bluuebunny/crossref_metadata_2025_split huggingface dataset:
Improvement in school‐size estimates of pelagic fish using information from sector‐scanning sonar
Authors: Hamano Akira , Nakamura Takeshi , Maeda Hiroshi 
Published: March 2003

AbstractSchool‐size estimates based on information from a sector‐scanning sonar were compared with those based on information from an echo sounder. Three pairs of size estimates of anchovy schools in the coastal waters, off Fukuoka Prefecture were shown as examples. They included the possibility of improving the size estimates by using information from sector‐scanning sonar to consider the size in the transverse direction. In these examples, the thickness and extent of the school varied in the transverse direction. A large difference was found between the estimates from the sounder information and those from the sector‐scanning sonar information, although whether or not the estimated size decreased differed according to each case. Also, whether the thickness information or the extent information is influential differed according to each case. The size information from the sector‐scanning sonar in the transverse direction caused a change in the estimated size from 66 to 16 (×103 m3, mainly by different extent), 305 to 146 (×103 m3, thickness increased but extent decreased), and 819 to 746 (×103 m3, three seemingly separated schools fused into one).
Experimental measurements of zebra mussel (Dreissena polymorpha) impacts on phytoplankton community composition
Authors: Bastviken David T. E. , Caraco Nina F. , Cole Jonathan J. 
Published: March 2003

1. To investigate direct effects of zebra mussel (Dreissena polymorpha) feeding activities on phytoplankton community composition, short‐term microcosm experiments were performed in natural water with complex phytoplankton communities. Both gross effects (without resuspension of mussel excretions) and net effects (with resuspension) were studied.2. Gross clearance rates were not selective; essentially all taxa were removed at similar rates ranging from 24 to 63 mL mussel–1 h–1. Net clearance rates were highly selective; different plankton taxa were removed at very different rates, ranging from 12 to 83% of the gross rates, leading to consistent changes in the phytoplankton community composition. Thus, although zebra mussels can cause most phytoplankton to decline, there is considerable variation among taxa in either pre‐digestive selection or post‐digestive survival.3. The direct, short‐term effects of zebra mussels on phytoplankton community composition are consistent with some of the major changes observed in the Hudson River since establishment of zebra mussels.4. We show, with simple calculations, how zebra mussel filtration rate, its selective efficiency on various taxa, and phytoplankton growth rates interact to produce changes in the phytoplankton composition.
Changes in the cycling of phosphorus in the Upper Kis‐Balaton Reservoir following external load reduction
Authors: Istvànovics Vera , Somlyçdy Làszlç 
Published: March 2003

1. The Upper Kis‐Balaton Reservoir was opened in 1985 to control eutrophication in Lake Balaton. High external TP load of the reservoir halved in 1991 due to improved sewage treatment. Annual TP retention efficiency of the reservoir dropped immediately from 50 to 20%, while the hypertrophic algal biomass started to decrease after 1995.2. We examine mass balances of the main forms of P in three consecutive areas (1, 2 and 3) of the reservoir. Biologically available P (BAP) includes soluble reactive P and algal P, whereas the rest of TP is considered to be non‐available (nBAP).3. Important pathways for P cycling varied in both space and time. A reduction in external load induced an enhanced net internal P load in the reservoir, and a variety of changes in the three areas. Thus, in the smallest Area 1, BAP retention dropped almost to zero, and the net sedimentation of nBAP decreased significantly. In Area 2 net BAP retention was characteristic before management, and net internal P load was observed afterwards. In Area 3 net internal P load has been substantial in some years ever since the reservoir was filled. The OECD model, corrected for internal P load, reasonably predicted the measured TP concentration in each area both before and after reduction in load.4. The external load‐algal biomass curve differed in the three areas. An immediate response occurred in the upstream Areas 1 and 2, while a delay of 4–5 years was observed in Area 3. Different long‐term sediment dynamics may underlay these load‐response relations in the three areas. Intense sediment redistribution, however, sets a serious constraint to the simple calculation of a mass balance. An evaluation of the long‐term sediment dynamics is needed in order to predict future performance of the reservoir.
Dry mass–length relationships for benthic insects: a review with new data from Catamaran Brook, New Brunswick, Canada
Authors: Johnston Thomas A. , Cunjak Richard A. 
Published: March 2003

