Browsing by Subject "Stable isotopes"

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  • Vesala, Risto; Kiheri, Heikki; Hobbie, Erik A.; van Dijk, Netty; Dise, Nancy; Larmola, Tuula (2021)
    Peatlands store one third of global soil carbon (C) and up to 15% of global soil nitrogen (N) but often have low plant nutrient availability owing to slow organic matter decomposition under acidic and waterlogged conditions. In rainwater-fed ombrotrophic peatlands, elevated atmospheric N deposition has increased N availability with potential consequences to ecosystem nutrient cycling. Here, we studied how 14 years of continuous N addition with either nitrate or ammonium had affected ericoid mycorrhizal (ERM) shrubs at Whim Bog, Scotland. We examined whether enrichment has influenced foliar nutrient stoichiometry and assessed using N stable isotopes whether potential changes in plant nutrient constraints are linked with plant N uptake through ERM fungi versus direct plant uptake. High doses of ammonium alleviated N deficiency in Calluna vulgaris and Erica tetralix, whereas low doses of ammonium and nitrate improved plant phosphorus (P) nutrition, indicated by the lowered foliar N:P ratios. Root acid phosphatase activities correlated positively with foliar N:P ratios, suggesting enhanced P uptake as a result of improved N nutrition. Elevated foliar delta N-15 of fertilized shrubs suggested that ERM fungi were less important for N supply with N fertilization. Increases in N availability in peat porewater and in direct nonmycorrhizal N uptake likely have reduced plant nitrogen uptake via mycorrhizal pathways. As the mycorrhizal N uptake correlates with the reciprocal C supply from host plants to the soil, such reduction in ERM activity may affect peat microbial communities and even accelerate C loss via decreased ERM activity and enhanced saprotrophic activity. Our results thus introduce a previously unrecognized mechanism for how anthropogenic N pollution may affect nutrient and carbon cycling within peatland ecosystems. (C) 2021 The Authors. Published by Elsevier B.V.
  • Saarela, Taija; Rissanen, Antti J.; Ojala, Anne; Pumpanen, Jukka; Aalto, Sanni L.; Tiirola, Marja; Vesala, Timo; Jäntti, Helena (2020)
    Freshwater ecosystems represent a significant natural source of methane (CH4). CH4 produced through anaerobic decomposition of organic matter (OM) in lake sediment and water column can be either oxidized to carbon dioxide (CO2) by methanotrophic microbes or emitted to the atmosphere. While the role of CH4 oxidation as a CH4 sink is widely accepted, neither the magnitude nor the drivers behind CH4 oxidation are well constrained. In this study, we aimed to gain more specific insight into CH4 oxidation in the water column of a seasonally stratified, typical boreal lake, particularly under hypoxic conditions. We used (CH4)-C-13 incubations to determine the active CH4 oxidation sites and the potential CH4 oxidation rates in the water column, and we measured environmental variables that could explain CH4 oxidation in the water column. During hypolimnetic hypoxia, 91% of available CH4 was oxidized in the active CH4 oxidation zone, where the potential CH4 oxidation rates gradually increased from the oxycline to the hypolimnion. Our results showed that in warm springs, which become more frequent, early thermal stratification with cold well-oxygenated hypolimnion delays the period of hypolimnetic hypoxia and limits CH4 production. Thus, the delayed development of hypolimnetic hypoxia may partially counteract the expected increase in the lacustrine CH4 emissions caused by the increasing organic carbon load from forested catchments.
