bluuebunny/crossref_metadata_2025_split huggingface dataset:
Landscape approaches to the analysis of aquatic ecosystems
Authors: JOHNSON LUCINDA , GAGE STUART 
Published: November 2003

1. In the mid‐1970s, Hynes (1975) wrote eloquently about the complex interactions between aquatic and terrestrial systems. Central theories in stream ecology developed thereafter have dealt with the longitudinal flow of energy, materials and organisms in streams, and, with the exception of the flood pulse concept (Junk, Bayley & Sparks, 1989), have largely ignored areas outside the riparian zone. The structure of the upland and activities occurring there play a more important part than previously recognized in regulating community structure and ecosystem processes in streams.2. These new perspectives are made possible by developments in hierarchy theory, patch dynamics, and the refinement of tools used to quantify spatial and temporal heterogeneity.3. Geographical information systems (GIS), image processing technology and spatial statistical techniques allow quantitative assessment of lateral, longitudinal and vertical components of the landscape that interact at several spatial and temporal scales to influence streams. When GIS is used in concert with geostatistics, multivariate statistics, or landscape models, complex relationships can be elucidated and predicted.4. To a certain extent, the tools discussed above have only automated functions that were previously performed manually. This suite of tools has improved the ability of aquatic ecologists to examine relationships and test theories over larger, more heterogeneous regions than were previously possible.5. At the local, state and federal level, management and regulatory frameworks are currently being re‐evaluated to incorporate this new perspective in resource management and policy decision making.6. We will discuss current and future trends in technologies and tools used for aquatic ecosystem research, and the use of techniques as they are applied in these regional assessments are also discussed.
Focusing environmental management budgets on non‐linear system responses: potential for significant improvements to freshwater ecosystems
Authors: STATZNER BERNHARD , CAPRA HERVÉ , HIGLER LAMBERTUS , ROUX A. 
Published: November 2003

1. The non‐linear responses of environmental systems to changes imposed upon them is well known to scientists. Environmental managers rarely act accordingly, however, because of communication problems, a lack of imagination and various other constraints. Therefore, we illustrate such non‐linear responses to demonstrate that gains in efficiency (benefit per money spent) can be made by integrating these characteristics into decision making.2. Identifying three measures that are currently the focus of large freshwater management budgets (waste‐water treatment, riparian buffer strips and discharge allocations to regulated rivers), we relate the costs of these measures to the environmental improvements achievable in running waters. For each of these measures, the environmental improvement achieved per currency unit significantly decreases with an increase in total money spent.3. Traditional environmental management ignores this system behaviour because it invests important parts of budgets in a particular measure before focusing on the next among other measures. We therefore advocate alternating investments in that measure which achieves the greatest environmental improvement in the next possible investment step. Compared with traditional management, this alternating decision‐making strategy will achieve greater environmental improvements for a given total budget.
Influence of ultraviolet‐B radiation on the drift response of stream invertebrates
Authors: KIFFNEY PETER , LITTLE EDWARD , CLEMENTS WILLIAM 
Published: November 2003

1. Recent studies have shown that ultraviolet (UV) radiation (280–400 nm) has increased by ≈ 8% in temperate regions over the past decade, but little effort has been devoted to understanding the ecological effects on temperate ecosystems. This research examined the effects of artificial ultraviolet‐B (UVB; 280–320 nm) radiation on the drift response of immature stream insects in laboratory microcosms.2. Two experiments involved natural populations of stream invertebrates, collected from the Cache la Poudre River (September 1994) and the Arkansas River (October 1995) in Colorado. UVB lamps were turned on from 10.00 to 14.00 h each day, and drifting animals were collected on days 1, 3, 5 and 7 during the exposure period. Levels of artificial UVB used in these experiments were similar to levels that stream organisms experience during clear, mid‐day conditions at Fort Collins, Colorado (longitude 105°30′; latitude 40°35′).3. Drift was significantly higher in microcosms exposed to UVB than in controls and was dominated by Baetis sp. (Ephemeroptera: Baetidae), Trichoptera (caddisflies) and Simulium sp. (Diptera: Simuliidae). The increased drift of some stream invertebrates in UVB‐exposed streams may be a behavioural response and/or a result of injury.4. Stream organisms may be particularly sensitive to predicted increases in UV radiation, because streams are generally shallow with clear water. As a result of this potential sensitivity, we recommend that research be directed to understanding the ecological effects of UV radiation on these habitats.
Sedimentation in a large lake: the importance of fluctuations in water level
Authors: GIBSON C.E. , GUILLOT J. 
Published: November 2003

