bluuebunny/crossref_metadata_2025 huggingface dataset:
Food quality for Eudiaptomus gracilis: the importance of particular highly unsaturated fatty acids
Authors: Von Elert Eric , Stampfl Paul
Published: March 2003

1. Development times and survival of nauplii and copepodites of the freshwater calanoid Eudiaptomus gracilis were measured on comparably sized Cryptomonas sp. and two strains of Chlamydomonasreinhardii under food saturated conditions (1 mg C L−1) to investigate the nutritional quality of these algae.  2. Cryptomonas sp. supported complete ontogenesis of nauplii to adults, whereas both strains of C. reinhardii were inadequate for the development of nauplii and copepodites and resulted in high mortality. The nutritional deficiency of both strains of C. reinhardii was compensated for by Cryptomonas sp. when the latter constituted ≥50% of dietary carbon. Pulses of Cryptomonas sp. had a similar compensatory effect.  3. In comparison to Cryptomonas sp., both strains of C. reinhardii were deficient in the three highly unsaturated fatty acids (HUFAs) stearidonic, eicosapentaenoic and docosahexaenoic acid. We manipulated the fatty acid content of C. reinhardii by externally adding these three HUFAs to the alga so that the fatty acid profile resembled that of Cryptomonas sp. This supplementation did not improve food quality, however, indicating that the nutritional deficiency of both strains of C. reinhardii for the ontogenesis of E. gracilis is not due to a lack of these three HUFAs.
Functional models for growth and food consumption of Atlantic salmon parr, Salmo salar, from a Norwegian river
Authors: Forseth T. , Hurley M. A. , Jensen A. J. , Elliott J. M.
Published: March 2003

1. The chief objectives were to analyse and model experimental data for maximum growth and food consumption of Atlantic salmon parr (Salmo salar) collected from a cold glacier fed river in western Norway. The growth and feeding models were also applied to groups of Atlantic salmon growing and feeding at rates below the maximum. The growth models were validated by comparing their predictions with observed growth in the river supplying the experimental fish.  2. Two different models were fitted, one originally developed for British salmon and the other based on a model for bacterial growth. Both gave estimates for optimum temperature for growth at 18–19 °C, somewhat higher than for Atlantic salmon from Britain. Higher optimal temperature for growth in salmon from a cold Norwegian river than from British rivers does not concur with predictions from the thermal adaptation hypothesis.  3. Model parameter estimates differed among growth groups in that the lower critical temperature for growth increased from fast to slow growing individuals. In contrast to findings for brown trout (Salmo trutta), the optimum temperature for growth did not decrease with decreasing levels of food consumption.  4. A new and simple model showed that food consumption (expressed in energy terms) peaked at 19.5–19.8 °C, which is similar to the optimal temperature for growth. Feeding began at a temperature 1.5 °C below the lower temperature for growth and ended about 1 °C above the maximum temperature for growth. Model parameter estimates for consumption differed among growth groups in a manner similar to the growth models. Maximum consumption was lower for Atlantic salmon than for brown trout, except at temperatures above 18 °C.  5. By combining the growth and food consumption models, growth efficiency was estimated and reached a maximum at about 14 °C for fast growing individuals, increasing to nearly 17 °C for slow growing ones, although it was lower overall for the latter group. Efficiency also declined with increasing fish size. Growth efficiency was generally higher for Atlantic salmon than for brown trout, particularly at high temperature.
Benthic macroinvertebrate biomass and wildfires: evidence for enrichment of boreal subarctic lakes
Authors: Scrimgeour Garry J. , Tonn William M. , Paszkowski Cynthia A. , Goater Cameron
Published: March 2003

1 We quantified the effects of forest fire on littoral benthic macroinvertebrate biomass on a boreal subarctic plateau in Alberta, Canada. Water chemistry and benthos were collected from six lakes, 1 and 2 years following a 1995 fire which burned about 91% of their catchments (i.e. recently burnt lakes), and from four other lakes whose catchments burned between 1961 and 1985 (i.e. previously burnt lakes). Seven lakes whose catchments had not burned since at least 1957 served as reference systems.  2 Total benthic macroinvertebrate biomass and biomass of Chironomidae were 1.5‐ and 2‐fold (P<0.05) greater within recently burnt lakes than in reference systems, whereas the biomass of Oligochaeta (P=0.06) and Amphipoda (P=0.07) were marginally higher in burnt than reference lakes. Burnt lakes had greater colour (P<0.05) and marginally (P=0.06) higher concentrations of soluble reactive phosphorus than reference lakes.  3 Nutrient diffusing substrata deployed in a previously and a recently burnt lake indicated that littoral epilithic communities were co‐limited by the availability of phosphorus (P) and nitrogen (N), although co‐limitation was stronger in the previously burnt than the recently burnt lake. Epilithic chlorophyll a on natural stone surfaces in the recently burnt lake was also 3.5 times higher (P<0.05) than that from the previously burnt lake.  4 Among all 17 lakes, total benthic biomass and biomass of Chironomidae, Amphipoda and Nematoda, were significantly (P<0.05) or marginally (P=0.06) related to soluble reactive phosphorus (SRP) but not dissolved inorganic nitrogen or colour. These regressions explained between 11% and 64% of variation in benthic biomasses.  5  Linear regressions and second‐order polynomials explained 18% and 24% of the variation in concentrations of SRP and water colour with time since fire, respectively, and between 22% and 70% of variation in total biomass and biomass of the five dominant invertebrate groups. These analyses suggest that benthic biomasses continue to be elevated for about 15–20 years following fire before declining to pre‐disturbance levels.
Tracing lake trophic history with a chironomid–total phosphorus inference model
Authors: Brooks Stephen J. , Bennion Helen , Birks H. John B.
Published: March 2003

1. In the absence of historical water chemistry data, predictive biological indicator groups preserved in lake sediments can be employed to reconstruct the history of lake eutrophication. Diatoms are well established in this role, but to augment diatom‐based inferences of nutrient status we investigate the potential use of chironomid midges (Insecta: Chironomidae).

