bluuebunny/crossref_metadata_2025_split huggingface dataset:
Problems with the use of terracotta clay saucers as phosphorus‐diffusing substrata to assess nutrient limitation of epilithic algae
Authors: Brown Glen G. , Maher William A. , Norris Richard H. , Mathieu  
Published: March 2003

1. We examined the diffusion properties of terracotta clay saucers, of types often used as components in phosphorus‐diffusing substrata for investigating nutrient limitation of epilithic algae.2. Laboratory experiments showed that phosphorus diffusion was low and inconsistent (0.06–2.6 mg P day−1) through clay saucers filled with agar containing orthophosphate. Similarly, in situ release of phosphorus from two types of terracotta clay saucers (Australian and Italian) was variable (2–8 mg P day−1; 5–25%) under three flow regimes (0, 0.1 and 0.3 m s−1) over 30 days, with most phosphorus being released during the first day. Clogging of pores by agar appears to prevent the diffusion of phosphorus through the terracotta clay saucers. However, the two types of terracotta clay saucer also irreversibly sorbed large quantities of phosphorus (40–140 mg P).3. Individual saucers can have markedly different physical and chemical properties both within and among terracotta types. Terracotta saucers also contain large quantities of iron, calcium and aluminium that are known binding agents for phosphorus. Variability in saucer composition and diffusion properties makes treatments difficult to replicate and weakens comparisons between studies that have used terracotta with different clay composition and manufacture.4. We recommend that phosphorus‐diffusing substrata should not be constructed from terracotta clay components.
Perch or plankton: top‐down control of Daphnia by yellow perch (Perca flavescens) or Bythotrephes cederstroemi in an inland lake?
Authors: Hoffman Joel C. , Smith Meghan E. , Lehman John T. 
Published: March 2003

1. Seasonal termination of the vernal clear‐water phase in Long Lake, Grand Traverse Co., Michigan coincided with severe size‐selective predation on juvenile Daphnia pulicaria from 0.8 to 1.8 mm in length. This could be caused by predation by age‐0 yellow perch (Perca flavescens) or by the exotic predatory zooplankter Bythotrephes cederstroemi.2. During the initial decline of Daphnia, Ivlev’s electivity coefficient for yellow perch from 15.0 to 20.0 mm in length was 0.50 for copepods and −0.75 for D. pulicaria.3. Bioenergetics modelling of both yellow perch and Bythotrephes demonstrates that, during the initial Daphnia decline, Bythotrephes consumed 1.5–5 times greater total mass than yellow perch. Furthermore, models in which Bythotrephes consumed juvenile Daphnia were more consistent with the timing of the Daphnia decline than those in which yellow perch consumed juvenile Daphnia.4. The invasion of Bythotrephes into Long Lake seems to be a significant perturbation, introducing effects that propagate throughout the food chain. Bythotrephes created a possible bottleneck for age‐0 yellow perch in late June by suppressing Daphnia.
Distribution and diel migration of macroinvertebrates within dense submerged vegetation
Authors: Marklund Ola , Blindow Irmgard , Hargeby Anders 
Published: March 2003

1. We studied vertical and horizontal distribution of macroinvertebrates within a dense stand of Chara spp. in Lake Krankesjön, southern Sweden. Invertebrates were sampled at three depths within the vegetation and at three distances from the vegetation edge during day and night in July and August. Corresponding samples of oxygen content of the water were taken.2. The densities (number of invertebrates per unit plant biomass) of most invertebrate taxa were generally lower in the upper layers of the vegetation than in the layers close to the sediment. The densities of several taxa (Asellus aquaticus, Cloëon sp. and Polycentropodidae), as well as total density of invertebrates, were higher at the edge than in the innermost parts of the macrophyte stand, whereas snail densities generally were highest at the innermost sites.3. Densities of A. aquaticus, Chironomidae larvae and Helobdella stagnalis generally increased at night. These taxa appear to undertake a diel vertical migration within the vegetation, towards, or even down to the sediment in daytime and up into the vegetation, in some cases to the vegetation surface, at night. Factors underlying the diel vertical migration are discussed, as are their ecological consequences.
Implications of Chaoborus pupation and ecdysis in cold water
Authors: Ouimet Chantal 
Published: March 2003

