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Small Rivers (small + river)
Selected AbstractsComposition and Longitudinal Patterns of Aquatic Insect Emergence in Small Rivers of Palawan Island, the PhilippinesINTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 4 2004Hendrik Freitag Abstract This study presents the first emergence trap samples from streams in the Philippines and Greater Sunda. Aquatic insect emergence from two small rivers and longitudinal patterns including estuaries are compared. A decline of total emergence towards estuaries was observed, affecting all major orders. Diptera, namely Chironomidae, dominated all sites. High abundances in Ceratopogonidae, Odonata, and Coleoptera were found, compared to other emergence studies from tropical and temperate latitudes. Ephemeroptera displayed a highly variable contribution to the emergence from Palawan as well as in other comparative studies either supported by the appropriate conditions for certain functional groups or limited by environmental variables such as pH. Trichoptera are likely to tolerate a wider range of environmental conditions and they are consequently able to fill further niches where Ephemeroptera are under-represented. Except for scarce abundances of Plecoptera observed in this and other studies from the tropics, no substantial differences in emergence composition at order level existed between temperate and tropical rivers, however, with a remarkable local variation. Components of riparian and non-aquatic insects and non-emergent fauna contributing to the collections are discussed based on trap features. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] ISTA 14,in-situ accumulation of PAHs in low-density polyethylene membranes in sedimentENVIRONMENTAL TOXICOLOGY, Issue 5 2010Damien A. Devault Abstract The use of passive samplers for the assessment of organic contaminants has been extended to solid matrixes for the past decade. Passive sampling is usually applied to sediment in laboratory experiments involving significant upheaval, whereas in-situ experiments remain rare. In this study, low-density polyethylene (LDPE) strips were deployed within the sediments of a small river contaminated with polycyclic aromatic hydrocarbons (PAHs). LDPE strips were deployed in the 3-cm depth sediment layer. Over a period of 36 days, LDPE strips were regularly retrieved and accumulated PAHs in LDPE were extracted and analyzed. Accumulations of hydrophobic contaminants in LDPE directly exposed in the sediment were observed. Accumulations in LDPE were observed for moderately hydrophobic PAHs with the highest concentrations in the sediment. Low accumulations were observed for more hydrophobic compounds, despite their presence in high concentrations in the sediment. This was explained by very low exchange rates and competitive interactions with particles in the sediment. © 2010 Wiley Periodicals, Inc. Environ Toxicol, 2010. [source] Snorkelling as a method for assessing spawning stock of Atlantic salmon, Salmo salarFISHERIES MANAGEMENT & ECOLOGY, Issue 3 2007P. ORELL Abstract, Reliability of underwater snorkel counts of adult Atlantic salmon, Salmo salar L., was analysed in the tributaries of the River Teno, close to the spawning period. In small (width 5,20 m) rivers, the replicated total counts of salmon were reasonably precise (CV = 5.4,8.5%), while in the medium-sized river (width 20,40 m) the precision of the counting method was considerably lower (CV = 15.3%). Low precision in a medium sized river was also observed in an experiment using marked live fish where the observation efficiency varied between 36.4% and 70.0%. In a small river, the detection efficiency of artificial fish silhouettes (test salmon) was almost perfect in pools (98%), but decreased in rapids (84%). Separate counts of males, females, grilse and large salmon were usually more variable than total counts, indicating that divers were more capable of locating a fish than properly identifying its sex and sea-age. The behaviour of adult salmon was favourable to conduct snorkel counts, as fish normally stayed still, or after hesitating, moved upstream (>95%of the cases) when encountering a diver. The high observation efficiency (>90%) and precision, favourable behaviour of salmon and congruence between snorkel counts and catch statistics in small rivers suggest that reliable data on Atlantic salmon spawning stock can be collected by snorkeling provided that the environmental conditions are suitable and the divers are experienced. [source] Factors affecting river entry of adult Atlantic salmon in a small riverJOURNAL OF FISH BIOLOGY, Issue 4 2007B. Jonsson In this study, effects of stock origin, fish size, water flow and temperature on time of river ascent of adult Atlantic salmon Salmo salar were tested. Brood stocks were collected in eight Norwegian rivers situated between 59 and 69° N. The fish were reared to smolts, individually tagged and released in the River Imsa, south-west Norway (59° N). Adults from all stocks approached the Norwegian coast concurrently, but Atlantic salmon ,70 cm in natural tip length entered coastal water slightly earlier during summer than smaller fish. Atlantic salmon <70 cm, however, ascended the river significantly earlier and at lower water flow and higher water temperature than larger fish. Although largest in size, the fish from the northern populations (62,69° N) ascended the