  • Kahilainen, Kimmo K.; Thomas, Stephen M.; Nystedt, Elina K. M.; Keva, Ossi; Malinen, Tommi; Hayden, Brian (2017)
    Resource polymorphism, whereby ancestral trophic generalists undergo divergence into multiple specialist morphs, is common in salmonid fish populations inhabiting subarctic lakes. However, the extent to which such resource specialization into the three principal lake habitats (littoral, profundal, and pelagic) affects patterns of contaminant bioaccumulation remains largely unexplored. We assessed total mercury concentrations (THg) of European whitefish (Coregonus lavaretus (L)) and their invertebrate prey in relation to potential explanatory variables across 6 subarctic lakes, of which three are inhabited by polymorphic (comprised of four morphs) and three by monomorphic populations. Among invertebrate prey, the highest THg concentrations were observed in profundal benthic macroinvertebrates, followed by pelagic zooplankton, with concentrations lowest in littoral benthic macroinvertebrates in both lake types. Broadly similar patterns were apparent in whitefish in polymorphic systems, where average age-corrected THg concentrations and bioaccumulation rates were the highest in pelagic morphs, intermediate in the profundal morph, and the lowest in the littoral morph. In monomorphic systems, age-corrected THg concentrations were generally lower, and showed pronounced lake-specific variation. In the polymorphic systems, we found significant relationships between whitefish muscle tissue THg concentration and gill raker count, resource use, lipid content and maximum length, whilst no such relationships were apparent in the monomorphic systems. Across all polymorphic lakes, the major variables explaining THg in whitefish were gill raker count and age, whereas in monomorphic systems, the factors were lake-specific. Whitefish resource polymorphism across the three main lake habitats therefore appears to have profound impacts on THg concentration and bioaccumulation rate. This highlights the importance of recognizing such intraspecific diversity in both future scientific studies and mercury monitoring programs. (C) 2017 Elsevier B.V. All rights reserved.
  • Kozak, Natalia; Ahonen, Salla A.; Keva, Ossi; ostbye, Kjartan; Taipale, Sami J.; Hayden, Brian; Kahilainen, Kimmo K. (2021)
    Subarctic lakes are getting warmer and more productive due to the joint effects of climate change and intensive land-use practices (e.g. forest clear-cutting and peatland ditching), processes that potentially increase leaching of peat- and soil-stored mercury into lake ecosystems. We sampled biotic communities from primary producers (algae) to top consumers (piscivorous fish), in 19 subarctic lakes situated on a latitudinal (69.0-66.5 degrees N), climatic (+3.2 degrees C temperature and +30% precipitation from north to south) and catchment land-use (pristine to intensive forestry areas) gradient. We first tested how the joint effects of climate and productivity influence mercury biomagnification in food webs focusing on the trophic magnification slope (TMS) and mercury baseline (THg baseline) level, both derived from linear regression between total mercury (log10THg) and organism trophic level (TL). We examined a suite of environmental and biotic variables thought to explain THg baseline and TMS with stepwise generalized multiple regression models. Finally, we assessed how climate and lake productivity affect the THg content of top predators in subarctic lakes. We found biomagnification of mercury in all studied lakes, but with variable TMS and THg baseline values. In stepwise multiple regression models, TMS was best explained by negative relationships with food chain length, climate-productivity gradient, catchment properties, and elemental C:N ratio of the top predator (full model R2 = 0.90, p < 0.001). The model examining variation in THg baseline values included the same variables with positive relationships (R2 = 0.69, p = 0.014). Mass standardized THg content of a common top predator (1 kg northern pike, Esox lucius) increased towards warmer and more productive lakes. Results indicate that increasing eutrophication via forestry-related land-use activities increase the THg levels at the base of the food web and in top predators, suggesting that the sources of nutrients and mercury should be considered in future bioaccumulation and biomagnification studies. (c) 2021 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY license (http:// creativecommons.org/licenses/by/4.0/).
  • Manninen, Sirkku; Zverev, Vitali; Kozlov, Mikhail (2022)
    Long-term exposure to primary air pollutants, such as sulphur dioxide (SO2) and nitrogen oxides (NOx), alters the structure and functions of forest ecosystems. Many biochemical and biogeochemical processes discriminate against the heavier isotopes in a mixture; thus, the values of delta C-13 and delta N-15 (i.e. the ratio of stable isotopes C-13 to C-12 and that of (15) N to (14) N, respectively) may give insights into changes in ecosystem processes and identify the immediate drivers of these changes. We studied sources of variation in the delta C-13 and delta N-15 values in the foliage of eight boreal forest C3 plants at 10 sites located at the distance of 1-40 km from the Monchegorsk nickel-copper smelter in Russia. From 1939-2019, this smelter emitted over 14,000,000 metric tons (t) of SO2, 250,000 t of metals, primarily nickel and copper, and 140,000 t of NOx. The delta C-13 value in evergreen plants and the delta N-15 value in all plants increased near the smelter independently of the plant mycorrhizal type. We attribute the pollution-related increase in the foliar delta C-13 values of evergreen species mainly to direct effects of SO2 on stomatal conductance, in combination with pollution-related water stress, which jointly override the potential opposite effect of increasing ambient CO2 concentration on delta C-13 values. Stomatal uptake of NOx and root uptake of N-15-enriched organic N compounds and NH4+ may explain the increased foliar delta N-15 values and elevated foliar N concentrations, especially in the evergreen trees (Pinus sylvestris), close to Monchegorsk, where the soil inorganic N supply is reduced due to the impact of long-term SO2 and heavy metal emissions on plant biomass. We conclude that, despite the uncertainties in interpreting delta C-13 and delta N-15 responses to pollution, the Monchegorsk smelter has imposed and still imposes a great impact on C and N cycling in the surrounding N-limited subarctic forest ecosystems.
