bluuebunny/crossref_metadata_2025 huggingface dataset:
Nutrient dynamics at the interface between surface waters and groundwaters
Authors: Dahm Clifford N. , Grimm Nancy B. , Marmonier Pierre , Valett H. Maurice , Vervier Philippe
Published: March 2003

1. The surface water/groundwater (SW/GW) interface is a crucial control point for lateral nutrient fluxes between uplands and aquatic ecosystems and for upstream/downstream (longitudinal) processes in lotic ecosystems.

2. Hydrological and biogeochemical dynamics of the SW/GW ecotone are linked to the degree of channel constraint and the sediment characteristics of the floodplain and stream bed.

3. The availability of specific chemical forms of electron donors and electron acceptors affects the spatial distribution of biogeochemical processes at the SW/GW interface. Temporal change in discharge is also a major factor affecting the rate and extent of these processes.

4. The magnitude of SW/GW interactions in lotic ecosystems is predicted to be a major determinant of solute retention. Channel morphology, stream bed composition and discharge are predicted to be important controls on SW/GW interactions.

5. Interdisciplinary research involving hydrologists, geomorphologists, aquatic ecologists, microbial ecologists and landscape ecologists is needed to further our present understanding of this critical interface linking terrestrial and aquatic ecosystems.
Response of stream fish to improved water quality: a comparison between the 1960s and 1990s
Authors: Eklöv A. G. , Greenberg L. A. , Brönmark C. , Larsson P. , Berglund O.
Published: March 2003

1. The effect of improved water quality on fish assemblages in streams in southern Sweden was assessed by comparing species composition at 161 sites and water quality at twenty‐nine sites in the 1960s and the 1990s.

2. Water quality had improved and there was an increase in the number of sites or catchments with brown trout (Salmo trutta), stone loach (Barbatula barbatula) and eel (Anguilla anguilla). The response was greatest for brown trout and was best explained by increased oxygen concentrations.

3. The number of sites with nine‐spined stickleback (Pungitius pungitius), ide (Leuciscus idus) and brook lamprey (Lampetra planeri) decreased between the 1960s and 1990s. The decrease was greatest for nine‐spined stickleback and was related to the increase in sites with trout, suggesting that nine‐spined stickleback may be sensitive to predation or competition.

4. Improved water quality has led to recolonization by brown trout, probably enabling biotic interactions to play a larger role in structuring fish assemblages. Improving water quality was an effective method for rehabilitating fish populations in streams where natural colonization was possible.
The hydrogeomorphic approach to functional assessment of riparian wetlands: evaluating impacts and mitigation on river floodplains in the U.S.A.
Authors: Hauer F. Richard , Smith R. Daniel
Published: March 2003

1. The ’hydrogeomorphic‘ approach to functional assessment of wetlands (HGM) was developed as a synthetic mechanism for compensatory mitigation of wetlands lost or damaged by human activities. The HGM approach is based on: (a) classification of wetlands by geomorphic origin and hydrographic regime (b) assessment models that associate variables as indicators of function, and (c) comparison to reference wetlands that represent the range of conditions that may be expected in a particular region. In this paper, we apply HGM to riparian wetlands of alluvial rivers.

2. In the HGM classification, riverine wetlands are characterized by formative fluvial processes that occur mainly on flood plains. The dominant water sources are overbank flooding from the channel or subsurface hyporheic flows. Examples of riverine wetlands in the U.S.A. are: bottomland hardwood forests that typify the low gradient, fine texture substratum of the south‐eastern coastal plain and the alluvial flood plains that typify the high gradient, coarse texture substratum of western montane rivers.

3. Assessment (logic) models for each of fourteen alluvial wetland functions are described. Each model is a composite of two to seven wetland variables that are independently scored in relation to a reference data set developed for alluvial rivers in the western U.S.A. Scores are summarized by a ’functional capacity index‘ (FCI), which is multiplied by the area of the project site to produce a dimensionless ’functional capacity unit‘ (FCU). When HGM is properly used, compensatory mitigation is based on the FCUs lost that must be returned to the riverine landscape under statutory authority.

4. The HGM approach also provides a framework for long‐term monitoring of mitigation success or failure and, if failing, a focus on topical remediation.

5. We conclude that HGM is a robust and easy method for protecting riparian wetlands, which are critically important components of alluvial river landscapes.
Α comparison of alternative techniques for prediction of the fauna of running‐water sites in Great Britain
Authors: Moss D. , Wright J. F. , Furse M. T. , Clarke R. T.
Published: March 2003

1. Early versions of the river invertebrate prediction and classification system (RIVPACS) used TWINSPAN to classify reference sites based on the macro‐invertebrate fauna, followed by multiple discriminant analysis (MDA) for prediction of the fauna to be expected at new sites from environmental variables. This paper examines some alternative methods for the initial site classification and a different technique for prediction.

2. A data set of 410 sites from RIVPACS II was used for initial screening of seventeen alternative methods of site classification. Multiple discriminant analysis was used to predict classification group from environmental variables.

3. Five of the classification–prediction systems which showed promise were developed further to facilitate prediction of taxa at species and at Biological Monitoring Working Party (BMWP) family level.

4. The predictive capability of these new systems, plus RIVPACS II, was tested on an independent data set of 101 sites from locations throughout Great Britain.

