bluuebunny/crossref_metadata_2025 huggingface dataset:
This is not the end of limnology (or of science): the world may well be a lot simpler than we think
Authors: Harris Graham
Published: March 2003

1.Reynolds (1998)recently wrote a short piece in this journal lamenting the state of the art of freshwater ecology. Others have recently foreshadowed the end of science altogether. It is my argument here that the end of science is not nigh and that there are fundamental advances to be made in understanding ecosystem function. Despite changes to the funding base of freshwater ecology over the years, the discipline can continue to make fundamental contributions to ecology. We have an excellent base of raw material to work with, however, collected.

2. As a rebuttal Reynolds (1997)I present evidence that ecosystems (and freshwater ecosystems in particular) may well be a lot simpler than we think. Buried deep within a very complex world there are some general modes of behaviour, determined by fundamental principles, which impart certain kinds of high level order and predictability.

3. By means of six propositions I argue the case for the existence of these fundamental principles and present empirical evidence for each.

4. In conclusion it is clear that there is a need for fundamental information about the role of biodiversity in ecosystem function. There is also a need to understand the interplay between environmental perturbations, biodiversity and functional groups which together determine the cycling of energy and materials within freshwater and estuarine systems. While we have considerable information about northern hemisphere aquatic ecosystems less is known about southern hemisphere systems.
Changes in agricultural intensity and river health along a river continuum
Authors: Harding JoN. S. , Young Roger G. , Hayes JohN. W. , Shearer Karen A. , Stark JohN. D.
Published: March 2003

1. The impact of agricultural activities on waterways is a global issue, but the magnitude of the problem is often not clearly recognized by landowners, and land and water management agencies.

2. The Pomahaka River in southern New Zealand represents a typical lowland catchment with a long history of agricultural development. Fifteen sites were sampled along a 119‐km stretch of the river. Headwater sites were surrounded by low‐intensity sheep farming, with high‐intensity pasture and dairying occurring in the mid‐reach and lower reaches.

3. Water clarity decreased significantly from about 6 m in the headwaters to less than 2 m in the lower reaches. Benthic sediment levels increased significantly downriver, peaking at 35 mg m−−2 below several tributaries with high‐intensity agriculture in their catchments. Periphyton levels were also significantly greater in the lower reaches than the headwaters, and coincided with increased nitrogen (DIN) and phosphorus (SRP) concentrations.

4. Macro‐invertebrate species richness did not change significantly throughout the river, but species composition did with Ephemeroptera, and to a lesser extent, Plecoptera and Trichoptera dominating the headwater sites (where there was high water clarity, and low nutrient and periphyton levels). Downriver these assemblages were replaced by molluscs, oligochaetes and chironomids.

5. Canonical correspondence analysis indicated that agricultural intensity and physical conditions associated with agriculture activity (e.g. impacted waters, high turbidity and temperature) were strongly associated with the composition of benthic assemblages at differing reaches down the Pomahaka River.

6. The present results indicate that quantifying agricultural intensity within a catchment, particularly relative livestock densities, may provide a useful tool for identifying threshold levels above which river health declines.
Predicting community characteristics from habitat conditions: fluvial fish and hydraulics
Authors: Lamouroux Nicolas , Olivier Jean‐Michel , Persat Henri , PouilLy MarC. , Souchon YveS. , Statzner Bernhard
Published: March 2003

1. One current approach to the prediction of community characteristics is to use models of key local‐scale processes (e.g. niche dimensions) affecting individuals and to estimate the effects of these attributes over larger scales. We tested this approach, focusing on how the hydraulic habitat structures fluvial fish communities.

2. We used a recent statistical habitat model to predict fish community characteristics in eleven reaches in the Rhône river basin in France. Predictions were made ‘blindly’ since most reaches were not used to calibrate the model. The model reflects species preferences for local hydraulics. We made predictions of the fish community from the local hydraulic conditions found in the reaches under low flow conditions. The overall abundance and the relative abundance (both as indices) of fish species, specific size classes and species traits (i.e. reproductive, trophic, morphological and others) were predicted. We summarized our predictions of the relative abundance of species as two ‘community structure indices’ using Principal Component Analysis.

3. Our predictions from low‐flow hydraulics were compared with long‐term observations of fish communities. The relative abundance of species actually observed depended largely on zoogeographic factors within the Rhône basin which could not be predicted by the model. The model predicted 13% of the variance in the indices of relative abundance at the species level and 23% of this variance at the trait level for all zoogeographic regions combined. However, when focused on reaches within a geographic region, the model explained up to 47% of the same variance. Therefore, geographic regions act as ‘filters’ on the relative abundance of species, but hydraulics do affect fish communities within a given geographical context.

4. For the synthetic ‘community structure indices’, we obtained good predictions from hydraulics independently of the geographical context (variance explained up to 95%). These indices were linked to simple key hydraulic characteristics of river reaches (Froude and/or Reynolds number). The indices enabled interpretations of the links between hydraulics, geomorphology, discharge and community patterns. These links were consistent with existing knowledge of species and their traits.

