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Introduction It is unclear whether tobacco in early pregnancy and alcohol use preceding pregnancy are associated with spontaneous abortion. The purpose was to investigate if use of tobacco and/or alcohol is associated with spontaneous abortion among women attending antenatal care, and if age and body mass index (BMI) attenuate the risk. Material and Methods A population-based cohort study based on data from the Swedish Pregnancy Register. All pregnant women having had the first antenatal visit from January 2014 to July 2018 were included (n = 525 604). The register had information about smoking and use of snuff before and in early pregnancy, as well as data on alcohol habits before pregnancy, measured by the Alcohol Use Disorders Identification Test (AUDIT), a validated questionnaire. Logistic regression analysis was used to estimate the association between lifestyle factors and spontaneous abortion, and multiple imputation was used to impute missing data. Results In total, 34 867 (6.6%) pregnancies ended in a spontaneous abortion after the first visit to maternal health care. At the first maternal healthcare visit, daily smoking was reported by 24 214 (5.1%), and 6403 (1.2%) used snuff. For 19 837 (4.2%) women, a high alcohol score was reported for the year preceding pregnancy. After adjusting for potential confounders and multiple imputation, use of tobacco was associated with spontaneous abortion; smoking 1–9 cigarettes/day (adjusted odds ratio [aOR] 1.11, 95% confidence interval [CI] 1.04–1.18), smoking 10 or more cigarettes/day (aOR 1.12, 95% CI 1.–1.26), and use of snuff (aOR 1.20, 95% CI 1.06–1.37). Higher AUDIT scores were not significantly associated with spontaneous abortion (AUDIT 6–9: aOR 1.03, 95% CI 0.97–1.10 and AUDIT 10 or more: aOR 1.07, 95% CI 0.94–1.22). Increasing maternal age showed the highest risk of spontaneous abortion from the age of 35, and BMI of 30 kg/m2 or more increased the risk. There were interactions between different lifestyle factors associated with spontaneous abortion that could either increase or decrease the risk of spontaneous abortion. Conclusions Smoking and use of snuff were associated with an increased risk of spontaneous abortion. The AUDIT scores preceding pregnancy were not associated with an increased risk of spontaneous abortion, which contradicts the results from previous studies.

Globally, lakes are warming and browning with ongoing climate change. These changes significantly impact a lake's biogeochemical properties and all organisms, including invertebrate consumers. The effects of these changes are essential to understand, especially during critical periods after and before the growing season, that is, autumn and spring, which can determine the composition of the invertebrate consumer community. In this study, we used a large-scale experimental pond system to test the combined effect of warming (+3°C) and increased input of terrestrial and coloured dissolved organic carbon (gradient of 1.6–8.8 mg/L in the ambient and 1.6–9.3 mg/L in the warm)—which causes browning—on zooplankton and benthic macroinvertebrate biomass and composition during the autumn and the following spring. Total zooplankton biomass decreased with warming and increased with browning, while total zoobenthos did not respond to either treatment. Warming and browning throughout the autumn had no overall interactive effects on zooplankton or zoobenthos. Autumnal warming decreased total pelagic consumer biomass, caused by a decrease in both Rotifera and Copepoda. In contrast, there was no effect on overall benthic consumer biomass, with only Asellus sp. biomass showing a negative response to warming. An autumnal increase in dissolved organic carbon led to increased total pelagic consumer biomass, which was related to increases in Daphnia sp. biomass but did not affect zoobenthos biomass. While we expected zooplankton and zoobenthos biomass to follow responses in primary and bacterial production to treatments, we did not find any relationship between consumer groups and these estimates of resource production. Our results suggest that consumer responses to warming and browning during autumn may lead to less overarching general changes in consumer biomass, and responses are mostly taxon-specific. This study gives novel insights into the effects of warming and browning on consumer biomass during autumn and spring and increases the understanding of the effects of climate change on invertebrate community biomass in the different habitats.

