bluuebunny/crossref_metadata_2025_split huggingface dataset:
Efficient estimation of temperature distribution, heat storage, thermocline migration and vertical eddy conductivities in stratified lakes
Authors: STAUFFER ROBERT E. 
Published: May 2006

SUMMARY1. Factorial designs were used to investigate the spatial and temporal components of temperature sampling error in two medium‐sized (maximum fetch = 9 and 11 km; maximum depth = 24 and 70m) Wisconsin lakes (Mendota and Green). Sampling designs were then optimized for estimating temperature distributions, thermocline migration, lake heat content, and vertical eddy conductivities in these and similar stratified lakes.2. Errors were at a minimum for: (i) isotherms positioned1/3‐1/2of the way down through the seasonal thermocline; (ii) at lake stations located near the node of the principal internal seiche; (iii) after an extended interval of low windpower. If seven spatially distributed lake stations were sampledn1,n2times during the two low‐power intervals bracketing a weather front, and the rime delay between revisits was randomized with respect to the period of the uninodal temperature seiches, the resulting standard error (cm) in Δ&#x005a;̄17(depth of 17° isotherm; an unbiased, minimum‐variance estimator for main thermocline migration) was (144/n1+ 144/n2)1/2. Ifn1=n2= 2 ‘revisits’, the resulting CV (coefficient of variation) was 5–10% for Δ&#x005a;̄17accompanying major individual cold fronts in early summer.3. When estimatingKz, the vertical eddy conductivity, the most important component of error relates to ΔHz, the change in heat content below depthz. The error in ΔHzis minimized in the same manner as for lake‐mean isotherm depth. Using the Mendota sampling design described above, the RMS error in ΔHzdecreases from ∼90 cal cm−2in the upper metalimnion to ∼35calcm−2near the base of the metalimnion. For seven take stations, andn1= n2= 2,Kzcan be estimated with a CV ∼10% bracketing a single major cold front. The CV decreases approximately as ΔHz−1, hence is roughly proportional to Δt−1or to (cumuiative windpower)−1.
Quantification of submerged wood in a lowland Australian stream system
Authors: O'CONNOR NICHOLAS A. 
Published: May 2006

SUMMARY1. The importance of submerged wood (snags) as macroinvertebrate habitat was evaluated in the Pranjip‐Creightons Creek system, a lowland stream system in northern Victoria. Snag surface area and biomass were measured at ten sites along the system. The first four upstream sites, located in the foothills of the Strathbogie Ranges, and the next three sites, on the northern Victorian riverine plain, were affected by streambank erosion and high sediment loads and contained little instream wood. A further three sites (Sites 8, 9 and 10) downstream on the riverine plain were not as affected by erosion and possessed extensive stands of riparian river redgum, Eucalyptus camaldulensis, which contributed large amounts of wood to the stream channel.2. Wood quantities at Site 8 were less than at Sites 9 and 10 downstream where the density of riparian redgum was greater. At Sites 9 and 10, snag surface area per m2 of stream bed was 0.57–0.92m2 and 0.38–0.71m2 depending on discharge. Total snag biomass in the stream channel at the same sites was 26 and 41kg m−2, respectively. Redgum was important to macroinvertebrates as habitat, at one site contributing 25% of total macroinvertebrate densities and over 30% of total macroinvertebrate biomass m−2 of stream bed.3. Estimations of nitrogen content and C:N ratios of decayed redgum were carried out to provide information on its putative nutritional quality to xylophagous macroinvertebrates. Decayed redgum wood has a comparatively high N content and therefore a low C:N ratio, but appeared to be unpalatable to most macroinvertebrates. Only two macroinvertebrate species, the chironomid larvae Stenochironomus sp. and Dicrotendipes sp., were found to consume decayed redgum.
Fluxes of bacteria and organic matter into a blackwater river from river sediments and floodplain soils
Authors: WAINRIGHT SAM C. , COUCH CAROL A. , MEYER JUDY L. 
Published: May 2006