5. In addition to the above validations, the habitat model partly explained the observed effects of impoundment on fish communities.

6. The present results show that stream hydraulics strongly impact fish community structure. Consequently, our findings confirm that community characteristics can be predicted using models of the local‐scale habitat requirements of the species forming the community.
Habitat use by crayfish in stream pools: influence of predators, depth and body size
Authors: Englund Göran , Krupa James J.
Published: March 2003

Crayfish in headwater streams are subjected to predation from two sources: (a) fish; and (b) terrestrial predators including wading birds and mammals. Field observations of the mortality of tethered crayfish of two size classes were used to examined how predation risks imposed by the two types of predators varied with water depth and crayfish size. We also examined the depth distribution of large and small crayfish in stream pools with and without predatory fish.

Predatory fish, mostly green sunfish,Lepomis cyctuellus, and creek chub,Semotilus atromaculatus, rapidly consumed tethered small crayfish (body length = 25–30 mm) in deep areas (0.4–0.7 m), but not in shallow areas (0.05–0.15 m) of stream pools. Tethered large crayfish (body length = 50–75 mm) suffered little mortality from fish at either depth. Terrestrial predators such as racoons,Procyou lotor, and herons,ButoridesandArdea, caused little crayfish mortality in deep areas, but rapidly consumed both small and large crayfish exposed in shallow areas.

A comparison of habitat use by crayfish in pools with and without fish suggests that small, but not large, crayfish shift their distributions to shallow water in the presence of fish. In pools without fish, the distribution of small crayfish was independent of depth, whereas large crayfish occupied deep water.
Morphological deformities occurring in Belarusian chironomids (Diptera: Chironomidae) subsequent to the Chernobyl nuclear disaster
Authors: Williams D. Dudley , Nesterovitch Andrei I. , Tavares Annette F. , Muzzatti Ernest G.
Published: March 2003

1. Chironomid larvae and adults were collected from several freshwater habitats around the Chernobyl site from 1990 to 1994 (4–8 years after a nuclear accident) and examined for morphological deformities.

2. Deformities were found in larvae of nine of the 13 species collected, and were most obvious in headcapsule structures, particularly the antennae, mentum, mandibles and epipharyngeal pectens.

3. In species of Chironomus, the most abundant genus, there was a positive linear relationship between the incidence of deformity and radiation level. Indices of severity of deformity showed similar trends. It is suggested that these deformities resulted largely from ingestion of irradiated, plant‐derived, fine particulate food.

4. Among adult male Ch. riparius, the deformity index decreased both with increasing time from the accident and with increasing distance from the reactor, although these trends were not statistically significant. There was also a trend of increased severity of deformity closer to the accident, both in time and space.

5. Overall, there was a greater incidence of deformity in the larvae than in the adults (e.g. 60 versus 20%, respectively, at the Krasnoselye site and 33 versus 20%, respectively, at the more distant Dron’ki site).

6. It was not possible to determine whether the deformities were inherited from previous generations or were somatic occurrences in each new generation as a consequence of the radiation that continues to pervade the region.
Nutrient limitation of bacterioplankton and phytoplankton in humic lakes in northern Sweden
Authors: Jansson Mats , Bergström Ann‐Kristin , Drakare Stina , Blomqvist Peter
Published: March 2003

1. Two small humic lakes in northern Sweden with concentrations of dissolved organic carbon (DOC) between 15 and 20 mg L–1 were fertilized with inorganic phosphorus (P) and inorganic nitrogen (N), respectively. A third lake was unfertilized and served as a control. In addition to this lake fertilization experiment, data from different regional surveys were used to assess the role of different limiting factors.

2. The P fertilization had no effects on bacterioplankton or phytoplankton, while phytoplankton were significantly stimulated by N fertilization. Inorganic nutrient limitation of bacterioplankton was a function of DOC concentration in water of the investigated region and nutrient‐limited bacteria were found only in lakes with DOC concentrations less than around 15 mg L–1

3. The fertilization experiments demonstrated that the DOC‐rich experimental lakes contained a bioavailable pool of P that was not utilized to its full potential under natural conditions. The overall mobilization of energy (bacterioplankton plus phytoplankton) in the experimental lakes was restricted by lack of inorganic N.
Fitness and sexual response to population density in Daphnia pulex
Authors: Berg  , Pálsson  , Lascoux
Published: March 2003

1. The switch between asexual and sexual reproduction is an important fitness component in cyclically parthenogenetic populations as it is the key to persistence in unstable habitats and because it influences population genetic characteristics such as linkage disequilibrium and population genetic structure.

2. Genetic variation for sexual and asexual reproductive rate (RC) was examined, under varying population density, in Daphnia pulex sampled from a rockpool system and two other distinct European localities.

3. Density affected the switch to sexual behaviour, as found in other studies and reduced Rc. Production of males was not correlated with sexual reproduction, promoting outcrossing.

