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Various approaches based on the natural variations of carbon isotopes ( 14 C and 13 C) in dissolved inorganic carbon (DIC) are routinely used to study groundwater dynamics and to estimate recharge rates by deriving groundwater ages. However, differences in 14 C activities in groundwater samples collected repeatedly from the same wells and discordantly young 14 C groundwater ages compared to noble gases led some authors to question the validity of radiocarbon dating. Poor sampling protocols and storage effects ( 14 C contamination) for radiocarbon analysis are a critical factor in explaining age determination discrepancies. We evaluated the impact of storage protocols on carbon isotope exchange with atmospheric carbon dioxide by comparing glass versus standard plastic field sampling bottles for various storage times before radiocarbon and 13 C analyses. The 14 C bias after 12 months in pre-evacuated glass vials was minimal and within analytical precision. However, storage of DIC samples in plastic sampling bottles led to marked changes in 14 C and 13 C contents (up to ∼15 pmC and ∼ 5 ‰, respectively, after 12 months), meaning contamination led to younger groundwater age estimations than it should have been. Protocols for sampling and storing DIC samples for radiocarbon using pre-evacuated glass bottles help avoid atmospheric 14 CO 2 contamination and microbial activity.

The seasonal coupling of plant and soil microbial nutrient demands is crucial for efficient ecosystem nutrient cycling and plant production, especially in strongly seasonal alpine ecosystems. Yet, how these seasonal nutrient cycling processes are modified by climate change and what the consequences are for nutrient loss and retention in alpine ecosystems remain unclear. Here, we explored how two pervasive climate change factors, reduced snow cover and shrub expansion, interactively modify the seasonal coupling of plant and soil microbial nitrogen (N) cycling in alpine grasslands, which are warming at double the rate of the global average. We found that the combination of reduced snow cover and shrub expansion disrupted the seasonal coupling of plant and soil N-cycling, with pronounced effects in spring (shortly after snow melt) and autumn (at the onset of plant senescence). In combination, both climate change factors decreased plant organic N-uptake by 70% and 82%, soil microbial biomass N by 19% and 38% and increased soil denitrifier abundances by 253% and 136% in spring and autumn, respectively. Shrub expansion also individually modified the seasonality of soil microbial community composition and stoichiometry towards more N-limited conditions and slower nutrient cycling in spring and autumn. In winter, snow removal markedly reduced the fungal:bacterial biomass ratio, soil N pools and shifted bacterial community composition. Taken together, our findings suggest that interactions between climate change factors can disrupt the temporal coupling of plant and soil microbial N-cycling processes in alpine grasslands. This could diminish the capacity of these globally widespread alpine ecosystems to retain N and support plant productivity under future climate change., (© 2024 The Authors. Global Change Biology published by John Wiley & Sons Ltd.)