5. Differences between the methods were often marginal but two gave the most consistently reliable outputs: the original TWINSPAN method, and the ordination method semi‐strong hybrid multidimensional scaling (SSH) followed by K‐means clustering.

6. Logistic regression, an alternative approach to prediction which does not require the prior development of a classification system, was also examined. Although its performance fell within the range offered by the other five systems tested, it conveyed no advantages over them.

7. This study demonstrated that several different multivariate methods were suitable for developing a reliable system for predicting expected probability of occurrence of taxa. This is because the prediction system involves a weighted average smoothing across site groupings.

8. Hence, the two most promising procedures for site classification, coupled to MDA, were both used in the exploratory analyses for RIVPACS III development, which utilized over 600 reference sites.
Quantified small‐scale turbulence inhibits the growth of a green alga
Authors: Hondzo Midhat , Lyn Dennis
Published: March 2003

1. Laboratory experiments were conducted to elucidate the effect of small‐scale turbulent fluid motion on the growth of laboratory cultures of the freshwater algae Scenedesmus quadricauda. Turbulent flow was generated using an oscillating‐grid apparatus. The experiments were performed under the range of fluid flow conditions similar to those occurring in nature. The only growth limiting factor was the effect of small‐scale fluid motion; all other environmental factors, such as light, temperature and nutrients, were kept constant.

2. Growth of Scenedesmus quadricauda, measured in terms of chlorophyll a concentration, was inhibited when the level of turbulence in the water column was increased. Algal growth was maximum in a quiescent fluid. The inhibitory effect of fluid motion was observed independently of flow regime (laminar, transitional, turbulent) in the water column.

3. Cell destruction and aggregation of dead and living cells of algae were observed in a turbulent flow. High shear rates, estimated from the dissipation of turbulent kinetic energy, caused the cell destruction, algal collision and agglomeration of algae. Data on Scenedesmus responses to small‐scale fluid motion will enhance and broaden our ability to develop predictive multispecies models for freshwater phytoplankton communities.
Prey selection and diel feeding of the freshwater jellyfish, Craspedacusta sowerbyi
Authors: Spadinger Reinhard , Maier Gerhard
Published: March 2003

1. The diet of the invasive freshwater jellyfish, Craspedacusta sowerbyi (Lankester), was assessed by analysing its stomach contents.

2. The medusae ingested various zooplankton and benthic prey in the 0.1–3.0 mm size range. The selectivity indices for prey showed that larger zooplankton (0.4–1.4 mm) and active prey such as copepods were preferred; small potential prey, and the loricate rotifer Keratella cochlearis in particular, were almost never consumed. Measurements suggest that spacing between the tentacle branches could determine prey selection. Another possibility is that some prey are too small or slow to activate nematocysts after collision with the predator. Prey > 1.4 mm can probably escape or are otherwise too large to be handled.

3. The medusae of Craspedacusta medusae stayed in deep water during daytime and migrated upwards at night. The greatest number of prey in freshwater jellyfish stomachs was detected at night.

4. Calculation of consumption rates, based on mean stomach contents and digestion times of 4–5 h, showed that, on average, one medusa takes 190 zooplankton prey day−−1 at a mean prey density of about 100 L−−1. At the observed medusae density of 1 m−−3, the cropping rate was about 0.2 zooplankton prey L−−1 day−−1.
Assessing the health of sediment ecosystems: use of chemical measurements
Authors: Maher W. , Batley G. E. , Lawrence I.
Published: March 2003

1. This paper outlines the use of chemical measurements as surrogate indicators of the health of sediment ecosystems.

2. For chemical measurements to be used for this purpose, links must be able to be made between adverse biological effects and the chemical composition of sediments.

3. Benchmark sediment quality guidelines allow decisions to be made about whether or not a sediment ecosystem is likely to be impacted. These guidelines are established using an effects database and a weight‐of‐evidence approach that gives ranges of chemical concentrations associated with known adverse biological effects.

4. If guidelines are exceeded the measured values are compared to concentrations of that contaminant in a comparable background or reference sediment. Exceedance of these concentrations leads to site‐specific estimates of contaminant bioavailability. If a potential problem is indicated, laboratory sediment bioassays are used to assess the likelihood that the sediment will harm biota.

5. Trace metals are used as an example of a sediment contaminant.
Development and testing of an Index of Stream Condition for waterway management in Australia
Authors: Ladson Anthony R. , White Lindsay J. , Doolan Jane A. , Finlayson Brian L. , Hart Barry T. , Lake P. Sam , Tilleard John W.
Published: March 2003

1. An Index of Stream Condition (ISC) has been developed to assist broad scale management of waterways by providing an integrated measure of their environmental condition.

2. The ISC provides scores for five components of stream condition: (i) hydrology (based on change in volume and seasonality of flow from natural conditions); (ii) physical form (based on bank stability, bed erosion or aggradation, influence of artificial barriers, and abundance and origin of coarse woody debris); (iii) streamside zone (based on types of plants; spatial extent, width, and intactness of riparian vegetation; regeneration of overstorey species, and condition of wetlands and billabongs); (iv) water quality (based on an assessment of phosphorus, turbidity, electrical conductivity and pH); and (v) aquatic life (based on number of families of macroinvertebrates).