River Imsa almost 1 month earlier than those from the south (59,60° N). They seemed less restricted by the environmental factors than the fish originating from the more southern rivers. There was no apparent trend among years in time of river ascent. Maximum ascent per day occurred at water discharges between 12·5 and 15 m3 s,1 and at water temperatures between 10 and 12·5° C. There was a significant positive correlation between water flow and river ascent during the first part of the upstream run from July to September with best correlation for September, when multiple regression analysis indicated that water temperature had an additional positive effect. Stock origin, fish size and water discharge were important variables influencing the upstream migration of Atlantic salmon in small rivers. [source] Snorkelling as a method for assessing spawning stock of Atlantic salmon, Salmo salarFISHERIES MANAGEMENT & ECOLOGY, Issue 3 2007P. ORELL Abstract, Reliability of underwater snorkel counts of adult Atlantic salmon, Salmo salar L., was analysed in the tributaries of the River Teno, close to the spawning period. In small (width 5,20 m) rivers, the replicated total counts of salmon were reasonably precise (CV = 5.4,8.5%), while in the medium-sized river (width 20,40 m) the precision of the counting method was considerably lower (CV = 15.3%). Low precision in a medium sized river was also observed in an experiment using marked live fish where the observation efficiency varied between 36.4% and 70.0%. In a small river, the detection efficiency of artificial fish silhouettes (test salmon) was almost perfect in pools (98%), but decreased in rapids (84%). Separate counts of males, females, grilse and large salmon were usually more variable than total counts, indicating that divers were more capable of locating a fish than properly identifying its sex and sea-age. The behaviour of adult salmon was favourable to conduct snorkel counts, as fish normally stayed still, or after hesitating, moved upstream (>95%of the cases) when encountering a diver. The high observation efficiency (>90%) and precision, favourable behaviour of salmon and congruence between snorkel counts and catch statistics in small rivers suggest that reliable data on Atlantic salmon spawning stock can be collected by snorkeling provided that the environmental conditions are suitable and the divers are experienced. [source] Assembly rules and community models for unicellular organisms: patterns in diatoms of boreal streamsFRESHWATER BIOLOGY, Issue 4 2005JANI HEINO Summary 1. Many studies have addressed either community models (e.g. Clementsian versus Gleasonian gradients) or assembly rules (e.g. nestedness, checkerboards) for higher plant and animal communities, but very few studies have examined different non-random distribution patterns simultaneously with the same data set. Even fewer studies have addressed generalities in the distribution patterns of unicellular organisms, such as diatoms. 2. We studied non-randomness in the spatial distribution and community composition of stream diatoms. Our data consisted of diatom surveys from 47 boreal headwater streams and small rivers in northern Finland. Our analytical approaches included ordinations, cluster analysis, null model analyses, and associated randomisation tests. 3. Stream diatom communities did not follow discrete Clementsian community types, where multiple species occur exclusively in a single community type. Rather, diatom species showed rather individualistic responses, leading to continuous Gleasonian variability in community composition. 4. Although continuous variability was the dominating pattern in the data, diatoms also showed significant nestedness and less overlap in species distribution than expected by chance. However, these patterns were probably only secondary signals from species' individualistic responses to the environment. 5. Although unicellular organisms, such as diatoms, differ from multicellular organisms in several biological characteristics, they nevertheless appear to show largely similar non-random distribution patterns previously found for higher plants and metazoans. [source] Predicting river water temperatures using stochastic models: case study of the Moisie River (Québec, Canada)HYDROLOGICAL PROCESSES, Issue 1 2007Behrouz Ahmadi-Nedushan Abstract Successful applications of stochastic models for simulating and predicting daily stream temperature have been reported in the literature. These stochastic models have been generally tested on small rivers and have used only air temperature as an exogenous variable. This study investigates the stochastic modelling of daily mean stream water temperatures on the Moisie River, a relatively large unregulated river located in Québec, Canada. The objective of the study is to compare different stochastic approaches previously used on small streams to relate mean daily water temperatures to air temperatures and streamflow indices. Various stochastic approaches are used to model the water temperature residuals, representing short-term variations, which were obtained by subtracting the seasonal components from water temperature time-series. The first three models, a multiple regression, a second-order autoregressive model, and a Box and Jenkins model, used only lagged air temperature residuals as exogenous variables. The root-mean-square error (RMSE) for these models varied between 