Degradation changes stable carbon isotope depth profiles in palsa peatlands

Peatland degradation indicated by stable isotope depth profiles and soil carbon loss

Abstract. Palsa peats are unique northern ecosystems formed under an arctic climate and characterized by a high biodiversity and sensitive ecology. The stability of the palsas are seriously threatened by climate warming which will change the permafrost dynamic and induce a degradation of the mires. We used stable carbon isotope depth profiles in two palsa mires of Northern Sweden to track environmental change during the formation of the mires. Soils dominated by aerobic degradation can be expected to have a clear increase of carbon isotopes (δ13C) with depth, due to preferential release of 12C during aerobic mineralization. In soils with suppressed degradation due to anoxic conditions, stable carbon isotope depth profiles are either more or less uniform indicating no or very low degradation or depth profiles turn to lighter values due to an enrichment of recalcitrant organic substances during anaerobic mineralisation which are depleted in 13C. The isotope depth profile of the peat in the water saturated depressions (hollows) at the yet undisturbed mire Storflaket indicated very low to no degradation but increased rates of anaerobic degradation at the Stordalen site. The latter might be induced by degradation of the permafrost cores in the uplifted areas (hummocks) and subsequent breaking and submerging of the hummock peat into the hollows due to climate warming. Carbon isotope depth profiles of hummocks indicated a turn from aerobic mineralisation to anaerobic degradation at a peat depth between 4 and 25 cm. The age of these turning points was 14C dated between 150 and 670 yr and could thus not be caused by anthropogenically induced climate change. We found the uplifting of the hummocks due to permafrost heave the most likely explanation for our findings. We thus concluded that differences in carbon isotope profiles of the hollows might point to the disturbance of the mires due to climate warming or due to differences in hydrology. The characteristic profiles of the hummocks are indicators for micro-geomorphic change during permafrost up heaving.

Simple SummaryStable isotopes were used to assess the assimilation of food in early juvenile seahorses of Hippocampus guttulatus reared under two feeding conditions: Artemia or copepods. The results suggest that copepods are more efficiently assimilated than Artemia since higher growth and survival were related to copepods feeding. Also, the consumption and assimilation of preys by juvenile seahorses could be traced using stable carbon isotopes as the stable carbon isotope values in seahorses approached the values of the corresponding diet. To our knowledge, it is the first study to assess nutrient assimilation in a seahorse species using stable isotopes.Nutritional issues are among the most critical factors in the initial survival of juvenile seahorses. Currently, there is a knowledge gap on the relationship between nutrient assimilation and the effects on initial mortalities and growth. In the present study, the stable isotope approach was used to assess the incorporation of two live preys (Artemia and copepods) in juvenile seahorses Hippocampus guttulatus. The changes in stable carbon isotope (δ13C) values were studied through two feeding experiments: feeding on Artemia or copepods (experiment 1), and shifting feeding from copepods to Artemia (experiment 2). In experiment 1, after 24–48 h of feeding, juvenile seahorses exhibited small but progressive changes in δ13C values towards those of the corresponding diet, indicating that the assimilation of the food offered was progressively enhanced from days 2–3. Similarly, in experiment 2, a diet shifting from copepods to Artemia caused an increase in δ13C values, reflecting a switch towards the isotopically enriched new diet (Artemia metanauplii). Differences in the assimilation efficiency of preys offered are discussed based on growth and survival rates. The enhanced growth performances and survivals achieved when the juveniles were fed on copepods could be related to higher efficient assimilation of copepods compared to Artemia. The present study demonstrates that the consumption and further assimilation of preys by juvenile seahorses could be traced using stable carbon isotopes. The research on nutrient assimilation of juvenile seahorses should enhance our knowledge on nutrient processes in developing seahorses for a better understanding of initial ontogeny in the early life stages of the species.

