bluuebunny/crossref_metadata_2025_split huggingface dataset:
Regional and temporal variation in pH, alkalinity and carbon dioxide in Danish streams, related to soil type and land use
Authors: REBSDORF A. , THYSSEN N. , ERLANDSEN M. 
Published: May 2006

SUMMARY 1. The Weichsel glaciation has divided Denmark into two regions with different susceptibility to acidification. East of the Weichselian terminal moraine, soils are usually clayey and calcareous, and the streams are alkaline (mean alkalinity 2.24 mmol 1‐‐1) and resistant to inputs of acidifying substances.2. Trend analysis of pH and alkalinity of water samples taken over 15 years in two streams with alkalinities above 1.5 mmol 1−1 in eastern Jutland, showed no trends of acidification.3. West of the terminal moraine the soils are sandy and leached and alkalinity is lower (mean 0.59 mmol 1−1). Although such streams with medium alkalinity are believed not to be vulnerable to acidification, we have documented significant decreases in their pH and alkalinity over 12 years.4. Trends of pH and alkalinity in four western streams with mean alkalinities between 0.05 and 0.79 mmol 1−1 showed annual decreases of 0.027 pH units and 4.7 nmol 1−1 in alkalinity.5. Overall, Danish streams contain about 7.9 times more calculated free CO2 (pCO2=10−2.6 atm) than water in equilibrium with air (pCO2= 10−3.5 atm). The calculated free CO2 content has increased significantly in western Danish streams over the study period (6.9 μmol 1−1 yr‐1). This increase cannot be explained by the prevailing global increase in atmospheric pCO2 which only can account for 0.54 pmol 1−1 yr−1 at maximum.6. Reasons for the ongoing stream acidification in the western part of Denmark are discussed. We suggest that atmospheric deposition causes stream acidification in a heath‐covered catchment without agriculture. In heavily cultivated regions the main acidification factor is argued to be proton production in the soil through nitrification of ammonium‐containing fertilizers.
Prey behaviour and size‐selective predation by fish
Authors: MACCHIUSI FRANK , BAKER ROBERT L. 
Published: May 2006

SUMMARY 1. We investigate the role of differential activity of chiro‐nomids as an explanation for the size selection of small larvae by fish.2. In the laboratory, pumpkinseed sunfish (Lepomis gibbosus L.) selectively consumed large larvae of Chironomus tentans Fab. when no tube‐building materials were available. Small larvae were selectively consumed when a mud substrate was provided but there was no difference in predation rates on large and small larvae in sand.3. Small larvae spent more time out of their tubes than large larvae in the presence of fish, which may explain the selection for small larvae in mud. Large larvae apparently compensated for decreased foraging activity in the presence of fish by increasing activity when fish were absent. Visibility of large larvae inside tubes may account for their increased mortality in sand.4. Our results suggest that differential activity is important in explaining the size‐selective mortality observed in the field.
Growth of the medicinal leech, Himudo medicinalis, under natural and laboratory conditions
Authors: WILKIN P. J. , SCOFIELD A. M. 
Published: May 2006

SUMMARY 1. The growth of the medicinal leech, Hirudo medicinalis L., was studied in the wild by a mark and recapture technique, and in the laboratory. Growth in the wild, even after 2 years, was generally small and variable.2. After being offered regular feeds of various preparations of bovine blood through a pig‐ileum membrane and being allowed to feed to satiation, hatchling leeches in the laboratory showed a saltatory pattern of weight gain with increases greatly in excess of those seen in the wild. Twelve of twenty‐five leeches starved from hatching survived for about 250 days. The ability to survive for long periods without feeding may well be important for the overwintering survival of late hatchlings.
A continuous‐flow system for measuring in vitro oxygen and nitrogen metabolism in separated stream communities
Authors: PRAHL C. , JEPPESEN E. , SAND‐JENSEN K. , MOTH‐IVERSEN T. 
Published: May 2006