Summary Objective Obesity is associated with reduced health‐related quality of life (HRQoL). Outcomes of nonsurgical weight loss treatment on HRQoL are inconsistent and it is unclear how much weight reduction, or what type of treatment, is required for significant improvements. This study aimed to evaluate the effects of a lifestyle intervention program on weight, eating behaviors, and HRQoL, and to describe participants' experiences of treatment. Methods This 2‐year intervention trial in persons with class II or III obesity comprised a 3‐month liquid low‐energy diet (880 kcal/d) followed by a 3‐month reintroduction to regular foods, combined with behavioral group treatment. Results Fifty‐five participants (73% women) were included, mean (SD) age 43.2 (12.4) years, and mean body mass index 42.0 (6.0) kg/m2. Mean weight loss at 6, 12, and 24 months was 18.9%, 13.7%, and 7.2%, respectively. Short‐ and long‐term effects on eating behavior were favorable. Twelve of 14 HRQoL domains were improved at 6 months, compared to eight domains at 12 months. After 24 months, 2 of 14 domains, physical and psychosocial functioning, were improved. The treatment program was well accepted by the participants. Conclusions Substantial weight loss after 6 months was associated with extensive improvements in HRQoL, comprising the physical, psychosocial, and mental domains. Significant weight regain was observed between 6 and 24 months follow‐up. Modest weight loss after 24 months was associated with moderate improvement in physical functioning and large improvement in psychosocial functioning. The effect on psychosocial functioning is most likely related to both weight loss and behavioral treatment.

Metabolic stoichiometry predicts that dissolved oxygen (O 2) and carbon dioxide (CO 2) in aquatic ecosystems should covary inversely; however, field observations often diverge from theoretical expectations. Here, we propose a suite of metrics describing this O 2 and CO 2 decoupling and introduce a conceptual framework for interpreting these metrics within aquatic ecosystems. Within this framework, we interpret cross-system patterns of high-frequency O 2 and CO 2 measurements in 11 northern lakes and extract emergent insights into the metabolic behavior and the simultaneous roles of chemical and physical forcing in shaping ecosystem processes. This approach leverages the power of high-frequency paired O 2-CO 2 measurements, and yields a novel, integrative aquatic system typology which can also be applicable more broadly to streams and rivers, wetlands and marine systems. Dissolved oxygen (O 2) remains one of the most studied attributes of aquatic ecosystems since the beginning of modern ecology. In 1957, G. E. Hutchinson famously wrote "A skillful limnologist can probably learn more about the nature of a lake from a series of oxygen determinations than from any other kind of chemical data" (Hutchinson 1957). The value of oxygen as an indicator of ecosystem function stems from its role in biogeochemical reactions, where it regulates

The ecology and biogeochemistry of lakes in the subarctic region are particularly sensitive to changes in the abundance and optical properties of dissolved organic matter (DOM). External input of c ...

Detailed knowledge of the flood period of Arctic rivers remains one of the few factors impeding rigorous prediction of the effect of climate change on carbon and related element fluxes from the lan ...

Headwater streams can be important sources of carbon dioxide (CO2) and methane (CH4) to the atmosphere. However, the influence of groundwater-stream connectivity on the patterns and sources of carb ...

Accounting for temporal changes in carbon dioxide (CO2) emissions from freshwaters remains a challenge for global and regional carbon budgets. Here, we synthesize 171 site-months of e...

Felt stigma is an internalized sense of shame about having an unwanted condition, along with fear of discrimination. The Stigma‐related Social Problems (SSP) scale was constructed to measure the impact of health‐related stigma on psychosocial functioning in people with different diseases and disorders. The performance of the SSP scale was tested in 3,422 subjects from the general population (Mid‐Swed Health Survey) and in subgroups according to gender, age, occupation, and education. The homogeneity and construct validity of the Distress and Avoidance scales were confirmed by exploratory factor analysis and the two factors were accurately reproduced across gender and age subgroups. The internal consistency reliability was high for both the Distress and Avoidance scales. Reliability coefficients were above the 0.90 standard for the Distress scale in all subgroups and for the Avoidance scale in most subgroups. The SSP scale is an instrument with sound psychometric properties that can be used to identify psychosocial disturbances.

