Measuring Terrestrial Subsidies to Aquatic Food Webs Using Stable Isotopes of Hydrogen

Abstract

Understanding river food webs requires distinguishing energy derived from primary production in the river itself (autochthonous) from that produced externally (allochthonous), yet there are no universally applicable and reliable techniques for doing so. We compared the natural abundance stable isotope ratios of hydrogen (deltaD) of allochthonous and autochthonous energy sources in four different aquatic ecosystems. We found that autochthonous organic matter is uniformly far more depleted in deuterium (lower deltaD values) than allochthonous: an average difference of approximately 100% per hundred. We also found that organisms at higher trophic levels, including both aquatic invertebrates and fish, have deltaD values intermediate between aquatic algae and terrestrial plants. The consistent differences between leaves and algae in deltaD among these four watersheds, along with the intermediate values in higher trophic levels, indicate that natural abundance hydrogen isotope signatures are a powerful tool for partitioning energy flow in aquatic ecosystems.

Strong evidence for terrestrial support of zooplankton in small lakes based on stable isotopes of carbon, nitrogen, and hydrogen

“…1 and Table S3). Dilution-regrowth cultures of phytoplankton (Methods) from these lakes confirmed the large fractionation for δ 2 H between water and algae reported (34,39), and there was little difference between deep and surface water phytoplankton. In the surface waters of both lakes, phytoplankton had a δ 2 H of near −200‰ with low variance (Table S3).…”

“…We assumed that POM is comprised of a mixture of phytoplankton and terrestrial material and solved for the 13 C and 15 N of phytoplankton algebraically (Table S2 for details). The consistency of ε H in these lakes and in the literature (5,15,39,60) justifies this approach.…”

“…Stable isotope ratios of organic samples were measured on isotope ratio mass spectrometers at the University of Alaska (δ 13 C and δ 15 N) and the University of Northern Arizona (δ 2 H). Methods for δ 2 H analysis followed those of Doucett et al (39) and Finlay et al (60), including a benchtop equilibration to correct for exchange of H atoms between samples and ambient water vapor (61)(62)(63). Water samples were analyzed for δ 2 H via cavityring-down laser spectroscopy.…”

Terrestrial organic matter support of lake food webs: Evidence from lake metabolism and stable hydrogen isotopes of consumers

“…Solid material for isotopic analysis was freeze-dried or dried at 65uC, homogenized when necessary and stored frozen until analysis. Analyses of the d 2 H of nonexchangeable H were carried out at the Colorado Plateau Stable Isotope Laboratory, Northern Arizona University, following Doucett et al (2007).…”

Hydrogen isotopes in individual amino acids reflect differentiated pools of hydrogen from food and water in Escherichia coli

“…This gap in knowledge contrasts with our more comprehensive understanding of the carbon (δ 13 C) and nitrogen (δ 15 N) isotope composition of animal tissues relative to their diets, for which a biochemical framework of isotopic discrimination has been described and tested in controlled feeding experiments. Determining the magnitude and variation in diet or water to tissue discrimination factors is essential to refine the use of δ 2 H to characterize animal movement patterns, and to explore further the potential of δ 2 H as a tracer of energy within and among ecosystems (7).…”