1.___We summarized previously published mass–length relationships for aquatic insects, and determined the relationship between dry body mass and body length for eight genera and seven families of benthic insects from Catamaran Brook, New Brunswick, Canada.2.___A power function was the most commonly used model in the earlier studies and best described the observed mass–length relationship for taxa from Catamaran Brook.3.___Predicted mass at length was highly variable (coefficient of variation_≥ 25%) among models developed in different studies for the same family group. This variability presumably resulted from both variation in the methods used to construct the models, and in the natural spatio‐temporal and taxonomic variation in mass at length, although the relative contributions of these two sources cannot be determined from existing data.4.___Several recommendations are made for the development and application of mass–length equations in future studies.
Zooplankton abundance in the River Danube, Austria: the significance of inshore retention
Authors: Reckendorfer W. , Keckeis H. , Winkler G. , Schiemer F. 
Published: March 2003

Summary1. Zooplankton density was examined in a free‐flowing section of the River Danube, Austria. Spatial and temporal patterns were used to identify mechanisms regulating zooplankton dynamics.2. Zooplankton abundance differed significantly between sampling sites. These differences were the result of variations in water residence time within the habitats. Inshore habitats with low flushing rates act as storage zones for zooplankton.3. The hydrological conditions govern the number and size of storage zones. In the study area, the highest availability of storage zones was observed at medium water level.4. Total zooplankton numbers, total rotifer numbers and the densities of the most abundant rotifer taxa were significantly positively related to the availability of adjacent storage zones.5. The present authors propose that inshore retention capacity, and the hydrological processes and mechanisms controlling the extent of inshore retention may be of major significance in regulated rivers with high water velocities, preventing substantial zooplankton growth in the main channel.
Temporal variability of stream bioassessments using benthic macroinvertebrates
Authors: Linke Simon , Bailey Robert C. , Schwindt John 
Published: March 2003

1. When using benthic macroinvertebrate communities for bioassessment, temporal variation may influence judgement as to whether or not a site is degraded.2. In a survey of sixteen reference and sixteen test sites in the upper Thames River catchment area (UTRCA) in south‐western Ontario, Canada, consistent differences between summer and winter samples were found for taxon richness (increase; P = 0.06) and the Family Biotic Index (decrease; P = 0.11). A bioassessment based on these results would indicate better water quality in the same streams in winter relative to summer. No consistent pattern of seasonal difference was detected for Simpson’s Diversity and Equitability, or percentage Dominant Taxon.3. The Reference Condition Approach to bioassessment uses predictive modelling to explain variation in reference communities with the environmental conditions at these sites as predictors. The community at a test site is compared with that predicted by the model. Several predictive models were constructed using simple geographic and habitat characteristics (i.e. catchment area, distance to source, stream width, substrate and habitat diversity) as predictors. By including season of sampling in the models, we increased their predictive power and the ability of the bioassessment to detect degradation. The best results were achieved when separate predictive models were built for each sampling season.
Light absorption and photosynthesis of a benthic moss community: importance of spectral quality of light and implications of changing light attenuation in the water column
Authors: Schwarz Anne ‐Maree , Markager Stiig 
Published: March 2003