0·53 and 1·70 °C and the second-order autoregressive model provided the best results. A statistical methodology using best subsets regression is proposed to model the combined effect of discharge and air temperature on stream temperatures. Various streamflow indices were considered as additional independent variables, and models with different number of variables were tested. The results indicated that the best model included relative change in flow as the most important streamflow index. The RMSE for this model was of the order of 0·51 °C, which shows a small improvement over the first three models that did not include streamflow indices. The ridge regression was applied to this model to alleviate the potential statistical inadequacies associated with multicollinearity. The amplitude and sign of the ridge regression coefficients seem to be more in agreement with prior expectations (e.g. positive correlation between water temperature residuals of different lags) and make more physical sense. Copyright © 2006 John Wiley & Sons, Ltd. [source] Composition and Longitudinal Patterns of Aquatic Insect Emergence in Small Rivers of Palawan Island, the PhilippinesINTERNATIONAL REVIEW OF HYDROBIOLOGY, Issue 4 2004Hendrik Freitag Abstract This study presents the first emergence trap samples from streams in the Philippines and Greater Sunda. Aquatic insect emergence from two small rivers and longitudinal patterns including estuaries are compared. A decline of total emergence towards estuaries was observed, affecting all major orders. Diptera, namely Chironomidae, dominated all sites. High abundances in Ceratopogonidae, Odonata, and Coleoptera were found, compared to other emergence studies from tropical and temperate latitudes. Ephemeroptera displayed a highly variable contribution to the emergence from Palawan as well as in other comparative studies either supported by the appropriate conditions for certain functional groups or limited by environmental variables such as pH. Trichoptera are likely to tolerate a wider range of environmental conditions and they are consequently able to fill further niches where Ephemeroptera are under-represented. Except for scarce abundances of Plecoptera observed in this and other studies from the tropics, no substantial differences in emergence composition at order level existed between temperate and tropical rivers, however, with a remarkable local variation. Components of riparian and non-aquatic insects and non-emergent fauna contributing to the collections are discussed based on trap features. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Habitat and abundance of Balitoridae in small rivers of central ThailandJOURNAL OF FISH BIOLOGY, Issue 10 2008F. W. H. Beamish Balitorids were collected, by electrofishing, from small rivers across central Thailand between October 2000 and March 2004. Total balitorid abundance for the 18 species averaged 3·8% of the cumulative total for all fishes. Balitorid species numbers and abundance varied directly with elevation to c. 400 m, substratum particle size and ambient silica concentration. Species numbers at stations were modest and few species were widely distributed. Species associations related significantly with elevation, temperature and ambient concentrations of dissolved oxygen and silica. Turbidity was also significant but probably an artefact. Habitat separation clearly occurs among some balitorids, particularly the less common species, and probably represents species-specific direct and indirect habitat effects. The more common balitorid species tended to occur in similar habitats where the significant factors approximated average values. For these species, coexistence is suggested to occur through food resource sharing possibly facilitated through adaptations. Balitorid distributions in low-order rivers are attributed to the direct and indirect influences of the environment on energy available for the performance of essential activities. [source] Factors affecting river entry of adult Atlantic salmon in a small riverJOURNAL OF FISH BIOLOGY, Issue 4 2007B. Jonsson In this study, effects of stock origin, fish size, water flow and temperature on time of river ascent of adult Atlantic salmon Salmo salar were tested. Brood stocks were collected in eight Norwegian rivers situated between 59 and 69° N. The fish were reared to smolts, individually tagged and released in the River Imsa, south-west Norway (59° N). Adults from all stocks approached the Norwegian coast concurrently, but Atlantic salmon ,70 cm in natural tip length entered coastal water slightly earlier during summer than smaller fish. Atlantic salmon <70 cm, however, ascended the river significantly earlier and at lower water flow and higher water temperature than larger fish. Although largest in size, the fish from the northern populations (62,69° N) ascended the River Imsa almost 1 month earlier than those from the south (59,60° N). They seemed less restricted by the environmental factors than the fish originating from the more southern rivers. There was no apparent trend among years in time of river ascent. Maximum ascent per day occurred at water discharges between 12·5 and 15 m3 s,1 and at water temperatures between 10 and 12·5° C. There was a significant positive correlation between water flow and river ascent during the first part of the upstream run from July to September with best correlation for September, when multiple