1. A sediment trap study was conducted in the central basin of Lower Lough Erne, Northern Ireland.2. The material caught was low in organic matter, ash weight was 77% of dry weight on average.3. Mass deposition of material was shown to be correlated with lake water level. When lake water level fell or rose above the middle range, the amount of material caught by the trap increased markedly. The effect was exaggerated by an unusually dry summer in 1995 which caused abnormally low water levels in the lake.4. Comparison of Erne data with Windermere shows similar deposition rate of many substances, but the deposition rate of iron is thirteen times higher in Erne than in Windermere, and iron made up 39% of the ash weight in the Erne trap data.5. Only 17% of the silica removed from the water column during diatom growth was recovered in the trap over the same time period.6. Trap data are compared with historical data for sediment deposition and the implications of sediment focusing are discussed.
Food selectivity and diel vertical distribution of Chaoborus edulis (Diptera, Chaoboridae) in Lake Malawi
Authors: IRVINE KENNETH 
Published: November 2003

1. Diel diet and vertical distribution patterns of the larval instars of Chaoborus edulis were studied in deep water near the central part of Lake Malawi, Africa.2. First instar larvae contained very little food in their crops and probably depended on reserves from the egg. Second, third and fourth instars fed on zooplankton and were size‐selective in their feeding. The mean size of prey eaten by the three instars was significantly different from each other, with larger instars feeding on larger prey. Smallest available prey was selected against and the upper size of prey was probably constrained by larval gape. Nauplii were not found in any of several thousand larvae examined. Phytoplankton did not form a significant part of the diet.3. There was a progressive and related increase in diel periodicity in feeding and vertical migrations of successive instar stages. Fourth instars migrated particularly large distances. Such migrations removed them from their zooplankton food supply but avoided predators. A refuge from predators is probably found in or near the permanent zero oxygen boundary, at depths greater than 200 m.
Field experiments on the mobility of benthic invertebrates in a southern English stream
Authors: WINTERBOTTOM JULIE , ORTON STUART , HILDREW ALAN 
Published: November 2003

1. In each of twenty‐six week‐long experiments, the colonization by macroinvertebrates of boxes of natural sediment in a stony stream was measured. The experiments took place between February and November 1992 and environmental conditions prevailing during the weeks (particularly discharge and temperature) differed widely.2. Colonization rate also varied widely between the weekly experiments and was sensitive to discharge, temperature and background benthic density, depending on the taxa considered.3. A ‘mobility index’ measured colonization rate independently of background benthic density. This index was most strongly and positively correlated with discharge for the abundant stonefly Leuctra nigra, the net‐spinning caddis Plectrocnemia conspersa and the Chironomidae, perhaps indicating that their mobility is physically driven by the influence of flow on drift.4. Mobility in a second stonefly (Nemurella pictetii) was greatest in summer, when flows were low but temperature was high. Peak mobility in this species occurred during an ochreous bloom on the stream bed. It is likely the mobility of N. pictetii is more active than the other taxa.5. There were thus differences among taxa in their mobility at baseflow and in their susceptibility to flow fluctuations. The population consequences of differences in mobility among taxa are discussed.
Predators can induce swarming behaviour and locomotory responses in Daphnia
Authors: PIJANOWSKA JOANNA , KOWALCZEWSKI ANDRZEJ 
Published: November 2003