1. The underwater light climate and benthic moss communities of Grane Langsø were investigated in May 1997 to determine the potential effects on benthic production of changing water column attenuation and spectral quality of light.2. A reduction in water clarity in the lake since the 1960s was manifested as a marked increase in the attenuation of blue light, relative to red light, which can be attributed to increased dissolved organic carbon.3. The biomass of the benthic moss community ranged from a maximum of 195 gDW m−2 at a depth of 4 m to 39 g DW m−2 at a depth of 10 m and Drepanocladus exannulatus contributed 70% of the biomass at all depths.4. Absorption of PAR by D. exannulatus was maximal in the highly pigmented youngest parts of the plant and these correspondingly showed the highest rates of net photosynthesis. The absolute amount of chlorophyll‐a per g dry weight was greater at 10 m than 2 m, but the ratio of accessory pigments to chlorophyll‐a did not change. Deep growing plants did not show adaptation to changed light quality.5. Increased attenuation of blue light and the resultant overall decrease in water clarity is likely to impact negatively on net annual production of benthic macrophytes of Grane Langsø. Any further increase in dissolved organic carbon concentration has the potential to markedly decrease the depth to which mosses grow by reducing the length of time in a year during which net photosynthesis occurs.
Fouling mussels (Dreissena spp.) colonize soft sediments in Lake Erie and facilitate benthic invertebrates
Authors: Bially Andrew , Macisaac Hugh J. 
Published: March 2003

Summary

We conducted survey and transplant studies to determine whether colonization and residency on soft sediments by introduced, fouling mussels (Dreissena polymorpha and D. bugensis) were affected by physical disturbance, and whether Dreissena presence in turn influenced the diversity and population densities of other benthic invertebrates. Surveys revealed that colony density was typically higher at moderate depths than at shallower and greater ones. However, the largest, midsummer colonies and greatest coverage of sediments by mussels occurred at deeper sites.
Disturbance of transplanted colonies varied by depth and colony size, with deeper and larger colonies experiencing the lowest destruction rates. Colony destruction rate was positively correlated with current velocity adjacent to the lakebed.
Absence of mussel colonies at shallow sites was not determined by recruitment or substrate limitation, as recruit density was higher and sediment characteristics more suitable for postveliger settlement at shallow than at deeper sites. Rather, seasonal storms have much stronger effects in shallow than in deep water.
Mussel residency on soft sediment has profound effects on invertebrate biodiversity. Invertebrate species (taxon) richness and total abundance were positively correlated with mussel colony area. Mussel‐sediment habitat supported between 462 and 703% more taxa, and between 202 and 335% more individuals (exclusive of Dreissena) than adjacent soft‐sediment lacking mussels.
Results from this study illustrate that physical disturbance directly limits the distribution of mussels on soft sediments, and the diversity and abundance of other benthic invertebrates in consequence.
A geomorphic template for the analysis of lake districts applied to the Northern Highland Lake District, Wisconsin, U.S.A.
Authors: Riera JoaN. L. , Magnuson JohN. J. , Kratz TiM. K. , Webster Katherine E. 
Published: March 2003

1. We tested the degree to which a lake's landscape position constrains the expression of limnological features and imposes a characteristic spatial pattern in a glacial lake district, the Northern Highland Lake District in north‐central Wisconsin.2. We defined lake order as a metric to analyze the effect of landscape position on limnological features. Lake order, analogous to stream order, is based solely on geographical information and is simple to measure.3. We examined the strength of the relationship between lake order and a set of 25 variables, which included measures of lake morphometry, water optical properties, major ions, nutrients, biology, and human settlement patterns.4. Lake order explained a significant fraction of the variance of 21 of the 25 variables tested with ANOVA. The fraction of variance explained varied from 12% (maximum depth) to 56% (calcium concentration). The variables most strongly related to lake order were: measures of lake size and shape, concentrations of major ions (except sulfate) and silica, biological variables (chlorophyll concentration, crayfish abundance, and fish species richness), and human‐use variables (density of cottages and resorts). Lake depth, water optical properties, and nutrient concentrations (other than silica) were poorly associated with lake order.5. Potential explanations for a relationship with lake order differed among variables. In some cases, we could hypothesize a direct link. For example, major ion concentration is a function of groundwater input, which is directly related to lake order. We see these as a direct influence of the geomorphic template left by the retreat of the glacier that led to the formation of this lake district.6. In other cases, a set of indirect links was hypothesized. For example, the effect of lake order on lake size, water chemistry, and lake connectivity may ultimately explain the relation between lake order and fish species richness. We interpret these relationships as the result of constraints imposed by the geomorphic template on lake development over the last 12 000 years.7. By identifying relationships between lake characteristics and a measure of landscape position, and by identifying geomorphologic constraints on lake features and lake evolution, our analysis explains an important aspect of the spatial organization of a lake district.
Assessing introgression of foreign strains in wild Atlantic salmon populations: variation in microsatellites assessed in historic scale collections
Authors: Martinez  , Dumas  , Beall  , Garcia‐Vazquez  
Published: March 2003

