trait scores explained by intensity of disturbance was generally higher in sites with less refugia available and lower in sites further from the headwaters. The percentage of variance explained was higher in sites recently subject to a major high discharge disturbance, suggesting that disturbances tend to strengthen the pattern of preponderance of resilience/resistance traits.

5. We mapped insect taxa onto the two‐dimensional templet, following Grime et al.’s triangular terrestrial plant classification. The full variety of resistance and resilience traits were represented in insect species throughout the templet, but taxa associated with more disturbed conditions generally displayed a larger number of resilience and resistance traits, combined, than taxa associated with more stable stream beds.
Facilitation of periphyton production by tadpole grazing: functional differences between species
Authors: KUPFERBERG SARAH
Published: November 2003

1. This study examined how interactions between resources that vary in edibility, and herbivores that vary in ability to acquire resources, control primary productivity. In a northern California river, grazing on Cladophora glomerata, a relatively inedible filamentous green alga, and its more nutritious epiphytic diatoms, was manipulated by exposing cobbles to tadpoles (Rana boylii or Hyla regilla) or excluding tadpoles.

2. Rana indirectly facilitated Cladophora by removing diatoms, whereas Hyla did not significantly change biomass relative to controls. Algal ash‐free dry mass on cobbles in Rana treatments was 65 and 72% greater than on controls in two years of investigation (1991 and 1993). Rana decreased epiphytic diatom biovolume by 56% and detritus by 87%.

3. Because nitrogen excretion rates of Hyla and Rana were similar, the differences in effect between the two species were probably due to their roles as consumers rather than as recyclers.

4. The net effect of Rana on periphyton was a 10% increase in areal specific primary productivity (mg O2 h–1 m–2);Hyla caused an 18% decrease. Rana decreased biomass‐specific productivity (mg O2 h–1 g–1) 44%;Hyla had no effect.

5. In tadpole exclosures, grazers such as baetid mayfly larvae (mostly Centroptilum sp.) were 4.7 (1991) and 1.8 (1993) times more abundant, and midge larvae (Chironomidae) were 2.5 (1991) and 2 (1993) times more abundant than in Rana enclosures. Invertebrate assemblages in Hyla enclosures, however, were similar to exclosures. Few predatory insects and fish colonized Rana enclosures. Path analyses indicated that Rana affected macroinvertebrates via both interference and exploitation of epiphytic diatoms.
Changes in the crustacean zooplankton community of Harp Lake, Canada, following invasion by Bythotrephes cederstrœmi
Authors: YAN NORMAN , PAWSON TREVOR
Published: November 2003

1. Detecting the impacts of invading Bythotrephes cederstrœmi (Crustacea, Onychopoda, Cercopagididae) on zooplankton in North American lakes has been hampered by the brevity of pre‐invasion data, and by the difficulty of distinguishing the effects of the invader from other stresses. The data from Harp Lake in Ontario, Canada, circumvent these difficulties. Bythotrephes appeared in the lake in 1993. There is a 15‐year pre‐invasion data set, and no significant complicating concurrent stresses.

2. The species composition and the size structure of the crustacean zooplankton community of Harp Lake changed after the invasion. Several small species either declined dramatically in abundance (e.g. Bosmina longirostris, Tropocyclops extensus) or disappeared (Chydorus sphaericus, Diaphanosoma birgei, Bosmina (Neobosmina) tubicen). In contrast the abundance of the larger cladocerans Holopedium gibberum and Daphnia galeata mendotae and the hypolimnetic copepod Leptodiaptomus sicilis increased. Several univariate and all multivariate summarizations of zooplankton abundance, biomass and size structure highlighted the uniqueness of the post‐invasion community.

3. The alterations in the zooplankton community could not be attributed to changes in lake acidity, thermal regimes, penetration by ultraviolet light, nutrient status, fish stocking or the abundances of native invertebrate predators, but they were correlated with Bythotrephes abundance, both within and among years. Hence, we hypothesize that the invasion by Bythotrephes has significantly altered the crustacean zooplankton community of Harp Lake.
Allozyme variability in brown trout Salmo trutta in Chile
Authors: FAUNDEZ V. , BLANCO G. , VÁZQUEZ E. , SÁNCHEZ J.A.
Published: November 2003

1. Brown trout ova were imported during the last century from different locations in Europe to establish populations in Chilean rivers (South America). The rivers are currently occupied by naturalized populations that have adapted to very different environmental conditions, such as areas of semi‐desert in the north, or rainy and cold areas in the south.