1. Cold water acted differently to delay and lengthen the pupation period for the larvae of two species of the zooplankton predator Chaoborus (Diptera: Chaoboridae). During Chaoborus pupation, the zooplankton community is released from predation, while the dark‐coloured Chaoborus pupae are more susceptible to their own predators.2. Fourth instar larvae of Chaoborus americanus and C. trivittatus, collected from an oligotrophic lake, were reared individually at 5 °C in the dark. Chaoborus americanus was also reared at 9 and 12 °C under spring photoperiod conditions (L : D, 16 : 8 h). Individuals were observed through pupation to emergence (ecdysis) or death.3. Chaoborus americanus pupated at 5, 9 and 12 °C with substantial emergence only at 12 °C. In comparison, C. trivittatus emerged at 5 °C. Light was not a necessary cue for pupation and ecdysis, contrary to previous reports. Cold water delayed the onset and lengthened and increased the variability of the duration of pupation.4. In Shirley Lake, C. americanus pupated in late June–early July while C. trivittatus pupated first in April and again in June–July.5. Chaoborus americanus pupae needed a temperature cue to complete ecdysis. The ecdysis temperature threshold helps to explain the difference in pupation timing, and the geographical distribution, of C. americanus and its relatively inflexible life history contrasted with C. trivittatus. Delayed predator pupation in years with low spring temperature can affect the community dynamics of the prey.
Colonization, riparian habitat selection and home range size in a reintroduced population of European beavers in the Loire
Authors: Fustec J. , Lode T. , Le Jacques D. , Cormier J. P. 
Published: March 2003

1. Colonization in a reintroduced population of European beavers in the Loire Valley was studied between 1974 and 1999. It followed a discontinuous remoteness model and a scattered distribution, beavers occupying only 25% of the river system over the 2800 km explored.2. After 5 years, the colonization rate reached 104.2% year–1 of new sites occupied (SD 75% year–1), before dropping over the next 20 years. Nevertheless, the number of new colonies per km (0.125) remained stable throughout the years.3. Populus nigra, Salix alba and Fraxinus angustifolia were the dominant woody species in beaver sites, often associated with some herbaceous species.4. The length of willow grove dominated by S. alba and P. nigra (x) was the best predictor of beaver home range (y), fitting the equation y=−0.742x + 5.9. Long‐term maintenance of the population requires a minimum of 1.79‐km of willows per colony.5. In cutting tree trunks, beavers stimulate shoot development from the remaining stumps. They rejuvenate riparian forests, increase the number of tree stems and help stabilize the banks. Their effect on woody plant morphogenesis may have consequences for the helophyte communities used as food or habitat by other aquatic species.
Macroinvertebrate stream communities along regional and physico‐chemical gradients in Western Greenland
Authors: Friberg Nikolai , Milner Alexander M. , Svendsen Lars M. , Lindegaard Claus , Larsen Søren Erik 
Published: March 2003

1. Macroinvertebrates were collected and physico‐chemical variables measured at 16 stream sites in Western Greenland during July 1999. Eight sites were located on Disko Island in an arctic oceanic climate and eight sites in the Kangerlussuaq area close to the icecap where the climate is arctic continental. The streams had different water sources (glacial, groundwater, snowmelt and lake water).2. The streams showed pronounced differences in water temperature (2.2–17.3 °C), concentrations of suspended solids (0–2400 mg L−1), and conductivity (10–109 μS cm−1). Principal component analysis (PCA) analysis of the physico‐chemical variables separated the Disko Island sites into a distinct group, whereas the sites in the Kangerlussuaq area were more dispersed.3. A total of 56 macroinvertebrate species were found, including 31 species of Chironomidae, the most abundant of which was Orthocladius thienemanni. Diamesa sp. was only the sixth most abundant chironomid taxon. Species composition varied between sites, and abundance varied from about 20 individuals m−2 in a glacier fed stream to more than 16 000 m−2 in a lake outlet.4. The macroinvertebrate communities of the 16 streams were separated into five TWINSPAN groups reflecting water source, irrespective of region. Lake outlets and ground‐water‐fed streams had the highest species richness and abundance, temperature and bed stability, while glacier‐fed streams were characterized by low species richness, abundance, temperature, bed stability and high concentrations of suspended solids. Macroinvertebrate species richness was positively correlated with water temperature and negatively with bed stability. Conductivity was positively correlated with invertebrate abundance.5. The results of this study suggest that the source of stream water can be used to predict invertebrate community composition in Greenlandic streams and thus the effects of changes in water balance and flow regime, and to identify sites of special conservation interest.
Trends of macroinvertebrate community structure in glacier‐fed rivers in relation to environmental conditions: a synthesis
Authors: Milner Alexander M. , Brittain John E. , Castella Emmanuel , Petts Geoffrey E. 
Published: March 2003