2. Canonical correspondence analysis (CCA) of modern chironomid assemblages in surface sediments from 44 lakes in the English Midlands and Wales, U.K., shows that five environmental variables (total phosphorus (TP), bottom dissolved oxygen, maximum lake depth, Secchi depth and surface water temperature) make a statistically significant (P < 0.05) contribution to explaining the variance in the chironomid data, of which TP makes the largest contribution (29%).

3. The relationship is used to develop a series of weighted averaging (WA) and partial least squares (PLS), (WA‐PLS) models to infer log10TP. The models are evaluated by leave‐one‐out (jack‐knifing) cross‐validation. The simplest minimal adequate model is provided by WA with unweighted inverse deshrinking of root mean square error of prediction (RMSEPjack=0.34 and r2jack=0.60).

4. Using this model, the trophic history of Betton Pool, Shropshire, U.K., is reconstructed from the mid‐19th century to the present day and the results from the chironomid‐TP model are compared with inferences from a diatom‐TP model (Bennion, Juggins & Anderson, 1996). Both reconstructions suggest that there was a gradual rise in TP since 1850 AD until about 1974, followed by a more pronounced and rapid increase that has continued until the present. Inferred TP values from the WA chironomid inference model agree with diatom‐inferred values.

5. The study demonstrates that fossil chironomid assemblages can be used to investigate quantitatively the trophic history of lakes.
Sulphate reduction and sulphur cycling in lake sediments: a review
Authors: Holmer Marianne , Storkholm Peter
Published: March 2003

1. The concentration of sulphate is low in lakes and sulphur cycling has often been neglected in studies of organic matter diagenesis in lake sediments. The cycling of sulphur is, however, both spatially and temporally dynamic and strongly influences many biogeochemical reactions in sediments, such as the binding of phosphorus. This review examines the control of sulphate reduction and sulphur cycling in sediments of lakes with different trophic status.

2. The factors that control the rate of sulphate reduction have not been identified with certainty in the various environments because many factors are involved, e.g. oxygen and sulphate concentrations, temperature and organic matter availability.

3. Sulphate reduction is less significant under oligotrophic conditions, where mineralization is dominated by oxic decomposition. The supply of organic matter may not be sufficient to support sulphate reduction in the anoxic parts of sediments and, also, sulphate availability may control the rate as the concentration is generally low in oligotrophic lakes.

4. There is a potential for significant sulphate reduction in eutrophic lakes, as both the availability of organic matter and sulphate concentration are often higher than in oligotrophic lakes. Sulphate is rapidly depleted with sediment depth, however, and methanogenesis is generally the most important process in overall carbon mineralization. Sulphate reduction is generally low in acidic lakes because of low sulphate availability and reduced microbial activity.

5. It is still unclear which of the forms of sulphur deposits are the most important and under which conditions burial occurs. Sulphur deposition is controlled by the rate of sulphate reduction and reoxidation. Reoxidation of sulphides occurs rapidly through several pathways, both under oxic and anoxic conditions. Only a few studies have been able to examine the importance of reoxidation, but it is hypothesized that most of the reoxidation takes place under anoxic conditions and that disproportionation is often involved. The presence of sulphide oxidizing bacteria, benthic fauna and rooted macrophytes may substantially enhance oxic reoxidation. Deposition of sulphur is generally higher in eutrophic than in oligotrophic lakes because of a number of factors: a higher rate of sulphate reduction, enhanced sedimentation of organic sulphur and less reoxidation as a result of reduced penetration of oxygen into the sediments, a lack of faunal activity and rooted macrophytes.
Effects of nutrient enrichment and leaf quality on the breakdown of leaves in a hardwater stream
Authors: Royer Todd V. , Minshall G. Wayne
Published: March 2003

1. The breakdown of leaf litter in streams is influenced strongly by leaf quality and the concentration of dissolved nutrients, primarily inorganic nitrogen (N) and phosphorus (P) in the water. We examined the effect of nutrient enrichment on the breakdown of three species of leaves in a hardwater, nutrient‐rich stream. The rate of microbial respiration was also measured on the decomposing leaves.

2. The breakdown rates of dogwood (Cornus stolonifera), aspen (Populus tremuloides) and birch (Betula occidentalis), k‐values of 0.0461, 0.0307 and 0.0186 day–1, respectively, were unaffected by nutrient enrichment and generally faster than reported previously. Microbial respiration on the leaves was greater than reported previously for leaves of congeneric species. It appears that leaf breakdown in the study stream was not nutrient limited.

