bluuebunny/crossref_metadata_2025 huggingface dataset:
Trophic interactions in rockpool food webs: regulation of zooplankton and phytoplankton byNotonectaandDaphnia
Authors: Arnér Marie , Koivisto Sanna , Norberg Jon , Kautsky Nils
Published: March 2003

We studied trophic interactions in experimental rockpools with three different food web structures: phytoplankton and small‐bodied zooplankton; phytoplankton, small‐bodied zooplankton and Daphnia; and phytoplankton, small‐bodied zooplankton, Daphnia and Notonecta. Nutrients, primary productivity, chlorophyll a and zooplankton species composition and biomass were measured over eight weeks.

2. Daphnia had a negative impact on other zooplankton and reduced the phytoplankton biomass and primary productivity. In the absence of Daphnia, small‐bodied zooplankton species were abundant, in particular cyclopoid copepods. Concentrations of dissolved nutrients were lower and the standing crop of primary producers was higher when Daphnia was absent.

3. The presence of the invertebrate predator Notonecta produced a top‐down effect which was similar to that reported for planktivorous fish, i.e. a selective reduction of daphnids followed by an increase of small‐bodied zooplankton species and phytoplankton biomass.

4. The study showed that consumer regulation of Daphnia by Notonecta and of algae by Daphnia are important, but also demonstrated that trophic level biomasses were controlled by a combination of predation and resource limitation.
Dispersal and recruitment ofTasiagma ciliata(Trichoptera: Tasimiidae) in rainforest streams, south‐eastern Australia
Authors: Hughes Jane M. , Bunn Stuart E. , Hurwood David A. , Cleary Cath
Published: March 2003

1. This study examined genetic variation within and among populations of the caddis fly Tasiagma ciliata (Tasimiidae: Trichoptera) from rainforest streams in south‐east Queensland, Australia.

2. Very low levels of genetic differentiation at large spatial scales, between subcatchments and between catchments, indicated that dispersal by the winged adults is widespread. However, significant genetic differentiation at the smallest spatial scale examined, within reaches in a single stream, suggested limited movement by larvae within streams.

3. A patchy distribution of deviations from Hardy–Weinberg equilibrium and differences in patterns among allozyme loci suggested that populations in particular reaches were the result of only a few matings.

4. These results are surprising, given the large numbers of larvae present within a single reach. We suggest that stochastic effects of recruitment may underlie much of the spatial and temporal variation in population numbers in these rainforest streams.
Locomotion in Elliptio complanata (Mollusca: Unionidae): a reproductive function?
Authors: Amyot Jean‐pierre , Downing John A.
Published: March 2003

1. Temporal variation in the spatial aggregation of the freshwater bivalve Elliptio complanata was studied at a sandy site in an oligotrophic lake over three years.

2. Epibenthic populations varied in aggregation over the season bringing animals closer together during spawning. The complex link between movements of mussels and aggregation dynamics suggested a functional reproductive role for horizontal locomotion of unionid mussels in lentic systems.

3. The rate of locomotion did not differ systematically among males, females or hermaphrodites, and was independent of gravidity, whether compared during spawning, after spawning or throughout the ice‐free season.

4. In spite of the high reproductive output of mussels and the energetic cost of locomotion, no relationship was found between the rate of movement of spawning gravid mussels and reproductive output.
Estimating age and growth in long‐lived temperate freshwater crayfish using lipofuscin
Authors: Belchier Mark , Edsman Lennart , Sheehy Matt R. J. , Shelton Peter M. J.
Published: March 2003

1. In ecological studies on freshwater crayfish, determination of basic population parameters is often complicated by the lack of a suitable age estimation method.

2. Previously, lipofuscin age pigment in the olfactory lobe cell masses (OLCM) of short‐lived tropical crayfish has been used for accurate age determination. Here we present the first test of this method on a longer‐lived, temperate species, the signal crayfish, Pacifastacus leniusculus.

3. Confocal fluorescence microscopy and image analysis of histological sections were used to quantify OLCM lipofuscin in a reference sample of Swedish P. leniusculus from several known year‐classes, reared under naturally variable temperature conditions. Lipofuscin concentration was linearly associated with age (r2 = 92.4%) and produced much more accurate age estimates than conventional body size‐based procedures.

4. A model derived from the crayfish of known‐age was used to estimate the ages of wild P. leniusculus from an English stream. The relationship between lipofuscin‐estimated age and carapace length suggested relatively slow growth in this wild population, consistent with a high population density and severe competition. The analysis also extended the known longevity of P. leniusculus to approximately 16 years.

5. The lipofuscin method for determining age and growth may be widely applicable to freshwater crayfish, with probable further potential both within and outside the Crustacea.
In situ studies on heart rate and locomotor activity in the freshwater crayfish, Astacus astacus (L.) in relation to natural fluctuations in temperature and light intensity
Authors: Bojsen Berit H. , Witthøfft Hanne , Styrishave Bjarne , Andersen Ole
Published: March 2003

1. By the aid of a computer technique, the in situ variations in heart rate and locomotor activity were recorded continuously for 7 days in sixteen individuals of the crayfish, Astacus astacus (Linnaeus 1758), in association with natural changes in water temperature and light intensity.

