bluuebunny/crossref_metadata_2025_split huggingface dataset:
Stream macroinvertebrate communities in a conifer‐afforested catchment in Ireland: relationships to physico‐chemical and biotic factors
Authors: Clenaghan  , Giller  , O’halloran  , Hernan  
Published: March 2003

1. The influence of land use and physico‐chemical factors on stream macroinvertebrates was analysed at fifteen sites over a 2‐year period in a single conifer‐afforested catchment in Ireland, in an area subject to very low levels of atmospheric pollution.2. Macroinvertebrate assemblages were classified using two‐way indicator species analysis into five major groupings that were related to distance from headwaters and land use. Trends in macroinvertebrate community composition were related to changes in physico‐chemical and biotic characteristics of the river and its tributaries using canonical correspondence analysis.3. Local ecological factors (e.g. acid water, moss, shading or agricultural runoff), longitudinal trends in stream physico‐chemistry (related to distance from headwaters, geology and land use) and season (related to life history patterns of the invertebrates) were the explanatory variables of spatio‐temporal patterns in macroinvertebrate community composition in the catchment.4. Spatial variation in macroinvertebrate density, taxon richness, diversity and evenness was investigated in relation to environmental characteristics of the study sites using Spearman’s rank correlation, principal components analysis and stepwise multiple regression. Invertebrate density and richness increased with distance from the headwater and associated increases in pH, water hardness and nutrients. Macroinvertebrate density and richness also increased with increasing moss weight. Invertebrate diversity and evenness increased with shading of the channel.5. The increase in macroinvertebrate density and richness and changes in community composition were particularly marked over a relatively short (1.2 km) distance in one tributary, and were concurrent with a rapid increase in stream pH of 1.7 units.6. Although macroinvertebrate communities at conifer‐afforested sites were not impoverished in the same way as those in some other parts of Europe, they differed from the communities found above and below the plantation. This appeared to be owing to the primary importance of local ecological factors and the effect that the longitudinal position of these forest sites within the river system had on their physico‐chemical and biotic nature.
Surface water–groundwater exchanges in three dimensions on a backwater of the Rhône River
Authors: Dole‐olivier M. ‐J. 
Published: March 2003

1. Hydrological exchange between the surface stream and the hyporheic zone is well documented in the main channel of rivers, especially at the reach scale. Hydrological processes of advection/convection occur at different scales, and in secondary channels of large rivers little is known about these exchanges in the hyporheic zone on a broad scale (i.e. kilometres). This work studied exchanges of water and biota in a secondary channel on a large scale (4 km), using a three‐dimensional framework.2. The exchanges of water were described using physicochemical indicators of surface and groundwaters. Samples of water and biota were taken in three dimensions: (i)verticallyfrom benthic (i.e. 0.20 m below the surface of the substratum) to hyporheic (0.50 m) and deep interstitial (1.0 m) zones; (ii)laterallyfrom the right to the left bank (i.e. right, middle and left positions); and (iii)longitudinallyfrom upstream to downstream (seven stations regularly distributed along the channel).3. The physicochemical indicators clearly revealed hydrological heterogeneity in the longitudinal and vertical dimensions, whereas lateral variability was not significant.4. Spatial distribution of biota exhibited strong longitudinal variations that were not gradual as predicted by an upstream/downstream continuum, but patchy and discontinuous. No significant differences were found between the three positions across the channel.5. Analyses of both physicochemical and faunal data sets produced matched ordination of samples and stations, indicating that interstitial–surface flow relationships appear to be an important governing factor in the distribution of interstitial biota at this broad scale.6. Results are discussed in relation to the hypothetical three‐dimensional models of the hyporheic zone in rivers. Contrasting with other observations on the main channel (where advection/convection patterns are dominated by morphological changes of the river‐bed morphology), it is proposed that water exchanges in backwaters are more likely to be related to local modifications of stream‐bed porosity.
Methane release from stands of water horsetail (Equisetum fluviatile) in a boreal lake
Authors: Hyvönen T. , Ojala A. , Kankaala P. , Martikainen P. J. 
Published: March 2003