4. Genetic variation was found for the response to density, both within and between populations. There was substantial variation within the rockpools despite their demographic instability, indicating rapid recovery of life‐history variation or maintenance during bottlenecks.
Species traits in relation to habitat variability and state: neotropical juvenile fish in floodplain creeks
Authors: Mérigoux Sylvie , Dolédec Sylvain , Statzner Bernhard
Published: March 2003

1. Ecological theory predicts that (1) proportions of fish having particular life history strategies should vary with habitat conditions, and (2) biological traits of species should change across spatio‐temporal variability gradients (River Habitat Templet).

2. We used data on juvenile fish and biological traits of the species, temporal (i.e. hydrology) and spatial (e.g. depth, bottom substrate, litter type) habitat variability and state (i.e. mean conditions) to test these predictions for communities comprising 57 fish taxa in floodplain creeks of the Sinnamary River (French Guiana).

3. We did not confirm predictions on habitat use according to groupings based on life history strategies. However, we found 10 significant relationships between species traits and habitat variability (e.g. size at maturity, diameter of mature oocytes, parental care and relative body height decreased with increasing temporal variability; size at maturity and mean diameter of mature oocytes increased with increasing spatial variability). In addition, state variables such as mean water level, dissolved oxygen, mean width or mean depth could explain much of the variation in species traits.

4. Thus, our results generally supported the River Habitat Templet but suggested that state, in addition to variability, should be included in habitat descriptions.
Viruses in the plankton of freshwater and saline Antarctic lakes
Authors: Laybourn‐Parry Johanna , Hofer Julia S. , Sommaruga Ruben
Published: March 2003

1. Virus‐like particle (VLP) abundances in nine freshwater to saline lakes in the Vestfold Hills, Eastern Antarctica (68° S) were determined in December 1999. In the ultra‐oligotrophic to oligotrophic freshwater lakes, VLP abundances ranged from 1.01 to 3.28 × 106 mL–1 in the top 6 m of the water column. In the saline lakes the range was between 6.76 and 36.5 × 106 mL–1. The lowest value was found in meromictic Ace Lake and the highest value in hypersaline Lake Williams. Virus to bacteria ratios (VBR) were lowest in the freshwater lakes and highest in the saline lakes, with a maximum of 23.4 in the former and 50.3 in the latter.

2. A range of morphologies among VLP was observed, including phages with short (Podoviridae) and long tails, icosahedric viruses of up to 300 nm and star‐like particles of about 80 nm diameter.

3. In these microbially dominated ecosystems there was no correlation between VLP and either bacterial numbers or chlorophyll a. There was a significant correlation between VLP abundances and dissolved organic carbon concentration (r=0.845, P < 0.01).

4. The data suggested that viruses probably attack a spectrum of bacteria and protozoan species. Virus‐like particle numbers in the freshwater lakes were lower than values reported for lower latitude systems. Those in the saline lakes were comparable with abundances reported from other Antarctic lakes, and were higher than most values published for lower latitude lakes and many marine systems. Across the salinity spectrum from freshwater through brackish to hypersaline, VLP concentrations increased roughly in relation to increasing trophy.

5. Given that Antarctic lakes have a plankton almost entirely made up of bacteria and protists, and that VLP abundances are high, it is likely that viruses play a pivotal role in carbon cycling in these extreme ecosystems.
Flight activity of insects along a mountain stream: is directional flight adaptive?
Authors: Winterbourn Michael J. , Crowe Anna L. M.
Published: March 2003

1. Flight activity of Trichoptera, Plecoptera and Ephemeroptera was studied by sticky trapping for 12 months at five sites along a New Zealand mountain stream. Over 19 000 insects were captured by the traps, which were located in forest and grassland reaches, including a reach with intermittent flow.

2. Most species occurred predominantly in forest or grassland, although some were trapped throughout the stream. Longitudinal distributions of adults and their larvae were strongly correlated.

3. Flight periods of 24 caddisflies, three mayflies and four stoneflies ranged from 2 to 12 months. Six species were trapped in all months and 17 (55%) in more than 5 months.

4. The most abundant forest‐dwelling caddisfly species were over‐represented on the downstream sides of sticky traps located in, and immediately below, forest indicating a majority was flying upstream. Upstream flight compensates for downstream drift of larvae and should maximize the likelihood that forest‐dwelling species will locate preferred habitat for egg, larval and/or adult development. Unlike the caddisflies, the stonefly Spaniocerca zelandica was over‐represented on the upstream sides of traps, suggesting that some adults may float or fly downstream following emergence.

5. In contrast to forest‐dwelling species, only one common caddisfly (Oxyethira albiceps) was over‐represented on the downstream sides of traps at grassland sites. Unlike the forest‐dwelling species, most species taken at the downstream sites probably came from a variety of sources, including a nearby stream.
Food limitation of planktonic rotifers: field experiments in two mountain ponds
Authors: Cordova Susan E. , Giffin Joy , Kirk Kevin L.
Published: March 2003

1. Resource competition is thought to be important in controlling zooplankton population dynamics and structuring zooplankton communities. Resource competition requires that resources are limiting. Ten field experiments were conducted to determine the presence and intensity of resource limitation of herbivorous planktonic rotifers in two mountain ponds. The intensity of food limitation was measured as Δr, the difference between population growth rates in food supplemented versus control enclosures.

