Hydrogen isotope discrimination in aquatic primary producers: implications for aquatic food web studies

• Published in: Aquatic sciences 2014-04, Vol.76 (2), p.217-229
• Main Authors: Hondula, K. L, Pace, M. L, Cole, J. J, Batt, R. D
• Format: Article
• Language: English
• Subjects: Algae; Animal and plant ecology; Animal, plant and microbial ecology; Aquatic ecosystems; aquatic food webs; Aquatic plants; Biological and medical sciences; Biomedical and Life Sciences; body water; Deuterium; Ecology; ecosystems; Food chains; Food webs; Fresh water ecosystems; Freshwater & Marine Ecology; Fundamental and applied biological sciences. Psychology; General aspects; Hydrogen; Isotopes; Lagoons; lakes; Life Sciences; macroalgae; Marine & Freshwater Sciences; microalgae; Oceanography; Organic matter; Phytoplankton; Research Article; rivers; subsidies; Synecology; Terrestrial ecosystems; Terrestrial environments; Transpiration; uncertainty; Vegetation; Water bodies; watersheds
• ISSN: 1015-1621; 1420-9055
• DOI: 10.1007/s00027-013-0331-6

Large differences in δ ²H of primary producers between aquatic and terrestrial ecosystems are used to identify subsidies, discriminate organic matter sources, and reduce uncertainty in food web studies. Previous investigations of hydrogen isotope ratios suggest there may be predictable differences between the δ ²H of water and organic matter for different types of primary producers. We define the difference in the net isotopic discrimination between water and bulk organic matter (om) as: ΔH = (δ ²Hₒₘ − δ ²Hwₐₜₑᵣ) ÷ (1 + δ ²Hwₐₜₑᵣ ÷ 1,000). We summarized ΔH values from published literature and we measured the δ ²H of water and primary producers in order to compare ΔH among aquatic and terrestrial primary producers. Measurements were made from three water body types (lake, river, coastal lagoon) and their associated watersheds. Although we predicted a large and equivalent net isotopic discrimination for aquatic primary producers, we found considerable variability among groups of aquatic producers. Macroalgae, benthic microalgae, and phytoplankton had more negative ΔH values (i.e. greater isotopic discrimination) than both aquatic macrophytes and terrestrial vegetation. The more positive δ ²Hₒₘ and hence lower ΔH of terrestrial vegetation was expected due to relative increases in the heavier isotope, deuterium, during transpiration. However, the more positive values of δ ²Hₒₘ and relatively low ΔH in aquatic macrophytes, even submerged species, was unexpected. Marine macroalgae had high variability in δ ²Hₒₘ as a group, but low variability within distinct species. Variability among types of primary producers in δ ²Hₒₘ and in ΔH should be assessed when hydrogen is used in isotopic studies of food webs.