Background: Freshwater ecosystems are amongst the most threatened habitats on Earth; nevertheless, they support about 9.5% of the known global biodiversity while covering less than 1% of the globe's surface. A number of anthropogenic pressures are impacting species diversity in inland waters and, amongst them, the spread of invasive alien species is considered one of the main drivers of biodiversity loss and homogenisation in freshwater habitats.Crayfish species are widely distributed freshwater invaders and, while alien species introductions occur mostly accidentally, alien crayfish are often released deliberately into new areas for commercial purposes. After their initial introduction, crayfish species can rapidly establish and reach high-density populations as a result of their adaptive functional traits, such as their generalist diet.The Louisiana crayfish Procambarusclarkii (Girard, 1852) is globally considered one of the worst invaders and its impact on recipient freshwater communities can vary from predation and competition with native species, to modification of food webs and habitat structure and introduction of pathogens. Native to the south United States and north Mexico, P.clarkii has been introduced in Europe, Asia and Africa, determining negative ecological and economic impacts in the majority of invaded habitats where it became dominant within the receiving benthic food webs. Due to its flexible feeding strategy, P.clarkii exerts adverse effects at different trophic levels, ultimately affecting the structure and dynamics of invaded food webs. It is, therefore, paramount to evaluate the ecological consequences of P.clarkii invasion and to quantify its impact in a spatially explicit context., New Information: In the past decades, the analysis of stable isotopes of carbon, nitrogen and other elements has become a popular methodology in food web ecology. Notably, stable isotope analysis has emerged as a primary tool for addressing applied issues in biodiversity conservation and management, such as the assessment of the trophic ecology of non-indigenous species in invaded habitats. Here, we built two geo-referenced datasets, resolved respectively at the population and individual scale, by collating information on δ 13 C and δ 15 N values of P.clarkii within invaded inland waters. The population-scale dataset consists of 160 carbon and nitrogen isotopic values of the Louisiana crayfish and its potential prey, including living and non-living primary producers and benthic invertebrates. The dataset resolved at individual scale consists of 1,168 isotopic records of P.clarkii . The isotopic values included within the two datasets were gathered from 10 countries located in Europe, Asia, Africa and North America, for a total of 41 studies published between 2005 and 2021. To the best of the authors' knowledge, this effort represents the first attempt to collate in standardised datasets the sparse isotopic information of P.clarkii available in literature. The datasets lend themselves to being used for providing a spatially explicit resolution of the trophic ecology of P.clarkii and to address a variety of ecological questions concerning its ecological impact on recipient aquatic food webs., (Cristina Di Muri, Paloma Alcorlo, Roberta Bardelli, Jordi Catalan, Esperança Gacia, Maria Teresa Guerra, Ilaria Rosati, David X. Soto, Salvatrice Vizzini, Giorgio Mancinelli.)

Climate change and associated droughts threaten the ecology and resilience of natural saline lakes globally. There is a distinct lack of research regarding their ecological response to climatic events in the Global South. This region is predicted to experience climatic events such as El Niño-Southern Oscillation (ENSO) more often and with greater severity with the potential to alter the structure and functioning of aquatic ecosystems significantly. From 2015 to 2016 South Africa experienced one of the most severe country-wide droughts as a result of a strong ENSO event. Our study aimed to investigate the effect of this supra-seasonal drought on the trophic structure of fish communities in a naturally saline shallow lake of a Ramsar wetland using stable isotope techniques. Fishes and potential basal sources were collected from the lake, during predrought conditions in 2010 and after severe drought (recovery phase; 2017). The δ 13 C and δ 15 N values of food web elements were determined and analysed using Bayesian mixing models and Bayesian Laymen metrics to establish the proportional contribution of C 3 and C 4 basal sources to the fish (consumer) diets, and examine the fish community in terms of isotopic niche and trophic structure, respectively. Fish consumers relied predominantly on C 3 basal sources in the predrought and shifted to greater reliance on C 4 basal sources, decreased isotopic niche space use and a reduction in trophic length in the recovery phase. Drought altered the type and abundance of the basal sources available by limiting sources to those that are more drought-tolerant, reducing the trophic pathways of the food web with no significant alterations in the fish community. These results demonstrate the resilience and biological plasticity of Lake Nyamithi and its aquatic fauna, highlighting the importance of freshwater inflow to saline lakes with alterations thereof posing a significant threat to their continued functioning., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier B.V. All rights reserved.)