The contribution of terrestrially derived carbon to micro-crustacean zooplankton biomass (i.e., allochthony) has been previously studied in lakes, reservoirs, and estuaries, but little is known abo ...

Phosphorus (P) often limits the biomass of primary producers in freshwater lakes. However, in unproductive northern lakes, where anthropogenic nitrogen (N) deposition is low, N instead of P can lim ...

Global warming and land use scenarios suggest increased 21st century nitrogen (N) inputs to aquatic systems. Nitrogen affects in-lake processing and, potentially, atmospheric exchange of greenhouse ...

Anthropogenic activities are increasing inorganic nitrogen (N) loadings to unproductive boreal lakes. In many of these lakes phytoplankton are N limited, consequently N fertilization may affect eco ...

1. Arctic and sub‐Arctic lakes in northern Europe are increasingly threatened by climate change, which can affect their biodiversity directly by shifting thermal and hydrological regimes, and indirectly by altering landscape processes and catchment vegetation. Most previous studies of northern lake biodiversity responses to environmental changes have focused on only a single organismal group. Investigations at whole‐lake scales that integrate different habitats and trophic levels are currently rare, but highly necessary for future lake monitoring and management. 2. We analysed spatial biodiversity patterns of 74 sub‐Arctic lakes in Norway, Sweden, Finland, and the Faroe Islands with monitoring data for at least three biological focal ecosystem components (FECs)—benthic diatoms, macrophytes, phytoplankton, littoral benthic macroinvertebrates, zooplankton, and fish—that covered both pelagic and benthic habitats and multiple trophic levels. 3. We calculated the richnessrelative (i.e. taxon richness of a FEC in the lake divided by the total richness of that FEC in all 74 lakes) and the biodiversity metrics (i.e. taxon richness, inverse Simpson index (diversity), and taxon evenness) of individual FECs using presence–absence and abundance data, respectively. We then investigated whether the FEC richnessrelative and biodiversity metrics were correlated with lake abiotic and geospatial variables. We hypothesised that (1) individual FECs would be more diverse in a warmer and wetter climate (e.g. at lower latitudes and/or elevations), and in hydrobasins with greater forest cover that could enhance the supply of terrestrial organic matter and nutrients that stimulated lake productivity; and (2) patterns in FEC responses would be coupled among trophic levels. 4. Results from redundancy analyses showed that the richnessrelative of phytoplankton, macrophytes, and fish decreased, but those of the intermediate trophic levels (i.e. macroinvertebrates and zooplankton) increased with decreasing latitude and/or elevation. Fish richnessrelative and diversity increased with increasing temporal variation in climate (temperature and/or precipitation), ambient nutrient concentrations (e.g. total nitrogen) in lakes, and woody vegetation (e.g. taiga forest) cover in hydrobasins, whereas taxon richness of macroinvertebrates and zooplankton decreased with increasing temporal variation in climate. 5. The similar patterns detected for richnessrelative of fish, macrophytes, and phytoplankton could be caused by similar responses to the environmental descriptors, and/or the beneficial effects of macrophytes as habitat structure. By creating habitat, macrophytes may increase fish diversity and production, which in turn may promote higher densities and probably more diverse assemblages of phytoplankton through trophic cascades. Lakes with greater fish richnessrelative tended to have greater average richnessrelative among FECs, suggesting that fish are a potential indicator for overall lake biodiversity. 6. Overall, the biodiversity patterns observed along the environmental gradients were trophic‐level specific, indicating that an integrated food‐web perspective may lead to a more holistic understanding of ecosystem biodiversity in future monitoring and management of high‐latitude lakes. In future, monitoring should also focus on collecting more abundance data for fish and lower trophic levels in both benthic and pelagic habitats. This may require more concentrated sampling effort on fewer lakes at smaller spatial scales, while continuing to sample lakes distributed along environmental gradients. Special Issue.

Air–water gas exchange velocities (k) are critical components of many biogeochemical and ecological process studies in aquatic systems. However, their high spatiotemporal variability is difficult t ...

This study aimed to evaluate changes in mental health over 2 years in adolescents undergoing gastric bypass.