2. Rotifers were significantly food limited (Δr > 0) in most experiments. The intensity of food limitation varied between species. In Grady Lake, mean Δr was 0.26 day−1 for Polyarthra vulgaris and 0.43 day−1 for an unidentified Synchaeta sp. In L1 Pond, mean Δr was 0.07 day−1 for Keratella cochlearis and 0.28 day−1 for S. oblonga. The frequent and intense food limitation suggests that edible phytoplankton in both ponds were often present at low densities, were of low nutritional quality, or both. The intensity of food limitation often changed rapidly over time, indicating rapid temporal variation in resource availability.

3. For P. vulgaris, Δr was not correlated with its population growth rate in Grady Lake. Thus, although food limitation was common, population dynamics may have been more strongly affected by other factors. For K. cochlearis, Δr increased as population density increased, suggesting the existence of intraspecific resource competition that may regulate population dynamics.
Response of plankton communities to whole‐lake Ca(OH)2 and CaCO3 additions in eutrophic hardwater lakes
Authors: Zhang Ying , Ghadouani Anas , Prepas Ellie E. , Pinel‐Alloul Bernadette , Reedyk Sharon , Chambers Patricia A. , Robarts Richard D. , Méthot Ginette , Raik Assia , Holst Meike
Published: March 2003

1. The impact of whole‐lake lime (slaked lime, Ca(OH)2, and/or calcite, CaCO3) addition on plankton communities was evaluated in eutrophic hardwater lakes on the North American Boreal Plain.

2. Two lakes received a single treatment of lime (Ca(OH)2 at 74 or 107 mg L–1), two lakes received multiple treatments with Ca(OH)2 and/or CaCO3 (5–78 mg L–1), and four lakes were untreated and served as reference systems.

3. Over the long‐term (> 1 year), phytoplankton biomass was reduced in multiple‐dose lakes, but not in single‐dose lakes. Cyanobacteria typically dominated the algal community in the years before, during and after lime treatment in both single‐ and multiple‐dose lakes.

4. In the single‐dose lakes, randomized intervention analysis showed no significant change in the biomass of zooplankton after lime addition.
Effect of dissolved organic carbon quality on microbial decomposition and nitrification rates in stream sediments
Authors: Strauss Eric A. , Lamberti Gary A.
Published: March 2003

1. Microbial decomposition of dissolved organic carbon (DOC) contributes to overall stream metabolism and can influence many processes in the nitrogen cycle, including nitrification. Little is known, however, about the relative decomposition rates of different DOC sources and their subsequent effect on nitrification.

2. In this study, labile fraction and overall microbial decomposition of DOC were measured for leaf leachates from 18 temperate forest tree species. Between 61 and 82% (mean, 75%) of the DOC was metabolized in 24 days. Significant differences among leachates were found for labile fraction rates (P < 0.0001) but not for overall rates (P=0.088).

3. Nitrification rates in stream sediments were determined after addition of 10 mg C L–1of each leachate. Nitrification rates ranged from below detection to 0.49 μg N mL  sediment–1 day–1and were significantly correlated with two independent measures of leachate DOC quality, overall microbial decomposition rate (r=–0.594,P=0.0093) and specific ultraviolet absorbance (r=0.469,P=0.0497). Both correlations suggest that nitrification rates were lower in the presence of higher quality carbon.

4. Nitrification rates in sediments also were measured after additions of four leachates and glucose at three carbon concentrations (10, 30, and 50 mg C L–1). For all carbon sources, nitrification rates decreased as carbon concentration increased. Glucose and white pine leachate most strongly depressed nitrification. Glucose likely increased the metabolism of heterotrophic bacteria, which then out‐competed nitrifying bacteria for NH4+. White pine leachate probably increased heterotrophic metabolism and directly inhibited nitrification by allelopathy.
Persistence and stability of lotic invertebrate communities in New Zealand
Authors: SCARSBROOK M.R.
Published: March 2003

1. Persistence and stability of lotic invertebrate communities were determined at an annual time scale over a 9‐year period (1990–98) at 26 river sites over the northern half of New Zealand. In addition, a number of water quality variables were measured monthly and flow information collected continuously over the same period at each site.

2. The aim of the study was to describe the levels of interannual variability in invertebrate communities, and relate community changes to variability in environmental conditions. The consequences of this temporal variability for the sensitivity of predictive models were also investigated.

3. Levels of change in environmental conditions varied significantly between years, but were relatively similar across sites. In contrast, community persistence (similarity between years in species assemblage composition), and stability (similarity between years with respect to relative abundance of species in the community) both varied significantly between sites, but changes between years were similar. Community stability was highest at sites with relatively harsh flow conditions (high coefficient of variation, high relative size of floods), and was also greater in communities dominated by Ephemeroptera.

4. Relationships between change in environmental conditions and changes in community composition and structure were relatively weak for most individual sites. However, when average levels of change for each of the 26 sites were used, communities showed greater persistence under conditions where flow conditions remained relatively constant. Water quality changes had no significant effect on community persistence when assessed for all 26 sites combined.