1. Genetic variation at five microsatellite loci was analysed in a collection of scales (1970–97) sampled from Atlantic salmon adults returning to the Nivelle River (South France).2. Native and foreign fish (from an allochthonous Scottish stock introduced into the river to increase population size) were clearly identified as all foreign individuals released in the river were physically marked.3. Introgression of foreign genes into the native gene pool has occurred, although the reproductive success of foreign Atlantic salmon in the wild was lower than that of native individuals.4. The utility of old scale samples for investigating the impact of foreign stocking on wild fish populations is demonstrated in this work.
Activity profiles of bacterioplankton in a eutrophic river
Authors: Sinsabaugh  , Foreman  
Published: March 2003

1. The significance of microbial diversity in processing dissolved organic matter (DOM) is largely unknown. We investigated the range of functional diversity in the bacterioplankton from a eutrophic river by profiling extracellular enzyme activities (EEA) and substrate‐induced respiration (SIR) patterns.2. The EEA profiles consisted of assays for 21 hydrolases, measured using fluorogenic substrates arrayed on 96‐well microplates. Commercially available BiOLOG® GN and ECO plates, which contained 120 different substrates, were used for the SIR profiles.3. The EEA data were more dynamic than the SIR. Five enzymes, leucine aminopeptidase, alkaline phosphatase, alanine aminopeptidase, arginine aminopeptidase and β‐glucosidase, showed consistently high activity; ten others were ubiquitous at lower activity levels; the remainder were detected intermittently. The SIR data showed less temporal variability. With one exception (citrate), the 20 substrates that generated the largest responses were all saccharides or their derivatives.4. The EEA and SIR data did not generally correlate. Both methods were effective for ordinating bacterioplankton although, unlike the SIR, the EEA ordination followed a clear temporal trajectory.5. Because the SIR profiles are based on a culture response, whilst the EEA profiles measure activity of the extant community, the latter appear to be more directly linked to the mechanics of DOM processing.
Chironomid‐based inference models for estimating end‐of‐summer hypolimnetic oxygen from south‐central Ontario shield lakes
Authors: Quinlan Roberto , Smol John P. 
Published: March 2003

1. Subfossil chironomid head capsules were sampled from surficial sediments from 86 boreal shield lakes in south‐central Ontario, Canada. Lake characteristics ranged from shallow to very deep (> 80 m), ultraoligotrophic to mesotrophic, and with end‐of‐summer hypolimnetic oxygen conditions ranging from near‐saturation to anoxic.2. Subfossil chironomid assemblages, comprising 44 taxa from 59 lakes, were analysed using multivariate ordination techniques such as redundancy analysis (RDA) and canonical correspondence analysis (CCA). Forward selection in RDA and CCA both showed that measures of oxygen, such as end‐of‐summer volume‐weighted hypolimnetic oxygen concentration (VWHO) and bottom oxygen concentration (botO2), were the strongest explanatory variables for the chironomid data. Maximum depth and major ion chemistry were also important explanatory variables.3. Oxygen inference models were developed using partial‐least‐squares regression (PLS), weighted‐averaging partial‐least‐squares regression (WA‐PLS), and weighted averaging regression (WA). Models were developed using both the full 44 taxa assemblage (which included littoral taxa) and using only 15 profundal‐type taxa.4. Cross‐validated models (jackknifing) using full‐assemblage or profundal‐only taxa had similar statistical power (similar root mean squared error of prediction, RMSEP). The best models had moderate predictive power, with an r2jack as high as 0.56, and an RMSEP as low as 2.15 mg L–1 for [VWHO], and an r2jack of 0.49 and an RMSEP of 0.24 for log([botO2] + 1).5. Reconstruction of [VWHO] and [botO2] using a previously published chironomid profile that showed strong lake response to land‐clearance and logging suggests that oxygen inference models are reliable and accurate, reflecting the qualitative changes occurring in subfossil assemblages. However, the profundal‐only models may be misleading in situations where the ratio of littoral‐to‐profundal subfossils changes drastically in response to lake disturbance.
Inter‐biome comparison of factors controlling stream metabolism
Authors: Mulholland P. J. , Fellows C. S. , Tank J. L. , Grimm N. B. , Webster J. R. , Hamilton S. K. , Martí E. , Ashkenas L. , Bowden W. B. , Dodds W. K. , Mcdowell W. H. , Paul M. J. , Peterson B. J. 
Published: March 2003