Methods for identifying origin, movement, and foraging areas of animals are essential for understanding ecosystem connectivity, nutrient flows, and other ecological processes. Telemetric methods can provide detailed spatial coverage but are limited to a minimum body size of specimen for tagging. In recent years, stable isotopes have been increasingly used to track animal migration by linking landscape isotope patterns into movement (isoscapes). However, compared to telemetric methods, the spatial resolution of bulk stable isotopes is low. Here, we examined a novel approach by evaluating the use of compound-specific hydrogen and carbon stable isotopes of fatty acids (δ 2 H FA and δ 13 C FA ) from fish liver, muscle, brain, and eye tissues for identifying site specificity in a 254 km 2 sub-alpine river catchment. We analyzed 208 fish (European bullhead, rainbow trout, and brown trout) collected in 2016 and 2018 at 15 different sites. δ 13 C FA values of these fish tissues correlated more among each other than those of δ 2 H FA values. Both δ 2 H FA and δ 13 C FA values showed tissue-dependent isotopic fractionation, while fish taxa had only small effects. The highest site specificity was for δ 13 C DHA values, while the δ 2 H isotopic difference between linoleic acid and alpha-linolenic acid resulted in the highest site specificity. Using linear discrimination analysis of FA isotope values, over 90% of fish could be assigned to their location of origin; however, the accuracy dropped to about 56% when isotope data from 2016 were used to predict the sites for samples collected in 2018, suggesting temporal shifts in site specificity of δ 2 H FA and δ 13 C FA . However, the predictive power of δ 2 H FA and δ 13 C FA over this time interval was still higher than site specificity of bulk tissue isotopes for a single time point. In summary, compound-specific isotope analysis of fatty acids may become a highly effective tool for assessing fine and large-scale movement and foraging areas of animals.

Evaluation of trace metal pollution in an environmentally complex context may require the use of a suite of indicators. Common reed, Phragmites australis, is a well-known biomonitor of sediment pollution. Here, we show its potential for also assessing air pollution. The plant panicles, holding silky hairs with high surface to volume ratio, are appropriate collectors of atmospheric contaminants, which perform independently from root bioconcentration. We applied the dual value of common reed as an indicator of trace metal pollution to the case of a chlor-alkali plant in the Ebro river bank (Spain). This factory had historically damped waste to the shallow Flix reservoir. Extensive common reed meadows are growing on the top of the waste, in a nearby nature reserve across the reservoir and a meander immediately downriver. Three replicated individuals from a total of 11 sites were sampled, and the trace metal content measured in the main plant compartments (roots, rhizomes, stems, leaves, and panicles). Panicles and roots showed a much larger concentration of trace metals than the other plant compartments. Levels of Hg, Cu, and Ni were markedly higher in panicles at the factory and nearby points of the reserve and lowered at the meander. In contrast, Cd, Zn, and Mn in roots increased from the factory to the meander downriver. We conclude that panicles show recent (less than a year) airborne pollution, whereas roots indicate the long-term transport of pollutants from the waste in the shoreline of the factory to downriver sedimentation hotspots, where they become more bioavailable than in the factory waste. The Hg spatial pattern in panicles agree with air measurements in later years, therefore, confirming the panicles suitability for assessing airborne pollution and, consequently, Phragmites as a potential dual biomonitor of air and sediments., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Eutrophication is a globally significant challenge facing aquatic ecosystems, mostly associated with human induced enrichment of these ecosystems with nitrogen and phosphorus. Given the complexity of assigning eutrophication issues to local primary N sources in field-based studies, this paper proposes a multi-stable isotope and biological framework to track nitrogen biogeochemical transformations, inputs and fate of nitrate in groundwater-dependent shallow lakes. Three representative freshwater ecosystems from the Pampa Plain (Argentina), with different land uses and topographic features were selected. Groundwater (N = 24), lake (N = 29) and stream (N = 20) samples were collected for isotope (δ 15 N-NO 3 - and δ 18 O-NO 3 - , δ 18 O-H 2 O) and hydrogeochemical (major ions and nutrients) determinations, and in the case of surface water, also for biological determinations (chlorophyll-a, fecal coliforms and nitrifying bacteria abundance). Both chemical and isotopic characteristics clearly indicated that denitrification was limited in lakes and streams, while evidence of assimilation in shallow lakes was confirmed. The results suggested that groundwater denitrification plays a role in the nitrate concentration pattern observed in the Pampeano Aquifer. The proportional contribution of nitrate sources to the inflow streams for all years were estimated by using Bayesian isotope mixing models, being ammonium nitrified in the system from soil and fertilizers ~50 - 75 %, sewage/manure ~20 - 40 % and atmospheric deposition ~5 - 15 %. In this sense, agricultural practices seem to have a relevant role in the eutrophication and water quality deterioration for these watersheds. However, limnological, bacterial and algal variables, assessed simultaneously with isotopic tracers, indicated spatio-temporal differences within and between these aquatic ecosystems. In the case of Nahuel Rucá Lake, animal manure was a significant source of nitrogen pollution, in contrast to La Brava Lake. In Los Padres Lake, agricultural practices were considered the main sources of nitrate input to the ecosystem., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)