  • Etu-Sihvola, H.; Salo, K.; Naito, Y. I.; Kytokari, M.; Ohkouchi, N.; Oinonen, M.; Heyd, V.; Arppe, L. (2022)
    In this article, we present the results of an isotopic study of diet for the early medieval (Merovingian, Viking, Early Christian) humans buried in the unique Luistari cemetery at Eura (ca. 600-1400 CE), southwestern Finland, the largest cemetery of the region. Isotope analysis was conducted on 37 humans for dentine and bone collagen (delta C-13, delta N-15, and delta S-34), and five of them were also studied using compound-specific nitrogen isotope analysis. Dental enamel and/or bone carbonate delta C-13 values were studied from altogether 65 humans, five cattle, and five sheep/goats. The bone and dentine collagen and carbonate data show that throughout the centuries, freshwater fish was a stable part of the diet for the population. Our results do not show systematic dietary differences between estimated males and females, but differences can be large on the individual level. We also discovered a possible temporal change in the enamel carbonate delta C-13 values that could be related to the increasing role of carbohydrates (e.g., crops) in the diet. Luistari burials are well comparable to contemporary Swedish Viking trading communities like Birka in their higher protein intake. But contrary to the wider Viking network, they do not show the same marine signal.
  • Asevedo, Lidiane; Ranzi, Alceu; Kalliola, Risto; Pärssinen, Martti; Ruokolainen, Kalle; Cozzuol, Mário Alberto; Rodrigues do Nascimento, Ednair; Negri, Francisco Ricardo; Souza-Filho, Jonas P.; Cherkinsky, Alexander; Trindade Dantas, Mario Andre (2021)
    We report the first radiocarbon datings and carbon (d13C) and oxygen (d18O) stable isotopes data to reconstruct the paleoecology of medium to large herbivorous mammals from late Quaternary of southwestern Amazon (Acre and Rond^onia states, Brazil). AMS 14C dates for Neochoerus sp. (29,072 - 27,713 Cal yr BP), Notiomastodon platensis (25,454 - 24,884 Cal yr BP) and Eremotherium laurillardi (11,320 - 11,131 Cal yr BP) support the Lujanian ages. All fossils have low d13C and d18O isotopic values that suggest C3-dominated environments from closed canopy forests to wooded savannas, agreeing with paleovegetation reconstitution. Most species were browsers (piC3¼100%; Niche breadth, BA¼0), where the key species with the largest body mass, N. platensis (~6,300 kg) and E. laurillardi (~3,500 kg), possibly had a more generalized browser diet in closed-canopies to woodlands. Their diet distinguished from the C3/C4 generalist Trigodonops lopesi (~1,900 kg), which foraged in wooded savannas (piC3¼70%; BA¼0.72), similarly with its relative Toxodon platensis (~1,800 kg) that had a browse-dominated mixed feeder diet (piC3 84%, BA 0.38) in Peruvian and Bolivian Amazon localities. Palaeolama major (~280 kg) was possibly a strictly folivorous within forest canopies, whereas Tapirus sp. (~250 kg) and Mazama sp. (~40 kg) were browsers in closed-canopies to woodlands. Holmesina rondoniensis (~120 kg) was a browser but not restricted, where could also feed on herbaceous from understories in woodlands, and Neochoerus sp. (~200 kg) feeding predominantly herbaceous plants in wooded savannas (piC3¼~69%; BA¼0.75). We estimate that the interspecific competition could have been avoid by different feeding strategies, although more investigations are still needed to better understand their ecological interactions in the habitats of the southwestern Amazon during the late Quaternary.