2. In this first study in this geographical area, electrophoretic variability of proteins encoded by twenty‐five loci was screened in seven populations from northern to southern Chile.

3. The results show significant heterogeneity of allelic frequencies between populations in seven of eleven polymorphic loci detected. The estimated value of genetic diversity 0.1274 (HT) is higher than that observed in populations from areas of natural distribution of this species. However, only 12.64% of this genetic diversity was found between samples (GST), indicating a low genetic divergence among Chilean populations. The observed associations among the Chilean and ‘modern’ group of European populations suggests the probable origin of the new populations.
Features of the underwater light climate just below the surface in some New Zealand inland waters
Authors: RØRSLETT BJØRN , HAWES IAN , SCHWARZ ANNE‐MAREE
Published: November 2003

1. Using sampling rates of 8–64 Hz we found clear indications of extensive and high frequency fluctuations of underwater photosynthetically active radiation (PAR) just below the surface (0.016–1.1 m) in some New Zealand water bodies. High variability and flashing occurred down to at least 3 m depth.

2. PAR variability increased under the influence of bright sunshine if wind roughening of the surface took place. Concomitantly, the average PAR levels declined by about 10%. However, even when the surface was shaded, high variability of PAR persisted.

3. Under a calm surface, PAR irradiance followed a log normal distribution. This occurred independently of the presence of direct sunlight. However, when the surface was roughened by wind in sunshine, PAR immediately switched to a Gumbel (extreme value type EV1) distribution.

4. Neither wave action nor wave focusing of incident irradiance would explain the wide range of PAR close to the water surface, although both factors add to the PAR variability.

5. The data indicate that transmittance through the surface is highly variable at the temporal and spatial scales studied, and that the irregularity of the air–water interface is instrumental in bringing about the observed fluctuations of PAR just below the surface.
Inorganic carbon limitation of photosynthesis in lake phytoplankton
Authors: HEIN METTE
Published: November 2003

1. Inorganic carbon availability influences species composition of phytoplankton in acidic and highly alkaline lakes, whereas the overall influence on community photosynthesis and growth is subject to debate.

2. The influence of total dissolved inorganic carbon (DIC) and free CO2 on community photosynthesis was studied in six Danish lakes during the summer of 1995. The lakes were selected to ensure a wide range of chlorophyll a concentrations (1–120 μg l–1), pH (5.6–9.6) and DIC concentration (0.02–2.5 mm). Photosynthesis experiments were performed using the 14C technique in CO2‐manipulated water samples, either by changing the pH or by adding/removing CO2.

3. Lake waters were naturally CO2 supersaturated during most of the experimental period and inorganic carbon limitation of photosynthetic rates did not occur under ambient conditions. However, photosynthesis by phytoplankton in lakes with low and intermediate DIC concentrations was seriously restricted when CO2 concentrations declined. Similarly, photosynthesis was limited by low CO2 concentrations during phytoplankton blooms in the hardwater alkaline lakes.
The response of benthic macroinvertebrates to pollution in developing countries: a multimetric system of bioassessment
Authors: THORNE RICHARD , WILLIAMS PETER
Published: November 2003

1. A variety of bioassessment metrics were tested using family‐level macroinvertebrate data, gathered by standard colonization units, and associated physicochemical data from pollution gradients in three rivers in developing countries.

2. Graphical methods of evaluation were used to evaluate the metrics with respect to these pollution gradients.

3. In general, the macroinvertebrate communities sampled displayed a similar response to pollution to that observed in well‐studied temperate areas.

4. Of the twenty metrics tested seven described the pollution gradients adequately. Four of these seven metrics, which do not supply duplicate information, were selected for use in a multimetric system of bioassessment.

5. A multimetric system is proposed and tested using the original macroinvertebrate data. It performs well in the assessment of the pollution status of the study sites and the description of the pollution gradient. However, local modifications are likely to enhance its performance.
Depth limits and minimum light requirements of freshwater macrophytes
Authors: MIDDELBOE ANNE LISE , MARKAGER STIIG
Published: November 2003

1. Data for maximum colonization depth (Zc) of five groups of submerged macrophytes and light attenuation were collected for forty‐five Danish lakes and 108 non‐Danish lakes. The macrophyte groups were bryophytes, charophytes, caulescent angiosperms, rosette‐type angiosperms and Isoetes spp.