3. Nitrogen‐based measures of leaf quality, such as percentage N and carbon (C)/nitrogen ratio, did not correspond to measured breakdown rates among the three leaf types. The best predictors of relative breakdown rates were percentage lignin and the percentage of the total carbon that occurred as lignin. We suggest that, when leaf breakdown is not nutrient limited, measures of carbon quality (i.e. lignin‐based measures) are a better assessment of overall leaf quality than are N‐based measures.

4. Previous studies have indicated that the enzymes produced by aquatic hyphomycetes (microfungi) operate most efficiently at a basic pH and in the presence of calcium ions. The hardwater conditions (pH=8.6, total hardness > 300 mg CaCO3 L–1) and abundance of dissolved NO3 and soluble reactive phosphorous (SRP) (approximately 50 μg L–1, each) in the study stream appear to have provided conditions that resulted in a high respiration rate and rapid breakdown of leaf litter.
A proximate cue for oviposition site choice in the bitterling (Rhodeus sericeus)
Authors: Smith Carl , Rippon Karina , Douglas Alex , Jurajda Pavel
Published: March 2003

1. We investigated two possible proximate cues used for oviposition site choice by females of the bitterling (Rhodeus sericeus), a freshwater fish that spawns on the gills of live unionid mussels. The two cues were the flow velocity and/or oxygen content of water emerging from the exhalant siphon of a mussel.

2. Field observations showed that female bitterling always inspected the exhalant siphons of mussels before they spawned in them. Siphon inspection was not always a prelude to spawning and it may serve as a means of assessing mussel quality. Female skimming behaviour, swimming over a mussel without spawning, may also be used to assess mussel quality, although the mechanism for this is unclear.

3. Measurements of the flow velocity of water emerging from the exhalant siphons of four mussel species (Anodonta anatina, A. cygnea, Unio pictorumandU. tumidus) showed a significant difference among species, withU. tumidushaving the highest mean flow velocity andU. pictorumthe lowest.

4. Measurements of the change in oxygen concentration of water entering a mussel inhalant siphon and leaving its exhalant siphon in field and laboratory studies showed a significant difference among the four mussel species, withA. cygneaexhibiting a significantly higher change in oxygen concentration than the other species.

5. The presence of bitterling embryos in the gills of a mussel significantly increased its oxygen consumption whereas larval glochidia had no significant effect. We discuss oxygen availability as a possible proximate cue for oviposition site choice in bitterling.
Comparison of bacterial production in sediments, epiphyton and the pelagic zone of a lowland river
Authors: Fischer Helmut , Pusch Martin
Published: March 2003

1. The microbial metabolism of organic matter in rivers has received little study compared with that of small streams. Therefore, we investigated the rate and location of bacterial production in a sixth‐order lowland river (Spree, Germany). To estimate the contribution of various habitats (sediments, epiphyton, and the pelagic zone) to total bacterial production, we quantified the contribution of these habitats to areal production by bacteria.

2. Large areas of the river bottom were characterized by loose and shifting sands of relatively homogenous particle size distribution. Aquatic macrophytes grew on 40% of the river bottom. Leaf areas of 2.8 m2 m−2 river bottom were found in a 6.6 km river stretch.

3. The epiphyton supported a bacterial production of 5–58 ng C cm−2 h−1. Bacterial production in the pelagic zone was 0.9–3.9 μg C L−1 h−1, and abundance was 4.0–7.8 × 109 cells L−1. Bacterial production in the uppermost 2 cm of sediments ranged from 1 to 8 μg C cm−3 h−1, and abundance from 0.84 to 6.7 × 109 cells cm−3. Bacteria were larger and more active in sediments than in the pelagic zone.

4. In spite of relatively low macrophyte abundance, areal production by bacteria in the pelagic zone was only slightly higher than in the epiphyton. Bacterial biomass in the uppermost 2 cm of sediments exceeded pelagic biomass by factors of 6–22, and sedimentary bacterial production was 17–35 times higher than in the overlying water column.

5. On a square meter basis, total bacterial production in the Spree was clearly higher than primary productivity. Thus, the lowland river Spree is a heterotrophic system with benthic processes dominating. Therefore, sedimentary and epiphytic bacterial productivity form important components of ecosystem carbon metabolism in rivers and shallow lakes.

6. The sediments are focal sites of microbial degradation of organic carbon in a sand‐bottomed lowland river. The presence of a lowland river section within a river continuum probably greatly changes the geochemical fluxes within the river network. This implies that current concepts of longitudinal biogeochemical relationships within river systems have to be revised.
Lime treatment and its effects on the chemistry and biota of hardwater eutrophic lakes
Authors: Prepas Ellie E. , Pinel‐Alloul Bernadette , Chambers Patricia A. , Murphy Tom P. , Reedyk Sharon , Sandland Greg , Serediak Mark
Published: March 2003

1. The main focus of this study was to investigate the effects of single and multiple moderate doses of lime (slaked lime, Ca(OH)2, and/or calcite, CaCO3) on eutrophic hardwater lakes. This information would contribute to strategies to manage phytoplankton and macrophyte biomass in eutrophic lakes.

2. Water chemistry and biota were monitored for up to 7 years after initial lime treatment and results were compared with reference systems.

3. Complementary studies investigated the effect of lime on macrophytes in ponds, irrigation canals and microcosm experiments.

4. When water pH was kept within its natural range (≤ 10), single and multiple lime applications to lakes and ponds controlled macrophyte biomass, without negatively affecting invertebrate communities.