3. The ISC is intended for use by managers at state and regional levels and can be used to report on stream condition, assist with priority setting, judge the long‐term effectiveness of rehabilitation programs and assist with adaptive management. The best available scientific information was used by a multidisciplinary group of scientists and managers to create a stream assessment procedure that can be used routinely by people with limited scientific training.

4. ISC development included trials in four catchments in Victoria, Australia. Over 80 stream reaches were assessed and the results were used to refine the ISC to improve the ease of measurement and ensure that outcomes met the expectations of users. The ISC is now available to be used more widely for reporting on stream condition.
Climate sensitivity of Oak Mere: a low altitude acid lake
Authors: Carvalho Laurence , Moss Brian
Published: March 2003

1. Hydrologically open lakes in temperate regions are not considered as sensitive to climate change as closed‐basin lakes in semiarid regions.

2. Oak Mere is an acid lake in lowland UK. It has no surface inflow or outflow but is connected to the regional groundwater. It is a high landscape, hydrologically open lake.

3. This paper describes how Oak Mere responded to drought with rapid and substantial changes in acidity and nutrients. Decreases in pH and catchment‐derived nutrients appear to be a response to the relative amount of catchment‐derived minerals compared with those received in direct precipitation.

4. The extreme sensitivity of the site appears to be due to negligible groundwater inputs, low buffering capacity and a short retention time.

5. The paper demonstrates that high landscape sites may represent the most sensitive hydrologically open lakes to climate change. This not only has consequences for acidification and eutrophication studies. These sites may also be considered valuable in that they potentially offer an important new archive for palaeoclimate studies, with a sensitivity previously considered unavailable in low altitude temperate regions.
Physiological responses to variable environments: storage and respiration in starving rotifers
Authors: Kirk Kevin L. , Ellis John , Taylor Jennifer
Published: March 2003

1. Zooplankton exist in environments where food availability varies greatly over time, and success depends in part on the ability to store resources when food is abundant and to conserve them when food is scarce. This paper reports on interspecific differences in the size of stored reserves, and in respiration rate during food deprivation, of four species of planktonic rotifers.

2. The size of reserves varied from 42 to 71% of initial (well‐fed) body mass. Interspecific differences in reserve size explained some of the previously observed differences in starvation time.

3. The initial response of respiration rate to food deprivation was quite variable between species. Brachionus calyciflorus was the only species to conserve energy by decreasing respiration rate in response to food deprivation. In contrast, the respiration rate of starved Asplanchna priodonta increased, while that of A. silvestrii and Synchaeta pectinata did not change, during food deprivation.

4. Theory predicts that temporal variation in resource level may facilitate the coexistence of competing species. This theory depends upon trade‐offs between traits that confer competitive success in different environments. Although rotifers show a trade‐off between competitive ability and maximum population growth rate, we found no evidence for trade‐offs between either of those two traits and the size of reserves.
Importance of landscape position and legacy: the evolution of the lakes in Taylor Valley, Antarctica
Authors: Lyons Wberry , Fountain& ReW. ,   dagger, & Peter Doran ,   Dagger, Priscu& JohN. C. ,   sect, Neumann Klaus , Welch Kathleen A.
Published: March 2003

1. The major factor influencing the chemical composition and evolution of the major lakes in Taylor Valley, Antarctica, is their location within the landscape. Present‐day microclimatic variation and its manifestation over the past 6000 years have led to the differences observed in these lakes today.

2. Geographical and topographical variables within the Taylor Valley magnify subtle changes in the hydrological balances of these lakes. Even short‐term variation of the surface temperatures and albedo greatly impact the run‐off into the lakes, leading to positive or negative water balances.

3. The legacy of past climatic changes has had a profound effect on the ecology of the lakes today.
Factors influencing the temporal coherence of five lakes in the English Lake District
Authors: George D. G. , Talling J. F. , Rigg E.
Published: March 2003

1. The lakes in the Windermere catchment are all deep, glacial lakes but they differ in size, shape and general productivity. Here, we examine the extent to which year‐to‐year variations in the physical, chemical and biological characteristics of these lakes varied synchronously over a 30–40‐year period.

2. Coherence was estimated by correlating time‐series of the spring, summer, autumn and winter characteristics of five lakes: Esthwaite Water, Blelham Tarn, Grasmere and the North and South Basins of Windermere. Three physical, four chemical and two biological time‐series were analysed and related to year‐to‐year variations in a number of key driving variables.

3. The highest levels of coherence were recorded for the physical and chemical variables where the average coherence was 0.81. The average coherence for the biological variables was 0.11 and there were a number of significant negative relationships. The average coherence between all possible lake pairs was 0.59 and average values ranged from 0.50 to 0.74. A graphical analysis of these results demonstrated that the coherence between individual lake pairs was influenced by the relative size of the basins as well as their trophic status.

4. A series of examples is presented to demonstrate how a small number of driving variables influenced the observed levels of coherence. These range from a simple example where the winter temperature of the lakes was correlated with the climatic index known as the North Atlantic Oscillation, to a more complex example where the summer abundance of zooplankton was correlated with wind‐mixing.