  • Kivilä, Elissa Henriikka; Luoto, Tomi P.; Rantala, Marttiina V.; Nevalainen, Liisa (2020)
    High latitude freshwater systems are facing changes in catchment-mediated allochthonous input, as well as physical and chemical controls triggered by on-going climate change, which may alter their carbon processing and ecological characteristics. To explore changes in chironomid functional responses and carbon utilization in relation to longterm environmental change, we studied a sediment core covering ca. 2000 years from a tundra lake in northern Finland, which was analysed for sediment geochemistry, isotopic composition of chironomid remains and their functional assemblages. We aimed to relate changes in chironomid functional feeding assemblages and resource utilization, based on Bayesian stable isotope modelling, and determined that the long-term resource utilization was more controlled by sediment geochemistry (resource availability) and climatic variables, reflecting changes in habitat and lake ontogeny, rather than the functional feeding assemblage composition. Change horizons were observed for both sediment geochemistry and functional assemblage composition. However, different timing of these changes suggests different drivers affecting the dynamics of primary production and chironomid community functionality. We also compared the recent warming period to Medieval Climate Anomaly (MCA), observing divergent patterns, which suggests that MCA may not be a good analogue for changes induced by on-going climate warming.
  • Karcher, Denis B.; Roth, Florian; Carvalho, Susana; El-Khaled, Yusuf C.; Tilstra, Arjen; Kürten, Benjamin; Struck, Ulrich; Jones, Burton H.; Wild, Christian (2020)
    While various sources increasingly release nutrients to the Red Sea, knowledge about their effects on benthic coral reef communities is scarce. Here, we provide the first comparative assessment of the response of all major benthic groups (hard and soft corals, turf algae and reef sands-together accounting for 80% of the benthic reef community) to in-situ eutrophication in a central Red Sea coral reef. For 8 weeks, dissolved inorganic nitrogen (DIN) concentrations were experimentally increased 3-fold above environmental background concentrations around natural benthic reef communities using a slow release fertilizer with 15% total nitrogen (N) content. We investigated which major functional groups took up the available N, and how this changed organic carbon (C-org) and N contents using elemental and stable isotope measurements. Findings revealed that hard corals (in their tissue), soft corals and turf algae incorporated fertilizer N as indicated by significant increases in delta N-15 by 8%, 27% and 28%, respectively. Among the investigated groups, C-org content significantly increased in sediments (+24%) and in turf algae (+33%). Altogether, this suggests that among the benthic organisms only turf algae were limited by N availability and thus benefited most from N addition. Thereby, based on higher C-org content, turf algae potentially gained competitive advantage over, for example, hard corals. Local management should, thus, particularly address DIN eutrophication by coastal development and consider the role of turf algae as potential bioindicator for eutrophication.
  • Rapo, Aleksi (Helsingin yliopisto, 2021)
    The geographical origin of food can be determined by analyzing stable isotope ratios of hydrogen and oxygen from water samples that have been extracted from food matrices. A geographical gradient is formed from isotope ratios of water constituents, due to the small mass differences of the different isotopes, which can be also seen in the growing plants in certain regions. Finnish Food Authority has established a method for differentiating domestic and foreign strawberry samples, which uses a database that was created for Finnish strawberries. To produce a representative water sample from food, almost all of the water needs to be extracted from the matrix. The aim of this master’s thesis was to establish and optimize the extraction process of water from strawberry samples with a cryogenic vacuum extraction (CVE). The secondary objective was to test if isotopic values of Finnish strawberries differ from that of foreign strawberry samples and thus be used for determining the domesticity of strawberries. The performance of the cryogenic vacuum extraction procedure was confirmed with three validation tests which tested extraction effect on the sample’s isotope ratios of hydrogen and oxygen, cross-contamination between extraction units and suitable sample fixing materials. The optimization did not reach acceptable accuracy as there were no significant differences between the experimental runs for the Box-Behnken design (BBD). The reason showing ineffective modelling of the design remains unknown, especially as the response surface diagram shows clearly the optimal and minimal trends of the tested factors for δ2H. However, this was not so evident for δ18O. The ranges of tested factors may partly explain this discrepancy. Nonetheless, the differentiation of foreign and domestic strawberry samples was successful with principal component analyses. However, several factors concerning cryogenic vacuum extraction and water extraction in general, such as recovery of water, sample pretreatment, sample storage, different sample matrices and coextracted compounds as well as extraction parameters, need to be addressed in future studies.