2. All sixteen crayfish investigated were found to express circadian rhythmicity in heart rate with a periodicity of ≈ 24 h. For 88% of the animals investigated, rhythmicity was significant (P < 0.05). Ninety‐three per cent of the crayfish showed circadian rhythmicity in locomotor activity with a 24 ± 2 h periodicity and, for 67% of the animals, this rhythmicity was significant (P < 0.05). In general, the expression of circadian rhythms was associated with nocturnal behaviour, heart rates and locomotor activity levels being higher at night than by day.

3. A positive correlation was observed between heart rate and locomotor activity. Temperature and light intensity exerted positive and negative influences on heart rate in A. astacus, respectively.

4. In the first experiment, 84% of the variation in heart rate could be explained by the changes in locomotor activity, temperature and light intensity. In the second experiment 35% of the variation in the heart rate was explained using these parameters.
Macrophyte growth and sediment phosphorus and nitrogen in a Canadian prairie river
Authors: Carr Geneviève M.
Published: March 2003

1. The role of sediment phosphorus (P) and nitrogen (N) in regulating growth of rooted macrophytes in a Canadian prairie river was investigated by means of in situ observations and artificial stream fertilization experiments.

2. Biomass and percentage cover of rooted macrophytes in the South Saskatchewan River increased downstream of a municipal sewage treatment plant, with maximum abundance occurring between 25 and 100 km downstream of the outfall. Biomass in the river was related to sediment P but not N concentration, although sites of maximum biomass did not coincide with sites of maximum sediment P concentration.

3. Artificial stream experiments revealed that while biomass was unaffected by addition of N to the sediment, it was enhanced by the addition of P to sediments, and further enhanced with the addition of N and P together, indicating a primarily P‐limited system, with secondary N limitation when P is in excess.

4. Macrophyte biomass increased linearly with increasing sediment P concentration in the artificial streams, and tissue P concentration peaked at ≈ 400 μg g–1. Biomass did not respond to increasing sediment N concentration, and only a weak relationship was observed between tissue N and sediment N, with maximum tissue N corresponding to ≈ 140 μg g–1 sediment exchangeable N.

5. A lack of concurrence between the sediment P concentration producing maximum biomass and tissue P concentration in situ vs. under experimental conditions indicates that other environmental factors have an important role in regulating macrophyte growth in rivers. Thus, while nutrient control may be one element in a river macrophyte control programme, a holistic ecosystem approach should be adopted to account for the other factors that may affect the growth of rooted plants.
Biological assessment of freshwater ecosystems using a reference condition approach: comparing predicted and actual benthic invertebrate communities in Yukon streams
Authors: Bailey Robert C. , Kennedy Matthew G. , Dervish Michael Z. , Taylor And Ronald M.
Published: March 2003

1. The reference condition approach to bioassessment is based on comparing a biological community found at a test site to the range of communities observed at a set of reference sites. A community descriptor (e.g. number of taxa) is estimated for the test site. If the value of the descriptor falls outside of a given boundary, or biocriterion, from the distribution of the descriptors for the reference sites, the test site fails.

2. The sensitivity of the reference condition approach can be increased by modelling and explaining variation in the community descriptor among the reference sites, and then using the predictive model to refine the expectation of the descriptor’s value at a test site.

3. This study applied the reference condition approach, with predictive modelling, to the bioassessment, using benthic macroinvertebrate (BMI) communities, of streams exposed to placer gold mining effluent in central Yukon Territory, Canada. The major changes to the stream caused by mining are increased turbidity and metal concentrations.

4. Among reference sites sampled from 1993 to 1995, a predictive model using year of sampling and simple geographical characteristics (distance to source of the stream, upstream catchment area, altitude, two‐way interactions) explained over half of the variation in each of five BMI community descriptors including richness (number of families), Simpson’s diversity, Simpson’s equitability, family biotic index and Bray–Curtis distance to the median reference community.

5. Biocriteria (other than Bray–Curtis distance to the median community) based on the predictive models failed a far greater proportion of sites currently exposed to placer mining (50–100%) than biocriteria not based on predictive models (7–71%). A similar increase in the sensitivity of the bioassessment was seen when evaluating sites previously exposed to placer mining effluent. The simplest, most sensitive

bioassessment of the effects of placer gold mining effluent on stream ecosystems

used richness (number of families) of the BMI community together with a predictive

model.
Effects of buried leaf litter and vertical hydrologic exchange on hyporheic water chemistry and fauna in a gravel‐bed river in northern New South Wales, Australia
Authors: Boulton Andrew J. , Foster J. G.
Published: March 2003

1. Large amounts of coarse particulate organic matter (CPOM) are buried in the sand and gravel beds of many rivers during spates. The effects of these patchily distributed resources on hyporheic invertebrates and water chemistry are poorly understood. Buried CPOM may provide local ‘hot‐spots’ of food for hyporheic detritivores and their predators, alter nutrient supply to nearby sediment biofilms, and generate habitat for some invertebrates.