5. The implications of these findings are discussed and a conceptual model developed to illustrate the principal factors influencing temporal coherence in lake systems. The model suggests that our ability to detect temporal coherence depends on the relative magnitude of three factors: (a) the amplitude of the year‐to‐year variations; (b) the spatial heterogeneity of the driving variables and (c) the error terms associated with any particular measurement.
Nocturnal drift of mayfly nymphs as a post‐contact antipredator mechanism
Authors: Huhta Arto , Muotka Timo , Tikkanen Pertti
Published: March 2003

1. The predominantly nocturnal constrained drift of stream invertebrates is commonly regarded as a behaviour that avoids encounters with visually foraging fish in the water column. The alternative explanation, that drift peaks are caused by bottom‐feeding, nocturnal predators, has rarely been tested.  2. We examined these hypotheses by collecting invertebrate drift in five streams in northern Finland: one with brown trout (Salmotrutta, a drift‐feeding fish), one with alpine bullhead (Cottuspoecilopus, a benthic fish), one with both species, and two fishless streams.  3. Drift by Baetis mayflies was aperiodic or slightly diurnal in both fishless streams on all sampling occasions. In contrast, drift was nocturnal in streams with trout and, to a lesser extent, in the stream with bullhead. Non‐dipteran prey drifted mainly nocturnally in all streams with fish, whereas Diptera larvae were less responsive to the presence of fish.  4. In laboratory experiments, bullheads were night‐active, causing a much higher frequency of drift by touching Baetis at night than during the day. Thus, increased nocturnal drift may serve to avoid both visual predators (a pre‐contact response) and benthic fish (a post‐contact response). In streams with bottom‐feeding fish, nocturnal drift should be caused by increased drift by night rather than by reduced drift by day.
Temporal and geographical variation in lake trophic status in the English Lake District: evidence from (sub)fossil diatoms and aquatic macrophytes
Authors: Bennion Helen , Monteith Donald , Appleby Peter
Published: March 2003

1. A sediment core (representing 250–300 years) was taken from each of three lakes of conservation interest and contrasting trophic status in the English Lake District: Wastwater, Bassenthwaite Lake and Esthwaite Water. Lithostratigraphic analyses, radiometric dating and analysis of fossil diatoms were carried out.  2. Transfer functions, based on the diatoms, were used to reconstruct total phosphorus (TP) and, thus, eutrophication at the study lakes. In Wastwater, changes in lake pH were also reconstructed.  3. The lakes were also classified according to their present macrophyte flora, the latter being compared with previous records.  4. The fossil diatoms of Wastwater were continuously dominated by taxa typical of oligotrophic, circumneutral waters, indicating that the lake has not been enriched or acidified in the last 250 years. The aquatic macrophyte flora has probably remained unchanged since before the Industrial Revolution.  5. The diatom assemblages of both Bassenthwaite Lake and Esthwaite Water began to change in the mid‐1800s. Further change occurred from the 1960s, at the onset of a recent period of eutrophication. These two lakes have experienced continued nutrient enrichment throughout the 1970s, 80s and 90s, largely associated with increasing phosphorus inputs from sewage effluent. There is no evidence of any recovery in response to recent reductions in external nutrient loads.  6. Only in Esthwaite Water has the change in aquatic macrophytes been pronounced.  7. Palaeolimnological reconstruction is useful in determining background conditions and natural variation in lake ecosystems.
The responses of a lotic mayfly Nousia sp. (Ephemeroptera: Leptophlebiidae) to moving water and light of different wavelengths
Authors: Barmuta Leon A. , Mckenny Claire E. A. , Swain Roy
Published: March 2003

1. Although laboratory studies of the behaviour of aquatic macroinvertebrates are common, there has been little critical evaluation of the importance of test conditions to them. We used a common Australian leptophlebiid mayfly, Nousia sp., to investigate responses to light, wavelength of light, presence or absence of cover and still or flowing water.

2. Nousia sp. showed substantial qualitative differences in behaviour, as measured by movement, when there was no refuge (in the form of a crevice beneath a tile) present in the experimental arena.

3. We found no evidence of diel periodicity in activity in Nousia sp.

4. Nousia sp. did not respond to infra‐red, red or green light at a flux density of 18–19 μmol m–2 s–1.

5. Nymphs were three times more likely to remain stationary in flowing water (mean velocity 0.10 m s–1) than in still water.

6. We conclude that generalized assumptions about test conditions for experiments designed to quantify laboratory behaviour in benthic macroinvertebrates are unjustified and that evaluation of the individual requirements of test species should be conducted routinely.
Problems with the application of diatom‐total phosphorus transfer functions: examples from a shallow English lake
Authors: Sayer Carl D.
Published: March 2003

1. A diatom‐total phosphorus transfer function has been applied to a sedimentary diatom sequence from Groby Pool, a small shallow lake in Leicestershire, U.K.

2. Extensive aquatic plant records exist for Groby Pool dating back over two centuries. These records, in conjunction with selected aquatic pollen and herbarium diatom data, provide independent, qualitative evidence for the progression of eutrophication and its effects on aquatic plant communities and habitat structure.

3. Before 1800, Groby Pool was probably mesotrophic with clear water and a diverse submerged macrophyte community, but subsequently it experienced considerable nutrient enrichment. Key evidence for this includes: (i) historical plant records indicating the loss of species associated with mesotrophic waters and their replacement by others typical of eutrophic conditions, (ii) a significant increase in the percentage of planktonic diatoms in the lake sediment record (particularly Cyclostephanos dubius) after 1890, and (iii) increases in percentages of Stephanodiscus parvus and Cocconeis placentula in the second half of the twentieth century.