1. Generalized additive models (GAMs) were used to predict macroinvertebrate taxonomic richness and individual taxon diversity at the reach level across seven European glacier‐fed river sites from a set of 11 environmental variables. Maximum water temperature and channel stability were found to explain the most deviance in these models.2. Using this information, and data from other recent studies of glacier‐fed rivers, a modified conceptual model based on Milner & Petts (1994) is presented which predicts the occurrence of macroinvertebrate families and subfamilies as determined by maximum water temperature (Tmax) and channel stability. This deterministic model only applies to the summer meltwater period when abiotic variables drive community structure.3. Where maximum water temperature is below 2 °C, Diamesinae chironomids are typically the sole inhabitants, but where Tmax >2 °C but <4 °C Orthocladiinae are found and, where channels are more stable, Tipulidae and Oligochaeta also occur. Above 4 °C Perlodidae, Taeniopterygidae, Baetidae, Simuliidae and Empididae can be expected to be part of the glacier‐fed river community, particularly in Europe.4. At other times of the year when environmental conditions ameloriate, glacial rivers support higher macroinvertebrate abundance and diversity, with a number of taxa present that are not found during the summer melt period.5. Dispersal constraints influence macroinvertebrate assemblages of many glacier‐fed rivers located on islands and in some alpine areas.
Resource competition among saline‐lake diatoms under varying N/P ratio, salinity and anion composition
Authors: Saros Jasmine E. , Fritz Sherilyn C. 
Published: March 2003

1. A series of resource competition experiments were performed with four diatom taxa isolated from saline lakes in the Northern Great Plains of North America. Three variables were tested in a factorial design: N/P ratio (6 : 1, 12 : 1, 24 : 1, 48 : 1), salinity (5, 8, 11‰), and anion composition (sulphate versus bicarbonate‐dominated medium).2. Coexistence of Chaetoceros elmorei, Cyclotella quillensis, and Cymbella pusilla occurred at the two lowest N/P ratios. These three taxa have similar N requirements and thus competitive exclusion by the taxon with the lowest N requirement may have required more time.3. Anomoeoneis costata, which had the highest nitrogen requirements and slowest growth rate of these four taxa, declined in all cases. Cyclotella biovolume concentration consistently declined at the two highest N/P ratios, indicating a higher P requirement, which is consistent with its distribution pattern.4. In general, we found opposite trends with respect to all variables for Chaetoceros, a taxon that mainly inhabits sulphate systems, versus Cymbella, a bicarbonate‐associated taxon. Our results suggest that Cymbella may be found mainly in bicarbonate systems because of a higher C requirement, whereas Chaetoceros may be less abundant in these systems, in part, because of competitive interactions with bicarbonate‐associated taxa.
Predicting the spatial dominance of phytoplankton in a light limited and incompletely mixed eutrophic water column using the PROTECH model
Authors: ELLIOTT J. A. , IRISH A. E. , REYNOLDS C. S. 
Published: March 2003