Understanding the degree to which aquatic and terrestrial primary production fuel tropical aquatic food webs remains poorly understood, and quantifying the relative contributions of autochthonous and allochthonous inputs is methodologically challenging. Carbon and nitrogen stable isotope ratios ( δ 13 C, δ 15 N) can provide valuable insights about contributions of terrestrial resources and trophic position, respectively, but this approach has caveats when applied in typical complex natural food webs.Here, we used a combination of C, N, and H ( δ 2 H) stable isotope measurements and Bayesian mixing models to estimate the contribution of terrestrial (allochthonous) and aquatic (autochthonous) inputs to fish and invertebrate communities in the Congo River (and some tributaries).Overall, our results show that we gained power to distinguish sources by using a multiple tracer approach and we were able to discriminate aquatic versus terrestrial sources (esp. including hydrogen isotopes). Fish δ 2 H values were clearly correlated with their food preferences and revealed a high level of variation in the degree of allochthony in these tropical aquatic communities.At the community level, it is clear that terrestrial C 3 plants are an important source fueling the Congo River food web. However, in order to better constrain source contribution in these complex environments will require more robust constraints on stable isotope values of algal and methane-derived C sources., Competing Interests: None declared., (© 2019 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd.)

Anthropogenic nitrogen inputs into Lake Winnipeg, Canada, from watershed sources have increased during the last decades, contributing to eutrophication. These nutrient N inputs include loadings from agriculture (inorganic fertilizer and animal waste) and urban sources (wastewater discharge from sewage treatment plants). The aim of this study was to evaluate the sources and seasonal patterns of dissolved nitrates in two major contributors to Lake Winnipeg; the Assiniboine and Red rivers. The relative contribution of nitrate sources was estimated using Bayesian isotope mixing models incorporating δ 15 N and δ 18 O values of dissolved nitrate. Overall, δ 15 N values of nitrate in the rivers ranged from -2 ‰ to +20 ‰, and δ 18 O values ranged from -20 ‰ to +20 ‰, which indicated variable contribution of nitrate sources, depending on the river reach and seasonal period of sampling. The results indicated that nitrate in the Assiniboine River originated up to 62 % from waste or municipal sources (i.e. manure and/or waste water discharge), whereas ca. 40 % of nitrate in the Red River originated predominantly from inorganic agricultural fertilizers. These different source contributions were temporally variable, with a decrease in fertilizer loading following spring snowmelt. We found higher proportions of inorganic fertilizers in the Assiniboine River watershed during flooding, which has relevant implications for water nutrient management in response to stochastic flooding events., (Crown Copyright © 2018. Published by Elsevier B.V. All rights reserved.)

