Variation in Zn, C, and N isotope ratios in three stream insects

R Douglas Evans,Wei Wang,R Bastian Georg,Hayla E Evans,Dietrich Albert Volmer

doi:10.1139/facets-2016-0023

Abstract

Total Zn concentrations and Zn isotope ratios were measured, using multicollector inductively coupled plasma (ICP)-mass spectrometry (MS), in three species of aquatic insects collected from a stream in Peterborough, Ontario, Canada. Total Zn levels averaged 193 ± 88 μg/g dry weight (dw) in water striders (Heteroptera: Gerridae, Aquarius remigis) and were significantly higher than the concentrations measured in stonefly nymphs (Plecoptera: Perlidae, Acroneuria abnormis) and caddisfly larvae (Trichoptera: Limnephilidae, Pycnopsyche guttifer), i.e., 136 ± 34 μg/g dw and 125 ± 26 μg/g dw, respectively. Average delta values for 66Zn/64Zn in the water striders were approximately 0.7‰ lighter (−1.2‰ ± 1.0‰) and were significantly different than those measured for stoneflies (−0.45‰ ± 0.62‰) and caddisflies (−0.51‰ ± 0.54‰). Nitrogen isotope ratios were significantly different ( P < 0.05) among the three species suggesting differences in trophic positioning. Similar to the Zn isotope ratios, δ 13C values for the water striders (−28.61‰ ± 0.98‰) were significantly different than those of the stoneflies and caddisflies, i.e., −30.75‰ ± 1.33‰ and −30.68‰ ± 1.01‰, respectively. The data suggest that the differences observed in Zn ratios relate to food source for these insects. Similar to their carbon sources, Zn in water striders appears to be primarily of terrestrial origin, and of aquatic origin for the other two species.

Highlights

With the tremendous advances in mass spectrometry (MS) techniques over the past few decades, the use of stable isotope ratios to determine the cycling and ultimate fate of elements in the aquatic environment has grown exponentially
Total Zn, δ66Zn, δ15N, and δ13C values were determined on individual insects, Fig. 1. (a) Monthly average total Zn concentrations and (b) δ66Zn (‰) in stoneflies, caddisflies, and water striders collected from Jackson Creek, Peterborough, in May, June, July, and August 2009
Average total Zn concentrations (Fig. 1a) were highest in the water striders (193 ± 88.5 μg Zn/g dw, n = 34) and were significantly higher (P < 0.05) than those measured in the stoneflies (136 ± 34 μg Zn/g dw, n = 38) and caddisflies (125 ± 26 μg Zn/g dw, n = 40), which were not significantly different from each other

Summary

Introduction

With the tremendous advances in mass spectrometry (MS) techniques over the past few decades, the use of stable isotope ratios to determine the cycling and ultimate fate of elements in the aquatic environment has grown exponentially. Variations in stable isotope ratios of 13C/12C (δ13C) and 15N/14N (δ15N) have been used extensively to examine food sources, trophic structure, and energy transfer and efficiency in lakes (Vander Zanden et al 1999; Vander Zanden and Rasmussen 1999, 2001; Post 2002), reservoirs (Saito et al 2001), and marine systems (Das et al 2003). Interest in the sources and trophic transfer of contaminants in aquatic systems has led to studies in which δ15N and (or) δ13C values were coupled with measurements of total metal concentrations in both freshwater and marine biota (e.g., Power et al 2002; Das et al 2003; Quinn et al 2003; Larsson et al 2007; Jardine et al 2009, 2012; Senn et al 2010; Jones et al 2014).

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