Freshwater pearl mussels as a stream water stable isotope recorder
Auteurs
L. Pfister, F. Thielen, E. Deloule, N. Valle, E. Lentzen, C. Grave, J.-N. Beisel, and J. J. McDonnell
Référence
Ecohydrology, vol. 11, no. 7, art. no. UNSPe2007, 2018
Description
For several decades, stable isotopes have been a commonly used and effective tool for flow path analysis, stream water source apportionment, and transit time analysis. The Global Network of Isotopes in Precipitation repository now has monthly precipitation isotope time series extending over several years and even decades in some settings. However, stream water isotope composition time series remain rather short with only very few data sets spanning over more than a few years. A critical challenge in this respect is the collection of stream water isotope data sets across a wide variety of headwater streams and for long durations. We rely on a new approach for stream signal reconstruction based on freshwater mussels, specifically the freshwater pearl mussel Margaritifera margaritifera. We use secondary ion mass spectrometry (SIMS) to quantify oxygen isotope ratios in pearl mussel shell growth bands. In our study area, the observed seasonal variability in precipitation delta O-18 values ranges between -15 parts per thousand and -3 parts per thousand. This input signal is strongly damped in stream water, where observed values of delta O-18 range between -10 parts per thousand and -6.5 parts per thousand. These values are consistent with our measured average shell-derived stream water delta O-18 of -7.19 parts per thousand. Along successive growth bands, SIMS-based stream water delta O-18(w) values varied within a seasonal range of -9 parts per thousand to -5 parts per thousand. The proposed SIMS-based shell analysis technique is obviously well suited for analysing isotopic signatures of O in shell material-especially from the perspective of reconstructing historical series of in-stream isotope signatures.