2. To examine potential short‐term effects on hyporheic water chemistry, nutrient concentrations and invertebrate assemblage composition, leaf packs were buried in downwelling (surface water infiltrating the hyporheic zone) and upwelling (hyporheic water emerging to the surface) zones at two sites along a gravel‐bed river in northern New South Wales. At one site, pits were excavated to simulate leaf burial (procedural control) and plastic ‘leaves’ were buried to test whether invertebrates might respond to leaves as refuges rather than food. Hyporheic CPOM, sediment size fractions, and interstitial silt content were also quantified at these sites.

3. Dry weights of naturally buried CPOM (leaf litter and wood fragments) varied substantially (0.6–71.7 g L–1 sediment). Amounts of CPOM did not differ between up‐ vs. downwelling zones or between sites. Hyporheic dissolved oxygen saturation was generally high (> 75%), and was lower in upwelling zones. The hyporheos was dominated taxonomically by water mites (≈ 20 species), whereas small oligochaetes were most abundant (40% of total abundance). Tiny instars of elmid beetle larvae and leptophlebiid mayfly nymphs were also common. Before experimental manipulation, faunal composition differed between up‐ and downwelling zones. In upwelling zones, bathynellaceans and blind peracarids were found, whereas small individuals of the surface benthos were common in samples from downwelling zones. This validated stratification of the experiment across zones of hydrologic exchange.

4. Twenty days after leaf burial, there was no effect of the treatments at either site on changes in most variables, including mean numbers of taxa and individuals per sample. Similarly, changes in faunal composition of the hyporheos in the treatments paralleled those in the controls except for a weak response in the buried leaves treatment in the upwelling zone at site 1. Artificially buried leaf litter does not seem to influence hyporheic water chemistry or fauna at these two sites. It is probable that naturally buried leaf litter is swiftly processed soon after entrainment and that repeating this experiment immediately after a flood may yield different results.
Aquatic bryophytes in Himalayan streams: testing a distribution model in a highly heterogeneous environment
Authors: Suren A. M. , Ormerod S. J.
Published: March 2003

1. Aquatic bryophytes were sampled from 108 streams spanning over 3000 m of altitude in four regions of Nepal. Richness, cover and community composition were related to physicochemistry using multiple regression, DECORANA ordination and TWINSPAN. The performance of a hierarchically scaled descriptive model, developed in New Zealand for predicting bryophyte distribution, was examined in this highly heterogeneous Himalayan region.

2. Community composition and cover varied highly significantly with altitude, streambed stability and alkalinity, with evidence of effects of riparian land use on bryophyte cover. Cover was greatest in streams at low to middle altitudes with steep slopes (> 15°), high stability and low conductivity (< 60 μS cm–1), where communities were dominated by two Isopterygium spp., two Philonotis spp., Mnium punctatum and Lejeuneaceae.

3. Richness, by contrast, increased significantly but weakly at high altitude and moderate stability, where streams were dominated by Eurynchium praelongum, Rhynchostegium spp., Fissidens grandifrons and Hygroamblystegium spp. Richness and cover were lowest in unstable streams at the lowest altitude, where no single taxon was consistently most abundant.

4. Although these results were similar to those in the descriptive model developed for bryophytes in New Zealand, subtle differences were apparent. Substrate size, although influencing the presence of bryophytes in New Zealand streams, appeared to be unimportant in Nepal. By contrast, streambed stability was more important in Nepal than New Zealand, perhaps reflecting pronounced monsoonal floods, and subsequent increased frequency of bed movement in the former. A suggested habitat template indicates that large plant size and vegetative reproduction may be responsible for the widespread distribution of some species, even into unstable Himalayan streams.
Perspectives and predictions on the microbial ecology of the hyporheic zone
Authors: Storey R. G. , Fulthorpe R. R. , Williams D. D.
Published: March 2003

1. Studies of hyporheic microbial ecology have suggested an important role for hyporheic microbial processes in stream ecosystem functioning. Using evidence from microbial communities in other aquatic habitats, some predictions are made concerning the diversity of microbial types and microbial processes likely to occur in the hyporheic zone, and the relative importance of these various types to the hyporheic ecosystem.

2. It is predicted that the biofilm growth form of interstitial micro‐organisms will create a variety of microniches, allowing coexistence of a great diversity of microbial types, and promoting the activity of some otherwise poor competitors. It is further predicted that the confluence of reduced groundwaters and aerobic surface waters will favour chemolithotrophic processes in the hyporheic zone, but that these will contribute significantly to hyporheic production only if surface water is very low in dissolved organic carbon, or the groundwater is extremely reduced, such as by the influence of riparian wetlands. A variety of anaerobic respiratory pathways, such as nitrate, ferric ion, sulphate and even methanogenic respiration will be employed in the hyporheic zone, with biofilm dynamics permitting these to occur even in aerobic sediments. Anaerobic pathways may account for a significant proportion of total hyporheic organic matter mineralization.

