Insights from stable isotope analysis have resulted in significant advances in the study of biogeochemistry, ecology, and environmental science. In particular, compound-specific isotope analysis (CSIA) of organic compounds have emerged as powerful tools for providing unprecedented accuracy in the understanding of ecological and environmental dynamics across aquatic and terrestrial systems. In this session, we bring together a diverse group of scientists who have used stable isotope analysis, including bulk and CSIA, to develop novel theoretical and applied approaches to solving broad, overarching questions relating to ecology, evolution, and sustainability in aquatic ecosystems.
Lead Organizer: Yoshito Chikaraishi, Hokkaido University (ychikaraishi@lowtem.hokudai.ac.jp)
Co-organizers:
Kyung-Hoon Shin, Hanyang University (shinkh@hanyang.ac.kr)
Shawn Steffan, University of Wisconsin-Madison (steffan@entomology.wisc.edu)
Hyuntae Choi, Hokkaido University (htchoi@lowtem.hokudai.ac.jp)
Presentations
09:00 AM
DECONVOLVING PROPORTIONAL CONTRIBUTIONS TO THE FLUX OF MARINE SINKING ORGANIC PARTICLES AT THREE SITES OFF EASTERN CANADA USING COMPOUND SPECIFIC NITROGEN ISOTOPE ANALYSIS (8349)
Primary Presenter: Owen Sherwood, Dalhousie University (owen.sherwood@dal.ca)
Constraining the mechanisms and rates of particulate organic matter (POM) export and carbon sequestration is a fundamental concern in marine biogeochemistry. Compound-specific nitrogen isotope analysis of amino acids (d15N-AA) is a potentially powerful way to disentangle the proportional contributions of different source materials to the downward flux of POM, particularly when particle disaggregation and degradation processes can render visual identification difficult. We compiled new and previously published d15N-AA and associated geochemical data from long-term (9 – 12 months) sediment traps deployed off Eastern Canada (Gulf of Maine, St Lawrence Estuary, and Labrador Sea), which together span gradients in proximity to land (1 – 175 km) and trap depth (130 – 915 m). Fluxes of particulate organic carbon and nitrogen decreased exponentially with depth, as expected. However, d15N-AA based indices of trophic position and microbial resynthesis varied little, which implies common origins and excellent preservation of d15N-AA signatures in the POM during export and sinking. Mixing model analysis of the d15N-data revealed a dominance of zooplankton fecal pellets (>70%) relative to phytoplankton (<15%) or other sources contributing to the sinking POM at all sites. Results are in broad agreement with other recent sediment trap d15N-AA investigations from sites in the Pacific Ocean and support the idea, based on visual analysis of sediment trap particles and biogeochemical models, that fecal pellets are the dominant form of POM export in many ocean regions.
09:15 AM
Organic Carbon Storage in the sediment Upo Wetland revealed by using the 13C Fingerprinting Technique of Essential Amino Acids (8092)
Primary Presenter: Minhwa Gu, Hanyang university (alsmin317@gmail.com)
The use of fossil fuels for global energy production has increased the concentration of CO2 released into the atmosphere. Consequently, there has been an increase in the concentration of anthropogenic greenhouse gases in the atmosphere, which contributes to the increase in global average temperature. Therefore, carbon sinks and storage have been investigated to mitigate atmospheric CO2 concentrations and reduce average temperature increases. This study aims to determine the potential of wetlands as a new carbon sink using stable isotope ratios. Four core samples were collected at Upo Wetland in June and August 2023. Radiocarbon, total organic carbon concentration, and stable carbon isotope of essential amino acids (δ13CEAA) were analyzed from the sediment core samples. Cores No. 3, 4, and 5 indicate that sediment depths of approximately 0.2-0.4m were deposited over about 100 years, whereas core No. 2 showed the equivalent time to 1m sediment depth. Moreover, all four cores displayed organic carbon content exceeding 1% at deeper depths than 3m, indicating that Upo Wetland has the potential to store organic carbon for a long time. The each basal source contribution of organic carbon was determined using 13C fingerprinting of essential amino acids δ13CEAA, with the freshwater phytoplankton, terrestrial plants, fungi, and bacteria serving as end-members. The sediments were found to be primarily composed of organic carbon from phytoplankton, accounting for over 90% of the total organic carbon source. Terrestrial plants contributed 0.7-5.3%, while bacteria and fungi contributed 0.4-2.3% and 0.6-3.8%, respectively. This indicates that the organic matter in the sediment of Upo Wetland is predominantly derived from phytoplankton. As a result, Upo Wetland seems to be a long term depository of organic carbon produced by the microalgal community.