4. Diatom‐inferred total phosphorus (DI‐TP) estimates were inconsistent with the qualitative evidence for eutrophication at Groby Pool. In particular the DI‐TP profile was thought to overestimate phosphorus during the period of dominance by small Fragilaria spp. before 1890, and to misjudge the timing and direction of subsequent changes in nutrient loading.

5. This study highlights some of the problems associated with the application of diatom‐TP transfer functions to sedimentary diatom sequences from shallow lakes. The major problem relates to the frequent dominance of non‐planktonic diatoms in the sediments of these systems, many species of which (particularly small Fragilaria spp.) appear to be more sensitive to changes in habitat availability than to phosphorus. Potential ways of improving diatom‐TP models via altered approaches to sampling are suggested.
Can life‐history traits predict the fate of introduced species? A case study on two cyprinid fish in southern France
Authors: Rosecchi Elisabeth , Thomas Frédéric , Crivelli Alain J.
Published: March 2003

1. The ecological and economic costs of introduced species can be high. Ecologists try to predict the probability of success and potential risk of the establishment of recently introduced species, given their biological characteristics.

2. In 1990 gudgeon, Gobio gobio, were released in a drainage canal of the Rhône delta of southern France. The Asian topmouth gudgeon, Pseudorasbora parva, was found for the first time in the same canal in 1993. Those introductions offered a unique opportunity to compare in situ the fate of two closely related fish in the same habitat.

3. Our major aims were to assess whether G. gobio was able to establish in what seemed an unlikely environment, to compare populations trends and life‐history traits of both species and to assess whether we could explain or could have predicted our results, by considering their life‐history strategies.

4. Data show that both species have established in the canal and have spread. Catches of P. parva have increased strongly and are now higher than those of G. gobio.

5. The two cyprinids have the same breeding season and comparable traits (such as short generation time, small body, high reproductive effort), so both could be classified as opportunists. The observed difference in their success (in terms of population growth and colonization rate) could be explained by the wider ecological and physiological tolerance of P. parva.

6. In conclusion, our field study seems to suggest that invasive vigour also results from the ability to tolerate environmental changes through phenotypic plasticity, rather than from particular life‐history features pre‐adapted to invasion. It thus remains difficult to define a good invader simply on the basis of its life‐history features.
Food quality, feeding preferences, survival and growth of shredders from temperate and tropical streams
Authors: Graça  , Cressa  , Gessner  , Feio  , Callies  , Barrios
Published: March 2003

1. The importance of leaf quality to the nutritional ecology of lotic shredders is well established for temperate species but virtually unknown for tropical taxa. In the present study, we compared the feeding behaviour and performance of two tropical and two temperate shredders in a series of pair‐wise experiments.

2. Specifically, we tested whether leaf conditioning status (stream‐conditioned versus unconditioned leaves) and geographical origin (temperate Alnus glutinosa versus tropical Hura crepitans leaves) affect the food preference, survivorship, and growth of selected shredders from low and high latitudes in a consistent manner. The animals used in experiments were the caddis‐flies Nectopsyche argentata and Phylloicus priapulus from Venezuela, Sericostoma vittatum from Central Portugal, and the amphipod Gammarus pulex from Northern Germany.

3. In general, all shredders exhibited the same high preference for conditioned over unconditioned leaves, irrespective of the geographical origin of the leaf or shredder species.

4. A corresponding tendency for higher growth was found for sets of animals offered conditioned leaves, with the differences in growth being clearer in the two tropical shredders. Survivorship of the two temperate species was consistently high (> 83%) regardless of the diet offered, whereas the tropical shredders survived better on conditioned (77–90%) as compared with unconditioned (54–87%) leaves, although not significantly so.

5. With the exception of the temperate S. vittatum, shredders did not select or perform better on leaves to which they had previously been exposed, indicating a potential adaptation to native leaf species is over‐ridden by intrinsic leaf properties.

6. Taken together, the results of this study suggest that tropical shredders may exhibit the same basic patterns of food exploitation as their temperate counterparts. Consequently, current concepts relating to the role of shredders in stream detritus dynamics may well be applicable to tropical streams, although essentially derived from temperate systems.
The functional role of burrowing bivalves in freshwater ecosystems
Authors: Vaughn Caryn C. , Hakenkamp Christine C.
Published: March 2003

1. Freshwater systems are losing biodiversity at a rapid rate, yet we know little about the functional role of most of this biodiversity. The ecosystem roles of freshwater burrowing bivalves have been particularly understudied. Here we summarize what is known about the functional role of burrowing bivalves in the orders Unionoida and Veneroida in lakes and streams globally.

2. Bivalves filter phytoplankton, bacteria and particulate organic matter from the water column. Corbicula and sphaeriids also remove organic matter from the sediment by deposit feeding, as may some unionids. Filtration rate varies with bivalve species and size, temperature, particle size and concentration, and flow regime.

3. Bivalves affect nutrient dynamics in freshwater systems, through excretion as well as biodeposition of faeces and pseudofaeces. Excretion rates are both size and species dependent, are influenced by reproductive stage, and vary greatly with temperature and food availability.

