bluuebunny/crossref_metadata_2025_split huggingface dataset:
Microbial respiration within a floodplain aquifer of a large gravel‐bed river
Authors: Craft James A. , Stanford Jack A. , Pusch Martin 
Published: March 2003

1. Aerobic respiration, productivity and the carbon turnover rate of microbial biofilms were determined at hyporheic and phreatic sites in the Kalispell Valley alluvial aquifer along a transect extending 3.9 km laterally from the main channel of the Flathead River, a sixth order river in Montana (U.S.A.). The effect of experimentally increasing bioavailable organic carbon (acetate) on the respiration rate of biofilms in this carbon‐poor [dissolved organic carbon (DOC) < 2 mg L−1] aquifer was also measured.2. Chambers containing natural substratum were placed in‐situ and allowed to colonise for 20 weeks. After 4, 12 and 20 weeks, they were taken to the laboratory where oxygen flux was measured in a computer‐controlled, flow‐through respirometry system.3. Respiration ranged from 0.01 to 0.33 mg O2 dm−3 h−1 across sites, with means ranging from 0.10 to 0.17 mg O2 dm−3 h−1. Productivity estimates ranged from 0.18 to 0.32 mg C dm−3 day−1 (mean 0.25, SE 0.03). The total organic carbon (TOC) of the microbial biofilms ranged from 18.2 to 29.7 mg C dm−3. Turnover rate ranged from 3.2 to 5.6 year−1 with a mean of 4.2 year−1.4. At the hyporheic site very close to the river, respiration did not significantly increase when samples were supplemented with labile carbon. Respiration increased with increasing DOC addition at hyporheic sites more distant from the river, suggesting a carbon‐limitation gradient within the hyporheic zone. Microbes at the phreatic site did not respond to increasing DOC addition, suggesting that the phreatic biofilm is adapted to low carbon availability.5. Comparing the volume of the alluvial aquifer (about 0.7 km3) to that of the river benthic sediments (to 0.25 m depth, which amounts to about 1.6 × 10−4 km3) within the Flathead Valley, leads to the conclusion that interstitial microbial productivity is orders of magnitude greater than benthic productivity. Alluvial aquifers are often voluminous and microbial production is an enormous component of ecosystem production in rivers such as the Flathead.
Zooplankton biomass and community structure in a Danube River floodplain system: effects of hydrology
Authors: BARANYI CHRISTIAN , HEIN T. , HOLAREK C. , KECKEIS S. , SCHIEMER F. 
Published: March 2003

1. Zooplankton density and biomass was examined in a Danube River floodplain section with highly variable hydrological dynamics. Temporal patterns were analysed to assess the effects of hydrological conditions on zooplankton community structure and the differential response of the two major zooplankton taxa, rotifers and crustaceans.2. Calculated floodplain water age was used as an integrated parameter describing hydrological conditions and connectivity.3. Total zooplankton biomass, crustacean biomass and crustacean species number were significantly positively related to water age. Rotifer biomass followed a hump‐shaped relationship with water age, and rotifer species number decreased with increasing water age.4. Rotifers dominated the community in periods of low to medium water ages. In periods of higher water ages the community was dominated by crustaceans.5. We propose that the hydrological regime of floodplains is crucial for zooplankton biomass patterns and succession, through the alternation of washing‐out effects, taxon‐specific potential of reproduction and biological interactions. Flood events and high water levels reset the community to an early successional phase.
Development and evaluation of a diatom‐conductivity model from lakes in West Greenland
Authors: RYVES D. B. , MCGOWAN S. , ANDERSON N. J. 
Published: March 2003