5. Single lime treatments at moderate dosages of lakes and ponds resulted in variable and mostly temporary changes in chlorophyll a (chl a) and phosphorus (P) concentration. Although sediment P release was reduced in single‐dose lakes during the first winter following treatment, reductions appeared temporary.

6. Multiple treatments of lakes and ponds were effective at reducing both chl a and P concentrations over longer periods. Mean winter P release rate was also reduced after initial treatment.

7. In laboratory studies, sediment cores were incubated with eight different treatments to assess P release. Redox‐sensitive treatments were no more effective at lowering total P concentration in overlying water than some redox‐insensitive treatments. Lime reduced total P concentrations, but was not as effective as treatments with alum.

8. The use of lime in managing macrophyte and phytoplankton biomass in shallow, hardwater lakes and ponds may be preferable over other treatments, because lime is economical and non‐toxic as long as pH is kept within a natural range.
Ecology of glacier‐fed rivers: current status and concepts
Authors: Brittain John E. , Milner Alexander M.
Published: March 2003

1. This paper is an introduction to a special issue of Freshwater Biology containing papers dealing with various aspects of the ecology of glacier‐fed rivers.

2. Using similar field protocols, a wide range of glacier‐fed systems were studied across Europe from the French Pyrenees to Svalbard within the framework of the European Commission project, Arctic and Alpine Stream Ecosystem Research (AASER). Recent investigations from other parts of Europe together with New Zealand and Greenland are also reported. This work has advanced our knowledge of the functioning of these types of rivers and has led to the modification and quantification of the conceptual model of Milner & Petts (1994).

3. Glacier‐fed rivers, by virtue of the dominance of physical variables in shaping macroinvertebrate communities, are not only good indicators of climate change, but also may be suitable testing grounds for examining ecological concepts.
Longitudinal distribution of macroinvertebrate assemblages in a glacially influenced stream system in the Italian Alps
Authors: Maiolini Bruno , Lencioni Valeria
Published: March 2003

1. The longitudinal distribution of macroinvertebrates was investigated in June, August and September 1996 and 1997 in the Conca glacial stream and its tributary (Italian Alps; 46°N, 10°E). The principal aim was to test the Milner & Petts (1994) model that predicts the succession of faunal groups downstream of the glacial snout in relation to water temperature and channel stability. The effect of a non‐glacial tributary on the taxonomic richness and density patterns occurring in the glacial stream was also considered.

2. Channel stability showed an atypical longitudinal trend in the Conca glacial stream, being high in the upper part with Pfankuch Index values between 30 and 33. Water temperature exceeded 6 °C at all stations, with average values below 2 °C occurring only within 700 m from the glacial snout.

3. Taxonomic richness and diversity increased downstream. Taxonomic richness in the glacial stream (at about 1.5 km from the glacier) was comparable with the tributary and the reach after the confluence. Abundance also increased downstream in the glacial stream, but not as greatly as the number of taxa.

4. At higher taxonomic levels, the community structure in the tributary stations appeared to be similar to the two stations in the glacial stream just upstream of the confluence. The effect of the tributary was evident mainly at the genus or species level of the Chironomidae community. Some taxa found in the non‐glacial stream (e.g. Cricotopus fuscus, Eukiefferiella coerulescens, Metriocnemus sp., Paratrichocladius rufiventris, P. skirwitensis, Rheocricotopus effusus and Smittia sp.) were found also in the Conca stream but only after the confluence.

5. The upper glacial reach (within 700 m from the glacier snout) was dominated by the chironomid Diamesa spp. Less than 400 m from the glacier other Diamesinae (Pseudokiefferiella parva) and a few Orthocladiinae, especially Orthocladius (Euorthocladius) rivicola gr., colonized the stream. Some Diamesinae maintained relatively dense populations at mean water temperature around 5 °C, while some Orthocladiinae colonized reaches with mean water temperature <3 °C.

6. Contrary to the Milner & Petts (1994) model, Dipteran families such as Empididae and Limoniidae were more abundant in the upper stations than Simuliidae; non‐insects such as Nematoda and Oligochaeta were also numerous at some sites. Leuctridae, Taeniopterygidae and Nemouridae were the first Plecoptera to appear upstream, while Chloroperlidae were restricted to the lower reaches. Among Ephemeroptera, Heptageniidae were more abundant than Baetidae in the glacial sites.

7. In this glacial system channel stability and maximum temperature did not show the expected longitudinal trend and thus a typical kryal community was confined within 700 m from the glacier snout where summer mean water temperature was below 4 °C.
Longitudinal and seasonal distribution patterns of the benthic fauna of an alpine glacial stream (Val Roseg, Swiss Alps)
Authors: Burgherr Peter , Ward J. V.
Published: March 2003

1. Seasonal changes in longitudinal patterns of environmental conditions and macroinvertebrate community distributions were examined in an alpine glacial stream (Roseg River, Switzerland).

2. Physico‐chemical parameters reflected seasonal changes in glacial influence via shifts in water sources and flowpaths (glacial meltwater versus ground water), and were best described by turbidity, particulate phosphorus and specific conductance. High nitrogen concentrations indicated snowmelt was the main water source in June.