4. Bioturbation of sediments through bivalve movements increases sediment water and oxygen content and releases nutrients from the sediment to the water column. The physical presence of bivalve shells creates habitat for epiphytic and epizoic organisms, and stabilizes sediment and provides refugia for benthic fauna. Biodeposition of faeces and pseudofaeces can alter the composition of benthic communities.

5. There is conflicting evidence concerning the role of resource limitation in structuring bivalve communities. Control by bivalves of primary production is most likely when their biomass is large relative to the water volume and where hydrologic residence time is long. Future studies should consider exactly what bivalves feed upon, whether feeding varies seasonally and with habitat, and whether significant overlap in diet occurs. In particular, we need a clearer picture of the importance of suspension versus deposit feeding and the potential advantages and tradeoffs between these two feeding modes.

6. In North America, native burrowing bivalves (Unionidae) are declining at a catastrophic rate. This significant loss of benthic biomass, coupled with the invasion of an exotic burrowing bivalve (Corbicula), may result in large alterations of ecosystem processes and functions.
Population dynamics of Bythotrephes cederstroemii in south‐east Lake Michigan 1995–1998
Authors: Pothoven Steven A. , Fahnenstiel Gary L. , Vanderploeg Henry A.
Published: March 2003

1. Population characteristics (density, size, reproductive patterns) of the predatory cladoceran Bythotrephes cederstroemii in south‐east Lake Michigan were monitored at an offshore station (110 m) in 1995–98 and at a nearshore station (45 m) in 1997–98.

2. The mean density of B. cederstroemii at the offshore station was generally highest in July–September (145–914 m−2) and at the nearshore station in October–November (168–1625 m−2). In 1995 and 1998, density was also high at the offshore station in November (211–284 m−2). Fish predation may limit B. cederstroemii in nearshore regions in the summer. The maximum annual densities of B. cederstroemii for 1995–98 were generally similar to those reported from the late 1980s, when the species arrived in Lake Michigan.

3. Body size increased rapidly each year to a maximum in August. Thereafter, body size declined and converged for stage‐2 and 3 individuals, suggesting food scarcity or size‐selective fish predation was affecting large individuals.

4. Most reproduction occurred asexually (90%), and by stage 2 or 3 females (99%). Asexual brood size was highest when B. cederstroemii first appeared each year, and decreased in August, when larger neonates were produced. There appeared to be differences in reproductive mode for stage 2 and 3 females, with a higher percentage of stage 2 females reproducing sexually.
The macroinvertebrate communities of two contrasting Norwegian glacial rivers in relation to environmental variables
Authors: Brittain John E. , Saltveit Svein J. , Castella Emmanuel , Bogen Jim , Bønsnes Truls E. , Blakar Inggard , Bremnes Trond , Haug Ingrid , Velle Gaute
Published: March 2003

1. Macroinvertebrate communities in two Norwegian glacial rivers, one in the western fjords (Dalelva) and one in the eastern mountains (Leirungsåi), were investigated during three time periods in 1996 and 1997.

2. Channel stability variables (substratum heterogeneity/Pfankuch index/hydraulic stress) and water temperature accounted for 54% of the total inertia in the principal components analysis (PCA) ordination of environmental variables. The importance of these variables was confirmed by cluster analysis.

3. The two rivers were well separated in the ordinations, with Leirungsåi showing much greater heterogeneity. This is explained by differences in altitudinal range, terrestrial vegetation and the importance and nature of tributary inputs.

4. Channel stability and temperature were also important in determining faunal communities in the two glacial rivers, supporting the main determining variables in the conceptual model of glacial streams (Milner & Petts, 1994). However, clear temporal differences were apparent in the data, the two rivers being more similar during the summer period of high discharge dominated by glacial meltwater. During spring and especially during autumn environmental conditions and the macroinvertebrate fauna differed both within and between rivers.

5. Diamesinae dominated in the upper reaches of both rivers, with Orthocladiinae becoming more common downstream. The dominance of Diamesinae persisted further down Dalelva because of the continued influence of glacial tributaries, whereas in Leirungsåi the influence of non‐glacial tributaries led to a change towards a greater proportion of Orthocladiinae. Lakes modified macroinvertebrate communities in both river systems.
Species richness and spatial distribution of blackflies (Diptera: Simuliidae) in streams of Central Amazonia, Brazil
Authors: Hamada Neusa , McCreadie John W. , Adler Peter H.
Published: March 2003

1. The spatial distribution and species richness of blackflies were evaluated at 58 stream sites in Central Amazonia, Brazil. Samples were taken along a north–south axis of approximately 130 km and a east–west axis of approximately 220 km.

2. Based on stream‐site characteristics, the occurrence of larvae of the six most frequently collected species was highly predictable (79.3–91.5% accuracy in prediction of occurrence). The predictive value of stream size and the presence of impoundments agrees with results of similar work in the Holarctic Region, suggesting a general responses of blackflies to environmental parameters.