SUMMARY.
1. This paper describes a continuous‐flow system that we have used extensively for measurement of oxygen exchange and nitrogen transformations in different communities of lowland streams, i.e. the water, the sediment, and the macrophyte—biofilm community. The system, which is set up on the stream bank, consists of several macrophyte and sediment chambers equipped with a double‐flow system that ensures an internal water velocity close to that in the stream and which, by continuously renewing the water, mimics diel fluctuation in stream temperature and water chemistry. Water temperature and dissolved oxygen are measured continuously and the data stored on magnetic tape. Water samples are collected in a refrigerator and analysed using standard chemical procedures.2. The application of the system is illustrated using results obtained during a 2‐day summer experiment in a shallow macrophyte—rich stream. The biological processes in the stream were mainly associated with the macrophyte—biofilm community and the sediment, those in the water being negligible. Oxygen release was confined to the macrophyte—biofilm community, the sediment consuming oxygen both by day and by night. Whole‐system gross production and dark respiration occurred at similar rates (6–7g O2 m−2 day−1), net balance being about zero. Inorganic nitrogen was consumed both by the sediment and to a greater extent by the macrophytes, the diel average consumption being 1g N m−2 day−1.3. The sum of the activity in the macrophyte and sediment chambers corresponded to the overall activity of the stream section as determined by upstream/downstream mass balance. This indicates that the results obtained with the continuous‐flow chambers realistically describe the oxygen and the nitrogen metabolism of the stream.
Extracellular enzyme activity associated with suspended matter in the River Rhine
Authors: ADMIRAAL W. , TUBBING G.M.J. 
Published: May 2006

SUMMARY.
1. Spatial and temporal variations in exoenzymatic proteolysis and alkaline phosphatase activity in the River Rhine were measured fluorometrically using L‐leucyi (ß‐naphthylamide and methylumbelliferyl phosphate (MUFP), respectively, as test substances.2. Extracellular proteolytic activity measured in the lower 150‐km reach of the river during 1988 followed the changes in the concentration of particulate nitrogen associated with the occurrence of phytoplankton blooms. Alkaline phosphatase activity was not related to the concentration of particulate phosphate and correlated weakly with particulate nitrogen and phytoplankton concentrations.3. Seasonal observations (1989) in the lower River Rhine and transport studies in a 660‐km‐long reach of the river (1990) indicated that the variations in the exoenzyme activities were unrelated (or not closely related) to fluctuating bacterial numbers. Exoproteolytic activity correlated well with thymidine incorporation and algal density, confirming indications in the literature that the exoenzyme activity is related to the overall metabolic rate of the bacterial populations.4. The exoproteolytic activities in the Rhine are similar to the highest observed in eutrophic freshwaters, indicating a rapid turnover of proteins in the river. Bacterial phosphatase activities, measured with MUFP, were similar to those in the few marine and inland waters studied so far. However, phosphate‐limited algal blooms, such as reported for the plume of the Rhine in the North Sea, are likely to contribute substantially to hydrolysis of natural organic phosphates.
The fauna of North American temperate cold springs: patterns and hypotheses
Authors: GLAZIER D.S. 
Published: May 2006

SUMMARY.
1. The relative abundance of six classes of macroinvertebrates in fifteen mid‐Appalachian and thirteen other North American cold springs is briefly reviewed. In both surveys peracaridans, molluscs, and triclads dominated the hard‐water limestone springs, whereas insects dominated the relatively acidic soft‐water springs.2. A hypothetical framework is offered to explain the dominance of non‐insect taxa in hard‐water limestone springs. The importance of a non‐emergent lifestyle and high population densities in springs is emphasized. Some evidence is offered in support of the proposed hypotheses, but most of the testing remains to be done.
Spring bloom development of microbenthic algae and associated invertebrates in two reaches of a small lowland stream with contrasting sediment stability
Authors: IVERSEN TORBEN MOTH , THORUP JENS , KJELDSEN KARINA , THYSSEN NIELS 
Published: May 2006