1. The area around Kangerlussuaq (Søndre Strømfjord; West Greenland, 67°N 51°W) contains thousands of lakes ranging from coastal, dilute (conductivity < 30 μS cm–1) oligotrophic systems to subsaline (∼4000 μS cm–1), closed basin lakes close to the ice sheet margin. In closed basins, salinity (or conductivity) is often a proxy for effective moisture, and thus palaeorecords of lake conductivity can provide valuable palaeoclimatic data. Little or nothing is known about the recent history of these lakes and hence it is difficult to evaluate how they will respond to effects of future changes.2. Over 100 lakes have been sampled (1996–2000) between the ice sheet and the outer coast for a variety of water chemical and limnological variables. Surface sediments were taken from a subset of 40 lakes and analysed for diatoms. Diatom responses to 28 environmental variables were analysed by multivariate ordination techniques and indicate that the main gradient is highly correlated to conductivity (explaining ∼12% of species variance). Despite the relatively short gradient (24–4072 μS cm–1), diatom assemblages exhibit a clear response to conductivity. The most saline lakes do not contain a true saline flora.3. We developed a range of weighted averaging (WA) and weighted‐averaging partial least squares (WA‐PLS) models from this training data set and found two component WA‐PLS models performed best. The effects of data transformation and omission of dissolution susceptible species (Diatomaspp.) on model performance were also examined. The error statistics for the preferred WA‐PLS (2) model (r2jack=0.88, root mean square error of prediction (RMSEP)=0.217 log μS cm–1) compare well with other published models.4. A210Pb‐dated short core from a meromictic, subsaline lake (Braya Sø; location 67°N, 51°W, max. depth 23 m; conductivity 2600 μS cm–1) was analysed for diatoms. Diatom preservation is poor and some taxa (e.g.Diatomaspp.) are badly corroded. Lake water conductivity was reconstructed using WA‐PLS models. Diatom‐inferred conductivity ranges from 1800 to 4400 μS cm–1over the last 600 years (extrapolated210Pb chronology).5. The Kangerlussuaq area of West Greenland is an important area for palaeoclimatic research, located as it is between the Greenland ice sheet (ice core records) and the Davis Straits to the west. The development of a statistically robust transfer function for diatoms and conductivity will enable the reconstruction of conductivity from the many subsaline lakes around the head of the fjord and, hence, regional estimates of changing palaeoprecipitation.
The influence of ventilation systems on water depth penetration of emergent macrophytes
Authors: STRAND V. VRETARE 
Published: March 2003

1. Roots of emergent macrophytes depend on oxygen transported from aerial parts by diffusion and, in some species, by pressurised ventilation. The aim of this study was to determine if species with pressurised ventilation grow in deeper water in situ than species lacking this ability.2. Species with pressurised ventilation grew significantly deeper than species lacking pressurised ventilation, and this was true in substrates with low as well as high redox potential.3. Two species with low or non‐detectable flow rates (Schoenoplectus lacustris and Equisetum fluviatile, respectively) were found in unexpectedly deep water. Thus, pressurised ventilation is not a prerequisite for growth in deep water. It is, however, suggested that species with pressurised ventilation have a competitive advantage in deep water resulting in long‐term competitive exclusion of species lacking pressurised ventilation.
Can filter‐feeding fishes improve water quality in lakes?
Authors: HAMBRIGHT K. D. , BLUMENSHINE S. C. , SHAPIRO J. 
Published: March 2003

1. In this paper we examine the potential of a cichlid fish species (Sarotherodon galilaeus) to both maintain positive growth rates through filter‐feeding on phytoplankton and improve water quality in Lake Kinneret through suppression of dinoflagellate (Peridinium gatunense) blooms.2. Seasonal plankton consumption byS. galilaeusfrom Lake Kinneret was examined experimentally by monitoring changes in plankton assemblages during 24 h in 5‐m3mesocosms containing varying densities of fish. Taxon‐specific grazing rates ranged from 0 to 17 mg gfish day–1, with mean total consumption of 1.6% fish body weight per day. During the spring bloom ofP. gatunense,S. galilaeusconsumed mostly (94%) netphytoplankton (≥20 μm). The remaining 6% consisted mostly of nanophytoplankton (<20 μm). During the summer and fall, net‐ and nanophytoplankton accounted for 54 and 42%, respectively, of the diet ofS. galilaeus. Zooplankton and flagellated and ciliated protozoans made up the remaining 4%.3. Simulations using a fish bioenergetics model indicated that consumption rates (C) were near maximum in spring (90%Cmax), while consumption was reduced in summer‐fall (59%Cmax).Sarotherodon galilaeusobtains sufficient energy through filter‐feeding year‐round, although most growth (≥60%) occurs during the springP. gatunensebloom.4. Despite efficient feeding onP. gatunenseand nanophytoplankton byS. galilaeus, estimates of instantaneous plankton mortality caused by ingestion were two orders of magnitude lower than maximum potential plankton growth rates. Thus the potential for theS. galilaeuspopulation in Lake Kinneret to positively affect water quality through algal suppression is low.
Predation on mayfly nymph, Baetis rhodani, by native and introduced Gammarus: direct effects and the facilitation of predation by salmonids
Authors: KELLY DAVID W. , DICK JAIMIE T. A. , MONTGOMERY W. IAN 
Published: March 2003