The macronutrients that Arctic herbivores invest in their offspring are derived from endogenous reserves of fat and protein (capital) that females build prior to the period of investment or from foods they consume concurrently with investment (income). The relative contribution from each source can be influenced by temporal and environmental constraints on a female's ability to forage on Arctic breeding areas. Warming temperatures and advancing Arctic phenology may alter those constraints. From 2011 to 2014, we examined relationships among spring temperature, timing of migration and reproduction, and the sources of nutrients females deposited in eggs for three sympatric species of geese that nested in northern Alaska. Compared to lesser snow geese (Anser caerulescens caerulescens) and greater white-fronted geese (Anser albifrons frontalis), black brant (Branta bernicla nigricans) were more likely to initiate follicle development during migration, resulting in fewer days between their arrival in the Arctic and the onset of incubation and requiring a relatively greater capital investment in eggs. Delaying follicle development until after their arrival in the Arctic provided snow geese and white-fronted geese an opportunity to forage near their nesting area and to deposit exogenous nutrients in eggs. With warmer spring temperatures, brant invested more capital in eggs, but snow geese invested less capital. Brant likely used capital to meet costs associated with earlier onset of follicle development when phenology was advanced, whereas snow geese used capital to compensate for poor foraging conditions during colder Arctic springs. Global warming is likely to reduce the quality of lower latitude marine habitats where brant acquire endogenous reserves and advancing Arctic phenology may increase their reliance on those reserves during reproduction. Near-term warming in northern Alaska may improve foraging conditions and favor the reproductive strategies of some herbivores such as snow geese and white-fronted geese that mainly invest Arctic nutrients in their offspring., (Published 2018. This article is a U.S. Government work and is in the public domain in the USA.)

Changes in the isotopic composition (δ 13 C and δ 15 N) in biofilm, macro-invertebrates and resident salmonids were used to characterize temporal dynamics of marine derived nutrients (MDNs) incorporation between stream reaches with and without MDN inputs. Five Atlantic rivers were chosen to represent contrasting MDN subsidies: four rivers with considerable numbers of anadromous fishes; one river with little MDN input. Rainbow smelt Osmerus mordax, alewife Alosa pseudoharengus, sea lamprey Petromyzon marinus and Atlantic salmon Salmo salar, were the primary anadromous species for the sampled rivers. Regardless of the spatial resolution or the pathway of incorporation, annual nutrient pulses from spawning anadromous fishes had a positive effect on isotopic enrichment at all trophic levels (biofilm, 1·2-5·4‰; macro-invertebrates, 0·0-6·8‰; fish, 1·2-2·6‰). Community-wide niche space shifted toward the marine-nutrient source, but the total ecological niche space did not always increase with MDN inputs. The time-integrated marine-nutrient resource contribution to the diet of S. salar parr and brook trout Salvelinus fontinalis ranged between 16·3 and 36·0% during anadromous fish-spawning periods. The high degree of spatio-temporal heterogeneity in marine-nutrient subsidies from anadromous fishes lead to both direct and indirect pathways of MDN incorporation into stream food webs. This suggests that organisms at many trophic levels derive a substantial proportion of their energy from marine resources when present. The current trend of declining anadromous fish populations means fewer nutrient-rich marine subsidies being delivered to rivers, diminishing the ability to sustain elevated riverine productivity., (© 2017 The Fisheries Society of the British Isles.)

Rationale: Determination of non-exchangeable hydrogen isotopic compositions (δ 2 H values) of bulk complex organic materials is difficult due to uncontrolled H isotope exchange between the organic material and ambient water vapor. A number of calibration keratinous materials with carefully measured hydrogen isotopic compositions of the non-exchangeable fraction were proposed to enable stable isotope laboratories to normalize their 2 H measurements. However, it was recently reported that high-temperature carbon-reactor methods for measuring the hydrogen isotopic composition of nitrogenous organic materials is biased by the production of HCN in the reactor. As a result, the reported values of these calibration materials needed to be re-evaluated., Methods: We evaluated the non-exchangeable δ 2 H VSMOW values of keratins EC1 (CBS) and EC2 (KHS), USGS hair standards, and a range of other nitrogenous widely used organic laboratory calibration materials (collagen and chitin) using pre-treatment with a preparation device designed to eliminate residual moisture and quantify exchangeable H., Results: The revised non-exchangeable δ 2 H VSMOW values of EC-1 (CBS) and EC-2 (KHS) keratin standard materials were -157.0 ± 0.9 and -35.3 ± 1.1 ‰, respectively. The revised values of USGS42 and USGS43 were -72.2 ± 0.9 and -44.2 ± 1.0 ‰, respectively, in excellent agreement with previous results., Conclusions: For routine H isotope analyses, with proper sample pre-treatment, we show that the Comparative Equilibration approach can provide accurate and reproducible non-exchangeable δ 2 H values among laboratories regardless of the reactor type used. © 2017 Her Majesty the Queen in Right of Canada Rapid Communications in Mass Spectrometry © 2017 John Wiley & Sons Ltd. Reproduced with the permission of the Environment and Climate Change Canada., (© 2017 Her Majesty the Queen in Right of Canada Rapid Communications in Mass Spectrometry © 2017 John Wiley & Sons Ltd. Reproduced with the permission of the Environment and Climate Change Canada.)