SUMMARY1. The Ogeechee River, in south‐eastern Georgia, U.S.A, is a blackwater river with an extensive floodplain that is inundated regularly during winter months. Previous studies have shown that low to moderate bacterial production rates cannot support the relatively high suspended bacteria concentrations observed (107−‐108 cells ml−1), suggesting an allochthonous source of bacteria. We report the results of a combination of field and flume experiments which demonstrate that river sediments and floodplain soils are significant sources of suspended bacteria during seasonal flooding. Benthic bacteria are also entrained by normal discharges. There are sizeable fluxes of POC and DOC from river sediments and floodplain soils.2. Bacterial, POC and DOC fluxes (14, 250, and 790 mg Cm−2 h−1, respectively) were substantial when water was percolated upward through floodplain soils.3. Simulation of overland flow using a flume demonstrated further fluxes of bacteria and POC from floodplain soils (up to 61 and 10700 mg Cm−2h−1, respectively) and river sediments, but did not yield additional DOC from floodplain soils.4. These laboratory results are supported by experiments in which we measured significant increases in concentrations of bacteria and DOC in a downstream direction in (i) the main river channel during a winter flood in 1986, and (ii) a floodplain slough (channel side‐arm) which re‐entered the main channel 800m from its initial divergence. Inputs of bacteria and DOC from the surrounding floodplain were estimated to be up to 3500 kg DOC h−1, and 4000 kg bacteria Ch−1 over a 50‐km reach.5. These previously unmeasured fluxes of organic carbon help to explain the high concentrations of suspended bacteria in the Ogeechee River.
Diatom communities along stream longitudinal gradients
Authors: MOLLOY JENNIFER M. 
Published: May 2006

SUMMARY1. Summer diatom communities on artificial substrates were sampled weekly for a month in three first‐ to sixth‐order tributaries of the Kentucky River to determine how community structure varied with stream size.2. Diatom cell abundances were generally higher in the headwaters. Species diversity increased in a downstream direction in two of the streams, and in an upstream direction in the third. However, diversity in general seemed more closely related to current regimes than to stream size per se, with highest species diversity at intermediate current velocities.3. Variation in diatom accumulation rates was greater in downstream communities than in the headwater assemblages of two streams, suggesting that downstream communities may experience greater fluctuations in abundance, at least under low‐flow conditions.4. Patterns of species distributions suggested a relationship between morphological growth forms (guilds) and stream size, as well as the influence of current. Achnanthes spp., Eunotia spp., erect, and stalked taxa were more commonly associated with headwater assemblages. Filamentous and centric diatoms occurred with greater frequency downstream.
The coexistence of Bosmina and Ceriodaphnia in a south Andes lake
Authors: BALSEIRO E.G. , MODENUTTI B.E. , QUEIMALIÑOS C.P. 
Published: May 2006

SUMMARY1. The coexistence of Bosmina and Ceriodaphnia was studied in relation to phytoplankton succession in a small lake (Laguna Ezquerra) in the araucanian region of Argentina.2. The study involved field sampling and single species cultures of each of the two cladocerans in lake water under laboratory conditions.3. Ceriodaphnia showed a unimodal cycle while Bosmina had a bimodal pattern during 4 months of coexistence. Ceriodaphnia exhibited a direct relationship between clutch size and biovolume of edible algae, whereas Bosmina's fecundity was related to the density of flagellates.4. We found that the fecundity of these species responded differently to laboratory and field conditions. The fecundity of Ceriodaphnia followed the same pattern in both the field and laboratory, whereas Bosmina showed higher fecundity values in laboratory experiments.5. Our results are in good agreement with predictions derived from Northern Hemisphere studies, indicating that food‐limited populations of daphnids and Bosmina can coexist for extended periods in spatially homogeneous environments.6. The variation in food availability, measured as biovolume of edible algae, determines the loss of Ceriodaphnia and the persistence of Bosmina.
Immobilization and mineralization of dissolved free amino acids by stream‐bed biofilms
Authors: FIEBIG DOUGLAS M. , MARXSEN JORGEN 
Published: May 2006