Stable isotope stratigraphy of Holocene speleothems: examples from a cave system in Rana, northern Norway

Assessing the main factors that control carbon dynamics in soils is an urgent problem in the context of modern climate change. The analysis of stable carbon isotope (δ13С) composition is one of the approaches to understanding this dynamics. The study was carried out in the landscapes of the southeastern slope and foothills of the Primorskii Range, characterized by contrasting physico-geographical conditions. Climatic parameters, spatial variations in the composition of stable carbon isotopes and their distribution in soil profiles, and soil physicochemical properties controlling carbon dynamics have been analyzed. The soil humus horizons formed in mountainous tundra and steppe landscapes manifest the highest δ13С values (–24.72 and –23.97…–24.75‰); whereas the lowest (–25.61…–27.18‰) values are registered in the mountainous taiga soils. Based on the calculation of linear dependence between δ13С values and the total carbon content in soil, which varies with the depth, the carbon turnover intensity was determined using the slope of linear regression. It was revealed that under the contrasting conditions of mountainous tundra and steppe landscapes, the climate (deficiency of heat and moisture) has a significant impact on the intensity of organic matter transformation, blocking the effect of edaphic (soil profile) factors. Under more favorable climatic conditions of mountainous taiga landscapes, the dynamics of organic matter in soils is controlled mainly by edaphic factors.

Since the invention of the isotope ratio mass spectrometer, isotope analysis has shed light on many key processes in the Earth’s ecosystems. Stable isotope analysis was first applied in the field of chemistry and geochemistry, while the use of isotopic fractionation for various biochemical reactions was elaborated later. The knowledge gained from isotope research led to a better understanding of the dynamics of the biosphere and to the more efficient study of interactions between the geosphere and biosphere. In soil research, stable isotopes are ideally suited to provide a wider insight into the element cycles in soil ecosystems. Stable carbon isotopes, in particular, have been in the focus of soil research, since soil organic matter (SOM) plays an important role not only in soil fertility, soil water management and many other physical, chemical and biological soil functions, but also in the global carbon cycle. If processes connected with these soil functions are isotopically labelled with stable carbon isotopes, the key reactions of C input, exchange and output in the soil and other soil organic matter functions can be studied accurately. Moreover, analysing the isotopic composition of CO2 exchange between the soil and the atmosphere helps to predict ecosystem responses to global changes.

Impact of Salinity on Respiration and Organic Matter Dynamics in Soils is More Closely Related to Osmotic Potential than to Electrical Conductivity

Effects of lipid extraction on human bone collagen: Comparing stable carbon and nitrogen isotope values with and without lipid extraction

Numerical simulations of transport and isotope fractionation provide a method to quantitatively interpret vadose zone pore water stable isotope depth profiles based on soil properties, climatic conditions, and infiltration. We incorporate the temperature‐dependent equilibration of stable isotopic species between water and water vapor, and their differing diffusive transport properties into the thermodynamic database of the reactive transport code TOUGHREACT. These simulations are used to illustrate the evolution of stable isotope profiles in semiarid regions where recharge during wet seasons disturbs the drying profile traditionally associated with vadose zone pore waters. Alternating wet and dry seasons lead to annual fluctuations in moisture content, capillary pressure, and stable isotope compositions in the vadose zone. Periodic infiltration models capture the effects of seasonal increases in precipitation and predict stable isotope profiles that are distinct from those observed under drying (zero infiltration) conditions. After infiltration, evaporation causes a shift to higher δ18O and δD values, which are preserved in the deeper pore waters. The magnitude of the isotopic composition shift preserved in deep vadose zone pore waters varies inversely with the rate of infiltration.

Numerical simulations of transport and isotope fractionation provide a method to quantitatively interpret vadose zone pore water stable isotope depth profiles based on soil properties, climatic conditions, and infiltration. We incorporate the temperature-dependent equilibration of stable isotopic species between water and water vapor, and their differing diffusive transport properties into the thermodynamic database of the reactive transport code TOUGHREACT. These simulations are used to illustrate the evolution of stable isotope profiles in semiarid regions where recharge during wet seasons disturbs the drying profile traditionally associated with vadose zone pore waters. Alternating wet and dry seasons lead to annual fluctuations in moisture content, capillary pressure, and stable isotope compositions in the vadose zone. Periodic infiltration models capture the effects of seasonal increases in precipitation and predict stable isotope profiles that are distinct from those observed under drying (zero infiltration) conditions. After infiltration, evaporation causes a shift to higher δ18O and δD values, which are preserved in the deeper pore waters. The magnitude of the isotopic composition shift preserved in deep vadose zone pore waters varies inversely with the rate of infiltration.

