Field testing cellulose-water oxygen isotope relations in periphyton for paleohydrological reconstructions

• DOI: 10.1007/s10933-021-00207-8
• Publication Date: 2021-07-09T14:23:52Z
• Authors: Cory A. M. Savage; Casey R. Remmer; James V. Telford; Mitchell L. Kay; Eva Mehler; Brent B. Wolfe; Roland I. Hall
• Keywords: δ18O; Periphyton

The oxygen isotope composition (δ18O) of aquatic cellulose extracted from lake sediment cores has long been used to reconstruct past hydrological responses to climate variation and anthropogenic (e.g. mining, agriculture, forestry) disturbance. Application of this method depends upon a constant oxygen isotope fractionation factor between aquatic cellulose and lake water, often reported as α18Ocell-lw = 1.028. Prior field-based assessments of α18Ocell-lw, however, commonly relied on one-time measures of lake water δ18O, which introduces uncertainties because values may not represent lake water δ18O at the time of cellulose synthesis. We field-tested the use of α18Ocell-lw = 1.028 across a broad hydrological gradient of lakes within the Peace-Athabasca Delta (PAD), west-central Canada, where we constrained cellulose production by periphyton on artificial substrates to bracketed measurements of lake water δ18O collected in late May 2015 and late June 2015. Cellulose-inferred lake water δ18O, calculated using α18Ocell-lw of 1.028 ± 0.0015, corresponded with the range of measured lake water δ18O in 36 of 52 (75%) of our study lakes. Agreement improved to 86% for ‘clean cellulose’ samples that appeared to be of higher quality (i.e. those with minimal minerogenic material). Mean apparent α18Ocell-lw calculated for clean cellulose samples, using both May lake water δ18O (1.0286) and the May–June mean lake water δ18O (1.0275), did not differ significantly from 1.028, but was significantly, albeit slightly, below 1.028 using June lake water δ18O (1.0264). Closer correspondence of apparent α18Ocell-lw, calculated using May and May–June average lake water δ18O, suggested rapid and early colonization and cellulose production by periphyton. For samples that were a mixture of cellulose and minerogenic material, mean apparent α18Ocell-lw was significantly below 1.028 for these corresponding lake water δ18O measurements, but differences were small and would potentially lead to under-estimation of cellulose-inferred lake water δ18O by only 1–2‰ in sediment stratigraphic records. Overall, strong agreement observed between the cellulose-inferred and directly measured lake water δ18O supports application of α18Ocell-lw = 1.028 ± 0.0015 and lends confidence to paleohydrological reconstructions using this method in lakes of the PAD and elsewhere.