SUMMARY1. Radiolabelled (14C) amino acids were used to investigate the influence of sediment size as well as dissolved free amino acid (DFAA) concentration and composition on immobilization and mineralization of DFAAs by biofilms from a first‐order stream.2. Over time (240 min), biofilms on stony substrata immobilized a DFAA mixture more effectively than those on sandy substrata, however proportional mineralization of immobilized DFAAs was higher for sandy substrata (36 v 20%).3. Using stony substrata, the DFAA mixture was immobilized more rapidly than glycine alone at ‘near‐natural’ amino acid concentrations (c. 37 μgl−1), as well as enriched concentrations (1 and 100 mg 1‐−1). Instantaneous rates of glycine immobilization and mineralization were not saturated at glycine enrichments of up to 980 mgl−1.4. With both the amino acid mixture and glycine alone, proportional mineralization of the immobilized amino acids increased on enrichment to Img 1‐−1 (DFAA mixture: from 25 to 37%; glycine alone: from 50 to 54%), but then fell on further enrichment to 100mgl−1 (DFAA mixture: 11%; glycine alone: 7%).5. Results are discussed in terms of the potential trophic utility of immobilized DFAAs as well as the apparent roles of biotic and abiotic immobilization mechanisms. Immobilization and mineralization responses to variables investigated in this study give an insight into potential variability of carbon immobilization and retention in stream‐bed sediments. This is fundamental to an understanding of how DOC may become available to higher trophic levels.
Reversal of eutrophication in Lake Geneva: evidence from the oligochaete communities
Authors: LANG CLAUDE , REYMOND OLIVIER 
Published: May 2006

SUMMARY1. In Lake Geneva (Switzerland), total phosphorus concentrations have decreased from 90 mg m−3 in 1979 to 55 mg m−3 in 1990.2. To assess the effects of this improvement, tubificid and lumbriculid communities were sampled in 1982 and in 1991 in the same areas, at a depth of 40 m.3. Abundance of mesotrophic species (mostly Potamothrix vejdovskyi) and of eutrophic species (mostly Potamothrix hammoniensis) was lower in 1991 than in 1982; in contrast, oligotrophic species (mostly Peloscolex velutinus) were more abundant in 1991 than in 1982.4. The changes recorded in 1991 were the same as those associated with a decrease of organic sedimentation.5. Mean relative abundance of oligotrophic species increased from 17% in 1982 to 41% in 1991. According to these values, Lake Geneva was mesoeutrophic in 1982, but mesotrophic in 1991.
Nutrients, algae and grazers in some British streams of contrasting pH
Authors: WINTERBOURN MICHAEL J. , HILDREW ALAN G. , ORTON STUART 
Published: May 2006

SUMMARY1. The relationship between algal biomass accumulation, invertebrate colonization, and stream‐water pH was investigated in seven streams in three regions of England and Wales. Possible nutrient limitation of algal production at all sites was examined with diffusion substrata.2. Periphyton assemblages on experimental substrata after 30 days were dominated by diatoms, notably Eunotia spp., at all sites. Algal pigment concentration (chlorophyll a and phaeopigments) was not correlated with stream‐water pH, and mean concentrations on control (unenriched) substrata ranged from 0.08 to 1.94 μg cm−2.3. The growth response of periphyton to nutrient additions was site specific. Algal production was stimulated by nutrient additions at sites in the English Lake District and Llyn Brianne (south‐west Wales), but not in the Ashdown Forest (southern England).4. Larval Chironomidae were the main invertebrates retrieved from substrata at all sites. Within all three regions, larval abundance was positively related to algal pigment concentration (biomass). Abundance of the stonefly Nemurella pictetii was also positively correlated with algal biomass at the one site where it occurred.5. Our results indicate that epilithic algal production in small, oligotrophic streams is unlikely to be determined primarily by pH. Neither do they support the view that an absence of grazers from acid streams is necessarily due to an inadequate food supply.
Mortality of the terrestrial adult and aquatic nymphal life stages of Baetis vernus and Baetis rhodani in the Breitenbach, Germany (Insecta: Ephemeroptera)
Authors: WERNEKE ULRICH , ZWICK PETER 
Published: May 2006

SUMMARY1. The mortality of Baetis vernus Curtis and Baetis rhodani Pictet during the terrestrial‐aerial and aquatic life stages was studied at the Breitenbach near Schlitz, Hesse, Germany. The number of females emerging from the stream was recorded with emergence traps. To estimate mortality of females of both species during terrestrial life, numbers of emerging females were compared with numbers of females returning to the stream for oviposition, as shown by numbers of egg masses found in the stream.2. Mortality of female B. vernus during their terrestrial life stage was 98.8%. It was 91.2 and 96.6%, respectively, during the first and second generations of B. rhodani.3. To estimate the mortality of both sexes of B. rhodani during the aquatic life stage, the number of eggs laid by the first generation was compared with the number of adults emerging during the second generation.4. Mortality during the aquatic phase (both sexes combined) of B. rhodani was 91.1%.5. Mortality during the terrestrial life stages was at least as high, if not higher than during the aquatic stages. Evidently, there is a considerable export of organic material into the terrestrial environment around the stream. Mortality during terrestrial life may be an important regulator of population size.
Mixotrophic algae in three ice‐covered lakes of the Pocono Mountains, U.S.A.
Authors: BERNINGER ULRIKE‐G. , CARON DAVID A. , SANDERS ROBERT W. 
Published: May 2006