1. In a series of laboratory experiments, we assessed the predatory nature of the native Irish amphipod, Gammarus duebeni celticus, and the introduced G. pulex, towards the mayfly nymph Baetis rhodani. We also investigated alterations in microhabitat use and drift behaviour of B. rhodani in the presence of Gammarus, and indirect predatory interactions with juvenile Atlantic salmon, Salmo salar.2. In trials with single predators and prey, B. rhodani survival was significantly lower when Gammarus were free to interact with nymphs as than when Gammarus were isolated from them. The invader G. pulex reduced the survival of B. rhodani more rapidly than did the native G. d. celticus. Both Gammarus spp. were active predators.3. In `patch' experiments, B. rhodani survival was significantly lower both when G. pulex and G. d. celticus were present, although the effect of the two Gammarus species did not differ. Again, active predation of nymphs by Gammarus was observed. Significantly more nymphs occurred on the top and sides of a tile, and per capita drifts were significantly higher, when Gammarus were present. Baetis rhodani per capita drift was also significantly higher in the presence of the introduced G. pulex than with the native G. d. celticus.4. Gammarus facilitated predation by salmon parr of B. rhodani by significantly increasing fish–nymph encounters on exposed gravel and in the drift. There were no differential effects of the two Gammarus spp. on fish –B. rhodani encounters or consumption.5. We conclude that Gammarus as a predator can have lethal, nonlethal, direct and indirect effects in freshwaters. We stress the need for recognition of this predatory role when assigning Gammarus spp. to a `Functional Feeding Group'.
Phosphorus dynamics in Danish lakes and the implications for diatom ecology and palaeoecology
Authors: Bradshaw Emily G. , Anderson N. John , Jensen Jens Peder , Jeppesen Erik 
Published: March 2003

SUMMARY 1. Seasonal phosphorus variability may be considerable in eutrophic lakes and patterns are influenced by internal, as well as external, nutrient loading. The strong seasonality of planktonic diatoms, with main growth periods in the spring and also in the autumn in meso‐ to eutrophic lakes, means that the measure of total phosphorus (TP) that is most relevant for diatom ecology may not be adequately assessed by single or few measurements during the year.2. The diatom species assemblage of surface sediments can be used to infer in‐lake nutrient concentrations. Weighted averaging (WA) and weighted averaging partial least squares (WAPLS) regression and calibration models for diatoms and annual mean TP were developed for a 29‐site data set of Danish lakes based on (a) all diatom species and (b) planktonic species only. Jack‐knifed error statistics were: =0.37, root mean squared error of prediction (RMSEP)=0.28 log10μg TP L−1 and mean bias=0.04 log10μg TP L−1 for the WAPLS 2‐component model based on all species; =0.23, RMSEP= 0.32log10μg TP L−1 and mean bias=0.07 log10μg TP L−1 for the WA model with tolerance downweighting based on planktonic species only. These are comparable with similar, published data sets.3. A subset of 23 sites was used to develop models based on seasonal TP measurements. Mean spring TP concentrations gave only slightly improved RMSEP values for models based on all species and plankton‐only (0.24 log10μg TP L−1 and 0.29 log10μg TP L−1, respectively).4. Weighted averaging models derive environmental optima, for individual species, which are not necessarily of ecological relevance. However, good water chemistry data are required to model species' responses adequately and to develop calibration data sets.
Modulation of the bacterial response to spectral solar radiation by algae and limiting nutrients
Authors: Medina‐Sánchez J. M. , Villar‐Argaiz M. , Carrillo P. 
Published: March 2003