3. Macroinvertebrate densities and taxon richness were highest during spring (4526 m–2 and 16 taxa, all sites combined) and late autumn/early winter (8676–13 398 m–2 with 16–18 taxa), indicating these periods may be more favourable for these animals than summer when glacial melting is maximal. Diamesa spp. (Chironomidae) dominated the fauna at the upper three sites (>95% of zoobenthos) and were abundant at all locations. Other common taxa at lower sites (1.2–10.6 km downstream of the glacier terminus) included other chironomids (Orthocladiinae, Tanytarsini), the mayflies Baetis alpinus and Rhithrogena spp., the stoneflies Leuctra spp. and Protonemura spp., blackflies (Simulium spp., Prosimulium spp.), and Oligochaeta.

4. Co‐inertia analysis revealed a strong relationship between environmental conditions and benthic macroinvertebrate assemblages. Furthermore, it elucidated temporal variability in longitudinal response patterns, as well as a similarity in temporal patterns among individual sites.

5. Our results suggest that zoobenthic gradients are not solely related to temperature and channel stability. Seasonal shifts in sources and pathways of water (i.e. extent of glacial influence), and periods of favourable environmental conditions (in spring and late autumn/early winter) also strongly influenced zoobenthic distributions.
Macrobenthic invertebrate richness and composition along a latitudinal gradient of European glacier‐fed streams
Authors: Castella Emmanuel , Adalsteinsson Hákon , Brittain John E. , Gislason Gisli M. , Lehmann Anthony , Lencioni Valeria , Lods‐Crozet Brigitte , Maiolini Bruno , Milner Alexander M. , Olafsson Jon S. , Saltveit Svein J. , Snook Deborah L.
Published: March 2003

1. The influence of 11 environmental variables on benthic macroinvertebrate communities was examined in seven glacier‐fed European streams ranging from Svalbard in the north to the Pyrenees in the south. Between 4 and 11 near‐pristine reaches were studied on each stream in 1996–97.

2. Taxonomic richness, measured at the family or subfamily (for Chironomidae) levels for insects and higher levels for non‐insects, increased with latitude from Svalbard (3 taxa) to the Pyrenees (29 taxa).

3. A Generalized Additive Model (GAM) incorporating channel stability [Pfankuch Index (PFAN)], tractive force, Froude number (FROU), water conductivity (COND), suspended solids (SUSP) concentration, and maximum temperature explained 79% of the total deviance of the taxonomic richness per reach. Water temperature and the PFAN of stability made the highest contribution to this deviance. In the model, richness response to temperature was positive linear, whereas the response to the PFAN was bell‐shaped with an optimum at an intermediate level of stability.

4. Generalized Additive Models calculated for the 16 most frequent taxa explained between 25 (Tipulidae) and 79% (Heptageniidae) of the deviance. In 10 models, more than 50% of the deviance was explained and 11 models had cross‐validation correlation ratios above 0.5. Maximum temperature, the PFAN, SUSP and tractive force (TRAC) were the most frequently incorporated explanatory variables. Season and substrate characteristics were very rarely incorporated.

5. Our results highlight the strong deterministic nature of zoobenthic communities in glacier‐fed streams and the prominent role of water temperature and substrate stability in determining longitudinal patterns of macroinvertebrate community structure. The GAMs are proposed as a tool for predicting changes of zoobenthic communities in glacier‐fed streams under climate or hydrological change scenarios.
Characterizing nitrogen dynamics, retention and transport in a tropical rainforest stream using an in situ15N addition
Authors: Merriam Jeffrey L. , McDowell William H. , Tank Jennifer L. , Wollheim Wil M. , Crenshaw Chelsea L. , Johnson Sherri L.
Published: March 2003

1. This study was part of the Lotic Intersite Nitrogen eXperiment (LINX); a series of identical 15NH4 tracer additions to streams throughout North America. 15NH4Cl was added at tracer levels to a Puerto Rican stream for 42 days. Throughout the addition, and for several weeks afterwards, samples were collected to determine the uptake, retention and transformation pathways of nitrogen in the stream.

2. Ammonium uptake was very rapid. Nitrification was immediate, and was a very significant transformation pathway, accounting for over 50% of total NH4 uptake. The large fraction of NH4 uptake accounted for by nitrification (a process that provides energy to the microbes involved) suggests that energy limitation of net primary production, rather than N limitation, drives N dynamics in this stream.

3. There was a slightly increased 15N label in dissolved organic nitrogen (DON) the day after the 15NH4 addition was stopped. This DO15N was < 0.02% of DON concentration in the stream water at the time, suggesting that nearly all of the DON found in‐stream is allochthonous, or that in‐stream DON production is very slow.

4. Leptophlebiidae and Atya appear to be selectively feeding or selectively assimilating a very highly labelled fraction of the epilithon, as the label found in the consumers became much higher than the label found in the food source.

5. A large spate (>20‐fold increase in discharge) surprisingly removed only 37% of in‐stream fine benthic organic matter (FBOM), leaves and epilithon. The fraction that was washed out travelled downstream a long distance (>220 m) or was washed onto the stream banks.