1. A phytoplankton community model [Phytoplankton RespOnses To Environmental CHange (PROTECH)] was used to examine the effect of a wide range of varied light intensities and mixed depths upon simulated phytoplankton populations. Two different column lengths of the simulated water body were examined (the upper 5 m and the whole 14.5 m water column) for each scenario.2. The hypotheses tested were that: (i) under low light intensity and/or deep mixing the simulated community will be dominated by a phytoplankter with a low critical light intensity; (ii) at high light intensity and shallow mixing the simulated community will be dominated by small, fast‐growing phytoplankters; (iii) under all conditions, except deep mixing, the largest proportion of phytoplankton biomass will be found near the surface.3. It was found under most conditions that, although there was a bloom in the upper column (dominated by algae such as Chlorella, Ceratium or Rhodomonas), the largest phytoplankton biomass in the water column was located 9 m below the surface and consisted of solely Asterionella. This bloom was missed by the 5‐m samples. Thus, using the whole column sample lengths, hypothesis (i) was not rejected but hypotheses (ii) and (iii) were refuted.4. The inclusion of specific movement characteristics of phytoplankton in the model allowed the possibility of the dominance of multiple spaces within the water column and should be included in any model‐based investigation of this topic. Further, the results from the model suggest that a reduced depth of mixing creates greater environmental heterogeneity, allowing more species to persist.
Mortality and growth responses of Daphnia carinata to increases in temperature and salinity
Authors: HALL CATHERINE J. , BURNS CAROLYN W. 
Published: March 2003

1. Daphnia carinata King, a freshwater cladoceran, occurs in Lake Waihola, a tidal lake with seasonal fluctuations in temperature (4–21 °C), and salinity (30–2000 mg L–1 Cl). We hypothesise that these fluctuations influence the seasonal changes in D. carinata abundance.2. To test this hypothesis, adults and juveniles were exposed to combinations of temperature and salinity. We measured mortality of adults and juveniles, growth of juveniles over 20 days, and their age at first reproduction.3. The salinity tolerance of adult D. carinata was temperature‐dependent. Juveniles were more sensitive to salinity, but more tolerant of temperature increases.4. Growth rates were higher at elevated temperatures, but reduced by elevated salinities. The onset of reproduction was earlier at elevated temperatures.5. We conclude that seasonal changes in temperature and salinity contribute to seasonal population changes of D. carinata.
Detritivores in Kenyan highland streams: more evidence for the paucity of shredders in the tropics?
Authors: DOBSON MIKE , MAGANA ADIEL , MATHOOKO JUDE M. , NDEGWA FIDENSIO K. 
Published: March 2003

1. The relationship between coarse particulate organic matter (CPOM) standing stock and benthic macroinvertebrate assemblages in Kenyan highland streams was determined by sampling seven sites on three rivers (2000–2700 m a.s.l.). Taxa recorded were allocated to functional feeding groups using published literature, mouthpart analysis and examination of gut contents. Patterns were compared with five structurally similar streams in three areas of Europe (south‐west France, south‐east England, north‐east England).2. Number of individuals and proportion of detritivores in Kenyan streams were equivalent to, or greater than, those in European sites. Shredders were, however, almost completely absent from Kenyan sites, despite high standing stocks of CPOM. Shredders were abundant in all European sites.3. The phenomenon of low shredder abundance has been observed in other tropical streams in south‐east Asia and Central and South America but, in contrast to these regions, the African rivers studied were devoid of shrimps or fish which may occupy the shredding niche elsewhere.4. These preliminary data suggest that shredder‐mediated detritus processing, which is a key functional component of streams in the North Temperate Zone, does not operate in East African streams. There are three possible reasons for this. The first is that tropical African rivers are functionally different to those in temperate regions. This could be because of enhanced microbial activity replacing shredder activity at high temperatures. Alternatively, it could be a result of low palatability of detrital inputs from dominant riparian trees in the region. The second and third are methodological: that our allocation to functional feeding groups is incorrect, and that our sampling methods missed a potentially key shredding taxon – the freshwater crab Potamonautes sp.
Groundwater controls on nutrient cycling in a Mojave desert stream
Authors: JONES JEREMY B. 
Published: March 2003