Hydrogen isotope (δ 2 H) measurements of consumer tissues in aquatic food webs are useful tracers of diet and provenance and may be combined with δ 13 C and δ 15 N analyses to evaluate complex trophic relationships in aquatic systems. However, δ 2 H measurements of organic tissues are complicated by analytical issues (e.g., H exchangeability, lack of matrix-equivalent calibration standards, and lipid effects) and physiological mechanisms, such as H isotopic exchange with ambient water during protein synthesis and the influence of metabolic water. In this study, δ 2 H (and δ 15 N) values were obtained from fish muscle samples from Lake Winnipeg, Canada, 2007-2010, and were assessed for the effects of species, feeding habits, and ambient water δ 2 H values. After lipid removal, we used comparative equilibration to calibrate muscle δ 2 H values to nonexchangeable δ 2 H equivalents and controlled for H isotopic exchange between sample and laboratory ambient water vapor. We then examined the data for evidence of trophic δ 2 H enrichment by comparing δ 2 H values with δ 15 N values. Our results showed a significant logarithmic correlation between fork length and δ 2 H values, and no strong relationships between δ 15 N and δ 2 H. This suggests the so-called apparent trophic compounding effect and the influence of metabolic water into tissue H were the potential mechanisms for δ 2 H enrichment. We evaluated the importance of water in controlling δ 2 H values of fish tissues and, consequently, the potential of H isotopes as a tracer of provenance by taking account of confounding variables such as body size and trophic effects. The δ 2 H values of fish appear to be a good tracer for tracking provenance, and we present a protocol for the use of H isotopes in aquatic ecosystems, which should be applicable to a broad range of marine and freshwater fish species. We advise assessing size effects or working with fish of relatively similar mass when inferring fish movements using δ 2 H measurements.

The painted lady, Vanessa cardui, is a migratory butterfly that performs an annual multi-generational migration between Europe and North Africa. Its seasonal appearance south of the Sahara in autumn is well known and has led to the suggestion that it results from extremely long migratory flights by European butterflies to seasonally exploit the Sahel and the tropical savannah. However, this possibility has remained unproven. Here, we analyse the isotopic composition of butterflies from seven European and seven African countries to provide new support for this hypothesis. Each individual was assigned a geographical natal origin, based on its wing stable hydrogen isotope (δ 2 H w ) value and a predicted δ 2 H w basemap for Europe and northern Africa. Natal assignments of autumn migrants collected south of the Sahara confirmed long-distance movements (of 4000 km or more) starting in Europe. Samples from Maghreb revealed a mixed origin of migrants, with most individuals with a European origin, but others having originated in the Sahel. Therefore, autumn movements are not only directed to northwestern Africa, but also include southward and northward flights across the Sahara. Through this remarkable behaviour, the productive but highly seasonal region south of the Sahara is incorporated into the migratory circuit of V. cardui., (© 2016 The Author(s).)