3. Although only 19.0% of interstream variation in species richness was explained by a regression model, results suggested that species richness was greater in larger, cooler, faster, covered streams with rocky beds than in smaller, warmer, slower, open streams with sandy bottoms. Overall, the species richness of blackflies (11 species in total) was lower than in the temperate zone suggesting, for some taxa at least, that aquatic communities do not follow the terrestrial pattern of greater species richness in the tropics.
Microbial respiration within a floodplain aquifer of a large gravel‐bed river
Authors: Craft James A. , Stanford Jack A. , Pusch Martin
Published: March 2003

1. Aerobic respiration, productivity and the carbon turnover rate of microbial biofilms were determined at hyporheic and phreatic sites in the Kalispell Valley alluvial aquifer along a transect extending 3.9 km laterally from the main channel of the Flathead River, a sixth order river in Montana (U.S.A.). The effect of experimentally increasing bioavailable organic carbon (acetate) on the respiration rate of biofilms in this carbon‐poor [dissolved organic carbon (DOC) < 2 mg L−1] aquifer was also measured.

2. Chambers containing natural substratum were placed in‐situ and allowed to colonise for 20 weeks. After 4, 12 and 20 weeks, they were taken to the laboratory where oxygen flux was measured in a computer‐controlled, flow‐through respirometry system.

3. Respiration ranged from 0.01 to 0.33 mg O2 dm−3 h−1 across sites, with means ranging from 0.10 to 0.17 mg O2 dm−3 h−1. Productivity estimates ranged from 0.18 to 0.32 mg C dm−3 day−1 (mean 0.25, SE 0.03). The total organic carbon (TOC) of the microbial biofilms ranged from 18.2 to 29.7 mg C dm−3. Turnover rate ranged from 3.2 to 5.6 year−1 with a mean of 4.2 year−1.

4. At the hyporheic site very close to the river, respiration did not significantly increase when samples were supplemented with labile carbon. Respiration increased with increasing DOC addition at hyporheic sites more distant from the river, suggesting a carbon‐limitation gradient within the hyporheic zone. Microbes at the phreatic site did not respond to increasing DOC addition, suggesting that the phreatic biofilm is adapted to low carbon availability.

5. Comparing the volume of the alluvial aquifer (about 0.7 km3) to that of the river benthic sediments (to 0.25 m depth, which amounts to about 1.6 × 10−4 km3) within the Flathead Valley, leads to the conclusion that interstitial microbial productivity is orders of magnitude greater than benthic productivity. Alluvial aquifers are often voluminous and microbial production is an enormous component of ecosystem production in rivers such as the Flathead.
Zooplankton biomass and community structure in a Danube River floodplain system: effects of hydrology
Authors: BARANYI CHRISTIAN , HEIN T. , HOLAREK C. , KECKEIS S. , SCHIEMER F.
Published: March 2003

1. Zooplankton density and biomass was examined in a Danube River floodplain section with highly variable hydrological dynamics. Temporal patterns were analysed to assess the effects of hydrological conditions on zooplankton community structure and the differential response of the two major zooplankton taxa, rotifers and crustaceans.

2. Calculated floodplain water age was used as an integrated parameter describing hydrological conditions and connectivity.

3. Total zooplankton biomass, crustacean biomass and crustacean species number were significantly positively related to water age. Rotifer biomass followed a hump‐shaped relationship with water age, and rotifer species number decreased with increasing water age.

4. Rotifers dominated the community in periods of low to medium water ages. In periods of higher water ages the community was dominated by crustaceans.

5. We propose that the hydrological regime of floodplains is crucial for zooplankton biomass patterns and succession, through the alternation of washing‐out effects, taxon‐specific potential of reproduction and biological interactions. Flood events and high water levels reset the community to an early successional phase.
Development and evaluation of a diatom‐conductivity model from lakes in West Greenland
Authors: RYVES D. B. , MCGOWAN S. , ANDERSON N. J.
Published: March 2003

1. The area around Kangerlussuaq (Søndre Strømfjord; West Greenland, 67°N 51°W) contains thousands of lakes ranging from coastal, dilute (conductivity < 30 μS cm–1) oligotrophic systems to subsaline (∼4000 μS cm–1), closed basin lakes close to the ice sheet margin. In closed basins, salinity (or conductivity) is often a proxy for effective moisture, and thus palaeorecords of lake conductivity can provide valuable palaeoclimatic data. Little or nothing is known about the recent history of these lakes and hence it is difficult to evaluate how they will respond to effects of future changes.

2. Over 100 lakes have been sampled (1996–2000) between the ice sheet and the outer coast for a variety of water chemical and limnological variables. Surface sediments were taken from a subset of 40 lakes and analysed for diatoms. Diatom responses to 28 environmental variables were analysed by multivariate ordination techniques and indicate that the main gradient is highly correlated to conductivity (explaining ∼12% of species variance). Despite the relatively short gradient (24–4072 μS cm–1), diatom assemblages exhibit a clear response to conductivity. The most saline lakes do not contain a true saline flora.

3. We developed a range of weighted averaging (WA) and weighted‐averaging partial least squares (WA‐PLS) models from this training data set and found two component WA‐PLS models performed best. The effects of data transformation and omission of dissolution susceptible species (Diatomaspp.) on model performance were also examined. The error statistics for the preferred WA‐PLS (2) model (r2jack=0.88, root mean square error of prediction (RMSEP)=0.217 log μS cm–1) compare well with other published models.