SUMMARY 1. The response of bacterial production (measured as [3H]TdR incorporation rate) to spectral solar radiation was quantified experimentally in an oligotrophic high‐mountain lake over 2 years. Bacterial responses were consistent: ultraviolet‐B (UVB) was harmful, whereas ultraviolet‐A (UVA) + photosynthetically active radiation (PAR) and PAR enhanced bacterial activity. Full sunlight exerted a net stimulatory effect on bacterial activity in mid‐summer but a net inhibitory effect towards the end of the ice‐free period.2. Experiments were undertaken to examine whether the bacterial response pattern depended on the presence of algae and/or was modulated by the availability of a limiting inorganic nutrient (phosphorus, P). In the absence of algae, [3H]TdR incorporation rates were significantly lower than when algae were present under all light treatments, and the consistent bacterial response was lost. This suggests that the bacterial response to spectral solar radiation depends on fresh‐C released from algae, which determines the net stimulatory outcome of damage and repair in mid‐summer.3. In the absence of algae, UVB radiation inhibited bacteria when they were strongly P‐deficient (mean values of N : P ratio: 46.1), whereas it exerted no direct effect on bacterial activity when they were not P‐limited.4. P‐enrichment of lake water markedly altered the response of bacteria to spectral solar radiation at the end of ice‐free period, when bacteria were strongly P‐deficient. Phosphorus enrichment suppressed the inhibitory effect of full sunlight that was observed in October, both in whole lake water (i.e. including algae) and in the absence of algae. This indicates that the bacterial P‐deficiency, measured as the cellular N : P ratio, was partly responsible for the net inhibitory effect of full sunlight, implying a high bacterial vulnerability to UVB.
Phenotypic plasticity and constancy of life‐history traits in laboratory clones of Daphnia magna Straus: effects of neonatal length
Authors: Barata C. , Baird D. J. 
Published: March 2003

1. The phenotypic constancy of four laboratory Daphnia magna clones in fitness‐related life‐history traits, such as age and clutch size at maturity, was studied among consecutive experimental runs in differing food environments. 2. A significant part of the observed clonal and genetic‐by‐environmental variation in age and clutch size at maturity was explained by experimentally uncontrollable variations in neonatal body length. 3. Despite food availability, neonatal length determined the number of instars invested to maturity and thus maturation age. Clonal differences in neonatal length and thus in maturation instar occurrence across environments explained most of the clonal variability observed in maturation age. 4. Although interclonal differences in clutch size existed, most of the phenotypic plasticity observed for clutch size was mediated by clonal differences in neonatal length. 5. Clonal differences in neonatal length and in the occurrence of maturation instars across environments dramatically affected the body length of instar IM‐2 where provisioning of eggs take place. Since clutch size is determined from clutch mass and clutch mass was strongly related to the body length of instar IM‐2, clonal differences across environments in body length of instar IM‐2 mirrored clonal differences across environments in clutch size. 6. The results reported in the present study show that maternally mediated traits such as neonatal length affect how genotypes respond to different environmental selection regimes (genetic‐by‐environmental interaction). Future research needs to focus on the effects of neonatal length on the heritability or genetic variation of the reaction norms, since prediction of the response to selection is a key research objective in quantitative genetic studies.
Haematological health state indices of reproducing Great Tits: methodology and sources of natural variation
Authors: Ots I. , MurumÄgi A. , HÕrak P. 
Published: March 2003