Background: Fish fin is a widely used, non-lethal sample material in studies using stable isotopes to assess the ecology of fishes. However, fish fin is composed of two distinct tissues (ray and membrane) which may have different stable isotope values and are not homogeneously distributed within a fin. As such, estimates of the stable isotope values of a fish may vary according to the section of fin sampled., Methods: To assess the magnitude of this variation, we analysed carbon (δ13C), nitrogen (δ15N), hydrogen (δ2H) and oxygen (δ18O) stable isotopes of caudal fin from juvenile, riverine stages of Atlantic salmon (Salmo salar) and brown trout (Salmo trutta). Individual fins were sub-sectioned into tip, mid and base, of which a further subset were divided into ray and membrane., Findings: Isotope variation between fin sections, evident in all four elements, was primarily related to differences between ray and membrane. Base sections were13C depleted relative to tip (~1‰) with equivalent variation evident between ray and membrane. A similar trend was evident in δ2H, though the degree of variation was far greater (~10‰). Base and ray sections were 18O enriched (~2‰) relative to tip and membrane, respectively. Ray and membrane sections displayed longitudinal variation in 15N mirroring that of composite fin (~1‰), indicating that variation in15N values was likely related to ontogenetic variation., Conclusions: To account for the effects of intra-fin variability in stable isotope analyses we suggest that researchers sampling fish fin, in increasing priority, 1) also analyse muscle (or liver) tissue from a subsample of fish to calibrate their data, or 2) standardize sampling by selecting tissue only from the extreme tip of a fin, or 3) homogenize fins prior to analysis.

We present a novel approach for nitrogen (δ(15)N) and oxygen (δ(18)O) isotopic analysis of nitrate in water based on the isotopic analysis of N2O produced from the conversion of NO3(-) by cultured denitrifying bacteria and off-axis integrated cavity output spectroscopy (OA-ICOS). The headspace N2O was manually injected into an OA-ICOS isotopic N2O laser analyzer through a syringe septum port. Sample analysis time was ∼300 s. The use of OA-ICOS technology yields accurate and precise δ(15)N and δ(18)O results for dissolved nitrate samples when nonlinearity issues are considered. This new isotope analytical technique thus improves the isotopic analysis of nitrates by (i) providing accurate measurements of δ(15)N and δ(18)O without preconcentration, (ii) eliminating interferences by other gas substances (i.e., H2O and CO2), and (iii) reducing extensive maintenance and costs of isotope ratio mass spectrometers (IRMS). This approach will greatly streamline the identification and quantification of nitrate sources in aquatic systems.

A steady-state mass-balance model describing controls on the stable hydrogen isotopic ratios (δ(2)H) of tissues in fish was previously developed but physiological effects related to fish size and growth had not been tested. Here, we assessed the influence of size (or growth rate) on tissue δ(2)H composition of a fish species (Poecilia reticulata) and the incorporation of metabolic products derived from dietary lipids (water, NADH). Sampled tissues were obtained from individuals that grew at different rates while raised on an isotopically homogeneous commercial diet (lipid-free fraction, δ(2)H=-95±2 ‰; and dietary lipids,-198±11 ‰) under different controlled water hydrogen isotopic composition (δ(2)H=-128±3 ‰;+17±5 ‰; and+202±5 ‰). Our findings suggested that fish growth rate was correlated positively with the degree of incorporation of metabolic products from dietary lipids that, in turn, influenced both fish tissue protein and lipid δ(2)H values. We conclude that δ(2)H measurements of lipids (and, subsequently, of body water) in fish could become a physiological tool that provides insights into fish growth rates.