3. The role of fungi in hyporheic dynamics is, as yet, almost completely unstudied. However, it is expected that they will be important in breaking down buried particulate organic matter (POM), which may account for a large proportion of total stream POM.

4. Physicochemical conditions in hyporheic sediments appear to be highly heterogeneous, and this heterogeneity may be very important in the cycling of certain nutrients, especially nitrogen, which involves a series of steps requiring different conditions.

5. Various new techniques are now available by which biofilm dynamics and in situ microbial processes may be measured. Studies are recommended of intact microbial communities both at the microscale of the biofilm and at the scale of the heterogeneities occurring in hyporheic sediments. Studies are needed that measure actual rates of microbial processes under in situ conditions.
Competitive abilities and related strategies in four aquatic plant species from an intermediately disturbed habitat
Authors: Greulich S. , Bornette G.
Published: March 2003

1. High species richness in disturbed habitats is commonly attributed to the coexistence of species with diverse competitive abilities and, more generally, to the coexistence of different plant strategies sensu Grime (1977, 1979). The present study tests this assumption for the case of intermediately disturbed, species‐rich macrophyte habitats.

2. Four species, Sparganium emersum, Hippuris vulgaris, Groenlandia densa and Luronium natans that coexist solely in one flood‐disturbed, cut‐off channel of the Upper Rhone River (France) were selected for this study. Apart from this common, disturbed habitat, they presented different distribution patterns within the floodplain. The present study aimed to establish both a hierarchical ranking of their competitive abilities and their respective strategies according to the C‐S‐R‐model.

3. The study was carried out during one growth season in a de Wit experimental design with supplementary monitoring of growth characteristics. Whereas a clear ranking of species competitiveness could not be established, the experiment revealed differences in their traits and strategies.

4. S. emersum possesses the traits of a competitor, whereas the other species present intermediate secondary strategies, with a C‐R‐strategy in G. densa, a C‐S‐strategy in H. vulgaris, and a C‐S‐R or S‐R‐strategy in L. natans. These strategies are well matched to the distribution of the species within the floodplain, since the distribution of S. emersum reaches far into weakly disturbed and undisturbed, and supposedly competition intensive sites, whereas Luronium occupies a habitat that is both disturbed and relatively nutrient‐poor. Only the presence of Hippuris in disturbed habitats seems not to correspond to the established strategy, but this might be explained by its need for only moderately intensive competition and by particularities of its regeneration strategy. The revealed differences in strategy may also make it possible to interpret the patchy pattern in vegetation cover within disturbed habitats.
Effect of water temperature on the mass emergence of the mayfly, Ephoron shigae, in a Japanese river (Ephemeroptera: Polymitarcyidae)
Authors: Watanabe N. C. , Mori I. , Yoshitaka I.
Published: March 2003

1. Winged stages of Ephoron shigae were collected every day during their emergence period during a 6‐year period from 1989 to 1994, by net sweeps or a light trap along the Asahi‐gawa River in western Japan. Emergence occurred mainly in September.

2. Coefficients of determination (r2) were calculated for the regression of the mean date of emergence against cumulative degree‐days during various periods from late March to early September.

3. In both sexes the highest values of r2 were obtained for regression with degree‐days from late June to late August. This indicates that thermal conditions during the late instars affected the emergence timing most strongly. The timing of emergence can be well predicted from the cumulative degree‐days during summer.
Hydrological connectivity, and the exchange of organic matter and nutrients in a dynamic river–floodplain system (Danube, Austria)
Authors: Tockner Klement , Pennetzdorfer Doris , Reiner Niko , Schiemer Fritz , Ward J. V.
Published: March 2003

1. The relationship between hydrological connectivity, and the exchange processes of suspended sediments, organic matter and nutrients (NO3‐N) was investigated in a dynamically connected river–floodplain segment of the Danube over a 15‐month period in 1995 and 1996 in the Alluvial Zone National Park, Austria.

2. Based on water level dynamics and water retention times, three phases of river–floodplain connectivity were identified: disconnection (phase I), seepage inflow (phase II) and upstream surface connection (phase III). The frequency of occurrence of these phases was 67.5%, 29.3% and 3.2%, respectively, during the study period.

3. A conceptual model is presented linking hydrological connectivity with ecological processes. Generally, the floodplain shifts from a closed and mainly biologically controlled ecosystem during phase I to an increasingly open and more hydrologically controlled system during phases II and III. Phase I, with internal processes dominating, is designated the ‘biotic interaction phase’.

4. Phase II, with massive nutrient inputs to the floodplain yet relatively high residence times, and therefore, high algal biomass, is classified as the ‘primary production phase’. This demonstrates that water level fluctuations well below bankfull may considerably enhance floodplain productivity.