6. While uptake of 15NH4 was very rapid, retention was low. Quebrada Bisley retained only 17.9% of the added 15N after 42 days of 15N addition. Most of this was in FBOM and epilithon. Turnover rates for these pools were about 3 weeks. The short turnover times of the primary retention pools suggest that long‐term retention (>1 month) is minimal, and is probably the result of N incorporation into shrimp biomass, which accounted for < 1% of the added 15N.
Invertebrate food webs along a stream resource gradient
Authors: Rosi‐Marshall Emma J. , Wallace J. Bruce
Published: March 2003

1. The flow of energy through food webs with similar species can vary with both space and time. The river continuum concept (RCC) provides a useful framework for predicting variability in the biota and food availability along streams. We estimated the flow of organic matter (g m−2 year−1) through food webs, arrayed along a stream, that had different resource inputs. Four sites were sampled along the Little Tennessee River, North Carolina, U.S.A.: two fifth order sites, one sixth and one seventh order site. The dominant resource is leaf detritus in the upstream reach (the upstream fifth order site), algae in the mid‐reaches (the downstream fifth and sixth order sites), and suspended material downstream (seventh order site).

2. Eleven genera, contributing from 50 to 66% of the total macroinvertebrate secondary production of each site, were studied. We estimated organic matter flow from resource to consumer by combining previously measured rates of invertebrate secondary production with gut content analyses and assimilation efficiencies.

3. Organic matter flow through food webs increased in a downstream direction, while the structure of the food webs remained constant. The total food consumed by the taxa analysed increased from 34 g m−2 year−1 at the upstream site to 730 g m−2 year−1 at the most downstream site. We estimate that the organic matter consumed by the entire macroinvertebrate community ranged from 66 to 1164 g m−2 year−1. These results indicate that there is variation in the magnitude of organic matter flow through the food webs along this river continuum.

4. The dominant food resource consumed also changed along the gradient. Leaf detritus consumption decreased from 58% of the total consumption upstream to 6% downstream, whereas consumption of amorphous detritus increased from 18 to 64%. The proportion of animal material consumed also increased from 3 to 27%. The total consumption of autochthonous resources (diatoms and filamentous algae) increased along the continuum (from 6.41 to 34.05 g m−2 year−1). We conclude that these results are related to variation in resource availability, dietary shifts and invertebrate secondary production. These results link resource availability to energy flow, a relationship originally suggested by the RCC.
Consumption of cyanobacteria by roach (Rutilus rutilus): useful or harmful to the fish?
Authors: Kamjunke Norbert , Schmidt Katja , Pflugmacher Stephan , Mehner Thomas
Published: March 2003

1. The ability of roach to use cyanobacterial food is generally believed to be one reason for the dominance of roach over perch in eutrophic European lakes. The aim of this study was to test whether cyanobacteria really are a suitable food for juvenile roach. Special attention was paid to differences between the two cyanobacteria species Aphanizomenon and Microcystis which are common in eutrophic lakes and are ingested by roach there.

2. We performed growth and behaviour experiments with juvenile roach fed with zooplankton and the different cyanobacteria. Growth rate with Aphanizomenon was lower than with Daphnia but significantly higher than without food, whereas growth rate with Microcystis was as low as without food.

3. In cultivation experiments of roach faeces, Microcystis was found not to have been digested and grew exponentially after passing through the gut whereas Aphanizomenon stayed at low biomass. Differences in growth were not related to the toxin content of cyanobacteria. Investigations of roach motility showed no differences whether fed with Aphanizomenon or Microcystis.

4. In contrast to Microcystis, Aphanizomenon can be regarded as a suitable food source for juvenile roach probably because of its better digestability. We conclude that the ability to feed on cyanobacteria is not a general competitive advantage for roach, but the outcome depends on the species composition of the cyanobacteria.
Sources of nutrients to rooted submerged macrophytes growing in a nutrient‐rich stream
Authors: Madsen Tom Vindbæk , Cedergreen Nina
Published: March 2003

1. The relative contribution of roots and leaves to nutrient uptake by submerged stream macrophytes was tested in experiments where plants were grown in an outdoor flow‐channel system. Water was supplied from a nutrient‐rich stream with inorganic nitrogen and phosphorus concentrations typical of Danish streams.

2. Four submerged macrophyte species were tested, Elodea canadensis, Callitriche cophocarpa, Ranunculus aquatilis and Potamogeton crispus, and all species were able to satisfy their demand for mineral nutrients by leaf nutrient uptake alone. This was evident from manipulative experiments showing that removal of the roots had no negative impact on the relative growth rate of the plants. Further, the organic N and P concentrations of the plant tissue was constant with time for the de‐rooted plants.

3. Enrichment of water and/or sediment had no effect on the relative growth rate of two species, E. canadensis and C. cophocarpa, indicating that in situ nutrient availability was sufficient to cover the needs for growth. Despite the lack of a response in growth rate, a reduced root/shoot biomass ratio was observed with nutrient enrichment of water and/or sediment, and an increased tissue‐P concentration in response to open‐water enrichment.

4. The open‐water nutrient concentrations of the stream in which the experiments were performed are in the upper part of the range found for Danish farmland streams (the majority of Danish streams). Still, however, the negligible effect of nutrient enrichment on the growth of submerged macrophytes observed suggests that mineral nutrient availability might play a minor role in controlling macrophyte growth in most Danish streams.
Sexual reproduction in Daphnia pulex (Crustacea: Cladocera): observations on male mating behaviour and avoidance of inbreeding
Authors: WINSOR GEOFFREY L. , INNES DAVID J.
Published: March 2003

1.  Mating behaviour in Daphnia appears to rely on random contact between males and sexual females rather than diffusible pheromones. Males may be able to discriminate sexually receptive females from females in other developmental stages and increase their mating efficiency. Males may also use chemical signals to avoid mating with females from the same clone and avoid the severe inbreeding depression that has been documented for intraclonal mating. The present study used experiments to test for the avoidance of intraclonal mating and assess male mating efficiency in D. pulex.