Dissolved organic carbon (DOC) concentrations in lakes are changing globally, but little is known about potential ecosystem impacts.We evaluated the relationship between DOC and whole-lake primary ...

Nutrient limitation of primary producers and their consumers can have a large influence on ecosystem productivity. The nature and strength of nutrient limitation is driven both by external factors (e.g., nutrient loading) and internal processes (e.g., consumer-driven nutrient regeneration). Here we present results from a field study in 10 low productive headwater lakes in northern subarctic Sweden, where nitrogen (N) deposition is low and phytoplankton is primarily N-limited. We assessed the carbon:nitrogen:phosphorus (C:N:P) stoichiometry of seston and zooplankton and estimated the N:P ratio of consumer-driven nutrient regeneration. Based on stoichiometric models, the estimated elemental imbalances between seston and zooplankton suggest that zooplankton were mainly N-limited and regenerated nutrients with low N:P ratios (median 11.9, atomic ratio). The predicted N:P regeneration ratios were consistent with results from phytoplankton nutrient limitation bioassays in mid-summer, i.e., the N:P regeneration was predicted to be low when phytoplankton were N-limited, and high when phytoplankton were P-limited. During other seasons, when water discharge was high, nutrient loading from the surrounding catchments apparently had the strongest effect on phytoplankton nutrient limitation. We propose that lakes with higher N:P ratios than the open ocean is an effect of N deposition, that N-limitation of consumers and phytoplankton is further enhanced by low nutrient regeneration N:P ratios, and that in the absence of N deposition, lake and ocean N:P stoichiometry are similar.

Climate change is expected to not only raise water temperatures, but also to cause brownification of aquatic ecosystems via increased inputs of terrestrial dissolved organic matter. While efforts h ...

Response to Comment : Terrestrial support of pelagic consumers in unproductive lakes- Uncertainty and potential in assessments using stable isotopes

The aim of this study was to predict the combined effects of enhanced nitrogen (N) deposition and warming on phytoplankton development in high latitude and mountain lakes. Consequently, we assessed, in a series of enclosure experiments, how lake water nutrient stoichiometry and phytoplankton nutrient limitation varied over the growing season in 11 lakes situated along an altitudinal/climate gradient with low N-deposition (1 kg N ha(-1) yr(-1) ) in northern subarctic Sweden. Short-term bioassay experiments with N- and P-additions revealed that phytoplankton in high-alpine lakes were more prone to P-limitation, and with decreasing altitude became increasingly N- and NP-colimited. Nutrient limitation was additionally most obvious in midsummer. There was also a strong positive correlation between phytoplankton growth and water temperature in the bioassays. Although excess nutrients were available in spring and autumn, on these occasions growth was likely constrained by low water temperatures. These results imply that enhanced N-deposition over the Swedish mountain areas will, with the exception of high-alpine lakes, enhance biomass and drive phytoplankton from N- to P-limitation. However, if not accompanied by warming, N-input from deposition will stimulate limited phytoplankton growth due to low water temperatures during large parts of the growing season. Direct effects of warming, allowing increased metabolic rates and an extension of the growing season, seem equally crucial to synergistically enhance phytoplankton development in these lakes.

Objective. To validate the Swedish versions of the Incontinence Impact Questionnaire (IIQ-7) and Urogenital Distress Inventory (UDI-6). Design and setting. Prospective study, university hospital. Population and method. We analyzed reliability, validity, and responsiveness in a clinical sample of 96 women with urinary incontinence. Main outcome measures. Construct and criterion validity, reliability via test-retest and internal consistency. Responsiveness via calculation of effect size. Result. Test-retest reliability ranged from moderate to almost perfect. Cronbach's alpha was 0.39 (UDI-6) and 0.83 (IIQ-7). Effect size calculation of change after treatment demonstrated good responsiveness. The effect size at six months was moderate in the Stress Urinary Incontinence group and small in the Urge Urinary Incontinence + Mixed Urinary Incontinence group. There was a moderate to strong correlation between UDI-6 and IIQ-7 and treatment satisfaction at six, 12, and 24 months for both groups. Conclusion. The UDI-6 scale did not produce the same solid result in the psychometric analysis as the IIQ-7 scale, but these newly translated Swedish forms of UDI-6 and IIQ-7 show good responsiveness and are easy to administer and to fill out.