SUMMARY1. The occurrence and grazing activity of mixotrophic (phagotrophic) algae in three icecovered freshwater lakes of different trophic status were examined (oligotrophic Lake Giles, mesotrophic Lake Lacawac, eutrophic Lake Waynewood), Microbial population densities were low (4.1–7.2 × 105 bacteria ml−1 and 1.2–2.4 × 103 nanoplanktonic protists ml−1). All three nanoplankton communities were dominated by chloroplast‐bearing forms (60–96%).2. Mixotrophs formed up to 48% of the phototrophic nanoplankton in Lake Lacawac and were responsible for up to ∼90% of the observed uptake of bacteria‐sized particles. The abundance of mixotrophic algae in Lakes Giles and Waynewood were extremely low (3 and 2% of the phototrophic algae, respectively), and heterotrophs dominated nanoplankton bacterivory.3. The overall impact of nanoplankton feeding activity on the bacterial assemblage was low under the ice in Lakes Giles and Waynewood. Removal rates of bacteria based on our particle uptake experiments were 1.0 and 4.0% of the bacterial standing stock day−1 in these lakes, respectively. Removal rates were higher in Lake Lacawac and ranged from 4.9 to 11% of the bacterial standing stock day−1 on 2 successive sampling days.
Non‐annual external annuli in the freshwater musselsAnodonta grandis grandisandLampsilis radiata siliquoidea*
Authors: DOWNING WILLIAM L. , SHOSTELL JOSEPH , DOWNING JOHN A. 
Published: May 2006

SUMMARY1. Two species of freshwater mussels,Lampsilis radiata siliquoideaandAnodonta grandis grandiswere measured and permanently marked with pointed, plastic tape positioned at the postero‐lateral edge of the shell. Mussels were returned to original conditions at two sites in an oligotrophic lake, retrieved at yearly intervals, re‐measured, and external annuli that had been added since marking were counted.2. External annuli were formed much less frequently than annually; the overall median number of annuli formed each year was 0.5. In one of the four populations studied, the rate of annulus formation was >1 in small animals and <1 in large ones. Many mussels showed no new external annuli at all, even several years after marking.3. Ford‐Walford plots of shell annuli did not yield consistent indices of shell growth. Repeated measurement of mussels in successive years showed that estimates of growth based on shell annuli consistently overestimated real shell growth.
Ecology of invertebrate predators in a Coastal Plain stream
Authors: SMITH LANE C. , SMOCK LEONARD A. 
Published: May 2006

SUMMARY1. The spatial and temporal abundance patterns, production and feeding habits of invertebrate predators were determined in a sand‐bottomed, headwater stream in Virginia, U.S.A.2. Annual mean density and biomass of predators in debris dams were 3897 individuals m−2 and 2.5 g dry mass m−2, respectively, but only 711 individuals m−2 and 0.2 gm−2 on the sediment. Predator production was 8.36 gm−2yr−1 in debris dams compared to 1.52 gm−2yr−1 on the sediment. Annual predator production, weighted by habitat availability, was 1.73gm−2yr−1.3. The predominant taxa in terms of production were the chironomids Thienemannimyia spp, complex, Ablabesmyia parajanta, Zavrelimyia sp., and the odonate Cordulegaster maculata. Chironomidae and Odonata together comprised 77% of the production of the predator guild.4. Based on gut content analysis and calculations of the trophic basis of production, estimated predator production was supported mostly by Chironomidae (38%), detritus (20%), unidentifiable insects (14%), and Ephemeroptera (11%). Total food ingestion by predators was 9.8 gm−2yr−1, 63% of which was detritus and 37% of which was animal material on an areal basis. The predator guild consumed an estimated 94% of primary invertebrate consumer production on the channel surface of the stream.
Limiting nutrients for periphyton growth in sub‐alpine, forest, agricultural and urban streams
Authors: CHESSMAN BRUCE C. , HUTTON PRIMROSE E. , BURCH JOANNE M. 
Published: May 2006