1. We studied whole‐ecosystem metabolism in eight streams from several biomes in North America to identify controls on the rate of stream metabolism over a large geographic range. The streams studied had climates ranging from tropical to cool‐temperate and from humid to arid and were all relatively uninfluenced by human disturbances.2. Rates of gross primary production (GPP), ecosystem respiration (R) and net ecosystem production (NEP) were determined using the open‐system, two‐station diurnal oxygen change method.3. Three general patterns in metabolism were evident among streams: (1) relatively high GPP with positive NEP (i.e. net oxygen production) in early afternoon, (2) moderate primary production with a distinct peak in GPP during daylight but negative NEP at all times and (3) little or no evidence of GPP during daylight and a relatively constant and negative NEP over the entire day.4. Gross primary production was most strongly correlated with photosynthetically active radiation (PAR). A multiple regression model that included log PAR and stream water soluble reactive phosphorus (SRP) concentration explained 90% of the variation in log GPP.5. Ecosystem respiration was significantly correlated with SRP concentration and size of the transient storage zone and, together, these factors explained 73% of the variation in R. The rate of R was poorly correlated with the rate of GPP.6. Net ecosystem production was significantly correlated only with PAR, with 53% of the variation in log NEP explained by log PAR. Only Sycamore Creek, a desert stream in Arizona, had positive NEP (GPP: R > 1), supporting the idea that streams are generally net sinks rather than net sources of organic matter.7. Our results suggest that light, phosphorus concentration and channel hydraulics are important controls on the rate of ecosystem metabolism in streams over very extensive geographic areas.
Physico‐chemistry and aquatic insects of a glacier‐fed and a spring‐fed alpine stream
Authors: Füreder Leopold , Schütz Cornelia , Wallinger Manfred , Burger Rainer 
Published: March 2003

1. Physico‐chemical conditions and benthic macroinvertebrates were studied in two adjacent alpine streams in the Tyrolean Alps, Austria, for 2 years, and aquatic insect emergence was recorded for 1 year.2. In the spring‐fed system, maximum discharge and increased concentrations of suspended solids, nitrate and particulate phosphorus occurred during snowmelt in June. In the glacier‐fed stream, high discharge and strong diel fluctuations in flow and concentrations of suspended solids created a harsh and unstable environment during summer. Glacial ablation, variation in groundwater inflow, and water inputs from tributaries draining calcareous rocks caused water chemistry to vary both seasonally and longitudinally in glacier‐fed Rotmoosache.3. A total of 126 aquatic or semi‐aquatic invertebrate taxa were collected, 94 of which were found in the glacier‐fed stream and 120 in the spring‐fed stream. Chironomid abundance was 2–8 times and taxa richness 2–3 times lower in the glacier‐fed stream than in the spring‐fed stream, as was the number of chironomid taxa (72 versus 93 total).4. These results broadly support the conceptual model by Milner & Petts (1994) concerning glacier‐fed stream systems. However, single samples and seasonal means showed relatively high invertebrate abundance and richness, especially during winter, indicating a considerable degree of spatial and temporal variability.5. We suggest that the seasonal shifts from harsh environmental conditions in summer to less severe conditions in autumn and a rather constant environment in winter are an important factor affecting larval development, life‐history patterns and the maintenance of relatively high levels of diversity and productivity in glacier‐fed streams.