SUMMARY.
The microbenthic algal biomass and the invertebrate fauna were quantified during an algal spring bloom in two reaches of a small Danish lowland stream which, although similar with regard to stream velocity, water chemistry and irradiance, differed with regard to substrata and sediment stability. Due to channelization, one reach (Ellerup I) had low variation in depth, unstable sand midstream and mud along the banks; the other reach (Ellerup II) had more variable depth and more different and stable substrata.
At Ellerup I, maximum mean algal biomass was 74 ± 28 mg chl m −2. Algal biomass primarily developed in muddy areas near the banks, whereas midstream algal biomass remained low.
At Ellerup II, maximum mean algal biomass was 161 ± 41 mg chl m−2 on fine‐grained sediments and 64 ± 21 mg chl m−2 on stones. Algal biomasses near the banks and midstream were similar, but seasonal development on the two main substrata was significantly different, suggesting that algal development on the two substrata was regulated by different factors.
At Ellerup I, the invertebrate fauna was dominated by Oligochaeta and invertebrate density and diversity were generally higher near the banks than midstream. Such differences did not occur at Ellerup II, where total invertebrate density was significantly higher than at Ellerup I and the fauna was dominated by Orthocladiinae, Simuliidae and Baetis sp.
It was concluded that stream channelization and maintenance, through their effects on sediment variation and stability, profoundly affect algal biomass distribution and development and invertebrate distribution, density and community structure.
Calibration of FST‐hemispheres against bottom shear stress in a laboratory flume*
Authors: STATZNER B. , KOHMANN F. , HILDREW A.G. 
Published: May 2006

SUMMARY.
Fliesswasserstammtisch (FST)‐hemispheres of identical size but different densities were exposed on a horizontal plane on the pebble‐covered bottom of a laboratory flume at streaming to shooting, turbulent and fully developed flow. The heaviest hemisphere moved was used as an indicator of shear stress, a flow force acting on the flume bottom.
The relationship between shear stress and hemisphere density was practically the same for three different sets of hemispheres, namely one prototype set newly prepared for the calibrations, one prototype set intensively used in the field prior to calibrations, and one randomly selected new set bought commercially.
Shear stress (y, dyn cm−2) was related to hemisphere density (x, g cm−3) by y= x2.85 (n= 69; r2= 0.993). For lighter hemispheres this relationship was better explained by the linear model y= 7.32x– 6.60 (n= 35; r2=0.983).
Invertebrate recolonization of small patches of defaunated hyporheic sediments in a Sonoran Desert stream
Authors: BOULTON A.J. , STIBBE S.E. , GRIMM N.B. , FISHER S.G. 
Published: May 2006

SUMMARY.
Fine mesh (63 nm) traps filled with defaunated sediment and open to recolonization from upstream, downstream or below were buried 30 cm deep in the hyporheic zone of a gravel run in a desert stream and recovered after 1, 3, 7, 14 and 27 days. Temporal changes in organic matter and faunal composition and abundance were compared among treatments and with those in completely closed ‘control’ traps.
Closed traps consistently contained tittle detritus (<30mg AFDM per 5000 cm3). Traps facing upstream accumulated significantly more organic matter than those facing below or downstream, indicating downstream hyporheic transport of fine particulate detritus.
Upstream‐facing traps also captured significantly greater numbers of taxa and individuals. Low numbers of most taxa recolonized from all three directions within 1 day; total densities of individuals in the traps increased before levelling off after 2 weeks.
The prediction that taxa with planktonic epigean relatives (e.g. cyclopoid copepods) would predominate in upstream facing traps was unsupported, nor did unpigmented, blind phreatic forms preferentially colonize traps from below. Two closely related taxa exhibited major differences in recolonization dynamics, illustrating the risk of masking such trends when pooling data for more than one taxon.
Experimental manipulations such as this supplement the predominantly descriptive studies of the hyporheos, and demonstrate the complex dynamics of organic matter and biota in the hyporheic zone that must be considered in analyses of most stream ecosystems.
Emigration and immigration can be important determinants of benthic diatom assemblages in streams
Authors: JAN STEVENSON R. , PETERSON CHRISTOPHER G. 
Published: May 2006

SUMMARY.
Interspecific differences in diatom abundances in stream drift (plankton), immigration, and natural benthic assemblages were compared to assess the importance of emigration and immigration in benthic diatom community dynamics. Water samples were collected throughout a 24‐h period to measure diel changes in diatom drift abundances and to estimate benthic diatom emigration rates. Immigration was assessed with 24‐h colonization of bare tiles.
Dissimilarity in species composition of drift, immigration, and natural substrate assemblages indicated differential emigration and immigration among diatom species.
A mathematical model indicated that reproduction by diatoms in the plankton could not account for diel drift peaks and that diel variation in drift was an informative measure of benthic diatom emigration.
Emigration and immigration of some species constituted substantial proportions of diatom abundances on natural substrata. We conclude that emigration into the drift and immigration onto substrata can be important processes that regulate benthic diatom species composition and standing crop in streams.
An experimental study of the influence of periphytic algae on invertebrate abundance in a Hong Kong stream
Authors: DUDGEON DAVID , CHAN IVAN K.K. 
Published: May 2006