1. A cornerstone concept of ecological immunology is that immune function, interacting with various aspects of individual health state, plays a central role in the life‐history trade‐offs between conflicting demands of survival and reproduction. In order to develop this research, more knowledge about the applicability and usefulness of different health state assays is needed. 2. Eleven, mostly hemato‐serological, health state indices are described and their suitability for sensing the condition of breeding Great Tits (Parus major L.) in terms of measurement precision, constancy in time, diurnal variation, and sex‐ and site‐related differences, is examined. 3. Measurement errors for the plasma albumin content, residual body mass, heterophile/lymphocyte ratio and total plasma protein content were relatively small compared with the total variation, suggesting these indices to be most adequate for ecological research. Measurement precision was lowest for the heterophile count and ‘buffy coat’ layer height (relative amount of leucocytes in total blood volume). Buffy coat layer height correlated weakly (r=0·21) with total leucocyte count estimated from blood smears and therefore appeared inappropriate for estimation of the leucocyte number. 4. Body mass (residual in respect to size) and intensity of Haemoproteus blood parasite infection were the least variable state indices during the nestling period (for both, the correlation between the values measured on the 8th and 15th days of the nestling period=0·71). Haematocrit, heterophile count and albumin/globulin ratio showed no individual constancy across the nestling period, while other traits revealed moderate but statistically significant correlations between 8th‐ and 15th‐day values. 5. Leucocyte (both lymphocyte and heterophile) counts were higher among females captured at night compared with those captured during the day. 6. Females had higher intensities of Haemoproteus infection, higher heterophile counts and higher heterophile/lymphocyte ratios than males. Contrary to published information, females had higher haematocrits than males. 7. Haematocrit values in both sexes, as well as total plasma protein and albumin concentrations in males, differed significantly between Great Tits breeding in urban habitat and rural woodlands, respectively.
Haematological health state indices of reproducing Great Tits: a response to brood size manipulation
Authors: HÕrak P. , Ots I. , Murumägi A. 
Published: March 2003

1.A brood size manipulation experiment was performed in two Great Tit (Parus majorL.) populations in order to evaluate the effect of raising different numbers of nestlings on parental health state.2.Brood enlargement resulted in elevated heterophile:lymphocyte ratios and decreased lymphocyte number in the peripheral blood, indicating that increased reproductive effort causes immunosuppression.3.Haematocrit increased in response to brood enlargement, suggesting a response to the requirement of elevated oxygen‐carrying capacity of the blood during increased work load.4.Parental body mass revealed a tendency to decrease in response to brood enlargement.5.No effect of brood size manipulation on total leucocyte count, heterophile count, intensity ofHaemoproteusblood parasite infection or plasma proteins could be detected.6.Health state indices were more sensitive to brood size manipulation in the Great Tits breeding in a rural habitat than urban birds.
Seasonal patterns of nitrogen fixation in termites
Authors: Curtis A. D. , Waller D. A. 
Published: March 2003

1. Termite nitrogenase activity was highest in autumn and spring (≈ 3 μg N2 fixed termite fresh mass (g)–1 day–1) and lowest in winter and summer (≈ 0·8 μg N2 fixed termite fresh mass (g)–1 day–1). 2. The nitrogenase activity of worker termites was significantly higher than all other castes (1·58 ± 0·27 μg N2 fixed termite fresh mass (g)–1 day–1). 3. Worker termites constituted the largest proportion of all the castes throughout the study period (≈ 90%). 4. The localized input of fixed nitrogen by termites may reach 15·3 mg N log–1 day–1 and 5·6 g N log–1 year–1.
Random walks and the gas model: spacing behaviour of Grey‐Cheeked Mangabeys
Authors: Barrett L. , Lowen C. B. 
Published: March 2003

1.Simple mechanical models (random walks and the ‘gas model’) were used to investigate the movement patterns and intergroup encounter rates of a high‐ and low‐density subpopulation of Grey‐Cheeked Mangabeys (Cercocebus albigena johnstoni,Lydeker) at two sites in the Kibale Forest, Western Uganda.2.Random walk simulations showed that the presence of conspecific groups could act as ‘social barriers’ which constrained group movements, and promoted high levels of site attachment to a specific home range area.3.Encounter rate models showed that in the low‐density subpopulation (Kanyawara), intergroup encounters occurred no more frequently than expected if groups were moving randomly and independently of each other. This was in contrast to previous analyses which suggested that Grey‐Cheeked Mangabeys employed a social spacing mechanism (mediated by male loud calls) in order to reduce the frequency of encounter to below chance levels.4.Encounters in the high‐density subpopulation (Ngogo) were found to occur less frequently than expected at short range (within 100 m). This was suggested to be due to the operation of a territorial mate defence strategy by males at this site.