1. Groundwater fluxes of nitrogen and dissolved organic carbon (DOC) were investigated in Grape Vine Canyon Stream in the Mojave Desert focusing on the rate of inputs and the fate of groundwater‐derived nutrients in the stream. Discharge rates from different ground waters were measured using an end‐member mixing model coupled with injections of a conservative solute tracer into the stream channel.2. In surface water, nitrate concentration averaged 1.13 mg N L–1 and DOC concentration averaged 1.82 mg C L–1.3. Groundwater discharge into Grape Vine Canyon Stream was derived from three sources. Nitrate concentration varied among the three groundwater sources with mean concentrations of 0.56, 0.94 and 0.08 mg N L–1. DOC, in contrast, did not vary among ground water sources, with an overall average concentration of 2.96 mg C L–1.4. In the surface stream, nitrate concentration was two‐fold greater than the concentration predicted from groundwater input, indicating that in‐stream processes generated nitrate. Stream DOC concentration was lower than predicted based upon groundwater input rate. The production of nitrate and loss of DOC suggest that DOC is lost through mineralisation of dissolved organic matter, possibly resulting in the mineralisation of dissolved organic nitrogen to ammonium and subsequent transformation to nitrate via nitrification. In further support of this hypothesised linkage, DOC loss explained 80–89% of the variance in nitrate production in Grape Vine Canyon Stream.
Effects of riparian leaf dynamics on periphyton photosynthesis and light utilisation efficiency
Authors: HILL WALTER R. , DIMICK SARAH M. 
Published: March 2003

1. Streambed light regimes change dramatically when riparian trees gain leaves in spring and lose them in autumn. This study examined the effect of these changes on periphyton photosynthetic characteristics, primary production, and light utilisation efficiency in two eastern Tennessee streams.2. Photosynthesis–irradiance responses were measured at intervals covering leaf emergence and abscission in spring and autumn. Photosynthetic efficiency (αchl) increased with declining streambed irradiances during spring leaf emergence, but returned to pre‐emergence values after autumn leaf fall. The onset of photosaturation (Ik) displayed the opposite pattern, decreasing during leaf emergence and increasing after leaf fall. Both αchl and Ik were closely associated (P < 0.01) with daily integrated streambed irradiance, as were periphyton carotenoids. Internal shading by photoprotective carotenoids is hypothesised to account for lower αchl when streambed irradiances are high.3. An in situ shading experiment confirmed that the temporal changes observed in periphyton photosynthetic characteristics and carotenoids were primarily the result of changing light levels and not other environmental factors (e.g. nutrients, temperature).4. Daily chlorophyll‐specific primary production (PPchl) was calculated with P–I models and recorded streambed irradiances. In both streams, PPchl was the highest in early spring when trees were leafless, and then declined markedly as leaves emerged, reaching a minimum in summer. PPchl increased after leaf abscission, but was still lower than it was in early spring, when the sun was higher and daylength was longer. A hyperbolic tangent equation fit to PPchl and daily integrated irradiance (r2=0. 85) suggested that primary production was light saturated at 4–8 mol m–2 d–1.5. Light utilisation efficiency (Ψ) increased 10‐fold during leaf emergence. Photosaturation at high irradiances and photoacclimation at lower irradiances were responsible for a negative hyperbolic relationship between Ψ and daily integrated irradiance.
Essential fatty acid content and the phosphorus to carbon ratio in cultured algae as indicators of food quality for Daphnia
Authors: PARK SANGKYU , BRETT MICHAEL T. , MÜLLER‐NAVARRA DÖRTHE C. , GOLDMAN CHARLES R. 
Published: March 2003

1. A series of experiments examined growth of Daphnia magna on three algal diets (Rhodomonas minuta, Scenedesmus acutus and Synechococcus sp.) at varying physiological states [nitrogen and phosphorus (P) limitations] to test whether variation in algal fatty acid and/or elemental composition can predict Daphnia growth.2. These algae differed widely in their essential fatty acid (EFA) composition while phosphorus (P) or nitrogen limitation had only a small influence on their ω3‐polyunsaturated fatty acid (PUFA) content.3. Individually, algal ω3‐PUFA content explained 69% of the variation in the normalised growth of D. magna, while algal phosphorus content explained 11% of the variation. Quantitative models for D. magna growth used both algal ω3‐PUFA content and algal C : P ratio as food quality indices. Together, algal ω3‐PUFA content and C : P ratio explained 70% of the variation in the normalised growth rate of D. magna.4. Our results indicate that EFA influenced algal food quality much more strongly than P. The EFA and mineral P impacts appear to be independent.