SUMMARY1. Small cages (294cm2) containing unglazed clay quarry tiles were used to investigate the influence of periphytic algae on macroinvertebrate abundance in a Hong Kong stream. Algal biomass was manipulated by shading cages with plastic sheets. Individual cages were assigned to one of three treatment groups: unshaded, shaded and deeply shaded. Invertebrate densities and algal biomass within cages were monitored after 23, 37 and 65 days.2. Multiple‐regression analysis revealed that algal biomass, invertebrate morphospecies richness and total abundance declined with greater shading intensity. The responses of individual invertebrate taxa varied: some (especially Trichoptera) were unaffected by shading, whereas grazers (Baetidae, Psephenidae and Elmidae) declined as shading increased.3. Significant regressions of the densities of individual taxa upon algal and detrital standing stocks in cages had positive slopes, but algal biomass increased during the study while detrital standing stocks declined. Abundance of invertebrates declined or remained rather stable over time. Density increases resulting from a positive association with algae were apparently offset by declines in abundance correlated with reductions in detritus.4. Declines in algal biomass were associated with greater shading to which animals may respond directly. To uncouple the link between scarcity of algae and reduction of light intensity, the plastic covers on two groups of cages (deeply shaded and unshaded) which had been placed in the stream for 28 days were reversed so that cages which had been shaded became unshaded and vice versa. The cages were recovered on day 33, Only Coleoptera demonstrated a positive association with atgae inside cages; no relationship between population densities and algal biomass or light intensity was apparent for other taxa. However, the design may have been confounded by deposition of sediment in the cages (due to declining stream discharge) which reduced population densities of colonizers.5. This study documents changes in invertebrate abundance and morphospecies richness in response periphyton and detritus standing stocks within patches. Summation of such responses may account for observed variations in benthic communities among Hong Kong streams which differ in the extent of shading by riparian vegetation.
Indirect effects of fish on foraging behaviour and leaf processing by the isopod Lirceus fontinalis
Authors: SHORT T.M. , HOLOMUZKI J.R. 
Published: May 2006

SUMMARY1. We examined whether the isopod, Lirceus fontinalis, an important facultative shredder in low‐order streams in the eastern United States, responded to chemical cues of the skin mucus of five fish species varying in relatedness and feeding habits, and if fish‐induced alterations in the foraging activity of isopods indirectly affected leaf processing.2. In the laboratory, isopods generally responded to the presence of fish mucus by reducing their activity. Isopods were most responsive in water containing the skin mucus of predatory sunfish (Lepomis) and least responsive in water treated with mucus from algivorous stonerollers (Campostoma anomalum).3. Rates of leaf disc breakdown by isopods in the laboratory were significantly reduced when isopods were exposed to chemical cues of confined green sunfish (L. cyanellus).4. The rate of leaf processing in a fishless reach of a headwater stream was four to five times greater by isopods 7—10mmTL (total length) than those ≤ 5mm TL. Rates of leaf processing by isopods in low‐order streams may be affected directly by the size structure of the isopod population and indirectly by the presence of fish.
Effects of drying and freezing autumn leaves on leaching and colonization by aquatic hyphomycetes
Authors: BÄRLOCHER FELIX 
Published: May 2006

SUMMARY1. Drying or freezing autumn‐shed leaves of Betula papyrifera, Ulmus americana and Acer saccharum increased the leaching of soluble substances. The difference between fresh and treated leaves was most pronounced in birch.2. Dried and frozen leaves supported more species of aquatic hyphomycetes during early decay, and conidium production from these fungi was higher.3. Anguillospora filiformis was the most prolific spore producer on most samples. It declined in later stages of decay, when Articulospora tetradadia became more common. Crucella subtilis, an unspecialized parasite of aquatic hyphomycetes, was quite common in many samples.4. In the autumn of 1990, 50% of elm and maple leaves, and 30% of birch leaves were shed before the air temperature dropped below 0°C; 10% (elm, maple) to 30% (birch) experienced more than one freezing period before being shed.5. Water‐soluble extracts from leaves inhibited radial growth of four fungal species. Maple extracts generally had the greatest inhibitory effect, followed by birch and elm.
Changes in the abundance and composition of cyclopoid copepods following fish manipulation in eutrophic Lake Væng, Denmark
Authors: HANSEN ANNE‐METTE , JEPPESEN ERIK 
Published: May 2006