Large numbers of the Globe Skimmer dragonfly (Pantala flavescens) appear in the Maldives every October-December. Since they cannot breed on these largely waterless islands, it has recently been suggested that they are "falling out" during a trans-oceanic flight from India to East Africa. In addition, it has been suggested that this trans-oceanic crossing is just one leg of a multi-generational migratory circuit covering about 14,000-18,000 km. The dragonflies are presumed to accomplish this remarkable feat by riding high-altitude winds associated with the Inter-tropical Convergence Zone (ITCZ). While there is considerable evidence for this migratory circuit, much of that evidence is circumstantial. Recent developments in the application of stable isotope analyses to track migratory dragonflies include the establishment of direct associations between dragonfly wing chitin δ(2)H values with those derived from long-term δ(2)H precipitation isoscapes. We applied this approach by measuring wing chitin δ(2)H values in 49 individual Pantala flavescens from the November-December migration through the Maldives. Using a previously established spatial calibration algorithm for dragonflies, the mean wing δ(2)H value of -117±16 ‰ corresponded to a predicted mean natal ambient water source of -81 ‰, which resulted in a probabilistic origin of northern India, and possibly further north and east. This strongly suggests that the migratory circuit of this species in this region is longer than previously suspected, and could possibly involve a remarkable trans-Himalayan high-altitude traverse.

Comparative studies of biomonitors of trace metal contamination are relatively scarce. We took advantage of a point source pollution in a reservoir (Flix, Spain) to compare trace metal (Hg, Pb, Cd, Se, As, Zn, Cu, Cr) bioaccumulation patterns among 16 food web components. Our results indicate that most organisms are suitable for Hg biomonitoring, whereas other metals are better monitored by only some of them. Biofilms and zebra mussel were the organisms with larger and more diverse biomonitoring capacity. However, we show that using groups of biomonitors increase the scope and strengths of the conclusions and specific goals can be better addressed. We conclude providing an overview of the strengths and weaknesses of the main organisms considered for biomonitoring trace metals in rivers and reservoirs., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Large amounts of industrial waste containing high concentrations of mercury, cadmium and organochlorine residues were dumped in a reservoir adjacent to a chlorine-alkali plant in the village of Flix(Catalonia, Spain), situated at the shore of the lower Ebro river. Effects of these contaminants to aquatic river invertebrates were assessed by integrating analyses of metals and organochlorine residues in field collected zebra mussels and crayfish with a wide range of biomarkers. Biological responses included levels of metallothioneins, activities of ethoxyresorufin-O-deethylase, oxidative stress biomarkers (glutathione content, enzymatic activities of superoxide dismutase, catalase, glutathione s-transferase, glutathione peroxidise and glutathione reductase), levels of lipid peroxidation and of DNA strand breaks. The results obtained evidenced similar response patterns in mussels and crayfish with increasing toxic stress levels from upper parts of the river towards the meander located immediately downstream from the most polluted site, close to the waste dumps. The aforementioned stress levels could be related with concentrations of mercury, cadmium, hexachlorobenzene, polychlorobiphenyls and dichlorodiphenyltrichloroethanes from 4- to 195-fold greater than local background levels. The response of biomarkers to these pollutant concentrations differences was reflected in high activities and levels of antioxidant enzymes, metallothioneins, lipid peroxidation and DNA strand breaks and decreased levels of glutathione., (Copyright 2009 Elsevier Ltd. All rights reserved.)

Large amounts of industrial waste containing high concentrations of mercury (up to 436 microg/g) are dumped in a reservoir adjacent to a chlor-alkali plant in Flix (Catalonia, Spain), on the lower Ebro River. In order to assess the spatial redistribution of mercury from the point source and its bioavailability to the aquatic food web, zebra mussels (Dreissena polymorpha) were collected at several sites. The highest total Hg (THg) and methylmercury (MeHg) concentrations ever reported for zebra mussels were found (THg: 0.02 to 0.81 microg/g ww; MeHg: 0.22 to 0.60 microg/g ww). At the most polluted site, close to the waste dump, the mean values were 20 times greater than the local background level. Concentrations decreased with increasing mussel size at all sites. The MeHg/THg ratio was ca. 60% (range: 50-80%). A comparison of similar size classes clearly indicated the hot spots of Hg bioavailability to the aquatic food web and downstream transport.