2.  Three clones were examined for the avoidance of intraclonal mating by providing males with an opportunity to mate with females of the same or two different clones. The proportion of intraclonal matings did not differ from the proportion of interclonal matings, suggesting that D. pulex males do not use kin discrimination to avoid mating with females from the same clone.

3.  The proportion of mated females decreased with increasing numbers and density of sexual females when exposed to a single male. This observation suggests that a male spends more time pursuing and copulating with sexually receptive females than non‐receptive females and there is insufficient time to mate with all sexual females. The decrease in proportion of females mated could also be the result of sperm depletion in the male. Sperm depletion is unlikely to occur in nature because sexually receptive females are much rarer than in the experimental conditions.
Gradients in stream fish assemblages across a Mediterranean landscape: contributions of environmental factors and spatial structure
Authors: MAGALHÃES M. FILOMENA , BATALHA DIOGO C. , COLLARES‐PEREIRA MARIA JOÃO
Published: March 2003

1. Despite wide recognition that fish assemblages are influenced by factors operating over a range of spatial scales, little effort has been devoted to quantifying large‐scale variation and the multiscale dependencies of assemblage patterns and processes. This is particularly true for Mediterranean streams, where seasonally predictable drying‐up may lead to a strong association between assemblage attributes and large‐scale factors affecting the distribution of population sources and extinction likelihood.

2. The contribution of large‐scale factors to stream fish assemblage variation was quantified across a Mediterranean landscape, in south‐west Portugal. Fish abundance and species composition were estimated at 166 sites across third‐ to sixth‐order streams, in March–July 1998. Variance partitioning by redundancy analyses was used to analyse assemblage variation against three sets of predictor variables: environmental (catchment position, and geomorphic and hydrological factors), large‐scale spatial trends and neighbourhood effects.

3. Environmental variables and spatial trends accounted for 34.6% of the assemblage variation across the entire region, and for 36.6 and 57.8% within the two largest catchments (Mira and Seixe). Neighbourhood effects were analysed at the catchment scale, increasing the explained variation to 56.1% (Mira) and 70.7% (Seixe).

4. A prevailing environmental gradient was reflected in an increase in the abundance of all species and size‐classes in relation to catchment position, with more fish present in larger streams and in downstream reaches. Variables describing geomorphic and hydrological settings were less important in explaining assemblage variation.

5. Spatial trends always accounted for the smallest fraction of assemblage variation, and they were probably associated with historical barriers to fish dispersal. The strong neighbourhood effects may be related to spatially autocorrelated habitat conditions, but they are also a likely consequence of fish emigration/extinction and colonisation processes.

6. These results emphasise that a substantial proportion of fish assemblage variation in Mediterranean streams may be explained by large‐scale factors, irrespective of microhabitats and local biotic interactions. It is suggested that this pattern results to a large extent from the seasonal drying‐up, with the summer shortage of surface water limiting fish occurrence in headwaters, and consequently the key core areas for fish concentrating in larger streams and tributaries adjacent to large streams because of neighbourhood effects.
Are distribution patterns linked to dispersal mechanism? An investigation using pond invertebrate assemblages
Authors: RUNDLE S. D. , FOGGO A. , CHOISEUL V. , BILTON D. T.
Published: March 2003

1. Dispersal ability influences the distribution and abundance of organisms, but empirical investigations of the relationship between dispersal ability and the composition of ecological assemblages are scarce. Here, we compare between‐site variation in the species richness and community composition of actively and passively dispersing pond invertebrates.

2. Coleoptera (active dispersers) and microcrustacea (passive dispersers) were sampled over a season from 16 ponds within a 4‐km radius in south‐west England. Species richness and community composition were related to environmental variables using regression and Canonical Correspondence Analysis (CCA), respectively.

3. Coleopteran species richness was significantly and positively correlated with pond permanence and maximum area, whereas microcrustacean species richness was relatively equal across sites and did not correlate with environmental variables. The frequency of species' occurrence between sites was the same for both groups, which suggests that active and passive dispersers exhibited the same degree of dispersal.

4. Between‐site variation in community composition was non‐random for both groups, with pond permanence and area, together, explaining similar proportions of between‐site variation for Coleoptera. Permanence was correlated most strongly with microcrustacean community composition and a high proportion (25%) of microcrustacean species were more numerous in smaller, more ephemeral ponds.

5. These data suggest that, at small spatial scales, Coleoptera which can undertake multiple dispersal events, are more likely to colonise large, more permanent ponds than passively dispersing microcrustacea. For microcrustacea, other traits (in this case those permitting existence in ephemeral habitats) may over‐ride the influences of dispersal in driving between‐site variation in species composition.
The effect of bladderwort (Utricularia) predation on microcrustacean prey
Authors: Harms Sabine
Published: March 2003

SUMMARY 1. The effects of the carnivorous plant Utricularia (bladderwort) on its microcrustacean and macroinvertebrate prey were studied under seminatural and natural conditions. The results suggest that Utricularia is a strong interactor in littoral communities that influences its prey populations by direct predation and indirect facilitation.