5. Finally, since transport of particulate matter is mainly restricted to short flood pulses above bankfull level, phase III has been defined as the ‘transport phase’.

6. The floodplain served as a major sink for suspended sediments (250 mt ha−−1 year−−1), FPOM (96 mt ha−−1 year−−1), particulate organic carbon (POC; 2.9 mt ha−−1 year−−1) and nitrate‐nitrogen (0.96 mt ha−−1 year−−1), but was a source for dissolved organic carbon (DOC; 240 kg ha−−1 year−−1), algal biomass (chlorophyll‐a; 0.5 kg ha−−1 year−−1) and CPOM (21 kg

ha−−1 year−−1). Considerable quantities of DOC and algal biomass were exported to the river channel during phase II, whereas particulate matter transport was largely restricted to the short floods of phase III.

7. The Danube Restoration Project will create a more gradual change between the individual phases by increasing hydrological connectivity between the river channel and the floodplain, and is predicted to enhance productivity by maintaining a balance between retention and export of nutrients and organic matter.
What happens to allochthonous material that falls into streams? A synthesis of new and published information from Coweeta
Authors: Webster J. R. , Benfield E. F. , Ehrman T. P. , Schaeffer M. A. , Tank J. L. , Hutchens J. J. , D’Angelo D. J.
Published: March 2003

1. ,One of two things can happen to allochthonous material once it enters a stream: it can be broken down or it can be transported downstream. The efficiency with which allochthonous material is used is the result of these two opposing factors: breakdown and transport.

2. ,The present synthesis of new and published studies at Coweeta Hydrologic Laboratory compares biological use versus transport for four categories of particulate organic material: (1) large wood (logs); (2) small wood (sticks); (3) leaves; and (4) fine particulate organic matter (FPOM).

3. ,Over 8_years, logs showed no breakdown or movement.

4. ,The breakdown rate of sticks (≤3_cm diameter) ranged from 0.00017 to 0.00103_day−1, while their rate of transport, although varying considerably with discharge, ranged from 0 to 0.1_m_day−1.

5. ,Based on 40 published measurements, the average rate of leaf breakdown was 0.0098_day−1. The leaf transport rate depended on stream size and discharge.

6. ,The average respiration rate of FPOM was 1.4_mg_O2_g_AFDM−1_day−1 over a temperature range of 6–22_°C, which implies a decomposition rate of 0.00104_day−1. Transport distances of both corn pollen and glass beads, surrogates of natural FPOM, were short (<_10_m) except during high discharge.

7. , Estimates of transport rate were substantially larger than the breakdown rates for sticks, leaves and FPOM. Thus, an organic particle on the stream bottom is more likely to be transported than broken down by biological processes, although estimates of turnover length suggest that sticks and leaves do not travel far. However, once these larger particles are converted to refractory FPOM, either by physical or biological processes, they may be transported long distances before being metabolized.
Small‐scale movements of lotic macroinvertebrates with variations in flow
Authors: Lancaster Jill
Published: March 2003

1. The small‐scale movements and distribution patterns of invertebrates were observed in an attempt to identify the various mechanisms by which organisms may use flow refugia during flow disturbances. The microdistribution of lotic macroinvertebrates was examined in two replicate, non‐circulating laboratory flumes with variations in flow among microhabitat patches (≈ 0.015–0.035 m2). The discharge in one experimental flume was manipulated to mimic spates and alter near‐bed flow patterns; the other flume acted as a control. After an initial settling period, the position and behaviour of animals within the flumes was recorded before, during and after a simulated spate. Three species with contrasting flow microhabitat preferences and movement behaviour were examined.

2. At low discharge, the microdistribution of all three study species in flumes was broadly consistent with field observations. In the field, the optimum current speed was lowest for adults of the dytiscid beetle, Oreodytes sanmarkii, and highest for mayfly nymphs, Ephemerella ignita, with nymphs of the stonefly, Leuctra inermis, most abundant at intermediate velocities. In the flumes, O. sanmarkii occurred only in very low velocity areas, L. inermis occurred widely throughout the flumes with highest density in low velocity areas and E. ignita also occurred throughout the flumes, but maximum density was in moderately high velocity areas.

3. Increased discharge did not reduce the total number of individuals in experimental versus control flumes for any of the three species studied, although total numbers did decrease over the observation period in both treatments. Simulated spates resulted in a change in the microdistribution of O. sanmarkii and E. ignita, but not L. inermis, such that numbers were reduced in very high velocity microhabitats and animals accumulated in lower flow areas, analogous to flow refugia. These distributional shifts were attributed to movements of individuals among microhabitats.