regression analysis indicated that water temperature had an additional positive effect. Stock origin, fish size and water discharge were important variables influencing the upstream migration of Atlantic salmon in small rivers. [source] Effects of sediment eluates and extracts from differently polluted small rivers on zebrafish embryos and larvaeJOURNAL OF FISH BIOLOGY, Issue 1 2002M. Strmac The effects on newly fertilized eggs, embryos and larvae of zebrafish Danio rerio following exposure to sediment samples from the more heavily contaminated River Körsch, southern Germany, occurred earlier and were more prominent than in samples from the less contaminated Krähenbach. Dose- and time-related effects following exposure to Körsch sediment eluates and extracts included: (1) hatching failure and subsequent death of larvae exposed to undiluted aqueous sediment eluates and reduced hatching rates at sediment extract concentrations 0·0125%; (2) increased mortality after exposure to 25 and 50% dilutions of aqueous sediment eluates, and dilutions of 0·00625% sediment extracts; (3) reduction of heart beat frequency for 50% dilutions of sediment eluates and concentrations of 0·025% extracts; (4) increased frequency of heart and yolk sac oedema after exposure to 0·0125% sediment extracts. Since adverse effects of sediment extracts observed in zebrafish laboratory tests correlated with reproductive failure in natural populations of brown trout Salmo trutta f. fario in the severely polluted River Körsch, early life stages tests with zebrafish appear to be a suitable tool to assess the contamination rate of natural sediments. [source] Dispersion patterns of parasites in 0+ year three-spined sticklebacks: a cross population comparisonJOURNAL OF FISH BIOLOGY, Issue 6 2002M. Kalbe Two ciliates and 16 metazoan parasites were identified in 434 0+ year three-spined sticklebacks Gasterosteus aculeatus collected from two small rivers and four lakes located in Schleswig-Holstein, Germany. By repeated sampling and analysis of dispersion patterns of six frequently occurring parasites no consistent evidence was found for mortality induced by a single parasite species. Linear log-variance to log-mean abundance ratios with slopes of c. 2 indicated negative binomial distributions for five of the six parasites. The numbers of these six parasites were combined as multiples of S.D. of each parasite species over all samples to form an ,individual parasitation index' (IPI), which showed that only in one locality a slight decrease in parasite burden occurred between September and April. In two of the lake populations, however, there was a distinct decline in the degree of dispersion in spring samples. This indicates that a combination of different species might cause parasite-induced host mortality, undetectable by patterns obtained from single species. There were differences in parasite diversity and intensity of infection among river compared to lake populations suggesting a role for parasites as selective agents in the ecological divergence of three-spined sticklebacks. [source] Benchmarking habitat quality: observations using River Habitat Survey on near-natural streams and rivers in northern and western EuropeAQUATIC CONSERVATION: MARINE AND FRESHWATER ECOSYSTEMS, Issue S1 2010Paul J. Raven Abstract 1.Some ecological effects of physically modifying rivers are still unclear, partly due to scale factors, but also because the character of high quality habitat is poorly understood. 2.Surveys at 278 sites on 141 near-natural streams and rivers in northern and western Europe were carried out between 1994 and 2009 to benchmark the habitat quality assessment system used for River Habitat Survey (RHS). 3.The objectives were to establish if RHS was suitable outside the UK, investigate if 500 m was still valid as the survey length, suggest a benchmarking strategy and recommend improvements to habitat quality assessment protocols. 4.Some modifications to RHS are needed to take account of differences in hydrological conditions, land-use and, most importantly, riparian habitat structure found in mainland Europe. 5.On average, 82,87% of channel attributes and 87,98% of channel and bank features were recorded within the first of consecutive RHS sites, confirming that 500 m is an effective sample length for characterizing small rivers. 6.Stream-flow character appeared to influence the distribution of several in-channel features, with greater diversity and between-site variation associated with rivers of mixed flow-types. To account for local variation and for effective use of survey time, it is recommended that two or more consecutive RHS sites are used for benchmarking purposes. 7.A suite of assessment protocols with agreed criteria and analytical rules, linked to specific objectives (e.g. nature conservation, geomorphic condition), is needed to establish the character and habitat quality of rivers in a consistent fashion. 8.A multi-discipline benchmarking programme using hydro-ecological regions in Europe would build on existing knowledge and help to improve both the inter-calibration and local application of quality assessment protocols. Data-sharing by hydrologists, river ecologists and fluvial geomorphologists would improve the basis for managing rivers in support of the European Water Framework Directive and Habitats Directive. Copyright © 2010 John Wiley & Sons, Ltd. [source] | |||||||||||||