4. A210Pb‐dated short core from a meromictic, subsaline lake (Braya Sø; location 67°N, 51°W, max. depth 23 m; conductivity 2600 μS cm–1) was analysed for diatoms. Diatom preservation is poor and some taxa (e.g.Diatomaspp.) are badly corroded. Lake water conductivity was reconstructed using WA‐PLS models. Diatom‐inferred conductivity ranges from 1800 to 4400 μS cm–1over the last 600 years (extrapolated210Pb chronology).

5. The Kangerlussuaq area of West Greenland is an important area for palaeoclimatic research, located as it is between the Greenland ice sheet (ice core records) and the Davis Straits to the west. The development of a statistically robust transfer function for diatoms and conductivity will enable the reconstruction of conductivity from the many subsaline lakes around the head of the fjord and, hence, regional estimates of changing palaeoprecipitation.
The influence of ventilation systems on water depth penetration of emergent macrophytes
Authors: STRAND V. VRETARE
Published: March 2003

1. Roots of emergent macrophytes depend on oxygen transported from aerial parts by diffusion and, in some species, by pressurised ventilation. The aim of this study was to determine if species with pressurised ventilation grow in deeper water in situ than species lacking this ability.

2. Species with pressurised ventilation grew significantly deeper than species lacking pressurised ventilation, and this was true in substrates with low as well as high redox potential.

3. Two species with low or non‐detectable flow rates (Schoenoplectus lacustris and Equisetum fluviatile, respectively) were found in unexpectedly deep water. Thus, pressurised ventilation is not a prerequisite for growth in deep water. It is, however, suggested that species with pressurised ventilation have a competitive advantage in deep water resulting in long‐term competitive exclusion of species lacking pressurised ventilation.
Can filter‐feeding fishes improve water quality in lakes?
Authors: HAMBRIGHT K. D. , BLUMENSHINE S. C. , SHAPIRO J.
Published: March 2003

1. In this paper we examine the potential of a cichlid fish species (Sarotherodon galilaeus) to both maintain positive growth rates through filter‐feeding on phytoplankton and improve water quality in Lake Kinneret through suppression of dinoflagellate (Peridinium gatunense) blooms.

2. Seasonal plankton consumption byS. galilaeusfrom Lake Kinneret was examined experimentally by monitoring changes in plankton assemblages during 24 h in 5‐m3mesocosms containing varying densities of fish. Taxon‐specific grazing rates ranged from 0 to 17 mg gfish day–1, with mean total consumption of 1.6% fish body weight per day. During the spring bloom ofP. gatunense,S. galilaeusconsumed mostly (94%) netphytoplankton (≥20 μm). The remaining 6% consisted mostly of nanophytoplankton (<20 μm). During the summer and fall, net‐ and nanophytoplankton accounted for 54 and 42%, respectively, of the diet ofS. galilaeus. Zooplankton and flagellated and ciliated protozoans made up the remaining 4%.

3. Simulations using a fish bioenergetics model indicated that consumption rates (C) were near maximum in spring (90%Cmax), while consumption was reduced in summer‐fall (59%Cmax).Sarotherodon galilaeusobtains sufficient energy through filter‐feeding year‐round, although most growth (≥60%) occurs during the springP. gatunensebloom.

4. Despite efficient feeding onP. gatunenseand nanophytoplankton byS. galilaeus, estimates of instantaneous plankton mortality caused by ingestion were two orders of magnitude lower than maximum potential plankton growth rates. Thus the potential for theS. galilaeuspopulation in Lake Kinneret to positively affect water quality through algal suppression is low.
Predation on mayfly nymph, Baetis rhodani, by native and introduced Gammarus: direct effects and the facilitation of predation by salmonids
Authors: KELLY DAVID W. , DICK JAIMIE T. A. , MONTGOMERY W. IAN
Published: March 2003

1. In a series of laboratory experiments, we assessed the predatory nature of the native Irish amphipod, Gammarus duebeni celticus, and the introduced G. pulex, towards the mayfly nymph Baetis rhodani. We also investigated alterations in microhabitat use and drift behaviour of B. rhodani in the presence of Gammarus, and indirect predatory interactions with juvenile Atlantic salmon, Salmo salar.

2. In trials with single predators and prey, B. rhodani survival was significantly lower when Gammarus were free to interact with nymphs as than when Gammarus were isolated from them. The invader G. pulex reduced the survival of B. rhodani more rapidly than did the native G. d. celticus. Both Gammarus spp. were active predators.

3. In `patch' experiments, B. rhodani survival was significantly lower both when G. pulex and G. d. celticus were present, although the effect of the two Gammarus species did not differ. Again, active predation of nymphs by Gammarus was observed. Significantly more nymphs occurred on the top and sides of a tile, and per capita drifts were significantly higher, when Gammarus were present. Baetis rhodani per capita drift was also significantly higher in the presence of the introduced G. pulex than with the native G. d. celticus.

4. Gammarus facilitated predation by salmon parr of B. rhodani by significantly increasing fish–nymph encounters on exposed gravel and in the drift. There were no differential effects of the two Gammarus spp. on fish –B. rhodani encounters or consumption.

5. We conclude that Gammarus as a predator can have lethal, nonlethal, direct and indirect effects in freshwaters. We stress the need for recognition of this predatory role when assigning Gammarus spp. to a `Functional Feeding Group'.