Long-term overfishing and environmental pollution has led to a high degree of change in Laizhou Bay fisheries resource structures. Since 1980, small pelagic fish have become the new dominant species in this area.These small pelagic fish play a connecting role in the food chain and are often one of the key groups in marine ecosystems. Research on the trophic level of Engraulidae and Clupeidae fish in Laizhou Bay based on stomach content analysis has provided useful but dated information. More up-to-date research is now necessary. Based on bottom trawl surveys in Laizhou Bay during summer and autumn, 2011, the stable isotope signatures of four Engraulidae and Clupeidae species revealed that the stable carbon isotope ratios ranged from 21.97‰ to 11.67‰,while stable nitrogen isotope ratios ranged from 8.54‰ to 15.95‰. ANOVA analysis revealed that δ13C and δ15N varied significantly among the four species(P0.05). Linear regression analysis between fork length and stable isotopic ratios showed that Sardinella zunasi and Konosirus punctatus had significant ontogenetic variation in terms of δ15N(P0.05), while Setipinna taty and Thrissa kammalensis did not(P0.05). The S. zunasi trophic level ranged from 2.80 to 4.88, with the average being 3.52±0.46; the K. punctatus trophic level ranged from 2.71to 4.29, with the average being 3.34±0.33; the T. kammalensis trophic level ranged from 3.38 to 4.42, with the average being 3.97±0.28; the S. taty trophic level ranged from 3.28 to 4.13, with the average being 3.76±0.23.According to the stable carbon and nitrogen isotope results, we can draw the following conclusions:(1) The stable carbon isotope values showed that K. punctatus trophic level range( 20.92 to 11.67) almost covers that of the remaining three species( 21.97 to 16.8), meaning that K. punctatus inhabits a wide depth range which is different to that of other pelagic fish;(2) The K. punctatus trophic level decreases with increasing fork length while that of S. zunasi increases with increasing fork length, no such changes were observed in the other two species;(3) The T. kammalensis trophic level is about 0.7 times larger than that reported from the traditional stomach content analysis, which may be related to increased feeding on shrimp. The trophic level of the other three species was slightly higher according to the stable isotope results, but not significantly so.

We measured the stable carbon and nitrogen isotope ratios for muscles of the upland buzzards (Buteo hemilasius) and their potential food sources, plateau pikas (Ochotona curzoniae), Qinghai voles (Lasiopodomys fuscus), plateau zokors (Myospalax fontanierii), and several passerine bird species at the alpine meadow in Maduo county, Guoluo prefecture of Qinghai province, People's Republic of China, to provide diet information of upland buzzards, highlighting different diet composition of upland buzzards exposed to different locations. The results demonstrated that stable carbon isotope ratios of upland buzzards, passerine birds, plateau pikas, plateau zokors, and Qinghai voles were -24.42 +/- 0.25parts per thousand, -22.89 +/- 1.48parts per thousand, -25.30 +/- 1.47parts per thousand, -25.78 +/- 0.22parts per thousand, and -25.41 +/- 0.01parts per thousand, respectively, and stable nitrogen isotope ratios were 7.89 +/- 0.38parts per thousand, 8.37 +/- 2.05parts per thousand, 5.83 +/- 1.10parts per thousand, 5.23 +/- 0.34parts per thousand, and 8.86 +/- 0.06parts per thousand, respectively. Fractionation of stable carbon and nitrogen isotope ratios between upland buzzards and their food were 1.03parts per thousand and 2.11parts per thousand, respectively. Based on mass balance principle of stable isotopes and the Euclidean distance mixing model, upland buzzards depended mainly on plateau pikas as food (74.56%). Plateau zokors, Qinghai voles, and passerine birds only contributed a small proportion (25.44%) to diets of upland buzzards. The results were closely accordant with analyses of stomach contents and food pellets, which firmly supported the feasibility of using stable carbon and nitrogen isotope ratios to investigate diet information of upland buzzards. Another study based on stable carbon isotopes showed that upland buzzards living in the Haibei prefecture (another prefecture located in the southeast Qinghai province) mainly preyed on passerine birds (64.96% or more) as food supply. We were alarmed by the preliminary results that widespread poisoning activities of small mammals could reshape the food composition of upland buzzards, influencing the stability and sustainability of the alpine meadow. Bio-control on rodent pests should be carried out rather than the chemical measures.

