bluuebunny/crossref_metadata_2025_split huggingface dataset:
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.