2. The data showed systematic differences among the groups in the relationship of Zc to water transparency. In lakes with low transparency (Secchi disc transparency (Zs) less than 7 m) caulescent angiosperms and charophytes penetrated deepest followed by bryophytes and Isoetes spp. In more transparent lakes bryophytes grew deepest, followed by charophytes, caulescent angiosperms and Isoetes spp. Rosette‐type angiosperms had the lowest Zc in all types of lakes. Charophytes and caulescent angiosperms had similar depth limits in lakes with Zs < 4 m but charophytes grew deeper in more transparent lakes. The depth limits of both groups were independent of light penetration in lakes with very low transparency (Zs < 1 m). The annual light exposure for the deepest growing macrophytes (bryophytes) was 20–95 mol photons m–2.

3. The relationship between Zc, macrophyte type and lake transparency could be explained by three distinct processes regulating Zc. In lakes with low transparency (Zs < 1 m), tall macrophytes (caulescent angiosperms and charophytes) compensate for light limitation by shoot growth towards the water surface and Zc is therefore independent of transparency. In lakes with medium transparency (1 m < Zs < 4 m) Zc for angiosperms, charophytes and Isoetes spp. is constrained by light attenuation in the water column, corresponding to a linear relationship between Zc and Zs. This pattern also applies to bryophytes, despite lake transparency. In transparent lakes, the minimum light requirement at Zc increased with increasing transparency for angiosperms, charophytes and Isoetes spp.

4. The minimum light requirements among submersed macrophytes (including marine macroalgae) depend on their plant‐specific carbon value (plant biomass per unit of light‐absorbing surface area) for the species/group, indicating that the light requirements of submersed plants are tightly coupled to the plants’ possibility to harvest light and hence to the growth form.

5. The light requirements increased on average 0.04% surface irradiance per degree increase in latitude corresponding to an average decrease in Zc of 0.12 m per degree latitude.
Field experiments on flow refugia in streams
Authors: WINTERBOTTOM JULIE , ORTON STUART , HILDREW ALAN , LANCASTER JILL
Published: November 2003

1. Field experiments were carried out to determine whether animals move into areas of low shear stress during periods of peak flow and therefore avoid hydraulic disturbance.

2. Flow at the scale of 0.05 m2 patches was reduced experimentally by creating artificial ‘refugia’. Invertebrate colonization of cages with 1.1 mm mesh sides, which provided such potential refugia by reducing hydraulic forces within the cage, was compared with colonization of cages with coarser (15 mm) mesh which did not restrict the flow.

3. Colonization of these cages was tested over a series of weekly periods in two different streams. Nine trials were completed in a stream with abundant natural flow refugia (Broadstone Stream, SE England), and during three of these trials strong spates occurred. Six trials were completed in a stream with comparatively few natural flow refugia (Dargall Lane, SW Scotland), and peak flows were relatively less.

4. In Broadstone Stream, the relative colonization of refugium cages was greatest during periods of peak flow, suggesting animals had used these low‐flow areas as refugia during spates. Use of the artificial refugia did not occur in Dargall Lane, at least at the flows achieved during the trials.

5. Our results are consistent with the hypothesis that stream invertebrates accumulate in refugia during high flow disturbances. Whether their distribution among patches is altered by active or passive means remains unclear.
Responses of Daphnia pulex populations to toxic cyanobacteria
Authors: LAURÉN‐MÄÄTTÄ CAMILLA , HIETALA JAANA , ANDWALLS MARI
Published: November 2003

1. We studied the effects of toxic cyanobacteria, Microcystis aeruginosa, on Daphnia pulex populations. The experiment was performed at room temperature in laboratory microcosms to which we added toxic Microcystis in two pulses. Green alga, Scenedesmus obtusiusculus, was provided in two concentrations.

2. Microcystis exposure resulted in a decreased population density of Daphnia. The proportion of adolescents was higher in the Microcystis treatment than in the control, while the proportion of newborns did not differ significantly from the control. This indicates delayed maturation of Daphnia exposed to Microcystis. We found no significant impacts of cyanobacteria, food level or clonal origin on population variability after correcting for differences in population size.