Summary1. Annual and diel variations in methane (CH4) release in stands of Equisetum fluviatile were measured from June to November in Lake Pääjärvi, southern Finland, where E. fluviatile is the dominant emergent macrophyte. An estimate of total annual release of CH4 from stands of E. fluviatile in this lake was also made. Diel variation was measured twice (June and August), whereas measurements for annual variation were performed monthly. The hypothesis that a relationship exists between the productivity of stands and CH4 release was also tested, whereupon net ecosystem exchange (NEE) of CO2 as well as standing stock of E. fluviatile were determined, in addition to simultaneous recordings of air temperature and solar radiation.2. Seasonal variations in CH4 release were pronounced, with the highest release rate of 813 mg m–2 day–1 measured in July and the lowest 6.5 mg m–2 day–1 in November, when the shoreline was already frozen.3. Methane release rates were strongly correlated with mean air temperature in the measuring chambers and with total solar radiation. There was no significant correlation between the instantaneous radiation and CH4 release rates.4. The seasonal patterns of CH4 release and NEE of CO2 resembled each other, except in July when NEE suddenly dropped. The decrease in NEE coincided with the highest CH4 release rate measured and the highest temperature during the measuring period, i.e. 32 °C outside and 37 °C inside the chamber. Excluding this date, daily CH4 release was strongly correlated with NEE (r2 = 0.971).5. No diel changes in CH4 release rates were detected. In June and August the maximum release rates were 11.4 and 16.8 mg CH4 m–2 h–1, respectively.6. The standing stock of E. fluviatile at different times of the growing season was not correlated with CH4 efflux; the CH4 release rates could be related neither to the number of shoots, i.e. sufficient conduits for gas transport were always present, nor to the shoot biomass in the measuring chambers.7. For an estimate of the annual release, the monthly values measured at noon were integrated over the entire growing season; this resulted in 43.7 g CH4 m–2 for the annual emission. The total annual emission of CH4 from the area covered with E. fluviatile in Lake Pääjärvi was calculated to be ≈ 5000 kg.8. Significant amounts of CH4 are released from stands of E. fluviatile in boreal lakes. The CH4 release rate follows a seasonal pattern but there is no diel pattern. Methane release rate can be related to temperature, solar radiation and NEE of CO2, but not to the standing stock of E. fluviatile or the number of shoots.
Breeding in the crayfish,Austropotamobius pallipes:mating patterns, mate choice and intermale competition
Authors: Villanelli Fabio , Gherardi Francesca 
Published: March 2003

Summary1. The breeding behaviour of the white‐clawed crayfish, Austropotamobius pallipes, which is in decline throughout Europe, was analysed.2. Observations and experiments focused on: (i) several aspects of mating behaviour, showing the primary role of the female during courtship, the patterns of mature male receptivity and the possible existence of a mating stimulus produced by either a mating pair or a receptive female; (ii) the potential for mate choice either by males (males were not choosy, mating with the first receptive female they met) or by females (that rejected the smallest males and males with only one cheliped) and (iii) intermale fighting before copulation (larger males copulated more often, with the exception of some ’sneakers‘).3. Sperm competition occurred when a new male was presented with a female after a previous male‘s spermatophore had been deposited; the new male cleaned the rival male‘s spermatophore by feeding on it before copulation. This behaviour has also been observed in some pseudoscorpions, millipedes and collembolans, but always in cases where the spermatophore is deposited on the substratum.Introduction
Temporal and spatial variation in the epilithic biofilm of an acid stream
Authors: Ledger Mark E. , Hildrew Alan G. 
Published: March 2003