2. In an 8‐week enclosure experiment, effects on prey density were compared in three treatments with (1) U. vulgaris with intact trapbladders, (2) U. vulgaris without bladders and (3) no Utricularia present.

3. Utricularia predation caused a decrease in prey density over time, whereas presence of Utricularia without bladders increased prey density. In the controls without Utricularia, prey density was relatively constant over time.

4. Field samples were collected to quantify predation rates of three Utricularia species on two natural prey populations. Daily consumption rates on prey peaked from mid‐July to mid‐August for all Utricularia species, but were low in June and September. This pattern was explained mainly by a high number of trapbladders at this time, but also by a slight increase in the number of prey caught per bladder. Per capita prey mortality rates caused by Utricularia were substantial and ranged between 0.14 and 0.43 day−1 for copepods, 0.1–0.27 day−1 for ostracods and 0.04–0.2 day−1 for chydorid cladocerans.

5. Predation and facilitation effects were observed for total prey and separately for epiphytic and benthic prey. Planktonic microcrustaceans showed no response to Utricularia presence.
Aminopeptidase and phosphatase activities in basins of Lake Hiidenvesi dominated by cyanobacteria and in laboratory grown Anabaena
Authors: VAITOMAA JAANA , REPKA SARI , SAARI LUYDMILA , TALLBERG PETRA , HORPPILA JUKKA , SIVONEN KAARINA
Published: March 2003

1. Extracellular enzyme activities were examined in freshwater basins representing a transition from hypertrophy to mesotrophy and in axenic cyanobacterial cultures to evaluate the ecological role of extracellular enzyme activities of cyanobacteria.

2. Aminopeptidase activity was related to the trophic status of the lake basins. The activity was highest in the most eutrophic basin and decreased in the less nutrient‐rich basins. Cyanobacteria were the most important autotrophic organisms and aminopeptidase activity was positively associated with cyanobacterial biomass.

3. In an axenic Anabaena batch culture, nitrogenase activity was several orders of magnitude higher than leucine aminopeptidase activity. Nitrate did not have an effect on aminopeptidase activity or growth, but significantly reduced the rate of nitrogen fixation. A high phosphorus concentration at the beginning of the Anabaena batch‐culture experiment resulted in reduced phosphatase activity.

4. In Lake Hiidenvesi, aminopeptidase activity probably originated mostly from attached bacteria and less so from cyanobacteria.
Connectivity and biocomplexity in waterbodies of riverine floodplains
Authors: AMOROS C. , BORNETTE G.
Published: March 2003

1. In river corridors, water plays a key role in connecting various landscape patches. This `hydrological connectivity' operates on the four dimensions of fluvial hydrosystems: longitudinal, lateral, vertical, and temporal. The present review focuses on: (1) lateral connectivity that links the main course of a river with floodplain waterbodies; and (2) vertical connectivity, the exchanges between the surface and groundwater via infiltration into the alluvial aquifer and exfiltration of phreatic water from the hillslope aquifer.

2. The biocomplexity of fluvial hydrosystems results from interactions between processes operating at various spatial and temporal scales. Differences in the nature and intensity of hydrological connectivity contribute to the spatial heterogeneity of riverine floodplains, which results in high alpha, beta and gamma diversity. Differences in connectivity also provide complementary habitats that are required for the parts of life cycles and life‐cycles of some species. Hydrological connectivity also produces antagonistic effects, even within the same waterbody.

3. Two temporal scales are distinguished in connectivity dynamics. River level fluctuations within years lead to a pulsing connectivity that drives the functioning of floodplain ecosystems, namely the exchange of organic matter and inorganic nutrients and the shift between production and transport phases. On the scale of decades to centuries, the interactions between various processes increase the biocomplexity of floodplains; for example, river dynamics, which create highly connected waterbodies, compensate for succession that tends towards disconnection. Alternatively, river‐bed incision leads to the reduction of fluvial dynamics and to the disconnection of waterbodies, although river incision may increase vertical connectivity where waterbodies are supplied by the hillslope aquifer.
Island‐dominated landscapes of large floodplain rivers, a European perspective
Authors: GURNELL A. M. , PETTS G. E.
Published: March 2003

1. The landscapes of large floodplain rivers are characterised by heterogeneous environments related to the interplay of flood flows, sediment transport and vegetation dynamics.

2. The large rivers of Europe, and probably most rivers throughout the forest biomes, were characterised by islands but over the period of major human interference, many have become dominated by incision and narrowing so that they are now characterised by single‐thread and relatively simple channel forms.

3. Vegetation plays an active role in developing heterogeneous channel forms through (a) biotic processes such as seed dispersal, vegetative regeneration and succession and (b) abiotic effects such as increasing flow resistance inducing sedimentation, and decreasing bank erodibility.

4. In particular, accumulations of living driftwood (cf. dead driftwood accumulations and dispersed seedlings) accelerate sedimentation and island development.

5. River reaches with vegetated islands have a high habitat diversity.

6. The natural influences of flood disturbance, wood accumulation, vegetation growth, island development and tree die‐off, cause island‐dominated reaches to undergo cycles of island growth and decay that are related to cycles of aquatic habitat diversification and simplification.