1. Exposure to chemical cues released by fish induced a tendency to form and maintain aggregations in two Daphnia clones originating from habitats inhabited by fish (and invertebrate predators), while Daphnia from a clone originating from a fishless habitat did not aggregate in response to fish cues.2. Daphnia from one of the two clones responsive to fish cues, also aggregated in response to chemical cues released by invertebrate predators or to a substance released from homogenized Daphnia.3. Chemical cues released by predators and the substance released from homogenized conspecifics induced a significant decrease in Daphnia’s swimming speed and an increased readiness to perform a somersaulting escape behaviour, especially in response to light cues.
Nutrient transfer between parafluvial interstitial water and river water: influence of gravel bar heterogeneity
Authors: CLARET CÉCILE , MARMONIER PIERRE , BOISSIER JEAN‐MICHEL , FONTVIEILLE DOMINIQUE , BLANC PAUL 
Published: November 2003

1. Nutrient concentrations in interstitial water springs at the downstream ends of two gravel bars in the River Rhône were measured in order to estimate the importance of nutrient inputs [nitrate, dissolved organic carbon (DOC), biodegradable and refractory fractions of DOC] from the parafluvial zone (saturated sediments adjacent to the wetted channel, i.e. interstitial habitats of gravel bars) to the river as well as seasonal variations in these inputs.2. Compared with surface water, parafluvial water had lower concentrations of DOC (especially the refractory fraction) and generally higher concentrations of nitrate. These differences were at their lowest during winter.3. The influence of gravel bar geomorphological heterogeneity (grain size and spatial distribution of fine sediments) on parafluvial inputs was studied in terms of nutrient content and biofilm characteristics along transects across the gravel bars.4. A gravel bar located in a stable area of the river had low transversal heterogeneity and acted as a sink for DOC and as a source of nitrate. The low fine sediment content and the high oxygenation of interstitial water must have enabled aerobic processes such as mineralization of organic matter and nitrification to occur.5. In contrast, gravel bars located in a degradation zone of the river had a spatially variable structure, acting as a sink for DOC and nitrate because localized accumulation of fine sediment and ensuing hypoxic conditions induced anaerobic processes such as denitrification.6. This study highlights the important influence of geomorphological heterogeneity in gravel bars for nutrient transformations as well as nutrient exchanges between parafluvial interstitial systems and the adjacent river over a seasonal cycle.
Reproductive traits, habitat use and templet theory: a synthesis of world‐wide data on aquatic insects
Authors: STATZNER BERNHARD , HOPPENHAUS KERSTIN , ARENS MARIE‐FRANCOISE , RICHOUX PHILIPPE 
Published: November 2003