SUMMARY1. The seasonal cycle of cyclopoid copepods during and following an approximately 50% reduction in planktivorous fish biomass was studied in shallow, eutrophic Lake Vaeng, Denmark, from 1986 to 1990.2. The dominant cyclopoid copepods changed from Cyclops vicinus and Mesacyclops leuckarti during 1986–1989 to M. leuckarti and Megacyclops viridis in 1990. The abundance of cyclopoid copepods gradually increased from 1986 to 1988–89, decreased in autumn 1989 and markedly decreased in 1990.3. The increase in the abundance of cyclopoid copepods from 1986 to 1988 is attributed mainly to the reduction in fish predation pressure, there being no concomitant increase in edible phytoplankton. The appearance of M. viridis in 1990, and the general decrease in cyclopoid copepod density in autumn 1989 and in 1990, are attributed to the appearance of submerged macrophytes.4. Temperature, predation and availability of edible phytoplankton appear to determine whether C. vicinus or M. leuckarti dominates the cyclopoid copepod population of eutrophic Lake Væng.
Microcrustacea in flowing water: experimental analysis of washout times and a field test
Authors: RICHARDSON WILLIAM B. 
Published: May 2006

SUMMARY1. Flow‐chamber experiments were conducted to evaluate the ability of microcrustacea to maintain position in moving water. These results were compared to distributions of zooplankton and water velocity in a stream pool to determine the relationship of animal density to water movement and swimming ability.2. Cladocerans exhibited negative rheotaxis (directed behaviour against a current) but poor ability to maintain position at velocities >2.5cm s−1. Daphnia and Scapholeberis were better at avoiding washout than Moina and Diaphanosoma. At velocities <2.5cm s−1Eucyclops (Cyclopoida) tended to exhibit no rheotaxis.3. Washout of Daphnia was complete at velocities >2.5cm s−1, Scapholeberis >3.2cm s−1 and Eucyclops >7.75 cm s−1. Washout time of Daphnia and Scapholeberis was positively related to body size and negatively to water velocity and possession of eggs. Washout was inversely related to water velocity for Eucyclops.4. Highest densities of microcrustacea in a stream pool were found in non‐flowing or downstream zones of the pool. Benthic (Hydracarina, harpacticoid copepods, ostracods) and fast‐swimming (cyclopoids) forms were most common in flowing zones. Facultatively benthic Cladocera were abundant in regions of no flow. Rotifers and immature copepods were most abundant at the downstream end of the pool.5. Behavioural mechanisms for remaining in stream pools at times of high flow appear to include: (i) flow avoidance (Simocephalus, Chydorus, Scapholeberis and cyclopoids), (ii) use of benthic habitat (ostracods, harpacticoids, Hydracarina), (iii) strong swimming ability (cyclopoids).
Herbivory of invertebrates on submerged macrophytes from Danish freshwaters
Authors: JACOBSEN DEAN , SAND‐JENSEN KAJ 
Published: May 2006

SUMMARY1. Invertebrate herbivory on submerged freshwater macrophytes, measured as per cent leaf area lost, was determined for sixteen species and forty‐two populations of macrophytes during peak summer biomass in Danish streams and lakes.2. All seventeen Potamogeton populations and seventeen of the remaining twenty‐five non‐Potamogeton populations were grazed. Species of Potamogeton were significantly more heavily grazed (mean 4.2%) than non‐Potamogeton species (mean 0.8%). Herbivory losses were not significantly different between stream (mean 2.4%) and lake populations (mean 1.9%). Wide ranges in herbivory loss were observed between species from the same locality and within species from different localities. The location of main damage to either old or young leaves was not species specific but varied among localities. Additional data for four macrophyte populations showed that herbivory loss had a strong seasonal variation (e.g. 1.0–26.3% for Potamogeton perfoliatus), with maximum losses during May‐June.3. Although the mean defoliation percentages were low during the period of maximum macrophyte biomass, they were not systematically lower than encountered for terrestrial plants.