5. Results from this study suggest that lotic invertebrate communities fluctuate around a relatively stable state, at least over a 9‐year period. However, the extent of interannual variation in community composition and structure observed, along with the relatively low degree of cluster fidelity observed within a single region, suggests that predictive models based on reference site conditions extrapolated over several years should be applied with caution in New Zealand streams.
Catchment land‐use, macroinvertebrates and detritus processing in headwater streams: taxonomic richness versus function
Authors: HURYN ALEXANDER D. , BUTZ HURYN VIVIAN M. , ARBUCKLE CHRIS J. , TSOMIDES LEONIDAS
Published: March 2003

1. We used a litter bag technique to assess the effect of catchment land‐use (forest, wetland, agriculture, urban) on the processing of red maple (Acer rubrum L.) litter in 17 streams in Maine, U.S.A. Litter processing by fungi was predicted to increase with nutrient concentrations along a gradient of land use, from relatively unmodified to highly modified. Litter processing by litter‐shredding macroinvertebrates was predicted to decline along this gradient because of a decline in their taxonomic richness and biomass.

2. Land use was associated with the anticipated gradient in nutrient and macroinvertebrate attributes, and a significant relationship was found between land use and nitrate concentration. There was, however, no significant relationship between land use and soluble reactive phosphorus (SRP) concentration. Similarly, shredder taxonomic richness was significantly related to land use type, whereas shredder biomass showed no significant relationship to land use.

3. Attributes of the shredder assemblage structure and nutrient concentrations were both strong determinants of litter processing. Increasing biomass and taxonomic richness of shredders was significantly related to increasing rates of litter mass loss. Increasing concentrations of nitrate and SRP were significantly related to increasing rates of litter softening below threshold concentrations (approximately 0.20 mg NO3‐N L–1 and 5 μg SRP L–1).

4. The potentially additive effects of nitrate and SRP concentrations or shredder richness and biomass on litter processing rates were confounded by the lack of significant correlation between these pairs of variables. Consequently, rates of litter processing (as rates of softening or mass loss) did not vary systematically among different land use regimes.
Dispersal in drift‐prone macroinvertebrates: a case for density‐independence
Authors: HUMPHRIES S.
Published: March 2003

1. Studies of dispersal of macroinvertebrates in streams and rivers tend to be focused on drift, whilst benthic movements are usually considered to be less important.

2. Field‐enclosure experiments with the mayflyBaetis rhodaniindicate that net dispersal in this species is simply a proportional loss of individuals from the benthos.

3. Neither net upstream or downstream movements exhibited evidence of density‐dependence in the form of curvilinear relationships between initial and final densities.

4. The net number of animals moving upstream did not differ significantly from the net number moving downstream.

5. The probable mechanisms behind density‐independent dispersal are discussed, as are the implications for our understanding of population dynamics in relation to invertebrate drift.
Correlations between nutrient concentrations and zooplankton populations in a mesotrophic reservoir
Authors: CONDE‐PORCUNA J. M. , RAMOS‐RODRÍGUEZ E. , PÉREZ‐MARTÍNEZ C.
Published: March 2003

1. A year‐round study was conducted in a mesotrophic reservoir to determine the dynamics of zooplankton populations as a function of food availability (edible phytoplankton), nutrient concentration, temperature and hydraulic regime.

2. Rotifer biomass was correlated with soluble reactive phosphorus (SRP) concentration. The abundance of the rotifers Keratella cochlearis and Anuraeopsis fissa were not correlated with food availability (measured by chlorophyll and cell counts) but showed a strong dependence on P availability. Another rotifer, Synchaeta oblonga, and crustacean species were not related to nutrient availability but seemed to be dependent on food concentrations, especially of some phytoplankton taxa.

3. In this field study, rotifers seemed more susceptible than Daphnia or copepods to P‐limitation. Among rotifer species, Keratella seemed to be more susceptible than Anuraeopsis to P limitation. Different susceptibilities of zooplankton species to nutrient limitation may be important in explaining the dynamics of these organisms in natural situations. Further analyses are warranted to clarify the interactions between nutrient limitation and energy limitation among zooplankton.
Food web structure in riverine landscapes
Authors: WOODWARD GUY , HILDREW ALAN G.
Published: March 2003

1. Most research on freshwater (and other) food webs has focused on apparently discrete communities, in well‐defined habitats at small spatial and temporal scales, whereas in reality food webs are embedded in complex landscapes, such as river corridors. Food web linkages across such landscapes may be crucial for ecological pattern and process, however. Here, we consider the importance of large scale influences upon lotic food webs across the three spatial dimensions and through time.

2. We assess the roles of biotic factors (e.g. predation, competition) and physical habitat features (e.g. geology, land‐use, habitat fragmentation) in moulding food web structure at the landscape scale. As examples, external subsidies to lotic communities of nutrients, detritus and prey vary along the river corridor, and food web links are made and broken across the land–water interface with the rise and fall of the flood.