Abstract. Climate warming is degrading palsa peatlands across the circumpolar permafrost region. Permafrost degradation may lead to ecosystem collapse and potentially strong climate feedbacks, as this ecosystem is an important carbon store and can transition to being a strong greenhouse gas emitter. Landscape-level measurement of permafrost degradation is needed to monitor this impact of warming. Surface subsidence is a useful metric of change in palsa degradation and can be monitored using interferometric synthetic-aperture radar (InSAR) satellite technology. We combined InSAR data, processed using the ASPIS algorithm to monitor ground motion between 2017 and 2021, with airborne optical and lidar data to investigate the rate of subsidence across palsa peatlands in northern Sweden. We show that 55 % of Sweden's eight largest palsa peatlands are currently subsiding, which can be attributed to the underlying permafrost landforms and their degradation. The most rapid degradation has occurred in the largest palsa complexes in the most northern part of the region of study, also corresponding to the areas with the highest percentage of palsa cover within the overall mapped wetland area. Further, higher degradation rates have been found in areas where winter precipitation has increased substantially. The roughness index calculated from a lidar-derived digital elevation model (DEM), used as a proxy for degradation, increases alongside subsidence rates and may be used as a complementary proxy for palsa degradation. We show that combining datasets captured using remote sensing enables regional-scale estimation of ongoing permafrost degradation, an important step towards estimating the future impact of climate change on permafrost-dependent ecosystems.

Stable isotope analyses of bone collagen are often used in palaeoecological studies to reveal environmental conditions in the habitats of different herbivore species. However, such studies require valuable reference data, obtained from analyses of modern individuals, in habitats of well-known conditions. In this article, we present the stable carbon and nitrogen isotope composition of bone collagen from modern red deer (N = 242 individuals) dwelling in various habitats (N = 15 study sites) in Europe. We investigated which of the selected climatic and environmental factors affected the δ13C and δ15N values in bone collagen of the studied specimens. Among all analyzed factors, the percent of forest cover influenced the carbon isotopic composition most significantly, and decreasing forest cover caused an increase in δ13C values. The δ15N was positively related to the proportion of open area and (only in the coastal areas) negatively related to the distance to the seashore. Using rigorous statistical methods and a large number of samples, we confirmed that δ13C and δ15N values can be used as a proxy of past habitats of red deer.

Abstract. Prabowo H, Rahardjo BT, Mudjiono G, Rizali A. 2022. Stable isotope analysis to assess the trophic level of arthropod in sugarcane ratoon agroecosystem. Biodiversitas 23: 2871-2881. Arthropods represent one of the main components of soil inhabitants and play an important role in maintaining soil health, as well as providing ecosystem services. The description of the trophic level of the ratoon sugarcane agroecosystem is needed to describe the role of organisms in the ecosystem to maximize the role of detritivores, predators, and parasitoids in the ratoon sugarcane agroecosystem. The stable isotope approach is widely used in various studies to describe trophic levels in an agroecosystem. The stable isotope technique, especially the one that uses stable isotopes of carbon (?13C) and nitrogen (?15N), can measure the trophic position that integrates energy assimilation or mass flow through all the different trophic pathways leading to an organism. Stable isotopes ?13C and ?15N can be used to identify the roles of arthropods in the ratoon sugarcane agroecosystem by identifying the composition of both isotopes. The ratio of arthropod's carbon assimilation (?13C) to sugarcane ranges from-1.4 to-5.45‰. In contrast, the ratio of nitrogen assimilation (?15N) of arthropod to sugarcane ranges from 3.86 to 39.7‰. The values of stable isotope ?13C and ?15N on predator and parasitoids are varied. The stable isotope value of carbon (?13C) for predators varies from-10.14 to-11.62‰. In contrast, the predator's stable isotope value of nitrogen (?15N) varies from 9.17 to 18.1%. The parasitoids' carbon stable isotope value (?13C) varies from 10.5 to 11.05‰. In contrast, parasitoids' nitrogen stable isotope value (?15N) varies from 12.8 to 17.05‰. The value of carbon (?13C) stable isotope assimilation between herbivores and predators varies from 0.006 to 1.38‰. While the value of nitrogen (?15N) stable isotope assimilation varies in the range of 0.33 to 10.3‰. Furthermore, the value of carbon (?13C) stable isotope assimilation between herbivores and parasitoids varies in the range of 5.3 to 9.23‰. While the value of nitrogen (?15N) stable isotope assimilation varies in the range of 3.79 to 10.3‰. Isotope content (?13C) shows the food resources of arthropods in the agroecosystem, while isotope value (?15N) shows the roles of arthropods in the sugarcane ratoon agroecosystem. Carbon stable isotope values of predator and parasitoids are close to zero. While the stable nitrogen isotope (?15N) values on arthropods are averagely above 10‰, values are suspected of having roles as predators or parasitoids. Knowing the trophic level of predators and parasitoids through stable isotopes in agroecosystems can be used to conserve and optimize natural enemies to suppress the development of herbivores.