Summary1. The extent of spatial and temporal variation, and the taxonomic and biochemical composition of epilithic biofilm were determined in a first‐order, acidic stream in the Ashdown Forest, southern England.2. The biofilm had an autotrophic component consisting of acidobiontic diatoms, small coccoid green algae, zygnematacean filamentous green algae, and a heterotrophic component of bacteria. Fungi were absent.3. Diatoms were the dominant algal group in spring. These were succeeded by coccoid green algae in summer. Synchronous variation existed between algae and bacteria, suggesting a strong link between the two groups.4. Quantitative community descriptors (algal and bacterial densities, chlorophyll, ash‐free dry matter) and biochemical descriptors (protein, lipid and carbohydrate content) of biofilm presented a consistent temporal pattern in which biofilm biomass peaked in spring and early summer and decreased subsequently.5. Stepwise multiple regression revealed that temporal variation in the quantity of biofilm coating substrata was primarily associated with photosynthetically active radiation. The quantity of biofilm coating the upper surfaces of substrata increased with substratum particle size (small stones, large stones and bedrock). Smothering of algae by fine particulate organic matter, proximal shading by bed sediments, and physical disturbance are proposed as mechanisms that brought about the pattern.
Interactive effects of pH and leaf litter on a shredder, the scirtid beetle, Helodes pulchella, inhabiting tree‐holes
Authors: Paradise Christopher J. , Kuhn Kristen L. 
Published: March 2003

1. Scirtid beetles (Coleoptera: Scirtidae) are common inhabitants of water‐filled treeholes and interact with other detritivores in a processing chain commensalism. The strength of the commensalism is determined by resource quantity and the organisms involved have different tolerances to low pH. To determine the effects and interactions of resource quantity and pH on one of these leaf‐shredding scirtid beetles, Helodes pulchella (Guerin), leaf litter and pH were varied independently in experimental microcosms which mimic treehole habitats.2. Helodes pulchella growth was affected by both resources and pH in two similar experiments conducted in different years. Scirtid larvae grew more slowly in low resource treatments and also grew more slowly in low pH treatments. Scirtid survival was not affected by pH, but was lower in high resource microcosms in the 1997 experiment. Consumption of leaf litter was much higher in high resource microcosms, even though not all leaf litter was consumed in low leaf litter treatments.3. Thus, water chemistry and leaf litter quantity could have strong effects on resource availability through effects on these beetle facilitators, in turn affecting other insects living in these detritus‐based communities.
Mixotrophic cryptophytes and their predators in the Dry Valley lakes of Antarctica
Authors: Roberts Emily C. , Laybourn‐Parry Johanna 
Published: March 2003

1. The ingestion rates of planktonic, mixotrophic cryptophytes in two perennially ice‐covered Antarctic lakes in the McMurdo Dry Valleys, were investigated during the summer of 1997–1998.2. In Lake Fryxell, which is meromictic, ingestion rates increased with depth in November and were highest in a cryptophyte maximum close to the chemocline. In Lake Hoare, which is unstratified and freshwater, there was no significant difference in ingestion rates with depth. In both lakes, the highest ingestion rates occurred in early summer, decreasing in December and January. Ingestion rates varied between 0.2 bacteria cell−1 h−1 and 3.6 bacteria cell−1 h−1.3. During November, mixotrophic cryptophytes removed up to 13% of bacterial biomass day−1 and had a greater grazing impact than heterotrophic nanoflagellates (HNAN). As summer progressed, the grazing impact of cryptophytes and HNAN became similar.4. The maximum depth of cryptophytes in Lake Fryxell was predated by a population of the ciliate Plagiocampa. Plagiocampa had an ingestion rate of 0.13–0.19 cryptophytes cell−1 h−1. The grazing impact on the cryptophyte community was insignificant. However, the ciliate appeared to be indulging in temporary mixotrophy, sequestering the cryptophytes for a number of weeks before digesting them.5. It is suggested that mixotrophy is an important survival strategy in the extreme lake ecosystems of the McMurdo Dry Valleys.
Predicting the structure and diversity of young‐of‐the‐year fish assemblages in large rivers
Authors: Gozlan R. E. , Mastrorillo S. , Copp G. H. , Lek S. 
Published: March 2003

1. Interactions between environmental variables and 0+ fish assemblages in the upper River Garonne (France) were quantified during late August 1995.2. The abundance and diversity of the fish assemblages in floodplain channels were modelled using Artificial Neural Network (ANN) analysis and nine variables: the abundance of the six dominant species, fish specific richness, overall abundance of 0+ fish and the Shannon index of diversity. Multiple regression analysis was also used to assess ANN performance.3. Using 596 samples, correlation coefficients (r adjusted) between observed and estimated values of the nine dependent parameters were all highly significant (P < 0.01). Expected values from the tested data were significantly related to the observed values. The correlation coefficient between observed and estimated values (r) varied from 0.70 to 0.85.4. The ANN provided a high quality prediction, despite the complex nature of the relationship between microhabitat composition and fish abundance.5. Garson’s algorithm was used to provide the explanatory power needed in ecology when using black‐box models. Parameters contained in the models (i.e. weighting) were used to determine the relative contributions of explanatory variables and thus to ascertain the structure of fish communities.
Effects of artificial ultraviolet‐B radiation on experimental aquatic microcosms
Authors: De Lange Hendrika J. , Verschoor Antonie M. , Gylstra Ronald , Cuppen Jan G. M. , Van Donk Ellen 
Published: March 2003