3. We identify several avenues of potentially fruitful research, particularly the need to quantify energy flow and population dynamics. Stoichiometric analysis of changes in C : N : P nutrient ratios over large spatial gradients (e.g. from river source to mouth, in forested versus agricultural catchments), offers a novel method of uniting energy flow and population dynamics to provide a more holistic view of riverine food webs from a landscape perspective. Macroecological approaches can be used to examine large‐scale patterns in riverine food webs (e.g. trophic rank and species–area relationships). New multivariate statistical techniques can be used to examine community responses to environmental gradients and to assign traits to individual species (e.g. body‐size, functional feeding group), to unravel the organisation and trophic structure of riverine food webs.
Remote sensing of riverine landscapes
Authors: MERTES LEAL A. K.
Published: March 2003

1. The fashion for examining riverine landscapes is changing as our technical instruments, from microprobes to satellites, expands to be able to examine the spatial and temporal relationships among biota, hydrology and geomorphology across scales from microhabitats to channel units to valleys to catchments.

2. The range of successful applications from remote sensing analyses of riverine landscapes has especially increased with the launch of many new instruments that record data across the electromagnetic spectrum. Engineering of the instruments has also improved such that knowledge of the radiometric properties of the digital data is more complete as a result of better instrumentation and installation of on‐board calibrations systems for many instruments.

3. With the development of faster processing on cheaper computers, it is now common for comprehensive data sets to be processed through algorithms that previously could only be applied to relatively small (<1 Mbyte) rasters of data. This technical advance is especially important for the statistical algorithms such as principal components and spectral mixture analysis that can decompose gradients in the spectral data. The combined effect is the production of regional views of riverine landscapes separated into components of water, vegetation and soil.

4. The landscape properties of riverine landscapes that have been most successfully measured with remote sensing data include community and habitat level classification and connectivity of waterbodies with optical and radar data. Laser and radar altimetric data measured from aircraft provide land elevations at resolutions as fine as decimetres. A remaining challenge is to achieve an exact match between the categories of landscape classification from the remote sensing analysis and data from field surveys or model outputs.

5. In contrast to many landscape properties, several water properties are now routinely measured as absolute values (water surface elevation, temperature, surface sediment concentration and algal concentration) with remote sensing. New analyses of both passive and active radar data in addition have led to measurements of inundation and wetness that are providing valuable insight into the dynamics of flooding and its effect on riverine landscapes.

6. Finally, an effective examination of the variability in landscape cover includes additional analyses of remote sensing products using pattern metrics that measure the scale of patchiness and distribution of the landscape properties. These types of variability measures at the regional scale contribute to an increased understanding of the way in which spatial heterogeneity of riverine landscapes varies across scales and how landscape filters (sensu Poff, 1997) influence the evolution of these diversity patterns.
Re‐establishing and assessing ecological integrity in riverine landscapes
Authors: JUNGWIRTH M. , MUHAR S. , SCHMUTZ S.
Published: March 2003

1. River–floodplain systems are among the most diverse and complex ecosystems. The lack of detailed information about functional relationships and processes at the landscape and catchment scale currently hampers assessment of their ecological status.

2. Intensive use and alteration of riverine landscapes by humans have led to severe degradation of river–floodplain systems, especially in highly industrialised countries. Recent water‐related regulations and legislation focussing on high standards of ecological integrity back efforts to restore or rehabilitate these systems.

3. Most restoration projects in the past have suffered from a range of deficits, which pertain to project design, the planning process, the integration of associated disciplines, scaling issues and monitoring.

4. The so‐called `Leitbild' (i.e. a target vision) assumes a key role in river restoration and the assessment of ecological integrity in general. The development of such a Leitbild requires a multistep approach. Including explicitly the first step that defines the natural, type‐specific reference condition (i.e. a visionary as opposed to an operational Leitbild), has great practical advantages for restoration efforts, primarily because it provides an objective benchmark, as is required by the European Water Framework Directive and other legal documents.

5. Clearly defined assessment criteria are crucial for evaluating ecological integrity, especially in the pre‐ and postrestoration monitoring phases. Criteria that reflect processes and functions should play a primary role in future assessments, so as to preserve and restore functional integrity as a fundamental component of ecological integrity.

6. Case studies on the Kissimmee River (U.S.A.), the Rhine River (Netherlands and Germany), and the Drau River (Austria) are used to illustrate the fundamental principles underlying successful restoration projects of river–floodplain systems.
Colonisation of freshwater habitats by the European eel Anguilla anguilla
Authors: Ibbotson Anton , Smith Jim , Scarlett Peter , Aprhamian Miran
Published: March 2003

1. The spatial distribution of European eels in 18 U.K. rivers was related to distance from tidal limit using a negative exponential model. This function accounted for between 19 and 90% of the variation in eel density where quantitative data was available. For semiquantitative data the negative exponential function was a significant predictor of eel densities in only six out of 10 cases, although all rivers showed a consistent decline in abundance with distance upstream from the tidal limit.