4. Both active and passive modes of movement contributed to the accumulation of E. ignita and O. sanmarkii in low flow microhabitats (i.e. flow refugia). Some nymphs of E. ignita actively crawled from high to low flow microhabitats. Both species drifted between microhabitats. Drift entry could be active or passive, whereas regaining the substratum was active: O. sanmarkii swam down and E. ignita altered its body posture to promote sinking.
Effects of ice duration on plankton succession during spring in a shallow polymictic lake
Authors: Adrian Rita , Walz Norbert , Hintze Thomas , Hoeg Sigrid , Rusche Renate
Published: March 2003

1. Long‐term records of air temperature and ice phenology (ice duration), and phyto‐ and zooplankton time series (1979–1997) were used to study the effects of ice duration on the successional pattern within plankton communities during spring in a shallow polymictic lake.

2. Water temperature in March was significantly lower after cold winters when compared to average or mild winters. Mean water temperature in April was not significantly different after mild, average or cold winters, but showed an overall significant negative correlation with ice duration.

3. Ice duration affected the timing and the magnitude of the peak abundance of diatoms, rotifers and daphnids during spring, but had no direct effects on the timing and maximum of chlorophytes, cryptophytes, cyanobacteria, bosminids and cyclopoid copepods.

4. Plankton groups which appeared first in the seasonal succession (i.e. diatoms, rotifers and daphnids) reached maximum abundance earlier after mild and average winters. The peak abundance of diatoms was negatively correlated with ice duration, whereas that of rotifers and daphnids was independent of the conditions during the preceding winter.

5. Temperature alone was generally a poor predictor of the timing and magnitude of both phyto‐ and zooplankton maxima. Turbulence may be important in the timing and the magnitude of peaks in diatoms, while total algal biomass was the most important determinant for the timing of the rotifer maximum. The magnitude of the daphnid maxima were significantly influenced by water temperature in March and April, and by rotifer abundance. The magnitude of the bosminid maximum was correlated with food availability and predation, whereas the timing of the maximum was more closely related to water temperature in May.

6. We conclude that, as a result of the low heat storage capacity of shallow lakes, the effects of winter on planktonic communities are short lived, and soon overtaken by the prevailing weather and by biotic interactions.
What is river health?
Authors: Norris Richard H. , Thoms Martin C.
Published: March 2003

1. Traditionally the assessment of river water quality has been based solely on the measurement of physical, chemical and some biological characteristics. While these measurements may be efficient for regulating effluent discharges and protecting humans, they are not very useful for large‐scale management of catchments or for assessing whether river ecosystems are being protected.

2. Measurements of aquatic biota, to identify structural or functional integrity of ecosystems, have recently gained acceptance for river assessment. Empirical evidence from studies of river ecosystems under stress suggests that a small group of biological ecosystem‐level indicators can assess river condition. However, physical and chemical features of the environment affect these indicators, the structure and function of which may be changed by human activities.

3. The term ‘river health’, applied to the assessment of river condition, is often seen as being analogous with human health, giving many a sense of understanding. Unfortunately, the meaning of ‘river health’ remains obscure. It is not clear what aspects of river health sets of ecosystem‐level indicators actually identify, nor how physical, chemical and biological characteristics may be integrated into measures rather than just observations of cause and effect.

4. Increased examination of relationships between environmental variables that affect aquatic biota, such as habitat structure, flow regime, energy sources, water quality and biotic interactions and biological condition, are required in the study of river health.
Predicting diatom communities at the genus level for the rapid biological assessment of rivers
Authors: Chessman Bruce , Growns IvoR. , Currey Julie , Plunkett‐Cole Nicola
Published: March 2003

1. Diatoms were sampled in the spring of 1994 and the autumn of 1995 at 137 pristine or near‐pristine reference sites on large and small streams at various altitudes in eastern New South Wales and Victoria. Scrapings were taken from five firm substrata across a range of microhabitat conditions at each site on each occasion. For each substratum, 100 valves were identified to genus level.

2. Multivariate statistical models were constructed to predict the probability of occurrence of each genus at a given site under near‐pristine conditions on the basis of physical features of the site that are not affected by human activity. Model predictions were compared with the flora observed at the reference sites and at 55 test sites affected by varying degrees of human disturbance.

3. Test sites were characterized more by the presence of genera not predicted by the model than by the absence of predicted genera. The degree of departure from model predictions was related mainly to increasing alkalinity, electrical conductivity, hardness and pH of river water. We therefore conclude that the main effect of human activity on the composition of diatom communities in the rivers of coastal south‐eastern Australia has been to increase genus richness through enrichment with alkaline salts.

4. The models did not perform as well as similar models applied to river macroinvertebrates at the family level, perhaps because of greater temporal variability in diatom communities and differences in the environmental variables to which diatoms and macroinvertebrates respond. Means of improving the current models are discussed.
Assessment of river health: accounting for perturbation pathways in physical and ecological space
Authors: Townsend Colin R. , Riley Ralph H.
Published: March 2003

1. A full understanding of changes to river ecosystem structure and functioning along the continuum from relatively pristine to profoundly perturbed requires knowledge of physical, chemical and ecological properties at many spatial and temporal scales. Perturbations may span broad spatio‐temporal scales or be spatially and temporally discrete.