1. The effects of prolonged ultraviolet‐B (UVB) radiation on freshwater communities were studied in indoor microcosms (600 L) with artificial light sources, simulating a clear, shallow, mesotrophic aquatic ecosystem. A range of six intensities (in duplicate) of UVB radiation, ranging from 0 (control) to 9.56 kJ m−2 day−1 at the water surface, was applied for 8 weeks. The UVB radiation levels, attenuation, shading and scattering were comparable to those in Dutch shallow freshwater systems. Physical, chemical and biological variables were monitored weekly.2. The UVB treatment did not affect the abundance, species composition or biovolume of the phytoplankton or zooplankton communities, nor did it affect the periphyton or the macroinvertebrate community. A few species showed a significant response on some of the sampling dates, but there was no negative UVB effect at the community level. Overall, the ecosystems in the microcosms were not affected by the UVB treatment.3. In a bio‐assay, a laboratory clone of Daphnia pulex, not subjected to UVB radiation, was fed with seston from the microcosms. Daphnia pulex feeding on seston from the control microcosms grew faster, had better survival and better reproduction than D. pulex feeding on seston from the UVB treated microcosms. The phytoplankton–zooplankton interaction may have been influenced by the UVB treatment.4. The dissolved oxygen content (DOC) concentrations in the microcosms were around 5 mg L−1. The DOC levels in Dutch systems rarely fall below 10 mg L−1. This might provide sufficient protection against the detrimental effects of increased UVB radiation.
Foraging strategies and growth inhibition in five daphnids feeding on mixtures of a toxic cyanobacterium and a green alga
Authors: DeMott William R. 
Published: March 2003

1. Laboratory experiments were used to study the feeding, growth and reproduction of five daphnids in mixtures of a toxic cyanobacterium, Microcystis aeruginosa, and a green alga, Scenedesmus acutus. The mixtures included 0%, 20%, 50%, 80% and 100% Microcystis with a total food concentration of 0.5 mg C L−−1 in each treatment. The feeding rate was measured after 1 and 24 h of acclimatization to the mixtures.2. Toxic Microcystis inhibited feeding in all the species, but they exhibited an unexpected diversity and complexity in the pattern of feeding inhibition. Daphnia magna exhibited the strongest inhibition of feeding after 1 h of exposure to toxic food, but had substantially recovered after 24 h in the same mixtures. This pattern of inhibition and recovery may balance the benefits of reduced ingestion of toxin with the disadvantage of a reduced energy intake.3. All five daphnids grew quickly in the Scenedesmus control, whereas growth and reproduction declined with an increasing proportion of the toxic alga in the diet. Daphnia pulicaria showed the least inhibition of growth and reproduction, D. pulex showed the strongest inhibition and the three remaining species exhibited intermediate sensitivity.4. Estimates of gross growth efficiency (GGE; growth/ingestion) provided a means for discriminating between the effects of feeding inhibition and direct toxicity on zooplankton growth. Daphnia pulex exhibited a sharp decline in GGE, suggesting that growth inhibition was a result of both feeding inhibition and direct toxicity. In contrast, D. magna exhibited a nearly constant GGE, indicating that feeding inhibition accounted for its decline in growth. However, two Daphnia species (i.e. D. pulicaria and D. galeata) exhibited improbable increases in GGE with toxic cyanobacteria, suggesting that their feeding rates were underestimated.Growth assays with sensitive and resistant zooplankton species are proposed for testing the potential impacts toxic cyanobacteria in lakes.
Distribution of recreational boating across lakes: do landscape variables affect recreational use?
Authors: Reed‐Andersen TarA. , Bennett Elena M. , Jorgensen Bradley S. , Lauster George , Lewis David Bruce , Nowacek David , Riera Joan L. , Sanderson Beth L. , Stedman Richard 
Published: March 2003

