An evaluation of deuterium as a food source tracer in temperate streams of eastern Canada

Stable H isotope ratios (D/H, expressed as delta D) hold promise as an additional tool for elucidating food sources for consumers in aquatic ecosystems. We tested the applicability of delta D as a food source tracer in streams of New Brunswick, Canada. First, we analyzed delta D and delta(13)C in biofilm and terrestrial leaves and compared signal-to-noise ratios (variability within sources vs variability between sources) between the 2 elements. Signal-to-noise ratios were roughly similar, and 23 of the 31 sites had isotopically distinct food sources based on delta D compared to 20 of 31 based on delta(13)C. Second, we used mixing models to estimate % aquatic H and % aquatic C for benthic invertebrates at a subset of sites. of 16 samples, only 1 had delta(13)C that was outside the range of the 2 food sources (yielding % aquatic C > 100%), but 12 of the 16 samples had delta D outside the range of the food sources, a result suggesting confounding effects of water and lipids on total body H content. Last, we analyzed delta D in laboratory-reared consumers (brook trout and water striders) and in their diet before and after lipid extraction to estimate diet-tissue fractionation. Large differences between consumer and diet were apparent before lipid extraction, but no significant differences were found after lipid extraction. All of these measures indicate that delta D could serve as a complementary, but not alternative, isotopic method for estimating food sources for consumers in streams. Further laboratory trials are needed to explore the influence of lipids on delta D values.