09:30 AM
NITROGEN ISOTOPES OF AMINO ACIDS IN (SUB-) FOSSIL BIVALVE (ARCTICA ISLANDICA) SHELLS (8223)
Primary Presenter: Qian Huang, University of Mainz (qhuang01@uni-mainz.de)
Compound-specific nitrogen isotope analysis of individual amino acids (CSIA-δ15NAA) overcomes challenges of bulk δ15N and enables precise estimates of the nitrogen isotope baseline and the trophic position (TP) from organisms of the food web. By applying this technique to the organics of bivalve mollusk shells, it allows to reconstruct the variability of the nitrogen sources in aquatic ecosystems and changes in the basal food web through time. An essential prerequisite to reconstructing these ecological variables using bivalve shells is to understand if the pristine isotope signals can be retrieved from shell organics. Intra-crystalline organic matrix (intra-OM), which is trapped within biomineral units and less likely contaminated, might be a good candidate for CSIA-δ15NAA of (sub-) fossil shells. Here we present the δ15NAA and AA composition data from the total organics and isolated intra-OM of radiocarbon dated sub-fossil shells, which are then compared to the results of modern shells. By analyzing the nitrogen isotope values in the source AA, phenylalanine, as well as the estimated TP of the fossil specimens, we explore potential changes in the marine basal food web in the northern North Sea during the Holocene. This study provides perspectives on the CSIA method in palaeoceanographic and palaeoecological studies.
09:45 AM
Stable isotopes of eye lens layers track the individual component of dietary niche shifts, a case study in recently evolved species of arctic char (7886)
Primary Presenter: Gregoire Saboret, Eawag (gregoire.saboret@eawag.ch)
Stable isotopes significantly advance diet characterization, but tracking individual changes over time remains challenging. Micro-dissection of eye lenses has emerged as a cost-efficient tool for reconstructing individual dietary shifts, as they act as inert records of carbon and nitrogen isotope ratios over growth. However, their potential and applicability in the wild remain elusive. In this study, we used eye lens isotopes in well-characterized ecosystems (lakes and rivers) in Greenland to reconstruct the individual dietary shifts of Arctic char. Our results align with population data, and bulk muscle tissue’s isotopic content closely resembles that of the outermost layer, supporting its interpretation. We applied this methodology in a lake with two recently evolved sister species of Arctic char, one planktivorous and one piscivorous. While the juvenile diet remains unknown due to capture difficulties, we found that juveniles of both species occupy a unique isotopic niche, partly overlapping (30-40%), and two trophic levels less than adult piscivores (Δδ15N ~ 8 ‰), surpassing previous assumptions. Using linear mixed models, we demonstrate that diet is influenced by individual history (i.e., previous diet) and genetic factors (species). Furthermore, our examination of the individual components reveals that dietary plasticity is subject to selection pressure, with the piscivorous species exhibiting less predictable trajectories. Our study illustrates the importance of integrating individual isotopes over time to understand ecological and evolutionary processes.
10:00 AM
Development of compound-specific isotope analysis of sugars: for illustrating nutritional cycles between sugars and amino acids in organisms (7867)
Primary Presenter: Hyuntae Choi, Hokkaido University (htchoi@lowtem.hokudai.ac.jp)
Recent studies have suggested that stable isotope analysis of individual amino acids (AAs) can be used to identify the fate of organic matter in the trophic transfer and the resource utilization of organisms in the food web, with a considerably small error, for diverse marine and terrestrial settings. Such identification have been increasingly advanced by understanding the isotopic fractionation of amino acids (and their precursors and products) associated with metabolic processes in organisms. One of major organic molecules that have used for life energy sources as well as precursors and products of amino acids is ‘glucose’, and it is simply expected that the carbon isotope ratios of glucose can be useful for better understanding the isotope ratios of non-essential amino acids associated with biosynthesis and metabolic loading in consumer species. However, the isotope analysis of sugars, including glucose, by using isotope ratio mass spectrometry/gas chromatography (GC/IRMS) is still challenging, because of technical difficulties in preparation for the isotope analysis including the artificial isotopic fractionation during derivatization of sugars. Here, we review (1) potential of the carbon isotope analysis of sugars for better understanding the nutritional cycle between sugars and amino acids in organisms, (2) the carbon isotope analysis of sugars on the GC/IRMS system, and (3) the challenges for reducing the technical difficulties.
10:15 AM
Lipid degradation in organisms quantified via position-specific carbon isotope analysis of fatty acid (7881)
Primary Presenter: Yuko Takizawa, Hokkaido University (takizaway@lowtem.hokudai.ac.jp)
The isotopic composition of organic compounds is defined by the sum of the isotope ratio of the substrates and isotopic fractionation in biosynthesis and degradation processes. Since the 1990s, scientists in biogeochemistry have utilized compound-specific isotope analysis (CSIA) to trace the delivery and to evaluate biosynthetic pathways of organic compounds in natural samples. In the last decade, the CSIA of amino acids has quantified 'degradation' based on the relationship between degradation flux (e.g., deamination) and 15N-enrichment in amino acids, which contributes to the quantitative assessment of "protein (and amino acid) utilization" for diverse organisms and environments. On the other hand, organisms utilize not only proteins (amino acids) but also sugars and lipids in the adaptation to the environmental change and in the response to the growth stage in their life. In the current study, we are challenging the quantification of 'lipid degradation' by using ‘position-specific’ carbon isotope ratios of fatty acids. In this presentation, we would like to share the latest findings, including isotopic fractionation during lipid degradation, a new analytical method, and preliminary data for biological samples. These results will contribute to a better understanding of organisms' physiological responses to environmental changes on the Earth.
SS35A - Tracing Ecological and Environmental Dynamics Via Stable Isotope Analysis
Description
Time: 9:00 AM
Date: 4/6/2024
Room: Meeting Room MN