  • Jaatinen, Kim; Öst, Markus; Hobson, Keith A. (2016)
    Background: Species-specific strategies for financing the costs of reproduction are well understood, forming a continuum ranging from high to low reliance on stored nutrients. Animals relying mostly on stored reserves are termed 'capital breeders', whereas 'income breeders' rely mostly on concurrent intake when financing the costs of reproduction. The role and adaptive value of individual variation in these strategies remain elusive. Life-history theory posits that capital breeding should be favoured when offspring reproductive value peaks, typically occurring early in the season, and that current income should increasingly be used with progressing season. Because resource limitation may hamper flexible resource allocation, a corollary prediction is that only good-condition individuals may show the expected seasonal shift in resource use. To test this prediction, we examined stable isotopes (delta C-13 and delta N-15) in blood and lipid-free egg yolk of breeding eider females (Somateria mollissima) from the Baltic Sea to assess the role of individual variation in the use of proteins from local diet vs. stored reserves. Results: We show for the first time that individuals from a single population differ in their utilization of stored reserves and concurrent intake to finance the costs of reproduction. Consistent with our prediction, heavy females predominantly used stored reserves for producing egg yolks early in the season, increasingly relying on local feeding with later onset of breeding, whereas light females showed no seasonal change in allocation strategy. Conclusions: Stable isotope profiling at the individual level is a powerful tool for monitoring relative changes in investment strategies through time, showing promise as an early warning indicator of ecological change in food webs.
  • Arppe, Laura; Karhu, Juha A.; Vartanyan, Sergey; Drucker, Dorothée G.; Etu-Sihvola, Heli; Bocherens, Hervé (2019)
    The world's last population of woolly mammoths (Mammuthus primigenius) lived on Wrangel Island persisting well into the Holocene, going extinct at ca. 4000 cal BP. According to the frequency of 'radiocarbon dated mammoth remains from the island, the extinction appears fairly abrupt. This study investigates the ecology of the Wrangel Island mammoth population by means of carbon, nitrogen and sulfur isotope analyses. We report new isotope data on 77 radiocarbon dated mammoth specimens from Wrangel Island and Siberia, and evaluate them in relation to previously published isotope data for Pleistocene mammoths from Beringia and lower latitude Eurasia, and the other insular Holocene mammoth population from St. Paul Island. Contrary to prior suggestions of gradual habitat deterioration, the nitrogen isotope values of the Wrangel Island mammoths do not support a decline in forage quality/quantity, and are in fact very similar to their north Beringian forebears right to the end. However, compared to Siberian mammoths, those from Wrangel Island show a difference in their energy economy as judged by the carbon isotope values of structural carbonate, possibly representing a lower need of adaptive strategies for survival in extreme cold. Increased mid-Holocene weathering of rock formations in the central mountains is suggested by sulfur isotope values. Scenarios related to water quality problems stemming from increased weathering, and a possibility of a catastrophic starvation event as a cause of, or contributing factor in their demise are discussed. (C) 2019 The Authors. Published by Elsevier Ltd.
  • Kahilainen, K. K.; Thomas, S. M.; Harrod, C.; Hayden, B.; Eloranta, A. P. (2019)
    The trophic ecology of piscivorous Arctic charr (Salvelinus alpinus (L.); charr) in the food webs of large subarctic lakes is not well understood. We assessed charr diets, parasites, growth, maturity, and stable isotope ratios in Fennoscandian subarctic lakes dominated by monomorphic or polymorphic whitefish (Coregonus lavaretus (L.)) populations. Charr density was low in all lakes, except in profundal habitats. Charr shifted to piscivory at small size (16-25 cm total length) and consumed a range of prey-fish sizes (2-25 cm). Cannibalism was observed in a few individuals from one monomorphic whitefish lake. Charr matured at 37-51 cm (5-8 years old), grew to 52-74 cm maximum observed length and 47-83 cm asymptotic length. Charr increased total area of convex hull and core stable isotopic diversity area of the fish community by 51-98% and 44-51% in monomorphic whitefish lakes, but only 8-11% and 7-10% in polymorphic whitefish lakes. The difference was due to increasing food-chain length in monomorphic whitefish lakes, whereas reliance on littoral carbon did not change. Charr were the top piscivores in monomorphic whitefish lakes, but played a less important role in polymorphic whitefish lakes, which contained a more diverse predator fauna.