1. Using world‐wide data on the reproductive biology of 131 species (in eight orders) of aquatic insects, we used multivariate analyses to examine: (i) relationships among reproductive traits determining life cycle, fecundity, morphology, behaviour and physiology; (ii) relationships among traits determining spatial and temporal habitat characteristics at different scales; and (iii) the relationship between reproductive and habitat‐use traits. This provided a test of predictions of the habitat templet concept on trends of species traits along gradients of habitat heterogeneity.2. The major trends observed in the relationships among reproductive traits were that larger females had larger eggs, which were more vulnerable to perturbations such as droughts and often laid in cocoons. In addition, they laid the eggs in larger numbers of smaller clutches than smaller females. Other traits (e.g. egg number or incubation time) did not show clear trends.3. Females that deposited eggs at sites of low local temporal heterogeneity (within plants) used, at the same time, gross habitats of high temporal heterogeneity (temporary waters). In contrast, traits in habitat use hardly differed on well‐known gradients of temporal heterogeneity along running waters (from source to estuary). The number of habitat units used by ovipositing females generally increased with the spatial scale considered, most species oviposited in a single small habitat unit but in several gross habitats.4. A significant (P < 0.01) relationship between traits in reproduction and habitat use demonstrated that habitat acted as a templet for reproductive strategies. This relationship was dominated by larger females having larger, unattached eggs which were more vulnerable to droughts and were oviposited in temporally more stable small‐scale habitats (within wood or macrophytes, or within cocoons spun by the female) but more unstable large‐scale habitats (primarily temporary waters). Thus, only on the small habitat scale did some of our observations correspond to the predictions of the habitat templet concept (e.g. larger size or higher vulnerability in more stable habitats). However, many species had traits in reproduction that did not show trends as predicted by the concept.5. This and other recent studies of the relationships between traits of freshwater organisms and the heterogeneity of their habitats have shown that habitat acts as a templet for species life history traits. However, many of the details observed in these studies did not correspond to predictions of the templet concept because of trade‐offs among the traits and scale problems in the description of habitat heterogeneity. Therefore, future studies should focus on groups of organisms which are as similar as possible in the trade‐offs among their species traits and on the potential relationships of habitat heterogeneity across multiple scales.
Longitudinal patterns of organic matter transport and turnover along a New Zealand grassland river
Authors: YOUNG ROGER , HURYN ALEXANDER 
Published: November 2003

1. We determined the longitudinal pattern of organic matter concentration, quality, size composition and spiralling length along a 310‐km grassland river system (Taieri River, New Zealand).2. Organic seston concentration (0.24–4.05 mg ash‐free dry mass (AFDM) l–1) and dissolved organic carbon (DOC) concentration (2.3–5.7 mg C l–1) showed no obvious longitudinal patterns. In contrast, there was a significant downstream increase in inorganic seston concentration (0.13–13.73 mg ash l–1), presumably because of a downstream increase in the proportion of the catchment developed for agriculture.3. Although there was a trend toward increasing particle size in the first 25 km of the river continuum, organic seston was primarily composed of ultrafine particles (0.6–30 μm) at all study sites. The ratio of coarse (> 250 μm) to ultrafine organic seston decreased logarithmically down the continuum. Organic content generally decreased with particle size. Ultrafine particles, however, had significantly higher organic fractions than fine (60–100 μm) and very fine (30–60 μm) particles.4. Daily organic carbon turnover length ranged from 10 to 98 km and increased downstream. This is consistent with other studies along river continua and suggests that organic carbon turnover length is largely controlled by the relationship between channel dimensions and discharge, rather than the presence of specific retention devices.5. Concentrations and nutritional quality of organic seston and concentrations of DOC were highest in an unconstrained floodplain reach in the upper river. These data suggest that new material enters the river channel in this reach, potentially providing an important energy source for the river community downstream. The effect of this reach on the longitudinal pattern of organic matter concentration and quality emphasizes how changes in channel form can alter river ecosystem structure and function.
Predation on meiobenthic assemblages: resource use of a tanypod guild (Chironomidae, Diptera) in a gravel stream
Authors: SCHMID P.E. , SCHMID‐ARAYA J.M. 
Published: November 2003