SUMMARY1. Nutrient‐diffusing artificial substrata were used in summer and autumn to assess limiting nutrients for periphytic algal growth in streams draining sub‐alpine, forested, agricultural and urban catchments in eastern Victoria, Australia.2. Chlorophyll a density was primarily limited by nitrogen in most cases; often phosphorus was secondarily limiting. One sub‐alpine, one forest and one agricultural stream were primarily phosphorus limited in at least one season. Added trace elements and vitamins did not increase chlorophyll density.3. The dominant filamentous algal genera did not differ greatly between various nutrient enrichments. However, the relative abundance of Stigeodanium spp. was sometimes increased on substrata containing the limiting nutrient.4. The results suggest that nutrient limitation is a widespread phenomenon in Victorian streams, and that limiting nutrients can be inferred from stream‐water nitrogen to phosphorus ratios in many instances.
Susceptibilities of different‐sized ciliates to direct suppression by small and large cladocerans
Authors: JACK JEFFREY D. , GILBERT JOHN J. 
Published: May 2006

SUMMARY

Laboratory experiments compared the susceptibilities of six ciliates and the rotifer Keratella cochlearis to predation and interference from Daphnia pulex and Bosmina longirostris.
Susceptibilities of the ciliates to D. pulex were similar to or less than that of the rotifer, and decreased with increasing ciliate size. Most ciliates were just as susceptible to B. longirostris as to the much larger D. pulex. The jumping response of the oligotrich Strobilidium gyrans appeared to be an effective defence against B. longirostris.
Clearance rates of B. longirostris and D. pulex on different ciliate species at a density of 1,3 ciliates ml−1 ranged from 1–30 to 5–24ml ind.−1 day−1, respectively. In natural plankton communities, cladocerans could impose high mortality rates on ciliates and shift the size structure of ciliate assemblages towards larger and less susceptible species.
Effects of a forest disturbance on shredder production in southern Appalachian headwater streams
Authors: STOUT BEN M. , BENFIELD E.F. , WEBSTER J.R. 
Published: May 2006

SUMMARY

The effects of a forest disturbance were investigated by comparing production of leaf‐shredding aquatic insects in three streams draining a mature hardwood forest and three streams draining an 11‐year‐old, cable‐logged clearcut.
Reference streams contained significantly greater mean annual standing crop of leaf material and significantly more slow‐processing leaf material than disturbed streams. Disturbed streams had a significantly higher mean annual standing crop of fast‐processing leaf material than the reference streams.
Leaf‐shredding cranefly (Tipula abdominalis), caddisfly (Pycnopsyche gentilis), and stonefly (Tallaperla maria) larvae comprised over 95% of shredder biomass in all streams. Total shredder production was significantly greater (P<0.05) in disturbed versus reference streams, but individual production rates were not significantly different between stream types.
Pycnopsyche gentilis larvae were present at higher densities and achieved significantly greater annual biomass in disturbed versus references streams, Biomass of P. gentilis was significantly correlated with the standing crop of fast‐processing, early successional leaf material in samples, whereas biomass of other shredders was correlated significantly with medium or slow‐processing leaf species characteristic of later stages of forest succession.
Exploration and rehabilitation of hydraulic habitats in streams using principles of fluvial behaviour
Authors: NEWBURY ROBERT , GABOURY MARC 
Published: May 2006

SUMMARY

The combination of elements from geomorphology, open‐channel hydraulics, and hydraulic habitat requirements of stream fish forms the basis for an ecologically sound ‘soft engineering’ of river channels.
Interpreting and mapping the hydraulic geometry of streams and locally varied flow conditions can be accomplished with plane table surveys and customized field‐data sheets. This information can serve to manage hydraulic habitats preferred by fish.
The use of fluvial characteristics to design preferred hydraulic habitats is illustrated in two examples: (i) a walleye (Stizostedion vitreum vitreum Mitchill) spawning rehabilitation project undertaken in a stream channelized as a lowland drainage canal, and (ii) a trout (Salvelinus fontinalis Mitchill and Oncorhynchus mykiss Walbaum) habitat‐enhancement project to create additional holding and resting areas for adult fish in a stream paved with glacially deposited boulders modified by a road crossing.
In both examples the ‘soft engineering’ of the river channels enhanced the hydraulic fish habitat.