1. Because people impact lake ecosystems, it is important to consider factors influencing the human use of freshwater resources. We investigated the influence of the landscape position, as well as lake area, recreational facilities, and distance to highways and urban centres, on lake use by boaters in the Northern Highland Lake District of Wisconsin, U.S.A.2. In aerial surveys of ninety‐nine randomly selected lakes, we did not see boats on over half of the lakes. Of the lakes with boats, we found a strong correlation between the number of boats and lake area. Recreational boats tended to be found on large, accessible lakes with good boating facilities. Boats were not seen on small, stained lakes with few recreational facilities.3. Regression models showed that lake size and landscape position explained 63% of the variability in the average number of boats per lake and landscape position explained 24% of the variability in boat density on all ninety‐nine lakes. Social variables representing the quality of boating facilities and the perception of good fishing explained 70% of the variability in number of boats per lake and 54% of the variation in boat density on all lakes. A combined model using both physical and social variables increased the explanatory power for both number and density. Lake use by boaters was correlated with landscape position, the quality of fishing and the availability of recreational facilities. When the analysis was restricted to the forty‐six lakes where boats were found, only the availability of recreational facilities proved a significant predictor of boat density.4. Our results suggest that lake choice by recreational boaters may be best predicted by a combination of the location of a lake in a regional hydrologic landscape, and considerations of available facilities and perceptions regarding fishing.
Integration of lakes and streams in a landscape perspective: the importance of material processing on spatial patterns and temporal coherence
Authors: Kling George W. , Kipphut George W. , Miller Michael M. , O'Brien W. JohN. 
Published: March 2003

1. We studied the spatial and temporal patterns of change in a suite of twenty‐one chemical and biological variables in a lake district in arctic Alaska, U.S.A. The study included fourteen stream sites and ten lake sites, nine of which were in a direct series of surface drainage. All twenty‐four sites were sampled between one and five times a year from 1991 to 1997.2. Stream sites tended to have higher values of major anions and cations than the lake sites, while the lake sites had higher values of particulate carbon, nitrogen, phosphorous and chlorophyll a. There were consistent and statistically significant differences in concentrations of variables measured at the inlet versus the outlet of lakes, and in variables measured at upstream versus downstream sites in the stream reaches which connect the lakes. In‐lake processing tended to consume alkalinity, conductivity, H+, DIC, Ca2+, Mg2+, CO2, CH4, and NO3–, and produce K+ and dissolved organic carbon (DOC). In‐stream processing resulted in the opposite trends (e.g. consumption of K+ and DOC), and the magnitudes of change were often similar to those measured in the lakes but with the opposite sign.3. Observed spatial patterns in the study lakes included mean concentrations of variables which increased, decreased or were constant along the lake chain from high to low altitude in the catchment (stream sites showed no spatial patterns with any variables). The strongest spatial patterns were of increasing conductivity, Ca2+, Mg2+, alkalinity, dissolved inorganic carbon and pH with lake chain number (high to low altitude in the basin). These patterns were partly determined by the effect of increasing catchment area feeding into lakes further downslope, and partly by the systematic processing of materials in lakes and in the stream segments between lakes.4. Synchrony (the temporal coherence or correlation of response) of variables across all lakes ranged from 0.18 for particulate phosphorus to 0.90 for Mg2+ the average synchrony for all twenty‐one variables was 0.50. The synchronous behaviour of lake pairs was primarily related to the spatial location or proximity of the lakes for all variables taken together and for many individual variables, and secondarily, to the catchment to lake area ratio and the water residence time.5. These results illustrate that, over small geographic areas, and somewhat independent of lake or stream morphometry, the consistent and directional (downslope) processing of materials helps produce spatial patterns which are coherent over time for many limnological variables. We combine concepts from stream, lake and landscape ecology, and develop a conceptual view of landscape mass balance. This view highlights that the integration of material processing in both lakes and rivers is critical for understanding the structure and function of surface waters, especially from a landscape perspective.