We quantified the utilization of terrestrial organic matter (OM) in the food web of a humic lake by analyzing the metabolism and the consumers' stable isotopic (C, H, N) composition in benthic and pelagic habitats. Terrestrial OM inputs (3 g C m(-2) d(-1)) to the lake greatly exceeded autochthonous OM production (3 mg C m(-2) d(-1)) in the lake. Heterotrophic bacterial growth (19 mg C m(-2) d(-1)) and community respiration (115 mg C m(-2) d(-1)) were high relative to algal photosynthesis and were predominantly (> 85%) supported by terrestrial OM in both habitats. Consequently, terrestrial OM fueled most (85%) of the total production at the base of the lake's food web (i.e., the sum of primary and bacterial production). Despite the uncertainties of quantitatively estimating resource use based on stable isotopes, terrestrial OM clearly also supported around half the zooplankton (47%), macrozoobenthos (63%), and fish (57%) biomass. These results indicate that, although rates of terrestrial OM inputs were around three orders of magnitude greater than that of autochthonous OM production, the use of the two resources by higher trophic levels was roughly equal. The disproportionally low reliance on terrestrial OM at higher trophic levels, compared with its high rates of input and high support of basic biomass production in the lake, suggests that autochthonous resources could not be completely replaced by terrestrial resources and indicates an upper limit to terrestrial support of lake food webs.

Ecology Letters (2012) Abstract A majority of the worlds lakes are supersaturated with respect to carbon dioxide (CO2). By experimental manipulation of the CO2 concentration in supersaturated borea ...

Ecology Letters (2010) Abstract Carbon of terrestrial origin often makes up a significant share of consumer biomass in unproductive lake ecosystems. However, the mechanisms for terrestrial support ...

1. Air temperature will probably have pronounced effects on the composition of plankton communities in northern lake ecosystems, either via indirect effects on the export of essential elements from ...

We investigated productivity at the basal trophic level in 15 unproductive lakes in a gradient ranging from clear-water to brown-water (humic) lakes in northern Sweden. Primary production and bacterial production in benthic and pelagic habitats were measured to estimate the variation in energy mobilization from external energy sources (primary production plus bacterial production on allochthonous organic carbon) along the gradient. Clear-water lakes were dominated by autotrophic energy mobilization in the benthic habitat, whereas humic lakes were dominated by heterotrophic energy mobilization in the pelagic habitat. Whole-lake (benthic + pelagic) energy mobilization was negatively correlated to the light-extinction coefficient, which was determined by colored terrestrial organic matter in the lake water. Thus, variation in the concentration of terrestrial organic matter and its light-absorbing characteristics exerts strong control on the magnitude, as well as on the processes and pathways, of energy mobilization in unproductive lakes. We suggest that unproductive lakes in general are sensitive to input of terrestrial organic matter because of its effects on basal energy mobilization in both benthic and pelagic habitats.

Recent accelerated decay of discontinuous permafrost at the Stordalen Mire in northern Sweden has been attributed to increased temperature and snow depth, and has caused expansion of wet minerotrop ...

This study quantified new biomass production of algae and bacteria in both benthic and pelagic habitats of clear-water lakes to contrast how carbon from the atmosphere and terrestrial sources regulates whole-lake metabolism. We studied four small unproductive lakes in subarctic northern Sweden during one summer season. The production of new biomass in both benthic and pelagic habitats was calculated as the sum of autotrophic production by algae and heterotrophic production by bacteria using allochthonous organic carbon (OC). Whole-lake production of new biomass was dominated by the benthic habitat (86% +/- 4% [mean +/- SD]) and by primary production (77% +/- 9%). Still, heterotrophic bacteria fueled by allochthonous OC constituted a significant portion of the new biomass production in both benthic (19% +/- 11%) and pelagic habitats (51% +/- 24%). In addition, overall net production (primary production minus respiration) was close to zero in the benthic habitats but highly negative (-163 +/- 81 mg C x m(-2) x d(-1)) in pelagic regions of all lakes. We conclude (1) that allochthonous OC supported a significant part of total production of new biomass in both pelagic and benthic habitats, (2) that benthic habitats dominated the whole-lake production of new biomass, and (3) that respiration and net CO2 production dominated the carbon flux of the pelagic habitats and biomass production dominated the benthic carbon flux. Taken together, these findings suggest that previous investigations have greatly underestimated the productivity of clear-water lakes when benthic autotrophic production and metabolism of allochthonous OC have not been measured.