2. The relevant scale for study depends on the manner in which perturbations move through two kinds of pathways – through the physical space of the catchment hierarchy and through the ecological space of river food webs. Different kinds of perturbation (e.g. inputs of sediment, nitrogen or phosphorus, changes to shading or discharge) vary in the degree and manner in which they are propagated downstream and through food webs.

3. The fundamental importance of disturbance regimes and refugia to river health is now clear and managers need to take this into account when devising river management schemes.

4. A comparison of the physics, chemistry and ecology of streams in catchments of native tussock and exotic pasture grassland in New Zealand serves to emphasize (i) the extreme complexity of interacting factors resulting from land use change, (ii) the importance of disturbance regime (not encapsulated in biotic indices) and biogeographic patterns (usually unmeasured) in determining ecosystem structure and functioning, and (iii) the lack of concordance between any single index of health and various fundamental features of ecosystem functioning.

5. Practical considerations limit most evaluations of river health to a small suite of indices, though it is important that researchers continue to evaluate the spatial, temporal and biological limitations of these indices. The vagaries of history and geography (extinction and colonization trajectories in relation to natural disturbance regimes) and the complexity of interacting physical, chemical and ecological responses to perturbation suggest that multi‐scale, multi‐temporal studies of river function offer the best opportunity to evaluate river health.
An overview of river health assessment: philosophies, practice, problems and prognosis
Authors: Boulton Andrew J.
Published: March 2003

1. Philosophically, the term ‘river health’ is useful because it is readily interpreted by the general public and evokes societal concern about human impacts on rivers. The common goal of achieving healthy rivers unites ecologists and the general public because the value of the ecologists’ contributions is clear (and, hence, funded). The difficulty arises in the choice of relevant symptoms because there is a wide variety that can be measured with varying accuracy at a broad range of spatial scales. These indicators may respond to impacts at different time scales, and no single indicator is a ‘silver bullet’ that reveals river health unequivocally.

2. In practice, choice of indicator often shows personal bias, technical considerations, and constraints of knowledge. Selection of appropriate spatial and temporal scales for these measures is crucial. Although most measurements are spot samples (e.g. concentration, abundance, species richness), assessment of river health based on changes in ecological processes such as post‐disturbance recovery rate or nutrient spiralling lengths may be more suitable in some cases.

3. Problems include validation of the indicator, its response time at a range of scales, and the reliability of its measurement. Assessment of river health should be accurate, timely (warning of deterioration instead of waiting until the patient is terminal), rapid (so that the response is swift), and inexpensive. The connectedness of running waters with their floodplains and catchments must be explicitly recognized. Hydrological and geomorphological modifications of rivers usually affect their health by severing or impairing the linkages, and the ‘cure’ may lie in addressing these causes. Often, we need landscape‐level data for management because this is the scale where cumulative effects of impacts are evident.

4. The prognosis is uncertain. We need to explore further the use of integrative measures of river health, and focus on establishing a link between the measure and impaired ecological integrity. Ecosystem‐level variables (e.g. estimates of production or respiration) show promise and recent technological advances make these more accessible. Data analytical approaches (e.g. multimetric vs. predictive models) need further debate but must not overlook the importance of high quality and relevant input data. Appropriate choice of indicators, rigorous sampling and analysis, and careful data interpretation must be matched with effective communication to policy‐makers and the public. When this occurs, the concept of ‘river health’ becomes more than just a rhetorical tool.‘
Bioenergetics and phenology of reproduction of the introduced red swamp crayfish, Procambarus clarkii, in Do·ana National Park, Spain, and implications for species management
Authors: Gutiérrez‐Yurrita Pedro J. , Montes Carlos
Published: March 2003

1. The red swamp crayfish, Procambarus clarkii (Girard), is a North American species which was introduced into the Lower Guadalquivir, Spain, in 1974. Procambarus clarkii has become a key species since it has greatly altered the functioning and structure of the ecosystems it has invaded.

2. Since P. clarkii spawn spontaneously throughout the year, it is to be expected that their ecological impact on the ecosystem may vary depending of the timing of habitat flooding (e.g. temporary freshwater marsh, and temporary or permanent pond). The objective of the present study was to understand the reproductive phenology and bioenergetics of P. clarkii in Do·ana National Park, Spain, freshwater ecosystems, and consequently, propose some management plans for their populations.

3. Five stages of ovarian development were detected. Final ovarian maturation occurred a few days before spawning and spawning was synchronized among mature females of all populations. Egg numbers hatched in pleopods ranged from 450 to 550. Timing of juvenile release from pleopods varied greatly (10–35 days).

4. Gravid females support most of their metabolic needs by catabolizing carbohydrates (overall mean of O:N = 30.39), and to a lesser extent, lipids. The aerobic and excretory metabolisms of gravid females were lower than those of immature animals of similar weight.