2. The spatial distribution of different age groups of European eel in River Severn showed an initial rapid dispersion into freshwater followed by a much slower dispersion rate. Movement of the population upstream by a wave‐form migration process does not occur in this system. Instead colonisation of freshwaters can be seen as a two‐phase dispersion. Phase‐1 is a rapid dispersion upstream driven by density at the point source. Phase‐2 commences once the eels become yellow eels and is equivalent to random diffusion of particles.

3. These processes have important implications for the penetration of freshwaters with reduced numbers of eel larvae arriving on the coast of Europe and North America. Eel abundance will decrease more in freshwaters in an upstream direction whilst it may remain stable or decrease to a lesser extent in estuaries. They are also able to explain the demography of eels migrating upstream over weirs and the observations of varying sex ratios within catchments. We conclude that a dispersion model dependent on age, temperature, difficulty of migration, habitat quality and density of eels should be an important part of freshwater eel management.
Short‐term and long‐term effects of zooplanktivorous fish removal in a shallow lake: a synthesis of 15 years of data from Lake Zwemlust
Authors: Van De Bund Wouter J. , Van Donk Ellen
Published: March 2003

SUMMARY 1. Removal of zooplanktivorous fish (mainly bream) in 1987 from a shallow eutrophic lake in the Netherlands, Lake Zwemlust, resulted in a quick switch from a turbid state with cyanobacteria blooms to a clear state dominated by macrophytes.

2. The clear state was not stable in the long term, however, because of high nutrient loadings.

3. In 1999, another removal of zooplanktivorous fish (mainly rudd) had similar effects as in 1987, although macrophytes returned more slowly.

4. In the years directly following both interventions there was a ‘transition period’ of very clear water with high densities of zooplanktonic grazers in the absence of macrophytes; low oxygen concentrations indicate that during those years primary production was low relative to heterotrophic activity.

5. The transition period appears to provide the light climate necessary for the return of macrophytes.

6. Reduction of nutrient loading is necessary to improve water quality in Lake Zwemlust in the long term. In the short term, repeated fish stock reduction is a reasonable management strategy to keep Lake Zwemlust clear.
Differences in the exploitation of bream in three shallow lake systems and their relation to water quality
Authors: Lammens E. H. R. R. , Van Nes E. H. , Mooij W. M.
Published: March 2003

SUMMARY 1. The development of bream populations, water transparency, chlorophyll‐a concentration, extent of submerged vegetation and densities of the zebra mussel, Dreissena polymorpha, were analysed in three shallow eutrophic lake systems subject to different fish management.

2. In Lake Veluwemeer, the bream population was reduced from c. 100 to 20 kg ha−1 after 5 years of fishing. The mortality caused by the fishery was estimated at 38% of bream >15 cm in addition to a 13% natural mortality of bream >17 cm. The decline was followed by an expansion of the Chara beds present in the shallow parts, an increase in water transparency in the open‐water zone, an increase in the density of zebra mussels and a decrease in chlorophyll‐a concentrations.

3. The newly created Lake Volkerak showed trends opposite to those in Lake Veluwemeer. Bream colonised the lake in 1988 and reached a biomass of c. 140 kg ha−1 in 1998. The water transparency decreased from a maximum of 3 m to c. 1 m and the chlorophyll‐a concentration increased from 5 to 45 μg L−1. Submerged vegetation colonised up to 20% of the total lake area in the first 5 years after creation of the lake in 1987 but decreased to 10% as turbidity increased.

4. Seine fishery in the Frisian lake system did not appear to affect the bream population despite annual catches as high as 40–50 kg ha−1. The estimated natural mortality of fish >15 cm was 15% and mortality by fishery was 26%. The high loss was apparently compensated by good recruitment and high growth rates resulting from a c. 1 °C higher water temperature during the years when bream were removed by fishing. There was only a slight decrease in chlorophyll‐a concentrations and a slight increase in water transparency.

5. The results of this study suggest that the effects of bream exploitation in eutrophic lakes can vary depending on the efficiency of the fishery, recruitment success and temperature regime. In the absence of fishery, bream dominated the fish community in the study lakes and apparently prevented D. polymorpha and submerged vegetation from establishing because of physical disturbance, enhanced internal P‐loading and resettling of resuspended sediments.
Phytoplankton–zooplankton seasonal timing and the ‘clear‐water phase’ in some English lakes
Authors: Talling J. F.
Published: March 2003

SUMMARY 1. An examination is made of the relative seasonal timing of the postwinter increase of phytoplankton and zooplankton populations in four English lake basins. It centres upon weekly sampling over 20 years and rough counts of larger Crustacea, as copepods and cladocerans, from filtered samples that were used for chlorophyll a (Chl) estimation.