We used stable carbon (δ13C) and nitrogen (δ15N) isotopes to assess the importance of benthic algae for the zooplankton individual growth in winter in a shallow, clear subarctic lake. The δ13C values of calanoid (Eudiaptomus graciloides) and cyclopoid (Cyclops scutifer) zooplankton in autumn suggest a food resource of pelagic origin during the ice-free period. The zooplankton δ13C values were high in spring compared to autumn. E. graciloides did not grow over winter and the change in δ13C was attributed to a decrease in lipid content during the winter. In contrast, the increase in δ13C values of C. scutifer over the winter was explained by their growth on organic carbon generated by benthic algae. The δ15N of the C. scutifer food resource during winter was low compared to δ15N of the benthic community, suggesting that organic matter generated by benthic algae was mainly channelled to zooplankton via 15N-depleted heterotrophic bacteria. The results demonstrate that benthic algae can sustain zooplankton metabolic demands and growth during long winters, which, in turn, may promote zooplankton growth on pelagic resources during the summer. Such multi-chain omnivory challenges the view of zooplankton as mainly dependent on internal primary production and stresses the importance of benthic resources for the productivity of plankton food webs in shallow lakes.

We studied a small subarctic lake to assess the magnitude of winter respiration and the organic carbon (OC) source for this respiration. The concentration and stable isotopic composition (d13C) of ...

This study investigates the allocation of allochthonous organic carbon (AlloOC) to pelagic respiration and biomass production in unproductive lakes. Metabolic process rates and stable isotopic composition (δ13C) of crustacean zooplankton and respired CO2 were measured in the epilimnion of 13 forest lakes in northern Sweden. The δ13C of zooplankton was low (−31.2 to −38.0‰) compared to that of respired CO2 (−28.4 to −30.6‰), implying that the relative importance of AlloOC was lower for zooplankton (ca 40%) than for respiration (ca 80%). Combining δ13C and carbon flux data revealed that a large amount of metabolized AlloOC was lost in respiration, compared to the amount transferred to zooplankton (

1. Both the pelagic and benthic net dissolved inorganic carbon (DIC) productions were measured in situ on four occasions from June to September 2004, in the unproductive Lake Diktar-Erik in subarct ...

We carried out short-term (2 d) experiments in nine unproductive lakes in northern Sweden in order to investigate organic carbon sources supporting lake water respiration. Surface water was incubated in gas-tight bottles in the dark, and the concentration and isotopic composition (d13C) of dissolved inorganic carbon (DIC) were measured at the start and end of the incubations. Keeling plot analyses revealed that the d13C of the respired carbon was between 228.4% and 230.6% in the lakes and that the respired carbon was mainly of allochthonous organic carbon (AlloOC) origin. The respiration of AlloOC corresponded well with metabolic imbalances indicated by negative net ecosystem production (NEP) values in the lake waters. Keeling plot analysis of DIC accumulating in the hypolimnion of two lakes during summer stratification showed d13C values of around 226.6% for excess DIC, implying that the accumulation of DIC was mainly derived from respiration of AlloOC. Our data provide direct evidence that net heterotrophy of these lakes is caused by input and respiration of AlloOC. We conclude that the Keeling plot method is a powerful technique that enables characterization and quantification of the organic carbon sources contributing to respiration in aquatic systems.