3. Juveniles of the two clones studied showed different sensitivities to toxic Microcystis in the acute test. However, in the population experiment we did not find clonal differences between Microcystis and control treatments in the relative proportion of juveniles.

4. The number of ephippia produced per adult was highest in the treatments with Microcystis. This indicates that cyanobacterial toxins may be one of several factors inducing ephippia formation, acting directly or through inhibition of feeding.
Grazer control and nutrient limitation of phytoplankton biomass in two Australian reservoirs
Authors: MATVEEV VLADIMIR , MATVEEVA LILIAN
Published: November 2003

1. Grazer and nutrient controls of phytoplankton biomass were tested on two reservoirs of different productivity to assess the potential for zooplankton grazing to affect chlorophyll/phosphorus regression models under Australian conditions. Experiments with zooplankton and nutrients manipulated in enclosures, laboratory feeding trials, and the analysis of in‐lake plankton time series were performed.

2. Enclosures with water from the more productive Lake Hume (chlorophyll

a = 3–17.5 μg l–1), revealed significant zooplankton effects on chlorophyll a in 3/6, phosphorus limitation in 4/6 and nitrogen limitation in 1/6 of experiments conducted throughout the year. Enclosures with water from the less productive Lake Dartmouth (chlorophyll a = 0.8–3.5 μg l–1), revealed significant zooplankton effects in 5/6, phosphorus limitation in 5/6 and nitrogen limitation in 2/6 of experiments.

3. While Lake Hume enclosure manipulations of the biomass of cladocerans (Daphnia and Diaphanosoma) and large copepods (Boeckella) had negative effects, small copepods (Mesocyclops and Calamoecia) could have positive effects on chlorophyll a.

4. In Lake Hume, total phytoplankton biovolume was negatively correlated with cladoceran biomass, positively with copepod biomass and was uncorrelated with total crustacean biomass. In Lake Dartmouth, total phytoplankton biovolume was negatively correlated with cladoceran biomass, copepod biomass and total crustacean biomass.

5. In both reservoirs, temporal variation in the biomass of Daphnia carinata alone could explain more than 50% of the observed variance in total phytoplankton biovolume.

6. During a period of low phytoplankton biovolume in Lake Hume in spring–summer 1993–94, a conservative estimate of cladoceran community grazing reached a maximum of 0.80 day–1, suggesting that Cladocera made an important contribution to the development of the observed clear‐water phase.

7. Enclosure experiments predicted significant grazing when the Cladocera/Phytoplankton biomass ratio was greater than 0.1; this threshold was consistently exceeded during clear water phase in Lake Hume.

8. Crustacean length had a significant effect on individual grazing rates in bottle experiments, with large Daphnia having highest rates. In both reservoirs, mean crustacean length was negatively correlated with phytoplankton biovolume. The observed upper limit of its variation was nearly twice as high compared to other world lakes.
Coprophagy: a supplementary food source for two freshwater gastropods?
Authors: BRENDELBERGER HEINZ
Published: November 2003

1. The freshwater pulmonate snail Radix peregra voluntarily and regularly fed on its faeces, whereas Bithynia tentaculata (Prosobranchia) did not.

2. With high‐quality faeces as food (faeces with C : N‐values below ten) Radix could grow and survived for 11 weeks. Growth was 24–30% of that achieved with control food (lettuce, Chlamydomonas and Tetramin), and body mass was close to the expected value.

3. As with real food, the percentage organic content of faeces was reduced during gut passage, with the exception of very low‐quality faeces.

4. Faeces contained living cells of green algae (Chlamydomonas reinhardii) and diatoms (Achnanthes lanceolata, Eunotia pectinalis), which survived the gut passage of R. peregra and B. tentaculata. Faecal material was also rich in bacteria, with up to 150 × 106 cells mg–1 dry mass. Bacteria increased in abundance in faeces which had been evacuated for 7 days or more.

5. A further degradation of partly digested food in the faeces was indicated by the activity of the extracellular digestive enzymes cellobiase and chitobiase. These enzymes hydrolysed material with an activity of 0.2–14.5 pkat mg–1 faecal dry mass in 1–12‐day‐old faeces. In faeces of Bithynia fed control food or incubated sycamore leaves, chitobiase activity was correlated with bacterial abundance.