5. Analysis suggested that several factors influence the spawning of crayfish at the monitored sites. The major factors are water regime and temperature. Red swamp crayfish appear to be a spontaneous spawning species which may adjust their reproductive cycle to the timing of flooding, enhancing the utilization of available resources.

6. Populations of P. clarkii in Do·ana National Park could be controlled by the management of the water regime and by devising a fishing scheme which would maintain an appropriate population structure.
Species traits for future biomonitoring across ecoregions: patterns along a human‐impacted river
Authors: Dolédec Sylvain , Statzner Bernhard , Bournard Michel
Published: March 2003

1. Current budgets for environmental management are high, tend to increase, and are used to support policy and legislation which is standardized for large geographic units. Therefore, the search for tools to monitor the effects of this investment is a major issue in applied ecology. Ideally, such a biomonitoring tool should: (1) be as general as possible with respect to its geographic application; (2) be as specific as possible by separating different types of human impact on a given ecosystem; (3) reliably indicate changes in human impact of a particular type; and (4) be derived from a sound theoretical concept in ecology.

2. We developed an approach to biomonitoring which matches these ‘ideal’ characteristics by focusing on numerous, general biological species traits (e.g. size, number of descendants per reproductive cycle, parental care, mobility) and on the habitat templet concept, which relates trends in these general species traits to disturbance patterns. Using the French Rhône River and benthic macroinvertebrates as an example, we have used the data to demonstrate a general framework and the potential of our approach rather than to produce a ready‐made tool. Our data covered a large river and its major tributaries, which has a catchment that crosses ecoregions, and known gradients and discontinuities in human impact.

3. We applied multivariate analyses to evaluate how the distribution of species traits in invertebrate communities could discriminate environmental differences along the Rhône in comparison to traditionally used approaches (e.g. community structure, based on species abundances, or ecological species traits, such as velocity preferences and pollution tolerance). Invertebrate community structure expressed in terms either of the abundance or the traits of species reliably indicated differences in overall human impact. The community structure based on biological traits was less confounded by natural spatial gradients and reliably indicated human impact, while community structure based on ecological traits was the most confounded by natural spatial gradients and was the poorest indicator of human impact. Community structure based on species abundances was an intermediate indicator of human impact.

4. These results indicate that a revision of biomonitoring approaches which have been based on a single aspect of the biological responses may be warranted. The biological traits of species could separate the different types of human impact. Therefore, the use of these traits in biomonitoring could improve existing multi‐metric approaches. Future research has to show if the general applicability of species traits allows the development of a unique biomonitoring tool for running waters of the European Union, for running waters in temperate climates on several continents, for freshwater, marine and terrestrial systems, and/or for global biodiversity assessment.
Substratum patch selection in the lacustrine mussels Elliptio complanata and Pyganodon grandis grandis
Authors: Downing John A. , Van Leeuwen Hendrik , Di Paolo L. Antonio
Published: March 2003

1. Sediment selection was investigated under controlled conditions in two common lake‐dwelling species of freshwater mussels (Bivalvia: Unionidae), Elliptio complanata and Pyganodon grandis grandis.  2. Sediment choice was determined in six independent experiments under controlled conditions by distributing mussels randomly or evenly in tanks containing patches of sand and mud, and following their movement among sediment patches in experiments lasting between 30 and 45 days.  3. In all experiments, both species were found most frequently in muddy sediment patches. Movement toward muddy patches occurred rapidly: an average of nearly 80% of Pyganodon grandis grandis were found in mud after 30 days. Elliptio complanata moved rapidly to patches of mud at the start of experiments, but occupation of muddy sediments appeared to decrease after about 30 days.  4. Our results contrast with many field studies that suggest populations of lake‐dwelling freshwater mussels infrequently inhabit mud and silt. We therefore postulate that large‐scale mussel distribution in lakes is influenced most strongly by factors other than sediment composition.
Variation in growth rates of the zebra mussel, Dreissena polymorpha, within Lake Wawasee
Authors: Garton David W. , Johnson Ladd E.
Published: March 2003

1. Field experiments conducted in Lake Wawasee in 1995 and 1996 measured the response of shell growth of Dreissena polymorpha to environmental gradients.  2. Shell growth decreased with initial shell length in four mussel size classes ranging between 8 and 22 mm, and decreased with depth, with mussels in shallow water (<4 m) having growth rates nearly twice those of mussels in deeper water (4–7 m).  3. Growth occurred early in the spring–summer period (May–June) with relatively little shell added later in the summer (July–September), and varied significantly among sites within Lake Wawasee, but not between the 2 years of this study.  4. Rank order of sites was consistent for both years implying that environmental conditions responsible for variation in shell growth were stable within Lake Wawasee.  5. Cage design did not have a significant effect on mussel shell growth nor did the distance of growth cages above the bottom (0.5–0.75 m above the bottom versus directly on the bottom).  6. This study demonstrates the sensitivity of adult mussel growth to subtle variation in environmental conditions occurring within and among lakes, with potential consequences for mussel population dynamics and community structure and function.