The increasing accessibility and use of microarrays in transcriptomics has accentuated the need for purpose-designed storage and analysis tools. Here we present UPSC-BASE, a database for analysis and storage of Populus DNA microarray data. A microarray analysis pipeline has also been established to allow consistent and efficient analysis (from small to large scale) of samples in various experimental designs. A range of optimized experimental protocols is provided for each step in generating the data. Within UPSC-BASE, researchers can perform standard and advanced microarray analysis procedures in a user-friendly environment. Background corrections, normalizations, quality-control tools, visualizations, hypothesis tests and export tools are provided without requirements for expert-level knowledge. Although the database has been developed primarily for handling Populus DNA microarrays, most of the tools are generic and can be used for other types of microarray. UPSC-BASE is also a repository of Populus microarray information, providing data from 21 experiments on a total of 407 microarray hybridizations in the public domain of the database. There are also an additional 10 experiments containing 347 hybridizations, where the automatically analysed data are searchable.

Climate change is predicted to be dramatic at high latitudes. Still, climate impact on high latitude lake ecosystems is poorly understood. We studied 15 subarctic lakes located in a climate gradien ...

We used stable carbon (d 13 C) and nitrogen (d 15 N) isotopes to assess the energy sources supporting the top consumer (Arctic char, Salvelinus alpinus) in nine subarctic lakes in northern Sweden. The d 13 C of littoral (epipelic algae) and pelagic (bacterioplankton and phytoplankton) energy sources were clearly separated in the lakes, as reflected in habitat-specific consumers (zoobenthos, zooplankton). Char were enriched in 13 C compared with pelagic energy sources and prey and isotopically more similar to littoral energy sources and prey. The contribution of littoral energy sources to char body carbon was estimated to range between 62% and 94% among the lakes. The reliance on littoral energy sources was independent of char size and did not change when char coexisted with a small-sized prey fish (nine-spined stickleback, Pungitus pungitus). The strong reliance of top consumers in subarctic lakes on littoral energy sources may be due to the higher energy mobilization and larger sizes of primary consumers in littoral than in pelagic habitats. The energy flow through the ecosystem, i.e., from the energy mobilizers at the base of the food web to top energy consumers, is of fundamental importance for the function of lake ecosystems. Mobilization and transfer of energy within the food web sets the limit for production at higher trophic levels, and the presence of several diverse energy-flow pathways may affect ecosystem properties such as food-web dynamics and nutrient cycling (Polis et al. 1997). Still, energy flow between benthic and pelagic compartments has received little attention, reflecting both methodological constraints and a scarcity of whole-lake studies (Vadeboncoeur et al. 2002). Research into lake energy flow has largely focused on pelagic food webs. Pelagic energy mobilization derives from photosynthesis and from bacterioplankton growing on allochthonous organic carbon (Tranvik 1989; Jones 1992; Karlsson et al. 2002). The energy mobilization at the base of the food web is consumed, redistributed in the food web, and subsequently transferred to top consumers such as fish. However, recent studies have shown that benthic resources are of great importance for lake food webs, since fish communities may make considerable use of zoobenthos (Schindler and Scheuerell 2002). In the profundal zone, exploitation of benthic resources can be regarded as mainly comprising the re

1. To assess the use of stable nitrogen isotopes (δ15N) for reconstructing trophic relationships in planktonic food webs, crustacean zooplankton species and pelagic dissolved and particulate matter ...

We compared the stable carbon isotopic composition (delta(13)C) of crustacean zooplankton with that of potential carbon sources in 15 lakes in northern Sweden with different dissolved organic carbo ...

We examined the relationship between planktonic primary production (PP) and bacterial production (BP) in 16 subarctic lakes along an altitude gradient extending from colored coniferous forest lakes to clearwater high alpine lakes. We tested the hypothesis that there was a shift from low to high PP:BP ratios along this gradient. The clearwater alpine lakes had low PP:BP ratios, generally well below 1.0, while the highest ratios were found in the forest lakes. In contradiction to our hypothesis, the pelagic systems of the clearwater lakes were thus dominated by bacterial energy mobilization from external carbon sources. In this respect the alpine lakes were similar to highly humic lakes. We suggest that the relationship between C, N, and P plays a critical role in determining the PP:BP ratio, and that the N:P ratio in particular can be critical for development of PP or BP dominance in the pelagic systems of unproductive lakes.