6. Coprophagy is considered to be a suitable strategy for further degradation and utilization of refractory material for which one gut passage is too short and/or too inefficient.
Annual production of leaf‐decaying fungi in a woodland stream
Authors: SUBERKROPP KELLER
Published: November 2003

1. Fungi are thought to be important mediators of energy flow in the detritus‐based food webs of woodland streams. However, until recently, quantitative methods to assess their contribution have been lacking. Growth rates of leaf‐decaying fungi can be estimated from rates of acetate incorporation into ergosterol which, together with estimates of fungal biomass from ergosterol concentrations, enables calculation of fungal production. In this study, I used this method to estimate total production of leaf‐decaying fungi over an annual cycle in a small woodland stream, Walker Branch, Tennessee, U.S.A. To calculate fungal biomass and production on an areal basis, I determined the amount of leaf litter occurring in the stream by sampling transects randomly selected in each of ten 10‐m sections every 20–50 days. Subsamples of leaves chosen from five of the transects were used to determine ergosterol concentrations and in situ rates of acetate incorporation into ergosterol.

2. Leaf litter, fungal biomass m–2, and fungal production m–2 were highly seasonal. Leaf litter ranged from 249 g m–2 in November to less than 5 g m–2 during the summer. Fungal biomass as percentage of leaf litter ranged from 4.4 to 8.8% during the year, but on an areal basis ranged from 11 to 13 g m–2 during November to January to 0.25 g m–2 in June, primarily due to the seasonal variation in amount of leaf litter present. Fungal growth rates averaged 2.6% day–1 (0.9–7.0% day–1) during the year. Daily production of leaf‐decaying fungi ranged from 0.49 g m–2 in November, when the amount of leaf litter was at its maximum, to 0.006 g m–2 during the summer when the amount of leaf litter was low. Annual production of leaf‐decaying fungi was 34 g m–2, with an annual production to biomass ratio (P/B) of 8.2.

3. Fungal spore concentrations in the stream were also seasonal and were correlated with amount of leaf litter m–2 and fungal biomass m–2. Spore concentrations varied between one and four spores ml–1 throughout most of the year, but increased to eighteen spores ml–1 shortly after the greatest amount of leaf litter was present in the stream during November.
Habitat segregation and interactive effects of multiple predators on a prey assemblage
Authors: GONZÁLEZ MARÍA , TESSIER ALAN
Published: November 2003

1. In a field experiment we examined the interactive effects of two common predators of zooplankton, bluegill sunfish (Lepomis macrochirus) and Chaoborus spp. on the growth rate and habitat use of three congeneric prey species (Daphnia). Bluegill and Chaoborus both consume Daphnia, but bluegill also prey on Chaoborus. The prey species, Daphnia pulicaria, D. rosea and D. retrocurva, differed in body size and vertical distribution. We expected the largest species, D. pulicaria, to be most vulnerable to fish predation and the smallest species, D. retrocurva, to be most vulnerable to Chaoborus predation.

2. As we expected, the population growth rate of D. pulicaria was significantly reduced by fish. However, Chaoborus also significantly reduced the growth rate of this species. No significant interaction effect was detected, indicating that the effect of these predators was additive. The growth rates of D. rosea and D. retrocurva were significantly reduced by Chaoborus, but a significant interaction effect indicated that the effect of Chaoborus was stronger in the absence of fish than when fish were present. Therefore the impact of Chaoborus and fish on D. rosea and D. retrocurva was non‐additive. The interactive effect of the two predators on D. retrocurva was greater in magnitude than on D. rosea.

3. In the absence of predators, the three Daphnia species showed no differences in mean habitat depth between day and night. Both predators significantly affected diel habitat use of D. pulicaria and D. rosea. Fish caused both of these Daphnia species to move deeper during the day, whereas Chaoborus caused Daphnia to move into shallower water at night. Daphnia retrocurva tended to migrate upwards at night in all predator treatments, but no significant differences in migration were observed among the predator treatments. The effects of predators on habitat use were not interactive for any prey species.

4. Our results suggest that body size, habitat use and the diel migratory response to predators are important factors mediating the interactive effects of multiple predator types on zooplankton.