1. Three predatory chironomid species constituted numerically 8.8% (± 95% CL 2.2) of the macro‐ and meiobenthic community at the sediment surface and in the hyporheic zone of Oberer Seebach, a gravel stream in Lower Austria. Larvae of Thienemannimyia geijskesi (Goetghebuer) and Nilotanypus dubius (Meigen) occurred in higher densities in sediment depths between 10 and 40 cm, whereas Conchapelopia pallidula (Meigen) achieved higher densities at the sediment surface. The three species completed one generation in a year.2. A total of ninety‐seven prey species and instars were identified by gut analyses, of which forty‐one benthic rotifer species constituted 69.5% of individuals and twenty‐three chironomid species and their instars, 22.9%. The three tanypod species showed shifts from mainly rotifer species in early instars to chironomids and diverse other meio‐ and macrofaunal taxa in later instars. Rather than shifting towards larger prey sizes, growing predators expanded their upper size thresholds and continued to include smaller prey species in their diet. The extent to which tanypod instars fed on similar prey size classes declined with increasing larval size. Predation by tanypods amounted to 2.2% (± 95% CL 0.1) of the combined prey densities and prey consumption averaged 1.32 (bootstrap 95% CL 1.26–1.39) individuals per predator individual.3. Preferences for microhabitat flow differed between predator species and in the prey assemblage. Prey densities and densities of T. geijskesi and C. pallidula were highest in pool areas, whereas N. dubius achieved high densities in riffle sites.4. Tanypod larvae fed non‐selectively among prey types. To test the significance of observed size(instar)‐specific spatial and dietary overlap values amongst tanypod species, simulations were generated from random models for pairs of intra‐ and interspecific associations of individuals and groups of prey and predator species. Groups and individuals of tanypod instars fed near randomly on groups of prey types and a high proportion (P > 0.60) of prey individuals are quasi‐randomly chosen by tanypods in those patches. Tanypod instar‐pairs did not show a sustained trophic resource partitioning in time, thus reducing the degree of competitive interactions for food in this predator guild. Spatially segregated and non‐segregated tanypod instars formed random aggregations independent of each other at different flow microhabitats.5. Species‐rich prey assemblages such as benthic rotifers and larval chironomids increased the probability of non‐selective feeding upon a wide spectrum of prey species by tanypods. Prey choice was governed by prey availability and tanypod individuals fed on many species at rather even proportions independent of each other.
Development and application of a nutrient‐diffusing bioassay for large rivers
Authors: SCRIMGEOUR GARRY , CHAMBERS PATRICIA 
Published: November 2003

1. Laboratory and field experiments were performed to develop and then apply a nutrient‐diffusing substratum (NDS) design suitable for use in large, fast‐flowing rivers.2. Initial laboratory experiments quantified diffusion of PO4 and NO3 from new and previously used clay pots, which were soaked in deionized distilled water. Mean release rates initially exceeded 2.4 and 725 μmol l–1 day–1 P and 0.22 and 18 μmol l–1 day–1 N from new and used pots, respectively, but declined rapidly with increasing time spent in deionized distilled water and were below detectable levels after about 18 and 29 days, respectively.3. A phosphorus (P) dose–response experiment in a P‐limited reach of the Athabasca River, Alberta, Canada showed that epilithic biomass and macroinvertebrate density on NDS increased with increasing concentrations of KH2PO4 up to about 0.5 m. Beyond this threshold, biomasses and densities were unaffected by initial KH2PO4 concentration. Coefficients of variation of epilithic biomass estimates declined with increasing KH2PO4 whereas invertebrate density appeared to be unaffected by KH2PO4 levels.4. Release rates of both P and N from NDS filled with 0.5 m KH2PO4 or 0.5 m NaNO3 declined at a log‐negative rate from about 5000 μmol N‐NO3 l–1 day–1 and 3500 μmolP‐PO4 l–1 day–1 on day 2, to 200 μmol l–1 day–1 for both N and P on day 32.5. After development, we used the diffusing substrata to identify spatial patterns in nutrient limitation at seven sites along a 120 km reach in the Athabasca River, that receives two known point‐source nutrient inputs. NDS consisting of N, P, N + P and unenriched controls were attached to the river bottom for 22–23 days and then retrieved and sampled for epilithic chlorophyll a. Physicochemical parameters and epilithic biomasses on upper stone surfaces were also quantified when NDS were deployed and retrieved from each site.6. Sites located immediately downstream of the two point source inputs had higher water column concentrations of PO4 and epilithic biomasses than the site immediately upstream; epilithic biomass was positively related to PO4 in the late autumn (r2= 0.58) but not in early autumn. Sites located immediately below nutrient inputs were not nutrient‐limited, whereas upstream reference sites were P‐limited.