2. Typically, a spring maximum of phytoplankton, dominated by diatoms and earlier in the shallower lakes, is accompanied or followed by a maximum of copepods and then one of cladocerans dominated by the Daphnia hyalina–galeata complex. Regarding timing, the maximum of copepods has no apparent relation with phytoplankton abundance (Chl). The maximum of cladocerans appears to be largely independent of variation in the phytoplankton maximum, but is generally associated with a minimum in Chl. Evidence for some direct causality in this inverse correlation after the spring phytoplankton maximum is best displayed by the shallow Esthwaite Water in which the peaks of Chl and cladocerans are separated further than in the deep Windermere basins where phytoplankton growth is delayed. In Esthwaite Water, and possibly often in Windermere, a principal minimum in Chl is ascribable to grazing by Daphnia.

3. The typical inverse relationship of Chl and cladocerans is lost in some years when relatively inedible large phytoplankters (e.g. colonial chrysomonads, filamentous cyanophytes) are abundant and Chl minima are less pronounced, although maxima of cladocerans still occur. Conversely, available edible phytoplankters include various small forms grouped as μ‐algae and Cryptomonas spp.; their probable depletions by Daphnia appear to be sequential and may limit the latter's maxima, whose inception is temperature‐dependent.

4. The spring–summer maxima of cladocerans and minima of Chl are generally coincident with a main seasonal maximum of Secchi disc transparency and light penetration – to which removal of non‐phytoplankton particles by filtering cladocerans may contribute.
Ciliate populations in temporary freshwater ponds: seasonal dynamics and influential factors
Authors: Andrushchyshyn Oksana , Magnusson A. Katarina , Williams D. Dudley
Published: March 2003

SUMMARY 1. The ciliate populations of two temporary ponds in southern Ontario were studied throughout their aquatic phases in 2001. Pond I (∼1 ha) held water for 98 days, whereas Pond II (∼0.25 ha) held water for 34 days. Populations were assessed both within the ponds themselves and within a series of enclosures in which invertebrate predator pressure was manipulated.

2. In the natural pond water, total ciliate abundance in Pond II rose rapidly from day 1 increasing two orders of magnitude by day 7. In contrast, total abundance in Pond I began at the same level as in Pond II but increased much more slowly, reached a plateau of around 500 individuals L−1, and increased again late in the hydroperiod.

3. Despite being only 500 m apart, the two ponds were fairly dissimilar in terms of their species richness and species composition. Pond I contained 50 species compared with 70 species for Pond II, with only 24 species shared. Additional species occurred within the enclosures raising the total species richness to 145 species; 88 from Pond I, 104 from Pond II, with 47 species (30%) in common. Pond II contained more mid‐sized ciliates (50–200 μm), whereas Pond I was dominated by smaller ciliates, especially in mid‐May and early June. In Pond I, cumulative species richness throughout the hydroperiod was highest in the predator addition enclosures (65 ± 4 species), followed by the partial‐predator exclusion enclosures (50 ± 4). Lowest species richness was found in the control enclosures (39 ± 2) and in the pondwater controls (39 ± 0). Differences between the ciliates in the natural pond water and the enclosures appeared to be related to a greater concentration of phytoplankton within the enclosures (perhaps resulting from extensive growth of duckweed, Lemna, outside), and higher densities of zooplankters in the pond.

4. The physicochemical environment influenced species richness, total abundance and the number of rare species (27 in Pond II versus 13 in Pond I). Variation in ciliate abundance in Pond I could be explained by the number of days after filling (39%) and enclosure treatment (23%). These two parameters also explained 72% of the variation in species richness in Pond I (46 and 26%, respectively). Sixty‐five per cent of the variation in abundance in Pond II could be explained by the measured parameters: number of days after filling 27%, pH 19%, and nitrate levels 12%. Fifty‐two per cent of the variation in species richness was explained by the environmental parameters, of which pH was the most influential. Species succession was a strong feature of both ponds and its relationship to environmental variables and the presence of other organisms is discussed.

5. Addition of invertebrate predators resulted in higher abundance and higher species richness for a limited time period in one of the ponds – suggesting that differences in foodweb dynamics may influence ciliate community composition.
Effects of a fertility‐reducing baculovirus on sperm numbers and sizes in the Indian Meal Moth, Plodia interpunctella
Authors: Sait S. M. , Gage M. J. G. , Cook P. A.
Published: March 2003

1. A dose‐dependent decrease in male fertility occurs in the Indian Meal Moth, Plodia interpunctella, when sub‐lethally infected with granulovirus during the larval stage.

2. Here, the causes for this decline are investigated by examining eupyrene and apyrene sperm numbers and sizes produced by males across four levels of viral challenge.

3. The results could not explain how reduced male fertility is caused in this host–pathogen interaction. While a reduction in both eupyrene and apyrene sperm numbers from all virus‐treated males was found, this was not significant and neither was there a difference in sperm lengths across the four treatments. There were also no differences in the variances of sperm numbers or lengths between the doses, and no associations between sperm numbers or lengths and body size were found.

4. A significant correlation between eupyrene and apyrene numbers was found, but this was independent of dose. Significant between‐male variance in apyrene sperm lengths was found, indicating that individual males differ in the range of apyrene sperm sizes they produce.

5. It is suggested that further intracellular and behavioural study is needed to identify the causes of the granulovirus‐induced reduction in fertility of P. interpunctella.